Complex formation in the indolo[2,3-b]quinolines--methylene blue systems in aqueous solutions

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Computational Chemistry

Background:

• Methylene blue (MB) is a widely used dye with applications in various scientific fields.
• Indoloquinolines are heterocyclic compounds with potential biological and chemical significance.
• Understanding molecular interactions in solution is crucial for predicting chemical behavior.

Purpose of the Study:

• To investigate the complex formation between methylene blue and indoloquinolines in aqueous solutions.
• To determine the stoichiometry and association constants of the MB-indoloquinoline complex.
• To correlate experimental findings with theoretical calculations of electronic properties.

Main Methods:

• UV-Vis spectroscopy was employed to monitor spectral changes upon mixing MB and indoloquinolines.
• Spectroscopic data were analyzed using Benesi-Hildebrand, Scott, and Scatchard linearization methods.
• Ab initio calculations were performed to determine the electronic properties of indoloquinolines.

Main Results:

• Complex formation between MB and indoloquinolines was confirmed by changes in absorption spectra.
• A 1:1 complex stoichiometry was established at low reactant concentrations.
• An isosbestic point was observed, supporting the formation of a single complex species.
• Association constants were determined and correlated with calculated electronic properties of indoloquinolines.

Conclusions:

• Methylene blue and indoloquinolines form stable 1:1 complexes in aqueous solution.
• The observed spectral changes are indicative of specific molecular interactions.
• Computational analysis provides insights into the electronic factors governing complex stability.