(Georgia Institute of Technology, 1993-05-01)
Levine, Yehudi K.; Kolinski, Andrzej; Skolnick, Jeffrey
A Monte Carlo dynamics (MCD) scheme has been applied in a study of the effects of unsaturated double bonds on the internal conformational dynamics and orientational order of hydrocarbon chains arranged in a monolayer on the surface of an impenetrable interface. The MCD algorithm makes use of the high coordination {2 1 0} lattice for the representation of both sp³ and sp² valence states of the carbon atoms. The chain dynamics are considered to arise from a superposition of local conformational rearrangements. The simulations reproduced the principal features of the experimentally observed order parameter profiles of the C–H bonds on taking into account the intramolecular conformational energy of the molecules and excluded volume effects. The results show that the introduction of a rigid, planar, unsaturated segment enhances the orientational order in the monolayer. The extent of the enhancement is larger for the trans unsaturated chains than for the cis unsaturated ones. The increase in orientational order is accompanied by a marked increase in the effective rotational correlation times, indicating that the unsaturated segments undergo slow and restricted motion. In addition, the C–H bonds of the saturated chain segment between the cis double bond and the headgroup of the chain undergo slower motions than the corresponding vectors in the saturated and trans unsaturated chains. This arises from the anchoring of the headgroup at the impenetrable monolayer interface.
(Georgia Institute of Technology, 1992-07-15)
Rey, Antonio; Kolinski, Andrzej; Levine, Yehudi K.; Skolnick, Jeffrey
Brownian dynamics simulations of isolated 18-carbon chains have been performed, both for
saturated and unsaturated hydrocarbons. The effect of one or several (nonconjugated)
double bonds on the properties of the chains is discussed in terms of both equilibrium and
dynamic properties. The introduction of a cis double bond increases the relaxation
rates of the unsaturated chain with respect to the saturated alkane. On the other hand,
coupling effects in the torsional transitions around a trans double bond make the dynamics of
this unsaturated chain very similar to the saturated one. Based on these results, the
parameters and moves of a dynamic Monte Carlo algorithm are tuned to reproduce the
observed behavior, providing an efficient method for the study of more complicated systems.
(Georgia Institute of Technology, 1991-09-01)
Levine, Yehudi K.; Skolnick, Jeffrey; Kolinski, Andrzej
A Monte Carlo dynamics study of the motions of hydrocarbon chains containing cis double bonds is presented. The simulations utilize the high-coordination {2 1 0} lattice for the simultaneous representation of the tetrahedrally bonded carbon atoms and the planar unsaturated segment. Results on single chains undergoing free motion in space and tethered to an impenetrable planar interface are reported. The introduction of a cis double bond into a hydrocarbon chain induces a slowdown in the dynamics. The simulations show this to be a universal result independent of the representation of the chain on the lattice. In contrast, polyunsaturated chains are found to be more mobile than saturated ones.