Synthesis Of Green-fluorsecent Carbon Dots And Their Interactions With Bovine Serum Albumin

Aiming at improving the disadvantage of fluorescent carbon dots（CDs） whichsynthesis complicated and has low fluorescence intensity. In this article, a novelsolvothermal approach to synthesize green-fluorescent CDs was developed usingL-ascorbic acid as the carbon source, ethanol solution as the solvent. And thenmodified with branched polyethyleneimine (PEI) to improve their fluorescenceproperty and functionalize them with amino-group. After that, this paper investigatesthe interaction between BSA and the two products including the action mechanism,action zone, acting force and binding sites through using several spectroscopictechniques. The result of these researches is helpful to understand the impact on thestructure of BSA, as well as has an important and guiding significance to know theCDs’ application in the Bio field.The main research results and conclusions are as follows:1. The as-prepared CDs were characterized by infrared spectrum (IR), ultravioletand visible spectrophotometer (UV), transmission electron microcopy (TEM) andX-Ray Powder Diffraction(XRD). The results indicated that the synthesized CDshave small size of4nm, good monodispersity and uniform size distribution. At thesame time, this paper investigate the impact on the CDs of pH. The PEI-CDs werecharacterized by infrared spectrum (IR), ultraviolet and visible spectrophotometer(UV), transmission electron microcopy (TEM) and X-Ray Powder Diffraction. Theresults indicated that the fluorescence intensity and the fluorescence quantum yield ofthe CDs has been raised.2.The interaction of CDs with bovine serum albumin (BSA) have beendetailedly studied by fluorescence quenching technique(FS) in combination withUV-Vis absorption spectroscopy, circular dichroism (CD) spectroscopy under thesimulative physiology-ical conditions. The results showed that the quenching of BSAfluorescence by CDs was found to be a static quenching procedure. Based onmeasuring fluorescence spectra of protein, the binding constants were calculated to be1.582and2.287×104L·mol-1at300and310K, respectively. Their binding sites n are about equal to1at two temperatures. According to the Van’t Hoff equation, thethermodynamic parameters were estimated, which indicated that CDs interacted withBSA mainly through hydrophobic forces.The entropy increase and the free energyreducing in this combining process proved it is a spontaneous procedure. The bindingdistance between BSA and CDs was calculated to be2.23nm according to the theoryof F rster’s non-radiation energy transfer. The displacement experiments pointed outthat CDs could bind to the SiteⅠof BSA. CD spectra and asynchronous fluorescencespectrospcopy demonstrate that CDs induced secondary structure of BSA moleculesin the micro-change.It shows the CDs has potential toxicity to biosome.3. To study the interaction mechanism of BSA with PEI-CDs underphysiological conditions by fluorescence quenching in combination with UV-Visabsorption, CD spectroscopy. According to the formula of Stern-Volmer, the resultsshowed that the quenching of BSA fluorescence by PEI-CDs was found to be adynamic quenching procedure. Calculated the binding constants of the PEI-CDssystem was1.773and5.859×104L·mol-1at300and310K, respectively. Theirbinding sites n are about equal to1at two temperatures. According to the Van’t Hoffequation, the thermodynamic parameters were calculated, which indicated thatPEI-CDs interacted with BSA mainly through hydrophobic forces. The entropyincrease and the free energy reducing in this combining process proved it is aspontaneous procedure. The binding distance between BSA and PEI-CDs wascalculated to be5.26nm according to the theory of F rster’s non-radiation energytransfer. The displacement experiments suggested that PEI-CDs could bind to theSiteⅠof BSA. CD spectra and asynchronous fluorescence spectrospcopy demonstratethat PEI-CDs induced secondary structure of BSA molecules in the micro-change. Itshows the PEI-CDs has potential toxicity to biosome.