Interaction of phospholipid dispersions with water-soluble porphyrins as monitored by their Raman temperature profiles

Raman scattering spectra of 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) dispersions, mixed with water-soluble porphyrins, i.e. cationic copper(II)-5,10,15,12-tetrakis(4-N-methylpyridyl) and anionic silver(II)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrins, were measured in the 2800-3100 cm(-1) C-H stretching vibration region as a function of the temperature within the 5-55 degrees C range. Temperature profiles of Raman data were constructed from a quantitative data treatment based on factor analysis. This method is shown to be more efficient than the commonly used approach employing peak intensity ratios. Parameters of the gel phase to liquid crystal phase transition determined from Raman temperature profiles were used to monitor the porphyrin influence on DPPG and DPPC structures. Both negatively and positively charged porphyrins significantly perturb DPPC and DPPG dispersions, causing significant downshift of the transition temperature and broadening of the transition region. Water-soluble porphyrins are assumed to set at the outside part of phospholipid dispersions and interact via coulombic forces with charged lipid heads. For the cationic CuTMPyP, the strongest effect has been observed for negatively charged DPPG. In contrast, anionic AgTPPC4 has been found to interact more efficiently with DPPC possessing both positive and negative charges.