The interaction of amino acids with macrocyclic pH probes of pseudopeptidic nature

The fluorescence quenching, by a series of amino acids, of pseudopeptidic compounds acting as probes for cellular acidity has been investigated. It has been found that amino acids containing electron-rich aromatic side chains like Trp or Tyr, as well as Met quench the emission of the probes mainly via a collisional mechanism, with Stern–Volmer constants in the 7–43 M−1 range, while other amino acids such as His, Val or Phe did not cause deactivation of the fluorescence. Only a minor contribution of a static quenching due to the formation of ground-state complexes has been found for Trp and Tyr, with association constants in the 9–24 M−1 range. For these ground-state complexes, a comparison between the macrocyclic probes and an open chain analogue reveals the existence of a moderate macrocyclic effect due to the preorganization of the probes in the more rigid structure

Organogel–quantum dots hybrid materials displaying fluorescence sensitivity and structural stability towards nitric oxide

Nanoparticle doped hybrid organogels were prepared using the pseudopeptidic macrocycle 1 and CdSe/ ZnS quantum dots (QDs). The new semi-solid materials show the same thermal stability and excellent optical transparency as compared to the parent organogel in the absence of the nanoparticles, but they are fluorescent due to the presence of embedded semiconductor nanocrystals. The fluorescence lifetime of a QD–organogel composite is reported for the first time, and it was found to be similar to that of the QDs in solution in a related solvent, independent of the concentration of gelator. The chemical sensing ability of the hybrid organogels towards gaseous nitric oxide was investigated by steady-state fluorescence spectroscopy. The gels show fluorescence sensitivity towards NO ranging from 0.05 to 0.5 (vol%). The results reported herein constitute a proof of principle of the potential of the hybrid supramolecular soft materials to develop nitric oxide sensor devices of practical application, especially because the semi-solid state of the organogel is preserved after interaction with the analyte. This is remarkable since, for the vast majority of organogels with analytical capabilities reported so far, the signaling mechanism relies upon the disassembly of the supramolecular structure

Coordination behaviour of new open chain and macrocyclic peptidomimetic compounds with copper (ii)

Two valine-derived bis(amino amides) ligands have been prepared and fully characterized. Both compounds contain additional functionalities that implement their basicity and their water solubility. Besides, compound 1 is an open chain ligand, while 2 is a macrocycle. Their protonation constants as well as their stability constants for the formation of the corresponding Cu2+ complexes have been determined potentiometrically. Important differences are associated to the macrocyclic effect and to the additional functionalities in the spacer. The presence of an additional amine group and/or the inclusion of a carboxylic side chain in this spacer increase the stabilities of the Cu2+complexes, suggesting its participation in the interaction with the metal. Thus, 2 is the first pseudopeptidic cyclophane of this family displaying the ability to form highly stable metal complexes in water. UV-Vis and ESI-MS were used for analyzing the complex species detected in the speciation diagram