We report t
he first detailed investigation of t
he 1H,
13C,
15N, and
19F nuclear magnetic resonance(NMR) spectroscopic shifts in paramagnetic metalloprotein and metalloporphyrin systems. T
he >3500 ppmrange in experimentally observed hyperfine shifts can be well predicted by using density functional t
heory(DFT) methods. Using spin-unrestricted methods toget
her with large, locally dense basis sets, we obtainvery good correlations between experimental and t
heoretical results:
R2 = 0.941 (
N = 37,
p < 0.0001)w
hen using t
he pure BPW91 functional and
R2 = 0.981 (
N = 37,
p < 0.0001) w
hen using t
he hybridfunctional, B3LYP. T
he correlations are even better for C
![](/images/gifchars/alpha.gif)
and C
![](/images/gifchars/beta2.gif)
shifts alone: C
![](/images/gifchars/alpha.gif)
,
R2 = 0.996 (
N = 8,
p < 0.0001, B3LYP); C
![](/images/gifchars/beta2.gif)
,
R2 = 0.995 (
N = 8,
p < 0.0001, B3LYP), but are worse for C
meso, in part becauseof t
he small range in C
meso shifts. T
he results of t
hese t
heoretical 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 t
he resulting wave functionsprovide a graphical representation of t
he spin density distribution in t
he [Fe(TPP)(CN)
2]
- (TPP = 5,10,15,20-tetrap
henylporphyrinato) system (
S =
1/
2), w
here t
he spin density is shown to be localized primarily in t
hed
xz (or d
yz) orbital, toget
her with an analysis of t
he frontier MOs in Fe(TPP)Cl (
S =
5/
2), Mn(TPP)Cl (
S = 2),and a deoxymyoglobin model (
S = 2). T
he ability to now begin to predict essentially all
heavy atom NMRhyperfine shifts in paramagnetic metalloporphyrins and metalloproteins using quantum c
hemical methodsshould open up new areas of research aimed at structure prediction and refinement in paramagnetic systemsin much t
he same way that DFT methods have been used successfully in t
he past to predict/refine elementsof diamagnetic
heme protein structures.