Surface‐enhanced Raman scattering characteristics of CuO : Mn/Ag heterojunction probed by methyl orange: effect of Mn2+ doping

Interest in the synthesis of hybrid substrates for surface‐enhanced Raman scattering (SERS) has surged recently. Hereof, in the present work, a hybrid SERS substrate CuO : Mn/Ag heterojunction has been synthesised. To accomplish this, the nanostructred Ag island film and CuO : Mn nanoparticles are synthesised by vacuum thermal evaporation method and sol–gel method respectively, and thereafter, a heterojunction between the CuO : Mn and Ag is fabricated by adsorption of CuO : Mn (10^‐3 m in ethanol) on Ag island film. Further, the SERS sensitivity of CuO : Mn/Ag heterojunctions has been studied by probing methyl orange. We observed that with Mn‐doping in the lattice of CuO, the SERS signal is enhanced considerably because of ferromagnetic ordering in CuO : Mn. DFT/B3LYP/6‐311 G(d, p) method is used to calculate the energy of HOMO and LUMO level of methyl orange. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonpremixed flame control with microjets

The hydrodynamic control of buoyant nonpremixed flames is investigated by injecting high-momentum fluid through a central microjet. The resulting flame characteristics are mapped for jets of different strengths. The flame height decreases linearly with an increase in the microjet Froude number as the flow changes from a buoyancy-dominated to a momentum-controlled regime. The flame luminosity is reduced by injecting stronger microjets. The jets alter the flame structure by establishing strong entrainment of the ambient air from the quiescent surroundings. The introduction of an inert species as the microjet fluid has a similar qualitative effect as air. Microjet assistance is as effective as partial premixing for reducing the flame height and luminosity.     

N‐Alkoxyheterocycles As Irreversible Photooxidants

Irreversible photooxidation based on N–O bond fragmentation is demonstrated for N‐methoxyheterocycles in both the singlet and triplet excited state manifolds. The energetic requirements for bond fragmentation are studied in detail. Bond fragmentation in the excited singlet manifold is possible for ππ* singlet states with energies significantly larger than the N–O bond dissociation energy of ca 55 kcal mol^?1. For the nπ* triplet states, N–O bond fragmentation does not occur in the excited state for orbital overlap and energetic reasons. Irreversible photooxidation occurs in the singlet states by bond fragmentation followed by electron transfer. Irreversible photooxidation occurs in the triplet states via bimolecular electron transfer to the donor followed by bond fragmentation. Using these two sensitization schemes, donors can be irreversibly oxidized with oxidation potentials ranging from ca 1.6–2.2 V vs SCE. The corresponding N‐ethylheterocycles are characterized as conventional reversible photooxidants in their triplet states. The utility of these sensitizers is demonstrated by irreversibly generating the guanosine radical cation in buffered aqueous solution.     

A palladium-catalyzed three-component cross-coupling of conjugated dienes or terminal alkenes with vinyl triflates and boronic acids

A three-component coupling of vinyl triflates and boronic acids to alkenes catalyzed by palladium is reported. Using 1,3-dienes, selective 1,2-alkene difunction-alization is observed, whereas the use of terminal alkenes results in 1,1-alkene difunctionalization. The reaction outcome is attributed to the formation of stabilized, cationic Pd-π-allyl intermediates to regulate β-hydride elimination.     

Supramolecular polymerization from polypeptide-grafted comb polymers

The helical and tubular structures self-assembled from proteins have inspired scientists to design synthetic building blocks that can be "polymerized" into supramolecular polymers through coordinated noncovalent interactions. However, cooperative supramolecular polymerization from large, synthetic macromolecules remains a challenge because of the difficulty of controlling the structure and interactions of macromolecular monomers. Herein we report the synthesis of polypeptide-grafted comb polymers and the use of their tunable secondary interactions in solution to achieve controlled supramolecular polymerization. The resulting tubular supramolecular structures, with external diameters of hundreds of nanometers and lengths of tens of micrometers, are stable and resemble to some extent biological superstructures assembled from proteins. This study shows that highly specific intermolecular interactions between macromolecular monomers can enable the cooperative growth of supramolecular polymers. The general applicability of this strategy was demonstrated by carrying out supramolecular polymerization from gold nanoparticles grafted with the same polypeptides on the surface.     

Synthesis of fullerene@gold core-shell nanostructures

A "direct encapsulation" method was developed for the synthesis of highly stable water-soluble fullerene@gold core-shell nanostructures, with gold nanoshells showing either closed or porous morphology. This gold nano-shell coating formed a "nano-oven", capable of decomposing encapsulated fullerene molecules rapidly when irradiated by laser. We envisaged this being a useful tool for chemical reactions as well as a novel scaffold for nano-material synthesis.     

First principle studies toward the design of a new class of carbene superbases involving intramolecular H···π interactions

The higher basicity of carbenes has been exploited with H···π non-bonding interactions to design a new class of organic superbases. This simple molecular architecture gains a basicity comparable to some of the known functionalized nitrogen superbases and phosphazenes.     

A facile approach for morphosynthesis of Pd nanoelectrocatalysts

A facile approach has been developed for synthesis of highly-structured, anisotropic Pd nanostructures. The dendritic Pd nanostructures show superior performance toward oxidation of formic acid and methanol for fuel cell application.     

Point-to-plane corona discharge for high-speed reacting flow visualization

We present the results of a novel technique for the high-speed visualization of a flame reaction zone using a streamer-initiated point-to-plane unipolar pulsed corona discharge. Our results show images of the flame front under conditions of natural hydrodynamic flame instability, as well as external air flow modulation induced flame instability. This technique can potentially be used as a high-speed 2-D flow visualization diagnostic tool to monitor flow instabilities in reacting and non-reacting fluids that have a density gradient. We also show that this technique does not modify the flame characteristics in any measurable way, if the high electric field region of the streamer/corona discharge is located in the downstream region.     

Investigation of hydrogen bond effects on the hyperpolarizability of 2-Aminopyridinium maleate (2APM) complex and determining the non-linear optical susceptibility of the molecular crystal of 2APM

2-Aminopyridinium maleate (2APM) is a recently discovered organic acid-base complex that crystallizes in a non-centrosymmetric space group Pc and hence has a nonzero second-order optical susceptibility. In 2APM the cation (aminopyridinium ion) is connected to the anion (maleate ion) through hydrogen bonds (N1-H10–O2 and N2-H12–O1), we have calculated the molecular properties of 2APM for varying strength of these hydrogen bonds. It is observed that the molecular hyperpolarizabilty varies for varying strength of these hydrogen bonds. These observations are interpreted in terms of the change in nature of the hydrogen bond interaction as its strength is varied. Macropscopic second-order optical susceptibility (d ₀) of 2APM is obtained using the calculated value of molecular hyperpolarizability and the reported crystal structure of 2APM. In order to study the influence of molecular packing on the macroscopic non-linear optical property of the crystal, susceptibility calculations are repeated for 2-methyl-4nitroaniline (MNA) crystal, which is a very well known non-linear optical organic crystal with an exceptionally high value of second-order optical susceptibility. A comparison between the non-linear optical property of 2APM and MNA crystals is given. Comparing the values of d ₀ of 2APM crystals with that of urea shows that the nonlinear optical response of 2APM crystals will be nearly 10 times that of a urea crystal.