Transition-metal-induced fluorescence resonance energy transfer in a cryptand derivatized with two different fluorophores

A laterally nonsymmetric aza cryptand has been derivatized with one 7-nitrobenz-2-oxa-1,3-diazole (fluorophore(1)) and one/two anthracenes (fluorophore(2)) to obtain 1 and 2. Their emission characteristics are probed in the presence of a number of transition metals and proton. In the case of 1, Cu(II), Zn(II), Cd(II), and proton afford a large enhancement of fluorescence, whereas Fe(II) and Ag(I) exhibit one order of magnitude less enhancement. In contrast, 2 gives a large enhancement with Cu(II), Ag(I), and proton. The enhancement is observed in the diazole moiety even when the anthracene fluorophore is excited because of substantial fluorescence resonance energy transfer from anthracene to the diazole moiety. Compounds 1 and 2 can be termed as the second-generation fluorescence signaling systems.     

Mesoporous silica as a membrane for ultra-thin implantable direct glucose fuel cells

The design, fabrication and characterization of an inorganic catalyst based direct glucose fuel cell using mesoporous silica coating as a functional membrane is reported. The desired use of mesoporous silica based direct glucose fuel cell is for a blood vessel implantable device. Blood vessel implantable direct glucose fuel cells have access to higher continuous glucose concentrations. However, reduction in the implant thickness is required for application in the venous system as part of a stent. We report development of an implantable device with a platinum thin-film (thickness: 25 nm) deposited on silicon substrate (500 μm) to serve as the anode, and graphene pressed on a stainless steel mesh (175 μm) to serve as the cathode. Control experiments involved the use of a surfactant-coated polypropylene membrane (50 μm) with activated carbon (198 μm) electrodes. We demonstrate that a mesoporous silica thin film (270 nm) is capable of replacing the conventional polymer based membranes with an improvement in the power generated over conventional direct glucose fuel cells.     

Fabrication of multi-structure nanocarbons from carbon xerogel: a unique scaffold towards bio-imaging

A novel route has been developed to fabricate different carbon nanostructures having individual morphology of carbon nanoparticles: nanofullerene, nanocube, nanoleaf and porous nanorods, through the combustion of carbon xerogel with nitric acid. These fabricated nanostructures exhibited bright green fluorescence under the exposure of UV light.     

Synthetic Studies on Ophiobolins1. Synthesis of 1β (H) -3,7α,11β-Trimethyl-CIS-Bicyclo [6.3.0] Undecan-4-One

In our synthetic studies towards ophiobolin F (1), we report here a stereospecific synthesis of 1β(H)-3,7α,llβ-trimethyl-cis bicyclo [6.3.0]undecan-4-one (2) with defined stereochemistry at each of the four contiguous asymmetric centres and particularly with A/B cis ring juncture as present in (1). It may be mentioned here that no synthetic studies towards developing the characteristic ring systems present in ophiobolins have been reported so far.     

Charged polystyrene nanoparticles: role of ionic comonomers structures

Emulsion copolymerizations of styrene were carried out with four structurally different ionic comonomers namely acrylic acid (AAc), methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), and sodium styrene sulfonate (NaSS) to study the effect of monomer structure on the copolymerization kinetics and size, morphology, charge density, and the self-assembly of the particles. The copolymerization kinetics was found to be highly dependent upon the ionic comonomer structure, and the nature of this dependence altered from homogeneous to micellar nucleation regime. The decrease in particle size (D) with increasing surfactant concentration (S) was observed in all the cases; however, the exponents of D vs. S were not similar for all the cases. In the homogeneous nucleation regime, exponents followed the order as AAc (0.446) > MAA (0.396) > NaSS (0.252) > HEMA (0.241), whereas the order was almost reversed in the micellar nucleation regime as NaSS (0.406) > HEMA (0.228) > AAc (0.206) > MAA (0.172). The hydrophobic/hydrophilic character and the steric factors were found to be the driving force for the variation in D vs. S exponents with ionic comonomer structure. The presence of charges on the particle surface contributed by the ionic comonomers triggered the self-assembly of the particles upon sedimentation and diffracted visible light obeying Bragg's law.     

Synthetic studies toward potent cytostatic macrolide rhizopodin: stereoselective synthesis of the C16-C28 fragment

A stereoselective synthesis of the C16-C28 fragment of cytostatic C₂-symmetric macrolide rhizopodin is described. Enantioselective addition of a chiral thiazolidinethione derived titanium enolate to acetal, Evans’ aldol reaction, Horner-Wadsworth-Emmons reaction, and Mukaiyama aldol reaction were applied as key steps.     

Total synthesis of (+)-mupirocin H from D-glucose

Enantioselective total synthesis of mupirocin H is accomplished starting from D-glucose featuring strategic application of D-glucose derived chirality, diastereoselective Still-Barrish hydroboration, and further elaboration of carbon chain to furnish a phenyltetrazolyl sulfone intermediate, which on coupling with (2S,3S)-2-methyl-3-(triisopropylsilyloxy)butanal under Julia-Kocienski olefination conditions gave an advanced E-olefinic intermediate selectively. The E-olefin was transformed to the 4-hydroxynitrile, a prefinal substrate, which on acid-catalyzed oxidative lactonization furnished the target molecule mupirocin H in 19 steps from known compound 6 (longest linear sequence) with an overall yield of 4.96%.     

Sonochemical synthesis and application of rhodium–graphene nanocomposite

Abstract  

Highly water dispersible rhodium–graphene nanocomposite have been successfully synthesized by the simple reduction of Rh³⁺ salt on poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymer or pluronic-stabilized graphene oxide (GO) nanosheets with borohydride. Rhodium nanoparticles, having average size of 1–3 nm, are homogeneously distributed through out the graphene sheets. Some porous structures of graphene sheets have also been observed after the reduction of pluronic-stabilized GO in the presence of metal ions. The material is very effective for hydrogenation of arenes, especially for benzene as the substrate material at the room temperature and 5 atm pressure of hydrogen.     

Work fluctuation theorem for coloured noise driven open systems

We have studied work fluctuation behaviour in the presence of internal thermal noise as well as external coloured noise. The external coloured noise may have both Gaussian or non-Gaussian characteristics. We have investigated the dependence of position and work fluctuations on the properties of both the environments. For thermal noise driven systems, there is a maximum in the variation of mean square fluctuation of work (MSFW) as a function of damping strength at intermediate times, while at asymptotic long times MSFW monotonically increases in the same damping regime. But for external noise, MSFW monotonically decreases as a function of damping strength at intermediate times, whereas at long times it becomes almost independent of damping strength.Another interesting observation is that for the external noise driven systems, noise correlation time and damping strength have similar roles in the dynamics.     

119Sn Mössbauer characterization of self assembled organotin(IV) complexes with Schiff bases containing amino acetate skeletons

Several organotin(IV) compounds, viz., diorganotin(IV) compounds of the types Ph₂SnLH (monomer), ⁿBu₂SnLH·OH₂ (monomer), [Me₂SnLH·OH₂]₂ (centrosymmetric dimer), [ⁿBu₂SnLH]₃ (cyclic trinuclear), [Ph₂SnLH] _n (polymer), {[ⁿBu₂Sn(LH)]₂O}₂ (centrosymmetric tetranuclear), dinuclear di-/tri-mixed organotin(IV) compounds Ph₂SnLH·Ph₃SnCl (monomer) and triorganotin(IV) compounds of the types [Bz₃SnLH]₂ (centrosymmetric dimer) and [Me₃SnL¹H] _n (Polymer) (LH = Schiff base carboxylate) have been studied in the solid state at liquid nitrogen temperature using ¹¹⁹Sn Mössbauer spectroscopy. The tin coordination geometry of the compounds determined from crystallography was correlated with the ¹¹⁹Sn Mössbauer results.