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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Alanine Radicals. 2. The Composite Polycrystalline Alanine EPR Spectrum Studied by ENDOR, Thermal Annealing, and Spectrum Simulations
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Alanine Radicals. 2. The Composite Polycrystalline Alanine EPR Spectrum Studied by ENDOR, Thermal Annealing, and Spectrum Simulations

机译：丙氨酸自由基。 2.通过ENDOR，热退火和光谱模拟研究了复合多晶丙氨酸丙氨酸EPR光谱

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Radiation-induced free radical formation in the amino acid l-α-alanine has been studied using powder and single-crystal X-, K-, and Q-band electron paramagnetic resonance (EPR) spectroscopy, X-band powder electron-nuclear double resonance (ENDOR), thermal annealing, and EPR spectrum simulations. The spectra obtained after room temperature irradiations are composite, consisting of resonances from mainly three radicals denoted R1, R2, and R3. R1 is the well-known, stable room-temperature species formed by deamination from a protonated alanine anion radical. On the basis of simulations of EPR spectra obtained at X-, K-, and Q-bands, the room-temperature EPR spectrum seems to consist of about 55% of R1. Upon thermal annealing, the R1 resonance disappears faster than those of the other two components. The R2 species is presumably formed in the oxidative chain of radiation-induced events by net H-abstraction from the central alanine carbon atom. Q-band EPR was used to determine the g-tensor of R2. This species contributes about 35% to the resonance recorded at room temperature. Upon thermal annealing this radical decays slower than R1, resulting in the predominance of R2 in spectra obtained after prolonged warming at 480 K. Powder ENDOR was used to verify that the dominating species remaining after thermal annealing at this temperature indeed is R2 and not a successor species of either of the room-temperature radicals. The R3 species was previously assigned to an N-deprotonated version of R2 being additionally protonated at the carboxyl group. Detailed spectral data for this resonance are missing but a set of parameters based on available data and otherwise estimated using literature values for similar products was constructed. Simulations indicated that 5-10% of the room-temperature resonance could be ascribed to R3. R3 is more heat-resistant than the R1 and R2 radicals, and after prolonged annealing at 480K it was estimated that the resulting resonance consisted of about 51% R2 and 43% R3. The remaining part (about 6%) of the resonance was due to R1. These numbers must, however, be considered as tentative because of the lack of precise spectral data for R3.
机译：使用粉末和单晶X-，K-和Q-带电子顺磁共振（EPR）光谱研究了X-带粉末电子-核双电子对氨基酸l-α-丙氨酸中辐射诱导的自由基的形成共振（ENDOR），热退火和EPR频谱模拟。室温辐照后获得的光谱是合成的，主要由三个基本原子（分别表示为R1，R2和R3）的共振组成。 R1是众所周知的，稳定的室温物质，是通过从质子化的丙氨酸阴离子自由基中脱氨基形成的。根据在X，K和Q波段获得的EPR光谱的模拟，室温EPR光谱似乎由R1的55％组成。经过热退火后，R1共振消失的速度比其他两个组件更快。 R2物种可能是通过从中心丙氨酸碳原子中净吸氢而在辐射诱发事件的氧化链中形成的。 Q波段EPR用于确定R2的g张量。该物质对室温下记录的共振贡献约35％。在进行热退火后，该自由基的衰变速度比R1慢，导致在480 K长时间加热后获得的光谱中R2占优势。粉末ENDOR用于验证在此温度下进行热退火后剩余的主导物种确实是R2，而不是后继物种。室温自由基之一的种类。先前将R3物种分配给R2的N去质子化版本，并在羧基上进一步质子化。缺少该共振的详细光谱数据，但是构建了一组基于可用数据的参数，否则使用相似产品的文献值进行估算。模拟表明，室温共振的5-10％可以归因于R3。 R3比R1和R2自由基更耐热，并且在480K长时间退火后，估计所产生的共振由大约51％的R2和43％的R3组成。共振的其余部分（约6％）归因于R1。但是，由于缺少R3的精确光谱数据，因此这些数字必须视为临时的。

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