Oxidative Elimination And Reductive Addition Of Thiol-Terminated Polymer Ligands On Gold Nanoparticles

Gold nanoparticles(AuNPs)have exhibited a broad range of applications in chemical and biological sensing,catalysis,optoelectronics,therapeutics,and diagnostics.The optical,electronic,and catalytic properties of the AuNPs,as well as their colloidal stability and self-assembly are significantly influenced by the surface capping ligands.Polymer ligands not only can stabilize AuNPs in different solvents,but also govern the stimulus-responsive self-assembly and surface patterning of AuNPs,resist the serum protein adsorption,and enhance their bio-compatibility,blood circulation time,and tumor delivery efficiency.Polymers have been tethered to the surface of AuNPs via the“grafting-to”method by the interaction between thiol(-SH)end group of polymers and AuNPs,e.g.,polystyrene,polyethylene oxide,poly(lysine methacrylamide),polyacrylamide,and polypeptides.The interactions between the thiol group and AuNPs surface are of great importance.Self-assembled monolayers(SAM)of small molecular alkane thiols on the Au surfaces have been utilized in various applications.Alkanethiol of SAMs were found to be oxidized to sulfonates and detached from the Au surface after 1-2 weeks storage at room temperature in air.Compared to alkanethiols of SAM,thiol-terminated polymer ligands with relatively lower packing density on AuNPs,which show less chemical stability.The thiol-terminated polymer can be detached from AuNPs and caused AuNPs to aggregate after oxidation.However,the chemical properties of the AuNPs surface and the changes of polymer ligands during the oxidation process have not been explored.In organometallic chemistry,oxidative addition and reductive elimination of ligands for transition-metal complex is a general strategy in many catalyzed reactions,such as Heck reaction,Suzuki reaction,Sonogashira coupling,etc.,organic ligands can coordinate and decoordinate with metal centers through the reversible redox process.However,a similar redox process has not been explored for the polymer ligands on AuNPs.In-depth understanding of the redox properties of thiol-terminated polymers on AuNPs will open new opportunities for their long-term stabilities,redox-responsive self-assembly,and chemically controlled manipulation of surface ligands.In this thesis,the mechanism of the oxidative elimination and reductive addition of polymers on the surface of AuNPs has been studied.We developed a method for the reversible assembly of various thiol-terminated polymer grafted metal particles.We also studied how to improve the stability and the antifouling performance of thiol-terminated polymer grafted AuNPs in the serum.Meanwhile,we synthesized cyclic polymers and their linear counterparts,and explored the differences in stability of AuNPs modified by cyclic polymers and their linear counterparts.The dissertation consists of the following parts:1.This work studied the mechanism of oxidative elimination of thiol-terminated polymer on the surface of AuNPs.When the oxidizing reagent interacts with AuNP@PS,it will attack the Au-Au bond on the surface of AuNPs,causing the polymer to detach from the surface of AuNPs as PS-S-Au(I)chain and resulting in the assembly of AuNP@PS.We also studied the effects of molecular weight,incubation solvents,and the types of thiol end-group polymers on the oxidative elimination of thiol-terminated polymer on AuNPs surface.Moreover,we developed a method to inhibit the oxidative elimination of polymers and improve the colloidal stability of AuNPs.This work clarified the mechanism of oxidative elimination of thiol-terminated polymer on the surface of AuNPs,and deepened the understanding of the interaction between thiol-terminated polymer grafted AuNPs and environmental media.2.This work studied the mechanism of polymer re-grafted on the surface of AuNPs assemblies after oxidative elimination.Furthermore,a method to realize the disassembly of AuNP assembly was developed.By adding a reducing agent,the oxide residues on the surface of the assemblies desorbed,the thiol-terminated polymer re-grafted to the surface of the AuNPs assemblies to realize the disassembly of the assembly.Meanwhile,we developed a simple and universal method to realize the reversible assembly of various thiol-terminated polymer grafted metal NPs by oxidative elimination-reduction addition mechanism.This work provided a deep understanding of the redox characteristics of thiol-terminated polymers on metal NPs.It will open new opportunities for the long-term stabilities,redox-responsive self-assembly,and chemically controlled manipulation of surface ligands of metal NPs.3.This work synthesized thiol-terminated polyethylene glycol grafted AuNPs(AuNP@PEG)to study the oxidative elimination of PEG on the surface of AuNPs in serum.The experimental results show that peroxide and hydroxyl radicals can lead to the detachment of PEG from the AuNP surface,and decrease the antifouling performance of AuNP@PEG in serum.After modified the surface of AuNP@PEG with antioxidants,the stability and antifouling performance of AuNP@PEG in serum were enhanced.The work provides a feasible method for improving the stability of AuNP@PEG in the blood and the efficiency of treatment in in-vivo experiments.4.This work synthesized P(FpP)32 linear macromolecules and P(~PFp R)28 cyclic macromolecules.By theoretical calculations and experiments,we studied the differences in physicochemical properties of the two macromolecules.By breaking the balance between the dipole-dipole interaction and the excluded volume effect of the P(~PFp R)28 macrocycles,P(~PFp R)28 macrocycles self-assembled into nanotubes in a face-to-face fashion.Moreover,we explored the stability of AuNPs modified by cyclic polymers and their linear counterparts.Compared with linear macromolecules,cyclic macromolecules can provide better colloidal stability for AuNPs due to their excluded volume effect.