DFT study on the reactivity of iron porphyrins tuned by ring substitution

Study of geometric, electronic structures and vibrations of 4, 4′, 4′′, 4′′′-(porphine-5,10,15,20 tetrayl) tetrakis (benzene sulfonic acid) compound by computational and experimental techniques

The optimized geometry and vibrational frequencies of a substituted compound of tetraphenylporphine namely 4, 4[Formula: see text], 4[Formula: see text], 4[Formula: see text]-(porphine-5,10,15,20 tetrayl) tetrakis (benzene sulfonic acid) have been investigated using density functional theory. The vibrational spectra of tetraphenylporphine and its substituted complex were simulated to study the substitution effects of sulfonic acid group at the peripheral sites of tetraphenylporphine. Experimentally, vibrational properties of these molecules have been studied using infrared absorption spectroscopic technique. The vibrational frequencies obtained from the theoretical studies generally agree with the experimental values. For substituted molecules, due to a change in charge distribution, ring vibrations accompanied by the S–O motions also appear at the higher wavenumbers. In the lower region, C–H bending vibrations diminish and SO3 group vibrations arise. The electronic absorption spectra of the substituted tetraphenylporphine in different solvents have been studied using UV-vis spectroscopy. In addition to dipole-dipole and electrostatic interactions, hydrogen bonding plays a key role in molecular-solvent interactions. The energy gap between the highest occupied and lowest unoccupied molecular orbitals and natural bonding orbital analysis show the intermolecular charge transfer interactions. The molecular electrostatic potential and solvent accessible surface area analysis were made in order to study the interaction sites of the molecules. The current-voltage characteristics for the substituted molecule were also plotted. It was found that substituted tetraphenylporphine show good photoconductivity.

Effect of CO adsorption on properties of transition metal doped porphyrin: A DFT and TD-DFT study

The structural, electronic and optical properties of transition metal doped porphyrin (TM@P; TM = Mn, Co, Fe, Cu, Ni, Zn) as well as the effect of CO adsorption on TM@P properties have been investigated using the density functional theory (DFT). The presented results include adsorption energies, bond lengths, electronic configurations, magnetic moments, density of states, frontier molecular orbitals, and UV-Vis. spectra. Our calculation results show that, the CO molecule favors to be adsorbed on TM-doped Porphyrin with its carbon head. The most energetically stable adsorption of CO is reported for Fe doped Porphyrin. The interaction between CO molecules with TM@P is attributed to donation-back donation as well as charge transfer mechanisms. Mn, Co and Fe-doped porphyrins have visible active nature which may be affected by CO adsorption, whereas, Ni, Cu and Zn-doped porphyrins have UV active nature which not affected by CO adsorption. These results may be meaningful for CO removal and detection.

Optical activity of Co-porphyrin in the light of IR and Raman spectroscopy: A critical DFT investigation

A critical investigation on the structure, electronic properties and optical activities of a series of transition metal doped porphyrins (TMP; TM=Fe, Co, Ni) in the light of infrared and Raman spectroscopy is performed, under density functional formalism. The structure and electronic properties are studied in terms of ionization potential, electron affinity, chemical hardness (η), binding energies of the transition metals (BE_TM) etc. The origin of the optical activities, especially the visibly active cobalt porphyrin is addressed through critical study on their infrared and Raman spectra. The information availed from the spectral analysis will certainly ease their possible synthesis and useful applications in the sensor and optoelectronic domains.

Small ligand-globin interactions: reviewing lessons derived from computer simulation

In this work we review the application of classical and quantum-mechanical atomistic computer simulation tools to the investigation of small ligand interaction with globins. In the first part, studies of ligand migration, with its connection to kinetic association rate constants (kon), are presented. In the second part, we review studies for a variety of ligands such as O2, NO, CO, HS(-), F(-), and NO2(-) showing how the heme structure, proximal effects, and the interactions with the distal amino acids can modulate protein ligand binding. The review presents mainly results derived from our previous works on the subject, in the context of other theoretical and experimental studies performed by others. The variety and extent of the presented data yield a clear example of how computer simulation tools have, in the last decade, contributed to our deeper understanding of small ligand interactions with globins. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.

π Back-bonding of iron(II) complexes supported by tris(pyrid-2-ylmethyl)amine and its nitro-substituted derivatives

The electronic and geometric structures of a series of iron(II) complexes supported by tetradentate tris(pyrid-2-ylmethyl)amine-type ligands with different numbers of 4-nitropyridine groups, [(PyCH(2))(3-n)(4-NO(2)PyCH(2))(n)N] (n = 0-3), were examined by X-ray absorption fine-structure and variable-temperature (1)H NMR spectroscopies and theoretical calculations to reveal how the low-spin state is stabilized through π back-bonding interactions between iron(II) and 4-nitropyridine donor group(s).

The structures and stabilities of the complexes of biologically available ligands with Fe(III)-porphine: an ab initio study

Fe(III) porphine complexes and a limited number of Fe(II) porphine complexes were investigated at the 'MP2/LB'//B3LYP/SB level of theory, where SB and LB represent small and large basis sets, 6-31+G(d) and 6-311+G(2df,2p), respectively. Solvation effects were incorporated by the IEFPCM procedure. Most of the ligands whereby the heme prosthetic group is bound in biological systems were modeled in the study. These include H(2)O, Im (imidazole), CH(3)NH(2), CH(3)CO(2)(-), CH(3)S(-), CH(3)PhO(-), OH(-), and Cl(-). Fe(III) porphine, 2(+), and the pentacoordinated complexes, 2(+)(Im), 2(+)(CH(3)NH(2)), and 2(+)(H(2)O), have quartet ground states. The pentacoordinated complexes with negatively charged ligands all have high spin hextet ground states. All of the hexacoordinated complexes have low spin doublet ground states, with the exception of 2(+)(H(2)O)(2) and 2(+)(H(2)O)(Im) which have intermediate spin quartet ground states. None of the pentacoordinated complexes, 2(+)(OH(-)), 2(+)(CH(3)PhO(-)), and 2(+)(CH(3)S(-)), are predicted to form stable hexacoordinated complexes in water with any of the ligands of the present study. The most stable species in water is 2(+)(OH(-)). The hydroxide may be displaced by CH(3)PhOH and CH(3)SH at physiological pH, and by Cl(-), CH(3)CO(2)(-), and Im under acidic conditions, but not by CH(3)NH(3)(+). The relevance of the present results for the pH-dependent transitions of cytochrome c and the fragments, NAcMP8, and NAcMP11, the resting state of cytochrome P450, and the bonding interactions between heme and Aβ, is discussed.

Unravelling the intrinsic features of NO binding to iron(II)- and iron(III)-hemes

Electrospray ionization of appropriate precursors is used to deliver [Fe (III)-heme] (+) and [Fe (II)-hemeH] (+) ions as naked species in the gas phase where their ion chemistry has been examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. In the naked, four-coordinate [Fe (II)-hemeH] (+) and [Fe (III)-heme] (+) ions, the intrinsic reactivity of iron(II)- and iron(III)-hemes is revealed free from any influence due to axial ligand, counterion, or solvent effects. Ligand (L) addition and ligand transfer equilibria with a series of selected neutrals are attained when [Fe (II)-hemeH] (+), corresponding to protonated Fe (II)-heme, is allowed to react in the FT-ICR cell. A Heme Cation Basicity (HCB) ladder for the various ligands toward [Fe (II)-hemeH] (+), corresponding to -Delta G degrees for the process [Fe (II)-hemeH] (+) + L --> [Fe (II)-hemeH(L)] (+) and named HCB (II), can thus be established. The so-obtained HCB (II) values are compared with the corresponding HCB (III) values for [Fe (III)-heme] (+). In spite of pronounced differences displayed by various ligands, NO shows a quite similar HCB of about 67 kJ mol (-1) at 300 K toward both ions, estimated to correspond to a binding energy of 124 kJ mol (-1). Density Functional Theory (DFT) computations confirm the experimental results, yielding very similar values of NO binding energies to [Fe (II)-hemeH] (+) and [Fe (III)-heme] (+), equal to 140 and 144 kJ mol (-1), respectively. The kinetic study of the NO association reaction supports the equilibrium HCB data and reveals that the two species share very close rate constant values both for the forward and for the reverse reaction. These gas phase results diverge markedly from the kinetics and thermodynamic behavior of NO binding to iron(II)- and iron(III)-heme proteins and model complexes in solution. The requisite of either a very labile or a vacant coordination site on iron for a facile addition of NO to occur, suggested to explain the bias for typically five-coordinate iron(II) species in solution, is fully supported by the present work.