Homobimetallic complexes of ligand having O- and S-donor sites with same and different di- and trialkyl/aryltin(IV) moiety: their synthesis, spectral characterization and biological activities

Homobimetallic complexes with oxygen and sulphur donor ligand have been synthesized at room temperature under stirring conditions using R₂SnCl₂ (R?=?Me, n-Bu) and R₃SnCl (R?=?Me, n-Bu, Ph) in 1:1 molar ratio. The synthesized complexes have been characterized by elemental analysis, IR and multinuclear NMR (¹H, ¹³C) spectroscopy. These complexes have also been screened for their biological activities. IR data show that the ligand acts in a bidentate manner and exhibits trigonal bipyramidal geometry in solid state which is also confirmed by semi-empirical study. NMR data show that reported complexes exhibit tetrahedral geometry in solution. Results of antimicrobial screening activities indicated that complexes (6) and (7) are very effective antibacterial and antifungal agents, respectively, and they might indeed be a potential source of antimicrobial agents, while the complex (3) exhibits significant free radical scavenging ability with lower IC₅₀ value of 99.47?±?1.2???g/mL. Results of cytotoxicity/haemolytic activity showed the significant value of % haemolysis for complex (7) (18.101?±?2.3), while complex (4) was found to be least cytotoxic (5.733?±?1.0). Only a few colonies are observed in mutagenicity testing by Ames test.     

Effect of magnetic field-dependent viscosity on revolving ferrofluid

The effect of magnetic field-dependent viscosity on the revolving axi-symmetric steady flow of ferrofluid in a disc is investigated by solving the boundary layer equations using Neuringer-Rosenweig model. Besides numerically calculating the velocity components and pressure for different values of magnetic field-dependent viscosity with variation in dimensionless parameter α (Karman’s parameter), we also have calculated the thickness of the boundary layer and the total volume flowing outward the z-axis. Here, the solutions of non-linear differential equations are obtained in the form of asymptotic series.     

Synthesis,characterziation, semi-empirical quantum-mechanical study and biological activity of organotin(IV) complexes with 2-ethylanilinocarbonylpropenoic acid

Seven different organotin(IV) complexes have been synthesized by reacting 2-ethylanilinocarbonylpropenoic acid with R₂SnCl₂/R₃SnCl under reflux conditions. The organotin(IV) complexes along with ligand have been characterized by different techniques including elemental analysis, FT-IR and multinuclear NMR (¹H and ¹³C). IR data show that complexation occurs through -COO site and the ligand is bidentate which is also confirmed by the semi-empirical quantum-mechanical study. ¹H and ¹³C NMR data confirm the tetrahedral geometry of complexes in solution. The complexes as well as the ligand were also checked for various     

Self-assembled monolayers of Aβ peptides on Au electrodes: an artificial platform for probing the reactivity of redox active metals and cofactors relevant to Alzheimer's disease

The water-soluble hydrophilic part of human Aβ peptide has been extended to include a C-terminal cysteine residue. Utilizing the thiol functionality of this cysteine residue, self-assembled monolayers (SAM) of these peptides are formed on Au electrodes. Atomic force microscopy imaging confirms formation of small Aβ aggregates on the surface of the electrode. These aggregates bind redox active metals like Cu and cofactors like heme, both of which are proposed to generate toxic partially reduced oxygen species (PROS) and play a vital role in Alzheimer's disease. The spectroscopic and electrochemical properties of these Cu and heme bound Aβ SAM are similar to those reported for the soluble Cu and heme bound Aβ peptide. Experiments performed on these Aβ-SAM electrodes clearly demonstrate that (1) heme bound Aβ is kinetically more competent in reducing O(2) than Cu bound Aβ, (2) under physiological conditions the reduced Cu site produces twice as much PROS (measured in situ) than the reduced heme site, and (3) chelators like clioquinol remove Cu from these aggregates, while drugs like methylene blue inhibit O(2) reactivity of the heme cofactor. This artificial construct provides a very easy platform for investigating potential drugs affecting aggregation of human Aβ peptides and PROS generation by its complexes with redox active metals and cofactors.     

Continuous stationary phase gradients for planar chromatographic media

A simple, elegant method for the formation of a continuous stationary phase gradient for use in chromatographic separations is described. Its applicability to separation science is demonstrated using thin-layer chromatography as a test case. Gradient stationary phases were formed on activated High Performance Thin-Layer Chromatography (HP-TLC) plates using a newly developed methodology termed "controlled rate infusion". Specifically, the SiOH groups on the activated HP-TLC plates were reacted with 3-aminopropyltriethoxysilane (APTEOS) in a time dependent fashion by using a programmable syringe pump to control the rate of APTEOS infusion into the deposition reservoir. The shape (profile) of the gradient was controlled by the rate of infusion and imaged by taking advantage of the concentration-dependent color formation reaction between amine groups and ninhydrin. The advantages of such gradients in optimizing the retention and separation of various components in different mixtures were illustrated using mixtures of (1) four weak acids and bases and (2) three widely used over-the-counter drugs. The separation of the individual components on the gradient stationary phase was clearly improved relative to those on either traditional normal-phase TLC plates or uniformly amine-modified TLC plates. Precise control over component retention and separation was also demonstrated by strategically modifying the steepness of the gradient.     

Synthesis of powdered silver nanoparticles using hydrogen in aqueous medium

Environmentally benign one-pot protocol is used in the synthesis of silver nanoparticles (AgNPs) in powder form, involving the reduction of silver nitrate in the presence of fully hydrolyzed polyvinyl alcohol (PVA) as stabilizer by hydrogen (H₂) as reducing agent in aqueous medium. Fully hydrolyzed biodegradable PVA has extremely low cytotoxicity, making it a favorable stabilizer from green perspective. In the present methodology, essentially naked silver nanoparticles are obtained in good yield. The prepared silver nanoparticles were characterized by TEM, XRD, EDAX, UV–Vis spectroscopy and DLS histogram, and studied for its activity as a recyclable catalyst for synthesis of different enaminones.     

Cyano‐Bridged ‘Oximato’ Complexes: Synthesis,Structure, and Catalase‐Like Activities

The reaction of the ‘oximato’‐ligand precursor A (Fig. 1) and metal salts with KCN gave two mononuclear complexes [ML(CN)(H₂O)_n](ClO₄) ( 1 and 2 ; L={N‐(hydroxy‐κO)‐α‐oxo‐N′‐[(pyridin‐2‐yl‐κN)methyl[1,1′‐biphenyl]‐4‐ethanimidamidato‐κN′}; M=Co^II ( 1 ), Cu^II ( 2 ); n=2 for Co^II, n=0 for Cu^II; Figs. 2 and 3). The new cyano‐bridged pentanuclear ‘oximato’ complexes [{ML(H₂O)_n(NC)}₄M¹(H₂O)_x](ClO₄)₂ ( 3 – 6 ) and trinuclear complexes [{ML(H₂O)_n(NC)}₂M¹L](ClO₄) ( 7 – 10 ) ([M¹=Mn^II, Cu^II; x=2 for Mn^II, x=0 for Cu^II] were synthesized from mononuclear complexes and characterized by elemental analyses, magnetic susceptibility, molar conductance, and IR and thermal analysis. The four [ML(CN)(H₂O)_n]⁺ moieties are connected by a metal(II) ion in the pentanuclear complexe 3 – 6 , each one involving four cyano bridging ligands (Fig. 4). The central metal ion displays a square‐planar or octahedral geometry, with the cyano bridging ligands forming the equatorial plane. The axial positions are occupied by two aqua ligands in the case of the central Mn‐atom. The two [ML(CN)(H₂O)_n]⁺ moieties and an ‘oximato’ ligand are connected by a metal(II) ion in the trinuclear complexes 7 – 10 , each one involving two cyano bridging ligands (Fig. 5). The central metal ions display a distorted square‐pyramidal geometry, with two cyano bridging ligands and the donor atoms of the tridentate ‘oximato’ ligand. Moreover catalytic activities of the complexes for the disproportionation of hydrogen peroxide (H₂O₂) were also investigated in the presence of 1H‐imidazole. The synthesized homopolynuclear Cu^II complexes 6 and 10 displayed eficiency in disproportion reactions of H₂O₂ producing H₂O and dioxygen thus showing catalase‐like activity.     

Additive free microwave assisted synthesis of nanocrystalline Mg(OH)2 and MgO

A novel approach for additive free synthesis of nanocrystalline magnesium hydroxide (MH) and magnesium oxide (MgO) using microwave technique is herein reported. Use of 13-propanediol as a solvent played multiple roles circumventing the additional requirement of any extraneous species such as base and other capping agents. The prepared nanomaterials were well characterised using TEM, XRD, EDAX, Raman spectroscopy and FT-IR analysis.     

A Reversibly Porous Supramolecular Peptide Framework**

The ability to use bio-inspired building blocks in the assembly of novel supramolecular frameworks is at the forefront of an exciting research field. Herein, we present the first polyproline helix to self-assemble into a reversibly porous, crystalline, supramolecular peptide framework (SPF). This framework is assembled from a short oligoproline, adopting the polyproline II conformation, driven by hydrogen-bonding and dispersion interactions. Thermal activation, guest-induced dynamic porosity and enantioselective guest inclusion have been demonstrated for this novel system. The principles of the self-assembly associated with this SPF will be used as a blueprint allowing for the further development of helical peptide linkers in the rational design of SPFs and metal-peptide frameworks.