Molecular Engineering for Catalysis and Biosensors Development of new generations of catalysts and nanostructured materials will be useful for a wide range of processes that are transforming our society, and thus, represent an extremely challenging issue which requires the close and active collaboration between interdisciplinary research groups. In this project, the experimental studies will be focused in the synthesis of discrete molecules, molecular clusters and nanostructured materials with desired molecular properties to be functional as biosensors or catalysts.
Our goal is to employ the supramolecular principles with nanosized structures in order to design hybrid electrodes and sensing ensembles with improved sensitivity and/or selectivity and for the targeting of organic – inorganic molecules. Relevant systems will be studied in detail, taking into account functional aspects such as, enhanced coordination of functionalized molecular self-assembly at solid and nanostructure surfaces, electronic and optoelectronic properties, and biosensor probes utilizing discrimination by polarity and size.
These strategies are opening frontier research for smart materials linking molecular engineering, supramolecular chemistry, and nanotechnology.
Several interesting results were obtained in our previous Milenium Nuclueus Molecular Engineering and Supramolecular Chemistry for Catalysis, Electrocatalysis, Remediation and Energy Conversion.
In the area of Catalysis an Electrocatalysis we obtained interesting results in reinterpreting the role of the Catalyst formal potential (Linares-Flores et al. J. Phys. Chem. C 2012, 116, 7091-7098) where we studied the thiocyanate electrooxidation catalyzed by Cobalt macrocyclic complexes. We observed that several parameters, like functionalized Co-phthalocyanine which shows the highest catalytic activity and the appropriate energy gap allows an efficient adduct formation and the subsequent electron transfer. This result is quite. We also studied the enhancement of the catalytic activity of Fe phthalocyanine (FePc) for the oxygen reduction anchored to Au(111) surface via conjugated self-assembled monolayers (SAM) of aromatic thiols compared to the reduced catalytic activity of Cu-phtahalocyanines (Ponce et al. J. Phys. Chem. C 2012, 116, 15329-15341). Scanning tunneling microscopy (STM) studies confirm the functionalization of the 4-aminothiphenol (4-ATP) by FePc. STM images reveal that FePc molecules are chemically anchored to 4-ATP monolayers, probably having an umbrella type orientation respect to the Au(111) surface. The electrocatalytic studies carried out with Au(111)/4-ATP/FePc and Au(111)/MDPP/FePc modified electrodes show that the oxygen reduction takes place by the transfer of 4-electrons to give water in contrast with the 2-electron transfer process for the bare gold. Thus, the modified electrodes promotes a 4-electron transfer process. The catalytic activity of the electrodes increases as: Au < Au/FePc <Au/4-ATP/FePc < Au/MDPP/FePc. In contrast, the less active CuPc shows almost the same activity in all three electrodes configurations.
We re-interpreted the well-known volcano correlations for the hydrazine catalyzed by Cobalt macrocyclic complexes catalysts and found that the highest catalytic activity is observed when the catalyst formal potential matches the reversible potential of the reaction. This clearly shows that the formal potential of the catalysts needs to be tuned or to be very close to the reversible potential of the target molecule to an electron-transfer process. (Recio et al., ECS Electrochemistry Lett. 2013, 2, H16-H18).
In the area of dye sensitized solar cells (DSSC) we have obtained interesting results. We succeeded with the synthesis of a binuclear Ru(II) complex with the [2,6-Bis(2-benziimidazolyl) pyridyl ligand (Dr. Delgadillo and undergraduate students at Universidad La Serena). Our calculation done at the Universidad Andres Bello indicates that this complex could a useful dye for dye-sensitized solar cells (DSCs). We also study several ruthenium-tris-(2,2-bipyridine) substituted complexes which do or do not have an anchoring group to get attached to the semiconductor surface. It was observed that the complexes that have electron-donor substituent might be more efficient to donate electrons if they are anchored to a semiconductor than those complexes that have electron-acceptor substituent. Therefore, the results suggest that these dyes with electron-donor substituents will give better yields in photocurrent generation. (Schott et al., J. Phys. Chem. A 2012, 116, 7436-7442).
We presented a novel method to capture the differences between direct and indirect photoinjection mechanisms in a fully atomistic picture. A model anastase TiO2 nanoparticle (NP) functionalized with different dyes was chosen. We show that a linear depéndence of the rate of electron injection with respect to the square of the applied field intensity can be viewed as a signature of a direct electron injection mechanism. Dyes involved in both direct (type-I) and indirect (type-II) mechanisms were studied. (Belen Oviedo et al., J. Phys. Chem. Lett. 2012, 3, 2548-2555).
In another study we explore the effects of some peripheral substituents on a Ni-porphyrazine dimer family. The simulated UV-vis absorption spectra exhibit the usual B or Soret and Q bands seen in the usual Gouterman´s description. We explained the effects of electron donor groups over the UV shift of the B and Q bands. (Zarate et al. Polyhedron 2013, 50, 131-138).
We also proposed a series of sensitizer candidates for DSSC by studying peripheral substituted diZinc pyrazinoporphyrazine-phthalocyanine complexes. The aim of this work was to provide a useful theoretical basis for the design and screening of new potential dye candidates to be used as sensitizers in solar cells. The results indicate that those dyes where their LUMOs are above the conduction band of the semiconductor are capable of electron injection into TiO2. In this article we proposed that several complexes are very promising to act as sensitizers. (Zarate et al., J. Phys. Chem. A 2013, 117, 430-438).
We also initiated the study of many structural aspects and properties of fluorene, a useful material for photovoltaic applications. ( (a) Barboza et al. Internat. J. Quantum Chem. 2012, 112, 3434-3438; (b) Barboza et al. Chem. Phys. Lett. 2012, 538, 67-71).
We also studied structural and electronic properties of a family of single walled one-dimensional (1D) ceria (Ce) nanotubes (NTs) by means of periodic DFT calculations. Gold (Au) atoms were deposited on both the outer and inner surfaces of a prototypical NT, where the interaction energy was equal to -1.4 eV. This result indicates that these surfaces appears to be easily reduced with the formation of cationic Au+ species, which allows us to postulate that these surfaces are attractive for catalytic purposes. (Plata et al., J. Phys. Chem. Lett. 2012, 3, 2092-2096).
New research in biomedicine: In an interesting experiment we used the paramagnetic [Re6Se8I6]3- cluster, which we predicted in 2003 its luminescent behavior (Arratia-Perez et al. J. Chem. Phys. 118, 7425, 2003) and we thought that it could be a useful dyes for DSCs. It was these predicted luminescent and reactivity properties that induced our curiosity to use it as sensor in cancer research. We then evaluated and observed the efficacy of the Re6Se8I63- cluster, to selectively increase tumor cell death, leaving non-tumoral cells unaffected, and we also observed the red luminescense. Thus, we explored its intracellular localization by taking advantage of its revealed luminescence. Comparative studies of the cytotoxic effects of the Re6Se8I63- cluster when exposed to the tumorigenic cell line HepG2, endothelial cell-derived cell line (EA cells) and non-tumor primary endothelial cells (HUVEC) revealed that the cytotoxicity was highest for HepG2 and lowest for HUVEC. In addition, cells tend to uptake the cluster into their nuclei, where we found significant evidence of direct non-intercalating DNA binding. Finally, DNA laddering experiments suggested that the cluster induced apoptotic-like cell death. Our results suggest that the Re6Se8I63- cluster could be useful for the development of novel and efficient metal-based antitumor drugs for the diagnosis and treatment of cancers. These findings represent the first attempts of a new and exciting field of research of inorganic multinuclear clusters in cancer research. (Echeverria et al. New J. Chem. 2012, 36, 927-932). We are currently performing some biodisponibility, bioavalibility and cytotoxicity experiments to gain important information about the action mechanism. The early detection of cancer is one of most important goals in moden life, we have found that a rhenium based cluster detects skin and hepatic cancer in 24-48 hrs. We are currently working in-vivo to establish the biodisponibility and cytotoxicity response on living organism.
We also synthesized aluminosilicates nanotubes decorated with quantum dots (QDs) for imaging and treatment of pathogenic bacteria. This work described for the first time the use of single-walled aluminosilicates nanotubes (SWNT) as a one-dimensional template for the in situ growth of mercaptopropionic acid-capped CdTe QDs and their antimicrobial activity on bacteria. We tested these CdTe QDs with three opportunistic multi-resistant pathogens such as: Salmonella typhimurium, Acinetobacter baumannii, and Pseudomonas aeruginosa. Growth inhibition test were conducted by exposing growing bacteria to CdTe QDs/SWNT showing that these nano-structured composite is a potential antimicrobial agent for heavy metal-resistant bacteria. (Geraldo et al. J. Nanopart. Res. 2012, 14: 1286-6). Thus, we are opening a new area of exciting research in bionanomedicine.
We feel that we are contributing to the development of science in Chile by training highly qualified young scientist working in multidisciplinary research.