Bryce David L, Sward Gregory D
Department of Chemistry and Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
J Phys Chem B. 2006 Dec 28;110(51):26461-70. doi: 10.1021/jp065878c.
Trends in the chlorine chemical shift (CS) tensors of amino acid hydrochlorides are investigated in the context of new data obtained at 21.1 T and extensive quantum chemical calculations. The analysis of chlorine-35/37 NMR spectra of solid L-tryptophan hydrochloride obtained at two magnetic field strengths yields the chlorine electric field gradient (EFG) and CS tensors, and their relative orientations. The chlorine CS tensor is also determined for the first time for DL-arginine hydrochloride monohydrate. The drastic influence of 1H decoupling at 21.1 T on the spectral features of salts with particularly small 35Cl quadrupolar coupling constants (CQ) is demonstrated. The chlorine CS tensor spans (Omega) of hydrochloride salts of hydrophobic amino acids are found to be larger than those for salts of hydrophilic amino acids. A new combined experimental-theoretical procedure is described in which quantum chemical geometry optimizations of hydrogen-bonded proton positions around the chloride ions in a series of amino acid hydrochlorides are cross-validated against the experimental chlorine EFG and CS tensor data. The conclusion is reached that the relatively computationally inexpensive B3LYP/3-21G* method provides proton positions which are suitable for subsequent higher-level calculations of the chlorine EFG tensors. The computed value of is less sensitive to the proton positions. Following this cross-validation procedure, /CQ(35Cl)/ is generally predicted within 15% of the experimental value for a range of HCl salts. The results suggest the applicability of chlorine NMR interaction tensors in the refinement of proton positions in structurally similar compounds, e.g., chloride ion channels, for which neutron diffraction data are unavailable.
在21.1 T下获得的新数据以及广泛的量子化学计算的背景下，研究了氨基酸盐酸盐中氯化学位移（CS）张量的趋势。对在两种磁场强度下获得的固体L-色氨酸盐酸盐的氯-35/37 NMR光谱进行分析，得到了氯电场梯度（EFG）和CS张量及其相对取向。还首次测定了一水合DL-精氨酸盐酸盐的氯CS张量。证明了在21.1 T下的1H去耦对具有特别小的35Cl四极耦合常数（CQ）的盐的光谱特征有显著影响。发现疏水性氨基酸盐酸盐的氯CS张量跨度（Ω）大于亲水性氨基酸盐的跨度。描述了一种新的实验-理论结合程序，其中对一系列氨基酸盐酸盐中氯离子周围氢键质子位置的量子化学几何优化与实验氯EFG和CS张量数据进行交叉验证。得出的结论是，计算成本相对较低的B3LYP/3-21G*方法提供的质子位置适用于随后对氯EFG张量进行的更高层次计算。计算值对质子位置不太敏感。按照这种交叉验证程序，对于一系列HCl盐，/CQ(35Cl)/通常在实验值的15%范围内预测。结果表明，氯NMR相互作用张量适用于在中子衍射数据不可用的情况下，对结构相似的化合物（如氯离子通道）中的质子位置进行细化。
