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Toassess the potential use of O–H stretching modes of aromaticalcohols as ultrafast local probes of transient structures and photoacidity,we analyze the response of the O–H stretching mode in the 2-naphthol-acetonitrile(2N–CH3CN) 1:1 complex after UV photoexcitation.We combine femtosecond UV-infrared pump–probe spectroscopyand a theoretical treatment of vibrational solvatochromic effectsbased on the Pullin perturbative approach, parametrized at the densityfunctional theory (DFT) level. We analyze the effect of hydrogen bondingon the vibrational properties of the photoacid–base complexin the S0state, as compared to O–H stretching vibrationsin a wide range of substituted phenols and naphthols covering the3000–3650 cm–1frequency range. Ground statevibrational properties of these phenols and naphthols with varioussubstituent functional groups are analyzed in solvents of differentpolarity and compared to the vibrational frequency shift of 2N inducedby UV photoexcitation to the 1Lbelectronicexcited state. We find that the O–H stretching frequency shiftsfollow a linear relationship with the solvent polarity function F0= (2ε0– 2)/(2ε0+ 1), where ε0is the static dielectricconstant of the solvent. These changes are directly correlated withphotoacidity trends determined by reported pKavalues and with structural changes in theO···N and O–H hydrogen-bond distances inducedby solvation or photoexcitation of the hydrogen-bonded complexes. [ABSTRACT FROM AUTHOR]

Reduction potentials and pKavalueswere calculated for intermediates and products along three major pathwaysfor guanine oxidation using the B3LYP and CBS-QB3 levels of theorywith the SMD implicit solvation model. N-methylatednucleobases were used as models for nucleoside species. Ensemble averagedreduction potentials at pH 7 (E7) wereobtained by combining calculated standard reduction potentials withcalculated pKavalues in addition to accountingfor tautomerization energies. Calculated pKavalues are reasonable based on experimental estimates and chemicalintuition. Pathway A leads to guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp).The first step is the oxidation of 8-oxoguanine which proceeds bythe loss of an electron followed by the loss of two protons and lossof another electron, yielding 8-oxopurine. The calculated E7values for the remaining intermediates andproducts are at least 0.3 V higher than that of guanine, indicatingthat further oxidation of these species is unlikely. Pathway B leadsto two formamidopyrimidine isomers (FAPyG and 2,5FAPyG). Species alongthis pathway have calculated reduction potentials that are much lowerthan the oxidation potential for guanine and would likely be veryshort-lived in an oxidatively stressed environment. Pathway C leadsto reduced spiroiminodihydantoin and 5-carboxamido-5-formamido-2-iminohydantoin (2Ih).Similar to pathway A, the calculated reduction potentials for speciesalong this pathway are at least 0.4 V higher than that of guanine. [ABSTRACT FROM AUTHOR]