To gain more understanding into the mechanism that enables the dramatic resonant Raman enhancement of totally symmetric modes observed in hemozoin (malaria pigment) and other related heme supramolecular arrays when applying near-infrared excitation wavelengths, the iron(III) porphyrins Fe(TPP)Cl, [Fe(TPP)](2)O, Fe(OEP)Cl, and [Fe(OEP)](2)O along with β-hematin (synthetic hemozoin or malaria pigment) were analyzed in the solid state using resonance Raman spectroscopy. The critical finding was that from the model compounds investigated, all except [Fe(OEP)](2)O exhibited the enhancement of the totally symmetric mode ν(4) when exciting the molecules with 782 and 830 nm laser lines. Through a detailed comparison of X-ray crystallographic structures, it is proposed that intermolecular noncovalent interactions play an integral role in enabling excitonic interactions to occur in these heme supramolecular systems. Comparison of the solid- and solution-phase electronic spectra in the near-IR region indicated more absorbance in the solid state between 800 and 900 nm. The electronic spectrum of [Fe(OEP)](2)O shows minimal absorbance in this region compared to that of the other compounds. All heme derivatives investigated have similar structure with a five-coordinate high-spin iron(III) ion. The crystallographic data indicate no significant differences in porphyrin geometry between TPP and OEP derivatives studied. However, [Fe(OEP)](2)O contains less supramolecular interactions in comparison to the other species. The supramolecular bonding enhances the probability of through-space interactions between the transition dipoles from electronic transitions of extended π systems. Our results indicate that the intensity of ν(4) is in part strongly affected by C-H···X hydrogen bonding interactions when X is an electron-donating entity. Such information may have important implications in the design and monitoring of antimalarial drugs that specifically interfere with hemozoin formation.
The solvent-induced changes in the optical and spectroscopic properties of 1,2-benzenedicarboxylic anhydride are studied using time dependent Hartree-Fock and density functional theory calculations within the framework of two reaction field procedures. To investigate the influence of the cavity shape, the Onsager reaction field is compared with the polarized continuum model (PCM). It is observed that solvent polarity has noticeable effects on the vibrational properties as well as the linear and nonlinear optical characteristics of the molecule. Furthermore, the Onsager and PCM procedures may lead to contradicted harmonic vibrational frequencies; in the case of the studied molecule the Onsager model predicts the blue-shifted CH stretching band while PCM leads to red-shifted CH stretching mode.
The geometrical parameters and static electric properties of several metal porphyrin halides, including Fe(III) porphine chloride (FePCl), Fe(III) porphine bromide (FePBr), Fe(III) tetraphenylporphine chloride (FeTPPCl), aluminum phthalocyanine chloride (AlPcCl), gallium(III) phthalocyanine chloride (GaPcCl), and manganese(III) phthalocyanine chloride (MnPcCl), were investigated using density functional theory (DFT) methods. It was observed that FePBr and MnPcCl showed the highest total hyperpolarisabilities among the studied porphyrins. To investigate the effect of substituted phenyl groups on the nonlinear optical (NLO) responses of porphyrins, the optical properties of FeTPPCl and FePCl were compared using UBLYP/cc-pVDZ+LanL2DZ level of theory. Moreover, the polarised continuum model (PCM) was employed to study the influence of solvation on the optical properties of FePCl.
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