DPPTE Thiolipid Self-Assembled Monolayer: A Critical Assay.
Supported lipid membranes represent an elegant way to design a fluid interface able to mimic the physicochemical properties of biological membranes, with potential biotechnological applications. In this work, a diacyl phospholipid, the 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE), functionalized with a thiol group, was immobilized on a gold surface. In this molecule, the thiol group, responsible for the Au-S bond (45 kJ/mol) is located on the phospholipid polar head, letting the hydrophobic chain protrude from the film. This system is widely used in the literature but is no less challenging, since its characterization is not complete, as several discordant data have been obtained. In this work, the film was characterized by cyclic voltammetry blocking experiments, to verify the SAM formation, and by reductive desorption measurements, to estimate the molecular density of DPPTE on the gold surface. This value has been compared to that obtained by quartz crystal microbalance measurements. Ellipsometry and impedance spectroscopy measurements have been performed to obtain information about the monolayer thickness and capacitance. The film morphology was investigated by atomic force microscopy. Finally, Monte Carlo simulations were carried out, in order to gain molecular information about the morphologies of the DPPTE SAM and compare them to the experimental results. We demonstrate that DPPTE molecules, incubated 18 h below the phase transition temperature (T = 41.1 ± 0.4 °C) in ethanol solution, are able to form a self-assembled monolayer on the gold surface, with domain structures of different order, which have never been reported before. Our results make possible rationalization of the scattered results so far obtained on this system, giving a new insight into the formation of phospholipids SAMs on a gold surface.
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Raffaella
R
Lettieri
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Floriana
F
Di Giorgio
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Alessandra
A
Colella
Department of Physics, Chemistry and Biology (IFM), University of Linköping , 581 83 Linköping, Sweden.
Roger
R
Magnusson
Ångström Laboratory, Department of Chemistry, Uppsala University , Box 538, SE-75121 Uppsala, Sweden.
Fredrik
F
Bjorefors
Institute of Structure of Matter, CNR, Department of Physics, University of Rome Tor Vergata , 00133 Rome, Italy.
Ernesto
E
Placidi
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Antonio
A
Palleschi
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Mariano
M
Venanzi
Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Emanuela
E
Gatto