Michail G. Arnaudov

Linear-dichroic infrared spectral analysis of Cu(I)–homocysteine complex

The interaction between homocysteine (HCysSH) and Cu(II) leads to the formation of a yellow complex [Cu(I)(HCysS-SCysH)2]Cl (1) after redox processes in the Cu(II)-homocysteine system resulting in dimerization of the ligand and formation of a mononuclear Cu(I) complex with two dimers. The structure of (1) was obtained by IR-LD spectral analysis of a solid amorphous sample oriented in nematic liquid crystal medium. The original technique for orientation developed here and the polarized IR spectra thus obtained, permit the determination of the complexation sites and coordination mode of diamagnetic complexes. In the complex (1), Cu(I) is coordinated through the two O atoms of one COO- group of each of the ligands and the metal ion coordination sphere represents a distorted tetrahedron.

Validation of reducing-difference procedure for the interpretation of non-polarized infrared spectra of n-component solid mixtures

Validation of reducing-difference procedure based on subtracting of non-polarized infrared (IR) spectra of n-component solid mixtures is presented. The accuracy and precision are established. The limits of detection are 3.0, 2.5, 1.5 and 1.0wt.% for 5-, 4-, 3-and 2-component mixtures, respectively. Smoothing procedures for IR spectral analysis, based on Savitzky-Golay or Fourier methods are applied as well. The mean values and relative standard deviations for peak position (nu(i)) and integral absorbance (A(i)) obtained by this data processing approach have been examined using Students t-test.

Linear-dichroic infrared and NMR spectroscopic analysis of an Au(III) complex of glycylmethioninylglycine

A solid state, linear dichroic IR analysis of a mononuclear Au(III) complex of the tripeptide glycylmethioninylglycine (GlyMetGly) oriented in a nematic liquid crystal has been carried out. Structural results are compared with 1H and 13C NMR data. The ligand coordinates to Au(III) as a tridentate in [Au(C9H17N3O4S)Cl]Cl2, binding through S, and the N- and O-atoms of neighbouring CONH– and COO− groups. The fourth position is occupied by a terminal Cl− ligand.

IR-SPECTRAL STUDY OF SELF-ASSOCIATION EFFECTS OF 2-AMINOPYRIDINE IN SOLUTION

Abstract A comparative IR-spectral study of solute-solute hydrogen bond formation in carbon tetrachloride and chloroform solutions of 2-amino-pyridine is reported. The presence of chain-like self-associates is confirmed in contrast to the solid state where the stabilization of the cyclic dimeric structure takes place. This conclusion is suggested on the basis of the NH2 stretching region data obtained by changing the solute concentration as well as by comparing with the corresponding data about melted and solid state 2-aminopyridine and 3-aminopyridine samples.

Tautomerism in 1‐Phenyl‐3‐Substituted Pyrazol‐5‐ones: FT‐Infrared Spectral Analysis and Ab Initio Calculations

Abstract A comparative IR‐spectral study of 3‐phenyl‐(DPhP) and 3‐methyl‐(MPhP) substituted 1‐phenyl‐pyrazol‐5‐ones both in solution and in the solid state was performed. It is shown that aprotic solvents stabilized the oxo (CH) tautomers, but the protic ones shifted the tautomeric equilibrium to the hydroxy (OH) forms. A zwitterion structure of MPhP in solid was determined to exist, rather than the CH‐tautomer, DPhP. In addition, accompanying quantum chemical calculations (at the Hartree‐Fock level of theory and with the 6‐31G** basis set) suggest that the last phenomenon is a result of a steric hindrance caused by the bulky phenyl substituent at the 3‐position of the pyrazolone ring.

Fourier deconvolution of infrared spectra using a reference band

Abstract A method of Fourier deconvolution of infrared (IR) spectra using a reference band is developed. The deconvolution function is given by an expression of the type exp[−(Δx)ρ], where Δ is the deconvolution half-width and the parameter ρ is determined by the experimental reference band shape. The specific experimental conditions are additionally taken into account by the ratio R(x), in which deconvolution function is modified with the normalized experimental interferogram of the reference spectrum. The proposed procedure allows overdeconvolution to be controlled. The reference band is selected either from the IR spectrum being studied or from the spectrum of another compound. Two principal restrictions are included: the reference band should be symmetric and must be recorded under the same conditions as the IR spectrum, subject to the deconvolution.

A reducing-difference IR-spectral study of 4-aminopyridine

The IR-spectra of 4-aminopyridine (4-AP) in solution and in the solid state have been analyzed, using the reducing-difference procedure. Defining a more precise band assignment of a part of the characteristic frequencies of 4-AP, the data obtained proved in particular a Fermi-resonance splitting of the symmetric NH2-stretch.

IR-Spectral Study of 2-Aminopyridine and Aniline Complexes with Palladium (II)

Abstract An IR-spectral study of sulphato- and chloro complexes of palladium (II) with 2-aminopyridine and aniline, respectively, is reported. The results obtained confirm the bidentate co-ordination of both 2-aminopyridine and SO4 group in the case of sulphato-2-aminopyridine-palladium (II) leading to polynuclear structure of the complex in solution. The comparative investigation of sulphato-dianiline-palladium (II) suggests that the self-dependent ability of the SO4 2- ion for bridging co-ordination can stabilize chain-like complexes of palladium (II) only in the solid state.

IR-LD-spectral study on the self-association effects of 2-aminopyridine

Abstract The IR-linear dichroic (LD) spectral study of 2-aminopyridine, dissolved and oriented in a nematic liquid crystal mixture, is accomplished in order to clarify the kind of solute-solute hydrogen bond interaction. The formation of head-to-tail open associates in 2-aminopyridine solution is proved by the reduction subtracting procedure applied to the polarized and unpolarized spectra. The comparative IR-LD study of oriented 2-aminopyridine samples in the solid state, where the stabilization of a cyclic dimeric structure takes place, is in accordance with the upper conclusion.

IR- and UV-Spectral Study on the Mechanism of 2-Aminopyridine Complexation with Palladium (II)

Abstract The IR-spectra of Pd (II) complexes with 2-aminopyridine, obtained both in sulphuric acid and alkaline solution are studied in the region 1700- 1400 cm−1. The structural conclusions are based on comparison with the IR- and UV-spectra of the free ligand and aminopyridinium sulphate, as well as of trans-dichloro-di-2-aminopyridine-palladium and deuterated at the amino group analogues of the investigated compounds.