Fluorescence Study of the Fluidity and Cooperativity of the Phase Transitions of Zwitterionic and Anionic Liposomes Confined in Sol−Gel Glasses

Abstract

The current work makes use of different fluorescent reporter molecules and fluorescent spectroscopic techniques to characterize the thermotropic, physical, and dynamical properties of large unilamellar liposomes formed from either 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-glycerol] (DMPG) encapsulated in sol-gel matrixes. In particular, cooperativity of the phase transition is analyzed from steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), the interfacial properties are studied by measuring the spectral shift of Laurdan, and the structural organization (heterogeneity) of the lipid bilayer is determined from the fluorescence lifetime of trans-parinaric acid (t-PnA). In addition, information regarding order and dynamical properties in the bulk hydrophobic core is obtained from time-resolved fluorescence anisotropy of t-PnA and 3-(4-(6-phenyl)-1,3,5-hexatrienyl)-phenylpropionic acid (PA-DPH). The spectroscopic study reveals that upon encapsulation, the basic thermodynamic properties as well as the fluidity of the lipid bilayer practically remain intact for DMPG liposomes but not for DMPC liposomes, whose lipid bilayer exhibits large gel-fluid heterogeneity. On the basis of these experimental results, electrostatic interactions between phospholipid polar heads and the porous surface of the host matrix seem to play a capital role for the preservation of the structural integrity of encapsulated bilayer.

Micellization of Zonyl FSN-100 fluorosurfactant in aqueous solutions

“…Since the lengths of both hydrophilic and hydrophobic chains of FSN-100 are variable, we measured quantitative 1 H, 13 C, and 19 F NMR spectra of 20 mg/mL FSN-100 solution in D 2 O with TFE as an internal standard in order to determine the fluorine and hydrogen content in the used FSN-100 sample; all the spectra are shown in the Supplementary material. The integral over the isolated signal of CH 2 CF 2 protons was used to calculate the molar concentration of FSN-100 with respect to the known concentration of TFE.…”

“…Fig. 3a shows the concentration changes of the 19 (the concentration dependence is shown in Fig. 3b).…”

“…Inset in Fig. 8 shows the anisotropy decay of 5 M DPH in 10 g L −1 aqueous solution of FSN-100 and its fit by the formula [19]:…”

Photophysics of a β-carboline based non-ionic probe in anionic and zwitterionic liposome membranes

“…In recent years, a variety of research has been performed successfully to study the incorporation of various fluorophores into the liposome membranes (Nassar et al, 1998;Sujatha and Mishra, 1998;Lakowicz, 1999;Chattopadhyay, 2003;Mukherjee and Chattopadhyay, 2005;Moyano et al, 2006;Esquembre et al, 2007). Lipid vesicles are closed systems consisting of one or more lamellae containing the amphiphiles.…”

“…To characterize interaction behavior, location of the probe molecules of the membrane, different spectroscopic techniques have been extensively used, among which fluorescence technique is perhaps the most sensitive one (Lakowicz, 1999;Mukherjee and Chattopadhyay, 2005;Moyano et al, 2006;Esquembre et al, 2007). It is known that the local microenvironment surrounding a probe molecule influences its electronic structure and hence its photophysics (Mallick et al, 2004(Mallick et al, , 2005aDas et al, 2007a,b).…”