Polarity studies on the head group of single-layered phosphatidylcholine-α-tocopherol vesicles

Bellemare, F.; Fragata, M.

doi:10.1016/0021-9797(80)90437-3

Cited by 47 publications

(22 citation statements)

References 23 publications

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“…Values for the rate constants (k Q ) of α-Toc and carotenoids for scavenging 1 O 2 in DMPC liposomes and EtOH solution were measured by the technique of Young et al (9) using Equations 1 and 2: [2] where S 0 and S α-T or S Car denote the slopes of first-order plots of disappearance of DPBF in the absence and presence of α- (11) and tert-BuOH (3.0 × 10 4 s −1 ) (12) for the RB system and PDA system, respectively, because 1 O 2 is generated at a polar membrane surface in the RB system and a hydrophobic membrane inner region in the PDA system. The micropolarity of the environment around the OH-groups of α-Toc in liposomes close to the membrane surface was inferred to be equal to that in EtOH (13), in which the dielectric constant is higher than that in tert-BuOH. Table 1 shows the k Q values for carotenoids and α-Toc in EtOH solution and liposomes.…”

Section: Resultsmentioning

confidence: 95%

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α‐tocopherol in liposomes

Fukuzawa

Inokami

Tokumura

et al. 1998

Lipids

104

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The (1)O2 quenching rate constants (kQ) of alpha-tocopherol (alpha-Toc) and carotenoids such as beta-carotene, astaxanthin, canthaxanthin, and lycopene in liposomes were determined in light of the localization of their active sites in membranes and the micropolarity of the membrane regions, and compared with those in ethanol solution. The activities of alpha-Toc and carotenoids in inhibiting (1)O2-dependent lipid peroxidation (reciprocal of the concentration required for 50% inhibition of lipid peroxidation: [IC50](-1)) were also measured in liposomes and ethanol solution and compared with their kQ values. The kQ and [IC50](-1) values were also compared in two photosensitizing systems containing Rose bengal (RB) and pyrenedodecanoic acid (PDA), respectively, which generate (1)O2 at different sites in membranes. The kQ values of alpha-Toc were 2.9 x 10(8) M(-1) s(-1) in ethanol solution and 1.4 x 10(7) M(-1) s(-1) (RB system) or 2.5 x 10(6) M(-1) s(-1) (PDA system) in liposomes. The relative [IC50](-1) value of alpha-Toc in liposomes was also five times higher in the RB system than in the PDA-system. In consideration of the local concentration of the OH-group of alpha-Toc in membranes, the kQ value of alpha-Toc in liposomes was recalculated as 3.3 x 10(6) M(-1) s(-1) in both the RB and PDA systems. The kQ values of all the carotenoids tested in two photosensitizing systems were almost the same. The kQ value of alpha-Toc in liposomes was 88 times less than in ethanol solution, but those of carotenoids in liposomes were 600-1200 times less than those in ethanol solution. The [IC50](-1) value of alpha-Toc in liposomes was 19 times less than that in ethanol solution, whereas those of carotenoids in liposomes were 60-170 times less those in ethanol solution. There were no great differences (less than twice) in the kQ and [IC50](-1) values of any carotenoids. The kQ values of all carotenoids were 40-80 times higher than that of alpha-Toc in ethanol solution but only six times higher that of alpha-Toc in liposomes. The [IC50](-1) values of carotenoid were also higher than that of alpha-Toc in ethanol solution than in liposomes, and these correlated well with the kQ values.

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Section: Resultsmentioning

confidence: 95%

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α‐tocopherol in liposomes

Fukuzawa

Inokami

Tokumura

et al. 1998

Lipids

104

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“…34 Several studies have shown that the relative permittivity of the ester carbonyl region of phosphatidylcholine vesicles is about 30. [35][36][37] If 1 or 2 were to bind to this region of the liposome, then a moderate amount of ion pair extraction would be expected. However, methylene blue has been shown to bind to a region of a phosphatidylcholine bilayer with an effective relative permittivity of about 75.…”

Section: Resultsmentioning

confidence: 99%

The Effect of lonic Strength on Liposome–Buffer and 1-Octanol–Buffer Distribution Coefficients

Austin¹,

Barton²,

Davis³

et al. 1998

Journal of Pharmaceutical Sciences

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The distribution of salmeterol and proxicromil between unilamellar vesicles of dioleoylphosphatidylcholine (DOPC) and aqueous buffer at pH 7.4 has been studied, using an ultrafiltration method, as a function of compound concentration, DOPC concentration, and buffer ionic strength. The binding of these ionized lipophilic compounds to neutral DOPC vesicles induces a surface charge, which causes the observed membrane distribution coefficient D(mem)obs to vary significantly with bound compound to DOPC ratio and with ionic strength. This variability is shown to be well-described with use of the Gouy-Chapman theory of the ionic double layer and is contrasted with the ideal behavior shown by the neutral compound clofibrate. Increasing ionic strength is also shown to increase the observed 1-octanol-buffer distribution coefficients D(o/w)obs of proxicromil but through a very different mechanism involving the extraction of ion pairs. This study highlights the experimental difficulty in determining concentration-independent liposome distribution coefficients of ionized lipophilic compounds and describes when deviations will be significant and how observed values may be corrected for such effects. The general effect of ionic strength on membrane-buffer distribution and 1-octanol-buffer distribution is discussed with particular reference to the very different propensity for ion pair formation shown by the two systems, and the most suitable experimental conditions that should be used with each system.

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“…E1 is calculated from Eq. 2 to be 25, which is reasonable for the polar region of the membrane (19,(22)(23)(24)(25) ality that produces the large Madelung constant. Thus the conductivity is limited by the space charge (8,26,27) and a clear theoretical discussion is presented by de Levie and co-workers (28)(29)(30)(31).…”

Section: Discussionmentioning

confidence: 96%

Photogating of ionic currents across a lipid bilayer.

Drain

Christensen

Mauzerall

1989

Proc. Natl. Acad. Sci. U.S.A.

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Photoformation of metalloporphyrin cations in a lipid bilayer increases the ionic currents of negative and decreases those of positive hydrophobic ions. At low concentrations of the mobile hydrophobic ion, a 30% change in conductivity is observed that decreases with increasing concentration of positive tetraphenylphosphonium ion and increases drastically with increasing concentration of negative tetraphenylboride ion. In the region of saturated conductance of boride ion, the increase in conductivity is 3.6-fold. A 15-fold increase is observed with the protonophore carbonyl cyanide 3-chlorophenylhydrazone. In this case the net charge gated is 300 times greater than the photogenerated charge in the bilayer membrane. Thus there is a net gain in this organic field effect phototransistor. The gating can also be accomplished by continuous light or chemical oxidants. Photogating is explained as space charge effects inside the bilayer.There is great interest in the movement of ions across cell membranes since these currents are associated with the activity ofall metabolically functional cells. In addition, there is much work aimed at understanding the chemical properties ofthese membranes (1). The planar lipid bilayer membrane as developed by Mueller et al. (2) has proven to be remarkably useful as a model ofthe cell membrane. It was discovered that small ions cross these membranes by two mechanisms: ion channels that can be gated by voltage or receptors (3, 4) and ion carriers that are not gated (5). We now show that the latter ionic currents, exemplified by currents of large hydrophobic ions, can be gated by photoinduced charge generation inside the membrane. The photogating effect is explained by local electrostatic effects in the bilayer membrane. The pigment/ bilayer/hydrophobic ion system is an example of an organic field effect phototransistor (6).Much work has been carried out on the mechanism by which ion carriers or hydrophobic ions cross the lipid bilayer (7-11). The large radius of these ionic species decreases the Born electrostatic charging energy of the ion, thus enabling them to traverse the hydrocarbon core of the membrane (10). It is striking that for hydrophobic ions of similar size, the conductivity of negative ions is 102-103 times that of positive ions (7,8,12,13). This observation has been explained by a dipolar potential, originating in ordered ester carbonyl groups, which is positive toward the hydrocarbon core (12). Most studies of the kinetics of ion crossing monitor either current relaxations after an applied voltage step or voltage relaxations after a charge pulse (7,9). These techniques, although very useful, are limited by capacitive transients and by ambiguity of interpretation (14). The present technique avoids the former problem and allows a direct measure of the transients in the change of conductivity. EXPERIMENTALThe 4-ml plastic membrane cell was separated by a Teflon divider with a 1-mm2 hole in the center and had glass slides for windows. A bilayer was formed from a solut...

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Polarity studies on the head group of single-layered phosphatidylcholine-α-tocopherol vesicles

Cited by 47 publications

References 23 publications

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α‐tocopherol in liposomes

Rate constants for quenching singlet oxygen and activities for inhibiting lipid peroxidation of carotenoids and α‐tocopherol in liposomes

The Effect of lonic Strength on Liposome–Buffer and 1-Octanol–Buffer Distribution Coefficients

Photogating of ionic currents across a lipid bilayer.

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