Detection of amitraz,a formamidine-based pesticide using chromogenic spray reagent by thin-layer chromatography

JPC – Journal of Planar Chromatography – Modern TLC - In the present study, we developed a simple, sensitive and selective thin-layer chromatographic method for the detection and...     

Structure, function, and stability of enzymes covalently attached to single-walled carbon nanotubes

We describe the structure, activity, and stability of enzymes covalently attached to single-walled carbon nanotubes (SWNTs). Conjugates of SWNTs with three functionally unrelated enzymes-horseradish peroxidase, subtilisin Carlsberg, and chicken egg white lysozyme-were found to be soluble in aqueous solutions. Furthermore, characterization of the secondary and tertiary structure of the immobilized proteins by circular dichroism and fluorescence spectroscopies, respectively, and determination of enzyme kinetics revealed that the enzymes retained a high fraction of their native structure and activity upon attachment to SWNTs. The SWNT-enzyme conjugates were also more stable in guanidine hydrochloride (GdnHCl) and at elevated temperatures relative to their solution counterparts. Thus, these protein conjugates represent novel preparations that possess the attributes of both soluble enzymes-high activity and low diffusional resistance-and immobilized enzymes-high stability-making them attractive choices for applications ranging from diagnostics and sensing to drug delivery.     

Strategies to design pyrazolyl urea derivatives for p38 kinase inhibition: a molecular modeling study

The p38 protein kinase is a serine–threonine mitogen activated protein kinase, which plays an important role in inflammation and arthritis. A combined study of 3D-QSAR and molecular docking has been undertaken to explore the structural insights of pyrazolyl urea p38 kinase inhibitors. The 3D-QSAR studies involved comparative molecular field analysis (CoMFA) and comparative molecular similarity indices (CoMSIA). The best CoMFA model was derived from the atom fit alignment with a cross-validated r ² (q ²) value of 0.516 and conventional r ² of 0.950, while the best CoMSIA model yielded a q ² of 0.455 and r ² of 0.979 (39 molecules in training set, 9 molecules in test set). The CoMFA and CoMSIA contour maps generated from these models provided inklings about the influence of interactive molecular fields in the space on the activity. GOLD, Sybyl (FlexX) and AutoDock docking protocols were exercised to explore the protein–inhibitor interactions. The integration of 3D-QSAR and molecular docking has proffered essential structural features of pyrazolyl urea inhibitors and also strategies to design new potent analogues with enhanced activity.     

LNA (locked nucleic acid) and analogs as triplex-forming oligonucleotides

The triplex-forming abilities of some conformationally restricted nucleotide analogs are disclosed and compared herein. 2'-Amino-LNA monomers proved to be less stabilising to triplexes than LNA monomers when incorporated into a triplex-forming third strand. N2'-functionalisation of 2'-amino-LNA monomers with a glycyl unit induced the formation of exceptionally stable triplexes. Nucleotide analogs containing a C2',C3'-oxymethylene linker (E-type furanose conformation) or a C2',C4'-propylene linker (N-type furanose conformation) had no significant effect on triplex stability proving that conformational restriction per se is insufficient to stabilise triplexes.     

Template-directed oligonucleotide strand ligation, covalent intramolecular DNA circularization and catenation using click chemistry

The copper-catalyzed azide-alkyne cycloaddition reaction has been used for the template-mediated chemical ligation of two oligonucleotide strands, one with a 5'-alkyne and the other with a 3'-azide, to produce a DNA strand with an unnatural backbone at the ligation point. A template-free click-ligation reaction has been used for the intramolecular circularization of a single stranded oligonucleotide which was used as a template for the synthesis of a covalently closed DNA catenane.     

Poly(ethylene glycol) (PEG) as an efficient and recyclable reaction medium for the synthesis of dibenz[b,f]-1,4-oxazepine

Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction solvent for the synthesis of dibenz[b,f]-1,4-oxazepine (2a). PEG-400 as a promoter provided 89% of 2a within 8 h. We compared the reactivity of PEG-400 with 18-crown-6, tetra-n-butylammonium bromide and ionic liquids as phase transfer catalysts. Further, we investigated our protocol with various PEGs, with molecular weight 200, 300, 1000, 2000, 8000, 10,000, and 20,000. The reaction provided excellent yields with low as well as high molecular weight PEGs. We also studied the effect of various organic cosolvents (polar protic/aprotic/non-polar) on the reactivity of PEG-400 for the synthesis of 2a.     

Low-pressure gas chromatography: Recent trends and developments

In the past few years, low-pressure gas chromatography (LP-GC) has been applied for the fast analysis of various pollutants in different environmental and food matrices. A typical LP-GC set-up involves the use of a short microbore column (typically 0.5–1 m × 0.10 mm internal diameter) at the injector side connected with a zero dead-volume connector to a short megabore column (typically 10 m × 0.53 mm) to be used with higher gas velocities. This set-up maintains atmospheric injection conditions, while the analytical column is operated under low-pressure conditions that are compatible with mass-spectrometer analyzers. Although the use of LP-GC results in a loss of separation efficiency, it offers a 3–5-fold reduction in analysis time for organic compounds and thus increased sample throughput and enhancement of the signal-to-noise ratio leading to improved detection limits. Considering the significance of, and the potential interest in, this topic, this review briefly describes the concept of LP-GC. Furthermore, we explore recent developments and applications of LP-GC, with a focus on the use of various column systems and analyzers. Finally, we critically evaluate the prospects for, and the limitations of, LP-GC.     

Asymmetric Synthesis of Monofluorinated Carbocyclic Alcohols and Vicinal Difluorinated Heterocycles and Carbocycles

A straightforward method to access novel families of enantioenriched cis-monofluorinated carbocyclic alcohols has been developed through ATH/DKR in up to 97 % yield, up to 99 : 1 dr and enantioinductions up to 97 % ee. Trans-difluorinated indans, tetrahydronaphthalenes, tetrahydroquinolines and chromans have been synthesized as well by deoxofluorination of the corresponding cis-fluoro alcohols. The reaction was performed on a series of variously substituted 3-fluorochromanols, 3-fluorotetrahydroquinolinols, 2-fluoro inden-1-ols and 2-fluoro 1,2,3,4-tetrahydronaphthalen-1-ols in up to 86 % yields, with diastereoselectivities up to 97 : 3 and enantioselectivities up to >99 % ee.     

Capturing the Polarization Response of Solvated Proteins under Constant Electric Fields in Molecular Dynamics Simulations

We capture and compare the polarization response of a solvated globular protein ubiquitin to static electric (E-fields) using atomistic molecular dynamics simulations. We collectively follow E-field induced changes, electrical and structural, occurring across multiple trajectories using the magnitude of the protein dipole vector ( P _p ). E-fields antiparallel to P _p induce faster structural changes and more facile protein unfolding relative to parallel fields of the same strength. While weak E-fields (0.1–0.5 V/nm) do not unfold ubiquitin and produce a reversible polarization, strong E-fields (1–2 V/nm) unfold the protein through a pathway wherein the helix:β-strand interactions rupture before those for the β1-β5 clamp. Independent of E-field direction, high E-field induced structural changes are also reversible if the field is switched off before P _p exceeds 2 times its equilibrium value. We critically examine the dependence of water properties, protein rotational diffusion and E-field induced protein unfolding pathways on the thermostat/barostat parameters used in our simulations.     

Transient temperature distribution in an internally and externally insulated cylindrical shell

This paper presents the analytical solution for unsteady state temperature distribution in a cylindrical shell having thin layer of thermal insulation coating at the inner and outer surfaces. The formula has been derived assuming different initial temperatures of shell and insulation coating while the contact between them has also been assumed to be imperfect. The internal and external surfaces of the shell and coatings are exposed to the convective boundary conditions of third kind.The generalized formula obtained has been used to obtain the warming-up-period of the cylindrical wall of a Diesel engine coated internally and externally by ceramic insulation material. A plot of Temperature-time history and heat flow rates have been obtained. The problem considered has got its application in the transient thermal analysis of an adiabatic engine. Any other similar problem in metallurgical, aeronautical, furnace design, boiler design applications may be solved by the formula obtained.Nomenclature a ₁, a ₂, a ₃ thermal diffusivity of shell, inner and outer insulation coatings - A ₁(, ) to A ₆(, ) as defined in equation (4) - B _g , B _w Biot's numbers on inner and outer surfaces - C ₁, C ₂, C ₃ Specific heat of shell, inner and outer insulation coatings - F ₀ Fourier's number, F ₀ = a ₁ t/R ₂ ² - G(s) as defined in equation (4) - h _g , h _w heat transfer coefficients at inner and outer surfaces - K ₁, K ₂, K ₃ coefficient of thermal conductivity of shell, inner and outer insulation coatings - ratio defined as, - thermal activeness ratio, - L ₁ to L ₂₁ Factors defined in equation (4) - m ₂, m ₃ thermal contact resistances at interfaces, (kcal/m² hr°C)^–1 - M ₂, M ₃ dimensionless contact coefficients, M ₂ = m ₂ K ₂/₂, M ₃ = m ₃ K ₃/₃ - P factor defined in equation (7) - Q ₁, Q ₂, Q ₃, Q ₄ heat flow rates at inner, interfaces and outer surfaces - R ₁, R ₂, R ₃, R ₄ Interfaces, inner and outer radii - r radial co-ordinate - s Laplace parameter - t time - T ₁(r, t), T ₂(r, t), T ₃(r, t) temperatures in shell, inner and outer insulation coatings - T ₁₀, T ₂₀, T ₃₀ initial temperatures in shell, inner and outer insulation coatings - T _g , T _w gaseous and water side temperatures - U _m (, x) as defined in equation (4) - V _m (, x) as defined in equation (4) - W _m (, x) as defined in equation (4) - x, x ₁ dimensionless radii, x = r/R ₂ and x ₁ = R ₁/R ₂ Greek symbols ₂, ₃ thicknesses of the insulation coatings, ₂ = (R ₁ – R ₃), = (R ₄ – R ₂) - , dimensionless radii, = (r – R ₃)/₂, = (r – R ₂)/₃ - ₁₀, ₂₀, ₃₀, _g initial temperatures ₁₀ = ( T ₁₀ – T _w ); ₂₀ = (T ₂₀ – T _w ); ₃₀ = T ₃₀ – T _w ; _g = T _g – T _w ) - ₁(x, F ₀), ₂(, F ₀), ₃(, F ₀) temperature symbols defined as ₁ = ( T ₁ (r, t) – T _w ); ₂ = (T ₂ (r, t) – T _w ); ₃ = T ₃ (r, t) – T _w ) - Laplace transformation of ₁(x, F ₀), ₂(, F ₀) and ₃(, F ₀) - defined as, - defined as - defined as, - ₁, ₂, ₃ densities of shell, inner and outer insulation coatings - angle defined in equation (5) - _n factor defined in equation (7)