2-Ketogluconic acid production by acetobacter pasteurianus

Production of 2-ketogluconic acid in batch fermentation was investigated.Acetobacter pasteurianus ATCC 6438, which produces selectively 2-ketogluconic acid only, was used. The optimal pH for glucose dehydrogenation to gluconate by resting cells was 5.0 and for gluconate dehydrogenation to 2-ketogluconate 4.25. When glucose medium was used, the 89% yield was achieved after 90 h. For the optimal productivity, medium containing glucose and gluconate with the molar glucose:gluconate ratio 7.4 was proposed, and the yield of 92% after 56 h was achieved. This composition of medium led to the elevation of dissolved oxygen concentration during fermentation. It consequently resulted in elevated gluconate dehydrogenase activity being discussed as the rate-limiting activity of the batch production.     

Bounds on fourth-generation fermion masses in the standard model

In the standard model, if the ratios of Yukawa couplings to gauge couplings are bounded functions of the renormalization point, then the fourth-generation fermion massesm _U , m _D , andm _L (in GeV) are constrained to lie within a domain approximately given by (m _U /213)^4.8+(m _D /209)^4.8+(m _L /161)^2.4<1.     

Alkoholbestimmung

Ohne Zusammenfassung     

Frozen orbital effects in the computation of excitation energies of the iron atom

The limitations arising from the use of a frozen orbital approximation applied to 3s and 3p electrons of the iron atom are investigated at the CI level.     

Stereochimie de la cycloadditton des diarylnitrilimines sur les n-alkyl et les dialkyl-1,2 dihydro-1,2 isoquinoleines

The PMR spectroscopic properties (60 MHz) of cycloadducts of diarylnitrilimins towards 1,2-dihydroisoquinolines mono alkylated at the N-atom or dialkylated at the C¹ -carbor and N-atoms have been studied.Date allow us to determine the stereochemistry of the cycloaddition reaction which is regio and diastereospecific. Configuration and conformation of the cycloadducts are specified.     

Elemental concentrations in nbs biological and environmental standard reference materials

Elemental concentrations reported by 325 investigators in 16 NBS SRM's are summarized. Mean values, standard deviations and comparative data from NBS and other reviews are provided.     

The Rayleigh—Schrödinger BK method applied to the lower electronic states of pyrrole

A second-order Rayleigh—Schrödinger B_K method (RS B_K) is described and applied to computing the lower electronic states of pyrrole. This method is more nearly size consistent than the previously used Brillouin—Wigner B_K (BW B_K) method. Pyrrole RS B_K excitation energies compare closely to BW B_K, second-order perturbation theory, and extrapolated CI energies. To provide insight into the origin of the bands in the experimental absorption spectrum, absorption coefficients and second moments are also reported.     

(+)-Echinobetaine B: isolation, structure elucidation, synthesis and preliminary SAR studies on a new nematocidal betaine from a southern Australian marine sponge, Echinodictyum sp

The principle nematocidal agent present in a southern Australian marine sponge of the genus Echinodictyum has been isolated and identified as the novel betaine (+)-echinobetaine B (6), and the structure assigned by spectroscopic analysis has been confirmed by total synthesis. Preliminary SAR conclusions are drawn from analysis of synthetic intermediates and the known marine metabolites zooanemonin (12) and norzooanemonin (13), and the new sponge metabolite norzooanemonin methyl ester (14). The latter compound is reported for the first time from a selection of Australian sponges, including an Axinyssa sp., a Niphates sp., an Axinella sp. and a Ptilocaulis sp.     

A theoretical study of paths for decomposition and rearrangement of dihydroxycarbene

The transition states for fragmentation of dihydroxycarbene [C(OH)₂] to H₂ and CO₂ and for the rearrangement of this carbene to formic acid were located by ab initio calculations. The relative energies of the transition states were determined at several levels of theory and the basis set dependence of the energies is discussed. At the best level of theory; using a basis set of double-zeta quality augmented by polarization functions and with the inclusion of extensive CI, we found that the transition state for fragmentation was considerably higher in energy than that for rearrangement. This finding is at variance with the predictions of the Woodward--Hoffmann rules because fragmentation represents an “allowed” reaction, whereas rearrangement is “forbidden.” In conformity with the Woodward–Hoffman rules, the transition state for rearrangement was found to be close in energy to H· + ·CO₂H. The even higher energy of the transition state for concerted fragmentation to H₂ and CO₂ is attributed to the need for the latter fragment to remain substantially bent in order to permit H₂ formation while maintaining a modicum of OH bonding. Difficulties in locating the transition state for concerted fragmentation are discussed and a new method for finding transition states is proposed.     

Highly stereoselective asymmetric synthesis of (R)-(−)-mevalolactone

An asymmetric synthesis of ($\text{R}$)-(?)-mevalolactone in over 87% enantiomeric purity is described.