Adsorption of methylene blue dye from aqueous solution by agricultural waste: Equilibrium,thermodynamics, kinetics,mechanism and process design

The adsorption of methylene blue (MB) dye from aqueous solution onto a cashew nut shell (CNS) was investigated as a function of parameters such as solution pH, CNS dose, contact time, initial MB dye concentration and temperature. The CNS was shown to be effective for the quantitative removal of MB dye, and the equilibrium was reached in 60 min. The experimental data were analysed by two-parameter isotherms (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models) using nonlinear regression analysis. The characteristic parameters for each isotherm and the related correlation coefficients were determined. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also evaluated, the sorption process was found to be spontaneous and exothermic. Pseudo-first-order, pseudo-second-order and Elovich kinetic models were used to analyze the adsorption process. The results of the kinetic study suggest that the adsorption of MB dye matches the pseudo-second-order equation, suggesting that the adsorption process is presumably chemisorption. The adsorption process was found to be controlled by both surface and pore diffusion. Analysis of adsorption data using a Boyd kinetic plot confirmed that the external mass transfer is a rate determining step in the sorption process. A single-stage batch adsorber was designed for different CNS doses to effluent volume ratios using the Freundlich equation. The results indicated that the CNS could be used effectively to adsorb MB dye from aqueous solutions.     

A Note on Prehomomorphisms

We show that if G is a free group with basis X then any map θ from X to an inverse monoid S extends to a monoid prehomomorphism ψ: G\rightarrow S. As an application we give an affirmative answer to a problem of M. Petrich. 1980 Mathematics Subject Classification: Primary 20M10. September 14, 1999     

X-Ray Crystallographic Investigation of Fully Acetylated N-(2-Deoxy-2-Acetamido-β-D-Glucopyranosyl)Alkanamides as N-Glycoprotein Linkage Region Analogs

To understand the structural significance of the linkage region of N-glycoproteins, three title sugar amides have been prepared as analogs and their molecular assembly and crystal structures have been solved to explore the effect of acetyl protection and aglycon variation on the conformation, particularly of the N-glycosidic linkage. Comparative analysis of these structures with those of free sugar amides reported earlier showed that conformation of the amido aglycon moiety is not altered significantly by the masking of hydroxyl groups in the form of acetate. The bifurcated antiparallel pattern involving N?H…O and C?H…O hydrogen bonds, a hallmark of the N-glycoprotein models GlcNAcβNHAc and GlcNAcβAsn, is absent in all of the fully protected title alkanamides. The asymmetric unit of the tri-O-acetylated GlcNAcβNHAc contains two different conformations, in one of which the double-pillared hydrogen bond network involving C1 and C2 acetamido groups is antiparallel, while it is parallel in the other. The co-occurrence of a molecular assembly motif—a double-pillared parallel and antiparallel hydrogen bonding pattern—is hitherto unknown in the crystal structures of N-glycoprotein linkage region models and analogs.     

Low-temperature neutron diffraction structures of N-glycoprotein linkage models and analogues: structure refinement and trifurcated hydrogen bonds

The biological addition of oligosaccharide moieties to asparagine residues of N-glycoproteins influences the properties and bioactivities of these macromolecules. The low-temperature neutron crystal structures of three N-glycoprotein linkage models and analogues provide accurate characterization of the three-dimensional structure of the conserved GlcNAc-Asn linkage. These first crystal structures of N-acetylated carbohydrates obtained by neutron diffraction provide high-resolution geometrical parameters that can be used for force-field parametrization and subsequent molecular dynamics simulation of N-glycoproteins. The correct localization of hydrogen atoms demonstrates the occurrence of trifurcated hydrogen bonds and hydrophobic contacts.     

35Cl NQR frequency and spin lattice relaxation study in 3,4-dichloronitrobenzene as a function of temperature and pressure

³⁵Cl NQR frequency and spin lattice relaxation time in 3,4-dichloronitrobenzene have been measured as a function of temperature and pressure. Two NQR signals were observed in the temperature range 77 to 300 K and pressure up to 5.1 kbar at 300 K. The contributions to the relaxation from the torsional motion of the molecule and reorientational motion of the nitro group have been analyzed on the basis of the Woessner and Gutowsky model. The temperature dependence of the average torsional lifetimes of the molecules, transition probabilities, and the activation energy for the reorientation of the nitro group was estimated. The pressure dependence of the NQR frequency in 3,4-Dichloronitrobenzene shows a nonlinear increase in NQR frequency with increase in pressure, indicating increased contribution from the static effects at higher pressures. A thermodynamic analysis of the data was carried out to determine the constant-volume temperature coefficients of the NQR frequency. The spin–lattice relaxation was found to be weakly dependent on pressure.     

Local Controllability of Functional Integrodifferential Equations in Banach Space

In this paper, we establish a set of sufficient conditions for the local controllability of functional integrodifferential equations in Banach space. The results are obtained by using the methods of analytic semigroups, fractional powers of operators, and a fixed-point argument. These results generalize previous results on bounded linear operators to unbounded linear operators in which the equation involves a nonlinear delay term. An application to a partial integrodifferential equation is given.     

Photoaquation of methylated cis-dichlorobis(1,10-phenanthroline)rhodium(III)chloride compounds by direct population of a photoactive triplet excited state

Photoaquation in compounds II and III by direct excitation into a photoactive triplet excited state is reported. The location of the singlet to triplet transition in compound III is estimated by a combination of the action spectrum for photoaquation in the region between 520 and 600 nm and the phosphorescence spectrum at 77 K. The significant increment of the reactivity (10-fold) of the triplet states in II and III as compared to that in I is explained in terms of increasing sigma-donation from the phen ligands stabilizing the pentacoordinated rhodium intermediate formed by chloride expulsion.