Organic Reactions on Silica in Water

A simple and efficient copper-catalyzed amination of aryl halides by aqueous ammonia in water

The copper(I) iodide/1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazine (CuI–L2) system catalyzed the cross-coupling reactions between aryl halides and aqueous ammonia in water to produce primary aromatic amines in good yields. The protocol was simple and efficient, avoiding the need for inert atmosphere, additional base, or other additives.

Structural manipulation of colloidal silica

Structural properties of the nanosized silica Ludox TMA with novel functionalizations have been investigated. Silica is stabilized in aqueous solution at a pH value higher than the pK(a) of silicic acid. A surface modification consisting of poly(p-benzamide)s functionalized with derivatized nucleobases on the C-terminus and cationic pyridinium functions on the N-terminus of the polymer chain was carried out. Due to the negatively charged surface, strong physisorption of the cationic pyridinium functions occurs. It is possible to stabilize diluted solutions of silica without agglomeration in solvents with various polarities by using pyridinium cations. Defined structures could be created according to the hydrogen donor/acceptor potential of the introduced nucleobase. Surprisingly the interactions between the same nucleobases are already sufficient for strong particle-particle interactions. Dramatic effects on the structural behavior are characterized by PCS, (S)TEM and EFTEM.

Synthesis of a Series of Highly Substituted Cyclohexanols via Michael Addition in an Aqueous Medium

The Michael addition of active methylene compounds or nitromethane to chalcones in an aqueous medium and catalysed by tetrabutyl ammonium hydroxide (TBAOH) to afford highly substituted cyclohexanols is described. The protocol provides an efficient route for the synthesis of highly substituted cyclohexanols, with short reaction time, and a range of different substrates in the absence of toxic organic solvents.

Tris(hydroxymethyl)aminomethane-functionalized silica particles and their application for hydrophilic interaction chromatography

A new method is presented for synthesizing a highly hydrophilic silica-based material for use in hydrophilic interaction chromatography. Porous silica particles used as a starting substrate were modified with 3-bromopropyl trichlorosilane and grafted with glycidyl methacrylate by controlled ("living") atom transfer radical polymerization in order to introduce an oxirane-carrying reactive tentacle layer on the silica surface. The grafted material was thereafter subject to an oxirane ring opening reaction with tris(hydroxy-methyl)aminomethane in dimethylformamide to yield a polymer-bound equivalent of the well known and highly hydrophilic "TRIS" buffering substance. Chemical characterization was done by diffuse reflectance FT-IR, X-ray photoelectron spectroscopy, elemental analysis, and (1)H NMR. Porosity and surface area examination was done with Brunauer-Emmett-Teller. Chromatographic application of the material was evaluated by separations of nucleic bases, small organic acids, and common nucleotides under mixed hydrophilic interaction chromatography and weak anion exchange conditions.

Development of heterogeneous olympic medal metal nanoparticle catalysts for environmentally benign molecular transformations based on the surface properties of hydrotalcite

In this review, we describe the development by our research group of highly functionalized heterogeneous Olympic medal metal (gold, silver, and copper) nanoparticle catalysts using hydrotalcite as a support, aimed towards Green and Sustainable Chemistry. Olympic medal metal nanoparticles can cooperate with the basic sites on the hydrotalcite surface, providing unique and high performance catalysis in environmentally-benign organic transformations such as aerobic oxidation of alcohols, lactonization of diols and selective deoxygenation of epoxides and nitro aromatic compounds.

Effect of humidity on the interaction of dimethyl methylphosphonate (DMMP) vapor with SiO2 and Al2O3 surfaces, studied using infrared attenuated total reflection spectroscopy

Infrared attenuated total reflection spectroscopy has been used to study the interaction of DMMP vapor with SiO(2), Al(2)O(3), and AlO(OH) vs relative humidity (RH) and DMMP partial pressure (P/P(0)). For SiO(2) the growth with increasing RH of ice-like and liquid-like layers is seen in agreement with previous work. H↔D exchange during exposure to H(2)O and D(2)O indicates that the ice-like layer is more resistant to exchange, consistent with stronger H-bonding than in the liquid-like layer. Exposure of nominally dry SiO(2) to D(2)O indicates the existence of adsorbed H(2)O that does not exhibit an ice-like spectrum. The ice-like layer appears only at a finite RH. Exposure of SiO(2) to DMMP in the absence of intentionally added H(2)O shows the formation of a strongly bound molecular species followed by a liquid-like layer. The strong interaction involves SiO-H···O═P bonds to surface silanols and/or HO-H···O═P bonds to preadsorbed molecular H(2)O. At a finite RH the ice-like layer forms on SiO(2) even in the presence of DMMP up to P/P(0) = 0.30. DMMP does not appear to penetrate the ice-like layer under these conditions, and the tendency to form a such a layer drives the displacement of DMMP. Amorphous Al(2)O(3) and AlO(OH) do not exhibit an ice-like H(2)O layer. Both have a higher surface OH content than does SiO(2), which leads to higher coverages of H(2)O or DMMP at equivalent RH or P/P(0). At low P/P(0), for which adsorption is dominated by Al-OH···O═P bonding, a-Al(2)O(3) interacts with DMMP more strongly than does AlO(OH) as a result of the higher acidity of OH sites on the former. Up to RH = 0.30 and P/P(0) = 0.30, DMMP appears to remain bonded to the surface rather than being displaced by H(2)O. H(2)O appears to have little or no effect on the total amount of DMMP adsorbed on any of these surfaces, up to an RH of 0.30 and a P/P(0) of 0.30. The results have implications for the transport of DMMP and related molecules on oxide surfaces in the environment.

Inorganic nanoparticle-based contrast agents for molecular imaging

Inorganic nanoparticles (NPs) including semiconductor quantum dots (QDs), iron oxide NPs and gold NPs have been developed as contrast agents for diagnostics by molecular imaging. Compared with traditional contrast agents, NPs offer several advantages: their optical and magnetic properties can be tailored by engineering the composition, structure, size and shape; their surfaces can be modified with ligands to target specific biomarkers of disease; the contrast enhancement provided can be equivalent to millions of molecular counterparts; and they can be integrated with a combination of different functions for multimodal imaging. Here, we review recent advances in the development of contrast agents based on inorganic NPs for molecular imaging, and also touch on contrast enhancement, surface modification, tissue targeting, clearance and toxicity. As research efforts intensify, contrast agents based on inorganic NPs that are highly sensitive, target-specific and safe to use are expected to enter clinical applications in the near future.

Self-assembly of palladium nanoparticles on periodic mesoporous organosilica using an in situ reduction approach: catalysts for ullmann reactions in water

A Si--H functionalized phenyl-bridged periodic mesoporous organosilica [H-PMO(Ph)] is synthesized via a surfactant-directed assembly approach. Pd nanoparticles are then immobilized onto the PMO catalyst [Pd/H-PMO(Ph)] by a Si--H in situ reduction method. The Ullmann reaction, in water as medium, is used to investigate the catalytic performance of Pd/H-PMO(Ph). The results show that the Pd/H-PMO(Ph) catalyst has excellent catalytic activity and selectivity, which can be attributed to synergetic effects derived from the highly dispersed catalytic species and the hydrophobic microenvironments. Furthermore, the catalyst could be conveniently recovered and recycled five times without significant loss of activity and selectivity.

Ionic Liquids Derivative of 1H-Imidazole as Novel Reagents, Catalysts and Solvents

Ionic liquids are becoming widely used in chemical processes. Taking this into account we focus on recent advances in the synthesis and the investigation of 1H-imidazole derived ionic liquids. The fi rst part of this paper focuses on describing the developments in the synthesis and physical properties of 1,3-disubstituted imidazolium salts. The second part describes the application of these unique reagents, as catalysts and solvents in organic chemistry.