Prof. Melissa A. Pasquinelli

The focus of our research is to design and utilize a variety of multiscale simulation tools at the molecular to mesoscopic scales for applications in nanotechnology, textiles, biomedical engineering, and toxicology. These multiscale modeling tools relate the physical and chemical interactions of molecules such as polymers and proteins to (1) their functional properties, including biological, electrical, mechanical, biocompatible, and toxicological; and (2) their role in processes, such as molecular recognition and self-assembly mechanisms.

Current projects include:

* Optimize the mechanical and physical properties of nanocomposites containing carbon nanotubes.

* Nanostructured membranes for energy applications.

* Simulations of the stain removal process.

* Development of software tools for deriving structure-property relationships.

* Study the toxicology of textiles and materials based on nanotechnology by predicting their effects on human health.

Postdoctoral Research:
Many biological processes are mediated by electron transfer (ET) reactions, including respiration, hormone biosynthesis, DNA repair, and drug metabolism. We are developing and utilizing computational methods that connect the electron transfer process to other dynamic processes. For fixed molecular geometries, electron transfer theories are relatively well established, and we are exploring the extension of these theories to systems with large-scale structural reorientation. Biological electron transfer is frequently coupled to protein conformational changes, such as protein-protein docking. These conformational changes can be triggered by physiochemical signals; a common regulatory signal for enzyme activity is protein phosphorylation. Whether protein phosphorylation affects intermolecular electron transfer has not been thoroughly investigated. We are using our computational methods to study how protein phosphorylation control affects an electron transfer chain in a mitochondrial steroid hydroxylase system, adrenodoxin (AdX) with its cytochrome P450 redox partners, CYP11A1 and CYP11B1.

Thesis Research:
We developed a computational technique, called the effective particle approach, that enables structure-property relationships to be extracted from quantum chemistry calculations. This approach views an excited state as containing one or more effective particles that move on an energy landscape with a position-dependent effective mass. For the 1Bu state of conjugated polymers, the effective particle is an exciton, or bound electron-hole pair. The form of the particle is defined by the relative motion of the electron and hole, and its delocalization is described by its center-of-mass motion. This technique yields computational savings as well as interpretive advantages. Effective particles are used to generate energy landscapes and effective mass profiles that provide insight into how the structure of a material relates to its photophysical properties. Calculations on a carbonyl defect in polyacetylene and PPV quantify the degree to which the carbonyl attracts an electron and repels a hole, thereby promoting charge separation that is strongly influenced by dielectric solvation. Landscapes and effective masses for a meta defect and torsional disorder in PPV reveal that even relatively small torsional defects have fairly large effects on the energy and reduced mass landscapes. Combined with a scattering formalism, these effective particles were used to investigate whether biexcitons are stable and can be observed in two-photon spectroscopy. The results indicate that biexciton states are not stable in the limit of long chains but could be stabilized on short chains by confinement effects.

Other Research Interests:
- Interrelationships among the structure, dynamics, and function of proteins and other materials, and bioinformatic approaches to probing these connections
- The electronic, optical, and magnetic properties of biological systems and molecular electronics
- Drug design and delivery
- Excited state processes, including photoinduced proton/electron transfer, isomerization, and other structural reorientations
- Nonlinear optics

Experienced with molecular simulation techniques such as Brownian dynamics, electronic structure theory, configuration interaction theory, Monte Carlo sampling, protein electrostatics and interactions, geometry optimization, and PATHWAYS model of electron transfer

Proficient in C++, knowledgeable in object-oriented design, and familiar with Fortran

Skilled with many scientific software programs, including Gaussian98, University of Houston Brownian Dynamics (UHBD), MOPAC, Cerius2, Sybyl, Origin, Mathcad, Mathematica, Maple

Experienced with Windows 2000 and Linux

Skilled with LaTeX and HTML

Strong verbal and written communication abilities