Biliverdin chiral derivatives as chiroptical switches for pH and metal cation sensing

Year: 2021

Authors: Ghidinelli S., Abbate S., Mazzeo G., Boiadjiev SE., Lightner DA., Longhi G.

Autors Affiliation: Univ Brescia, Dipartimento Med Mol & Traslaz, Viale Europa 11, I-25123 Brescia, Italy; CNR, Ist Nazl Ottica INO, Res Unit Brescia, Via Branze 45, I-25123 Brescia, Italy; Reg Hlth Inspectorate, 7 Prince Al Battenberg 1 Str, Pleven 5800, Bulgaria; Univ Nevada, Chem Dept, Reno, NV 89557 USA.

Abstract: A series of six optically active derivatives of the bile pigment biliverdin, namely (beta S,beta ’ S)-dimethylmesobiliverdin-XIII alpha, cyclic esters of linear diols [HO(CH2)(n)OH] where n = 1-6, have been investigated by vibrational circular dichroism (VCD) and density functional theory (DFT) calculations. The results were correlated with the length (n) of the diester belt, the verdin helicity and an M reversible arrow P conformational equilibrium – as previously shown by electronic circular dichroism (ECD). Furthermore, ECD spectra have been found to be quite sensitive to solvent nature and pH. TD-DFT calculations of the protonated/deprotonated verdins with n = 1 and 2 diester belts respectively have allowed one, moreover, to explain the spectroscopic data in terms of a change in the M reversible arrow P equilibrium. Finally, the set of investigated compounds, together with other chirally functionalized non-belted biliverdin analogs, has also been found to be sensitive to the presence of metal ions, with which the verdins chelate. On the basis of ECD and VCD data, we propose that the spectroscopic changes observed are consistent with self-association (dimerization) of the verdin molecules promoted by the metal cations, as bolstered by DFT calculations, and for which a dimerization constant of 73 000 M-1 is evaluated. We envision the use of current chiroptical spectroscopies in connection with chiral biliverdin derivatives as natural sensors or probes of the micro-environmental conditions, such as pH or the presence of metal ions.

Journal/Review: PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Volume: 23 (36)      Pages from: 20138  to: 20151

More Information: We acknowledge the use of CINECA facilities at Bologna, Italy: ISCRA Grants IsC76_Bv-Me3 and IsC63_SELFASS and support from the Big & Open Data Innovation Laboratory (BODaI-Lab), University of Brescia, granted by Fondazione Cariplo and Regione Lombardia. Support from the Italian MIUR (PRIN 2017, Project Physicochemical Heuristic Approaches: Nanoscale Theory of Molecula r Spectroscopy (PHANTOMS), prot. 2017A4XRCA) is acknowledged.
KeyWords: Circularly-polarized Luminescence; Pyrrole Pigments; Linear Tetrapyrroles; Phytochrome Model; Optical-activity; Bile-pigments; Chemistry; Dichroism; Bilirubin; Stereochemistry
DOI: 10.1039/d1cp02571f

Citations: 9
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