On-line preconcentration of mercury by sorption on an anion-exchange resin loaded with 1,5-bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide and determination by cold-vapour inductively coupled plasma atomic emission

1,5-Bis[(2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex) has been used for the on-line preconcentration of mercury from biological samples and waters prior to its determination by inductively coupled plasma atomic emission spectroscopy. The metal was eluted from the column using a solution of 2 M HNO(3) and mixed on-line with SnCl(2). The optimum experimental conditions were evaluated for the continuous preconcentration of Hg, the direct generation of mercury vapour and the final determination of this element by ICP-AES. The enrichment, together with low blank levels of the optimized procedure, allow the simple determination of this toxic element at concentrations down to a few nanograms per milliliter. The proposed method has a linear calibration range 5-1000 ng ml(-1) of mercury, with a detection limit of 4 ng ml(-1) (S/N=3) and a sampling rate of 40 h(-1), investigated with a 9 ml sample volume. The precision of the method (evaluated as the relative standard deviation obtained after analyzing ten series of ten replicates) was +/-3.6% at the 10 ng ml(-1) level of Hg(II) and +/-1.3% at the 100 ng ml(-1) level. The accuracy of the method was examined by the analysis of certified reference materials.     

Determination of yeast assimilable nitrogen content in wine fermentations by sequential injection analysis with spectrophotometric detetection

An automated method for measuring the primary amino acid concentration in wine fermentations by sequential injection analysis with spectrophotometric detection was developed. Isoindole-derivatives from the primary amino acid were formed by reaction with o-phthaldialdehyde and N-acetyl- L-cysteine and measured at 334 nm with respect to a baseline point at 700 nm to compensate the observed Schlieren effect. As the reaction kinetic was strongly matrix dependent the analytical readout at the final reaction equilibrium has been evaluated. Therefore four parallel reaction coils were included in the flow system to be capable of processing four samples simultaneously. Using isoleucine as the representative primary amino acid in wine fermentations a linear calibration curve from 2 to 10 mM isoleucine, corresponding to 28 to 140 mg nitrogen/L (N/L) was obtained. The coefficient of variation of the method was 1.5% at a throughput of 12 samples per hour. The developed method was successfully used to monitor two wine fermentations during alcoholic fermentation. The results were in agreement with an external reference method based on high performance liquid chromatography. A mean-t-test showed no significant differences between the two methods at a confidence level of 95%.     

Conformational selection of glycomimetics at enzyme catalytic sites: experimental demonstration of the binding of distinct high-energy distorted conformations of C-, S-, and O-glycosides by E. Coli beta-galactosidases

We show that the conformational features of the molecular complexes of E. coli beta-galactosidase and O-glycosides may differ from those formed with closely related compounds in their chemical nature, such as C- and S-glycosyl analogues. In the particular case presented here, NMR and ab initio quantum mechanical results show that the 3D-shapes of the ligand/inhibitor within the enzyme binding site depend on the chemical nature of the compounds. In fact, they depend on the relative size of the stereoelectronic barriers for chair deformation or for rotation around Phi glycosidic linkage.     

Conformational differences between O- and C-glycosides: the alpha-O-man-(1-->1)-beta-Gal/alpha-C-Man-(1-->1)-beta-Gal case--a decisive demonstration of the importance of the exo-anomeric effect on the conformation of glycosides

The conformational behavior of alpha-O-Man-(1-->1)-beta-Gal (1) and its C-analogue (2) has been studied using J/NOE NMR data, molecular mechanics, molecular dynamics, and ab initio calculations. The population distribution around the glycosidic linkages of 1 and 2 is rather different, especially for the alpha-Man linkage. A lower limit for the exo-anomeric effect in water has been experimentally determined.     

Development of a Sequential Injection Analysis Device for the Determination of Total Polyphenol Index in Wine

A sequential injection analysis method is developed for the determination of the total polyphenol index in wines. The determination is based on the Folin-Ciocalteu reaction, which is monitored spectrophotometrically. Interactions between experimental variables and their optimal levels were investigated using factorial designs. The proposed system is fully computerised and is able to monitor polyphenol index in real samples of white, sweet and red wines. The calibration graph is linear from 5 to 200mg·L^–1 using Tannic acid as standard, with a detection limit of 3.2mg·L^–1. Interferences are studied. For validation purposes the proposed methodology was applied to the determination of the total polyphenol index in different types of wines and compared with earlier alternatives in order to assess their performance.     

Insights into the Dynamics and Molecular Recognition Features of Glycopeptides by Protein Receptors: The 3D Solution Structure of Hevein Bound to the Trisaccharide Core of N‐Glycoproteins

Protein‐carbohydrate interactions are at the heart of a variety of essential molecular recognition events. Hevein, a model lectin related to the superantigen family, recognizes the trisaccharide core of N‐glycoproteins ( 1 ). A combined approach of NMR spectroscopy and molecular modeling has permitted us to demonstrate that an Asn‐linked Man(GlcNAc)₂ ( 2 ) is bound with even higher affinity than (GlcNAc)₃. The molecular recognition process entails conformational selection of only one of the possibilities existing for chitooligosaccharides. The deduced 3D structure of the hevein/ 2 complex permits the extension of polypeptide chains from the Asn moiety of 2 , as well as glycosylation at Man O‐3 and Man O‐6 of the terminal sugar. Given the ubiquity of the Man(GlcNAc)₂ core in all mammalian N‐glycoproteins, the basic recognition mode presented herein might be extended to a variety of systems with biomedical importance.     

A Geometric Approach to Integrability of Abel Differential Equations

A geometric approach is used to study the Abel first-order differential equation of the first kind. The approach is based on the recently developed theory of quasi-Lie systems which allows us to characterise some particular examples of integrable Abel equations. Second order Abel equations will be discussed and the inverse problem of the Lagrangian dynamics is analysed: the existence of two alternative Lagrangian formulations is proved, both Lagrangians being of a non-natural class. The study is carried out by means of the Darboux polynomials and Jacobi multipliers.     

Analysis of the Composition of Lyophilisates Obtained from Aloe arborescens Gel of Leaves of Different Ages from Controlled Crops

The aim of the study is to evaluate the composition of lyophilisates obtained from Aloe arborescens leaf gel at the age of one to four years. The leaves were obtained from controlled crops, which allowed to exclude environmental factors as variables. It was confirmed that the lyophilisates obtained from different years of Aloe arborescens leaf gel varied in chromatographic analyses in terms of aloin A and aloenin A content (high-performance liquid chromatography with diode-array detection HPLC-DAD, high-performance liquid chromatography with tandem mass spectrometric detection HPLC-MS/MS). Similarly, while testing the phenolic acids and the sum of polyphenols content, differences in their levels in leaf gel lyophilisates from plants of individual years were observed (spectrophotometric method UV-VIS). The lyophilisate composition analysis showed that the one-year-old leaves were characterized by the highest content of aloin A and aloenin A. While the content of polyphenols, including phenolic acids, was higher in the leaves of older plants. The antioxidant potential of the tested lyophilisates was assessed simultaneously. Regardless of the research model used (CUPRAC, DPPH, ABTS), an antioxidant effect was noted for Aloe arborescens leaves.