Asymmetric acyl-transfer promoted by readily assembled chiral 4-N,N-dialkylaminopyridine derivatives

The development of a new class of chiral 4-N,N-dialkylaminopyridine acyl-transfer catalysts capable of exploiting both van der Waals (pi) and H-bonding interactions to allow remote chiral information to stereochemically control the kinetic resolution of sec-alcohols with moderate to excellent selectivity (s = 6-30). Catalysts derived from (S)-alpha,alpha-diarylprolinol are considerably superior to analogues devoid of a tertiary hydroxyl moiety and possess high activity and selectivity across a broad range of substrates.     

Production of fuel alcohol from wheat by VHG technology

Very high gravity (VHG) wheat mashes containing more than 300 g of dissolved solids per liter were prepared and fermented with active dry yeast at 20, 25, 30, and 35°C with and without yeast extract as nutrient supplement. At 20°C, mashes with 38% (w/v) dissolved solids end-fermented without any nutrient supplementation and maximum ethanol yields of 23.8% (v/v) were obtained. With increasing temperatures, the sugar consumption decreased. Addition of yeast extract stimulated the rate of fermentation at all temperatures, but did not increase the total amount of sugar consumed. The stimulatory effect of yeast extract on cell multiplication decreased with increasing sugar concentration, and virtually no difference in cell number was observed between yeast extract-supplemented and unsupplemented mashes at sugar concentrations above 33% (w/v). The fermentative capacity of the yeast (expressed as maximum specific rate of sugar consumption) remained the same at all sugar concentrations in unsupplemented mashes, but decreased in yeast extract-supplemented mashes at sugar concentrations below 33% (w/v). When the sugar concentration was above 33% sugar (w/v), the fermentative capacity in yeast extract-supplemented mashes was greater than that observed in unsupplemented samples.     

Theoretical study of the dissociation of nitric acid at a model aqueous surface

The issue of acid dissociation of nitric acid at an aqueous surface is relevant in various portions of the atmosphere in connection with ozone depletion. This proton-transfer reaction is studied here via electronic structure calculations at the HF/SBK+(d) level of theory on the HNO(3) x (H(2)O)(3) model reaction system embedded in clusters comprising 33, 40, 45, and 50 classical, polarizable waters with an increasing degree of solvation of the nitrate group. Free energy estimates for all the cases examined favor undissociated, molecular nitric acid over the 0-300 K temperature range, including that relevant for the upper troposphere, where it is connected to the issue of the mechanism of nitric acid uptake by water ice aerosols. The presence of molecular HNO(3) at 300 K at the surface is further supported by vibrational band assignments in good agreement with a very recent surface-sensitive vibrational spectroscopy study of diluted HNO(3)/H(2)O solutions.     

Further studies on the synthesis of quinazolines from 2-fluorobenzonitriles

Recently, we reported that appropriately substituted 2-fluorobenzonitriles undergo cyclization with guanidine carbonate to afford 2,4-diaminoquinazolines usually in good to excellent yield. This paper describes the preparation of a variety of new 2,4-diaminoquinazolines substituted at positions five or seven. In addition, the reactions of selected 2-fluorobenzonitriles with formamidine acetate or acetamidine acetate were examined. The results obtained demonstrate that the analogous 4-amino- and 2-methyl-4-aminoquinazolines can be prepared by this approach but that the yields are considerably lower than when guanidine carbonate is employed as the cyclization reagent.     

Microscopic theory of brownian motion: Mori friction kernel and langevin-equation derivation

A derivation of the phenomenological Langevin equation for the momentum of a brownian particle from the generalized Langevin equation of Mori is presented. This derivation requires a detailed examination of the Mori friction kernel (or memory function). It is demonstrated, on the basis of prior work of Mazur and Oppenheim, that the Mori kernel does not admit of a well behaved expansion in the ratio of bath- and brownian-particle masses. In addition, the Mori kernel is found to decay on the slow time scale of the brownian-particle momentum. Both features, which contradict standard assumption, are traced to the influence of coupling to nonlinear powers of the momentum and preclude a Langevin-equation derivation solely on the basis of time-scale separation arguments. The Langevin-equation is recovered, however, when the small magnitude of slowly decaying contributions is taken into account.