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D Tyler McQuade

Publications and source records attributed to D Tyler McQuade.

15 recordsLinked to original sources
PubMed2006

Microcapsule enabled multicatalyst system.

We present a new microencapsulated catalyst and report its use in a tandem multicatalyst reaction. Using an encapsulation technique, we developed an active, site-isolated amine catalyst that is capable of catalyzing the addition of nitromethane to an aldehyde. When a second Lewis acid catalyst is added, the nitroalkene intermediate is trapped and converted to the corresponding Michael adduct. We show that if the amine catalyst is not encapsulated, the two catalysts cannot function together. Moreover, if the two reactions are performed in sequence rather than in tandem, the first reaction results in an undesired dinitro product and the desired Michael adduct is not formed.

Journal Article↗
PubMed2006

Microencapsulated linear polymers: "soluble" heterogeneous catalysts.

A new strategy for supporting catalysts based on the microencapsulation of linear polymers is presented. In this paper, we present a DMAP capsule that is capable of catalyzing acylation reactions. The catalyst is compared to DMAP on cross-linked and linear polystyrene, as well as small molecule DMAP. Rapid optimization through modification of encapsulation conditions is demonstrated. The optimization provides a dynamic range of catalysis from 90 to 300% of the rate of DMAP on polystyrene.

Capsules↗
PubMed2006

Rapid self-assembly of core-shell organosilicon microcapsules within a microfluidic device.

The preparation of hierarchically structured organosilicon microcapsules from commercially available starting materials is described. Using a microfluidic device, an emulsion of dichlorodiphenylsilane is formed in a continuous phase of aqueous glycerol. The silane droplets undergo hydrolysis, condensation, and crystallization within minutes to form self-assembled, core-shell microcapsules. The microparticles have been characterized with light and electron microscopy, nuclear magnetic resonance spectroscopy (NMR), diffusion-ordered NMR spectroscopy (DOSY), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). The characterization data show that the microcapsule walls consist of amorphous, oligomeric poly(diphenylsiloxane) surrounded by a spiny layer of crystalline diphenylsilanediol. Glycerol is occluded within the wall material but is not covalently bound to the silicon components. Glycerol is a crucial element for producing low-dispersity microcapsules with well-ordered surface spines, as the use of methyl cellulose as viscomodifier yields amorphous surfaces.

Journal Article↗
PubMed2006

Investigating PdEnCat catalysis.

The catalytic behavior of three commercially available PdEnCat catalysts was explored. When the three-phase test was used, it was demonstrated that these microencapsulated palladium catalysts act as heterogeneous sources, or reservoirs, for soluble, catalytically active species. In addition, kinetic data coupled with transmission electron microscopy and solvent-dependent investigations were used to support this conclusion.

Journal Article↗
PubMed2006

Removable colored coatings based on calcium alginate hydrogels.

This article describes the creation of a nontoxic, biodegradable coating using calcium alginate and FD&C approved dyes. The coating is robust but is rapidly removed upon treatment with disodium ethylenediamine tetraacetate (EDTA). Dye leaching from calcium alginate films was studied, and it was determined that the efficiency of dye retention is proportional to the degree of cross-linking. Degradation rates were studied on calcium alginate beads serving as a model for a coating. We determined that degradation rates depend on the gel's cross-linking and on the amount of EDTA used. Bead size also influenced the degradation rates; smaller beads degraded faster than larger beads. We show that the coating can be used as an easily removable and environmentally friendly logotype on an artificial turf surface. Applications of these coatings can be extended to food, cosmetic, medicinal, and textile uses and to wherever nontoxic, easily removable colored coating is desired.

Alginates↗
PubMed2005

Crystallization of bacteriorhodopsin solubilized by a tripod amphiphile.

Bacteriorhodopsin (bR) is solubilized efficiently as a monomer by a novel surfactant, a tripod amphiphile (TPA), which permits the formation of purple hexagonal bR crystals under several conditions. The crystals, although small, diffract to 2.5 A resolution using synchrotron radiation. TPA may be useful for the solubilization, purification, and crystallization of other membrane proteins.

Bacteriorhodopsins↗
PubMed2005

Interfacial polymerization within a simplified microfluidic device: capturing capsules.

A simple approach to a microfluidic device is described. The device is composed of flexible tubing and a needle inserted orthogonal to the long axis of the tubing. This design is well suited to creating oil-water interfaces allowing the formation of laminar flows and monodisperse emulsions. The system is characterized by mapping the phases observed as a function of organic phase flow and Reynolds number. In addition, the device allows interfacial polymerization reactions to capture low coefficient of variation capsules. The shell structure and surface are examined by scanning electron microscopy.

Journal Article↗
PubMed2005

One-pot multi-step synthesis: a challenge spawning innovation.

Creating one-pot synthetic routes is a challenge that is already spawning new chemistry, enzymes, materials, and mechanistic insight. Through one-pot reactions, the chemical products that add value to our lives can be produced with less waste and greater economic benefits. Within this Emerging Area, we describe models for designing one-pot reactions as well as advanced catalysts created to facilitate their realization.

Catalysis↗
PubMed2005

A new interpretation of the Baylis-Hillman mechanism.

[reaction: see text] On the basis of reaction rate data, we have proposed a new mechanism for the Baylis-Hillman reaction involving the formation of a hemiacetal intermediate. We have determined that the rate-determining step is second order in aldehyde and first order in DABCO and acrylate. We have shown that this mechanism is general to aryl aldehydes under polar, nonpolar, and protic conditions using both rate data and two isotope effect experiments.

Journal Article↗
PubMed2005

Baylis-Hillman mechanism: a new interpretation in aprotic solvents.

Using reaction rate data collected in aprotic solvents, we have determined that the Baylis-Hillman rate-determining step is second order in aldehyde and first order in DABCO and acrylate. On the basis of these data, we have proposed a new mechanism involving a hemiacetal intermediate. The proposed mechanism was then supported using two different kinetic isotope experiments.

Acrylates↗
PubMed2003

A comparison of crystalline- and graft polymer-based chemosensors.

Herein, we report a highly sensitive luminescent thin film chemosensor constructed out of a small-molecule donor/acceptor system. Two types of films were compared: one using a small-molecule crystalline donor/acceptor pair and the other using a donor-graft polymer/small-molecule acceptor pair. The acceptor selected for this proof of concept responds to acid, causing its absorption and emission bands to red-shift, which increases spectral overlap with the donor. This increase in overlap greatly enhances energy transfer from the acceptor to the donor. Signal amplification was ascertained by measuring the ratio of acceptor fluorescence when the donor was excited versus direct excitation of the acceptor. Both types of films exhibited large amplification. For the polymeric system, the mechanism of energy migration was investigated by the use of steady-state fluorescence spectroscopy. The mechanism was determined to be dominated by an exciton-hopping process.

Journal Article↗
PubMed2003

Synthesis and characterization of cross-linked reverse micelles.

The design and synthesis of a new cross-linkable amphiphile is reported. Solutions of the amphiphile in a toluene/water mixture form reverse micelles as indicated by dynamic light scattering and NMR spectroscopy. As indicated by dynamic light scattering, TEM, and NMR spectroscopy data, these reverse micelles can be cross-linked without drastically changing the radius of the reverse micelles. Mixed reverse micelles are also characterized and cross-linked. The cross-linked reverse micelles are demonstrated to facilitate phase transfer and can be used to site isolate a catalyst.

Journal Article↗
PubMed2002

Structural control in thin layers of poly(p-phenyleneethynylene)s: photophysical studies of Langmuir and Langmuir-Blodgett films.

We present the relationship between the spatial arrangement and the photophysical properties of fluorescent polymers in thin films with controlled structures. Eight surfactant poly(p-phenyleneethynylene)s were designed and studied. These detailed studies of the behavior of the polymers at the air-water interface, and of the photophysical properties of their transferred LB films, revealed key structure-property relationships. Some of the polymers displayed pi-aggregates that are characteristic of an edge-on structure at the air-water interface. Monolayer LB films of these polymers showed greatly reduced quantum yields relative to solution values. Other polymers exhibited a highly emissive face-on structure at the air-water interface, and did not form pi-aggregates. The combination of pressure-area isotherms and the surface pressure dependent in situ UV-vis spectra of the polymers at the air-water interface revealed different behavioral details. In addition, the UV-vis spectra, fluorescence spectra, and quantum yields of the LB films provide design principles for making highly emissive films.

Alkynes↗