Study of acid-base properties of morin by tristimulus colorimetry

Acid-base properties of morin in aqueous solutions have been studied by means of chemical tristimulus colorimetry, and the ionization constants have been determined. The pK values have been assigned to the corresponding functional groups, and their dissociation scheme has been suggested. Diagram of distribution of ionic and molecular forms of morin at pH 1–13 has been constructed. Spectral parameters of equilibrium acid-base forms of morin have been determined.     

A tristimulus colorimetric study of the acid–base properties of 6,7-dihydroxybenzopyrylium chlorides in solutions

The acid–base equilibria of 6,7-dihydroxybenzopyrylium chloride derivatives in solutions are studied by tristimulus colorimetry. The ionization constants of their functional groups are determined. Possible schemes of the equilibria and the distribution diagrams of the ion-molecular forms of the reagents are proposed depending on the pH of the medium. It is shown that tristimulus colorimetry can be used to determine the protonation and hydroxylation constants of the dyes. The relation between these constants and the charges on the oxygen atoms and 2-C atoms of the benzopyrylium ring is established.     

Sulfonephthalein dyes: Part VII. Chromogenic Reactions of Semi-Glycicethymol Blue

The chromogenic reactions of semi-glycinethymol blue have been studied spectrophotometrically and by complementary tristimulus colorimetry. The separation of the dye from a commercial product of glycinethymol blue is described. The five dissociation constants were determined; the means of the pK_a (H_iI) values for i= 5, 4, 3, etc. are —1.5, 0.3, 1.5, 7.5, and 12.7, respectively. Colour reactions with some metal ions are reported; the reaction with copper(II) is suggested for the determination of the composition of commercial samples of glycinethymol blue.     

Microionization constants of sulphonamides

The macroionization constants and thermodynamic parameters of twelve commercial sulphonamides were determined by potentiometric titration at 15 degrees , 25 degrees and 35 degrees and by spectrophotometry at 25 degrees , in aqueous solution of ionic strength 0.1 (NaClO(4)). The microionization constants and the tautomeric constants (concentration ratios of zwitterion to uncharged or neutral species) were obtained according to the Edsall method combined with complementary tristimulus colorimetry. By utilizing the microionization constants, the species distribution as a function of pH were calculated for the three kinds of sulphonamides.     

Moisture induced solid phase degradation of l-ascorbic acid Part 1: a kinetic study using tristimulus colorimetry and a quantitative HPLC assay

l-Ascorbic acid was found to degrade in the solid phase with discoloration under the influence of moisture in proportion to the moisture content. This degradation pattern was different to that in solution and followed zero order kinetics. The exclusion of air reduced the rate of reaction suggesting the degradation may proceed via an oxidative route but no evidence was found for the presence of dehydroascorbic acid. A method was developed for the determination of dehydroascorbic acid using an automated precolumn reduction reaction with dl-dithiothreitol. The degradation was found to be zero order and activation energy was been measured at 37.57 kJ mol(-1) by high performance liquid chromotography (HPLC) assay and 33.30 kJ mol(-1) by tristimulus colorimetry, resulting in a 12.8% difference between the two methods. Tristimulus colorimetry was more sensitive to the onset of degradation than HPLC assay, but it is non-specific. The purpose of this study was to obtain kinetic data on the rate of degradation of l-ascorbic acid alone under the influence of moisture and air and to identify whether tristimulus colorimetry could be used as a rapid and non-destructive means of monitoring for the degradation of l-ascorbic acid in the solid phase. Further studies to determine the degradation pathway and to identify the degradation products are to be reported in subsequent papers.     

光声光谱技术在色分析研究中的应用

现行测色法多以常规光谱为基础。通过测量样品对光的透射或反射率以及光源的能量分布,叠合色匹配函数,来寻找颜色的三刺激量,由此获取样品的色别、色饱和度和明度的信息。这些方法的共同特点是定向输入光子,并计量定向输出光子的情况。为了能将测定范围扩展到那些高反射、散射、漫射、辐射和层状样品,对一般常规光谱法是困难的。我们因此提出了光声测色法(PAC)。     

Determination of plutonium oxidation states in dilute nitric acid by complementary tristimulus colorimetry

The preparation of reference standards for use in complementary tristimulus colorimetry for plutonium is described. Plutonium(III) and (VI) are prepared by hydrazine reduction and silver(II) oxidation, respectively, of plutonium(IV). Plutonium(V) is prepared by reduction of plutonium(VI) with ascorbic or sulphurous acid. A method for computerizing tristimulus colorimetry is presented, and the technique is extended to three dimensions ("quadristimulus colorimetry").     

数码比色法测定环境及生物样品中的氰化物浓度

在传统氰化物检测方法的基础上,提出了一种新的方法—数码比色法。在一定条件下,苦味酸与氰化物生成黄色化合物,用数码相机对显色溶液拍照,通过数码比色,进行灰度处理,照片的三原色值与氰化物的浓度成线性关系,可以直接分析出其氰化物的浓度。对唾液样品测定,其回收率为98.18%,对照品测定的相对标准偏差RSD为1.5%。研究结果表明,数码比色法具有准确度和精密度都比较理想,方便快速、环境友好等特点。     

Application of simplified complementary tristimulus colorimetry to chemical kinetics in solution-II Determination of rate constants of consecutive irreversible first-order reactions

A simple but highly reproducible method based on simplified complementary tristimulus colorimetry is proposed for determination of the rate constants of two consecutive irreversible first-order reactions. For the binary system the complementary colour points can be calculated in the same manner as in conventional tristimulus colorimetry. Hence the mole fractions of the three reacting species can be calculated as a function of time. Application of the method is illustrated by the assay of xanthine oxidase with hypoxanthine.     

The brilliant blue FCF ion-molecular forms in solutions according to the spectrophotometry data

The brilliant blue FCF acid–base properties in aqueous solutions have been studied and its ionization constants have been defined by tristimulus colorimetry and spectrophotometry methods. The scheme of the acid–base dye equilibrium has been proposed and a diagram of the distribution of its ionic-molecular forms has been built. It has been established that the dominant form of the dye was the electroneutral form, which molar absorptivity (ε₆₂₅ = 0.97 × 10⁵) increases with the increase of the dielectric permittivity of the solvent. It has been shown that the replacement of polar solvents by less polar ones is causing a bathochromic shift of the maximum absorption band of the dye, the value of which is correlated with the value of the Hansen parameter. Tautomerization constants have been defined in a number of solvents and associated with the value of the Dimroth-Reichardt parameter.     

吡啶酮系偶氮染料腙体结构中亚胺基质子的交换和解离动力学

吡啶酮系偶氮染料腙体结构中, 亚胺基质子能与水分子中的质子发生交换和解离。用核磁双共振实验测定了交换速率(ka)和活化能(E0)。两者均与染料结构、pH值、温度、溶剂性质和水含量等因素有关。在重氮和偶合组分一的亲电取代基和溶液中的碱都能促进交换反应。本文进一步解释了该系列染料的变色机理和染料具有不同的pH值。     

Ground and excited state complexation of ketocyanine dyes with alkaline earth metal ions

Electronic absorption and emission spectral characteristics of two ketocyanine dyes have been studied in solution in the presence of alkaline earth metal ions. Absorption spectral studies indicate complex formation between the ions and the dyes in the ground state. Values of the equilibrium constant and the enthalpy change characterizing dye (S0)-metal ion interaction have been determined from the absorption spectral data. In the presence of the metal ions the fluorescence spectrum of the dyes shows two bands pointing to the existence of two emitting species, viz., the solvated and the complexed dye in solution. Time-resolved studies of the dyes in solution containing the metal ions can be explained by a two-state model and indicate the presence of two emitting species in equilibrium. Values of the equilibrium constant for the interaction of metal ion and the dyes in the S1 state have also been estimated.     

Microscopic acid dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds, and 3,4-dihydroxyphenylalanine (DOPA)

The dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds and of DOPA were determined by potentiometric titration and complementary tristimulus colorimetry at 25 degrees and mu = 0.1 (NaClO(4)) in aqueous solution. The thermodynamic parameters were calculated from the values of the dissociation constants at various temperatures. The dissociation constants and corresponding thermodynamic parameters for the first phenol group of the catechols showed almost the same values as those of the phenol derivatives. In the dissociation of the second phenol group of the catechols, formation of an intramolecular hydrogen bond was indicated. The microscopic acid dissociation constants of 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylpropionic acid were calculated by two different methods. In the physiological pH-region (pH 7.2-7.4), 3,4-hydroxyphenylpropionic acid is present in the carboxylate form, and the two possible monophenolate anions are present to the extent of about 45% and 40%, respectively, at pH 11.0. The twelve micro-constants for the eight chemical species from DOPA were similarly evaluated.     

Spectral and photochemical properties of hydroxylated 2-styrylquinoline derivatives

The spectral and photochemical properties of 2-(4-hydroxystyryl)quinoline 1 and 2-(2-hydroxystyryl)quinoline 2 have been studied. The trans-cis photoisomerization quantum yield for 1 and 2 in the neutral form is 0.2–0.5, and it is reduced by a factor of 6–7 by protonation, presumably, owing to the competitive process of hydroxyl group deprotonation in the excited state and the formation of quinoid tautomers. The quantum yield of the back cis-trans photoisomerization in the protonated form varies insignificantly. The neutral, protonated, and deprotonated forms of 1 have been used for to simulate a molecular logic gate, the half-adder with chemical inputs and absorbance as outputs.     

Application of simplified complementary tristimulus colorimetry to chemical kinetics in solution-I: analysis of reaction mixtures and determination of first- or pseudo first-order rate constants

A graphical method is described which allows estimation of the number of reacting light-absorbing species from the plots of complementary colour points which are obtained with the use of simplified complementary tristimulus colorimetry (SCTS method) from absorption spectra of a series of kinetics solutions. It is shown that the mole function of the reactant or the product at any time can be calculated from the complementary colour points, so that the rate constant can also be determined. The present method has some advantages over the common approach to the determination or reaction rates in presence of a colour impurity.     

Potentiometric study of silver ion co-ordination by azo dyes

The stability constants of the silver(I) complexes of five azo dyes have been determined by means of potentiometric equilibrium measurements with silver electrodes in 75% vlv acetone-water solution. Each azo dye molecule was shown to co-ordinate at most three silver ions. The sequence of the stepwise stability constants indicated an effect stabilizing complexes with high silver content.     

Effect of cooperative hydrogen bonding in azo-hydrazone tautomerism of azo dyes

Azo-hydrazone tautomerism in azo dyes has been modeled by using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level of theory. The most stable tautomer was determined both for model compounds and for azo dyes Acid Orange 7 and Solvent Yellow 14. The effects of the sulfonate group substitution and the replacement of the phenyl group with naphthyl on the tautomer stability and on the behavior in solvent have been discussed. Intramolecular hydrogen bond energies have been estimated for the azo and hydrazone tautomers to derive a relationship between the tautomer stability and the hydrogen bond strength. The transition structures for proton transfer displayed resonance assisted strong hydrogen bonding properties within the framework of the electrostatic-covalent hydrogen bond model (ECHBM). Evolution of the intramolecular hydrogen bond with changing structural and environmental factors during the tautomeric conversion process has been studied extensively by means of the atoms-in-molecules (AIM) analysis of the electron density. The bulk solvent effect was examined using the self-consistent reaction field model. Special solute-solvent interactions were further investigated by means of quantum mechanical calculations after defining the first-solvation shell by molecular dynamics simulations. The effect of cooperative hydrogen bonding with solvent molecules on the tautomer stability has been discussed.     

Ion-exchanger colorimetry-II microdetermination of chromium in natural waters

Ion-exchanger colorimetry for chromium(VI) with 1,5-diphenylcarbohydrazide has been developed for the determination of chromium at mug/l. concentrations in natural water samples. About 90% of the chromium(VI) in a 1-litre sample solution is concentrated in 200-400 mesh Dowex 50W-X4 resin within half an hour. It is possible to obtain higher sensitivity by employing a larger amount of sample solution. Total chromium can be determined by oxidizing chromium(III) to chromium(VI) with ceric sulphate.     

Hydrogen bond directed self-assembly of core-substituted naphthalene bisimides with melamines in solution and at the graphite interface

A series of red and blue highly fluorescent core-substituted naphthalene bisimide dyes has been synthesized and they have been investigated as supramolecular building blocks. NMR and UV-Vis titration experiments of these dyes with complementary melamines revealed the formation of triple hydrogen bonds (DAD-ADA arrays) in solution. At stoichiometric ratios, ditopic melamine receptors could dissolve otherwise insoluble bisimides by means of hydrogen bonding, even in aliphatic solvents. At the solution/graphite interface, one-dimensional chains of hydrogen bonded naphthalene bisimides and two-dimensional adlayers of ditopic melamines are formed for the pure compounds but little evidence for heterocomplexes between the two complementary building blocks could be obtained.     

UV-Vis spectroscopic and chemometric study on the aggregation of ionic dyes in water

The monomer-dimer equilibrium in several ionic dyes (Methylene Blue, Acridine Orange, Nile Blue A, Neutral Red, Rhodamine 6G and Safranine O) has been investigated by means of UV-Vis spectroscopy. The data have been processed by a recently developed method for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. In the cases of Acridine Orange a second chemometric approach has been used as a reference. It is based on a decomposition of the recorded spectra into a product of target and projection matrices using non iterative partial least squares (NIPALS). The matrices are then rotated to give the correct concentrations, spectral profiles of the components and the equilibrium constant. The dimeric constants determined by the two methods were in excellent agreement, evidencing the accuracy of the analysis. From the calculated dimeric constant and monomer and dimer spectra, the structures of the dimeric forms of the studied dyes are estimated.