Antioxidant properties of gold nanoparticles studied by ESR spectroscopy

The Au-containing nanocomposites were synthesized by UV irradiation followed by the thermal treatment of chitosan oligomer solutions doped by HAuCl₄. The size of the formed gold nanoparticles depends on the concentration of the dopant, which is proved by UV—Vis absorption spectroscopy and small-angle X-ray scattering (SAXS). The antioxidant activity of the gold nanoparticles with respect to hydroxy radicals significantly depends on the specific surface of the particles, which was found using the secondary radical spin-trapping technique. The change in the ^·OH radical concentration was monitored by the intensity of the ESR signal of the adduct of the spin trap (α-phenyl-N-tert-butylnitrone) with the Me^·radicals formed in the reaction of ^·OH with DMSO. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 509–512, March, 2008.     

A microcomputer aided microwave spectrometer controlled by a larger computer

Hewlett-Packard 8460A microwave spectrometer has been connected to a microcomputer based on the Motorola MC6800 microprocessor. The microcomputer is programmed to control frequency and Stark voltage and to perform $\text{A}\text{D}$ conversion, storage and accumulation of intensities.The microcomputer is connected to a larger local computer, the RC4000, from which it may be loaded with a program, started and stopped, and from which data transfer between the storages of the two computers is controlled. This transfer may be performed, while the microcomputer is running a spectrum.     

Determination of polyphenols in oats by near-infrared spectroscopy (NIRS) and two-dimensional correlation spectroscopy

Two-dimensional correlation spectroscopy (2DCOS) and near-infrared spectroscopy (NIRS) were used to determine the polyphenol content in oat grain. A partial least squares (PLS) algorithm was used to perform the calibration. A total of 116 representative oat samples from four locations in China were prepared and the corresponding near-infrared spectra were measured. Two-dimensional correlation spectroscopy was employed to select wavelength bands for the PLS regression model for the polyphenol determination. The number of PLS components and intervals was optimized according to the coefficients of determination (R²) and root mean square error of cross validation (RMSECV) in the calibration set. The performance of the final model was evaluated using the correlation coefficient (R) and the root mean square error of validation (RMSEV) in the prediction set. The results showed the band corresponding to the optimal calibration model was between 1350 and 1848?nm and the optimal spectral preprocessing combination was second derivative with second smoothing. The optimal regression model was obtained with an R² of 0.8954 and an RMSECV of 0.06651 in the calibration set and R of 0.9614 and RMSEV of 0.04573 in the prediction set. These measurements reveal the calibration model had qualified predictive accuracy. The results demonstrated that the 2DCOS with PLS was a simple and rapid method for the quantitative determination of polyphenols in oats.     

Rotamers of some radical-ions as evidenced by optical and ESR spectroscopy

Conformational isomerizations of radical-ions are studied both experimentally and theoretically. The representative systems of stilbenes, polyenes, and non-planar alicyclic compounds will be reviewed first. Then, the result of the study on the radical-cations of 1,4-dithiacyclohexane and ethane-1,4-dithiol will be presented. It is found that the former cation suffers a change from a chair form to a boat form and the latter from an anti- or a gauche-form to a cis form even in a rigid matrix. The conformational changes are manifested by drastic changes in the electronic absorption and ESR spectra. The strong “through-space” interaction between the lone pair orbitals of the sulfur atoms is responsible for the conformational changes. Ab initio MO calculations lend support to the analysis of the experimental results.     

Saturation ESR spectroscopy of PA12 polyamide

This work presents the results of our EPR study of polyamide 12 (PA12) -[NH-(CH₂)₁₁-CO]_n-NH-(CH₂)₁₁-CO-. In this study the spin probe method with “conventional” or “continuous saturation” at low temperatures (4-260 K) was used. The aim of our investigation was to determine if it possible to obtain the saturation effects and establish experimental conditions by using commercial ESR spectrometers. We also wanted to know what information about the relaxation processes in polymeric materials could be obtained. We have found that the information about the relaxation processes (below frequency ≈10⁴ Hz) at low-temperatures in polymers could be obtained. The process, which could be associated with mobility of the spin probe is probably connected with the process called γ (in PA12 as yet unrecorded by using others methods). This process in other systems is usually connected with mobility of the methylene sequences and could be used to study the amorphous regions of PA12.     

The nitrosation of N-alkylureas: Evidence for a proton transfer mechanism

The kinetics of the nitrosation of methyl, ethyl, propyl, butyl, and allyl urea were studied by conventional and stopped-flow spectrophotometry in the presence or absence of acetate or mono-, di-, or trichloroacetate anions. In the presence of a large excess of urea, the observed rate equation was where K_a is the acidity constant of nitrous acid and K_R that of the carboxylic acid. The ureas exhibited the reactivity order methylurea ≫ (ethylurea ≅ propylurea ≅ butylurea) ≫ allylurea. Experiments in D₂O afforded values of k/k = exp(0.130hv⌅/kT)], where v⌅ is the frequency of R₃N H stretching (2700–2250 cm⁻¹) in the protonated urea. This result, the observed catalysis by carboxylate ions and the value of the Bronsted parameter β(0.45) show the rate-controlling step of these reactions to be the transfer of a proton from the protonated N-alkyl-N-nitrosourea to the solvent or to the organic anion, if present. The observed order of substrate reactivities is explicable in terms of the capacity of the protonated N-alkyl-N-nitrosourea for forming a hydrogen bond with the water molecule to which the proton will be transferred, and the degree to which the formation of such bonds is hindered by the hydrophobic alkyl chain of the nitrosourea. © 1996 John Wiley & Sons, Inc.     

Comparison of photo- and radiation-induced radical formation in polyethylene by ESR spectroscopy

The behaviors of free radicals produced in polyethylene irradiated with ultraviolet light and electron beams were compared in connection with primary processes of radical formation and trapping regions of free radicals. In the case of irradiation with ultraviolet light, an ESR spectrum observed at ?196°C immediately after irradiation is an eight-line spectrum due to alkyl radicals of the type ? CH₂? ?H? CH₃, while in the case of ionizing radiation, a six-line spectrum due to ? CH₂? ?H? CH₂? was observed. The former radicals are produced by the Norrish type I reaction of the carbonyl groups contained in the polymer, followed by radical rearrangement; and the latter are formed by dissociation of hydrogen atom from the excited state of the polymer or ion-molecular reactions. From the sensitivity to oxygen molecules, it was deduced that free radicals are trapped in amorphous regions after ultraviolet irradiation, but mainly in crystalline regions after irradiation with electron beams. Saturation studies of ESR spectra seem to support this conclusion.     

ESR spectroscopy of the C60 cation produced by photoinduced electron transfer

In this study the existence of the C60 cation produced by photochemically induced electron transfer in the presence of different sensitising molecules is proved for the first time by using ESR spectroscopy. It is demonstrated for triphenylpyryliumtetrafluoroborate (TPP) by this spectroscopic method that the electron transfer from C60 to TPP occurs without an application of a cosensitiser. Furthermore it is shown that the addition of alcohols causes a new radical in the system C60/TPP. The stationary concentration of the C60 cation diminishes even in the presence of a cosensitiser to such a low concentration that it is not detectable by ESR spectrosopy. The spectroscopic study of the sensitiser/C60 system is also extended to the reaction products.     

Oxygen species adsorbed on CeX zeolites identified by ESR spectroscopy

Two kinds of paramagnetidc O^?₂ ions have been identified by contacting molecular oxygen with CeX zeolite heat treated at 200°C in vacuo. The first O^?₂ species corresponds to the usual O^?₂ ions adsorbed on cerium oxide with the following parameters: g₁ = g_? ≈ 2.035 ± 0.002, g₂ = g₃ = g_⊥ = 2.0095 ± 0.0005 and a hyperfine pattern of six and eleven lines centred about g₃ and split by about 78 Oe, the other two components being not resolved. The second paramagnetic species of much higher intensity (larger by 2 or 3 orders of magnitude) presents rather ESR parameters and hyperfine structure. One has: g₁ = 2.0242, g₂ = 2.0208 and g₃ = 2.0112 ± 0.0003; c₁ = 24 ± 3, c₂ = 66 ± and c₃ = 12 ± 3 Oe. The six and eleven hyperfine line pattern which has been observed shows that the unpaired spin is qually distributed between two oxygen nuclei. The g tensor values are interpreted in terms of almost complete averaging of g₁ and g₂ components due to rotational motion at ?196°C about axis (3 (χ_ξ). The species is attributed to O^?₂ ion formed according to the equilibrium:

. The Ce ions are located in cationic sites SII within the zeolite supercages and are only weakly bonded to the oxygen leading to rotational motion and to case of desorption, the species reversibly disappearing by outgassing at room temperature.     

MECHGEN: computer aided generation and reduction of reaction mechanisms

The paper describes selection rules implemented in a software generating "possible reaction mechanism", i.e. a set of elementary reactions chosen from all stoichiometrically possible reactions. The novelty of the approach lies in the fact that the user has to define all species involved (reactants, intermediates, products), and the rules applied with user-set limits reduce the resulting mechanism to a reasonable set of possible elementary reactions. The computer code consists of five parts: (i) definition of species, and introducing its characteristics (structure and thermodynamic data); (ii) definition of the reacting system and generation of all stoichiometrically possible reactions; (iii) reduction of the mechanisms using complexity and thermodynamic constraints based on user-set limits; (iv) calculation of the resulting pathways (routes of the various atoms or groups of atoms transferred from one species to another); and (v) tools to help visualization of the process by finding those elementary processes which realize a given pathway. Reasonable flexibility is ensured for using selection rules based on various criteria with limits set by the user. The various pathways are shown (in a matrix form), which offers an overview of the entire process.     

Analysis of building stone decay by computer assisted IR spectroscopy

The development of an automatic identification system for infrared spectra of inorganic sulphates and the first results are briefly described.     

Identification of irradiated sage tea (Salvia officinalis L.) by ESR spectroscopy

The use of electron spin resonance (ESR) spectroscopy to accurately distinguish irradiated from unirradiated sage tea was examined. Before irradiation, sage tea samples exhibit one asymmetric singlet ESR signal centered at g=2.0037. Besides this central signal, two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. Irradiation with increasing doses caused a significant increase in radiation-induced ESR signal intensity at g=2.0265 (the left satellite signal) and this increase was found to be explained by a polynomial varying function. The stability of that radiation-induced ESR signal at room temperature was studied over a storage period of 9 months. Also, the kinetic of signal at g=2.0265 was studied in detail over a temperature range 313–353 K by annealing samples at different temperatures for various times.     

Local structure analysis of Cu(II)-diazepam complexes by ESR spectroscopy

CuL(2)X(2) (L = 7-chloro-1,3-dihydro-1-methyl-5-phenyl-3H-1,4-benzodiazepin-2-one, also known as diazepam, X = Cl, Br) complexes have been prepared and investigated by ESR spectroscopy. Powder ESR spectra of these complexes suggest a planar-rhombic distorted local symmetry. The CH(3)Cl solutions spectra show the presence of pseudo-tetrahedral species with a 3d(xy)+4p(z) mixture ground state for the paramagnetic electron. The anisotropic spectra obtained for the Cu(II)-diazepam solution adsorbed on NaY zeolite confirm the existence of a CuN(2)X(2) chromophore.     

Local structure analysis of Cu(II)-diazepam complexes by ESR spectroscopy

CuL₂X₂ (L = 7-chloro-1,3-dihydro-1-methyl-5-phenyl-3H-1,4-benzodiazepin-2-one, also known as diazepam, X = Cl, Br) complexes have been prepared and investigated by ESR spectroscopy. Powder ESR spectra of these complexes suggest a planar-rhombic distorted local symmetry. The CH₃Cl solutions spectra show the presence of pseudo-tetrahedral species with a 3d_xy+4p_z mixture ground state for the paramagnetic electron. The anisotropic spectra obtained for the Cu(II)-diazepam solution adsorbed on NaY zeolite confirm the existence of a CuN₂X₂ chromophore.     

Noncovalent paramagnetic complexes: detection of halogen bonding in solution by ESR spectroscopy

Halogen-bonded complexes between aliphatic and aromatic iodoperfluorocarbons and persistent nitroxide radicals have been detected by ESR spectroscopy in solution. Quantitative data indicate that nitroxides behave as strong electron donors in halogen bonding, giving rise to interactions whose strength is close to that of strong hydrogen bonds. These results point to a novel design of supramolecular paramagnetic species.     

Two-dimensional electrophoresis aided by personal computer analysis for screening of mutant proteins in inherited diseases

A rapid and reproducible method of two-dimensional electrophoresis was developed for screening of abnormal proteins expressed in fibroblasts from patients with inherited diseases. After silver staining, the electrophoresis gel was subjected to semiautomatic digitizer-personal computer analysis: scanning with an image sensor video camera connected to a digitizer, followed by quantitative determination and statistical analysis with a personal computer. The protein spots analyzed by this method showed quantitative variations of various degrees, particularly in 2 of 247 spots examined. Seven spots were not always detected in control and pathological cells in this study. Slight variations in molecular weight were observed in 3 different spots.     

ESR spectroscopy of FeIII ions in sodium silicate glasses

The state of Fe^III ions doped in sodium silicate glasses of the composition (100 ? x)Na₂O-xSiO_2?y Fe₂O₃ (x = 75, 81 mol.%; y = 0.05?13 wt.%) was studied by electron spin resonance (ESR). X-band ESR spectra exhibited three resonance signals at g ≈ 2.0, 4.3, and 6. The computer simulation of ESR spectra was performed on the basis of spin-Hamiltonian of rhombic symmetry. The nature of observed signals was interpreted as a combination of five types of Fe^III complexes. Three of them were clustered iron ions and two other were isolated paramagnetic ones. The ratio of observed forms was found for different glass compositions and various total amounts of Fe^III ions in a matrix containing 0.55, 2.5, 4, 7, and 13 wt.% of Fe₂O₃.     

Confirmation of the cation radicals of hexamethylethane and hexamethyldisilane by ESR and other spectroscopy

Unambiguous ESR spectra of cation radicals of hexamethylethane and hexamethyldisilane were obtained for γ-irradiated solutions in CCl₃F at 77 and 140 K. INDO calculations, optical measurements, and comparison with photoelectron spectra are consistent with the observed ESR spectra.