Ferenc Billes

Vibrational spectroscopy of triazoles and tetrazole

Abstract This work deals with the analysis of vibrational spectra of three five membered nitrogen heterocycles, the parent compounds: 1,2,3-triazole, 1,2,4-triazole and tetrazole, and their N-deuterated derivatives. The infrared spectra of these compounds were recorded in condensed states, while the Raman spectra were measured without polarization and using both parallel and perpendicular polarizations of scattered light. The fundamental vibrational frequencies were calculated applying the density functional theory with the Becke3P86 functional and the 6-311G(d,p) basis set. The results of the calculations were utilized in the assignment of the vibrational fundamentals, and the measured fundamental frequencies were used to refine the vibrational force constants. The considerable association of these compounds in condensed phase caused shifts of some fundamental frequencies of the isolated molecules. Nevertheless, the relative mean deviations between the measured and calculated frequencies were about 1 % or less for every investigated molecule.

Vibrational spectroscopic calculations on pyrogallol and gallic acid

Abstract Infrared and Raman spectra of pyrogallol and gallic acid were recorded. Optimized geometries, vibrational frequencies and infrared intensities were calculated utilizing the post-HF DFT method with the Becke3P86 functional and the 6-311G(d,p) basis set for one of the possible conformers of both molecules. Normal coordinate analysis was carried out. The results of the calculations were applied to simulate the infrared spectra.

A comparative study on the vibrational spectroscopy of pyridazine, pyrimidine and pyrazine

Abstract In this work, the authors deal with the vibrational spectroscopy of the three diazine parent compounds, i.e. that of pyridazine, pyrimidine and pyrazine. Infrared spectra were recorded in vapour and condensed phases, and Raman spectra were measured in condensed phase using both parallel and perpendicular polarization of light. The vibrational fundamental frequencies were calculated applying ab initio quantum-chemical methods: Moller–Plesset perturbation and local density functional methods. The results of the calculations were applied to the assignment of the vibrational fundamentals and the measured fundamental frequencies were used to refine the vibrational force constants. The main deviations between the recalculated and the measured frequencies are about 2.5% or smaller.

Vibrational analysis and spectra of orotic acid

The IR and Raman spectra of polycrystalline anhydrous orotic acid and its N1, N3, and O12 trideuterated isotopomer are recorded in the 4000-40 cm(-1) spectral interval as part of a series of vibrational analyses of nucleosides, nucleotides, and related compounds carried out in our laboratory. The frequencies of the fundamental transitions and the potential energy distributions of the 39 normal modes of orotic acid and its isotopomer are calculated by an ab initio density functional theory Becke3P86/6-311G** treatment. Assignments of the vibrational modes are proposed that consider the results of these calculations and the observed spectra. The results of the ab initio treatment are related to crystallographic and spectral data, and they are compared with previous assignments for similar molecules.

Vibrational spectroscopic and quantum chemical study of the chlorine substitution of pyrazine

Abstract Vibrational spectroscopy of pyrazine and its two chlorine derivatives, the 2-chloropyrazine and the 2,6-dichloropyrazine have been investigated. The substituent effect and the chlorine isotopic effect were investigated, too. Infrared spectra were recorded in condensed and in vapour (pyrazine, 2-chloropyrazine) phase, Raman spectra in condensed one. In the case of pyrazine and 2-chloropyrazine the spectra were excited both with parallel and perpendicular polarised light. The optimised geometry and the force field of the investigated molecules were calculated using the density functional theory with the Becke3P86 functional and the 6-311G** basis set. The results of the calculations were applied to the assignment of the vibrational fundamentals. The measured spectral data were used to refine the vibrational force constants. The intermolecular interactions of the compounds shifted the fundamental frequencies of the isolated molecules.

Vibrational spectra and harmonic force fields of pyrrolidine derivatives: Comparison between HF, MP2 and DFT force fields

Abstract Infrared and Raman spectra are reported for the isotopic species of pyrrolidine-d 0 (PY) and -d 1 and for N -methylpyrrolidine-d 0 (NMP), -d 2 , -d 3 and -d 8 . A complete assignment of the experimentally observed bands to normal modes is presented and discussed in particular in the CH/CD stretching region. The molecular structures and harmonic force fields were calculated ab initio at the Hartree–Fock (HF), the second order Moller–Plesset (MP2) and the density functional theory (DFT) level with the 6-31G* basis set. The force fields were fitted by use of 7 (PY) and 4 (NMP) independent scale factors. The spectra calculated with the DFT force fields are in better agreement with the experiment than those calculated by the MP2 and HF force fields. Though some scaled fundamental frequencies show larger deviations from the experimental ones, the mean percentage deviations of calculated frequencies from experimental fundamentals are less than 2.6% for all isotopic species of PY and NMP under study. The results indicate that density functional theory is a reliable tool to get a deeper insight in the assignment of vibrational spectra and the nature of normal modes of pyrrolidine derivatives.

The influence of L-ascorbic acid on the antibacterial-toxic activity of aflatoxins on adsorbent layer.

Aims:  To substantiate the role of formaldehyde (HCHO) and its reaction products in the mechanism of the antibacterial‐toxic effect of aflatoxins B1 (AFB1), B2, G1 and G2.

Vibrational analysis of benzothiazoline-2-thione

Abstract Infrared and Raman spectra of solid benzothiazoline-2-thione (BTT) have been measured in the range 4000–50 cm −1 and 4000–200 cm −1 , respectively. Force constants and vibrational frequencies of BTT and 2-mercapto-benzothiazole have been determined by means of quantum chemical calculations on the basis of the density functional theory. An assignment has been made for the normal vibrations using the calculated vibrational frequencies and the potential energy distribution. In spite of the probability of the existence of 2-mercapto-benzothiazole within a tautomeric equilibrium, there is no indication of its presence besides the neat BTT.

A simple method of boron determination in mineral waters using Victoria blue 4R

The reaction of the tetrafluoroborate anion with Victoria blue 4R (VB4R) reagent was investigated, and a new, simple, rapid and sensitive method was developed for the spectrophotometric determination of boron. The method is based on the reaction of boric acid with fluoride, which forms the tetrafluoroborate anion, and that is followed by the extraction of with VB4R into benzene and subsequent spectrophotometric detection. The optimum conditions for the conversion of boron to tetrafluoroborate anion as well as for complex formation and extraction of with VB4R were found. The molar absorptivity of the investigated complex is 9.6 × 104 L mol−1 cm−1 at 610 nm. The absorbance of the coloured extracts obeys Beers law in the range 0.03–0.55 mg L−1 of B(III). The limit of detection calculated from a blank test (n = 10; P = 0.95) based on 3 s is 0.02 mg L−1 of B(III). Under appropriate extraction conditions, the majority of metals (excluding probably tantalum and some others) did not form extractable fluoride complexes with VB4R. Therefore, the presence of small quantities of metals should not interfere with the determination of boron in the presence of a sufficient surplus of fluoride. Exceptions, however, are metal ions such as Sn(IV), Ti(IV), Sn(II), Zr(IV), Hg(II), Hg(I), Tl(I), etc., which strongly hydrolysed under experimental conditions. Some anions formed complexes with the cation of VB4R and are easily extractable using benzene. Examples of such ions are , I−, SCN−, Br−, bromate, chlorate, iodate and perrhenate. These anions strongly interfere with boron determination and therefore must first be extracted with VB4R before boron determination. The boron must then be converted to and extracted with VB4R into benzene for determination. The Cl−, , , CH3COO− and anions are extracted in very small amounts or not at all, and do not interfere with boron determination. The reaction mechanism was also discussed. Quantum chemical calculations were carried out for VB4R, and the optimised molecular structure and atomic net charges were calculated. The possible position of the protonation of VB4R as well as the possible position for dipole-ion interaction (associate building) between the reagent and the anion was predicted. The method was used for the determination of boron in commercial brand mineral waters.

Bioautographic detection of antimicrobial compounds in the edible Shiitake mushroom (Lentinus edodes)

The shiitake mushroom is well known for its health-beneficial effects. In this study we examined its antimicrobial activity by use of bioautography. After bioactivity detection we identified one major antimicrobial compound by use of infrared spectroscopy and gas chromatography. It shares similarity with well-known fatty acids.