In‐line coupled single drop liquid–liquid–liquid microextraction with capillary electrophoresis for determining fluoroquinolones in water samples

A simple in‐line single drop liquid–liquid–liquid microextraction (SD‐LLLME) coupled with CE for the determination of two fluoroquinolones was developed. The method is capable to quantify trace amount of analytes in water samples and to improve the sensitivity of CE detection. For the SD‐LLLME, a thin layer of organic phase was used to separate a drop of 0.1 M NaOH hanging at the inlet of the capillary from the aqueous donor phase. By this way, the analytes were extracted to the acceptor phase through the organic layer based on their acidic/basic dissociation equilibrium. The drop was immersed into the organic phase during 10 min for extraction and then it is directly injected into the capillary for the analysis. Parameters such as type and volume of organic solvent phase, aqueous donor, and acceptor phases and extraction time and temperature were optimized. The enrichment factor was calculated, resulting 40‐fold for enrofloxacin (ENR) and sixfold for ciprofloxacin (CIP). The linear range were 20–400 μg/L for ENR and 60–400 μg/L for CIP. The detection limits were 10.1 μg/L and 55.3 μg/L for ENR and CIP, respectively, and a good reproducibility was obtained (4.4% for ENR and 5.6% for CIP). Two real water samples were analysed applying the new method and the obtained results presented satisfactory recovery percentages (90–100.3%).     

The formation of non-soluble complexes between polyethyleneimine-anions and their potential use to isolate enzymes

The aqueous solution behavior of polyethyleneimine (a synthetic cationic polymer) in the presence of anions with two or more electrical charges (citrate, phosphate, sulphate, malate, malonate and succinate) was studied by means of turbidimetry and light scattering. Polyethyleneimine forms non-soluble complexes with these anions, which behave as a pseudo-polyampholyte with an isoelectrical pH value dependent on the type of anion. The effect of pH, polymer concentration and ionic strength on the non-soluble complexes formation was examined. The complex precipitation pH range was between 3.5 and 8.0 and also depended on the type of anion. The complex formation was inhibited by the ionic strength in agreement with the electrostatic mechanism of the non-soluble complex formation. Model proteins with isoelectric pH from 1 to 10 were assayed in orden to be precipitated by these complexes. It was found that the non-soluble polyethyleneimine-anion complexes have the property to precipitate macromolecules charged with an opposite electrical charge.     

Influence of synthesis conditions on the cross-link architecture of silsesquioxanes prepared by in situ water production route

The esterification reaction between carboxylic acids and alcohols has been used as the source of water for the hydrolysis-condensation reactions of difunctional and trifunctional organosilanes. Diphenylsilanediol (DPDO) has been reacted with methacryloxypropyltrimethoxysilane (MPTMS) and glycidoxypropyltrimethoxysilane (GPTMS) and the obtained products have been characterized by vibrational spectroscopy (FT-IR, FT-Raman) nuclear magnetic resonance (NMR) and gel permeation chromatography. The relation between water availability from the in situ water production process (ISWP) and silsesquioxanes morphology has been evaluated in the case of DPDO/MPTMS mixtures, changing molecular features of acids and alcohols. These measurements have shown that the pK of the carboxylic acid used in the esterification reaction has a valuable influence on the silanes cross-linking ability. Acids with low pK values and heteroatoms substituents favor the silane hydrolysis and allow the growth of high molecular weight species. Using acetic acid/ethanol mixture leads to the best results for DPDO/MPTMS reaction, with a narrow distribution of silsesquioxane species. Under the same conditions, the reaction of DPDO with GPTMS produces polymeric species and only avoiding the presence of the difunctional precursor allows to limiting the silsesquioxanes species growth.     

Electrochemical genosensors for the detection of Bonamia parasite. Selection of single strand-DNA (ssDNA) probes by simulation of the secondary structure folding

A post-PCR nucleic acid work by comparing experimental data, from electrochemical genosensors, and bioinformatics data, derived from the simulation of the secondary structure folding and prediction of hybridisation reaction, was carried out in order to rationalize the selection of ssDNA probes for the detection of two Bonamia species, B. exitiosa and B. ostreae, parasites of Ostrea edulis.Six ssDNA probes (from 11 to 25 bases in length, 2 thiolated and 4 biotinylated) were selected within different regions of B. ostreae and B. exitiosa PCR amplicons (300 and 304 bases, respectively) with the aim to discriminate between these parasite species. ssDNA amplicons and probes were analyzed separately using the “Mfold Web Server” simulating the secondary structure folding behaviour. The hybridisation of amplicon-probe was predicted by means of “Dinamelt Web Server”. The results were evaluated considering the number of hydrogen bonds broken and formed in the simulated folding and hybridisation process, variance in gaps for each sequence and number of available bases. In the experimental part, thermally denatured PCR products were captured at the sensor interface via sandwich hybridisation with surface-tethered probes (thiolated probes) and biotinylated signalling probes. A convergence between analytical signals and simulated results was observed, indicating the possibility to use bioinformatic data for ssDNA probes selection to be incorporated in genosensors.     

Urea-, squaramide-, and sulfonamide-based anion receptors: a thermodynamic study

In this work, we compare the anion-binding capabilities of receptors 1-5, characterized by similar structures, but possessing different hydrogen-bond-donor moieties (urea, squaramide, and sulfonamide). The presence of chromophoric substituents on the receptor's skeleton allowed the determination of association constants by performing UV/Vis titrations with the investigated anions on solutions of the receptors in pure acetonitrile. Additional quantitative studies of the anion-binding properties of receptors 1-5 were performed by isothermal titration calorimetry (ITC). The experimental results indicated that 1 and 2 formed 1:1 hydrogen-bonded complexes with most of the anions investigated. In the case of receptors 3-5, the formation of the 1:1 adduct was observed only with anions of low basicity (i.e., chloride, bromide, iodide, and hydrogen sulfate). With more basic anions (i.e., acetate and dihydrogen phosphate), both spectrophotometric and ITC titrations accounted for the deprotonation of the sulfonamide group, involving the formation of the conjugated base of the receptor.     

Development and validation of a high-performance liquid chromatography-tandem mass spectrometry method for the determination of the novel inhibitor of angiogenesis E-3810 in human plasma and its application in a clinical pharmacokinetic study

E-3810, 6-[[7-[(1-aminocyclopropyl)methoxy]-6-methoxy-4-quinolyl]oxy]-N-methyl-naphthalene-1-carboxamide, is a novel, potent, dual inhibitor of vascular endothelial growth factor and fibroblast growth factor receptors with antiangiogenic properties, now under early clinical evaluation as an anticancer agent. To investigate its clinical pharmacokinetics, a high-performance liquid chromatography-tandem mass spectrometry method was developed and validated to measure the drug in human plasma on the basis of simple protein precipitation with methanol after addition of deuterated E-3810 as internal standard. The method requires a small volume of sample (100 μl) and is rapid and selective, allowing good resolution of peaks in 5 min. It is sensitive, precise, and accurate, with overall precision, expressed as CV%, always ≤7.1%, accuracy in the range 92.7%-104.4%, and high recovery, close to 100%. The limit of detection is 0.01 ng/ml, and the lower limit of quantitation is 2.0 ng/ml. The assay was validated in the range from the lower limit of quantitation up to 500.0 ng/ml. This is the first method developed and validated for analyzing E-3810 in human plasma. The method has been successfully applied to study E-3810 pharmacokinetics in cancer patients with solid tumors who are receiving daily oral doses of the drug during the phase I trial.     

Pyridinium/urea-based anion receptor: methine formation in the presence of basic anions

The influence of the positively charged N-methylpyridinium substituent on the anion binding tendencies of urea-based receptors has been investigated by comparing molecules 1 and 2. These receptors have been studied in acetonitrile, by performing UV-vis. and (1)H NMR titrations with several anions. UV-vis. titrations have also been performed in DMSO, MeOH and CHCl(3)/CH(3)CN mixture (1/1, v/v). In the case of 1, the presence of both H-donor and H-acceptor groups (urea and pyridine, respectively) favours aggregation and the formation of dimers in the solid state. In solution, this tendency to aggregate reduces affinity for anions with respect to the similar urea-based receptor 3. The methylation of the pyridyl group of 1 leads to the pyridinium-containing receptor 2. The pyridinium positive charge enhances the acidity of urea and increases anion affinity, as evidenced by the comparison of the binding constants. Both receptors (1-2) form stable adducts with all investigated anions. However, in the case of 2, the formation of 1?:?1 adducts with basic anions, such as acetate and fluoride, is followed by a proton transfer process. Quite interestingly, deprotonation does not involve the urea group, thus preserving the 1?:?1 adduct, as demonstrated by the (1)H NMR measurements. In particular, the proton transfer process takes place at the methylene group linking the pyridinium fragment to the receptor's skeleton. (1)H NMR studies indicate the formation of a stable neutral methine species, characterised by the loss of aromaticity by the pyridyl ring. These results open new perspectives in the field of anion recognition, as receptor 2 may by applied to the monitoring of both bound anion (through the urea unit) and excess anion in solution (through the development of the yellow methine species).     

Molecular recognition probes of solvation thermodynamics in solvent mixtures

High-throughput UV-Vis experiments using four molecular recognition-based probes, made by the combination of two hydrogen bond acceptors, tri-n-butylphosphine oxide and N,N'-bis(2-ethylhexyl)acetamide, and two hydrogen bond donors, 4-phenylazophenol and 4-nitrophenol, were performed. The association constants for the 1 : 1 H-bond interaction involved in each probe system were measured in mixtures of a polar and non-polar solvent, di-n-hexyl ether and n-octane, respectively. Similar behaviour was observed for all four systems. When the concentration of the polar solvent was low, the association constant was identical to that observed in pure n-octane. However, once the concentration of the polar solvent exceeded a threshold, the association constant decreased linearly with the concentration of di-n-hexyl ether. Selective solvation in mixtures can be understood based on the competition between the multiple competing equilibria in the system. In this case, solvation thermodynamics are dominated by competition of the ether for solvation of H-bond donors. For the more polar solute, 4-nitrophenol, the selective solvation starts at lower concentrations of the polar solvent compared with the less polar solute, 4-phenylazophenol. Thus the speciation and hence the properties of systems containing multiple solutes and multiple solvents can be estimated from the H-bond properties and the concentrations of the individual functional groups.     

The solution stability of copper(I) and silver(I) complexes with N-heterocyclic carbenes

The tris-benzimidazolium cage LH(3)(3+), in MeCN solution, in the presence of OH(-), forms with Cu(I) and Ag(I) ions complexes of formula [M(I)(LH)](2+), in which each metal is linearly coordinated by two carbenes and one imidazolium N-H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [M(I)(LH)](2+) complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with Cu(I) and Ag(I) with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH(+), was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of Ag(I) are more stable than those of Cu(I). A significant cooperative effect has been observed with the formation of the [Ag(I)Q(2)](+) complex.