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11.
The recently proposed Harbola–Sahni local potential in its exchange-only version [Phys. Rev. Lett. 62 , 689 (1989)] is found to give the static dipole and quadrupole polarizabilities for the Neisoelectronic series in excellent agreement with the corresponding Hartree–Fock estimates. © 1992 John Wiley & Sons, Inc. 相似文献
12.
By means of exponential laws we show a Bianchi Type I model of the universe where we define overall deceleration and Hubble's parameters that have constant values. We employ a convenient relation for defining the radius of the universe. Pressure and density have constant values, too. 相似文献
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Appleby I Boulton LT Cobley CJ Hill C Hughes ML de Koning PD Lennon IC Praquin C Ramsden JA Samuel HJ Willis N 《Organic letters》2005,7(10):1931-1934
Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield. 相似文献
16.
Samuel Natelson 《Microchemical Journal》1991,44(3)
When glutamic acid is amidinated, guanidinoglutaric acid is formed. This is readily converted by boiling in water to its lactam [2-imino-4-oxo-5-(3′-propane acid) imidazolidine; GGAL]. In the present study GGAL is dehydrated to form a second lactam, anhydro-GGAL (AGGAL), with trifluoroacetic anhydride. The molecular weight of this compound was ascertained gravimetrically by precipitation with flavianic acid and by mass spectrography to be 153.14. UV and infrared spectra and hydrogen and 13C NMR studies determined its structure as an imidazolidine ring fused to a pyrrol ring, 2-imino-4-oxo-imidazolidine-1,5-pyrrolidone-8. On paper electrophoresis, GGAL traveled to the anode, while AGGAL traveled to the cathode. On TLC plates (butanol 60, H2O 25, acetic 15), the Rf value of GGAL was 0.42 and that of AGGAL was 0.38, confirming that AGGAL was more basic than GGAL. The preparation of 1,3-di-(phenylcarbamoyl)-GGAL is also described. 相似文献
17.
R. R. Mendel Kimball A. Milton James H. Reid Mark A. Samuel 《Zeitschrift fur Physik C Particles and Fields》1986,32(4):517-520
Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τντ/B(D→μνμ,B(F→τντ/B(D→μνμ can be sensitive to tau-neutrino masses of 30 MeV or greater. 相似文献
18.
Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate. 相似文献
19.
Most common diseases appear to result from complex, poorly understood interactions between genetic and environmental factors. Relatively few factors have been unequivocally linked with disease risk or outcome. Evidence from various studies using different experimental approaches has been interpreted as showing that, apart from its harmful effects on the pathogenesis of the common skin cancers, ultraviolet radiation (UVR) may exert a beneficial effect on development of various internal cancers and other pathologies. This concept is supported by parallel studies showing that hypovitaminosis D is linked with increased risk of various diseases including insulin resistance and multiple sclerosis. These findings suggest that, first, host factors such as skin pigmentation that affect UVR-induced synthesis of vitamin D and, second, polymorphism in genes that mediate the effectiveness of vitamin D action are susceptibility candidates for a variety of diseases. Collectively, these data suggest the hypothesis that, via effects on vitamin D synthesis, UVR exposure has beneficial effects on susceptibility and outcome to a variety of complex diseases. We describe evidence from studies in various diseases, but mainly from prostate cancer patients, that supports this hypothesis, but we emphasize that, although supportive data are available, the concept is unproven. Indeed, other explanations are possible. However, given the potentially important public health implications of the hypothesis and the potential for the development of novel therapeutic modalities, we believe the concept is worthy of further investigation. 相似文献
20.
Samuel Natelson 《Microchemical Journal》1982,27(4):466-483
The existence of homoserine lactone in Pisum sativum seedlings is demonstrated. L-Homoserine lactone reacts with hydroxylamine, at neutral or alkaline pH, to form homoserine hydroxamic acid. Procedures are described for preparing L-homoserine lactone and L-homoserine hydroxamic acid. The hydroxamic acid yields a color with maximum absorbance at 492 nm with Fe3+ in 0.25 N HCl. This reaction permitted assay for total homoserine and homoserine lactone. Six-day old Pisum sativum seedlings, with cotyledons removed, were extracted with 90% ethanol. Evaporation of the ethanol and addition of Na2SO4 solution and toluene and centrifugation removed protein lipids and esters. After clarification with activated charcoal, homoserine lactone content was estimated by reaction with NH2OH and Fe3+ reagents. For total homoserine, protein precipitation was with 2 N HCl and toluene. Evaporation to dryness at 60 °C under vacuum converted all homoserine to the lactone. The values found for total homoserine (μmols/g, wet weight) and preformed lactone (%) with the various growth media used were as follows: nitrate 87.4 (14.7%), NH2OH 75.2 (6.3%), water 70.5 (7.9%), urea 56.4 (18.9%). Acetic anhydride added to homoserine hydroxamic acid forms acetohydroxamic acid, which yields a color with maximum absorbance at 505 nm with Fe3+. This color reaction is seven times as sensitive as the reaction of Fe3+ with homoserine hydroxamic acid itself. 相似文献