Poly(diacetylene)-nanofibers can be fabricated through photo-irradiation using natural polysaccharide schizophyllan as a one-dimensional mold

Schizophyllan interacts with various 1,4-diphenylbutadiyne derivatives to induce their chirally-twisted packing. A series of referential experiments using other polysaccharides (amylose, pullulan, dextran, etc.) and a carbohydrate-appended detergent (dodecyl-beta-d-glucopyranoside) indicates that these 1,4-diphenylbutadiyne derivatives are accommodated within a tubular cavity constructed by a helical superstructure of schizophyllan. In these 1,4-diphenylbutadiyne derivatives, 1,4-bis(p-propionamidophenyl)butadiyne can be easily polymerized through UV-irradiation, in which schizophyllan acts as a one-dimensional mold to produce the corresponding poly(diacetylene)s with fibrous morphologies. Detailed investigations on this unique approach to prepare the nanofibers revealed that it includes two individual processes, that is, 1) UV-mediated polymerization of encapsulated 1,4-bis(p-propionamidophenyl)butadiyne to produce immature nanofibers and 2) their reorganization through hydrophobic interfiber interactions into ordered nanofibers. The other 1,4-diphenylbutadiyne derivatives could not be polymerized through UV-irradiation, indicating that the p-propionamido-functionalities play substantial roles for a suitable packing of the monomer for the polymerization. The other 1,4-diphenylbutadiyne derivatives, however, can be also polymerized through gamma-ray irradiation in the presence of schizophyllan to give the corresponding poly(diacetylene)-nanofibers, emphasizing the wide applicability of the schizophyllan-based strategy for polymerization of various 1,4-diphenylbutadiyne derivatives.     

Effects of addition of hydrophobic sucrose fatty acid oligoesters on crystallization rates of n-hexadecane in oil-in-water emulsions

Ultrasonic velocity measurements were made on crystallization rates of n-hexadecane dispersed in an oil-in-water (O/W) emulsion (20 wt.% oil and 80 wt.% water) in which Tween 20 was employed for emulsification. Highly hydrophobic emulsifiers, sucrose fatty acid oligoesters involving stearic acid (S-170), lauric acid (L-195) and oleic acid (O-170) moieties, were added to n-hexadecane in an attempt to modify the crystallization rate of n-hexadecane. The crystallization process of n-hexadecane was monitored by variations in the ultrasonic velocity values, which increase with increasing amount of crystal fractions in the oil phase of the emulsion. In comparison with the results of the O/W emulsion systems with the additive P-170 (a sucrose palmitate) (N.Kaneko et al., J. Crystal Growth 197 (1999) 263), the following results were obtained: (a) the addition of S-170 accelerated the nucleation in the emulsion system in the same manner as P-170, no acceleration was revealed with the additive O-170, and L-195 showed moderate effects; (b) the rate of crystal growth was retarded by S-170 and L-195, but not by O-170; (c) the effects of acceleration of nucleation occurred singly in the emulsion system, but not in the bulk system; and (d) the acceleration of nucleation was exhibited through two stages with increasing concentrations of the additives. These results showed the remarkable influence of the fatty acid chain structures of sucrose oligoesters on the acceleration of heterogeneous nucleation of n-hexadecane in the O/W emulsions. The heterogeneous nucleation effected by the addition of S-170 and P-170 was discussed taking into account the adsorption at the oil-water interface and the formation of reversed micelles of the sucrose oligoesters added in the oil phase.     

Determination of cefixime and its metabolises by high-performance capillary electrophoresis

Cefixime (CX), an oral cephalosporin antibiotic, and its metabolites in human digestive organs were separated by various modes of high-performance capillary electrophoresis. The zone electrophoresis mode in phosphate buffer (pH 6.8) containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate gave the best separation, permitting the complete resolution of CX and all of five metabolites. On the other hand, the plain zone electrophoresis mode in phosphate buffer (pH 6.8) offered a simple procedure for the direct determination of urinary CX concentration using intact urine samples.     

Dielectric analysis of sheep erythrocyte ghost. Examination of applicability of dielectric mixture equations

The purpose of this study is to confirm the applicability of dielectric mixture equations in dielectric analysis of biological cell suspensions. Two dielectric mixture equations, the Pauly-Schwan (P-S) equation and the Hanai-Asami-Koizumi (H-A-K) equation were tested using sheep erythrocyte ghosts whose internal solution is identical with the external solution. Dielectric measurements were carried out for the ghost suspensions over a frequency range 10 kHz to 100 MHz; a single dielectric relaxation was found between 100 kHz and 10 MHz. From the dielectric relaxation, the conductivity and permittivity of the ghost interior and the capacitance of the cell membrane were calculated following the P-S and H-A-K equations. When the H-A-K equation was employed (and as expected from the property of the ghosts), the estimated internal conductivity was in good agreement with the external conductivity at volume fractions up to about 0.7. With the P-S equation, on the other hand, the same results as above were obtained but only at low volume fractions below about 0.3. In addition, the H-A-K equation provided a better simulation for the observed relaxation curves than did the P-S equation, especially at high volume fractions. It is, therefore, concluded that the H-A-K equation is applicable to a wider range of volume fraction than is the P-S equation.     

Molecular manipulation of two- and three-dimensional silica nanostructures by alkoxysilylation of a layered silicate octosilicate and subsequent hydrolysis of alkoxy groups

A novel methodology for constructing molecularly ordered silica nanostructures with two-dimensional (2-D) and three-dimensional (3-D) networks has been developed by using a stepwise process involving silylation of a layered silicate octosilicate with alkoxytrichlorosilanes [ROSiCl(3), R = alkyl] and subsequent reaction within the interlayer spaces. Alkoxytrichlorosilanes react almost completely with octosilicate, bridging two closest Si-OH (or -O(-)) sites on the silicate layers, to form new five-membered rings. The unreacted functional groups, Si-Cl and Si-OR, are readily hydrolyzed by the posttreatment with a water/dimethyl sulfoxide (DMSO) or water/acetone mixture, leading to the formation of two types of silicate structures. The treatment with a water/DMSO mixture produced a unique crystalline 2-D silicate framework with geminal silanol groups, whereas a water/acetone mixture induced hydrolysis and subsequent condensation between adjacent layers to form a new 3-D silicate framework. The 2-D structure is retained by the presence of DMSO molecules within the swelled interlayer spaces and is transformed to a 3-D silicate upon desorption of DMSO. The structural modeling suggests that both of the 3-D silicates contain new cagelike frameworks where solvent molecules are trapped even at high temperature (up to 380 degrees C, in the case of acetone). Both 2-D and 3-D silica structures are quite different from known layered silicates and zeolite-like materials, indicating the potential of the present approach for precise design of various silicate structures at the molecular level.     

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.     

Folding Dynamics of 10‐Residue β‐Hairpin Peptide Chignolin

Short peptides that fold into β‐hairpins are ideal model systems for investigating the mechanism of protein folding because their folding process shows dynamics typical of proteins. We performed folding, unfolding, and refolding molecular dynamics simulations (total of 2.7 μs) of the 10‐residue β‐hairpin peptide chignolin, which is the smallest β‐hairpin structure known to be stable in solution. Our results revealed the folding mechanism of chignolin, which comprises three steps. First, the folding begins with hydrophobic assembly. It brings the main chain together; subsequently, a nascent turn structure is formed. The second step is the conversion of the nascent turn into a tight turn structure along with interconversion of the hydrophobic packing and interstrand hydrogen bonds. Finally, the formation of the hydrogen‐bond network and the complete hydrophobic core as well as the arrangement of side‐chain–side‐chain interactions occur at approximately the same time. This three‐step mechanism appropriately interprets the folding process as involving a combination of previous inconsistent explanations of the folding mechanism of the β‐hairpin, that the first event of the folding is formation of hydrogen bonds and the second is that of the hydrophobic core, or vice versa.     

Direct Observation of Foam Film Rupture by Several Types of Antifoams Using a Scanning Laser Microscope

It is well known that the stability of a pseudoemulsion film, a thin liquid film formed between an antifoam particle and air, can be important during defoaming action. We have compared the bursting behavior of a two-dimensional thin liquid film from an aqueous surfactant solution on a glass plate, in which six types of antifoam particles have been dispersed, using laser microscopic techniques. The used antifoams were a silicone oil, a mixed-type antifoam (mixture of silicone oil and hydrophobic solid particles), a hydrophobic silica, and a silicone-based solid antifoam (prepared by interfacial polymerization with oil and water). The antifoaming performance of these six types of antifoams, measured by the glass cylinder shaking test, was in the order: the mixed-type antifoam >== the silicone-based solid antifoam > the hydrophobic silica >== the silicone oil. Pseudoemulsion film rupture was observed at the film thickness less than 0.1 μm for both the silocone oil and the hydrophobic silica. In the case of particles with rough edges (the silicone-based antifoam), pseudoemulsion film on the top of the particles can be easily ruptured at a convex part of the solid surface. Furthermore, solid particles existing on the surface of an oil droplet in the mixed-type antifoams form marked projections and these projections give rise to distortion of the thinning film. As soon as the distortion of the thinning film took place on the top of the antifoam droplet, the pseudoemulsion film can be instantaneously ruptured. Referring to the antifoaming mechanisms for mixed-type antifoams, both steps from the pseudoemulsion film formation to the lens formation and from the counter pseudoemulsion film formation to the bridge formation would be very fast and cause a very high antifoaming efficiency. Copyright 1999 Academic Press.     

A convenient synthesis of 5,14-methano-16-oxo-1,5,6-benzoxadiazonino[3,4-b]quinoxalines utilizing a 1,3-dipolar cycloaddition reaction and an intramolecular alcoholysis

The reaction of the hydrazones 5a-c with 2-chloroacrylonitrile produced the 1,2-diazepino[3,4-b]quinoxaline hydrochlorides 6a-c , which were transformed into the 5,6,7,13-tetrahydro-5,14-methano-16-oxo-1,5,6-benzoxadiazonino[3,4-b]quinoxalines 7a-c , respectively. The oxidation of 7a-c with diethyl azodicarboxylate afforded the 7,13-dihydro-5,14-methano-16-oxo-1,5,6-benzoxadiazonino[3,4-b]quinoxalines 8a-c , respectively. Compounds 7a-c and 8a-c were also obtained by a one-pot synthesis from 5a-c and 6a-c , respectively.     

A facile synthesis of novel pyrazolo[5′,1′:3, 4]-[1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines

The reaction of the 3-substituted 4-aminopyrazolo[5, 1-c][1, 2, 4]triazines 1a-d with thiosemicarbazide hydrochloride in acetic acid gave new pyrazolo[5′,1′:3, 4][1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines 3, 4 and 6 , which were converted into the 5-oxo derivatives 5 and 7 by hydrolysis in hydrochloric acid/acetic acid.