Verbenanone,an octahydro-5H-chromen-5-one from a Hawaiian-plant associated fungus FT431

Verbenanone (1), a new secondary metabolite with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.     

Development of a light-up fluorescent probe for HRAS G-quadruplex DNA

The development of small-molecule G-quadruplex DNA probes has attracted significant attention in recent years. However, G-quadruplexes can display a wide variety of topologies, which process different structures and functions. Therefore, selective discrimination one G-quadruplex structure over another is promising. Herein, we reported the design, synthesis and biological evaluation of a long-chain fatty amine functionalized triphenylamine-quinolinium conjugate 1b. Significant enhancement of the fluorescence intensity (over 180 fold) was observed when 1b bound with HRAS G-quadruplex DNA, while much weaker enhancements were presented in the presence of other G-quadruplexes (45–90-fold) and single/double-stranded DNAs (less than 20-fold), indicating 1b had an excellent selectivity to HRAS. The details of the interactions were investigated by UV–Vis, FID and CD analysis. The results show 1b could interact and stabilize HRAS structure mainly by π-π stacking binding mode. The introduced amine chain of the structure core was found to be better in the terms of inducing selectivity toward G-quadruplex structure. In addition, the application of 1b as a fluorescent agent for living cell imaging was also demonstrated.     

Bienzyme-based visual and spectrophotometric aptamer assay for quantitation of nanomolar levels of mercury(II)

The article describes a bienzyme visual system for aptamer-based assay of Hg(II) at nanomolar levels. The detection scheme is based on the finding that Hg(II) ions captured by aptamer-functionalized magnetic beads are capable of inhibiting the enzymatic activity of uricase and thus affect the formation of H₂O₂ and the blue product, i.e., oxidized tetramethylbenzidine. This strategy allows for a visual detection of Hg(II) at nanomolar levels without additional amplification procedure. Measuring the absorbance at 650 nm, the logarithmic calibration plot is linear in the concentration range of 0.5–50 nM and the limit of detection (LOD) is 0.15 nM. This is as low as the LOD obtained by atomic fluorescence spectrometry (AFS). The ions K⁺, Mg²⁺, Na⁺, Ca²⁺, Cu²⁺, Zn²⁺, Fe³⁺, Al³⁺, Co²⁺, AsO₂ ^?, Ni²⁺, Cd²⁺ and Pb²⁺ do not have a significant effect on color formation. The method was applied to the analysis of (spiked) river water, lake water, mineral water, tap water and certified reference water samples, and the results agreed well with those obtained by AFS or certified values, with recoveries ranging from 97% to 109%. The relative standard deviation for five parallel detections at a 10 nM Hg(II) level is 5.2%.

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Graphical abstract A bienzyme-based visual aptasensor was fabricated for label-free detection of nanomolar Hg²⁺ in water samples without any amplification or enrichment procedure.

     

A capillary coated with a metal-organic framework for the capillary electrochromatographic determination of cephalosporins

The authors have developed a rapid and reliable method for the capillary electrochromatographic determination of cephalosporin antibiotics in environmental waters. An open-tubular capillary column was modified with the complex [Cu(mal)(bpy)], a copper(II) complex with malic acid and 4,4′-bipyridyl, by an amide coupling method to act as the stationary phase. The simultaneous determination of the cephalosporins formulations, namely cefapirin (CP), ceftiofur (EFT) and cefixime (CFM) in environmental water samples was accomplished in buffer of pH 5.0 by applying a voltage of 8 kV and with DAD detection. Detection limits typically are 0.1 μg?mL^?1.The method was applied to the analysis of cephalosporins in spiked water samples from Kunming Lake to give recoveries betwen 88 and 106%.

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Graphical abstract A metal-organic framework (MOF) was synthesized from copper(II), malic acid and 4,4′-bipyridyl and used as stationary phase of capillary electrochromatography (CEC) by covalent immobilization on the capillary inner walls. Compared to an uncoated fused-silica capillary, improved separation of cephalosporin antibiotics can be accomplished.

     

Photometric determination of free cholesterol via cholesterol oxidase and carbon nanotube supported Prussian blue as a peroxidase mimic

Microchimica Acta - The authors describe a photometric method for the determination of free cholesterol based on the oxidation of cholesterol by the catalytic action of the enzyme...     

Template-directed syntheses of two 3D metal oxalates: in situ N-methylation and crystal structures

Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn₂(C₂O₄)₃]·4H₂O (1), and (dmdabco)[Co₂(C₂O₄)₃]·4H₂O (2) (C₂O₄^2? = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco²⁺ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes.     

Determination of Protonation Constants of O-Phospho-<Emphasis Type="SmallCaps">l</Emphasis>-serine in Aqueous Solution: Potentiometry,Microcalorimetry, NMR Spectroscopy and Quantum Chemical Calculations

O-Phospho-l-serine is one of the naturally occurring phosphorylated amino acids, having important pharmacological activity and bioactivity. The protonation constants of O-phospho-l-serine were determined by means of potentiometric titrations at 25 °C and ionic strength of 0.5 mol·L^?1 (NaCl). The heat effects of the protonation reaction of the O-phospho-l-serine were measured by direct calorimetry. NMR spectroscopy has demonstrated that the first protonation site occurs at the nitrogen atom in the amino group, followed by one of the oxygen atoms in the phosphono group, and finally the carboxyl oxygen atom. This trend is in good agreement with the enthalpy of protonation and quantum chemical calculations. These data will help to predict the speciation of O-phospho-l-serine in physiological systems.     

Geometry of spacelike generalized constant ratio surfaces in Minkowski 3-space

Generalized constant ratio surfaces are defined by the property that the tangential component of the position vector is a principal direction on the surfaces. In this work, we study these class of surfaces in the 3-dimensional Minkowski space L³. We achieve a complete classification of spacelike generalized constant ratio surfaces in L³.     

Multi-recurrence and van der Waerden systems

We explore recurrence properties arising from dynamical approach to the van der Waerden theorem and similar combinatorial problems. We describe relations between these properties and study their consequences for dynamics. In particular, we present a measure-theoretical analog of a result of Glasner on multi-transitivity of topologically weakly mixing minimal maps. We also obtain a dynamical proof of the existence of a C-set with zero Banach density.     

Novel approach to the synthesis of istaroxime

Istaroxime 1, a novel cardiotonic agent with high efficiency and low toxicity was synthesized from dehydroepiandrosterone 2 using a novel approach that included epoxidation, ring-opening, substitution, and oximation. The new protocol without gas protection was milder than the reported approaches. The overall yield of the method was 24.1%.