Spectrophotometric determination of acidity constants by two-rank annihilation factor analysis

Annihilation of the contribution of one chemical component from the original data matrix is a general method in rank annihilation factor analysis (RAFA). However, RAFA is not applicable for studying the protonation equilibria of multiprotic acids. In this work, a two-rank annihilation factor analysis (TRAFA) method was proposed for determination of the acidity constants of diprotic acids. After recording the electronic absorbance spectra of the acids at different pH, the contributions of both H₂A and A²⁻ were annihilated from the absorbance data, which made feasible the determination of two successive acidity constants. The method was validated by analysis of simulated data and its application to the determination of the acidity constants of calmagite, as a reference compound. A close agreement was obtained between the resulted values by TRAFA and the declared values. Indeed, the method was used for determination of the acidity constants of two new chromenone derivatives in binary solvents mixtures of methanol and water. The effects of changing solvent composition on acidity constant data were explained by linear solvation free energy relationships (LSFER) utilizing solvatochromic parameters.     

Experimental and computational study of the pKa of coumaric acid derivatives

The dissociation constant (pK_a) of a drug is a key parameter in drug discovery and pharmaceutical formulation. The hydroxy substituent has a significant effect on the acidity of hydroxycinnamic acid. In this work, the acidic constants of coumaric acids are obtained experimentally by spectrophotometry using the chemometric method and calculated theoretically using ab initio quantum mechanical method at the HF/6‐31G* level of theory in combination with the SMD continuum solvation method. Rank annihilation factor analysis (RAFA) is an efficient chemometric technique based on the elimination of the contribution of one of the chemical components from the data matrix. RAFA cannot be performed because the pure spectrum of HA^? is not available. So, two‐rank annihilation factor analysis (TRAFA) is proposed for the determination of the pK_a OF H₂A. A comparison between the pK_a values obtained previously by TRAFA for the molecules o‐coumaric acid (4.13, 9.58), m‐coumaric acid (4.48, 10.35), and p‐coumaric acid (4.65, 9.92) makes it clear that there is good agreement between the results obtained by TRAFA and ab initio quantum mechanical method.     

Tautomerization equilibria in aqueous micellar solutions: a spectrophotometric and factor-analytical study

The keto-enol equilibria of benzoylacetone (BZA) as a model for 1,3-dicarbonyl compounds are studied in aqueous acid and cationic micellar solution. Evolving factor analysis (EFA), multivariate curve resolution-alternating least-squares (MCR-ALS), and rank annihilation factor analysis (RAFA) are used for complete resolving of measured spectrophotometric data. The acidity constants of the enolic, KaE, and ketonic, KaK, forms of BZA and also the tautomerization constant, Kt, and its related thermodynamic parameters have been determined by using EFA and MCR-ALS methods and spectral variation of BZA solutions in various pHs and temperatures. The concentration and spectral profiles of all species were calculated without any assumption about chemical models. The spectral variation of BZA solutions as a function of cationic micelle concentration sufficiently beyond its critical micelle concentration is analyzed according to the partition model for distribution between water and micellar pseudo-phase and RAFA. The outputs of using RAFA on measured rank deficient data are the spectrum of enolic form in the micellar pseudo-phase, free from contribution of the enolic form in the aqueous phase, the partition coefficient of enolic form, KdE, between the micelle and water phases, and the tautomerization constant in the micellar pseudo-phase, Ktm.     

Spectrophotometric determination of acidity and tautomeric constants and hydrogen bonding strength for a new Schiff base using hard modeling and multivariate curve resolution alternative least squares methods

The equilibria of a new Schiff base derived from 3,6-bis((aminoethyl)thio)pyridazine were studied spectrophotometrically with the aid of factor-analytical methods. Hard modeling program was used for determination of the acidity constants of the Schiff base in dimethylformamide (DMF)/water mixture (30:70 v/v). In this method acidity constant equations act as hard models and the score vectors obtained by decomposing of absorbance data matrix will be linear combinations of equilibrium concentrations of species that exist in the absorption matrix. Two rank annihilation factor analysis (TRAFA) was used as a standard method to investigate the accuracy of the method. The tautomerization constant, K_t, of the Schiff base solution in various DMF/water mixtures has also been determined using spectral variations of the Schiff base solutions in various volume ratios of water with the aid of evolving factor analysis (EFA) and multivariate curve resolution alternative least squares (MCR-ALS) methods. In addition the intramolecular hydrogen bonding strength and its related thermodynamic parameters have been determined using MCR-ALS and spectral variation of the Schiff base solutions in different temperatures.     

三维荧光二阶校正法用于未知混合物中苯酚含量的测定

将三维荧光光谱技术与秩消失因子分析、广义秩消失因子分析和交替三线性分解3种二阶校正方法相结合,建立了测定未知混合物中苯酚含量的三维荧光二阶校正新方法。设定在激发波长240~280 nm和发射波长280~360 nm范围内测定未知混合物中苯酚的三维荧光光谱,构建三维响应数据阵,运用基于三线性分解的二阶校正算法进行解析。结果表明,当模拟样品的组分数为2时,秩消失因子分析、广义秩消失因子分析和交替三线性分解3种方法测定苯酚的预测均方根误差分别为0.33,1.18和0.15,平均回收率分别为101.6%,115.6%和101.9%;当组分数为3时,3种方法的预测均方根误差则分别为1.61,1.80和0.51,平均回收率分别为134.2%,133.9%和107.1%;将其分别应用于实际样品中苯酚的测定,结果满意,且交替三线性分解法的测定结果优于秩消失因子分析法和广义秩消失因子分析法。     

Investigation of the Effect of Inclusion of Eriochrome Black T with β-Cyclodextrin on Its Complexation Reaction with Ca2+ and Mg2+ Using Rank Annihilation Factor Analysis

Rank annihilation factor analysis (RAFA) was used to investigate the effects of inclusion of eriochrome black T (EBT) on its complexation reaction with Ca²⁺ and Mg²⁺ at different pH values. Addition of β-cyclodextrin (β-CD) to Ca-EBT or Mg-EBT caused decomposition of the 1:1 metal complex and increase in EBT concentration in solution due to the formation of EBT-β-CD inclusion complex. In order to perform RAFA, concentration profiles were calculated by optimizing the value of the conditional stability constant and inclusion constant. The rank of original data matrix reduces by one by removing the information from the complex form (Ca-EBT or Mg-EBT). The performance of the method was evaluated by using synthetic data as well as experimental data and good results were obtained. The proposed method is capable of the simultaneous spectrophotometric determination of formation constant of a complex and the equilibrium constant of the competing reaction in solution.     

秩消因子分析—荧光光度测定某些食物中的营养元素硒

本文应用秩消因子分析－荧光光度法测定了食物中营养元素硒的含量，与文献〔１〕报道的ＤＡＮ－荧光光度法测定结果比较，具有良好的统计学一致性，从而为简化实验操作，改善痕量硒测定的准确性和灵敏度提供了新的可能。     

Rank annihilation factor analysis for spectrophotometric study of complex formation equilibria

The use rank annihilation factor analysis (RAFA) for spectrophotometric studies of complex formation equilibria are proposed. One-step complex formation and two successive and mononuclear complex formation systems studied successfully by proposed methods. When the complex stability constant acts as an optimizing object, and simply combined with the pure spectrum of ligand, the rank of original data matrix can be reduced by one by annihilating the information of the ligand from the original data matrix. The residual standard deviation (R.S.D.) of the residual matrix after bilinearization of the background matrix is regarded as the evaluation function. The performance of the method has been evaluated by using synthetic data. For two-step successive complex formation systems, the effects of noise level and equilibrium constants K₁ and K₂ on output of algorithm are investigated. The applicability of method for resolving the two-step successive complex formation systems with full spectral overlapping of two complex species also is shown. Spectrophotometric studies of murexide-calcium, dithiazone-nickel and methyl thymol blue (MTB)-copper are used as experimental model systems with different complexation stoichiometries and spectral overlapping of involved components.     

Potentiometric study of the protonation and distribution equilibria of d-gluconic-delta-lactone acid in sodium perchlorate solutions at 25 degrees C and construction of a thermodynamic model

The protolytic behavior of d-gluconic-delta-lactone acid has been studied by means of automated potentiometric titrations at different ionic strengths in the range 0.1相似文献   

Spectrophotometric investigation of the effect of beta-cyclodextrin on the intramolecular cyclization reaction of catecholamines using rank annihilation factor analysis

The catalytic effect of β-cyclodextrin (β-CD) on the intramolecular cyclization reaction of catecholamines dopamine, methyldopa and levodopa after their oxidation with periodate was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The method was based on the effect of β-CD concentration on the intramolecular cyclization reaction of the investigated catecholamines after their oxidation with potassium periodate. In order to perform RAFA, concentration profiles were calculated by optimizing the value of formation constant. The rank of original data matrix can be reduced by one by annihilating the information of the cyclization reaction in the absence of β-CD. The rate constant for the reactions in the presence and absence of β-CD was also determined. The best estimation of rate constant in the presence of β-CD reduces the rank of the system to zero (noise level). The method was evaluated using synthetic data as well as experimental data and good results were obtained.     

Rank annihilation factor analysis for multicomponent kinetic‐spectrophotometric determination using difference spectra

In this work rank annihilation factor analysis (RAFA) is used to analyze difference spectra of kinetic‐spectrophotometric data. Annihilation of the contribution of one chemical component from the original data matrix is a general method in RAFA. However, sometimes RAFA is not suitable for studying rank deficient data such as kinetic‐spectrophotometric measurements. On the other hand, in order to apply RAFA for the determination of an analyte in an unknown sample, a standard two‐way matrix of the analyte with rank one should generally be available. This is not usually attainable for kinetic‐spectrophotometric monitoring of complexation reactions. Processes monitored by difference spectroscopy always have the spectrum of the initial stage subtracted from each spectrum in the data matrix. In this work we show that, for kinetic‐spectrophotometric data of complexation reactions, the spectrum of ligand (reactant) itself can be used as initial spectrum for subtraction. The obtained difference matrix of sample and that of analyte of interest will be full‐rank and rank 1, respectively. Therefore the system can be analyzed by RAFA. The proposed method was investigated with simulated data at the first stage. The method was then applied in the analysis of experimental kinetic‐spectrophotometric data of a complexation reactions of Co(II) and Ni(II) with chromogenic reagent 1‐(2‐pyridylazo) 2‐naphthol in order to do multi‐component determination of these ions in various real samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanisms of photoinduced protolytic interactions of 2,5-diphenyloxazoleortho-hydroxy derivatives in media of various acidities

The mechanism of photoinduced intra- and intermolecular protolytic interactions ofortho-hydroxy derivatives of 2,5-diphenyloxazole in an aqueous alcohol medium was studied over a wide range of acidity from pH ∼13 toH ₀ of ∼−7. The spectral parameters of protolytic forms and equilibrium constants were obtained, and rate constants for the primary photochemical processes (excited-state intra- and intermolecular proton transfer reactions) were evaluated. It was shown that the spectral characteristics of oxazoleortho-hydroxy derivatives in an acidic medium are formed as a result of competition and interchange of intra- and intermolecular protolytic interactions. The phototautomeric form in strongly acidic solutions was found to be produced by dissociation of the cationic form with the protonated oxazole ring.     

A new algorithm for the determination of protolytic constants from spectrophotometric data in multiwavelength mode: Calculations of acidity constants of 4-(2-pyridylazo)resorcinol (PAR) in mixed nonaqueous-water solvents

A new efficient, simple and versatile algorithm is presented for determination of the protolytic constants from spectrophotmetric data in multiwavelength mode based on the combining of hard and soft modeling. The algorithm was checked by determining the acidity constants of a triprotic acid from theoretical and real absorption-pH data. The real spectral data are obtained from photometric titration of different solutions of 4-(2-pyridylazo)resorcinol (PAR) by a standard base solution under an inert atmosphere. The algorithm starts the minimization process using an user supplied number of components and initial guesses of the unknown parameters and refined in a least squares manner. New algorithm is implemented in the new version of DATAN package (version 3.1). The validity of the obtained results was checked by some well known programs such as DATAN 2.1, SPECFIT/32, SQUAD, a modified version of difference spectra and a A-pH curve method. The comparison of the outputs of the DATAN 3.1 with the other programs reveals that there is a very good agreement between the obtained results and mentioned programs.     

Determination of rate constants from two-way kinetic-spectral data by using rank annihilation factor analysis

Rank annihilation factor analysis (RAFA) is applied to resolve the two-way kinetic-spectral data measured from spectroscopic reactions and acquire rate constants and the absorption spectrum of each component. A two-step first-order consecutive reaction is studied in this paper. When the first step rate constant acts as an optimizing object, and simply combined with the pure spectrum of reactant, the rank of the original data matrix can be reduced by one by annihilating the information of reactant from the original data matrix. The residual standard deviation (R.S.D.) of the residual matrix after bilineaization of the background matrix is regarded as the evaluation function. Owing to the correlation between kinetic functions of species in the reaction, two optimal resolutions, corresponding to the rate constants of the first and second step, respectively, can both be obtained in one computing process. Given the kinetic parameters, the absorption spectrum of each component including the intermediate can be obtained through least square regression. This approach can also be applied to reaction systems where the intermediate or the final product doesnot absorb. The performance of the method has been evaluated by using synthetic data. Electrodegradation of phenol solution and alkaline hydrolysis of dimethyl phthalate were also studied by the present method.     

Spectrophotometric determination of the formation constants of some transition metal cations with a new synthetic Schiff base in dichloromethane and chloroform using rank annihilation factor analysis

The complex formation between a new synthesized Schiff base and the cations Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺ in dichloromethane (DCM) and chloroform solutions was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The results of mole ratio plots and continuous variation data show the stoichiometry of complexation were found to be 1:1, and 2:1 metal ion to ligand. The stoichiometry was obtained as 1:1 metal ion to ligand ratio for Co²⁺, Ni²⁺ and Zn²⁺ in chloroform and 2:1 for Cu²⁺. In DCM the stoichiometry was obtained as 1:1 for Co²⁺ and 2:1 for Ni²⁺ and Zn²⁺ and a consecutive 2:1 metal ion to ligand ratio was obtained for Cu²⁺. Formation constants of these complexes were estimated by application of RAFA on spectrophotometric data. In this process the contribution of ligand was removed from the absorbance data matrix when the complex stability constant acts as an optimizing object and simply combined with the pure spectrum of the ligand, the rank of the original data matrix can be reduced by one by annihilating the information of the ligand from the original data matrix.     

Influence of mobile phase acid-base equilibria on the chromatographic behaviour of protolytic compounds

A review about the influence of mobile phase acid-base equilibria on the liquid chromatography retention of protolytic analytes with acid-base properties is presented. The general equations that relate retention to mobile phase pH are derived and the different procedures to measure the pH of the mobile phase are explained. These procedures lead to different pH scales and the relationships between these scales are presented. IUPAC rules for nomenclature of the different pH are also presented. Proposed literature buffers for pH standardization in chromatographic mobile phases are reviewed too. Since relationships between analyte retention and mobile phase pH depends also on the pKa value of the analyte, the solute pKa data in water-organic solvent mixtures more commonly used as chromatographic mobile phase are also reviewed. The solvent properties that produce variation of the pKa values with solvent composition are discussed. Chromatographic examples of the results obtained with the different procedures for pH measurement are presented too. Application to the determination of aqueous pKa values from chromatographic retention data is also critically discussed.     

利用减秩因子分析法同时优化确定化学反应级数和速率常数

通过对反应过程中在线测得的动力学谱-光谱二维数据矩阵进行主成分分析，可确定化学反应过程存在的组分数。提出用优化动力学参数-减秩因子分析法解析二维数据矩阵，对未知动力学模型的复杂反应可同时优化求解第一步反应的级数和速率常数。模拟二维数据验证了该方法的可行性。该方法用于高锰酸钾氧化溴化钠的反应过程中测得的二维数据的解析，结果表明：高锰酸钾的还原过程符合0级反应模型。     

Multiwavelength spectrophotometric determination of protolytic constants of 4-(2-pyridylazo) resorcinol (PAR) in binary DMF-water mixtures

A multiwavelength spectrophotometric titration method was applied to study the protolytic constants of 4-(2-pyridylazo) resorcinol(PAR), in binary DMF + water mixtures. UV-vis absorption spectra of PAR solution were recorded in the course of pH-metric titration of acidic solutions of PAR with standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated from the fitting of the pH-spectral titration data with appropriate mass balance equations by a home written program according to an established target factor analysis. To precise determination of number of absorptive components a recently developed statistical indicator function (IND function) was used. A glass electrode calibration procedure based on a four-parameter equation pH=α+SpcH+JH⁺[H⁺]+JOH⁻Kw/[H⁺] based on the Gran's plots was used to obtain pH readings in the concentration scale (p_cH). It has been observed that there is an inverse relationship between second and third protolytic constants and mole fraction of DMF. The effect of the solvent on the protolytic constants was discussed.     

Electronic absorption study on acid-base equilibria for some keto and thioketo pyrimidine derivatives. Experimental and theoretical evidence of enolization and solute-solvent interactions

The UV-vis spectra of recently synthesized 1-amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-one, (I), and 1-amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-thione (II), were studied in aqueous methanol (5%, v/v, methanol) and pure methanol. The nature of the electronic transitions and the role of carbonyl oxygen of I and thiocarbonyl sulfur of II in the behavior of the observed UV-vis spectra were discussed. The carbonyl group at position 2 of I and the thiocarbonyl group of II were found to be enolized instead of protonation. Quantum chemical calculations showed agreement with the experimental evidence. However, the carbonyl group of the benzoyl moiety at position 5 of both compounds underwent neither enolization nor protonation. Acid-base equilibria of the compounds against varying pH have been examined in detail. The pKa values of all related equilibria were determined at room temperature and an ionic strength of 0.10 M from the pH-dependence of the absorbance values using the Henderson-Haselbalch equation and graphical logarithmic analysis. The mean acidity constants for the protonated forms of the compounds were determined as pKa1=4.214 and pKa2=6.678 for I and pKa1=3.739 and pKa2=6.258 for II. The mean acidity constants (pKa3) for the enol form of I and the thioenol form of II were determined as 11.278 and 11.063, respectively. The preferred dissociation mechanisms were discussed based on the data of UV-vis spectroscopy and a mechanism was proposed for each compound. The formation of intramolecular and intermolecular hydrogen bonding were found with I but not with II. The intramolecular bonding stabilizing the enol form was favoured at pH values corresponding to pKa1 and above. On the other hand, the intermolecular hydrogen bonding stabilizing the free form of the carbonyl group was favoured at all pH values.     

Determination of Sudan I in chilli powder from solvent components gradual change-visible spectra data using second order calibration algorithms

It was discovered that a second order spectra data matrix of Sudan I produced from the solvent components gradual change-visible absorption spectra can be expressed as the combination of two bilinear data matrices. Based on this discovery, a new method for the determination of Sudan I in gray systems using second order calibration algorithms has been developed. The second order calibration algorithms were based on the popular parallel factor analysis (PARAFAC) and rank annihilation factor analysis (RAFA), respectively. In the method described here, the components of the solvent were changed gradually by adding ethanol into cyclohexane, the absorption spectra of Sudan I and chilli samples in a series of cyclohexane-ethanol mixed solvents with various ethanol volume fractions were recorded, and then the second order data were obtained from the solvent components gradual change-visible absorption spectra. Thus, the concentration of Sudan I in a gray system could be determined from the spectra matrices using second order calibration algorithms. This method is simple, convenient and dependable. The method has been used to determine Sudan I in chilli powder with satisfactory results.