Relationship between adenine and silver cluster fluorescence

PAC Gym

Silver and nucleic acids form clusters with varying fluorescence and optical spectra. To study the effect of the adenine nucleobase on these properties, a violet cluster bound to DNA strands with the sequence AxC4, with X varied from 1 to 3, was examined. UV/vis spectroscopy indicated absorptions at 435 nm that degraded to 420 nm over time, suggesting bonding similarities between the clusters. Each of the three clusters was excited at 545 nm using a fluorometer, and the resulting emissions, each around 465 nm, increased greatly from A1C4 to A2C4 and to a lesser extent from A2C4 to A3C4, showing a direct correlation between the number of adenines and fluorescence. Analysis of the decay time using time-correlated single-photon counting (TCSPC) also supported a direct relationship between the number of adenines and fluorescence. A Job plot obtained from circular dichroism showed that the number of unreduced silver atoms bonded to the oligo strands was similar regardless of the number of adenines. This suggests that the adenines may favor binding with the reduced silver species while the cytosines tend toward the unreduced silver species. These results suggest that, although there may be structural similarities between these clusters, larger adenine-silver clusters tend towards fluorescence. More information about the bonding characteristics of adenine and silver is needed to determine the reason for the relationship between number of adenines and fluorescence.