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Sannicolo F.,University of Milan | Arnaboldi S.,University of Milan | Benincori T.,University of Insubria | Bonometti V.,University of Milan | And 8 more authors.
Angewandte Chemie - International Edition | Year: 2014

The typical design of chiral electroactive materials involves attaching chiral pendants to an electroactive polyconjugated backbone and generally results in modest chirality manifestations. Discussed herein are electroactive chiral poly-heterocycles, where chirality is not external to the electroactive backbone but inherent to it, and results from a torsion generated by the periodic presence of atropisomeric, conjugatively active biheteroaromatic scaffolds, (3,3-bithianaphthene). As the stereogenic element coincides with the electroactive one, films of impressive chiroptical activity and outstanding enantiodiscrimination properties are obtained. Moreover, chirality manifestations can be finely and reversibly tuned by the electric potential, as progressive injection of holes forces the two thianaphthene rings to co-planarize to favor delocalization. Such deformations, revealed by CD spectroelectrochemistry, are elastic and reversible, thus suggesting a breathing system. A jolt upon recognition: Torsion in the electroactive backbone endows poly-heterocycle films with high chiroptical activity, which is reversibly tunable by the electric potential, and outstanding enantiorecognition capability with about 100 mV between two enantiomeric ferrocenyl amino probes, in any order, in alternating sequences, and as a racemate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molinari P.,Dip. del Farmaco | Vezzi V.,Dip. del Farmaco | Sbraccia M.,Dip. del Farmaco | Gro C.,Dip. del Farmaco | And 4 more authors.
Journal of Biological Chemistry | Year: 2010

The addictive potential of opioids may be related to their differential ability to induce G protein signaling and endocytosis. We compared the ability of 20 ligands (sampled from the main chemical classes of opioids) to promote the association of μ and δ receptors with G protein or β-arrestin 2. Receptor-arrestin binding was monitored by bioluminescence resonance energy transfer (BRET) in intact cells, where pertussis toxin experiments indicated that the interaction was minimally affected by receptor signaling. To assess receptor-G protein coupling without competition from arrestins, we employed a cell-free BRET assay using membranes isolated from cells expressing luminescent receptors and fluorescent Gβ1. In this system, the agonist-induced enhancement of BRET (indicating shortening of distance between the two proteins) was Gα-mediated (as shown by sensitivity to pertussis toxin and guanine nucleotides) and yielded data consistent with the known pharmacology of the ligands. We found marked differences of efficacy for G protein and arrestin, with a pattern suggesting more restrictive structural requirements for arrestin efficacy. The analysis of such differences identified a subset of structures showing a marked discrepancy between efficacies for G protein and arrestin. Addictive opiates like morphine and oxymorphone exhibited large differences both at δ and μ receptors. Thus, they were effective agonists for G protein coupling but acted as competitive enkephalins antagonists (δ) or partial agonists (μ) for arrestin. This arrestin-selective antagonism resulted in inhibition of short and long term events mediated by arrestin, such as rapid receptor internalization and down-regulation. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

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