A SERS probe of adenyl residues available for intermolecular interactions. Part I—adenyl ‘fingerprint’

<jats:title>Abstract</jats:title><jats:p>This work validated a SERS probe able to compare adenyl reactivity in DNA and RNA. A Creighton silver colloid including adenine (A) [or 2<jats:sup>′</jats:sup>‐deoxyadenosine 5<jats:sup>′</jats:sup>‐phosphate (pdA)] from 2 × 10<jats:sup>−3</jats:sup> to 2 × 10<jats:sup>−8</jats:sup> <jats:sc>M</jats:sc> is stabilized in the absence or presence of chloride. Concentration‐dependent SER spectral profiles reveal how A may interact with (Ag)<jats:sub><jats:italic>n</jats:italic></jats:sub><jats:sup>+</jats:sup> sites. At concentration ≥2 × 10<jats:sup>−5</jats:sup> <jats:sc>M</jats:sc> adsorption of (A)<jats:sub><jats:italic>n</jats:italic></jats:sub> clusters prevents the colloid from undergoing salt effects. Adsorption via N1/N3 is allowed whereas C6NH<jats:sub>2</jats:sub> is involved in self‐association. At [A] <2 × 10<jats:sup>−5</jats:sup> <jats:sc>M</jats:sc> with chloride, hydrogen bonding between chloride and the C6NH<jats:sub>2</jats:sub> group enhances C6N electronegativity, which assists C6N/N7 cooperative adsorption. Complex A(Cl<jats:sup>−</jats:sup>) entities compete with individual chloride ions for adsorption on silver. Very similar C6N/N7 adenyl adsorption occurs for pdA but only above 2 × 10<jats:sup>−5</jats:sup> <jats:sc>M</jats:sc>. Chloride–adenyl bonding is reduced and pdA self‐association is weaker than adenine self‐association. Steric factors, repulsive electrostatic forces and phosphate competitive reactivity with respect to chloride may explain the much higher pdA concentration needed to saturate the silver surface compared with A. Mg<jats:sup>2+</jats:sup>–phosphate complexation entails concentration‐dependent opposite effects on adenyl reactivity with (Ag)<jats:sub><jats:italic>n</jats:italic></jats:sub><jats:sup>+</jats:sup> sites. Cytosine, thymine and guanine base or corresponding nucleotides deliver weaker SER spectra and much higher SERS responses for chloride adsorption compared with A or pdA. This reveals a weaker adsorption of the oxo bases, assumed to result from alternative oxo and nitrogen interactions with the (Ag)<jats:sub><jats:italic>n</jats:italic></jats:sub><jats:sup>+</jats:sup> sites. Copyright © 2001 John Wiley & Sons, Ltd.</jats:p>