Conformation and configuration at the central amine nitrogen of a nucleotide adduct of the carcinogen 2-(acetylamino)fluorene as studied by 13C and 15N NMR spectroscopy

Photodecomposition of Pigment Yellow 74, a Pigment Used in Tattoo Inks¶

Tattooing has become a popular recreational practice among younger adults over the past decade. Although some of the pigments used in tattooing have been described, very little is known concerning the toxicology, phototoxicology or photochemistry of these pigments. Seven yellow tattoo inks were obtained from commercial sources and their pigments extracted, identified and quantitatively analyzed. The monoazo compound Pigment Yellow 74 (PY74; CI 11741) was found to be the major pigment in several of the tattoo inks. Solutions of commercial PY74 in tetrahydrofuran (THF) were deoxygenated using argon gas, and the photochemical reaction products were determined after exposure to simulated solar light generated by a filtered 6.5 kW xenon arc lamp. Spectrophotometric and high-pressure liquid chromatography (HPLC) analyses indicated that PY74 photodecomposed to multiple products that were isolated using a combination of silica chromatography and reversed-phase HPLC. Three of the major photodecomposition products were identified by nuclear magnetic resonance and mass spectrometry as N-(2-methoxyphenyl)-3-oxobutanamide (o-acetoacetanisidide), 2-(hydroxyimine)-N-(2-methoxyphenyl)-3-oxobutanamide and N,N''-bis(2-methoxyphenyl)urea. These results demonstrate that PY74 is not photostable in THF and that photochemical lysis occurs at several sites in PY74 including the hydrazone and amide groups. The data also suggest that the use of PY74 in tattoo inks could potentially result in the formation of photolysis products, resulting in toxicity at the tattoo site after irradiation with sunlight or more intense light sources.

A circular dichroism study on the conformation of d(CGT) modified with N-acetyl-2-aminofluorene or 2-aminofluorene

The trinucleotide d(CGT) was modified by covalent binding of the carcinogen N-acetyl-2-aminofluorene (AAF) or 2-aminofluorene (AF) at the C8 position of the guanine base. The conformations of d(CGT)-AAF and -AF were studied by comparing the absorption and circular dichroism properties with those of dCMP + dGMP-AAF or -AF + dTMP in a molar ratio of 1:1:1 and AAF- and AF-containing dGMP. For both AAF- and AF-d(CGT) complexes the results show significant stacking interactions between the fluorene residue and the base(s) and are discussed in terms of the conformation of d(CGT)-AAF and -AF. In d(CGT)-AF we observe a clear interaction between AF and thymine, whereas the C-G stack is still intact. In the case of d(CGT)-AAF the C-G stack is weakened and the glycosidic rotation angle of dGuo-C8-AAF is most probably syn. The specific fluorene-base interactions persist at elevated temperatures. The carcinogen-base interactions are stronger in the AAF-carrying d(CGT) than in the case of the deacetylated complex. This is consistent with the higher mobility of the AF-adduct and its conformationally heterogeneous appearance in DNA.

Structure of oxidatively damaged nucleic acid adducts. 3. Tautomerism, ionization and protonation of 8-hydroxyadenosine studied by 15N NMR spectroscopy

Natural abundance 15N NMR spectroscopy and ancillary spectroscopic techniques have been employed to study the solution structure of 8-hydroxyadenosine. 8-Hydroxyadenosine is a naturally occurring oxidized nucleic acid adduct that is generally implied to have an 8-hydroxy tautomeric structure. 15N NMR chemical shifts and coupling constants, however, indicate that the modified base exists as an 8-keto tautomer. The pH dependence of 15N NMR and UV spectra showed the presence of two pKa's, at 2.9 and 8.7, corresponding to protonation at N1 and ionization at N7, respectively. The latter results in the formation of an 8-enolate structure. Unusual upfield shifts of the 1H and 15N resonances of the NH2 group, and a reduction in the one-bond coupling constant 1JN6-H6, is indicative of an unfavorable steric or electronic interaction between the NH2 group and the adjacent N7-H proton. This interaction results in a subtle change in the structure of the NH2 group. In addition to being a possible mechanism for alteration of hydrogen bonding in oxidized DNA, this type of interaction gives a better understanding into N7-N9 tautomerism of adenine. Furthermore, the structure of 8-hydroxyadenosine has been related to possible mechanisms for mutations.

Visualization of an AAF induced frameshift mutation: molecular views of base displacement in B-DNA from minimized potential energy calculations

Energy minimized structures of base displacement in an AAF modified B-DNA dodecamer are presented. A rational search strategy, beginning with a global search of the conformation space of the modified deoxydinucleoside monophosphate, together with model building by computer graphics, has been employed. A number of different minimum energy conformations have been located which reveal base displaced structures. These show fluorene interstrand stacking, fluorene inter- and intrastrand stacking, and non-stacked fluorene situated in the denatured bulge. The local helix axis is bent to various extents in the different forms, and one or two base pairs are fully denatured. One structure of special interest offers a molecular view that suggests how AAF can induce the -2 deletion mutation observed in AAF modified E. coli.

Energy minimized structures of carcinogen-DNA adducts: 2-acetylaminofluorene and 2-aminofluorene

Energy minimized structures of DNA modified by the aromatic amines 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF), for which no experimental atomic resolution data exist, are presented. These have been computed with a new molecular mechanics program specifically designed to define distortions imposed by such adducts, and employing a rational strategy for searching the conformation space of a DNA molecule with covalently linked carcinogen. In alternating G-C sequences, the AAF adduct prefers to reside at the exterior of an undeformed Z-helix. It can also induce base displacement with attendant denaturation and helix bending in sequences that disfavor the Z form, but undeformed B helices are excluded. The AF adduct, by contrast, prefers the major groove of an unperturbed B-helix, but can also induce carcinogen-base stacking in single stranded regions of the DNA, such as at the replication fork. The different biological properties of these two adducts may be related to their distinct

1H NMR study of self-association and restricted internal rotation of the C8-substituted deoxyguanosine 5'-monophosphate adduct of the carcinogen 2-(acetylamino)fluorene

The high-field 1H NMR spectra of a nucleotide-carcinogen adduct formed from 2-(acetylamino)fluorene (8-(N-fluoren-2-ylacetamido)-2'-deoxyguanosine 5'-monophosphate) have been examined in aqueous solution as a function of concentration at high and low temperatures. An anomalous concentration dependence of NMR spectra was observed at concentration levels over 1 mM. These spectral characteristics have been analyzed in terms of changes in self-association and in the interconversions between torsional diastereomers associated with the central nitrogen. Association constants have been computed. Stacking interactions, which involve both the fluorene and guanine rings, are strong, cooperative and highly temperature-dependent. Deacetylation alters the mode of stacking. Several effects of solvent and aggregation on the conformation at the central nitrogen are discussed.