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- Electrodeposition of polyaniline on self-assembled monolayers on graphite for the voltammetric detection of iron(II)Publication . Camacho, Cláudia S.; Mesquita, José C.; Rodrigues, JoãoConducting polyaniline (PANI) prepared by potentiodynamic electropolymerization on unmodified graphite, and on graphite modified by self-assembled monolayers (SAMs) of 3-mercapto-1-propanesulfonic acid sodium salt (MPS) or 4-aminothiophenol (4-ATP), has been studied by cyclic voltammetry and electrochemical impedance. For the various PANI-modified electrodes, the electropolymerization behaviour of aniline is not significantly different, as well as the polyaniline redox behaviour. Despite that, the films electrodeposited on self-assembled seem to be thinner than those directly obtained on graphite. The 4-aminothiophenol self-assembled exerts more influence on polyaniline, particularly through a relative enhancement of the redox couple benzoquinone/hydroquinone. It was verified by cyclic voltammetry that Fe(II) is detected with the several PANI-modified electrodes. The comparison of the Fe(II) redox voltammetry on the different PANI-modified electrodes shows that does not significantly depend on of the modified electrode used. Complementarily, there is a relative increase in current of the redox couple Fe(II)/Fe(III) on polyaniline compared to that observed in graphite, suggesting an electrocatalytic process. However, that effect may be explained by an increase in surface area. Nevertheless, our results have shown clearly, with polyaniline, an increase in the reversible nature of the voltammetry of the redox couple Fe(II)/Fe(III).
- Use of half-generation PAMAM dendrimers (G0. 5–G3. 5) with carboxylate end-groups to improve the DACHPtCl2 and 5-FU efficacy as anticancer drugsPublication . Camacho, Cláudia; Tomás, Helena; Rodrigues, JoãoThe DACHPtCl2 compound (trans-(R,R)-1,2-diaminocyclohexanedichloroplatinum(II)) is a potent anticancer drug with a broad spectrum of activity and is less toxic than oxaliplatin (trans-l-diaminocyclohexane oxalate platinum II), with which it shares the active metal fragment DACHPt. Nevertheless, due to poor water solubility, its use as a chemotherapeutic drug is limited. Here, DACHPtCl2 was conjugated, in a bidentate form, with half-generation PAMAM dendrimers (G0.5–G3.5) with carboxylate end-groups, and the resulting conjugates were evaluated against various types of cancer cell lines. In this way, we aimed at increasing the solubility and availability at the target site of DACHPt while potentially reducing the adverse side effects. DNA binding assays showed a hyperchromic effect compatible with DNA helix’s disruption upon the interaction of the metallodendrimers and/or the released active metallic fragments with DNA. Furthermore, the prepared DACHPt metallodendrimers presented cytotoxicity in a wide set of cancer cell lines used (the relative potency regarding oxaliplatin was in general high) and were not hemotoxic. Importantly, their selectivity for A2780 and CACO-2 cancer cells with respect to non-cancer cells was particularly high. Subsequently, the anticancer drug 5-FU was loaded in a selected metallodendrimer (the G2.5COO(DACHPt)16) to investigate a possible synergistic effect between the two drugs carried by the same dendrimer scaffold and tested for cytotoxicity in A2780cisR and CACO-2 cancer cell lines. This combination resulted in IC50 values much lower than the IC50 for 5-FU but higher than those found for the metallodendrimers without 5-FU. It seems, thus, that the metallic fragment-induced cytotoxicity dominates over the cytotoxicity of 5-FU in the set of considered cell lines.
- New insights into the blue intrinsic fluorescence of oxidized PAMAM dendrimers considering their use as bionanomaterialsPublication . Camacho, Cláudia S.; Urgellés, Marta; Tomás, Helena; Lahoz, Fernando; Rodrigues, JoãoLike other bionanomaterials, dendrimers are usually labelled with fluorescent compounds in order to be optically detected within cells. However, this process can interfere with their biological properties, so it is crucial to find other solutions for their traceability. Here, the blue intrinsic fluorescence of amine terminated poly(amidoamine) (PAMAM) dendrimers was enhanced using oxidative treatment with ammonium persulfate (APS). The effects of dendrimer generation (G3, G4, and G5) and pH on the spectroscopic behavior of both pristine and APS-treated PAMAM dendrimers were studied in aqueous solution. Overall, the results pointed out that there are at least two types of emitting electron-rich hetero-atomic sub-luminophores (HASLs) confined within the dendrimer scaffold that have very close maximum emission wavelengths and whose emission properties strongly depend on pH. The APS treatment significantly enhanced the fluorescence intensity by leading to the protonation of the interior of the dendrimer. However, fluorescence intensity was not only dependent on the number of HASLs in the dendrimer scaffold (i.e., on dendrimer generation), but also on the rigidification suffered by the dendrimer due to the acidic environment (at low pH values, APS-treated G4 was indeed the most emissive species). Moreover, photoluminescence studies with lyophilized samples were also conducted, which confirmed the coexistence of more than one type of HASLs emitting in the dendrimer structure. The APS treatment affected these HASLs to a different extent. Time-resolved fluorescence experiments always showed higher average lifetimes of HASLs for APS-treated dendrimers than for pristine ones, in accordance with the fluorescence intensity results. On the other hand, the fraction and lifetimes of HASLs in APS-treated dendrimers were similar in solution and the lyophilized form. This behaviour was different for the pristine dendrimers that presented increased luminescence upon aggregation. Finally, the highly emissive oxidized dendrimers were shown not only to be much less cytotoxic and hemotoxic than pristine dendrimers but also to be detectable inside cells upon excitation with UV light.
- Polímeros condutores em monocamadas automontadas para a determinação de compostos de interesse ambientalPublication . Camacho, Cláudia Sofia; Mesquita, José Carlos Almeida; Rodrigues, João Manuel Cunha
- Biological Effects in Cancer Cells of Mono- and Bidentate Conjugation of Cisplatin on PAMAM Dendrimers: A Comparative StudyPublication . Camacho, Cláudia; Maciel, Dina; Tomás, Helena; Rodrigues, JoãoCisplatin (cis-diamminedichloroplatinum(II)) is a potent chemotherapeutic agent com monly used to treat cancer. However, its use also leads to serious side effects, such as nephrotoxicity, ototoxicity, and cardiotoxicity, which limit the dose that can be safely administered to patients. To minimize these problems, dendrimers may be used as carriers for cisplatin through the coordination of their terminal functional groups to platinum. Here, cisplatin was conjugated to half-generation anionic PAMAM dendrimers in mono- and bidentate forms, and their biological effects were as sessed in vitro. After preparation and characterization of the metallodendrimers, their cytotoxicity was evaluated against several cancer cell lines (A2780, A2780cisR, MCF-7, and CACO-2 cells) and a non-cancer cell line (BJ cells). The results showed that all the metallodendrimers were cytotoxic and that the cytotoxicity level depended on the cell line and the type of coordination mode (mono- or bidentate). Although, in this study, a correlation between dendrimer generation (number of carried metallic fragments) and cytotoxicity could not be completely established, the monodentate coordina tion form of cisplatin resulted in lower IC50 values, thus revealing a more accessible cisplatin release from the dendritic scaffold. Moreover, most of the metallodendrimers were more potent than the cisplatin, especially for the A2780 and A2780cisR cell lines, which showed higher selectivity than for non-cancer cells (BJ cells). The monodentate G0.5COO(Pt(NH3 )2Cl)8 and G2.5COO(Pt(NH3 )2Cl)32 metallodendrimers, as well as the bidentate G2.5COO(Pt(NH3 )2 )16 metallodendrimer, were even more active towards the cisplatin-resistant cell line (A2780cisR cells) than the correspondent cisplatin sensitive one (A2780 cells). Finally, the effect of the metallodendrimers on the hemolysis of human erythrocytes was neglectable, and metallodendrimers’ interaction with calf thymus DNA seemed to be stronger than that of free cisplatin.
- Anticancer prodrug nanoscale platform using low-generation dendrimers and/or platinum derivatives. Synthesis, cytotoxicity and synergetic effectsPublication . Camacho, Cláudia; Rodrigues, João Manuel Cunha; Tomás, Helena Maria Pires Gaspar