Modelling interactions between a PBB and fullerenes

Fullerenes have many uses including in medical and electronic nanodevices. High pressure liquid chromatography (HPLC) columns are generally used to extract a certain structure of fullerne from a mixture of them. In this paper, we investigate the interactions between various types of fullerenes and a station phase in HPLC known as pentabromobenzyl (PBB). The Lennard-Jones potential and a continuum approach are employed to determine the van der Waals energy of these interactions within the HPLC columns. The equilibrium configurations for any given distance between a fullerene and the centre of a PBB are obtained. Results of this study may assist the design of a chromatography column for fullerene separation.     

Wave-like deformations for oscillating carbon nanotubes

Carbon nanostructures such as nanotubes and fullerenes, represent future materials because of their remarkable mechanical, electrical and thermal properties. Double-walled carbon nanotubes are widely studied as possible gigahertz oscillators, where the inner tube oscillates within the outer tube. These oscillators are believed to generate frequencies in the gigahertz range and typically of the order of 1–74 GHz. They are also known to generate wave-like formations on the outer surface. In this paper, we study such induced deformations on the surface of the outer tube, as generated by the moving inner tube. Following previous authors we assume that double-walled carbon nanotubes can be modelled as transversely isotropic linearly elastic materials. Using a previously derived approximate force distribution for the resultant van der Waals forces arising from the interatomic interactions, we solve a dynamic linearly elastic problem, and show that the resulting solution exhibits wave-like behaviour.     

A continuous model for the joining of two fullerenes

The successful design of many novel nano-electronic devices will require a thorough understanding of the geometric joining issues of certain nano-structures. In this paper, we adopt a continuous approach and we employ the calculus of variations to model the nanostructure obtained by the joining of two fullerenes. We model the fullerenes as spheres and we assume symmetric defects on both fullerenes so that the three-dimensional problem is axially symmetric and can therefore be reduced to a problem in two dimensions. We propose two models depending upon the curvature of the join profile which can be either positive or both positive and negative. However, there is at present no experimental or simulation data to verify the theoretical connecting structures predicted by this study.     

Toroidal molecules formed from three distinct carbon nanotubes

In order to design nanotori for nanomechanical systems, perhaps involving oscillating components, precise physical parameters for the nanotori are necessary. Toroidal shaped molecules of carbon have been investigated previously by the present authors as constructed by connecting elbow sections formed from joining armchair and zigzag nanotubes through a pentagonal–heptagonal pair defect. In this paper, we extend this design by constructing the elbow structures from three distinct carbon nanotubes. Since for a toroidal molecule, there is a constraint on the bend angles in the elbow sections to add up to 360°, particular elbow types which can accommodate this requirement are (5,0)–(4,4)–(7,0) and (3,3)–(6,0)–(4,4). We adopt a least squares approach for the bond length to minimise the variation from the ideal carbon–carbon bond length, which is taken to be σ = 1.42 Å. Moreover, formulae for the mean generating radius of the nanotori and the mean radius of the nanotubes are obtained from certain integral expressions. This purely geometrical approach can be formally directly related to certain numerical energy minimisation methods used by a number of authors.     

Enantiodivergent Synthesis of Benzoquinolizidinones from L-Glutamic Acid

Benzoquinolizidinone systems were synthesized in both enantiomeric forms from L-glutamic acid. The key chiral arylethylglutarimide intermediate was synthesized from dibenzylamino-glutamate and homoveratrylamine. Aldol reaction of the glutarimide afforded a mixture of syn and anti-aldol adducts. Subsequent regioselective hydride reduction of the glutarimide carbonyl followed by N-acyliminium ion cyclization afforded a product with opposite absolute configurations at C3 and C11b. Cope elimination of the dibenzylamino group then converted the two diastereomers into enantiomers.     

Novel <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="Italic">N</Emphasis>-acetylglucosaminidases from <Emphasis Type="Italic">Vibrio harveyi 650</Emphasis>: Cloning,expression, enzymatic properties,and subsite identification

Background  

Since chitin is a highly abundant natural biopolymer, many attempts have been made to convert this insoluble polysaccharide into commercially valuable products using chitinases and β-N-acetylglucosaminidases (GlcNAcases). We have previously reported the structure and function of chitinase A from Vibrio harveyi 650. This study t reports the identification of two GlcNAcases from the same organism and their detailed functional characterization.     

Continuum modelling of spherical and spheroidal carbon onions

Carbon nanostructures are of considerable interest owing to their unique mechanical and electronic properties. Experimentally, a wide variety of different shapes are obtained, including both spherical and spheroidal carbon onions. A spheroid is an ellipsoid with two major axes equal and the term onion refers to a multi-layered composite structure. Assuming structures of either concentric spherical or ellipsoidal fullerenes comprising n layers, this paper examines the interaction energy between adjacent shells for both spherical and spheroidal carbon onions. The Lennard-Jones potential together with the continuum approximation is employed to determine the equilibrium spacing between two adjacent shells. We also determine analytical formulae for the potential energy which may be expressed either in terms of hypergeometric or Legendre functions. We find that the equilibrium spacing between shells decreases for shells further out from the inner core owing to the decreasing curvature of the outer shells of a concentric structure.     

Modelling adsorption of a water molecule into various pore structures of silica gel

Silica gel is widely used in commercial applications as a water adsorbent due to its properties including hydrothermally stable, high water sorption capacity, low regeneration temperature, low cost and wide range of pore diameters. Since the water sorption capacity of silica gel strongly depends on the pore size and structure, which can be controlled during synthesis, this paper study the effect of pore shapes and dimensions of silica gel upon the adsorption of a water molecule aiming at maximising the water sorption capacity. In particular, we consider three types of pore structures, namely cylindrical, square prismatic and conical pores. On using the Lennard-Jones potential and a continuum approximation, we find that the minimum radii for a water molecule to be accepted into cylindrical, square prismatic and conical pores are 4.009, 3.7898 and 4.4575 Å, respectively. For cylindrical and square prismatic pores, the critical radii which maximise the adsorption energy are 4.5189 and 4.1903 Å, respectively. Knowledge of these critical pore sizes may be useful for the manufacturing process of silica gel that will maximise the water sorption capacity.     

Modeling the join curve between two co-axial carbon nanotubes

Making use of an applied mathematical model, we employ a calculus of variations technique to join two co-axial nanotubes. Due to the axial symmetry of the tubes, the three-dimensional problem can be reduced to a problem in two dimensions. The curvature squared for the join region is minimized for a prescribed join length and given tube radii. In this model, a certain non-dimensional parameter B arises, which approximately has the same numerical value when compared with the standard method for the joining between any two carbon nanotubes of different radii. This value occurs in consequence of adopting an angle of inclination of 9.594°, which occurs in the conventional method for joining two carbon nanotubes of different radii and which is necessary to accommodate a single pentagon. The simple calculus of variations model described here provides a general framework to connect nanotubes or other nanostructures.     

Encapsulation behaviours of nanoparticles entering two-section carbon nanotubes

Carbon nanotubes are special nanostructures due to their unique mechanical and electronic properties. One of the proposed applications is a container for drug delivery. In this paper, we consider two-section carbon nanotubes for their uses as nanocapsules to encapsulate a single atom and a C $_{60}$ fullerene. The Lennard-Jones function and the continuous approach are employed to determine the molecular interactions. Moreover, the explicit forms of their interaction energies are determined. The suction energies are utilised to determine the encapsulated conditions of both nanoparticles, where they depend on the radii of the particle and the nanocapsule. This theoretical study can be thought of as the first step to design the nanocapsule for the drug delivery devices.