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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >EPR and ENDOR Studies of Single Crystals of α-Glycine X-ray Irradiated at 295 K
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EPR and ENDOR Studies of Single Crystals of α-Glycine X-ray Irradiated at 295 K

机译：295 K照射的α-甘氨酸X射线单晶的EPR和ENDOR研究

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摘要

Single crystals of the amino acid α-glycine H↑(+)↓(3)N-CH↓(2)-C00↑(-) were X-ray irradiated at 280 K and studied at 295 K and at 100 K using EPR, ENDOR, and EIE techniques. Five radicals were detected and characterized. Two of these are well known from previous studies, the oxidation product H↑(+)↓(3)N-CH-COO↑(-) (radical I) and the reduction product CH↑(2)-COO↑(-) (radical II). It is shown that at 295 K the ENDOR and EIE spectra from radical I are characteristic of efficient W↓(1x) cross relaxation induced by rapid rotation of the amino group. This allows for the determination of the absolute signs of the hyperfine coupling constants of radical I. The other three radicals are two geometrical conformations of the product H↓(2)N-CH-COOH (radicals III and IV) and a species suggested to be the dimer product H↑(+)N-CH↓(2)-CO-CH-COO↑(-) (radical V). Radical III exhibits spectral parameters related to those previously reported by M. Brustolon et al. (J. Phys. Chem. 1997, 101, 4887). However, on the basis of our analysis of ENDOR and EIE spectra from normal as well as from partially deuterated crystals, the structural assignment for radical III is different from that suggested by these authors. A comparison with a new radical species recently observed and characterized in irradiated crystals of the amino acid L-α-alanine indicates that the new alanine radical and radical III presented here have similar structures. A review of the mechanistic aspects of radical formation in glycine is given, and the newly detected species (radicals Ⅲ-V) are tentatively fitted into this scheme.
机译：用280 K的X射线对氨基酸α-甘氨酸H↑（+）↓（3）N-CH↓（2）-C00↑（-）的单晶进行了X射线照射，并使用EPR在295 K和100 K下进行了研究。 ，ENDOR和EIE技术。检测并表征了五个自由基。其中两个是先前研究中众所周知的，氧化产物H↑（+）↓（3）N-CH-COO↑（-）（自由基I）和还原产物CH↑（2）-COO↑（-） （自由基II）。结果表明，在295 K处，基团I的ENDOR和EIE光谱是氨基快速旋转引起的有效W↓（1x）交叉弛豫的特征。这可以确定基团I的超精细偶合常数的绝对符号。其他三个基团是乘积H↓（2）N-CH-COOH（基团III和IV）的两个几何构型，并且建议一个基团是二聚产物H↑（+）N-CH↓（2）-CO-CH-COO↑（-）（自由基V）。自由基III显示出与M.Brustolon等人先前报道的那些有关的光谱参数。 （J.Phys.Chem.1997，101，4887）。但是，根据我们对正常晶体和部分氘代晶体的ENDOR和EIE光谱的分析，基团III的结构分配与这些作者所建议的不同。与最近观察到并在氨基酸L-α-丙氨酸的辐照晶体中表征的新的自由基种类的比较表明，此处显示的新的丙氨酸自由基和自由基III具有相似的结构。综述了甘氨酸中自由基形成的机理，并对新发现的物种（自由基Ⅲ-Ⅴ）进行了初步尝试。

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