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A combined experimental and computational approach utilizing CO2 infrared gas lasers and chemometric multivariate analysis was employed to detect chemicals and their concentrations in the open atmosphere under controlled release conditions. Absorption spectra of four organic gases were collected in the laboratory by lasing 40 lines of a Synrad 15 W CO2 laser in the 9.3 to 10.8 micron range. Several chemometric calibration models were constructed based on this IR data using the Partial Least Squares computational technique. The chemometric models were used to analyze in near real time the field DIAL data acquired over this exact wavelength range at round trip distances of 7 and 13 km. It will be shown that the ability to predict the chemicals and their respective concentrations depends on a variety of factors. In 39 of the 45 experiments, the identities of the released chemicals were correctly identified without predictions of false positives or false negatives. Under the best field conditions, we achieved predictions of absolute concentrations within 30% of the actual values.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Time-resolved electronic absorption, infrared, resonance Raman, and magnetic circular dichroism spectroscopies are applied to characterization of the intermediate which is formed within 20 ps after photodissociation of CO from cytochrome a3 of reduced cytochrome oxidase. This intermediate decays with the same halflife (ca. 1 microsecond(s)) as the post- photodissociation CuB+-CO species previously observed by time-resolved infrared. The transient UV-Vis spectra, kinetics, infrared, and Raman evidence suggest that an endogenous ligand is transferred from CuB to Fea3 when CO binds to CuB, forming a cytochrome a3 species with axial ligation which differs from the reduced unliganded enzyme. The time-resolved magnetic circular dichroism results suggest that this transient is high spin and therefore five coordinate. Thus it is inferred that the ligand from CuB binds on the distal side of cytochrome a3 and displaces the proximal histidine imidazole. This remarkable mechanistic feature is an additional aspect of the previously proposed 'ligand shuttle' activity of the CuB/Fea3 pair. The authors suggest that the ligand shuttle may play a functional role in redox-linked proton translocation by the enzyme. More detail on this work is presented elsewhere.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Time-resolved infrared spectroscopy (TRIRS) has been employed to study the reactions of small molecules with the cytochrome a3-CuB site of cytochrome c oxidase (CcO). All phases of these reactions have been investigated, from ultrafast phenomena (hundreds of femtoseconds) to relatively slow processes (milliseconds). The ligation dynamics immediately following photodissociation have been studied using a TRIRS technique with time resolution of less than 1 ps. The rate of photoinitiated transfer of CO from Fea32+ to CuB+ was measured directly by monitoring the development of the transient CuB+-CO absorption. The development of a stationary CuB+ spectrum which is constant until the CO dissociates from CuB+ occurs in less than 1 ps, indicating that the photoinitiated transfer of CO is remarkably fast. This unprecedented ligand transfer rate has profound implications with regard to the structure and dynamics of the cytochrome a3-CuB site, the functional architecture of the protein and coordination dynamics in general. The photodissociation and recombination of CN- has also been studied using a real-time TRIR technique. The CN- recombination rate of 430 s-1 is consistent with a recombination pathway similar to the one we have previously proposed for CO, in which a long-lived barrier to recombination is formed by the binding of an endogenous ligand L to Fea32+. The authors suggest the rate determining step for CN- recombination is the thermal dissociation of the Fea32+-L bond.