Chemical Functionalisation of Vinyl Polymers to Obtain Heparin-Like Materials

Vinyl polymers such as poly(ethylene-co-vinyl alcohol) (EVAL) and polyallylamine (PALA) both commercially available were chemically modified by introduction of carboxylic and sulfonate groups to obtain polymeric materials with improved haemocompatibility. The introduction of carboxyl groups was carried out by reaction of EVAL's hydroxy groups with acrylonitrile followed by basic hydrolysis of  CN groups. Amino groups of PALA were transformed into sulfonate groups by reaction with pyridine-SO₃ complex. Influence of reagents molar ratio, temperature and reaction time on the carboxylation degree was evaluated. In particular, yields of 86% (EVAL-CN 0.52) and 30% (EVALCOOH 0.16) were obtained for the cyanoethylation and the hydrolysis reaction of the  CN groups, respectively, whereas a sulfonation of 24% of the PALA amino groups was found. The functionalised polymers were characterized by physicochemical measurements. Preliminary biological tests proved the importance of strong acidic groups on the anticoagulant properties of the polymeric materials.     

A Novel qNMR Application for the Quantification of Vegetable Oils Used as Adulterants in Essential Oils

Essential oils (EOs) are more and more frequently adulterated due to their wide usage and large profit, for this reason accurate and precise authentication techniques are essential. This work aims at the application of qNMR as a versatile tool for the quantification of vegetable oils potentially usable as adulterants or diluents in EOs. This approach is based on the quantification of both ¹H and ¹³C glycerol backbone signals, which are actually present in each vegetable oil containing triglycerides. For the validation, binary mixtures of rosemary EO and corn oil (0.8–50%) were prepared. To verify the general feasibility of this technique, other different mixtures including lavender, citronella, orange and peanut, almond, sunflower, and soy seed oils were analyzed. The results showed that the efficacy of this approach does not depend on the specific combination of EO and vegetable oil, ensuring its versatility. The method was able to determine the adulterant, with a mean accuracy of 91.81 and 89.77% for calculations made on ¹H and ¹³C spectra, respectively. The high precision and accuracy here observed, make ¹H-qNMR competitive with other well-established techniques. Considering the current importance of quality control of EOs to avoid fraudulent practices, this work can be considered pioneering and promising.     

Relaxed Krylov subspace approximation

Recent computational and theoretical studies have shown that the matrix-vector product occurring at each step of a Krylov subspace method can be relaxed as the iterations proceed, i.e., it can be computed in a less exact manner, without degradation of the overall performance. In the present paper a general operator treatment of this phenomenon is provided and a new result further explaining its behavior is presented. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The electron transfer rate of large TPA based compounds: a joint theoretical and electrochemical approach

A series of triphenylamine (TPA) based compounds is investigated by means of density functional theory and cyclic voltammetry. Using the Nicholson's formalism, the measured deltaE(p) are correlated with B3LYP/6-31G* calculated reorganisation energies (lambda), elucidating the trend followed by the electron transfer rate of these compounds. Besides the direct dependency upon the dimension of the cationic fragment contributing to the hole stabilisation, the lambdas are tuned by the symmetry local to the TPA units, as evidenced by the structural relaxation of the cations. MDTAB shows the interesting combination of low ionisation potential (IP) and low lambda. This can make this compound interesting for practical applications in organic light emitting diode (OLEDs) devices, due to the direct correlation of the IP and lambda with the hole transfer efficiency to the anode, along with the hole mobility.     

Lewis acid-promoted synthesis and reactivity of beta-O-benzylhydroxylamino imides derived from D-glyceraldehyde

This paper describes the synthesis and use of beta-hydroxylamino imides derived from D-glyceraldehyde possessing a number of reactive sites that operate synergistically or alternatively to bring about highly regio- and diastereoselective transformations to give an optically pure aziridine-2-imide, a dihydro pyrimidine-2,4-dione, or a lactone. Both the syntheses, via the diastereoselective 1,4-conjugate addition of O-benzyl hydroxylamine to alpha,beta-unsaturated imides, and transformations can be simply tuned by choosing between different Lewis acids.     

Substituent effects on ionisation and (13)C NMR properties of some monosubstituted phenols A potentiometric, spectrophotometric and (13)C NMR study

The pK(a) values of ionisation of a set of phenols ortho, meta and para substituted are studied by spectrophotometry and (13)C NMR spectroscopy. A dual substituent analysis of equilibrium and NMR results, according to the Swain and Lupton procedure, is presented. The results of this analysis allow the assignment of the contribution of field and resonance contributions, both on equilibrium constants and chemical shifts.     

'On-off-on' fluorescent indicators of pH windows based on three separated components

'On-off-on' fluorescent indicators for pH windows are obtained with ternary systems in which the three separated components are Cu2+, a tetraaza ligand and the fluorophore Coumarin 343: protonation of Coumarin 343, its coordination to Cu2+ and its displacement from Cu2+ by OH- give an inverse bell-shaped variation of emission with pH.     

Enantioselective separation of rivastigmine by capillary electrophoresis with cyclodextrines

Different beta-cyclodextrines (beta-cyclodextrin, heptakis (2,3,6-tri-O-methyl)-beta-cyclodextrin, hydroxypropyl-beta-cyclodextrin, and sulfated beta-cyclodextrin) were investigated as additives for the enantioselective separation of the R-form from rivastigmine ((S)-N-ethyl-3-[(1-dimethylamino) ethyl]-N-methyl-phenyl carbamate), contained as impurity in this drug, which is used for the treatment of Alzheimer's disease. Electrophoresis was performed in an acidic background electrolyte (triethanolammonium phosphate, 75 mM, pH 2.5) with various concentrations of the additives. The electrophoretic mobilities measured are typical functions of the additive concentrations, with complex constants (obtained by fitting the appropriate binding curve on the data) ranging between about 180 and 770 M(-1). Best separation was obtained with 7.5 mM beta-cyclodextrin, with the R-enantiomer as impurity migrating before the main S-compound. Intra- and interday reproducibility (n = 6 and 18, respectively) of migration time and peak area was in the low percentage range, linearity of the calibration line for the quantitation of the impurity in the range between 2.3 and 50 microg/ml, expressed by the linear correlation coefficient, was 0.9998. The limits of detection and quantitation, respectively, were 0.7 and 2.3 microg/ml, corresponding to 0.05 and 0.15%, m/m of the R- relative to the S-compound. Analysis can be carried out at 18 degrees C in less than 19 min.     

Monitoring the redox-driven assembly/disassembly of a dicopper(I) helicate with an auxiliary fluorescent probe

The assembly/disassembly of a dicopper(I) helicate with a bis-bidentate imine-quinoline ligand is driven by the Cu(II)/Cu(I) redox change and is signaled by a fluorescent probe bearing a -COO(-) group (coumarine 343). The probe coordinates the Cu(II) center of the monomeric complex, which quenches its emission (fluorescence off), and is released upon reduction and formation of the Cu(I) helicate (fluorescence on).