Linked Life Data

12105911

Source:http://linkedlifedata.com/resource/pubmed/id/12105911

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
28
pubmed:dateCreated
2002-7-10
pubmed:abstractText
The interaction of the lipophilic cyclophane 1 with several acetylcholine (ACh) and tetramethylammonium (TMA) salts has been investigated in deuteriochloroform to ascertain the influence of the counterion on the cation-pi interaction. Reliable association constants have been measured for 17 salts of commonly used anions; corresponding binding free energies -DeltaG degrees ranged from over 8 kJ mol(-1) down to the limit of detection. The dramatic dependence of the binding energy on the anion showed that the latter takes part in the process with a passive and adverse contribution, which inhibits cation binding even to complete suppression in unfavorable cases. Thermodynamic parameters for the association of 1 with TMA picrate demonstrate that binding is enthalpic in origin, showing a substantial enthalpy gain (DeltaH degrees = -16.7 kJ mol(-1)) and an adverse entropic contribution (DeltaS degrees = -27.9 J mol(-1) K(-1)). A correlation has been found between the "goodness" of anions as binding partners and the solubility of their salts. Conversion of the anion into a more charge-dispersed species, for example, conversion of chloride into dialkyltrichlorostannate, improves cation binding substantially, indicating that charge dispersion is a main factor determining the influence of the anion on the cation-pi interaction. DFT computational studies show that the variation of the binding free energy of TMA with the counterion is closely accounted for by the electrostatic potential (EP) of the ion pair: guest binding appears to respond to the cation's charge density exposed to the receptor, which is determined by the anion's charge density through a polarization mechanism. A value of -DeltaG degrees = 38.6 kJ mol(-1) has been extrapolated for the free energy of binding of TMA to 1 in chloroform but in the absence of a counterion. The transmission of electrostatic effects from the ion pair to the cation-pi interaction demonstrates that host-guest association is governed by Coulombic attraction, as long as factors (steric, entropic, solvation, etc.) other than pure electrostatics are not prevalent.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0002-7863
pubmed:author
pubmed:issnType
Print
pubmed:day
17
pubmed:volume
124
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
8307-15
pubmed:dateRevised
2008-11-21
pubmed:meshHeading
pubmed:year
2002
pubmed:articleTitle
Binding of acetylcholine and tetramethylammonium to a cyclophane receptor: anion's contribution to the cation-pi interaction.
pubmed:affiliation
CNR, Istituto di Chimica dei Composti Organometallici, Dipartimento di Chimica Organica, Università di Firenze, Polo Scientifico, I-50019 Sesto Fiorentino, Firenze, Italy.
pubmed:publicationType
Journal Article