7 research outputs found
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Time-resolved infrared studies of the dynamics of ligand binding to cytochrome c oxidase
Time-resolved infrared spectroscopy (TRIRS) has been employed to study the reactions of small molecules with the cytochrome a{sub 3}-Cu{sub B} 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 TRIR technique with time resolution of less than 1 ps. The rate of photoinitiated transfer of CO from Fe{sub a3}{sup 2+} to Cu{sub B}{sup +} was measured directly by monitoring the development of the transient Cu{sub B}{sup +}-CO absorption. The development of a stationary Cu{sub B}{sup +}-CO spectrum which is constant until the CO dissociates from Cu{sub B}{sup +} 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 a{sub 3}-Cu{sub B} site, the functional architecture of the protein and coordination dynamics in general. The photodissociation and recombination of Cn{sup {minus}} has also been studied using a real-time TRIR technique. The CN{sup {minus}} recombination rate of 430 s{sup {minus}1} is consistent with a recombination pathway similar to the one they have previously proposed for CO. The authors suggest the rate determining step for CN{sup {minus}} recombination is the thermal dissociation of the Fe{sub a3}{sup 2+}-L bond. 25 refs., 7 figs
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Laser-induced reactions in a deep UV resist system: Studied with picosecond infrared spectroscopy
One of the most technologically important uses of organic photochemistry is in the imaging industry where radiation-sensitive organic monomers and polymers are used in photoresists. A widely-used class of compounds for imaging applications are diazoketones; these compounds undergo a photoinduced Wolff rearrangement to form a ketene intermediate which subsequently hydrolyses to a base-soluble, carboxylic acid. Another use of organic molecules in polymer matrices is for dopant induced ablation of polymers. As part of a program to develop diagnostics for laser driven reactions in polymer matrices, we have investigated the photoinduced decomposition of 5-diazo-2,2-dimethyl-1,3-dioxane-4,6-dione (5-diazo Meldrum`s acid, DM) in a PMMA matrix using picosecond infrared spectroscopy. In particular, irradiation of DM with a 60 ps 266 nm laser pulse results in immediate bleaching of the diazo infrared band ({nu} = 2172 cm{sup -1}). Similarly, a new band appears within our instrument response at 2161 cm{sup -1} (FWHM = 29 cm{sup -1}) and is stable to greater than 6 ns.; we assign this band to the ketene photoproduct of the Wolff rearrangement. Using deconvolution techniques we estimate a limit for its rate of formation of {tau} < 20 ps. The linear dependence of the absorbance change with the pump power (266 nm) even above the threshold of ablation suggest that material ejection take place after 6ns
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Picosecond infrared spectroscopy as probe for photochemical or thermal reactions in solid matrices
Spectroscopy in the mid-IR on timescales from pico to milliseconds has been developed for the study of laser-material interactions over broad timescales. To reach these timescales the authors have employed two configurations: (1) for the ps to ns timescale a one and a two stage difference frequency mixing setup is employed, (2) for the longer timescale, CW mid-IR laser diodes have been used. In general, they excite the sample with one pulse at 1064/266/355 nm and probe some time later in the mid IR (2900--800 cm{sup {minus}1}). In the case of photochemical reaction, they excite the sample directly in the UV. Alternatively, they initiate thermal reactions by pumping a heater dye at 1.064 {micro}m, which quickly converts the photon energy into heat. The potential of this technique to study reactions in the solid state was demonstrated for a photochemically induced (266 nm) reaction (Wolff rearrangement of a {alpha}-diazo-ketone to {alpha}-keto-ketene) in a polymer matrix. Thermal initiation resulted in a similar reaction. The position, amplitude and width of the product bands changed, they believe due to additional side reactions and temperature effects
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Picosecond infrared study of carbonmonoxy cytochrome c oxidase: Ligand transfer dynamics and binding orientations
Cytochrome c oxidase (CcO), an enzyme which catalyzes the reduction of dioxygen to water in the terminal step of the respiratory chain, combines several fundamental chemical processes in performing its function. The coordination chemistry and ligation dynamics of the cytochrome {alpha}{sub 3}-Cu{sub B} site, where O{sub 2} and other small molecules such as CO, NO and isocyanates can bind, are essential to the function of the enzyme. Recent time-resolved infrared (TRIR) and visible absorption measurements have shown that coordination to Cu{sub B}{sup +} is an obligatory mechanistic step for CO entering the cytochrome {alpha}{sub 3} heme site and departing the protein after photodissociation. The timescale (> 10{sup {minus}7} s) of the TRIR measurements precluded observation of the ligation dynamics immediately following photodissociation. Here we report a picosecond timescale TRIR study of these events. The results reveal that the photoinitiated ligand transfer of CO from Fe{sub a3}{sup 2+} to Cu{sub B}{sup +}, which are believed to lie 4--5 {Angstrom} apart, occurs within 1 ps. 9 refs., 2 figs