MAGNETIC SPIN-SPIN INTERACTIONS OF COENZYME B12

本项目的目标是阐明 两个顺磁物质之间的磁自旋-自旋相互作用 在辅酶B12的均裂钴-碳键断裂中形成 和相关的模型化合物， 光诱导的模型膜。 了试验研究 计划使用多频率（Q波段、X波段、S波段和L波段） 电子自旋共振（ESR）谱 辅酶B12和具有已知结构的模型化合物， X射线测定。 类似的研究将在 辅酶B12和模型化合物分散在两个不同的 脂质双层：L-α-二肉豆蔻酰磷脂酰胆碱a 饱和脂肪和蛋黄磷脂酰胆碱 脂质 关于ESR测量，线形将 使用矩阵对角化技术计算，或者 微扰法 钴自由基自旋的值 耦合常数J 0将由两种线型确定， 模拟和ESR面积的温度依赖性 信号. 两个自旋之间的偶极距离 三重态将估计使用两个线型模拟 和比较的相对强度的一般关系 半场线和全场线。 的相对 然后可以将Co（II）和自由基的位置 从“磁几何”的想法，这是很好的确定 定义为多频ESR线型。 另外我们 旨在确定参数Δ eta不等于Δ S 不等于钴的键离解能 辅酶B12和模型化合物的碳键 光解均裂速率的温度依赖性 模型膜中的分裂。 参与或 轴向配体苯并咪唑在活化中的贡献 和均裂率是感兴趣的，这将被确定 使用碱基对辅酶B12模型化合物和碱基关闭辅酶B12模型化合物。 这些研究可能会导致更好地了解辅酶B12 在生化系统中。

The objectives of this project are to elucidate the nature of magnetic spin-spin interactions between two paramagnetic species formed in homolytic cobalt-carbon bond cleavage of coenzyme B12 and related model compounds in a polycrystalline state or in model membranes induced by light. Experimental studies are planned using multi-frequency (Q-band, X-band, S-band and L-band) electron spin resonance (ESR) spectroscopy on polycrystalline coenzyme B12 and model compounds with known structures based on X-ray determinations. Similar studies are to be performed on coenzyme B12 and with model compounds dispersed in two different lipid bilayers: L-alpha-dimyristoylphosphatidylcholine a saturated lipid and egg yolk phosphatidylcholine an unsaturated lipid. With regard to the ESR measurements, the lineshapes will be calculated using either matrix diagonalization techniques or perturbation methods. The values of the cobalt-radical spin-spin coupling constants, J0, will be determined from both lineshape simulation and the temperature dependence of the area of the ESR signals. The dipolar distance between the two spins in the triplet state will be estimated using both lineshape simulation and a general relationship comparing the relative intensity of the half-field line vs. the full-field line. The relative positions of the Co(II) and the free radical can then be determined from the "magnetic geometry" idea which is well defined by multi-frequency ESR lineshapes. In addition, we intend to determine parameters delta eta not equal to, delta S is not equal to and the bond dissociation energies of the cobalt- carbon bond of coenzyme B12 and the model compounds from the temperature dependence of the rate of homolysis by photolytic cleavage in model membranes. The participation or the contribution of the axial ligand benzimidazole in the activation and the rate of homolysis is of interest which will be determined using both base-on and base-off coenzyme B12 model compounds. These studies may lead to a better understanding of coenzyme B12 in biochemical systems.