Immobilization of Urease from Pigeonpea (<Emphasis Type="Italic">Cajanus cajan</Emphasis>) on Agar Tablets and Its Application in Urea Assay

The pigeonpea urease was immobilized on agar, a common gelling substance. The tablet strips were used as moulds to cast agar tablets of uniform shape and size. The time and temperature of solidification of agar was 6 min and 44 degrees C, respectively. The 5 % agar (w/v) and 0.019 mg protein/agar tablet yielded an optimum immobilization of 51.7%. The optimum pH was shifted through 0.2 U (from 7.3 to 7.5) towards basic side upon immobilization. The optimum temperature of soluble and immobilized urease was 30 degrees C and 60 degrees C, respectively, showing the improvement in thermal stability of urease. There was an increase in K m from 3.23 to 5.07 mM after immobilization. The half-lives of soluble and immobilized urease were 21 and 53 days, respectively, at pH 7.3 and 4 degrees C. The urea was estimated in different blood samples with the help of immobilized urease and the results were consistent with those from clinical pathology laboratory through an autoanalyzer (Zydus Co., Rome, Italy).     

Nanostructured copper phthalocyanine-sensitized multiwall carbon nanotube films

We report a detailed study of the interaction between surface-oxidized multiwall carbon nanotubes (o-MWCNTs) and the molecular semiconductor tetrasulfonate copper phthalocyanine (TS-CuPc). Concentrated dispersions of o-MWCNT in aqueous solutions of TS-CuPc are stable toward nanotube flocculation and exhibit spontaneous nanostructuring upon rapid drying. In addition to hydrogen-bonding interactions, the compatibility between the two components is shown to result from a ground-state charge-transfer interaction with partial charge transfer from o-MWCNT to TS-CuPc molecules orientated such that the plane of the macrocycle is parallel to the nanotube surface. The electronegativity of TS-CuPc as compared to unsubsubtituted copper phthalocyanine is shown to result from the electron-withdrawing character of the sulfonate substituents, which increase the molecular ionization potential and promote cofacial molecular aggregation upon drying. Upon spin casting to form uniform thin films, the experimental evidence is consistent with an o-MWCNT scaffold decorated with phthalocyanine molecules self-assembled into extended aggregates reminiscent of 1-D linearly stacked phthalocyanine polymers. Remarkably, this self-organization occurs in a fraction of a second during the spin-coating process. To demonstrate the potential utility of this hybrid material, it is successfully incorporated into a model organic photovoltaic cell at the interface between a poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester bulk heterojunction layer and an indium-tin oxide-coated glass electrode to increase the light-harvesting capability of the device and facilitate hole extraction. The resulting enhancement in power conversion efficiency is rationalized in terms of the electronic, optical, and morphological properties of the nanostructured thin film.     

"Fingertip"-guided noncovalent functionalization of carbon nanotubes by dendrons

Noncovalent functionalization of carbon nanotubes (CNTs) by dendrons was demonstrated. Certain types of dendrons successfully functionalized CNT surfaces through the noncovalent interactions between the peripheries of the dendrons and the sidewalls of CNTs. Dendrons have a unique anisotropic shape and an orthogonal functional group at their apex, and thus can generate a certain spacing between the functional groups upon immobilization on surfaces. Atomic force microscope (AFM) imaging, dispersion experiments, and MicroRaman spectroscopy were employed for the characterization of the functionalization. The binding was found to be governed by the chemical nature of the terminal groups, namely, the "fingertips", through a comparison study on the adsorption efficiency of the dendron analogs. Functional groups such as the carboxylic acid group and the benzyl amide group were effective for the cooperative binding. AFM analysis showed that the average spacing generated by the dendrons was 14-15 nm at a particular adsorption condition. Assembling streptavidin on the tubes through the dendrons and biotin confirmed the realization of the regulated spacing as well as the elimination of unwanted aggregation. The noncovalent functionalization of CNTs by a dendron can be a new approach toward sensible nanobiodevices, not only by introducing biomolecular probes on CNTs without disruption of the electronic network of the tubes, but also by providing the immobilized probe molecules with a space ample enough to minimize steric hindrance for the unhindered interaction with their target species.     

Coagulation of nanoparticles in reverse micellar systems: a Monte Carlo model

The process of formation of nanoparticles obtained by mixing two micellized, aqueous solutions has been simulated using the Monte Carlo technique. The model includes the phenomena of finite nucleation, growth via intermicellar exchange, and coagulation of nanoparticles after their formation. Using the model, an exploratory study has been conducted to analyze whether the coagulation of nanoparticles is the reason for the formation of nanoparticles whose sizes are comparable to the size of the reverse micelles. The model explains the possible mechanism of coagulation of semiconductor nanoparticles formed within reverse micelles and its effect on the evolution of their size with time. The model is predictive in nature, and the simulation results compare well with those observed experimentally.     

Synthesis and self-assembly of [60]fullerene containing sulfobetaine polymer in aqueous solution

A well-defined poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA-b-C60) was synthesized using the atom transfer radical polymerization (ATRP) technique and betainized with 1,3-sulfobetaine to yield a Bet-PDMAEMA-b-C60. The solution properties were then studied by light transmittance, viscometric, 1H NMR laser light scattering, and transmission electron macroscopic techniques. It was found that Bet-PDMAEMA-b-C60 exhibits an upper critical solution temperature (USCT) similar to that observed for Bet-PDMAEMA in aqueous solution. However, the modification of Bet-PDMAEMA with a C60 molecule increases the UCST of Bet-PDMAEMA in solution, which is a function of the solution ionic strength. Addition of a small amount of salt increases the UCST, similar to polyelectrolyte systems, while the presence of an excess amount of salt leads to a decrease in the UCST, attributed to the antipolyelectrolyte effect of polyampholytes. In aqueous salt solution, Bet-PDMAEMA-b-C60 chains self-assemble into micelles that coexist with unimeric Bet-PDMAEMA-b-C60 chains. TEM studies revealed that the system agglomerates when the temperature exceeds the UCST.     

Spectroscopic evaluation of manganese(II) complexes derived from semicarbazones and thiosemicarbazones

Manganese(II) complexes having the general composition Mn(L)2X2 [where L=isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD) and X=Cl-, 1/2SO(4)2-] have been synthesized. All the complexes were characterized by elemental analyses, molar conductance, magnetic moment susceptibility, EI-mass, 1H NMR, IR, EPR and electronic spectral studies. All the complexes show magnetic moments corresponding to five unpaired electrons. The possible geometries of the complexes were assigned on the basis of EPR, electronic and infrared spectral studies.     

On periodic solutions of nonlinear second order differential systems

The paper deals with the second order differential systems with periodic boundary conditions. In the first part of the paper four different methods are employed to find the unique solution of the linear systems. One of the methods is a shooting type which converts the periodic boundary value problem into its equivalent initial value problem. In the second part of the paper several sufficient conditions are provided for the existence and uniqueness for the nonlinear systems. The technique developed for the linear systems to convert into its equivalent initial value problem is used in an iterative way for the nonlinear systems. It is shown that the iterations converge quadratically.     

The incorporation of learning in production planning models

Production managers employ numerous aggregate planning models to smooth work loads and minimize labor and inventory costs. Some of the more recently developed models incorporate the learning that occurs during repetitive work. This article discusses the history of both aggregate planning and learning models, the various combined models, and their appropriateness to a given environment.     

Aurivillius family of layered perovskites,BiREWO6 (RE = La,Pr, Gd,and Dy): Synthesis,characterization, and photocatalytic studies

The present work deals with the synthesis, characterization, and photocatalytic studies of layered perovskites belonging to Aurivillius family. Layered perovskites of various chemical compositions, BiREWO₆ (RE = La, Pr, Gd, and Dy), were synthesized by an ethylene glycol–assisted sol–gel method. These materials were characterized by X-ray diffraction, scanning electron microscopy–energy dispersive spectroscopy (EDS), Fourier transform infrared, Raman, and ultraviolet–visible diffuse reflectance techniques. The composition of all these materials was obtained from EDS. The unit cell lattice parameters were attained from Rietveld refinement program, Fullprof.2k, by refining the d-lines of BiREWO₆. The band gap energy of these samples was obtained from the Kubelka–Munk plot. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue. The mechanistic degradation pathway of methylene blue was studied using radical quenchers.