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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).

Proton transfer along biological interfaces is exceptionally difficult to unravel from both experimental and theoretical perspective [1]. In addition to rather scarce computational studies, experimental endeavours are mostly focused on the incorporation of membrane- anchored pH-sensitive dyes that detect the arrival of a migrating proton. Evidently, the establishment of a probe-free method would serve as considerable breakthrough in deepening our knowledge on lateral proton transfer. In this regard, we have examined lipid multibilayers of 1, 2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) in the absence and the presence of small amount of palmitic acid (PA) (2 %) in buffers of pH values 4 ≤ pH ≤ 9 by FT- IR spectroscopy. Depending on the pH value, PA can be protonated (COOH) or deprotonated (COO−) and, consequently, placed at different depth of a lipid bilayer [3]. The presence of such small amount of PA should not significantly modify characteristic undulations of DPPC multibilayers surface [4], but accompanying proton transfer is expected to leave its signature. The latter are indirectly detected by FT-IR spectroscopy coupled with MCR-ALS with EFA analysis (Fig. 1) that is very sensitive and powerful tool in discerning of coupled events [5]. Experimental observations are corroborated by molecular dynamics (MD) simulations and calorimetric measurements.