Flavylium-Supported Poly(<i>N</i>‑isopropylacrylamide): A Class of Multistimuli Responsive Polymer

A new multistimuli responsive polymer was prepared by means of the free-radical copolymerization of <i>N</i>-isopropylacrylamide and a vinyl flavylium derivative. The polymer shows response to temperature (conferred by the <i>N</i>-isopropylacrylamide units) and pH and light stimuli (conferred by the flavylium moieties). The polymer follows the typical pH dependent network of chemical reactions of flavylium compounds in water that was studied by means of UV–vis spectroscopy and stationary fluorescence emission. Regarding the temperature response, the presence of the flavylium cation in the polymeric chains reduces the LCST, and it is possible to take advantage of this effect to photo-collapse partially the polymer by irradiating the system in defined ranges of pH and temperature

Thermodynamic Aspects of Aurophilic Hydrogelators

The complexes [Au­(4-pyridylethynyl)­(phosph)] (phosph = PTA (<b>1</b>), DAPTA (<b>2</b>)) are known to produce supramolecular aggregates and gels in water. We studied the impact of these aggregation processes in the absorption spectra, ¹H NMR (at different temperatures and concentrations), and DLS and estimated the equilibrium constant for a single step aggregation of the molecule (<i>K</i> = 26760 and 2590 M^–1 for <b>1</b> and <b>2</b>, respectively, at 25 °C). We present spectroscopic evidence for the presence of Au···Au contacts in the aggregates: the recorded changes on ¹H 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 (Δ<i>G</i> ∼ −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 <b>1</b> is stronger than the aggregation of monomer <b>2</b> and the existence of aurophilic interactions

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

<p>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).</p

Polarized Supramolecular Aggregates Based on Luminescent Perhalogenated Gold Derivatives

The reaction of [Au­(C₆F₅)­(tht)] (tht = tetrahydrothiophene) with 1,3,5-triaza-7-phosphaadamantane (PTA) and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]­nonane (DAPTA) leads to the formation of [Au­(C₆F₅)­(phosph)] (phosph = PTA, <b>1</b>; phosph = DAPTA, <b>2</b>). The compounds are slightly soluble in water and aggregate at higher concentrations, giving rise to the formation of needle- and rodlike structures (<b>1</b>) and well-organized spherical aggregates (<b>2</b>). Compounds <b>1</b> and <b>2</b> were reacted with AgPF₆, giving rise to the formation in all cases of luminescent water-soluble 1:1 Au···Ag heterometallic complexes, as evidenced by X-ray crystal structure determination. The use of different silver salts that differ on the counterion induces changes in the resulting luminescence and aggregation morphology