Elisabet Aguiló

From Au(I) organometallic hydrogels to well-defined Au(0) nanoparticles

The reaction of water soluble phosphine 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) with [Au(CC–C5H4N)]n yields a luminescent water soluble phosphine gold(I) alkynyl complex [Au(4-pyridylethynyl)(DAPTA)] that leads to the formation of a luminescent hydrogel. A small variation of the phosphine structure (introduction of acetyl groups) with respect to the previously reported complex [Au(4-pyridylethynyl)(PTA)] has a clear effect on the observed properties: (i) a great increase in the hydrogel entanglement structure has been observed; (ii) the different cross-linking structures give rise to specific emission properties. The hydrogel was characterized by different techniques (1H-NMR, absorption and emission spectroscopy, optical microscopy, fluorescent microscopy (FM) and SEM). FM together with microspectrofluorimetry measurements has determined different emissive properties that vary according to the cross-linking process. Thermal treatments of the hydrogel produce well-defined metallic gold nanoparticles with a remarkable narrow size distribution, which have been characterized by SEM, TEM and X-ray photoelectron spectroscopy (XPS). At 200 °C, Au particles measuring 1.0 ± 0.2 nm were obtained. Au nanoparticles were also formed as a result of electron beam irradiation.

Alkynyl gold(I) phosphane complexes: Evaluation of structure–activity-relationships for the phosphane ligands, effects on key signaling proteins and preliminary in-vivo studies with a nanoformulated complex

Gold alkynyl complexes with phosphane ligands of the type (alkynyl)Au(I)(phosphane) represent a group of bioorganometallics, which has only recently been evaluated biologically in more detail. Structure-activity-relationship studies regarding the residues of the phosphane ligand (P(Ph)3, P(2-furyl)3, P(DAPTA)3, P(PTA)3, P(Et)3, P(Me)3) of complexes with an 4-ethynylanisole alkyne ligand revealed no strong differences concerning cytotoxicity. However, a relevant preference for the heteroatom free alkyl/aryl residues concerning inhibition of the target enzyme thioredoxin reductase was evident. Complex 1 with the triphenylphosphane ligand was selected for further studies, in which clear effects on cell morphology were monitored by time-lapse microscopy. Effects on cellular signaling were determined by ELISA microarrays and showed a significant induction of the phosphorylation of ERK1 (extracellular signal related kinase 1), ERK2 and HSP27 (heat shock protein 27) in HT-29 cells. Application of 1 in-vivo in a mouse xenograft model was found to be challenging due to the low solubility of the complex and required a formulation strategy based on a peanut oil nanoemulsion.

Thermodynamic aspects of aurophilic hydrogelators.

The complexes [Au(4-pyridylethynyl)(phosph)] (phosph = PTA (1), DAPTA (2)) are known to produce supramolecular aggregates and gels in water. We studied the impact of these aggregation processes in the absorption spectra, (1)H NMR (at different temperatures and concentrations), and DLS and estimated the equilibrium constant for a single step aggregation of the molecule (K = 26760 and 2590 M(-1) for 1 and 2, respectively, at 25 °C). We present spectroscopic evidence for the presence of Au···Au contacts in the aggregates: the recorded changes on (1)H NMR and the appearance of new absorption bands assigned to (σ*Au···Au-π*) have been attributed to the short (Au···Au) average distances in the aggregates. Relativistic density functional theory computations support the existence of short Au···Au distances and reveal charge-transfer in the aurophilic interactions. The free energy for a single step aggregation was calculated from the experimental data, and the value obtained (ΔG ∼ -20 kJ/mol) is in good agreement with the expected values in the order of the energies found for hydrogen bonds. The DFT computations confirm the experimental findings that aggregation of monomer 1 is stronger than the aggregation of monomer 2 and the existence of aurophilic interactions.

Gold(I)-complex–titania hybrid photocatalyst for hydrogen production

The integration of TiO2 with a AuI complex containing a thiocoumarin moiety resulted in a very efficient photocatalyst for the generation of H2. The molecular structure of the complex was preserved under the photoreaction owing to the strong AuI−S bond. The AuI complex played a determinant role in the photogeneration of H2 by accepting the photoinduced electrons originated in TiO2 upon light exposure. This is the first example of a AuI complex semiconductor hybrid photocatalyst. The rate of H2 generation under dynamic conditions from water/ethanol is approximately one order of magnitude superior on a metal basis to that obtained over conventional TiO2 decorated with Au metal nanoparticles.

Exploiting Metallophilicity for the Assembly of Inorganic Nanocrystals and Conjugated Organic Molecules

The accurate engineering of interfaces between inorganic nanocrystals and semiconducting organic molecules is currently viewed as key for further developments in critical fields such as photovoltaics and photocatalysis. In this work, a new and unconventional source of interface interaction based on metal-metal bonds is presented. With this aim, an Au(I) organometallic gelator was exploited for the formation of hydrogel-like nanocomposites containing inorganic nanoparticles and conjugated organic molecules. Noteworthy, the establishment of metallophilic interactions at the interface between the two moieties greatly enhances interparticle coupling in the composites. Thus, we believe that this new hybrid system might represent a promising alternative in several fields, such as in the fabrication of improved light-harvesting devices.

Reversible Self-Assembly of Water-Soluble Gold(I) Complexes

The reaction of the gold polymers containing bipyridyl and terpyridyl units, [Au(C≡CC15H10N3)]n and [Au(C≡CC10H7N2)]n, with the water-soluble phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H2O) and dimethyl sulfoxide (DMSO), through different intermolecular interactions, with an impact on the observed luminescence displayed by the supramolecular assemblies. A detailed analysis carried out by NMR studies performed in different DMSO/deuterated H2O mixtures indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramolecular environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from density functional theory calculations carried out in DMSO and H2O. Small-angle X-ray scattering (SAXS) experiments performed in the same mixture of solvents are in agreement with the formation of aggregates in all cases. The aromatic units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramolecular assemblies. Interaction with the Zn2+ cation is observed to disassemble the aggregates, while encapsulating agents competing for Zn2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramolecular assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn2+.

Modulation of supramolecular gold(I) aggregates by anion’s interaction

Abstract The gold complexes [Au(4-pyridylethynyl)(PTA)] and [Au(4-pyridylethynyl)(DAPTA)] (PTA = 1,3,5-triaza-7-phosphaadamantane; DAPTA = 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) were used as host in molecular recognition processes of sodium hexametaphosphate (HMP) and a single-stranded 24-long oligonucleotide. Experiments were performed by absorption titrations and looking at the resulting host:guest adducts by polarised optical, fluorescence and scanning electron microscopy. The resulting information indicates that different types of interactions are present with the two different guest molecules. In the case of HMP, the compounds aggregate giving rise to larger structures, favouring exciton splitting coupling and the formation of head to tail interactions. In the case of oligonucleotide studies, the formation of smaller supramolecular structures is observed, with less contribution of aurophilic contacts and organised in a parallel way (head to head interactions organised by the presence of the oligonucleotide).

Rhodium(I) macrocyclic and cage-like structures containing diphosphine bridging ligands

Three series of rhodium organometallic complexes, mono-(1c, 2c, 5c, 6c), di-(1a-6a) and tetranuclear (1b, 5b, 6b), containing six different diphosphines 1,1′-bis(diphenylphosphino)methane or dppm (1), 1,2-bis(diphenylphosphino)ethane or dppe (2), 1,4-bis(diphenylphosphino)butane or dppb (3), bis(diphenylphosphino)acetylene or dppa (4), 1,2-bis(diphenylphosphino)benzene or dppbz (5) and 4,5-bis(diphenylphosphino)-9,9′-dimethylxanthene or xantphos (6) were successfully synthesised. These Rh(I) complexes were characterised by conventional techniques. The influence of the flexibility/rigidity of these P-donor ligands was carefully analysed, including their effect on both synthesis and catalysis. The luminescent properties of the dinuclear and tetranuclear complexes were investigated, and only those containing dppa, dppbz and xantphos displayed luminescence. Structures of the dinuclear complexes were modelled by using DFT methods in order to elucidate the most reasonable conformation. The different types of complexes were applied in the catalytic hydrogenation of (E)-4-phenylbut-3-en-2-one, showing high activity and similar catalytic behaviour. No cooperative effect could be inferred.Graphical AbstractThree series of 1D, 2D and 3D rhodium complexes were successfully synthesised, and their emission properties were analysed. The large number of isomeric forms of the 2D were analysed by DFT methods. Their use in catalytic hydrogenation of (E)-4-phenylbut-3-en-2-one was studied showing high selectivity towards the formation of 4-phenylbutan-2-one.