ISSN:
1432-1424
Keywords:
phospholipid bilayers
;
dehydration
;
carbohydrates
;
glycerol
;
merocyanine spectra
;
liposome size
;
anisotropy parameter
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The interaction of permeant molecules such as glycerol and urea and nonpermeants such as trehalose, sucrose, lactose and glucose with dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine (EPC) bilayers was studied by means of infrared spectroscopy in solid samples. The properties of the liposomes formed upon rehydration in different polyol solutions were determined by dynamic light scattering, fluorescence anisotropy, absorbance at 450 nm and merocyanine 540 spectra. Phospholipid samples dehydrated in the presence of urea and glycerol give Δv 1/2 values for the antisymmetric stretch (P=0 stretch) in the IR spectra; lower values are found for hydrated phospholipids. In contrast, the same procedure in the presence of carbohydrates, gives Δv 1/2 values close or higher to those found for hydrated phospholipids, following the sequence glucose〉sucrose〉trehalose. This order is similar to that found in hydrated bilayers for the 570/500 nm ratio determined in the MC 540 spectra as a function of the number of OH equatorial groups of the sugars. Liposomes lyophilized in the presence of those carbohydrates and rehydrated in buffer solution showed an increase in the 570/530 absorbance ratio in the MC spectra at temperatures below that corresponding to the gel-liquid crystalline transition. This is interpreted as an exposure of hydrophobic regions due to the carbohydrate-phospholipid interaction. In these conditions, the size at which liposomes spontaneously stabilize is a function of the type and concentration of the polyols in the aqueous solution. These changes in size are connected with packing and mechanical constraints of the bilayer for some of the sugars assayed. Similar results to those obtained with lyophilized liposomes were found after aging liposomes in high sugar concentration solutions. A clear distinction can be made between the effect of permeant and nonpermeant molecules in regard to size, packing and hydrophobic region exposure.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870420
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