CPL of Mellein and Related Natural Compounds: Analysis of the ESIPT Phenomenon

Year: 2024

Authors: Mazzeo G., Fusi M., Bloino J., Evidente A., Abbate S., Longhi G.

Autors Affiliation: Univ Brescia, Dept Mol & Translat Med, Viale Europa 11, I-25123 Brescia, Italy; Scuola Normale Super Pisa, I-56125 Pisa, Italy; Natl Res Council CNR, Inst Biomol Chem, Via Campi Flegrei 34, I-80078 Pozzuoli, Na, Italy; Natl Inst Opt, Brescia Res Unit, CNR, via Branze 45, I-25123 Brescia, Italy.

Abstract: (R)-(-)-Mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein obtained from fungi, i. e. from Diplodia globulosa, were investigated as a class of natural products presenting ESIPT (excited state intramolecular proton transfer) phenomenon, through fluorescence and CPL (circularly polarized luminescence). The study was preceded by the assessment of the absolute configuration through ECD and VCD (electronic and vibrational circular dichroism) spectroscopies in addition to NMR spectra. It is found that ESIPT takes place in these systems very rapidly, and no dual fluorescence has been observed. The experimental study is backed up by TD-DFT calculations of ECD and CPL spectra, plus MD calculations to follow proton transfer in the excited state and careful analysis of the puckering dynamics of the lactone ring. Deprotonated forms of the three compounds were also investigated by the same chiroptical experimental and theoretical methods, showing how one can find in natural compounds not only biological activity but also biologically compatible sensing probes. The ESIPT mechanism is studied via CPL, Fluorescence and DFT calculations on mellein and hydroxy derivatives, natural compounds belonging to the isocoumarin family. ESIPT takes place very rapidly, and no dual fluorescence is observed. Deprotonated forms were also considered and results were compared to those of previously investigated narciclasine. image

Journal/Review: CHEMPHYSCHEM

More Information: Funding was provided by the Italian Ministry of University and Research (MUR) through the PRIN 2022 program, project Enhancing Circularly Polarised Emitters Quantum Efficiency Exploiting Singlet-Triplet Inversion (INVESTCPE), prot. 2022CXHY3A. The Big & Open Data Innovation Laboratory (BODaI-Lab) of University of Brescia is acknowledged for providing access to CINECA high-performance computing facilities. The CINECA award under the ISCRA (IsCb3_VCDoCOMS) initiative is also acknowledged.
KeyWords: ESIPT; CPL; Fluorescence; ECD; VCD; MD; Ring Puckering; Cremer-Pople coordinates
DOI: 10.1002/cphc.202400543


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