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61.
The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pK(a) values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of D-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.  相似文献   
62.
Wu R  Zou H  Ye M  Lei Z  Ni J 《Electrophoresis》2001,22(3):544-551
A mode of capillary electrochromatography (CEC), based on the dynamical adsorption of surfactants on the uncharged monolithic stationary phases has been developed. The monolithic stationary phase, obtained by the in situ polymerization of butyl methacrylate with ethylene dimethacrylate, was dynamically modified with an ionic surfactant such as the long-chain quaternary ammonium salt of cetyltrimethylammonium bromide (CTAB) and long-chain sodium sulfate of sodium dodecyl sulfate (SDS). The ionic surfactant was adsorbed on the surface of polymeric monolith by hydrophobic interaction, and the ionic groups used to generate the electroosmotic flow (EOF). The electroosmotic mobility through these capillary columns increased with increasing the content of ionic surfactants in the mobile phase. In this way, the synthesis of the monolithic stationary phase with binary monomers can be controlled more easily than that with ternary monomers, one of which should be an ionic monomer to generate EOF. Furthermore, it is more convenient to change the direction and magnitude of EOF by changing the concentration of cationic or anionic surfactants in this system. An efficiency of monolithic capillary columns with more than 140000 plates per meter for neutral compounds has been obtained, and the relative standard deviations observed for to and retention factors of neutral solutes were about 0.22% and less than 0.56% for ten consecutive runs, respectively. Effects of mobile phase composition on the EOF of the column and the retention values of the neutral solutes were investigated. Simultaneous separation of basic, neutral and acidic compounds has been achieved.  相似文献   
63.
Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for C–C bond formation. A decarboxylative cross-coupling method is described to afford substituted alkynes from various carboxylic acids using copper catalysts CuCl and Cu(acac)2. The photoexcitation of copper acetylides with electron-rich NEt3 as a ligand provides a general strategy to generate a range of alkyl radicals from RAEs of carboxylic acids, which can be readily coupled with a variety of aromatic alkynes. The scope of this cross-coupling reaction can be further expanded to aliphatic alkynes and alkynyl silanes using a catalytic amount of preformed copper-phenylacetylide. In addition, DFT calculations revealed the favorable reaction pathway and that the bidentate acetylacetonate ligand of the copper intermediate plays an important role in inhibiting the homo-coupling of the alkyne.

Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for Cu-catalysed C–C bond formation.  相似文献   
64.
A selective and sensitive high-performance liquid chromatography-electrospray ionization mass spectrometry (MS) for the determination of nisoldipine in human plasma is first presented. With nimodipine as the internal standard, nisoldipine is extracted from plasma with ethyl acetate. The organic layer is evaporated and the residue is resuspended in the mobile phase of methanol-water (80:20, v/v). An aliquot of 40 microL is chromatographically analyzed on an Agilent ODS C18 reversed-phase column (5 microm, 250- x 4.6-mm i.d.) by means of selected-ion monitoring mode MS. The calibration curve of nisoldipine in plasma exhibits a linear range from 0.5 to 20.0 ng/mL with a correlation coefficient of 0.9995. The limit of detection is 0.2 ng/mL. The within- and between-day variations (relative standard deviation) are less than 9.28% and 11.13% (n = 5), respectively. The developed method is validated through successful use for the analysis of nisoldipine contained in biological fluids resulting from a phase-I human pharmacokinetic study.  相似文献   
65.
倪良  卢洁 《物理化学学报》1996,12(2):146-151
讨论了沸点升高法测定混和溶剂化热和汽化熵的原理,并用拟静态法测定了乙醇-丙酮,并-四氯化碳和苯,甲苯三组混和溶剂在不同组成下的正常沸点,根据沸点数据求得了混和泶微分汽化热和汽化熵,实验结果表明,二元混和溶剂与理想溶液偏离不大时,其正常汽化熵符合Trouton规则。  相似文献   
66.
本文报告了298.1 K下甲酸钠(C_1), 乙酸钠(C_2)、丙酸钠(C_3)、丁酸钠(C_4)、戊酸钠(C_5)、已酸钠(C_6)和庚酸钠(C_7)七个盐对水溶液中乙醇、丙酮和乙腈三个溶质的活度系数的影响。实验方法是, 固定水溶液中乙醇、丙酮和乙腈的浓度(摩尔分数约为0.05), 用气相色谱法检测不同盐浓度下平衡气相中溶质分压的变化, 从而得出溶质的盐效应活度系数γ。本文给出了一个可以连续取样的气液平衡装置的设计。由实验结果可见, 不同碳链大小的脂肪酸根离子的盐效应作用差别很大。C_1、C_2的盐效应主要由于静电作用; 对C_3、C_4盐, 除静电作用外,它们的疏水基与溶质疏水基的相互作用对盐效应有显著影响; C_5、C_6和C_7的盐效应则反映了疏水离子的特色, 疏水水化、疏水相互作用、疏水离子形成的聚集体与不同官能团的特定相互作用等几项因素, 导致儿个溶质盐效应的差异。  相似文献   
67.
金属玻璃TM-Met(TM为过渡金属原子,Met为类金属原子,如硼、磷等)由于其优异性能已成为非晶态研究的重要课题之一。实验研究表明,类金属原子与过渡金属原子构成非晶态合金(即金属玻璃)后,平均原子磁矩随Met的含量在一定范围内的变化呈线性下降关系.相当多的文献用“电荷转移刚性能带”模型来解释.认为金属玻璃的能带是  相似文献   
68.
自从1969年Lchn等合成穴醚[2,2,2]似来.人们对穴醚的研究越来越感到兴趣.由于空腔效应,穴醚具有很强的配位能力和较高的选择性,它对于研究无机离子在生物体内的传输过程具有重要的意义,而且有可能用于离子的识别和分离.  相似文献   
69.
Ni ZH  Kou HZ  Zheng L  Zhao YH  Zhang LF  Wang RJ  Cui AL  Sato O 《Inorganic chemistry》2005,44(13):4728-4736
Two new cyano-bridged heterobinuclear complexes, [Mn(II)(phen)2Cl][Fe(III)(bpb)(CN)2] x 0.5CH3CH2OH x 1.5H2O (1) and [Mn(II)(phen)2Cl][Cr(III)(bpb)(CN)2] x 2H2O (2) [phen = 1,10-phenanthroline; bpb(2-) = 1,2-bis(pyridine-2-carboxamido)benzenate], and four novel azido-bridged Mn(II) dimeric complexes, [Mn2(phen)4(mu(1,1)-N3)2][M(III)(bpb)(CN)2]2 x H2O [M = Fe (3), Cr (4), Co (5)] and [Mn2(phen)4(mu(1,3)-N3)(N3)2]BPh4 x 0.5H2O (6), have been synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic studies. Complexes 1 and 2 comprise [Mn(phen)2Cl]+ and [M(bpb)(CN)2]- units connected by one cyano ligand of [M(bpb)(CN)2]-. Complexes 3-5 are doubly end-on (EO) azido-bridged Mn(II) binuclear complexes with two [M(bpb)(CN)2]- molecules acting as charge-compensating anions. However, the Mn(II) ions in complex 6 are linked by a single end-to-end (EE) azido bridging ligand with one large free BPh4(-) group as the charge-balancing anion. The magnetic coupling between Mn(II) and Fe(III) or Cr(III) in complexes 1 and 2 was found to be antiferromagnetic with J(MnFe) = -2.68(3) cm(-1) and J(MnCr) = -4.55(1) cm(-1) on the basis of the Hamiltonian H = -JS(Mn)S(M) (M = Fe or Cr). The magnetic interactions between two Mn(II) ions in 3-5 are ferromagnetic in nature with the magnetic coupling constants of 1.15(3), 1.05(2), and 1.27(2) cm(-1) (H = -JS(Mn1)S(Mn2)), respectively. The single EE azido-bridged dimeric complex 6 manifests antiferromagnetic interaction with J = -2.29(4) cm(-1) (H = -JS(Mn1)S(Mn2)). Magneto-structural correlationship on the EO azido-bridged Mn(II) dimers has been investigated.  相似文献   
70.
信息拓扑指数与烷烃分子热力学性质的关系   总被引:13,自引:0,他引:13  
Two topological information indices were constructed based on Randic and Wiener indices, and the values of topological information indices for 85 alkanes were calculated. The thermodynamic properties such as the standard enthalpies of formation, the standard entropies and the standard free energies of formation for these alkanes were also correlated with these topological and information indices. It is found that the thermodynamic properties calculated for both gaseous and liquid states of the 85 alkanes are in excellent agreement with the experimental values through the regression analysis.  相似文献   
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