Stability of chlorophyll a at the gas-water interface in pure and mixed monolayers. An evaluation of interfacial pH
- Centre de Recherche Paul Pascal-C.N.R.S., Pessac (France)
- Ecole Normale Superieure, Lyon (France)
- Univ. of Notre Dame, IN (United States)
The stability of chlorophyll a, Chl a, in neat and mixed lipid monolayers at the nitrogen-water interface has been measured using Langmuir trough and HPLC techniques. In neat monolayers, at subphase pH less than 8, Chl a degrades rapidly to produce pheophytin a, Phe a. Above this pH, Chl a appears to hydrolyze, giving a new product, Chl a{sub hyd}, spectroscopically similar to the parent compound. This latter process appears to involve alteration at the pentanone ring peripheral to the porphyrin structure. For mixed monolayer studies, four oleoyl-bearing lipids with headgroups differing in charge have been used to explore the influence of such headgroups on these two pH dependent processes. It has been shown that L-{alpha}-dioleoylphosphatidyl-DL-glycerol markedly increases pheophytinization while eliminating the formation of Chl a{sub hyd}. By contrast, positively charged dioleoyl-N-(3-trimethylammoniopropyl)carbamoylglycerol serves to generate formation of Chl a{sub hyd} with no production of Phe a. In neutral but polar 1,2-dioleoyl-sn-glycerol monolayers, product yields were observed that are consistent with the larger acidity in the region of Chl a. Finally, L-{alpha}-dioleoylphosphatidylcholine, which bears a zwitterionic headgroup, significantly enhanced apparent Chl a hydrolysis. These results are interpreted in terms of alterations by the host lipid in pH local to Chl a. 27 refs., 12 figs.
- OSTI ID:
- 437377
- Journal Information:
- Journal of Physical Chemistry, Vol. 100, Issue 47; Other Information: PBD: 21 Nov 1996
- Country of Publication:
- United States
- Language:
- English
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