Preparation of DPPC lipid monolayer in water trough has been done by dropping method and compared with compression method. Monolayer was studied by surface pressure isotherm, fluorescence microscopy, Brewster angle microscopy, and infrared external reflection spectroscopy. Results of these measurements showed that dropping method gave better results compared to compression method. In dropping method, transition from liquid expanded state to liquid condensed is gradual compared to sharp one in compressed method. During monolayer formation, adjustment and interaction between hydrophilic part of lipid and water and among hydrophobic part of lipid molecule are slow, stable, and more natural as worked out from surface area versus pressure isotherm. At a given molecular area, surface pressure is less compared to compression method thus monolayer is in more fluidic state in dropping method than compression method. The observation was supported by all techniques described above.

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The interactions of phospholipid monolayers (dipalmitoyl phosphatidyl choline; DPPC and dimyristoyl phosphatidyl choline; DMPC) with volatile anesthetic isoflurane were investigated using quartz crystal microbalance (QCM) and quartz crystal impedance (QCI) methods. The quartz crystal oscillator was attached horizontally on the surface of DPPC and DMPC monolayer formed on the water surface. Physisorption of isoflurane hydrate at the DPPC monolayer surface was monitored in terms of frequency and resistance change of quartz crystal on addition of anesthetics isoflurane. Both frequency and resistance change showed the elastic nature of DPPC monolayer. Measurement of DMPC monolayer-isoflurane hydrate revealed the expandable nature of DMPC monolayer. Variation of frequency and impedance of DPPC and DMPC monolayer on addition of isoflurane which proved a two-step change has occurred at monolayer surface at isoflurane concentration of <8 mM that has been attributed to isoflurane aggregation at monolayer/water interface. Isoflurane hydrates formed in the process have capability to affect the interfacial properties of monolayer such as existence of structured water.

We have investigated the interactions between phospholipid monolayers and volatile anest-hatics. Two monolayers (dihexadecyl phosphate (DHP) and dipalmitoyl phosphatidyl choline (DPPC) and two anesthetics (halothane and enflurane) were used to observe these interac-tions using a highly sensitive quartz crystal microbalance (HS-QCM). The concentration of each anesthetic in aqueous solution was kept at 4 mM. The frequency of QCM showed no change when halothane was added to the DHP monolayer, however, it responded and de-creased when interaction occurred with DPPC monolayer. In case of enflurane addition the frequency decreased in both the monolayers of DHP and DPPC. The frequency change followed the following order of monolayer-anesthetic interactions: DHP-halothane <DPPC-halothane <DHP-enflurane <DPPC-enflurane. These re-sults showed that the response of anesthetics to the monolayers i.e. the physisorption not only depends on the anesthetic structure, the type of anesthetic hydrate formed, but also the hydrophilic polar group structure of the monolayer or the monolayer/water interface had an important role in physisorption