Triplet topology of self-assembled zinc porphyrin-pyridylfullerene complex

This work extends a recent EPR study on light-driven electron and energy transfer in a self-assembled zinc porphyrin-pyridylfullerene (ZnP-PyrF) complex. We report on a triplet line shape analysis of the photoexcited PyrF monomer and the ZnP-PyrF complex dissolved in isotropic and anisotropic matrixes of different polarity, namely, toluene, tetrahydrofuran (THF), and the nematic liquid crystals (LCs), E-7 and ZLI-4389. The line shape of the unbound *(3)PyrF obtained in both isotropic matrixes exhibits triplet parameters similar to those obtained for other monoadducts of C(60) under similar experimental conditions. On the other hand, 8(3)PyrF oriented in the LCs shows a complicated line shape, which is attributed to two conformers: (a) an axial dominant (85%) configuration characterized by triplet parameters, similar to those obtained in the isotropic matrixes and (b) a bent configuration associated with spin density localized about the poles accompanied by sign reversal of the ZFS parameter D of the *(3)C(60) moiety. Further, since in both LCs the ZnP-PyrF complex mainly exhibits a conformation with axial symmetry, the differences between the electron and the energy transfer routes in each LC are attributed to their different polarity. This study reflects the strength of LC matrixes to serve as a topological tool, enabling us to determine the conformers' distribution and to differentiate between electron and energy transfer routes.     

Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions

Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 x 10(8) M(-1) s(-1) and 1.4 x 10(9) M(-1) s(-1), respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.     

Theory of spike timing-based neural classifiers

We study the computational capacity of a model neuron, the tempotron, which classifies sequences of spikes by linear-threshold operations. We use statistical mechanics and extreme value theory to derive the capacity of the system in random classification tasks. In contrast with its static analog, the perceptron, the tempotron's solutions space consists of a large number of small clusters of weight vectors. The capacity of the system per synapse is finite in the large size limit and weakly diverges with the stimulus duration relative to the membrane and synaptic time constants.     

微尺度色谱通道截面形状优化

本文将基于体积平均方法的理论模型与拓扑优化工具结合,以减小弥散系数为优化目标对微尺度色谱通道的截面形状进行了优化。优化结果表明色谱通道截面形状优化可以明显削弱通道内弥散过程。优化得到的截面形状明显不同于常见的矩形截面,具体形状取决于流动阻力系数的数值,流动阻力系数越大,截面的宽高比越大。将优化截面用于微尺度色谱设计可以显著改善分离速度及分离精度。     

Equilibrium,kinetics, and mechanism of the malonic acid–iodine reaction

The equilibrium constant for the reaction CH₂(COOH)₂ + I₃^? ? CHI(COOH)₂ + 2I^? + H⁺, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO₄), is (2.79 ± 0.48) × 10^?4M². Stopped-flow kinetic measurements at 25°C and ionic strength 1.00M with [H⁺] = (2.09-95.0) × 10^?3M and [I^?] = (1.23-26.1) × 10^?3M indicate that the rate of the forward reaction is given by (k₁[I₂] + k₃[I₃^?]) [HOOCCH₂COO^?] + (k₂[I₂] + k₄[I₃^?]) [CH(COOH)₂] + k₅[H⁺] [I₃^?] [CH₂(COOH)₂]. The values of the rate constants k₁-k₅ are (1.21 ± 0.31) × 10², (2.41 ± 0.15) × 10¹, (1.16 ± 0.33) × 10¹, (8.7 ± 4.5) × 10^?1M^?1·sec^?1, and (3.20 ± 0.56) × 10¹M^?2·sec^?1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by k_en[CH₂(COOH)₂], with k_en = 2.0 × 10^?3 + 1.0 × 10^?2 [CH₂(COOH)₂]. An intramolecular mechanism, featuring a six-member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.     

A generalization of Malho’s method for obtaining large cardinal numbers

Mahlo used a method by which fixed points of an enumeration of regular cardinals were employed to get a hierarchy of “large cardinals.” He also employed a second method which, in a certain sense, is much stronger than the first. Here the methods are investigated and generalized and the relations between them are clarified. This stronger method turns out to be a kind of “least upper bound” to all “fixed-points operations.” Possibilities of strengthening these processes in a natural way are pointed out.     

The X-ray structure of methyl shoreate and the stereochemistry of eichlerianic acid,cabraleone and ocotillone

An X-ray structure determination of methyl shoreate has shown that this compound has 20S,24R stereochemistry in the side chain. Ocotillone therefore possesses the same configuration, whereas eichlerianic acid and cabraleone must have 20S,24S stereochemistry. A previous wrong assignment is thereby corrected.