Linked Life Data

2713405

Source:http://linkedlifedata.com/resource/pubmed/id/2713405

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
1989-6-15
pubmed:abstractText
As models for chlorophyll a (Chl a), methyl ester ClFe(III)pheophorbides (1, pheophorbide a; 2, mesopheophorbide a; and 3, mesopyropheophorbide a) were examined by Fourier transform infrared (FTIR) absorption and resonance Raman (RR) spectroscopy. The infrared (IR) chlorin band above 1600 cm-1, assigned as a Ca-Cm mode (Andersson et al. (1987) J. Am. Chem. Soc. 109, 2908-2916) is shown to be metal-sensitive and responsive to spin state and coordination number for dihydroporphyrins, as well as being diagnostic for the chlorin vs. porphyrin or bacteriochlorin macrocycle. Frequency variations for this metallochlorin IR band thus parallel those of the v10 RR mode of porphyrins in their predictive utility. Qy excitation SERRS spectra of Chl a were compared with Qy excitation RR spectra of 1 and methyl Ni(II)pyropheophorbide a. The data demonstrate that 5-coordinate ClFe(III)pheophorbides are better models for chlorophylls than are ruffled 4-coordinate Ni(II)pheophorbides. Major spectral differences between the three chlorophyll models are associated with the C-9 keto and/or C-10 carbomethoxy vibrational modes. The approx. 1700 cm-1 IR band was formerly assigned solely to v(C = O) of the C-9 keto group. However, this IR feature shifts down to approx. 1685 cm-1 and nearly doubles in intensity when the C-10 carbomethoxy is removed, as for 3. Similar frequency downshifts coupled with intensity increases in the IR are found in the literature on chlorophylls. RR spectra of pheophorbides having the C-10 carbomethoxy group (1 and 2) have bands at both approx. 1700 and approx. 1735 cm-1. However, the C-9 keto v(C = O) mode of pyrophorbins also downshifts to approx. 1685 cm-1, as in the IR spectra. The approx. 1735 cm-1 ester RR mode disappears in the case of pyrophorbins, and is never RR active for nonconjugated esters of porphyrins or chlorins. These data demonstrate an interaction between the C-10 and C-9 carbonyls of phorbins. They also indicate that phorbins tend toward conjugation of the C-10 ester. Biological examples of such conjugation effects have recently been reported, e.g., for the Chl a pi-cation radical (Heald et al. (1988) J. Phys. Chem. 92, 4820-4824). Because the phorbin E ring is the major structural feature distinguishing chlorophylls from non-photosynthetic systems, the participation of the C-10 ester in ring conjugation is suggestive of its biological importance.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0006-3002
pubmed:author
pubmed:issnType
Print
pubmed:day
8
pubmed:volume
974
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
163-79
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1989
pubmed:articleTitle
Spectroscopic analysis of chlorophyll model complexes: methyl ester ClFe(III)pheophorbides.
pubmed:affiliation
Department of Chemical and Biological Sciences, Oregon Graduate Center, Beaverton 97006-1999.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't