Theoretical study of halophilic reactions of stable silylenes with chloro- and bromocarbons

A theoretical study of the mechanism of the reaction of stable silylenes with halocarbons has been carried out using the B3LYP density functional method. The main findings are as follows: (1) Lewis acid-base complexes formed between silylenes and halocarbons do not play a role in silylene insertion chemistry into halocarbons; therefore, the acid-base complex mechanism proposed by West et al. (J. Am. Chem. Soc. 2002, 124, 4186) is not appropriate to describe the disilane formation reaction. (2) The disilane formation reactions follow the energetically favorable general reaction pathway (X = halogen): (i) Y2Si: + HCX3 --> TS1 --> Y2XSi-CHX2. (ii) Y2Si: + Y2XSi-CHX2 --> TS2 --> Y2XSi-SiY2CHX2. (3) The observed preference of stable silylenes to undergo C-X bond insertion rather than C-H bond has been investigated. The theoretical findings suggest that this preference is a result of the thermodynamic factor. (4) Stable silylenes prefer to insert into a C-Br rather than a C-Cl bond because the energy barrier to insertion is lower, and the reaction is more exothermic.     

A computational study of cycloaddition reactions of d8 metal tetroxide (iron, ruthenium, osmium) complexes with C60

The potential energy surfaces of the cycloaddition reactions MO(4)(NC(5)H(5))(2) + C(60)→ MO(4)(NC(5)H(5))(2)(C(60)) (M = Fe, Ru, and Os) have been studied at the B3LYP/LANL2DZ level of theory. It has been found that there should be two competing pathways in these reactions, which can be classified as a [6,5]-attack (path A) and a [6,6]-attack (path B). Our theoretical calculations indicate that, given the same reaction conditions, the cycloaddition reaction of C(60)via [6,6]-attack is more favorable than that via [6,5]-attack both kinetically and thermodynamically. This is in good agreement with the available experimental observations. A qualitative model, which is based on the theory of Pross and Shaik, has been used to develop an explanation for the barrier heights. As a result, our theoretical findings suggest that the singlet-triplet splitting ΔE(st) (= E(triplet)- E(singlet)) of the d(8) MO(4)(NC(5)H(5))(2) and C(60) species can be a guide to predict their reactivity towards cycloaddition. Our model results demonstrate that the reactivity of d(8) metal tetroxide cycloaddition to C(60) decreases in the order FeO(4)(NC(5)H(5))(2) > RuO(4)(NC(5)H(5))(2) > OsO(4)(NC(5)H(5))(2). In consequence, we show that both electronic and geometric effects play a decisive role in determining the energy barriers as well as the reaction enthalpy.     

Characterization of the SiOT Angle and Cation Effects on 29Si Chemical Shifts Of Zeolites

The quantitative relationships between ²⁹Si chemical shifts and (a) the SiOT (T = Al or Si) angles and (b) the nature of the cations of the alkali forms of zeolites can be account for by the changes of charge density and p electron population of the Si atoms as calculated by the extended Hückel method on cluster models.     

Comparison of epithelial and fibroblastic cell behavior on nano/micro-topographic PCL membranes produced by crystallinity control

In this study, the relationship between the cellular morphology and the material surface topography was investigated. Poly(ε-caprolactone) (PCL) membranes were prepared in a wide range of surface wettabilities by means of crystallinity-controlled solvent casting process. Membrane surfaces were characterized by atomic force microscope (AFM), scanning electron microscope (SEM), and static/dynamic water contact angle measurements. It was found that solvent evaporation and non-solvent (methanol) addition to the solvent (THF) are the most decisive parameters to change the surface topography. The non-solvent addition and the decrease in solvent evaporation temperature from room temperature to -20 °C caused increased polymeric chain mobility and crystallization time. Such changes in crystallization parameters led to the formation of micro/nano-sized features on the membrane. Cell culture studies indicated that in contrast to Madin Darby kidney (MDBK) epithelial cells, L929 mouse fibroblast preferred rough and porous surfaces.     

A regenerable immobilized NADH model. II. Reduction of α,α,α-trifluoroacetophenone by immobilized 1,4-dihydronicotinamide in aprotic solvent

A regenerable dihydronicotinamide, immobilized on a macroreticular polystyrene resin was used for the reduction of trifluoroacetophenone (TFA) in acetonitrile. Practical reutilization of the polymeric reagent (91% per cycle) was obtained when magnesium perchlorate was added to the reaction of the immobilized dihydropyridine with TFA. A possible explanation of the role of Mg ion in the reaction of benzyldihydronicotinamide and its polymeric analog is presented. This explanation also accounts for the results of other NADH model reactions, described in the literature, and for the role of the Zn ion in the enzyme liver alcohol dehydrogenase (LADH).     

On an alternative functional equation

Aequationes mathematicae -     

On the boundedness and continuity of convex functions and additive functions

Aequationes mathematicae -