37 research outputs found
Comportamento hidrológico de bacias hidrográficas: integração de métodos e aplicação a um estudo de caso
Bioactivity of the organic extracts of Annona vepretorum on Tetranychus urticae (Acari: Tetranychidae)
Importantes caracterÃsticas de chuva para a conservação do solo e da água no municÃpio de São Manuel (SP)
Efeito da pimenta rosa associada a diversas dosagens de antibióticos em frangos de corte
Krigagem e inverso do quadrado da distância para interpolação dos parâmetros da equação de chuvas intensas
Physicochemical properties and antioxidant capacity of propolis of stingless bees (Meliponinae) and Apisfrom two regions of Tocantins, Brazil
Sistemas produtivos de caprinocultura leiteira no semiárido nordestino: controle integrado das parasitoses gastrointestinais visando contornar a resistência anti-helmÃntica
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Bis- and tris-(methylphosphonic) acid derivatives of a 14-membered tetraazamacrocycle containing pyridine: synthesis, protonation and complexation studies
Two N-methylphosphonic acid derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized, H4L1 and H6L2. The protonation constants of these compounds and the stability constants of complexes of both ligands with Ni2+, Cu2+ and Zn2+ were determined by potentiometric methods at 298 K and ionic strength 0.10 mol dm(-3) in NMe4NO3. The high overall basicity of both compounds is ascribed to the presence of the phosphonate arms. H-1 and P-31 NMR spectroscopic titrations were performed to elucidate the sequence of protonation, which were complemented by conformational analysis studies. The complexes of these ligands have stability constants of the order of or higher than those formed with ligands having the same macrocyclic backbone but acetate arms. At pH = 7 the highest pM values were found for solutions containing the compound with three acetate groups, followed immediately by those of H6L2, however, as expected, the increasing pH favours the complexes of ligands containing phosphonate groups. The single-crystal structure of Na-2[Cu(HL1)]NO3.8H(2)O has shown that the coordination geometry around the copper atom is a distorted square pyramid. Three nitrogen atoms of the macrocyclic backbone and one oxygen atom from one methylphosphonate arm define the basal plane, and the apical coordination is accomplished via the nitrogen atom trans to the pyridine ring of the macrocycle. To achieve this geometric arrangement, the macrocycle adopts a folded conformation. This structure seems consistent with Uv-vis-NIR spectroscopy for the Ni2+ and the Cu2+ complexes and with the EPR for the latter