Modeling the carotid sinus baroreceptor

A mathematical model that describes the relationship between sinus pressure and nerve discharge frequency of the carotid sinus baroreceptor is presented. It is partly based upon the single-fiber data obtained by Clarke from the sinus nerve of a dog. The model takes into account what is currently known about the physiology of the baroreceptor. It consists of two nonlinear ordinary differential equations and eight free parameters. With one set of values for these eight parameters, the model reproduces well the experimental results reported by Clarke for positive ramp pressure inputs. Only three parameters needed to be adjusted in order to fit the dynamic data. The remaining five were obtained from static and steady-state data.

Abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by methyl radicals and chlorine atoms: photochlorination of 1-methylbicyclo[2.1.1]hexane

Photolysis of acetone has been used as a source of methyl radicals to study the abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by methyl radicals. The reaction was found to have an activation energy of 10.3 kcal/mole and a pre-exponential factor that is typical of other abstraction reactions. The absolute rate of abstraction of hydrogen atoms from bicyclo[2.1.1]hexane by chlorine atoms at room temperature was measured to be 8.1 × 1010 l mole−1 s−1. The photochlorination of 1-methylbicyclo-[2.1.1]hexane in solution gave both the 1-chloromethyl and 2- or 3-chloro-1-methylbicyclohexanes. The relative rates of attack at the methyl and the 2- or 3- position were determined to be 1:2.1. It is pointed out that the rate parameters for the abstraction of an H atom from bicyclo[2.1.1]hexane by a methyl radical are slower than for cyclopentane, as would be expected for a highly strained hydrocarbon, whereas the abstraction by chlorine is slightly faster than the rate for cyclopentane.

INFRARED STUDY OF THE PHOTOCHEMISTRY OF TETRAMETHYLCYCLOBUTAN-1,3-DIONE

The photolysis of tetramethylcyclobutan-1,3-dione was investigated in a nitrogen matrix at 4°K and in solution in cyclohexane at room temperature. Infrared spectra of the reactant after irradiation showed the formation of carbon monoxide, dimethylketene, tetramethylethylene, and a compound with an intense absorption at 1 840 cm−1 which has been identified as tetramethylcyclopropanone. Since the dimethylketene that was formed was also capable of undergoing secondary photolysis, the effect of light (mainly 2 537 Å) on dimethylketene in solution or in a nitrogen matrix, was also studied. It has been found that in solution 0.2 of the molecules of tetramethylcyclobutandione which decompose, do so to give two molecules of dimethylketene, while approximately the same number of molecules decompose to tetramethylcyclopropanone and carbon monoxide. The remainder of the molecules seem to give tetramethylethylene and carbon monoxide in a concerted process.