Elucidation of the structure is a central problem in the study of natural and synthesized products, since enantiomers, due to their different spatial orientation, can exhibit markedly varying biological and pharmacological properties. Circular dichroism is a widely used tool for determination of spatial structure of molecules. This method is based on different absorption of left- and right-handed light by chiral molecules. However, CD spectra can be measured only if the molecule has both electric and magnetic transition moments. Organic molecules often do not have magnetic transition moment, and their CD spectra are silent. In this case, CD spectra can still be measured using chirality transfer or induced chirality (ICD). Intrinsically achiral metalloporphyrins are able to exhibit optical activity by inducing circular dichroism (CD) signal by axial coordination of a chiral guest. Due to a unique set of physicochemical properties metalloporphyrins are often used as a key element in chemical sensors [1]. Besides detection of small molecules in gas phase and in solution [2], the porphyrin-based supramolecular systems have found a wide application as various chirality probes [3,4]. On the example of mono- and bis-metalloporphyrins ICD spectra will be rationalized based on TD-DFT approach. Will be shown how significant is an influence of a guest conformation on a CD profile of mono-porphyrins. Will be discussed synergy between axial ligation and peripheral substitution. Will be considered how distortion of porphyrin unit is reflected on CD spectra of mono- and bis-porphyrin complexes. Will be shown how critical it is for CD spectra simulations to determine the relative position of porphyrin subunits in bis-porphyrin complexes.
References:
[1] Paolesse R, Nardis S, Monti D, Stefanelli M, Di Natale C. Chem. Rev. 2017; 117: 2517–2583.
[2] D’Amico A, Di Natale C, Paolesse R, Macagnano A, Mantini A. Sens. Actuator B-Chem. 2000; 65: 209–215.
[3] Hembury GA, Borovkov VV, Inoue Y. Chem. Rev. 2008; 108: 1–73.
[4] Borovkov V, Symmetry 2014; 6: 256–294.
