Formation of 2,2-difluoro-3-hydroxymethylbenzo-1,4-oxathianes from 2-(α-trifluoromethylvinylthio)phenols)

It is shown that 2,2-difluoro-3-hydroxymethylbenzo-1,4-oxathianes are formed together with 3-trifluoromethylbenzo-1,4-oxathianes whenortho-(-trifluoromethyl--chloroethylthio)phenols are boiled with excess aqueous alkali. The mechanism of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1457–1459, August, 1994.     

Synthesis of Gels in the System Na2O-ZrO2-SiO2

Gels have been synthesized in the SiO₂-Na₂O-ZrO₂ system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO₄ unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses.     

Effects of pretreatments and modifiers on electrochemical properties of carbon paste electrodes

The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed.     

Crosslinked polystyrene with improved mechanical properties

The synthesis of some divinyl monomers—bis(vinylphenyl)ethane ( 2 ), bis(vinylbenzyloxy)hexane ( 3a ), and bis(vinylbenzyloxy)dodecane ( 3b ) is reported. Copolymers of the new monomers and styrene were evaluated as an alternative to divinylbenzene-crosslinked polymers for use as matrices and absorbents. The mechanical properties and the amount of residual double bonds in the copolymers were compared. It was found that the new copolymers, unlike the divinylbenzene-crosslinked polymers, retained their mechanical strength even at high crosslinking degrees. Stress at break values of 79, 68, and 18 N/mm² were found for the polymers crosslinked with 20 mol % of 3a, 2 , and divinylbenzene; 5, 25 and 45% of the divinyl units in these polymers were left as pendant double bonds. Porous styrene– 2 copolymers were synthesized and shown to have lower surface areas than the corresponding divinylbenzene-crosslinked polymers. The pore size distribution showed that this was due to the absence of the smallest pores which are found in the divinylbenzene-crosslinked polymers in between heavily crosslinked nodules. © 1993 John Wiley & Sons, Inc.     

Phase transition of polycarbonate in blends with liquid crystal

Phase transition temperatures of polycarbonate film consisting of micron-sized liquid crystalline droplets were investigated using differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) methods. Both a decrease in (T _g ) and (T _m ) of the polycarbonate with an increase of liquid crystal (LC) content in the sample were observed. The decrease ofT _g is related to the plastifying effect of a low molecular weight LC substance remaining soluble in the polycarbonate matrix. A fraction of the liquid crystal contained in the droplets was estimated on the basis of theT _g decrease.     

Resolution of lymphocyte subpopulations derived from rat spleen by polyamine-graft-PHEMA copolymer

The retention behavior of lymphocyte subpopulations, B cell, T cell and null cell, derived from rat spleen to polyamine-graft-poly(2-hydroxyethyl methacrylate) copolymer (HA) surface was investigated, focusing on the conformational transition of the polyamine side chain as well as the protonation of amino groups in the polyamine grafts. Furthermore, the availability of HA was discussed as a column adsorbent for separation of lymphocyte subpopulations derived from spleen. The conformational transition of polyamine grafts significantly influenced the mode of retention of lymphocyte subpopulations. When polyamine grafts existed in an aggregated conformation (protonatin degree α < 0.5), the retention of lymphocyte subpopulations was decreased in the order B cell> null cell> T cell. On the other hand, when polyamine existed in an extended conformation into the aqueous interior from the matrix interface (α > 0.5), T cell retention became greater than null cell retention, resulting in a decreased B cell> T cell> null cell order. These results indicate that the differential retention of spleen lymphocyte subpopulations is attributed to their differential responses to the change in matrix interface accompanied by the protonation of amino groups. Furthermore, spleen lymphocytes were compared with lymph node lymphocytes in terms of resolution efficacy by an HA copolymer column.     

Determination of degree of conversion as a function of depth of a photo-initiated dental restoration composite—III application to commercial Prodigy Condensable™

In this third work, we evaluated the degree of conversion (DC) versus depth of dental filling composite named Prodigy Condensable™ using infrared spectroscopy. Confirming previous results, there was a gradual reduction of DC with increasing depth but the composite exhibited extreme values of DC, an upper value (45.9%) on the surface and a lower one (6.1%) at a depth of 5 mm. The composite presented the worst performance among materials studied. The composite formulation was 80% of inorganic fillers and BisfenolA/dimethacrylate (BisGMA) (18%)/triethyleneglycoldimethacrylate (TEGDMA) (2.0%) as monomers. As stated before, type/ratio/viscosity of monomers and type, amount, size and size distribution of fillers all together had an important role in the cure reaction contributing to the final performance of the composite.     

Solvothermal synthesis of new metal organic framework structures in the zinc-terephthalic acid-dimethyl formamide system

Two new metal organic framework (MOF) structures have been obtained from the Zn-terephthalic acid (H₂BDC)-dimethyl formamide (DMF) system and examined by single-crystal X-ray diffraction: Zn(C₈H₄O₄)(C₃H₇NO), 1, monoclinic C2/m, a=11.1369(5), b=14.0217(7), , β=106.316(1)°, , , Z=4, R₁=0.060, wR₂=0.169, S=1.27; Zn(HCO₂)₃(C₂H₈N), 2, trigonal , a=8.1818(1), , , , Z=6, R₁=0.014, wR₂=0.039, S=1.11. Contrary to previously published structures in the same system, the crystals were obtained by solvothermal synthesis at 381 K. Structure 1 consists of 2-D layers stacked in an offset manner to accommodate DMF moieties coordinated to Zn²⁺ within voids in adjacent layers. Structure 2 consists of a 3-D network constructed from Zn²⁺ ions bridged by deprotonated formic acid moieties. Over time, the structure of 1 rearranges to Zn(C₈H₄O₄)(C₃H₇NO)(H₂O) [monoclinic P2₁/n, a=6.6456(2), b=15.2232(5), , β=104.110(2)°, , , Z=4, R₁=0.048, wR₂=0.100, S=1.07], which is identical to the known MOF-2 structure, obtained by crystallization at ambient conditions. The three structures were determined from crystals with similar crystal habits picked from a single solvothermal synthesis batch. The study demonstrates that MOF syntheses can give not only multiple crystal structures under different conditions, but also that numerous different structures, including some that are metastable, can be formed under identical conditions.     

Dinuclear Cobalt(III) Complexes Showing a Co2O2 Metallacycle

The heptadentate Schiff base H₃L reacts with cobalt(II) acetate in methanol to form the discrete dinuclear complex Co₂L(OAc)₂(OMe)(H₂O)₂ ( 1 ·2H₂O). The reaction of 1 ·2H₂O with NMe₄OH·5H₂O in methanol gives rise to displacement of the acetate by methanolate groups, yielding Co₂L(OMe)₃(H₂O) ( 2 ·1H₂O). Recrystallizations of the Schiff base, 1 ·2H₂O and 2 ·H₂O in different solvents, produce single crystals of H₃L, 1 ·2.5H₂O and 2 ·2MeOH, respectively. The crystal structures of 1 ·2.5H₂O and 2 ·2MeOH show the cobalt atoms double bridged by and endogenous phenol oxygen atom and an exogenous methanolate oxygen donor, giving rise to Co₂O₂ cores with Co···Co distances of ca. 2.87 Å.     

Bound water measurements for aqueous protein solutions and food gels

The role of aqueous media in the stabilization of globular proteins and formation of gels was studied by absorption millimeter spectroscopy. This method allowed to measure bound water, the fraction of water which had decreased rotational mobility owing to the presence of solute. Hydration data for globular proteins were compared with data obtained previously for low-weight molecules and groups. It was found that rotational mobility of water molecules in the hydration shells of various kinds of solutes (groups) decreased in the following order: water structure breaking compounds>polar groups>unfolded proteins>globular proteins>non-polar groups. Time courses of the storage modulus were determined for the chemical acidification by glucono-δ-lactone (GDL) of milk samples prepared from skimmed milk powder (SMP). Gelation of unheated milk was a monotonous process that started at pH 4.9. Heat-treated milk from SMP (16 and 14 g per 100 ml) acidified by GDL (3 g per 100 ml) at 43 °C gave non-monotonous kinetics of gelation with two phases corresponding to the mechanisms induced by denatured whey proteins at pH>5 and by casein–casein interactions at pH 4.8–4.9. For heat-treated milk, measurement of bound water gave two stages of decrease in water mobility. Additional hydration of SMP during acidification gave 0.15–0.2 g and 0.8 g bound H₂O per gram of SMP for unheated and heat-treated milk, respectively.