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

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-Agnq 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 Eb was obtained for the complexes between the Ptr0 and Ag32+ (-50.8 kcal mol- 1), between Ptr-1 and Ag32+ (-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 S0 -> S1 transitions of Ag5+ 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.

Automated summary

Metal nanoclusters have been widely used in biosensing, bioimaging, and diagnostics due to their small size, great biocompatibility, and sensitivity to the biomolecular environment. In this study, the interaction between silver nanoclusters and pterin compounds was investigated using quantum chemistry methods. It was found that different pterin atoms selectively bind to silver nanoclusters depending on the cluster's charge and size. These findings suggest that the absorption and vibrational spectra of silver-pterin complexes can be exploited for biosensor development.