Metal dependence of the nonplanar distortion of octaalkyltetraphenylporphyrins

Journal Article · Tue Jan 26 23:00:00 EST 1993 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00055a030· OSTI ID:6443194

Sparks, L D; Shelnutt, J A ^[1]; Medforth, C J; Senge, M O; Smith, K M ^[2]; Park, M S; Ondrias, M R ^[3]; Chamberlain, J R ^[4]

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1. Sandia National Laboratories, Albuquerque, NM (United States) Univ. of New Mexico, Albuquerque (United States)
2. Univ. of California, Davis (United States)
3. Univ. of New Mexico, Albuquerque (United States)
4. Sandia National Laboratories, Albuquerque, NM (United States)

The biological activity of porphyrins and related tetrapyrroles in proteins may be modulated by nonplanar conformational distortions; consequently, two aspects of nonplanarity have been investigated in the highly nonplanar octaalkyltetraphenylporphyrins (OATPPs). In the first part, the effect of the central metal ion (M = Ni(II), Co(II), Cu(II), Zn(II), Co(III), Fe(III)) on the conformation of the OATPP macrocycle has been determined. Crystallographic studies reveal that the sterically encumbered, nonplanar porphyrin 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin (OETPP) remains sufficiently flexible to show a small decrease in nonplanarity for large metal ions. This decrease in nonplanarity for the OETPP metal complexes is predicted by using a molecular mechanics force field derived from structural and vibrational data for planar metalloporphyrins. A detailed analysis of the crystal structures of the Co(II) and Cu(II) complexes of OETPP reveals that the metal-dependent changes in bond lengths and bond angles are qualitatively similar to the changes observed for the OEP complexes. As the metal size increases, both OEPs and OETPPs exhibit expansion of the meso bridges (increases in the C[sub [alpha]]-C[sub m] bond length and the C[sub [alpha]]-C[sub m]-C[sub [alpha]] bond angle) and a movement of the coordinating nitrogen atoms away from the metal atom (increases in the M-N bond length and the C[sub [alpha]]-N-C[sub [alpha]] bond angle and a decrease in the N-C[sub [alpha]] bond length). In the second part, a combination of molecular mechanics and INDO/CI molecular orbital calculations successfully predicts the optical spectra of a series of highly substituted OATPPs with increasing nonplanar distortion. The successes of these calculations indicates the importance of including both the macrocycle conformation and the peripheral substituents in the INDO calculations. 62 refs., 10 figs., 6 tabs.

• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6443194
• Journal Information: Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 115:2; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
BOND ANGLE
BOND LENGTHS
CARBOXYLIC ACIDS
CHARGED PARTICLES
COBALT COMPLEXES
COMPLEXES
CONFIGURATION INTERACTION
COPPER COMPLEXES
DIMENSIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IONS
IRON COMPLEXES
LENGTH
MATHEMATICAL MODELS
MOLECULAR STRUCTURE
NICKEL COMPLEXES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
ZINC COMPLEXES