Vibrational spectroscopic studies of conformation of poly(oxyethylene). II. Conformation–spectrum correlations

Detailed normal-coordinate analysis has been carried out on a large number of conformers of model molecules of poly(oxyethylene); the model molecules treated are CH₃(OCH₂CH₂)_nOCH₃ with n = 2,3, and 6. The systematic treatment provides well-defined correlations between conformation and vibrational spectra of poly(oxyethylene). The vibrations in the region 1050–800 cm^?1, which are associated with the C? O and C? C stretching and CH₂ rocking modes, are highly dependent on the conformation of the polymer chain. On the basis of these correlations, the infrared and Raman spectra of the molten state and of the aqueous solution are interpreted in terms of the conformational states. The analysis indicates that the following conformational fragments are present in these phases: GT-TG (T: trans; G: gauche), TT-TG, GT-GG, TT-TT, and TT-GG for the CH₂? CH₂? O? CH₂? CH₂ group, and TGT and TGG for the O? CH₂? CH₂? O group. Conformational fragments GT-TG′ and GT-G′G′ are also possible in the analogy to GT-TG and GT-GG.     

Size- and shape-dependent activity of metal nanoparticles as hydrogen-evolution catalysts: mechanistic insights into photocatalytic hydrogen evolution

The catalytic activity of Pt nanoparticles (PtNPs) with different sizes and shapes was investigated in a photocatalytic hydrogen‐evolution system composed of the 9‐mesityl‐10‐methylacridinium ion (Acr⁺–Mes: photocatalyst) and dihydronicotinamide adenine dinucleotide (NADH: electron donor), based on rates of hydrogen evolution and electron transfer from one‐electron‐reduced species of Acr⁺–Mes (Acr^.–Mes) to PtNPs. Cubic PtNPs with a diameter of (6.3±0.6) nm exhibited the maximum catalytic activity. The observed hydrogen‐evolution rate was virtually the same as the rate of electron transfer from Acr^.–Mes to PtNPs. The rate constant of electron transfer (k_et) increased linearly with increasing proton concentration. When H⁺ was replaced by D⁺, the inverse kinetic isotope effect was observed for the electron‐transfer rate constant (k_et(H)/k_et(D)=0.47). The linear dependence of k_et on proton concentration together with the observed inverse kinetic isotope effect suggests that proton‐coupled electron transfer from Acr^.–Mes to PtNPs to form the Pt? H bond is the rate‐determining step for catalytic hydrogen evolution. When FeNPs were used instead of PtNPs, hydrogen evolution was also observed, although the hydrogen‐evolution efficiency was significantly lower than that of PtNPs because of the much slower electron transfer from Acr^.–Mes to FeNPs.     

Disproportionation of dipyrrolylquinoxaline radical anions via the internal protons of the pyrrole moieties

Disproportionation of dipyrrolylquinoxaline radical anions occurs via hydrogen atom transfer from the pyrrole moiety to the quinoxaline moiety to produce monodeprotonated dipyrrolylquinoxaline anions and monohydrodipyrrolylquinoxaline anions. In contrast, simple quinoxaline radical anions without pyrrole moieties are stable, and disproportionation occurs only in the presence of external protons.     

Photocatalytic hydrogen evolution under highly basic conditions by using Ru nanoparticles and 2-phenyl-4-(1-naphthyl)quinolinium ion

Photocatalytic hydrogen evolution with a ruthenium metal catalyst under basic conditions (pH 10) has been made possible for the first time by using 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh(+)-NA), dihydronicotinamide adenine dinucleotide (NADH), and Ru nanoparticles (RuNPs) as the photocatalyst, electron donor, and hydrogen-evolution catalyst, respectively. The catalytic reactivity of RuNPs was virtually the same as that of commercially available PtNPs. Nanosecond laser flash photolysis measurements were performed to examine the photodynamics of QuPh(+)-NA in the presence of NADH. Upon photoexcitation of QuPh(+)-NA, the electron-transfer state of QuPh(+)-NA (QuPh(?)-NA(?+)) is produced, followed by formation of the π-dimer radical cation with QuPh(+)-NA, [(QuPh(?)-NA(?+))(QuPh(+)-NA)]. Electron transfer from NADH to the π-dimer radical cation leads to the production of 2 equiv of QuPh(?)-NA via deprotonation of NADH(?+) and subsequent electron transfer from NAD(?) to QuPh(+)-NA. Electron transfer from the photogenerated QuPh(?)-NA to RuNPs results in hydrogen evolution even under basic conditions. The rate of electron transfer from QuPh(?)-NA to RuNPs is much higher than the rate of hydrogen evolution. The effect of the size of the RuNPs on the catalytic reactivity for hydrogen evolution was also examined by using size-controlled RuNPs. RuNPs with a size of 4.1 nm exhibited the highest hydrogen-evolution rate normalized by the weight of RuNPs.     

Regio- and stereoselective multisubstituted enol ester synthesis

Regio- and stereoselective cohalogenation of alkynes with NXS (X = Br, I) was achieved, and the stereoselectivity of the resulting alkenes was dependent on the substituent on the alkyne. Cohalogenation and successive cross-coupling gave multisubstituted enol esters in a one-pot process.     

Culcitiolides A-D, four new eremophilane-type sesquiterpene derivatives from Senecio culcitioides

Four new eremophilane-type sesquiterpenes, culcitiolides A-D, were isolated from the stem of Senecio culcitioides Sch. Bip (Asteraceae). Their structures were established by detailed 2D NMR spectroscopic and single-crystal X-ray experiments. These compounds were assessed for inhibitory activity against nuclear factor kappaB (NF-kappaB). Culcitiolides C and D at 20 microM showed 97 and 100% inhibition of NF-kappaB activity, respectively.     

Isolation of antitrypanosomal compounds from Vitis repens, a medicinal plant of Myanmar

Bioactivity-guided fractionation of an ethanolic extract of Vitis repens led to the isolation of resveratrol (1), 11-O-acetyl bergenin (2), and stigmast-4-en-3-one (3). The compounds were examined for their in vitro antitrypanosomal activities against trypomastigotes of Trypanosoma evansi. Resveratrol showed antitrypanosomal activity with an IC50 value of 0.13 microM, whereas 11-O-acetyl bergenin and stigmast-4-en-3-one exhibited IC50 values of 0.17 and 0.15 microM, respectively.     

Preparation of mesoporous silicas using food grade emulsifiers and its application for enzyme supports

A novel mesoporous silica (TMPS) was synthesized via self-assembly using a myristic acid ester of pentaglycerol. The ester is obtained from catalytic esterification and it is commercially available as a food grade emulsifier. TMPS material was employed for preparation of a biocatalyst in order to examine the ability as an enzyme support in comparison with the other mesoporous silica materials having a channel or a cage-like pore system. The used TMPS materials possessed the interconnected channel-like pore system with the pore sizes of 9.2, 12, and 16 nm. The materials successfully entrapped lipase into their mesopores with the high loadings. The resultant lipase/TMPS conjugates functioned as the biocatalyst for hydrolysis of p-nitrophenyl propionate (p-NPP), having the higher activity than those of the used mesoporous silica conjugates. The high activities were ascribed to the textural properties such as the small particle length, large pore size and the three-dimensional pore connectivity that permit the accessibility of p-NPP to the immobilized lipases during the reactions. Consequently, we concluded that TMPS materials are of the suitable mesoporous support for the enzymes.     

Bioactive Polymeric Metallosomes Self-Assembled through Block Copolymer-Metal Complexation

Spontaneous formation of polymeric metallosomes with uniform size (～100 nm) was found to occur in aqueous medium through the reaction of an anticancer agent, (1,2-diaminocyclohexane)platinum(II) (DACHPt), with a Y-shaped block copolymer of ω-cholesteroyl-poly(l-glutamic acid) and two-armed poly(ethylene glycol) (PEGasus-PLGA-Chole). Circular dichroism spectrum measurements revealed that the PLGA segment forms an α-helix structure within the metallosomes, suggesting that secondary-structure formation of metallocomplexed PLGA segment may drive the self-assembly of the system into vesicular structure. These metallosomes can encapsulate water-soluble fluorescent macromolecules into their inner aqueous phase and eventually deliver them selectively into tumor tissues in mice, owing to the prolonged blood circulation. Accordingly, fluorescent imaging of the tumor was successfully demonstrated along with an appreciable antitumor activity by DACHPt moieties retained in the vesicular wall of the metallosomes, indicating the potential of metallosomes as multifunctional drug carriers.     

Utilization of photoinduced charge-separated state of donor-acceptor-linked molecules for regulation of cell membrane potential and ion transport

The control of ion transport across cell membranes by light is an attractive strategy that allows targeted, fast control of precisely defined events in the biological membrane. Here we report a novel general strategy for the control of membrane potential and ion transport by using charge-separation molecules and light. Delivery of charge-separation molecules to the plasma membrane of PC12 cells by a membranous nanocarrier and subsequent light irradiation led to depolarization of the membrane potential as well as inhibition of the potassium ion flow across the membrane. Photoregulation of the cell membrane potential and ion transport by using charge-separation molecules is highly promising for control of cell functions.