Multi-technique characterization of poly-L-lysine dendrigrafts-Cu(II) complexes for biocatalysis.

Poly-L-lysine is a biocompatible polymer used for drug or gene delivery, for transport through cellular membranes, and as nanosized magnetic resonance imaging contrast agents. Cu(II)-poly-L-lysine complexes are of particular interest for their role in biocatalysis. In this study, poly-L-lysine dendrigrafts (DGLs) at different generations (G2, G3, and G4) are synthesized and characterized in absence and presence of Cu(II) by means of electron paramagnetic resonance (EPR), UV-Vis, potentiometric titration and circular dichroism (CD). The analysis is performed as a function of the [Cu(II)]/[Lys] (=R) molar ratio, pH and generation by identifying differently flexible complexes in different dendrimer regions. The amine sites in the lateral chains become increasingly involved with the increase of pH. The good agreement and complementarity of the results from the different techniques provide an integrate view of the structural and dynamic properties of Cu(II)-DGL complexes implementing their use as biocatalysts.

Characterization of the TiO2/dye/electrolyte interfaces in dye-sensitized solar cells by means of a titania-binding nitroxide.

Dye-sensitized solar cells (DSSCs) have been characterized in several literature examples by using relatively complex methods and/or modified DSSC conditions with respect to the usual working ones. In this study, we propose a method for the investigation of the interfaces TiO2/dye/electrolyte in a DSSC at its usual working conditions. This method implies the use of a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra of the spin probe 4-carboxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-carboxy-TEMPO, indicated as 4-cT). This probe well-mimics the dyes in their interactions with TiO2 surface, but does not perturb dye adsorption onto TiO2 surface, as verified by UV-vis measurements. First, we investigated the interacting ability toward 4-cT of commercially available TiO2 used for assembling the DSSC. It was found that interactions are modulated by the different distribution of interacting sites at the solid surface and powder aggregation. Further, experiments on 4-cT were carried out in the presence of a series of other molecules coded as N3, N719, and D149, which are commonly used as dyes in DSSCs. Then, the effect of solutions added to the electrodes was investigated. On the basis of the interactions occurring at the TiO2/dye/electrolyte interfaces, we selected the ingredients of the DSSCs. Electrical and EPR characterizations of these DSSCs miniaturized to enter the EPR cavity, together with time-dependent laser-light on-off experiments, were carried out, which demonstrated the ability of the EPR analysis to monitor the types and strengths of the interactions occurring at the cell's different interfaces. This method using the standard continuous wave EPR technique at room temperature may be profitably used to characterize the quality and performances of a DSSC.

Copper(II) complexes with 4-carbomethoxypyrrolidone functionalized PAMAM-dendrimers: an EPR study.

The internal flexibility and interacting ability of PAMAM-dendrimers having 4-carbomethoxypyrrolidone-groups as surface groups (termed Gn-Pyr), which may be useful for biomedical purposes, and ion traps were investigated by analyzing the EPR spectra of their copper(II) complexes. Increasing amounts (with respect to the Pyr groups) of copper(II) gave rise to different signals constituting the EPR spectra at room and low temperature corresponding to different coordinations of Cu(2+) inside and outside the dendrimers. At low Cu(2+) concentrations, CuN4 coordination involving the DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a CuN3O coordination. CuN2O2 coordination into the external dendrimer layer was also contributing to G3- and G4-Pyr spectra. The structures of the proposed copper-dendrimer complexes were also shown. G4-Pyr displays unusual binding ability toward Cu(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr and its peculiar binding ability leads to a potential use in biomedical fields.