Metalation of alkyl aryl sulfones: qualitative and quantitative product determination

The metalation of methyl phenyl sulfone (I) and methyl naphthyl sulfone (II) was investigated under a variety of conditions. The product species were determined qualitatively and quantitatively after characterization with some electrophilic agents. After the primary metalation at the methyl position, species of various metalation degrees were prsent simultaneously, including the 1,1,1-trimetalated derivatives. With high LiR/sulfone ratios, in addition to the products of the primary metalation, compounds arising from metalation of the aromatic ring were formed as well as those from reduction, cleavage, etc.     

Ethylene-butadiene copolymerization with three-component catalyst systems Al[N(CH3)2]3, Al(C2H5)Cl2 and vanadium chlorides

The ethylene butadiene copolymerization with systems of three components Al[N(CH₃)₂]₃, Al(C₂H₅)Cl₂ and VOCl₃ or VCl₄, is described. In the resulting copolymers, the butadiene units are substantially in trans-1,4 configuration. Although it is possible to obtain copolymers with a wide range of composition, attention was paid to products with a low content of unsaturation (less than 2% mole of butadiene). These copolymers are highly homogeneous. They show high crystallinity of the polyethylene type and they can be crosslinked with conventional sulphur recipes.     

Synthesis of unsymmetrical methylene derivatives of benzopyran‐4‐ones from mannich bases

The formation of methylene‐bis derivatives of benzopyran‐4‐ones from their Mannich bases was studied. On these grounds, unsymmetrical methylene derivatives have been synthesized by reacting Mannich bases of benzopyran‐4‐ones with structurally related compounds lacking the dialkylaminomethyl group.     

Effects of organic solvents on ultrafiltration polyamide membranes for the preparation of oil-in-water emulsions

Hydrophilic ultrafiltration membranes made of polyamide with molecular weight cutoff 10 and 50 kDa have been studied for the preparation of oil-in-water emulsions by a cross-flow membrane emulsification technique. Isooctane and phosphate buffer were used as disperse and continuous phase, respectively. The permeation of apolar isooctane through the polar hydrophilic membrane was achieved by pretreatment of membranes with a gradient of miscible solvents of decreasing polarity to remove water from the pores and replace it with isooctane. Four different procedures were investigated, based on the solvent mixture percentage and contact time with membranes. After pretreatment, the performance of the membranes in terms of pure isooctane permeate flux and emulsion preparation was evaluated. The influence of organic solvents on polyamide (PA) membranes has been studied by SEM analysis, which showed a clear change in the structure and morphology of the thin selective layers. The effects proved stronger for PA 10 kDa than for 50 kDa. In fact, similar pretreatment procedures caused larger pore size and pore size distribution for PA 10 kDa than for 50 kDa. The properties of emulsions in terms of droplet size distribution reflected the membrane pore sizes obtained after pretreatment. The correlation between pore size and droplet size, for the physicochemical and fluid dynamic conditions used, has been evaluated.     

Syntheses and properties of ethylene sulphide-isobutylene sulphide copolymers and their unsaturated terpolymers

The synthesis with anionic catalysts and the characterization of ESIBS copolymer and ESIBSATE terpolymer are reported (ES, IBS, ATE and PS = ethylene sulphide, isobutylene sulphide, 3-allyloxy-1,2-epithiopropane and propylene sulphide respectively). For ESIBS copolymer with 35–55% ES, nearly amorphous structures, were obtained. Microstructures, investigated by ¹³C-NMR, have been compared with that of the ESPS copolymer; the ESIBS copolymer has greater blockiness than ESPS. Some preliminary results on the properties of ESIBSATE unsaturated terpolymer are also reported and compared with those of the known ESPSATE terpolymer. The good swelling values shown by the former are related to the possibility of obtaining amorphous structures with a high ES content.     

Bioelectrochemical Characterization of Horseradish and Soybean Peroxidases

Heme peroxidase are ubiquitous enzymes catalyzing the oxidation of a broad range of substrates by hydrogen peroxide. In this paper the bioelectrochemical characterization of horseradish peroxidase (HRP) and soybean peroxidase (SBP), belonging to class III of the plant peroxidase superfamily, was studied. The homogeneous reactions between peroxidases and some common redox mediators in the presence of hydrogen peroxide have been carried out by cyclic voltammetry. The electrochemical characterization of the reactions involving enzyme, substrate and mediators concentrations allowed us to calculate the kinetic parameters for the substrate–enzyme reaction (K_MS) and for the redox mediator–enzyme reaction (K_MM). A full characterization of the direct electron transfer kinetic parameters between the electrode and enzyme active site was also performed by opportunely modeling data obtained from cyclic voltammetry and square wave voltammetry experiments. The experimental data obtained with immobilized peroxidases show enhanced direct electron transfer and excellent electrocatalytical performance for H₂O₂. Despite the structural similarities and common catalytic cycle, HRP and SBP exhibit differences in their substrate affinity and catalytic efficiency. Basing on our results, it can be concluded that peroxidase from soybean represents an interesting alternative to the classical and largely employed one obtained from horseradish as biorecognition element of electrochemical mediated biosensors.     

Partially disposable biosensors for the quick assessment of damage in foodstuff after thermal treatment

A novel approach towards a quick, easy and reliable solution to the quite complex problems connected with the Amadori's compounds and furosine formation in several foodstuff is here proposed and based on enzymatic reactions, either as far as L-lysine release after partial hydrolysis from proteic material of the food matrix (bioavailable L-lysine), or as far as the determination of total and free L-lysine is concerned.The contribution proposes the use of specific L-lysine sensitive bioelectrodes for the evaluation of the possible heat damage through the rapid measure of L-lysine consumption. The L-lysine biosensor has been realized by immobilizing the enzyme L-lysine-α-oxidase (LOx) on an amperometric H₂O₂ sensitive electrode.The bioelectrode-enzymatic reaction arrangement allows to perform determinations of L-lysine and bioavailable L-lysine in foodstuff from different sources and after different thermal treatments in a very rapid inexpensive and reliable way in the range 1.0–33 ppm, with a limit of detection LOD = 0.5 ppm, so that a considerable number of samples can be easily monitored quickly and with very low costs.     

Interactions between carbonic anhydrase and some decarboxylating enzymes as studied by a new bioelectrochemical approach.

This work presents the results of a study, carried out by recently developed amperometric bioelectrodes, on the interactions between carbonic anhydrase (CA) and the decarboxylating enzymes arginine decarboxylase (ADC), L-lysine decarboxylase (LDC), and L-ornithine decarboxylase (ODC). These are all pyridoxal-phosphate dependent enzymes and catalyze the decarboxylation reaction of the respective amino acids, to give carbon dioxide and the corresponding diamine (agmatine, cadaverine, and putrescine, respectively). The rate of each decarboxylase catalyzed reaction was measured by monitoring the production of the respective diamine by a plant tissue diamino oxidase (DAO) based bioelectrode. DAO is the enzyme which catalyzes the oxidation of agmatine, cadaverine, and putrescine with the production of NH and H2O2. DAO-based bioelectrodes consist of an amperometric H2O2 electrode, coupled to the biocatalytic membrane formed by a whole plant tissue (lentil cotyledon) containing the enzyme DAO, immobilized on a dialysis membrane by polyazetidine prepolymer (PAP). The bioelectrodes were calibrated and characterized in standard solutions of agmatine, cadaverine, and putrescine. Kinetic studies to measure decarboxylase activity were performed in the presence of different concentrations of ADC, LDC, and ODC, resulting in a lowest detection limit of 10, 25, and 10 U l(-1), respectively. The effect of bovine CA II (bCAII) was evaluated in the presence of 500 U l(-1) of each decarboxylase, showing a marked increase of the rate of the decarboxylation reaction. These results suggest that (i) CA can be used to enhance the performance of decarboxylase-based biosensors, and (ii) it possibly plays further physiological roles, acting synergistically, at specific cellular and subcellular sites, with low-activity decarboxylating enzymes.     

The Structure of the Elusive Urease–Urea Complex Unveils the Mechanism of a Paradigmatic Nickel‐Dependent Enzyme

Urease, the most efficient enzyme known, contains an essential dinuclear Ni^II cluster in the active site. It catalyzes the hydrolysis of urea, inducing a rapid pH increase that has negative effects on human health and agriculture. Thus, the control of urease activity is of utmost importance in medical, pharmaceutical, and agro‐environmental applications. All known urease inhibitors are either toxic or inefficient. The development of new and efficient chemicals able to inhibit urease relies on the knowledge of all steps of the catalytic mechanism. The short (microseconds) lifetime of the urease–urea complex has hampered the determination of its structure. The present study uses fluoride to substitute the hydroxide acting as the co‐substrate in the reaction, preventing the occurrence of the catalytic steps that follow substrate binding. The 1.42 Å crystal structure of the urease–urea complex, reported here, resolves the enduring debate on the mechanism of this metalloenzyme.