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31.
Boyd DR Sharma ND Llamas NM Coen GP McGeehin PK Allen CC 《Organic & biomolecular chemistry》2007,5(3):514-522
Enantiopure trans-dihydrodiols have been obtained by a chemoenzymatic synthesis from the corresponding cis-dihydrodiol metabolites, obtained by dioxygenase-catalysed arene cis-dihydroxylation at the 2,3-bond of monosubstituted benzene substrates. This generally applicable, seven-step synthetic route to trans-dihydrodiols involves a regioselective hydrogenation and a Mitsunobu inversion of configuration at C-2, followed by benzylic bromination and dehydrobromination steps. The method has also been extended to the synthesis of both enantiomers of the trans-dihydrodiol derivatives of toluene, through substitution of a vinyl bromine atom of the corresponding trans-dihydrodiol enantiomers derived from bromobenzene. Through incorporation of hydrogenolysis and diMTPA ester diastereoisomer resolution steps into the synthetic route, both trans-dihydrodiol enantiomers of monohalobenzenes were obtained from the cis-dihydrodiols of 4-haloiodobenzenes. 相似文献
32.
Udit AK Hagen KD Goldman PJ Star A Gillan JM Gray HB Hill MG 《Journal of the American Chemical Society》2006,128(31):10320-10325
We report analyses of electrochemical and spectroscopic measurements on cytochrome P450 BM3 (BM3) in didodecyldimethylammonium bromide (DDAB) surfactant films. Electronic absorption spectra of BM3-DDAB films on silica slides reveal the characteristic low-spin FeIII heme absorption maximum at 418 nm. A prominent peak in the absorption spectrum of BM3 FeII-CO in a DDAB dispersion is at 448 nm; in spectra of aged samples, a shoulder at approximately 420 nm is present. Infrared absorption spectra of the BM3 FeII-CO complex in DDAB dispersions feature a time-dependent shift of the carbonyl stretching frequency from 1950 to 2080 cm(-1). Voltammetry of BM3-DDAB films on graphite electrodes gave the following results: FeIII/II E(1/2) at -260 mV (vs SCE), approximately 300 mV positive of the value measured in solution; DeltaS degrees (rc), DeltaS degrees , and DeltaH degrees values for water-ligated BM3 in DDAB are -98 J mol(-1) K(-1), -163 J mol(-1) K(-1), and -47 kJ mol(-1), respectively; values for the imidazole-ligated enzyme are -8 J mol(-1) K(-1), -73 J mol(-1) K(-1), and -21 kJ mol(-1). Taken together, the data suggest that BM3 adopts a compact conformation within DDAB that in turn strengthens hydrogen bonding interactions with the heme axial cysteine, producing a P420-like species with decreased electron density around the metal center. 相似文献
33.
This paper studies four n-job, m-machine flowshop problems when processing times of jobs on various machines follow certain
conditions. The objective is to obtain a sequence, which minimizes total elapsed time under no-idle constraint. Under no-idle
constraint, the machines work continuously without idle-interval. We prove two theorems. We introduce simple algorithms without
using branch and bound technique. Numerical examples are also given to demonstrate the algorithms. 相似文献
34.
Udit Surya Mohanty 《Applied Surface Science》2006,252(16):5907-5916
The effect of Al on the electrochemical corrosion behaviour of Pb-free Sn-8.5 Zn-0.5 Ag-XAl-0.5 Ga solder in 3.5% NaCl solution was investigated by using potentiodynamic polarization techniques. The X content in the solder varied from 0.1 to 3 wt.%. Polarization studies revealed that an increase in Al content upto 1.5 wt.% decreased the corrosion current density (Icorr), corrosion rate of the solder and shifted the corrosion potential (Ecorr) towards more noble values. However, higher content of Al, i.e. 3 (wt.%) in the five-element solder enhanced the corrosion rate and resulted in a significant increase in the Ecorr towards more negative values. Passivation behaviour was noticed in all the solders having varying Al content, but the passive film formed at 1.5 wt.% Al was most stable due to its low passivation current density (ip) and low critical current density (icc) value in comparison to the other solders. XPS and Auger depth profile results revealed that the passive film consisted of oxides/hydroxides of Al and Zn formed on the surface of the solder with Sn being formed in the subsequent layer. Considerable aluminium segregation occurred towards the surface principally as Al2O3/Al(OH)3 with increase in Al content to 1.5 wt.% in the five element solder. The formation of Al2O3 seemed to prevent the oxidation of zinc on the surface of the solder. 相似文献
35.
For each n 4 there exists a finite 2-group Gn such that itsnth dimension subgroup does not coincide with its nth lowercentral subgroup. This settles the dimension subgroup conjecturenegatively for all n4. 相似文献
36.
The sphingolipid backbone is readily assembled by E-selective olefin cross metathesis of a suitable building block. 相似文献
37.
Derek R. Boyd Peter B. Coulter Narain D. Sharma W.Brian Jennings Valerie E. Wilson 《Tetrahedron letters》1985,26(13):1673-1676
Steric and mesomeric effects have a marked influence upon the formation of oxaziridine (normal pathway) or nitrone (abnormal pathway) products from the imine-peroxyacid reaction; n.m.r. studies of the thermal isomerization of oxaziridines to nitrones provide evidence of a pseudo-abnormal oxidation pathway. 相似文献
38.
Summary A thin-layer Chromatographic investigation was carried out on Silica Gel-G plates for metal dithizonates and the technique was applied for detecting metals present in autopsy tissues in cases of suspected suicide and homicide. Rf values of the common metal complexes in four Chromatographic solvents and the colour of their respective spots on the TLC plate are reported.
Zusammenfassung Die Dünnschichtchromatographie von Metalldithizonaten auf Silicagel G-Platten wurde mit dem Ziel untersucht, Metalle in Leichenteilen nach Selbstmord oder Mord nachweisen zu können. Die Rf-Werte der Dithizonate üblicher Metalle in vier zur Chromatographie verwendeten Lösungsmitteln und die Farbe der Chromatogrammflecken wurden angegeben.相似文献
39.
Swarup Narain Tewari 《Mikrochimica acta》1961,49(1):37-40
Summary The separation by paper chromatography and identification of reducing sugars in urine is described.
Zusammenfassung Die papierchromatographische Trennung und Identifizierung reduzierender Zucker im Harn wird beschrieben.
Résumé On décrit la séparation par Chromatographie sur papier et l'identification des sucres réducteurs dans l'urine.相似文献
40.
Hao Liu Jian Xu Jiali Jiang Jun Yin Ravin Narain Yuanli Cai Shiyong Liu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1446-1462
Well‐defined amphiphilic PCL‐b‐(PDMA)2 and (PCL)2‐b‐PDMA Y‐shaped miktoarm star copolymers and PCL‐b‐PDMA linear diblock copolymer were synthesized via a combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP), where PCL is poly (ε‐caprolactone) and PDMA is poly(2‐(dimethylamino)ethyl methacrylate). All of these three types of copolymers have comparable PCL contents and overall molecular weights. The PCL block is hydrophobic while the PDMA block is hydrophilic, and they behave like polymeric surfactants and self‐assemble into PCL‐core micelles in aqueous media. The chain architectural effects on the micellization properties, including the aggregation number, size, polydispersity, and micelle densities of (PCL29)2‐b‐PDMA45, PCL61‐b‐(PDMA24)2, and PCL56‐b‐PDMA49 in dilute aqueous solution, were then explored by dynamic and static laser light scattering (LLS). The intensity–average hydrodynamic radius, 〈Rh〉, the aggregation number per micelle, Nagg, and the core radius, Rcore, of the PCL‐core micelles all increased in the order PCL61‐b‐(PDMA24)2 < (PCL29)2‐b‐PDMA45 < PCL56‐b‐PDMA49. The surface area occupied per soluble PDMA block at the core/corona interface increased in the order PCL61‐b‐(PDMA24)2 < PCL56‐b‐PDMA49 < (PCL29)2‐b‐PDMA45. PCL61‐b‐(PDMA24)2 micelles had the largest overall micelle density, possibly because of that the presence of two soluble PDMA arms at the junction point favors the bending of the core–corona interface and thus the formation of densely‐packed core‐shell nanostructures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1446–1462, 2007 相似文献