Effects of Solvent Polarity and Microenvironment on the Excited-State Dynamics and UV Photodegradation of Serotonin (5-Hydroxytryptamine)
Abdourahmane Khonté *
Laboratoire Matériaux, Electrochimie et Photochimie Analytique, Université A. Diop de Bambey (UADB), Bambey, Sénégal and Laboratoire OPTIMAG, Université de Brest (UBO), 6 Av. Victor Le Gorgeu, 29285 Brest Cedex, France.
Diégane Sarr
Laboratoire Matériaux, Electrochimie et Photochimie Analytique, Université A. Diop de Bambey (UADB), Bambey, Sénégal.
Pape Abdoulaye Diaw
Laboratoire Matériaux, Electrochimie et Photochimie Analytique, Université A. Diop de Bambey (UADB), Bambey, Sénégal.
Diène Diégane Thiaré
Laboratoire de Photochimie et d’Analyse (LPA), Faculté des Sciences et Techniques, Université Cheikh Anta Diop (UCAD), BP 5005, Dakar, Sénégal.
Jean Pierre Bakhoum
Laboratoire de Photochimie et d’Analyse (LPA), Faculté des Sciences et Techniques, Université Cheikh Anta Diop (UCAD), BP 5005, Dakar, Sénégal.
Ndeye Arame Diop
Laboratoire Matériaux, Electrochimie et Photochimie Analytique, Université A. Diop de Bambey (UADB), Bambey, Sénégal.
Atanasse Coly
Laboratoire de Photochimie et d’Analyse (LPA), Faculté des Sciences et Techniques, Université Cheikh Anta Diop (UCAD), BP 5005, Dakar, Sénégal.
Philippe Giamarchi
Laboratoire OPTIMAG, Université de Brest (UBO), 6 Av. Victor Le Gorgeu, 29285 Brest Cedex, France.
*Author to whom correspondence should be addressed.
Abstract
Serotonin, like many small organic molecules, can undergo photochemical transformations under UV irradiation. Photodegradation of pharmaceuticals and biologically active compounds is an active research field due to concerns about drug stability under light exposure and the environmental fate of pharmaceutical residues in water systems. This study investigates the photophysical and photochemical behaviour of serotonin (5-HT) in various environments, including aqueous, organic, and micellar media. Using UV–vis absorption and fluorescence spectroscopy, key parameters such as dipole moments, Stokes shifts, and fluorescence lifetimes were determined. Solvatochromic analysis was performed with Lippert-Mataga, Bakhshiev, and related models, revealing significant intramolecular charge redistribution upon excitation (dipole moment increase to ~7.8 D). Photolysis kinetics were studied under controlled conditions, showing first- and second-order behaviours depending on the medium. Half-lives ranged from 24 s in aqueous pH 7 solutions to over 1900 s in micellar systems, illustrating enhanced photostability in hydrophobic microenvironments. The localisation of serotonin at the micelle–water interface was identified as a key factor governing its photochemical response. Quantitative data are summarised in tables for spectroscopic parameters, dipole moments, and kinetic constants, providing clarity and reproducibility. The findings offer insights into the influence of solvent polarity, pH, and micellar structures on serotonin’s stability and reactivity, with implications for neurochemistry, pharmacology, and photobiology. Overall, this comprehensive study demonstrates the utility of spectrofluorimetric methods in evaluating biomolecular photostability and provides a framework for designing safer drug formulations sensitive to light.
Keywords: Photochemical, Solvatochromic analysis, Bathochromic shifts, Half-life, molecular mobility