Menaquinones
(naphthoquinones, MK) are isoprenoids that play key
roles in the respiratory electron transport system of some prokaryotes
by shuttling electrons between membrane-bound protein complexes acting
as electron acceptors and donors. Menaquinone-2 (MK-2), a truncated
MK, was synthesized, and the studies presented herein characterize
the conformational and chemical properties of the hydrophobic MK-2
molecule. Using 2D NMR spectroscopy, we established for the first
time that MK-2 has a folded conformation defined by the isoprenyl
side-chain folding back over the napthoquinone in a U-shape, which
depends on the specific environmental conditions found in different
solvents. We used molecular mechanics to illustrate conformations
found by the NMR experiments. The measured redox potentials of MK-2
differed in three organic solvents, where MK-2 was most easily reduced
in DMSO, which may suggest a combination of solvent effect (presumably
in part because of differences in dielectric constants) and/or conformational
differences of MK-2 in different organic solvents. Furthermore, MK-2
was found to associate with the interface of model membranes represented
by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles.
MK-2 adopts a slightly different U-shaped conformation within reverse
micelles compared to within solution, which is in sharp contrast to
the extended conformations illustrated in literature for MKs.
The interaction of benzoic acid and benzoate with model membrane systems was characterized to understand the molecular interactions of the two forms of a simple aromatic acid with the components of the membrane. The microemulsion system based on bis(2ethylhexyl)sulfosuccinate (AOT) allowed determination of the molecular positioning using 1D NMR and 2D NMR spectroscopic methods. Benzoic acid and benzoate were both found to penetrate the membrane/water interfaces; however, the benzoic acid was able to penetrate much deeper and thus is more readily able to traverse a membrane. The Langmuir monolayer model system, using dipalmitoylphosphatidylcholine, was used as a generic membrane lipid for a cell. Compression isotherms of monolayers demonstrated a pH dependent interaction with a lipid monolayer and confirming the pH dependent observations shown in the reverse micellar model system. These studies provide an explanation for the antimicrobial activity of benzoic acid while benzoate is inactive. Furthermore, these studies form the framework upon which we are investigating the mode of bacterial uptake of pyrazinoic acid, the active form of pyrazinamide, a front line drug used to combat tuberculosis.
Must the concept of the study of new media seem so thoroughly ordinary? What does it mean to study new media other than to study media that exist now? Prompted by the 10th anniversary of New Media & Society, this article aims to help rethink and elongate the history of new media studies by merging new media studies and media history literatures.The recursive definition and use of the term `new media' are reviewed. New media need to be understood not as emerging digital communication technologies, so much as media with uncertain terms and uses. Moreover, by recognizing that new media studies quickly become history and that most media history is already new media history, this article calls for a use of both literatures to focus on the renewable nature of media in history. It reflects on a complementary attitude toward history meant to help usher in a sounder future of the study of the past.
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