Subramaniam Sujatha

Axial ligand modified high valent tin(IV) porphyrins: synthesis, structure, photophysical studies and photodynamic antimicrobial activities on Candida albicans

Herein, we report the synthesis, structure, photophysical properties and photodynamic antimicrobial activities on Candida albicans of axial ligand modified high valent tin(IV) porphyrins, namely SnIV(OH)2T(4-CMP)P (1), SnIV(OH)2T(4-CP)P (2) and SnIV(O-NO2Ph)2T(4-CMP)P (3). The newly synthesized porphyrins were characterized by various spectroscopic methods and single crystal X-ray diffraction analysis. The crystal structures of the precursor porphyrin, SnIV(Cl)2T(4-CMP)P and 3 are well stabilized by various intermolecular interactions and porphyrin 3 shows complementary bonding interactions between the nitro groups (N⋯O) forming a one-dimensional array. The fluorescence lifetime of 3 is lower compared to other porphyrins which indicates that there is a considerable interaction between the tin(IV) porphyrin core and nitrophenyl system and this could be the reason for its significant phototoxicity. This is further evident from X-ray crystallography and DFT calculations. In the presence of light, tin(IV) porphyrins significantly inhibited the growth of C. albicans in liquid as well as in the solid agar medium and the growth inhibitory effects were much less under dark conditions. The porphyrin internalization as well as localization within the Candida cells were examined by fluorescence microscopic analysis. Our results suggest that the mechanism behind the photodynamic inactivation of C. albicans could be through the generation of singlet oxygen species within the cells.

Synthesis, structure, electrochemical, DNA interaction and antimicrobial studies of fluorinated trans-dicationic pyridinium porphyrins

A series of trans-pyridyl porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2′/3′/4′-pyridyl)porphyrin (1–3), trans-dicationic pyridinium porphyrins, 5,15-di(pentafluorophenyl)-10,20-bis(2′/3′/4′-N-methylpyridyl)porphyrins (4–6) and their copper(II) and zinc(II) derivatives were synthesized. These compounds were characterized using various spectroscopic methods, electrochemical and single crystal X-ray crystallographic studies. The trans-dicationic porphyrin derivatives exhibit red shifted absorption spectra over the simple pyridyl porphyrins. The reduction potentials of trans-pyridyl porphyrins are more positive than those of MTPPs. Crystal structure of 3c is forming networks of molecules through Zn–N coordination displaying large number of channels. The intermolecular interactions involving fluorine contributes considerably to the crystal packing in all the structures which was confirmed by computational Hirshfeld surface analysis. The dicationic porphyrins were further explored for its DNA interaction abilities and antimicrobial activities. The UV-visible and fluorescence spectroscopic titrations indicate that the porphyrins bind with the calf thymus DNA by outside groove binding mode with or without self-stacking. The intrinsic binding constants Kb of these dicationic porphyrins to DNA was found to be in the range of 105 to 106 M−1. The results reveal that among the three sets of porphyrins (4–6), the 3-/4-pyridyl derivatives display higher DNA binding activities compared to the 2-pyridyl analogues. The photocleavage experiments disclose that the porphyrins employ 1O2-mediated mechanism in cleaving DNA and the freebase and zinc(II) derivatives show better photoinduced cleavage ability compared to its copper(II) analogues. The dicationic porphyrins also show significant antimicrobial activities than those of non-fluorinated analogues.

Fluorinated meso-tetraaryl Pt(II)-porphyrins: structure, photophysical, electrochemical, and phosphorescent oxygen sensing studies

Fluorinated Pt(II)-porphyrins (F1–F8) were synthesized, characterized; photophysical and electrochemical studies were conducted. The electronic absorption spectra of the complexes exhibited an intense Soret band (392–402 nm) and two hypsochromically shifted visible (Q) bands (508–510 and 538–541 nm). They also exhibited two emission bands (701–721 nm and 651–658 nm), corresponding to the T → S0 transition. The cyclic voltammetric studies of the porphyrins revealed the order of electron deficiency is as follows; F2 > F7 ≈ F8 > F5 > F4 > F3. The crystals of F3, F4, and F7 were structurally characterized and the crystal packing was mainly controlled by F⋯H, O⋯H, O⋯O, C⋯H close contacts. The oxygen sensing studies of the synthesized Pt(II)-porphyrins demonstrate that the highest sensitivity was observed for F8 compared to other complexes. The modified Stern–Volmer or two-site model provides the highest weighted quenching constant (KSV) of 0.068 Torr−1 for F8, which is twofold of the reference compound F1.

Protonation and axial ligation intervened fluorescence turn-off sensing of picric acid in freebase and tin(IV) porphyrins

Freebase and tin(IV)-porphyrins are examined for the selective detection of picric acid and their affinity is revealed by spectroscopic titrations and X-ray structures. The sensing is mediated through protonation and axial ligation in 1–5 and 6–9 respectively. Fluorescent lifetime studies show that the quenching is dynamic in the freebase and static in tin(IV)-porphyrins.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs

A series of mono- and di-brominated BODIPYs (1–5) was synthesized and characterized with a view to study the performance of dyes towards antibacterial activity. Regioselective bromination at the 2- and 2,6-positions of the BODIPY core was achieved with quantitative yield. The bromination of meso-(4-hydroxyphenyl) BODIPY (5) yielded an unexpected dibromo derivative, where the bromine groups were installed at the 3,5-positions of the phenyl ring rather than the 2,6-positions of the BODIPY core, which is confirmed and supported by UV-visible, fluorescence, and 1H NMR spectroscopic analyses, electrochemical studies, and also by single crystal X-ray crystallography. We observed a red shift of ∼16 nm in the absorption and 20–29 nm in the emission spectra in CH2Cl2 for the installation of each bromine group at the BODIPY core. The small difference between the first reduction potentials of the parent and dibromo derivative (5 and 5b) reveal that dibromination does not occur on the pyrrolic moiety. The intermolecular interactions involving C⋯H, F⋯H, H⋯H, and Br⋯H are the key factors in stabilizing the molecular crystal packing. The antibacterial properties of these dyes were investigated and the brominated derivatives showed better antibacterial effects than their corresponding parent BODIPYs, particularly the unusual dibromo derivative, 5b.

CCDC 1041763: Experimental Crystal Structure Determination

Related Article: Rahul Soman, Subramaniam Sujatha and Chellaiah Arunkuma|2016|J.Porphyrins Phthalocyanines|20|833|doi:10.1142/S1088424616501017

Structural, spectroscopic and electrochemical investigations on fluorinated meso-tetraaryl porphyrins

Two series of meso-phenyl fluorinated porphyrins and their metal complexes, 5,10,15,20-tetrakis(2′,4′,6′-trifluorophenyl)porphyrin, MT(2′,4′,6′-TFP)Ps (2a–2d) and 5,10,15,20-tetrakis[3′,5′-bis(trifluoromethylphenyl)]porphyrin, MT(3′,5′-BTFMP)Ps (3a–3d); where M = 2H; Ni(II); Cu(II) and Zn(II) have been synthesized and characterized using various spectroscopic techniques including UV-visible, fluorescence and 1H NMR and mass spectrometry. Electronic absorption spectra of porphyrins show the typical Soret (B) and visible (Q) bands. Free ligands and zinc(II) derivatives display two well-defined emission bands around 600–660 nm and 650–720 nm upon exciting the Soret band. Porphyrins, 1d, 2a, 2b, 2c, 3a and 3d were structurally characterized by single crystal XRD analysis, and various intermolecular interactions present in them were quantified on the basis of Hirshfeld surfaces and 2D fingerprint plots. Electrochemical studies were performed and the HOMO–LUMO energy gap is high for all the porphyrins compared ...

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions

Crystal engineering is an emerging area of research in material, biological, and pharma‐ ceutical chemistry that involves synthesis of new materials, analysis of its structure including intermolecular interactions using X‐ray crystallography as well as computa‐ tional methods. It has been shown that the intermolecular interactions involving organic fluorine such as C−F∙∙∙H, F∙∙∙F, and C−F∙∙∙π play an important role in stabilizing the supramolecular assemblies, especially in the absence of strong intermolecular forces. Recently, non‐covalent interactions involving conjugated aromatic system such as porphyrins have been studied intensively. The synthetic porphyrins are of widespread attention because of their close resemblance to naturally occurring tetrapyrrolic pigments and they find various materials and biological applications. In this book chapter, we disclose our recent findings on detailed crystal structure analysis of a few series of fluorinated porphyrins using single‐crystal XRD as well as computational Hirshfeld surface analysis to understand the role of close contacts involving fluorine in the molecular crystal packing.

Structural elucidation and study of intermolecular interactions in meso-tetratolylporphyrins

Synthesis and crystal structure analysis of meso-tetratolylporphyrins, 1–5 combined with computational Hirshfeld surface analysis were investigated. The crystal packing of porphyrins 1, 3 and 4 are arranged in an “orthogonal fashion” whereas 2 and 5 are in a “slip-stack or off-set fashion” through various intermolecular interactions. Compound 2 exhibits saddle geometry whereas 5 showed a domed geometry as evident from the single crystal X-ray diffraction studies. The enhancement of non-planarity in 2 is probably due to the presence of numerous intermolecular interactions caused by the presence of trifluoroacetate anions on both faces of the porphyrin in addition to the bulky bromine groups at the β-pyrrole positions. In 5, the non-planarity is merely due to the metal coordination at the porphyrin core as pentacoordinated MnIII center with a chloro ligand in the axial position. Hirshfeld surface analysis was performed in order to analyze the various intermolecular interactions present in these porphyrins and the result was discussed.