Abstract

The effects of increasing gramicidin D (gD) concentration on the partial specific volume, vo, and the adiabatic
compressibility coefficient of the lipid, βS
lipid of the bilayer reveals a continual decrease in ?o and βS
lipid (within the
range of concentration studied) with concentration, except between 5 and 7.5 %, where a very slight decrease was
observed. At gD concentrations higher than 5 mol%, the isothermal compressibility coefficient, βT
lipid is greater than
βS
lipid at the gel-fluid region by ? 10 – 20 % in the entire temperature range covered. The maximum value of the
relative volume fluctuation of 12 % is reached for DPPC at the main transition, and is strongly dampened upon
addition of gD. A gradual decrease in the calculated relative volume fluctuations with gD concentration at Tm is
observed between concentrations 1 and 10 mol%.

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