Amendment in Singular Value Decomposition Approach for FTIR Spectra of Heat-treated Indomethacin–Cimetidine Mixture: Study of Solid Intermolecular Interaction

Purpose: The transmission Fourier-transform infrared (FTIR) spectrum contains complexed signals for molecular structures and intermolecular interactions. Their interrelated signals were attempted to be recognized using the singular value decomposition (SVD) procedure. Methods: Cimetidine (CIM) and indomethacin (INM) mixtures are known to be co-amorphous, and their eutectic mixtures were studied using the SVD computation for the FTIR spectra of KBr tablets containing CIM, INM, and their mixture pre-heated before and after their phase transition temperatures. Results: The SVD approaches can recognize the evidence that the cyano substituent of CIM and the carboxylic acid group of INM were involved in intermolecular interactions in the solid phase. CIM crystals were in the stable A-form polymorph, where the conformation takes the cyanoguanidyl group and imidazole ring contact. The presence of acidic INM likely influences the intramolecular interaction of CIM to the intermolecular interaction between INM and CIM. Conclusions: The present analyses for the FTIR spectra provided the structurally based characteristics, highlighting the validity of the SVD approach in interpreting the intermolecular interactions between CIM and INM.