Relationship between competitive adsorption by carbon black from aqueous solution and formation of molecular compounds in the solid phase for aminopyrine and barbituric acid derivatives.

Abstract

As an approach to an understanding of the combined effects of drugs, the competitive adsorption of aminopyrine (AM) and barbituric acid derivatives (BA) by carbon black (CB) from aqueous solution was investigated in relation to the formation of molecular compounds between AM and BA. The formation of molecular compounds of AM with various BA compounds was confirmed by differential scanning calorimetry (DSC), powder X-ray diffractometry and infrared absorption spectrometry. All adsorption isotherms of AM and BA were in good accordance with Langmuir's equation. From the results of perturbation experiments (20°to 40°transition), it was considered that the mechnaisms of adsorption of AM and BA by CB were "chemisorption" and "physical adsorption, " respectively. In competitive adsorption, the decrease of BA adsorbed was larger for compounds that formed molecular compounds with AM than for those that did not. It was considered that adsorption was influenced by an interaction between AM and BA molecules at the surface of CB ; the greatest effect in competitive adsorption was seen with AM and barbital, which also formed a molecular compound most readily.