Adsorption of Carbon Tetrachloride on Pyridinium Montmorillonite

Effect of substitution of Na⁺ by pyridinium on the surface and pore structures of montmorillonite is studied by CCl₄ vapor adsorption.     

Bistable ferroelectric liquid crystal photoswitch triggered by a dithienylethene dopant

The spontaneous polarization (PS) of a ferroelectric liquid crystal is modulated reversibly by photocyclization of the dopant 1,2-bis[5'-(4' '-heptyloxyphenyl)-2'-methylthien-3'-yl]perfluorocyclopentene. The magnitude of PS photomodulation increases with dopant concentration up to 3 mol %, and the resulting photoswitch is fatigue resistant and bistable. To the best of our knowledge, this is the first example of a bistable ferroelectric liquid crystal photoswitch to be reported in the literature.     

Dynamic mechanical and thermal behavior of thermotropic polyesters based on 4,4-alkane-1-ω-diylbis(4-hydroxybenzoic acid) and 4,4-(pentane-1,5-diyloxy)dibenzoic acid

Thermotropic polyesters based on 4,4^′-alkane-1-ω-diylbis(4-hydroxybenzoic acid) and 4,4^′-(pentane-1,5-diyloxy)dibenzoic acid were studied by dynamic mechanical spectroscopy, X-ray scattering, differential scanning calorimetry and polarizing microscopy. The effect of structure changes in the mesogenic group as well as in the flexible spacer, in particular the incorporation of Cl atoms into the mesogen, introduction of ether oxygen into spacer and the number of CH₂ groups in spacer was investigated. More complex mechanical and thermal behaviour was found on second heating scan than on first cooling of the isotropic melt; higher values of mechanical functions were observed in the isotropic state than in the nematic state of melts. While an even number of CH₂ groups and the presence of ether oxygen in spacer shifts the transition temperatures to higher values, the incorporation of Cl atoms into the mesogen leads to disappearance of ordered structure and the polymers behave as amorphous materials.     

Migration of 99Tc in a Weak Loess Aquifer: A Field Column Experiment

The migration of ⁹⁹Tc in a weak loess aquifer was investigated in-situ with undisturbed aquifer medium columns. The columns were obtained horizontally at a depth of 3236 m in an Underground Research Facility (URF). Quartz containing ³H (HTO) and ⁹⁹Tc (in the form of ⁹⁹TcO₄ ^-) was introduced into one end of the columns and the columns were covered tightly. Aquifer water was introduced into the columns directly from an experimental shaft in the UFR. Effluents from the columns were collected and the activity of ³H and ⁹⁹Tc were determined with a liquid scintillation analyzer. The breakthrough curves of ³H and ⁹⁹Tc indicate that ⁹⁹Tc migrates a little faster than that ³H does in the aquifer.     

Diverse redox-active molecules bearing O-, S-, or Se-terminated tethers for attachment to silicon in studies of molecular information storage

A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Attachment of the molecules to electroactive surfaces requires control over the nature of the tether (linker and surface attachment group). We have synthesized a collection of redox-active molecules bearing different linkers and surface anchor groups in free or protected form (hydroxy, mercapto, S-acetylthio, and Se-acetylseleno) for attachment to surfaces such as silicon, germanium, and gold. The molecules exhibit a number of cationic oxidation states, including one (ferrocene), two [zinc(II)porphyrin], three [cobalt(II)porphyrin], or four (lanthanide triple-decker sandwich compound). Electrochemical studies of monolayers of a variety of the redox-active molecules attached to Si(100) electrodes indicate that molecules exhibit a regular mode of attachment (via a Si-X bond, X = O, S, or Se), relatively homogeneous surface organization, and robust reversible electrochemical behavior. The acetyl protecting group undergoes cleavage during the surface deposition process, enabling attachment to silicon via thio or seleno groups without handling free thiols or selenols.     

A rapid access to chiral alkylidene cyclopentenone prostaglandins involving ring-closing metathesis reaction

A synthesis of the alkylidene cyclopentenone prostaglandin TEI 9826 has been realized. The synthesis involved the preparation of the chiral 1,5-diene 8 using a stereoselective Claisen rearrangement from the allylic alcohol 6 giving the ester 7 after vinylation. Then a key RCM reaction allowed the preparation of the cyclopentenol 9 which, after oxidation, gave the cyclopentenone 10, precursor of the prostaglandin.     

Thermal properties of tetrahydroperparine derivatives

The thermal behaviour of tetrahydroperparine (THP) and its derivatives with various acids has been investigated. The acid is liberated from the formate derivative basically in two steps, while the other aliphatic acids are released quantitatively before the thermal decomposition of the THP molecule. The thermoanalytical curves, electrical conductivity data measured in the molten phase, and infrared spectra prove that while part of the formic acid is hydrogen-bonded the other part is bound ionically in the molecule. It may be assumed that the marked biological activity of the compound can be explained by this difference in the nature of the bonds.     

Potentiometric response of graphite electrodes coated with modified polymer films

Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10^?1–1 × 10^?5 M sodium thiocyanate.     

Continuous Selective Heating of the Dispersion Medium in a Unit Constituted by Heater and Mass-Exchange Apparatus

A new method for heat exchange between dispersed flows and a unit for continuous selective heating, comprising a heater and a mass-exchange apparatus, was proposed. A mathematical model of the unit was developed for the cases of direct-flow and counterflow heaters. Analytical solutions to the model equations were obtained. The parameters affecting the result of continuous selective heating of the dispersion medium in the unit were determined.     

Application of parallel processing techniques to improving the efficiency of MM2 molecular mechanics calculations

The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc.