Studies on the encapsulation of various anions in different fullerenes using density functional theory calculations and Born-Oppenheimer molecular dynamics simulation

The density functional theory (DFT)-based Becke's three parameter hybrid exchange functional and Lee-Yang-Parr correlation functional (B3LYP) calculations and Born-Oppenheimer molecular dynamics (BOMD) simulations have been performed to understand the stability of different anions inside fullerenes of various sizes. As expected, the stability of anion inside the fullerene depends on its size as well as on the size of the fullerene. Results show that the encapsulation of anions in larger fullerenes (smaller fullerene) is energetically favorable (not favorable). The minimum size of the fullerene required to encapsulate F(-) is equal to C(32). It is found from the results that C(60) can accommodate F(-), Cl(-), Br(-), OH(-), and CN(-). The electron density topology analysis using atoms in molecule (AIM) approach vividly delineates the interaction between fullerene and anion. Although F(-)@C(30) is energetically not favorable, the BOMD results reveal that the anion fluctuates around the center of the cage. The anion does not exhibit any tendency to escape from the cage.     

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.     

ON QUOTIENTS OF BRAID GROUPS

ABSTRACT.

Let G be the group ?[t, t ^?1] x ?. By studying the action of the braid group B_n on the set Gⁿ , we obtain representations of B_n into a wreath product of the symmetric group and the general linear group over ?[t, t ^?1]. This in particular recovers the Burau representation of the braid group. Furthermore, some quotients of the braid group are obtained by using the representations found.     

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.