Submitted on October 14, 2004
Revised on November 26, 2004
Accepted on December 7, 2004
Interaction of long-chain nicotinates with dipalmitoylphosphatidylcholine (DPPC)
Hans-Joachim Lehmler, Azarih Fortis-Santiago, Dhananjaya Nauduri, and Paul M. Bummer
Department of Occupational and Environmental Health, University of Iowa, Iowa City, Iowa 52242
Corresponding Author: hans-joachim-lehmler{at}uiowa.edu
The interaction of four long-chain nicotinates, compounds which are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine was investigated in monolayers at the air-water interface and in fully hydrated bilayers. For the monolayer studies, the compression isotherms of mixtures of the respective nicotinate with DPPC were recorded at various compositions on a hydrochloric acid subphase (pH = 1.9 to 2.1, 37 ± 2°C). The headgroup of the nicotinates (24-29Å2/molecule) is larger compared to the hydrophobic tail (20Å2/molecule). The pure nicotinates exhibit a temperature- and chain-length dependent transition from an expanded to a condensed phase. Analysis of the concentration dependence of the average molecular area at constant film pressure and the concentration dependence of the breakpoint of the phase transition from the expanded to the condensed state suggests that all four DPPC-nicotinate mixtures are partially miscible at the air-water interface. Although a complex phase behavior with several phase transitions was observed, the Differential Scanning Calorimetry (DSC) studies of the four mixtures are also indicative of partial miscibility of DPPC and the respective nicotinate. Overall, the complex phase behavior most likely results from the head-tail mismatch of the nicotinates and the geometric packing constraints in the two-component lipid bilayer.
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