Investigation and characterization by TG/DTG–DTA and DSC of the fusion of Riboflavin, and its interaction with the antibiotic norfloxacin in the screening of cocrystal

Abstract

This work synthesized and characterized the NOR-RIB 1:1 (mol-mol) cocrystal. During a study of the reagents, Riboflavin (RIB) melted at 304°C, which is different from the temperature previously reported in the literature (280-290°C); therefore, this compound was characterized individually. Subsequently, the cocrystal was synthesized with the active pharmaceutical ingredient (API) norfloxacin (NOR) with the RIB coformer, and the mechanochemical synthesis route was adopted. NOR, RIB, and the cocrystal were characterized by thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), DSC coupled to a microscope (photo-DSC), mid-infrared spectroscopy (MIR), and powder X-ray diffraction. The results of thermal analysis showed that the RIB starts decomposition process (260°C) and then melts (304°C). The MIR found that beginning at 295°C, the RIB passes into the form of a decomposition intermediate; therefore, the melting point observed in the DSC curve is related to this decomposition material. The cocrystal presented thermal stability (200°C) lower than the API (235°C) and the coformer (260°C). The DSC curve did not contain a melting peak. The bands at 1726 cm-1 (C=O of the carboxylic acid) for the NOR, and the band at 3326 cm-1 (stretch O-H), among others, were not visible for the cocrystal in the MIR spectrum, indicating interactions in these regions. The X-ray diffractograms showed a new diffraction pattern, which proved the obtainment of a new phase and cocrystal formation.

Structural Insights and Intermolecular Energy for Some Medium and Long-Chain Testosterone Esters

“…The second exothermic peak, with maxima (544 °C, TEna), (537 °C, TCyp), (540 °C, TDec), (540 °C, TUnd), can be associated with the decomposition and oxidation of the remaining material simultaneously with a less significant loss of mass. Similar thermal behavior has been reported for other active pharmaceutical ingredients such as riboflavin and norfloxacin [ 36 ].…”

Crystal Structure and Intermolecular Energy for Some Nandrolone Esters

“…Further wide exothermic events (roughly around 450 • C) are attributable to decomposition and oxidation of the remaining samples accompanied with a small mass loss among the remaining materials. A similar behavior was highlighted for other pharmaceutical compounds, such as riboflavin and norfloxacin [33].…”

Cocrystals Enhance Biopharmaceutical and Antimicrobial Properties of Norfloxacin

“…Making a relationship between the cocrystal reproduced in this article, which followed the process previously described by Basavoju and collaborators [ 14 ], and the other NFX cocrystals described in the literature so far [ 15 , 16 , 17 , 18 , 19 , 20 ], we can mention that most of them also used organic solvents for its preparation, such as chloroform [ 17 ], toluene [ 18 ], and ethanol [ 20 ], which is, therefore, considered a common practice among authors. When evaluating the DSC/TG results, it can be observed that, after desolvation of the cocrystal at ~110 °C, we have a temperature interval until its melting occurs at 143 °C, which suggests the hypothesis of the existence of an anhydrous cocrystal between these two temperatures that could be isolated and obtained through the use of thermal analysis techniques, offering a possible proposal for an NFX–INA cocrystal without the presence of the CHCl 3 solvent and an interesting topic for future studies.…”

“…The objective was to improve factors like dissolution, solubility, and antimicrobial properties, which were evaluated by colorimetric microdilution assay. There are reports in the literature of the formation of some NFX cocrystals, such as a cocrystal solvated with isonicotinamide/chloroform [14], a salt cocrystal with saccharin [15], a dual-drug cocrystal with ciprofloxacin [16] a cocrystal with riboflavin [17], another with resorcinol [18], an NFX cocrystal with two known isomers of nicotinic acid (picolinic acid and isonicotinic acid) [19], and a cocrystal with nicotinamide, cinnamic acid, and sorbic acid [20]. All these NFX crystals cited are listed in more detail in Table 1.…”