Study On The Intraction Between CdS Quanta Dots And EcoRI

Bio-nanotechnology has generated great research interest in now days. The CdSQDs quantum dots because of their unique size-dependent photochemical properties,their high ratio between surface area/total volume and the high surface energy,allowing a strong biomolecule absorption. So, it could be a good supporter forbio-nanotechnology. EcoRI was an important biomacromolecule in lives cellsconsidered to be part of a defense system that protects bacterial cells against foreignDNA. But the physiological function of EcoRI was depended on the secondarystructure. Hence, investigating the interaction between EcoRI and CdS QDs and theEcoRI conformational structure change was meaningful for nanopaticles as areporter application to exploring biological process. These works mainly covered thefollowing areas:1. In the first part, synthesized water soluble fluorescent quantum dots (QDs),and studied the interaction between QDs and proteins and the conformationalstructure of protein in the bioconjugate. UV vis spectroscopy, the fluorescencequenching method, CD spectra, gel electrophoresis and Fourier transform infrared(FTIR) spectroscopic techniques were used to systematically investigate theinteraction between type II restriction endonuclease (EcoRI) and CdS QDs andconformational structure of EcoRI in the EcoRI CdS QDs bioconjugates. The resultsindicated that electrostatic interactions played a major role in the binding reaction atpH6.0, and the nature of quenching was static, resulting in forming CdSQDs–EcoRI bioconjugates. FTIR and CD spectra studies indicated some decrease ofα-helical and turn structures accompanied by the increase of β-sheet structures ofEcoRI in the bioconjugates. This result showed the interaction between EcoRI andCdS QDs resulted in a change in the secondary of EcoRI after it was conjugated withCdS QDs, but the enzyme activity was kept.2. In the second part, I performed an array of measurements to quantify theinteraction of model CdS QDs having a certain range of nanopaticle diameters withEcoRI. We find that the CdS QDs strongly associate with EcoRI where theequilibrium constant, KD, as well as the degree of cooperativity of particle-proteinbinding (Hill constant, n), depends on particle size. We also find that the differentcurvature of the QDs surface could lead to EcoRI undergo different conformational changes from their native structure. The decreasing in α-helix content more or lessaffects the activity of EcoRI from the result from gel electrophoresis.3. In the second part, using solvothermal method synthesized fluorescentquantum dots (QDs), which had different function group. And I studied theinteraction between QDs and proteins and the conformational structure of protein inthe bioconjugate. From the image of polyacrylamide gel electrophoresis, thebingding force was different, and dependence with the function group. UsingUV vis spectroscopy, the fluorescence quenching method, CD spectra, gelelectrophoresis and Fourier transform infrared (FTIR) spectroscopic techniques wereused to systematically investigate the interaction between EcoRI and CdS QDs andconformational structure of EcoRI in the EcoRI CdS QDs bioconjugates. The resultsindicated that the nature of quenching was static, but the Ksv and Ka were different.CdS QDs contain hydroxyl group, the hydrogen bonds and Vander Waalsinteractions played a major role in the binding reaction at pH6.0, however, whencontain methyl group, the hydrophobic force played a major role. FTIR spectrastudies indicated some decrease of α-helical structures accompanied by the increaseof β-sheet and turn structures of EcoRI in the bioconjugates.