On the main analytical characteristics for solving enological problems

Peer reviewe

Mixed columns made to order in gas chromatography. IV. Isothermal selective separation of alcoholic and acetic fermentation products

The FORTRAN program described In Part I of this series has been modified so that it may either find the best combined phases made up from two, three, or four simple phases, for the isothermal separation of all the solutes contained in a mixture, or else it may find the best combined phases for the separation of only a group of selected mixture components. The program has been applied to the separation by direct injection of the 20 more important components (b.p. up to 145°C) found in alcoholic and acetic fermentation samples. A couple of mixed bed columns have been found that achieve the separation of the 20 components plus four proposed internal standards In samples containing up to 40% ethanol. Comparison with other analytical procedures found in the literature shows that the couple of columns found by the computer represents the best choice for the detection and quantitative determination of volatile components of wine and distillates, as well as cognac, brandy, rum, whisky, beer, and vinegar. Chromatograms showing the capabilities of the two columns are included

Tethered ligands reveal glutamate receptor desensitization depends on subunit occupancy

Cell signaling is often mediated by the binding of multiple ligands to a multi-subunit receptor. The probabilistic nature and slow rate of binding of diffusible ligands at low concentrations can impede attempts to determine how ligand occupancy controls signaling in such protein complexes. We describe a solution to this problem that uses a photoswitched tethered ligand as a “ligand clamp” to induce rapid and stable binding and unbinding at defined subsets of subunits. We applied the approach to study gating in ionotropic glutamate receptors (iGluRs), ligand-gated ion channels that mediate excitatory neurotransmission and plasticity at glutamatergic synapses in the brain. We probed gating in two kainate-type iGluRs, GluK2 homotetramers and GluK2/GluK5 heterotetramers. Ultrafast (sub-millisecond) photoswitching of an azobenzene-based ligand on specific subunits provided a real-time measure of gating and revealed that partially occupied receptors can activate without desensitizing. The findings have implications for signaling by locally released and spillover glutamate