Synthesis and characterization of coordination polymers based on coinage metal ions and thio-derivatives of guanosine and uridine

Abstract

This work focuses on the search for new materials with useful optical and electronic properties based on nucleic acid-based components for possible use in nanotechnology. Towards this, two coordination polymers have been prepared using 6-thioguanosine, as a ligand, and univalent coinage metal ions of Ag(I) and Cu(I). [Ag(I)-6- thioguanosine]n was structurally characterized using mass spectroscopy, UV-Vis, FTIR, CD, SEM and AFM. This material has shown to have a polymeric onedimensional chain structure with Ag(I) ions coordinating two sulfur atoms. In addition, these chains form long polymeric strands when individually associate in parallel and also, they form helixes with a left-handed orientation. Additionally, the optical properties of the material showed luminescence emission suggesting that [Ag(I)-6- thioguanosine]n possess chiro-optical properties. A similar material was obtained in the reaction of Cu(I) ions to give the corresponding coordination polymer, [Cu(I)-6-thioguanosine]n as confirmed by characterization by mass spectroscopy, UV-Vis, FTIR, CD, SEM and AFM characterization. These showed the formation of a one-dimensional coordination polymer with Cu(I) ions bringing three sulfur atoms in form of fibres, that can associate one on top of another to form longer polymer chains. In this case, the material was fluorescence and electrically conductive after an oxidative doping process. Both systems formed metallo-supramolecular hydrogels when prepared at high concentrations, from 15 to 60 mM. They both were analyzed structurally by rheology, UV-Vis and CD confirming the formation of polymeric strands. In addition, these compounds were analyzed under AFM and they showed the formation of large onedimensional fibres that entangled by self-assembling to form the characteristic fibrillar ii network of a hydrogel. Also, both systems showed luminescence emission that combined with their chiral features showed CPL emission properties. Only [Cu(I)-6- thioguanosine]n displayed electrical conductivity without doping and this confirmed its nanowire behavior. As a promising application for these materials, a prototype of a nanowire-based gas sensor was prepared to detect ozone and VOCs. Firstly, [Cu(I)-6-thioguanosine]n was used as a potential gas sensor but it was discarded due to the poor stability and degradation shown to sense ozone and a time-dependent response for VOCs. Instead, a nanocomposite based on [Au(I)-6-thioguanosine]n and Multi-Walled Carbon Nanotubes (MWCTNs) was prepared and characterized structurally by AFM, Raman spectroscopy and SEM. A sensor based on [Au(I)-6-thioguanosine]n/MWCNTs was also built and this showed a stable response and high sensitivity for VOCs, especially for ethanol. Finally, two coordination polymers were prepared using a thio-modified nucleoside prepared synthetically, 4-thiouridine. [Ag(I)-4-thiouridine]n and [Au(I)-4-thiouridine]n complexes were structurally characterized using mass spectrometry, UV-Vis, FTIR, CD, SEM and AFM. In the case of [Ag(I)-4-thiouridine]n, the system formed a hydrogel with a structure based on coordination polymer similar to that formed with 6- thioguanosine. These are individual one-dimensional chains that self-assemble intertwining forming a supramolecular network. For [Au(I)-4-thiouridine]n, the structural analysis concluded with the formation of aggregates and it suggested the formation of Au(I) thiolate polymers that interact through aurophilic interactions. In addition, the optical properties of both Ag(I) and Au(I) systems showed higher luminescence emissions compared to the 4-thiouridine isolated confirming chiro-optics features of coinage-metal thiolate coordination polymers.