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The early diagnosis of diseases related to phosphate metabolism is very important for preventing, in most cases, severe kidney failure and cardiovascular events that have an increased risk of death. In this work, we present biofunctionalized quantum dots (b-QDs) prepared with chitosan and its chemically modified derivatives to detect and capture phosphate in water media. Chitosan (CHI), N,N,N-trimethylchitosan (TMC) and carboxymethylchitosan (CMC) were used as ligands for producing colloidal CdS nanocrystals in aqueous systems. UV-Visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), fluorescence microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), zeta potential analysis (ZP), and transmission electron microscopy (TEM) were used to characterize the colloidal QDs.Additionally, in vitro assays based on the b-QDs were designed and used to evaluate phosphate ion adsorption. The results clearly indicated that chitosan and chitosan derivatives were effective in nucleating and stabilizing CdS QDs in aqueous colloidal suspensions with an average nanocrystal size ranging from 2.2 to 3.6 nm. The photoluminescent behavior of the CdS bioconjugates was highly dependent on the chemical functionality introduced in the chitosan-derivative polymer. Moreover, the presence of different chemical groups in chitosan significantly affected the capacity of the bioconjugates to bind phosphates. Finally, a "pseudo in vivo" assay was designed using an artificial biomembrane based on phospholipid bilayers to preliminarily assess the possibility of using the bioconjugates to biolabel cell membranes. Therefore, a new class of fluorescent biosorbent nanohybrids was developed using chemically functionalized chitosan conjugated to quantum dots for potential applications in biochemical analysis and nanomedicine.

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Gold complexes that could act as antitumor agents have attracted great attention. Heterocyclic compounds and their metal complexes display a broad spectrum of pharmacological properties. The present study reports the preparation and characterization of four novel gold(I) complexes containing tertiary phosphine and new ligands 5-adamantyl-1,3-thiazolidine-2-thione, 3-methyladamantane-1,3,4-oxadiazole-2-thione. Spectroscopic data suggest that gold is coordinated to the exocyclic sulfur atom in all cases, as confirmed by X-ray crystallographic data obtained for complex (1) and supported by quantum-mechanical calculations. The cytotoxicity of the compounds has been evaluated in comparison to cisplatin and auranofin in three different tumor cell lines, colon cancer (CT26WT), metastatic skin melanoma (B16F10), mammary adenocarcinoma (4T1) and kidney normal cell (BHK-21). The gold complexes were more active than their respective free ligands and able to inhibit the thioredoxin reductase (TrxR) enzyme, even in the presence of albumin. Molecular modeling studies were carried out to understand the interaction between the compounds and the TrxR enzyme, considered as a potential target for new compounds in cancer treatment. The docking results show that the adamantane ring is essential to stabilize the ligand-enzyme complex prior the formation of covalent bond with gold center. The structure of the new gold compounds was established on the basis of spectroscopic data, DFT calculations and X-ray diffraction. TrxR inhibition was evaluated and the results correlated with the assays in tumor cells, suggesting the TrxR as possible target for these compounds.

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