Electrically excited halogen with halogens

The mechanism of action of inhalational anesthetics is unknown. The diversity of chemical structures (inert gas xenon hydrocarbons halogenated hydrocarbons) possessing anesthetic activity appears to rule out involvement of specific receptors. According to one hypothesis, uptake into the hydrophobic interior of the plasmalemma of neurons results in inhibition of electrical excitability and impulse propagation in the brain. This concept would explain the correlation between anesthetic potency and lipophilicity of anesthetic drugs (A). However, an interaction with lipophilic domains of membrane proteins is also conceivable. Anesthetic potency can be expressed in terms of the minimal alveolar concentration (MAC) at which 50% of patients remain immobile following a defined painful stimulus (skin incision). Whereas the poorly lipophilic N2O must be inhaled in high concentrations (>70% of inspired air has to be replaced), much smaller concentrations (<5%) are required in the case of the more lipophilic halothane. 

When an electric discharge is passed through a cold diatomic gas at low pressure it is partially dissociated into atoms in this way reasonable concentrations of O, H, D, N, halogen or other atoms can be produced in a chemically inert diluent. The recombination of these atoms, and their reaction with other molecules can be observed as the gas flows down a long tube. Many of the reactions produce molecules in excited electronic states the resulting chemiluminescence can be used to measure the concentration of atomic species as a function of distance, and hence time, down the tube. Dr Clyne describes this important technique, which has produced direct measurements of the rates of many exothermic reactions of atoms and free radicals at room temperature and below. The reverse of the recombination steps are, of course, the dissociation reactions whose kinetics at high temperatures were described in the first chapter if the ratio of forward and reverse rate constants is equal to the equilibrium constant, the temperature dependence of these rates can be deduced over very wide ranges of temperature. 

---