ABSTRACT
1,2-Didodecanolyl-sn-glycero-3-phosphoryl-1'-(3'-O-L-alanyl)-sn-glycerol (Ala-PG) has been synthetized. Its ionic properties have been studied at the air-water interface through film compressions and surface potential measurements as a function of subphase pH and ionic content (NaCl, Na2MoO4, CaCl2). The existence of the polar head in a loop conformation allowing for interactions between phosphate and amino groups is suggested. Ionic properties of Ala--PG clearly depended on subphase ionic strength but no specific interactions between either cations or anions in the subphase and phosphate or amino groups in the film could be detected. Results are interpreted in terms of ion-pair interactions at the interface between these two groups and anions and cations from the subphase. Occurrence of charge separation between these two groups, induced by increasing subphase ionic strength, is postulated. Since the molecular packing appeared independent of the subphase ionic content over a large domain of pH (3--7) and surface pressure (pi greater than 5 dyne/cm) and since the lipid can be considered as zwitterionic or slightly positive below pH 5--6, it is suggested that in the parent bacteria, grown under acidic conditions, Ala--PG could play a role in maintaining the membrane integrity and in preventing the passive diffusion of protons.
Subject(s)
Phosphatidylglycerols , Alanine , Calcium Chloride , Chemical Phenomena , Chemistry , Hydrogen-Ion Concentration , Molybdenum , Osmolar Concentration , Pressure , Sodium ChlorideABSTRACT
Ionic properties of didodecanoylphosphatidylglycerol (C12PG), didodecanolyphosphatidyl-l'-propanol (C12PP), di-(12-methyl, 13-methyl)-pentadecanoylphosphatidylglycerols (C15PG) and dihexadecanoylphosphatidylglycerol (C16PG) have been studied at the air-water interface using titration experiments at constant ionic strength and film expansion experiments at constant pH, with Li+, Na+, K+ and Cs+ in the subphase. For each lipid, the apparent pK in the surface is strongly dependent on the subphase salt concentration and differs from expected intrinsic pK in the bulk. Discrimination between alkaline cations is observed. These results can be accounted for by strong surface potentials, which are satisfactorily calculated by using the Gouy and Chapman theory of the diffuse double layer. The comparison of C12PP and PG expansion data shows the importance of the glycerol residue of PG ionic properties, favouring penetration of cations in the films. Lipids in the liquid-crystalline state, such as C12-and C15PG, do not interact with alkaline cations as does C16PG in the gel phase. In particular, film condensations bring about a clear-cut discrimination between Na+ and K+. Results are discussed with regard to cation penetration and the structure of water at the interface. The importance on membrane functions of these strong surface potentials generated by PG monolayers is suggested.
Subject(s)
Phosphatidylglycerols , Air , Binding Sites , Cations, Monovalent , Fatty Acids , Glycerol , Hydrogen-Ion Concentration , Micrococcus , Molecular Conformation , Osmolar Concentration , Structure-Activity Relationship , Surface Properties , Thermodynamics , WaterABSTRACT
The author presents some thoughs on the experience resulting from a 3 year individual supervision in the "Centre de Guidance Infantile" (Child Guidance Center) of the University of Louvain. The aim of the supervision is essentially the formation for child and adolescent psychotherapy. This supervision is done inside the Center, to be consistant, but this structure is causing some problems of interference : problems of responsability from the supervisors to the Center, to the patients ; problems of authority for the supervised ; problems of affective relationships between supervisors and supervised. To resolve these difficulties, the supervisors have established spontaneously regulations enabling them to limit as much as possible these interferences.
