TIME-DOMAIN ELECTRON-PARAMAGNETIC-RESONANCE AS A PROBE OF ELECTRON-ELECTRON SPIN-SPIN INTERACTION IN SPIN-LABELED LOW-SPIN IRON PORPHYRINS
TIME-DOMAIN ELECTRON-PARAMAGNETIC-RESONANCE AS A PROBE OF ELECTRON-ELECTRON SPIN-SPIN INTERACTION IN SPIN-LABELED LOW-SPIN IRON PORPHYRINS
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DOI：
10.1021/ja00112a019
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发表时间：
1995-02-22
影响因子：
15
通讯作者：
EATON, SS
中科院分区：
文献类型：
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作者：
RAKOWSKY, MH;MORE, KM;EATON, SS
通过双脉冲自旋回波光谱法在 8 至 70 K 之间测量低自旋铁 (III) 卟啉自旋标记配合物的硝氧基自由基电子自旋弛豫时间，并通过饱和恢复在 8 至 120 K 之间测量硝氧基自由基电子自旋弛豫时间。低自旋 Fe-III(TPP)(MeIm)(2)（TPP = 四苯基卟啉；MeIm = 甲基咪唑）的弛豫时间通过饱和恢复在 10 到 28 K 之间测量，并通过电子自旋回波在 10 到 25 K 之间测量。在低温下，铁电子自旋弛豫速率相对于电子-电子自旋-自旋分裂而言较慢。随着温度升高，Fe(III) 的弛豫速率变得与自旋-自旋分裂相当，然后大于自旋-自旋分裂，这使连续波 EPR 光谱中的分裂崩溃，导致硝酰基自旋-回波衰减率先增大后减小。在整个检查的温度范围内，与 Fe(III) 的相互作用增加了硝酰基的自旋晶格弛豫率 (1/T-1)。测量的 Fe(III) 弛豫时间用于分析自旋回波衰减和相互作用硝酰基的饱和恢复 (T-1) 数据中随温度变化的变化，并确定自旋间距离 r。所检查的四种复合物的 r 值在 10.5 至 15 埃之间，通过自旋回波和饱和恢复获得的值之间具有良好的一致性。对于每种化合物，r 值与该自旋标记卟啉的其他数据一致。对硝酰基自旋回波和饱和恢复数据的分析还提供了在速率太快而无法通过饱和恢复或电子自旋回波光谱直接测量的温度下铁弛豫速率的值。这些数据证明了时域 EPR 测量作为缓慢弛豫自旋与相对快速弛豫金属离子（例如低自旋 Fe(III)）之间距离的探针的强大功能。
Nitroxyl free radical electron spin relaxation times for spin-labeled complexes of low-spin iron(III) porphyrins were measured between 8 and 70 K by two-pulse spin-echo spectroscopy and between 8 and 120 K by saturation recovery. Relaxation times for low-spin Fe-III(TPP)(MeIm)(2) (TPP = tetraphenylporphyrin; MeIm = methylimidazole) were measured between 10 and 28 K by saturation recovery and between 10 and 25 K by electron spin-echo. At low temperature the iron electron spin relaxation rates are slow relative to the electron-electron spin-spin splitting. As temperature is increased, the relaxation rates for the Fe(III) become comparable to and then greater than the spin-spin splitting, which collapses the splitting in the continuous wave EPR spectra and causes an increase and then a decrease in the nitroxyl spin-echo decay rate. Throughout the temperature range examined, interaction with the Fe(III) increases the spin-lattice relaxation rate (1/T-1) for the nitroxyl. The measured relaxation times for the Fe(III) were used to analyze the temperature-dependent changes in the spin-echo decays and in the saturation recovery (T-1) data for the interacting nitroxyl and determine the interspin distance, r. The values of r for the four complexes that were examined were between 10.5 and 15 Angstrom, with good agreement between values obtained by spin-echo and saturation recovery. For each of the compounds the value of r is consistent with other data for that spin-labeled porphyrin. Analysis of the nitroxyl spin-echo and saturation recovery data also provide values of the iron relaxation rates at temperatures where the rates are too fast to measure directly by saturation recovery or electron spin-echo spectroscopy. These data demonstrate the power of time-domain EPR measurements as a probe of distance between a slowly-relaxing spin and a relatively rapidly relaxing metal ion such as low-spin Fe(III).