A study of antimony complexed to soil-derived humic acids and inorganic antimony species along a Massachusetts highway

Antimony is a toxic metalloid and is often present in inorganic forms such as more toxic Sb(III) and less toxic Sb(V). Auto brake linings are major contributors to antimony emissions along heavily traveled highways. In this study the distribution of water extractable Sb(III) and Sb(V) species along a Massachusetts highway was investigated. Antimony complexed to roadside soil-derived humic acids was studied by ion chromatography (IC) and size exclusion chromatography (SEC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). Thirty surface soil and soil core samples along route 116 in western Massachusetts were collected. Two soil-derived humic acids were extracted from the roadside soils. Elevated levels of nitric acid-extractable Sb (range: 2.9-24.9 µg/kg) and Pb (range: 10.4-2420 mg/kg) were found in the soil along the road and correlated well with highway traffic patterns. Sb(V) was the dominant species present in both surface and soil core samples, and is mostly confined to the top 20-cm layer of soil. HA mediated Sb(III) to Sb(V) oxidation was relatively fast and demonstrated pseudo-first order kinetics, where pseudo rate constant k is 3.033 h^-1. Antimony bound to soil-derived humic acid molar mass fractions was identified.     

Morphological and phase evolution of TiO2 nanocrystals prepared from peroxotitanate complex aqueous solution: Influence of acetic acid

Nanosized anatase and rutile TiO₂ having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H₂O₂) in water/isopropanol media by a facile sol-gel process. The TiO₂ nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO₂ are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given.     

Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water = 80:19.3:0.7 at [K⁺] = 0.02 M enabled to measure the potential change in a wide range of pOH (=−log [OH⁻]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.     

Nir-chemical imaging study of acetylsalicylic acid in commercial tablets

Near Infrared Chemical Imaging (NIR-CI) is demonstrating an increasing interest in pharmaceutical research since it meets the challenging analytical needs of pharmaceutical quality and may serve as a versatile adjunct to conventional NIR spectroscopy in many fields.The direct analysis of samples by using hyperspectral imaging techniques, which provide a NIR spectrum in each pixel of the image, generates a big amount of information from one sample. Focusing the interest in pharmaceutical research, several chemometric algorithms are demonstrating their usefulness extracting the relevant information (i.e. quantitative determination of the component in one sample) in tablets with only one sample and without damaging it.In this work, a quantitative method to analyze different commercial Acetylsalicylic acid tablets is proposed by using Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) method to the hyperspectral image and without any previous calibration model. For this purpose, a large concentration range of active pharmaceutical ingredient (ASA, Acetylsalicylic acid in this work), between 82% and 12%, was covered depending on the manufacturer. MCR-ALS allowed obtaining a concentration maps for acetylsalicylic acid and therefore, consequent analysis of the ASA distribution in the tablet was developed by using the histograms of the distribution of concentration.Results certified the good distribution of ASA despite the different origins of the tablets. Moreover, the obtained values of concentration showed a very good concordance with the nominal value of ASA. As a matter of fact, the quality of the results demonstrated the useful of encompassing NIR-CI techniques with MCR-ALS and, consequently, the well development on the production of Acetylsalicylic acid tablets.     

Kinetic study of uranium speciation in model solutions and in natural waters using Competitive Ligand Exchange Method

Kinetic speciation of uranium in model solutions containing uranium and humic acid (HA) and in natural waters has been investigated by Competitive Ligand Exchange Method (CLEM). In alkaline freshwaters, most of uranium species were uranium-carbonate species, which were labile in the CLEM experiment. The uranium speciation of every sample was characterized either as “labile” or “non-labile” uranium complexes depending on the dissociation rate coefficients of the complexes. The results showed that as the U(VI)/HA ratio was decreased, the dissociation rate coefficients decreased and the labile fraction decreased as well. When the U(VI)/HA ratio was 0.1, the labile fraction of the U(VI)-HA increased with increasing pH; however, there was no pH effect on the dissociation of U(VI)-HA complexes at lower U(VI)/HA ratios. Chelex-100 had some limitations in its use for the study of dissociation of U(VI)-HA complex at very low U(VI)/HA ratios. By developing an analytical method and procedure for quantitative determination of kinetic parameters for the dissociation of uranium-HA complexes in model solutions and natural waters, this work has made a substantial contribution to analytical chemistry.     

Poly(3-methylthiophene)/palladium sub-micro-modified sensor electrode. Part II: Voltammetric and EIS studies, and analysis of catecholamine neurotransmitters, ascorbic acid and acetaminophen

Promising voltammetric sensors based on the modification of Pt and poly(3-methylthiophene) (PMT) electrodes with Pd nanoparticles were achieved for the determination of catecholamine neurotransmitters, ascorbic acid and acetaminophen. Electrochemistry of the indicated compounds was studied at these electrodes and interesting electrocatalytic effects were found. Furthermore, simple, easily prepared one electrochemical step Pd-modified Pt electrode (Pt/Pd) is reported for the first time. Cyclic voltammetry (CV) and chronocoulometry (CC) were used for the determination of the apparent diffusion coefficients in different electrolytes at these electrodes and the values are in the range from 10⁻⁴ to 10⁻⁵ cm² s⁻¹. Furthermore, it was found that the method of polymer formation had a substantial effect on the synergism between the polymer film and the loaded metal particles towards the oxidation of dopamine (DA) in different supporting electrolytes. This was confirmed by the CV, CC and EIS (electrochemical impedance spectroscopy) as well as SEM (Scanning Electron Microscopy) results. Pt and PMT electrodes modified with Pd nanoparticles showed excellent results for the simultaneous determination of tertiary and quaternary mixtures of the studied compounds.     

The synthesis of substituted phenols from pyranone precursors

The syntheses of various substituted phenols from pyranone precursors, namely 4H-pyran-4-one, 3-(benzyloxy)-2-methyl-4H-pyran-4-one (benzyl-maltol), 2,6-dimethyl-4H-pyran-4-one and diethyl 4-oxo-4H-pyran-2,6-dicarboxylate (diethyl chelidonate) are presented. A variety of pronucleophiles were used in combination with tert-butanol as solvent and potassium tert-butoxide as base, using conventional heating methods and microwave conditions.     

Application of ortho-chloro-β-aroylthioamides in synthesis(II): an efficient one-pot, three-component synthesis of tricyclic thiochromeno[2,3-b]pyridine derivatives

Tricyclic thiochromeno[2,3-b]pyridine derivatives have been successfully synthesized in an unusual one-pot multicomponent cascade reaction from ortho-halo-β-aroylthioamides, Meldrum's acid, and aromatic aldehydes. The reaction presumably proceeds via Knoevenagel condensation-Michael addition-cyclocondensation-decarboxylation-rearrangement-intramolecular S_NAr reaction sequence. High bond forming efficiency of this reaction makes it attractive for the synthesis of thiochromeno[2,3-b]pyridine derivatives in a single step operation.     

Synthesis of hexahydrocarbazoles by cyclisation of 3-(but-3-enyl) indole derivatives

A new cyclisation of 3-(but-3-enyl) indole derivatives that produces policyclic compounds with a hexahydrocarbazole structure is described. In this reaction three stereogenic centres are generated in one step, and this process can be considered as evidence of the biogenetic relationship between anominine and tubingensin A.     

Hydroxy-α-amino acids modified by ionic liquid moieties: recoverable organocatalysts for asymmetric aldol reactions in the presence of water

New chiral ionic liquids bearing proline, serine or threonine moieties were synthesized. Compounds that contain 1-dodecylimidazolium or 4-(5-n-nonyl)-pyridinium cations and NTf₂ or PF₆ anions efficiently catalyze the asymmetric aldol reaction between aldehydes and ketones in the presence of water to generate aldols with high distereo- (up to 98:2) and enantioselectivity (up to >99% ee). 4-Hydroxyproline modified by the 4-(5-n-nonyl)-pyridinium hexafluorophosphate moiety retains its activity and selectivity over at least eight reaction cycles.