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The study by means of 'H nuclear magnetic resonance (NMR) of the histidines of phospholipase A2 isolated from porcine, bovine and equine pancreas is reported. Assignment of the histidine resonances was achieved by comparison of different enzymes and the use of paramagnetic probes. pH titration curves for various histidyl resonances were obtained and compared in the presence and absence of calcium. Calcium is shown to lower the pKa of the active site histidine. The NMR results are compared with the known X-ray three-dimensional structure for the bovine enzyme.Phospholipase A2 is an enzyme, present in high concentrations in snake and bee venoms and in mammalian pancreas, which catalyses the hydrolysis of the fatty acid ester bond at the 2-position of 3-snphosphoglycerides [l]. The enzyme is secreted by the pancreas as a zymogen and zymogens from a number of mammals have been purified. The amino acid sequences of porcine, bovine and equine pancreatic phospholipase A2 and of the corresponding zymogens have been determined [2-41. From the porcine pancreas an isoproenzyme occurring in a 5:95 ratio compared with the more abundant zymogen was isolated [5] and its amino acid sequence determined [6]. The zymogens are converted into the active enzymes by the action of trypsin which splits a peptide bond Arg-Ala with the removal of the N-terminal heptapeptide from the molecule [7]. In Table 1 the primary structures of equine, bovine and porcine phospholipases are shown. The three-dimensional structure and disulfide bond connections of the bovine enzyme have recently been elucidated [8].Inactivation studies using p-bromophenacyl bromide [9] have shown that His-48 is involved in the active site of phospholipase A2. This active site was also found to pre-exist for a main part already in the zymogen and, in fact, both zymogen and enzyme hydrolyse monomeric substrates at comparable rates. The rate of hydrolysis is dramatically increased in the case of the enzyme if the substrate is in micellar form [lo]. Calcium ions are specifi-Abbreviarions NMR, nuclear magnetic resonance; ppm, partsEnzyme Phosphohpase A2 (EC 3 1 1 4).per million cally required for catalytic activity and bind in a 1 : l molar ratio to the active enzyme and to the zymogen with similar affinities and producing similar conformational changes. His-48 was shown to be located very close to the metal ion binding site Proton nuclear magnetic resonance is the technique of choice for the study of proteins in detail in aqueous solution. In general, the low-field or aromatic region of a protein 'H NMR spectrum is the easiest to interpret because, apart from the exchangeable protons, only histidyl, tyrosyl, phenylalanyl and tryptophanyl residues give resonances in that region. The exchangeable protons can be removed by working in 2H20. The application of this technique to obtain knowledge of the environments and pKa values of histidyl groups in various proteins has been particularly successful due to the fact that the C-2 proton resonances of histidyl residues normally li...

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The microwave-assisted catalytic hydrogenation of the isoxazolidine-fused meso-tetrakis(pentafluorophenyl)chlorin afforded directly a mono-annulated chlorin with a singular 1-methyl-2,3-dihydro-1H-benzo[b]azepine ring that resulted from the cleavage of the isoxazolidine N-O bond followed by an intramolecular nucleophilic aromatic substitution of an o-F atom. The subsequent treatment of the mono-annulated chlorin with NaH induced a second intramolecular nucleophilic aromatic substitution, generating a bis-annulated chlorin having an additional 2H-pyran ring.

Mixed bisadducts resulting from the sequential addition of a nitrone and an azomethine ylide to the porphyrin macrocycle were efficiently obtained, in a site selective approach.

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Poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable flexible, and tough polymer is herein used, for the first time, to encapsulate and protect isocyanate derivatives. Isocyanates are essential building blocks widely employed in the chemical industry for the production of high-performing materials. Microencapsulation of isocyanates eliminates the risks associated with their direct handling and protects them from moisture. In light of this, and having in mind eco-innovative products and sustainability, we present a straightforward process to encapsulate isophorone diisocyanate (IPDI) using this biodegradable polymer. Spherical and core-shell microcapsules (MCs) were produced by an emulsion system combined with the solvent evaporation method. The MCs present a regular surface, without holes or cracks, with a thin shell and high isocyanate loadings, up to 79 wt%. Additionally, the MCs showed very good isocyanate protection if not dispersed in organic or aqueous solutions. Effects of various process parameters were systematically studied, showing that a higher stirring speed (1000 rpm) and emulsifier amount (2.5 g), as well as a smaller PBAT amount (1.60 g), lead to smaller MCs and narrower size distribution.

TiO 2-P25 supported Pd/C (P25@Pd/C) composite was prepared by the solid state dispersion method. The prepared composite was characterized by XRD, Raman, PL, SEM and DRS measurements. The photocatalytic activity of the composite was tested towards Naphthol Blue Black (NBB) azo dye degradation under visible light. The photocatalytic activity of P25 was highly influenced by Pd/C. Almost complete degradation was achieved with P25@Pd/C in 120 min, and found to be more efficient when compared with pristine Degussa-P25. The composite was reused in four cycles without loss of activity. A mechanism was proposed for NBB degradation by P25@Pd/C composite under visible light.