Supramolecular chirogenesis in zinc porphyrins: Complexation with enantiopure thiourea derivatives, binding studies and chirality transfer mechanism

Abstract

Complexation of three (1[Formula: see text],2[Formula: see text]-2-aminocyclohexyl arylthioureas (aryl [Formula: see text] 3,5-bis(trifluoromethyl)phenyl; phenyl; 3,5-dimethylphenyl) as the guests to ZnTPP and ZnOEP hosts has been studied by means of UV-vis, CD spectroscopies and computational simulation. The complexation proceeds via coordination of the primary amino group to the zinc ion of the metalloporphyrin and induces a moderate circular dichroism signal in the Soret band of the porphyrins. The association constants increase with larger electron-withdrawing properties of the porphyrin host and larger electron-donating ability of the guest, indicating predominantly electrostatic (Lewis acid-base) character of the complexation. Computational study of the (1[Formula: see text],2[Formula: see text]-2-aminocyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea and ZnTPP complex revealed slight asymmetric distortion of the porphyrin plane caused by the chiral guest and additional [Formula: see text]–[Formula: see text] interactions between the host and guest molecules. The calculated CD spectrum for the same system reproduces the experimentally observed one.

Benchmarking computational methods and influence of guest conformation on chirogenesis in zinc porphyrin complexes

“…However, this stacking interaction is of a lesser strength than other possible interaction, such as Hbonding, as illustrated by the geometry of the most stable conformer for L-Phe-OMe with the host A. Similarly, to the published studies, in our case the guest conformation plays a critical role in determining the shape of the CD spectra, 135 but in the case of all complexes studied the lowest-energy conformer made up more than 70% of the Boltzmann distribution. Thus, the CD spectra of the lowestenergy conformers in Figure 7 coincided with the average curve simulated using the cc-pVTZ basis set.…”

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation

“…In general, the porphyrin plane is flexible [138–142] and relatively modest energies of 10.2 kcal mol −1 are required for the out of plane deformation of a free base porphyrin [143] . The deformations can occur as a result of the influence of the environment, [60,144,145] bulky substituents, [32,47–52,146] and complexation of an axial ligand [98,139,147] . Apparently, the out of plane deformations weaken the macrocycle π‐electronic system through reducing the overlap of neighboring p z orbitals, [138] and hence may generate chirality in achiral porphyrins.…”

“…reported only one ECD signal for ligated zinc porphyrin complexes without peripheral chromophoric substituents and two bisignated ECD bands for ligated zinc porphyrin complexes with peripheral chromophoric substituents, which were fixed in a certain position by hydrogen bonds. The bisignated ECD bands were also measured in the works of Konrad et al, [98] . Imai et al [157] .…”

“…In our previous works[ 98 , 99 ] we showed that the conformation of a chiral guest determines the shape of the induced ECD spectra of achiral porphyrins upon axial ligation. In the present work we discuss the electronic and geometry factors and their respective contribution, which may affect the porphyrin electronic transitions and subsequently the corresponding ECD spectra.…”

Supramolecular Chirogenesis in Bis-Porphyrin: Crystallographic Structure and CD Spectra for a Complex with a Chiral Guanidine Derivative

“…The UV-Vis and CD spectra were simulated using the Gaussian16 [61] software and TD-DFT method [62][63][64]. For spectra simulations, the ωB97X-D functional [65] and cc-pVDZ basis set [66][67][68] with the SMD solvent model [69] were used, since this level of theory showed good agreement with experimental data [56,57,70]. The first 10 excited states were calculated in order to ensure that the B band region of the spectrum was covered.…”