The Study on the Structure and Physical Properties of Indigo Carmine

This study explores the structure-activity relationship of Indigo Carmine (IC) at the molecular level, aiming to enhance the understanding of its physical and chemical properties. The molecular structure of IC was analyzed using Density Functional Theory (DFT), specifically the GGA-BLYP method at the DZ basis set level. Geometric structural parameters, including bond lengths, bond angles, and dihedral angles, were obtained through theoretical calculations. For example, the calculated C-S bond length is 1.81 Å, and the C=O bond length is 1.220 Å, both of which align closely with experimental values. Infrared (IR) spectrum analysis revealed the presence of pyrrole and benzene ring structures in IC. The high vibrational frequencies indicate strong chemical bonds within the molecule, making them resistant to breakage and demonstrating relatively low reactivity. However, redox reactions can occur under specific conditions due to the π bonds formed by the p orbitals of carbon atoms at positions C(7) and C(8). Additionally, the calculated LogP value for Indigo Carmine is 3.06060. The study examined the molecular configuration, dipole moment, hydrophobic parameter, infrared spectroscopy, and frontier orbital structure in detail. The findings highlight IC's unique physical and chemical properties, identifying the primary sites of redox reactions as the C and D rings.