Vibrational spectral studies of L-citrullinium perchlorate

Infrared and Raman spectra of L-citrullinium perchlorate crystals have been recorded at room temperature. The vibrational assignments of the observed wavenumbers are proposed on the basis of group theoretical analysis. The presence of carbonyl group indicates that the molecule exists in the ionic form. The shifting of stretching and bending wavenumbers indicates the presence of extensive hydrogen bonding in the crystal. The anion fundamentals however continue to be degenerated. This suggests that its symmetry is not affected in the crystal.     

Solvent and substituent effects on spectroscopical changes of some diazoaminobenzene derivatives

A series of diazoaminobenzene derivatives (seven) in which the substituents have a wide range of electronic characters are set out to understand the involvement of the substituent identity in controlling the changes in their electronic absorption spectra. The interactions between the diazoamino group and the different groups account for some spectral shifts. The UV-vis spectrum of each compound is measured in several solvents with wide variations of solvent polarity parameters to examine the role of the chemistry of the solvent in these spectroscopical changes. The electronic transitions are assigned and the solvent induced spectral shifts are analyzed in relation to the different solute-solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlating the different parameters. The results help to assign the solute-solvent interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic character of the substituent and the chemical nature of the solvent are the major factors for the observed solvatochromism.     

Chemometric approach to evaluate the parameters affecting electrospray: application of a statistical design of experiments for the study of arginine ionization

The effects of different experimental parameters on arginine electrospray ionization have been investigated with response surface modelling design. This chemometric technique allows a study of the effects of selected experimental variables and their interactions on the response of an experiment by performing a limited number of analyses. Six variables were studied: methanol content in the liquid phase, formic acid concentration, electrospray voltage, orifice voltage, mobile phase flow rate, and sheath gas flow rate. Signal abundance and signal-to-noise ratio of the protonated molecule and the protonated dimer were measured from the electrospray mass spectra and these four responses were tested by the design. The factor that exhibits the greatest influence on MH+ abundance is shown to be the liquid flow rate whereas the formation of protonated dimer is mainly controlled by the percentage of methanol in the mobile phase. A strong synergic effect of methanol content and formic acid concentration in the liquid has also been demonstrated in the study of noise level. Moreover, the capabilities of the multicriteria optimization method have been demonstrated through a successful prediction of a set of optimal experimental conditions.     

Determination of antihypertensive mixtures by use of a chemometrics-assisted spectrophotometric method

A simple multivariate calibration method for analysis of two types of hypotensive mixture is described. The mixtures are composed of chlorthalidone with atenolol or chlorthalidone with both amiloride hydrochloride and atenolol. The components of the mixtures result in substantial spectral overlap—between 87.5 and 91.0%. Resolution of the mixtures under investigation has been accomplished mainly by using CLS and PCR methods. The components in each mixture have been simultaneously determined in three commercial dosage forms with high accuracy and without interference from commonly encountered excipients and additives. Good recoveries were obtained with both synthetic mixtures and commercial tablets. The results obtained were compared with those from pharmacopeial methods and found to be in good agreement. The results obtained from CLS and PCR were also compared with those obtained from a ¹D spectrophotometric method.     

The Fibonacci sequence modulo π, chaos and some rational recursive equations

In this paper, we provide the closed form solution to the inter-related equations Both of these equations were suggested as open problems in the book by Kocic and Ladas [V.L. Kocic, G. Ladas, Global Behavior of Nonlinear Difference Equations of High Order with Applications, Kluwer Academic, Dordrecht, 1993]. We also give the closed form solution to the equations studied by X. Li and D. Zhu [X. Li, D. Zhu, Two rational recursive sequences, Comput. Math. Appl. 47 (2004) 1487–1494].     

On a functional equation generalizing the class of semistable distributions

With ?(p),p≥0 the Laplace-Stieltjes transform of some infinitely divisible probability distribution, we consider the solutions to the functional equation ?(p-e ^?pβΠ _i=1 ^m ?^γi (c _i p) for somem≥1,c _i>0, γ _i >0,i=1., …,m, β ε ®. We supply its complete solutions in terms of semistable distributions (the ones obtained whenm=1). We then show how to obtain these solutions as limit laws (r → ∞) of normalized Poisson sums of iid samples when the Poisson intensity λ(r) grows geometrically withr.     

Binary,ternary and quaternary complexes invloved in the systems pyridoxamine-glycine-imidazole with some bivalent metal ions

Equilibrium-based computer models using MINIQUAD-75 program were utilized to determine the stoichiometry and formation constants involved in the systems pyridoxamine(Pm)-glycine (Gly)-imidazole (lmd) with CO(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions. The data were obtained from potentiometric pH titration of the various binary and ternary quaternary systems under physiological-like conditions (0.15 M NaNO₃-37°C). Various composition ratios of metal and ligands were used. The ligand concentrations did not exceed 4 times the concentration of metal ion in the binary systems and 4 times of the metal ions in ternary systems. In case of the quaternary systems only imidazole concentrations were two or four times the concentrations of metal ions keeping those of other ligands equal to that of metal ions. The stability constants of the quaternary species are discussed in terms of binary and ternary constants as are the effect of ring size on the stability of mixed ligand species. In addition, electrostatic as well as statistical effects also are mentioned and the biological implications of these model equilibria are described.     

Energie de cohésion des composés MAX (M ≡ Ca,Sr,Ba; A ≡ H,F; X ≡ Cl,Br,I) de structure PbFCl

The Madelung constant, the electrostatic and repulsive energies of the compounds MAX, with the PbFCI structure (D⁷_4h), are calculated and compared with the experimental cohesive energy. This calculation yields a crude estimate of the Van der Waals energy. The special case of CaHBr is discussed.     

Effect of magnetic field on nonlinear interactions of electromagnetic and surface waves in a plasma layer

Investigation is made for nonlinear interaction between incident radiation and a surface wave in a magnetized plasma layer. Both interacting waves are ofP polarization. We get the generated currents and fields at combination frequencies analytically. Unlike theS-polarized interacting waves, the magnetic field affects the fundamental waves and leads to an amplification of generated waves when their frequencies approach the cyclotron frequency.