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

Time resolved fluorescence of naproxen in organogel medium

The interaction between non-steroidal anti-inflammatory drug naproxen and the self assembled fibrillar network created by a low molecular weight organogelator has been probed by means of time resolved fluorescence spectroscopy

Bacterial base excision repair enzyme Fpg recognizes bulky N7-substituted-FapydG lesion via unproductive binding mode

Fpg is a bacterial base excision repair enzyme that removes oxidized purines from DNA. This work shows that Fpg and its eukaryote homolog Ogg1 recognize with high affinity FapydG and bulky N7-benzyl-FapydG (Bz-FapydG). The comparative crystal structure analysis of stable complexes between Fpg and carbocyclic cFapydG or Bz-cFapydG nucleoside-containing DNA provides the molecular basis of the ability of Fpg to bind both lesions with the same affinity and to differently process them. To accommodate the steric hindrance of the benzyl group, Fpg selects the adequate rotamer of the extrahelical Bz-cFapydG formamido group, forcing the bulky group to go outside the binding pocket. Contrary to the binding mode of cFapydG, the particular recognition of Bz-cFapydG leads the BER enzymes to unproductive complexes which would hide the lesion and slow down its repair by the NER machinery

Photoluminescence of CdSe/ZnS core–shell quantum dots stabilized in water with a pseudopeptidic gemini surfactant

The use of pseudopeptidic gemini surfactants as stabilizers of hydrophobic quantum dots in water is discussed. Compound 1a acts as an intercalator with hydrophobic ligands of QDs transferring them from toluene to pure water yielding a fluorescent nanoparticle resistant to quenching by chloride anion (up to 0.1 M)

Quantum dot–polymethacrylate composites for the analysis of NOx by fluorescence spectroscopy

A new type of hybrid materials composed by core–shell (CdSe/ZnS) quantum dots adsorbed on polymethacrylate surfaces has been synthesized and characterized, specially by means of time-resolved fluorimetry. The ability of such materials to sense NO and NOx has been tested, with promising results. Fluorescence quenching measurements afford limits of detection of ca. 0.1 ppm for NO and of ca. 1.0 ppm for NOx, which opens the way for the development of new materials with analytical applications

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

Recognition of Free Tryptophan in Water by Synthetic Pseudopeptides: Fluorescence and Thermodynamic Studies

Pseudopeptidic receptors containing an acridine unit have been prepared and their fluorescence response to a series of amino acids was measured in water. Free amino acids, not protected either at the C or the N terminus, were used for this purpose. The prepared receptors display a selective response to tryptophan (Trp) versus the other assayed amino acids under acidic conditions. The macrocyclic nature of the receptor is important as the fluorescence quenching is higher for the macrocyclic compound than for the related open-chain receptor. Notably, under the experimental acidic conditions used, both the receptor and guest are fully protonated and positively charged; thus, the experimental results suggest the formation of supramolecular species that contain two positively charged organic molecular components in proximity stabilized through aromatic–aromatic interactions and a complex set of cation-anion-cation interactions. The selectivity towards Trp seems to be based on the existence of a strong association between the indole ring of the monocharged amino acid and the acridinium fragment of the triprotonated form of the receptor, which is established to be assisted by the interaction of the cationic moieties with hydrogen sulfate anions

Nitric oxide sensitive fluorescent polymeric hydrogels showing negligible interference by dehydroascorbic acid

A series of nitric oxide (NO) sensitive polymeric hydrogels have been synthesized and their properties described. The new materials are based on a poly(2-hydroxyethyl methacrylate) matrix entrapping the DAF-FM (4-amino-5-methylamino-2′,7′-difluorofluorescein) fluorescent probe. Some of the developed materials show sensitivities in the range ca. 50–75 nM towards NO dissolved in aerated phosphate buffer (PBS), being nitrous anhydride the reactive species under such conditions. Remarkably, the sensitivity of the fluorescent polymers is not influenced by dehydroascorbic acid, a molecule of biological importance, which has been reported to be a common interfering species capable to react with well known probes for NO

Improved polyHEMA-DAQ films for the optical analysis of nitrite

A series of crosslinked poly(2-hydroxyethyl methacrylate) films containing 1,2-diaminoantraquinone (DAQ) have been synthesized and characterized spectroscopically by FT-IR and UV-vis. Their response towards nitrite anion in acidic medium has been evaluated by means of time-resolved UV-vis spectroscopy. This kinetic analysis has provided a tool for the dynamic characterization of nitrite-sensitive films which could have application in biomedical analysis (nitrite monitoring of biological fluids) and environmental science (control of nitrite levels in drinking water). © 2009 Elsevier Ltd. All rights reserved

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