Conversion of methanol into hydrocarbons over zeolite H-ZSM-5: ethene formation is mechanistically separated from the formation of higher alkenes

The widely debated reaction mechanism for the conversion of methanol to hydrocarbons over acidic zeolite H-ZSM-5 has been investigated using isotopic labeling. The mechanistic findings for H-ZSM-5 are clearly different from those previously described at a detailed level for H-beta and H-SAPO-34 catalysts. On the basis of the current set of data, we can state that, for H-ZSM-5, ethene appears to be formed exclusively from the xylenes and trimethylbenzenes. Moreover, propene and higher alkenes are to a significant extent formed from alkene methylations and interconversions. This implies that ethene formation is mechanistically separated from the formation of higher alkenes, an insight of utmost importance for understanding and possibly controlling the ethene/propene selectivity in methanol-to-alkenes catalysis.     

Controllability of Neutral Evolution Integrodifferential Systems with State Dependent Delay

In this paper, we address the problem of controllability of neutral evolution integrodifferential systems with state dependent delay in a Banach space. The results are obtained by using the theory of resolvent operators.     

DFT computations,vibrational spectra,monomer, dimer,NBO and NMR analyses of antifungal agent: 3,5-Dibromosalicylic acid

The experimental and theoretical study on the structures and vibrations of 3,5-dibromosalicylic acid (DBSA) are presented. The FT-IR and FT-Raman of the title compound have been recorded. The molecular structures, vibrational wavenumbers, infrared intensities, Raman activities were calculated. The energies of DBSA are obtained for all the eight conformers from density functional theory with 6-311++G(d,p) basis set calculations. From the computational results, C1 or C5 forms are identified as the most stable conformers of DBSA. The spectroscopic and theoretical results are compared with the corresponding properties for DBSA monomer and dimer of C1 (or C5) conformer. Intermolecular hydrogen bonds are discussed in dimer structure of the molecule. NBO analysis is useful to understand the intramolecular hyperconjugative interaction between lone pair O9 and C7O8. The calculated HOMO–LUMO energies reveal charge transfer occurs within the molecule. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The isotopic chemical shift computed by ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the DBSA molecule, calculated using the gauge invariant atomic orbital (GIAO) method, also shows good agreement with experimental observations.     

A Mechanics Based Model for Study of Dynamics of Milling Operations

A unified mechanics based model with multiple degrees of freedom is developed and numerically simulated to study workpiece-tool interactions during milling of ductile workpieces with helical tools. A refined orthogonal cutting model is used at each section of the tool, and the milling forces are determined by using a spatial integration scheme along the axis of the tool. Both regenerative and loss of contact effects are considered in determining the cutting forces, which makes the model well suited for a wide range of milling operations. The model also allows for partial engagement of a tool with a workpiece, which is an important feature needed for milling operations with helical tools. Time domain simulations are carried out by using the developed model to predict the stability boundaries in the space of the tool spindle speed and the axial depth of cut. Poincaré sections are used to determine loss of stability from period-one motions to other motions such as two-period quasiperiodic motions, as a control parameter is varied.     

Boundary controllability of integrodifferential systems in Banach spaces

Sufficient conditions for boundary controllability of integrodifferential systems in Banach spaces are established. The results are obtained by using the strongly continuous semigroup theory and the Banach contraction principle. Examples are provided to illustrate the theory.     

An Experimental Design Approach to Quantitative Expression for Quality Control of a Multicomponent Antidiabetic Formulation by the HILIC Method

A rapid and reproducible hydrophilic liquid chromatography (HILIC) process was established for concomitant determination of remogliflozin etabonate (RE), vildagliptin (VD), and metformin (MF) in a formulation. A face-centered central composite experimental design was employed to optimize and predict the chromatographic condition by statistically studying the surface response model and design space with desirability close to one. A HILIC column with a simple mobile phase of acetonitrile (65% v/v) and 20 mM phosphate buffer (35% v/v, pH 6, controlled with orthophosphoric acid) was used to separate RE, VD, and MF. RE, VD, and MF were separated in 3.6 min using an isocratic mode mobile phase flow at a flow rate of 1.4 mL at room temperature, and the analytes were examined by recording the absorption at 210 nm. The developed HILIC method was thoroughly validated for all parameters recommended by ICH, and linearity was observed in the ranges 20–150 µg/mL, 10–75 µg/mL, and 50–750 µg/mL for RE, VD, and MF, respectively, along with excellent regression coefficients (r² > 0.999). The calculated percentage relative deviation and relative error ascertained the precision and accuracy of the method. The selectivity and accuracy were further confirmed by the high percentage recovery of added standard drugs to the formulation using the standard addition technique. The robustness of the HILIC processes was confirmed by developing a half-normal probability plot and Pareto chart, as the slight variation of a single factor had no significant influence on the assay outcomes. Utilization of the optimized HILIC procedure for concurrent quantification of RE, VD, and MF in solid dosage forms showed accurate and reproducible results. Hence, the fast HILIC method can be regularly employed for the quality assurance of pharmaceutical preparations comprising RE, VD, and MF.     

Theory of laser action in scattering gain media

A laser model based on feedback produced by scattering has been developed to explain the narrow linewidth emission and input-output behavior observed in scattering gain media. The model is based on the transient two-level laser equations and includes the detailed spectral properties of the dye gain system. Monte Carlo methods were employed to calculate the threshold gain required for modeling the input-output and linewidth emission characteristics.     

Controllability of nonlinear systems to affine manifolds

Controllability to an affine manifold involves controlling a system to a target defined by the generalized boundary condition x=r, where :C ⁿ R ⁿ is a bounded linear operator on the continuous functions, as defined for ordinary differential equations by Kartsatos. In this paper, sufficient conditions are obtained for such controllability for linear systems and for a class of nonlinear perturbations of linear systems.     

Synthesis,characterization and charge-transfer photochemistry of trans-aquo azido-N,N′-trimethylenebis(naphthylideneiminato)chromium(III)

A new Cr^III complex, viz. trans-[Cr(naphprn)(H₂O)₂]ClO₄·2H₂O, (1) {naphprn=N,N-trimethylenebis(naphthylideneimine)} has been synthesized and characterized. Aquo ligand substitution of ( 1 ) by the azide ligand gave rise to trans-[Cr(naphprn)(N₃)(H₂O)], ( 2 ). Irradiation of ( 2) in DMF gave nitrido(naphprn)chromium(V) ( 3 ). Solutions of ( 3 ) showed e.p.r. spectra at room temperature (g _iso=1.9865). The i.r. spectra showed disappearance of a band at 2067cm^–1 showing the breakdown of NN and appearance of a new band at 1074cm^–1which is assigned to the Cr¹⁴N, stretching frequency indicating the formation of a nitrido chromium(V) complex, ( 3). The u.v.–vis. spectrum of complex ( 3 ) exhibited a d–d band maximum at 553nm (=120M^–1cm^–1). The rate of formation of ( 2 ) was found to be 5.0×10^–3M^–1s^–1 in an aqueous acidic medium at [Cr^III]=0.5×10^–3M; [N₃ ^–]=0.01–0.15M; [H⁺]=0.001M and I=0.2M (LiClO₄). The rate of photo-decomposition of ( 2 ) to give rise to ( 3 ) was found to be 0.15×10^–3s^–1 in DMF.