IIBYT   23944
INSTITUTO DE INVESTIGACIONES BIOLOGICAS Y TECNOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Water and membrane dynamics of polyethylene glycol (PEG) grafted vesicles
Autor/es:
CLOP, E. M.; CHATTAH, A, K.; PERILLO, M. A.
Lugar:
San Miguel, Tucumán
Reunión:
Congreso; XLI Reunion de la Sociedad Argentina de Biofísica; 2012
Institución organizadora:
Sociedad Argentina de Biofísica
Resumen:
PEG grafted phospholipids are used in nanoparticles formation for drug encapsulation and transport1. PEG chains form an interphasial hydrophilic layer that prevents aggregation and nonspecific binding2. Recently, from NMR measurements of spin-lattice relaxation times (T1) of PEG6000 solutions, we reported the presence of two molecular populations, both in water and in PEG as well as a PEG6000 aggregation also supported by dynamic light scattering3. In the present work we study the water dynamics by NMR in vesicles formed by binary mixtures DPPC:PE-PEG (9:1) where PE (dipalmitoylphosphatidylethanolamine) is covalently modified with PEG of different molecular masses (350, 1000 and 5000 Da.). 1H-T1 was measured in a 400 MHz Bruker spectrometer. Liposomes were dispersed in D2O, enabling the spectral resolution of signals belonging to protons from phospholipids polar head (PH) and hydrocarbon chain (HC), PEG moiety and residual H2O.. The results showed the presence of two components (T1A and T1B, long and short times respectively) both in water and in phospholipids. The presence of this two populations could be explained either by an equilibrium between two molecular conformations (phase coexistence), or by the presence of different supramolecular aggregates. 1D 31P-NMR spectra allowed us to discard the coexistence of different types of supramolecular aggregates (e.g. micelles and vesicles) showing a typical spectra for bilayers in PE-PEG350 and PE-PEG1000, and a typical isotropic spectra of micelles for PE-PEG5000. Moreover the Epifluorescence Microscopy (EM) on Langmuir monolayers of binary mixtures of DPPC containing PE-PEG with the three different chain lengths, exhibited phase coexistence at lateral pressures () compatible with typical equilibruim  of bilayers. This fact allowed us to postulate that the two proton populations observed by NMR corresponded to the different phase domains observed by EM in monolayers. 1. Kim et al., Biomaterials (2009) 30,5751–5756. 2. Woodle et al., Bioch. et Biophys.Acta (1992), 1113,171-199. 3. Clop et al, J. Phys. Chem. B (2012) 116, 11953−11958. Acknowledgement: Secyt-UNC, CONICET, FONCYT.