Sangbum Han

Multidentate ionic surfactant mediated extraction and dispersion of gold nanoparticles in organic solvents.

Resorcinarenes with three different quaternary ammonium headgroups were synthesized and evaluated for their ability to stabilize gold nanoparticles in organic and aqueous medium. Aqueous dispersions of citrate stabilized gold nanoparticles of dimensions up to 29 nm could be extracted into organic solvents by resorcinarenes functionalized with tetrapyridinium tetrabromide (1), tetratrimethylammonium tetrabromide (2), and tetratributylammonium tetrabromide (3). Such nanoparticles were characterized by TEM, EDS, UV-vis, and IR. Their long-term dispersion stability varied significantly and depended on the nature of the resorcinarene headgroup, and in particular nanoparticles extracted by resorcinarene 1 were stable for several weeks. Nanoparticles passivated by resorcinarenes 1 and 2 were also stable in the presence of thiourea for several hours in both aqueous and organic medium. This is notable as thiourea is known to result in the instantaneous aggregation of citrate stabilized nanoparticles. Remarkably nanoparticles stabilized by resorcinarenes 1 and 2 could be precipitated and redispersed in chloroform without any visible aggregation. The critical parameters controlling the extraction of the nanoparticles into the organic phase have also been evaluated. The resorcinarene surfactant mediated facile phase transfer of gold nanoparticles described here can be readily applied for the stabilization of other citrate stabilized mono- and bimetallic nanoparticles, thus providing opportunities to disperse and stabilize relatively larger nanoparticles in organic solvents using ionic surfactants opening up new applications.

Direct synthesis of hollow polymeric nanocapsules of variable shell thickness and rigidity

The thiol-ene photopolymerization of resorcinarene cavitand thiol with various alkene building blocks led to the formation of hollow nanocapsules of varying thickness and rigidity, depending on the valency of the alkenes.

Tunable gold nanostructures with nanocapsules as template reaction vessels

Hollow, polymeric, thiol-ene resorcinarene nanocapsules can act as template reaction vessels for the synthesis of gold nanoshells or spherical aggregates of gold nanoparticles depending on the reaction conditions. The spherical nanoparticle aggregates were evaluated as catalysts in the biphasic reduction of 4-nitrophenol.

Resorcinarene amine stabilized nanodiamond dispersions in organic solvents: applications in diamond film growth

Nanodiamonds of widely differing sizes (4 to >100 nm), shapes, and origin could be extracted from aqueous dispersions into toluene by a multidentate resorcinarene amine surfactant, in the absence of any elaborate covalent functionalization or extreme conditions. Resorcinarene amine encapsulated nanodiamonds displayed excellent dispersion stability in non-polar organic solvents for several months. The IR spectral analysis of these extracted and further precipitated nanodiamonds suggests that the carboxylic acid groups present on the nanodiamond surfaces are electrostatically stabilized by the resorcinarene amine surfactant. Such nanodiamond dispersions can also act as nucleation sources for the fabrication of continuous diamond films by CVD growth. Notably, this process resulted in diamond films with better uniformity, smaller grain size and reduced surface roughness when compared to the films prepared with unmodified nanodiamonds as nucleating agents.

Brust–Schiffrin synthesis of catalytic bipodal PdPt nanoparticles with some mechanistic insights

Brust–Schiffrin reduction of Pd and Pt precursors in the presence of resorcinarene amine surfactant led to the formation of substantially Pt rich, PdPt bimetallic nanoparticles of a V-shape or variants on the V-shape. New insights into this reaction are provided on the basis of reversed Brust–Schiffrin syntheses, DLS, UV-vis, and NMR analysis. Based on our experiments we conclude that the resorcinarene amine surfactant is part of the inverse micelle formed from TOABr and it also selectively complexes with the Pd salts prior to their reduction. Remarkably, the composition of the bipodal nanoparticles could be varied substantially by varying the reaction conditions. These anisotropic Pt rich PdPt bimetallic nanoparticles are expected to play a major role in catalytic and electrocatalytic applications and preliminary evidence shows that they are effective in mediating Suzuki cross-coupling reactions.

Synthesis, morphological control, dispersion stabilization and in situ self-assembly of noble metal nanostructures using multidentate resorcinarene surfactants

SYNTHESIS, MORPHOLOGICAL CONTROL, DISPERSION STABILIZATION AND IN SITU SELF-ASSEMBLY OF NOBLE METAL NANOSTRUCTURES USING MULTIDENTATE RESORCINARENE SURFACTANTS Sangbum Han Old Dominion University, 2016 Director: Dr. Balasubramanian Ramjee In this dissertation, a detailed investigation on the influence of various macrocyclic resorcinarene surfactants in determining the morphology, stabilization and self-assembly of monoand bimetallic nanoparticles was undertaken. Chapter 2 describes the influence of resorcinarene surfactants functionalized with amineand thiolheadgroups in determining the morphology of monometallic Pt nanoparticles synthesized via the Brust-Schiffrin reaction. We found that while resorcinarene benzylthiol can lead to the formation of highly branched Pt nanostructures, resorcinarene amine can lead to the formation of anisotropic crystalline Pt nanoparticles. Further, we have evaluated the influence of resorcinarene ligands in determining the catalytic activity of these nanoparticles. Chapter 3 evaluates the role of multidentate resorcinarene surfactants in influencing the morphology and composition of catalytic bimetallic nanoparticles synthesized via a BrustSchiffrin reduction. We have successfully shown the Pt rich V-shaped PdPt nanoparticles and Pd rich spherical PdPt nanoparticles produced in the presence of resorcinarene amine surfactant. Our detailed mechanistic investigations show newer insights into the formation of anisotropic nanostructures under Brust-Schiffrin reaction conditions. These anisotropic Pt rich bimetallic nanoparticles can act as excellent, stable catalysts for Suzuki cross coupling reactions. Chapter 4 describes the development of novel multidentate resorcinarene quaternary ammonium salts to stabilize metal nanoparticles in both organic and aqueous medium. We have shown that ionic resorcinarene surfactants can phase-transfer citrate stabilized gold colloids from aqueous dispersions into organic solvents, and their long term dispersion stability depends on the nature of the ionic resorcinarene headgroup. To better understand the interaction of resorcinarene

Highly fluorescent resorcinarene cavitand nanocapsules with efficient renal clearance

Nanomaterial based imaging approaches hold substantial promise in addressing current diagnostic and therapeutic challenges. One of the key requirements for the successful clinical translation of nanomaterials is their complete clearance from the body within a reasonable time period preferably via the renal filtration route. This article describes the synthesis of highly fluorescent, water soluble, resorcinarene cavitand nanocapsules and demonstrates their effective renal clearance in mice. The synthesis and functionalization of nanocapsules was accomplished in a one-pot operation via thiol-ene reactions without involving self-assembly, sacrificial templates or emulsions. Water soluble resorcinarene cavitand nanocapsules obtained by this approach were covalently functionalized with Alexa Fluor 750. Highly fluorescent nanocapsules with hydrodynamic diameters of 122 nm and 68 nm and extinction coefficients of 1.3 × 10(9) M(-1) cm(-1) and 1.5 × 10(8) M(-1) cm(-1) respectively were prepared by varying the reaction conditions. The in vivo biodistribution and clearance of these nanocapsules in mice followed by whole-body fluorescence imaging showed that they were both cleared renally within a few hours. Given the inherent encapsulation capabilities of nanocapsules, the renal clearance demonstrated in this work opens up new opportunities for their theranostic applications especially for targeting and treating the urinary tract.