Adsorption of collagen onto single walled carbon nanotubes: a molecular dynamics investigation

Classical molecular dynamics (MD) simulation has been carried out to understand the adsorption of collagen like peptides onto single walled carbon nanotubes (CNT) in an aqueous environment. It is observed that the triple helical structure of all the model collagen like peptides (CPs) has been unaltered upon adsorption onto CNT. The model CPs do not wrap around the CNT, however, the axis of the triple helix subtends a cross angle with respect to the axis of the CNT. The interaction between the CPs and CNT as well as that between the CPs and water molecules was observed by MD simulation snapshots. The inherent nature of the interaction of CPs with CNT facilitates the penetration of CPs into the water/CNT interface. During this process, water molecules trapped between the CPs and CNT are appreciably displaced. Although, hydrophobic-hydrophobic interaction is crucial for the interaction, the role of πR (R = OH and NH(2)) interactions are also observed from the geometrical parameters. The sequence specific interaction of CPs with CNT is evident from the results. It is found that the length of the CNT, curvature of the CNT and length of the CPs do not significantly influence interaction between the two systems. Overall the findings provide important information for the development of nanocomposite materials from collagen and CNT.     

Saturation of the free exciton resonance in GaAs

The transmission of 500 ns pulses through GaAs-AlGaAs heterostructures has been studied as a function of light intensity (0.015 to 50 kW/cm²) and wavelength (810 to 840 nm). The intrinsic exciton absorption (λ=818 nm at 10°K) can be modeled by the sum of a small unsaturable background and a dominant term which saturates as a Bloch resonance with a saturatiom parameter of about 150 W/cm².     

Generalized statistics variational perturbation approximation using q-deformed calculus

A principled framework to generalize variational perturbation approximations (VPAs) formulated within the ambit of the nonadditive statistics of Tsallis statistics, is introduced. This is accomplished by operating on the terms constituting the perturbation expansion of the generalized free energy (GFE) with a variational procedure formulated using q-deformed calculus. A candidate q-deformed generalized VPA (GVPA) is derived with the aid of the Hellmann-Feynman theorem. The generalized Bogoliubov inequality for the approximate GFE are derived for the case of canonical probability densities that maximize the Tsallis entropy. Numerical examples demonstrating the application of the q-deformed GVPA are presented. The qualitative distinctions between the q-deformed GVPA model vis-á-vis prior GVPA models are highlighted.     

An efficient synthesis of 1,8-dioxo-octahydro-xanthene derivatives promoted by a room temperature ionic liquid at ambient conditions under ultrasound irradiation

The condensation reaction involving an aldehyde and diketone was efficiently promoted by the Ionic liquid, [Hbim]BF(4) (IL) as a reaction medium with methanol as co-solvent at ambient temperature under ultrasonic irradiation to afford the corresponding 1,8-dioxo-octahydro-xanthene (xanthene) derivatives in excellent yields. The advantages of this method include among others the use of a recyclable, non-volatile ionic liquid, which promotes this protocol under ambient temperature without the requirement of any added catalyst. The reaction times and yields are compared with p-TSA catalyzed synthesis of xanthenes under thermal conditions, which is also reported for the first time under our reaction conditions.     

Achiral Trisubstituted Thioureas as Secondary Ligands to CuI Catalysts: Direct Catalytic Asymmetric Addition of α‐Fluoronitriles to Imines

Thioureas have emerged as effective hydrogen‐bonding catalysts over the last two decades, and they are broadly utilized in asymmetric catalysis. We report that achiral trisubstituted thioureas function as beneficial secondary ligands to Cu^I catalysts, thereby enabling highly diastereo‐ and enantioselective addition of α‐fluoronitriles to imines. The structure of the thiourea significantly affects the reaction outcome, and kinetic experiments indicate that the thioureas enhance the stereocontrol by binding to the Cu^I complex. The reaction products can be readily transformed into valuable β‐amino acid derivatives bearing a fluorinated tetrasubstituted stereogenic center.     

Mechanochemical metathesis synthesis and characterization of nano-structured MnV2O6·xH2O (x=2, 4)

A solid-state metathesis approach for the synthesis of hydrated MnV₂O₆·xH₂O (x=2, 4) materials driven by mechanochemical activation energy has been demonstrated. The metathesis pathway of forming the desired product is confirmed by the presence of high lattice energy by-product such as NaCl. The structural, optical, and chemical properties of the synthesized materials are examined by powder X-ray diffraction, X-ray photoelectron spectroscopy, thermo gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and diffused reflectance measurements in the UV–vis range. The valence state of Mn and V was determined to be +2 and +5, respectively, for the title compounds and the bandgap values determined showed these materials are likely to be semiconductors.