IR and UV-VIS spectroscopic characterization of norbadione A and study of the electronic properties of other pigments derived from pulvinic acid

Pulvinic acid-derivative pigments are characterized by the presence of one or more units of pulvinic acid ( 1 ) in their molecular structures. Due to their highly conjugated structures, this class of pigments presents significant photochemical properties, including the absorption of UV radiation with high coefficient ab-sorption bands. Here, the spectroscopic characterization of norbadione A ( 2 ), a naphtalenoid pulvinic acid derivative isolated from the fungus Pisolithus tinctorius, was made by comparison of its IR and UV-VIS data obtained from experimental and theoretical procedures. Linear correlation between the experimental and theoretical wavenumbers obtained in the IR spectroscopic analyses presented a coefficient of determina-tion (R 2) of 0.99576 with a linear equation y = 0.9729x + 37.26261, confirming the proposed chemical structure of norbadione A ( 2 ). All fundamental vibrational modes were assigned using theoretical quan-tum calculations. The experimental UV-VIS spectrum of 2 presented bands at 270, 371, and 419 nm, and quantum chemical calculations enabled the assignment of the electronic transitions in each band. Addi-tionally, the electronic properties of pulvinic acid ( 1 ) and its derivatives norbadione A ( 2 ), badione A ( 3 ), bisnorbadioquinone A ( 4 ), and pisoquinone ( 5 ) were investigated. For all compounds, the Frontier Molec-ular Orbitals and Fukui functions were calculated at a B3LYP/6-311 ++ G(d,p) computational level in the gas phase. Distinct regions of HOMO and LUMO molecular orbitals were observed, which means that the molecules may have different reactivity; also that the reactivity of the derivative compounds is greater than the precursor acid 1 .(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

This study characterized the spectroscopic properties of norbadione A (2), a naphtalenoid pulvinic acid derivative isolated from Pisolithus tinctorius, and confirmed its proposed chemical structure through comparison of experimental and theoretical data. The electronic properties of pulvinic acid (1) and its derivatives were also investigated using quantum chemical calculations.