Synthesis and reactivity of 2-(porphyrin-2-yl)-1,3-dicarbonyl compounds

A simple and efficient procedure for the synthesis of porphyrins bearing 1,3-dicarbonyl moieties at the β-position is described. The new compounds were further functionalized and new derivatives containing an heterocyclic ring, an ethyl acetate residue or a 2-oxopropyl group at the β-position have been obtained.     

Geminate rebinding in R-state hemoglobin: kinetic and computational evidence for multiple hydrophobic pockets

Biphasic geminate rebinding of CO to myoglobin upon flash photolysis has been associated to ligand distribution in hydrophobic cavities, structurally detected by time-resolved crystallography, xenon occupancy, and molecular simulations. We show that the time course of CO rebinding to human hemoglobin also exhibits a biphasic geminate rebinding when the protein is entrapped in wet nanoporous silica gel. A simple branched kinetic scheme, involving the bound state A, the primary docking site C, and a secondary binding site B was used to calculate the microscopic rates and the time-dependent population of the intermediate species. The activation enthalpies of the associated transitions were determined in the absence and presence of 80% glycerol. Potential hydrophobic docking cavities within the alpha and beta chains of hemoglobin were identified by computational modeling using xenon as a probe. A hydrophobic pocket on the distal side of the heme, corresponding to Xe4 in Mb, and a nearby site that does not have a correspondence in Mb were detected. Neither potential xenon sites on the proximal side nor a migration channel from the distal to proximal site was located. The small enthalpic barriers between states B and C are in very good agreement with the location of the xenon sites on the distal side. Furthermore, the connection between the two xenon sites is relatively open, explaining why the decreased mobility of the protein with viscosity only slightly perturbs the energetics of ligand migration between the two sites.     

Determination of chlorite in drinking water by differential pulse voltammetry on graphite

The chlorite ion is an unavoidable by-product of the disinfection of drinking water by means of chlorine dioxide. The maximum concentration values of chlorite accepted in many countries regulations range from 0.2 to 1.0 mg L^–1. A simple, inexpensive and quickly set up voltammetric procedure for the on-site determination of chlorite in drinking water networks is described. This procedure is suitable for the whole range of applications in drinking water plants. A useful cell for on-field analysis has been developed. Surface morphology and behaviour of carbon-based working electrodes have been investigated by voltammetry and atomic force microscopy (AFM). Actual samples of different types of water networks have been analysed for chlorite concentration.     

Fine tuning the structure of the Cu2+ complex with the prion protein chicken repeat by proline isomerization

The interaction between the single hexarepeat unit of chicken prion protein [ChPrP(54-59)] and Cu(II) was investigated by NMR, finding different coordination modes for the trans/trans and cis/trans isomers.     

The dimeric and tetrameric octarepeat fragments of prion protein behave differently to its monomeric unit

Potentiometric and spectroscopic data have shown that octarepeat dimer and tetramer are much more effective ligands for Cu(II) ions than simple octapeptide. Thus, the whole N-terminal segment of prion protein due to cooperative effects, could be more effective in binding of Cu(II) than simple peptides containing a His residue. The gain of the Cu(II) binding by longer octarepeat peptides derives from the involvement of up to four imidazoles in the coordination of the first Cu(II) ion. This type of binding increases the order of the peptide structure, which allows successive metal ions for easier coordination.     

Screening of acetogenin-producing plants in Brazilian flora

The acetogenins are strongly bioactive natural compounds present in the bark, roots, leaves, and seeds of manyAnnonaceae plants. They are modified fatty acids and their cytotoxicities have been determined for different biological models including the in vitro growth inhibition of several human cancer cell lines. Very low acetogenin yield (< 0.1 g%) has been found previously in native phytobiomass, and we have now investigated the nonpredatory exploitation of the seeds as acetogenin sources characterizing the seed triacylglycerols (dominant fraction; > 90% of the whole lipid extracts) as potential valuable by-products.     

Removal of Mn(II) and Cd(II) from wastewaters by natural and modified clays

The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents, by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q ₀ parameter, which is related to the sorption capacity, corresponding to 6.3 mg g^{− 1} for K-10/Cd(II), 4.8 mg g^{− 1} for K-10/Mn(II), 11.2 mg g^{− 1} for NT-25/Cd(II) and 6.0 mg g^{− 1} for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction, a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L^{− 1} solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent.