Development of an HPTLC‐based diagnostic method for invasive aspergillosis

A rapid, sensitive and specific high‐performance thin‐layer chromatographic (HPTLC) method was developed and validated for determination of gliotoxin in Aspergillus infected immunocompromised patients with invasive aspergillosis (IA). Densitometric analysis of gliotoxin was carried out in the absorbance mode at 254 nm after single‐step extraction with chloroform. The method uses TLC aluminum plates pre‐coated with silica gel 60F‐254 as a stationary phase and toluene–isoamyl alcohol–methanol (10:0.5:0.5, v/v/v) as mobile phase, which gives compact spot of gliotoxin (R_f = 0.51). The calibration curve was linear (r² ≥ 0.994) between peak area and concentration in the tested range of 100–1000 ng spot^?1 with minimum detectable range 0.025 ng μ^?1 of serum sample. The mean ± SD value of slope and intercept of the standard chromatogram of gliotoxin were found to be 523.2 ± 1.555635 and 915.8 ± 30.68843, respectively. The developed method is simple, rapid, precise and less costly than earlier diagnostic methods, and different serum samples can be run on a single TLC plate for comparative analysis. The proposed method can be used to analyze gliotoxin in patient serum for easy, rapid and cost‐effective diagnosis of IA. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability‐indicating HPTLC method for quantitative estimation of silybin in bulk drug and pharmaceutical dosage form

In the present study a novel stability‐indicating high‐performance thin‐layer chromatography (HPTLC) method for quantitative determination of silybin in bulk drug and nanoemulsion formulation has been developed and validated on silica using solvent chloroform–acetone–formic acid (9 : 2 : 1 v/v/v) (R_f of silybin 0.46 ± 0.05) in the absorbance mode at 296 nm. The method showed a good linear relationship (r² ± 0.999) in the concentration range 25–1500 ng per spot. It was found to be linear, accurate, precise, specific, robust and stability‐indicating and can be applied for quality control and standardization of several multi‐component hepatoprotective formulations as well as for stability testing of different dosage forms. The method proposed was also used to investigate the kinetics of acidic and alkaline degradation processes by quantification of drug at different temperature to calculate the activation energy and half‐life for silymarin degradation. Copyright © 2009 John Wiley & Sons, Ltd     

Anodic Sampling and TLC Identification of Dental Alloys

JPC – Journal of Planar Chromatography – Modern TLC - Knowledge of the composition of an incorporated alloy is a precondition for avoiding polymetallism in subsequent prosthetic...     

Block copolymers of poly(ethylene terephthalate)-poly(butylene terephthalate). II. Small-angle light-scattering studies

Small-angle light-scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusual H_v patterns with the four lobes along the polarizer directions, while at later stages they showed the usual H_v patterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster-crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superstructure.     

A polyhedron with alls—t cuts as vertices,and adjacency of cuts

Consider the polyhedron represented by the dual of the LP formulation of the maximums–t flow problem. It is well known that the vertices of this polyhedron are integral, and can be viewed ass–t cuts in the given graph. In this paper we show that not alls–t cuts appear as vertices, and we give a characterization. We also characterize pairs of cuts that form edges of this polyhedron. Finally, we show a set of inequalities such that the corresponding polyhedron has as its vertices alls–t cuts.Work done at the Department of Computer Science and Engineering, Indian Institute of Technology, Delhi, India.     

Evaluation of thermodynamic functions for complexation reactions involving bivalent metal ions and ethyl-2,3-dioxobutyrate-2 p -bromophenylhydrazone

Complexation reactions of bivalent metal ions and ethyl-2,3-dioxobutyrate-2p-bromophenylhydrazone (EDOB-2p-BPH) have been studied potentiometrically in 50% (v/v) ethanol/water medium at different ionic strengths with respect to NaClO₄ and at different temperatures and their stability constants determined. The method of Bjerrum and Calvin as modified by Irving and Rossotti has been used to determine then andpL values. S_min values which have the same significance as ‘T²’ have also been calculated. The thermodynamic stability constants and standard free energy change (ΔG) have also been calculated. ΔG values are negative in all cases indicating that the reactions are spontaneous. The ligand field stabilization energy (δH) has also been calculated for the 3d transition metals.     

Accurate numerical estimation of interphase momentum transfer in Lagrangian–Eulerian simulations of dispersed two-phase flows

The Lagrangian–Eulerian (LE) approach is used in many computational methods to simulate two-way coupled dispersed two-phase flows. These include averaged equation solvers, as well as direct numerical simulations (DNS) and large-eddy simulations (LES) that approximate the dispersed-phase particles (or droplets or bubbles) as point sources. Accurate calculation of the interphase momentum transfer term in LE simulations is crucial for predicting qualitatively correct physical behavior, as well as for quantitative comparison with experiments. Numerical error in the interphase momentum transfer calculation arises from both forward interpolation/approximation of fluid velocity at grid nodes to particle locations, and from backward estimation of the interphase momentum transfer term at particle locations to grid nodes. A novel test that admits an analytical form for the interphase momentum transfer term is devised to test the accuracy of the following numerical schemes: (1) fourth-order Lagrange Polynomial Interpolation (LPI-4), (3) Piecewise Cubic Approximation (PCA), (3) second-order Lagrange Polynomial Interpolation (LPI-2) which is basically linear interpolation, and (4) a Two-Stage Estimation algorithm (TSE). A number of tests are performed to systematically characterize the effects of varying the particle velocity variance, the distribution of particle positions, and fluid velocity field spectrum on estimation of the mean interphase momentum transfer term. Numerical error resulting from backward estimation is decomposed into statistical and deterministic (bias and discretization) components, and their convergence with number of particles and grid resolution is characterized. It is found that when the interphase momentum transfer is computed using values for these numerical parameters typically encountered in the literature, it can incur errors as high as 80% for the LPI-4 scheme, whereas TSE incurs a maximum error of 20%. The tests reveal that using multiple independent simulations and higher number of particles per cell are required for accurate estimation using current algorithms. The study motivates further testing of LE numerical methods, and the development of better algorithms for computing interphase transfer terms.     

Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]+: Experimental and Computational Studies of their Hydricities,Interaction with CO2, and Photochemistry

We prepared two geometric isomers of [Ir(tpy)(ppy)H]⁺, previously proposed as a key intermediate in the photochemical reduction of CO₂ to CO, and characterized their notably different ground‐ and excited‐state interactions with CO₂ and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]⁺, reacts with CO₂ to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH₃CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]⁰ species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO₂ and produces CO with the same catalytic efficiency.     

Milling Bifurcations from Structural Asymmetry and Nonlinear Regeneration

This paper investigates multiple modeling choices for analyzing the rich and complex dynamics of high-speed milling processes. Various models are introduced to capture the effects of asymmetric structural modes and the influence of nonlinear regeneration in a discontinuous cutting force model. Stability is determined from the development of a dynamic map for the resulting variational system. The general case of asymmetric structural elements is investigated with a fixed frame and rotating frame model to show differences in the predicted unstable regions due to parametric excitation. Analytical and numerical investigations are confirmed through a series of experimental cutting tests. The principal results are additional unstable regions, hysteresis in the bifurcation diagrams, and the presence of coexisting periodic and quasiperiodic attractors which is confirmed through experimentation.