Barbiturate interaction with phosphatidylcholine.

A hydrogen-bonding interaction between phenobarbital or pentobarbital with phosphatidylcholine in chloroform is indicated by the effects of added phosphatidylcholine on the infrared and proton magnetic resonance spectra of these barbiturates. The nitrogenbound proton of the barbiturate and the orthophosphate moiety of the phosphatidylcholine molecule appear to be involved. The more pronounced effect with the two barbiturates occurs in the proton magnetic resonance spectra of phenobarbital with increased amounts of phosphatidylcholine. A plot of the chemical shift of phenobarbital N-H against the concentration of phosphatidylcholine is linear and gives an extrapolated shift of 260 Hz (2.6 ppm) at 35 degrees C for a phosphatidylcholine-phenobarbital ratio of unity, pure 1:1 complex. It is suggested that the general depressant nature of barbiturates may be accounted for by their association in a similar fashion with a number of other phosphate-containing molecules.