University of Warmia and Mazury Olsztyn, Faculty of Mathematics and Computer Science, Sloneczna 54, PL-10710 Olsztyn, Poland.
J Chem Phys. 2012 Jun 28;136(24):244509. doi: 10.1063/1.4730034.
In order to study to what extent mechanisms of molecular motion can be unambiguously revealed by (2)H NMR spectroscopy, (2)H spectra for proteins (chicken villin protein headpiece HP36, selectively methyl-deuterated at leucine-69, C(δ) D(3)) and binary systems of high viscosity (benzene-d(6) in tricresyl phosphate) have been carefully analyzed as illustrative examples (the spectra are taken from the literature). In the first case, a model of restricted diffusion mediated by jumps between rotameric orientations has been tested against jump- and free diffusion models which describe rotational motion combined with jump dynamics. It has been found that the set of (2)H spectra of methyl-deuterated at leucine-69 chicken villin protein headpiece HP36 can be consistently explained by different motional models as well as by a gaussian distribution of correlation times assuming isotropic rotation (simple brownian diffusion model). The last finding shows that when the possible distribution of correlation times is not very broad one might not be able to distinguish between heterogeneous and homogenous (but more complex) dynamics by analyzing (2)H lineshapes. For benzene-d(6) in tricresyl phosphate, the dynamics is heterogeneous and it has been demonstrated that a gaussian distribution of correlation times reproduces well the experimental lineshapes, while for a Cole-Davidson distribution the agreement is somewhat worse. For inquires into the sensitivity of quadrupolar NMR spectral analysis (by "quadrupolar NMR spectroscopy we understand NMR spectroscopy of nuclei possessing quadrupole moment), the recently presented theoretical approach [Kruk et al., J. Chem. Phys. 135, 224511 (2011)] has been used as it allows simulating quadrupolar spectra for arbitrary motional conditions by employing the stochastic Liouville equation.
为了研究分子运动机制在何种程度上可以通过（2）H NMR 光谱来明确揭示，我们以（2）H 谱为实例（这些谱图均取自文献），对蛋白质（鸡绒毛蛋白头部 HP36，在亮氨酸-69 处被选择性氘代甲基化，C（δ）D（3））和高黏度二元体系（三磷酸三异辛酯中的苯-d（6））的（2）H 谱进行了仔细分析。在第一种情况下，我们对受限扩散模型（通过旋转构象之间的跳跃来介导）进行了测试，还对旋转运动与跳跃动力学相结合的跳跃和自由扩散模型进行了测试。结果发现，通过不同的运动模型以及假设各向同性旋转的相关时间分布为高斯分布（简单的布朗扩散模型），可以一致地解释亮氨酸-69 处被氘代甲基化的鸡绒毛蛋白头部 HP36 的一组（2）H 谱。最后一个发现表明，当可能的相关时间分布不是很宽时，通过分析（2）H 线谱，可能无法区分不均匀和均匀（但更复杂）动力学。对于三磷酸三异辛酯中的苯-d（6），动力学是不均匀的，结果表明，相关时间的高斯分布很好地再现了实验线谱，而对于 Cole-Davidson 分布，吻合度稍差。为了探究四极矩 NMR 光谱分析的灵敏度（通过“四极矩 NMR 光谱学”，我们理解为具有四极矩的核的 NMR 光谱学），我们使用了最近提出的理论方法[Kruk 等人，J. Chem. Phys. 135, 224511（2011）]，因为它允许通过使用随机刘维尔方程，对任意运动条件下的四极矩谱进行模拟。
