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Biomedical subjects

T G Spiro

Publications and source records attributed to T G Spiro.

At least 109 records · Page 6Linked to original sources
PubMed1979

Absence of heme-localized strain in T state hemoglobin: insensitivity of heme-imidazole resonance Raman frequencies to quaternary structure.

Substitution of pentadeuterated 2-methylimidazole in (2-methylimidazole)-Fe(II)-protoporphyrin IX, a model complex for deoxyHb, shifts three bands in the low-frequency resonance Raman spectrum 380 leads to 373 cm-1, 348 leads to 345 cm-1, and 220 leads to 218 cm-1. The first of these is assigned primarily to Fe-imidazole stretching, and the other two are assigned to porphyrin deformation modes with substantial Fe-pyrrole stretching contributions. The three bands are observed in deoxyHb and Mb. The Fe-pyrrole modes are at essentially the same frequencies in the two proteins, but the Fe-imidazole mode is 6 cm-1 lower in deoxyHb than Mb, implying a slight alteration in the heme-imidazole linkage. No change greater than 2 cm-1 is observed when Hb Kempsey is switched from the R to the T state. This observation places an upper limit on the energy stored in the Fe-imidazole bond of T state deoxyHb, which is estimated to be less than 0.2 kcal/mol (less than 836.8 J/mol).

Chemical Phenomena↗
PubMed1978

Electronic and resonance Raman spectra of iron(III) complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide.

Resonance Raman electronic absorption and circular dichroism spectra and pH titration curves are reported for the trianionic ferric complexes of enterobactin, catechol, and N-methyl-2,3-dihydroxybenzamide (MDHB). The spectral signatures of the enterobactin and MDHB complexes are virtually identical and differ from those of the catechol complex in ways that reflect the influence of the amide group on the electronic structure. Excitation in either the visible charge-transfer bands or the near-ultraviolet pi-pi* bands enhances Raman bands associated with benzene ring modes, although the relative enhancements differ markedly in the two regions. The data stronly support a structural model in which iron is bound exclusively to the phenolate oxygen atoms in all three complexes.

Benzamides↗
PubMed1977

Resonance coherent anti-Stokes Raman scattering spectra of fluorescent biological chromophores: Vibrational evidence for hydrogen bonding of flavin to glucose oxidase and for rapid solvent exchange.

Coherent anti-Stokes Raman scattering (CARS) spectra are reported for flavin adenine dinucleotide (FAD) and glucose oxidase (beta-D-glucose:oxygen 1-oxidoreductase; EC 1.1.3.4), in resonance with the 450 nm flavin absorption band. Several isoalloxazine ring modes were observed (1635, 1584, 1507, 1416, and 1359 cm(-1)). A 12 cm(-1) increase in one component of the 1359 cm(-1) band upon binding to glucose oxidase was attributed to hydrogen bonding of the N3 proton to a protein acceptor. This interpretation is consistent with deuteration results. Smaller decreases (5-7 cm(-1)) on binding were observed for the 1635 and 1416 cm(-1) modes (and also a 1297 cm(-1) mode of deuterated FAD) and were attributed to environmental effects. Deuteration of bound FAD was observed within 5 min of mixing glucose oxidase with D(2)O, demonstrating ready access to solvent. Lorentzian CARS peaks were observed with omega(as) at the peak of the 450 nm absorption band, a condition which corresponds to maximum resonance enhancement if the peak corresponds to the envelope of 0-1 vibronic transitions. If omega(1) was tuned to the peak, then dispersion lineshapes were observed, reflecting a loss of Raman enhancement relative to the electronic background.

Journal Article↗
PubMed1976

Coherent anti-Stokes Raman scattering (CARS) spectra, with resonance enhancement, of cytochrome c and vitamin B12 in dilute aqueous solution.

Coherent anti-Stokes Raman scattering (CARS) spectra have been obtained for ferrocytochrome c and cyano cobalamin in aqueous solution at millimolar concentrations, using a pair of tunable dye lasers pumped by a pulsed nitrogen laser. Resonance enhancement was obtained by tuning the omega1 laser to the visible absorption bands of the samples. The spectral features correspond to those observed in the conventional resonance Raman spectra. It appears that CARS spectroscopy, with its advantageous fluorescence rejection, can be usefully applied to biological samples by exploiting resonance enhancement. While the background scattering from water is 10 times higher than that of benzene and other aromatic solvents, it is actually at the low end of the scale for most liquids. The anomalously low background of aromatic liquids is thought to result from competition by the unusually efficient stimulated Raman scattering which they display. Off-resonance spectra for both cobalamin and cytochrome c contain negative peaks, i.e., absorption bands in the background. These are interpreted as inverse Raman processes induced by the omega1 photons in the presence of the continuum provided by the background scattering. While both CARS and the inverse Raman effect are subject to resonance enhancement, the wavelength dependence of CARS is evidently steeper.

Cytochrome c Group↗
PubMed1975

The copper coordination group in "blue" copper proteins: evidence from resonance Raman spectra.

Tunable dye laser excitation in the intense similar to 600-nm absorption band of azurin, plastocyanin, and ceruloplasmin provides resonance enhanced Raman spectra. They consist of a complex set of bands, at least three or four in number, between 350 and 473 cm-1, which are assignable to Cu-N or Cu-O bond stretching, and a weak band near 270 cm-1, which probably arises from Cu-S stretching. A weak band at 765 cm-1 found in plastocyanin may arise from C-S stretching. Analysis of the Raman intensity pattern, as well as of the nature of the resonant electronic transition, leads to a model of the "blue" copper site involving approximately trigonal-bipyramidal coordination, with a sulfur and two nitrogen ligands in the equatorial plane, and less strongly bound nitrogen or oxygen ligands at axial positions. This arrangement would be well poised for stabilization of Cu(I) upon reduction.

Azurin↗