Cyclic Acid Dimer Research Articles

4-carboxyanilinium phosphite: A structural, vibrational, thermal and computational study

A new organo- phosphite adduct, 4-carboxyanilinium dihydrogen phosphite (4-CAPI) was synthesized and characterized by single-crystal X-ray diffraction, FTIR and DSC. 4-CAPI crystallises in the Triclinic space group, P-1, Z = 4, with two 4-CA cations and two H2PO3− anions in an asymmetric unit. In 4-CAPI crystal the organic layer containing 4-CA cations and the inorganic layer containing phosphite anions are connected through a three-dimensional network of strong charge-assisted N–H⋯O and C–OH⋯O hydrogen bonds. The cations, 4-CA exists as a cyclic acid dimer. The infrared vibrational frequencies of 4-CAPI were assigned and the spectral features of 4-CAPI obtained suggest presence of a stronger NH⋯O and C–OH⋯O hydrogen bond interactions thus corroborating with the x-ray result. The intermolecular interaction topology of 4-CAPI has been quantitatively analyzed using the computational tool of energy framework analysis, A very high values of interaction energies are found for the hydrogen bonded anion–cation pairs. The major contribution is from electrostatic interaction.

Structural, vibrational and thermal study of Bis(4-Carboxyanilinium) sulphate a new organo-sulphate adduct of 4-amino benzoic acid

Bis(4-carboxyanilinium) sulphate (B4-CASO4), a new organo-sulphate adduct of 4-amino benzoic acid, was synthesized and characterized by single-crystal X-ray diffraction, DSC and FTIR. B4-CASO4 crystallises in the monoclinic space group, P21/c, Z = 4, with two 4-CA cations and a sulphate anion in an asymmetric unit. These cations, 4-CA was found to exist as a cyclic acid dimer. In B4-CASO4 crystal the 4-CA cations and sulphate anions are connected through a three-dimensional network of strong charge-assisted N–H…O and C–OH…O hydrogen bonds. The infrared vibrational frequencies of B4-CASO4 were assigned and comparison of the spectral features of 4-ABA and B4-CASO4 suggest presence of a stronger NH…O and C–OH…O hydrogen bond interactions in B4-CASO4. Using the computational tool of energy framework analysis, the intermolecular interaction topology has been quantitatively analysed. A very high values of interaction energies are found for the hydrogen bonded anion-cation pairs in the crystal structure of B4-CASO4. The DSC, IR and computational results corroborate well with the structural data of B4-CASO4.

Vibrational spectroscopic investigation of polymorphs and cocrystals of indomethacin

Context:Identification of optimal solid form of an active pharmaceutical ingredient and form control are very important in drug development. Thus, the structural information of these forms and in-depth insight on the modes of molecular interactions are necessary, and vibrational spectroscopic methods are well suited for this purpose.Objective:In-depth structural analysis of different solid forms of indomethacin (IND) using Raman and infrared (IR) spectroscopy is the objective. We have investigated the modes of molecular interactions in polymorphs (α and γ), amorphous and discovered cocrystals of IND with nicotinamide (NIC) and trans-cinnamic acid (CIN) coformers.Materials and methods: The solid forms of IND have been prepared; their purity has been verified by differential scanning calorimetry and powder X-ray diffractometry and then studied in the solid-state by Raman and IR spectroscopy. The modes of the interactions were closely investigated from the vibrational data.Results: The key vibrational features of IND solid forms have been specified. The IR (C=O) band at 1713 cm−1 attributed to cyclic acid dimer of γ IND has disappeared in IND–NIC/CIN whilst retained in IND–SAC cocrystal.Discussion:IND cocrystallizes in different conformations and crystal lattices with different coformers. The cyclic acid dimer of IND has been kept on its cocrystallization with saccharin and it could have been broken with NIC and CIN.Conclusions: The complementary nature of Raman and IR spectroscopy allowed unambiguous investigation of the chemical composition of pharmaceutical materials which is of particular importance in the absence of detailed structural information, as in the case of IND–NIC and IND–CIN.