title: One-dimensional random walk of a synthetic small molecule toward a thermodynamic sink.
abstract: We report on the spontaneous intramolecular migration of α-methylene-4-nitrostyrene from amine group to amine group along oligoethyleneimine tracks up to eight repeat units in length (number of amine footholds, n = 3, 5, 9). Each track consists of n - 1 aliphatic secondary amine footholds plus a naphthylmethylamine group foothold situated at one end of the track. Under basic conditions the α-methylene-4-nitrostyrene unit undergoes a series of reversible intramolecular Michael-retro-Michael reactions between adjacent amine groups that move it up and down the track. For n = 3 and 5 it is possible to monitor the population of every positional isomer on the track by (1)H NMR spectroscopy. On the longest track (n = 9) the fraction of walkers on each end-foothold can be quantified with respect to those on the inner footholds. In all cases the naphthylmethylamine foothold acts as a thermodynamic sink with the steady-state distribution significantly biased in favor of the walker at that site. The dynamics of the walker migration is well described by the random walk of a Brownian particle in one dimension.
authors.affiliation: School of Chemistry, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JJ, United Kingdom.
authors.forename: Araceli G
authors.initials: AG
authors.lastname: Campaña
authors.forename: David A
authors.initials: DA
authors.lastname: Leigh
authors.forename: Urszula
authors.initials: U
authors.lastname: Lewandowska
mesh_terms: D015394:Molecular Structure; D008970:Molecular Weight; D013343:Styrenes / Q000138:chemical synthesis* / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D013343:Styrenes