Metalation Of Free Base Porphyrins Research Articles

Investigation of antimicrobial potential of nanocomposites based on functionalization of graphene oxide with zinc porphyrin complexes

Herein, zinc porphyrin complexes were synthesised by passing through the formation of free base porphyrin ligands and metalation of free base porphyrins with zinc metal ions. The synthesised zinc porphyrin complexes were functionalised with graphene oxide leading to the formation of zinc porphyrin anchored graphene oxide hybrid nanocomposites. The zinc porphyrins complexes were anchored with graphene oxide through the particular functional group present at the periphery of zinc porphyrins (hydroxyl and carboxyl functional groups in Pr1 and Pr2 respectively). 1H NMR and UV–visible spectroscopic techniques have monitored the successful formation of free base porphyrins and their matching zinc-integrated metalloporphyrin complexes. Various spectroscopic techniques like, photophysical properties (UV–Visible spectroscopy and Fluorescence spectroscopy), Fourier transform infrared (FT-IR), powdered X-ray diffraction (P-XRD) patterns, FE-SEM and EDAX analysis were used to examine the intrinsic characteristics of the prepared nanocomposites. The in-vitro antimicrobial activity of the synthesized complexes and nanocomposites was tested against Staphylococcus aureus gram-positive strain, Klebsiella pneumonia, and Escherichia coli. By working on the antimicrobial behaviour, it has been observed that the compound containing –COOH substitute has shown enhanced antimicrobial activity. The in silico molecular docking studies of the synthesized compounds with the S. aureus nucleoside diphosphate kinase receptor showed strong interactions via hydrogen bonding, π − π interactions and hydrophobic interactions. Molecular dynamics (MDs) simulations were used to study the dynamic behaviour of the complexes as well as nanocomposites which revealed the stability of docked structures with S. aureus nucleoside diphosphate kinase receptor. The in-silico pharmacokinetics studies showed the drug-likeness, non-toxic nature and safe oral administration of the synthesized compounds.

Thermally induced intra-molecular transformation and metalation of free-base porphyrin on Au(111) surface steered by surface confinement and ad-atoms.

We investigated chemical transformations of a fluorinated free-base porphyrin, 5,10,15,20-tetrakis(4-fluorophenyl)-21,23H-porphyrin (2H-4FTPP) under a Au(111) surface confinement and including gold adatoms by using an experiment and density functional theory based first-principles calculations. Annealing of 2H-4FTPP led to cyclodehydrogenation of the molecule to a π-extended fused aromatic planar compound, 2H-4FPP, and metallation of the porphyrin ring by Au atoms to Au-4FPP complex. Noticeable lowering of bond-dissociation energies of the pyrrole's C–H bonds of the Au(111) supported molecule with respect to their values in the gas phase explained the observed on-surface planarization. Our findings also indicate that Au adatoms may catalyze cleavage of C–H/F bonds in temperature-initiated processes on Au surfaces. BDEs and explicit inclusion of Au adatoms helps to rationalize thermally induced chemical reactions on the respective surface.

ChemInform Abstract: Surface‐Mediated in Situ Metalation of Porphyrins at the Solid‐Vacuum Interface

AbstractReview: 43 refs.

Surface-Mediated in Situ Metalation of Porphyrins at the Solid-Vacuum Interface.

The investigation of porphyrin derivatives at the solid-vacuum interface has become a vivid research field with the prospect to tailor functional molecular architectures and as prototype examples to study the fundamental properties of porphyrin derivatives in regard to their vital role in many natural processes. The functional properties of the porphyrin derivatives are mainly determined by the central metal atom. Thus, the recent exploration of the surface-confined in situ metalation of porphyrins is an important step toward the realization of molecule-based functional devices. The corresponding metalation reaction of free base porphyrin derivatives can be conveniently realized in situ in ultrahigh vacuum by post- or predeposition of metal atoms or directly with substrate atoms in the so-called self-metalation. Moderate heating above room temperature (RT) might be necessary either to realize the transport of the metal to the porphyrin via diffusion or to overcome an activation barrier determined by the redox reaction itself. Surface science techniques like scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD) are powerful tools to scrutinize the reaction and give valuable insights into the metalation process. For example, the completed metalation can be reflected in an enhanced apparent height of the corresponding porphyrin in STM or can be evidenced by characteristic changes in the N 1s region in XPS. These signatures allow monitoring of the progress of the metalation, and it was found that the reaction generally proceeds with very high yield. Surface diffusion of the coadsorbed metal atoms mediates the reaction and is crucial for the high yields of the corresponding reactions with pre- and postadsorbed metals. It was also demonstrated that the completed metalation can indeed significantly alter the adsorption behavior and the electronic properties and thus the functionality of the porphyrin molecules. These alterations can be used to monitor the kinetics of a particular porphyrin self-metalation reaction by STM and to estimate the activation barrier for that reaction based on isothermal measurements at different temperatures. Also TPD measurements of the H2 and D2 signals allow for the determination of corresponding activation energies for the metalation of free base porphyrins and their deuterized analogues. Gas phase DFT calculations of the metalation of the "bare" free base porphyrin macrocycle identify intermediate reaction steps with the transfer of the first hydrogen atom to the metal center being the main barrier to overcome. The values from these calculations are in fair agreement with experimentally determined ones. However, TPD based results indicate that exchanges of deuterium and hydrogen between the central nitrogen and the surface occur, which indicate an active role of the surface and challenge the findings from gas phase DFT. The in situ metalation of porphyrins at the solid-vacuum interface is established as a novel and convenient route to tailor functional molecular architectures. With different surface science techniques detailed insights into the surface-mediated metalation reaction were achieved for this class of prototype functional molecules.

Polyethylene-glycol-Stabilized Ag Nanoparticles for Surface-Enhanced Raman Scattering Spectroscopy: Ag Surface Accessibility Studied Using Metalation of Free-Base Porphyrins

Silver nanoparticles (Ag NPs) stabilized with a permeable layer of long-chain polyethylene glycol (PEG) represent a new generation of surface-enhanced Raman scattering (SERS) substrates for bioanalytical applications. This paper will shed light on their efficiency in the SERS detection of biomolecules. Two types of thiol-terminated PEG (average molecular weight 5000 g/mol) were used. Metalation of free-base porphyrins (10–9–10–6 M) of different size and charge was employed as the probe of accessibility of the Ag-PEG NP surface. The influence of NaCl (0.01 M) on the system was examined. The metalation was significantly decreased by the interaction of porphyrins with propionylamino groups of PEG1, while no interaction with the neutral chain of PEG2 was observed. Sterical hindrance of the porphyrin side groups seemed to cause a rather perpendicular porphyrin orientation on both types of Ag-PEG NP surfaces, inhibiting the metalation. Moreover, chloride anions influenced the structure of the polymer coating and improved the porphyrin accessibility on the Ag-PEG1 NPs. Finally, the studied Ag-PEG NPs remained isolated even after addition of porphyrins and chlorides, therefore being favorable for SERS applications inside the living cells.

Do Sitting-Atop Metalloporphyrin Complexes Exist? Observation of N−H- - -π Bonding in Arene Solvates of a Diprotonated Porphyrin Dication

The existence of sitting-atop metalloporphyrin complexes, the proposed intermediates in the metalation of free-base porphyrins, has been explored via the microscopic reverse reaction, i.e., protonation of metalloporphyrins with a strong acid. The reaction of M(Tp-TP) (M = Zn, Cu, Ni; Tp-TP = dianion of tetra-p-tolylporphyrin) with mesitylenium carborane salts produced only the demetalated porphyrin in its diprotonated form, [H4Tp-TP][carborane]2 (carborane = CHB11H5Cl6-, CHB11H5Br6-, CHB11Cl11-). In arene solvents, the H4Tp-TP2+ dication shows an unusually upfield shifted 1H NMR resonance at ca. -6 ppm, which X-ray crystallography reveals to arise from N-H- - -pi hydrogen bonding of the acidic protons to arene solvent molecules.