(15)N and (1)H Solid-State NMR Investigation of a Canonical Low-Barrier Hydrogen-Bond Compound: 1,8-Bis(dimethylamino)naphthalene.
(15)N and (1)H Solid-State NMR Investigation of a Canonical Low-Barrier Hydrogen-Bond Compound: 1,8-Bis(dimethylamino)naphthalene.
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典型低势垒氢键化合物的 (15)N 和 (1)H 固态 NMR 研究：1,8-双(二甲氨基)萘。
DOI：
10.1021/acs.jpcb.5b06171
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Hong,Mei
中科院分区：
文献类型：
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作者：
White,PaulB;Hong,Mei
强或低势垒氢键经常被提出来解释蛋白质中的酶催化和质子转移反应。到目前为止，1H化学位移和标量耦合已被用作强氢键的主要NMR光谱特征。本文报道了用固体核磁共振法同时测定1，8-双（二甲氨基）萘（DMAN）的15N和1H化学位移和N-H键长。我们将DMAN与三种不同的抗衡阴离子络合，以研究化学环境对氢键长度和化学位移的影响。所有三种DMAN化合物都表现出显着延长的N-H距离相比，共价键的长度，和1HN化学位移大于1017 ppm，与DMAN阳离子中的强NHN氢键一致。然而，3种化合物的15N和1H化学位移以及精确的N-H距离存在差异，且15N化学位移对质子局域化的依赖性与有机化合物的一般趋势相反，表明抗衡阴离子对氢键的电子结构有显著影响.这些数据提供了有用的NMR基准强H-键，并提醒对化学位移的唯一依赖，以确定强H-键的蛋白质，因为相邻的侧链可以施加类似的影响，在DMAN中的大体积的有机阴离子的化学位移。相反，N-H键长应该与化学位移一起测量，作为H键强度的更基本参数。
Strong or low-barrier hydrogen bonds have often been proposed in proteins to explain enzyme catalysis and proton-transfer reactions. So far1H chemical shifts and scalar couplings have been used as the main NMR spectroscopic signatures for strong H-bonds. In this work, we report simultaneous measurements of15N and1H chemical shifts and N–H bond lengths by solid-state NMR in15N-labeled 1,8-bis(dimethylamino)naphthalene (DMAN), which contains a well-known strong NHN H-bond. We complexed DMAN with three different counteranions to examine the effects of the chemical environment on the H-bond lengths and chemical shifts. All three DMAN compounds exhibit significantly elongated N–H distances compared to the covalent bond length, and the1HNchemical shifts are larger than ∼17 ppm, consistent with strong NHN H-bonds in the DMAN cation. However, the15N and1H chemical shifts and the precise N–H distances differ among the three compounds, and the15N chemical shifts show opposite dependences on the proton localization from the general trend in organic compounds, indicating the significant effects of the counteranions on the electronic structure of the H-bond. These data provide useful NMR benchmarks for strong H-bonds and caution against the sole reliance on chemical shifts for identifying strong H-bonds in proteins since neighboring side chains can exert influences on chemical shifts similar to those of the bulky organic anions in DMAN. Instead, N–H bond lengths should be measured, in conjunction with chemical shifts, as a more fundamental parameter of H-bond strength.