Calorimetric and spin-label ESR studies of PEG:2000-DPPE containing DPPC/lyso-PPC mixtures |
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Authors: | Manuela Pantusa Rosa Bartucci Luigi Sportelli |
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Institution: | (1) Laboratorio di Biofisica Molecolare, Dipartimento di Fisica and UdR-CNISM, Università della Calabria, 87036 Rende (CS), Italy |
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Abstract: | The thermotropic behavior of dipalmitoylphosphatidylcholine (DPPC) multibilayers containing up to 10 mol% of lyso-palmitoylphosphatidylcholine
(lyso-PPC) with and without low content of poly(ethylene glycol:2000)-grafted dipalmitoylphosphatidylethanolamine (PEG:2000-DPPE)
has been studied by high sensitivity differential scanning calorimetry (DSC) and electron spin resonance (ESR) using the spin
probe di-tert-butyl-nitroxide (DTBN). The three lipids, dispersed in buffer at appropriate concentrations, form thermosensitive liposomes
used as site-specific drug-delivery systems. Without polymer–lipids, the DPPC main transition temperature is downshifted of
1.2–1.3 °C at the highest lyso-PPC content. The molar enthalpy and the cooperative unit of the DPPC main transition first
decrease rapidly, then more slowly and finally slightly increase with lyso-PPC content. Moreover, in the mixed dispersions,
the membrane fluidity increases at any temperature. The addition up to 5 mol% of PEG:2000-DPPE to DPPC/10 mol% lyso-PPC mixtures
does not affect neither the thermotropic phase behavior nor the transition cooperativity and the fluidity of the dispersions. |
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Keywords: | DPPC Lyso-PPC Polymer– lipid DSC Spin-probe ESR Transition cooperativity Membrane fluidity |
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