A new oligophenyleneethynylene (OPE)-based Pd(II) pyridyl complex has been synthesized, and its self-assembly has been investigated in solution, in the bulk state, and on surfaces. Detailed analysis of concentration- and temperature-dependent UV-vis studies in methylcyclohexane supported by DFT calculations demonstrate for the first time that cooperative supramolecular polymerization processes can be driven by metallophilic interactions.

Weak C-H···X hydrogen bonds are important stabilizing forces in crystal engineering and anion recognition in solution. In contrast, their quantitative influence on the stabilization of supramolecular polymers or gels has thus far remained unexplored. Herein, we report an oligophenyleneethynylene (OPE)-based amphiphilic Pt(II) complex that forms supramolecular polymeric structures in aqueous and polar media driven by π-π and different weak C-H···X (X=Cl, O) interactions involving chlorine atoms attached to the Pt(II) centers as well as oxygen atoms and polarized methylene groups belonging to the peripheral glycol chains. A collection of experimental techniques (UV/Vis, 1D and 2D NMR, DLS, AFM, SEM, and X-Ray diffraction) demonstrate that the interplay between different weak noncovalent interactions leads to the cooperative formation of self-assembled structures of high aspect ratio and gels in which the molecular arrangement is maintained in the crystalline state.

Micellization of three didodecyl dicationic dibromide gemini surfactants with different methylene spacer lengths, 12-s-12,2Br- where s = 3-5 methylene groups, has been investigated in water-ethylene glycol, EG, mixtures with weight percentages of EG up to 50%. Subsequently, effects of the addition of the organic solvent on the micellar growth of these surfactants and on the surfactant concentration range where sphere-to-rod transitions occur were studied by means of steady-state and time-resolved fluorescence quenching and spectroscopic measurements. Results show that an increase in the weight percentage of ethylene glycol added to aqueous 12-s-12,2Br- (s = 3-5) micellar solutions causes the sphere-to-rod transition to occur at higher surfactant concentrations than in pure water. The diminution in the average aggregation number, N(agg), when wt % EG increases, provoked by the decrease in the interfacial Gibbs energy contribution to DeltaG degrees M, is the main factor responsible for this observation. The decrease in N(agg) is accompanied by a decrease in the ionic interactions and the extra packing contribution to the deformation of the surfactants tails, making formation of cylindrical micelles less favorable. Besides, an increase in the solvent content and polarity of the interfacial region does not favor formation of direct ion pairs, decreasing the tendency of micelles to grow.

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription High-fidelity Noncovalent Synthesis of Hydrogen-bonded Macrocyclic AssembliesCarlos Montoro-García, Jorge Camacho-García, Ana M. López-Pérez, Nerea Bilbao, Sonia RomeroPérez, María J. Mayoral and David González-Rodríguez* Abstract: A hydrogen-bonded cyclic tetramer is assembled with remarkably high effective molarities from a properly designed dinucleoside monomer. This self-assembled species exhibits an impressive thermodynamic and kinetic stability and is formed with high fidelities within a broad concentration range.

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The spontaneous hydrolysis of phenyl chloroformate was studied in water−ethylene glycol (EG) micellar solutions of hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and dodecyltrimethylammonium bromide, the percentage by weight of EG varying within the 0−50% range. The dependence of the observed rate constant on the surfactant concentration was investigated in all the water−EG mixtures. In addition to the kinetic measurements, conductivity, spectroscopic, and fluorescence measurements were done to obtain information about the micellar solutions used as reaction media. For the three surfactants studied, an increase in the amount of EG present in the mixture resulted in an increase in the critical micelle concentration and in an increase in the micellar ionization degree but in a decrease in the aggregation number of micelles. The polarity of the bulk−micelle interface region seems to increase somewhat by increasing the percentage by weight of EG. A simple pseudophase model was useful in rationalizing the micellar kinetic effects observed. The adjustable parameters obtained from the fittings of the experimental data show that the reaction rate in the micellar pseudophase was similar for all the water−EG cationic micellar solutions investigated. The equilibrium binding constant for the phenyl chloroformate molecules to the micellar aggregates decreases as the amount of EG in the mixture increases, this decrease being responsible for the diminution in the observed rate constant when the amount of EG present in the mixture increases.

The absorption and fluorescence spectra of a set of dehydro and fully aromatic P-carboline (9Hpyrido[3,4-b] indole) derivatives have been investigated in aqueous solutions of varying acidity. Within the pH -range, cationic (nitrogen protonation) and neutral species are evidenced from both absorption and fluorescence spectra. Additional zwitterionic species can also be detected from the fluorescence spectra. In highly basic media, outside the pH -range, anionic species (pyrrolic nitrogen deprotonation) are formed. Ground state ionization constants for the different acid-base equilibria involving these species have been determined spectrophotometrically at 25 "C. Lowest excited singlet state pK,s have been estimated from the Forster-Weller cycle. The influence of structural variations on the spectra and on the acid-base properties of these compounds is discussed.As a continuation of the preceding paper,' we report now the results of our investigations on the acid-base properties and spectral characteristics of dehydro-(DB, 1) and fully aromatic (BC, 2) p-carbolines (9H-pyrido[3,4-b]indoles). Because of their extended x-electron systems, the acid-base and spectral properties of these compounds differ markedly from those of the less aromatic tetrahydro-P-carbolines (THBC 3), pre-' Taken from preceding paper. Taken from ref. 33.

The kinetics of exciplex formation of N 9 -methyl-1-methyl-9H-pyrido [3,4-b]indole, MHN, in the presence of the proton donor hexafluoro2-propanol, HFIP, in cyclohexane has been studied by UV-vis, steady-state, and time-resolved fluorescence measurements. The results conclusively show the formation of a 1:2 ground-state proton-transfer hydrogen bonded complex, PTC, between the pyridinic nitrogen of the substrate and the proton donor. The formation of these complexes is a necessary prerequisite for the exciplex to be observed. Thus, upon excitation of PTC, an excited-state equilibrium is established between PTC* and a cation like exciplex, CL*, λ em . 410 nm. This excited-state reaction is assisted by a proton donor molecule. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the excited-state kinetics of this phototautomeric process has been analyzed in detail.