Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

Platinum (Pt)-containing conjugated polymers were synthesized by the dehydrochlorination coupling polymerization of cis- and trans-dichlorobis(N-(p-(diphenylphosphino)benzoyl)-l-valine methyl ester)platinum(II) {cis-PtL2Cl2and trans-PtL2Cl2, L = P(Ph)2-p-C6H4CONHCH[CH(CH3)2]CO2CH3} with 1,4-diethynylbenzene, aiming at obtaining polymers with controlled geometry at the Pt centers. In the polymerization of cis-PtL2Cl2, the geometry at the Pt centers was controlled by the amine used in the polymerization and the reaction temperature. The formed polymer with trans-Pt centers exhibited a circular dichroism signal at the main chain chromophore region in CH2Cl2/MeOH mixed solvent. Based on the crystal packing state and non-covalent interaction analysis of a model compound, the chiroptical activity is attributed to aggregation stabilized by intermolecular π-π, CH-π, and hydrogen-bonding interactions between the phosphine ligands.

DOI： 10.1021/acs.organomet.2c00173

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Cu complexes with p-dimethylaminophenolate ligands were synthesized by the reaction of Cu-II ions with the ligands under inert gas atmosphere and characterized. The complexes showed a valence state change from Cu-II-phenolate to Cu-I-phenoxyl radical on loss of the coordinated solvent. The Cu-I-phenoxyl radical species showed the characteristic properties and reactivities.

DOI： 10.1039/d2cc01409b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Structures of La(III) and Ba(II) complexes and their stabilities were investigated to develop a stable chelating ligand for Ac(III) and Ra(II) which are of interest in nuclear medicine using alpha particles. The La(III) and Ba(II) complexes (1 and 2) with a diaza-18-crown-6 ether bearing pyridine phosphonic acid ethyl ester pendant arms (L1) and the complexes (3 and 4) with a diaza-18-crown-6 ether bearing pyridine phosphonate pendant arms ((H(2)L2)(2-)) were synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. The La(III) complexes, 1 and 3, exhibited 11-coordinate structures, whereas the Ba(II) complexes, 2 and 4 exhibited 11- and 10-coordinate geometries, respectively. Potentiometric titrations were performed to determine the acid-base equilibrium and the complex formation constants of the La(III) and Ba(II) complexes. In addition, the speciation analysis of the complexes was performed and the pH dependencies of the fractions in the aqueous solutions were investigated. For the La(III) complexes, the species with the ligand bearing pyridine phosphonate pendant arms were observed to be more stable than those with the ligand bearing pyridine phosphonate ester pendant arms. The Ba(II) complexes showed the opposite trend. The species with the pyridine phosphonate ester ligand were observed to be more stable than the species with the pyridine phosphonate type ligand.

DOI： 10.1246/bcsj.20210414

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

The cured resins of ethynylene-linked mono-, di- and tri-functional benzoxazines were thermally more stable than the resins obtained from the analogous benzoxazines without a triple bond.

DOI： 10.1039/d2py00840h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A highly regioselective and stereoselective difunctionalization reaction of 1,3-diene with amine and disilane to form C-N and C-Si bonds via a one-step Pd/Cu/O-2 system is disclosed. The difunctionalization reaction affords allylic silanes, including the allylic amine moiety, in up to 92 % yield in the absence of any acid, base, or external ligand. The developed synthetic methodology can be scaled to 100 g in high yield with high Z-selectivity, which demonstrates the feasibility of the reaction for industrial applications.

DOI： 10.1002/chem.202100043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

<p>The reaction of Ni(<sc>ii</sc>)-(phenol)(phenolate) complexes with O₂ gave the Ni(<sc>ii</sc>)-phenoxyl radical complexes assisted by CH₃OH. This reaction was concluded to undergo <italic>via</italic> the proton transfer–electron transfer type mechanism without redox of the Ni ion.</p>

DOI： 10.1039/D1DT00105A

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

Ring-opening metathesis polymerization (ROMP) of norbornene derivatives is useful for preparing thermally stable and transparent polymeric materials with good moldability. This study deals with the ROMP of the norbornene monomer 1 bearing a platinum(Pt)-acetylide complex moiety using the Grubbs thirdgeneration catalyst. The product, poly(norbornene) [poly(1)], was investigated as a sensitizer for triplettriplet annihilation upconversion (TTA-UC), together with the copolymers of 1 and 2-norbornene 2. All the polymers exhibited bright photoluminescence under N-2. The phosphorescence of poly(1) was remarkably quenched, while that of poly(1-co-2)s was hardly quenched in CHCl3 solution. The phosphorescence of cast films of the polymers was highly responsive to oxygen, indicating possible application as oxygen sensing materials. The luminescence colors of the films were tunable between yellow and orange by copolymerization of 2 as a matrix. The polymers served as excellent sensitizers of TTA-UC with 9,10-diphenylanthracene as an emitter.

DOI： 10.1039/D1PY00665G

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

Chirally regulated pi-conjugated polymers containing platinum (Pt) complex moieties have great potential as chiroptically functional materials. In this study, novel platinum-containing conjugated polymers, poly(1a-2) and poly( 1b-2), were synthesized by the dehydrochlorination coupling polymerization of dichloro(4,4'-tertbutyl-2,2'-bipyridyl)platinum (1a) and dichloro(4,4'-dinonyl-2,2'bipyridyl)platinum (lb) with N-[ 3,5-bis(4-ethynylphenylethynyl)benzoyl] -L-alanine dodecylamide (2), and their chiral secondary structures in solutions were investigated. Poly(1a-2) exhibited bisignate circular dichroism (CD) signals assignable to the main chain chromophore (300-450 nm) in dimethylformamide (DMF)/MeOH = SO/SO (v/v). The presence of particles of Z-average = 30 nm was confirmed in this solution. These results indicated that poly (1a-2) formed chirally regulated aggregates. Single-crystal X-ray analysis of the model compound and density functional theory (DFT) calculations were carried out to examine the mode of aggregation of the polymers.

DOI： 10.1021/acs.macromol.0c00911

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

A novel benzoxazine derivative, 9,10-bis(6-ethynyl-3-pheny1-3,4-dihydro-1,3-benzoxazine)anthracene (1a), was synthesized by the Sonogashira-Hagihara coupling reaction of 9,10-dibromoanthracene and 6-ethynyl-3-phenyl-3,4-dihydro-1,3-benzoxazine. A CH2Cl2 solution of 1a luminesced with a high quantum yield (Phi = 81%). Compound 1a afforded solventinsoluble cross-linked polybenzoxazine 1b by the bulk polymerization at 250 degrees C. Solution polymerization of a dilute solution of 1a at 200 degrees C afforded solvent-soluble samples, accompanied by a decrease of photoluminescence intensity. The weight loss values of 1a and 1b were 81 and 87%, respectively, under nitrogen at 500 degrees C. We believe that the present study will lead to thermally stable curing resins whose degree of curing can be estimated with the naked eye by observing the decrease of photoluminescence.

DOI： 10.1021/acs.macromol.0c00910

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

A triarylamine bearing three benzofuran rings was designed and successfully prepared in 64% yield. It exhibited absorption at 385 nm, and blue emission at around 440nm with a fluorescence quantum yield of 0.57. This compound showed high heat resistance and reversible one-electron oxidation. Upon one-electron chemical oxidation, a near-infrared absorption was revealed due to a persistent radical cation species. DFT calculations also supported the experimental data.

DOI： 10.1246/cl.200161

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Platinum (Pt) containing novel conjugated polymers, poly(1-2a)-poly(1-2d) having bipyridine ligands were synthesized by the Sonogashira-Hagihara coupling polymerization of [Pt(4,4'-dibromo-2,2'-bipyridine)((R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline)(trifluoromethanesulfonate)(2)] (1) coordinated with 4,4'-dibromo-2,2'-bipyridine/(R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline [(R,R)-QuinoxP*] and 1,4-diethynylbenzene (2a), 1,4-diethynyl-2,5-bis(heptyloxy)benzene (2b), 1,4-diethynyl-2,5-bis(2-ethylhexyloxy)benzene (2c), and 1,4-diethynyl-2,5-bis(2-(2-methoxyethoxy)ethoxy)benzene (2d). Poly(1-2d) exhibited circular dichroism signals derived from (R,R)-QuinoxP* and the conjugated main chain around 290 and 440 nm in DMF, respectively. The simulated CD spectroscopic pattern of a low molecular model compound, M1-Pt, agreed well with the observed spectra. The TEM images of poly(1-2d) in the solid state exhibited dispersed patterns with sizes around 10 nm. Concentrated solutions of polymer 1-2d in DMF and CHCl3 partly exhibited patterns assignable to the formation of lyotropic liquid crystals.

DOI： 10.1021/acs.macromol.0c00096

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Reaction of Cu(ClO4)(2).6 H2O with a tripodal 2N2O ligand, H2Me2NL, having a p-(dimethylamino)phenol moiety, in CH2Cl2/MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2NL)(H2O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O-2 in CH2Cl2/MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic Cu-II EPR signals of the dx2-y2 ground state in CH2Cl2/MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the Cu-II-(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2Cl2 solution of 1 exhibits distortion from the dx2-y2 ground state and a temperature-dependent equilibrium between the Cu-II-(dimethylamino)phenolate and the Cu-I-(dimethylamino)phenoxyl radical. From these results, Cu-II-phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O-2 via the Cu-I-phenoxyl radical species.

DOI： 10.1002/chem.201903077

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

In order to gain new insights into the effect of the pi-pi stacking interaction of the indole ring with the phenoxyl radical moiety as seen in the active form of galactose oxidase, we have prepared Ni(s) complexes of a methoxy substituted salen-type ligand containing a pendent indole ring on the dinitrogen chelate backbone and characterized their one-electron oxidized forms. The X-ray crystal structure analysis and the other physicochemical experiments of the Ni(s) complex revealed no significant intramolecular interaction of the indole ring with the coordination plane. On the other hand, the X-ray crystal structures of the oxidized Ni(ii) complex exhibited the pi-pi stacking interaction of the indole ring mainly with one of the two phenolate moieties. While the phenoxyl radical electron was delocalized on the two phenolate moieties in the Ni(s)-salen coordination plane, the phenolate moiety in close contact with the indole moiety was considered to be the initial oxidation locus, indicating that the indole ring interacted with the phenoxyl radical by pi-pi stacking. The UV vis NIR spectrum of the oxidized Ni(ii) complex with the pendent indole ring was different from that of the complex without the side chain indole ring, but the differences were rather small in comparison with the oxidized Cu(ii)-salen complexes with the pi-pi stacking interaction of the indole ring. Such differences are due to the electronic structure difference, the localized radical electron on one of the phenolate moieties in the oxidized Cu(ii) complexes being more favorable for then pi-pi stacking interaction.

DOI： 10.1039/C9DT01887E

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

In order to gain new insights into the effect of the pi-pi stacking interaction of the indole ring with the Cu-II-phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a Cu-II complex of a methoxy-substituted salen-type ligand, containing a pendent indole ring on the dinitrogen chelate backbone, and characterized its one-electron-oxidized forms. The X-ray crystal structures of the oxidized Cu-II complex exhibited the pi-pi stacking interaction of the indole ring mainly with one of the two phenolate moieties. The phenolate moiety in close contact with the indole moiety showed the characteristic phenoxyl radical structural features, indicating that the indole ring favors the pi-pi stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized Cu-II complex with the pendent indole ring was significantly different from those of the complex without the side-chain indole ring, and the absorption and CD spectra exhibited a solvent dependence, which is in line with the phenoxyl radical-indole stacking interaction in solution. The other physicochemical results and theoretical calculations strongly support that the indole ring, as an electron donor, stabilizes the phenoxyl radical by the pi-pi stacking interaction.

DOI： 10.1002/chem.201900733

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Using a novel tandem reduction-cyclization, we synthesized t-butyl 3-alkyloxindole-3-carboxylates from the di-t-butyl 2-alkyl-2-(2-nitrophenyl)malonate. Introduction of an alpha-substituent to the di-t-butyl 2-(2-nitrophenyl)-malonates and addition of acid promoted reactivity. This methodology was successfully applied to gram-scale-synthesis of the t-butyl 3-methyloxindole-3-carboxylate 1 and 3-hydroxyrnethy1-3-methyloxindole 2 without silica gel column chromatography.

DOI： 10.3987/COM-17-S(T)2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The Sonogashira-Hagihara coupling polymerization of a D-hydroxyphenylglycine-derived diiodoarylene monomer and platinum-containing diethynylphenylene monomers with various substituents, HCuCC6H4- CuC-Pt(PR3) 2-CuC-C6H4-CuCH, 1: R = C4H9, 2: R = C8H17, 3: R = cyclohexyl, 4: R = phenyl, and 5: R = 4-methoxyphenyl, gave the corresponding polymers 1'-5' with number-average molecular weights of 4600-22 000. The polymers were soluble in CHCl3, CH2Cl2, THF and DMF. CD/ UV-vis spectroscopic analysis and dynamic light scattering measurements revealed that 1'-5' formed chirally regulated unimolecular structures in THF/ toluene mixtures, while formed chiral aggregates in THF/ MeOH mixtures. The conjugation of the polymer main chain was longer for monomers with aryl groups bonded to P compared to monomers with alkyl groups bonded to P. The relationship between the HOMO-LUMO gaps and phosphine ligands was reasonably explained by DFT calculations. The polymers exhibited photoluminescence with quantum yields ranging from 0.003% to 0.9%. The photoluminescence intensity was controlled by changing the phosphine substituents. The thermal stability of the polymers increased and the refractive index decreased as the alkyl chain length of the phosphine ligand was increased.

DOI： 10.1039/c7py01886j

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Control of the conformation of polymers can be achieved by the ligand exchange reaction of optically active poly(phenyleneethynylene) 1' containing -Pt(PPh3)(2)- moieties in the main chain. Polymer 1' was reacted with 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), and 1,4-bis(diphenylphosphino)butane (dppb) to give the corresponding polymers 2', 3', and 4' containing -Pt-(dppe)-, -Pt(dppp)-, and -Pt-(dppb)- moieties in the main chain, respectively. Polymers 1' and 2' exhibited negligibly small circular dichroism (CD) signals in THF, indicating the absence of regulated chiral structures, while polymers 3' and 4' exhibited strong CD signals in THF. The dynamic light scattering (DLS) analysis of the polymer solutions indicated that polymer 3' formed a chirally regulated one-handed helix intramolecularly bridged with dppp, and polymer 4' formed aggregates intramolecularly and/or intermolecularly bridged with dppb.

DOI： 10.1021/acs.macromol.7b02249

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Society of Japan  

A synthetic method for 1,2-dihydroisoquinolines via the 6-endo-dig cyclization of 2-alkynylaldimines and nucleophilic addition has been developed. When the 2-alkynylaldimines were reacted with various nucleophiles such as nitromethane, dimethyl malonate, phenylacetylene, hydrosilane, allylstannane, and ketene silyl acetal in the presence of a rhenium catalyst, the corresponding 1,2-dihydroisoquinolines were obtained in moderate to good yields.

DOI： 10.1246/cl.180200

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A copper(II) complex of (R)-N-(2-pyridylmethyl) pipecolate (pmpi) was prepared, and its structure was revealed by X-ray crystal structure analysis. Mixed ligand complexes were then prepared from this complex and (R)- and (S)-N-(t-butoxycarbonyl) leucinate (BocLeu). The (R)-BocLeu complex is less soluble in aqueous acetonitrile and more soluble in acetone than the (S)-BocLeu complex, and the reason was discussed on the basis of their structures. Recrystallization of the reaction mixture consisting of Cu(II) ion, pmpi, and (RS)-BocLeu from aqueous acetonitrile gave the (R)-BocLeu complex and that from acetone gave the (S)-BocLeu complex. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ica.2017.06.052

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-Blackwell  

Methylthiophenoxyl radical plays an important role as the active form of galactose oxidase (GO), which catalyzes oxidation of a primary alcohol to the corresponding aldehyde. Although many metal(II)-phenoxyl radical species have been reported, only a few studies have been reported on the properties of methylthiophenoxyl radical-metal complexes. We have prepared the group 10 metal (Ni, Pd and Pt) complexes of a salen-type ligand with a methylthio group at para-position of the two phenolate moieties and characterized them by X-ray crystal structure analyses and various spectroscopic methods in order to understand the role of the methylthio moiety in phenoxyl radical metal complexes. The corresponding p-methoxy substituted derivatives have been also characterized for comparison. All the one-electron oxidized group 10 metal methylthiophenolate complexes have a relatively localized radical site on one of the two phenolate moieties in comparison to the one-electron oxidized complexes of p-methoxy derivatives and exhibit different properties dependent on the central metal ions.

DOI： 10.1002/slct.201701986

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION CRYSTALLOGRAPHY  

The crystal structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts show that these four compounds exist as racemic compounds around room temperature. The two ammonium salts are arranged around a 2(1) screw axis, forming a helical column which consists of ammonium ions and single enantiomeric anions similar to the crystals of the ammonium salts of optically active N-acetyl-L-isoleucine and N-acetyl-D-alloisoleucine. The ammonium ion and the carboxylate ion in the helix are connected by three hydrogen bonds, the fourth hydrogen bond being formed between the ammonium ion and an external acetyl amino group of the neighboring helical column. The fourth hydrogen bond is formed between the ammonium ion and an external acetyl amino group of the neighboring 2(1) column. Ammonium N-acetyl-DL-alloisoleucinate was revealed to exist as an unstable racemic compound due to conformational similarity between the racemic and optically active compounds in the solid state and was optically resolved by fractional crystallization at 293 K.

DOI： 10.1107/S2052520616007319

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Tryptophan (Trp), an essential amino acid, has an indole ring with a high electron density and is frequently seen at the proximal position of the metal site in metalloproteins. For example, the indole ring of Trp has been reported to interact weakly with Cu(I) in a Cu chaperone CusF. Another aromatic amino acid, tyrosine (Tyr), has a phenol ring, which is an important metal binding site in various metalloproteins. Although the structures of the aromatic rings are different, they both have a weakly acidic moiety and perform some similar roles in biological systems, such as radical formation and electron transfer. In this review, we focus on these and other properties of the indole and phenol rings in metal-containing systems. (C) 2015 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jinorgbio.2015.03.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WALTER DE GRUYTER GMBH  

Various Pd-C complexes have been developed to date, affording deep insights into the reaction intermediates in useful catalytic reactions in organic syntheses. Cyclopalladation is one of the most famous Pd-C bond formation reactions to generate the palladacycles. Indole is an electron-rich aromatic ring involved in the side chain of an essential amino acid, tryptophan (Trp), and Trp and its derivatives are important in biological systems, such as electron transfer in protein, cofactors for conversion of biological molecules and so on. Pd catalysts are also useful for syntheses of such indole derivatives, and the mechanisms are considered to be through the Pd-C intermediates. However, the detailed properties and formation mechanisms of Pd-indole species are still unclear. With these points in mind, we focus on Pd(II)-indole-C2 carbon bond formations using various Pd(II) complexes having an indole moiety, especially on the recent studies on the kinetic analyses for these cyclopalladation reactions and their detailed mechanisms.

DOI： 10.1515/pac-2014-5020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

One-electron oxidized salophen-type complexes, [Cu(salophen)](+) (H(2)salophen = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminobenzene), and its methoxy derivatives, [Cu(MeO-salophen)](+) and [Cu(salophen-(MeO)(2))](+) (H2MeO-salophen = N, N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-diaminobenzene, H(2)salophen-(MeO)(2) = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diamino-4,5-dimethoxybenzene), have been synthesized and structurally characterized, and their reactivities have been investigated. The solid state structures of the one-electron oxidized forms of these complexes suggested that [Cu(salophen)](+) and [Cu(MeO-salophen)](+) can be assigned to relatively localized Cu(II)-phenoxyl radical complexes, while [Cu(salophen-(MeO)(2))](+) is the diiminobenzene radical complex. On the other hand, [Cu(salophen)](+) in solution showed a different electronic structure from that of the solid sample, the radical electron being delocalized over the whole pi-conjugated ligand. The reaction of these oxidized complexes with benzyl alcohol has been investigated in the presence of a large excess of substrate, which revealed the difference in the kinetic behavior between the complexes. The mechanisms of the oxidation have been discussed on the basis of the electronic and geometrical structures and the reaction kinetics.

DOI： 10.1039/c3dt52338a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The Pd(II) complexes of three new N,N,O-donor ligands with a pendent indole ring and participation of the indole ring in Pd(II) binding have been studied by synthetic, structural, and kinetic methods. The reactions of ligands, 2-[N-2-(1-methylimidazolyl)methyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino] ethyl-3-indole (Hieip), 2-[N-2-(1,4,5-trimethylimidazolyl)methyl-N-2-hydroxy-3, 5-di(tert-butyl)benzylamino]ethyl-3-indole (HMe3-ieip) and 2-[N-2-(6-methypyridyl)-methyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino] ethyl-3-indole (HMe-iepp), with [PdCl2(CH3CN)2] at room temperature gave the complexes [Pd(ieip)Cl], [Pd(Me3-ieip) Cl] and [Pd(Me-iepp)Cl], respectively, as reddish-brown crystals. The X-ray crystal structure analyses and 1H NMR spectra revealed that all the complexes have a phenolate coordination in a square-planar geometry and that the pendent indole ring has no characteristic intramolecular interaction with the Pd(II) ion and the coordinated pyridine and imidazole moieties. The distortion of the coordination plane is in the order [Pd(ieip)Cl] &lt
[Pd(Me 3-ieip)Cl] &lt
[Pd(Me-iepp)Cl]. Heating a solution of each of the phenolate complexes gave yellow crystals, which were shown to be the indole-C2 binding complex by X-ray analysis. The Pd(II)-O(phenolate) to Pd(II)-C(indole) conversion characteristics of these complexes depends on the nitrogen donor properties of the trans position of the coordinated indole moiety, and the order of the conversion rate of Pd-indole binding complexes is in good correlation with the coordination plane distortion. On the basis of kinetic studies, the influence of the aromatic nitrogen donors to form the indole-C2 binding complexes and the detailed mechanism of the conversion were discussed. © 2013 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ica.2013.07.032

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The Pd(II) complexes of a 2N-donor ligand containing a pendent indole, 3-(2-pyridylmethylamino)ethylindole (L), were synthesized and characterized. Reaction of the ligand with [PdCl(2)(CH(3)CN)(2)] at room temperature gave [Pd(L)Cl(2)] (1) as pale yellow crystals. The X-ray crystal structure analysis and (1)H NMR spectrum of 1 revealed that the complex has a 2N2Cl-donor set in a square-planar geometry and that the pendent indole ring has no characteristic intramolecular interaction with the Pd(II) ion and the coordinated pyridine moiety. Refluxing a solution of 1 in CH(2)Cl(2)/DMF for a few hours under basic conditions gave yellow crystals, which were shown to be an indole-C2 binding complex [Pd(L)Cl] (2) by X-ray analysis. Conversion of complex 1 to 2 in DMSO was observed upon dilution of the solution of complex 1. From solution equilibrium and kinetic studies the initial step of the conversion by dilution has been assigned to the replacement of a coordinated Cl ion with the DMSO molecule. The ligand replacement easily occurred at low concentrations of 1. The complex with a coordinated solvent molecule exhibited a high reactivity and formed a stable Pd-C bond with the indole ring located close to the Pd(II) center. We discussed the concentration dependent formation of the indole-C2 binding complex 2 and its detailed mechanism. (C) 2011 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.ica.2011.07.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The neutral and one-electron oxidized group 10 metal, Ni(II), Pd(II) and Pt(II), six-membered chelate Salpn (Salpn = N,N&apos;-bis(3,5-di-tert-butylsalicylidene)-1,3-propanediamine) complexes have been investigated and compared to the five-membered chelate Salen (N,N&apos;-bis(3,5-di-tert-butylsalicylidene)-1,2-ethanediamine) and Salcn (N,N&apos;-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) complexes. Reaction of the Salpn complexes with 1 equivalent of AgSbF(6) affords the oxidized complexes which exist as ligand radical species in solution and in the solid state. The solid state structures of the oxidized complexes have been determined by X-ray crystal structure analysis. While the Ni and Pt analogues exhibit an essentially symmetric coordination sphere contraction upon oxidation, the oxidized Pd derivative exhibits an asymmetric metal binding environment demonstrating at least partial ligand radical localization. In comparison to the oxidized Salen and Salcn complexes, the propyl backbone of the Salpn complexes leads to a larger deviation from a planar geometry in the solid state. The electronic structure of the oxidized Salpn complexes was further probed by UV-vis-NIR measurements, electrochemistry, EPR spectroscopy, and theoretical calculations. The intense NIR band for the one-electron oxidized Salpn complexes shifts to lower energy in comparison to the 5-membered chelate analogues, which is attributed to lower metal d(xz) character in the beta-LUMO for the Salpn series. The reactivity of the one-electron oxidized Salpn complexes with exogenous ligands was also studied. In the presence of pyridine, the oxidized Ni analogue exhibits a shift in the locus of oxidation to a Ni(III) species. The oxidized PtSalpn complex rapidly decomposes in the presence of pyridine, even at low temperature. Interestingly, electronic and EPR spectroscopy suggests that the addition of pyridine to the oxidized Pd analogue results in initial dissociation of the phenoxyl radical ligand, likely due to the increased flexibility of the propyl backbone.

DOI： 10.1039/c0dt01574a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

A simple procedure is described to obtain D- and L-allothreonine (D- and L-aThr). A mixture of N-acetyl-D-allothreonine (Ac-D-aThr) and N-acetyl-L-threonine (Ac-L-Thr) was converted to a mixture of their ammonium salts and then treated with ethanol to precipitate ammonium N-acetyl-L-threoninate (Ac-L-Thr center dot NH3) as the less-soluble diastereoisomeric salt. After separating Ac-L-Thr center dot NH3 by filtration, Ac-D-aThr obtained from the filtrate was hydrolyzed in hydrochloric acid to give D-aThr of 80% de, recrystallized from water to give D-aThr of &gt;99% de. L-aThr was obtained from a mixture of the ammonium salts of Ac-L-aThr and Ac-D-Thr in a similar manner.

DOI： 10.1271/bbb.100295

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An X-ray crystal structural analysis revealed that (2S,3S)-N-acetyl-2-amino-3-methylpentanoic acid (N-acetyl-L-isoleucine; Ac-L-Ile) and (2R,3S)-N-acetyl-2-amino-3-methylpentanoic acid (N-acetyl-D-alloisoleucine; AC-D-aIle) formed a molecular compound containing one Ac-L-Ile molecule and one Ac-D-aIle molecule as an unsymmetrical unit. This molecular compound is packed with strong hydrogen bonds forming homogeneous chains consisting of Ac-L-Ile molecules or Ac-D-aIle molecules and weak hydrogen bonds connecting these homogeneous chains in a fashion similar to that observed for Ac-L-Ile and Ac-D-aIle. Recrystallization of an approximately 1:1 mixture of Ac-L-Ile and Ac-D-aIle from water gave an equimolar molecular compound due to its lower solubility than that of Ac-D-aIle or especially Ac-L-Ile. The results suggest that the equimolar mixture of Ac-L-Ile and Ac-D-aIle could be obtained from an Ac-L-Ile-excess mixture by recystallization from water.

DOI： 10.1271/bbb.90389

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

To photomodulate the interaction of the phosphatidylinositol 3-kinase SH3 domain with a peptide ligand, a cyclic peptide (cyclic-1)with a photolabile side chain-to-side chain linker was synthesized. The conformation of cyclic-1 differs from that of the parent linear peptide, but becomes identical by UV-irradiation. Accordingly, the binding affinity of cyclic-1 to the SH3 domain increased upon conversion of the cyclic to a linear flexible structure by irradiation (Kd: 3.4 +/- 1.7 and 0.9 +/- 0.3 mm, respectively). These results confirm the usefulness of a photocleavable peptide for photocontrol of peptide-protein interactions. Copyright (C) 2009 European Peptide Society and John Wiley & Sons, Ltd.

DOI： 10.1002/psc.1132

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Zinc(II) complexes of N(3)O-donor tripodal ligands, 2,4-di(tert-butyl)-6-{[bis(2-pyridyl) methyl] aminomethyl} phenol (HtbuL), 2,4-di(tert-butyl)-6-{[(6-methyl-2-pyridyl) methyl]-(2-pyridyl) methylaminomethyl} phenol (HtbuLMepy), and 2,4-di(tert-butyl)-6-{[bis(6-methyl-2-pyridyl) methyl] aminomethyl} phenol (HtbuL(Mepy)(2)), [Zn(tbuL)Cl] center dot CH(3)OH (1), [Zn(tbuLMepy)Cl] (2), and [Zn(tbuL(Mepy)(2))Cl] (3), respectively, were prepared and structurally characterized by the X-ray diffraction method. All the complexes were found to have a mononuclear structure with a coordinated phenolate moiety, the geometry of the Zn(II) center being 5-coordinate trigonal-bipyramidal. The Zn(II) binding ability of the ligands with and without 6-methyl-2-pyridylmethyl moieties was evaluated for similar ligands, which lacked the t-butyl groups at the 2-and 4-positions of the phenol moiety, by the stability constants determined by potentiometric titration at 25 degrees C (I = 0.1 M (KNO(3))). The stability of the complexes was found to be in the order L &gt; LMepy &gt; L(Mepy)(2), reflecting the steric hindrance of the 6-methyl group of the pyridine ring. Complexes 1, 2, and 3 were converted to the phenoxyl radicals upon oxidation with Ce(IV), giving a phenoxyl radical pi-pi* transition band at 394-407 nm. ESR and resonance Raman spectra established that the radical species had a Zn(II)-phenoxyl radical bond. The cyclic voltammograms showed similar quasi-reversible redox waves with E(1/2) = 0.68, 0.67, and 0.63 V (versus Ag/AgCl) for 1, 2, and 3, respectively, corresponding to the formation of the phenoxyl radical, which displayed a first-order decay. The half-lives, 58.6, 25.8, and 15.6 min at -40 degrees C for 1, 2, and 3, respectively, follow the order of the stability constants of the complexes, indicating that the metal(II) -phenoxyl radical stability is in close relationship with the complexation properties of the present series of N(3)O-donor ligands. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.ica.2008.11.006

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The Pt(II) complexes of 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl) benzylamino] ethylindole (Htbu-iepp), and 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl) benzylamino] ethylindole (Htbu-miepp) (H denotes an ionizable hydrogen), were synthesized, and the structure of [Pt(tbu-iepp) Cl] (1) was determined by X-ray analysis. Complex 1 prepared in CH(3)CN was revealed to have the C2 atom of the indole ring bound to Pt(II) with the Pt(II)-C2 distance of 1.981(3) angstrom. On the other hand, [Pt(tbu-miepp) Cl] (2) was concluded to have a phenolate coordination instead of the C2 atom of the indole ring by (1)H NMR spectra. Reaction of 1 with 1 equiv. of Ce(IV) in DMF gave the corresponding one-electron oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at 567 nm, indicating the formation of the Pt(II)-indole-pi-cation radical species. The half-life, t(1/2), of the radical species at -60 degrees C was calculated to be 43 s (k(obs) = 1.6 x 10(-2) s(-1)). (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.ica.2008.01.046

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Adduct formation of ternary Pt(II) complexes composed of an amino acid and an aromatic diimine, [Pt(A)(DA)] (A = glycinate (Gly), alaninate (Ala), valinate, or arginine (Arg); DA = 2,2&apos;-bipyridine (bpy) or 1,10-phenanthroline (phen)), with flavin mononucleotide (FMN) and anthraquinone-2-sulfonate (AQS) were investigated by spectroscopic, X-ray diffraction, and electrochemical methods. The Pt(II) complexes formed 1:1 [Pt(A)(DA)]-FMN adducts by stacking with the aromatic moiety of FMN, and the stability constants, logK, for the systems with [Pt(A)(phen)] (A = Gly, Ala, and Arg) and [Pt(Arg)(bpy)] were determined to be 2.83(8)-3.42(6) from (1)H NMR spectra at 25 degrees C in D(2)O (I = var.). The structure of the adduct [Pt(Ala)(phen)](AQS) (1) was determined by X-ray analysis to involve a p-p stacking interaction between coordinated phen and AQS with the distance of 3.400(7) angstrom and a hydrogen bond between the sulfonate moiety of AQS and the amino group of coordinated Ala. Cyclic voltammetry of the 1: 1 [Pt(A)(DA)]-FMN systems in a phosphate buffer (pH 7.0) showed that the potentials, E(1/2), for the two-electron redox process of FMN shifted to higher values by 18-31 mV as compared with the value for free FMN. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.ica.2008.03.054

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Indole is an electron-rich aromatic compound with characteristic properties and is widely distributed in natural products and in proteins as the important constituent of essential amino acid tryptophan. it is known to form a hydrophobic environment in proteins and to be involved in enzymatic reactions. In addition to the redox activities and various weak interactions, it shows versatile metal binding abilities through the nitrogen and carbon atoms. This review focuses on the properties of the indole ring in and around the coordination sphere and the structures and bonding modes of Cu(I), Cu(II), Pd(II), and Pt(II) complexes of indole-containing ligands. Reactivities of indole-containing Cu(I) complexes with dioxygen, indole-radical formation by oxidation of Pd(II) and Pt(II) Complexes, and the effects of the proximal indole ring on the reactivity of the Cu(I) center are also reviewed. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ccr.2008.04.012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

D-Alloisoleucine was obtained from L-isoleucine by acetylation and epimerization by acetic anhydride followed by separation of the diastereoisomeric ammonium salts using the solubility difference. The structure-solubility relationship of diastereoisomeric salts was explained by X-ray crystal structure analysis. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tetasy.2008.05.004

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Intramolecular M(II)center dot center dot center dot H-C interactions (M(II)=Cu(II), Pd(II)) involving a side chain alkyl group of planar d(8) and d(9) metal complexes of the N-alkyl (R) derivatives of N,N-bis(2-pyridylmethyl)amine with an N3Cl donor set were established by structural and spectroscopic methods. The methyl group from the branched alkyl group (R = 2,2-dimethylpropyl and 2-methylbutyl) axially interacts with the metal ion with the M center dot center dot center dot C and M center dot center dot center dot H distances of 3.056(3)-3.352(9) and 2.317(1)-2.606(1) angstrom, respectively, and the M-H-C angles of 122.4-162.3 degrees. The Cu(II) complexes showing the interaction have a higher redox potential as compared with those without it, and the H-1 NMR signals of the interacting methyl group in Pd(II) complexes shifted downfield relative to the ligand signals. Dependence of the downshift values on the dielectric constants of the solvents used indicated that the M(II)center dot center dot center dot H-C interaction is mainly electrostatic in nature and may be regarded as a weak hydrogen bond. Implications for possible environmental effects of the leucine alkyl group at the type I Cu site of fungal laccase are also discussed. (C) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jinorgbio.2007.11.022

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Copper(II) complexes of N4-donor ligands containing imidazole moieties, 4-[bis(1-methylimidazole-2-yl-methyl)aminomethyl]imidazole (Him-im(2)) and 4-[bis(1-methylimidazole-2-yl-methyl)aminoethyl]imidazole (Hhis-im2), were prepared, and [Cu(Him-im(2))Cl]ClO4 (1) and [Cu(Hhis-im(2))Cl]ClO4 (2) were structurally characterized by the X-ray diffraction method. Complexes 1 and 2 have a mononuclear structure with a coordinated chloride ion. The geometry of the Cu(II) center in 1 was found to be 5-coordinate trigonal-bipyramidal, whereas that of 2 was square-pyramidal. Complexes 1 and 2 showed different absorption and EPR spectra in MeOH, indicating that these compounds in solution maintain the structures revealed in the solid state. On the other hand, the reaction of Him-im(2) with Cu(ClO4)(2) center dot 6H(2)O under basic conditions gave a tetranuclear Cu(II) complex, [Cu-4(im-im(2))(4)](ClO4)(4) (3), whereas using the ligand Hhis-im(2) gave two kinds of polynuclear complexes [Cu-4(his-im(2))(4)](ClO4)(4) (4) and [Cu-6(his-im(2))(6)](ClO4)(6) (5) exhibiting discretely different structures. X-ray crystal structure analysis of the polynuclear complexes revealed their cyclic structures bridged by the imidazolate moiety. The geometry difference of the Cu(II) centers between 1 and 2 is thus concluded to determine the structures of tetranuclear complexes 3 and 4, respectively. Temperature dependent magnetic susceptibility measurements of complexes 3, 4, and 5 have shown an antiferromagnetic exchange interaction with a coupling constant of J=-32.5, -27.1 and -22.8 cm(-1), respectively. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ica.2007.03.058

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A ligand, 4-methoxy-4 ',4 ''-bis[N,N-bis(2-pyridylmethyl) aminomethyl]triphenyl-amine, and its palladium and copper dinuclear complexes were designed and prepared in order to examine intramolecular interactions between an organic cation radical and the metal ion. Novel NMR techniques, COSY and NOESY, were applied to the palladium complex to examine its conformation in solution. The palladium complex was found to prefer a folded conformation at ambient temperature, indicating the occurrence of intramolecular stacking interaction. CV measurements of the copper complex showed reversible Cu-I/Cu-II and TPA/TPA(+) redox couples. The spin-spin interaction in the radical pendant copper complex generated upon one electron oxidation of the copper complex was examined by cw-ESR measurements. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.10.031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A ligand, 4-methoxy-4 ',4 ''-bis[N,N-bis(2-pyridylmethyl) aminomethyl]triphenyl-amine, and its palladium and copper dinuclear complexes were designed and prepared in order to examine intramolecular interactions between an organic cation radical and the metal ion. Novel NMR techniques, COSY and NOESY, were applied to the palladium complex to examine its conformation in solution. The palladium complex was found to prefer a folded conformation at ambient temperature, indicating the occurrence of intramolecular stacking interaction. CV measurements of the copper complex showed reversible Cu-I/Cu-II and TPA/TPA(+) redox couples. The spin-spin interaction in the radical pendant copper complex generated upon one electron oxidation of the copper complex was examined by cw-ESR measurements. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.10.031

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An attempt was made to use a simple procedure to obtain (R)- and (S)-2-aminobutanoic acids [(R)- and (S)-11 which are non-proteinogenic ct-amino acids and are useful as chiral reagents in asymmetric syntheses. Compound (RS)-1 p-toluenesulfonate [(RS)-2], which is known to exist as a conglomerate, was optically resolved by replacing crystallization with (R)- and (S)-methionine p-toluenesulfonate [(R)- and (S)-3] as optically active co-solutes. When (S)-3 was employed as the cosolute, (R)-2 was preferentially crystallized from a supersaturated solution of (RS)-2 in 1-propanol, as was (S)-2 in the presence of (R)-3. (R)- and (S)-2 recrystallized from 1-propanol were treated with triethylamine in methanol to give (R)- and (S)-1 in optically pure forms.

DOI： 10.1271/bbb.60701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Group 10 metal(II) complexes of H(2)tbu-salen (H(2)tbu-salen = N,N'-bis(3',5'-di-tert-butylsalicylidene)ethylenediamine) and H(2)tbu-salcn (H(2)tbu-salcn = N,N'-bis(3',5'-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) containing two 2,4-di(tert-butyl)phenol moieties, [Ni(tbu-salen)] (1a), [Ni(tbu-salcn)] (1b), [Pd(tbu-salen)] (2a), [Pd(tbu-salcn)] (2b), and [Pt(tbu-salen)] (3), were prepared and structurally characterized by X-ray diffraction, and the electronic structures of their one-electron-oxidized species were established by spectroscopic and electrochemical methods. All the complexes have a mononuclear structure with two phenolate oxygens coordinated in a very similar square-planar geometry. These complexes exhibited similar absorption spectra in CH2Cl2, indicating that they all have a similar structure in solution. Cyclic voltammograms of the complexes showed a quasi-reversible redox wave at E-1/2 = 0.82-1.05 V (vs Ag/AgCl), corresponding to formation of the relatively stable one-electron-oxidized species. The electrochemically oxidized or Ce(IV)-oxidized species of 1a, 2a, and 3 displayed a first-order decay with a half-life of 83, 20, and 148 min at -20 degrees C, respectively. Ni(II) complexes 1a and 1b were converted to the phenoxyl radicals upon one-electron oxidation in CH2Cl2 above -80 degrees C and to the Ni(III)-phenolate species below -120 degrees C. The temperature-dependent conversion was reversible with the Ni(III)-phenolate ground state and was found to be a valence tautomerism governed by the solvent. One-electron-oxidized 1b was isolated as [Ni(tbu-salcn)]NO3 (4) having the Ni(II)-phenoxyl radical ground state. One-electron-oxidized species of the Pd(II) complexes 2a and 2b were different from those of the Ni(II) complexes, the Pd(II)-phenoxyl radical species being the ground state in CH2Cl2 in the range 5-300 K. The one-electron-oxidized form of 2b, [Pd(tbu-salcn)]NO3 (5), which was isolated as a dark green powder, was found to be a Pd(II)-phenoxyl radical complex. On the other hand, the ESR spectrum of the one-electron-oxidized species of Pt(II) complex 3 exhibited a temperature-independent large g anisotropy in CH2Cl2 below -80 degrees C, while its resonance Raman spectrum at -60 degrees C displayed nu(8a) of the phenoxyl radical band at 1600 cm(-1). These results indicated that the ground state of the Pt(II)-phenoxyl radical species has a large distribution of the radical electron spin at the Pt center. One-electron oxidation of 3 gave [Pt(tbu-salen)]NO3 (6) as a solid, where the oxidation state of the Pt center was determined to be ca. +2.5 from the XPS and XANES measurements.

DOI： 10.1021/ja067022r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Ternary Cu(II) complexes containing an aromatic diimine (DA = di(2-pyridylmethyl)amine (dpa), 4,4'-disubstituted 2,2'-bipyridine (Y(2)bpy; Y = H (bpy), Me, Cl, N(Et)(2), CONH2 or COOEt) or 2,2'-bipyrimidine) and an aromatic amino acid (AA = L-phenylalanine (Phe), p-substituted phenylalanine (XPhe; X = NH2, NO2, F, Cl or Br), L-tyrosine (Tyr), L-tryptophan (Trp) or L-alanine (Ala)) were characterized by X-ray diffraction, spectroscopic and potentiometric measurements. The structures of [Cu(dpa)(Trp)]ClO4 center dot 2H(2)O and [Cu((CONH2)(2)bpy)(Phe)]ClO4 center dot H2O in the solid state were revealed to have intramolecular pi-pi interactions between the Cu(II)-coordinated aromatic ring moiety, Cu(DA) (M pi), and the side chain aromatic ring of the AA (L pi). The intensities of M pi-L pi interactions were evaluated by the stability constants of the ternary Cu(II) complexes determined at 25 degrees C and I = 0.1 M (KNO3), which revealed that the stability enhancement of the Cu(DA)(AA) systems due to the interactions is in the order (CONH2)(2)bpy &lt; bpy &lt; Me(2)bpy &lt; (Et2N)(2)bpy with respect to DA. The results indicate that the electron density of coordinated aromatic diimines influences the intensities of the stacking interactions in the Cu(DA)(AA) systems. The M pi-L pi interactions are also influenced by the substituents, X, of L pi and are in linear relationship with their Hammett sigma(p) values with the exception of X = Cl and Br.

DOI： 10.1039/b612394e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In view of the interesting metal-binding properties of lichen substances and the indole ring as a potential ligand, we studied the Pd(II) complexes of indole-containing ligands, N-(indole-3-ethyl)-Delta(2,11)-enaminousnic acid (IEU) and 4-[2-(indol-3-yl)-ethylamino]pent-3-en-2-one (IEP) obtained by condensation of tryptamine with usnic acid and its model acetylacetone, respectively. Reactions of Pd( II) with IEU and IEP gave isomeric complexes resulting from coordination of the C( 3) atom of the indole ring in the 3H-indole form, Pd-2(IEUH-2)(2) (1 and 2) and Pd-2(IEPH-2)(2) (3 and 4) (IEUH-2 and IEPH-2 denote doubly deprotonated forms of IEU and IEP, respectively). Complexes 1-4 were determined, from the NMR and MS spectra, to have dimeric structures doubly bridged by the indole rings, which were stacked in different orientations. X-ray crystal structure analysis of 3 and 4 established that they are indole-bridged dimers of the [C, N, O]-donor palladacycles with the Pd(II) centers in a square-planar geometry formed by a CN2O donor set and are anti and synisomers with respect to the bridging indole rings, respectively. On the basis of the spectral similarity with 4, 1 and 2 were concluded to be stereoisomers assuming the synform with the same donor set. The results demonstrate the metal binding and stacking abilities of the indole ring and the stereoisomerism from the sp(3) C(3) atom formed upon coordination.

DOI： 10.1021/ic060595k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200463071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200463071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The Pd(II) complexes of new 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-iepp), 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-miepp), 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]methylindole (Htbu-impp), and 3- (N-2-pyridylmethyl-N-4-hydroxybenzylamino)ethylindole (Hp-iepp) (H denotes a dissociable proton), were synthesized, and the structures of [Pd(tbu-iepp)Cl] (1a), [Pd(tbu-iepp-c)Cl] (1b), [Pd(tbu-miepp)Ci] (3), and [Pd(p-iepp-c)Cl] (4) (tbu-iepp-c and p-iepp-c denote tbu-iepp and p-iepp bound to Pd(II) through a carbon atom, respectively) were determined by X-ray analysis. Complexes la prepared in CH2Cl2/CH3CN and 3 prepared in CH3CN have a pyridine nitrogen, an amine nitrogen, a phenolate oxygen, and a chloride ion in the coordination plane. Complex 1b prepared in CH3CN has the same composition as 1 a and was revealed to have the C2 atom of the indole ring bound to Pd(II) with the Pd(II)-C2 distance of 1.973(2) Angstrom. The same Pd(II)-indole C2 bonding was revealed for 4. Interconversion between 1a and 1b was observed for their solutions, the equilibrium being dependent on the solvent used. Reaction of 1b and 4 with 1 equiv of Ce(IV) in DMF gave the corresponding one-electron-oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at similar to550 nm, indicating the formation of the Pd(II)-indole pi-cation radical species. The half-lite, t(1/2), of the indole radical species at room temperature was calculated to be 20 s (k(obs) = 3.5 x 10(-2) s(-1)) for 1b. The cyclic voltammogram for 1b in DMF gave two irreversible oxidation peaks at E-pa = 0.68 and 0.80 V (vs Ag/AgCl), which were ascribed to the oxidation processes of the coordinated indole and phenolate moieties, respectively.

DOI： 10.1021/ja031587v

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The Pd(II) complexes of new 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-iepp), 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-miepp), 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]methylindole (Htbu-impp), and 3- (N-2-pyridylmethyl-N-4-hydroxybenzylamino)ethylindole (Hp-iepp) (H denotes a dissociable proton), were synthesized, and the structures of [Pd(tbu-iepp)Cl] (1a), [Pd(tbu-iepp-c)Cl] (1b), [Pd(tbu-miepp)Ci] (3), and [Pd(p-iepp-c)Cl] (4) (tbu-iepp-c and p-iepp-c denote tbu-iepp and p-iepp bound to Pd(II) through a carbon atom, respectively) were determined by X-ray analysis. Complexes la prepared in CH2Cl2/CH3CN and 3 prepared in CH3CN have a pyridine nitrogen, an amine nitrogen, a phenolate oxygen, and a chloride ion in the coordination plane. Complex 1b prepared in CH3CN has the same composition as 1 a and was revealed to have the C2 atom of the indole ring bound to Pd(II) with the Pd(II)-C2 distance of 1.973(2) Angstrom. The same Pd(II)-indole C2 bonding was revealed for 4. Interconversion between 1a and 1b was observed for their solutions, the equilibrium being dependent on the solvent used. Reaction of 1b and 4 with 1 equiv of Ce(IV) in DMF gave the corresponding one-electron-oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at similar to550 nm, indicating the formation of the Pd(II)-indole pi-cation radical species. The half-lite, t(1/2), of the indole radical species at room temperature was calculated to be 20 s (k(obs) = 3.5 x 10(-2) s(-1)) for 1b. The cyclic voltammogram for 1b in DMF gave two irreversible oxidation peaks at E-pa = 0.68 and 0.80 V (vs Ag/AgCl), which were ascribed to the oxidation processes of the coordinated indole and phenolate moieties, respectively.

DOI： 10.1021/ja031587v

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Adduct formations of Pt-II complexes containing an aromatic diimine (DA) and an L-amino acid (A) with an aromatic carboxylate (AR) or a mononucleotide (NMP) has been studied by synthetic, structural, spectroscopic, and calorimetric methods. Several adducts between Pt-II complexes, [Pt(DA)(L-A)] (charges are omitted; DA=2.2'-bipyrimidine (bpm); A=L-arginine (L-Arg), L-alaninate (L-Ala), and AR (=indole-3-acetate (IA), gentisate (GA)) or GMP were isolated as crystals and structurally characterized by the X-ray diffraction method. GMP in [Pt(bpm)(Arg)](GMP).5H(2)O was revealed to be bound through the pi-pi stacking and guanidinium-phosphate hydrogen bonds. ne [Pt(DA)(A)]-AR and -NMP systems in aqueous solution exhibited NMR upfield shifts of the aromatic ring proton signals due to stacking. The stability constants (K) for the adducts were determined by absorption and NMR spectra and calorimetric titrations. The log K values were found to be in the range 1.40-2.29 for AR and 1.8-3.3 for NMP, the order for NMP being GMP &gt; AMP &gt; CMP &gt; UMP. The DeltaHdegrees values were negative for all the systems studied, and the values for AR (= IA and GA) were more negative than those for NMP, indicating that ARs are stronger electron donors than NMPs. Comparison of the log K values for [Pt(bpm)(L-Arg)] and [Pt(bpm)(L-Ala)] (Ala = alaninate) indicated that the Arg moiety further stabilized the adducts by the guanidinium-carboxylate or -phosphate hydrogen bonds. The combined effects of weak interactions on the stability of the adducts in solution are discussed on the basis of the thermodynamic parameters and solid state structures.

DOI： 10.1002/chem.200304728

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Structures and stabilities of ternary copper(II) complexes, Cu(DP)(DA), where DP and DA denote dipeptides with an aromatic amino acid residue and bidentate nitrogen donor ligands, respectively, have been studied by synthetic, crystallographic, potentiometric, and spectroscopic methods. The X-ray crystal structure analysis of [Cu(gly.(L)-tyr)(bzp)] (gly.(L)-tyr = glycyl-(L)-tyrosinate, bzp = N-benzyl-N-2-pyridylmethylamine) revealed that the complex has a distorted square-pyramidal structure exhibiting an intramolecular edge-to-face stacking interaction between the pyridine ring of bzp and the phenol ring of gly.(L)-tyr around the Cu(II) center. [Cu(gly.(L)-tyr)(bzmp)] (bzmp = N-benzyl-N-6-methyl-2-pyridylmethylamine) was also revealed to have a similar structure and an intramolecular CH-pi-type interaction between the methyl group of bzmp and the phenol ring of gly.(L)-tyr. The absorption spectra of the ternary Cu(H)-DP-DA systems in water showed that the ternary complexes have a shoulder peak near 900 nm, supporting that the Cu(II) center has a square-pyramidal geometry. From the stability constants for the ternary Cu(II) complexes determined by pH titration at 25 degreesC and I = 0.1 M (KNO3), Cu(gly.(L)-tyr)(DA) and Cu(gly.(L)-trp)(DA) (DA = ligands with one or two aromatic rings) were found to be stabilized relative to Cu(gly.gly)(DA) (gly.gly = glycylglycinate), which has been concluded to be due to the contribution of the edge-to-face or CH-pi interactions within the complexes in solution. (C) 2002 Elsevier Science B.V. All rights reserved.

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Synthetic, structural, and spectroscopic studies were performed on the copper(H) and palladium(II) complexes of various 2N1O-donor tripod-like ligands containing a pyridine or a dimethylamine nitrogen, a tertiary amine nitrogen, and a phenolate oxygen as donor atoms and a pendent indole ring. [Pd(impp)Cl].3H(2)O.CH3CN (impp = N-2-pyridylmethyl-N-2-hydroxybenzyl-3-aminomethylindole) and two other Pd(II) complexes and a Cu(II) complex were isolated as crystals and structurally characterized by the X-ray diffraction method. The indole moiety of the Pd(II) complexes was found to be located close to the pyridine ring or the dimethylamino group and away from the phenolate moiety. H-1 NMR spectra of the Pd(II) complexes in CD3CN exhibited large upfield shifts of the pyridine and dimethylamino proton signals due to the pendent indole ring, supporting that the complexes in solution have a stacked structure similar to that found in the solid state. These findings indicated that the aromatic ring stacking interactions or CH-pi interactions exist between the indole and the pyridine rings or the methyl groups, respectively. [Cu-2(impp)(2)](ClO4)(2).H2O was revealed to have a dimeric structure with the indole moiety close to both the Cu(II) center and the pyridine ring, which suggests the possibility that the Cu(II) ion may undergo metal-aromatic ring interactions. (C) 2002 Published by Elsevier Science B.V.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

The metal binding properties of a phenolic lichen substance usnic acid (UA) and its acetyl and enamine derivatives 9-O-acetylusnic acid (MAUA), 7,9-di-O-acetylusnic acid (DAUA), Delta(2,11)-enaminousnic acid (EUA), and N-substituted Delta(2,11)-enaminousnic acids have been studied by synthetic and spectroscopic methods, and the structures of copper(II) and palladium(II) complexes have been established by the X-ray diffraction method. Cu(II) reacted with UA and DAUA to give the binary complexes Cu(UA)(2).H2O and Cu(DAUA)(2), respectively, and Cu(bpy) (bpy=2,2'-bipyridine) formed ternary complexes with UA and DAUA. Pd(II) also reacted with UA, DAUA, EUA, and N-substituted Delta(2,11)-enaminousnic acids to give the corresponding binary complexes. All the isolated complexes are insoluble in water and soluble in most organic solvents. They exhibited very strong absorption and circular dichroism spectral peaks in the UV region. The H-1-NMR spectrum in CDCl3 of the Pd(II) complex of N-phenyl-Delta(2,11)-enaminousnic acid (PEUA), Pd(PEUA)(2).C6H6, showed that the C-4-proton signal suffered a large upfield shift (0.86 ppm) due to the ring current effect of the N-phenyl moiety. X-Ray crystal structure analysis has been performed for Cu(bpy)(UA)(ClO4).CH3OH, Pd(MEUA)(2).C6H6, and Pd(PEUA)(2).C6H6. Cu(bpy)(UA)(ClO4).CH3OH has a square-pyramidal structure with the two nitrogen atoms of bpy and the two oxygen atoms of the mono-deprotonated B ring of UA in the equatorial positions, while Pd(II) binds with two molecules of MEUA or PEUA in the trans configuration through the nitrogen and oxygen atoms with deprotonation. The N-phenyl ring of PEUA in Pd(PEUA)(2).C6H6 was revealed to be located close to the C-4 proton as indicated by H-1-NMR. Isolation of Cu-2(bpy)(2)(UA)(NO3)(2).2H(2)O suggests that UA has two metal binding sites that can form polymeric complexes. The present results substantiate the metal binding ability and the structures of the complexes of usnic acid and other substances from lichens as biomonitors of environmental metal ions. (C) 2002 Elsevier Science Inc. All rights reserved.

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Electrostatic ligand-ligand interactions in ternary copper(II) complexes, Cu(AA)(PA), where AA refers to an aromatic amino acid (AA = 3,5-diiodo-L-tyrosinate (L-I(2)tyr), L-tyrosinate (L-Tyr), or L-phenylalaninate (L-Phe)) and PA refers to an amino acid with a polar or charged side-chain (PA = L-argininate (L-Arg), omega-protonated L-lysinate (L-LysH), L-asparaginate (L-Asn), L-glutaminate (L-Gln), or L-alaninate (L-Ala)), have been studied by potentiometric and spectroscopic methods. The stability constants for Cu(AA) (PA) were determined by pH titrations at 25 degrees C and I = 0.1 M (KNO3). The stability enhancement due to electrostatic interactions in Cu(AA) (PA) has been evaluated by several methods including the constant K for the following hypothetical equilibrium calculated from the determined overall stability constants of the relevant ternary complexes:
Cu(AA) (L-Ala) + C(L-Phe) (PA) reversible arrow(K) Cu(AA) (PA) + Cu(L-Phe) (L-Ala)
While the log K values were small or negative for Cu(L-I(2)tyr) (L-Asn), Cu(L-I(2)tyr) (L-Gln), and Cu(L-Tyr) (PA) with the protonated phenol OH group, large positive log K values were obtained for Cu(L-I(2)tyrO(-))(L-Arg) (0.40) and Cu(L-I(2)tyrO(-))(L-LysH) (0.41) with the deprotonated phenol moiety, which indicates that they are stabilized by intramolecular electrostatic interactions between the oppositely charged side groups of the coordinated ligands. Comparison of the H-1 NMR spectra of Pd(L-I(2)tyrO(-))(L-LysH) and Pd(L-Ala)(L-LysH) in D2O indicated the interaction between the diiodophenolate moiety of I(2)tyrO(-) and the protonated omega-amino group of LysH. The circular dichroism spectra observed in the d-d region for these complexes exhibited an anomalously large negative maximum near 600 nm, supporting the existence of such interactions in the complexes in solution. Contribution of the iodo groups to the interactions was discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Structures and spectroscopic studies have been carried out on ternary copper(II) complexes, Cu(DA)(AA), with aromatic amino acids (AA = 3,5-diiodo-L-tyrosinate (L-I(2)tyr), 3-iodo-L-tyrosinate (L-Ityr), L-tyrosinate) and diamines (DA = 1,10-phenanthroline, 2,2'-bipyridine (bpy), 2-(aminomethyl)pyridine, histamine (hista), or ethylenediamine). The charge transfer (CT) absorption bands observed in the near UV region and the CD spectral magnitude anomaly observed in the d-d region indicated an effective aromatic ring stacking interaction between the side-chain phenol ring of AA and the aromatic diamine DA in the complexes in solution. Two complexes, [Cu(bpy)(L-Ityr)(H2O). NO3 . CH3OH . H2O (1) and [Cu(hista)(L-I(2)tyrO(-))(H2O)](2) . 2H(2)O (2), where O- represents the deprotonated form of the phenol hydroxyl group, were isolated as single crystals, and their structures were determined by X-ray analysis. Both 1 and 2 crystallized in the monoclinic space group P2(1), with a = 7.549(1) Angstrom, b = 11.431(1) Angstrom, c = 14.292(2) Angstrom, beta = 100.08(1)degrees, and Z = 2 for 1 and a = 9.9642(9) Angstrom, b = 15.825(1) Angstrom, c = 12.451(1) Angstrom, beta = 91.565(7)degrees, and Z = 2 for 2. The molecular structures of 1 and 2 revealed the intramolecular aromatic ring stacking between DA and the iodinated phenol ring of Ityr and I(2)tyrO(-), respectively, in correspondence with the solution spectral observations. The stacking with hista was found to be weaker than that with bpy from the interplanar distances in 1 and 2 and the CT band intensities in solution. The molecular and crystal structures revealed some intermolecular iodine-aromatic ring and iodine-oxygen interactions as well as some hydrogen bonds involving the phenol hydroxyl group.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN BIOCHEMICAL SOC  

The site-directed mutants of negative. patches on silene plastocyanin (PC) were used to investigate the change of interactions between photosystem I (PSI) and PC during the course of evolution from cyanobacteria to plants. The net charges of two highly conserved negative patches (#42-45 and #59-61) on silene PC were systematically modified from -4 to +1. PSI complexes from cucumber and Chlamydomonas reinhardtii were efficient electron accepters for silene PC. The increase of net charge on the negative patch (#42-45) of silene PC decreased the reduction rates of PSI from cucumber and Chlamydomonas, while the modification of the other negative patch (#59-61) had no effect. Though the addition of MgCl2 decreased the reduction rate of cucumber PSI, the decrease was severely diminished in the case of Chlamydomonas PSI, and the reduction rate increased with increasing concentration of MgCl2 when the net charge of the negative patch (#42-45) was modified to +1. The PSI complexes from Anabaena variabilis and Synechosystis sp, PCC 6803 were inefficient electron acceptors for silene PC and their rates were almost independent of the net charge of the negative patches, as well as the ionic strength of the reaction mixtures. Silene PC specifically cross-linked to the PsaF subunit of PSI complexes from cucumber, Chlamydomonas, Anabaena, and Synechosystis sp, PCC 6803. Modification of the negative patch (#42-45) inhibited the formation of cross-linked, adducts in all the cases examined, whereas modification of the other negative patch (#59-61) had essentially no effect. Based on these results, the changes of electrostatic interactions between PC and PSI during the course of evolution from cyanobacteria to plants are discussed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Ternary copper(II) complexes containing an acidic amino acid (A) and a basic amino acid (B), Cu(A)(B), where A refers to ethylenediamine-N-monoacetic acid (EDMA) and DL-2,3-diaminopropionic acid (DAP) and B to L-arginine (L-Arg) and L-lysine (L-Lys), have been investigated by absorption and circular dichroism (CD) spectral, solution equilibrium, and X-ray diffraction methods with emphasis on ligand-ligand interactions. Deviations of the CD spectral magnitudes from additivity were observed for the systems Cu(A)(B) where ligand-ligand hydrogen bonds or electrostatic interactions exist between the oppositely charged side chains. Evaluation of the stability enhancement by such intramolecular interactions has been made by considering the following hypothetical equilibrium (charges are omitted): Cu(A)(B') + Cu(A')(B) half arrow right over half arrow left Cu(A)(B) + Cu(A')(B') (K), where A' and B' are ligands without an interacting side chain group such as valine (Val) and ethylenediamine, respectively, and ligand-ligand interactions are possible only in Cu(A)(B). The log K value which is defined to be equal to zero in the absence of interactions was calculated for each Cu(A)(B) from the overall stability constants of the relevant ternary complexes determined at 25-degrees-C and I = 0.1 M (KNO3) to be in the order Cu(DAP)(L-Arg) (0.63) &gt; Cu(EDMA)(L-Arg) (0.15) approximately Cu(EDMA)(L-Lys) (0.14) approximately Cu(DAP)(L-Lys) (0.16) &gt; Cu(EDMA)(L-Val) approximately Cu(DAP)(L-Val) approximately 0. The stability difference between Cu(EDMA)(L-Arg) and Cu(DAP)(L-Arg) was inferred to be due to steric requirements for intramolecular ligand-ligand interactions. X-ray crystal structure analysis has been performed on [Cu(EDMA)(L-Arg)ClO4].1/2C2H5OH(1)and[CU(L-Arg)2](NO3)2.3H2O(2). Complex 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1) with four molecules in a unit cell of dimensions a = 7.824(3) angstrom, b = 24.979(3) angstrom, and c = 10.617(4) angstrom. The Cu(II) ion is in a slightly distorted square-pyramidal geometry with the two nitrogen atoms of EDMA and the nitrogen and oxygen atoms of L-Arg coordinated at the equatorial positions and the carboxylate oxygen atom of EDMA coordinated at an axial position. A perchlorate oxygen atom weakly coordinates at the other axial site. The coordinated carboxylate group of EDMA is hydrogen-bonded to the positively charged guanidinium group of L-Arg of a neighboring complex molecule with the N...O distances of 2.89 and 2.85 A. Complex 2 crystallizes in the monoclinic space group C2 with four molecules in a unit cell of dimensions a = 26.680(3) angstrom, b = 7.320(1) angstrom, c = 12.772(1) angstrom, and beta = 92.08(1)-degrees. The Cu(II) ion has a square-planar geometry with the two nitrogen and two oxygen atoms of two coordinated L-Arg molecules in a cis configuration with respect to the amino groups, which are hydrogen-bonded to an uncoordinated nitrate ion. The side chain guanidinium group is also hydrogen-bonded to two uncoordinated nitrate ions with the N...O distances of 2.84-2.97 angstrom. On the basis of the log K values and the crystal structures, intermolecular interactions involving the arginine guanidinium group were inferred to be more specific than those involving the lysine ammonium group, and their biological implication was discussed.

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：FEDERATION AMER SOC EXP BIOL  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER SCIENCE INC  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER SCIENCE INC  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER SCIENCE INC  

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