Regeneration of NADH and ketone hydrogenation by hydrogen with the combination of hydrogenase and alcohol dehydrogenase

Applied Biochemistry and Biotechnology - The regeneration of nicotinamide-adenine dinucleotide (reduced form, NADH) by the reaction of NAD with hydrogen gas was carried out in the presence of the...     

One-step preparation of 3-alkoxypyrazine-2-carbonitriles from pyrazine-2,3-dicarbonitriles and related reactions

A series of 5,6-disubstituted 3-alkoxypyrazine-2-carbonitriles ( 2a-i ) were prepared from 5,6-disubstituted pyrazine-2,3-dicarbonitriles ( 1a-d ) by direct substitution with alcohols. Treatment of 1 with amines gave either pyrrolopyrazines ( 3a,b ) or substitution products ( 4,5 ). In a low temperature range, 1 afforded imidates and related compounds ( 6–11 ). The preference among these reactions depended on the 5,6-substituents and on the reaction conditions.     

Headspace solid-phase microextraction-gas chromatography--mass spectrometry analysis of the volatile compounds of Evodia species fruits

In this study the investigation of the aroma compounds of dried fruits of Evodia rutaecarpa (Juss.) Benth. and E. rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang (i.e. E. officinalis Dode) (Rutaceae family) was carried out to identify the odorous target components responsible for the characteristic aroma of these valuable natural products. To avoid the traditional and more time-consuming hydrodistillation, the analyses were carried out by means of headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The SPME headspace volatiles were collected using a divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fiber. The extraction conditions were optimized using a response surface experimental design to analyze the effect of three factors: extraction temperature, equilibrium time and extraction time. The best response was obtained when the extraction temperature was around 80 degrees C, equilibrium time near 25 min and extraction time close to 18 min. Analyses were performed by GC-MS with a 5% diphenyl-95% dimethyl polysiloxane (30 m x 0.25 mm I.D., film thickness 0.25 microm) capillary column using He as the carrier gas and a programmed temperature run. The main components of the HS-SPME samples of E. rutaecarpa (concentration >3.0%) were limonene (33.79%), beta-elemene (10.78%), linalool (8.15%), myrcene (5.83%), valencene (4.73%), beta-caryophyllene (4.62%), linalyl acetate (4.13%) and alpha-terpineol (3.99%). As for E. officinalis, the major compounds were myrcene (32.79%), limonene (18.36%), beta-caryophyllene (9.92%), trans-beta-ocimene (6.04%), linalool (5.88%), beta-elemene (7.85%) and valencene (4.62%).     

Dynamics of iodine anions in KI and LiI aqueous solutions studied by <Superscript>127</Superscript>I nuclear resonant quasi-elastic scattering

The dynamics of iodine ions in potassium iodide (KI) and lithium iodide (LiI) aqueous solutions have been studied through ¹²⁷I nuclear resonant quasi-elastic scattering (NRQES). A newly developed Si (12 2 2) double crystal monochromator for ¹²⁷I 57.6 keV excitation is used. Broadening due to a diffusive motion is measured in the energy spectra of the NRQES from the solutions.     

Stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with carbon nucleophiles

The stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with allyltributylstannane and with ketene silyl acetals in the presence of a Lewis acid are described. Both the reactions occurred regioselectively at the allylic position via an S_N2 process giving rise to a single product, respectively. Treatment of the products by the latter reaction with p-TsOH afforded various 3,4-anti- and 3,4-syn-disubstituted γ-lactones in a highly stereoselective manner and high yields.     

Thermoreversible gelation with hydrogen‐bonded zipper‐like crosslink junctions

Thermoreversible gelation of polymer chains bearing hydrogen‐bonding functional groups is studied by off‐lattice Monte Carlo simulation with semiflexible bead‐and‐spring model chains. To see the formation of zipper‐like sequential crosslink junctions (domino effect), we introduce stabilization energy ?Δε between the nearest neighboring hydrogen‐bonded beads along a chain in addition to the ordinary pairwise hydrogen‐bond energy ?ε. It is found that the condition nθ/ = 2 is fulfilled at the sol/gel transition point, where is the average zipper length, θ the zipper content per chain, and n the total number of beads on a chain. It is also shown that, at low temperature, zipper growth dominates the nucleation of new zippers, and as a result, there is another transition from a three‐dimensional network to a pairwisely bound state (network/pair transition). © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3331–3336, 2005     

Amphiphilic p-sulfonatocalix[4]arene-coated CdSe/ZnS quantum dots for the optical detection of the neurotransmitter acetylcholine

Water-soluble CdSe/ZnS (core-shell) semiconductor quantum dots surface-modified with tetrahexyl ether derivatives of p-sulfonatocalix[4]arene were synthesized for the optical detection of the neurotransmitter acetylcholine.     

Discovery of (E)-9,10-dehydroepothilones through chemical synthesis: on the emergence of 26-trifluoro-(E)-9,10-dehydro-12,13-desoxyepothilone B as a promising anticancer drug candidate

We provide a full account of the discovery of the (E)-9,10-dehydro derivatives of 12,13-desoxyepothilone B (dEpoB), a new class of antitumor agents with promising in vivo preclinical properties. The compounds, which are to date not available by modification of any of the naturally occurring epothilones, were discovered through total chemical synthesis. We describe how our investigations of ring-closing metathesis reactions in epothilone settings led to the first and second generation syntheses of (E)-9,10-dehydro-12,13-desoxyepothilone congener 6. With further modifications, the synthesis was applied to reach a 26-trifluoro derivative compound (see compound 7). To conduct such studies and in anticipation of future development needs, the total synthesis which led to the initial discovery of compound 7 was simplified significantly. The total synthesis methodology used to reach compound 7 was then applied to reach more readily formulated compounds, bearing hydroxy and amino functionality on the 21-position (see compounds 45, 62, and 63). Following extensive in vitro evaluations of these new congeners, compound 7 was nominated for in vivo evaluations in xenograft models. The data provided herein demonstrate a promising therapeutic efficacy, activity against large tumors, nonrelapseability, and oral activity. These results have identified compound 7 as a particularly promising compound for clinical development. The excellent, totally synthetic, route to 7 makes such a program quite feasible.     

Loss of regularity for p-evolution type models

The goal of the paper is to study the loss of regularity for special p-evolution type models with bounded coefficients in the principal part. The obtained loss of regularity is related in an optimal way to some unboundedness conditions for the derivatives of coefficients up to the second-order with respect to t.     

Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D₂O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111