甘氨酸在乙醇—水混合溶剂中离解常数的测定

本文利用电位滴定法测定了２５℃，ＫＣｌ离子强度Ｉ＝０．１ｍｏｌ．Ｌ＾－１时，甘氨酸在纯水及８个乙醇－水混合溶剂中的二级离解常数ｐＫａ，对应的碱离解常数ｐＫｂ和混合溶剂的质子自递常数ｐＫ。实验结果表明：在所研究的浓度范围内，随着混合溶剂中乙醇含量的增加，甘氨酸的酸离解常数及溶剂的质子自递常数逐渐减小，碱离解常数则逐渐增大。     

1,3-二苯基-4-酰基-5-吡唑酮螯合剂离解常数和两相分配常数的测定

在水-二氧六环混合体系中,用电位滴定法测定了四种新的β－二酮螯合剂在二氧六环不同含量时的离解常数,通过外推,求得它们在纯水中的离解常数。采用两相滴定法,测定了它们在氯仿、苯和正己烷三种有机溶剂与水之间的两相分配常数。     

水/乙醇混合溶剂中氨基酸离解的取代基效应

用LKB-2277BioActivityMonitor测定了298.15K时甘氨酸,丙氨酸和丝氨酸在水/乙醇混合溶剂中的离解焓,计算了相应的离解熵。根据三个氨基酸分别与某一参考酸之间的质子交换反应,重点讨论了溶剂结构变化对取代基效应焓,熵变化的影响。实验结果表明在水/乙醇混合溶剂的最大结构化区域,取代基效应最为显著。认为在混合溶剂的富水区大块的似冰山结构的水分子簇的寿命大大延长。     

氨基苯甲酸异构体在水-乙醇混合溶剂中的离解焓和熵

利用流动混合微量热法测定298.15K时单取代氨基苯甲酸邻,间,对三个异构体在水-乙醇混合溶剂中两个官能团分步离解的离解焓,结合相应的Gibbs自由能数据计算离解熵,从溶剂效应和取代基位置效应探讨其离解热力学行为。     

αNG和βNG在混合溶剂中的离解常数及其铜(Ⅱ)、镍(Ⅱ)络合物的稳定性研究

在25℃和0.1M高氯酸钠存在下,用pH法测定了N-β-萘氨基乙酸二氧六圜-水混合溶剂中的表观酸性离解常数及其与铜(Ⅱ)、镍(Ⅱ)络合物的稳定常数,讨论了该络合物的稳定性。     

电导法测定杂多酸在非水溶液中的离解常数

本文以电导法测定了１２－磷钨、１２－硅钨酸在一些醇、酯、醛、酮等含氧有机溶剂以及乙腈中的离解常数，得到的结果表明，两种酸在同种溶液中的离解常数接近，磷钨酸的略高，同一种酸在不同溶剂中的离解常数则与溶剂的介电常数有密切关系。在醚中，因杂多酸与溶剂发生缔合作用，用电导法得不到其离散常数。     

强酸与多元酸混合物中各组分酸含量测定方法研究

各级离解常数均大于10~(-7),而且相邻两级的离解常数之比K_(a1)/K_(a2)只有几十倍的多元酸与强酸混合情况下,提出通过测量多元酸的半中和点,分别测定各组分酸含量的酸碱滴定法。     

难溶有机物在水中离解常数及其分配系数的测定

离解常数是弱酸、弱碱很重要的物理常数,特别是有机试剂,因其分析性能与离解常数有很大的关系,所以测定新试剂的离解常数尤为必要。离解常数的测定常用电位滴定法和光度法。就光度法来说,目前绝大多数报道的是测     

对、间位卤代苯甲酸在水-乙醇混合溶剂中电离过程的焓、熵贡献

用LKB-2277Bioactivity Monitor测定了25℃时间氯、对氯和对氟苯甲酸在水-乙醇混合溶剂中的标准电离焓, 计算了相应体系的标准电离熵。利用Hammett方程对溶剂中酸的取代基常数σ进行了计算, 求取了对应的焓、熵取代基常数σH和σS值及熵反应常数ρS, 利用内部-环境模型和上述常数对溶剂效应和取代基效应进行了解释。     

介质对配合物稳定性的影响I.Cu(SCN)^+-NaNO3-C2H5OH-H2O体系

本文用分光光度法测定了25℃时配阳离子Cu(SCN)^+在乙醇-水介质中的稳定常数.乙醇在混合溶剂中的重量百分数为0,5,10,15,20和25.用NaNO3调节溶液离子强度I=0.2--2.0mol.dm^-^3.实验的pH=1.5--1.6.本文提出了基于Pitzer方程式的曲线拟合法,确定混合溶剂中配合物的热力学稳定常数.讨论了该常数和一级介质效应与溶液组成和介电常数的关系.     

Determination and comparison of stability constants of tungsten(VI) and molybdenum(VI) with nitrilotriacetic acid and glutamic acid at different ionic strengths

The formation constants of species formed in the systems H⁺?+?W(VI)?+?nitrilotriacetic acid (NTA) and H⁺?+?NTA have been determined in aqueous solution for pH?=?4–9 at 25°C and different ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 NaClO₄, using potentiometric and spectrophotometric techniques. It was shown that tungsten(VI) forms a mononuclear 1?:?1 complex with NTA of the type WO₃L^3? at pH?=?7.5. The composition of the complex was determined by the continuous variations method. The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1?:?1 complex with glutamic acid of the type MoO₃L^2? at pH?=?6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25°C and at ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 sodium perchlorate. In both complex formation reactions the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.     

A study of some problems in determining the stoicheiometric proton dissociation constants of complexes by potentiometric titrations using a glass electrode

Possible errors in the measurement of acid dissociation constants by potentiometric titration techniques have been considered, with particular references to nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). Unknown junction potentials can arise when pH measurements are carried out using a glass electrode with saturated calomel reference electrode which have been previously calibrated with a standard buffer solution. The magnitude of the influence of these unknown potentials has been demonstrated and an experimental procedure recommended which gives meaningful results.The precision of calculated acid dissociation constants will also be influenced by the presence of cationic species (e.g. H₄L⁴), the total acid strength, the absolute values of the constants and the value accepted for the auto-dissociation constant of water (K_w). All these factors have been considered quantitatively and their effect on metal complex formation constants, calculated from these acid dissociation constants, noted. The proton dissociation constant of the cationic species of NTA (i.e. H₄L⁺) has been found to have the value of pK₀=0.80 at 20° and μ=0.10 M.     

Thermodynamic, kinetic and pH studies on the reactions of NCS-, N3-, and CH3CO2- with Fusarium galactose oxidase

Thermodynamic and kinetic studies on the X- = NCS-, N3-, and CH3CO2- replacement of H2O/OH- at the CuII exogenous site of the tyrosyl-radical-containing enzyme galactose oxidase (GOaseox) from Fusarium (NRR 2903), have been studied by methods involving UV-vis spectrophotometry (25 degrees C), pH range 5.5-8.7, I = 0.100 M (NaCl). In the case of N3- and CH3CO2- previous X-ray structures have confirmed coordination at the exogenous H2O/OH- site. From the effect of pH on the UV-vis spectrum of GOaseox under buffer-free conditions, acid dissociation constants of 5.7 (pK1a; coordinated H2O) and 7.0 (pK2a; H+Tyr-495) have been determined. At pH 7.0 formation constants K(25 degrees C)/M-1 are NCS- (480), N3- (1.98 x 10(4)), and CH3CO2- (104), and from the variations in K with pH the same two pKa values are seen to apply. No pK1a is observed when X- is coordinated. From equilibration stopped-flow studies rate constants at pH 7.0 for the formation reaction kf(25 degrees C)/M-1 s-1 are NCS- (1.13 x 10(4)) and N3- (5.2 x 10(5)). Both K and kf decrease with increasing pH, consistent with the electrostatic effect of replacing H2O by OH-. In the case of the GOaseox Tyr495Phe variant pK1a is again 5.7, but no pK2a is observed, confirming the latter as acid dissociation of protonated Tyr-495. At pH 7.0, K for the reaction of four-coordinate GOaseox Tyr495Phe with NCS- (1.02 x 10(5) M-1) is more favorable than the value for GOaseox. Effects of H+Tyr-495 deprotonation on K are smaller than those for the H2O/OH- change. The pK1a for GOasesemi is very similar (5.6) to that for GOaseox (both at CuII), but pK2a is 8.0. At pH 7.0 values of K for GOasesemi are NCS- (270 M-1), N3- (4.9 x 10(3)), and CH3CO2- (107).     

Mechanism of indium(III) exchange between NTA and transferrin: a kinetic approach

The equilibria and kinetics for the process of In(3+) exchange between nitrilotriacetic acid (NTA) and bovine serum transferrin (T) have been investigated in aqueous solution containing sodium bicarbonate. The metal exchange equilibria have been measured by difference ultraviolet spectroscopy at 25 degrees C, pH=7.4, and I=0.2 M (NaClO4). The acid dissociation constants of NTA and the binding constants of In(III) to NTA have also been measured. Kinetic experiments revealed that the process of In(3+) uptake by transferrin from [In(NTA)2](3-) is biphasic, the fast phase being completed in a few seconds, the slow phase lasting for hours. The fast phase has been investigated by the stopped-flow method and results in monoexponential kinetics. It involves rapid interaction of the 1:1 complex ML (M=In, L=NTA) with TB (T=transferrin, B=CO3(2-)) to give a quaternary intermediate MLTB which then evolves to an "open" MTB* ternary complex complex with expulsion of L. In turn, this complex interconverts to a "closed", more stable, form MTB. Neither the prevailing complex M2L nor the TB2 form of transferrin are directly involved in the exchange process but act as metal and protein reservoirs. The pH dependence of the reaction has been also investigated. The slow phase has not been investigated in detail; it takes several hours to go to the completeness, its slowness being ascribed to metal redistribution between the C-site and N-site of the protein, and/or metal release from polynuclear In(III) species.     

Equilibria and structure of the lanthanide(III)-2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetraacetate complexes: formation of alkoxo-bridged dimers in solid state and solution

The complex formed between 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid (H4L-OH) and Nd3+ at pH 7.5 was found to be a dinuclear dimer in the solid state by X-ray crystallography. In the complex K4[Nd2(L-O)2(H2O)2].14H2O each ligand is coordinated to both Nd3+ atoms with an iminodiacetate group (the Nd3+-Nd3+ distance is 3.9283(8) A). The alcoholic OH groups are deprotonated, and the alkoxo oxygens are coordinated to both Nd3+ in a bridging position. The Nd3+ ions are nine-coordinated with one water molecule per Nd(III) ion in the inner sphere. The complex K4[Nd2(L-O)2(H2O)2].14H2O has an inversion center, and the space group is P1. Two of the K+ counterions are six-coordinated, while the other two K+ ions are eight-coordinated; polar polymeric water-K+ layers are formed between the apolar ligand layers via the bridging water molecules. The dinuclear dimer complexes are also present in aqueous solution. The proton relaxivities of the Gd3+ complex decrease with the increase of pH, and at pH > 6, the low relaxivity values indicate the probable absence of H2O in the inner sphere and the predominance of the eight-coordinated dimer species [Gd2(L-O)2].4- The results of ESI-TOF MS studies of the complexes of La3+, Nd3+, and Lu3+ proved the formation of dinuclear dimers in dilute (0.25 mM) solutions. pH-potentiometric titrations indicate the formation of complexes with 1:1 (Ln(L-OH)-, Ln(HL-OH), and Ln2(L-O)24-) and 2:1 (Ln2(L-O)+) metal-to-ligand ratios. The stability constants of the Ln(L-OH)- species increase from La3+ (log K = 10.19) to Lu3+ (log K = 14.08). The alcoholic OH group of the Ln(L-OH)- species dissociates at unusually low pH values. The pH range of dissociation shifts to lower and lower pH's with the increasing atomic number of the lanthanides. This pH range is about 4-7 for the La3+ complex and 1-4 for the Lu3+ complex. The results of 1D and 2D 1H and 13C NMR studies of the La3+ complex, the number and multiplicity of signals, and the values of coupling constants are in agreement with the dinuclear dimer structure of the complex in solution.     

胶束溶液中某些氨基酸和二肽的解离常数

用ｐＨ电位法测定了在ＳＤＳ（十二烷基磺酸钠）胶束溶液中甘氨酰丙氨酸和六种氨基酸（甘氨酸、丙氨酸、缬氨酸、亮氨酸、异亮氨酸、苯丙氨酸）的两级酸解离常数ｐＫａ１和ｐＫａ２,发现与水溶液相比,ｐＫａ值均显著增加,即ＳＤＳ胶束形成强烈抑制质子解离,结合＾１ＨＮＭＲ测定结果,讨论了ｐＫａ１和ｐＫａ２随ＳＤＳ浓度的变化规律以及与各配体自身结构的关系。     

In Process Citation

The proton concentration resulting from the dissociation of a moderately strong dibasic acid can be precisely determined by means of an acid-base indicator by differential spectrophotometry. The dissociation constants are then calculated by linear regression of the appropriate function. The method was tested on the first two dissociation constants of protonated O-phosphoserine in aqueous solution (25 degrees , KNO(3) 0.1M): the values found are pK(1) = 0.72 (3sigma = 0.08) and pK(2) = 2.14(6) (3sigma = 0.01).     

M(NTEA)配合物的NMR研究

用ＮＭＲ方法研究了氨三乙氧基乙酸（ＮＴＥＡ）的质子解离过程及其与Ｌａ３＋、Ｙ３＋、Ｌｕ３＋和Ｃａ２＋的配合作用．ＮＴＥＡ的氮原子和羧基的质子解离常数分别为８．８和３．０．当ｐＨ＞３．０时，Ｌａ３＋、Ｙ３＋和Ｌｕ３＋配合物能稳定形成（＞５０％），而Ｃａ２＋配合物则需出＞５．在ｐＨ３～６范围内，配合物与配体间的交换反应处于慢－中介交换速率区间，通过变温谱模拟得到了其交换反应的动力学参数．     

The acid stability constants of Alizarin Fluorine Blue

Two recent attempts to determine the dissociation constants of 3-aminomethylalizarin-N,N-diacetic acid are discussed and the results compared with values that can be predicted from earlier work on iminodiacetic acid derivatives and from the absorption spectra of the reagent at different pH values. Results of a potentiometric and spectrophotometric study to determine the stability constants of the various protonated species of the reagent in aqueous solution at ionic strengths 0.1 and 0.5 (potassium chloride) are: log K(H)(HL) = 12.1, log K(H)(H(2)L) = 9.81, log K(H)(H(3)L) = 5.47, log K(H)(H(4)L) = 2.54, and log K(H(2)L)(H(5)L(2)) = 2.2 at ionic strength 0.5.     

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be logbeta(210) = 7.33 +/- 0.10 at an ionic strength of 0.1 mol/l (NaClO(4)) and at 21 degrees C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.