Fluoride-selective polymeric membrane electrodes based on Zr(IV)- and Al(III)-salen ionophores of various structures

Al(III)- and Zr(IV)-salophens of novel structures were tested as anion-selective ionophores. It was shown that these compounds are highly selective to fluoride and give selectivity greatly deviating from classical Hofmeister pattern, when doped into the polymeric membrane of ion-selective electrode (ISE). The following selectivity sequence has been recorded for both ionophores: F⁻ > ClO₄⁻ > SCN⁻ > NO₃⁻ ≈ Br⁻ ≈ Cl⁻. The results of potentiometric and spectrophotometric measurements allow to conclude that the nature and structure of salophen ligands influence stability of ISE working parameters. An increase in salophen ligands lipophilicity results in prolongation of the ISE lifetime, most likely due to slower ionophore decomposition caused by the hydrolysis of imine bonds in salophen structure. Ion-selective electrodes (ISEs) with the most successful Al(III)-salophen exhibited a stable, fast and near-Nernstian fluoride response and a functional lifetime near 3 weeks and selectivity coefficients with as follows: −2.8 (Y⁻ = Br⁻), −2.7 (Cl⁻), −2.8 (NO₃⁻), −1.5 (SCN⁻), −1.3 (ClO₄⁻), which is better than for other ones based on Zr(IV)- and Al(III)-salophens and salens described to date.     

Flow injection chemiluminescence determination of the total phenolics levels in plant-derived beverages using soluble manganese(IV)

This study established a flow injection (FI) methodology for the determination of the total phenolic content in plant-derived beverages based on soluble manganese(IV) chemiluminescence (CL) detection. It was found that mixing polyphenols with acidic soluble manganese(IV) in the presence of formaldehyde evoked chemiluminescence. Based on this finding, a new FI-CL method was developed for the estimation of the total content of phenolic compounds (expressed as milligrams of gallic acid equivalent per litre of drink) in a variety of wine, tea and fruit juice samples. The proposed method is sensitive with a detection limit of 0.02 ng mL⁻¹ (gallic acid), offers a wide linear dynamic range (0.5-400 ng mL⁻¹) and high sample throughput (247 samples h⁻¹). The relative standard deviation for 15 measurements was 3.8% for 2 ng mL⁻¹ and 0.45% for 10 ng mL⁻¹ of gallic acid. Analysis of 36 different samples showed that the results obtained by the proposed FI-CL method correlate highly with those obtained by spectrophotometric methods commonly used for the evaluation of the total phenolic/antioxidant level. However, the FI-CL method was found to be far simpler, more rapid and selective, with almost no interference from non-phenolic components of the samples examined.     

Analysis of mechanisms with flexible beam-like links,rotary joints and assembly errors

The paper presents a method of modelling dynamics of mechanisms in which assembly errors can occur. One of the features of the method is that such errors can be included when the kinematics of the mechanism is modelled. A closed kinematic chain consisting of flexible and rigid links with one joint displaced and turned is discussed. Use of joint coordinates together with the rigid finite element method for discretisation of flexible links has allowed us to considerably decrease the size of the problem. Numerical simulations are carried out in order to analyse the influence of inaccurate assembly on the load on joints of a four-bar linkage.     

Synthesis of O-[4,6-Di-O-Acetyl-4-O-(2,3,4,6-Tetra-O-Acetyl-β-D-Galactopyranosyl)-2-Deoxy-2-Hydroxyimino-D-Arabino-Hexopyranosyl]-N-Benzyloxycarbonyl-L-Serine Methyl Esters And Their Transformations

ABSTRACT

3,6-Di-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-2-deoxy-2-hydroxyimino-α- and -β-D-arabino-hexopyranosides of N-benzyloxycarbonyl-L-serine methyl ester as well as of ethanol have been synthesised from D-lactal hexaacetate via nitrosyl chloride, followed by condensation with L-serine derivatives and ethanol, respectively. The compounds of L-serine thus obtained were modified at C-2 and C-3 to afford L-serine derivatives attached to disaccharides containing terminal α-D-gluco-, 2-acetamido-α-D-gluco-, β-D-manno, 2-acetamido-β-D-manno-pyranosyl, 3-azido-2-hydroxyimino-α-D-arabino-, and α-D-ribo-hexopyranosyl residues.     

The hydrogen‐bonding network in deacetyl­cephalothin

The structural analysis of deacetyl­cephalothin [systematic name: (6R,7R)‐3‐hydroxy­methyl‐8‐oxo‐7‐(2‐thio­phen‐2‐yl­acetyl­amino)‐5‐thia‐1‐aza­bicyclo­[4.2.0]oct‐2‐ene‐2‐carboxylic acid], C₁₄H₁₄N₂O₅S₂, shows that the geometry of the central bicyclic moiety is close to the geometry exhibited by other biologically active cephalosporin antibiotics. The mol­ecules are arranged in a helical chain running parallel to the 2₁ axis via a strong O—H⋯O hydrogen bond. The main helices are zipped together via N—H⋯O inter­actions, forming infinite layers. The supramolecular architecture is stabilized by O—H⋯S and C—H⋯O hydrogen bonds.     

Crystal Structure and Solid State 13C Nmr Analysis of Methyl 3,4,6-Tri-O-Acetyl-2-Deoxy-2-(3-Phenylureido)-β-D-Glucopyranoside

ABSTRACT

The X-ray diffraction analysis of methyl 3,4,6-tri-O-acetyl-2-deoxy-(3-phenylureido)-β-D-glucopyranoside was performed and showed that the molecules are associated by two NHz.O=C hydrogen bonds. One molecule with disorder of an acetyl group at C-4 was found in the asymmetric crystal unit. The signals in ¹³C CPMAS NMR spectrum are duplicated indicating that local symmetry is lower than those of the crystal.     

A concise synthesis of tetrahydroisoquinoline-1-carboxylic acids using a Petasis reaction and Pomeranz–Fritsch–Bobbitt cyclization sequence

A sequence of two reactions: the Petasis reaction, in which an aminoacetaldehyde acetal was used as the amine component, followed by Pomeranz–Fritsch–Bobbitt cyclization, has been shown to be a convenient and simple method for the synthesis of tetrahydroisoquinoline-1-carboxylic acids. Using this method several acids have been prepared in good to excellent yields and characterized as hydrochloride salts.     

Spectrochemical properties and solvatochromism of bis(salicylidene-2-amino-3-methylpyridine)copper(II)

The title complex, denoted as [Cu(Msap)₂], is a deep brown solid soluble in common solvents like chloroform, toluene, benzene, dioxane, acetone, methanol, ethanol, 2-propanol, dimethylformamide, dimethyl sulfoxide, and acetonitrile that is a necessary condition for solvatochromism observation. The complex has been characterized by elemental analysis, molar conductivity, ultraviolet, and visible spectroscopy. The available X-ray data for similar compounds show that copper atom adopts planar coordination geometry. The molar conductivities indicate their non-electrolytic properties. The electronic spectra have been used to study the coordination properties of donor atoms and their bonding abilities, as well as solvatochromism. The results obtained show that the interactions of metal with donors depend on solvent polarity and the color changes are subtle.