Thermodynamics and biological properties of the aqueous solutions of new glucocationic surfactants

Thermodynamic properties of aqueous solutions of newly synthesized compounds, namely, N-[2-(beta-D- glucopyranosyl)ethyl]-N,N-dimethyl-N-alkylammonium bromides with hydrophobic tails of 12(C(12)DGCB) and 16 (C(16)DGCB) carbon atoms, determined as a function of concentration by means of direct methods, are reported here. Dilution enthalpies, densities, and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes, and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudophase-transition approach. From a comparison with the corresponding acetylated compounds N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)ethyl] -N,N-dimethyl-N-dodecylammonium bromide (C(12)AGCB) and N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-hexadecylammonium bromide (C(16)AGCB), the role played in the micellization process by the acetylated glycosyl moiety was inferred: it enhances the hydrophobic character of the molecule and lowers the change in enthalpy of micelle formation by about 1.5 kJ mol(-1). By comparing the volume Of C(12)DGCB with those of DEDAB and DTAB, the volumes taken up by the (beta-D-glucopyranosyl)ethyl and beta-D-glucopyranosyl groups were found to be 133 and 99 cm(3) mol(-1), respectively. Regarding the interaction with DPPC membranes, it seems that the sugar moiety of the hexadecyl deacetylated compound gives rise to hydrogen bonds with the oxygen atoms of the lipid phosphates, shifting the phase transition of DPPC from a bilayer gel to a bilayer liquid crystal to lower temperatures. C(16)AGCB induces significantly greater changes than C(16)DGCB in the structure of liposomes, suggesting the formation of domains. The interaction is strongly enhanced by the presence of water. Neither compound interacts strongly with DNA or compacts it, as shown by EMSA assays and AFM images. Only C(16)AGCB is able to deliver little DNA inside cells when coformulated with DOPE, as shown by the transient transfection assay. This might be related to the ability Of C(16)AGCB to form surfactant-rich domains in the lipid structure.