大分子晶体的德拜-瓦勒因子的统计期望值和E(hkl)值
Statistical expectation value of the Debye-Waller factor and E(hkl) values for macromolecular crystals.
作者信息
Blessing R H, Guo D Y, Langs D A
机构信息
Hauptman-Woodward Research Institute, Buffalo, New York 14203, USA.
出版信息
Acta Crystallogr D Biol Crystallogr. 1996 Mar 1;52(Pt 2):257-66. doi: 10.1107/S0907444995014053.
If the unit-cell distribution of atomic mean-square displacement parameters B = 8pi(2)<u(2)> is assumed to be normal, with mean micro = and variance sigma(2) = <(B-)(2)>, the statistical expectation value of the Debye-Waller factor W(2) = exp(-2Bs(2)), where s = (sin theta)/lambda, is <W(2)> = exp[-2( micro - sigma(2)s(2))s(2)]. This result has been incorporated into procedures for scaling and normalizing measured Bragg intensities to their Wilson expectation values. The procedures can determine both isotropic micro (B) and sigma(B) and anisotropic micro (U(ij)) and sigma(U(ij) distribution parameters. Tests with experimental data and refined structural models for several protein crystals show that the procedures yield reliable normalized structure-factor amplitudes for direct-methods applications, with values of R = summation operator (h)||E(o)| - |E(c)||/ summation operator (h)|E(o)| averaging approximately 5%.
如果假设原子均方位移参数(B = 8\pi^{2}\langle u^{2}\rangle)的晶胞分布呈正态分布，其均值(\mu=\langle B\rangle)，方差(\sigma^{2}=\langle(B - \langle B\rangle)^{2}\rangle)，那么德拜 - 瓦勒因子(W(2)=\exp(-2Bs^{2}))（其中(s = (\sin\theta)/\lambda)）的统计期望值为(\langle W(2)\rangle=\exp[-2(\mu - \sigma^{2}s^{2})s^{2}])。该结果已被纳入将测量的布拉格强度按威尔逊期望值进行标度和归一化的程序中。这些程序能够确定各向同性的(\mu(B))和(\sigma(B))以及各向异性的(\mu(U_{ij}))和(\sigma(U_{ij}))分布参数。对几种蛋白质晶体的实验数据和精修结构模型进行测试表明，这些程序可为直接法应用产生可靠的归一化结构因子振幅，(R=\sum_{h}||E_{o}|-|E_{c}||/\sum_{h}|E_{o}|)的值平均约为(5%)。
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