Study On The Clustering Induced Luminescence Of Natural Compounds Bovine Serum Albumin And Dextran

In recent years,intrinsic emission from unorthodox luminogens without traditional conjugated building blocks is drawing increasing attention due to the fundamental importance and technical applications.More and more unconventional luminogens have been found and synthesized continuously by researchers,however,the emission mechanism is still controversial.In this contribution,the photophysical properties of natural compounds bovine serum albumin(BSA)and dextran containing different nonconventional chromophores were systematically studied,and the mechanism of their unique cluster-triggered luminescence(CTE)phenomenon was discussed in depth.And its have shown excellent application prospects in the fields of anti-counterfeiting and oxygen sensing.The main contents include:(1)It is a textbook knowledge that protein emission stems from three aromatic amino acid residues of tryptophan(Trp),tyrosine(Tyr),and phenylalanine(Phe),with predominant contribution from Trp.Recently,inspired by the intrinsic visible emission of nonaromatic amino acids and poly(amino acids)in concentrated solutions and solid states,we revisited the protein emission,especially in the aggregate state.For this purpose,the protein represented by BSA was studied.Our work outlines new perspectives for protein emission,other than previously prevailing concerns on the UV luminescence from aromatic amino acid residues,bright visible PL with concentration enhanced emission and aggregation-induced emission(AIE)features is identified.BSA is almost nonluminescent in dilute solutions even upon cooling to 77 K,but becomes highly emissive in concentrated solutions and solids,and the PL efficiency of the powders can be effectively enhanced through further pressurization.Intriguingly,distinct persisten room temperature phosphorescence(p-RTP)is observed from the amorphous BSA powders in vacuum or the tablet even at ambient conditions.Based on these properties,proof-of-concept applications of proteins in anticounterfeiting and sensing are demonstrated.This study uncovers the crucial role of nonaromatic amino acid residues to the luminescence of natural proteins at their aggregated states,which is almost ignored in the past.This visible emission can be rationalized by the CTE mechanism.(2)To further reveal the general fundamental principle of biomolecule luminescence under different conditions,the luminescent properties of another nonconventional luminogens dextran were systematically studied.The fluorescent intensity of dextran is enhanced with increasing concentrations,gelation or the molecular weight,and the dextran can exhibit an extremely p-RTP in an amorphous state,which is closely related to the ability of the inter-chain oxygen atom clustering of dextran.It can be confirmed by the analysis of the single crystal structure that the short contacts of O···O can result in an effective 3D through space electronic communication channel and collectively contribute to generate optically excitable conjugates with rigidified conformations,thus offering bright visible emission upon UV illumination.These newly discovered characteristics not only reveal the general laws of biomolecule luminescence under different conditions,but also verify the rationality of the CTE mechanism,and also further deepen the aggregation and molecular packing of dextran polymer segments under different conditions.These results should be enlightening for the development of new luminogens free of polycyclic(hetero)aromatic hydrocarbons.