Nakul C. Maiti

J- and H-Aggregates of Porphyrins with Surfactants: Fluorescence, Stopped Flow and Electron Microscopy Studies

The interaction of cationic surfactants such as CTAB (cetyl trimethyl ammonium bromide) with tetrakis-(4-sulfonato phenyl) porphine (H4TPPS2−), a dianion, leads to the formation of two premicellar aggregates of porphyrin when [CTAB] is below CMC (critical micelle concentration) and a micellized monomer when [CTAB] is above CMC. The premicellar aggregates are labeled as J- and H-aggregates because of their characteristic spectroscopic properties. Simple inorganic cations such as K+, Ba2+, Ca2+ and Zr4+ also induce the formation of the J-aggregate but not of the H-aggregate. The formation of the J-aggregate is preceded by kinetic intermediates, while no intermediate was observed prior to the formation of the H-aggregate. The rate of formation of the H-aggregate was faster than that of the J-aggregate. The fluorescence depolarization (anisotropy) properties of the monomer and the H- and J-aggregates were studied and compared. The size and structure of the J-aggregate were examined by transmission electron mi...

Melatonin inhibits matrix metalloproteinase‐9 activity by binding to its active site

The zinc‐dependent matrix metalloproteinases (MMPs) are key enzymes associated with extracellular matrix (ECM) remodeling; they play critical roles under both physiological and pathological conditions. MMP‐9 activity is linked to many pathological processes, including rheumatoid arthritis, atherosclerosis, gastric ulcer, tumor growth, and cancer metastasis. Specific inhibition of MMP‐9 activity may be a promising target for therapy for diseases characterized by dysregulated ECM turnover. Potent MMP‐9 inhibitors including an indole scaffold were recently reported in an X‐ray crystallographic study. Herein, we addressed whether melatonin, a secretory product of pineal gland, has an inhibitory effect on MMP‐9 function. Gelatin zymographic analysis showed a significant reduction in pro‐ and active MMP‐9 activity in vitro in a dose‐ and time‐dependent manner. In addition, a human gastric adenocarcinoma cell line (AGS) exhibited a reduced (~50%) MMP‐9 expression when incubated with melatonin, supporting an inhibitory effect of melatonin on MMP‐9. Atomic‐level interaction between melatonin and MMP‐9 was probed with computational chemistry tools. Melatonin docked into the active site cleft of MMP‐9 and interacted with key catalytic site residues including the three histidines that form the coordination complex with the catalytic zinc as well as proline 421 and alanine 191. We hypothesize that under physiological conditions, tight binding of melatonin in the active site might be involved in reducing the catalytic activity of MMP‐9. This finding could provide a novel approach to physical docking of biomolecules to the catalytic site of MMPs, which inhibits this protease, to arrest MMP‐9‐mediated inflammatory signals.

Novel Anti-inflammatory Activity of Epoxyazadiradione against Macrophage Migration Inhibitory Factor INHIBITION OF TAUTOMERASE AND PROINFLAMMATORY ACTIVITIES OF MACROPHAGE MIGRATION INHIBITORY FACTOR

Background: Macrophage migration inhibitory factor (MIF) is responsible for proinflammatory reactions in many infectious and non-infectious diseases. Results: Epoxyazadiradione, a limonoid, inhibits the tautomerase activity of both human and malarial MIF and prevents MIF-induced proinflammatory reactions. Conclusion: Epoxyazadiradione bears therapeutic potential against MIF-induced proinflammatory reactions. Significance: This novel molecule is a significant addition in the discovery of anti-inflammatory drugs. Macrophage migration inhibitory factor (MIF) is responsible for proinflammatory reactions in various infectious and non-infectious diseases. We have investigated the mechanism of anti-inflammatory activity of epoxyazadiradione, a limonoid purified from neem (Azadirachta indica) fruits, against MIF. Epoxyazadiradione inhibited the tautomerase activity of MIF of both human (huMIF) and malaria parasites (Plasmodium falciparum (PfMIF) and Plasmodium yoelii (PyMIF)) non-competitively in a reversible fashion (Ki, 2.11–5.23 μm). Epoxyazadiradione also significantly inhibited MIF (huMIF, PyMIF, and PfMIF)-mediated proinflammatory activities in RAW 264.7 cells. It prevented MIF-induced macrophage chemotactic migration, NF-κB translocation to the nucleus, up-regulation of inducible nitric-oxide synthase, and nitric oxide production in RAW 264.7 cells. Epoxyazadiradione not only exhibited anti-inflammatory activity in vitro but also in vivo. We tested the anti-inflammatory activity of epoxyazadiradione in vivo after co-administering LPS and MIF in mice to mimic the disease state of sepsis or bacterial infection. Epoxyazadiradione prevented the release of proinflammatory cytokines such as IL-1α, IL-1β, IL-6, and TNF-α when LPS and PyMIF were co-administered to BALB/c mice. The molecular basis of interaction of epoxyazadiradione with MIFs was explored with the help of computational chemistry tools and a biological knowledgebase. Docking simulation indicated that the binding was highly specific and allosteric in nature. The well known MIF inhibitor (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1) inhibited huMIF but not MIF of parasitic origin. In contrast, epoxyazadiradione inhibited both huMIF and plasmodial MIF, thus bearing an immense therapeutic potential against proinflammatory reactions induced by MIF of both malaria parasites and human.

Effects of non-planarity and β-substitution on the singlet-excited-state properties of basket-handle porphyrins

The combined effects of non-planarity in the porphyrin macrocycle and β-substitution on the photophysical properties of a series of basket-handle porphyrins are described. The introduction of a short chain across the periphery of the porphyrin ring induces deformation in the porphyrin ring and β-substitution further enhances the degree of deformation. The perturbations in the porphyrin π-system resulted in red-shifted emission bands, low quantum yields and reduction in singlet-excited-state lifetimes. A time-resolved fluorescence study invoked the possibility for an intramolecular electron transfer from the porphyrin ring to the bridging phenyl group which acts as an acceptor owing to the presence of electron-withdrawing substituents. The quenching of the fluorescence yields is interpreted in terms of enhancement in the non-radiative rates. The structure calculated using molecular mechanics reveals the enforced deformation caused by short bridging groups and β-substitution, supporting the observed photophysical properties.

Synthesis and bio-evaluation of human macrophage migration inhibitory factor inhibitor to develop anti-inflammatory agent

Macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine, is involved in the development of an array of inflammatory disorders including rheumatoid arthritis, inflammatory bowel disease, psoriasis, multiple sclerosis and sepsis. The synthesis of MIF-inhibitor is a rationale approach to develop novel anti-inflammatory agent to treat multitude of inflammatory diseases. In this work, we have synthesized and evaluated MIF-inhibitory activity of a series of small molecules containing isoxazoline skeleton. Mode of binding of this inhibitor to human MIF (huMIF) was determined by docking studies. The synthesized molecules inhibit tautomerase activity of huMIF. The anti-inflammatory activity of the most active inhibitor, 4-((3-(4-hydroxy-3-methoxyphenyl)-4, 5-dihydroisoxazol-5-yl) methoxy) benzaldehyde (4b) was evaluated against huMIF-induced inflammation in a cellular model (RAW 264.7 cell). Compound 4b significantly inhibits huMIF-mediated NF-κB translocation to the nucleus, up-regulation of inducible nitric oxide synthase and nitric oxide production in RAW 264.7 cell which are the markers for inflammation. The compound 4b is not cytotoxic as evident from cell viability assay. Hence, the compound 4b has potential to be a novel anti-inflammatory agent.

Mechanistic Studies of Cu(II) Binding to Amyloid-β Peptides and the Fluorescence and Redox Behaviors of the Resulting Complexes

Due in large part to the lack of crystal structures of the amyloid-beta (Abeta) peptide and its complexes with Cu(II), Fe(II), and Zn(II), characterization of the metal-Abeta complex has been difficult. In this work, we investigated the complexation of Cu(II) by Abeta through tandem use of fluorescence and electron paramagnetic resonance (EPR) spectroscopies. EPR experiments indicate that Cu(II) bound to Abeta can be reduced to Cu(I) using sodium borohydride and that both Abeta-Cu(II) and Abeta-Cu(I) are chemically stable. Upon reduction of Cu(II) to Cu(I), the Abeta fluorescence, commonly reported to be quenched upon Abeta-Cu(II) complex formation, can be regenerated. The absence of the characteristic tyrosinate peak in the absorption spectra of Abeta-Cu(II) complexes provides evidence that the sole tyrosine residue in Abeta is not one of the four equatorial ligands bound to Cu(II), but remains close to the metal center, and its fluorescence is sensitive to the copper oxidation state and perturbations in the coordination sphere. Further analysis of the quenching and Cu(II) binding behaviors at different Cu(II) concentrations and in the presence of the competing ligand glycine offers evidence supporting the operation of two binding regimes which demonstrate different levels of fluorescence recovery upon addition of the reducing agent. We provide results that suggest the fluorescence quenching is likely caused by charge transfer processes. Thus, by using tyrosine to probe the coordination site, fluorescence spectroscopy provides valuable mechanistic insights into the oxidation state of copper ions bound to Abeta, the binding heterogeneity, and the influence of solution conditions on complex formation.

Fluorescence study of some deformed zinc (II) porphyrins

Abstract The effect of deformation in the porphyrin ring on the emission properties of a series of zinc(II) derivatives of basket handle porphyrins is reported. Emission from the upper excited S2 state is observed in all zinc(II) deformed porphyrins. The porphyrin ring deformation results in red shifts of both the S1 and S2 emission bands and perturbed lifetimes of the S1 state. Decreased quantum yields and increased intersystem crossing rates are also caused by porphyrin ring deformation. The decrease in the S1 fluorescence yields can be interpreted in terms of an enhancement of the non-radiative rate, whereas a reduction in the energy gap between the S2 and S1 states results in low S2 quantum yields relative to planar derivatives.

Dipeptide derived from benzylcystine forms unbranched nanotubes in aqueous solution

The essence of modern nanotechnology is manifested in the formation of well-ordered nanostructures by a process of self-association. Peptides are among the most useful building blocks for organic bionanostructures such as nanotubes, nanospheres, nanotapes, nanofibrils, and other different ordered structures at the nanoscale. Peptides are biocompatible, chemically diverse, and much more stable and can be readily synthesized on a large scale. Also, they have diverse application in biosensors, tissue engineering, drug delivery, etc. Here, we report a short cystine-based dipeptide, which spontaneously self-associates to form straight, unbranched nanotubes. Such self-assembled nanobiomaterials provide a novel possibility of designing new functional biomaterials with potential applications in nanobiotechnology. The formation of nanotubes in solution state has been demonstrated by atomic force microscopy and scanning electron microscopy. Infrared absorption and circular dichroism demonstrated the intermolecular β-sheet-like backbone hydrogen bonding in juxtaposing and stacking of aromatic side chains.

ZnI2-Catalyzed Diastereoselective [4 + 2] Cycloadditions of β,γ-Unsaturated α-Ketothioesters with Olefins.

The potential of β,γ-unsaturated α-ketothioesters participating in hetero-Diels-Alder reaction has remained unexplored. We report herein the first study of a ZnI2-catalyzed highly diastereoselective inverse electron demand hetero-Diels-Alder reaction of β,γ-unsaturated α-ketothioesters with olefins to access highly substituted 3,4-dihydro-2H-pyrans. All the reactions proceed with cis-selectivity in moderate to excellent yields. Under similar reaction conditions, terminal alkynes undergo direct conjugate 1,4-addition to yield δ,ε-acetylenic α-ketothioesters. Furthermore, the utility of these cycloadducts has been demonstrated by an NBS-MeOH mediated stereospecific efficient access to fully substituted pyran rings. The product bromoethers undergo E2 elimination with DBU, resulting in substituted 3,6-dihydro-2H-pyrans. In addition, the thioester moiety of the products has been used for further transformations, such as amidations and Fukuyama coupling reactions.

Synthesis, characterization and cytotoxicity study of magnetic (Fe3O4) nanoparticles and their drug conjugate

An easy synthesis of magnetic nanoparticles (Fe3O4) is described. Transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and X-ray diffraction (XRD) have been used to study the well dispersed and uniformly spherical nanoparticles. 5-Fluorouracil (5-FU) has been successfully loaded onto the nanoparticles and cytotoxicity studies were performed using a standard MTT assay. The results indicate that 5-fluorouracil-loaded iron nanoparticles are a more potent anticancer drugversus5-fluorouracil alone.