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The two-phase reaction of NabMs (LOM~-= [(?s-C~H~)Co(P(0)(OCH3)213]-) in 1% H2SO4 with Ru04 in C C 4 affords the edge-sharing octahedral dimer [(LoM~)(HO)RU~(~-O)~RU~~(OH)(LOM~)] which is diprotonated by aqueous CF3SO3H to the corresponding salt [(~M~)(H~O)RU~~(~-O)ZRU~~(OH~)(LOM~)] [CF3S03]2. This dimer salt is oxidized by C6HJO in CH3CN to [(LoM~)(~)Ru~(c~-O)~RU~(O)(LOM~)] and reduced by alcohols, aldehydes, or triphenylphosphine in CH3CN to [(LOM~)(CH~CN)RUI~~(~-OH)~RU~I~(NCCH~)(LOM~)] [CF3S0312. In buffered aqueous solution, the diprotonated RuIV-RuW dimer reacts with formaldehyde to afford a triply bridged dimer, [(LOM~)RU~~~(L(-OH)~(L(-HCOO)RU~~~(LOM.)] [CF,S03]. The latter reaction appears to be autocatalytic via an inner-sphere mechanism. The RuI1I-Ru1If formate adduct is oxidized by AgCF3SO3 to the RuIv-RuIV analog [ (LoM~)Ru~~(~-~)~(c~-HCOO)RU~~(L~~,)] [CFpSO3], which slowly reacts with aqueous formaldehyde to regenerate the Ru1II-RuII1 adduct and free formate. The dimeric system in aqueous solution functions as an electrocatalyst for the oxidation of formaldehyde at low anodic potentials (near 0.0 V versus SCE at pH 8.5). Both RuIII-RuIII dimers have been characterized by X-ray crystallography. Crystal data: [ (LoM~) ( C H~C N ) R U~I~(~-O H )~-A, c = 13.457(3) A, a = 71.32(2)', /3 = 85.35(2)', y = 80.01(3)O, V = 1328.9(6) A3, 2 = 2, R(Fo) = 0.040; [ (LOM~)RU~~~(~-OH)~(CC-HCO~)RU~~~(LOM~)] [ CF3SO3]*2H20, R u~C O Z C~~H~~~Z~P~S F~, monoclinic, P21/n, with a = 14.356(2) A, b = 23.839(6) A, c = 15.284(3) A, /3= 115.44(1)', V -4723.5(18) A3, Z = 4, R(Fo) = 0.033. RU111(NCCH3)(Lo~,)] [CF3SO3]2, R U~C O~C~E H~, O~~N~P~S~F~, triclinic, Pi, with a = 8.626(3) A, b = 12.275(2)

The FTIR spectra of six argon-matrix-isolated flavonols were measured. Carbonyl stretching frequencies for the following compounds were the following:  flavone, 1669 cm-1; chromone, 1676 cm-1; 5-hydroxyflavone (5HF), 1660 cm-1; 3-hydroxyflavone (3HF), 1652 cm-1; 5-methoxyflavone (5MF), 1672 cm-1; and 3-methoxyflavone (3MF), 1658 cm-1. The 3HF carbonyl stretching frequency assignment represents a correction to the literature values:  (1628.6 cm-1 in an argon matrix and 1621 cm-1 in the liquid phase). ,− The hydroxyl stretch modes for 5HF and 3HF were observed at 2935 and 3320 cm-1, respectively, in agreement with the literature values. − While the hydroxyl stretch modes predict that the 5HF intramolecular-hydrogen bond to the carbonyl is stronger than that of 3HF, the carbonyl stretch frequency of 3HF is red-shifted more than that of 5HF. In analogy to hydroxyl-substituted flavones, methoxyl substitution at the flavone 3 position also results in a greater carbonyl red-shift than at the 5 position. Relative to the methoxyflavones, the effect of hydroxyl substitution on the carbonyl is clearly greater in 5HF than in 3HF. Density functional calculations at the B3LYP/6-31G(d) level are consistent with the experimental findings. Calculated OH···O intramolecular hydrogen bond distances and O−H···O angles were 1.70 Å and 149° for 5HF and 1.94 Å and 122° for 3HF, consistent with greater hydrogen-bonding in 5HF than in 3HF. Changes in the bond distances from 5MF to 5HF are consistent with hydrogen bonding, encouraging a resonance form resembling the excited-state proton-transfer tautomer of 5HF that weakens the carbonyl. Similarly, changes in the bond distances from 3MF to 3HF suggest that hydrogen bonding stabilizes a zwitterionic resonance form that also weakens its carbonyl. This zwitterionic resonance form of 3HF resembles the excited state proposed for its unusual fluorescence and could be responsible for the facile energy transfer to this state.

SAW1 is required for efficient removal by the Rad1-Rad10 nuclease of 3′ non-homologous DNA ends (flaps) formed as intermediates during two modes of double-strand break repair in S. cerevisiae, single-strand annealing (SSA) and synthesis-dependent strand annealing (SDSA). Saw1 was shown in vitro to bind flaps with high affinity, but displayed diminished affinity when flaps were short (< 30 deoxynucleotides [nt]), consistent with it not being required for short flap cleavage. Accordingly, this study, using in vivo fluorescence microscopy showed that SAW1 was not required for recruitment of Rad10-YFP to DNA double-strand breaks (DSBs) during their repair by SSA when the flaps were ~10 nt. In contrast, recruitment of Rad10-YFP to DSBs when flaps were ~500 nt did require SAW1 in G1 phase of cell cycle. Interestingly, we observed a substantial increase in colocalization of Saw1-CFP and Rad10-YFP at DSBs when short flaps were formed during repair, especially in G1, indicating significant recruitment of Saw1 despite there being no requirement for Saw1 to recruit Rad10. Saw1-CFP was seldom observed at DSBs without Rad10-YFP. Together these results support a model in which Saw1, and Rad1-Rad10 are recruited as a complex to short and long flaps in all phases of cell cycle, but that Saw1 is only required for recruitment of Rad1-Rad10 to DSBs when long flaps are formed in G1.