Chlorophyll b containing liposomes: Effect of thermal transitions on catalytic and spectral properties

Nicholls, Peter; West, J.; Bangham, A. D.

doi:10.1016/0005-2736(74)90058-3

Cited by 28 publications

(7 citation statements)

References 17 publications

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“…Several authors have discussed the location and orientation of chlorophyll a or b in black lipid bilayers (Cherry, Hsu & Chapman, 1972;Steinemann, Stark & L~uger, 1972), in unsonicated liposome membranes (Nicholls, West & Bangham, 1974;Lee, 1975) or in oriented lipid multilayers (Hoff, 1974). Using different experimental evidences, all agree on the location of the porphyrin ring close to the water-lipid interface with an angle of some 40 to 50 degrees between the porphyrin plane and the membrane surface.…”

Section: Molecular Basis Of Chlorophyll's Sensor Abilitymentioning

confidence: 98%

Pigment containing lipid vesicles

Walz

1977

J. Membrain Biol.

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It was shown previously (Walz, 1976) that chlorophyll a incorporated into the membrane of lecithin vesicles is a probe which detects the aggregational state of the lipids. This phenomenon is interpreted in terms of a solvatochromism, i.e., the effect of various solvents on the absorption spectrum of the solute. The sensor characteristics can be expressed by a set of solvatochromic coefficients, which are pertinent to the electronic transitions occuring in chlorophyll a on excitation with light, and by means of the absorption bands associated with these transitions. An unambiguous resolution of spectra into absorption bands is not yet practicable, but at least part of the bands can be approximated by Gaussian components which then allows us to estimate the solvatochromic coefficients. From these data and based on the currently available theoretical and experimental information about solvatochromism, it is concluded that the chromophore, i.e., the porphyrin ring of chlorophyll a, is located adjacent to the glycerol-ester moieties of the lecithin molecules in the membrane, and that the sensor ability relies on different orientations of the chromophore for lecithin in different states of aggregation.

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Section: Molecular Basis Of Chlorophyll's Sensor Abilitymentioning

confidence: 98%

Pigment containing lipid vesicles

Walz

1977

J. Membrain Biol.

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“…Cationic liposomes containing DOTAP or DOTAP and cholesterol in a 1:1 molar ratio were prepared using a previously described method [39]. The lipid was initially dried from chloroform, subsequently dispersed in PBS (pH 7,4) and shaken at a temperature above the gel-to-liquid-crystalline transition temperature of the lipid (50°C) for 10 min.…”

Section: Methodsmentioning

confidence: 99%

Characterization of cationic lipid DNA transfection complexes differing in susceptability to serum inhibition

2002

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BackgroundCationic lipid DNA complexes based on DOTAP (1,2-dioleoyl-3-(trimethyammonium) propane) and mixtures of DOTAP and cholesterol (DC) have been previously optimized for transfection efficiency in the absence of serum and used as a non-viral gene delivery system. To determine whether DOTAP and DC lipid DNA complexes could be obtained with increased transfection effciency in the presence of high serum concentrations, the composition of the complexes was varied systematically and a total of 162 different complexes were analyzed for transfection efficiency in the presence and absence of high serum concentrations.ResultsIncreasing the ratio of DOTAP or DC to DNA led to a dose dependent enhancement of transfection efficiency in the presence of high serum concentrations up to a ratio of approximately 128 nmol lipid/μg DNA. Transfection efficiency could be further increased for all ratios of DOTAP and DC to DNA by addition of the DNA condensing agent protamine sulfate (PS). For DOTAP DNA complexes with ratios of ≤ 32 nmol/μg DNA, peak transfection efficiencies were obtained with 4 μg PS/μg DNA. In contrast, increasing the amount of PS of DC complexes above 0.5 μg PS /μg DNA did not lead to significant further increases in transfection efficiency in the presence of high serum concentrations. Four complexes, which had a similar high transfection efficiency in cell culture in the presence of low serum concentrations but which differed largely in the lipid to DNA ratio and the amount of PS were selected for further analysis. Intravenous injection of the selected complexes led to 22-fold differences in transduction efficiency, which correlated with transfection efficiency in the presence of high serum concentrations. The complex with the highest transfection efficiency in vivo consisted of 64 nmol DC/ 16 μg PS/ μg DNA. Physical analysis revealed a predicted size of 440 nm and the highest zeta potential of the complexes analyzed.ConclusionsOptimization of cationic lipid DNA complexes for transfection efficiency in the presence of high concentrations of serum led to the identification of a DC complex with high transduction efficiency in mice. This complex differs from previously described ones by higher lipid to DNA and PS to DNA ratios. The stability of this complex in the presence of high concentrations of serum and its high transduction efficiency in mice suggests that it is a promising candidate vehicle for in vivo gene delivery.

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“… 12 , 13 The study of membranes is relevant to solar energy conversion. 12 , 14 − 19 Also, knowledge of ET across membranes is fundamental both for understanding the functioning of natural photosynthetic systems and for creating their artificial analogs. 12 , 20 The contribution of the fatty-acid chains of the phospholipids to ET is poorly understood.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, it is an essential process in all living organisms. − Extensive studies of ET have been performed on proteins, ,, DNA, , dendrimers, and artificial photosynthetic centers. , A consistent effort is devoted to the ET across lipid membranes . Most of studies on ET across biological membranes focus on natural or artificial redox-active complexes embedded in a lipid bilayer and on the effects of the presence of cations, on the processes of electron and proton transfer. , The study of membranes is relevant to solar energy conversion. ,− Also, knowledge of ET across membranes is fundamental both for understanding the functioning of natural photosynthetic systems and for creating their artificial analogs. , The contribution of the fatty-acid chains of the phospholipids to ET is poorly understood. The roles of the main types of chemical bonds, that is, hydrogen-, π-, and σ-bonds in ET are not well understood either. ,, …”

Section: Introductionmentioning

confidence: 99%

Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters

et al. 2020

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In this report, we present a method to characterize the kinetics of electron transfer across the bilayer of a unilamellar liposome composed of 1,2-dimyristoyl- sn -glycero-3-phosphocholine. The method utilizes synthetic phospholipids containing noninvasive nitroxide spin labels having the >N–O• moiety at well-defined distances from the outer surface of the liposome to serve as reporters for their local environment and, at the same time, permit measurement of the kinetics of electron transfer. We used 5-doxyl and 16-doxyl stearic acids. The paramagnetic >N–O• moiety is photo-oxidized to the corresponding diamagnetic oxoammonium cation by a ruthenium electron acceptor formed in the solution. Electron transfer is monitored by three independent spectroscopic methods: by both steady-state and time-resolved electron paramagnetic resonance and by optical spectroscopy. These techniques allowed us to differentiate between the electron transfer rates of nitroxides located in the outer leaflet of the phospholipid bilayer and of those located in the inner leaflet. Measurement of electron transfer rates as a function of temperature revealed a low-activation barrier (ΔG ‡ ∼ 40 kJ/mol) that supports a tunneling mechanism.

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Chlorophyll b containing liposomes: Effect of thermal transitions on catalytic and spectral properties

Cited by 28 publications

References 17 publications

Pigment containing lipid vesicles

Pigment containing lipid vesicles

Characterization of cationic lipid DNA transfection complexes differing in susceptability to serum inhibition

Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters

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