Characterization of the structural features of ripple phase of phosphocholine liposomes using FT-IR spectroscopy

Abstract

Molekule 1,2-dipalmitoil-sn-glicero-3-fosfokolina (engl. 1,2-dipalmitoyl-sn-glicero-3- phosphatidylcholine, DPPC) u vodenom mediju stvaraju hidrirane dvosloje koji se, ovisno o temperaturi, nalaze u određenoj fazi. Prijelaz DPPC-a iz faze gela (Lβ') u fazu fluida (Lα), odnosno glavni fazni prijelaz opažen pri temperaturi mekšanja (Tm), prekinut je valovitom fazom (Pβ') koja se opaža pri temperaturi pretprijelaza (Tp). Budući da su Tm i Tp iznimno osjetljive na ugradnju organskih molekula u lipidni dvosloj, posebice onih koje su kadre primati i otpuštati proton, u sklopu ovog diplomskog rada istraženi su višestruki hidrirani dvosloji DPPC lipida u odsutnosti i prisutnosti male količine palmitinske kiseline (engl. palmitic acid, PA) u puferima različitih pH vrijednosti. Tm i Tp određene su analizom vibracijskih potpisa metilenskih (νsCH2) i fosfatnih (νasPO2−) skupina iz temperaturno-ovisnih FT-IR spektara. Dobiveni podaci su djelomično upotpunjeni onima dobivenima iz razlikovno-pretražne kalorimetrije (engl. differential scanning calorimetry, DSC).1,2-dipalmitoyl-sn-glycero-3-phosphocoline form hydrated bilayers in an aqueous medium which, depending on the temperature, can be found in certain phase. The transition from gel (Lβ') to fluid phase (Lα), assigned as the main phase transition with a peak at melting point temperature (Tm), is interrupted by the ripple phase (Pβ') observed at the pretransition temeprature (Tp). Since Tm and Tp are extremely sensitive to the incorporation of organic molecules into the lipid bilayer, especially those capable of receiving and releasing a proton, multiple hydrated bilayers of DPPC lipids in the absence and presence of small amounts of palmitic acid (PA) in buffers of different pH values have been investigated across this thesis. Tm and Tp have been determined by the analysis of vibrational signatures of methylene (νsCH2) and phosphate (νasPO2−) groups from temperature-dependent FT-IR spectra. These data have been partially supplemented by those obtained from differential scanning calorimetry (DSC)