John A. Hyatt

Bio: John A. Hyatt is an academic researcher from Eastman Chemical Company. The author has contributed to research in topics: Cellulose & Cellulose triacetate. The author has an hindex of 23, co-authored 56 publications receiving 1923 citations. Previous affiliations of John A. Hyatt include Agricultural University of Athens & Eastman Kodak Company.

Liquid and supercritical carbon dioxide as organic solvents

Abstract: The nature of carbon dioxide in its liquid and supercritical states as a solvent for organic compounds was explored. Visible spectroscopy of solvatochromic dyes, ir spectroscopy of ketones and pyrrole, and the exo:endo ratio of a Diels-Alder reaction in CO/sub 2/ solutions were employed as probes of solvent polarity. For both liquid and supercritical CO/sub 2/, E/sub t/(30) similarly ordered 33.8 kcal/mol and Omega similarly 0.50; ..pi.. is near -0.5. Thus, CO/sub 2/ in these states behaves very much like a hydrocarbon solvent with very low polarizability. 52 references, 6 tables.

Mechanism of inhibition of P-glycoprotein mediated efflux by vitamin E TPGS: influence on ATPase activity and membrane fluidity.

Abstract: Efflux pump (e.g., P-gp, MRP1, and BCRP) inhibition has been recognized as a strategy to overcome multi-drug resistance and improve drug bioavailability. Besides small-molecule inhibitors, surfactants such as Tween 80, Cremophor EL, several Pluronics, and Vitamin E TPGS (TPGS 1000) are known to modulate efflux pump activity. Competitive inhibition of substrate binding, alteration of membrane fluidity, and inhibition of efflux pump ATPase have been proposed as possible mechanisms. Focusing on TPGS 1000, the aim of our study was to unravel the inhibitory mechanism by comparing the results of inhibition experiments in a Caco-2 transport assay with data from electron spin resonance (ESR) and from ATPase activity studies. ESR results, on Caco-2 cells using 5-doxyl stearic acid (5-SA) as a spin probe, ruled out cell membrane fluidization as a major contributor; change of membrane fluidity was only observed at surfactant concentrations 100 times higher than those needed to achieve full efflux inhibition. Concurr...

Acetoacetylation with 2,2,6-trimethyl-4H-1,3-dioxin-4-one: a convenient alternative to diketene

Abstract: La pyrolyse de la trimethyl-2,2,6 4H-dioxinne-1,3one-4 en presence de nucleophiles constitue une bonne methode de preparation de derives acetylacetates

Lipids and lipid-based formulations: optimizing the oral delivery of lipophilic drugs

Abstract: Highly potent, but poorly water-soluble, drug candidates are common outcomes of contemporary drug discovery programmes and present a number of challenges to drug development - most notably, the issue of reduced systemic exposure after oral administration. However, it is increasingly apparent that formulations containing natural and/or synthetic lipids present a viable means for enhancing the oral bioavailability of some poorly water-soluble, highly lipophilic drugs. This Review details the mechanisms by which lipids and lipidic excipients affect the oral absorption of lipophilic drugs and provides a perspective on the possible future applications of lipid-based delivery systems. Particular emphasis has been placed on the capacity of lipids to enhance drug solubilization in the intestinal milieu, recruit intestinal lymphatic drug transport (and thereby reduce first-pass drug metabolism) and alter enterocyte-based drug transport and disposition.

Supercritical and near-critical CO2 in green chemical synthesis and processing

Abstract: Carbon dioxide is often promoted as a sustainable solvent, as CO 2 is non-flammable, exhibits a relatively low toxicity and is naturally abundant. However, injudicious use of carbon dioxide in a process or product can reduce rather than enhance overall sustainability. This review specifically examines the use of CO 2 to create greener processes and products, with a focus on research and commercialization efforts performed since 1995. The literature reveals that use of CO 2 has permeated almost all facets of the chemical industry and that careful application of CO 2 technology can result in products (and processes) that are cleaner, less expensive and of higher quality.

Dissolution of wood in ionic liquids.

Abstract: The present paper demonstrates that both hardwoods and softwoods are readily soluble in various imidazolium-based ionic liquids (ILs) under gentle conditions. More specifically, a variety of ionic liquids can only partially dissolve wood chips, whereas ionic liquids such as 1-butyl-3-methylimidazolium chloride and 1-allyl-3-methylimidazolium chloride have good solvating power for Norway spruce sawdust and Norway spruce and Southern pine thermomechanical pulp (TMP) fibers. Despite the fact that the obtained solutions were not fully clear, these ionic liquids provided solutions which permitted the complete acetylation of the wood. Alternatively, transparent amber solutions of wood could be obtained when the dissolution of the same lignocellulosic samples was attempted in 1-benzyl-3-methylimidazolium chloride. This realization was based on a designed augmented interaction of the aromatic character of the cation of the ionic liquid with the lignin in the wood. After dissolution, wood can be regenerated as an ...