Vibrational circular dichroism of tetraphenylporphyrin in peptide complexes? A computational study

Abstract

The Raman and absorption spectra of tetraphenylporphyrin (TPP) were calculated and compared to experiment. The computation was based on the harmonic molecular force field and electric tensors obtained ab initio at the BPW91/6‐31G* level. Good agreement was found between experimental and calculated frequencies and intensities. In order to estimate whether induced optical activity in chiral complexes interferes with the signal of peptide vibrations, the vibrational circular dichroism (VCD) spectra of TPP were simulated. The magnetic field perturbation theory (MFP) and the gauge‐invariant atomic orbitals (GIAO) were used for the simulation. Such spectra were compared to theoretical VCD intensities of a model tripeptide as well to experimental spectra of a complex of the peptide and tetrakis(p‐sulfonatophenyl)porphyrin (TSPP). No significant contribution to VCD signal from the TPP residue was found in experimental spectra. Thus, possible peptide conformational changes occurring during the complexation can be monitored directly in the amide I frequency region. Chirality 12:191–198, 2000. © 2000 Wiley‐Liss, Inc.

Resonance Raman and vibrational mode analysis used to predict ligand geometry for docking simulations of a water soluble porphyrin and tubulin

“…Fortunately, the correlation of Raman peaks of porphyrins with their vibrational modes has been established previously. (Zhang, 2003, Saini, 2006, Bour, 2000) (Aydin, 2014, Rich, 2012 The DFT-calculated frequencies of vibrational modes tend to be overestimated when using the harmonic approximation. (Mroginski, 2006) In order to correct for this effect, the DFT-computed frequencies are scaled according to a scaling quantum mechanical factors (Kozlowski, 1999) in which the frequency is multiplied by a factor depending on the atomic motions involved in the vibrational mode.…”

Combined Use of Optical Spectroscopy and Computational Methods to Study the Binding and the Photoinduced Conformational Modification of Proteins When NMR and X-Ray Structural Determinations Are Not an Option

“…If one factors the experimental spectral width ($2-7 cm À1 ) which often spans multiple lines in the DFT spectrum, the challenge becomes the unambiguous correlation between the experimental and the computed spectra. In many cases as for instance with porphyrins (Bour et al, 2000;Saini, 2006;Zhang, Chen, He, & Liu, 2003), one can refer to published line assignments which enable to associate the experimental bands with the motions of certain atoms. The combination of the relative ordering provided by SVD, the atomic motions, and the scaling the vibrational frequencies obtained with DFT (Kozlowski et al, 1999) often reduced the possible choices of significant Raman bands to be analyzed (in the case of TSPP < 5).…”

Vibrational circular dichroism spectroscopy study of paroxetine and femoxetine precursors

“…Ab initio calculations of VCD spectra are no longer restricted to small molecules, 3,4 because they can be used for the interpretation of experimental results for medium sized systems, 5,6 as well as biopolymers. 7,8 The piperidine derivatives (3S,4R)-and (3R,4S)-4-(4-fluorophenyl)-3-hydroxylmethyl-1-methylpiperidine are the key intermediates in the synthesis of the antidepressive drugs paroxetine and femoxetine, respectively. Our previous VCD and NMR study 5 confirmed the absolute configuration of the (3R,4S)-enantiomer in solution, indicated its prevalent conformation, and implied that the hydroxyl group mediates intermolecular aggregation in concentrated solutions.…”

“…A simulation of the VCD intensities based on the Gaussian program package 13 was performed 6,7 for geometries optimized with the aid of the conformer searching routine implemented in the Spartan program.…”