Electron paramagnetic resonance studies of riboflavin and its derivatives

Guzzo, Anthony V.; Tollin, Gordon

doi:10.1016/0003-9861(64)90022-0

Cited by 23 publications

(10 citation statements)

References 4 publications

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“….I. Aside from a small decrease in the line separation (2.9 vs 3.5 gauss for the main splitting) the spectrum of I is very similar t o those previously obtained for unsubstituted and chlorine-substituted isoalloxazines (Guzzo and Tollin. 1964).…”

Section: Resultssupporting

confidence: 82%

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Tollin

Chan

Malefyt

et al. 1979

Photochem & Photobiology

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Abstract— 8‐Cyanoisoalloxazines have been previously shown to form highly stable radical species at basic pH. We have measured the electron spin resonance (EPR) spectra of the radical forms of 8‐cyano‐10‐methyl‐3‐sulfopropylisoalloxazine (I) at both acidic and basic pH. In both cases. the EPR spectra are similar to those obtained from unsubstituted isoalloxazines. with no indication of hyperfine splitting due to the cyano nitrogen. Laser photolysis of I in the presence of EDTA at basic pH generates two radical species. One of these decays rapidly by a first‐order process to produce thc stable radical. The rate of this decay depends upon the initial flavin concentration, thus suggesting a reaction of the radical with oxidized isoalloxazine. The rates of reaction of the radical species with added oxidants (O2, ferricyanide), and the pH‐dependence of stable radical formation, indicate that the rapidly‐decaying species is the anion radical of I, and that the stable radical is formed by its reaction with oxidized flavin. Laser photolysis of I at acidic pH, as well as of 8‐cyano‐5‐deaza‐isoalloxazine at acidic or basic pH, does not generate stable radical species. I‐Deazaisoalloxazines do not give radical transients at all upon laser photolysis.

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Section: Resultssupporting

confidence: 82%

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Tollin

Chan

Malefyt

et al. 1979

Photochem & Photobiology

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“…The spacing between the hyperfine structure lines are about 3.5 G or about the same as found for PlR-(R = H or CH,COOC,H5) [8,9,13,15,26]. The isotopic substitutions which have been applied previously for flavin free radicals have now also been used for chelates of 3-alkylated flavin (Fig.6).…”

Section: Hyperfine Interaction Within the Plavin Ligandmentioning

confidence: 62%

Flavin Radical Chelates as Studied by Electron Spin Resonance and Isotopic Substitution

Müller

Eriksson

Ehrenberg

1970

European Journal of Biochemistry

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The complexes formed between Zn2+ or Cd2+ and half-reduced flavins (isoalloxazines) in neutral aqueous as well as non-aqueous media were studied by electron spin resonance. Formation of 1 : 1 radical chelates between anionic radicals and Zn2+ as well as Cd2+ were found to occur. The stability constants at 20" for the chelates were estimated. A number of flavin derivatives were investigated. The spin density distribution was mapped by means of isotopic substitutions (ZH, 1 5 N , 6*Zn, 67Zn, 1Wd, 113Cd, and 114Cd). The spin distribution within the ligand is similar to that found earlier for the anionic flavin radical. Spin delocalization to the metals was observed and h y p e r h e coupling constants for magnetic isotopes determined by direct measurements and spectra simulations. The difference in spin delocalization between Zn and Cd is discussed.Evidence has accumulated indicating that flavin radicals (flavosemiquinones) occur as intermediates in the reactions of certain metal containing flavoenzyme [3-51. From microwave saturation experiments with electron spin resonance it was suggested [6] that metal-flavin interaction exists within the metalloflavoproteins. The nature of this interaction Among these five species, l?lR-, obtained by one equivalent reduction of Fl,,R, is the only one to show appreciable affinity for heavy metal ions [7,10,111 and therefore is capable of forming flavosemiquinone, or flavinradical, chelates (Mel?lR)+ (Fig.l).At neutral pH the free disproportionated system will "comproportionate') upon addition of d-metal Fig. 1. The structures of the oxidized, anionic radical and radical chelate form of flavins (isoalloxazines). Ring numbering system according to IUPAC-IUB nomenclature tentative rules, J . Biol. Chem. 241 (1966) 2987 is not yet understood and flavin chelates can therefore a t present not be excluded. The essential constituents of the half-reduced flavocoenzyme system a t equilibrium in dilute aqueous solution of pH 5 to 9 are the following molecular species : The quinonc Fl,,R (Fig.l), the hydroquinone Fl,,dRH, and its anion Fl,,RH-, and finally the semiquinonesl?lRHand PlR- (Fig

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“…For example, the relative positions of C-7-CH, and C-8-CH, in the Eu and Mo sequences conlpared to their positions in the C d sequence bear out the increased importance of electron delocalization (i.e., Fermi contact interaction) in the Mo complex. The C-7-CH, is spatially closer to a metal atom complexed at 0 -4 and N-5, but the n-electron spin density at position 7 is near 0.0 whereas it is near 0.15 at position 8 (1).…”

Section: The Flucine and Moclmentioning

confidence: 93%

sHigh resolution ¹H nuclear magnetic resonance studies of a flavine and its product with MoCl₄

Roberie¹,

Bhacca²,

Selbin³

1977

Can. J. Chem.

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The high resolution 1H nmr spectra of the substituted flavine, 3-N-methyltetraacetylriboflavine (3-Me-TARF), and its non-aqueous solution complexes with Gd(fod)3, Eu(fod)3, MoCl4, and MoCl4•2CH3(CH2)2CN, were studied in order to try to discern the binding sites of the flavine as it attaches to the molybdenum. Evidence was found that all three metal atoms, Gd(III), Eu(III), and Mo(IV), are attached in solution not only by the primary binding (chelating) sites of the flavine, viz., the O-4 and N-5 atoms, but also by an acetyl oxygen atom, at the C-4′ site of the ribityl side chain. 300 MHz spectra of the 3-Me-TARF have permitted the coupling constants for the side chain methine and methylene protons to be obtained.

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Electron paramagnetic resonance studies of riboflavin and its derivatives

Cited by 23 publications

References 4 publications

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Flavin Radical Chelates as Studied by Electron Spin Resonance and Isotopic Substitution

sHigh resolution ¹H nuclear magnetic resonance studies of a flavine and its product with MoCl₄

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Electron paramagnetic resonance studies of riboflavin and its derivatives

Cited by 23 publications

References 4 publications

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Some One Electron Reduction Products of Flavin Analogs: Cyanoisoalloxazines and Deazaisoalloxazines

Flavin Radical Chelates as Studied by Electron Spin Resonance and Isotopic Substitution

sHigh resolution 1H nuclear magnetic resonance studies of a flavine and its product with MoCl4

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sHigh resolution ¹H nuclear magnetic resonance studies of a flavine and its product with MoCl₄