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PubMed1983

Biological applications of picosecond spectroscopy.

Technological advances in picosecond spectroscopy have permitted the mechanisms of various chemical, physical and biological processes to be elucidated and understood to a greater degree than ever before. By means of picosecond emission, absorption and Raman spectroscopy, one can probe and measure directly the transient intermediates and kinetics of primary events in complex biological processes. A description of two current types of laser systems--solid-state and synchronously pumped dye lasers--and their application to determining the primary events in the biological processes of dissociation of oxy- and carboxymyoglobin, excited-state relaxation of porphyrins and visual transduction, illustrate the power of picosecond spectroscopy.

Carbon Monoxide↗
PubMed2005

Half or full core hole in density functional theory X-ray absorption spectrum calculations of water?

We analyze the performance of two different core-hole potentials in the theoretical modeling of XAS of ice, liquid and gas phase water; the use of a full core-hole (FCH) in the calculations, as suggested by Hetenyi et al. [B. Hetenyi, F. De Angelis, P. Giamozzi and R. Car, J. Chem. Phys., 2004, 120(18), 8632], gives poor agreement with experiment in terms of intensity distribution as well as transition energies, while the half core hole (HCH) potential, in the case of water, provides a better compromise between initial and final state effects, leading to good agreement with the experimental data.

Gases↗
PubMed1992

Evidence for copper and 3,4,6-trihydroxyphenylalanine quinone cofactors in an amine oxidase from the gram-negative bacterium Escherichia coli K-12.

The cofactors present in a amine oxidase induced in Escherichia coli K-12 by growth on 2-phenylethylamine have been studied by spectroscopic methods. E.s.r. spectroscopy establishes the presence of cupric copper while resonance Raman spectroscopy on the phenylhydrazine derivative of the enzyme provides strong evidence for the oxidized form of 3,4,6-trihydroxyphenylalanine (TOPA) quinone. The amine oxidase should accordingly be classified as EC 1.4.3.6. This is the first report of such an amine oxidase in a Gram-negative bacterium.

Amine Oxidase (Copper-Containing)↗
PubMed1996

Tissue spectroscopy for gastrointestinal diseases.

Tissue spectroscopy for gastrointestinal diseases has made rapid strides in methodology and technology, with recent studies showing very promising results for the detection of pre-cancers and cancers. Laser-induced fluorescence spectroscopy, elastic scattering spectroscopy, and Raman spectroscopy have all shown favorable results in the diagnosis of malignancies and dysplasia in a number of small studies, both in vitro and in vivo. While technical limitations have been encountered with each of the techniques, significant advances have been made in the last year that may allow a highly sensitive and specific diagnosis to be generated within seconds, allowing directed or guided biopsies or therapy during a single procedure. Large multicenter trials will be necessary to demonstrate the efficacy, usefulness, and efficiency of these new tools.

Biopsy↗
PubMed2004

Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates.

Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 x 10(10) on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.

Aniline Compounds↗
PubMed1978

Charge stabilization mechanism in the visual and purple membrane pigments.

The effects of charged groups of rhodopsin and bacteriorhodopsin on the potential energy surface of their chromophore are examined, taking into account the protein dielectric effect. It is found that the barriers for twisting double bonds of an isolated chromophore can be drastically reduced when the chromophore interacts with the protein charges. New types of local minima are found in the ground-state potential surface of the protein-chromophore complex. These minima correspond to "charge-stabilized intermediates" which are formed when a shift of the chromophore positive charge to the ring is stabilized by the ionization of a properly placed acidic group of the protein and by partial alternation of the bond lengths of the chromophore. It is suggested that the absorption of light by rhodopsin and bacteriorhodopsin may be used not only for isomerization about double bonds, but also for trapping such charge-stabilized intermediates. Thus, for example, it is concluded that prelumirhodopsin might be still in the cis configuration. Both the mechanism of the proton pump system of the purple membrane and the dark reaction of the visual and purple membrane pigments are considered. The connection between the finding of the present work and the mechanism of storage of light energy in photobiology is indicated.

Bacteriorhodopsins↗
PubMed1985

Active site structures of deoxyhemerythrin and oxyhemerythrin.

The physiologically active forms of the nonheme-iron, oxygen-transport protein hemerythrin have been studied by x-ray crystallographic techniques. At 3.9-A resolution, a difference electron-density map between the deoxy form and met form (methemerythrin) of the protein suggests only small differences in the binuclear iron complexes. The coordination of the iron atoms appears to be the same in both the deoxy and met forms, one iron of the complexes being pentacoordinate, the other iron being hexacoordinate. The iron atoms appear to be somewhat farther apart in the deoxy form. A 2.2-A resolution study of oxyhemerythrin shows that dioxygen binds to one iron atom--the pentacoordinate one in the met form of the protein, the same binding site found for azide in azidomethemerythrin.

Animals↗
PubMed1999

Iron coordination structures of oxygen sensor FixL characterized by Fe K-edge extended x-ray absorption fine structure and resonance raman spectroscopy.

FixL is a heme-based O(2) sensor protein involved in a two-component system of a symbiotic bacterium. In the present study, the iron coordination structure in the heme domain of Rhizobium meliloti FixLT (RmFixLT, a soluble truncated FixL) was examined using Fe K-edge extended x-ray absorption fine structure (EXAFS) and resonance Raman spectroscopic techniques. In the EXAFS analyses, the interatomic distances and angles of the Fe-ligand bond and the iron displacement from the heme plane were obtained for RmFixLT in the Fe(2+), Fe(2+)O(2), Fe(2+)CO, Fe(3+), Fe(3+)F(-), and Fe(3+)CN(-) states. An apparent correlation was found between the heme-nitrogen (proximal His-194) distance in the heme domain and the phosphorylation activity of the histidine kinase domain. Comparison of the Fe-CO coordination geometry between RmFixLT and RmFixLH (heme domain of RmFixL), based on the EXAFS and Raman results, has suggested that the kinase domain directly or indirectly influences steric interaction between the iron-bound ligand and the heme pocket. Referring to the crystal structure of the heme domain of Bradyrhizobium japonicum FixL (Gong, W., Hao, B., Mansy, S. S., Gonzalez, G., Gilles-Gonzalez, M. A., and Chan, M. K. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 15177-15182), we discussed details of the iron coordination structure of RmFixLT and RmFixLH in relation to an intramolecular signal transduction mechanism in its O(2) sensing.

Bacterial Proteins↗