Tuning of carbon bonds by substituent effects: an ab initio study

ABSTRACT

An ab initio study, at the MP2/aug-cc-pVTZ level of theory, is performed to study σ-hole bond in binary XH₃C···CNY complexes, where X = CN, F, NO₂, CCH and Y = H, OH, NH₂, CH₃, C₂H₅, Li. This type of interaction is labelled as ‘carbon bond’, since a covalently bonded carbon atom acts as the Lewis acid in these systems. The geometrical and energetic parameters of the resulting complexes are analysed in details. The interaction energies of these complexes are between ?4.97 kJ/mol in (HCC)H₃C···CNH and ?23.07 kJ/mol in (O₂N)H₃C···CNLi. It is found that the electrostatic interaction plays a key role in the overall stabilisation of these carbon-bonded complexes. To deepen the understanding of the nature of the carbon-bonding, the molecular electrostatic potential, natural bond orbital, quantum theory of atoms in molecules and non-covalent interaction index analyses are also used. Our results indicate that the carbon bond is favoured over the C-H···C hydrogen bond in the all complexes considered and may suggest the possible important roles of the C···C interactions in the crystal growth and design.     

Temperature tunable random laser using superconducting materials

We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very sensitive to the system temperature.     

Exploring the origin of tip‐enhanced Raman scattering; preparation of efficient TERS probes with high yield

Tip‐enhanced Raman scattering (TERS) spectroscopy is a promising technique for nanoscale chemical analysis. However, there are several challenges preventing widespread application of this technology, including reproducible fabrication of efficient TERS probes. These problems reflect a lack of clear understanding of the origins of, and the parameters influencing TERS. It is believed that the coating characteristics at the apex of the tip have a major effect on the near‐field optical enhancement and thus the TERS activity of a metalized probe. Here we show that the aspect ratio of the tip can play a significant role in the efficiency of TERS probes. We argue that the electrostatic field arising from the lightning‐rod effect has a substantial role in the observed TERS effect. This argument is supported by ‘edge‐enhanced Raman scattering’ which is shown for a noble metal film. Furthermore, it is reported that an associated tip‐surface‐enhanced Raman scattering effect can be achieved by using a TERS‐inactive metalized probe on a surface‐enhanced Raman spectroscopy‐inactive roughened surface. This observation can be explained by an interparticle enhancement of the electromagnetic field. Copyright © 2011 John Wiley & Sons, Ltd.     

Analytic study of sixth-order thin-film equation by tan(<Emphasis Type="BoldItalic">ϕ</Emphasis>/2)-expansion method

A improvement of the expansion methods, namely, the improved \(\tan (\phi (\xi )/2)\)-expansion method for solving the sixth-order thin-film equation is proposed. As a result, many new and more general exact traveling wave solutions are obtained including singular kink-type solutions. We obtained the further solutions comparing with other methods as Flitton and King (Eur J Appl Math 15:713–754, 2004) and Taha et al. (J King Saud Univ Sci 26:75–78, 2014). Recently this method is developed for searching exact traveling wave solutions of nonlinear partial differential equations. Abundant exact traveling wave solutions including kink and rational solutions have been found. These solutions might play important role in engineering and physics fields. Also the results demonstrate that the introduced method is powerful tools for solving the nonlinear partial differential equations.     

B-, N-doped and BN codoped C60 heterofullerenes for environmental monitoring of NO and NO2: a DFT study

ABSTRACT

Using density functional theory calculations, we investigate the gas sensing performance of B-, N-doped and BN-codoped C₆₀ fullerenes towards NO and NO₂ molecules. The calculated adsorption energies and net charge-transfer values indicate that NO and NO₂ molecules have a stronger interaction with the BN-codoped fullerenes compared to the B- or N-doped ones. It is also found that the electronic properties of the BN-codoped C₆₀ exhibit a larger sensitivity towards NO and NO₂ molecules. An increase in the concentration of doped/co-doped B and N atoms tends to weaken the gas sensing ability of these systems.     

Analytical solution of three-dimensional Navier–Stokes equations for the flow near an infinite rotating disk

In this letter, we will consider variational iteration method (VIM) and Padé approximant, for finding analytical solutions of three-dimensional viscous flow near an infinite rotating disk. The solutions is compared with the numerical (fourth-order Runge–Kutta) solution. The results illustrate that VIM–Padé is an appropriate method in solving the systems of nonlinear equations. It is predicted that VIM–Padé can have wide application in engineering problems (especially for boundary-layer and natural convection problems).     

Synthesis,characterization and application of a novel nanorod-structured organic–inorganic hybrid material as an efficient catalyst for the preparation of aminouracil derivatives

Research on Chemical Intermediates - In this work, a novel nanorod-structured organic–inorganic hybrid material namely nanorod-[SiO2-Pr-Im-SO3H][TFA] (N-[SPIS][TFA]) has been synthesized, and...