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    STUDIA CHEMIA - Ediţia nr.1 din 2005  
         
  Articol:   ATOMIC FORCE MICROSCOPY STUDIES OF LANGMUIR-BLODGETT FILMS. 4. THE INFLUENCE OF ALUMINUM SUBSTRATE ON DIPALMITOYL PHOSPHATIDYLCHOLINE NANOLAYERS.

Autori:  MARIA TOMOAIA-COTISEL, VASILICA-DANIELA POP, GHEORGHE TOMOAIA, AURORA MOCANU, CSABA RACZ, CRISTINA RAMONA ISPAS, OANA PASCU, OLIMPIA CRISTINA BOROŞTEAN.
 
       
         
  Rezumat:  The dipalmitoyl phosphatidylcholine (DPPC) nanolayers in the absence and in the presence of procaine (P), in concentration of 10-3 mole dm-3 in the aqueous phase of pH 5.6, have been investigated using Langmuir-Blodgett (LB) technique and atomic force microscopy (AFM). The LB films were vertically transferred from DPPC Langmuir nanolayers to a substrate made of glass covered by aluminum thin layer, at two controlled surface pressures, namely at a low surface pressure (of about 8 mN/m) corresponding to the main two-dimensional phase transition from expanded liquid (EL) to condensed liquid (CL) for pure DPPC nanolayers, and at a high surface pressure (around 70 mN/m) corresponding to the over compressed (advanced collapse) state of DPPC nanolayers. The structure of pure DPPC films show regular rounded condensed domains with densely packed DPPC molecules with polar groups on the solid substrate and methyl ends of the chains sticking out from the surface. Depending on the surface pressure the condensed domains coexist with less ordered features (primarily expanded liquid domains) at the main phase transition or with three layered domains under over compression at advanced collapse. In the presence of P, the stability of DPPC films is highly increased. This effect is shown by the increased collapse pressure of mixed DPPC and P nanolayers at the air/water interface. The nano-structures visualized by AFM observations on LB mixed films of DPPC and P reveal some specific molecular interactions between these biologically relevant compounds through hydrogen bonds and electrostatic attractions. In addition a strong adhesion between LB films and aluminum substrate was found which might further stabilize the LB films.  
         
     
         
         
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