Determination of lead in seawater by inductively coupled plasma optical emission spectrometry after separation and pre-concentration with cocrystallized naphthalene alizarin

An analytical method for separation and pre-concentration of lead in seawater for determination by inductively coupled plasma optical emission spectrometry has been investigated. Lead was retained in the solid phase (0.5 g) composed of co-precipitated naphthalene and alizarin red. The solid phase quantitatively sorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 ml of 2 mol l⁻¹ nitric acid. The effect of NaCl, KCl, BaCl₂, CaCl₂, Na₂SO₄, MgCl₂ and Na₃PO₄ on the sorption of Pb(II) in the solid phase was studied. A set of solutions containing varying amounts of electrolytes (0.5; 1.0; 3.0 and 5.0% m/v) with Pb (50 μg) was prepared and the recommended procedure applied. The Na₃PO₄ was found to interfere; the other electrolytes did not interfere up to 5% m/v. A pre-concentration factor of 40 was obtained in this analytical procedure. The limit of detection and limit of quantification for Pb(II) were 53 and 176 μg l⁻¹, respectively. Lead was determined in seawater samples collected in Salvador city, Bahia, Brazil. The precision, expressed as R.S.D., was 1.8–4.6%, and the recovery of lead added to seawater samples was 95–97%.     

The effects of lignin removal and drying on the porosity and enzymatic hydrolysis of sugarcane bagasse

The porosity of lignocellulosic materials is a key feature for the enzymatic hydrolysis of the constituent polysaccharides, being affected by its drying and lignin content. Here we evaluated the influence of both parameters in the porosity of sugarcane bagasse, using raw and chlorite-delignified samples. A fraction of these samples was air dried at room temperature and the remainder one was kept wet. All the samples were subjected to porometry (solute exclusion technique), determination of water retention value and assessment of enzymatic saccharification of polysaccharides. Samples with higher lignin contents had lower porosities and exhibited worse enzymatic conversions of polysaccharides. Mild drying collapsed only the smaller pores, which already were inaccessible to enzymes, and therefore did not affect the efficiencies of saccharification. Our results show that the lignin content plays an important role in the porosity of the material and that its removal improves the enzymatic saccharification of the constituent polysaccharides.     

[Pd(Fmes)2(tmeda)]: A Case of Intermittent C?H⋅⋅⋅F?C Hydrogen‐Bond Interaction in Solution

The X‐ray structure of the title compound [Pd(Fmes)₂(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF₃ groups of the Fmes ligand. The ¹⁹F NMR spectra in CD₂Cl₂ at very low temperature (157 K) detect restricted rotation for the two ortho‐CF₃ groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol^?1) to account for the rotational barrier observed (ΔH^≠=26.8 kJ mol^?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.     

Transition Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

A covalently‐linked salen–C₆₀ (H₂L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C₆₀ cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen–C₆₀ introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal–salen–C₆₀ complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene‐containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single‐, double‐ and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen–C₆₀ complexes in heterogeneous catalysis.     

Simple approach to study biomolecule adsorption in polymeric microfluidic channels

Herein a simple analytical method is presented for the characterization of biomolecule adsorption on cyclo olefin polymer (COP, trade name: Zeonor^®) substrates which are widely used in microfluidic lab-on-a-chip devices. These Zeonor^® substrates do not possess native functional groups for specific reactions with biomolecules. Therefore, depending on the application, such substrates must be functionalized by surface chemistry methods to either enhance or suppress biomolecular adsorption. This work demonstrates a microfluidic method for evaluating the adsorption of antibodies and oligonucleotides surfaces. The method uses centrifugal microfluidic flow-through chips and can easily be implemented using common equipment such as a spin coater. The working principle is very simple. The user adds 40 L of the solution containing the sample to the starting side of a microfluidic channel, where it is moved through by centrifugal force. Some molecules are adsorbed in the channel. The sample is then collected at the other end in a small reservoir and the biomolecule concentration is measured. As a pilot application, we characterized the adsorption of goat anti-human IgG and a 20-mer DNA on Zeonor^®, and on three types of functionalized Zeonor: 3-aminopropyltriethoxysilane (APTES) modified surface with mainly positive charge, negatively charged surface with immobilized bovine serum albumin (BSA), and neutral, hydrogel-like film with polyethylene glycol (PEG) characteristics. This simple analytical approach adds to the fundamental understanding of the interaction forces in real, microfluidic systems. This method provides a straightforward and rapid way to screen surface compositions and chemistry, and relate these to their effects on the sensitivity and resistance to non-specific binding of bioassays using them. In an additional set of experiments, the surface area of the channels in this universal microfluidic chip was increased by precision milling of microscale trenches. This modified surface was then coated with APTES and tested for its potential to serve as a unique protein dilution feature.     

Preconcentration of heavy metals ions from aqueous solutions by means of cellulose phosphate: an application in water analysis

Cellulose phosphate (CELLPHOS) was studied as a collector for analytical preconcentration of traces of Cd(II), Cr(III), Cu(II) and Ni(II) from aqueous sample solution. It has been proved that using chromatographic columns packed with CELLPHOS for preconcentration and 1.0 mol 1(-1) HCl for elution the adsorbed analytes are quantitatively enriched. An enrichment factor of 20 (100 ml sample, 5 ml concentrate) was achieved by this separation procedure, which was applied to a series of water analyses (river, sea, bog water).     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Chemoselective Staudinger-phosphite reaction of symmetrical glycosyl-phosphites with azido-peptides and polygycerols

In this paper we present the synthesis of glyco-phosphoramidate conjugates as easily accessible analogs of glyco-phosphorous esters via the Staudinger-phosphite reaction. This protocol takes advantage of synthetically accessible symmetrical carbohydrate phosphites in good overall yields, in which ethylene or propylene linkers can be introduced between phosphorous and galactose or lactose moieties. The phosphites were finally applied for the chemoselective reaction with azido-peptides and polyazido(poly)glycerols.     

Transition metal complexes with Girard reagent-based ligands

The ligand, salicylaldehyde Girard-T hydrazonium chloride, [H₂SalGT]Cl (1), and two complexes [Cu(HSalGT)X₂]·H₂O (X = Br(2); Cl(3)) were synthesized and their crystal structures were determined by single-crystal X-ray analysis. In the two isostructural complexes, the Cu(II) is located in a square-pyramidal environment, with the chelating ligand and one halogen atom in the basal plane and the second halogen in the apical position. The most apparent structural difference between the 1 and its complexes 2 and 3 is the orientation of the N(CH₃)₃ group: in 1, it is practically coplanar to the rest of the molecule, while in 2 and 3 it is oriented to the side of the axially bonded halogen, which can be explained by the C–H…X intramolecular interactions. The compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and electronic absorption spectra.