Multiwavelength spectrophotometric determination of acidity constants of some azo dyes

Application of a new version of GA-RBF neural network for simultaneous spectrophotometric determination of Zn(II), Fe(II), Co(II) and Cu(II) in real samples: An exploratory study of their complexation abilities toward MTB

The current study for the first time is devoted to the application of whole space genetic algorithm-radial basis function network (wsGA-RBFN) method to determine the content micro minerals of Zn(2+), Fe(2+), Co(2+) and Cu(2+) based on their complexes formation with methylthymol blue (MTB) spectrophotometrically in various pharmaceutical products and vegetable samples. Advantage of wsGA-RBFN compared to GA-RBFN is that centers can be located in any point of the samples spaces. Initially, the parameters controlling behavior of the system were investigated and optimum conditions were selected. Then, an exploratory analysis of complex systems was carried out by chemometrics approaches such as SVD, EFA, MCR-ALS and RAFA. The optimal parameters and conditions for constructing the proposed model of wsGA-RBFN were obtained from processing the data set of synthetic samples. Finally, wsGA-RBFN was successfully applied to the simultaneous determination of Zn(2+), Fe(2+), Co(2+) and Cu(2+) in tomato, white cabbage, red cabbage and lettuce and pharmaceutical products included iron, zinc, multi complete and B12 ampoule.

Electronic absorption spectroscopic behavior and acidity constants of some new dinitrophenylhydrazone derivatives

In the present study, UV-visible electronic spectra of three new 2,4-dinitrophenylhydrazone derivatives (C1, C2 and C3) have been studied. Different bands observed have been assigned to the proper electronic transitions. The solvatochromic behaviors of these compounds were investigated by studying their electronic spectra in several organic solvents with different polarities. The longer wavelength band is assigned to an intermolecular charge transfer transition. The solvated H-bonding complexes formed between dimethylformamide and 2,4-dinitrophenylhydrazone derivatives were also investigated. ΔG, and the Kf values of the molecular complexes formed in solution have been determined. Effects of temperature increase and concentration changes on the longer spectroscopic wavelength band of the studied compounds were investigated. In this work, the behavior of acidity constants of these compounds in different pH values is studied by a multiwavelength spectrophotometric method too.

Application of principal component-wavelet neural network in spectrophotometric determination of acidity constants of 4-(2-thiazolylazo)-resorcinol

The acidity constants of 4-(2-thiazolylazo)-resorcinol (TAR) were determined by the principal component-wavelet neural network (WNN). Biprotic acid mass balance equations, the distribution functions and the corresponding spectral profiles which were generated by a Gaussian model, have been considered to simulate all required absorbance-pH data. The simulated absorption-pH data matrix was used as training set whereas the TAR absorption-pH data was used as the test set of WNN model. The obtained acidity constants were in good agreement with the reported values of acidity constants in the literature and with those calculated by DATAN software. Artificial neural network (ANN) model has been also employed in this study and the results of WNN were compared with those obtained by ANN. It was found that WNN gives faster convergence and slightly better accuracy.

Multi-wavelength spectrophotometric determination of acidity constant of some newly synthesized Schiff bases and their QSPR study

The acidity constants of some newly synthesized Schiff base derivatives were determined by hard-model based multivariate data analysis of the spectrophotometric data in the course of pH-metric titration in 50% (v/v) methanol-water binary solvent. The employed data analysis method was also able to extract the pure spectra and pH-dependent concentration profiles of the acid-base species. The molecules that possess different substituents (both electron donating and withdrawing) on the ortho-, meta- and para-positions of one of the phenyl ring showed variable acidity constants ranging from 8.77 to 11.07 whereas the parent molecule had an acidity constant of 10.25. To investigate the quantitative effects of changing of substitution pattern on the acidity constant, a quantitative structure-property relation analysis was conducted using substituent constants and molecular descriptor. Some models with high statistical quality (measured by cross-validation Q(2)) were obtained. It was found that the acidity constant of the studied molecules in the methanol-water mixed solvent not only is affected by electronic features of the solutes but also by the lipophilic interaction between methanol part of solvent and the deprotonated solutes.

Solvatochromism and temperature effects on the electronic absorption spectra of some azo dyes

The UV-visible electronic spectra of some azo dyes have been studied. The different bands observed in the electronic spectra of the compounds in various organic solvents have been assigned to the proper electronic transitions. The solvatochromic behaviour of these compounds was investigated by studying their visible spectra in several pure and mixed organic solvents. The longer wavelength band displayed by para-nitro azo dyes is assigned to an intermolecular charge-transfer transition. The solvated H-bonding complexes formed between N,N-dimethylformamide and the para-nitro azo dyes were investigated. DeltaG and formation constant, the values of K(f) of the molecular complexes formed in solution have been determined. The effects of increase of temperature and concentration dependent spectroscopic changes on the longer wavelength visible band of para-nitro azo dyes were also investigated.