Homelessness in Richmond

Capstone presentation for the University of Richmond SSIR (Sophomore Scholars in Residence) Program.https://scholarship.richmond.edu/ssir-presentations-2017/1002/thumbnail.jp

Halogen Bonding Interactions for Aromatic and Non-Aromatic Explosive Detection

Improved sensing strategies are needed for facile, accurate and rapid detection of aromatic and nonaromatic explosives. Density functional theory was used to evaluate the relative binding interaction energies between halogen-containing sensor model molecules and nitro-containing explosives. Interaction energies ranged from –18 to –14 kJ/mol and highly directional halogen bonding interactions were observed with bond distances ranging between 3.0 and 3.4 Å. In all geometry optimized structures, the sigma-hole of electropositive potential on the halogen aligned with a lone pair of electrons on the nitro-moiety of the explosive. The computational results predict that the strongest interactions will occur with iodine-based sensors as, of all the halogens studied, iodine is the largest, most polarizable halogen with the smallest electronegativity. Based on these promising proof-of-concept results, synthetically accessible sensors were designed using1, 4-dihalobenzene (X= Cl, Br and I) with and without tetra-fluoro electron withdrawing groups attached to the benzene ring. These sensing molecules were embedded onto single walled carbon nanotubes that were mechanically abraded onto interdigitated array electrodes and these were used to measure the responses to explosive model compounds cyclohexanone and dimethyl-dinitro-benzene in nitrogen gas. Amperometric current-time curves for selectors and control molecules, including concentration correlated signal enhancement, as well as response and recovery times, indicate selector responsiveness to these model compounds, with the largest response observed for iodo-substituted sensors

Nanoaggregates of Diverse Asphaltenes by Mass Spectrometry and Molecular Dynamics

Asphaltene nanoaggregates from three diverse source materials-coal-derived asphaltenes dominated by aromatic carbon, petroleum asphaltenes with comparable abundances of aromatic and aliphatic carbon, and immature source-rock asphaltenes dominated by aliphatic carbon-are examined by means of surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) coupled with laser desorption laser ionization mass spectrometry ((LMS)-M-2). All three types of asphaltenes form nanoaggregates with aggregation numbers close to 7. Molecular dynamics calculations for proposed island molecular structures show the important roles that pi-stacking and alkane steric hindrance play in nanoaggregate formation and structure. These results are discussed in terms of entropy and enthalpy changes. All results are consistent with the Yen-Mullins model, which bodes well for its expanded use in oilfield reservoir evaluations