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101.
Exposure of aluminium-epoxide bonds to methanol, ethanol, ammonia and formamide has shown that the hydrogen bonding ability of the ‘solvent’ plays little part in determining the effect on bond strength. The strength of the bonds may be increased by short-term exposures to the alcohols. A mechanism is proposed to explain the data. 相似文献
102.
103.
The relationship between dental disease and cerebral vascular accident in elderly United States veterans 总被引:1,自引:0,他引:1
WJ Loesche A Schork MS Terpenning YM Chen C Kerr BL Dominguez 《Canadian Metallurgical Quarterly》1998,3(1):161-174
Enantiomers of N-methyl-N,alpha-methylbenzylbutyramide (1), 1-butyl-3-methyl-3'-alpha-methylbenzylurea (2), 1,2,3, 4-tetrahydro-1-naphthyl-N-butylcarbamate (3), 1,1'-bi-2-naphthyl-2, 2'-di-N-butylcarbamate (4), 1, 1'-bi-2-naphthyl-2-ol-2'-N-butylcarbamate (5), and 1, 1'-bi-2-naphthyl-2-butyrate-2'-N-butylcarbamate (6) are inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of 4-nitrophenyl butyrate and of electric eel acetylcholinesterase-catalyzed hydrolysis of acetylthiocholine in the presence of 5,5'-dithiobis-2-nitrobenzoate. For competitive inhibitors, values of the inhibition constant (Ki) and the enantiomeric ratio (Ecomp.) are investigated. For active site-directed irreversible inhibitors, values of the inhibition constant (Ki), the carbamylation constant (k2), the bimolecular rate constant (ki), and the enantiomeric ratio (E) are investigated. Toward both enzymes, compounds 1 are poor competitive inhibitors (Ki=102-104 microM) but have good enantioselectivities (Ecomp.=10-50, the preference for R). R-2 and S-2 are competitive inhibitors of acetylcholinesterase with Ki=26 and 80 microM, respectively (the preference for R) but are active site-directed irreversible inhibitors of cholesterol esterase with ki=4 and 16 M-1 sec-1, respectively (the preference for S). For those competitive inhibitions, both leaving group hydrophilic and hydrophobic binding sites of cholesterol esterase or both anionic substrate binding site and peripheral anionic binding site of acetylcholinesterase bind to N,N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors and the enzyme does not catalyze the hydrolysis of these inhibitors. The opposite stereopreference (S) for the inhibition of cholesterol esterase by compounds 2 may be due to the fact that N, N-methyl-alpha-methylbenzyl disubstituted amide parts of these inhibitors bind to the alkyl chain binding site of the enzyme. Compounds 3-6 are active site-directed irreversible inhibitors of cholesterol esterase (ki=1-13000 M-1 s-1) and peripheral anionic binding site-directed irreversible inhibitors of acetylcholinesterase (ki=1.7-1300 M-1 s-1). Compounds 3 have low enantioselectivities (E=1.3-1.4) for both enzymes. The stereopreference for atropisomers 4 and 6 is S-form toward both enzymes (E=2-30) and is identical to that of cholesterol esterase-catalyzed hydrolysis of 1,1'-bi-2-naphthyl-2,2'-diacylate. This stereopreference (S) may be due to the fact that the butyryl group or one of two butylcarbamate groups of S-atropisomers binds more effectively to the leaving group hydrophobic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase than that of R-atropisomers. The opposite stereopreference (R) for atropisomers 5 toward both enzymes may be due to a favorable interaction between the hydroxyl group of the inhibitors and the leaving group hydrophilic binding site of cholesterol esterase or the peripheral anionic binding site of acetylcholinesterase. 相似文献
104.
105.
Using data from a Swedish longitudinal project, we predicted timing of marriage and parenthood and age-35 career success from mother-rated shyness in 8–10 year old children. Results are compared with those previously found for Americans. Like shy American boys, shy Swedish boys married and became fathers later than nonshy boys. Unlike American boys, Swedish boys' adult careers were not affected by shyness. Like shy American girls, shy Swedish girls later married and became mothers at the same time as their peers. However, they also attained lower levels of education than nonshy girls. Results suggest that the life consequences of shyness depend upon its culturally defined gender and situation appropriateness. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
106.
107.
The API Coryne system, a commercially available system for the identification of coryneform bacteria, was used to identify 103 strains of Listeria spp. from clinical and environmental sources. All isolates were identified correctly to the genus or species level, although complete characterization also required tests for beta-hemolysis and CAMP reaction. 相似文献
108.
Management of patients irradiated for oral cancer should include consideration of their oral health prior to, and after, radiation therapy. Data from 130 patients, followed for a period of 1 to 10 years, are presented and evaluated. The philosophy of retention and maintenance of as many teeth as possible is supported by this data. Extraction of teeth with severe periodontal disease after irradiation also proves to be a relatively safe operation. Osteoradionecrosis tends to be limited in extent and is generally well tolerated by the patient when treated conservatively. A treatment regimen is presented that significantly reduces the morbidity from therapeutic irradiation of the jaws. A comprehensive dental evaluation and follow-up plan coupled with patient cooperation are instrumental to the success of this program. 相似文献
109.
A method is described for plotting graphs with a resolution of 30 characters per inch using an IBM 2741 communications terminal. 相似文献
110.
Plasma from cattle highly resistant to the tick Boophilus microplus conferred some resistance to unexposed calves. In contrast plasma from hosts of low resistance had no significant effect compared with plasma from unexposed donors. 相似文献