Organometallic surface functionalization of gold nanoparticles

Impact of photosensitizer orientation on the distance dependent photocatalytic activity in zinc phthalocyanine-nanoporous gold hybrid systems

Nanoporous gold powder was functionalized in a two-step approach by an azide terminated alkanethiol self-assembled monolayer (SAM) and a zinc(ii) phthalocyanine (ZnPc) derivative by copper catalyzed azide-alkyne cycloaddition (CuAAC). A series of different hybrid systems with systematic variation of the alkyl chain length on both positions, the alkanethiol SAM and the peripheral substituents of the ZnPc derivative, was prepared and studied in the photooxidation of diphenylisobenzofuran (DPBF). An enhancement by nearly one order of magnitude was observed for the photosensitized singlet oxygen (1O2) generation of the hybrid systems compared to the same amount of ZnPc in solution caused by the interaction of the npAu surface plasmon resonance and the excited state of the immobilized sensitizer. This interaction was shown to be distance dependent, with decreasing activity for short SAMs with alkyl chain lengths < 6 methylene groups caused by quenching of the excited state via electron transfer as well as decreasing activity for SAMs with n > 8 methylene groups due to decreasing energy transfer for long distances. An unexpected distance dependent behaviour was observed for the variation of the peripheral alkyl chain on the photosensitizer revealing a planar orientation of the immobilized photosensitizer on the nanoporous gold surface by a penta-coordinated central zinc ion through interaction with free azide groups from the self-assembled monolayer.

Transition metal complex/gold nanoparticle hybrid materials

Gold nanoparticles (AuNPs) are of considerable interest for diverse applications in areas such as medicine, catalysis, and sensing. AuNPs are generally surface-stabilized by organic matrices and coatings, and while the resultant organic compound (OC)/AuNP hybrids have been explored extensively, they are not suitable for certain applications (e.g. those necessitating reversible redox behaviour and/or long excited-state lifetimes), and they often suffer from low photo- and/or thermal stability. Transition metal complex (TMC)/AuNP hybrids have recently come to the fore as they circumvent some of the aforementioned shortcomings with OC/AuNP hybrids. This review summarizes progress thus far in the nascent field of TMC/AuNP hybrids. The structure and composition of extant TMC/AuNP hybrids are briefly reviewed and the range of TMCs employed in the shell of the hybrids are summarized, the one-phase, two-phase, and post-nanoparticle-synthesis synthetic methods to TMC/AuNP hybrids are discussed and contrasted, highlighting the advantages of variants of the last-mentioned procedure, and the utility of the various characterization techniques is discussed, emphasizing the need to employ multiple techniques in concert. Applications of TMC/AuNP hybrids in luminescence, electrochemical, and electro-optical sensing are described and critiqued, and their uses and potential in imaging, photo-dynamic therapy, nonlinear optics, and catalysis are assessed.

A click-based modular approach to introduction of peroxides onto molecules and nanostructures

Copper-promoted azide/alkyne cycloadditions (CuAAC) are explored as a tool for modular introduction of peroxides onto molecules and nanomaterials.

Gold nanocomposite assemblies using functionalized Ru(ii)-polypyridyl complexes

Ru(ii)-polypyridyl complexes with various surface anchoring functional groups were prepared and utilized as capping and engineering agents to attain surface functionalized gold nanocomposites (Au NCs) with unique morphologies.

Dendron-Mediated Engineering of Interparticle Separation and Self-Assembly in Dendronized Gold Nanoparticles Superlattices

Self-assembly of nanoparticles into designed structures with controlled interparticle separations is of crucial importance for the engineering of new materials with tunable functions and for the subsequent bottom-up fabrication of functional devices. In this study, a series of lipophilic, highly flexible, disulfide dendritic wedges (generations 0-4), based on 2,2-bis(hydroxymethyl)propionic acid, was designed to bind Au nanoparticles with a thiolate bond. By controlling the solvent evaporation rate, the corresponding dendron-capped Au hybrids were found to self-organize into hexagonal close-packed (hcp) superlattices. The interparticular spacing was progressively varied from 2.2 to 6.3 nm with increasing dendritic generation, covering a range that is intermediate between commercial ligands and DNA-based ligand shells. Dual mixtures made from some of these dendronized hybrids (i.e., same inner core size but different dendritic covering) yielded binary superlattice structures of unprecedented single inorganic components, which are isostructural with NaZn13 and CaCu5 crystals.

Binding Studies of Cucurbit[7]uril with Gold Nanoparticles Bearing Different Surface Functionalities

Host-guest interactions between a synthetic receptor, cucurbit[7]uril (CB[7]), and gold nanoparticles (AuNPs) have been quantified using isothermal titration calorimetry. AuNPs were functionalized with ligands containing tertiary or quaternary benzylamine derivatives, with electron donating or withdrawing groups at the para position of the benzene ring. Analysis of binding interactions reveals that functional groups at the para position have no significant effect on binding constant. However, headgroups bearing a permanent positive charge increased the binding of AuNPs to CB[7] ten-fold compared to monomethyl counterparts.

ICP-MS-based characterization of inorganic nanoparticles--sample preparation and off-line fractionation strategies

Validated and easily applicable analytical tools are required to develop and implement regulatory frameworks and an appropriate risk assessment for engineered nanoparticles (ENPs). Concerning metal-based ENPs, two main aspects are the quantification of the absolute mass concentration and of the “dissolved” fraction in, e.g., (eco)toxicity and environmental studies. To provide information on preparative aspects and on potential uncertainties, preferably simple off-line methods were compared to determine (1) the total concentration of suspensions of five metal-based ENP materials (Ag, TiO₂, CeO₂, ZnO, and Au; two sizes), and (2) six methods to quantify the “dissolved” fraction of an Ag ENP suspension. Focusing on inductively coupled plasma–mass spectrometry, the total concentration of the ENP suspensions was determined by direct measurement, after acidification and after microwave-assisted digestion. Except for Au 10 nm, the total concentrations determined by direct measurements were clearly lower than those measured after digestion (between 61.1 % for Au 200 nm and 93.7 % for ZnO). In general, acidified suspensions delivered better recoveries from 89.3 % (ZnO) to 99.3 % (Ag). For the quantification of dissolved fractions two filtration methods (ultrafiltration and tangential flow filtration), centrifugation and ion selective electrode were mainly appropriate with certain limitations, while dialysis and cloud point extraction cannot be recommended. With respect to precision, time consumption, applicability, as well as to economic demands, ultrafiltration in combination with microwave digestion was identified as best practice.

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Attaching high charge density metal ions to surfaces and biomolecules. Reaction chemistry of hypodentate cobalt diamine complexes

Hypodentate diamine cobalt(III) pentammine complexes [Co(NH3)5(NH2(CH2)(n)NH3)](ClO4)4 (8: a: n = 3; b: n = 4; c: n = 6; d: n = 8) have been synthesized via the reaction of [Co(NH3)5(OTf)](OTf)2 (TfOH = CF3SO3H) with the corresponding diamines. The analogous t-boc protected diamine complexes [Co(NH3)5(NH2(CH2)(n)NHt-boc)](ClO4)3 (7a-d) were prepared in 4-26% yield. Low yields for the formation of 7a-d are due to competing side reactions which also gave [Co(NH3)6](3+). Complexes 7a-d were deprotected using trifluoroacetic acid to give the corresponding hypodentate diamine complexes [Co(NH3)5(NH2(CH2)(n)NH3)](CF3CO2)0.5(ClO4)3.5 (9a-d). HBTU coupling of 8c with N-(t-boc)-L-phenylalanine gave an amino acid functionalized cobalt pentammine complex [Co(NH3)5(NH2(CH2)6NHt-boc)-L-phenylalanine)](ClO4)3 (10). All new complexes were characterized using UV-vis and (1)H NMR spectroscopy, and elemental analysis. Grafting of 8c onto 2.4 mm poly(ethylene-co-acrylic acid) (PEAA) beads was achieved via amide coupling. Complex 8c was coupled to thioctic acid via amide coupling and the resulting cobalt disulfide complex [Co(NH3)5(N-(6-aminohexyl)-5-(1,2-dithiolan-3-yl)pentanamide)](ClO4)3 (11) was attached to 10 nm Au nanoparticles. The amount of cobalt loading onto PEAA beads and Au nanoparticles was determined using ICP-MS and EDX.

Synthesis and coordinative layer-by-layer deposition of pyridine-functionalized gold nanoparticles and tetralactam macrocycles on silicon substrates

Coordination chemistry was applied to deposit pyridine-functionalized gold nanoparticles on silicon substrates. The particles were synthesized through the Brust/Schiffrin route with a subsequent ligand exchange reaction yielding well-defined particles of two different sizes. Multilayer deposition was carried out on a pyridine-terminated SAM, anchored on a hydroxyl-terminated silicon surface. Analogously, Hunter/Vögtle-type tetralactam macrocycle multilayers were deposited as well as mixed layers containing both either in an alternating sequence or as a macrocycle multilayer with a terminating nanoparticle layer. These composite layers were examined with respect to their ability to bind squaraine axles in the macrocycle cavities. The amount of guest bound is higher for the composite layer with alternating macrocycles and nanoparticles.