Charge-transfer mechanism for cytochrome c adsorbed on nanometer thick films. Distinguishing frictional control from conformational gating

Using nanometer thick tunneling barriers with specifically attached cytochrome c, the electron-transfer rate constant was studied as a function of the SAM composition (alkane versus terthiophene), the omega-terminating group type (pyridine, imidazole, nitrile), and the solution viscosity. At large electrode-reactant separations, the pyridine terminated alkanethiols exhibit an exponential decline of the rate constant with increasing electron-transfer distance. At short separations, a plateau behavior, analogous to systems involving -COOH terminal groups to which cytochrome c can be attached electrostatically, is observed. The dependence of the rate constant in the plateau region on system properties is investigated. The rate constant is insensitive to the mode of attachment to the surface but displays a significant viscosity dependence, change with spacer composition (alkane versus terthiophene), and nature of the solvent (H(2)O versus D(2)O). Based on these findings and others, the conclusion is drawn that the charge-transfer rate constant at short distance is determined by polarization relaxation processes in the structure, rather than the electron tunneling probability or large-amplitude conformational rearrangement (gating). The transition in reaction mechanism with distance reflects a gradual transition between the tunneling and frictional mechanisms. This conclusion is consistent with data from a number of other sources as well.     

Surface interaction forces mediated by poly(N-isopropylacrylamide) (PNIPAM) polymers: effects of concentration and temperature

Total internal reflection microscopy was used to directly measure the interaction potentials between a micron-sized silica sphere and a flat silica surface in the presence of a linear poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. When the PNIPAM concentration was low, no discernible forces were detected. A further increase in PNIPAM concentration resulted in a long-range attraction which was likely due to a combined of the reduced electrostatic interaction between the silica particle and the flat surface after the polymer adsorption and polymer bridges formation. On the other hand, for a fixed PNIPAM concentration, the interaction potential profiles between the particle and flat surface were once again characterized by attraction as temperature was increased. This attractive force can be explained in terms of the conformational changes of PNIPAM chains at the surfaces, which subsequently affected the polymer adsorption and enhanced the segment–segment interaction among the adsorbed polymer chains.     

Optimization of microwave-assisted extraction of polyphenols from apple pomace using response surface methodology and HPLC analysis

A simple and efficient microwave-assisted extraction of polyphenols from industrial apple pomace was developed and optimized by the maximization of the yield using response surface methodology. A Box-Behnken design was used to monitor the effect of microwave power, extraction time, ethanol concentration and ratio of solvent to raw material (g/mL) on the polyphenols yield. The results showed that the optimal conditions were as follows: microwave power 650.4?W, extraction time 53.7?s, ethanol concentration 62.1% and ratio of solvent to raw material 22.9:1. Validation tests indicated that the actual yield of polyphenols was 62.68±0.35?mg gallic acid equivalents per 100?g dry apple pomace with RSD=0.86% (n=5) under the optimal conditions, which was in good agreement with the predicted yield and higher than those of reflux and ultrasonic-assisted extraction methods. HPLC analysis indicated that the major polyphenols of apple pomace consisted of chlorogenic acid, caffeic acid, syrigin, procyanidin B2, (-)-epicatechin, cinnamic acid, coumaric acid, phlorizin and quercetin, of which procyanidin B2 had the highest content of 219.4?mg/kg.     

Four New Terpenoids from Xylaria sp. 101

One new diterpenoid, xylarenolide ( 1 ), and three new sesquiterpenoids, xylaranol A ( 2 ), xylaranol B ( 3 ), and xylaranic acid ( 4 ), were obtained from the fungal strain Xylaria sp. 101, which was isolated from the fruiting body of Xylaria sp. collected in Gaoligong Mountain, Yunnan Province. Their structures were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR experiments, and by HR‐Q‐TOF mass spectrometry. Their antimicrobial activities were evaluated.     

Two Novel Sesquiterpenoids from the Roots of Ferula ferulaeoides (Steud.) Korov.

Two new sesquiterpenoids, ferulactones A and B ( 1 and 2 , resp.), have been isolated from the roots of Ferula ferulaeoides (Steud.) Korov . Their structures and relative configurations were established by analysis of spectroscopic data. Their absolute configuration was assigned by application of the CD technique.     

Facile,efficient functionalization of polyethylene via regioselective copolymerization of ethylene with cyclic dienes

The copolymerizations of ethylene with cyclic dienes [dicyclopentadiene (DCPD) and 2,5‐norbornadiene (NBD)] using bis(β‐enaminoketonato)titanium complexes [PhN = C(R₂)CHC(R₁)O]₂TiCl₂ ( 1a : R₁ = CF₃, R₂ = CH₃; 1b : R₁ = t‐Bu, R₂ = CF₃; 1c : R₁ = Ph, R₂ = CF₃) have been investigated. In the presence of modified methylaluminoxane, these complexes exhibited high catalytic activities in the copolymerization of ethylene with DCPD or NBD, affording high molecular weight copolymers with unimodal molecular weight distributions. ¹H and ¹³C‐NMR spectra reveal ethylene/DCPD copolymerizations by catalysts 1a – c proceeds through the enchainment of norbornene ring. Catalysts 1a and 1c showed a tendency to afford alternating copolymers. More noticeably, catalysts 1b and 1c bearing bulky substituents on the ligands promote ethylene/NBD copolymerization without crosslinking, affording the copolymer containing intracyclic double bonds. The NBD incorporation as high as 27.2 mol % has been achieved by catalyst 1c . Moreover, the microstructures of the copolymers were further confirmed by the measurement of reactivity ratios and dyad monomer sequences as well as mean sequence lengths. The intracyclic double bonds of ethylene/DCPD or ethylene/NBD copolymers can be fully converted into polar groups such as epoxy, amine, silane, and hydroxyl groups under mild conditions. Convenient synthesis of hydroxylated polyethylene can be provided for the first time through the ring opening reaction of epoxide. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1764–1772, 2010     

New Epoxy‐Substituted Nitrogenous Bisabolene‐Type Sesquiterpenes from a Hainan Sponge Axinyssa sp.

Two new uncommon epoxy‐substituted nitrogenous bisabolene‐type sesquiterpenes, 3‐formamido‐7,8‐epoxy‐α‐bisabolane ( 4 ), 3‐isocyano‐7,8‐epoxy‐α‐bisabolane ( 5 ), together with three known related sesquiterpenes, 1 – 3 , were isolated from the Hainan sponge Axinyssa sp. Their structures were determined on the basis of extensive spectroscopic analyses and by comparison of their NMR data with those of structurally related compounds.     

New Sesquiterpenes from the Flowers of Chrysanthemum indicum L.

Two new guaianolides (=guaianolactones), chrysanthguaianolactone A and B ( 1 and 2 , resp.), and one new eudesmane sesquiterpene, chrysanthemdiol A ( 6 ), together with seven known sesquiterpenes were isolated from the flowers of Chrysanthemum indicum L. Their structures were elucidated on the basis of spectroscopic evidence.     

Neolignans and Caffeoyl Derivatives from Selaginella moellendorffii

Ten new phenolic compounds including the six neolignans 1 – 3 and 6 – 8 and four caffeoyl derivatives, i.e., myo‐inositol 1‐caffeate ( 9 ), myo‐inositol 6‐caffeate ( 10 ), myo‐inositol 5‐caffeate ( 11 ), and paucine 3′‐β‐D ‐glucopyranoside ( 12 ) were isolated from the whole plants of Selaginella moellendorffii (caffeic acid=3‐(3,4‐dihydroxyphenyl)prop‐2‐enoic acid). Their structures were established by spectroscopic and chemical methods.     

Polyethyleneimine functionalized protonated titanate nanotubes as superior carbon dioxide adsorbents

In this paper, protonated titanate nanotubes (PTNTs) were modified with polyethyleneimine (PEI) by wet impregnation method for CO(2) adsorption. Their micro-morphology and structural properties were characterized by a range of analytical techniques, including XRD, TEM, SEM, N(2) adsorption etc. Experimental results revealed that the functionalized PTNTs with 50wt.% PEI loaded exhibited a high CO(2) adsorption capacity of 130.8mg/g-sorbent at 100°C. Only a minor loss of its capacity was observed after five consecutive adsorption-desorption runs. The PEI was existed both in the internal and external mesoporous pores of PTNTs via chemical combination between amino group and enriched protons, which accounted for their good thermal stability at elevated temperatures. The results present herein imply that the PEI modified PTNTs could be appealing materials for capturing CO(2) from power plant flue gas.