Photophysical aspects of biological photosensitizer Kynurenic acid from the perspective of experimental and quantum chemical study

•Kynurenic acid (KA), an endogeneous and neuroactive NMDA receptor antagonist.•KA is an end product of “kynurenine pathway”.•Spectral ad theoretical studies of KA.•In S0 state, KA exists mainly in anionic form in water.•The presence of keto tautomer in S1 state.

In the present contribution, we have explored ground and excited state spectroscopic properties of an antiexcitotoxic and anticonvulsant drug, Kynurenic acid (KA), through steady-state absorption, emission and time-resolved emission spectroscopy and quantum chemical calculations. The main focus of this article is to illustrate the effects of various parameters such as the nature of the solvents and pH of the medium on the spectral properties of KA which confirms the presence of different neutral and ionic species in the ground and excited states. The molecule KA exists mainly as keto- or anionic form in the ground state, whereas the main contribution of its emission is arising from the keto tautomer in the excited state. Quantum chemical calculations by Density Functional Theory (DFT) method has been effectively employed to correlate the experimental findings. The ground and excited state properties of KA ascertained by means of experimental and theoretical method reveal that it resembles well with other two compounds, 4-hydroxyquinoline and xanthurenic acid formed by the decomposition of UV filters.

Graphical abstractExistence of various species such as keto, enol, anion of Kynurenic acid, a well-recognized antiexcitotoxic and anticonvulsant drug, and the byproduct of tryptophan metabolism has been established based on the steady state and time resolved absorption and fluorescence spectroscopy. Quantum chemical calculations support the experimental findings.Figure optionsDownload full-size imageDownload as PowerPoint slide