Solid-state NMR, Mossbauer, crystallographic, and density functional theory investigation of Fe-O2 and Fe-O2 analogue metalloporphyrins and metalloproteins
Solid-state NMR, Mossbauer, crystallographic, and density functional theory investigation of Fe-O2 and Fe-O2 analogue metalloporphyrins and metalloproteins
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DOI：
10.1021/ja9832820
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发表时间：
1999-04-28
影响因子：
15
通讯作者：
Oldfield, E
中科院分区：
文献类型：
--
作者：
Godbout, N;Sanders, LK;Oldfield, E
用固体核磁共振、穆斯堡尔谱、单晶X-射线衍射谱和密度泛函理论研究了以下Fe-O-2类似物：Fe(5，10，15，20-四苯基卟啉)(1-甲基咪唑)；Fe(5，10，15，20-四苯基卟啉)(1-甲基咪唑)(吡啶)；Fe(5，10，15，20-四苯基卟啉)(4-Fe-O-2类似物)(2，3，7，8，12，13，17，18-八乙基卟啉)(1-甲基咪唑)和Co(2，3，7，8，12，13，17，18-octaethylporphyrinate)(NO).我们的结果表明，两个含吡啶的四苯基卟啉的卟啉环是褶皱的，而另外三个化合物是平面的，并对其原因进行了讨论。固体核磁共振和穆斯堡尔谱结果通过DFT计算得到了很好的重现性，这使得能够测试金属卟啉和金属蛋白中Fe-O-2键的各种模型。我们没有发现在氧化型栅栏卟啉中有两个结合位点的证据，它们具有非常不同的电场梯度。然而，实验中的穆斯堡尔四极分裂可以很容易地解释为Fe-O-2单元的快速轴向旋转。与氧合肌球蛋白不同的是，PhNO中的穆斯堡尔四极分裂。由于铁的静态性质，肌红蛋白不会随温度变化。PhNO亚基，经Mb.[H-2(5)]PhNO的H-2核磁共振证实。O-2旋转到氧合肌球蛋白的第二(少数)位，可以通过简单的交换平均或电子机制减少实验中的四极分裂，而不会显著改变Fe-O-O键的几何构型，也不会改变四极分裂的符号。对CO、PhNO和O-2-金属卟啉络合物分子静电势的密度泛函计算表明，PhNO和O-2络合物中的氧位比CO系统中的氧位更具电负性，这有力地支持了这一观点，即O-2上的氢键将是血红素蛋白中O-2/CO区分的主要原因。
We have synthesized and studied via solid-state NMR, Mossbauer spectroscopy, single-crystal X-ray diffraction, and density functional theory the following Fe-O-2 analogue metalloporphyrins: Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(1-methylimidazole); Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(pyridine); Fe(5,10,15,20-tetraphenylporphyrinate)(4 Fe-O-2 analogue metalloporphyrins (2,3,7,8,12,13,17,18-octaethylporphyrinate) (nitrosobenzene)(1-methylimidazole) and Co(2,3,7,8,12,13,17,18-octaethylporphyrinate)(NO). Our results show that the porphyrin rings of the two tetraphenylporphyrins containing pyridine are ruffled while the other three compounds are planar: reasons for this are discussed. The solid-state NMR and Mossbauer spectroscopic results are well reproduced by the DFT calculations, which then enable the testing of various models of Fe-O-2 bonding in metalloporphyrins and metalloproteins. We find no evidence for two binding sites in oxypicket fence porphyrin, characterized by very different electric field gradients. However, the experimental Mossbauer quadrupole splittings can be readily accounted for by fast axial rotation of the Fe-O-2 unit. Unlike oxymyoglobin, the Mossbauer quadrupole splitting in PhNO . myoglobin does not change with temperature, due to the static nature of the Fe . PhNO subunit, as verified by H-2 NMR of Mb .[H-2(5)]PhNO. Rotation of O-2 to a second (minority) site in oxymyoglobin can reduce the experimental quadrupole splittings, either by simple exchange averaging, or by an electronic mechanism, without significant changes in the Fe-O-O bond geometry, or a change in sign of the quadrupole splitting. DFT calculations of the molecular electrostatic potentials in CO, PhNO, and O-2-metalloporphyrin complexes show that the oxygen sites In the PhNO and O-2 complexes are more electronegative than that in the CO system, which strongly supports the idea that hydrogen bonding to O-2 Will be a major contributor to O-2/CO discrimination in heme proteins.