Biomedical subjects

Osvaldo dos Santos

Publications and source records attributed to Osvaldo dos Santos.

3 recordsLinked to original sources

PubMed2003

Geometry-dependent phosphodiester hydrolysis catalyzed by binuclear copper complexes.

Two isomeric binuclear ligands PBTPA and MBTPA and their copper(II) complexes were prepared and examined for hydrolysis of a model phosphodiester substrate: bis(p-nitrophenyl)phosphate. A bell-shaped pH vs rate profile, which is in agreement with one mechanism proposed for bimetallonucleases/phosphatases, was observed for the binuclear complex of copper(II) and PBTPA. At pH 8.4, a maximum rate of 1.14 x 10(-6) s(-1)--more than 10(4)-fold over uncatalyzed reactions--was achieved. However, the analogous complex of MBTPA did not show significant rate enhancement. The binuclear complex of copper(II) and PBTPA also showed 10-fold acceleration over mononuclear complex of copper(II) and tris(2-pyridylmethyl)amine (TPA) catalyzed reaction. A phage phiX174 DNA assay showed that the complex of copper(II) and PBTPA promoted supercoiled phage phiX174 DNA relaxation under both aerobic and anaerobic conditions, in contrast to the hydrolytic inactivity of the mononuclear complex of copper(II) and TPA.

Catalysis↗

PubMed2002

Reaction of N3-benzoyl-3',5'-O-(di-tert-butylsilanediyl)uridine with hindered electrophiles: intermolecular N3 to 2'-O protecting group transfer.

The compound N3-benzoyl-3',5'-O-(di-tert-butylsilanediyl)uridine 2 was alkylated with various alkyl iodides in CH3CN in the presence of base. Normal 2'-O-alkylated products were obtained with methyl or benzyl iodide. If hindered alkyl iodides with beta-branching such as 2-ethylbutyl iodide were used as electrophiles under the same conditions, N3-alkyl-2'-O-benzoyl uridine derivatives were produced. This unexpected transformation is usually dormant with reactive alkylating agents, but expressed with sterically hindered, less reactive electrophiles. This unwanted reaction gives isomeric products whose spectra differ in only subtle ways from target compounds.

Alkylation↗

PubMed1997

Synthesis and Cyclic Voltammetry Studies of Copper Complexes of Bromo- and Alkoxyphenyl-Substituted Derivatives of Tris(2-pyridylmethyl)amine: Influence of Cation-Alkoxy Interactions on Copper Redox Potentials.

A combination of host-guest chemistry and coordination chemistry in the design of electrochemical sensors for alkali metal and ammonium ions is described. The sensor molecules are coordination complexes between a copper ion and a functionalized tripodal ligand. Upon presentation of the ion to the sensor molecule, a shift in the redox potential of the copper ion occurs. In the course of the study, three new alkoxyphenyl-substituted derivatives of the ligand tris(2-pyridylmethyl)amine (TPA) were prepared and characterized. The synthesis of the new ligands involved the preparation of bromopyridyl-TPA derivatives followed by Suzuki coupling with substituted phenylboronic acids. Cyclic voltammetry studies of copper complexes of the ligands indicated that steric effects played a dominant role in the overall determination of the copper redox couple. Studies of the alkoxyphenyl ligands indicated that small but reproducible changes in the copper redox couple occurred upon presentation of a guest cation that would be expected to form a complex with the copper-ligand complex.

Journal Article↗