D. J. Duchamp

A GC-MS Procedure for the Measurement of Dopamine in Mouse Striatal Tissue

Abstract A gas chromatographic-mass spectrometric (GC-MS) method for measuring dopamine levels in brain tissue has been developed. Deuterated dopamine was prepared by exchange of the aromatic hydrogens with deuterium. The method involves adding a known amount of deuterated dopamine to the extraction medium or vessel and extracting the brain sample. The sample is acylated with pentafluoropropionic anhydride, and an aliquot of the derivative in benzene injected into a gas chromatography-mass spectrometry-computer system. The ion fragments, m/e = 428 and 431 respectively, of the protium and deuterium form of dopamine pentafluoro-propionate are detected. From the relative intensities of the two forms the concentration of dopamine in the brain samples is determined. Trace amounts of selenium in biological samples were estimated by atomic absorption utilizing a Varian carbon rod flameless atomizer. Samples were digested with nitric perchloric acids, selenium was separated from the interfering sample matrices by...

Geometric and electronic structural characterization of (3-cyano-4,5-dimethyl pyrrol-2-yl) oxamic acid ethyl ester using X-ray diffraction and ab initio quantum mechanics

Abstract The crystal and molecular structure of (3-cyano-4,5-dimethyl pyrrol-2-yl) oxamic acid ethyl ester has been determined by X-ray diffraction techniques. The clear monoclinic crystals, space group P 2 1 / c , were found to contain four molecules in a unit cell of dimensions a = 12.9216(4), b = 4.5234(2), c = 23.1188(8) A and β = 119.585(2)°. A trial structure was obtained by direct methods and refined by crystallographic least squares to a final R index of 0.084. The distances and angles in the pyrrole ring are indicative of considerable electron delocalization. Two bifurcated hydrogen bonds are found in the crystal structure, each consisting of one intramolecular and one intermolecular acceptor. Molecular orbital calculations have been performed on the molecule by means of the ab initio molecular fragment method. The calculations indicate that the isolated molecule adopts a planar conformation. The sites of high density in the higher-occupied and lower-unoccupied molecular orbitals suggest that the pyrrole moiety could effectively act either as a donor or an acceptor in a π-type charge-transfer complex.