title: Analysis of Quil A-phospholipid mixtures using drift spectroscopy.
abstract: The aim of this study was to investigate molecular interactions between Quil A and phosphatidylcholine in the solid state using diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Analysis of the interactions was characterized on the different regions of phosphatidylcholine: hydrophobic chain, interfacial and headgroup regions. The spectra of the hydrocarbon region of phosphatidylcholine alone compared to that for the binary mixture of Quil A and phosphatidylcholine were similar. These findings suggest that Quil A did not cause conformational disorder of the fatty acyl chains of the phospholipid. In contrast, a shift in the wavenumber of the choline group and a broad band in this moiety indicate a modification of the phospholipid in the headgroup region due to interaction between Quil A and phosphatidylcholine. These results suggest possibly ionic interactions between the negatively charged glucuronic acid moiety of the Quil A molecule with the positively charged choline group. The findings could also be the result of conformational changes in the choline group because of the intercalation of sugar moieties in Quil A between the choline and phosphate groups due to hydrogen bonding. Shift of wavenumbers to lower values on the carbonyl group was observed suggesting hydrogen bonding between Quil A and phosphatidylcholine. The difference in degrees of wavenumber shift (choline>phosphate>carbonyl group) and observed broad bands indicated that Quil A preferentially interacted with phosphatidylcholine on the hydrophilic headgroup. Cholesterol influenced such interactions at relatively high concentration (60%, w/w).
authors.affiliation: School of Pharmacy, Tshwane University of Technology, Pretoria, South Africa. demanaph@tut.ac.za
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Demana
authors.forename: Nigel M
authors.initials: NM
authors.lastname: Davies
authors.forename: Sarah
authors.initials: S
authors.lastname: Hook
authors.forename: Thomas
authors.initials: T
authors.lastname: Rades
mesh_terms: D000276:Adjuvants, Immunologic / Q000032:analysis*; D002240:Carbohydrate Sequence; D002784:Cholesterol / Q000737:chemistry; D002794:Choline / Q000737:chemistry; D005227:Fatty Acids / Q000737:chemistry; D005612:Freeze Drying; D008969:Molecular Sequence Data; D010710:Phosphates / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000032:analysis*; D011208:Powders; D062605:Quillaja Saponins; D012503:Saponins / Q000032:analysis*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000276:Adjuvants, Immunologic; D005227:Fatty Acids; D010710:Phosphates; D010713:Phosphatidylcholines; D010743:Phospholipids; D011208:Powders; D062605:Quillaja Saponins; D012503:Saponins; C046386:Quil A; D002784:Cholesterol; D002794:Choline