In aqueous media, phospholipids are self-assembled into lipid bilayers. In biological membranes, proteins are hidden in lipid bilayers. It is well known that each protein and lipid have distinct characters. From the structures and functions study, it is revealed that different types of intermolecular interactions, viz. H-bond, van der Waals, hydrophobic, hydrophilic interactions play a significant role in the ability of these molecules. The DSC and dielectric spectroscopic techniques were used to study the gel-liquid crystal phase transition and the dynamics of DPPC molecules in aqueous media. The gel-gel pre-transition and gel-liquid crystal main transition were found from DSC study are strongly supported by x-ray measurement studied by Janiak et al. [Biochemistry, 15, 4575 (1976)] and present dielectric study from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions. From the complex dielectric study, four relaxation processes were observed from 40 Hz to 30 GHz frequency, which were ascribed to different molecular mechanisms, related to the structural units of the system. Surprisingly, relaxation process 3 observed near 10 MHz region due to motion of ions, which are related to the molecular motion of the lipid makes the bridge between lipid membrane and non-biological systems like ferroelectric liquid crystals. The process 3 is analogous to the variation of the soft mode observed in ferroelectric liquid crystals which was detected close to smectic-C*–smectic-A phase transition region. It is also interesting to find some physical properties of lipids such as depression of melting point, change of bilayer thickness, effect of domain structure, pH, etc. are strongly influenced by anesthetic molecules.
Dr. Shyamal Kumar Kundu is a Professor and Division chair in the Department of Physics, Galgotias University, Uttar Pradesh, India. Prior to that, he received Ph.D. degree from Indian Association for the Cultivation of Science, Kolkata, India. He was a postdoc at NCTU, Taiwan 2005, JSPS postdoc at Tokai University, Japan (2005-2007), Research Associate at Neutron Science Laboratory, The University of Tokyo, Japan (2007-2009), Research Scientist at the Jülich Center for Neutron Science (ICS-1), Forschungszentrum Jülich, Germany (2009-2012). He has received “Young Scientist Award” by Materials Research Society, Kolkata, India, “JSPS award” by JSPS, the Government of Japan and also “Bharat Ratna Dr. Abdul Kalam Gold Medal Award” by Global Economic Progress and Research Association, India. His scientific interests focus on the physical properties and the molecular dynamics of complex molecular systems like biomaterials, liquid crystals, gels, star like colloids and micelles. His expertise areas are Broadband Dielectric Spectroscopy, Rheology, Neutron Scattering and Light Scattering.