Resonance Raman spectra have been analyzed for vanadyl porphyrin cation radicals of octaethylporphyrin (OEP), meso-tetra-phenylporphyrin (TPP), and meso-tetrametisylporphyrin (TMP). The strength of the metal-oxo bond in these cation... more
Resonance Raman spectra have been analyzed for vanadyl porphyrin cation radicals of octaethylporphyrin (OEP), meso-tetra-phenylporphyrin (TPP), and meso-tetrametisylporphyrin (TMP). The strength of the metal-oxo bond in these cation radicals is demonstrated to be a function of radical type, a{sub 1u} or a{sub 2u}. Porphyrin ring mode νâ, which has previously been shown to be a marker for the radical type was used to identify the radicals. The a{sub 1u} OV(OEP) radical exhibited an upshift in the V{double bond}O stretching frequency resulting from the increased positive charge on the porphyrin, which reduces the porphyrin â vanadium electron donation and increases the O â vanadium donation. ν(V{double bond}O) frequency decreases were observed for the a{sub 2u} OV(TPP) and OV(TMP) radicals. These can be explained on the basis of mixing of the porphyrin Ï a{sub 2u} orbital with the vanadium d{sub z²} and oxygen p{sub z} orbitals, which is allowed in C{sub 4v} symmetry. This interaction decreases the bond strength in a {sub 2u} cation radicals, since an electron is removed from an orbital with partial V-O Ï-bonding character. Mixing of the porphyrin a{sub 1u} Ï orbital with metal or oxygen orbitals is forbidden. These results imply that porphyrin radical type is an important determinant of the Fe{double bond}O bond strength in heme protein cation-radical intermediates. 34 refs., 5 figs.
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... NMP and NMI exhibit reson-ance enhancement of (C)C,H bending vibrations, similar to NMA?; (2) are the wavenumber positions of these modes consistent with the assignment of the 1390 cm-' band in proteins as a (C)C,H vibration?;... more
... NMP and NMI exhibit reson-ance enhancement of (C)C,H bending vibrations, similar to NMA?; (2) are the wavenumber positions of these modes consistent with the assignment of the 1390 cm-' band in proteins as a (C)C,H vibration?; and (3) is there intensity enhancment of low ...
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Resonance Raman spectroscopy has been shown to be a sensitive structural probe for biomacromolecules with intense chromophores.'While most studies have involved excitation in visible absorption bands, the availability of laser... more
Resonance Raman spectroscopy has been shown to be a sensitive structural probe for biomacromolecules with intense chromophores.'While most studies have involved excitation in visible absorption bands, the availability of laser lines at 363.8 and 351. I nm from high-...
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... 40,41. Since the aquo ions are well-known to be high-spin, only the sextet state for Fe 3+ and the quintet state for Fe 2+ were ... A different approach to modeling the solvent effects is to add explicit water molecules to build a... more
... 40,41. Since the aquo ions are well-known to be high-spin, only the sextet state for Fe 3+ and the quintet state for Fe 2+ were ... A different approach to modeling the solvent effects is to add explicit water molecules to build a second hydration sphere and giving an Me(H 2 O) 18 ...
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Raman frequencies and intensities in methylcyclohexane solution and infrared frequencies in Nujol mull, have been obtained and assigned for the skeletal modes of (t-C4H9 Li)4 and (t-C4H9 Li)4. A normal coordinate analysis, neglecting... more
Raman frequencies and intensities in methylcyclohexane solution and infrared frequencies in Nujol mull, have been obtained and assigned for the skeletal modes of (t-C4H9 Li)4 and (t-C4H9 Li)4. A normal coordinate analysis, neglecting hydrogen atoms, gave an overall frequency fit of 2% with a reasonable set of valence force constants. The calculated eigenvectors were used to transform the Raman intensities into bond polarizability derivatives. Because of coordinate mixing and the inherent sign ambiguity of molecular polarizability derivatives, there are eight sets of bond polarizability derivatives which are consistent with the measured intensities. Only one set, however, gives reasonable polarizability derivatives for CC stretching and CCC bending, and also shows the requisite invariance to isotope substitution. This set gives a low value for the Li-Li polarizability derivative, and application of the delta function potential equation suggests that the extent of Li-Li bonding is small, amounting to perhaps 5% of the total bonding electron density in the Li4C4 cage. This conclusion is consistent with the failure to observe Li‒Li spin-spin coupling in (t-C4H9Li)4.
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Page 1. 2074 J. Am. Chem. SOC. 1993, 115, 2074-2075 culations were carried out using the CASSCF/4-31G method (with six-orbital active space comprising the four ethylenic p" orbitals and the two C p" orbitals of C atoms ...
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... 10) Fodor, S. P. A.; Rava, RP; Copeland, R. A,; Spiro, TG J. Raman Specfrosc., in press. ... Acknowledgment is made to the National Science Foundation (CHE-8317080, TNS andCHE-8106084, TGS) and to the National Institutes of Health (GM... more
... 10) Fodor, S. P. A.; Rava, RP; Copeland, R. A,; Spiro, TG J. Raman Specfrosc., in press. ... Acknowledgment is made to the National Science Foundation (CHE-8317080, TNS andCHE-8106084, TGS) and to the National Institutes of Health (GM 13498, TGS) for support of this ...
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... The dynamics of CO-hemoglobin photodissociation have recently been studied with time-resolved resonance Raman ... in terms of molecular tension in the T state,12 although possible changes in ... The origin of this shift was thought to... more
... The dynamics of CO-hemoglobin photodissociation have recently been studied with time-resolved resonance Raman ... in terms of molecular tension in the T state,12 although possible changes in ... The origin of this shift was thought to be a charge-transfer interaction between the ...
Multicopper oxidases (MCOs) catalyze the oxidation of a diverse group of metal ions and organic substrates by successive single-electron transfers to O2 via four bound Cu ions. MnxG, which catalyzes MnO2 mineralization by oxidizing both... more
Multicopper oxidases (MCOs) catalyze the oxidation of a diverse group of metal ions and organic substrates by successive single-electron transfers to O2 via four bound Cu ions. MnxG, which catalyzes MnO2 mineralization by oxidizing both Mn(II) and Mn(III), is unique among multicopper oxidases in that it carries out two energetically distinct electron transfers and is tightly bound to accessory proteins. There are two of these, MnxE and MnxF, both approximately 12kDa. Although their sequences are similar to those found in the genomes of several Mn-oxidizing Bacillus species, they are dissimilar to those of proteins with known function. Here, MnxE and MnxF are co-expressed independent of MnxG and are found to oligomerize into a higher order stoichiometry, likely a hexamer. They bind copper and heme, which have been characterized by electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), and UV-visible (UV-vis) spectrophotometry. Cu is found in two distinct type 2 (...
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Protein dynamics on the microsecond (μs) time scale were investigated by temperature-jump fluorescence spectroscopy as a function of temperature in two variants of a thermophilic alcohol dehydrogenase: W87F and W87F:H43A. Both mutants... more
Protein dynamics on the microsecond (μs) time scale were investigated by temperature-jump fluorescence spectroscopy as a function of temperature in two variants of a thermophilic alcohol dehydrogenase: W87F and W87F:H43A. Both mutants exhibit a fast, temperature-independent μs decrease in fluorescence followed by a slower full recovery of the initial fluorescence. The results, which rule out an ionizing histidine as the origin of the fluorescence quenching, are discussed in the context of a Trp49-containing dimer interface that acts as a conduit for thermally activated structural change within the protein interior.
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The dynamics of manganese solid formation (as MnOx) by the multicopper oxidase (MCO)-containing Mnx protein complex were examined by electron paramagnetic resonance (EPR) spectroscopy. Continuous-wave (CW) EPR spectra of samples of Mnx,... more
The dynamics of manganese solid formation (as MnOx) by the multicopper oxidase (MCO)-containing Mnx protein complex were examined by electron paramagnetic resonance (EPR) spectroscopy. Continuous-wave (CW) EPR spectra of samples of Mnx, prepared in atmosphere and then reacted with Mn(II) for times ranging from 7 to 600 s, indicate rapid oxidation of the substrate manganese (with two-phase pseudo-first-order kinetics modeled using rate coefficients of: k1obs = 0.205 ± 0.001 s(-1) and k2obs = 0.019 ± 0.001 s(-1)). This process occurs on approximately the same time scale as in vitro solid MnOx formation when there is a large excess of Mn(II). We also found CW and pulse EPR spectroscopic evidence for at least three classes of Mn(II)-containing species in the reaction mixtures: (i) aqueous Mn(II), (ii) a specifically bound mononuclear Mn(II) ion coordinated to the Mnx complex by one nitrogenous ligand, and (iii) a weakly exchange-coupled dimeric Mn(II) species. These findings provide new insights into the molecular mechanism of manganese mineralization.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full... more
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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... of Lead( 11) la Victor A. MaroniIb and Thomas G. Spiro Contributionfrom the Department of Chemistry, Princeton University, Princeton, New Jersey. Received May 28, 1966 ... 505 cm-'; this (12) RE Hester and R. A. Plane, Znorg.... more
... of Lead( 11) la Victor A. MaroniIb and Thomas G. Spiro Contributionfrom the Department of Chemistry, Princeton University, Princeton, New Jersey. Received May 28, 1966 ... 505 cm-'; this (12) RE Hester and R. A. Plane, Znorg. Chem., 3, 769 (1964). ...
Resonance Raman (RR) spectra are reported for radical cations of M" OEP (OEP= octaethylporphyrin; M= Zn, Mg, Ni, Cu) and for the perchlorate and bromide salts of [Co"'OEP]+, produced by... more
Resonance Raman (RR) spectra are reported for radical cations of M" OEP (OEP= octaethylporphyrin; M= Zn, Mg, Ni, Cu) and for the perchlorate and bromide salts of [Co"'OEP]+, produced by electrochemical and/or chemical oxidation. The enhancement ...
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... References. 1. PM Harrison. In: F. Gross, Editor, Iron Metabolism, Springer, New York (1964), p. 40. 2. CFA Bryce and RR Crichton. J. Biol. Chem. ... Biochem. J. 126 (1972), p. 151. View Record in Scopus | Cited By in Scopus (57). 7.... more
... References. 1. PM Harrison. In: F. Gross, Editor, Iron Metabolism, Springer, New York (1964), p. 40. 2. CFA Bryce and RR Crichton. J. Biol. Chem. ... Biochem. J. 126 (1972), p. 151. View Record in Scopus | Cited By in Scopus (57). 7. A. Mazur and A. Carleton. J. Biol. Chem. ...
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Introduction There is long-standing interest in understanding the structure and dynamics of x-radical species of tetrapyrrolic chro-mophores,' which play important roles in a number of biological processes.2 The x-anion and n-cation... more
Introduction There is long-standing interest in understanding the structure and dynamics of x-radical species of tetrapyrrolic chro-mophores,' which play important roles in a number of biological processes.2 The x-anion and n-cation radicals, produced by the addition and removal of ...
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The study of metalloproteins by resonance Raman (RR) spectroscopy began two decades ago, with the publication by Long and coworkers of the first RR spectrum of the iron-sulfur protein rubredoxin (1,2). This simple spectrum, which... more
The study of metalloproteins by resonance Raman (RR) spectroscopy began two decades ago, with the publication by Long and coworkers of the first RR spectrum of the iron-sulfur protein rubredoxin (1,2). This simple spectrum, which contained only four bands attributed to the Fe-S stretching and bending vibrations of the protein FeS(4) cluster, generated much interest because of the potential of RR spectroscopy for monitoring structures of metal centers in complex biological systems (3,4). The unique ability of this technique to study the coordination environment of transition metals in proteins derives from its dramatic increase in detection sensitivrty and selectivity for vibrations closely associated with atoms at the absorbing center(s) in the molecule. When the molecule is excited with a strong monochromatic light whose energy matches that of an electric-dipole allowed electronic transition, a vibronic coupling with the electronically excited state increases the probability of observing Raman scattering from vibrational transitions in the electronic ground state, and the modes that do show enhancement are localized on the chromophore (i.e., on the group of atoms that gives rise to the electronic transition). Since vibrational frequencies are sensitive to molecular bond strength, number of atoms, geometry, and coordination environment, the positions of the enhanced Raman bands can be used to monitor the chromophoric structure. Metalloproteins frequently exhibit allowed electronic transitions, owing to π-π* and/or ligand-metal charge-transfer (CT) transitions (5), and consequently, they give wide scope to the application of RR spectroscopy. A great many RR studies of heme proteins, cobalamin, chlorophylls, carotenoids, flavin nucleotides, the visual pigments, and bacteriorhodopsin, and a variety of iron and copper metalloprotein sites have been carried out in laboratories around the world (6-11).
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Resonance Raman and electron paramagnetic resonance studies on oxidized and ferricyanide-treated Clostridium pasteurianum ferredoxin. Vibrational assignments from 34S shifts and evidence for conversion of 4 to 3 iron-sulfur clusters via oxidative damage. Vibrational assignments from 34S shifts an...more
Resonance Raman spectra are reported for oxidized ferredoxin from Clostridium pasteurianum and for protein reconstituted with 34S2-, using 4579 A laser excitation. The spectra are of much higher quality than that previously reported, and... more
Resonance Raman spectra are reported for oxidized ferredoxin from Clostridium pasteurianum and for protein reconstituted with 34S2-, using 4579 A laser excitation. The spectra are of much higher quality than that previously reported, and the 34S shifts provide assignments of the Fe-S modes. After treatment with ferricyanide, the resonance Raman spectrum closely resembles that of the [3Fe-3S] protein, ferredoxin II from D. gigas; the 34S shifts aid in assignments of the [3Fe-3S] modes. The epr signal associated with the [3Fe-3S] cluster (g = 2.01) corresponds maximally to 0.80 spin/molecule. Anaerobic addition of excess sulfide to the reduced, ferricyanide-treated protein regenerates a [4Fe-4S]1+ epr spectrum, equivalent in intensity to the [3Fe-3S] signal. The ubiquitous occurrence of a g = 2.01 signal in preparations of [4Fe-4S] proteins can be attributed to variable amounts of [3Fe-3S] cluster generated by adventitious oxidation. The ready conversion of [4Fe-4S] to [3Fe-3S] cluste...
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... An example of recent work is G. Biedermann and L. Newman, Arkiv Kemi, 22, 203 (1964). (3) RW Holmberg, KA Kraus, and J. S. Johnson, J. Am. Chem. SOC., 78, 5506 (1956). (4) R. S. Tobias and S. Y. Tyree, Jr., ibid., 82, 3244 (1960). ...
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