Single and double hydrogen migration in the fragmentation of 3-methyl-2-butyl trifluoroacetate

Three of the main oxygen-containing fragments resulting from 3-methyl-2-butyl trifluoroacetate (11) had been identified previously as the 1-triflnoroacetoxyethyl cation (m/z 141, 12, product of simple cleavage), and the products of single (m/z 142) and double hydrogen transfer (m/z 143, protonated ethyl trifluoroacetate). Collisionally activated dissociation of m/z 142 and the isotopomers resulting from 11-2-d, 11-1-d₃, 11-5,6-d₆, and 11-¹⁸O₂ has established that m/z 142 is the oxygen protonated 1-trifluoroacetoxyethyl free radical (17) formed by hydrogen shift irom a γ-methyl group to oxygen in the molecular ion, rather than in a complex (18) between 12 and the 2-propyl free radical, as expected based on a mechanistic model existing in the literature. The second hydrogen transferred originates in the other γ-methyl group; its migration may occur, but does not have to, in the complex between 17 and a molecule of propene, prior to dissociation of the two fragments. Collision-activated dissociation has now shown that the m/z 140 ion observed in the spectrum is the molecular ion of vinyl trifluoroacetate, possibly formed by a hydrogen transfer from 12 to the 2-propyl radical in the complex 18. The hydrogen migration to oxygen exhibits no isotope effect, whereas the transfers to carbon atoms exhibit small primary and α secondary kinetic isotope effects. Exclusive migration of the tertiary hydrogen from C(3) occurs in the formation of 2-methylbutene cation radical (m/z 70) from the molecular ion. The hydrocarbon ion fragments and the heteroatom-containing fragments are formed from 11 by disjoint pathways.     

对固体圆二色光谱测试方法的再认识——兼谈“浓度效应”

对近期发展的固体圆二色(CD)光谱测试方法进行了概述、评价和比较, 着重探讨了“浓度效应”的存在使固体CD光谱失真的原因. 通过对本课题组和其他作者已报道的四种化合物的固体CD谱再测试的反思, 强调了依手性化合物的手性光谱学性质不同, 根据浓度梯度实验选择其合适测试浓度的必要性. 对固有手性的阻转异构化合物(S)-1,1'-联二萘酚(S-BINOL)进行了成膜法固体CD谱浓度梯度测试, 发现所得固体薄膜CD谱中也存在着“浓度效应”     

对固体圆二色光谱测试方法的再认识——兼谈“浓度效应”

对近期发展的固体圆二色(CD)光谱测试方法进行了概述、评价和比较, 着重探讨了“浓度效应”的存在使固体CD光谱失真的原因. 通过对本课题组和其他作者已报道的四种化合物的固体CD谱再测试的反思, 强调了依手性化合物的手性光谱学性质不同, 根据浓度梯度实验选择其合适测试浓度的必要性. 对固有手性的阻转异构化合物(S)-1,1'-联二萘酚(S-BINOL)进行了成膜法固体CD谱浓度梯度测试, 发现所得固体薄膜CD谱中也存在着“浓度效应”     

对固体圆二色光谱测试方法的再认识——兼谈“浓度效应”

对近期发展的固体圆二色(CD)光谱测试方法进行了概述、评价和比较, 着重探讨了“浓度效应”的存在使固体CD光谱失真的原因. 通过对本课题组和其他作者已报道的四种化合物的固体CD谱再测试的反思, 强调了依手性化合物的手性光谱学性质不同, 根据浓度梯度实验选择其合适测试浓度的必要性. 对固有手性的阻转异构化合物(S)-1,1'-联二萘酚(S-BINOL)进行了成膜法固体CD谱浓度梯度测试, 发现所得固体薄膜CD谱中也存在着“浓度效应”     

Solvation largely accounts for the effect of N-alkylation on the properties of nickel(II/I) and chromium(III/II) cyclam complexes

The source of the effect of N-alkylation on the redox properties of Ni(II/I) and Cr(III/II) cyclam complexes has been investigated using DFT calculations. The structures of the anhydrous and hydrated complexes were optimized in the gas phase, and single point calculations were performed in a polarized continuum. The main results are the following: the decrease in outer sphere solvation upon N-alkylation is the major source of the relative stabilization of the lower oxidation state complexes by the tertiary amine ligands; tertiary amine nitrogen donors are stronger sigma-donors than the secondary amines, as predicted from the inductive effect of alkyls; steric strain elongates the metal-nitrogen bonds in the tertiary complexes and decreases the ligand strain energies; and the site of water binding to the complexes differs because of their different electronic structures (i.e., in the Ni complexes, the water molecules bind to the M[bond]N[bond]H sites, whereas in the Cr complexes they bind to the central metal cation). Outer sphere hydrogen bonding of water to the ligands in the coordination sphere lowers the ionization potentials by charge delocalization.     

Volumes of restricted Minkowski sums and the free analogue of the entropy power inequality

In noncommutative probability theory independence can be based on free products instead of tensor products. This yields a highly noncommutative theory: free probability theory (for an introduction see [9]). The analogue of entropy in the free context was introduced by the second named author in [8]. Here we show that Shannon's entropy power inequality ([6, 1]) has an analogue for the free entropy (X) (Theorem 2.1).The free entropy, consistent with Boltzmann's formulaS=klogW, was defined via volumes of matricial microstates. Proving the free entropy power inequality naturally becomes a geometric question.Restricting the Minkowski sum of two sets means to specify the set of pairs of points which will be added. The relevant inequality, which holds when the set of addable points is sufficiently large, differs from the Brunn-Minkowski inequality by having the exponent 1/n replaced by 2/n. Its proof uses the rearrangement inequality of Brascamp-Lieb-Lüttinger ([2]). Besides the free entropy power inequality, note that the inequality for restricted Minkowski sums may also underlie the classical Shannon entropy power inequality (see 3.2 below).Research supported in part by grants from the National Science Foundation.     

简易型离子选择电极-流动注射分析仪的研制及卤水中氯、溴和碘的连续测定

本文设计研制了简单实用的流通池,组装了简易型离子选择电极—流动注射分析仪,对体系的分析特点和影响因素进行了考察。此装置性能可靠,能满足简单流注分析的需要,并建立了卤水中Cl~-、Br~-和I~-的连续测定方法。     

Precipitation and recrystallization of uniform CuCl particles formed by aggregation of nanosize precursors

Uniform, spherical CuCl particles were obtained by mixing aqueous solutions of CuCl ₂ and ascorbic acid in the presence of polyvinylpyrrolidone (PVP) as dispersing agent. The size and the uniformity of the resulting particles depended on the volume ratio of the reactant solutions, their concentrations, the distribution of the stabilizers, and the mixing method. The single jet precipitation yielded large spheres of broad size distributions, while the particles obtained by the double jet technique were rather uniform in size. The final colloidal CuCl particles were formed by the aggregation of nanocrystals, initially generated in the system. Depending on the pH of the reaction mixture, these particles slowly change to large CuCl crystals on aging in the mother liquor.     

五配位Cu(Ⅰ)配合物[Cu(4′-Phtpy)(PPh_3)_2](BF_4)的合成、结构及光谱性质研究

由[Cu(MeCN)2 (PPh3)2 ](BF4 )和 4′ 苯基 2,2′:6′,2″ 三联吡啶(4′ Phtpy)在室温下反应,合成了一个新颖的具有光致发光性能的五配位配合物[Cu(4′ Phtpy)(PPh3)2 ](BF4 ).对配合物进行了X射线衍射结构表征,并进行了红外光谱、紫外可见光谱、荧光光谱等光谱学分析.晶体属单斜晶系,空间群Pn,晶胞参数:a =1 0 80 7(6)nm,b =1 0 943 (6)nm,c=2 1610(12 )nm,α =90°,β =10 2 785(10 )°,γ =90°,V =2 492(2 )nm3,Z =2,Dc=1 3 5 4g·cm-3.配合物中,Cu(Ⅰ)与 4′ Phtpy的 3个N,2个PPh3的P配位呈变形三角双锥型结构,其轴向由Cu键合联吡啶的末端 2个N所组成,赤道平面由联吡啶的中心N原子和 2个PPh3的P原子所组成     

Structural Characterization of Anhydroicaritin Glycosides Using ESI—FT—ICR Mass Spectrometry

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to determine the structures of anhydroicaritin glycosides by the MS/MS experiments of anhydroicaritin glycosides and their methylated derivatives,With high accuracy FT-ICR-MS provides much information about the structures of compounds ,FT-ICR-MS shows the great potential application in the structural characterization of unknown compounds.