Direct measurement of isotopomer of intracellular metabolites using capillary electrophoresis time-of-flight mass spectrometry for efficient metabolic flux analysis

We have developed a metabolic flux analysis method that is based on (13)C-labeling patterns of the intracellular metabolites directly measured by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). The flux distribution of the central carbon metabolism in Escherichia coli was determined by this new approach and the results were compared with findings obtained by conventional GC-MS analysis based on isotopomer of the proteinogenic amino acids. There were some differences in estimation results between new approach using CE-TOFMS and conventional approach using GC-MS. These were thought to be attributable to variations in measured mass distributions between amino acids and the corresponding precursors and to differences in the sensitivity of the exchange coefficients to mass distributions. However, our CE-TOFMS method facilitates high-throughput flux analysis without requiring complicated sample preparation such as hydrolysis of proteins and derivatization of amino acids.     

A practical method for preparation of 4-hydroxyquinolinone esters

4-Hydroxyquinolinone esters are a common motif for many medicinal agents. Several methods exist for preparation of these compounds, generally involving the use of sodium hydride, which raises significant safety issues and limits their application to large-scale synthesis. In this note a practical, safe, and general method that employs a combination of diisopropylethylamine and sodium tert-butoxide is described. This allows for the synthesis of 4-hydroxyquinolinone esters and amides in good yields.     

Stereoselective ring-opening polymerization of a racemic lactide by using achiral salen- and homosalen-aluminum complexes

Highly isotactic polylactide or poly(lactic acid) is synthesized in a ring-opening polymerization (ROP) of racemic lactide with achiral salen- and homosalen-aluminum complexes (salenH(2)=N,N'-bis(salicylidene)ethylene-1,2-diamine; homosalenH(2)=N,N'-bis(salicylidene)trimethylene-1,3-diamine). A systematic exploration of ligands demonstrates the importance of the steric influence of the Schiff base moiety on the degree of isotacticity and the backbone for high activity. The complexes prepared in situ are pure enough to apply to the polymerizations without purification. The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral. However, analysis of the (1)H and (13)C NMR spectra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25 degrees C and that the complexes are achiral under the polymerization conditions. The flexibility of the backbone in the propagation steps is also documented. Hence, the isotacticity of the polymer occurs due to a chain-end control mechanism. The highest reactivity in the present system is obtained with the homosalen ligand with 2,2-dimethyl substituents in the backbone (ArCH==NCH(2)CMe(2)CH(2)N==CHAr), whereas tBuMe(2)Si substituents at the 3-positions of the salicylidene moieties lead to the highest selectivity (P(meso)=0.9(8); T(m)=210 degrees C). The ratio of the rate constants in the ROPs of racemic lactide and L-lactide is found to correlate with the stereoselectivity in the present system. The complex can be utilized in bulk polymerization, which is the most attractive in industry, although with some loss of stereoselectivity at high temperature, and the afforded polymer shows a higher melting temperature (P(meso)=0.9(2), T(m) up to 189 degrees C) than that of homochiral poly(L-lactide) (T(m)=162-180 degrees C). The "livingness" of the bulk polymerization at 130 degrees C is maintained even at a high conversion (97-98 %) and for an extended polymerization time (1-2 h).     

NMR chemical shift study of the methanol—benzene-d6 system

The OH proton chemical shifts of methanol referred to the CH₃ proton in the methanol — benzene-d₆ system have been measured from room temperature up to the supercritical region. MD simulations have also been performed at the same composition as experiment at 575 K. The chemical shift results in the supercritical region are in good agreement with those of pure methanol at the same density within experimental errors. The results of NMR and MD simulation suggest that the hydrogen-bonded structure of methanol is practically not affected by addition of benzene molecules.     

Radical polymerization behavior of N-vinylsaccharin

Synthesis and radical polymerization behavior of N-vinylsaccharin (1) are described. Radical homopolymerization of 1 was carried out in the presence of a radical initiator for 24 h to afford the polymer containing a saccharin moiety in the side group, which was insoluble in common organic solvents. Among the copolymers of 1 with various vinyl monomers such as vinyl acetate (VAc), methyl acrylate (MA), acrylonitrile (AN), and styrene (St), only the copolymer [copoly(1-St)] obtained from 1 and St was soluble in common organic solvents. In the copolymerization of 1 and St, the Q and e values of 1 were estimated to be 0.10 and −1.60, respectively. These values are similar to those of N-vinylphthalimide (Q = 0.36, e = −1.52). The reaction of copoly(1-St) with LiAlH₄ was carried out in THF for 24 h to convert the saccharin moiety into the ring-opened structure bearing hydroxy and sulfonamide groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3419–3426, 1999     

Nonstandard Point Counting for Algebraic Varieties

For varieties over a field k, we define motivic measures with values in ordered fields, using point counting over finite fields and taking the limits with respect to ultrafilters. Some properties and problems related to such measures are discussed. We define similar measures for algebraic dynamical systems by counting periodic points, and explain how they can be used to prove certain statements, such as the non-rationality of a motivic zeta function.     

Hawking radiation and tunneling mechanism for a new class of black holes in Einstein–Gauss–Bonnet gravity

We study Hawking radiation in a new class of black hole solutions in Einstein–Gauss–Bonnet theory. The black hole has been argued to have vanishing mass and entropy, but finite Hawking temperature. To check if it really emits radiation, we analyze Hawking radiation using the original method of quantization of a scalar field in the black hole background and with the quantum tunneling method, and confirm that it emits radiation at the Hawking temperature. A general formula is derived for the Hawking temperature and backreaction in the tunneling approach. Physical implications of these results are discussed.     

Iron-catalyzed decarbonylation reaction of aliphatic carboxylic acids leading to α-olefins

The catalytic decarbonylation reaction of aliphatic carboxylic acids can be carried out in the presence of an iron complex, and it proceeds smoothly to give α-olefins with high selectivity.