Calix[8]arene nanoreactor for Cu(I)-catalysed C-S coupling.

The catalytic activity of Cu(i) confined within a phenanthroline-containing calix[8]arene derivative was tested in C-S cross-coupling reactions. The substrate selectivity, solvent dependence, and catalyst loading differ significantly from those reported for bimetallic molecular systems. The putative monomeric complex represents the first calix[8]arene functionalised for endo-oriented metal chelation used as a nanoreactor.

Density Functional Theory and Electrochemical Studies: Structure-Efficiency Relationship on Corrosion Inhibition.

The relationship between structure and corrosion inhibition of a series of 30 imidazol, benzimidazol, and pyridine derivatives has been established through the investigation of quantum descriptors calculated with PBE/6-311++G**. A quantitative structure-property relationship model was obtained by examination of these descriptors using a genetic functional approximation method based on a multiple linear regression analysis. Our results indicate that the efficiency of corrosion inhibitors is strongly associated with aromaticity, electron donor ability, and molecular volume descriptors. In order to calibrate and validate the proposed model, we performed electrochemical impedance spectroscopy (EIS) studies on imidazole, 2-methylimidazole, benzimidazole, 2-chloromethylbenzimidazole, pyridine, and 2-aminopyridine compounds. The experimental values for efficiency of corrosion inhibition are in good agreement with the estimated values obtained by our model, thus confirming that our approach represents a promising and suitable tool to predict the inhibition of corrosion attributes of nitrogen containing heterocyclic compounds. The adsorption behavior of imidazole or benzimidazole heterocyclic molecules on the Fe(110) surface was also studied to elucidate the inhibition mechanism; the aromaticity played an important role in the adsorbate-surface complex.

Supramolecular fluorescence enhancement via coordination-driven self-assembly in bis-picolylcalixarene blue-emitting M2L2Xn macrocycles.

The lower-rim functionalised distal bis-(4-picolyl)-p-tert-butylcalix[4]arene () selectively and quantitatively self-assembles into a series of discrete [2 + 2] blue-emitting metallacycles of general formula M2L2Xn with diverse metal salts (M = Zn(2+), Pd(2+), Ag(+), and Cd(2+); X = Cl(-), NO3(-), ClO4(-), BF4(-) , CF3SO3(-), PF6(-), SbF6(-); n = 2, 4). Macrocycle assembly has been corroborated by 2D-DOSY NMR and ESI-MS analyses, which further indicate that the M2L2Xn entities are quite stable and persist as robust and discrete macrocyclic species in solution. While free units display modest blue emission (λmax = 307-405 nm), self-assembly of M2L2Xn results in amplified fluorescence (up to 13-fold). This remarkable enhancement may be primarily ascribed to the increase in conformational rigidity imposed on the units by supramolecular assembly formation upon metal coordination to the pyridyl groups; in addition, subtle intensity-emission modulation may be provided by the different metal components. Titrations aimed at exploring the possibilities for ratiometric detection of metal cations or sensing of nitroaromatic species, revealed that the M2L2Xn platform may be a suitable "turn-on/off" system. Our results provide valuable insights into luminescence enhancement within the context of coordination-driven assemblies, which may be engineered to increase their fluorescence by imposing rigidity on the chromophores.

Chloride-catalyzed, multicomponent self-assembly of arsenic thiolates.

We present the observation that chloride serves as a simple catalyst for the acceleration of a self-assembly reaction between AsCl3 and dithiolate ligands (H2L) to form As2L3 assemblies. Studies on a model monomeric arsenic complex suggest that chloride may accelerate ligand exchange dynamics in pnictogen thiolates in general.