Nuclear Magnetic Resonance Shifts in Paramagnetic Metalloporphyrins and Metalloproteins

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• 作者：Junhong Mao ; Yong Zhang ; and Eric Oldfield
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：November 20, 2002
• 年：2002
• 卷：124
• 期：46
• 页码：13911 - 13920
• 全文大小：312K
• 年卷期：v.124,no.46(November 20, 2002)
• ISSN：1520-5126

文摘

We report the first detailed investigation of the ¹H, ¹³C, ¹⁵N, and ¹⁹F nuclear magnetic resonance(NMR) spectroscopic shifts in paramagnetic metalloprotein and metalloporphyrin systems. The >3500 ppmrange in experimentally observed hyperfine shifts can be well predicted by using density functional theory(DFT) methods. Using spin-unrestricted methods together with large, locally dense basis sets, we obtainvery good correlations between experimental and theoretical results: R² = 0.941 (N = 37, p < 0.0001)when using the pure BPW91 functional and R² = 0.981 (N = 37, p < 0.0001) when using the hybridfunctional, B3LYP. The correlations are even better for C^{mages/gifchars/alpha.gif" BORDER=0>} and C^{mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">} shifts alone: C^{mages/gifchars/alpha.gif" BORDER=0>}, R² = 0.996 (N = 8,p < 0.0001, B3LYP); C^{mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">}, R² = 0.995 (N = 8, p < 0.0001, B3LYP), but are worse for C^meso, in part becauseof the small range in C^meso shifts. The results of these theoretical calculations also lead to a revision ofprevious heme and proximal histidine residue ¹³C NMR assignments in deoxymyoglobin which are confirmedby new quantitative NMR measurements. Molecular orbital (MO) analyses of the resulting wave functionsprovide a graphical representation of the spin density distribution in the [Fe(TPP)(CN)₂]^- (TPP = 5,10,15,20-tetraphenylporphyrinato) system (S = ¹/₂), where the spin density is shown to be localized primarily in thed_xz (or d_yz) orbital, together with an analysis of the frontier MOs in Fe(TPP)Cl (S = ⁵/₂), Mn(TPP)Cl (S = 2),and a deoxymyoglobin model (S = 2). The ability to now begin to predict essentially all heavy atom NMRhyperfine shifts in paramagnetic metalloporphyrins and metalloproteins using quantum chemical methodsshould open up new areas of research aimed at structure prediction and refinement in paramagnetic systemsin much the same way that DFT methods have been used successfully in the past to predict/refine elementsof diamagnetic heme protein structures.