Chain length effect of the counterion on the partial molal volume of alkanesulfonates

The partial molal volumes of two series of homologous surfactants, n-alkylammonium decanesulfonates and a, ?-alkanediammonium nonanesulfonates, were measured below and above their CMC in aqueous solution. Their counterions were n-alkylammonium and a, ?-alkanediammonium. The relationship between the partial molal volume and the chain length of the counterion below the CMC had an inflection point. The relationship between them, above the CMC, was almost linear. In the case of the alkylammonium salts, the values of the volume change of micellization were almost the same when the chain length of the counterions was shorter than the butyl, and increased with an increase in the chain length when it was longer than the propyl. In the case of the alkanediammonium salts, the volume change of micellization showed a small decrease with the chain length when it was shorter than octane, and was very large for the nonane ammonium salt. The large positive increase in the volume change with the increase in the chain length of the counterion can be explained by the hydrophobic interaction between the alkyl chain of the counterion and the hydrophobic core of the micelle.     

One‐Handed Helical Screw Direction of Homopeptide Foldamer Exclusively Induced by Cyclic α‐Amino Acid Side‐Chain Chiral Centers

Chiral cyclic α,α‐disubstituted amino acids, (3S,4S)‐ and (3R,4R)‐1‐amino‐3,4‐(dialkoxy)cyclopentanecarboxylic acids ((S,S)‐ and (R,R)‐Ac₅c^dOR; R: methyl, methoxymethyl), were synthesized from dimethyl L ‐(+)‐ or D ‐(?)‐tartrate, and their homochiral homoligomers were prepared by solution‐phase methods. The preferred secondary structure of the (S,S)‐Ac₅c^dOMe hexapeptide was a left‐handed (M) 3₁₀ helix, whereas those of the (S,S)‐Ac₅c^dOMe octa‐ and decapeptides were left‐handed (M) α helices, both in solution and in the crystal state. The octa‐ and decapeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2‐trifluoroethanol solution. The left‐handed (M) helices of the (S,S)‐Ac₅c^dOMe homochiral homopeptides were exclusively controlled by the side‐chain chiral centers, because the cyclic amino acid (S,S)‐Ac₅c^dOMe does not have an α‐carbon chiral center but has side‐chain γ‐carbon chiral centers.     

Optimization of in-gel protein digestion system in combination with thin-gel separation and negative staining in 96-well plate format

Improvement of in-gel digestion efficiency is highly desirable for one- or two-dimensional gel electrophoretic separation and mass spectrometric (MS) analysis in proteomics, because the resultant increases in sequence coverage and MS signal intensity lead to higher confidence in protein identification. Here an optimized in-gel digestion system, in combination with thin-gel separation and negative staining in a high-throughput format using 96-well plates, is described. The combination of negative staining and protein separation on a 0.9 mm thick gel showed a clear improvement in in-gel digestion efficiency in comparison with the more typical protocols such as the combination of silver staining and a 1.0 mm gel. In addition, the use of 96-well plates to increase throughput did not decrease the efficiency of this strategy when the stirring of the gel pieces in processes such as destaining, washing, gel-shrinking and peptide extraction was performed by sonication instead of shaking the plates. This procedure was optimized and applied to identify proteins of the postsynaptic density fraction; 105 proteins were identified after SDS-PAGE separation.     

Synthesis of styrene–acrylonitrile random copolymers (SAN) and polyarylate block copolymers and the control of their mechanical properties by morphology generation

The idea of repulsion in random copolymers was applied to the miscibility modification between polystyrene (PS) and polyarylate (PAr) segments of PS–PAr block copolymer (PAr–PS–PAr). Acrylonitrile (AN), which has a large positive interaction parameter against styrene, was used as a miscibility modifier toward PAr segments. AN was introduced into the carboxyl terminated telechelic‐PS at AN wt % ranging from 12 to 37 wt %. Based on these telechelic acrylonitrile–styrene random copolymers (SAN_x's where x represents AN wt %), SAN_x and PAr block copolymers (PAr–SAN_x–PAr's) were synthesized. The miscibility of SAN_x and PAr segments was estimated from the results of DSC with Fox's equation and spin–spin relaxation time measured by pulsed NMR. These results evidenced that the miscibility between PS and PAr segments can be modified by introducing AN into PS segments. The estimated volume fraction of the interfacial layer between SAN_x and PAr segments was increased as x was increased toward 24 wt %, around which the predicted miscibility reaches a maximum. Above that AN wt %, it began to decrease. The flexural strength increased as the miscibility between SAN_x and PAr segments increased. In particular, when x was between 20 and 30 wt %, PAr–SAN_x–PAr exhibited three times larger flexural strength than PAr–PS–PAr. The fracture behavior changed from brittle to ductile, even though the telechelic SAN_x by themselves exhibited almost the same fracture strength as the telechelic PS. The results of dynamic mechanical measurements and the percolation model suggested that around these AN wt % the continuum matrices in PAr–SAN_x–PAr changed from SAN_x phase to a cocontinuous phase of SAN_x and PAr. From these results, PAr–SAN_x–PAr was explained to perform such a high flexural strength by this phase change in the continuum matrices. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 127–137, 2000     

The First Fully Planar C5‐Conformation of Homooligopeptides Prepared from a Chiral α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=(2S)‐2‐Amino‐2‐ethylhexanoic Acid)

An optically active α‐ethylated α,α‐disubstituted amino acid, (S)‐butylethylglycine (=(2S)‐2‐amino‐2‐ethylhexanoic acid; (S)‐Beg; (S)‐ 2 ), was prepared starting from butyl ethyl ketone ( 1 ) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)‐Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C‐terminus, and a trifluoroacetyl group was used for the N‐terminus of the peptides. The structures of tri‐ and tetrapeptides 5 and 6 in the solid state were solved by X‐ray crystallographic analysis, and were shown to have a bent planar C₅‐conformation (tripeptide) and a fully planar C₅‐conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and ¹H‐NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl₃ solution was also a fully planar C₅‐conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α‐ethylated α,α‐disubstituted amino acid is a planar C₅‐conformation.     

Application of an Ion Beam Technique for the Design of Visible Light-Sensitive, Highly Efficient and Highly Selective Photocatalysts: Ion-Implantation and Ionized Cluster Beam Methods

As a new concept for the design of effective photocatalysts, an ion beam technology using accelerated metal ions, a metal ion implantation and an ionized cluster beam (ICB) method, have been applied to design unique photocatalysts. The metal ion implantation of TiO₂ and Ti-containing zeolites with highly accelerated metal ions (V⁺, Cr⁺, etc.) is useful in designing photocatalysts that can operate efficiently under visible light irradiation. Also, an ICB method with a low acceleration energy is useful in preparing transparent TiO₂ thin films on various types of substrates for the efficient photocatalytic degradation of pollutants diluted in water and air. The combination of the ICB method and metal ion implantation can develop the TiO₂ thin films that are able to operate not only under UV light but also under visible light irradiation.     

Three-way-output response system by electric potential: UV-vis, CD, and fluorescence spectral changes upon electrolysis of the chiral ester of tetracyanoanthraquinodimethane

The newly prepared tetracyanoanthraquinodimethane (TCNAQ) derivatives 1a,b with a chiral auxiliary are good electron acceptors and exhibit weak circular dichroism (CD) based on the absorption of TCNAQ. The twin-type electron acceptor 1c with two TCNAQ units shows larger ellipticity by exciton coupling. UV-vis, CD, and fluorescence spectra were changed drastically upon electrochemical reduction of 1c, which demonstrates the unprecedented three-way-output response system.     

Green polymers from Geobacillus thermodenitrificans DSM465--candidates for molecularly imprinted materials

Novel molecular recognition materials were prepared from water soluble proteins from thermophile G. thermodenitrificans DSM465 by an alternative molecular imprinting method. Water soluble proteins from G. thermodenitrificans DSM465 were converted into the molecularly imprinted materials by adopting 9-EA as a print molecule. The molecularly imprinted protein membranes recognized As in preference to Gs. The adsorption isotherms led to the conclusion that molecular recognition sites toward As were constructed by the presence of 9-EA during the membrane preparation process. The affinity constant between As and the molecular recognition site thus constructed was determined to be 1.75 x 10(5) mol(-1) dm(3). The results obtained in the present study suggest that water soluble proteins from G. thermodenitrificans DSM465 is one of environmentally-friendly 'green' polymers to be converted into molecular recognition materials by applying an alternative molecular imprinting method.     

Aromaticity and magnetotropicity of dicyclopenta-fused polyacenes

Most dicyclopenta-fused polyacenes are predicted to be moderately aromatic and diatropic, although they have no (4n + 2)-site conjugated circuits. We applied our graph theory of aromaticity and magnetotropicity to these molecules and found that these anomalous properties arise from a set of non-conjugated circuits, which contribute collectively to aromaticity and diatropicity. This result indicates that the conjugated circuit model is not always applicable to such non-alternant hydrocarbons. Dianions of dicyclopenta-fused polyacenes are more aromatic than their respective neutral species, because they are iso-pi-electronic with aromatic polyacenes.