Conformation, orientation and dynamics of dodecylphosphocholine in micellar aggregate: A 3.2 ns molecular dynamics simulation study

Abstract

A dodecylphosphocholine micelle of 86 monomers with 5776 water molecules has been simulated under NPT conditions for 3.2 ns using GROMACS2.0. The micelle was found to be very dynamic. Some of the C-C bonds, independent of their position in the DPC monomer, adopt <i>gauche </i>conformation and the <i>trans </i>↔ <i>gauche </i>transitions are quite frequent. An average of about 11 % of the C-C bonds in the micelle are observed to be in the <i>gauche </i>conformation (i.e., |dihedral angle|<120°). The terminal methyl groups are randomly distributed all over the micelle whereas the nitrogen atom of phosphocholine headgroup atoms is restricted to the interface region. Some of the monomers were found to lie on the surface. The shape of micelle, influenced by the packing considerations, shows deviations from spherical shape. The phosphocholine headgroup is well solvated and there is no water penetration into the micelle core. The overall features of the micelle of 86 DPC monomers conforms to the lattice model of micelle proposed by Dill and Flory [Dill K A, Flory P J

(1981)<i> Proc Natl Acad </i>Sci USA<i> </i>78, 676-680] and is similar to DPC micelles of smaller aggregate sizes except for the positional preference of the C-C bonds for the <i>gauche </i>conformation and the <i>trans ↔ gauche </i>transition times [Tieleman D P, van der Spoel D, Berendsen H J C (2000) <i>J Phys Chem B </i>104,6380-6388; Wymore T, Gao X F, Wong T C (1999) <i>J Mol</i> <i>Slrucf (Theochem) </i>485-486, 195-210]. It appears that packing considerations play a predominant role in determining the shape and dynamics of the micelle.

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