We develop an alternative polymer model to capture entanglements within the dissipative particle dynamics (DPD) framework by using simplified bond-bond repulsive interactions to prevent bond crossings. We show that structural and thermodynamic properties can be improved by applying a segmental repulsive potential (SRP) that is a function of the distance between the midpoints of the segments, rather than the minimum distance between segments. The alternative approach, termed the modified segmental repulsive potential (mSRP), is shown to produce chain structures and thermodynamic properties that are similar to the softly repulsive, flexible chains of standard DPD. Parameters for the mSRP are determined from topological, structural, and thermodynamic considerations. The effectiveness of the mSRP in capturing entanglements is demonstrated by calculating the diffusion and mechanical properties of an entangled polymer melt.

Molecular dynamics simulations were used to study the interactions of four green tea catechin compounds with lipid bilayers. Reported studies have shown that catechins are linked to beneficial health effects, specifically those related to interactions with the cell membrane. To better understand the molecular interaction of catechins with membranes, simulations were carried out of interactions of four catechin molecules [epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)] with a 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) lipid bilayer. The simulations show that catechins possess a strong affinity for the lipid bilayer. Some are absorbed into the bilayer. The molecular structure and aggregated condition of the catechins significantly influences their absorption, as well as their ability to form hydrogen bonds with the lipid headgroups. Insight into these molecular interactions helps to distinguish the structure-function relationship of the catechins with lipid bilayers and provides a foundation for a better understanding of the role of catechins in biological processes.

Molecular dynamics simulations were performed to study the interactions of bioactive catechins (flavonoids) commonly found in green tea with lipid bilayers, as a model for cell membranes. Previously, multiple experimental studies rationalized catechin's anticarcinogenic, antibacterial, and other beneficial effects in terms of physicochemical molecular interactions with the cell membranes. To contribute toward understanding the molecular role of catechins on the structure of cell membranes, we present simulation results for seven green tea catechins in lipid bilayer systems representative of HepG2 cancer cells. Our simulations show that the seven tea catechins evaluated have a strong affinity for the lipid bilayer via hydrogen bonding to the bilayer surface, with some of the smaller catechins able to penetrate underneath the surface. Epigallocatechin-gallate (EGCG) showed the strongest interaction with the lipid bilayer based on the number of hydrogen bonds formed with lipid headgroups. The simulations also provide insight into the functional characteristics of the catechins that distinguish them as effective compounds to potentially alter the lipid bilayer properties. The results on the hydrogen-bonding effects, described here for the first time, may contribute to a better understanding of proposed multiple molecular mechanisms of the action of catechins in microorganisms, cancer cells, and tissues.