Crystal polymorphism and spectroscopical properties of sulfonamides in solid state by means of First Principles calculations.

Sulfonamides are an important class of therapeutic agents. The increase in the number of new sulfonamide derivatives makes it necessary to study more rationally the chemical structure, because the solid forms often display different mechanical, thermal and physicochemical properties that can influence the bioavailability and stability of the drugs; consequently, the polymorphic structures are of great interest to the pharmaceutical industry because of their ability to modify the physical properties of the active pharmaceutical ingredient. The molecular interactions of these drugs in their crystal lattice are important for the stability of the crystals and polymorphism and for preparing composite complexes for optimizing the use of these drugs. In this work, the crystal structure of these drugs and crystal polymorphism is investigated. So, the crystal forms of antibiotics derivatives of the sulfonamides, sulfamethoxazole, sulfamethazine, sulfachloropyridazine, and sulfacetamide are studied at the molecular and supramolecular level by using computational modeling approach at quantum mechanical level. The spectroscopic properties of these systems are also studied explaining assignments of previous experimental data. The results of DFT calculations reproduce the crystal structures of sulfonamides determined experimentally and the polymorphism in these molecules have been clarified. Likewise, the main intermolecular interactions in all crystal forms of these sulfonamides are H-bonds among the sulfonic and amino groups and SNH groups, and also some π-π interactions. Also, these 3-D periodical models allow the exploration of the intermolecular interactions included in the crystal structures and some of these interactions can alter the vibration modes of the molecules. Therefore, the use of these models can be useful for experimental spectroscopy studies where use actual crystal solids.