NEGATIVE NUCLEAR OVERHAUSER EFFECTS AS PROBES OF MACROMOLECULAR STRUCTURE
NEGATIVE NUCLEAR OVERHAUSER EFFECTS AS PROBES OF MACROMOLECULAR STRUCTURE
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DOI：
10.1021/ja00766a063
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发表时间：
1972-01-01
影响因子：
15
通讯作者：
DADOK, J
中科院分区：
文献类型：
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作者：
BALARAM, P;BOTHNERB.AA;DADOK, J
在ω 2 tc 2 <<1（即，对于具有tc 2>> 10-nsec的小分子）的极端窄化极限中，f1（S）= 0.5，其对应于50%的最大增强。对于大分子，如球状蛋白质，相关时间很可能很长，并且/i（S）接近极限-1，即信号消失。霍夫曼和Forsen 9已经表明，由McConnell 10修改的用于化学交换的Bloch方程和由Solomon 8导出的用于一对相互弛豫自旋的方程是类似的。他们指出，对于标量相互作用W 0> W2，并且在化学交换和相互弛豫的情况下，两个自旋的磁化强度之间的耦合将具有相同的符号。这里已经表明，即使在偶极相互作用的情况下，只要调制耦合的相关时间足够长，W 0> W2。在化学交换系统中，如果交换率k> l/，则一个位点的原子核饱和导致第二个位点的信号饱和。在一个相互弛豫的自旋系统中，其特征在于长的运动相关时间，存在通过“触发器”机制的自旋饱和转移，这可以被视为类似于化学转移。这里提出的模型是定性的和一个警告的注意，必须健全的使用一个简单的双自旋系统来近似复杂的多自旋系统和随之而来的忽略交叉相关效应。已经进行了支持这种解释的额外实验。胰岛素芳香族共振的负分子内NOE，
In the extreme narrowing limit where co2tc2 «1 (ie, for small molecules having tc» 10~ n sec),/i (S)= 0.5, which corresponds to a maximum enhancement of 50%. For large molecules, such as globular proteins, the correlation times are likely to be long and/i (S) approaches the limit—1, ie, disappearance of the signal.Hoffman and Forsen9 have shown that the Bloch equations modified by McConnell10 for chemical exchange and the equations derived by Solomon8 for a pair of mutually relaxing spins are analogous. They pointed out that for scalar interactions W0> W2, and the coupling between the magnetizations of the two spins would have the same sign in the case of both chemical exchange and mutual relaxation. It has been shown here that W0> W2 even in the case of a dipolar interaction provided the correlation time modulating the coupling is sufficiently long. In a chemically ex-changing system saturation of the nucleus at one site results in a saturation of the signalat the second site provided3 the exchangerate k> l/. In a mutually relaxing spinsystem, characterized by long motional correlation times, there is a transfer of spin saturation by the “flip-flop” mechanism, which can be viewed as analogous to a chemical transfer. The model presented here is qualitative and a cautionary note must be sounded regarding the use of a simple twospin system to approximate complex multispin systems and the consequent neglect of cross correlation effects. Additional experiments supporting this interpreta-tion have been performed. Negative intramolecular NOE’s on the aromatic resonances of insulin and