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641.
[reaction: see text] Catalyst-free conjugate addition of thiols to alpha,beta-unsaturated carbonyl compounds in water is reported. beta-Sulfido carbonyl compounds were formed at room temperature, in short times and with excellent chemoselectivity. Competitive dithiane/dithiolane formation, transesterification, and ester cleavage were not observed. Water played a dual role in simultaneously activating the alpha,beta-unsaturated carbonyl compound and the thiol. This new methodology constitutes an easy, highly efficient, and green synthesis of beta-sulfido carbonyl compounds. 相似文献
642.
This work reports on the visible luminescence properties and energy transfer processes responsible for non-exponential nature of the decay curves and also quenching of luminescence intensity of the 5D3→7FJ transitions of Tb3+ ions in lead telluroborate (PTB) glasses containing different Tb3+ concentrations. The XRD and FT-IR spectra were measured to study the glassy nature and composition of the prepared glasses. The radiative properties are determined using the Judd-Ofelt theory to judge the suitability of studied glasses as practical photonic material. These parameters suggest that the PTBTb20 glass has the potential to produce intense green emission (544 nm) through the 5D4→7F5 transition. 相似文献
643.
This note is a follow-up on the paper [A. Borel, G. Harder, Existence of discrete cocompact subgroups of reductive groups over local fields, J. Reine Angew. Math. 298 (1978) 53-64] of A. Borel and G. Harder in which they proved the existence of a cocompact lattice in the group of rational points of a connected semi-simple algebraic group over a local field of characteristic zero by constructing an appropriate form of the semi-simple group over a number field and considering a suitable S-arithmetic subgroup. Some years ago A. Lubotzky initiated a program to study the subgroup growth of arithmetic subgroups, the current stage of which focuses on “counting” (more precisely, determining the asymptotics of) the number of lattices of bounded covolume (the finiteness of this number was established in [A. Borel, G. Prasad, Finiteness theorems for discrete subgroups of bounded covolume in semi-simple groups, Publ. Math. Inst. Hautes Études Sci. 69 (1989) 119-171; Addendum: Publ. Math. Inst. Hautes Études Sci. 71 (1990) 173-177] using the formula for the covolume developed in [G. Prasad, Volumes of S-arithmetic quotients of semi-simple groups, Publ. Math. Inst. Hautes Études Sci. 69 (1989) 91-117]). Work on this program led M. Belolipetsky and A. Lubotzky to ask questions about the existence of isotropic forms of semi-simple groups over number fields with prescribed local behavior. In this paper we will answer these questions. A question of similar nature also arose in the work [D. Morris, Real representations of semisimple Lie algebras have Q-forms, in: Proc. Internat. Conf. on Algebraic Groups and Arithmetic, December 17-22, 2001, TIFR, Mumbai, 2001, pp. 469-490] of D. Morris (Witte) on a completely different topic. We will answer that question too. 相似文献
644.
A theoretical model of diffusion and reaction in an anisotropic enzyme membrane is presented with particular emphasis on the
application of such membranes in enzyme electrodes. The dynamic response of systems in which the kinetics are linear, which
comprises the practical operating regime for enzyme electrodes in analysis, is investigated via an analytic solution of the
governing differential equations. The response is presented as a function of a single dimensionless group, Μ, that is the
membrane modulus. 相似文献
645.
Diacetone-D-glucose 1 gives 3- O -methylxanthate 2 on reaction with NaH/Me I. Reductive deoxygenation of compound 2 by Bu3SnH gives the corresponding 3-deoxy glucose derivative 3 and on acid-catalyzed regioselective deprotection of C-5,6-acetonide gives the diol 4. The diol on oxidative cleavage with NaIO4 gives the aldehyde 5, which on further condensation with benzylamine followed by reduction with NaBH4 gives the amine 7. Z-Protection of the amine followed by methanolysis gives methyl furanoside 9. Reaction of 9 with methanesulfonyl chloride/Et3N gives the corresponding C-3-O-mesylate derivative 10. Catalytic hydrogenation of compound 10 (Pd/C/H2/MeOH 3 kg) gives bicyclic oxaazo compound 11, due to deprotection of the N-benzyl- and Z-protecting groups and intramolecular nucleophilic displacement of the C-2- O-mesylate by the C-5 amine in a one-pot reaction. Z-Protection of the amine 11 followed by acid-catalyzed hydrolysis gives acetal 13. Reduction of acetal by use of NaBH4 gives Z-prolinol 14. Selective oxidation of diol 14 by (2,2,6,6-tetramethylpiperidin-1-yl)-oxyl (TEMPO)/[(bis)(acetoxy)iodo]benzene (BAIB) and NaClO2/NaH2PO4, followed by Z-deprotection, gives the title compound I in 3.5% overall yield from D-glucose. 相似文献
646.
Vaibhav B. Valodkar Gopal L. Tembe Marayil Ravindranathan Rajnath Ram Hoskote S. Rama 《Reaction Kinetics and Catalysis Letters》2003,80(2):285-291
L-phenyl alanine was anchored to P(S-DVB) resin and its complex with PdCl2 was prepared. The newly synthesized catalyst was found to be a versatile and recyclable catalyst for the hydrogenation of
1-octene and acetophenone. This chiral catalyst induced moderate enantioselectivity during the asymmetric reduction of acetophenone.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
647.
David G. Harris Ehab Morsy Gopal Pandurangan Peter Robinson Aravind Srinivasan 《Random Structures and Algorithms》2016,49(2):322-344
Basic graph structures such as maximal independent sets (MIS's) have spurred much theoretical research in randomized and distributed algorithms, and have several applications in networking and distributed computing as well. However, the extant (distributed) algorithms for these problems do not necessarily guarantee fault‐tolerance or load‐balance properties. We propose and study “low‐average degree” or “sparse” versions of such structures. Interestingly, in sharp contrast to, say, MIS's, it can be shown that checking whether a structure is sparse, will take substantial time. Nevertheless, we are able to develop good sequential/distributed (randomized) algorithms for such sparse versions. We also complement our algorithms with several lower bounds. Randomization plays a key role in our upper and lower bound results. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 49, 322–344, 2016 相似文献
648.
The concept of synthetic multifunctional pores as substrate-independent optical signal transducers of chemical reactions is introduced with emphasis on the combination with substrate-specific signal generation in biomolecular transformations. Comparison with the general electrochemical transduction, known from conventional biosensors, and the general optical transduction of analyte-specific biomolecular recognition (rather than transformation), known from immunosensing, reveals the fundamental nature of the concept as well as an attractive complementarity to existing methods. Examples with transferases, hydrolases, lyases, and even an isomerase demonstrate that optical transduction with synthetic multifunctional pores is general far beyond the substrate-specific signal generators of electrochemical transduction, that is, the oxidoreductases, and absolutely unproblematic. In part very recent breakthroughs are used to highlight the remarkable promise of synthetic multifunctional pores as optical transducers of biomolecular transformation with regard to practical sensing and screening applications. 相似文献
649.
Vijayanath S. Janaki K. Gopal Ramalingam Ragupathi C. Rangasamy Baskaran Alam Mohammed Mujahid 《Journal of Solid State Electrochemistry》2023,27(1):183-194
Journal of Solid State Electrochemistry - In the present study, a novel cost-effective and efficient configuration of dye-sensitized solar cell (DSSC) with zinc oxide–multi-walled carbon... 相似文献
650.
Existence and Non-existence of Positive Solutions for a Discrete Fractional Boundary Value Problem 下载免费PDF全文
In this work, we deal with two-point boundary problem for a finite nabla fractional difference equation. First, we establish an associated Green''s function and state some of its properties. Under suitable conditions, we deduce the existence and non-existence of positive solutions to the considered problem. Finally, we construct a few examples to illustrate the established results. 相似文献