The halogen bond between amantadine and iodine and its application in the determination of amantadine hydrochloride in pharmaceuticals.

It is proposed that molecular iodine as a donor could form halogen bonding complexes with amantadine (AMD) and amantadine hydrochloride (AMD-HCl) in chloroform and the resultant charge transfer bands (CT band) would be located at 259 and 253 nm, respectively. The halogen bonding interaction was explored by UV absorption, Raman and X-ray crystallography, and a new bonding model named N(+)···N(lep) bond in crystal was observed. The halogen bonding complexes were utilized in the development of simple and accurate spectrophotometry for the analysis of AMD/AMD-HCl. Compared with the traditional method based on the absorption of I3(-) at 290 and 365 nm, the new proposed spectrometry based on the CT band of halogen bonding complex was more sensitive and selective for the detection of AMD/AMD-HCl. Linear relationships with good correlation coefficients (>0.9994) were obtained between the absorbance and the AMD/AMD-HCl concentration in the range of 10-180 μg mL(-1) for AMD-HCl and 0.2-13 μg mL(-1) for AMD. The limit of detection (LOD) was 2.23 μg mL(-1) and limit of quantification (LOQ) was 7.45 μg mL(-1) for AMD-HCl. And because of the stronger bond constant between AMD and iodine than AMD-HCl, the method is more sensitive for AMD; the LOD was 0.02 μg mL(-1) and LOQ was 0.08 μg mL(-1) which was 100 times lower than that of AMD-HCl.