Eugene F. Brown

Molecular binding of catechins to biomembranes: relationship to biological activity.

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 Study on the Biophysical Interactions of Seven Green Tea Catechins with Lipid Bilayers of Cell Membranes

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 catechins 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.

Characteristics of thermal conductivity in classical water models

The thermal conductivities of common water models are compared using equilibrium (EMD) and non-equilibrium molecular dynamics (NEMD) simulation. A complete accounting for electrostatic contributions to the heat flux was found to resolve the previously reported differing results of NEMD and EMD Green-Kubo measurements for the extended simple point-charge (SPC/E) model. Accordingly, we demonstrate the influence of long-range electrostatics on the thermal conductivity with a simple coulomb cutoff, Ewald summation, and by an extended particle-particle particle-mesh method. For each water model, the thermal conductivity is computed and decomposed in terms of frequency-dependent thermodynamic and topological contributions. The rigid, three-site SPC, SPC/E, and transferable intermolecular potential (TIP3P-Ew) water models are shown to have similar thermal conductivity values at standard conditions, whereas models that include bond stretching and angle bending have higher thermal conductivities.

Online Course Design Informed by Students’ Epistemic Beliefs: A Case Study of a Thermodynamics Course

Online offerings of abstract engineering courses such as thermodynamics provide a medium to present course material using pedagogy that employs problem-based learning (PBL). This shift requires a student-centered approach to course design and delivery that addresses several key elements in the educational setting, including students’ self-efficacy as it relates to problem-solving and students’ epistemic beliefs as they relate to interacting with peers, instructors, and instruction. This paper reports results from a mixed-method study that collected data useful in design of an online course focused on teaching problem solving skills among students. The data were collected through qualitative and quantitative methods used to determine how students approach problem solving, the role of instructor in facilitating problem solving, and the role of peers and students’ use of technology as it relates to accomplishing course work related to problem solving. Results reveal that students are confident in their problem-solving skills but rely primarily on the instructor to show them how to solve problems. Analysis and discussion focus on how to change the manner in which the content of the course is designed and presented to improve students’ self-efficacy in problem solving and students’ epistemic beliefs through active engagement with materials and collaboration with peers and instructor.Copyright

Re-Establishment of the Nuclear Engineering Program at Virginia Tech

One of the first nuclear engineering programs in the United States was established at Virginia Tech in the mid-1950’s and continued until the mid-1980’s when it was abandoned due to a drop both in student interest and government support. In 2006, as a result of interest shown by the nuclear industry in Virginia, discussions were undertaken that led to the approval to offer Master’s and Doctorate Degrees in nuclear engineering in 2013. In parallel with these efforts, we began teaching undergraduate courses in anticipation of offering a minor in nuclear engineering to all Virginia Tech engineering and science students. Currently we have 140 undergraduate students taking nuclear engineering classes, nuclear engineering undergraduate research hours, and participating in nuclear-engineering-related senior design activities.Our program has been conceived and designed with the objective of providing the nuclear engineering workforce required to address the most important nuclear-related issues of our time including: enhancing the safe and productive use of nuclear energy; contributing to the development of advanced technologies for national and international nuclear security and safeguards; developing advanced medical devices for nuclear diagnostics and therapy; and the establishment of effective policies for the utilization of nuclear energy and its regulation.The Master’s degree program involves 7 courses and the equivalent of two semesters of thesis research for a total of 30 credit hours. The PhD program, which builds on the Master’s degree program, requires 5 additional courses, and the equivalent of 4 semesters of dissertation research for a total of 60 credit hours beyond the Master’s degree. The curriculum is supported by a rigorous, benchmarked assessment and evaluation process to assure that the goals of the program are attained.Currently five faculty members support the nuclear engineering program, and typical total enrollment in our graduate programs runs between 35 and 50 students. When we reach full strength, with the addition of two more nuclear engineering faculty members, we expect to be graduating 12 Master’s students and 7 PhD students per year.Copyright

A Study of Nanoparticle-Enhanced Heat Transfer

The study of the heat transfer characteristics of nanofluids, i.e. fluids that are suspensions of nanometer size particles, has gained significant attention in the search for new coolants that can effectively service a variety of needs ranging from the increasing heat transfer demands of ever smaller microelectronic devices to mitigating the effects of loss of coolant accidents in nuclear power plants. Experimental data has shown large increases in thermal conductivity and associated increases in the level of critical heat flux in nuclear reactors; however, in some cases the range of the applicability of the experimental results is uncertain and there is a lack of a theory by which this can be resolved. Complicating the theoretical description of heat transfer in nanofluids is the fact that fluids in the vicinity of the nanoparticles are a complex combination of phase transition, interfacial, and transport phenomena. This paper describes a study in which molecular dynamics simulations were used to enhance the understanding of the effect of nanoparticles on heat transfer. The molecular dynamics (MD) simulations presented here model a Lennard-Jones fluid in a channel where the walls are maintained at different temperatures. The heat flux is calculated for a variety of nanoparticle sizes and concentrations. The results are compared to experimental data in order to provide information that will more confidently bound the data and provide information that will guide the development of more comprehensive theories. We also anticipate that this work could contribute to the design of biosensors where suspended molecules are transported through micro- and nano-channels in the presence of heat transfer.Copyright

A Diffusion-Based Approach for Nanobead Drag Forces

A central process of the Bead ARray Counter (BARC) biosensor involves propelling a dilute solution of streptavidin-coated micron-scale beads through water. It is desirable to downsize these beads, leading to a basic engineering problem: What is the drag force acting on a nanoscale bead having an unknown hydrodynamic boundary condition? We use molecular dynamics simulation to estimate the drag force acting on a hypothetical biosensor “nanobead” without assuming a no-slip condition or a user-supplied slip parameter.Copyright