Monolayers (Langmuir films) behavior of multi-component systems composed of a bile acid with different sterols and with their 1:1 mixtures

Different physicochemical properties of Langmuir films (monolayers) composed of 10 mixed systems of a bile acid, deoxycholic acid (DC) with various plant sterols, such as stigmasterol (Stig), beta-sitosterol (Sito) and campesterol (Camp) and a stanol, cholestanol (Chsta) in addition to an animal sterol, cholesterol (Ch) [these sterols and Chsta are abbreviated as St] and DC with 1:1 St mixtures; (Ch+Chsta), (Ch+Stig), (Stig+Chsta), (Ch+Sito) and (Ch+Camp) on the substrate of 5M aqueous NaCl solution (pH 1.2) at 25 degrees C, were investigated in terms of mean surface area per molecule (A(m)), the partial molecular area (PMA), surface excess Gibbs energy (DeltaG((ex))), interaction parameter (I(p)) as well as activity coefficients (f(1) and f(2)) in 2-D phase of each binary (or ternary) component system and elasticity (Cs(-1)) of formed films; these were analyzed on the basis of the respective surface pressure (pi) versus A(m) isotherms as a function of mole fraction of Sts (X(st)) in the DC/St(s) mixtures at discrete surface pressures. Notable findings are: (i) all the binary component systems did form patched film type monolayers consisting of (a) DC-dominant film solubilizing a trace amount of St molecules and (b) St dominant film dissolving a small amount of DC molecules, (ii) DC in 2-D phase exhibited a transition from LE film to LC film at a constant pressure (pi(C)(1)) accompanied by compression and (iii) DeltaG((ex)) as well as I(p) was found to be greatly dependent on (a) the combinations of DC with different St species and (b) to be markedly varied by a difference in mixing ratio of DC to Sts. Compressibility (or elasticity) analyses and fluorescence microscopy images could support the above findings as well as interpretation.     

Effect of particle size on surface modification of silica nanoparticles by using silane coupling agents and their dispersion stability in methylethylketone

The effect of particle size on the reactivity of hexyltrimethoxysilane (C6S) with the particle surface was studied by using silica nanoparticles (SNPs) with different diameters (30 or 200 nm). In case of 30-nm SNPs, a large amount of isolated silanol was observed. On the other hand, in the case of 200-nm SNPs, the amount of hydrogen bonded silanol and hydrogen bonded water molecules at the surface of the SNPs increased. Since the hydrogen bonded silanol and the hydrogen bonded water enhanced the reaction of C6S with SNPs, the chemisorbed C6S on 200-nm SNPs was larger than that on 30-nm SNPs. Furthermore, the effects of surface modification on the dispersion stability in MEK were studied using viscosity measurements and surface force measurements by the AFM colloid probe method. The viscosity of the dilute SNPs/MEK suspension did not change by the chemisorptions of C6S; however, the viscosity of dense suspension reduced effectively by surface modification. It was estimated that the suspension viscosity reduced effectively when the mean particle surface distance in the suspension was near to the distance where the repulsive force appeared by the surface force measurements using the colloid probe AFM.     

Direct one-pot synthesis of alpha-siloxy-Weinreb amides from aldehydes

A one-pot method for synthesizing alpha-siloxy-Weinreb amides from aldehydes was developed with use of N,O-dimethylhydroxylamine and a masked acyl cyanide reagent bearing a tert-butyldimethylsilyl group avoiding the competitive reaction toward N-methoxy-N-methyl-2-amino-1-siloxymalononitrile.     

Polarizability and second hyperpolarizability evaluation of long molecules by the density functional theory with long-range correction

Polarizabilities and second hyperpolarizabilities of polyacetylene and a hydrogen chain are evaluated by density functional theory (DFT) using a hybrid generalized gradient approximation functional with correct long-range electron-electron interactions. The well known catastrophic overestimate of the hyperpolarizabilities for molecular systems of enhanced length is corrected by the two-electron repulsion operator decomposition technique, integrating the distance-dependent nonlocal exchange effects for long-range interaction, while neither the asymptotically corrected exchange functional for long-range interaction nor ordinary hybrid methods seem to be capable of overcoming the serious drawback of the DFT in polarizability/hyperpolarizability evaluation.     

Exploring enzymatic catalysis at a solid surface: a case study with transglutaminase-mediated protein immobilization

The factors affecting enzymatic protein immobilization with microbial transglutaminase (MTG) were explored. As model proteins, enhanced green fluorescent protein (EGFP) and glutathione S-transferase (GST) were chosen and tagged with a neutral Gln-donor substrate peptide for MTG (Leu-Leu-Gln-Gly, LLQG-tag) at their C-terminus. To create a specific surface, displaying reactive Lys residues, to be cross-linked with the Gln residue in the LLQG-tag of target proteins by MTG catalysis, a polystyrene surface was physically coated with beta-casein. Both recombinant proteins were immobilized onto the beta-casein-coated surface only in the presence of active MTG, indicating that those proteins were enzymatically immobilized to the surface. MTG-mediated protein immobilization markedly depends on the pH and ionic strength of the reaction media. The optimal pH range of MTG-mediated immobilization of both recombinant proteins was around 5, at which point the MTG-catalyzed reaction in aqueous solution is not normally preferred. By utilizing a pH-dependent change in EGFP fluorescence, we found that the apparent pH at the surface is likely to be lower than bulk pH, this difference is not attributed to an optimal pH shift in MTG-mediated immobilization. On the other hand, lower yields of protein immobilization at higher ionic strength suggest that electrostatic interaction is a key factor governing MTG catalysis at a solid surface. The results of this study indicate that, in enzymatic catalysis at a solid surface, the concentration of substrates at the surface can enhance the catalytic efficiency, and this could alter the pH dependence of enzymatic catalysis.     

Proton transfer and associated molecular rearrangements in the photocycle of photoactive yellow protein: role of water molecular migration on the proton transfer reaction

The mechanism of the proton transfer and the concomitant molecular structural and hydrogen bond rearrangements after the photoisomerization of the chromophore in the photocycle of photoactive yellow protein are theoretically investigated by using the QM/MM method and molecular dynamics calculations. The free energy surface along this proton-transfer process is determined. This work suggests the important role of the water molecular migration into the moiety of chromophore, which facilitates proton transfer by the hydrogen bond rearrangement and the hydration of the pB' state.     

Direct Ethanol Production from Ionic Liquid-Pretreated Lignocellulosic Biomass by Cellulase-Displaying Yeasts

Among the many types of lignocellulosic biomass pretreatment methods, the use of ionic liquids (ILs) is regarded as one of the most promising strategies. In this study, the effects of four kinds of ILs for pretreatment of lignocellulosic biomass such as bagasse, eucalyptus, and cedar were evaluated. In direct ethanol fermentation from biomass incorporated with ILs by cellulase-displaying yeast, 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) was the most effective IL. The ethanol production and yield from [Bmim][OAc]-pretreated bagasse reached 0.81 g/L and 73.4% of the theoretical yield after fermentation for 96 h. The results prove the initial concept, in which the direct fermentation from lignocellulosic biomass effectively promoted by the pretreatment with IL.     

Highly Sensitive and Robust Linear Probe for Detection of mRNA in Cells

A stemless linear probe was designed that robustly detects mRNA in cells with high sensitivity. The probe is modified at some positions with base surrogates prepared from D ‐threoninol, with anthraquinone moieties near the 5′‐ and 3′‐termini, and with perylene moieties. Even in cell lysate that involves various proteins and enzymes, background emission was very low. When the probe was hybridized with RNA, chromophores are intercalated between the base pairs, resulting in a remarkable light‐up signal. The signal‐to‐background ratio was as high as 1600 under our standard buffer conditions. In the HeLa cell lysate, the linear probe had sufficient signal‐to‐background ratio (S/B=40) for reliable mRNA detection. No degradation was observed after a 24 h incubation in HeLa cell lysate. In cells, a probe designed to target DsRed resulted in distinct blue fluorescence only in cells transfected with plasmid encoding DsRed; no fluorescence was observed in control cells.