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Biomedical subjects

Charles A Eckert

Publications and source records attributed to Charles A Eckert.

10 recordsLinked to original sources
PubMed2006

Molecular dynamics simulation of the cybotactic region in gas-expanded methanol-carbon dioxide and acetone-carbon dioxide mixtures.

Local solvation and transport effects in gas-expanded liquids (GXLs) are reported based on molecular simulation. GXLs were found to exhibit local density enhancements similar to those seen in supercritical fluids, although less dramatic. This approach was used as an alternative to a multiphase atomistic model for these mixtures by utilizing experimental results to describe the necessary fixed conditions for a locally (quasi-) stable molecular dynamics model of the (single) GXL phase. The local anisotropic pair correlation function, orientational correlation functions, and diffusion rates are reported for two systems: CO2-expanded methanol and CO2-expanded acetone at 298 K and pressures up to 6 MPa.

Acetone↗
PubMed2006

Switchable surfactants.

Many industrial applications that rely on emulsions would benefit from an efficient, rapid method of breaking these emulsions at a specific desired stage. We report that long-chain alkyl amidine compounds can be reversibly transformed into charged surfactants by exposure to an atmosphere of carbon dioxide, thereby stabilizing water/alkane emulsions or, for the purpose of microsuspension polymerization, styrene-in-water emulsions. Bubbling nitrogen, argon, or air through the amidinium bicarbonate solutions at 65 degrees C reverses the reaction, releasing carbon dioxide and breaking the emulsion. We also find that the neutral amidines function as switchable demulsifiers of an aqueous crude oil emulsion, enhancing their practical potential.

Journal Article↗
PubMed2006

The path forward for biofuels and biomaterials.

Biomass represents an abundant carbon-neutral renewable resource for the production of bioenergy and biomaterials, and its enhanced use would address several societal needs. Advances in genetics, biotechnology, process chemistry, and engineering are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally referred to as the biorefinery. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm.

Biomass↗
PubMed2006

Probing the cybotactic region in gas-expanded liquids (GXLs).

Gas-expanded liquids (GXLs) are a new and benign class of liquid solvents, which may offer many advantages for separations, reactions, and advanced materials. GXLs are intermediate in properties between normal liquids and supercritical fluids, both in solvating power and in transport properties. Other advantages include benign nature, low operating pressures, and highly tunable properties by simple pressure variations. The chemical community has only just begun to exploit the advantages of these GXLs for industrial applications. This Account focuses on the synergism of experimental techniques with theoretical modeling resulting in a powerful combination for exploring chemical structure and transport in the cybotactic region of GXLs (at the nanometer lengthscale).

Journal Article↗
PubMed2005

Green chemistry: reversible nonpolar-to-polar solvent.

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

Journal Article↗
PubMed2005

The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide.

Amidines have been reported to react with CO(2) to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO(2) detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO(2) and does not indicate that an isolable zwitterionic adduct between DBU and CO(2) forms either in the presence or the absence of water.

Journal Article↗
PubMed2002

Carbon dioxide as a solubility "switch" for the reversible dissolution of highly fluorinated complexes and reagents in organic solvents: application to crystallization.

Highly fluorinated organic or organometallic solid compounds can be made to dissolve in liquid hydrocarbons by the application of 20-70 bar of CO(2) gas. Subsequently releasing the gas causes the compounds to precipitate or crystallize, giving quantitative recovery of the solid. The resulting crystals can be of sufficient quality for single-crystal X-ray crystallography; the structures of Rh(2)(O(2)CCF(2)CF(2)CF(3))(4)(DMF)(2), Rh(2)(O(2)C(CF(2))(9)F)(4)(MeOH)(2), Cr(hfacac)(3), and P[C(6)H(3)(3,5-CF(3))(2)](3) have been determined from crystals grown in this manner.

Journal Article↗
PubMed2002

Phase-transfer catalyst separation by CO2 enhanced aqueous extraction.

CO2 is used to enhance the environmentally benign and efficient recovery of phase transfer catalysts with aqueous extraction; this method can alter the distribution of phase transfer catalysts so dramatically that even in dilute organic solutions they can be separated selectively from an organic reaction mixture with only a small fraction of the water required in a traditional aqueous extraction.

Journal Article↗