It is shown that the mutagen base analogue 2-aminopurine is hydrogen-bonded at its 1-ring position when annealed with cytosine in DNA. The presence of stably hydrogen-bonded regions proximal to the 2-aminopurine-cytosine base mispair is a prerequisite for the occurrence of two hydrogen bonds coupling the bases at their 1-3- and 2-2-positions. We consider the possibility that, in the resulting h...

Even though high-fidelity polymerases copy DNA with remarkable accuracy, some base-pair mismatches are incorporated at low frequency, leading to spontaneous mutagenesis. Using high-resolution X-ray crystallographic analysis of a DNA polymerase that catalyzes replication in crystals, we observe that a C • A mismatch can mimic the shape of cognate base pairs at the site of incorporation. This sha...

The present paper describes a new enzyme from animal tissues which catalyzes the keto-enol tautomeriaation of the phenylpyruvic acids. Preliminary accounts of this tautomerase have been published (1, 2). The enzyme has not yet proved to be essential in any biological reaction, but a physiological role may be expected since specific tautomers of a-keto acids are substrates or products in some re...

Infrared absorption spectra, in the vapour phase, have been recorded in the regions of NH, OH and carbonyl stretching frequencies, for a series of 1-substituted uracils and 9-substituted adenine and hypoxanthine, formal analogues of the natural nucleosides of uracil, adenine and hypoxanthine found in DNA and/or RNA. A number of related analogues was also examined, including the N-methyl derivat...

The analytical reagent Nitron is a mesoionic compound whose structure consists of a cationic triazolium unit with an anionic PhN substituent. We provide clear evidence for the existence of a singlet diaminocarbene tautomer whose structure is composed of a 1,2,4-triazol-5-ylidene unit bearing an NHPh substituent.

Oxidative damage to DNA yields guanine radical cations. Their gas-phase IR spectroscopic signature and acidity have been modelled by the radical cation of 9-methylguanine. Comparisons with quantum chemistry calculations suggest that radical cation formation produces the ground-state keto tautomer, which has an N-H acidity enhanced by ~470 kJ mol(-1).

An elusive free 4-(isopropylamino)imidazol-2-ylidene is engaged in a tautomeric equilibrium with its mesoionic tautomer, 4-(isopropylamido)imidazolium, which displays the typical reactivity of a cyclic diaminocarbene; once coordinated to a Rh(I) centre, it undergoes a smooth 4e(-) oxidation of its backbone to yield an amido-amidino-carbene, a weak electron donor viable only in its complexed form.

The ring-chain tautomerism of 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol (H(2)L(ring)) has been exploited to produce mononuclear complexes or, alternatively, dinuclear complexes, as desired, by varying the stoichiometry of the ligand. Cu(2+) and Zn(2+) stabilise the ring tautomeric form of the ligand in their mononuclear complexes M(HL(ring))(2). The structural characterisation ...

We present resonant two-photon ionization (R2PI), IR-UV, and UV-UV double resonance spectra of jet-cooled 2-aminopurine (2AP) as well as Fourier transform infrared (FTIR) gas phase spectra. 2AP is a fluorescing isomer of the nucleobase adenine. The results show that there is only one tautomer of 2AP which absorbs in the wavelength range 32,300-34,500 cm(-1). The comparison with the calculated I...

In this study, four arylazobenzylidene dyes (a-d) were synthesized with excellent yields in two steps using Knoevenagel condensation and azo-coupling reactions. Absorption spectra of these dyes with different substituents were investigated in organic solvents as a function of solvent polarity. The spectral features of synthesized arylazobenzylidene dyes were described according to azo-hydrazone...