Magnetic Circular Dichroism of Porphyrin Lanthanide M³⁺ Complexes

Abstract

Lanthanide complexes exhibit interesting spectroscopic properties yielding many applications as imaging probes, natural chirality amplifiers, and therapeutic agents. However, many properties are not fully understood yet. Therefore, we applied magnetic circular dichroism (MCD) spectroscopy, which provides enhanced information about the underlying electronic structure to a series of lanthanide compounds. The metals in the M(3+) state included Y, La, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; the spectra were collected for selected tetraphenylporphin (TPP) and octaethylporphin (OEP) complexes in chloroform. While the MCD and UV-VIS absorption spectra were dominated by the porphyrin signal, metal binding significantly modulated them. MCD spectroscopy was found to be better suited to discriminate between various species than absorption spectroscopy alone. The main features and trends in the lanthanide series observed in MCD and absorption spectra of the complexes could be interpreted at the Density Functional Theory (DFT) level, with effective core potentials on metal nuclei. The sum over state (SOS) method was used for simulation of the MCD intensities. The combination of the spectroscopy and quantum-chemical computations is important for understanding the interactions of the metals with the organic compounds.

Chiral sensing of amino acids and proteins chelating with EuIIIcomplexes by Raman optical activity spectroscopy

“…[4][5][6][7] However, the development of molecular biologically relevant probes based on lanthanides is not straightforward. For example, many europium(III) complexes decompose in the aqueous environment 8 or the luminescence in water solutions is strongly affected by interaction with the O-H groups. The Na 3 [Eu(DPA) 3 ] complex (Scheme 1) used here and similar tris-dipicolinate (DPA) complexes of lanthanides appear to be more universal because they are stable also in water.…”

Going beyond the vertical approximation with time‐dependent density functional theory

“…While up to now we focused on one‐photon absorption (OPA) and emission, the model PESs described in the previous sections can be used, in combination with TD‐DFT data, to simulate many other achiral and chiral, linear and nonlinear spectroscopies. This includes Electronic Circular Dichroism (ECD), Magnetic Circular Dichroism (MCD), Circularly Polarized Luminescence (CPL), Near Edge X‐ray Absorption Fine Structure (NEXAFS), Two‐Photon Absorption (TPA), and Two‐Photon Circular Dichroism (TPCD). Going in further detail, for nonlinear processes some additional approximations are required in order to write the spectra in a form equivalent to Eqs or .…”

Origin‐independent sum over states simulations of magnetic and electronic circular dichroism spectra via the localized orbital/local origin method

“…For example, the coordinate‐space grid may introduce a dependence on the origin . Recently, we found that the sum over states (SOS) approach provides a very efficient and accurate way of generating MCD spectra when the electronic excited states obtained from TDDFT computations are used . In test computations, we associated the Kohn–Sham determinant (very close to the Hartree–Fock one) with molecular ground state, and spin‐adapted TDDFT single excitations with excited electronic states.…”