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The reaction of CuII ion with dimethylaminophenolate ligands gave CuI–phenoxyl radical complexes under inert gas atmosphere in the absence of solvent coordination, and their electronic and geometric structures and reactivities were characterized.

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.

Five triphenyltriphenylamines with various substituents were investigated as precursors for near-infrared absorbing materials. Cyclic voltammetry (CV) studies showed that they all give stable radical cations in solution. The radical cations obtained by one-electron chemical oxidation of these compounds show strong absorption in the near-infrared region, and the position of the absorption is strongly influenced by the substituent. DFT (density functional theory) calculations suggest that the introduction of stronger electron-donating substituents would result in a smaller HOMO–SOMO energy gap and thus a larger long wavelength shift, which is consistent with the experimental results. On the other hand, strong electron-withdrawing substituents increase the HOMO–SOMO energy gap, resulting in a short wavelength shift. The position of the near-infrared absorption peak of the triphenylamine radical cation can be controlled to the longer or shorter wavelength direction depending on the substituent. A molecular design of near-infrared absorbing dyes utilizing the electronic effects of substituents is described.

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 third-generation catalyst. The product, poly(norbornene) [poly(1)], was investigated as a sensitizer for triplet–triplet annihilation upconversion (TTA–UC), together with the copolymers of 1 and 2-norbornene 2. All the polymers exhibited bright photoluminescence under N2. 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.

A reaction of Ni(ClO4)2·6H2O with a tripodal ligand having two di(tert-butyl)phenol moieties, H2tbuL, and 1 equivalent of triethylamine in CH2Cl2/CH3OH (1 : 1, v/v) under N2 gave a NiII-(phenol)(phenolate) complex, [Ni(HtbuL)(CH3OH)2]ClO4. The formation of the NiII-phenoxyl radical complex by O2 was observed in the reaction of this complex in the solid state. On the other hand, the NiII-phenoxyl radical complex [Ni(Me2NL)(CH3OH)2]ClO4 was obtained by the reaction of H2Me2NL having a p-(dimethylamino)phenol moiety with Ni(ClO4)2·6H2O in a similar procedure under O2, through the oxidation of the NiII-(phenol)(phenolate) complex. However, a direct redox reaction of the NiII ion could not be detected in the phenoxyl radical formation. The results of the reaction kinetics, XAS and X-ray structure analyses suggested that the O2 oxidation from the NiII-(phenol)(phenolate) complex to the NiII-phenoxyl radical complex occurs via the proton transfer–electron transfer (PT–ET) type mechanism of the phenol moiety weakly coordinated to the nickel ion.

Chirally regulated π-conjugated polymers containing platinum (Pt) complex moieties have great potential as chiroptically functional materials. In this study, novel platinum-containing conjugated po...

A novel benzoxazine derivative, 9,10-bis­(6-ethynyl-3-phenyl-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 (Φ = 81%). Compound 1a afforded solvent-insoluble cross-linked polybenzoxazine 1b by the bulk polymerization at 250 °C. Solution polymerization of a dilute solution of 1a at 200 °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 °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.

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 440 nm with a fluorescence quantum ...

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.

The site characterization around the Fukushima Daiichi nuclear power plant (FDNPP) was conducted to measure the dose rate of radioactive cesium using mobile gamma-ray spectrometry through a backpack survey based on a LaBr3(Ce) detector. Four sites were selected in the Fukushima prefecture with diverse dose rate levels in residence and non-residence areas. One reference site in Sendai city was also designated with a low dose rate in comparison with sites in the Fukushima prefecture. The ambient dose rate was distributed from several tens of dose rate to above 1 μGy h due to the radioactive cesium distributed on the ground of the Fukushima prefecture. To assess the dose rates of Cs and Cs using the backpack survey with a short acquisition time, a good correlation was identified between the dose rate of radioactive cesium and the gross count rate in specific regions of interest (ROIs) with gamma rays from radioactive cesium. The dose rates of Cs and Cs accounted for more than 25% of the ambient dose rate during the survey period. The ratio of the Cs dose rate to the Cs dose rate was shown to be about 30% for all survey sites.

Reaction of Cu(ClO4 )2 ⋅6 H2 O with a tripodal 2N2O ligand, H2 Me2 NL, having a p-(dimethylamino)phenol moiety, in CH2 Cl2 /MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me2 NL)(H2 O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me2 NL)(MeOH)]ClO4 (2), which could be obtained also from the isolated complex 1 by reaction with O2 in CH2 Cl2 /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 CuII EPR signals of the d x 2 - y 2 ground state in CH2 Cl2 /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 CuII -(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH2 Cl2 solution of 1 exhibits distortion from the d x 2 - y 2 ground state and a temperature-dependent equilibrium between the CuII -(dimethylamino)phenolate and the CuI -(dimethylamino)phenoxyl radical. From these results, CuII -phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O2 via the CuI -phenoxyl radical species.

Ground-based gamma-ray spectrometry using a LaBr3(Ce) detector was conducted to assess radioactive cesium deposition in soil contaminated by the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan. Five sites, including a reference site with relatively low contamination, were selected as having different levels of ambient dose rate due to significant effects of radioactive fallout of 134Cs and 137Cs. According to ICRU Report 53, the radioactivity in the ground and dose rate at 1 m above the ground were determined from the measured net count rates of gamma-rays induced from radioactive cesium. Because the radioactivity and dose rate depended on the depth profile of radioactive cesium in the ground, a database of possible radioactivity and dose rate could be established according to several depth distributions. A new approach to estimate the depth profile was then developed by directly calculating dose rates of 134Cs and 137Cs at the same geometry through dose rate spectroscopy and comparing them with the database of possible dose rates of radioactive cesium. Once the depth profile was determined, radioactivity was estimated from the database depending on the depth profile in the ground. The activity ratio between two radioactive cesium was shown to average about 0.112, in December 2017. It was in good agreement with the originally same released amount of 134Cs and 137Cs at the time of the FDNPP accident, when physical decay correction was applied to the results of the radioactivity assessment.

In order to gain new insights into the effect of the π-π stacking interaction of the indole ring with the CuII -phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a CuII 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 CuII complex exhibited the π-π 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 π-π stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized CuII 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 π-π stacking interaction.

A dust monitor with a silicon surface barrier detector (SSBD) is introduced at a nuclear fuel facility to detect airborne contamination of 238Pu and 239Pu released by past accidents. However, an SSBD frequently produces false alarms, especially in a room with high humidity. To develop a highly reliable dust monitor, we developed an alpha-particle spectrometer based on a cerium-doped Gd2Si2O7 (GPS) scintillator plate and a photomultiplier tube (PMT). The GPS scintillator plate is hexagonal and 50 mm in diameter, and the scintillator layer is approximately 40 μm. An output signal from the PMT is amplified by a preamp and transferred to an MCA. Then, an energy spectrum is displayed in real time. The 241Am alpha source, Rn progeny collected on the air filter, and a PuO2 particle were measured by our developed spectrometer. The energy resolution for 5.5-MeV alpha particles was ∼11.9% ± 0.2% of the FWHM. The efficiency was 92%, and it had a uniform sensitivity. By applying an energy window, the count-rate of the Rn progeny decreased by 77%. The GPS scintillator plate was able to measure the alpha spectrum even though the GPS scintillator got wet. Therefore, the alpha dust monitor using the GPS scintillator plate is ideal for detecting alpha-particle emitters in places lacking temperature and humidity controls, such as the outside of buildings.

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/O2 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.

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.

The Sonogashira–Hagihara coupling polymerization of a D-hydroxyphenylglycine-derived diiodoarylene monomer and platinum-containing diethynylphenylene monomers with various substituents, HCC–C6H4–CC–Pt(PR3)2–CC–C6H4–CCH, 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.

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 α-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-hydroxymethyl-3-methyloxindole 2 without silica gel column chromatography., Part of this work was supported by the Kansai University Subsidy for Supporting Young Scholars, 2015 “Development of macrocyclization reaction via a photoaffinity reaction”, JSPS KAKENHI Grant Number 15K18903, Grant-in-Aid for Young Scientists (B) – Japan and MEXT – Supported Program for the Strategic Research Foundation at Private Universities (2013–2017) – Japan., 2015年度関西大学若手研究者育成経費

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.

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.

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.

Ground-based gamma-ray spectrometry using a LaBr

Reaction of Cu(ClO

In order to gain new insights into the effect of the π–π stacking interaction of the indole ring with the phenoxyl radical moiety as seen in the active form of galactose oxidase, we have prepared Ni(II) 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(II) 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 π–π 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(II)-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 π–π 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 π–π 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 the π–π stacking interaction.

In order to gain new insights into the effect of the π-π stacking interaction of the indole ring with the Cu

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.

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.

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]

The crystal structures ofN-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 21screw axis, forming a helical column which consists of ammonium ions and single enantiomeric anions similar to the crystals of the ammonium salts of optically activeN-acetyl-L-isoleucine andN-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 21column. AmmoniumN-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.

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 [PdCl2(CH3CN)2] at room temperature gave [Pd(L)Cl2] (1) as pale yellow crystals. The X-ray crystal structure analysis and 1H 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 CH2Cl2/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.

This paper focuses on the effects of the PSt content of polystyrene (PSt)-poly (dimethylsiloxane) (PDMS) interpenetrateing network (IPN) polymer membranes, on the pervaporation (PV) characteristics during the removal of benzene from an aqueous solution of dilute benzene. When an aqueous solution of 0.05wt% benzene was permeated through the PSt-PDMS IPN membranes, they showed high benzene/water selectivity. Both the permeability and the benzene/water selectivity of the membranes were enhanced with increasing PSt content in the PSt-PDMS IPN membrane. The physicochemical mechanism of permeation and separation through the PSt-PDMS IPN membranes during PV is also discussed. The best normalized permeation rate, separation factor for benzene selectivity, and PV separation index of the PSt-PDMS IPN membrane were 1.27 × 10-6 kgm (m2hr)-1, 3293, and 41821, respectively. These PV characteristics are discussed from the viewpoint of the chemical and physical structure of the PSt-PDMS IPN membranes.

Zinc(II) complexes of N3O-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] · CH3OH (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 °C (I = 0.1 M (KNO3)). The stability of the complexes was found to be in the order L > LMepy > 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 π–π∗ 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 E1/2 = 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 °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 N3O-donor ligands.

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 © 2009 European Peptide Society and John Wiley & Sons, Ltd.

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.

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 CH3CN 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) A. 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 1H 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-π-cation radical species. The half-life, t1/2, of the radical species at −60 °C was calculated to be 43 s (kobs = 1.6 × 10−2 s−1).

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′-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, log K, 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 1H NMR spectra at 25 °C in D2O (I = var.). The structure of the adduct [Pt(Ala)(phen)](AQS) (1) was determined by X-ray analysis to involve a π–π stacking interaction between coordinated phen and AQS with the distance of 3.400(7) A 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, E1/2, for the two-electron redox process of FMN shifted to higher values by 18–31 mV as compared with the value for free FMN.

Intramolecular M(II)⋯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 N 3 Cl 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⋯C and M⋯H distances of 3.056(3)–3.352(9) and 2.317(1)–2.606(1) A, respectively, and the M–H–C angles of 122.4–162.3°. The Cu(II) complexes showing the interaction have a higher redox potential as compared with those without it, and the 1 H 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)⋯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 1 Cu site of fungal laccase are also discussed.

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-im 2 ), were prepared, and [Cu(Him-im 2 )Cl]ClO 4 ( 1 ) and [Cu(Hhis-im 2 )Cl]ClO 4 ( 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(ClO 4 ) 2 · 6H 2 O under basic conditions gave a tetranuclear Cu(II) complex, [Cu 4 (im-im 2 ) 4 ](ClO 4 ) 4 ( 3 ), whereas using the ligand Hhis-im 2 gave two kinds of polynuclear complexes [Cu 4 (his-im 2 ) 4 ](ClO 4 ) 4 ( 4 ) and [Cu 6 (his-im 2 ) 6 ](ClO 4 ) 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.

An attempt was made to use a simple procedure to obtain (R)- and (S)-2-aminobutanoic acids [(R)- and (S)-1] which are non-proteinogenic alpha-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 co-solute, (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.

Group 10 metal(II) complexes of H2tbu-salen (H2tbu-salen = N,N'-bis(3',5'-di-tert-butylsalicylidene)ethylenediamine) and H2tbu-salcn (H2tbu-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 E1/2 = 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 nu8a 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.

金沢大学医薬保健研究域 薬学系, Ternary Cu(ii) complexes containing an aromatic diimine (DA = di(2-pyridylmethyl)amine (dpa), 4,4′-disubstituted 2,2′-bipyridine (Y2bpy; 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)]ClO4·2H 2O and [Cu((CONH2)2bpy)(Phe)]ClO 4·H2O in the solid state were revealed to have intramolecular π-π interactions between the Cu(ii)-coordinated aromatic ring moiety, Cu(DA) (Mπ), and the side chain aromatic ring of the AA (Lπ). The intensities of Mπ-Lπ interactions were evaluated by the stability constants of the ternary Cu(ii) complexes determined at 25 °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 (CONH 2)2bpy < bpy < Me2bpy < (Et 2N)2bpy 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 Mπ-Lπ interactions are also influenced by the substituents, X, of Lπ and are in linear relationship with their Hammett σp values with the exception of X = Cl and Br. © The Royal Society of Chemistry

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)Cl] (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 1a prepared in CH(2)Cl(2)/CH(3)CN and 3 prepared in CH(3)CN have a pyridine nitrogen, an amine nitrogen, a phenolate oxygen, and a chloride ion in the coordination plane. Complex 1b prepared in CH(3)CN has the same composition as 1a 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) A. 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 approximately 550 nm, indicating the formation of the Pd(II)-indole pi-cation radical species. The half-life, 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.

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).5 H(2)O was revealed to be bound through the pi-pi stacking and guanidinium-phosphate hydrogen bonds. The [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>AMP>CMP>UMP. The DeltaH degrees 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.

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-π-type interaction between the methyl group of bzmp and the phenol ring of gly· l- tyr. The absorption spectra of the ternary Cu(II)–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 °C 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-π interactions within the complexes in solution.

Synthetic, structural, and spectroscopic studies were performed on the copper(II) 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]·3H2O·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. 1H 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–π interactions exist between the indole and the pyridine rings or the methyl groups, respectively. [Cu2(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.