稀土与多卤代变色酸双偶氮胂类试剂的配合反应研究

本文研究了稀土与卤代变色酸双偶氮胂类试剂的配合反应,测定了配合物的稳定常数,试剂的离解常数和配合物组成,讨论了试剂结构与配合物吸收光谱的关系和β型配合物的生成条件,从而探讨了该类试剂在高酸度下与稀土的配合反应机理.     

Dissociation constants of thymolphthalexone

For the dissociation constants of thymolphthalexone the following values have been found: pK(3) = 7.03 +/- 0.02, pK(4) = 8.05 +/- 0.09 (by potentiometric titration), pK(5) = 10.83 +/- 0.10, pK(6) = 12.99 +/- 0.11 (by spectrophotometry). They were determined at I = 0.4 and at 25 degrees.     

Acid dissociation and metal chelate formation equilibria of some halogenated diphenylthiocarbazones

The acid dissociation constants (K(a)) of di-p-fluoro-, di-p-chloro-, di-p-bromo-, di-p-iodo-and di-m-trifluoromethylphenylthiocarbazones and the equilibrium formation constants (K(f(1))) of their 1:1 complexes with Co(II), Ni and Zn have been determined at 25 degrees in 50% v v aqueous dioxan at 0.10 M ionic strength. Each of the electron-withdrawing substituents gives a reduction in pK(a) roughly proportional to its Hammett sigma value, and log K(f(1)) increases linearly with pK(a).     

Stability constants of the ternary complexes of CuDTPA, NiDCTA, CrEDTA, CoHEEDTA, NiHEEDTA and CuHEEEDT Aheedta with OH-

The acid dissociation constants of the metal chelates H(3)CuDTPA, H(2) NiDCTA, HCrEDTA, HCoHEEDTA, HNiHEEDTA and HCuHEEDTA were determined by potentiometric titration. The constants determined at an ionic strength of 0.1 were pK(a,1) = 2.1; pK(a,2) = 2.8 and pK(a,3) = 4.75 for H(3) CuDTPA (296 K), pK(a,1) = 2.16 for HCrEDTA (298 K); pK(a,1) = 1.6 and pK(a,2) = 2.0 for H(2) NiDCTA (298 K); pK(a,1) = 2.24 for HCoHEEDTA, pK(a,1) = 2.47 for HCuHEEDTA and pK(a,1) = 1.73 for HNi-HEEDTA. At high pH the formation of ternary hydroxo-complexes was observed for the chelates CrEDTA(-) (pK(a,1) = 7.35; pK(a,1) = 12.35), CoHEEDTA(-) (pK(a,1) = 11.74), NiHEEDTA(-) (pK(a,2) = 12,44) and CuHEEDTA(-) (pK(a,2) = 10.45).     

Free radical chemistry of flavan-3-ols: determination of thermodynamic parameters and of kinetic reactivity from short (ns) to long (ms) time scale

The physical chemistry and the free radical chemistry of the most abundant polyphenolic flavan-3-ols in food, catechin, its methylated metabolites, and several methylated analogues, have been investigated by laser flash photolysis and cyclic voltammetry studies. Two independent phenoxyl radicals formed upon oxidation of flavan-3-ols have been characterized and identified unambiguously: a short-lived resorcinol-like radical characterized by an absorption band at lambda = 495 nm and a long-lived catechol-like transient absorbing at lambda = 380 nm. The determination of all the thermodynamic constants of each phenolic function of flavan-3-ols, namely, redox potential (E degrees (3') = 0.13(5) V/SCE, E degrees (4') = 0.11(0) V/SCE, E degrees (5) = 0.28(5) V/SCE) and microscopic dissociation constants (pK(a3') = 9.02, pK(a4') = 9.12, pK(a5) = 9.43, pK(a7) = 9.58) were performed. These values are discussed and compared to the prediction of the density functional theory calculations made on the different species catechin, catechin phenoxyl, and catechin phenolate for each phenolic site.     

Macroscopic and microscopic ionization constants of the thiol and amine groups in 1-methyl-4-mercaptopiperidine

The acid dissociation constants of 1-methyl-4-mercaptopiperidine (pK(1) = 9.51, pK(2) = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (pK(A) = 9.59) and 1-methyl-4-(methylthio)piperidine (pK(B) = 10.18) have been determined potentiometrically in 3M sodium perchlorate (10% methanol) medium. The ultraviolet absorption of the mercaptide ion has been used to determine the relative proton affinity of the sulphur and nitrogen functions in 1-methyl-4-mercaptopiperidine under the same conditions, and its four microscopic constants (pK(a) = 9.49, pK(b) = 10.23, pK(c) = 11.34, pK(d) = 10.60) have been calculated; pK(A) has also been determined spectrophotometrically. From the results obtained, it can be concluded that the thiol group is more acidic than the amine group and that the Adams relation, K(a) + K(b) = K(1), holds very well when it is assumed that the spectrophotometric values for K(a), and K(b), can be replaced by K(A) and K(B) respectively.     

Protolytic reactions of 3,3'-dimethylnaphthidine and 3,3'-dimethoxybenzidine

The dissociation constants of diprotonated 3,3'-dimethylnaphthidine (DMN) and 3,3'-dimethoxybenzidine (DMB) have been determined spectrophotometrically. They are: pK(a1) = 2.62 +/- 0.03, pK(a2) = 3.33 +/- 0.09 for DMN: pK(a1) = 2.83 +/- 0.07, pK(a2) = 4.05 +/- 0.12 for DMB. The molar absorptivities (l.mole(-1).cm(-1)) of all forms of the indicators have been also determined: epsilon(B) = 1.68 x 10(4), epsilon(BH(+)) = 9.34 x 10(3), epsilon(BH(2+)(2)) = 1.80 x 10(3) at 300 nm for DMB; epsilon(B) = 7.33 x 10(3), epsilon(BH(+)) = 3.73 x 10(3), epsilon(BH(2+)(2)) = 0 at 330 nm for DMN.     

Accurate determination of low pK values by (1)H NMR titration

The NMR titration methodology to determine acid dissociation constants in aqueous solutions is extended for pK(a) values between 0 and 2, where potentiometric titrations are no longer applicable. (1)H NMR spectra are acquired for single samples of constant acid concentration (e.g. 0.02M), controlled ionic strength (I=1M with HNO(3)/NaNO(3)) and varying pH. To avoid biased pH readings due to the acid error of the glass electrode, true, concentration-based pH values are deduced by combination of the charge balance equation with information from (1)H NMR chemical shifts of the investigated acid. The method has been tested on histidine (pK(1)=1.83+/-0.02) and yielded the dissociation constant of dichloroacetic acid (pK=1.06+/-0.01) for the first time with good accuracy and precision. Dichloroacetic acid is recommended as an NMR spectroscopical "indicator molecule" for in situ monitoring the pH in strong acidic solutions of other equilibrium systems.     

Thermodynamic dissociation constants of isocaine, physostigmine and pilocarpine by regression analysis of potentiometric data

Concentration and mixed dissociation constant(s) of three drug acids, H(J)L, isocaine, physostigmine and pilocarpine, at various ionic strengths, I, in the range 0.03-0.81 and 25 degrees C have been determined with the use of regression analysis of potentiometric titration data when common parameter, pK(a), and group parameters E'(0), L(0), and H(T) are simultaneously refined. Internal calibration of the glass electrode cell in the concentration scale [H(+)] performed during titration was used. The estimate of ill-conditioned group parameters has a great influence on a systematic error in estimated pK(a) and therefore it makes the computational strategy important. As more group parameters are refined and a better fit achieved, a more reliable estimate of dissociation constants results. The thermodynamic dissociation constant, pK(a)(T), an ill-conditioned ion-size parameter, ?, and the salting-out coefficient, C, were estimated by non-linear regression of {pK(a), I} data and an extended Debye-Hückel equation. The goodness-of-fit test based on regression diagnostics is a measure of the reliability of parameters, and proves that reliable estimates for isocaine pK(a)(T)(=)8.96(1), ?=8(3) A and C=0.50(3) at 25 degrees C, for physostigmine pK(a)(T)(=)8.07(3), ?=19(26) A and C=0.64(3) at 25 degrees C, and for pilocarpine pK(a)(T)(=)7.00(1), ?=7(1) A and C=0.53(2) at 25 degrees C were found.     

Properties of 4-amino-4'-methyldiphenylamine as a redox indicator

The properties of 4-amino-4'-methyldiphenylamine as a redox indicator have been studied. The compound acts as a reversible, one-colour indicator, the oxidized form being red-violet, with molar absorptivity 6 x 10(3) l.mole(-1).cm(-1) at lambda(max) = 510 nm. The formal potential is described by the equation E = 0.735-0.059 pH. The two dissociation constants are pK(1) = -0.08 +/- 0.09 and pK(2) = 5.09 +/- 0.02. The relative error of titration of iron(II) with vanadium(V) is not larger than 0.2%.     

Spectrophotometric determination of the dissociation constants of n.n'-bis(2-hydroxyethyl)dithio-oxamide

The dissociation constants of N, N'-bis(2-hydroxyethyl)dithio-oxamide were determined by a spectrophotometric method. The dissociation constants were calculated by means of a weighted least squares technique. N, N'-Bis(2-hydroxyethyl)dithio-oxamide was found to be a dibasic acid with a thermodynamic dissociation constant pK1-11/04. At ionic strength μ - 0.5, pK1 - 10.71 and pK2 13.92.     

Intrinsic surface reaction equilibrium constants of structurally charged amphoteric hydrotalcite-like compounds

The relative equations among intrinsic surface reaction equilibrium constants (K in 1-pK model, K(a1)(int) and K(a2)(int) in 2-pK model, and *K(Na)(int) and *K(Cl)(int) in inert electrolyte chemical binding model), points of zero charge (PZC), and structural charge density (sigma(st)) for amphoteric solids with structural charge were established to investigate the effects of sigma(st) on intrinsic equilibrium constants and PZC. The intrinsic equilibrium constants of HTlc with general formulas [(Zn,Mg)(1-x)Al(x)(OH)(2)](Cl,OH)(x) and [Mg(1-x)(Fe,Al)(x)(OH)(2)](Cl,OH)(x) were evaluated. The following main conclusions were obtained. For amphoteric solids with structural charge, a point of zero net charge (PZNC) independent of electrolyte concentration (c) exists. A common intersection point (CIP) should appear among the acid-base titration curves at different c, and the pH at the CIP is pH(PZNC). The pK, pK(a1)(int), and pK(a2)(int) may be expressed as a function of pH(PZNC) and sigma(st), and these intrinsic equilibrium constants can be directly calculated from pH(PZNC) and sigma(st). The inert electrolyte chemical binding does not exist for amphoteric surfaces with structural charge. PZNC is not equal to the point of zero net proton charge (PZNPC) when sigma(st) not equal 0. pH(PZNC) > pH(PZNPC) when sigma(st)>0; pH(PZNC) < pH(PZNPC) when sigma(st)<0; and pH(PZNC) = pH(PZNPC) only when sigma(st)=0. With increasing c, the difference between pH(PZNC) and pH(PZNPC) decreases; i.e., pH(PZNPC) moves forward to pH(PZNC) with increasing c. For the HTlc samples studied, with increasing x, the pH(PZNC) and the pK(a1)(int) and pK(a2)(int) decrease, and the pK increases. These results can be explained on the basis of the affinity of metal cations for H(+) or OH(-) and the electrostatic interaction between the charging surface and H(+) or OH(-).     

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).     

Potentiometric determination of the dissociation constants of an asymmetric sorbent containing l-proline, and the stability constants of its Cu(II) complexes

The dissociation constants of the carboxyl groups (pK(a1) = 2.2, n = 1.8) and amino groups (pK(a2) = 9.5, n(2) = 1.6) of a sorbent prepared by reacting l-proline with a cross-linked chloromethylated styrene polymer have been determined by potentiometric titration. The potentiometrically measured stability constants of the Cu(II) complexes of the resin (logbeta(1) = 6.9 and log beta(2) = 12.4) were found to be close to the values for the Cu(II) complexes of N-benzyl-l-proline. For complexed resins of alpha-amino-acid type the pH-values of decomplexation do not appear to be directly correlated with the stability constants.     

Study of 1,4-dihydroxyanthraquinone as an acid-base indicator in isopropyl alcohol medium Evaluation of colour-change limits through complementary chromaticity parameters

The use of 1,4-dihydroxyanthraquinone as an acid-base indicator in isopropyl alcohol medium is proposed. The acid dissociation constants of the indicator in isopropyl alcohol solution are pK(a1) = 12.95 +/- 0.03 and pK(a2) = 15.96 +/- 0.07. The sharpness of the indicator transition is described by means of complementary chromaticity parameters. The indicator is used for determination of weak organic acids, with errors of less than 1%.     

Kinetic and equilibria studies of the aquation of the trinuclear platinum phase II anticancer agent [(trans-PtCl(NH(3))(2))(2)(mu-trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2))](4+) (BBR3464)

The hydrolysis profile of the bifunctional trinuclear phase II clinical agent [(trans-PtCl(NH(3))(2))(2)(mu-trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2))](4+) (BBR3464, 1) has been examined using [(1)H,(15)N] heteronuclear single quantum coherence (HSQC) 2D NMR spectroscopy. Reported are estimates of the rate and equilibrium constants for the first and second aquation steps, together with the acid dissociation constant (pK(a1) approximately equal to pK(a2) approximately equal to pK(a3)). The equilibrium constants for the aquation determined by NMR at 298 and 310 K (I = 0.1 M, pH 5.3) are similar, pK(1) = pK(2) = 3.35 +/- 0.04 and 3.42 +/- 0.04, respectively. At lower ionic strength (I = 0.015 M, pH 5.3) the values at 288, 293, and 298 K are pK(1) = pK(2) = 3.63 +/- 0.05. This indicates that the equilibrium is not strongly ionic strength or temperature dependent. The aquation and anation rate constants for the two-step aquation model at 298 K in 0.1 M NaClO(4) (pH 5.3) are k(1) = (7.1 +/- 0.2) x 10(-5) s(-1), k(-1) = 0.158 +/- 0.013 M(-1) s(-1), k(2) = (7.1 +/- 1.5) x 10(-5) s(-1), and k(-2) = 0.16 +/- 0.05 M(-1) s(-1). The rate constants in both directions increase 2-fold with an increase in temperature of 5 K, and rate constants increase with a decrease in solution ionic strength. A pK(a) value of 5.62 plus minus 0.04 was determined for the diaqua species [(trans-Pt(NH(3))(2)(OH(2)))(2)(mu-trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)-NH(2))(2))](6+) (3). The speciation profile of 1 under physiological conditions is explored and suggests that the dichloro form predominates. The aquation of 1 in 15 mM phosphate was also examined. No slowing of the initial aquation was observed, but reversible reaction between aquated species and phosphate does occur.     

葡萄糖水溶液中碳酸盐热力学研究 1.二氧化碳-碳酸氢钠-氯化钠-葡萄糖-水体系

在278.15～318.15K和一定离子强度范围内,测定了无液接电池Pt,(1-x)H~2+xCO~2│NaHCO~3(m~1),NaCl(M~2),.CO~2(m~3),葡萄糖(m~4)│AgCl-Ag的电动势,利用改进的Harned外推法和我们提出的多项式拟合法确定了二氧化碳在15%葡萄糖水溶液中的一级酸常数K 两种方法所得PK 值在实验误差范围内一致.PK 随温度变化符合经验方程PK =A~1+A~2/T+A~3T,并计算了二氧化碳在葡萄糖水溶液中解离过程的各热力学量.     

Purification of xylenol orange by preparative paper chromatography, and examination of its zirconium complex

Preparative paper chromatography is proposed as a suitable method for purification of Xylenol Orange (XO). The last three dissociation constants of pure XO have been determined with the aid of the program SPEKTFOT, the values found being pK(9) = 12.34; pK(8) = 10.66; pK(7) = 6.69 (0.1M KNO(3), 20 +/- 0.5 degrees ). The complexation of zirconium with the purified reagent has been studied and the co-existence of ML and M(2) L complexes proved by use of the program DALSFEK. The following conditional stability constants of the complexes and their molar absorptivities were computed: log beta'(ml) 4.58; log beta'(M(2)L) 11.59; (ML) 2.00 x 10(4); (M(2)L) 9.40x 10(4) l.mole(-1).cm(-1) at 550 nm.     

Application of RP-TLC technique for the determination of dissociation constants of 1-substituted pyrrolidin-2-one derivatives

The procedures for measuring dissociation constants (pK(a)) of twenty 1-substituted pyrrolidin-2-one derivatives are described. The dissociation constants of the compounds tested were determined using potentiometric titration, reversed-phase thin-layer chromatography (RP-TLC) and calculated using Pallas and Marvin programs. It was found that the RP-TLC method of determination of pK(a) could be considered as a feasible alternative to potentiometric titration. The Marvin program is a better tool for preliminary estimation of dissociation constant than the Pallas one.     

Temperature and substituent effects on the dissociation constants of 5-azorhodanine derivatives. Semi-empirical quantum mechanical calculation

Detailed analysis of the electronic structure and properties of some rhodanine derivatives (RDs) is presented. The aim of the present investigation is to pinpoint the electronic structural similarities and differences, among the series of the studied RDs that govern and determine their acidic, basic and co-ordinative properties. The geometries of the studied rhodanine were fully optimized at the level of AMI semi-empirical method. Relative stabilities of the enol/keto isomers have been calculated. Proton affinities and proton detachment energies were computed for the series of rhodanine studied, at the level of AM1 method and compared with the potentiometrically-determined proton-ligand dissociation constants. Zero-point energy and electron correlations have been taken into consideration. pK(H) have been found to increase with increasing electron-donating nature of the substituents. The resulting linear Hammett plots of pK(H) versus the Hammett constant sigma values indicate the co-planarity of the investigated molecules. The evaluated thermodynamic parameters (deltaG, deltaH and deltaS) indicate that the dissociation processes are non-spontaneous, endothermic and entropically unfavourable.