X-ray analysis of disodium cromoglycate.

Disodium cromoglycate (I; DSCG) was introduced in 1968 for the treatment of bronchial asthma. Evidence concerning its principal effects and possible mode of action has been described at some length in the recent literature (Cox, 1971 ; Cox & Altoanyan, 1970). Crystals of the compound exhibit a remarkable reversible water absorption (Cox, Woodard & McCrone, 1971), the number of water molecules per molecule of DSCG increasing from 5 or 6 at 30-70 % relative humidity (R.H.) to 9 at 90 % R.H. Above 93 % R.H. the crystals collapse to form a liquid crystal mesophase containing up to about 260 molecules of water per molecule of DSCG. The purpose of the present study is to determine the major structural features of the molecule in the crystal in the hope that this information will be valuable in future investigations into structure/activity relations and will help also in analysis of the transition from the crystalline to the liquid crystalline phase.