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Showing papers by "Oscar E. Piro published in 2004"


Journal ArticleDOI
TL;DR: In this article, the new dioxo(semicarbazone)vanadium(V) complexes cis-VO2L have been synthesized, characterized by 1H and 13C NMR and FTIR spectroscopy and tested for bioactivity as potential insulin mimetic agents.
Abstract: The new dioxo(semicarbazone)vanadium(V) complexes cis-VO2L, where L = salicylaldehyde semicarbazone (L1), salicylaldehyde 4-n-butylsemicarbazone (L2), or salicylaldehyde 4-(2-naphthyl)semicarbazone (L3), have been synthesized, characterized by 1H and 13C NMR and FTIR spectroscopy and tested for bioactivity as potential insulin-mimetic agents. All dioxovanadium(V) complexes exhibited essentially no in vitro insulin-mimetic activity, but the VO2L2 complex developed activity in the presence of ascorbic acid, similar to that of vanadyl sulfate. The molecular structure of the novel complex VO2L1 has been solved by X-ray diffraction methods. It crystallizes in the tetragonal space group P42/n with a = 12.7674(7), c = 11.5308(5) A, and Z = 8. The vanadium atom is in a distorted square-pyramidal coordination, with L1 acting as a tridentate ligand through its azomethyne nitrogen atom, carbonyl oxygen atom and deprotonated phenol oxygen atom. The coordination sphere is completed by two oxo ligands at cis positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

71 citations


Journal ArticleDOI
TL;DR: In this paper, the tautomeric forms of benzimidazole N-oxide derivatives in solution were studied using nuclear magnetic resonance (NMR) techniques and further insight into the molecular structures was provided by t...
Abstract: The tautomeric forms of benzimidazole N-oxide derivatives in solution were studied using nuclear magnetic resonance (NMR) techniques. Further insight into the molecular structures was provided by t...

23 citations


Journal ArticleDOI
TL;DR: In this article, the crystal structure of the Zn(II) cations was determined by single crystal X-ray diffractometry and their thermal behavior investigated by means of thermogravimetric and differential thermal analytical techniques.
Abstract: The crystal structure of the complexes [Zn(sac)2(im)2] (1) and [Zn(sac)2(bzim)2]2⋅2Et-OH⋅H2O (2) (sac = saccharinate anion; im = imidazole; bzim = benzimidazole; EtOH = ethanol) was determined by single crystal X-ray diffractometry. Complex 1 crystallizes in the monoclinic P2 1/n space group with a = 9.1585(5), b = 16.4409(6), c = 15.0249(5) A, β = 94.079(1)°, and Z = 4, whereas complex 2 belongs to the triclinic space group P1 with a = 10.8500(2), b = 12.4860(2), c = 13.5640(3) A, α = 115,696(1), β = 100.086(1), γ = 102.169(1)°, and Z = 1. In both complexes, the Zn(II) cations are in a slightly distorted tetrahedral ZnN4 environment, coordinated to two saccharinate anions and to two imidazole (1) and to two benzimidazole (2) molecules. The complexes were also characterized by means of infrared spectroscopy and their thermal behavior investigated by means of thermogravimetric and differential thermal analytical techniques.

23 citations


Journal ArticleDOI
TL;DR: In this paper, a tetraester calix[4]arene derivative with mixed pendant arms in its lower rim was synthesized and characterized by 1 H and 1 3 C NMR.
Abstract: A new calix[4]arene derivative containing mixed pendant arms in its lower rim, 5,11,17,23-tetra-tert-butyl-[25,27-bis(ethylethanoate)oxy-26,28-bis(ethylthioethoxy)]-calix[4]arene, 1, has been synthesized and characterizedby 1 H and 1 3 C NMR. 1 H NMR data carried out in CDCl 3 , CD 3 CN, CD 3 OD, and C 3 D 7 NO suggest that as far as acetonitrile is concerned, the hydrophobic cavity is likely to embrace a solvent molecule. It is shown that the hosting capacity of 1 toward metal cations is greater in acetonitrile than in N,N-dimethylformamide and in methanol. Thus, in the former solvent, complexation with various cations (Li + , Na + , Ag + , Ca 2 + , Cu 2 + , Hg 2 + , and Pb 2 + ) occurs while in the latter media, 1 interacts only with Ag + and Hg 2 + . This statement is corroborated by 'H NMR, conductance, calorimetric and potentiometric measurements. It is concluded that through molecular inclusion of acetonitrile in the hydrophobic cavity of 1, the hydrophilic cavity of the resulting adduct becomes more receptive to host metal cations than that of the free ligand. In propylene carbonate, the results show that the ligand loses its ability to interact with metal cations. Thus in acetonitrile, selective recognition of 1 for Hg 2 + is demonstrated to an extent that the selectivity for this cation is greater by factors of 1.8 x 10 3 , 1.9 x 10 3 , 6.9 x 10 3 , 1.8 x 10 4 , 4.1 x 10 4 and 4.5 x 10 4 , relative to Pb 2 + , Na + , Li + , Cu 2 + , Ag + , and Ca 2 + , respectively. This statement is supported by the thermodynamic characterization of the complexation process involving these systems in acetonitrile, N,N-dimethylformamide and in methanol. Thus, the medium effect on the binding process is carefully assessed. The results show that replacement of two ester groups in two alternate pendant arms of the tetraester calix[4]arene derivative by thioethyl moieties has altered significantly the binding capacity and the selective behavior of the latter relative to the former. Final conclusions are given.

20 citations


Journal ArticleDOI
TL;DR: In this paper, the reactions of several derivatives of 1,2,5-thiadiazole 1,1-dioxide were followed by cyclic voltammetry (CV) and UV-visible spectrophotometry in aprotic solvent solution.

18 citations


Journal ArticleDOI
TL;DR: In this paper, an estudo sistematico de fragmentacao dos derivados of N-oxidos of 1,2,5-oxadiazois por espectroscopia de massa, usando analogos marcados com deuterio for identificar algumas fragmentacoes criticas.
Abstract: Reportamos neste trabalho o estudo sistematico de fragmentacao dos derivados de N-oxidos de 1,2,5-oxadiazois por espectroscopia de massa, usando analogos marcados com deuterio para identificar algumas fragmentacoes criticas. Foi confirmada a perda neutra de CH2O a partir do N2-oxido de 3-hidroximetil-4-fenil-1,2,5-oxidiazol, usando o analogo mono-deuterado. A perda de OH, a partir do oxigenio do N-oxido, por um rearranjo b-H e d-H, foi claramente verificada a partir do N2-oxido de 3-(4-metilpiperazina-1-metil)-4-fenil-1,2,5-oxidiazol, usando-se o analogo tetra-deuterado adequado. O isomero N-oxido e analogos desoxigenados foram tambem usados para confirmar a participacao do fragmento oxido no processo de defragmentacao.

15 citations


Journal ArticleDOI
TL;DR: In this paper, a new synthetic procedure of 1-alkyl(aryl)-1H-4methylimidazole N 3 -oxide derivatives by cyclocondensation of α-amine-oximes and orthoesters was studied.
Abstract: A new synthetic procedure of 1-alkyl(aryl)-1H-4-methylimidazole N 3 -oxide derivatives by cyclocondensation of α-amine-oximes and orthoesters was studied. Low yields in the cyclization process were the result of predominant Z-stereoisomer around the oxime moiety of α-amineoxime reactants. Different attempts to improve these yields were assayed, mild conditions being those that produce the best results. Also, the special acidity of hydrogen-2 in the imidazole N 3 -oxide system was studied in solution by NMR spectroscopy. This property provides a convenient intermediate to access 2-substituted analogues.

14 citations


Journal ArticleDOI
TL;DR: In this paper, a metal-assisted synthesis of new functionalized diphosphane derivatives is described. But the reaction of the complex fac[Mn(CNtBu)-(CO) 3 {(PPh 2 ) 2 C-H}] with dimethyl acetylenedicarboxylate and methyl propiolate affords the compounds fac

10 citations


Journal ArticleDOI
TL;DR: Aqueous solution equilibrium of the quaternary system Cu(2+)/2-OH-Hip/Imz/H(+) was studied by potentiometric titrations.

9 citations


Journal ArticleDOI
TL;DR: In this paper, the X-ray structures of two sodium complexes (picrate as the counter-ion), isolated from water saturated chloroform with and without acetonitrile are reported for the first time.
Abstract: Distribution data for alkali metal picrates in the water–chloroform solvent system in the absence and in the presence of acetonitrile were used to determine the partition constants of the dissociated electrolytes in the mutually saturated solvents and the ion-pair formation constants in the water saturated organic phase. These data were compared with those previously reported in water–benzonitrile and water–dichloromethane solvent systems. The same experiments carried out in the presence of ethyl p-tert-butylcalix(4)arene tetraethanoate, EtCalix(4), led to the calculation of distribution and extraction constants in these solvent systems. The presence of acetonitrile in the organic phase enhances significantly the extraction constant to an extent that these are the highest values so far obtained in the solvent systems investigated. This enhancement in extraction is attributed to metal complex stabilization promoted by the presence of acetonitrile in the hydrophobic cavity of the ligand. The X-ray structures of two sodium complexes (picrate as the counter-ion), isolated from water saturated chloroform with and without acetonitrile are reported for the first time. In the first complex, the macro-cycle is sited on a crystallographic four-fold axis and hosts an acetonitrile solvent molecule in its calix and a sodium ion in its hydrophilic cavity. The metal is in a eight-fold Archimedean square anti-prism environment, coordinated to the phenol oxygen atom and to the carbonyl oxygen atom of the four rotationally symmetry related pendant arms. The macro-cycle of the other complex adopts a slightly distorted cone conformation and its hydrophilic cavity also hosts a sodium ion. But now the metal is in a seven-fold environment, coordinated to the four phenol oxygen atoms and to the carbonyl oxygen atoms of three pendant arms acting as bidentate ligands. The fourth, mono-dentate, pendant arm points away from the hydrophilic cavity and its terminal –CH2-CH3 group interacts hydrophobically with the calix of a neighboring complex giving rise to a supra-molecular polymeric structure in the lattice.

3 citations