Postprint version. Published in Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 154, Issue 1-2, August 1, 1999, pages 175-185.
NOTE: At the time of publication, the author Derek E. Gragson was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1016/S0927-7757(98)00895-4.
Vibrational sum frequency spectroscopy has been used in conjunction with dynamic surface tension measurements to study formation of a 1,2-dilauroyl-sn-phosphatidylcholine (DLPC) monolayer at a water–carbon tetrachloride interface. Surface tension measurements show that an aqueous solution of liquid crystalline phosphocholine vesicles (4.5 μM DLPC) requires several hours to form a tightly packed, fully equilibrated monolayer of DLPC monomers. Vibrational spectra of the interfacial region at different stages in the monolayer formation process indicate that the solvent structure undergoes dramatic re-organization as the monolayer forms. Initial adsorption of DLPC monomers severely disrupts the interfacial hydrogen bonding. Intensity in the OH stretching region oscillates in a systematic fashion during the first 2 h of monolayer formation before finally settling to a level characteristic of the fully equilibrated monolayer. Frequency shifts of the OH stretching vibration show that water molecules with their C2 axes aligned parallel to the interface experience a markedly different environment than those water molecules aligned perpendicular to the interface. This difference is attributed to the effect of the adsorbed, zwitterionic DLPC head-groups which, if aligned parallel to the interface, can stabilize in-plane water molecules.
Biochemistry | Chemistry