Internalization of a Preformed Atomically Precise Silver Cluster in Proteins by Multistep Events and Emergence of Luminescent Counterparts Retaining Bioactivity

A new synthetic protocol is introduced which preserves the secondary structure of protecting proteins encapsulating a luminescent atomically precise silver cluster. This was achieved by using a preformed triphenylphosphine (TPP) protected silver cluster as the precursor forming bovine serum albumin (BSA) and human serum albumin (HSA) protected Ag18 clusters. This is the first example of the formation of luminescent protein protected clusters in a neutral medium, without using any reducing agent, which results in minimal alteration of the protein structure during cluster growth. The cluster formed showed exceptional stability, unlike other silver clusters of this class. The formation of these red luminescent clusters was visualized by UV-vis and photoluminescence spectroscopy. The identification of Ag18 core was made through matrix assisted laser desorption ionization mass spectrometry (MALDI MS) and a plausible mechanism of the formation was identified by monitoring the systematic growth of the cluster co...