On the possibility that cyclodextrins' chiral cavities can be available on AOT n-heptane reverse micelles. A UV-visible and induced circular dichroism study

The formation of reverse micelles (RMs) of sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) in n-heptane including two different beta-cyclodextrin (beta-CD) derivatives (hydroxypropyl-beta-CD, hp-beta-CD, and decenyl succinyl-beta-CD, Mod-beta-CD) is reported. Both cyclodextrins can be incorporated into AOT RMs in different zones within the aggregate, while beta-CD cannot. Using UV-vis and induced circular dichroism (ICD) spectroscopy and different achiral molecular probes (some azo dyes, p-nitroaniline and ferrocene), it was possible to determine that Mod-beta-CD is located with its cavity at the oil side of the AOT RM interface, while for hp-beta-CD the cavity is inside the RM water pool. Among the molecular probes used, methyl orange (MO) was the only one which gave the ICD signal when dissolved in the AOT RMs with hp-beta-CD, so a detailed study of MO behavior in homogeneous media was also performed to compare with the microheterogeneous media. The solvatochromic behavior of the dye depends not only on the polarity of the media but also on other specific solvent properties. A Kamlet-Taft analysis shows that the MO absorption spectrum shifts to longer wavelength with an increase in the solvent polarity-polarizability (pi*) and the hydrogen donor ability (alpha) of the medium. MO appears to be almost 3 times more sensitive to the pi* parameter than to the alpha parameter. In addition, from the MO absorption spectral changes with the hp-beta-CD concentration, the association equilibrium constants in pure water (K11W) and inside the RMs (K11RM) were computed. The results show that K11W is almost 10 times larger than the value inside the RMs. The latter can be explained considering that MO resides anchored to the RM interface through hydrogen bond interaction with the hydration bound water. This study shows for the first time that the cyclodextrin chiral cavity is available for a guest in an organic medium such as the RMs; therefore, we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.     

Study of the replacement of weak ligands on square-planar organometallic nickel(II) complexes. Organo-nickel aquacomplexes

When trans-[NiRf2L2] (Rf = 3,5-C6Cl2F3; L = group 15 soft monodentate weak ligand such as SbPh3 or AsPh3) is dissolved in wet (CD3)2CO, isomerization (to give cis-[NiRf2L2]) and subsequent substitutions of L by (CD3)2CO or by water occur, and several complexes containing acetone and aqua ligands are formed. The isomerization takes place in a few seconds at room temperature. The substitution reactions on the cis isomer formed are faster. The kinetics of the equilibria between all of the participating species have been studied by 19F exchange spectroscopy experiments at 217 K, and the exchange rates and rate constants have been calculated. These data reflect the weakness of acetone compared to water and AsPh3. The data obtained are the first available for square-planar nickel(II) aquacomplexes. The bulkier AsCyPh2 ligand slows down the exchange processes while the displacement of AsMePh2 is clearly disfavored. Activation entropy studies support an associative ligand substitution. All of these data fit well with the previously reported relative activity of these complexes as catalysts in norbornene polymerization.     

Adsorptive stripping voltammetry of bovine serum albumin

The behaviour of bovine serum albumin in cyclic voltammetry and differential-pulse adsorptive stripping voltammetry is described. Under the optimized conditions, with an accumulation potential of +0.15 V (vs. Ag/AgCl) and accumulation times of 50 s or 120 s, linear calibration graphs were obtained for 1.0–4.0×10^?8 M BSA and 0.2–1.5×10^?8 M BSA, respectively.     

High-accuracy extrapolated ab initio thermochemistry. II. Minor improvements to the protocol and a vital simplification

The recently developed high-accuracy extrapolated ab initio thermochemistry method for theoretical thermochemistry, which is intimately related to other high-precision protocols such as the Weizmann-3 and focal-point approaches, is revisited. Some minor improvements in theoretical rigor are introduced which do not lead to any significant additional computational overhead, but are shown to have a negligible overall effect on the accuracy. In addition, the method is extended to completely treat electron correlation effects up to pentuple excitations. The use of an approximate treatment of quadruple and pentuple excitations is suggested; the former as a pragmatic approximation for standard cases and the latter when extremely high accuracy is required. For a test suite of molecules that have rather precisely known enthalpies of formation {as taken from the active thermochemical tables of Ruscic and co-workers [Lecture Notes in Computer Science, edited by M. Parashar (Springer, Berlin, 2002), Vol. 2536, pp. 25-38; J. Phys. Chem. A 108, 9979 (2004)]}, the largest deviations between theory and experiment are 0.52, -0.70, and 0.51 kJ mol(-1) for the latter three methods, respectively. Some perspective is provided on this level of accuracy, and sources of remaining systematic deficiencies in the approaches are discussed.     

Residues of a Pfaff system relative to an invariant subscheme

In this paper we give a purely algebraic construction of the theory of residues of a Pfaff system relative to an invariant subscheme. This construction is valid over an arbitrary base scheme of any characteristic.

     

TiO2膜电极光电催化降解苯甲酸的机理研究

利用自制纳米TiO2薄膜作电极, 对苯甲酸光电催化降解过程进行了系统研究. 同时利用扫描电镜(SEM)、X射线衍射图谱(XRD)和光电流-电压响应谱分析光催化剂的微观性质和光电性能. 选取较高的pH 10.5, 以利于苯甲酸降解中间产物的检测(GC/MS). 通过对比光电催化与单一的TiO2光催化体系中苯甲酸的降解动力学、总有机碳(TOC)的去除率、降解产物的生成(GC/MS)及活性自由基物种的产生(ESR), 提出光电催化降解苯甲酸的具体反应路径和氧化机理. 羟基化的苯甲酸在羟基自由基与活性氧自由基的共同作用下, 经由含六个碳原子的二酸(顺式己二烯二酸), 被进一步氧化成小分子酸和CO2.     

Antifungal activity of crown ethers

Some crown ethers were found to show significant antifungal activity against some wood-decay fungi, phytopathogenic fungi and eumycetes,Trichophytons for dermatomycosis. Their toxicity was evaluated by the paper disc method as well as by determining the values of ED₅₀, i.e., the concentration which inhibits the mycelium growth by 50%. The fungi examined areTyromyces palustris, Picnoporous coccineus, Coriolous versicolor, Pyricularia filamentosa, Fusarium sp., Trichophyton rubrum, Trichophyton sp., etc. Among the 26 crown ethers tested, 3,5-di-t-butyl-benzo-15-crown-5 showed relatively high activity, the highest ED₅₀ value of which being 8 M or 3 ppm. Other alkylbenzocrown ethers, dicyclohexyl crown ethers and Kryptofix 22DD also showed considerable activity. On the other hand, unsubstituted crown ethers, benzocrown ethers with a polar substituent, Kryptofix 222B and Kryptofix 221 were inactive.     

Hydrophobic interaction effects on the kinetics of ligand substitution in binary aqueous mixtures at pentacyano(piperidine)ferrate(II) ion

The kinetics of piperidine replacement by pyridine at the pentacyano(piperidine)-ferrate(II) complex ion was studied under pseudo-first order conditions in binary aqueous mixtures of methanol, t-butanol, p-dioxane, and glycerol, from a mole fraction of co-solvent from 0 to about 0.15. The observed variations can be explained considering the degree of hydrophobic interaction between released ligand and water molecules which changes according to the structure-forming or struucture-breaking effect of added co-solvent on water.