Isoniazid cocrystals with anti-oxidant hydroxy benzoic acids

• Cocrystals of isoniazid with four anti-oxidant hydroxy benzoic acids.
• Single crystal XRD studies of the isoniazid–hydroxy benzoic acid cocrystals.
• Infra-red (IR) studies of the isoniazid–hydroxy benzoic acid cocrystals.
• Differential Scanning Calorimetric (DSC) studies of the Isoniazid–hydroxy benzoic acid cocrystals.

Isoniazid is the primary constituent of “triple therapy” used to effectively treat tuberculosis. In tuberculosis and other diseases, tissue inflammation and free radical burst from macrophages results in oxidative stress. These free radicals cause pulmonary inflammation if not countered by anti-oxidants. Therefore, in the present study cocrystals of isoniazid with four anti-oxidant hydroxy benzoic acids have been reported. Gallic acid, 2,3-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and 3-hydroxybenzoic acid resulted in the formation of cocrystals when reacted with isoniazid. Cocrystal structure analysis confirmed the existence of pyridine–carboxylic acid synthon in the cocrystals of isoniazid with Gallic acid, 2,3-dihydroxybenzoic acid and 3-hydroxybenzoic acid. While cocrystal of 3,5-dihydroxybenzoic acid formed the pyridine–hydroxy group synthon. Other synthons of different graph sets are formed between hydrazide group of isoniazid and coformers involving NH⋯O and OH⋯N bonds. All the cocrystals were in 1:1 stoichiometric ratio.

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