Strategies for Photochemical and Thermal Modification of Materials

The modification of materials/surfaces is central to numerous applications ranging from opto-electronic devices to biomedical implants and drug delivery. Thus, there exists a high motivation for improving the methodologies which can be employed in order to modify surfaces in a selective and efficient fashion. One of the major goals of surface engineering is to control the chemical composition at the material interface. The fine control of the surface properties is a field of intense research as the performance of functional materials is strongly related to the processes and interactions that are occurring at the materials’ interface. In general, the modification or transformation of surfaces can be achieved via various chemical and physical methods. Although there is a general need for simple and convenient methods to covalently conjugate a molecule of interest to a surface, no single coupling strategy has been broadly adopted. Instead, numerous strategies have been reported in the literature. In an attempt to develop novel strategies to prepare functional materials via surface modifications we examined the potential of a series of photochemical and thermal reactions for such purposes. Methods described in this thesis are divided into two categories: Photochemical and Thermal. In the first chapter, these strategies are introduced. Since many of the modification methods deal with gold nanoparticles (AuNPs), a review of their properties and synthesis methods are also included. Two chapters (chapter 2 and 3) are devoted to the potential of diazirine for photochemical modification of materials and nanomaterials. In chapter 2, diazirine is employed to prepare robust hydrophobic cotton and paper surfaces by coating them with a highly fluorinated phosphonium salt using diazirine as the tether. In chapter 3, the same photochemical modification strategy is extended to nanomaterials by incorporating diazirine onto the surface of water soluble AuNPs. The synthesis and characterization of diazirine-AuNPs is described and it is demonstrated that upon irradiation, the photo generated carbene can be used for the insertion reaction which leads to interfacially modified AuNPs. Starting with chapter 4, we focus on “click-type” and more biologically friendly reactions for surface modification of water soluble AuNPs. Chapter 4 reports our efforts towards modification of small water soluble AuNPs using maleimide interfacial functionality. Both 1,3-dipolar cycloaddition and Diels Alder reactions are studied. In chapter 5, a novel strategy for modification of AuNPs via strain-promoted alkyne-nitrone cycloaddition (SPANC) is introduced. Nitrone functionalized AuNPs are synthesized and characterized. It is demonstrated in this chapter that one can take advantage of the nitrone moiety for interfacial SPANC (i-SPANC) reaction to prepare 18F-radiolabeled AuNPs with potential applications in positron emission tomography (PET). In the second part of chapter 5, the i-SPANC method is further extended to material chemistry by preparing AuNP-carbon nanotube (AuNP-CNT) hybrid nanomaterials

Nitrone Modified Gold Nanoparticles: Synthesis, Characterization and Their Potential as 18F-Labeled PET Probes via I-SPANC

A bioorthogonal gold nanoparticle template displaying interfacial nitrone functional groups for bioorthogonal interfacial strain-promoted alkyne-nitrone cycloaddition (I-SPANC) reactions has been synthesized. The Nitrone-AuNPs were characterized in detail using 1H NMR spectroscopy, TEM, TGA, and XPS and a nanoparticle raw formula was calculated. The ability to control the conjugation of molecules of interest at the molecular level onto the Nitrone-AuNPs template allowed us to create a methodology for the synthesis of AuNP-based radiolabeled probes with a high degree of loading using copper free, strained-promoted cycloaddition. To this end, we also describe the synthesis of a new prosthetic group containing a strained-alkyne capable of clicking hot 18F-label onto complementary azide or nitrone labelled agents

Insights on the Application of the Retro Michael-Type Addition on Maleimide-Functionalized Gold Nanoparticles in Biology and Nanomedicine

The glutathione-mediated retro Michael-type addition reaction is demonstrated to take place at the interface of small water-soluble maleimide-functionalized gold nanoparticles (Maleimide-AuNP). The retro Michael-type addition reaction can be blocked by hydrolyzing the Michael addition thioether adduct at the nanoparticle’s interface under reaction conditions that do not cause AuNP decomposition. This procedure “locks” the molecule of interest onto the Maleimide-AuNP template for potential uses in medical imaging and bioconjugation, ensuring no loss of the molecular cargo from the nanocarrier. On the other hand, the glutathione-mediated retro Michael-type addition reaction can be exploited for delivering a molecular payload. As a proof of concept, a fluorogenic molecular cargo was incorporated onto a Maleimide-AuNP and delivered via the glutathione-mediated retro Michael-type addition reaction

Photoinduced Carbene Generation from Diazirine Modified Task Specific Phosphonium Salts To Prepare Robust Hydrophobic Coatings

3-Aryl-3-(trifluormethyl)­diazirine functionalized highly fluorinated phosphonium salts (HFPS) were synthesized, characterized, and utilized as photoinduced carbene precursors for covalent attachment of the HFPS onto cotton/paper to impart hydrophobicity to these surfaces. Irradiation of cotton and paper, as proof of concept substrates, treated with the diazirine-HFPS leads to robust hydrophobic cotton and paper surfaces with antiwetting properties, whereas the corresponding control samples absorb water readily. The contact angles of water were determined to be 139° and 137° for cotton and paper, respectively. In contrast, water placed on the untreated or the control samples (those treated with the diazirine-HFPS but not irradiated) is simply absorbed into the surface. Additionaly, the chemically grafted hydrophobic coating showed high durability toward wash cycles and sonication in organic solvents. Because of the mode of activation to covalently tether the hydrophobic coating, it is amenable to photopatterning, which was demonstrated macroscopically