Stability-indicating liquid chromatography method development and validation for impurity profiling of montelukast sodium in bulk drug and tablet dosage form

Montelukast sodium (MLS) is a leukotriene receptor antagonist drug used in the treatment of asthma, bronchospasm, allergic rhinitis and urticaria. A reversed-phase high performance liquid chromatography method was developed to separate, identify and quantitative determination of MLS and its eight known organic impurities in tablet dosage form using a C₁₈ column and mobile phases consisting of a gradient mixture of pH 2.5 phosphate buffer and acetonitrile. The stability-indicating character of the developed method was proven using stress testing (1 m HCl at 80°C/30 min, 1 m NaOH at 80°C/30 min, H₂O at 80°C/30 min, 3% H₂O₂ at 25°C/1 min, dry heat at 105°C/10 h and UV–vis light/4 days) and was validated for specificity, quantitation limit, linearity, precision, accuracy and robustness. For MLS and its eight known impurities, the quantitation limits, linearity and recoveries were 0.015–0.03 μg/ml, correlation coefficient > 0.997 (R² > 0.995) and 85.5–107.0%, respectively. The developed chromatographic method is suitable for impurity profiling and also for assay determination of MLS in bulk drugs and pharmaceutical formulations. The mass values (m/z) of newly formed degradation products (DP1 and DP2) of montelukast sodium were identified using liquid chromatography–mass spectrometry.     

Optical tweezer for micro and nano scale rheology of biomaterials

Since the first proposal and demonstration of an optical trap to hold micron sized particles by Ashkin in 1986, optical tweezer-based techniques for control and manipulation of particles has seen tremendous progress and enabled the exploration of the structure and dynamics of materials at the nano length scale. In biophysical applications, these techniques have enabled a range of activities from measurements of very small forces (at sub-pN levels) at operation within cells thus assisting in the elucidation of intracellular transport mechanisms, to obtaining elastic parameters of biomolecules. The techniques have helped in gaining insights on the viscoelastic properties at micro and nano length scales of a range of soft materials such as colloids, polymer melts, bio membranes etc.     

Design,synthesis, antitubercular and antibacterial activities of pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives and in silico docking studies

Abstract

A novel series pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives have been designed, synthesized and confirmed by FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, MS, and elemental analysis. The synthesized compounds were screened for their antitubercular activity using microplate alamar blue assay method and antibacterial activity. Among the tested compounds, 4- fluorophenyl (8m), 4- chlorophenyl (8n) and 4-methoxyphenyl (8i) showed potent anti-TB activity (3.12?µg/mL) in comparison with reference drug, Pyrazinamide ((3.12?µg/mL). In addition, all compounds were docked into DprE1 (PDB code: 4KW5) to explore their binding interactions at the active site. The compounds exhibited essential key interactions as that of reported DprE1 inhibitors and hence, the synthesized compounds may be considered as molecular scaffolds for antitubercular activity. Compounds, 4-chlorophenyl (8n) and 4-flurophenyl (8m) showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus strains. In silico prediction of toxicities, druglikeness and drug score profiles of the tested compounds are promising.     

Evidence for two superconducting gaps in the unconventional superconductor PrPt4Ge12

We report the results of magnetization measurements on the unconventional superconductor PrPt₄Ge₁₂ in its superconducting state. A distinct positive curvature is observed in the temperature dependence of the lower critical field H _C1(T) and the upper critical field H _C2(T) around 5.5?K. The zero field critical current density J _C(T, H?=?0) is found to vary nearly linearly with temperature. We argue that these observed features are due to the existence of two superconducting gaps in the material. The normalized superfluid density is estimated from the temperature dependence of H _C1. Our detailed analysis of the normalized superfluid density using a two-gap model indicates the presence of line nodes in the larger gap. The H _C2(T) line can be fitted with the Usadel equations, and the positive curvature in H _C2(T) is shown to be consistent with the two-gap picture of superconductivity.     

On a continued fraction of order 12

We present some new relations between a continued fraction U(q) of order 12 (established by M. S. M. Naika et al.) and U(q ⁿ ) for n = 7, 9, 11, 13:     

T3P®-DMSO mediated one pot cascade protocol for the synthesis of 4-thiazolidinones from alcohols

Propylphosphonic anhydride (T3P®)-DMSO mediated oxidation of alcohols to carbonyl compounds and their subsequent cyclization with aryl/hetero aryl amines and thioglycolic acid to afford 4-thiazolidinones has been reported. Synthesis of 4-thiazolidinones directly from alcohols has been carried out for the first time. Mild reaction conditions, wide functional group tolerance, ease of work-up, and good yields are the noteworthy features of this protocol.     

Dielectrophoretic deformation of breast cancer cells for lab on a chip applications

This paper presents the development and experimental analysis of a curved microelectrode platform for the DEP deformation of breast cancer cells (MDA‐MB‐231). The platform is composed of arrays of curved DEP microelectrodes which are patterned onto a glass slide and samples containing MDA‐MB‐231 cells are pipetted onto the platform's surface. Finite element method is utilised to characterise the electric field gradient and DEP field. The performance of the system is assessed with MDA‐MB‐231 cells in a low conductivity 1% DMEM suspending medium. We applied sinusoidal wave AC potential at peak to peak voltages of 2, 5, and 10 V_pp at both 10 kHz and 50 MHz. We observed cell blebbing and cell shrinkage and analyzed the percentage of shrinkage of the cells. The experiments demonstrated higher percentage of cell shrinkage when cells are exposed to higher frequency and peak to peak voltage electric field.     

Validity of Taylor's dissipation-viscosity independence postulate in variable-viscosity turbulent fluid mixtures

G. I. Taylor's postulate [Proc. R. Soc. A 151, 421 (1935)] that dissipation is independent of viscosity at high Reynolds numbers is the foundation of many single-fluid turbulence theories and closure models. The validity of this key postulate in an important class of flows, turbulent mixtures, is not yet clearly established. We devise a simple numerical experiment of decaying turbulence in a mixture of two fluids of vastly different viscosities to examine dissipation scaling. Initially, the two fluids are segregated, and dissipation is directly proportional to viscosity. As turbulence evolves and fluids mix, the velocity gradients rapidly adapt to the viscosity field, and within one-half eddy turnover time, dissipation-viscosity independence is established. Viscosity-weighted velocity-gradient skewness is shown to be constant, leading to the validity of Taylor's postulate in turbulent mixtures.     

Fully explicit and self-consistent algebraic Reynolds stress model

A fully explicit, self-consistent algebraic expression (for Reynolds stress) which is the exact solution to the Reynolds stress transport equation in the weak-equilibrium limit for two-dimensional mean flows for all linear and some quasi-linear pressure-strain models, is derived. Current explicit algebraic Reynolds stress models derived by employing the weak-equilibrium assumption treat the production-to-dissipation (P/) ratio as a constant, resulting in an effective viscosity that can be singular away from the equilibrium limit. In this paper the set of simultaneous algebraic Reynolds stress equations in the weak-equilibrium limit are solved in the full nonlinear form and the eddy viscosity is found to be nonsingular. Preliminary tests indicate that the model performs adequately, even for three-dimensional mean-flow cases. Due to the explicit and nonsingular nature of the effective viscosity, this model should mitigate many of the difficulties encountered in computing complex turbulent flows with the algebraic Reynolds stress models.This research was supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-19480.