Low molecular weight organogels based on long-chain carbamates

Thermoreversible organogels were prepared from carbamates with alkyl side chains of different lengths. Gelation was possible only up to an alkyl side chain length of 12 carbons, beyond which crystallization occurs, due to the dominant van der Waals interaction between the alkyl chains. This is in contrast to other alkane-based organogels, in which gelating efficiency increased with the length of the alkane chain (see Abdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237). The critical concentration for gelation decreases drastically with an increase in the side chain length. Xerogels of these show birefringent fibers with uniform cross section and unlimited growth in one direction. The extent of this unlimited growth is affected by the length of the alkyl side chain in the carbamate, which finally ceases the gel formation ability of the carbamate. Cryogenic scanning electron microscopy images of the gels are similar to those of xerogels. From X-ray diffraction of the fibers, we propose that the growth direction is along the plane of hydrogen bonds between the carbamate molecules. The thickness of the fibers depends on the length of the alkyl side chain. Morphological differences are seen between gels prepared by slow cooling and quenching of the solution. Thus, the morphology of the fibrous xerogels of the carbamates can be tailored for specific applications, by the choice of the alkyl side chain length and the rate of cooling the solution.     

Joule-Thomson inversion curve prediction by using equation of state

In this paper five equations of state are tested for checking their ability to predict the Joule-Thomson inversion curve.These five equations of state are:Mohsennia-Modarres-Mansoori(MMM),Ji-Lemp(JL),modified Soave-Redlich-Kwang(SRK)equation of state by Graboski(MSRK1),modified SRK equation of state by Peneloux and Rauzy(MSRK2),and modified Peng-Robinson (PR)equation of state by Rauzy(PRmr).The investigated equations of state give good prediction of the low-temperature branch of the inversion curve,except for MMM equation of state.The high-temperature branch and the peak of the inversion curve have been observed,in general,to be sensitive to the applied equation of state.The values of the maximum inversion temperature and maximum inversion pressure are calculated for each component used in this work.     

Use of a Water-in-Oil Microemulsion as Mobile Phase in Complexation TLC of Amino Acids on Silica Layers Impregnated with Metal Cations

JPC – Journal of Planar Chromatography – Modern TLC - A water-in-oil microemulsion has been used for the first time as a mobile phase in thin-layer chromatography of amino acids. A new...     

Immobilized enzyme electrode for the determination of salicylate in blood serum

This determination of salicylate in blood serum is based on application of an immobilized enzyme electrode. Salicylate hydroxylase (E.C.1.14.13.1) is chemically immobilized onto a pig intestine mounted on an oxygen electrode. The signals are monitored amperometrically and the resulting output voltage is read using a simple adapter. The experimental parameters and possible interferences are discussed. Samples containing 1.0 × 10^?5?1.87 × 10^?3 M (1.6–300 μg ml^?1) salicylate were assayed with relative standard deviations between 1.3% and 6% and recoveries between 98.7 and 103%. Results obtained by the proposed method and by the established clinical method for randomly spiked pooled serum samples correlated well (r = 0.99).     

Selected valence electron split-shell molecular orbital calculations on the diatomic interhalogen molecules

Selected valence electron split-shell molecular orbital calculations have been performed on the diatomic interhalogen molecules in order to obtain their binding energies, equilibrium internuclear distances, vibrational force constants, dipole moments and nuclear quadrupole coupling constants. The results are compared with the corresponding closedshell values and with those of some previous semiempirical and nonempirical all valence electron calculations. It is observed that the selected valence electron split-shell molecular orbital method which involves the least amount of computations yields results in better agreement with experiment than other methods.     

Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

Thermochemistry of bis-arene- and arenetricarbonyl-chromium compounds containing hexamethylbenzene, 1,3,5-trimethylbenzene and naphthalene.

Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and iodination have led to values of the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol^?1) at 298K: [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (63±12); [Cr(η⁶-C₆(CH₃)₆)₂] : -(88±12); [Cr(1,2,3,4,4a,8a-η-C₁₀H₈)₂] = (407±11); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = -(258±8). Separate measurements by the vacuum sublimation microcalorimetric technique gave the following values for the enthalpy of sublimation at 298K (kJ mol^?1) : [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (104±1); [Cr(η⁶-C₆(CH₃)₆)₂] = (119±4); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = (107±3). From these and other data, the bond enthalpy contributions of the metal-ligand bonds in the gaseous metal complexes were evaluated as follows: [(η₆-C₆(CH₃)₆)-Cr] (155±7); [(η⁶-C₆H₃(CH₃)₃)-Cr] (151±6); [(1,2,3,4,4a, 8a-η-C₁₀H₈)-Cr](145±6) kJ mol^?1]The question of the transferability of the enthalpy contributions of chromium—ligand bonds between organochronium complexes is discussed with aid of information from structural and spectroscopic investigation. The limitations of the procedure are defined.The thermodynamic data are used to discuss various substitution, redistribution and exchange reaction of Cr(η-arene)₂ and [Cr(CO)₃(η-arene)] compounds.     

Kinetics of anation of chromium(III) by L-phenylalanine

Summary The kinetics of anation of chromium(III) species, [Cr(H₂O)₆]⁴⁺ and [Cr(H₂O)₅OH]²⁺, by L-phenylalanine in aqueous acid has been studied spectrophotometrically. Effects of varying [substrate], [ligand], [H⁺], , % ethanol and temperature were investigated. The kinetic data suggest a mechanism where outersphere-associations [between chromium(III) species and phenylalanine in the zwitterionic form] precede anation. Comparison of the results with published data suggest an I_a path for the [Cr(H₂O)₆]³⁺ reaction and I_d path for the [Cr(H₂O)₅OH]²⁺ reaction.