Chlorophyll model compounds: effects of low symmetry on the resonance Raman spectra and normal mode descriptions of nickel(II) dihydroporphyrins
Resonance Raman (RR) spectra are reported for a series of nickel(II) dihydroporphyrins with excitation in the B, Q/sub x/, and Q/sub y/ absorption regions. The molecules include trans-octaethylchlorin, ..gamma..,delta-deuteriated trans-octaethylchlorin, 9-deoxomethylmesopyropheophorbide a, methylmesopyropheophorbide a, and methylpyropheophorbide a. These molecules represent a series in which the structural complexities of chlorophyll a (reduced pyrrole ring, isocyclic ring, 9-keto group, and 2-vinyl group) are systematically added to the basic tetrapyrrole structure. All of the observed in-plane chlorin skeletal modes and vibrations of the isocyclic ring and vinyl group are assigned. Assignments are then proposed for chlorophyll a based on analogy to those of the Ni(II) complexes. In addition to the spectral assignments, normal coordinate calculations are performed on the various nickel(II) dihydroporphyrins. These calculations indicate that the forms of the normal coordinates of the metallochlorins bear little resemblance to those of the parent metalloporphyrins. In the low-symmetry environment which characterizes the reduced pyrrole pigments, a number of the vibrations are localized in semicircles or quadrants of the macrocycle rather than being delocalized over the entire ring. This vibrational localization is due to geometrical changes in the ..pi..-bonded system which occur as a result of reduction of one of the pyrrole rings and addition of the isocyclic ring.
- Research Organization:
- Carnegie Mellon Univ., Pittsburgh, PA
- OSTI ID:
- 6563047
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:8; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
CARBOXYLIC ACIDS
CHLOROPHYLL
DATA
DEUTERIUM COMPOUNDS
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INFORMATION
LASER SPECTROSCOPY
NICKEL COMPOUNDS
NORMAL-MODE ANALYSIS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
SIMULATION
SPECTRA
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
VIBRATIONAL STATES