Spectroscopic and Thermodynamic Studies of Chlorophyll Containing Monolayers and Vesicles

1979 ◽  
Vol 34 (5-6) ◽  
pp. 406-413 ◽  
Author(s):  
J. Luisetti ◽  
H. Möhwald ◽  
H. J. Galla
Keyword(s):  
Phase Transition ◽  
Absorption Spectrum ◽  
Lipid Bilayer ◽  
Chlorophyll A ◽  
Solubility Limit ◽  
Molar Ratio ◽  
Lipid Phase ◽  
Lipid Phase Transition ◽  
Fluorescence Measurements ◽  
Lipid Bilayer Vesicles

Abstract Absorption and fluorescence experiments on pheophytin and chlorophyll containing lipid bilayer vesicles are reported. Pheophytin aggregates on the vesicles are established from an additional red shifted band (at 695 nm) in the absorption spectrum. These aggregates contain pheophytin in an arrangement with the molecular planes of the porphyrin rings being parallel and cover about 10% of the vesicle surface. The lipid phase dissolves pheophytin up to a molar ratio of 15% above the lipid phase transition. This solubility limit decreases hardly on solidification of the lipid.For chlorophyll a containing vesicles the aggregates are not observed in the absorption spectrum. The chlorophyll solubility is about equal to that of pheophytin. This suggests that the phase separa­ tion indicated from fluorescence measurements at temperatures below the lipid phase transition does not lead to the formation of strongly bound chlorophyll aggregates.

scholarly journals Verapamil prevents the effects of daunomycin on the thermotropic phase transition of model lipid bilayers

1991 ◽  
Vol 279 (2) ◽  
pp. 413-418 ◽  
Author(s):  
J M Canaves ◽  
J A Ferragut ◽  
J M Gonzalez-Ros
Keyword(s):  
Phase Transition ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Drug Binding ◽  
Lipid Phase ◽  
Dependent Manner ◽  
Binding Studies ◽  
Scanning Calorimetry ◽  
Lipid Phase Transition ◽  
Fluorescence Depolarization

High-sensitivity differential scanning calorimetry and fluorescence-depolarization techniques were used to study how the presence of daunomycin and/or verapamil affect the thermotropic behaviour of dipalmitoyl phosphatidylcholine (DPPC) vesicles. Daunomycin, a potent anti-cancer agent, perturbs the thermodynamic parameters associated with the lipid phase transition: it decreases the enthalpy change, lowers the transition temperature and reduces the co-operative behavior of the phospholipid molecules. Verapamil, on the other hand, produces smaller alterations in the lipid phase transition. However, when daunomycin and verapamil are present simultaneously in the DPPC vesicles, it is observed that verapamil prevents, in a concentration-dependent manner, the alteration in the phospholipid phase transition expected from the presence of daunomycin in the bilayer. Furthermore, drug-binding studies suggest that the observed interference of verapamil in the daunomycin/phospholipid interaction occurs without a decrease in the amount of daunomycin bound to the lipid bilayer and without the formation of a daunomycin-verapamil complex. Because of the importance of drug-membrane interactions in anthracycline cytotoxicity, we speculate that the lipid bilayer of biological membranes may provide appropriate sites at which the presence of verapamil influences the activity of daunomycin.

Fatty acyl chain structure, orientational order, and the lipid phase transition in Acholeplasma laidlawii B membranes. A review of recent 19F nuclear magnetic resonance studies

1984 ◽  
Vol 62 (11) ◽  
pp. 1134-1150 ◽  
Author(s):  
P. M. Macdonald ◽  
B. D. Sykes ◽  
R. N. McElhaney
Keyword(s):  
Phase Transition ◽  
Fatty Acids ◽  
Nuclear Magnetic Resonance ◽  
Acyl Chain ◽  
Orientational Order ◽  
Membrane Lipid ◽  
Fatty Acyl ◽  
Fatty Acyl Chain ◽  
Lipid Phase ◽  
Lipid Phase Transition

The orientational order parameters of monofluoropalmitic acids biosynthetically incorporated into membranes of Acholeplasma laidlawii B in the presence of a large excess of a variety of structurally diverse fatty acids have been determined via 19F nuclear magnetic resonance (19F NMR) spectroscopy. It is demonstrated that these monofluoropalmitic acids are relatively nonperturbing membrane probes based upon physical (differential scanning calorimetry), biochemical (membrane lipid analysis), and biological (growth studies) criteria. 19F NMR is shown to convey the same qualitative and quantitative picture of membrane lipid order provided by 2H-NMR techniques and to be sensitive to the structural characteristics of the membrane fatty acyl chains, as well as to the lipid phase transition. Representatives of each naturally occurring class of fatty acyl chain structures, including straight-chain saturated, methyl-branched, monounsaturated, and alicyclic-ring-substituted fatty acids, were studied and the 19F-NMR order parameters were correlated with the lipid phase transitions (determined calorimetrically). The lipid phase transition was the prime determinant of overall orientational order regardless of fatty acid structure. Effects upon orientational order attributable to specific structural substituents were discernible, but were secondary to the effects of the lipid phase transition. In the gel state, relative overall order was directly proportional to the temperature of the particular lipid phase transition. Not only the overall order, but also the order profile across the membrane was sensitive to the presence of particular structural substituents. In particular, in the gel state specific fatty acyl structures demonstrated a characteristic disordering effect in the membrane order profile. These various observations can be merged to provide a unified picture of the manner in which fatty acyl chain chemistry modulates the physical state of membrane lipids.

Effect of Inhalation Anesthetics on Spin-Labeled Cholesterol Containing DPPC Vesicles

1988 ◽  
Vol 43 (3-4) ◽  
pp. 264-268 ◽  
Author(s):  
N. Gulfo ◽  
R. Bartucci ◽  
L. Sportelli
Keyword(s):  
Phase Transition ◽  
Diethyl Ether ◽  
Liquid Crystalline ◽  
Main Phase ◽  
Molar Ratio ◽  
Lipid Phase ◽  
Interfacial Region ◽  
Hydrophobic Core ◽  
Hydrophobic Region ◽  
Inhalation Anesthetics

We have investigated by means of electron spin resonance (ESR) spectroscopy the influence of three inhalation anesthetics, i.e. halothane, chloroform and diethyl ether, on the interfacial and hydrophobic region as well of 38 mol% cholesterol containing DPPC unilamellar vesicles. The study has been carried out in the temperature range 25-45 °C. The variation of the order parameter, S, vs temperature of the lipid phase indicates that with this content of cholesterol the characteristic gel → liquid crystalline main phase transition of DPPC, normally occurring at Tt ~ 41 °C, disappears. When halothane and chloroform are added to the vesicles suspension up to [DPPC]/[anesthetic] molar ratio of 1:1 the main phase transition, as detected with the stearic acid spin label I(12,3), reappears again and it results down shifted at Tt ~ 35 and 39 °C, respectively. In presence of diethyl ether, instead, the main phase transition is not observable also at the highest concentration of anesthetic used. Moreover, halothane and chloroform affect similarly the hydrophobic core of cholesterol-!- DPPC vesicles which, in turn, results to be different from the action exerted by diethyl ether in the same region. The ESR findings are discussed in terms of competitive effects shown by cholesterol and inhalation anesthetics. Moreover, the interfacial region of CHOL + DPPC vesicles results to be the target of anesthetics.

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