DPPC liposomes

Second-Order Quenching Rate Constants for the Quenching of 102 by Carotenoids in Unilamellar DPPC Liposomes, Benzene, and Triton X-100/405 Micelles... 

FIGURE 14.12 Decay of P-CAR + in unilamellar DPPC liposomes (a) without ascorbic acid, (b) with 10 xM ascorbic acid, (c) with 50 xM ascorbic acid, (d) with 150 xM ascorbic acid. Inset Quenching plot. 

Jizomoto and Hirano [3.41 ] tried to increase the amount of drug inclusions in liposomes by inserting Ca2+ ions in dipalmitoylphosphatidylcholine (DPPC) liposomes. The included volume (mL) per g of liposomes is called Vcap, and this can be increased as a function of the Ca2+ concentration up to ten fold of the minimum Vcap The increase in Vcap is attributed to the electrostatic repulsion between the Ca ions, which reduces the number of lamella and increases the diameter of the liposomes to a certain extent, but increases substantially. A calculated simulation of this thesis is in reasonable agreement with the measurements... 

Studies with the freeze dried DPPC liposomes in trehalose solution showed, that not Tg )f the amorphous sugar is the critical temperature during storage, but the bilayer transition emperature Tm. for the lyposomes determines the short term stability of the formulation. With trehalose as lyoprotectant and a low residual water content, Tm proved to be 10 to 30 °C below the onset of T . 30 min heating above Tm but well below T% decreased the retention of CF after rehydration. Tm< after the heating was reduced from 40 to 80 °C to below 25 °C. 

Jizomoto, H Hirano, K. Encapsulating of drugs by lyophilized empty dipalmitoyl-choline (DPPC) liposomes Effects of calcium ion. Chem. Pharm. Bull., 37 (11), p. 3066-3069,1989... 

Incidentally, ICD in DPPC liposomes is observed in the temperature range below Tm but not above. Consequently, the non-linear depression of ICD will be relevant to disordering of DPPC molecular arrangement. The change in ICD is a reversible process. Reverse photoisomerization to the trans isomer restores the initial ICD. 

Figure 3 Variation of P form fluorescence intensity of 1-naphthol ( - - ) and 22Na+ selfdiffusion rate (A-A-A) with temperature in DPPC liposome membrane. (The curve for 22Na+ self-diffusion rate has been adapted from Ref. 93 with permission from Elsevier Science. Figure reprinted with permission from Ref. 93a. Copyright 1998 American Chemical Society.)...

This possibility has been explored by Pappayee and Mishra [130], It was found that in DMPC and DPPC liposomes, simultaneous presence of both P and DP form fluorescence is observed in a pH interval of 11-13. Within this pH interval, the maximal fluorescence sensitivity (largest changes in neutral to anionic form fluorescence ratio) was observed at pH 12. At this pH, CBZ partitions well into the liposome membrane with a large Kp value of 2 X 106 M 1 for DMPC and 3 X 106 M 1 for DPPC liposomes. Fluorescence quenching studies with the hy-... 

Differential scanning calorimetry has also been used to study the interaction of DPPC liposomes with the neuromediators norepinephrine and 5-hydroxytryptamine and four antidepressant drugs (imipramine, indalpine, citalopram, and milnacipran) known to inhibit uptake of these neurotransmitters [39]. Changes in the thermograms, transition temperature maximum, Tt, and ATt were determined as a function... 

Several other examples of drug-membrane interactions have been reported. Using X-ray diffraction techniques, interactions with tetracyclines [75], pindolol [76], and chlorpromazine [77, 78] have been described. In these studies, it was shown that in the presence of chlorpromazine the bilayer thickness or lipid head group separation in DPPC liposomes is only 30 A, which is about 20 A smaller than two fully extended DPPC molecules. Chlorpromazine produced an interdigitated phase, which is in agreement with the observed effect of chlorpromazine on the shape of erythrocytes. 

I, DMPC liposomes II, DPPC liposomes III, DMPC/CHOL (1 1 mole ratio) liposomes ... 

The larger partition coefficient into lipids is because only the neutral form can efficiently partition into octanol. Ordered phospholipid bilayers can, however, take up both forms neutral and charged. The influence of anionic and cationic charge on the ability of amphiphilic drugs to partition and bind to DPPC liposomes was investigat-... 

When the interaction of the modifiers was studied on DPPS liposomes rather than DPPC liposomes, a major difference was the observed change in AH. This is exemplified in Figure 5.18. At lipid to drug molar ratios ranging from 1 0.01 to 1 0.1, the change in AH was observed for all studied compounds with the exception of verapamil and lidocaine. The decrease in AH of DPPS, indicating a new type of phospholipid organization, was paralleled by the formation of a new endothermic peak at... 

Another study on this same theme examined the effects of trehalose, glucose and hydroxyethyl starch on the motional properties of the phosphate headgroup of freeze-dried dipalmitoylphosphatidylcholine (DPPC) liposomes, this time employing 31P NMR.110 The work aimed to examine whether there... 

Mohr, K. and Struve, M., Differential influence of aruonic and cationic charge on the ability of amphiphilic drugs to interact with DPPC-liposomes, Biochem. Pharmacol., 41, 961,1991. 

Watkinson, A. C. et al. Evidence of phase separation of oleic acid in DPPC liposomes and excised stratum comeum from a small angle neutron scattering study. In Prediction of Percutaneous Penetration. R. C. Scott et al., eds. IBC London, 1991, pp. 380-385. 

In PC and 1,2-dipalmitoylphosphatidylcholine (DPPC) liposomes below the phase transition temperature, pyrene senses an environment similar to butanol and propanol, respectively, although above the transition temperatures the environment is less polar [49c]. 

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