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911.
Bentley TW Harris HC Ryu ZH Lim GT Sung DD Szajda SR 《The Journal of organic chemistry》2005,70(22):8963-8970
[reaction: see text] Rate constants and product selectivities (S = ([ester product]/[acid product]) x ([water]/[alcohol solvent]) are reported for solvolyses of chloroacetyl chloride (3) at -10 degrees C and phenylacetyl chloride (4) at 0 degrees C in ethanol/ and methanol/water mixtures. Additional kinetic data are reported for solvolyses in acetone/water, 2,2,2-trifluoroethanol(TFE)/water, and TFE/ethanol mixtures. Selectivities and solvent effects for 3, including the kinetic solvent isotope effect (KSIE) of 2.18 for methanol, are similar to those for solvolyses of p-nitrobenzoyl chloride (1, Z = NO(2)); rate constants in acetone/water are consistent with a third-order mechanism, and rates and products in ethanol/ and methanol/water mixtures can be explained quantitatively by competing third-order mechanisms in which one molecule of solvent (alcohol or water) acts as a nucleophile and another acts as a general base (an addition/elimination reaction channel). Selectivities increase for 3 as water is added to alcohol. Solvent effects on rate constants for solvolyses of 3 are very similar to those of methyl chloroformate, but acetyl chloride shows a lower KSIE, and a higher sensitivity to solvent-ionizing power, explained by a change to an S(N)2/S(N)1 (ionization) reaction channel. Solvolyses of 4 undergo a change from the addition/elimination channel in ethanol to the ionization channel in aqueous ethanol (<80% v/v alcohol). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions, calculated using Gaussian 03 (HF/6-31G(d), B3LYP/6-31G(d), and B3LYP/6-311G(d,p) MO theory). 相似文献
912.
The determination of citalopram, amitriptyline, clomipramine and their desmethyl metabolites after alkaline diethyl either extraction from plasma is achieved by high-performance liquid chromatography using two internal standards and mu Bondapak C18 as stationary phase. Elution is carried out isocratically at 0.5 or 1 ml/min with a mixture of acetonitrile-potassium dihydrogen phosphate-distilled water (45:50:5). Detection is monitored by absorption at 254 nm. The detection limit is less than 5 ng/ml for each compound. The coefficients of variation are between 1.3% and 9.4% for 8-360 ng/ml. Interference from 22 possible co-medications is discussed. The technique can be used for therapeutic monitoring of these antidepressants as well as in analytical toxicology. 相似文献
913.
914.
We continue our earlier paper [20] by proving the equivalence, for regularκ>ω, of the existence of (κ, 1) morasses with built-in ♦ sequences and a strengthening, SK◊ , of the forcing principle, SK◊ of [20]. We obtain various applications of SK◊, to wit: the existence of a stationary subset of [K+]<K with sup as coding function, the existence of a counterexample to Arhangel’skii’s conjecture (κ=ℵ1) and compactness, axiomatizability and transfer properties for the Magidor-Malitz language ℒ
(κ=ℵ1).
Research partially supported by NSF Grant MCS 8301042. 相似文献
915.
916.
917.
Stanley Sawyer 《Probability Theory and Related Fields》1978,42(4):279-292
Summary Let T be an infinite homogeneous tree of order a+1. We study Markov chains {X
n} in T whose transition functions p(x, y)=A[d(x,y)] depend only on the shortest distance between x and y in the graph. The graph T can be represented as a symmetric space of a p-adic matrix group; we prove a series of results using essentially the spherical functions of this symmetric space. Theorem 1.
d(X
n,x) n a.s., where >0 if A(0) 1, X
0=x. Assuming {X
n} is strongly aperiodic, Theorem 2. p
2(x, y)CRn/n3/2 for fixed x, y where R=(d) A(d)<1, and if E[d(X1, X0)2]<, Theorem 3. R(1–u, x, y) = (1–u)npn(x, y)=Ca–d[exp(–du/)+od(1)] as d=d(x,y) uniformly for 0u2. Using Theorem 3, we calculate the Martin boundary Dirichlet kernel of p(x, y) on T, which turns out to be independent of {itA(d)}. We also consider a stepping-stone model of a randomly-mating-and-migrating population on the nodes of T. If initially all individuals are distinct, then in generation n approximately half of the individuals of a given type are within n of a typical one and essentially all are within 2n.This work was partially supported by the National Science Foundation under grant number MCS 75-08098-A01For the academic year 1977–78: Department of Mathematics GN-50, University of Washington, Seattle, Washington 98195 USA 相似文献
918.
We look at the asymptotic behavior of the coefficients of the q-binomial coefficients (or Gaussian polynomials) \({\left(\begin{array}{c}{a+k}\\{k}\end{array}\right)_{q}}\), when k is fixed. We give a number of results in this direction, some of which involve Eulerian polynomials and their generalizations. 相似文献
919.
Vostrikov VV Grant CV Daily AE Opella SJ Koeppe RE 《Journal of the American Chemical Society》2008,130(38):12584-12585
Using the model alpha-helical peptide acetyl-GGALW5LALALALALALALW19LAGA-ethanolamide ("GWALP23"), we have compared the polarization inversion with spin exchange at magic angle method and geometric analysis of labeled alanines method for estimating the transmembrane helix orientation. For GWALP23 in bilayers of a short lipid, dilauroylphosphatidylcholine, we find general agreement between the two methods, with a static helix tilt of about 11degrees-13degrees with respect to the bilayer normal. 相似文献
920.