SELECTIVE SELF-ASSEMBLY AND ACID-BASE CONTROLLED DE- RETHREADING OF PSEUDOROTAXANES CONSTRUCTED USING MULTIPLE RECOGNITION MOTIFS/

Citation
Pr. Ashton et al., SELECTIVE SELF-ASSEMBLY AND ACID-BASE CONTROLLED DE- RETHREADING OF PSEUDOROTAXANES CONSTRUCTED USING MULTIPLE RECOGNITION MOTIFS/, Chemistry (Weinheim), 4(11), 1998, pp. 2332-2341
Citations number
48
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
ISSN journal
0947-6539
Volume
4
Issue
11
Year of publication
1998
Pages
2332 - 2341
Database
ISI
SICI code
0947-6539(1998)4:11<2332:SSAACD>2.0.ZU;2-4
Abstract
The selective self-assembly of a threadlike tetracation, containing tw o dialkylammonium (NH2+) centers and a 4,4'bipyridinium (bpym(2+)) uni t, with an assortment of macrocyclic polyethers has been investigated. Spectroscopic studies, supported by X-ray crystallographic analyses, have demonstrated the formation of pseudorotaxanes between the thread and the macrocyclic polyethers. In particular, the macrocyclic polyeth ers dibenzo[24]crown-8 (DB24C8) and bis-p-phenylene[34]crown-10 (BPP34 C10) associate selectively with the thread's NH2+ and bpym(2+) units, respectively, to generate novel multicomponent pseudorotaxane and pseu dopolyrotaxane superarchitectures as a consequence of hydrogen-bonding and charge-transfer interactions. BPP34C10's preference for bpym(2+) units is shared by several of its dinaphtho-containing crown-l0 congen ers, which self-assemble with the tetracationic thread to produce [2]p seudorotoxanes in which the bpym(2+) moiety is encircled by the macroc yclic polyether. The reversible acid - base controlled de/rethreading of [n]pseudorotaxanes based on the multifunctional tetracationic threa d has also been studied by H-1 NMR, absorption, and fluorescence spect roscopies. Only one DB24CS macrocycle is ejected from a [3]pseudorotax ane-created from the tetracationic thread and two DB24C8 molecules-whe n both of its DB24CS-encircled NH; centers are deprotonated with base, leading to a [2]pseudorotaxane whose bpym(2+) unit is associated with the remaining DB24C8 macroring, The [3]pseudorotaxane is reestablishe d upon reprotonation of the thread with a stoichiometric amount of aci d. Treatment of this species with an excess of acid causes protonation of the DB24C8 macrorings, which are completely dethreaded thereafter, Again, the dethreading process can be reversed upon neutralization of the surplus acid with base, Addition of dicyclohexano[24] crown-8 (DC y24C8) to a solution of the [3]pseudorotaxane induces the dethreading of one of the two DB24C8 macrocycles, so that a [4]pseudorotaxane is p roduced in which the tetracation's NH2+ and bpym(2+) units are encircl ed by DCy24C8 and DB24C8 macrorings, respectively Reversible acid- bas e de-/rethreading processes have also been observed for [2]pseudorotax anes bearing the dinaphtho-containing crown-10s.