Dynamics of order formation by colloidal adsorption onto a substrate studied with Brownian dynamics

Colloidal adsorption and spontaneous ordering of adsorbed particles on a substrate was simulated using a three-dimensional simulation model for colloidal dispersion system with an adsorptive surface under a specified bulk concentration, where the particle-particle and particle-substrate interactions were modeled on the DLVO theory. The key process for order formation is considered to be the adsorption of a particle that induces the transition from incomplete order to perfect order, and is found to involve a stochastic nature due to an energy barrier which must be overcome for the system to reach ordered state. Also, a model was developed to predict the energy barrier for order formation based on direct observation of the key process. Further, a model to describe the stochastic nature of the process was developed and its quantitative validity was demonstrated. Through the examination of the key process, it is concluded that the mechanism of the order formation is composed of two successive processes and the rate-determining step varies depending on the ionic strength.     

Influence of isosorbide dinitrate concentration on its skin permeability from adhesive matrix devices.

Adhesive matrix devices containing a model drug, isosorbide dinitrate (ISDN), were prepared with three different types of pressure sensitive adhesives (PSAs). ISDN permeation through excised hairless rat skin from the different devices was measured in vitro. For each PSA type, the steady state permeation rate of ISDN increased proportionally with an increase of ISDN concentration in the PSA and reached a maximum level at a certain concentration. Although the concentrations reaching the maximum skin permeation level varied among PSA types, the maximum rate for each PSA type was largely similar to that for ISDN aqueous suspension. The release rate of ISDN from devices was too fast to influence the skin permeation rate for all devices. In the PSA of devices showing maximum skin permeability, ISDN crystalline was observed by polarizing microscopy and differential scanning calorimetry. These results suggest that the skin permeation of ISDN from adhesive matrix devices was controlled by the thermodynamic activity of the drug in the PSAs.     

Ceric-ion-initiated grafting of methyl methacrylate onto (1 → 5)-α-D-ribofuranan and (1 → 5)-α-D-xylofuranan

We report herein studies of grafting of MMA onto (1 → 5)-α-D -ribofuranan and (1 → 5)-α-D -xylofuranan by ceric ion initiation both in water and in dimethyl sulfoxide (DMSO). In aqueous medium, the graft polymer having high grafting (%) can be obtained easily without adding any nitric acid. The degradation of polysaccharide by the acidic ceric ion solution is not serious; 73–82% of its original molecular weight remained after the polymerization. In DMSO, graft polymers having lower grafting (%) and lower molecular weight of grafts were obtained.     

Interaction of cubosomes with plasma components resulting in the destabilization of cubosomes in plasma

Cubosomes are novel dispersed nanoparticles with bicontinuous cubic phases of monoolein in their interior. We investigated their disintegration process in plasma by in vitro and in vivo studies. Cubosomes were incubated with whole plasma or plasma components such as HDL, LDL, and albumin. The lypolysis study indicated lipolytic activity of whole plasma towards cubosomes. Gel filtration chromatography revealed that HDL, LDL and albumin interacted with cubosomes. HDL affected cubosomes’ integrity and gave rise to smaller particles which contained the components of both cubosomes and HDL. Upon incubation with LDL, cubosomes fused with LDL. Albumin was shown to take up monoolein out of the particles. Cubosomes were disintegrated by whole plasma as a result of the interaction with plasma components. It was concluded that in vivo observation of a long circulation time of a hydrophobic substance in cubosomes was due to the sustained behavior of cubosome remnant particles.     

Crystal structure of poly(p-benzamide)

Redetermination of the crystal structure of poly(p-benzamide) was made by using newly collected intensity data. The molecular conformation is TCTC, where the internal rotation angles about the N? C bond of the amide group and about the virtual bond of N-phenyl-C are T (trans) and C (cis) conformations, respectively. Two molecular chains pass through a rectangular unit cell with dimension, a = 7.75 Å, b = 5.30 Å, c (fiber axis) = 12.87 Å, and the space group, P2₁2₁2₁-D. The reflection observed at the spacing of 010 may be attributed to the reflection due to another crystal polymorph or the diffuse scattering due to disorder. © 1993 John Wiley & Sons, Inc.     

Phase-death mode in two-coupled chemical oscillators studied with reactors of different volume and by simulation

The behavior of the phase-death mode (cessation of oscillations and transition to a steady state) in the two-coupled Belousov–Zhabotinsky reactions is studied in the asymmetric coupling. In an experiment, the types of synchronized modes and their regions were investigated as an extension of our previous study. This experiment is compared to a simulation using the two-coupled three-variable Oregonator models. The results confirm that the phase-death mode changes from “bistable” to “monostable” and reveal the stable region of the latter.     

Stereoselective synthesis of (Z)-fluoroalkenes directed to peptide isosteres: copper mediated reaction of trialkylaluminum with 4,4-difluoro-5-hydroxyallylic alcohol derivatives

Copper mediated alkyl-transfer reaction of trialkylaluminum (R₃Al) with (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative smoothly proceeded to give the corresponding 2-alkylated 4-fluoro-5-hydroxyhomoallylic alcohol derivative with completely Z and 2,5-syn selective manner. Regio- and stereoselective conversion of the C5-hydroxyl group of the fluoroolefin thus obtained to amino group could be achieved through one-pot mesylation and azidation reaction.     

Determination of chemical form of antimony in contaminated soil around a smelter using X-ray absorption fine structure.

Only limited information is available about the behavior of antimony (Sb) in contaminated soils. However, understanding the behavior of Sb in contaminated soils is important, because the toxicity or solubility of this element depends on its chemical state. In this study, we investigated the levels of Sb and the chemical forms of Sb in the soil around a smelter using X-ray absorption fine structure (XAFS) spectra. The highest Sb concentration in the contaminated soil was 2900 mg/kg dry soil. According to Sb-K edge X-ray absorption near edge (XANE) spectra, the Sb in the soil was in the form of Sb(V) compounds. The similarity of extended XAFS (EXAFS) spectra suggests that Sb speciation was independent of the sampling site, which indicates that Sb or Sb2O3 emitted from the smelter was converted into Sb(V) compounds in the soil.     

Photocyclization of n-[ω-(cycloalken-1-yl)alkyl]-and n-[ω-(inden-3-yl)alkyl]phthalimides : Synthesis of spiro-nitrogen multicyclic systems

Photolysis of the N-[ω-(cycloalken-1-yl)alkyl]phthalimides 6b-$\text{e}$ in each case gave a pair of stereoisomers of spiro-nitrogen multicyclic systems (9b-$\text{e}$) in moderate yields, whose stereochemistry was determined by means of chemical and spectroscopic analyses. Similarly, in N-[ω-(inden-3-yl)alkyl]-phthalimides (8), spiro-nitrogen macrocycles up to 13-membered 13a-$\text{c}$ were obtained in good yields