Picosecond Resonance Raman Evidence of the Structure of a Long-Lived Electronic Excited State of Low-Spin Fe(III)Heme O

The structure of the excited state of low-spin ferric heme o has been studied using picosecond time-resolved resonance Raman spectroscopy. The excited state has a lifetime of 10-30 ps, and the heme skeletal vibrations are shifted to lower frequencies relative to those in the electronic ground state. Based on the relatively small frequency shifts, we conclude that the relatively long-lived heme o excited state is not a porphyrin ππ* state. We propose that the heme o excited state is a charge transfer state, in which the heme iron donates an electron to the porphyrin macrocycle

Application of double-pulse laser-induced breakdown spectroscopy (DP-LIBS), Fourier transform infrared micro-spectroscopy and Raman microscopy for the characterization of copper-sulfides

The combined application of the structure sensitive techniques Fourier transform infrared μ-spectroscopy and Raman microscopy in conjunction with different approaches of laser-induced breakdown spectroscopy (LIBS) including the two-color double pulse (DP-LIBS) have been applied towards the characterization of whole ore copper-sulfide minerals. Discrete information from the surface of the whole ore minerals that lead to the establishment of infrared marker bands and from the surface of bioleached samples that allow the monitoring of jarosite and biofilm formation are provided by FTIR mapping experiments. Raman data can provide information related to the type of the mineral and of the secondary minerals formed on the surface of the ore. Of the four different LIBS approaches applied towards the characterization of the composition of the whole ore minerals, the DP-LIBS shows the highest sensitivity with increasing signals for both the Fe and Cu metals in the whole ore samples

Bacterial colonization on the surface of copper sulfide minerals probed by fourier transform infrared micro-spectroscopy

Biofilm formation is a molecular assembly process occurring at interfaces, such as in bioleaching processes. The real time monitoring of the marker bands of amide I/amide II by FTIR microspectroscopy during Acidithiobacillus ferrooxidans colonization on chalcopyrite surfaces revealed the central role of lipids, proteins and nucleic acids in bacterial cell attachment to copper sulfide surfaces. The Raman and FTIR spectra of the interactions of Acidithiobacillus ferrooxidans with bornite are also reported

Low-Power Picosecond Resonance Raman Evidence for Histidine Ligation to Heme A3 After Photodissociation of CO from Cytochrome C Oxidase

Several models have been proposed for the ligand dynamics in the heme a32+/Cu(B)1+ binuclear pocket in cytochrome oxidase following CO photodissociation. These range from straightforward heme pocket relaxation to a variety of ligand exchange processes that have been proposed to be of relevance to the proton pumping function of the enzyme. To provide discrimination between these models, we have used picosecond time-resolved, pump-probe resonance Raman spectroscopy to study the photolysis process in the enzyme isolated from beef heart and from Rhodobacter sphaeroides. The intermediate observed within 5 ps of photolysis with low-energy probe pulses (10-20 nJ/pulse) is the high-spin, five-coordinate heme a32+ to which a histidine is ligated, as indicated by the observation of the Fe-His vibration at 220 cm-1. Several control experiments demonstrate that the probe pulse energy is sufficiently low to avoid promoting any significant photochemistry during the spectral acquisition phase of the pump-probe experiment. From these observations, we conclude that histidine is ligated to high-spin heme a32+ on the picosecond time scale following photolysis. Since H376 is the proximal a32+ ligand in the CO complex, our results indicate that this proximal ligation survives photolysis and that the control of the access of exogenous ligands to the heme a3 site by means of a ligand exchange process can be ruled out. We observe similar picosecond transient resonance Raman spectra for the CO complex of Rb. sphaeroides cytochrome c oxidase. From these results and earlier time-resolved Raman and FTIR measurements, we propose a model for the relaxation dynamics of the heme as pocket that involves picosecond migration of CO to the Cu(B) center and relaxation of the a32+-proximal histidine bond on the microsecond time scale following CO photolysis

Ligand Dynamics in the Binuclear Site in Cytochrome Oxidase

The dioxygen-reduction mechanism in cytochrome oxidase relies on proton control of the electron-transfer events that drive the process. Recent work on proton delivery and efflux channels in the protein that are relevant to substrate reduction and proton pumping is considered, and the current status of this area is summarized. Carbon monoxide photo dissociation and the ligand dynamics that occur subsequent to photolysis have been valuable tools in probing possible coupling schemes for linking exergonic electron-transfer chemistry to endergonic proton translocation. Our picosecond-time-resolved Raman results show that the heme a3- proximal histidine bond remains intact following CO photo dissociation but that the local environment around the heme a3 center in the photoproduct is in a nonequilibrium state. This photoproduct relaxes to its equilibrium configuration on the same time scale as ligand release occurs from CUB' which suggests a coupling between the two events and a potential signaling pathway between the site of O2 binding and reduction and the putative element, CUB' that links the redox chemistry to the proton pump

Aldoxime Dehydratase: Probing the Heme Environment Involved in the Synthesis of the Carbon–Nitrogen Triple Bond

Fourier transform infrared (FTIR) spectra, "light" minus "dark" difference FTIR spectra, and time-resolved step-scan (TRS 2) FTIR spectra are reported for carbonmonoxy aldoxime dehydratase. Two C-O modes of heme at 1945 and 1964 cm -1 have been identified and remained unchanged in H 2O/D 2O exchange and in the pH 5.6-8.5 range, suggesting the presence of two conformations at the active site. The observed C-O frequencies are 5 and 16 cm -1 lower and higher, respectively, than that obtained previously (Oinuma, K.-I.; et al. FEBS Lett.2004, 568, 44-48). We suggest that the strength of the Fe-His bond and the neutralization of the negatively charged propionate groups modulate the ν(Fe-CO)/ν(CO) back-bonding correlation. The "light" minus "dark" difference FTIR spectra indicate that the heme propionates are in both the protonated and deprotonated forms, and the photolyzed CO becomes trapped within a ligand docking site (ν(CO) = 2138 cm -1). The TRS 2-FTIR spectra show that the rate of recombination of CO to the heme is k 1945 cm -1 = 126 ± 20 s -1 and k 1964 cm -1 = 122 ± 20 s -1 at pH 5.6, and k 1945 cm -1 = 148 ± 30 s -1 and k 1964 cm -1 = 158 ± 32 s -1 at pH 8.5. The rate of decay of the heme propionate vibrations is on a time scale coincident with the rate of rebinding, suggesting that there is a coupling between ligation dynamics in the distal heme environment and the environment sensed by the heme propionates. The implications of these results with respect to the proximal His-Fe heme environment including the propionates and the positively charged or proton-donating residues in the distal pocket which are crucial for the synthesis of nitriles are discussed