The heat effects of dissociation of maleic and fumaric acids

The heat effects of dissociation of maleic and fumaric acids at 298.15 K and several ionic strength values were determined calorimetrically in the presence of NaNO₃. The thermodynamic characteristics of dissociation at fixed ionic strengths and under standard conditions were calculated.     

The Heat Effects of Malonic Acid Dissociation

The heat effects of malonic acid dissociation at 298.15 K and several ionic strength values in the presence of NaClO₄ were determined calorimetrically. The thermodynamic characteristics of dissociation at fixed ionic strength values and at I = 0 were calculated.     

The heat effects of dissociation of N,N-bis-(carboxymethyl)aspartic acid

The heat effects of dissociation of N,N-bis-(carboxymethyl)aspartic acid were measured calorimetrically at 298.15 K and various solution ionic strengths. The standard thermodynamic characteristics of dissociation of the complexone studied were calculated at fixed and zero ionic strength values.     

The influence of the nature of the background electrolyte on the heat effects of dissociation of succinic acid

The results of calorimetric measurements were used to determine the heat effects of dissociation of succinic acid at 298.15 K and several ionic strength values in the presence of NaNO₃. The thermodynamic characteristics of dissociation at fixed ionic strength values and I = 0 were calculated.     

Dissociation constants of protolytic dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solution at 298 K

Protolytic dissociation constants of stepwise dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solutions at 298.15 K at ionic strengths of 0.1, 0.5, and 1.0 M on the NaCl background were measured by potentiometric titration. The thermodynamic dissociation constants were calculated. Using the obtained and published data, we discuss the effect of additional carboxy groups in the side chains of the molecule on the protolytic dissociation constants of peptides.     

The step dissociation constants of ethylenediamine-N,N′-diacetic-N,N′-dipropionic and ethylenediamine-N,N,N′,N′-tetrapropionic acids

The step dissociation constants of ethylenediamine-N,N′-diacetic-N,N′-dipropionic and ethylenediamine-N,N,N′,N′-tetrapropionic acids at 298.15 K and ionic strengths of 0.1, 0.5, and 1.0 (KNO₃) were determined potentiometrically. The results were extrapolated to zero ionic strength by the equation with one individual parameter. The thermodynamic constants of dissociation were calculated. The results are compared with the corresponding data on related compounds.     

一氯甲烷同步辐射光电离研究: 离子生成焓与键能的测定

本文报道超音速射流冷却条件下, 用同步辐射光研究CH3Cl光电离及其解离电离的动力学, 测得CH3Cl的电离能(IP)为11.28±0.01eV。通过测定CH3Cl光解离电离碎片的出现势(AP), 并结合有关已确认的热力学数据, 获得了它们的标准生成焓、离子型分子中的键能、中性分子或自由基中的键能及母体离子的解离能等热力学数据。对CH3Cl分子VUV光解离电离通道进行了分析。     

Thermochemical Study of Acid-Base Reactions of L-Valine in Salt Solutions

Heat effects of protonation and neutralization of L-valine were measured at 298.15 K, ionic strengths of the solutions of 0.25, 0.50, and 0.75, and on lithium, sodium, and potassium nitrate backgrounds. The heat effects of dissociation and neutralization of L-valine were extrapolated to zero ionic strength by a one-parameter equation to find standard enthalpies of dissociation and neutralization of L-valine in aqueous solution. Temperature-dependent and temperature-independent components of thermodynamic values were determined.     

Thermodynamics of stepwise dissociation of D,L-tryptophan in aqueous solution

The heat effects of the reaction of a solution of D,L-tryptophan with solutions of KOH and HNO₃ were measured by calorimetry at temperatures of 288.15, 298.15, and 308.15 K and ionic strength values of 0.25, 0.5, and 0.75 (KNO₃). The effect of the temperature and concentration of the background electrolyte on the heats of dissociation of amino acid was considered. The standard heat effects of ionization of D,L-tryptophan were determined by extrapolation to zero ionic strength. The standard thermodynamical characteristics of the stepwise dissociation of D,L-tryptophan were calculated.     

The dissociation of ethylenedithiodiacetic acid in aqueous solution

The dissociation of ethylenedithiodiacetic acid (H₂Edtda) was studied by potentiometric titration at 298.15 K and ionic strength values of 0.5, 1.0, and 1.5 against the background of sodium and lithium nitrates. The concentration and thermodynamic dissociation constants were determined.     

Dissociation pathways of protic ionic liquid clusters: Alkylammonium nitrates

Protic ionic liquids are promising candidates for many applications, including as spacecraft propellants. For both fundamental interest and understanding clustering and dissociation during electrospray‐based propulsion, it is useful to explore the dissociation pathways of protic ionic liquid clusters, as well as the factors affecting the relative contributions of each pathway to the observed MS/MS spectra. With that said, most of the published reports on ionic liquid cluster dissociation have focused on aprotic ionic liquids. The purpose of the current work is to explore the dissociation pathways (eg, loss of amine, nitric acid, or ion pair) of alkylammonium nitrates using energy‐resolved collision‐induced dissociation. Here, it was found that, in general, protic ionic liquids have multiple dissociation pathways—namely, protic ionic liquids can lose their neutralized cation (here, an alkylamine) or neutralized anion (here, nitric acid)—in addition to the ion pair dissociation familiar to aprotic salt and aprotic ionic liquid clusters. In general, increasing the basicity of the cation (here, through increasing the degree of alkylation) decreases the propensity to follow these alternative pathways. Interestingly, increasing the cluster size has a similar effect: as cluster size increases, nitric acid loss decreases. These results will help better model and design protic ionic liquids for electrospray‐based spacecraft propulsion and help provide a better understanding for the general behavior of protic ionic liquids versus aprotic ionic liquids within mass spectrometers.     

CH_2Cl_2对离子液体BmimPF_6中二茂铁电化学行为的影响

应用循环伏安和交流阻抗法研究有机溶剂二氯甲烷对二茂铁在离子液体1-丁基-3-甲基咪唑六氟磷酸盐(Bm imPF6)中电化学行为的影响.实验表明,二氯甲烷可促进离子液体的离子解离,减小离子液体粘度,增加离子液体电导率,加速二茂铁在离子液体中的扩散,增大氧化还原峰电流.由于电极界面双电层结构的变化,导致双电层电容增大,电极反应电阻减小,从而加速了界面电子传递反应.     

常压热解离化学电离源的研制及表征

自行研制了常压热解离化学电离源(TDCI),与商品化LTQ XL质谱仪成功联用,进一步考察了TDCI的性能,并对其应用领域进行了初步探索.TDCI-MS/MS谱图表明,离子液体可在现有实验条件下产生特征离子碎片;升高TDCI源偏置电压和温度,可以提高离子液体的信号强度.基于优化后的实验参数,常压热解离化学电离质谱方法(...     

Determination of cationic mobilities and pKa values of 22 amino acids by capillary zone electrophoresis

The effective mobilities of the cationic forms of common amino acids--mostly proteinogenic--were determined by capillary zone electrophoresis in acidic background electrolytes at pH between 2.0 and 3.2. The underivatized amino acids were detected by the double contactless conductivity detector. Experimentally measured effective mobilities were fitted with the suitable regression functions in dependence on pH of the background electrolyte. The parameters of the given regression function corresponded to the values of the actual mobilities and the mixed dissociation constants (combining activities and concentrations) of the compound related to the actual ionic strength. McInnes approximation and Onsager theory were used to obtain thermodynamic dissociation constants (pK(a)) and limiting (absolute) ionic mobilities.     

A thermochemical study of acid-base interactions in aqueous solutions of citric acid

The heat effects of interaction of a solution of citric acid with HNO₃ and KOH were measured calorimetrically at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO₃). The heat effects of acid dissociation were calculated using the universal HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.     

Dissociation behaviors of carboxyl and amine groups on carboxymethyl‐chitosan in aqueous system

Several carboxymethyl‐chitosan (CMCS) samples with different deacetylation degree and/or substituted degree were prepared from the carboxymethylation reaction of chitosan under soft conditions. The products were dissolved in standard HCl aqueous solution to carry out potentiometric titration by using NaOH as titrating solution at different ionic strengths. Then the dissociation behaviors of protonated carboxyl and amine groups were investigated under their degree of dissociation (α) and protonation constant (pK_α) had been calculated. Moreover, influences of the intrinsic and extrinsic parameters on the dissociation behavior of CMCS were also considered in this article. As a result, dissociations of carboxyl and amine on CMCS exhibited unusual behaviors in comparison with carboxyl of carboxymethyl‐cellulose and amine groups of chitosan, respectively. The pK_α values of carboxyl declined slightly at early dissociation stage but subsequently maintained constant. In contrast, the pK_α of ammonium increased with its dissociation degree despite that there was an inflexed change on its dissociation curve. The potentiometric behavior of carboxyl was hardly affected by variation of deacetylation degree or substituted degree. However, these intrinsic parameters played more important role on dissociations of ammonium on CMCS. The ionic strength of media could bring screening effect on dissociaciation of both sorts of ionizable groups of CMCS. By increasing the ionic strength of media, screening effect on dissociations increased significantly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1419–1429, 2008     

混合溶剂中弱电解质解离热力学(I)

溴酚蓝(BPB)是分析化学中常用的指示剂,它有一个等吸收点的特征吸收谱图,利用这种吸收谱图可以确定溴酚蓝热力学解离常数K°.用通常的化学法和电化学法测定弱电解质的解离度,不能区分没解离的部分是分子还是离子对.用分光光度法测定解离度,可以找出这个区别,因为分子和离子有不同的吸收光谱.在溶液中离子对的形成主要靠离子间的库伦力,而光学性质通常受库伦力影响不大.因此,用具有等吸收点的吸收谱图来确定弱电解质的解离度的方法被称作真解离度测定法.在pH=2—5范围内,溴酚蓝的解离是从第二个羟基上脱下质子的过程     

Photometric, colorimetric, and acid-base characteristics of nitroso-R-salt

Optical and colorimetric characteristics of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt) are studied in aqueous solutions at pH 4–10. Equations of calibration plots are obtained as the colorimetric functions of the concentration, and the molar coefficients of the colorimetric functions are calculated. The dissociation constants of nitroso-R-salt are determined by colorimetry at an ionic strength of 0.1–0.5, reduced to zero ionic strength, and compared with the literature data. Advantages of colorimetry over spectrophotometry in the determination of the dissociation constants of colored reagents are demonstrated.     

Determination of limiting ionic mobilities and dissociation constants of some local anaesthetics.

The limiting ionic mobilities and thermodynamic acid dissociation constants were calculated from isotachophoretic experiments for the local anaesthetics procaine, tetracaine, lidocaine, trimecaine, bupivacaine, cinchocaine, diperodone, diocaine, cocaine, psicaine-neu, tropacocaine, amylocaine, beta-eucaine and leucinocaine. The pH values at which the local anaesthetics with very similar limiting ionic mobilities can be isotachophoretically separated were determined from simulated mobility curves. The measuring apparatus employed a high-frequency contactless conductivity detector.     

Valence Bond Study of Dissociation Behavior and Spectroscopic Constants for the Ground States of LiF and NaF

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