The Department of Chemistry at the University of North Carolina at Chapel Hill, offers a wide range of research opportunities in theoretical and experimental physical chemistry. Our program has broadened from its traditional areas of excellence in molecular chemical physics to include research activities in biophysical and surface chemistry, and materials and environmental sciences. Experimental efforts within these areas utilize state-of-the-art instrumentation, such as high-resolution and ultra-fast laser systems, molecular beam techniques, mass spectrometry, ion-scattering, scanning probe microscopy, and magnetic resonance spectrometry.
Research in theoretical chemistry involves developing computational models of chromatin, the structure of complex fluids, and polymer dynamics. Students at UNC have access to high-performance computer workstations, as well as RENCI/UNC Research Computing, which is home to one of the best computing facilities in the world, including a 4160-processor Dell Linux cluster.
To study the interaction between melittin peptides and lipid bilayer, researchers in the Berkowitz Group, as published in the Journal of Physical Chemistry B, performed coarse-grained simulations on systems containing melittin interacting with a bilayer containing zwitterionic dipalmitoylphosphatidylcholine (DPPC) and anionic palmitoyloleoylphosphatidylglycerol (POPG) phospholipids in a 7:3 ratio. Eight different systems were considered: four at low and four at high peptide to lipid (P/L) ratios. In case of low P/L ratio the team did not observe any pore creation in the bilayer. In two out of four of the simulations with the high P/L ratio, appearance of transient pores in the bilayer was observed. These pores were created due to an assembly of 3–5 melittin peptides.
Not all of the peptides in the pores were in a transmembrane conformation; many of them had their termini residues anchored to the same leaflet, and these peptides assumed bent, U-shaped, conformations. We propose that when an assembly of melittin peptides creates pores, such an assembly acts as a "wedge" that splits the bilayer. The appearance of transient pores together with the translocation of peptides across the membranes is consistent with the mechanism proposed to explain graded dye leakage from large vesicles in the presence of melittin.
Femtosecond pump–probe microscopy is used by researchers in the Papanikolas Group to investigate the charge recombination dynamics at different points within a single needle-shaped ZnO rod. As described in The Journal of Physical Chemistry B, recombination in the tips of the rod occurs through an excitonic or electron–hole plasma state, taking place on a picosecond time scale. Photoexcitation in the larger diameter sections of the interior exhibit dramatically slower recombination that occurs primarily through defects sites, i.e., trap mediated recombination.
Transient absorption imaging shows that the spatial variation in the dynamics is also influenced by the cavity resonances supported within the hexagonal cross section of the rod. Finite element simulations suggest that these optical resonator modes produce qualitatively different intensity patterns in the two different locations. Near the end of the rod, the intensity pattern has significant standing-wave character, which leads to the creation of photoexcited carriers in the core of the structure. The larger diameter regions, on the other hand, exhibit intensity distributions in which the whispering gallery (WG) mode character dominates. At these locations, the photoexcited carriers are produced in subsurface depletion zone, where the internal fields separate the electrons and holes and lead to a greater degree of trap recombination on longer time scales.
Free Energy Barrier for Melittin Reorientation from a Membrane-Bound State to a Transmembrane State. Sheeba J. Irudayam, Tobias Pobandt, and Max L. Berkowitz. J. Phys. Chem. B, 2013, 117 (43), pp 13457–13463.
Interplay between Vibrational Energy Transfer and Excited State Deactivation in DNA Components. Brantley A. West, Jordan M. Womick, and Andrew M. Moran. J. Phys. Chem. A, 2013, 117 (29), pp 5865–5874.
Uncovering Molecular Relaxation Processes with Nonlinear Spectroscopies in the Deep UV. Brantley A. West, Brian P. Molesky, Paul G. Giokas, Andrew M. Moran. Chemical Physics, Volume 423, 23 September 2013, Pages 92-104.
Gas Phase Acidity Measurement of Local Acidic Groups in Multifunctional Species: Controlling the Binding Sites in Hydroxycinnamic Acids. Andres Guerrero, Tomas Baer, Antonio Chana, Javier González, and Juan Z. Dávalos. J. Am. Chem. Soc., 2013, 135 (26), pp 9681–9690.
Melittin Creates Transient Pores in a Lipid Bilayer: Results from Computer Simulations. Kolattukudy P. Santo , Sheeba J. Irudayam , and Max L. Berkowitz. J. Phys. Chem. B, 2013, 117 (17), pp 5031–5042.
Pump–Probe Microscopy: Spatially Resolved Carrier Dynamics in ZnO Rods and the Influence of Optical Cavity Resonator Modes. Brian P. Mehl, Justin R. Kirschbrown, Michelle M. Gabriel, Ralph L. House, and John M. Papanikolas. J. Phys. Chem. B, 2013, 117 (16), pp 4390–4398.
Interfacial Energy Conversion in RuII Polypyridyl-Derivatized Oligoproline Assemblies on TiO2. Da Ma, Stephanie E. Bettis, Kenneth Hanson, Maria Minakova, Leila Alibabaei, William Fondrie, Derek M. Ryan, Garegin A. Papoian, Thomas J. Meyer, Marcey L. Waters, and John M. Papanikolas. J. Am. Chem. Soc., 2013, 135 (14), pp 5250–5253.
Two-Dimensional Electronic Spectroscopy in the Ultraviolet Wavelength Range. Brantley A. West, and Andrew M. Moran. J. Phys. Chem. Lett., 2012, 3 (18), pp 2575–2581.
Direct Imaging of Free Carrier and Trap Carrier Motion in Silicon Nanowires by Spatially-Separated Femtosecond Pump–Probe Microscopy. Michelle M. Gabriel, Justin R. Kirschbrown, Joseph D. Christesen, Christopher W. Pinion, David F. Zigler, Erik M. Grumstrup, Brian P. Mehl, Emma E. M. Cating, James F. Cahoon, and John M. Papanikolas . Nano Lett., Article ASAP, DOI: 10.1021/nl400265b.
Tunable Energy Transfer Rates via Control of Primary, Secondary, and Tertiary Structure of a Coiled Coil Peptide Scaffold. Dale J. Wilger, Stephanie E. Bettis, Christopher K. Materese, Maria Minakova, Garegin A. Papoian, John M. Papanikolas, and Marcey L. Waters. Inorg. Chem., 2012, 51 (21), pp 11324–11338.