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351.
Hart BR Létant SE Kane SR Hadi MZ Shields SJ Reynolds JG 《Chemical communications (Cambridge, England)》2003,(3):322-323
Biomolecules have been attached to porous silicon by a new linking method that forms a direct Si-C bond on the surface and retains the photoluminescence of the porous silicon. 相似文献
352.
Raman and infrared spectroscopy were used to study the nature of hydrogen bonding and the cation inductive effect in solutions of LiCF(3)SO(3) dissolved in hexylamine, a primary amine, and dipropylamine, a secondary amine. Comparison of pure hexylamine and hexylamine dissolved in CCl(4) established that the Raman band maximum of the symmetric stretching mode, nu(s)(NH(2)), in pure hexylamine originates in molecules undergoing no hydrogen bonding interactions. The addition of LiCF(3)SO(3) to hexylamine or dipropylamine shifts the frequencies of the solvent NH stretching modes by two effects: the breaking of hydrogen bonds and the cation inductive effect. Comparison of the infrared and Raman spectra allows (to some degree) the separation of these two effects. During these studies, crystalline compounds of hexylamine:LiCF(3)SO(3) and dipropylamine:LiCF(3)SO(3) were discovered, and their structures were solved by single-crystal X-ray diffraction techniques. Vibrational spectra of these crystals and detailed structural knowledge of the cation-solvent interactions complement analogous spectroscopic studies of the solution phases. The cation-polymer and hydrogen bonding interactions of branched poly(ethylenimine) (BPEI) complexed with LiCF(3)SO(3) were modeled by the solutions of hexylamine and dipropylamine containing dissolved LiCF(3)SO(3). Specifically, lithium ion interactions with the primary and secondary amine groups in BPEI were modeled by the solution studies with hexylamine and dipropylamine, respectively. The analysis of the hexylamine system was particularly useful because the primary amine group of BPEI dominates the NH stretching region of the spectrum. 相似文献
353.
Summary Paper chromatographic procedures involving the use of butanolacetic acidwater (415 v/v) as solvent and 1 % aqueous uranyl acetate or uranyl nitrate solution as spray reagent, have been developed for detection of plant pigments when present in amounts of at least 5 g each. Quinones, flavones and some of their O-glycosides having at least one hydroxyl group adjacent to carbonyl group, have been easily detected. The colour intensity has been found to increase in the case of compounds containing vicinal hydroxyl groups. 相似文献
354.
A novel family of BINAP ligands were prepared with alkoxy- and acetoxy-derived substituents in the 3,3'-positions. They were prepared through a convergent synthesis starting from readily available 4-bromo-2-naphthol. These ligands afforded excellent enantioselectivities in the asymmetric hydrogenation of substituted olefins. The presence of the 3,3'-substituents was shown to be beneficial by a direct comparison with the parent unsubstituted BINAP. [reaction: see text] 相似文献
355.
Michael C. Hodgson Masood A. Khan Rudolf J. Wehmschulte 《Journal of Cluster Science》2002,13(4):503-520
A new series of amidoaluminum hydride complexes H
n
Al[N(SiHMe2)2]3–n
NMe3 (1, n=2; 2, n=1), Al[N(SiHMe2)2]3 (3), and [H2AlN(SiHMe2)2]2 (4) were prepared by the metallation of tetramethyldisilazane (Me2HSi)2NH with either H3AlNMe3 or H3Al2OEt2. The molecular structures of 1 and 2 were shown by X-ray crystal structure determination to be monomeric Lewis acid-base adducts with four coordinate aluminum centers and terminal amido groups. The molecular structure of 4 was found to be a dimer with bridging disilylamides in the solid state. Attempts to obtain crystals of [H2AlN(SiMe3)2]2, a bulkier analogue of 4, led to the isolation of the unusual alumoxane
2-(Me3Si)2 N-(AlH2)2-
3-O-Al(H)N(SiMe3)2OEt2 (6) in moderate yields. Thermolysis of 1 and 2 resulted only in the formation of ligand exchange and decomposition products, whereas thermolysis of 4 at 80°C afforded 1 equivalent of Me2SiH2 and a new species formulated as the imide complex [HAlNSiMe2H]
n
(7). Thermolysis of 4 in the presence of AlH3NMe3 gave Me2SiH2 and 7 at a higher reaction rate even at a lower temperature. 相似文献
356.
357.
In an alternative strategy to the use of delta-lactam urethanes for the preparation of homologues of AMPA-type glutamate antagonists, we have used 5-exomethylene derivatives of pyroglutamate esters. The homochiral pyrazole amino acid derivatives 18 and 19 have been prepared in this way. Although this synthesis yields products with a glycine residue separated from a heterocyclic ring by two carbon atoms, the substitution of the heterocyclic ring is different from that in compounds prepared from delta-lactam urethanes. The branched chain compounds 32 and 33 have also been prepared in this way but the second chiral centre is epimerised during the synthesis. An interesting reaction, giving the pyridone 27 from the imino ether 24 and tert-butyl acetoacetate, is also reported. 相似文献
358.
The dilithium salts of the phosphonate dianions [PhP(E)(N(t)Bu)(2)](2-) (E = O, S, Se) are generated by the lithiation of [PhP(E)(NH(t)Bu)(2)] with n-butyllithium. The formation of the corresponding telluride (E = Te) is achieved by oxidation of [Li(2)[PhP(N(t)Bu)(2)]] with tellurium. X-ray structural determinations revealed dimeric structures [Li(THF)(2)[PhP(E)(N(t)Bu)(2)]](2) in which the monomeric units are linked by Li-E bonds. In the case of E = Se or Te, but not for E = S, transannular Li-E interactions are also observed, resulting in a six-rung ladder. By contrast, for E = O, this synthetic approach yields the Li(2)O-templated tetramer [(THF)Li(2)[PhP(O)(N(t)Bu)(2)]](4).Li(2)O in THF or the tetramer [(Et(2)O)(0.5)Li(2)[PhP(O)(N(t)Bu)(2)]](4) in diethyl ether. The reaction of trimethylaluminum with PhP(E)(NH(t)Bu)(2) produces the complexes Me(2)Al[PhP(E)(N(t)Bu)(NH(t)Bu)] (E = S, Se), which were shown by X-ray crystallography to be N,E-chelated monomers. 相似文献
359.
In the solid state, OP[N(H)Me](3) (1a) and OP[N(H)(t)Bu](3) (1b) have hydrogen-bonded structures that exhibit three-dimensional and one-dimensional arrays, respectively. The lithiation of 1b with 1 equiv of (n)BuLi generates the trimeric monolithiated complex (THF)[LiOP(N(t)Bu)[N(H)(t)Bu](2)](3) (4), whereas reaction with an excess of (n)BuLi produces the dimeric dilithium complex [(THF)(2)Li(2)OP(N(t)Bu)(2)[N(H)(t)Bu]](2) (5). Complex 4 contains a Li(2)O(2) ring in an open-ladder structure, whereas 5 embraces a central Li(2)O(2) ring in a closed-ladder arrangement. Investigations of the lithiation of tris(alkyl or arylamido)thiophosphates, SP[N(H)R](3) (2a, R = (i)Pr; 2b, R = (t)Bu; 2c, R = p-tol) with (n)BuLi reveal interesting imido substituent effects. For the alkyl derivatives, only mono- or dilithiation is observed. In the case of R = (t)Bu, lithiation is accompanied by P-S bond cleavage to give the dilithiated cyclodiphosph(V/V)azane [(THF)(2)Li(2)[((t)BuN)(2)P(micro-N(t)Bu)(2)P(N(t)Bu)(2)]] (9). Trilithiation occurs for the triaryl derivatives EP[N(H)Ar](3) (E = S, Ar = p-tolyl; E = Se, Ar = Ph), as demonstrated by the preparation of [(THF)(4)Li(3)[SP(Np-tol)(3)]](2) (10) and [(THF)(4)Li(3)[SeP(NPh)(3)]](2) (11), which are accompanied by the formation of small amounts of 10.[LiOH(THF)](2) and 11.Li(2)Se(2)(THF)(2), respectively. 相似文献
360.
[Reaction: see text]. Several novel organoselenium and tellurium compounds were prepared and evaluated as mimetics of the selenoenzyme glutathione peroxidase, which protects cells from oxidative stress by reducing harmful peroxides with the thiol glutathione. The compounds were tested for catalytic activity in a model system wherein tert-butyl hydroperoxide or hydrogen peroxide were reduced with benzyl thiol and the rate of the reaction was measured by monitoring the formation of dibenzyl disulfide. Thus, aromatic derivatives 19, 22, 24, and 25 proved to be inferior catalysts compared to the parent cyclic seleninate ester 14 and spirodioxyselenurane 16. In the case of 19 and 22, this was the result of their rapid conversion to the relatively inert selenenyl sulfides 31 and 32, respectively. In general, hydrogen peroxide was reduced faster than tert-butyl hydroperoxide in the presence of the selenium-based catalysts. The cyclic tellurinate ester 27 and spirodioxytellurane 29 proved to be superior catalysts to their selenium analogues 14 and 16, respectively, resulting in the fastest reaction rates by far of all of the compounds we have investigated to date. Oxidation of 29 with hydrogen peroxide produced the unusual and unexpected peroxide 33, in which two hypervalent octahedral tellurium moieties are joined by ether and peroxide bridges. The structure of 33 was confirmed by X-ray crystallography. Although 33 displayed strong catalytic activity when tested independently in the model system, its relatively slow formation from the oxidation of 29 rules out its intermediacy in the catalytic cycle of 29. 相似文献