Molecular dynamics of solid furosemide (4-chloro-2-furfurylamino-5-sulfamoyl-benzoic acid) studied by NMR and DFT methods

This Letter reports the temperature dependencies of the relaxation time T1 (in the ranges: 100–440 K at 60 MHz; 20 K–RT at 24.667 MHz) and the second moment of the NMR line for protons (in the range: 100–350 K, 27 MHz) measured for a polycrystalline sample of 4-chloro-2-furfurylamino-5-sulfamoyl-benzoic acid (furosemide), form I. The minima in the temperature dependence of the T1 time revealed two activation processes related to the proton transfer in the O–H⋯O hydrogen bond (the low-temperature minimum) and a jumps of the –NH2 group (the high-temperature minimum). The reduction in the second moment value M2 indicated a global motion of the compound molecule, a quasi-isotropic tumbling motion.