Article

Rigid-rod anion-pi slides for multiion hopping across lipid bilayers.

Department of Organic Chemistry, University of Geneva, Geneva, Switzerland.
Organic & Biomolecular Chemistry (impact factor: 3.7). 09/2007; 5(18):3000-12. DOI:10.1039/b708337h
Source: PubMed

ABSTRACT Shape-persistent oligo-p-phenylene-N,N-naphthalenediimide (O-NDI) rods are introduced as anion-pi slides for chloride-selective multiion hopping across lipid bilayers. Results from end-group engineering and covalent capture as O-NDI hairpins suggested that self-assembly into transmembrane O-NDI bundles is essential for activity. A halide topology VI (Cl > F > Br approximately I, Cl/Br approximately Cl/I > 7) implied strong anion binding along the anion-pi slides with relatively weak contributions from size exclusion (F >or= OAc). Anomalous mole fraction effects (AMFE) supported the occurrence of multiion hopping along the pi-acidic O-NDI rods. The existence of anion-pi interactions was corroborated by high-level ab initio and DFT calculations. The latter revealed positive NDI quadrupole moments far beyond the hexafluorobenzene standard. Computational studies further suggested that anion binding occurs at the confined, pi-acidic edges of the sticky NDI surface and is influenced by the nature of the phenyl spacer between two NDIs. With regard to methods development, a detailed analysis of the detection of ion selectivity with the HPTS assay including AMFE in vesicles is provided.

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    Article: Experimental evidence for the functional relevance of anion-pi interactions.
    Ryan E Dawson, Andreas Hennig, Dominik P Weimann, Daniel Emery, Velayutham Ravikumar, Javier Montenegro, Toshihide Takeuchi, Sandro Gabutti, Marcel Mayor, Jiri Mareda, Christoph A Schalley, Stefan Matile
    [show abstract] [hide abstract]
    ABSTRACT: Attractive in theory and confirmed to exist, anion-pi interactions have never really been seen at work. To catch them in action, we prepared a collection of monomeric, cyclic and rod-shaped naphthalenediimide transporters. Their ability to exert anion-pi interactions was demonstrated by electrospray tandem mass spectrometry in combination with theoretical calculations. To relate this structural evidence to transport activity in bilayer membranes, affinity and selectivity sequences were recorded. pi-acidification and active-site decrowding increased binding, transport and chloride > bromide > iodide selectivity, and supramolecular organization inverted acetate > nitrate to nitrate > acetate selectivity. We conclude that anion-pi interactions on monomeric surfaces are ideal for chloride recognition, whereas their supramolecular enhancement by pi,pi-interactions appears perfect to target nitrate. Chloride transporters are relevant to treat channelopathies, and nitrate sensors to monitor cellular signaling and cardiovascular diseases. A big impact on organocatalysis can be expected from the stabilization of anionic transition states on chiral pi-acidic surfaces.
    Nature Chemistry 07/2010; 2(7):533-8. · 20.52 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

anion binding
 
anion-pi
 
anion-pi interactions
 
Anomalous mole fraction effects
 
detailed analysis
 
end-group engineering
 
hexafluorobenzene standard
 
high-level ab initio
 
ion selectivity
 
lipid bilayers
 
NDIs
 
O-NDI hairpins
 
phenyl spacer
 
pi-acidic edges
 
pi-acidic O-NDI rods
 
revealed positive NDI quadrupole moments
 
size exclusion
 
sticky NDI surface
 
strong anion binding
 
transmembrane O-NDI bundles
 

Virginie Gorteau