Studies on the interaction of mononuclear metal(II) complexes of amino­naphthoquinone with bio-macromolecules.

Three metal(II) complexes [CoLCl2], [CuLCl2] and [ZnL2Cl2] {L = 2­chloro­3­((3­dimethylamino)propylamino)naphthalene­1,4­dione} have been synthesized and characterized using analytical, thermal and spectral techniques (FT-IR, UV-Vis, ESR and ESI-MS). The structure of the L has been confirmed by single crystal XRD study. The complexes show good binding propensity to bovine serum albumin (BSA) having relatively higher binding constant values (104 M-1) than the ligand. Fluorescence spectral studies indicate that [CoLCl2] binds relatively stronger with CT DNA through intercalative mode, exhibiting higher binding constant (2.22 × 105 M-1). Agarose gel electrophoresis run on plasmid DNA (pUC18) prove that all the complexes showed efficient DNA cleavage via hydroxyl radical mechanism. The complexes were identified as potent anticancer agents against two human cancer cell lines (MCF7 and A549) by comparing with cisplatin. Co(II) complex demonstrated greater cytotoxicity against MCF7 and A549 cells with IC50 values at 19 and 22 µM, respectively.

Tetraphenylethylene conjugated p-hydroxyphenacyl: fluorescent organic nanoparticles for the release of hydrogen sulfide under visible light with real-time cellular imaging.

Hydrogen sulfide (H2S) behaves like a two-edged sword, at low concentrations it has beneficial and cytoprotective effects, while at higher concentrations it exhibits toxicity. Hence there is a keen interest in developing light responsive H2S donors with a spatio-temporal controlled release. Herein, we report visible light activatable tetraphenylethylene conjugated p-hydroxyphenacyl (TPE-pHP-H2S) nanoparticles for the release of hydrogen sulfide (H2S) with a real time monitoring ability. Our newly designed photoresponsive single component organic nanoparticle based H2S donor is built by integrating the tetraphenylethylene (TPE) moiety and p-hydroxyphenacyl (pHP) group so that it can display both aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) properties. Aggregation-induced emission enhancement was exhibited by our TPE-pHP-H2S NP donor, which was then explored for the cellular imaging application. The ESIPT by the pHP moiety provided unique advantages to our TPE-pHP-H2S NP donor which include (i) the excitation wavelength extended to >410 nm (ii) a large Stokes shift (iii) a low inner filter effect and (iv) real-time monitoring of H2S release by a simple fluorescent colour change. In vitro studies showed that the TPE-pHP-H2S NP donor presents excellent properties like real-time monitoring, photoregulated H2S release and biocompatibility.

Ultrasound-assisted synthesis of metal organic framework for the photocatalytic reduction of 4-nitrophenol under direct sunlight.

In this study, the metal organic framework MOF [Zn(BDC)(DMF)] crystal was synthesized via ultrasonic irradiation and solvothermal method. The synthesized MOF [Zn(BDC)(DMF)] crystal was characterized by PXRD, FTIR, FESEM-EDX, TGA, UV-DRS and BET. The catalytic activity of MOF [Zn(BDC)(DMF)] was investigated by 4-nitrophenol (4-NP) degradation under direct sunlight irradiation. The influence of various degradation parameters such as initial 4-NP concentration, dosage, pH and H2O2 concentration were investigated. The results indicated that the synthesized MOF [Zn(BDC)(DMF)] exhibited strong photocatalytic activity in the presence of NaBH4 under sunlight irradiation and the reduction of 4-NP to 4-aminophenol (4-AP) completed within 10 min. The study provides the synthesized MOF [Zn(BDC)(DMF)] crystal can be used as a high performance catalyst for the treatment of dyes in wastewater.

Metal complexes of naphthoquinone based ligand: synthesis, characterization, protein binding, DNA binding/cleavage and cytotoxicity studies.

Protein binding, DNA binding/cleavage and in vitro cytotoxicity studies of 2-((3-(dimethylamino)propyl)amino)naphthalene-1,4-dione (L) and its four coordinated M(II) complexes [M(II) = Co(II), Cu(II), Ni(II) and Zn(II)] have been investigated using various spectral techniques. The structure of the ligand was confirmed by spectral and single crystal XRD studies. The geometry of the complexes has been established using analytical and spectral investigations. These complexes show good binding tendency to bovine serum albumin (BSA) exhibiting high binding constant values (105 M-1) when compared to free ligand. Fluorescence titration studies reveal that these compounds bind strongly with CT-DNA through intercalative mode (Kapp 105 M-1) and follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > L. Molecular docking study substantiate the strength and mode of binding of these compounds with DNA. All the complexes efficiently cleaved pUC18-DNA via hydroxyl radical mechanism and the Cu(II) complex degraded the DNA completely by converting supercoiled form to linear form. The complexes demonstrate a comparable in vitro cytotoxic activity against two human cancer cell lines (MCF-7 and A-549), which is comparable with that of cisplatin. AO/EB and DAPI staining studies suggest apoptotic mode of cell death, in these cancer cells, with the compounds under investigation.

Role of de-N-acetylase PgaB from Aggregatibacter actinomycetemcomitans in exopolysaccharide export in biofilm mode of growth.

Aggregatibacter actinomycetemcomitans, a Gram-negative bacterium, is the causative agent of localized aggressive periodontitis. Attachment to a biotic surface is a critical first step in the A. actinomycetemcomitans infection process for which exopolysaccharides have been shown to be essential. In addition, the pga operon, containing genes encoding for biosynthetic proteins for poly-N-acetyl glucosamine (PNAG), plays a key role in A. actinomycetemcomitans virulence, as a mutant strain lacking the pga operon induces significantly less bone resorption. Among the genes in the pga operon, pgaB codes for a de-N-acetylase that is responsible for the deacetylation of the PNAG exopolysaccharide. Here we report the role of PgaB in regulation of virulence genes using a markerless, scarless deletion mutant targeting the coding region of the N-terminal catalytic domain of PgaB. The results demonstrate that the N-terminal, catalytic domain of PgaB is crucial for exopolysaccharide export.

Synthesis, characterization and DNA binding/cleavage, protein binding and cytotoxicity studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of aminonaphthoquinone.

The Co(II), Ni(II), Cu(II) and Zn(II) complexes of an aminonaphthoquinone ligand (L) have been prepared and characterized using analytical and spectral techniques. The structures of L and its Zn(II) complex are confirmed by single crystal X-ray diffraction study. The results indicate that Co(II), Ni(II) and Zn(II) complexes possess tetrahedral geometry while Cu(II) complex exhibits square planar structure. The interaction of L and its complexes with CT-DNA reveal that they could interact with CT-DNA through intercalation. The DNA cleavage studies of the L and its complexes indicate that the Cu(II) and Ni(II) complexes cleave the circular form of the DNA relatively to a greater extent than the other complexes. The results of the interaction of these compounds with bovine serum albumin (BSA) indicate that the complexes exhibit a strong binding to BSA over the L. The in vitro anticancer activities indicate that these compounds exhibit substantial activity against human breast (MCF7) and lung cancer (A549) cell lines. The characteristics of apoptosis in cell morphology have been observed using AO/EB and DAPI staining and the results suggest that an apoptotic mode of cell death with these compounds. The overall results and discussion indicate that coordination of metal ions with the ligand enhances the biological activity.

Structural and functional analysis of de-N-acetylase PgaB from periodontopathogen Aggregatibacter actinomycetemcomitans.

The oral pathogen Aggregatibacter actinomycetemcomitans uses pga gene locus for the production of an exopolysaccharide made up of a linear homopolymer of ß-1,6-N-acetyl-d-glucosamine (PGA). An enzyme encoded by the pgaB of the pga operon in A. actinomycetemcomitans is a de-N-acetylase, which is used to alter the PGA. The full length enzyme (AaPgaB) and the N-terminal catalytic domain (residues 25-290, AaPgaBN) from A. actinomycetemcomitans were cloned, expressed and purified. The enzymatic activities of the AaPgaB enzymes were determined using 7-acetoxycoumarin-3-carboxylic acid as the substrate. The AaPgaB enzymes displayed significantly lower de-N-acetylase activity compared with the activity of the deacetylase PdaA from Bacillus subtilis, a member of the CE4 family of enzymes. To delineate the differences in the activity and the active site architecture, the structure of AaPgaBN was determined. The AaPgaBN structure has two metal ions in the active site instead of one found in other CE4 enzymes. Based on the crystal structure comparisons among the various CE4 enzymes, two residues, Q51 and R271, were identified in AaPgaB, which could potentially affect the enzyme activity. Of the two mutants generated, Q51E and R271K, the variant Q51E showed enhanced activity compared with AaPgaB, validating the requirement that an activating aspartate residue in the active site is essential for higher activity. In summary, our study provides the first structural evidence for a di-nuclear metal site at the active site of a member of the CE4 family of enzymes, evidence that AaPgaBN is catalytically active and that mutant Q51E exhibits higher de-N-acetylase activity.

Design, synthesis, characterization and cation sensing behavior of amino-naphthoquinone receptor: Selective colorimetric sensing of Cu(II) ion in nearly aqueous solution with mimicking logic gate operation.

An amino-naphthoquione receptor (R1) has been rationally designed, synthesized and characterized using 1H and 13C NMR, LCMS and single crystal X-ray diffraction studies. The receptor exhibits an instantaneous colour change from yellow to blue selectively with Cu(II) ions in water-DMF (98:2% v/v) medium. The results of UV-Vis and fluorescence spectral studies indicates that the mechanism of sensing involves formation of a 1:1 complex between R1 and Cu(II) ion. The proposed mechanism has been confirmed through product analysis using FT-IR, UV-Vis, EPR and HRMS studies in addition to magnetic moment and elemental analysis measurements. The formed [Cu(R1)Cl2] possess a square planar geometry. The binding constant for the interaction of Cu(II) ion with the present unsubstituted quinone is found to be relatively higher than that with quinones containing electron withdrawing chlorine atom and electron releasing methyl group reported in literature. The detection limit of Cu(II) ion in aqueous solution by R1 is observed to be 8.7nM. The detection of Cu(II) ion by R1 in aqueous solution produces remarkable changes in the electronic and fluorescence spectra, which is applied to construct logic gate at molecular level.

Differentiation of mesenchymal stem cells under hypoxia and normoxia: lipid profiles revealed by time-of-flight secondary ion mass spectrometry and multivariate analysis.

Mesenchymal stem cells (MSC) have the ability to self-renew and differentiate into multiple cell types valuable for clinical treatment of rheumatic pathologies. To study the chondrogenic potential of MSC and identify the conditions that recreate the native cartilage environment, we used time-of-flight secondary ion mass spectrometry (TOF-SIMS) for label-free detection of cell-type- and environmental-condition-specific molecular profiles. We observed that coculture of human MSC and chondrocytes under standard culture conditions leads to improved extracellular matrix (ECM) deposition. In marked contrast, this effect was lost under low oxygen tension. This improved extracellular matrix deposition was associated with a significant decrease in lipids and in particular cholesterol under low oxygen tension as revealed by TOF-SIMS coupled to principal component analysis and discriminant analysis. We furthermore demonstrate that the higher cholesterol levels under normoxia might regulate fibroblast growth factor 1 (FGF-1) gene expression which was previously implemented in increased ECM production in the cocultures. In conclusion, our study shows an unexpected role of lipids as orchestrators of chondrogenesis in response to oxygen tension which is, at least in part, mediated through FGF-1.

Highly selective colorimetric sensing of Hg(II) ions in aqueous medium and in the solid state via formation of a novel M-C bond.

For the first time an easy-to-make receptor 2-chloro-3-(thiazol-2-ylamino)naphthalene-1,4-dione (R1) for highly selective sensing of Hg(ii) ions in aqueous solution and in the solid state through the formation of an Hg-C bond was developed. The Hg(ii) ion sensing properties of R1 were investigated using UV-Vis, fluorescence and (1)H & (13)C NMR spectral studies. The results indicated that the receptor selectively senses Hg(ii) ions via the formation of a 1 : 1 complex of moderate stability (Ka = 3.5 × 10(4) M(-1)). The NMR spectral studies indicated that complexation between R1 and Hg(ii) occurs through the formation of an Hg-C bond (after deprotonation), which was confirmed by a single crystal XRD analysis of the product. When Hg(ii) was added to a solution of R1 in DMF-water (1 : 9 v/v), a dramatic color change from pale brown to blue was observed, while many common cations and anions did not interfere with the recognition process. The detection limit was 0.3 µM, which is much lower than the permissible limit of Hg(ii) in drinking water (0.001 mg L(-1)) as recommended by the WHO. The simple grinding of R1 with Hg(ii) in the solid state also exhibited the same dramatic colour change which is easily detectable visually.

Anion induced azo-hydrazone tautomerism for the selective colorimetric sensing of fluoride ion.

The design, synthesis, characterization and their anion sensing properties of two receptors capable of exhibiting azo-hydrazone tautomerism are reported. The anion sensing properties have been investigated using electronic, fluorescence and nuclear magnetic spectral studies in addition to electrochemical and visual detection experiments. Both the receptors selectively bind fluoride ion with >100 nm red-shift in the electronic spectrum and the color changes from yellow to red. The results of the spectral studies revealed that the sensing mechanism involves fluoride ion induced change of chromophore from C=N (hydrazone form) to N=N (azo form) in these receptors leading to the visible color change. Density Functional Theory calculations were conducted to rationalize the optical response of the receptors.

Biosynthesis of antibacterial gold nanoparticles using brown alga, Stoechospermum marginatum (kützing).

Biological synthesis of gold nanoparticles by brown alga, Stoechospermum marginatum biomasses through a green route was reported in this study. The formation of the gold nanoparticles was observed within 10 min. The properties of prepared nanoparticles were characterized by photoluminescence spectra, Fourier Transform Infrared Spectroscopy, scanning electron microscopy, Transmission Electron Microscopy, X-ray diffraction, particle size analysis and quantified by Wavelength Dispersive X-ray Fluorescence Spectrophotometer. The synthesized gold nanoparticles were found to be photoluminescent. The formation of gold nanoparticles was confirmed by the presence of an absorption peak at 550 nm using UV-visible spectrophotometer. TEM image revealed that most of the particles are spherical in shape and some are hexagonal and triangle with size ranged from 18.7 to 93.7 nm. The nanoparticles were crystalline in nature and it was confirmed by XRD pattern and the presence of elemental gold (45.92%) was confirmed by WD-XRF. From the FTIR measurements it is noticed that the reduction has been carried out by hydroxyl groups present in the diterpenoids of the brown seaweed. Furthermore the biologically synthesized gold nanoparticles were found to be effective against bacterial pathogens.