“…On the other hand, the TMPyP spectra in the lower panel of Figure represent the case where the CD signal is induced by the TDC mechanism in chirally stacked porphyrin dyes. ,, The signal is nearly conservative and larger in magnitude by an order bigger than that of the TPP−Phe, as predicted by the computations. The elevating of the porphyrin symmetry to D 4 h by the copper ions, not explicitly considered in this work, does not seem to have a major effect on the induced CD.…”
Section: Resultsmentioning
confidence: 65%
“…The simulated intensity is somewhat larger, but this can be attributed to averaging over more conformations and a bigger experimental band width than that used for the simulations. 12 Experimental CD spectra: (top) 5.8 × 10 −5 M aqueous solution of the TPP-Phe porphyrin 12 and (bottom) the TMPyP (10 −5 M) complex with the polyglutamic acid (10 −3 M, pH = 4.8), with and without the presence of copper ions depicted by the full and dashed lines. , …”
Section: Resultsmentioning
confidence: 99%
“…Experimental CD spectra: (top) 5.8 × 10 −5 M aqueous solution of the TPP-Phe porphyrin 12 and (bottom) the TMPyP (10 −5 M) complex with the polyglutamic acid (10 −3 M, pH = 4.8), with and without the presence of copper ions depicted by the full and dashed lines. , …”
The optical activity in porphyrins can easily be induced by a chiral environment, but it is difficult to determine the underlying mechanisms purely on an experimental basis. Therefore, in this study, magnitudes of the perturbational, dipolar, and direct covalent contributions to the electronic circular dichroism (CD) are evaluated with the aid of quantum chemical computations. Electronic properties of model porphyrin chromophores are analyzed. Time-dependent density functional theory (TD DFT), particularly with the hybrid B3LYP functional, appeared suitable for estimation of the electronic excitation energies and spectral intensities. The transition dipole coupling (TDC) between chirally stacked porphyrins was determined as the most important mechanism contributing to their optical activity. This is in agreement with previous experimental observations, where chiral matrices often induce the stacking and large CD signals. About a 10 times smaller signal could be achieved by a chiral orientation of the phenyl or similar residues covalently attached to the porphyrin core. Also, this prediction is in agreement with known experiments. Perturbation models realized by a chirally arranged porphyrin and a point charge, or by a porphyrin and the methane molecule, provided the smallest CD signals. The electrically neutral methane induced similar CD magnitudes as those of the charge, but spectral shapes were different. For a complex of porphyrin and the alanine cation, a significant influence of the solvent on the resultant CD spectral shape was observed, while for the charge and methane perturbations, a negligible solvent effect was found. Detailed dependence of the induced optical activity on variations of geometrical parameters is discussed. The simulations of the induced porphyrin activity can thus bring important information about the structure and intermolecular interactions in chiral complexes.
“…On the other hand, the TMPyP spectra in the lower panel of Figure represent the case where the CD signal is induced by the TDC mechanism in chirally stacked porphyrin dyes. ,, The signal is nearly conservative and larger in magnitude by an order bigger than that of the TPP−Phe, as predicted by the computations. The elevating of the porphyrin symmetry to D 4 h by the copper ions, not explicitly considered in this work, does not seem to have a major effect on the induced CD.…”
Section: Resultsmentioning
confidence: 65%
“…The simulated intensity is somewhat larger, but this can be attributed to averaging over more conformations and a bigger experimental band width than that used for the simulations. 12 Experimental CD spectra: (top) 5.8 × 10 −5 M aqueous solution of the TPP-Phe porphyrin 12 and (bottom) the TMPyP (10 −5 M) complex with the polyglutamic acid (10 −3 M, pH = 4.8), with and without the presence of copper ions depicted by the full and dashed lines. , …”
Section: Resultsmentioning
confidence: 99%
“…Experimental CD spectra: (top) 5.8 × 10 −5 M aqueous solution of the TPP-Phe porphyrin 12 and (bottom) the TMPyP (10 −5 M) complex with the polyglutamic acid (10 −3 M, pH = 4.8), with and without the presence of copper ions depicted by the full and dashed lines. , …”
The optical activity in porphyrins can easily be induced by a chiral environment, but it is difficult to determine the underlying mechanisms purely on an experimental basis. Therefore, in this study, magnitudes of the perturbational, dipolar, and direct covalent contributions to the electronic circular dichroism (CD) are evaluated with the aid of quantum chemical computations. Electronic properties of model porphyrin chromophores are analyzed. Time-dependent density functional theory (TD DFT), particularly with the hybrid B3LYP functional, appeared suitable for estimation of the electronic excitation energies and spectral intensities. The transition dipole coupling (TDC) between chirally stacked porphyrins was determined as the most important mechanism contributing to their optical activity. This is in agreement with previous experimental observations, where chiral matrices often induce the stacking and large CD signals. About a 10 times smaller signal could be achieved by a chiral orientation of the phenyl or similar residues covalently attached to the porphyrin core. Also, this prediction is in agreement with known experiments. Perturbation models realized by a chirally arranged porphyrin and a point charge, or by a porphyrin and the methane molecule, provided the smallest CD signals. The electrically neutral methane induced similar CD magnitudes as those of the charge, but spectral shapes were different. For a complex of porphyrin and the alanine cation, a significant influence of the solvent on the resultant CD spectral shape was observed, while for the charge and methane perturbations, a negligible solvent effect was found. Detailed dependence of the induced optical activity on variations of geometrical parameters is discussed. The simulations of the induced porphyrin activity can thus bring important information about the structure and intermolecular interactions in chiral complexes.
At the interface of the toluene/water system, H4TPyP4+ and CuTPPS4− formed heteroaggregates, which could recognize the chirality of d- and l-phenylalanines (Phe) and other amino acids, though neither H4TPyP4+ nor CuTPPS4− could indicate the chirality of the amino acids. The composition of H4TPyP4+:CuTPPS4− in the aggregate was estimated as 1:1 as reported in an aqueous solution. But, CD spectra of the interfacial heteroaggregates were different from that in the aqueous solution, suggesting different chiral interaction. The present results suggest a new mode of the interfacial chiral reaction exhibited by the synergistic effect of the heteroaggregation of the inversely charged porphyrins.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
