Bending contributions hydration of phospholipid and block copolymer membranes: Unifying correlations between probe fluorescence and vesicle thermoelasticity

The temperature-dependent hydration of several pure, net-neutral membranes was studied by spectroscopic shifts of the amphiphilic probe 6-dodecanoyl-2 -(dimethylamino)-naphthalene (LAURDAN). A calibration scale for local polar ity was first established with LAURDAN in various organic solvents. For pho sphatidylcholine membranes above the gel-phase temperature, the log(local p olarity) was found to be inversely related to the bending-renormalized area elastic moduli.-A novel self-assembled polymer membrane broadens the corre lation, and the absence of any discontinuity in local polarity with tempera ture indicates that the polymer membrane is in a suitable fluid phase. Sepa rate correlations between the log(hydraulic permeability x membrane thickne ss) and the bending modulus, but not the area elastic moduli, strongly sugg est that, local bending fluctuations pf a membrane are coupled to membrane hydration. The results identify the importance of a collective response, me mbrane flexure, to a molecular-scale property, specifically, hydration.