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21.
Russell P. Newton Jalal A. Khan Dipankar Ghosh James I. Langridge A. Gareth Brenton Frank M. Harris Terence J. Walton 《Journal of mass spectrometry : JMS》1991,26(5):447-453
The determination of cytidine 3′,5′-cyclic monophosphate-specific phosphodiesterase activity by means of fast-atom bombardment (FAB) mass Spectrometry with mass-analysed ion kinetic energy (MIKE) spectrum scanning is described. Initial efforts to determine the activity of the enzyme by this method were unsuccessful owing to the obfuscation of sample-related peaks by peaks emanating from the incubation buffer and cation adducts; dilution of buffer and a desalting procedure overcame these difficulties. In the resulting positive-ion FAB mass spectra, characteristic peaks of the enzyme substrate and product could be readily identified and the protonated molecular ions selected for MIKE scanning. By spiking enzyme incubates with known amounts of substrate and product, and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the substrate/product ratio at the end of a series of phosphodiesterase incubations was determined. From the data obtained, the Km and Vmax of the phosphodiesterase were calculated as 6.08 mM and 11 μmol min?1 mg?1, respectively, showing good agreement with the analogous values of 8.06 mM and 5.8 μmol?1 min?1 mg?1 obtained by radioactive assay. 相似文献
22.
Terence C. Gibb Robert Greatrex Norman N. Greenwood Kenneth G. Snowdon 《Journal of solid state chemistry》1975,14(2):193-202
The magnetic and structural properties of the solid solution SrFexRu1?xO3?y (0 ? x ? 0.5) have been studied using 57Fe and 99Ru Mössbauer spectroscopy and other techniques. These phases, which are here reported for the first time, have a distorted perovskite structure. The iron substitutes exclusively as Fe3+ and thereby causes oxygen deficiency, but has little effect on the magnetic behaviour of the Ru4+ until x > 0.2, whereupon the metallic band system begins to revert to a localized electron structure. The properties of a sample with x = 0.3 are complex and intermediate in character. For x > 0.3 the oxygen deficiency is reduced by substantial oxidation to Ru5+ until at x = 0.5 the system corresponds to Sr2Fe3+Ru5+O6. 相似文献
23.
Thomas Gelbrich Terence L. Threlfall Michael B. Hursthouse 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o470-o472
The title compound anilinium chloride–4‐bromo‐N‐phenylbenzenesulfonamide (1/1), C6H8N+·Cl−·C12H10BrNO2S, displays a hydrogen‐bonded ladder motif with four independent N—H⋯Cl bonds in which both the NH group of the sulfonamide molecule and the NH3 group of the anilinium ion [N⋯Cl = 3.135 (3)–3.196 (2) Å and N—H⋯Cl = 151–167°] are involved. This hydrogen‐bonded chain contains two independent R42(8) rings and each chloride ion acts as an acceptor of four hydrogen bonds. 相似文献
24.
The cob(I) alamin (1(I)) -catalyzed2 transformation of the aldehyde 2 has been studied (cf. Table 1). Kinetic examinations showed a rapid isomerization of 2 to 3 (cf. Fig. 1 and 2). From the transformations in glacial AcOH, the two cyclopropanols 5 and 7 were isolated as main products (cf. Tables 1–3 and Fig. 1 and 2). Using large amounts of 1(I) , the aldehyde 4 was very slowly transformed. Accepting the intermediate formation of 6 interconnected Co-complexes, i. e. A , B , C , D , E and F (cf. Scheme), the generation of all the products observed can be explained. 相似文献
25.
A series of novel 4-amino-1,4-benzodiazepine-2,5-diones was synthesized via two pathways. The first method involved reductive alkylation of unsymmetrical hydrazines with glyoxylic acid, followed by Fisher esterification. The resulting N-aminoglycinate ethyl ester was subsequently o-nitrobenzoylated, reduced, and thermally cyclized to obtain 4-dialkylaminobenzodiazepinones. In the second method methylhydrazine was acetylated at Nα then benzoylated at Nβ to give 1,2-diacylhydrazines. Alkylation with ethyl bromoacetate and reduction of the nitro group, followed by thermal cyclization yielded 4-acetamidobenzodiazepinones. All title compounds were evaluated in mice in MES seizure and sc Met seizure threshold tests for anticonvulsant activity, and in the rotorod test for neurotoxicity. Activity and toxicity were both minimal. 相似文献
26.
[3-3H]-valine was efficiently synthesised from sodium α-ketoisovalerate. With a β-lactam negative mutant of C. acremonium, l-[1-14C-3-3H]-valine and dl-[1-14C-3-3H]-valine were independently incorporated into the Arnstein tripeptide dimer, i.e. Bis-δ-(l-α-aminodipyl)-l-cystinyl-bis-d-valine, with full retention of trieium at C-3 of the d-valine residue. This result strongly suggested retention of configuration at C-3 of valine when the tripeptide was biosynthesised, and further limited the number of possible mechanisms for the biosynthesis of penicillins. 相似文献
27.
An inexpensive flow-injection instrument for determining low concentrations of dissolved reactive phosphorus in natural waters is reported. The unique feature is the use of an inexpensive detector consisting of a flow cell and a simple photometer that incorporates a super-bright light-emitting diode as the source and a photodiode as the detector. The tin(II) chloride-molybdate method was optimized using a modified simplex optimization method. Silicate interference up to 5 mg Si l?1 was removed by addition of 0.10% (w/v) tartaric acid. Using the tartaric acid-modified optimized reagents, a detection limit of 0.6 μg P l?1 was achieved. The method was linear over the range 0–100 μg P l?1 with an excellent precision (r.s.d. 2.9% at 2.0 and 0.5% at 50 μg P l?1). An in-line pre-concentration anion-exchange column was used to obtain an even lower detection limit of 0.1 μg P l?1 and applied to the analysis of real samples. 相似文献
28.
Sadayuki Mori Tetsuya Karita Koichi Komatsu Nobuyuki Sugita Terence S. M. Wan 《合成通讯》2013,43(9):1475-1482
Under high pressure conditions, fullerene C60 smoothly reacts with 2H-pyran-2-one to give a [4+2] cycloadduct, which can be reduced to an alcohol derivative. 相似文献
29.
30.
Giles Auchmuty 《Numerical Functional Analysis & Optimization》2013,34(3-4):211-264
This paper describes, and analyzes, a method of successive approximations for finding critical points of a function which can be written as the difference of two convex functions. The method is based on using a non-convex duality theory. At each iteration one solves a convex, optimization problem. This alternates between the primal and the dual variables. Under very general structural conditions on the problem, we prove that the resulting sequence is a descent sequence, which converges to a critical point of the problem. To illustrate the method, it is applied to some weighted eigenvalue problems, to a problem from astrophysics, and to some semilinear elliptic equations. 相似文献