Simple electrooptical sensors for inorganic anions

[reaction: see text] Electrooptical sensors consisting of a conjugated chromophore undergoing a change in color and a redox-active moiety such as quinone fused to the chromophore were synthesized. Strong changes in colorimetric and electrochemical properties were observed in the presence of inorganic anions. A unique anion-specific response was observed for fluoride, pyrophosphate, and acetate. DFT (B3LYP/6-31G) calculations performed for both "on/off" states of a sensor-fluoride model are in good agreement with the observed electrochemical and spectroscopic data.     

Evaluation of automated synthesis for chain and step‐growth polymerizations: Can robots replace the chemists?

This article explores current challenges in the use of automated parallel synthesizers in polymeric materials research. Four types of polymerizations were investigated: carbodiimide‐mediated polyesterification, diphenol phosgenation, free radical, and reversible addition‐fragmentation chain‐transfer (RAFT). Synthetic challenges of condensation polymerization, such as liquid and solid dispensing accuracy, dropwise addition, and toxic chemical handling, were successfully met using the automated synthesizer. Both solid and liquid dosing of the diphenol and diacid were successful for polyarylate synthesis. The high precision of liquid dispensing made it possible to achieve stoichiometric balance using reagent stock solutions. For all reactions, molecular weights and their reproducibility were comparable to those obtained with manual synthesis. For RAFT polymerizations, solvent and mol ratio of chain transfer reagent to initiator were successfully optimized on the automated synthesizer and a library of over 60 polymethacrylate copolymer compositions was generated. Considerable savings in time relative to manual methods were achieved when generating polymer libraries (e.g., 4.5× faster for 96 polymethacrylates and 20× faster for 45 for polycarbonates). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 49–58, 2009     

A field deployable method for a rapid screening analysis of inorganic arsenic in seaweed

Inorganic arsenic (iAs) in 13 store-bought edible seaweed samples and 34 dried kelp (Laminaria digitata) samples was determined by a newly developed, field-deployable method (FDM) with the aid of a field test kit for arsenic in water. Results from the FDM were compared to results from speciation analysis achieved by using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The FDM consisted of a simple extraction method using diluted HNO₃ to quantitatively extract iAs without decomposing the organoarsenicals to iAs followed by the selective volatilisation of iAs as arsine (AsH₃) and subsequent chemo-trapping on a filter paper soaked in mercury bromide (HgBr₂) solution. Method optimization with a sub-set of samples showed 80–94% iAs recovery with the FDM with no matrix effect from organo-arsenic species in the form of dimethylarsinic acid (DMA) on the iAs concentration. The method displayed good reproducibility with an average error of ±19% and validation by HPLC-ICP-MS showed that the results from the FDM were comparable (slope = 1.03, R² = 0.70) to those from speciation analysis with no bias. The FDM can be conducted within an hour and the observed limit of quantification was around 0.05 mg kg^?1 (dry weight). This method is well suited for on-site monitoring of iAs in seaweed before it is harvested and can thus be recommended for use as a screening method for iAs in seaweed.

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Graphical abstract Screening seaweed for their inorganic arsenic concentration within one hour without bias has been made possible in the field by using a field deployable arsenic kit. Its accuracy and precision was compared to HPLC-ICPMS.

     

Synthesis,Crystal Structure and Vibrational Spectra of Barium Cyclotetraphosphate Hydrate Ba2(P4O12)∙3.5H2O

Barium tetrametaphosphate hydrate Ba₂(P₄O₁₂)∙3.5H₂O was synthesized as a single‐phase crystalline powder starting from an aqueous solution of barium hydroxide and phosphorus pentoxide at 300 K. Ba₂(P₄O₁₂)∙3.5H₂O crystallizes in a new structure type in which the Ba²⁺ ions form a distorted hexagonal diamond‐like arrangement with the (P₄O₁₂)^4– anions in the trigonal prismatic voids (Ba₂(P₄O₁₂)∙3.5H₂O, C2/c, Z = 4, a = 777.3(2), b = 1297.6(2), c = 1346.1(3) pm, b = 95.38(2)°, wR₂ = 0.071, R₁ = 0.018, 1180 reflections, 118 parameters). The vibrational spectra of Ba₂(P₄O₁₂)∙3.5H₂O and its thermal behavior up to 720 K are also reported.     

Effective Approximation for the Semiclassical Schrödinger Equation

The computation of the semiclassical Schrödinger equation presents major challenges because of the presence of a small parameter. Assuming periodic boundary conditions, the standard approach consists of semi-discretisation with a spectral method, followed by an exponential splitting. In this paper we sketch an alternative strategy. Our analysis commences with the investigation of the free Lie algebra generated by differentiation and by multiplication with the interaction potential: it turns out that this algebra possesses a structure which renders it amenable to a very effective form of asymptotic splitting: exponential splitting where consecutive terms are scaled by increasing powers of the small parameter. This leads to methods which attain high spatial and temporal accuracy and whose cost scales as \({\mathcal {O}}\!\left( M\log M\right) \) , where \(M\) is the number of degrees of freedom in the discretisation.     

Topotecan dynamics,tautomerism and reactivity—1H/13C NMR and ESI MS study

Topotecan (TPT) is in clinical use as an antitumor agent, hycamtin^?. Because of this, it requires both biologically and chemically useful information to be available. TPT acts by binding to the covalent complex formed by nicked DNA and topoisomerase I. This has a poisonous effect since inserted into the single‐strand nick and TPT inhibits its religation. We used NMR to trace TPT dynamics, tautomerism and solvolysis products in various solvents and conditions. Chemical stability was assessed in methanol and DMSO as compared to water, and the regioselectivity of the N‐ and O‐methylation was studied using various alkylating agents. The reaction products of quaternization of the nitrogen atom and methylation of the oxygen atom were characterized by means of ESI MS, ¹H/¹³C‐HMBC and ‐HSQCAD NMR. We have focused on the NMR characterization of TPT with an anticipation that its aggregation, tumbling properties and the intramolecular dipolar interactions will be a common feature for other compounds described in this article. These features can also be useful in tracing the interactions of this class of topoisomerase I (TopoI) poisons with DNA. Moreover, the results explained shed light on the recently disclosed problem of lack of stability of TPT in the heart tissue homogenate samples using the analytical assays developed for this class of compounds carried out in the presence of methanol. Copyright © 2010 John Wiley & Sons, Ltd.     

α‐Peptide–Oligourea Chimeras: Stabilization of Short α‐Helices by Non‐Peptide Helical Foldamers

Short α‐peptides with less than 10 residues generally display a low propensity to nucleate stable helical conformations. While various strategies to stabilize peptide helices have been previously reported, the ability of non‐peptide helical foldamers to stabilize α‐helices when fused to short α‐peptide segments has not been investigated. Towards this end, structural investigations into a series of chimeric oligomers obtained by joining aliphatic oligoureas to the C‐ or N‐termini of α‐peptides are described. All chimeras were found to be fully helical, with as few as 2 (or 3) urea units sufficient to propagate an α‐helical conformation in the fused peptide segment. The remarkable compatibility of α‐peptides with oligoureas described here, along with the simplicity of the approach, highlights the potential of interfacing natural and non‐peptide backbones as a means to further control the behavior of α‐peptides.     

Influence of the soft segment length on the properties of water‐cured poly(carbonate‐urethane‐urea)s

Poly(carbonate‐urethane‐urea)s (PCUU) based on oligocarbonate diols (M_n ≈ 2000) with different length of the hydrocarbon chain as soft segments were synthesized and investigated. Carbonate oligomerols were obtained in a two‐step method from dimethyl carbonate (DMC) and linear α,ω‐diols (1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, 1,9‐nonanediol, 1,10‐dekanediol and 1,12‐dodecanediol). Oligo(trimethylene carbonate) diol was synthesized using ring‐opening polymerization of trimethylence carbonate. PCUUs were obtained by prepolymer method using isophorone diisocyanate (IPDI) and water as a chain extender. Changes in polymers properties with increase of methylene group number between carbonate linkages were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and hardness measurements. The thermal stability was also analyzed by means of thermogravimetric analysis (TGA). Based on FTIR analysis influence of methylene groups number between carbonate linkages on phase separation and concentration of allophanate and biuret groups in the samples were investigated. The obtained poly(carbonate‐urethane‐urea)s exhibited very good mechanical properties. Tensile strength and elongation at break were 40 MPa and 400–600%, respectively, depending on the oligocarbonate used. Copyright © 2014 John Wiley & Sons, Ltd.