Determination Of Oxidation Degree Of Hyperbranched Polyethyleneimine And Its Effect On The Synthesis Of Gold Nanoclusters

Hyperbranched polyethyleneimine(hPEI),a typical ployamine contains a large number of amine groups,has been widely used in gene transfer,drug delivery,surface adsorption,nanomaterial synthesis,and so on.However,the natural oxidation of hPEI leads to the variation in molecular structure and function.Therefore,it is important to develop a simple and sensitive method for analysizing the oxidation of hPEI.Although fourier transform infrared spectroscopy and thermogravimetric analysis have been applied to study the oxidation of polymers,these traditional methods cannot directly observe the degree of oxidation of hPEI.This thesis proposes a fluorimetric method for quick and accurate analysis of the oxidation of hPEI.Meanwhile,the fluorescence mechanism of luminescent production from oxidized hPEI(F-hPEIox)is systematically studied.In addition,the electrostatic attraction between hPEI and gold core lead to the aggregation of gold core,which benefits the quick and large-scale preparation of near-infrared emitting gold nanoclusters(Au NCs).The versatility of the synthetic method is further verified,and the influence of the oxidation of hPEI on the synthesis of nanoclusters is investigated.The main research contents of this thesis are as follows:1.After protonation and heat treatment,the oxidized hPEI shows distinct fluorescence,and studies have found that the fluorescence is originated from the Schiff base groups during the treatment of oxidized hPEI(hPEIox),and the generation of Schiff base is confirmed by fluorescence spectra,ultraviolet-visible absorption spectra,infrared spectra and other characterization techiniques.On the basis of this phenomenon,a rapid fluorimetric method for analysizing the oxidation of hPEI is established.This method can also monitor the natural oxidation of hPEI and guide the use of hPEI reagents.2.An electrostatic attraction assisted gold core approaching strategy is proposed for rapid synthesis of Au NCs.Taking the GSH-HAuCl4 system as an example,fast preparation of near-infrared emissive Au NCs within 1.5 hours is achieved by introducing polyamine polymers(hPEI).This method is also suitable for large-scale preparation of other metal nanoclusters.The surface potential of hPEI is positively charged due to the abundant amine groups,which facilitates the electrostatic attraction between hPEI and negatively charged Au(?)-thiol complexes and subsequently rapid formation of Au NCs.It is found that the oxidized hPEI could not induce the formation Au NCs quickly,a possible reason is that the diminished positive charge weakens the electrostatic attraction and hinders the rapid formation of Au NCs.The proposed synthetic method for metal nanoclusters is simple and rapid,and the resulted Au NCs has large stokes shift and near-infrared emission.Moreover,large-scale synthesis of metal nanoclusters and other nanomaterials based on this tactic is now possible.