Bulletin of the American Physical Society
2007 Joint Fall Meeting of the Texas Sections of the APS and AAPT; Zone 13 of SPS
Volume 52, Number 16
Thursday–Saturday, October 18–20, 2007; College Station, Texas
Session F4: GEN2: Biological, Chemical and General Physics |
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Chair: Jaan Laane, Texas A&M University Room: Rudder Tower 504 |
Friday, October 19, 2007 3:30PM - 3:42PM |
F4.00001: The Structure of the Metal Transporter Tp34 and its Affinity for Divalent Metal Ions Gregory Knutsen, Ranjit Deka, Chad Brautigam, Diana Tomchick, Mischa Machius, Michael Norgard Tp34 is periplasmic membrane protein of the nonculitvatable spirochete \textit{Treponema pallidum}, the pathogen of syphillis. It was proposed that Tp34 is a divalent metal transporter, but the identity of the preferred metal ion(s) was unclear. In this study we investigated the ability of divalent metal ions to induce rTp34 dimerization using hydrodynamic techniques and determine the crystal structure of metal bound forms. Using analytical ultracentrifugation sedimentation velocity experiments, we determined that cobalt is superior to nickel at inducing the dimerization of rTp34. rTp34 was crystallized and selected crystals were incubated at a pH 7.5 with CuSO$_{4}$ and NiSO$_{4}$. Diffraction experiments were conducted and the processed electron density maps showed that copper was bound to the major metal binding site as well as to three additional minor binding sites. By contrast nickel was only bound to the major metal binding site in one monomer and to three additional minor sites. These results along with previous findings support evidence of Tp34 being involved with metal transport and/or iron utilization. [Preview Abstract] |
Friday, October 19, 2007 3:42PM - 3:54PM |
F4.00002: Maximum Entropy Principle for the Microcanonical Ensemble Donald Kobe, Michele Campisi We derive the microcanonical ensemble from the Maximum Entropy Principle using the phase space volume entropy of Gibbs. Maximizing (or extremizing) the entropy with respect to a general probability distribution and using the constraints of normalization and average energy, we obtain the condition that the energy is a constant E that characterizes the microcanonical ensemble. We justify the phase space volume entropy of Gibbs by showing that the combined first and second laws of thermodynamics is satified, a condition that Boltzmann called orthodicity. We also show that the entropy calculated from the Tsallis q-escort probability distribution approaches the phase space volume entropy in the limit as q approaches minus infinity. Our approach is in contrast to the commonly accepted derivation of the microcanonical ensemble from the Maximum Entropy Principle that assumes a priori that the energy E is a constant. Then the Shannon information theory entropy with only the constraint of normalization gives Laplace's Principle of Insufficient Reason for the states with the constant energy E. [Preview Abstract] |
Friday, October 19, 2007 3:54PM - 4:06PM |
F4.00003: Ultraviolet Absorption Spectra and the Quasi-planarity of Pyridine and its d$_{5}$ Isotopomer in its S$_{1}(\pi $,$\pi $*) Excited State Praveen Boopalachandran, Kathleen McCann, Jaan Laane The ultraviolet absorption spectra of pyridine-d$_{0}$ and --d$_{5}$ vapor have been recorded and analyzed in the 32,000 to 38,000 cm$^{-1}$ region. The electronic band origins are at 34,767 (d$_{0})$ and 34,945 cm$^{-1}$ (d$_{5})$ for the two isotopomers. For both molecules series of transitions for $\nu_{18}$, the out-of-plane ring-bending vibration, in the excited electronic state can be observed, and a one-dimensional potential energy function of the form V = ax$^{4}$ -- bx$^{2}$ can be determined, where x is the out-of-plane vibrational coordinate. In the S$_{0}$ electronic ground state pyridine is rigid and planar with $\nu_{18}$ at 403 cm$^{-1}$. In the S$_{1}(\pi $,$\pi $*) excited state $\nu_{18}$ drops to 59.5 cm$^{-1}$ and the molecule becomes floppy with a tiny barrier to planarity of 3 cm$^{-1}$ resulting in a quasi-planar structure. [Preview Abstract] |
Friday, October 19, 2007 4:06PM - 4:18PM |
F4.00004: Laser Induced Fluorescence and Ultraviolet Absorption Spectra, DFT Calculations, and Structure of 1,3-Benzodioxan Kathleen McCann, Martin Wagner, Jaebum Choo, Jaan Laane The laser induced fluorescence spectra, both excitation and dispersed, of jet-cooled 1,3-benzodioxan along with ultraviolet absorption spectra of the ambient temperature vapors have been recorded and analyzed. The focus of the study was on the low-frequency out-of-plane vibrational modes which are useful for determining the potential energy surface which governs the molecular structure. In the S$_{0}$ electronic ground state these have vibrational frequencies of 107.6 cm$^{-1}$ (ring-bending), 157.3 cm$^{-1}$ (ring-twisting), 275.1 cm$^{-1}$ (ring-flapping), and 350.2 cm$^{-1}$ (ring-twisting at the benzene ring). The corresponding values for the S$_{1}(\pi $,$\pi $*) excited state are 96.3, 102.2, 194.6, and 255.8 cm$^{-1}$ with the lower values reflecting a less rigid ring structure. DFT calculations predict a twisted structure and a barrier to planarity of 3475 cm$^{-1}$ for the S$_{0}$ ground state and this is consistent with the experimental data. [Preview Abstract] |
Friday, October 19, 2007 4:18PM - 4:30PM |
F4.00005: Exploration of Functionalized Nanoparticles for Fingerprint Detection Jacob Ajimo, Lun Ma, Xing Zhang, Kwan Cheng, Wei Chen We report an exploratory study on the use of water soluble luminescent nanoparticles for latent fingerprint detection. Thioglycolic acid coated CdTe and ZnS:Mn$^{2+}$ nanoparticles were used for fingerprint detection. Latent fingerprints on glass, aluminum and plastic substrates have been successfully labeled with the nanoparticles for periods ranging from 20 minutes to 24 hrs. The labeling is probably due to the amidation reaction between the functional carboxyl group of the nanoparticles with the amine groups of the biomaterials present in the fingerprint residues. The specificity of the nanoparticles at various wavelengths is displayed in the resulting images. The nanoparticles have high quantum yields, tunable fluorescence wavelength and are photo-stable which make them suitable for use in developing ultra-sensitive, target --specific and background suppressed latent fingerprint detection. [Preview Abstract] |
Friday, October 19, 2007 4:30PM - 4:42PM |
F4.00006: East Antarctic Ice Sheets: Potential for Sub-Glacial Water Based on Temperature Modeling Annette Borchard, Heather Haneman, Peter Burkett, Sridhar Anandakrishnan This project addressed the issue of whether a sub-glacial lake exists at a location about 10 km from the Amundsen-Scott Station in Antarctica. Computer modeling was used to predict the temperature at the base of the ice sheet to determine whether or not it was actually frozen and thus determine whether it would be possible to drill into the lake without contaminating any potential sub-glacial water systems. Temperature data from the AMANDA (Anarctic Muon and Neutrino Detector Array) and equations from Paterson, \textit{The Physics of Glaciers}, were used to build the model and approximate values which are not known well experimentally. The results indicated that there is a reasonable chance that liquid water exists at the base and thus that careful consideration should be taken before drilling at this site. [Preview Abstract] |
Friday, October 19, 2007 4:42PM - 4:54PM |
F4.00007: Nano-patterned elastic polymer Soyeun Park, Dave Kahn, Wolfgang Frey Polymers grown by surface-initiated polymerization have received increasing attention due to the ability to control chain length and achieve high-density grafting, which are both needed in a variety of chemical to biomedical applications, including the stabilization of colloids and the fabrication of cell adhesion-promoting surfaces for tissue engineering scaffolds. Interestingly, surface-grafted polymers on nanoislands have fundamentally unique properties due to the confinement effects. Growing polymers on homogeneous or micro-patterned surface with well-controlled length has been achieved successfully. However, the polymer growth in nano-scale patterns with well controlled length and lateral size has been challenging. By combining a surface-initiated polymerization, self-assembly, and nano-sphere lithography, we successfully developed a unique technique to grow polymers on a nano-patterned substrate. With this technique, we were able to fabricate polymer brushes with high grafting densities and the well controlled polymer length on laterally confined nano-islands. The polymer nano-islands were characterized, and the elastic properties of the nano-patterned polymer gel were investigated using AFM 2D-force spectroscopy. [Preview Abstract] |
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