Study of immobilized metal affinity chromatography sorbents for the analysis of peptides by on‐line solid‐phase extraction capillary electrophoresis‐mass spectrometry

Several commercial immobilized metal affinity chromatography sorbents were evaluated in this study for the analysis of two small peptide fragments of the amyloid β‐protein (Aβ) (Aβ(1–15) and Aβ(10–20) peptides) by on‐line immobilized metal affinity SPE‐CE (IMA‐SPE‐CE). The performance of a nickel metal ion (Ni(II)) sorbent based on nitrilotriacetic acid as a chelating agent was significantly better than two copper metal ion (Cu(II)) sorbents based on iminodiacetic acid. A BGE of 25 mM phosphate (pH 7.4) and an eluent of 50 mM imidazole (in BGE) yielded a 25‐fold and 5‐fold decrease in the LODs by IMA‐SPE‐CE‐UV for Aβ(1–15) and Aβ(10–20) peptides (0.1 and 0.5 μg/mL, respectively) with regard to CE‐UV (2.5 μg/mL for both peptides). The phosphate BGE was also used in IMA‐SPE‐CE‐MS, but the eluent needed to be substituted by a 0.5% HAc v/v solution. Under optimum preconcentration and detection conditions, reproducibility of peak areas and migration times was acceptable (23.2 and 12.0%RSD, respectively). The method was more sensitive for Aβ(10–20) peptide, which could be detected until 0.25 μg/mL. Linearity for Aβ(10–20) peptide was good in a narrow concentration range (0.25–2.5 μg/mL, R² = 0.93). Lastly, the potential of the optimized Ni(II)‐IMA‐SPE‐CE‐MS method for the analysis of amyloid peptides in biological fluids was evaluated by analyzing spiked plasma and serum samples.     

Modelling the electrophoretic migration behaviour of peptides and glycopeptides from glycoprotein digests in capillary electrophoresis-mass spectrometry

In this study, the classical semiempirical relationships between the electrophoretic mobility and the charge-to-mass ratio (m_e vs. q/M^α) were used to model the migration behaviour of peptides and glycopeptides originated from the digestion of recombinant human erythropoietin (rhEPO), a biologically and therapeutically relevant glycoprotein. The Stoke’s law (α = 1/3), the classical polymer model (α = 1/2) and the Offord’s surface law (α = 2/3) were evaluated to predict migration of peptides and glycopeptides, with and without sialic acids (SiA), in rhEPO digested with trypsin and trypsin–neuraminidase. The Stoke’s law resulted in better correlations for the set of peptides used to evaluate the models, while glycopeptides fitted better with the classical polymer model. Once predicted migration times with both models, it was easy to simulate their separation electropherogram. Results were later validated predicting migration and simulating separation of a different set of rhEPO glycopeptides and also human transferrin (Tf) peptides and glycopeptides. The excellent agreement between the experimental and the simulated electropherograms with rhEPO and Tf digests confirmed the potential applicability of this simple strategy to predict, in general, the peptide–glycopeptide electrophoretic map of any digested glycoprotein.     

Selective and sensitive chromo-fluorogenic sensing of anionic surfactants in water using functionalised silica nanoparticles

A new chromo-fluorogenic sensing protocol for anionic surfactants in aqueous environments using silica functionalised nanoparticles containing imidazolium and thiol groups has been developed.     

Structural and vibrational study of 2‐(2′‐ furyl)‐4,5‐1H‐dihydroimidazole

In this study 2‐(2′‐furyl)‐4,5‐1H‐dihydroimidazole (1) was prepared and then characterized by infrared, Raman, and multidimensional nuclear magnetic resonance (NMR) spectroscopies. The crystal and molecular structures of 1 were determined by X‐ray diffraction methods. The density functional theory (DFT) and second‐order Møller–Plesset theory (MP2) with Pople's basis set show that there are two conformers for the title molecule that have been theoretically determined in the gas phase, and that only one of them, conformer I, is present in the solid phase. NMR spectra observed for 1 were successfully compared with the calculated chemical shifts at the B3LYP/6‐311++G** level theorized for this conformer. The harmonic vibrational frequencies for the optimized geometry of the latter conformer were calculated at the B3LYP/6‐311++G** level in the approximation of the isolated molecule. For a complete assignment of the IR and Raman spectra in the solid phase of 1 , DFT calculations were combined with Pulay´s scaled quantum mechanics force field (SQMFF) methodology to fit the theoretical frequency values to the experimental ones. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of enantiopure imidazolines through a Ritter reaction of 2-(1-aminoalkyl)aziridines with nitriles

The Ritter reaction of enantiopure 2-(1-aminoalkyl)aziridines 1 with different nitriles afford enantiopure tetrasubstituted imidazolines 2. The opening of the aziridine ring takes place with total regio- and stereoselectivity. A mechanism to explain the described addition reaction is proposed. [reaction: see text]     

An intelligent flow analyser for the in-line concentration, speciation and monitoring of metals at trace levels

An intelligent and versatile flow system is proposed for the in-line speciation and/or concentration of metal ions at a wide range of concentrations without requiring manifold reconfiguration. On one hand, sample enrichment strategies are accomplished using packed-bed reactors, on the other hand speciation procedures are readily performed exploiting the selective complexation of the different oxidation states with the appropriate chromogenic reagents.

The potentials of the automated methodology were evaluated using the spectrophotometric monitoring of iron as a model of chemistry. Under the optimised physical and chemical variables, linear analytical curves over the ranges 0.025–0.5 or 2.0–40 mg l⁻¹ Fe were attained. The 3σ detection limit, the repeatability at the 0.5 mg l⁻¹ level, the enrichment factor for a sampling volume of 10 ml, and the maximum injection throughput were 8.4 ng ml⁻¹ Fe, 2.5%, 58.6 and 22 h⁻¹, respectively. The flowing system was applied to the speciation analysis of iron in waters, pharmaceutical formulations and agricultural products, using ICP-OES detection as an external reference method for total iron determination.

A remarkable feature of the expert system hereby presented is the ability to decide by itself if the pre-concentration and/or oxidation of the sample zone is required.