EPR and Quantum Chemical Studies of the pH-sensitive Imidazoline and Imidazolidine Nitroxides with Bulky Substituents

The X- and W-band electron paramagnetic resonance (EPR) spectroscopies were employed to investigate a series of imidazolidine nitroxide radicals with different number of ethyl and methyl substituents at positions 2 and 5 of a heterocycle in liquid and frozen solutions. The influence of the substituents on the line shape and width was studied experimentally and analyzed using quantum chemical calculations. Each pair of the geminal ethyl groups in the positions 2 or 5 of the imidazolidine ring was found to produce an additional hyperfine splitting (hfs) of about 0.2 mT in the EPR spectra of the nitroxides. The effect was attributed to the hfs constant of only one of four methylene hydrogen atoms of two geminal ethyl substituents not fully averaged by ethyl group rotation and ring puckering. In accordance with this assumption, the substitution of hydrogen atoms of CH₂ groups in 2,2,5,5-tetraethyl-substituted imidazolidine nitroxides by deuterium leads to the substantial narrowing of EPR lines which could be useful for many biochemical and biomedical applications, including pH-monitoring. W-band EPR spectra of 2,2,5,5-tetraethyl-substituted imidazolidine nitroxide and its 2,2,5,5-tetraethyl–d₈ deuterium-substituted analog measured at low temperatures demonstrated high sensitivity of their g-factors to pH, which indicates their applicability as spin labels possessing high stability.     

Real-time monitoring of diamond nucleation and growth using field-enhanced thermionic emission current

Diamond nucleation and growth in the combustion-flame method were monitored in real time using thermionic emission current from the deposited diamond films. It was observed that the emission current evolved over three periods, the incubation, the fast increase, and the saturation periods. Ball-shaped diamond particles, faceted diamond crystals, and diamond films with well-faceted crystals were formed in the three periods. The current from a diamond-seeded substrate started to increase immediately without an incubation period, confirming that the current is from the diamond. Therefore, the current could be used for real-time monitoring of the diamond nucleation and growth.     

Real-time monitoring of electro-mechanical effect in carbon-fiber reinforced polymer using HTS SQUID

Stress damage of cross-ply or quasi-isotropic carbon-fiber reinforced polymer laminates, commonly used in aerospace structures, has been monitored in real-time during quasi-static loading. The fiber displacement in the matrix due to mechanical loading have been detected using atomic force microscopy techniques. A correlation between mechanical and electrical effects in the material has been confirmed by electrical and magnetic measurement using an eddy current technique based on high critical temperature dc Superconducting Quantum Interference Device magnetometer.     

Real-time monitoring of ethane in human breath using mid-infrared cavity leak-out spectroscopy

We report on spectroscopic real-time analysis of ethane traces in exhaled human breath. Ethane is considered the most important volatile marker of free-radical induced lipid peroxidation and cell damage in the human body. Our measurements were carried out by means of mid-infrared cavity leak-out spectroscopy in the 3 μm region, a cw variant of cavity ring-down spectroscopy. The spectrometer is based on a CO overtone laser with tunable microwave sidebands. The resulting system proved to be an unique tool with high sensitivity and selectivity for rapid and precise breath testing. With a 5 s integration time, we achieved a detection limit on the order of 100 parts per trillion ethane in human breath. Thus, sample preconcentration is unnecessary. Time-resolved monitoring of the decaying ethane fraction in breath after smoking a cigarette is demonstrated. Received: 13 March 2001 / Published online: 9 May 2001     

Spectrum mobility in cognitive radio network using spectrum prediction and monitoring techniques

The spectrum mobility during data transmission is an integral part of the cognitive radio network (CRN) which is conventionally two types for instance reactive and proactive. In the reactive approach, the cognitive user (CU) switches its communication after the emergence of the primary user (PU), where the detection of emergence of PU relies either on spectrum sensing and/or monitoring. Due to certain limitations of the reactive approach such as: (1) loss at least one packet on the emergence of PU and (2) resource (bandwidth) wastage if the periodic sensing is used for mobility, the researchers have introduced the concept of proactive spectrum mobility. In this approach, the emergence of PU is predicted on the bases of pre-available spectrum information, and switching is performed before true emergence of the PU, in order to avoid even the single packet loss. However, the imperfect spectrum prediction is a major milestone for the proactive spectrum mobility. Recently, due to introduction of the spectrum monitoring simultaneous to the data transmission, the reactive approach has come into lime-light again, however, it suffers from the ‘single packet loss’ and ‘imperfect spectrum monitoring’ issues. Therefore in this paper, we have exploited the spectrum monitoring and prediction techniques, simultaneously for the spectrum mobility, in order to enhance the performance of cognitive radio network (CRN). In the proposed strategy, the decision results of the spectrum prediction and monitoring techniques are fused using AND and OR fusion rules, for the detection of emergence of PU during the data transmission. Further, the closed-form expressions of the resource wastage, achieved throughput, interference power at PU and data-loss for the proposed approaches as well as for the prediction and monitoring approaches are derived. Moreover, the simulation results for the proposed approaches are presented and validation is performed by comparing the results with prediction and monitoring approach. In a special case, when the prediction error is zero, the graphs of all metric values overlies the spectrum monitoring approach, which further validates the proposed approach.     

Temperature-induced changes in the EPR spectrum of the magnetic center in kaolin

Studies of kaolin have revealed an effect characterized by an unusual temperature-induced change of the EPR spectrum of the Fe3+ ion, which is the magnetic probe in kaolin-clay. At low temperature (T=4.2 K) a resonance line with an effective g-value g1=4.13 +/- 0.16 is observed. At high temperature (T=288 K) one observes a resonance line with the effective g-value g2=2.15 +/- 0.1. The transition from the low- to high-temperature spectrum is gradual and it is accompanied by a redistribution of the absorption intensity. The observed properties of the temperature dependence of the EPR spectrum are characteristic of systems with a multiminimum potential.     

EPR techniques applied to the study of chemistry and catalysis on oxide surfaces

The use of electron paramagnetic resonance (EPR) spectroscopy to study the chemistry of oxide surfaces and catalysis is discussed. Emphasis is placed on those aspects of the techniques that are directly related to the specificity of heterogeneous systems, investigations of surfaces and catalytic reactions. The characteristic features of EPR spectra of high-surface oxide materials are analyzed, and the typical means employed to increase the amount of extractable information are presented. A brief survey of new potentialities of continuous-wave EPR and typical applications is also provided.     

In vivo temporal EPR imaging of the brain of rats by using two types of blood-brain barrier-permeable nitroxide radicals

In vivo temporal EPR imaging was conducted on the brain of rats that received one of two kinds of blood-brain barrier-permeable nitroxide radicals via the tail vein-one is a water-soluble 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (hydroxymethyl-PROXYL); and the other is a non-water-soluble 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (PCAM). From temporal EPR imaging data, temporal changes in the distribution of the nitroxide radical in the cerebral cortex, striatum, and hippocampus in the brain were investigated. It was found that the half-lives of the three parts in the brain of hydroxymethyl-PROXYL are longer and their EPR signal intensities are greater than those of PCAM.     

便携式近红外光谱仪测定苹果酸度和抗坏血酸的研究

应用便携式近红外光谱分析仪对6种苹果进行无损检测,运用Kernel Isomap结合广义回归神经网络的方法分别建立苹果酸度和抗坏血酸定量分析模型.结果表明:采用Kernel Isomap方法能够使模型具有良好的预测能力.苹果酸度模型校正集相关系数Rc=0.9994,预测集相关系数Rp=0.979 9,RMSEP=0.0...     

Real-time monitoring the formation and decomposition processes of methane hydrate with THz spectroscopy

<正>Gas hydrates are crystalline clathrate compounds comprised of hydrogen-bonded water cavities,consisting of guest molecules trapped in a lattice of polyhedral water cages under elevated pressures and low temperatures[1].The structures of the gas hydrates are closely related to the types and sizes of the guest species,and three distinct structures,including cubic structure-Ⅰ(sⅠ),cubic structure-Ⅱ(sⅡ),and hexagonal structure-H(sH),are known to form[2].Being expected as a kind of future energy resource,natural gas     

Importance of volume limitation for tissue redox status measurements using nitroxyl contrast agents: a comparison of X-band EPR bile flow monitoring (BFM) method and 300 MHz in vivo EPR measurement

Methods proposed for in vivo redox status estimation, X-band (9.4 GHz) electron paramagnetic resonance (EPR) bile flow monitoring (BFM) and 300 MHz in vivo EPR measurement, were compared. The spin probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) was utilized for both methods, due to its suitable lipophilicity. EPR signal decay of a nitroxyl spin probe in the bile flow and in the liver region (upper abdomen) of several rat groups with different selenium status were measured by both the BFM and the in vivo EPR method, respectively. The nitroxyl radical clearance measured with in vivo EPR method may be affected not only by the redox status in the liver but also by information from other tissues in the measured region of the rat. On the other hand, the time course of nitroxyl radical level in the bile flow of rats was found to be a reliable index of redox status. Measurement site and/or volume limitation, which was achieved by the BFM method in this paper, is quite important in estimating reasonable EPR signal decay information as an index of tissue/organ redox status.     

联合动静态图像分析技术研究鳄鱼血红细胞形态功能随pH值的变化

采用多维显微成像技术,结合有关动、静态图像分析方法,通过测定鳄鱼血红细胞在不同pH值下其形态参数(包括红细胞的接触面积、周长、长轴、短轴、伸长率和圆度)和反映细胞变形能力的频颤变化,揭示了鳄鱼血红细胞形态结构与有关生理功能随环境pH值的变化情况.结果表明,鳄鱼红细胞无论形态结构还是变形能力都比人体的红细胞更耐受酸性环境...     

Temperature dependence of the low-field mobility in the presence of scattering on polar optical phonons. Calculation using Monte Carlo method

Temperature dependence of the low field mobility in the presence of scattering on polar optical phonons in GaAs and InAs is calculated with the help of a special modification of the Monte Carlo method. The obtained data are compared with known analytical approximations. The parabolic and the Kane dispersion laws are considered. It is shown that for both dispersion laws the low temperature approximation gives better results over the whole temperature interval studied. Reasons for widening of the region of applicability of the low-temperature approximation for the Kane dispersion law are studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–45, September, 1981.     

Improved techniques for in-situ monitoring and control of pH in the cane sugar manufacturing process

A pH sensor has been improved by using a pair of glass electrodes, appropriately fitted in a suitable assembly fabricated from a polymer material. An interface has been designed and developed for processing the signal from the pH sensor. The improved pH sensor and the interface forms the improved pH sensing system. The performance of the system is good and is a cost effective solution over pH measurement errors and problems. Details of the pH sensor, interface and the results of the field trials are presented in this paper.     

Kinetics and mechanisms of the sonolytic destruction of non-volatile organic compounds: investigation of the sonochemical reaction zone using several OH* monitoring techniques

This study investigates the sonolytic degradation mechanism of non-volatile organic compounds and reaction sites for its degradation using various tools that allow OH* to be monitored, such as: the spin-trapping method of OH* detection using non-volatile nitrone trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the hydrogen peroxide analytical methods and the p-chlorobenzoic acid (pCBA)-probe method. These methods can successfully monitor OH* produced during sonochemical processes, and identify the major reaction sites involving OH* of the three proposed reaction zones--within the cavity, in the bulk solution, and at the gas-liquid interfacial (shell) region. The patterns of hydrogen peroxide accumulation under the various conditions suggest that peroxides pre-form at the interfacial region, but the self-scavenging reaction by hydrogen peroxide simultaneously takes place in the same region. The simultaneously measured peroxide concentration, in the absence and presence of DMPO, and that of the DMPO-OH adduct indicated the peroxide production and DMPO-OH adduct formation reaction occur at the shell region. The sonolytic destruction efficiency of ultrasound coupled with Fe(II) has been also investigated. The coupled Fe(II)/ultrasound process was found to enhance the OH* production rate by 70% compared to the ultrasound process alone due to the reaction of Fe(II) with sonochemically produced hydrogen peroxide (Fenton's reaction). This accelerated reaction was also found to occur at the shell region rather than in the bulk solution. The enhancement effect of Fe(II)/ultrasound was also examined using pCBA as a probe. 2.8-fold and 3.6-fold increases of the pCBA degradation rate were observed at Fe(II) concentrations of 10 and 20 microM, respectively.     

Trace-gas analysis using diode lasers in the near-IR and long-path techniques

Room-temperature, near-infrared, semiconductor diode lasers continue to gain importance for gas monitoring applications owing to their compactness, ease of use, reasonable cost and compatibility with telecommunications-grade optical fiber components. They may probe overtone or combination vibrational bands for a large variety of atmospheric relevant molecular species. These spectral bands exhibit line strengths orders of magnitude lower than those of fundamental vibrations, occurring in the mid-infrared. As a consequence, they are often used in conjunction with long-path techniques, enabling one to perform high sensitivity local measurements through long absorption path-lengths. At this purpose, resonant optical cavities can be fruitfully employed. This paper is devoted to a discussion of the main features of cavity-enhanced absorption spectrometers, operating with near-infrared diode lasers. We report on the operating principle as well as the achievable performance of these devices, also compared to more traditional apparatus, based on the multiple reflection cells. Experimental results on water vapour and oxygen detection are reported.