三苯基硅自由基的电子自旋共振研究

有机硅自由基的电子自旋共振(ESR)的研究一直十分活跃,Bock等已做了大量工作。然而,对于三苯基硅自由基的ESR研究报道却甚少。采用X射线辐照单晶生成的三苯基硅自由基的ESR谱并未获得理想的超精细结构谱,而采用三苯基硅烷与二苯甲酮热反应仅获得Ph_2COSiPh_3自由基的ESR谱。本文报道在氯仿溶液中,用无水三氯化铝与三苯基硅醇或三苯基硅烷在室温下反应,获得三苯基硅烷正离子自由基(Ph_3Si~+)ESR的研究结果,并进行计算机模拟。     

On the carrier properties of perfluoropolyether-betaine mixed vesicles: the contribution of electron spin resonance spectroscopy

The carrier properties of mixed unilamellar vesicles of fluorocarbon-hydrocarbon surfactants built up with the ammonium salt of a perfluoropolyether and n-dodecylbetaine were investigated by electron spin resonance spectroscopy (ESR). The ESR-active lipophilic nitroxide 5-doxylstearic acid (5-DSA) was used as a model of a lipophilic drug to be carried and delivered into cell membranes. Healthy and malignant colorectal tissues were used as the target cells. Cell suspensions of living tissues were studied in physiological conditions. For the maintenance of the surgically removed tissues, McCoy’s 5A culture medium was used. 5-DSA probe was rapidly delivered from perfluoropolyether (PFPE)/betaine mixed vesicles to the membranes of both healthy and malignant colorectal cells. The analysis of the computed 5-DSA ESR line shapes ensured that no spectral differences occurred when 5-DSA was either introduced directly into the cells or through the intervention of vesicles. This well agreed for an unmodified physical status of the membranes where the probe was mainly localized.     

Kinetic study of radical polymerization of dialkyl fumarates using electron spin resonance spectroscopy

The radical polymerization of dialkyl fumarates (DRF) bearing various ester alkyl groups was kinetically studied. The propagation and termination rate constants were determined using electron spin resonance (ESR) spectroscopy. The introduction of the bulky ester alkyl groups such as a tert-butyl group decreased the termination rate constant as expected. However, it has also been revealed that the bulky groups promote propagation despite the steric repulsion. The propagation rate and mechanism are discussed in relation to the propagation manner, i.e., tacticity of the polymer. © 1996 John Wiley & Sons, Inc.     

Some observations of various 1,8 naphthoquino-dimethane biradicals by electron spin resonance spectroscopy

Photolysis of 8-methyl-1-naphthyldiazomethane at 4 K gives the triplet ESR spectrum of 1,8-naphthoquinodimethane but not that of 8-methyl-1-naphthylcarbene. Photolysis of either 8-methyl-1-azido-naphthalene or 8-amino-1-azidonaththalene does produce the triplet biradical spectra of 8-imino-1-naphthoquinomethane and 1,8-diiminonaphthoquinodimethane, in addition to the triplet nitrene spectra of 8-methyl-1-nitreno-naphthalene and 8-amino-1-nitreno-naphthalene. Curie Law analyses demonstrate that these biradicals are all ground state triplets. Hückel and INDO calculations pertaining to the biradicals are reported. Large charge transfer interactions were observed in the ESR spectra of 8 substituted-1-naphthyl nitrenes.     

Study of chloroquine binding to melanins by pyrolysis-gas chromatography and electron spin resonance spectroscopy

Structural differences in melanins were studied by Curie-point pyrolysis-gas chromatography-mass spectrometry, electron spin resonance spectroscopy and chloroquine binding. Pyrolysis-gas chromatographic data on the polymer allow the calculation of a UU index that expresses the relative amount of unindolized DOPA-derived units in the melanins.It is shown that the content of unindolized units in the polymer depends strongly on the oxidation time and DOPA concentration used during the melanin synthesis. Comparison of the chloroquine binding to melanins and the pyrolysis data showed that there is an inverse relationship between the affinity of chloroquine and the UU index.     

Advanced protocol for the detection of irradiated food by electron spin resonance spectroscopy

Using ESR (electron spin resonance) spectroscopy, we found various free radicals in a pepper before and after irradiation. The representative ESR spectrum of the pepper composed of a sextet centered at g=2.0, a singlet at the same g-value and a singlet at g=4.0. This reflects the evidence of three independent radicals in the pepper before irradiation. Upon gamma ray irradiation, a new pair of signals appeared. The progressive saturation behavior (PSB) at various microwave power levels indicates quite different relaxation behaviors of those signals. For the evaluation of radiation-induced radicals and irradiation effects we propose a new protocol using the PSB method. This would call for an advanced protocol for the detection of irradiated foods.     

Solvent-induced textural changes of as-synthesized mesoporous alumina, as reported by spin probe electron spin resonance spectroscopy

The effect of solvent used during the synthesis and postsynthesis treatment on textural properties of organized mesoporous aluminas was investigated and related to the behavior of spin probes studied by electron spin resonance (ESR) spectroscopy. It was found that the structure of surfactant aggregates serving in the as-synthesized precipitates as templates could be easily modified by treatment with different solvents. This treatment induces corresponding variations in surface areas, mesopore volumes, and mesopore diameters of the final products. The ESR spectrum of 5-doxyl stearic acid spin probe properly reflects the changes in template structure based on changes of the solvent used and represents an early indicator of the corresponding textural modifications of the mesoporous alumina.     

An electron spin resonance study of azaallyl radicals

The ESR spectrum of the 2-aza-allyl radical, Me2CNCMe₂, has been recorded. A series of 1-aza-allyl radicals have been generated by reaction of 2-alkyl-4,4-dimethyloxazolines with t-butoxyl radicals and their ESR spectra studied. In this reaction 2-alkyl-4,4-dimethyloxazolin-5-yl radicals are also formed.     

An electron spin resonance study of gamma-irradiated grapes

The ESR spectra of the seeds, skins and stalks of unirradiated and γ-irradiated Cape black grapes have been obtained. In the spectra of all parts of the grape a single line (g ca. 2.004) is observed both before and after irradiation. New spectral features are observed after irradiation with doses of between 2 and 10 kGy. Some of these features decline in intensity over a period of several days. However, in the case of stalks, new spectral features are readily observed over the shelf-life of the fruit and in samples irradiated to a dose of only 2kGy.     

The electrochemical behaviour and electron spin resonance spectroscopy of some heterocyclic organoboron compounds

Some heterocyclic organoboron compounds derived from the reaction of 1,2-disubstituted benzene with m-nitrophenyl boronic acid have been investigated electrochemically. All the compounds exhibit two irreversible reduction waves. Controlled-potential electrolysis at the plateau of the second wave leads to decomposition and formation of nitrophenyl boronic acid radical anions. Electron spin resonance spectroscopy has been carried out to investigate the nature of these radical anions.     

An electron spin resonance study of gamma-ray irradiated ginseng

Using electron spin resonance (ESR) spectroscopy, we revealed the presence of four radical species in gamma-ray irradiated ginseng (Agaliaceae). Before irradiation, the representative ESR spectrum of ginseng is composed of a sextet centered at g = 2.0, a sharp singlet at the same g-value, and a singlet at about g = 4.0. The first one is attributable to a hyperfine (hf) signal of Mn2+ ion (hf constant: 7.4 mT). The second one is due to an organic free radical. The third one is originated from Fe3+. Upon gamma-ray irradiation, a new ESR (the fourth) signal was detectable in the vicinity of g = 2.0 region. The progressive saturation behaviors of the ESR signals at various microwave power levels were indicative of different relaxation time for those radicals. The anisotropic ESR spectra were detected by the angular rotation of the sample tube. This is due to the existence of anisotropic microcrystalline in the ginseng powder sample.     

Tracking nitrogen-to-nickel ratio and prevalent paramagnetic species in synthetic diamonds by electron spin resonance at 90 K

Nitrogen and nickel are the main impurities in the type Ib synthetic diamonds obtained under high pressure and high temperature conditions using nickel-containing catalysts. Nitrogen enters the synthesized diamond from the air. The nickel/nitrogen ratio for the two types of diamonds, obtained with and without an aluminum getter that prevents the diamond crystal lattice from nitrogen penetration, was studied by electron spin resonance at 90 K.     

Automatic analysis of mixed spectra : Generalised spectral subtraction applied to electron spin resonance spectroscopy

A new technique is described for estimating the pure component spectra from a set of linearly independent spectra. The process is one of generalised spectral subtraction in which an iterative combination of multivariate linear least-squares analysis and matrix transformation is applied to the input data to give estimates of the number of independent components in the original mixed spectra. This technique is applicable to bipolar data (e.g. from e.p.r. spectra) as well as absorption spectra determined by any spectroscopic technique, provided that the spectra may be reasonably assumed to be an additive mixture of unknown pure components. Numerical model examples are given together with an experimental application to electron spin resonance.     

Studies on electron spin resonance spectroscopy of biradical molecules containing N-O and N-O moieties

The biradicals with ¹⁴N-Oxide and ¹⁵N-Oxide at the both ends of a molecule are synthesized for the molecular ruler of protein structure, and a potential device for quantum computing. We also establish a general synthetic method for reliable biradical formation. ESR spectra are recorded for the biradicals containing ¹⁵N-Oxide and ¹⁴N-Oxide with various interdistance separations. We find that two types of biradicals yielded different ESR spectra depending upon the distance between the ¹⁵N-O and ¹⁴N-O moieties in a molecule. This is due to electron spin dipole–dipole interaction occurring between the radicals. We also find that there is an indication of isotopic nuclear effects in the dipole–dipole interactions. The present study implies feasibility of the distance measurement between two different N-Oxides containing ¹⁴N and ¹⁵N isotopes. We conclude that quantum entanglement effects are observed through the dipolar interactions, which enable application of quantum computing devices operating in the liquid state.