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Ashley L Galloway

Publications and source records attributed to Ashley L Galloway.

8 recordsLinked to original sources
PubMed2006

Sodium ion internalized within phospholipid membranes.

Seven phospholipids, modified with ester groups in their hydrophobic chains, were synthesized and examined for their ability to promote sodium ion flux across vesicular membranes. It was found by 23Na NMR that only the phospholipids having short chain segments beyond their terminal ester groups catalyze sodium ion transfer by up to 2 orders of magnitude relative to a conventional phospholipid, POPC. The rates increase with the concentration of the ester-phospholipid admixed with POPC in the bilayer. More surprisingly, the rates increase with the time allowed for the vesicles to age. This was attributed to ester-phospholipid migrating in the bilayers to form domains that solubilize the sodium ion within the hydrocarbon interior of the membrane. Such membrane domains explain why shift reagent-modified NMR spectra display three 23Na signals representing sodium outside the vesicles, sodium within the vesicular water pools, and sodium within the membranes themselves.

Ion Transport↗
PubMed2005

Surface tension of aqueous amphiphiles.

Surface tension measurements show that at low concentrations a surfactant bearing two ester groups in its chain assembles into small aggregates or else rearranges at the air/water interface to occupy less area per molecule. Only at higher surfactant concentrations do bona fide micelles form. The air/water interface, it is argued, saturates abruptly and cooperatively (as does the aggregation into micelles at the higher concentrations) to give a "critical monolayer concentration". Yet saturation does not reduce the surface tension a great deal. The bulk of surface tension reduction is imparted by monomeric surfactant in the solution via a mechanism that is obscure but may be related in part to the mechanical perturbation of the saturated film during measurement.

Adsorption↗
PubMed2005

Characterizing the "shell phase" formed from amphiphilic picolinates.

The shell phase forms when certain picolinates are subjected to energy input (via sonication or vortexing) while exposed to a water/toluene mixture. A shell, about 600 A thick and containing the picolinate and (very likely) toluene, surround the water droplets that are always produced during the mixing process. Solubility in either phase appears to be deleterious to shell formation. The shells, stable for months, are not easily distorted but can be punctured, even skewered, with a syringe needle without destroying the sphere, yet there is enough mobility among the molecules to repair the physical damage after the needle is removed. This, plus the absence of evidence for crystallinity, suggests a solid or semisolid film forms when picolinates, with the aid of an aromatic solvent, are provided the energy to rearrange themselves on water droplet surfaces. Structure-activity comparisons among the 10 compounds studied indicate that chain-chain association and intermolecular hydrogen bonding are dominant forces in a side-by-side self-assembly of the molecules within the shells.

Anesthetics, Local↗
PubMed2004

Contiguous versus segmented hydrophobicity in micellar systems.

This paper addresses a question not yet posed systematically in surfactant chemistry: How do the colloidal properties of surfactants respond to insertion of non-hydrocarbon functionalities (i.e., ester groups) within chains that are normally entirely hydrocarbon? In answering this question, two classes of such chain-modified surfactants were discovered. One class forms only small aggregates with noncooperative self-assembly, low foaming, high areas of occupancy at the air/water interface, and weak solid-adsorption and solubilization properties. The other class is much more normal with regard to these properties and, in fact, can even exceed conventional surfactants in mesitylene solubilization. Differences between the two categories of chain-modified surfactants originate from the degree of segmentation of the hydrocarbon and, in particular, upon the location of the longest segment. Segmented hydrophobicity, having in principle a "hydrophobic potential" similar to that of a contiguous hydrophobicity of equal length, can induce aggregation but, concurrently, alters the mode of assembly into films and micelles.

Journal Article↗
PubMed2004

Ultrastructure in frozen/etched saline solutions: on the internal cleansing of ice.

Seawater, with its 3.5% salt content, freezes into hexagonal ice (Ih) that encloses concentrated brine within its matrix. When unsubmerged sea ice reaches a certain height and temperature, the brine drains downward through narrow channels. This mechanism was now modeled by frozen 2-3.5% saline as investigated by cryo-etch high-resolution secondary electron microscopy. Thus, saline was either plunge-frozen in liquid ethane at -183 degrees C or else high-pressure frozen to -105 degrees C in 5-6 ms. Ice from a freshly exposed surface was then subjected to a high-vacuum sublimation ("etching"), a procedure that removes pure bulk ice in preference to ice from frozen hydrated salt. After chromium-coating the etched surface with a 2-nm film, the sample was examined by cryo-HRSEM. Granular icy "fences" were seen surrounding empty areas where amorphous ice had originally resided. Since the fences, about 1-2 mum high, survived the etching, it is likely that they consist of frozen brine. The presence of such fences suggests that, during freezing, saline can purge itself of salt with remarkable speed (5-6 ms). Alternatively, channels (perhaps routed around submicroscopic crystallites of cubic ice (Ic) embedded in the amorphous ice at -105 degrees C) can guide the migration of salt to the periphery of ice patches. Macromolecules fail to form fences because they diffuse too slowly or because they are too large to pass through the channels.

Freeze Etching↗
PubMed2003

Relationship between rate and distance.

The activation energies for four Smiles reactions vary with the distance squared between the nucleophilic and electrophilic atoms (consistent with theoretical considerations and pertinent to organic and enzymatic catalyses).

Journal Article↗