Broadband sum frequency generation has been used to characterize glass surfaces functionalized with siloxanes containing terminal carboxylic acid and ester functional groups. ω-Ester silanes can be used in the preparations of ester-functionalized glass surfaces, which yield acid-functionalized surfaces via hydrolysis. This general methodology can be used in environmental, biochemical, or materials science surface chemistry to generate surfaces with tunable physical and chemical properties. Definitive characterization of these carboxylatefunctionalized glass surfaces can be performed in the C-H vibrational frequency region using sum frequency generation.

The synthesis, characterization, and oxidation reaction of a tropospherically relevant terpene bound to a glass surface are reported. Vibrational broadband sum frequency generation (SFG) is used to characterize the various terpene-modified glass surfaces and track their interaction with ozone. SFG spectra indicate that, although orientations of the surface-bound terpenes depend on the linker strategies employed, the CdC double bond is accessible to gas-phase ozone regardless of the strategy applied. Exposure of the terpene-functionalized surface to ppm levels of ozone at 1 atm and 300 K yields an initial reaction probability of approximately 1 × 10 -5 per surface collision, which is significantly higher than the corresponding gas-phase reaction involving 1-methyl-1-cyclohexene (5 × 10 -7 from gas-phase collision theory). The interaction of ozone with a saturated octyl silane-functionalized glass surface leads to a slight molecular reorientation, or tilting, of the terminal CH 3 groups on a much slower time scale. Our work demonstrates that SFG spectroscopy can be used to determine reaction probabilities of heterogeneous atmospheric reactions and bridges the gap between atmospheric chemistry and surface functionalization.

Organic adlayers can significantly alter the interactions of environmentally relevant surfaces with their surroundings. We present the first second harmonic and broadband sum frequency generation (SHG and BBSFG) study that illustrates how organic surface functional groups can control the mobility of the priority pollutant chromium(VI) in soil: Cr(VI) binds to ester- and acid-functionalized surfaces but not to alkane-functionalized surfaces. The implications with respect to toxic metal transport across organic adlayers at liquid-solid interfaces are that aqueous Cr(VI) can be retained by polar groups common in biopolymers but not by hydrophobic groups common in surfactants.

It is now known that the untreated discharge of pharmaceuticals into the environment can impact human health and development and lead to increased drug resistance in biota. Here, we present the first direct interface-specific studies that address the mobility of the widely used agricultural antibiotic morantel, which is commonly present in farm runoff. Surface-bound morantel was spectroscopically identified using second harmonic generation (SHG) via a two-photon resonance of its n-pi* transition and in the C-H stretching region by vibrational sum frequency generation (VSFG). Resonantly enhanced SHG adsorption isotherm measurements carried out at the silica/water interface between 6 x 10(-7) and 5 x 10(-5) M morantel concentration result in a free energy of adsorption of 42(2) kJ/mol at pH 7. Finally, real-time tracking of morantel interaction with the silica/water interface shows that the binding events are fully reversible, consistent with its high mobility in silica-rich soil environments. This work thus indicates that pharmaceuticals discharged into the environment can enter the groundwater supply of municipal water systems, at which point their removal is challenging. In addition, the high mobility of morantel in silica-rich soil environments could lead to developing increased interaction of this antibiotic with target organisms, which could respond by increased drug resistance.

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