The oxidation of a reduced pyridine nucleotide analog by flavins

Suelter, Clarence H.; Metzler, David E.

doi:10.1016/0006-3002(60)91518-3

Cited by 125 publications

(56 citation statements)

References 25 publications

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“…A special case in the present context is 10-(formylmethyl)-flavin (I), one of the key intermediates in the photolysis of riboflavin [21]. This compound has a basic pK of 3.5 because protonation goes along with reversible formation of the cyclic aminal Ia as shown in Scheme 2.…”

Section: The Photoreactive Speciwmentioning

confidence: 99%

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

Schöllnhammer¹,

Hemmerich²

1974

Eur J Biochem

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1. The method of "photohydroxylation" of azaheteroaromatics, known in the phenazine and alloxazine series, has been applied to flavin ( = isoalloxazine) derivatives FbxH. The products habe been identified as 6-and 9-hydroxyflavins (FlOx-6/9-OH). On this basis it was possible to assign a 6-hydroxyflavin structure to the new flavocoenzyme chromophores described by Mayhew et al. in the accompanying paper.2. I n agreement with the data obtained by Dekker et al. in a recent laser study on alloxazine, we find that the reaction proceeds via addition of water, alcohols or carboxylic acids by the lowest excited singlet state of flavin with synchronous intramolecular hydrogen shift from the site of RO-addition [= C(6) or C(9)l towards N(5) and subsequent oxidation of the 6/9-hydroxy-1 $-dihydroflavin formed.3. The photoaddition reaction occurs in competition with photodehydrogenation of available CH-bonds by the lowest excited flavin triplet, in which case the CH-substrate may be provided by the solvent ROH or, when R = H, by methyl groups of a second flavin molecule (= flavin autophotolysis). This photodehydrogenation may be suppressed by 0,-dependent triplet quenching and/or by applying a positive charge to the flavin (RFl,,H+, R = H or alkyl) in order to inhibit the reaction with itself.4. Differentiation of 6-and 9-hydroxyflavin isomers was possible by double resonance evaluation of the proton coupling between the residual Ar-H and the adjacent methyl group, by evaluation of the electron paramagnetic resonance hyperhe coupling for the residual Ar-H in the radical cations 1 ,5-RHlk6/9-OH, and by formation of cupric chelates from 6-hydroxy-flavin as compared to the lack of metal affinity in the 9-isomer. lH-Nuclear magnetic resonance, electron paramagnetic resonance and visible spectra and their dependence on the state of ionisation of hydroxyflavins are discussed. Hydroxyflavin anions as well as their N( 1)-alkylated meso-ionic derivatives are shown to exhibit characteristic long-wavelength absorption bands ranging from 50 to 800 nm with maxima around 600 nm and low molar absorption coefficients between 500 and 3000 M-bm-l (as compared to =lo4 for the first n, n* transition a t %400 nm), which might be readily mistaken for "flavin-substrate charge transfer'' bands. 5. 9-Methoxy-flavins could be spectroscopically related to 9 : 10-bridged cyclic hemiacetals obtained upon ring closure of 9-hydroxy groups with lob-carbonyl functions. Such cyclic hemiacetals can be trapped in the acid photolysis of 10-(hydroxyalky1)-flavins, e.g. riboflavin or flavocoenzymes, in a sequence of 10-side-chain dehydrogenation and N ( 1)-cycloaminal cation formation of the lob-carbonyl formed, which results in a quenching of the further photolysis in favor of 9-photoaddition.Since the discovery of covalent 8a-dimerization of riboflavin and its derivatives [3], evidence has been accumulating with respect to the reactivity of the benzenoid subnucleus of flavoquinone (Fl0,H) Abbreviations. EPR, electron paramagnetic resonance ; NMR, nuclear magnet...

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Section: The Photoreactive Speciwmentioning

confidence: 99%

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

Schöllnhammer¹,

Hemmerich²

1974

Eur J Biochem

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“…values of the corresponding protolytic equilibria of the lumiflavin triplet were found to be 4,4, ± 0·1 and 9·8 ± 0·15. 1974;accepted 19 August 1974) Quantum yield and product distribution of f1avin photoreactions are frequently found to be strongly pH dependent (Suelter and Metzler, 1960;Penzer, 1970;Carr and Metzler, 1970;Cairns and Metzler, 1971;Haas and Hemmerich, 1972).…”

Section: Determination Of the Pk Values Of The Lumiflavin Triplet Stamentioning

confidence: 99%

DETERMINATION OF THE pk VALUES OF THE LUMIFLAVIN TRIPLET STATE BY FLASH PHOTOLYSIS

Schreiner

Steiner

Kramer

1975

Photochem & Photobiology

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Lumiflavin was prepared by photolysis of an alkaline aqueous solution of riboflavin (Knowles and Roe, 1968). As a solvent we used triply distilled water, as buffers (0,2 M) (Schwabe, 1958): pH 1-3'7 sodium acetate, hydrochloric acid pH 3·7-5·6 sodium acetate, acetic acid pH 6-12 potassium dihydrogen phosphate, sodium hydroxide pH 13 potassium chloride, sodium hydroxide (E. Merck. Darmstadt, Germany). RESULTSDependence of the lumiflavin triplet -triplet absorption spectrum on pH. Figure I shows the transient change in absorption when lumiflavin soJutions of pH = 2, pH = 7, and pH = 13 are flashed. From this the triplet-triplet absorption spectra of the acid (pH = 2), neutral (pH = 7), Kramer and Maute, 1972). The flash energy could be varied between 300 J and 900 J. The half duration of the flash was about 4-6 JlS (3001) and 6 JlS (900 J). The cuvette was surrounded by a Kodak-Wratten filter No. 2A which absorbs light of wavelength shorter than 400 nm. Using the flash apparatus described above (kinetic spectrophotometry) the spectra were recorded point-by-point at intervals of 10 nm (half-width value 2·5 nm) in the spectral region from 300 to 780 nm; the spectra were corrected for stray light.The high buffer concentration ensures that the protolytic equilibria in the triplet state are really established.Oxygen was removed by bubbling nitrogen (>99,9%) through the solutions for 45 min. The results with solutions treated in this way were identical to those with solutions degassed by the 'freezepump-and-thaw' procedure.The flash apparatus was the same as described earlier (Fischer, 81 S. SCHREINER, U. STEINER and H. E. A. KRAMER* Institut fuer Physikalische Chemie der Universitaet Stuttgart, Germany•Author to whom correspondence should be addressed. DETERMINATION OF THE pK VALUES OF THE LUMIFLAVIN TRIPLET STATE BY FLASH PHOTOLYSISConsequently one has to assurne the existence of at least three different protolytic forms for the excited states, too. Kavanagh and Goodwin (1948) found a marked change of f1uorescence of lumiflavin and riboflavin in the regions of pH 2-4 and 9-10'5. The pK values of the lumiflavin triplet are still unknown. For f1avins, there are only a few investigations of the triplet state with respect to variation of the pH (Shiga and Piette, 1964; Lhoste et ai., 1966;Katan et al., 1971).In this paper we present the results of our investigations on the triplet-triplet absorption spectra of the acid ('LfH2+), the neutral ('LfH) and the basic ('Ln forms of the lumiflavin triplet as detected by flash photolysis.Abstract-The triplet-triplet absorption spectra in aqueous solution of the acid ('UH,+), the neutral ('UH) and the basic ('Ln forms of lumiflavin (6,7,9-trimethylisoalloxazine) were measured by flash photolysis. The pK. values of the corresponding protolytic equilibria of the lumiflavin triplet were found to be 4,4, ± 0·1 and 9·8 ± 0·15.

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“…The other three compounds (RF, FMF, CDRF), present in the aqueous phase, are determined by a three-component assay at 385, 410, 445 nm, corresponding to the absorption maxima of FMF, CDRF and RF, respectively [11]. The absorption maxima of RF and FMF (445 nm, pH 7.0) can be distinguished at pH 2.0 where FMF exists in a protonated form (pK a 3.5) [34] and thus can be assayed by this method. CMF is a minor product of the oxidation of FMF [13,17,35] and has not been considered in the assay scheme.…”

Section: Spectrophotometric Assaymentioning

confidence: 99%

Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study

Sheraz

Kazi

Ahmed

et al. 2014

Journal of Photochemistry and Photobiology A: Chemistry

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a b s t r a c tA study of the photodegradation of 5 × 10 −5 M riboflavin (RF) in 0.2-1.0 M phosphate buffer in the presence and absence of 2.50 × 10 −4 M caffeine at pH 6.0-8.0 has been carried out. RF in phosphate buffer is photodegraded simultaneously by normal photolysis (photoreduction) and photoaddition reactions giving rise to lumichrome (LC) and cyclodehydroriboflavin (CDRF) as the main final products, respectively. RF and its photoproducts, formylmethylflavin (FMF), lumiflavin (LF), LC and CDRF in degraded solution have been determined by a specific multicomponent spectrophotometric method with an accuracy of ±5%. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF are 5.47-15.05 × 10 −3 min −1 , 1.06-8.30 × 10 −3 min −1 and 4.31-8.05 × 10 −3 min −1 , respectively. An increase in phosphate concentration leads to an increase in the rate of formation of CDRF and alters the photodegradation of RF in favor of the photoaddition reaction. This photoaddition reaction is further enhanced in the presence of caffeine which results in a further decrease of the fluorescence of RF in phosphate buffer. Caffeine may facilitate the photoaddition reaction by suppression of the photoreduction pathway of RF.

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The oxidation of a reduced pyridine nucleotide analog by flavins

Cited by 125 publications

References 25 publications

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

Nucleophilic Addition at the Photoexcited Flavin Cation: Synthesis and Properties of 6- and 9-Hydroxy-Flavocoenzyme Chromophores

DETERMINATION OF THE pk VALUES OF THE LUMIFLAVIN TRIPLET STATE BY FLASH PHOTOLYSIS

Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study

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