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Updated: Apr 4, 2026
Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Redox activity and biomolecular affinity of gallium octacarboxyphthalocyanine hydroxide investigated by spectroscopic
Joanna Nackiewicz1, Marta Kliber-Jasik1, Małgorzata A Broda1
1Faculty of Chemistry and Pharmacy, Department of Physical Chemistry and Molecular Modeling, University of Opole, Oleska 48, Opole 45-052, Poland.
Abstract:
Gallium octacarboxyphthalocyanine hydroxide (Ga(OH)PcOC) was investigated using UV-vis and fluorescence spectroscopy supported by DFT calculations to elucidate its redox behaviour, aggregation properties, and interactions with biologically relevant molecules. The influence of pH and solvent environment on the spectroscopic characteristics of Ga(OH)PcOC was examined, revealing that the monomeric form dominates in the pH range 7-11, whereas coordinating solvents such as DMSO and DMF induce distinct bathochromic shifts of the Q-band. Reduction of Ga(OH)PcOC with NaBH4 leads to the formation of a stable anion-radical species, characterized by the appearance of near-infrared absorption bands and reversible oxidation by I2. Interactions with selected amino acids and bovine serum albumin (BSA) significantly affect the spectral profile and enhance the photostability of the complex, with aromatic amino acids exerting the strongest stabilizing effect. Fluorescence-quenching measurements indicate strong binding of Ga(OH)PcOC to BSA, with association constants on the order of 106 L/mol. DFT calculations at the M06-2X/6-31+G(d,p) level elucidated the structural and energetic features of Ga(OH)PcOC binding to amino acids. Axial interactions with zwitterionic amino acids showed a strong binding energy (∼34 kcal/mol in the gas phase) and caused a noticeable geometric distortion of the phthalocyanine core, especially its flattening. Dispersion forces were identified as key stabilizing factors in these interactions. Additionally, spectroscopic analysis of the redox processes of Ga(OH)PcOC in DMSO and its emission spectra provided insights into its electronic properties. These findings contribute to the understanding of the behaviour of Ga(OH)PcOC in various biological and chemical environments, highlighting the importance of solvent, pH, and molecular interactions in modulating its spectroscopic and structural characteristics.
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