Electron nuclear double resonance of ferric cytochrome P450CAM
Electron nuclear double resonance of ferric cytochrome P450CAM
复制标题
三价铁细胞色素 P450CAM 的电子核双共振
DOI：
10.1021/ja00523a046
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发表时间：
1980
影响因子：
15
通讯作者：
P. Debrunner
中科院分区：
文献类型：
--
作者：
R. Lobrutto;C. Scholes;G. Wagner;I. C. Gunsalus;P. Debrunner
1是相当敏感的性质的溶剂，一般来说，极性较小的溶剂与较大的微分位移。对于大多数实验，质子供体与1的比例保持< 1：1，希望通过利用缔合平衡常数的可能差异来最大化位移差异。然而，在大多数情况下，当加入更多的质子供体时，氮的NMR不等价性的程度增加。分裂也被发现，随着温度的降低而增加。当（R）（+）-3，3，3-三氟-2-甲氧基-2-苯基丙酸（2）为络合剂6时，观察到二氯甲烷中对映异构体的氮之间的位移差异为0.70 ppm，并且如预期的，当使用外消旋2代替（R）-（2）时，该差异消失。（+）-2和1的每种对映异构体的平均环境变得相同。在二甲基亚砜溶液中存在β-环糊精水合物的情况下，对映体氮的核磁共振不等效性很有趣，因为二甲基亚砜是一种出色的氢键受体，并且预计会饱和β-环糊精的氢键贡献能力。也许通过这种组合，存在将1的对映异构体之一的苯环优先插入β-环糊精的手性空隙中的某种趋势。光学活性酸与1络合产生的位移差异的来源尚不确定。1的X2 HCH 2C 6 H5部分的NMR表明在C-8-C-9键处的一种旋转构象的强烈偏好，从模型的检查来看，几乎可以肯定具有与吡啶环相对的苄基。[7]对于在α碳上具有手性中心的羧酸，在氢键络合物中非对映异构体中心将相距相当远。尽管如此，如果苄基基本上是单一构象，则将存在远离手性中心的实质性分子不对称性。当1与羧酸络合时，15 N NMR位移的23.6-67 ppm的总变化（见表I）在与吡啶3.8氢键结合的预期范围内相当多，并且可能仅代表小程度的实际质子转移和离子对形成。
1 are quite sensitiveto the nature of the solvent and, in general, the less polar solvents are associated with larger differential shifts. Formost experiments, the proportions of proton donor to 1 were kept< 1: 1with the hope of maximizing the shift differences through taking advantage of possible differences in the association equilibrium constants. In most cases, however, the degree of NMR nonequivalence of the nitrogens increased when more proton donor was added. The splittings were also found to increase with decreasing temperature. When (ft)(+)-3, 3, 3-trifluoro-2-methoxy-2-phenylpropionic acid (2) is the complexing agent, 6 a shift difference between the nitrogens of the enantiomers in dichloromethane of 0.70 ppm was observed, and this difference, as expected, disappeared when racemic 2 was used in place of (/?)-(+)-2 and the average surroundings of each enantiomer of 1 become identical. The NMR nonequivalence of the nitrogens of the enantio-mers in the presence of/3-cyclodextrin hydrate in dimethyl sulfoxide solution is interesting because dimethyl sulfoxide is an excellent hydrogen-bond acceptor and would be expected to saturate the hydrogen-bond-donating powers of the/3-cy-clodextrin. Perhaps with this combination there is some tendency for preferential insertion of the phenyl ring of one of the enantiomers of 1 into the chiral void of the/3-cyclodextrin. The origin (s) of the shift differences produced by com-plexing optically active acids with 1 is uncertain. The NMR of the X2HCH2C6H5 moiety of 1 indicates a strong preference for one rotational conformation at the C-8-C-9 bond which, from inspection of models, almost certainly has the benzyl group oppositeto the pyridine ring. 7 With a carboxylic acid having a chiral center at the a carbon, the diastereomeric centers would be rather far apart in a hydrogen-bonded com-plex. Nonetheless, if the benzyl group is in essentially a single conformation, there will be a substantial molecular dissym-metry extending away fromthe chiral center. The total change of 23.6-67 ppm in l5N NMR shift when 1 is complexed with carboxylic acids (see Table I) is pretty muchin the range ex-pected for hydrogen bonding to pyridine, 3· 8 and probably represents only a small degree of actual proton transfer and ion-pair formation.