Solution and solid state electronic absorption, magnetic circular dichroism, and resonance Raman spectroscopies have been used to probe in detail the excited state electronic structure of LMoO(bdt) and LMoO(tdt) (L ) hydrotris-(3,5-dimethyl-1-pyrazolyl)borate; bdt ) 1,2-benzenedithiolate; tdt ) 3,4-toluenedithiolate). The observed energies, intensities, and MCD band patterns are found to be characteristic of LMoO(S-S) compounds, where (S-S) is a dithiolate ligand which forms a five-membered chelate ring with Mo. Ab initio calculations on the 1,2-enedithiolate ligand fragment, -SCdCS -, show that the low-energy S f Mo charge transfer transitions result from one-electron promotions originating from an isolated set of four filled dithiolate orbitals that are primarily sulfur in character. Resonance Raman excitation profiles have allowed for the definitive assignment of the ene-dithiolate S in-plane f Mo d xy charge transfer transition. This is a bonding-to-antibonding transition, and its intensity directly probes sulfur covalency contributions to the redox orbital (Mo d xy ). Raman spectroscopy has identified three totally symmetric vibrational modes at 362 cm -1 (S-Mo-S bend), 393 cm -1 (S-Mo-S stretch), and 932 cm -1 (MotO stretch), in contrast to the large number low-frequency modes observed in the resonance Raman spectrum of Rhodobacter sphaeroides DMSO reductase. These results on LMoO(S-S) complexes are interpreted in the context of the mechanism of sulfite oxidase, the modulation of reduction potentials by a coordinated ene-dithiolate (dithiolene), and the orbital pathway for electron transfer regeneration of pyranopterin dithiolate Mo enzyme active sites.

Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the interactions between the sulfur -orbitals of arene dithiolates and high-valent transition metals as minimum molecular models of the active site features of pyranopterin Mo͞W enzymes. The compounds (Tp*)MoO(bdt) (compound 1), Cp 2Mo(bdt) (compound 2), and Cp 2Ti(bdt) (compound 3) [where Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, bdt is 1,2-benzenedithiolate, and Cp is 5 -cyclopentadienyl] provide access to three different electronic configurations of the metal, formally d 1 , d 2 , and d 0 , respectively. The gas-phase photoelectron spectra show that ionizations from occupied metal and sulfur based valence orbitals are more clearly observed in compounds 2 and 3 than in compound 1. The observed ionization energies and characters compare very well with those calculated by density functional theory. A ''dithiolate-folding-effect'' involving an interaction of the metal in-plane and sulfur-orbitals is proposed to be a factor in the electron transfer reactions that regenerate the active sites of molybdenum and tungsten enzymes. C oordination by the sulfur atoms of one or two ene-1,2-dithiolate (dithiolene) ligands of the novel substituted pyranopterin-dithiolate (''molybdopterin''; ref. 1) is a common structural feature of mononuclear molybdenum-containing enzymes (2-4). These enzymes catalyze a wide range of oxidation͞reduction reactions in carbon, sulfur, and nitrogen metabolism. Fig. 1 shows the structure of the active site of sulfite oxidase, a representative example (5, 6) of the coordination of the pyranopterin-dithiolate (hereafter abbreviated S 2 pdt; ref. 7). These structural results raise fundamental questions about the role of the S 2 pdt coordination in the overall catalytic cycle of molybdenum enzymes (8). The unusual ability of ene-1,2-dithiolate ligands to stabilize metals in multiple oxidation states has been recognized since the compounds were first investigated (9). Proposed roles for the S 2 pdt ligand include functioning as an electron transfer conduit from the metal to other prosthetic groups (10) and as a modulator of the oxidation͞reduction potential of the metal site (10). During catalysis, the metal center is proposed to pass through the M(VI͞V͞IV) oxidation states, i.e., the Mo d electron count changes from d 0 to d 1 to d 2 . Thus, studies of discrete metal dithiolate complexes encompassing these and related electron configurations may provide insight concerning metal thiolate bonding and reactivity in enzymes.Previous structural studies of model molybdenum complexes of the type (Tp*)MoE(1,2-dithiolate) [where E is O or NO, Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, and the 1,2-dithiolates are bdt (1,2-benzenedithiolate), bdtCl 2 (3,6-dichlorobenzenedithiolate), and qdt (2,3-quinoxalinedithiolate)] have shown that the fold angle of the dithiolate metallacycle along the S⅐⅐⅐S vector (Fig. 2) varies in a way that depends on the occupation of a d orbital that is in the equatorial pl...

Eighty drugs of abuse and metabolites were successfully measured by surface-enhanced Raman spectroscopy (SERS) using gold- and silver-doped sol-gels immobilized in glass capillaries. A method was developed that provided consistent detection of 50 ppb cocaine in saliva in a focused study. This general method was successfully applied to the detection of a number of additional drugs in saliva, such as amphetamine, diazepam, and methadone.

The number of drug-related emergency room visits in the United States doubled from 2004 to 2009 to 4.6 million. Consequently there is a critical need to rapidly identify the offending drug(s), so that the appropriate medical care can be administered. In an effort to meet this need we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect and identify numerous drugs in saliva at ng/mL concentrations within 10 minutes. Identification is provided by matching measured spectra to a SERS library comprised of over 150 different drugs, each of which possess a unique spectrum. Trace detection is provided by fused gold colloids trapped within a porous glass matrix that generate SERS. Speed is provided by a syringe-driven sample system that uses a solid-phase extraction capillary combined with a SERS-active capillary in series. Spectral collection is provided by a portable Raman analyzer. Here we describe successful measurement of representative illicit, prescribed, and over-the-counter drugs by SERS, and 50 ng/mL cocaine in saliva as part of a focused study.