Detection of fragmented genomic DNA by PCR-free piezoelectric sensing using a denaturation approach

Label-free and real-time DNA sequence detection in PCR-amplified DNA samples can now be achieved by different approaches. On the contrary, only few works have been reported dealing with direct sequence detection in nonamplified genomic DNA. Here, a piezoelectric biosensor for direct detection of sequences in nonamplified genomic DNA is described. The system relies on real-time and label-free detection of the hybridization reaction between an immobilized probe and the complementary sequence in solution. The DNA probe is immobilized on the sensing surface (10 MHz quartz crystals), while the complementary sequence is present in the genomic DNA, previously fragmented with restriction enzymes.     

Kinetics and Thermodynamics of Binding of a Model Tripeptide to Teicoplanin and Analogous Semisynthetic Antibiotics

The thermodynamics and kinetics of binding of model tripeptides epsilon-N-acetyl-alpha-N-dansyl-L-Lys-D-Ala-D-Ala (ADLAA) or alpha-N,epsilon-N-diacetyl-L-Lys-D-Ala-D-Ala (AALAA) to teicoplanin (1a) and a series of semisynthetic derivatives with (1b-f) or devoid of (2a-g) the glycidic side arms and modified at the terminal amino acids of the peptide backbone have been studied by fluorescence or UV spectroscopy. The binding process is suggested to occur via a two-step mechanism. The first, fast process is likely governed by an electrostatic interaction between the C- and N-termini of the peptide chain of the substrate and of the antibiotic, respectively, while the second slower one, accounts for the formation of the hydrogen bonds responsible of the major contribution to the overall binding energy. The binding constants with all modified derivatives are smaller than that with native teicoplanin. Larger modification of the overall binding constant are observed when the sugar residues are removed and, to a lower extent, when the N-terminus of the peptide chain is acylated. The kinetic process is very little affected by the modifications introduced.     

Synthesis of Highly Fluorinated Chloroformates and Their Use as Derivatizing Agents for Hydrophilic Compounds and Drinking‐Water‐Disinfection By‐Products

A rapid, safe, and efficient procedure was developed to synthesize, on a small scale, fluorinated chloroformates often required to perform analytical derivatizations. This new family of agents allows straightforward derivatization of highly polar compounds (with multiple hydroxy, carboxy, and amino substituents) in the aqueous phase, compatible with GC and GC/MS analysis. A goal of this work was to develop a derivatization procedure that would enable the detection and identification of highly polar disinfection by‐products in drinking water.     

Competitive Complexation by Ligand and Solvent: Polarographic Characterization of ATRP Catalyst Polyamine–Copper Complexes in Acetonitrile + Water Mixed Solvents

In the Atom Transfer Radical Polymerization (ATRP) technique, the suggested polymerization scheme is pivoted by a metal complex acting as a redox catalyst able to coordinate with the incipient radicals. The development of an a priori criterion of choice of the best (complex + solvent) combination is one of the current topics in this field. In this context we performed polarographic investigations on copper complexes with multidentate amino ligands (TMEDA and Me₆TREN, plus acetonitrile as a reference) in water and in water + acetonitrile mixed solvents. In the latter case we took into account the competition between the co-solvent acetonitrile [a weaker ligand, but concentrated, selectively stabilizing Cu(I)], and the polyamine [a stronger ligand, but diluted, preferentially stabilizing Cu(II)], achieving further stabilization of the complexed copper, with a narrow potential range of stability as Cu(I), which is modulated through the acetonitrile/polyamine ratio. An interpretative scheme is presented.     

Determination of triazines and dinitroanilines in waters by high-performance liquid chromatography after solid-phase extraction

A rapid and selective method for the simultaneous determination of triazines and dinitroanilines in real water matrices is suggested based on a preliminary adsorption on an RP-18 cartridge, an elution step using acetonitrile and HPLC separation with a Lichrosorb RP- Select B column and UV detection. The washing step cartridge is critical for triazines: terbutryn is eluted with quantitative recovery only after washing with an NH₃ solution. The degree of enrichment of the compounds studied has been determined: triazine recoveries are quantitative, while dinitroaniline recoveries are between 66% and 78% at the lowest fortification level. The detection limits for the ten herbicides are in the range 0.03-0.1 μg/l. The analysis time is 2 h.     

HPLC determination of catabolic amines in silage using their dansyl derivatives and an electrochemical detector

Summary The use of the electrochemical detector (EC) in the high performance liquid chromatography (HPLC) of dansyl derivatives of biogenic amines is reported. Isocratic and gradient elution patterns of synthetic mixtures of putrescine, cadaverine, 1,6-diaminohexane, tryptamine, histamine, tyramine, spermine and spermidine on a reversed phase column are shown. Hydrodynamic voltammograms of standard compounds are presented. The detection limits of the EC are compared with those of ultraviolet and spectrofluorimetric detectors. A chromatographic profile of amines from the proteolytic catabolism of maize silage byClostridia is shown.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Estimation of measurement uncertainty for the determination of aflatoxin M1 in milk using immunoaffinity clean-up procedures

A measurement uncertainty estimated for aflatoxin M₁ determination in milk sample has been calculated using data generated from analytical method validation studies. The protocol adopted is described in detail in document LGC/VAM/1998/088. The uncertainty budget was based on precision, trueness and ruggedness data. The individual contributions are described in detail. The expanded uncertainty for aflatoxin M ₁ at a concentration of 20 ng L⁻¹ was estimated as 2.81 ng L⁻¹. This was calculated using a coverage factor of two which gives a level of confidence of approximately 95%. Presented at AOAC Europe / Eurachem Symposium March 2005, Brussels, Belgium     

Inclusion Complexation of Carbaryl and β-Cyclodextrin in Solution and in the Solid State

This study was carried out with the aim ofinvestigating the interactions between-cyclodextrin and carbaryl, a carbamatepesticide, and their effect on some physico-chemicalproperties of carbaryl, such as aqueous solubility andlipophilicity. The interactions between carbaryl and-cyclodextrin were thoroughly investigated bothin solution and in the solid state. The effect of-cyclodextrin on the aqueous solubility ofcarbaryl was evaluated by the phase solubility method.The amount of carbaryl dissolved increased linearlywith the addition of -cyclodextrin according toan A_L type plot and without precipitation of thecomplex. The apparent stability constant of thecomplex was 289 ± 21 M^-1, assuming a 1 : 1stoichiometry; this value was confirmed by a methodbased on circular dichroism measurements.Equimolar carbaryl/-cyclodextrin solid systemswere prepared by physical-mixing and freeze-drying,and fully characterised by Differential ScanningCalorimetry, X-ray powder diffractometry and FourierTransform Infra-Red analysis. The results of the solidstate study demonstrated that the freeze-drying methodyields a system with a high degree of amorphisationand yields an inclusion complex.The dissolution profile of the pesticide was affectedby the physico-chemical properties of each solidsystem, the freeze-dried form dissolving more rapidly. However, the physical association of-cyclodextrin and carbaryl enhanced the aqueoussolubility of the insecticide as well.     

Application of special reduction procedures to metrological data

To improve the reduction of metrological data, that are typically grouped in series and cannot be considered as replicated data, a modelling procedure has been obtained by adding to the model representing the physical behaviour, common to all data, a specific term for each series. Such a procedure combines both the advantages of preserving the individuality of each series and of improving the variance estimate which arises from fitting the overall data. A non-parametric bootstrap method for the error analysis has been developed, which does not imply the assumption of the Normal distribution in the least squares estimation. Two examples of application of the method to thermodynamic data series are reported.