SPECIFIC ADSORPTION OF METACHROMATIC COMPOUNDS OF CHONDROITIN SULFATE BY INSOLUBLE CALCIUM SALTS

Abstract

A method has been found for specifically adsorbing from solution the metachromatic compounds of chondroitin sulfate and two metachromatic dyes. The specific adsorbants are CaHPO₄, CaCO₃, and CaC₂O₄. These adsorb only metachromatic compound and do not adsorb either dye or chromotrope alone. With these adsorbants it is easy to show that the metachromatic compound adsorbed contains dye and chromotrope in equivalent amounts even when the solution from which it was adsorbed contained a tenfold excess of chromotrope. This supports by an independent method the conclusion of an earlier ultracentrifugal study. The evidence presented shows that under the conditions studied there exists in solution a single metachromatic compound of methylene blue and chondroitin sulfate which obeys Beer's law over the concentration range 0.37 x 10^-4 to 7.2 x 10^-4M, and has a molar extinction coefficient at 570 mµ of 2.36 x 10⁴. Some less specific adsorbants are also mentioned; in addition to adsorbing the metachromatic compound, Ca₃(PO₄) also adsorbs chromotrope, and Al₂O₃, dye. The specific adsorbants provide a new tool for the study of metachromasia in solution and facilitate chemical analysis of adsorbable metachromatic compounds.