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| Max Berkowitz, University of North Carolina |
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Max Berkowitz received his M.Sc. in Physics from Novosibirsk State University in 1972 and his Ph.D. in Physical Chemistry from the Weizman Institute of Science in 1979. After a year and a half of a postdoctoral fellowship at Purdue University and three years work as a Visiting Assistant Professor at the University of Houston, he moved to the University of North Carolina (UNC) at Chapel Hill where he is now a Professor.
During twenty years at UNC the group of Max Berkowitz has been involved in studies of aqueous solutions in different environments using molecular dynamics computer simulation technique. Some interesting and sometimes surprising results were obtained from this work. Max and his former postdoctoral associate Lalith Perera demonstrated that small ions such as chloride, bromide or iodide are located on the surfaces of water clusters. Work on a study of a field dependent dielectric constant of water performed with his former student In-Chul Yeh resulted in a prescription for an effective use of a three dimensional Ewald summation algorithm for the case of slab geometry. Max also collaborated with Prof. R.G. Parr on establishing chemical notions in quantum Density Functional Theory such as hardness kernel, softness kernel etc. and the relationship between these notions. The study of hydration forces acting between biomembranes triggered his interest in the properties of these membranes.
Max Berkowitz is a Fellow of the American Physical Society.
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Complexes Between Lipids in Bilayers
Max Berkowitz, University of North Carolina
We postulate that hydrogen bonding plays an important role in condensation (complexation) processes taking place in biological membranes. To illustrate this postulate we consider two cases when simulations were performed on bilayers containing different mixtures of lipids. In the first case a mixed bilayer containing dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylserine (DPPS) at a ratio of 5:1 was simulated in NaCl electrolyte solution. Direct NH---O and CH---O hydrogen bonding between lipids was observed to serve as the basis of interlipid complexation. In the second case the simulations were performed on a DPPC-cholesterol bilayer mixture and a dilauroylphosphatidylcholine (DLPC)-cholesterol bilayer mixture, both having a cholesterol concentration of 40 mol %. Complexation of the simulated phospholipids with cholesterol was observed and visualized, exhibiting 2:1 and 1:1 stoichiometries. The most popular complex was found to be 1:1 in the case of DLPC, whereas the DPPC system carries a larger population of 2:1 complexes. The CH---O hydrogen bond plays a crucial role in the formation of these complexes as well. The aggregation and extension of a hydrogen-bonded network implies a possible means by which phospholipid:cholesterol domains form.
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