Voltammetric Sensing of Mercury and Copper Cations at Poly(EDTA‐like) Film Modified Electrode

Complexing polymer‐coated electrodes have been synthesized by oxidative electropolymerization of ethylenediamine tetra‐N‐(3‐pyrrole‐1‐yl)propylacetamide (monomer L ). The presence of four polymerizable pyrrole fragments on the same EDTA skeleton was thought to confer enhanced rigidity and controlled dimensionality to the resulting complexing materials, which were used for the electrochemical detection of Hg(II), Cu(II), Pb(II) and Cd(II) ions by means of the chemical preconcentration‐anodic stripping technique. The polyamide electrode material showed particularly a significant selectivity towards mercury ions, even in the presence of a large excess of other metal cations. Moreover, the use of imprinted polymer‐coated electrodes prepared by electropolymerization of L in the presence of metal cations turned out to significantly improve the detection limits, down to 5×10^?10 mol L^?1 for Hg(II) and Cu(II) species.     

Hydrolytic and photoinduced degradation of tribenuron methyl studied by HPLC-DAD-MS/MS

The paper studies, with the help of HPLC-DAD-MS/MS technique, the hydrolytic and photoinduced degradation processes that take place in aqueous solutions of tribenuron methyl, both when preserved in the dark and when undergoing solar box irradiation under conditions that simulate sun light. The results indicate that the degradation products formed by hydrolysis alone and by photoirradiation are the same, but kinetics of the hydrolysis reaction is much slower. The degradation products are identified as 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (P1), methyl 2-aminosulfonylbenzoate (P2), and saccharin (P3) and quantified. Ecotoxicological biotests performed on 0.1 microg L(-1) photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization.     

catena-Poly­[[di­aqua(1,10-phen­anthroline-N,N′)­manganese(II)]-μ-(thiosulfato-O:S)] and bis(2,2′-bipyridyl-N,N′)(tetra­thionato-O,O′)manganese(II)

The structures of [Mn(S₂O₃)₂(C₁₂H₈N₂)(H₂O)₂] and [Mn(S₄O₆)(C₁₀H₈N₂)₂] are presented. The former consists of pairs of polymeric chains formed by manganese polyhedra bridged by bidentate thio­sulfate anions, which are in turn related to each other by a pseudo-twofold screw axis. The latter has crystallographic twofold symmetry and consists of monomers in which manganese displays its typical octahedral coordination provided by the bidentate bites of two bi­pyridine bases and a tetra­thionate anion, which is, to our knowledge, the first chelating tetra­thionate to be reported in the literature.     

N-propargylic beta-enaminones: common intermediates for the synthesis of polysubstituted pyrroles and pyridines.

N-Propargylic beta-enaminones have been used as common intermediates for the synthesis of polysubstituted pyrroles and pyridines. Best results have been obtained using DMSO as solvent. In the presence of Cs(2)CO(3) N-propargylic beta-enaminones are cyclized to pyrroles in good to high yields, whereas omitting bases and using CuBr leads to the selective formation of pyridines.     

Carbohydrate-Based Scaffolds for the Generation of Sortiments of Bioactive Compounds

Summary.  The polyfunctionality and conformational rigidity of carbohydrates make this class of compounds ideal scaffolds for the production of sortiments¹ of bioactive compounds. Examples of carbohydrate-derived peptidomimetics of biological interest, such as somatostatin agonists and integrin antagonists, are presented. In order to have access to solid phase supported sortiments of compounds, orthogonally protected or unprotected carbohydrates were linked to polymers and reacted in the solid phase employing different regioselective strategies. Original bicyclic and tricyclic glycidic scaffolds were easily obtained starting from natural sugars such as D-arabinose and D-fructose. Manipulation of these conformationally blocked compounds afforded different carbohydrate-based derivatives, among which azidoacids are useful precursors of β-turn peptidomimetics. Received September 10, 2001. Accepted November 2, 2001     

EEG Fractal Analysis Reflects Brain Impairment after Stroke

Stroke is the commonest cause of disability. Novel treatments require an improved understanding of the underlying mechanisms of recovery. Fractal approaches have demonstrated that a single metric can describe the complexity of seemingly random fluctuations of physiological signals. We hypothesize that fractal algorithms applied to electroencephalographic (EEG) signals may track brain impairment after stroke. Sixteen stroke survivors were studied in the hyperacute (<48 h) and in the acute phase (∼1 week after stroke), and 35 stroke survivors during the early subacute phase (from 8 days to 32 days and after ∼2 months after stroke): We compared resting-state EEG fractal changes using fractal measures (i.e., Higuchi Index, Tortuosity) with 11 healthy controls. Both Higuchi index and Tortuosity values were significantly lower after a stroke throughout the acute and early subacute stage compared to healthy subjects, reflecting a brain activity which is significantly less complex. These indices may be promising metrics to track behavioral changes in the very early stage after stroke. Our findings might contribute to the neurorehabilitation quest in identifying reliable biomarkers for a better tailoring of rehabilitation pathways.     

Effects of pH and Carbon Source on <Emphasis Type="Italic">Synechococcus</Emphasis> PCC 7002 Cultivation: Biomass and Carbohydrate Production with Different Strategies for pH Control

Synechococcus PCC 7002 is an interesting species in view of industrial production of carbohydrates. The cultivation performances of this species are strongly affected by the pH of the medium, which also influences the carbohydrate accumulation. In this work, different methods of pH control were analyzed, in order to obtain a higher production of both Synechococcus biomass and carbohydrates. To better understand the influence of pH on growth and carbohydrate productivity, manual and automatic pH regulation in CO₂ and bicarbonate system were applied. The pH value of 8.5 resulted the best to achieve both of these goals. From an industrial point of view, an alternative way to maintain the pH practically constant during the entire period of cultivation is the exploitation of the bicarbonate-CO₂ buffer system, with the double aim to maintain the pH in the viability range and also to provide the amount of carbon required by growth. In this condition, a high concentration of biomass (6 g L^?1) and carbohydrate content (around 60 %) were obtained, which are promising in view of a potential use for bioethanol production. The chemical equilibrium of C-N-P species was also evaluated by applying the ionic balance equations, and a relation between the sodium bicarbonate added in the medium and the equilibrium value of pH was discussed.     

Immobilization and Stabilization of Beta-Xylosidases from Penicillium janczewskii

β-Xylosidases are critical for complete degradation of xylan, the second main constituent of plant cell walls. A minor β-xylosidase (BXYL II) from Penicillium janczewskii was purified by ammonium sulfate precipitation (30% saturation) followed by DEAE-Sephadex chromatography in pH 6.5 and elution with KCl. The enzyme presented molecular weight (MW) of 301 kDa estimated by size exclusion chromatography. Optimal activity was observed in pH 3.0 and 70–75 °C, with higher stability in pH 3.0–4.5 and half-lives of 11, 5, and 2 min at 65, 70, and 75 °C, respectively. Inhibition was moderate with Pb⁺² and citrate and total with Cu⁺², Hg⁺², and Co⁺². Partially purified BXYL II and BXYL I (the main β-xylosidase from this fungus) were individually immobilized and stabilized in glyoxyl agarose gels. At 65 °C, immobilized BXYL I and BXYL II presented half-lives of 4.9 and 23.1 h, respectively, therefore being 12.3-fold and 33-fold more stable than their unipuntual CNBr derivatives (reference mimicking soluble enzyme behaviors). During long-term incubation in pH 5.0 at 50 °C, BXYL I and BXYL II glyoxyl derivatives preserved 85 and 35% activity after 25 and 7 days, respectively. Immobilized BXYL I retained 70% activity after 10 reuse cycles of p-nitrophenyl-β-D-xylopyranoside hydrolysis.

     

Synthesis and biological evaluation of N-thia-carba-thymidine as an antiherpetic agent

As a continuation of our project aimed at the search for new antiviral agents, the synthesis and biological evaluation of N-thia-carba-thymidine ((1R,2S,4S,5S)-5-methyl-1-{6-thia-4-hydroxy-5-[(hydroxy)-methyl]bicyclo[3.1.0]hex-2-yl}-1,3-dihydropyrimidine-2,4-dione; compound 8) was carried out employing the carbocyclic enantioenriched intermediate (1R,4S)-4-phenylmethoxy-3-[(phenylmethoxy)methyl]cyclopent-2-en-1-ol, which in turn was prepared from (3R,4S) phenylmethoxy-3-[(phenylmethoxy)methyl]-cyclopent-1-ene. The title compound resulted to be a very potent antiherpetic agent exhibiting a similar potency to acyclovir as shown. The synthetic approach to obtain this carbanucleoside required a novel strategy to introduce a thiirane group fused to a functionalized five-membered ring.     

Biradicaloid Character of Thiophene‐Based Heterophenoquinones: The Role of Electron–Phonon Coupling

The quinoidal versus biradicaloid character of the ground state of a series of thiophene‐based heterophenoquinones is investigated with quantum‐chemical calculations. The role of the ground‐state electronic character on molecular structure and vibrational properties is emphasized. The vibrational activities are experimentally determined and their analysis is performed by taking advantage of the definition of a collective vibrational coordinate (the