A combination of surface-enhanced Raman spectroscopy (SERS), surfaceenhanced infrared spectroscopy (SEIRA), and density functional theory (DFT) calculations are used to study the adsorption and thin film growth of isoniazid (an antimicrobial used to treat tuberculosis) on silver nanostructures (SNS). It is known that an isoniazid crystal takes on a C1 configuration where one of the hydrogens at the end of the hydrozyl group (−NH-NH 2 ) form an intramolecular hydrogen bond with the only oxygen atom. DFT calculations involving combinations of isoniazid dimers, trimers, and tetramers are used to model and interpret the Raman spectrum of isoniazid powder. The DFT calculations highlight the importance of accurately modeling hydrogen-bonding interactions between adjacent hydrozyl groups as well as interactions involving the ring nitrogen and the hydrozyl group. SERS, SEIRA, and DFT calculations involving isoniazid dimers and four-metal silver clusters reveal that isoniazid takes on a T conformation in a monolayer adsorbed on SNS where the hydrozyl group is rotated around a single bond so that the −NH 2 is oriented down with respect to the oxygen atom. Further evidence from the SEIRA and DFT calculations illustrate that the multilayer of isoniazid deposited from acetone maintains a geometry similar to the T conformation. In addition to the polar solvent acetone, n-heptane, a solvent with nonpolar bonds, is used to study the interactions of isoniazid with the SNS. These studies reveal that isoniazid has a stronger affinity for SNS when using n-heptane as the deposition solvent. An increase in attraction between isoniazid and the SNS is probably accomplished by changing the angle of interaction of the NH 2 and −NH groups with respect to the SNS. It is believed that a lower level of solvation occurs when using n-heptane as a deposition solvent, which allows for increased isoniazid attraction to the SNS.

There is a need for increasing the number of transition metals that can be used as substrates for surface-enhanced infrared absorption (SEIRA). We present here microscopy and infrared experiments that show oblique-angle deposition of Ni onto CaF 2 or BaF 2 , which result in elongated Ni nanostructures (ENiNSs) that are partially aggregated and exhibit surface plasmon resonances in the midinfrared. SEIRA enhancement factors in the range of 10−20-fold were observed for a monolayer of the pnitrobenzoate ion adsorbed onto the ENiNS. Extending SEIRA to a metal such as Ni would yield different ways of studying Ni thin film and catalysis chemistry. This work also suggests that oblique-angle deposition might be used to create new SEIRA substrates from other metals. SECTION: Physical Processes in Nanomaterials and Nanostructures

A combination of surface-enhanced infrared absorption (SEIRA) and density functional theory (DFT) was used to study the adsorption of the dihydroxybenzene (DH) isomers on silver nanostructures (SNSs). No evidence was observed for the oxidation of any of the DH isomers during adsorption on SNSs. It was found that the SNSs weakened intermolecular hydrogen bonding in thin DH layers adsorbed on SNSs versus the bulk powders with the effect being more pronounced for para-dihydroxybenzene (PDH) than ortho-dihydroxybenzene (ODH) and meta-dihydroxybenzene (MDH). DFT simulations of the infrared spectra of ODH and MDH dimers were good reproductions of the SEIRA spectra and infrared spectra of ODH/MDH powder, but DFT dimer infrared simulations were less effective at modeling the PDH results due to the large variations of hydrogen bonding between PDH films formed on SNSs versus PDH powder. Hydrogen-bonding effects were observed between acetone and both PDH and ODH in thin layers adsorbed on SNSs, and C−H•••O hydrogen bonding was also seen between n-heptane and PDH and ODH in adsorption experiments on SNSs. These hydrogen-bonding effects were not detected between MDH and either acetone or n-heptane due to differences in resonance effects between MDH versus ODH and PDH.