Silver cluster interactions with Pterin: Complex structure, binding energies and spectroscopy.

[Display omitted] • Interactions between pterin (Ptr) and Ag clusters have been explored using quantum chemistry. • It has been established that Ptr-Ag 3 2+ complex is the most favorable one. • Presence of Ag clusters significantly red-shifts the absorption spectrum of Ptr. • SERS detection has potential benefits in both acidic and alkaline pH. Metal nanoclusters (NCs) are widely present today in biosensing, bioimaging, and diagnostics due to their small size, great biocompatibility, and sensitivity to the biomolecular environment. Silver (Ag) NCs often possess intense fluorescence, photostability, and low photobleaching, which is in high demand during the detection of organic molecules. Pterins are small compounds, which are used in medicine as biomarkers of oxidative stress, cardiovascular diseases, neurotransmitter synthesis, inflammation and immune system activation. It is experimentally possible to detect pterin (Ptr) through the adsorption on Ag colloid. We optimized geometries and evaluated the binding energy in Ptr-Ag n q complexes (n = 1–6; q = 0, +1, +2) using quantum chemistry methods. Different Ptr atoms were preferential for silver attachment depending on NC charge and size. The highest E b was obtained for the complexes between the Ptr0 and Ag 3 2+ (-50.8 kcal mol−1), between Ptr-1 and Ag 3 2+ (-64.8 kcal mol−1), which means that these complexes should be formed preferably in aqueous solutions in acidic and alkaline media, respectively. The colorimetric detection of pterin with silver clusters does not seem to be promising. However, intense S 0→ S 1 transitions of Ag 5 + complexes look promising for luminescent Ptr detection. SERS detection of pterin is better to be done at pH > 8 since deprotonated pterin Raman undergo more dramatic changes upon addition of Ag than the neutral pterin. The characteristics of absorption and vibrational spectra of silver-pterin should be exploited during biosensor development. [ABSTRACT FROM AUTHOR]