Near-edge X-ray absorption and dichroism in amino acids.
Near-edge X-ray absorption and dichroism in amino acids.
复制标题
氨基酸的近边 X 射线吸收和二色性。
DOI：
10.1107/s0909049598017567
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发表时间：
1999
影响因子：
2.5
通讯作者：
H. Ågren
中科院分区：
文献类型：
--
作者：
L. Yang;O. Plashkevytch;O. Vahtras;Vincenzo Carravetta;H. Ågren
含氮有机化合物形成了一类特殊的化合物，由于其潜在的技术用途和生物学重要性，已成为光谱研究的热点。近边X射线吸收光谱(NEXAFS)和圆二色谱(XCD)组成了两个光谱，能够提供此类样品的组成和结构信息。在目前的工作中，我们研究了一组与生物化学特别相关的有机化合物，即氨基酸，并探索了NEXAFS和XCD光谱可以以何种方式对此类化合物进行指纹识别。我们简要地回顾和讨论了最近在一系列论文中提出的关于C、N和O的K边的谱的理论结果(Plashkevych等人，1998；Carravetta等人，1998)。这些研究的动机也是因为观察到(Kirtley等人，1992)，DNA的氮边缘NEXAFS谱可以理解为多核苷酸谱的加权和，以及NEXAFS谱中的差异可用于定位氨基酸含量不同的蛋白质(Boese等人，1997)。除甘氨酸外，所有研究的氨基酸丙氨酸、半胱氨酸、丝氨酸、缬氨酸、甘氨酸、苯丙氨酸、组氨酸、酪氨酸和色氨酸都以两种光学活性形式存在，即相互镜像的D型和立方异构体。计算了旋转X射线吸收强度，并预测了这类分子的XCD光谱(Plashkevych等人，待发表)。采用直接原子轨道静态交换方法STEX。它基于吸收过程的单独通道描述，允许根据不同分子亚基的贡献轻松地分析光谱。STEX技术用于完全松弛不同位置的核孔势，并使用双基集算法，允许得到接近基集极限的结果。
Nitrogen-containing organic compounds form a special group of compounds that have become of interest for spectroscopic research owing to their potential technical use and biological importance. Near edge X-ray absorption (NEXAFS) and circular dichroism (XCD) spectroscopies constitute two spectroscopies with capability of giving information on composition and structure of such sampies. In the present work we address a particular set of organic compounds with special relevance for biochemistry, namely the amino acids, and explore in what way NEXAFS and XCD spectra can fingerprint such compounds. We briefly review and discuss recent theoretical results on spectra at the K edges of C, N and O, that were presented in a series of papers (Plashkevych et al., 1998; Carravetta et al., 1998) These studies were also motivated by the observations (Kirtley et al., 1992) that the nitrogen edge NEXAFS spectrum of DNA can be understood as a weighted sum of the polynucleotide spectra, and by the suggestion that differences in the NEXAFS spectra might be used for mapping proteins which differ in their amino acid content (Boese et al., 1997). Except for glycine, all the amino acids investigated alanine, cysteine, serine, valine, glycine, phenylalanine, histidine, tyrosine and tryptophan exist in two optically active forms, namely as Dand Lisomers that are mirror images of one another. The rotatory X-ray absorption intensities have been computed and XCD spectra for this class of molecules are predicted (Plashkevych et al., to be published). The direct atomic orbital static exchange approach STEX is employed. It is based on a separate channel description of the absorption process, which allows an easy analysis of the spectra in terms of contributions from different molecular subunits. The STEX technique is implemented for fully relaxed core hole potentials of the different sites, and for using the double basis set algorithm, allowing for close to basis set limit results.