Assignment and the effect of hydrogen bonding on the vibrational normal modes of flavins and flavoproteins

Abstract

are observed. If the vI were associated with a residual ground-state population, it is obvious that modes associated with the bpzo of this residual ground-state complex should also be observed and that their intensities (relative to the features labeled u, in Figure 4B) would closely approximate those observed in Figure 2D. We have confirmed the fact that the relative enhancements of bpyo and bpzo at 350.7 nm are very similar to those at 356.4 nm. Thus, it is not reasonable to argue that relative enhancements at 354.7 nm would be significantly different than at 356.4 nm. Therefore, the absence of wi features in Figure 4B is inconsistent with assignment of the v, features to a residual ground-state population.The TR3 spectrum of the heteroleptic partner complex, Ru-is also consistent with the Dallinger-Woodruff assignment of the u, modes. As can be seen in Figure 2H, the RR spectra of the ground-state species, excited at 356.4 nm, exhibits strong bands associated with both fragments, bpyo and bpzo. The TR3 spectrum ( Figure 4C) excited at 354.7 nm exhibits both u, and w, features, as is expected, given the interpretation that the 3MLCT state is properly formulated as [Ru3(bpy)-(bp~)(bpz-)]~+. To summarize this section, while it is obviously true that a residual population of ground-state species can contribute intensity to the features labeled v, and wI in the TR3 spectrum, these modes are'also enhanced in the spectrum of the 3MLCT state species, Le., even in the absence of a residual ground-state population. We have also confirmed the fact that the enhancements (relative to Sod2-internal standard) of the bpyo "neutral ligand" modes in the TR3 spectrum of R~( b p y ) ,~+ and Ru(bpy),(bp~)~+ (Figure 4, traces A and B, respectively) are identical within experimental error. Such behavior obviously supports the view that the origin of the "neutral ligand" modes in both cases is identical; Le., in both cases the fragment responsible for scattering is formulated as R~~+ ( b p y )~.Thus, the original (Dallinger-Woodruff) assignment of these features to modes of the neutral bipyridine fragments of the 3MLCT state is supported bq the present work.For a number of years we have studied the resonance Raman spectra of flavins and flavoproteins; these studies included investigation of the solvent effect on the 13 resonance Raman (RR) bands between 1700 and 1100 cm-'. These investigations led us to the conclusion that two bands, I1 and X, in the Raman spectrum of flavins are strongly influenced by the degree of hydrogen bonding. Other investigators have made similar suggestions based on shifts in these two bands and in others. We report the QCFF-?r calculations of 87 normal modes of lumiflavin (7,8,1O-trimethylisoalloxazine). We have also calculated resonance Raman intensities and isotope shifts of each resonance Raman active mode. The generally good agreement between calculated and observed values supports our assignment of the experimental bands. The QCFF-a assignments are in general agreement with earlier calculations leadin...

Resonance Raman Study on the Oxidized and Anionic Semiquinone Forms of Flavocytochrome b2 and l-Lactate Monooxygenase. Influence of the Structure and Environment of the Isoalloxazine Ring on the Flavin Function

“…be provided by band X. This band involves the stretching modes of the C4N3 and C2N3 bonds coupled with a bending mode of the N3H group (Abe & Kyogoku, 1987;Lively & McFarland, 1990). As previously proposed by Lively and McFarland (1990), it exhibits a rough sensitivity to the H-bonding state at the N3H site since an increase in H-bonding interaction produces an increase in the band X frequency.…”

“…c Average of Raman frequencies of DAOX complexed with benzoate derivatives (Nishina et al, 1981). d Mode assignment from Bowman and Spiro (1981), Abe and Kyogoku (1987), and Lively and McFarland (1990). e See Figure 7 for the atom labeling and ring numbering of the isoalloxazine macrocycle.…”

Raman mode‐selective spectroscopic imaging of coenzyme and enzyme redox states

“…On the basis of literature and calculations [24] , our approximate description of the Raman bands is given in Table 1, and a diagram describing the normal modes of fully reduced flavin is given in Fig. 3.…”

Resonance Raman spectra of the neutral and anionic radical semiquinones of flavin adenine dinucleotide in glucose oxidase revisited

“…Band X has been shown to correlate well to the strength of hydrogen-bonding at N(3)-H and to the total number of hydrogen-bonding interactions involving ring III of the isoalloxazine ring. 26,36 Tegoni et al 26 have pointed out that GO has the fewest hydrogen bonds to its flavin cofactor. The RR spectrum of tetraacetylriboflavin in the non-hydrogen-bonding solvent acetonitrile also has …”

“…This can again be explained by a weaker hydrogen-bonding environment of the FAD cofactor. 13,22,36 Further analysis of the vibrations of the flavin neutral radical semiquinone is not possible at this point due to the lack of vibrational mode assignments. Currently we are working in our lab on these vibrational mode assignments by isotopic labeling experiments and theoretical approaches.…”