DOSY study on dynamic catenation: self-assembly of a [3]catenane as a meta-stable compound from twelve simple components.

Synthesis of [2]catenane 6 has been successfully achieved by the combination of Pd complex 1 and pyridines 2 and 3 at a molar ratio of 2:1:1 in D20. A mixture of square molecule 4 (prepared from 1 and 2) and macrocycle 5 (obtained from 1 and 3), in which the final ratio of 1, 2, and 3 was kept 2:1:1 reorganizes in D2O/CD3OD (1:1) to form 6 within one day. However, the same mixture in D2O shows the formation of novel [3]catenane 7 along with the [2]catenane. In order to make 7, the theoretical ratio of components 1, 2, and 3 should be 3:1:2. Thus, deliberately maintaining such ratio of the above-mentioned molecules, a higher proportion of the [3]catenane is observed in D2O as found from 1H NMR spectra of the system. Reorganization of the twelve components to form [3]catenane is supported by studies with the DOSY method. This method is a first attempt to separate, from a mixture, either catenanes or any other supramolecular self-assembly structures. CSI-MS studies further support the assigned catenane super structures 6 and 7. All the results indicate that the [2]catenane is thermodynamically the most stable structure, while the [3]catenane is a meta-stable self-assembly.

Cavity-directed synthesis of labile silanol oligomers within self-assembled coordination cages.

This paper introduces a concept that is referred to as cavity-directed synthesis by showing the selective oligomerization of trialkoxysilanes, RSi(OMe)3 (7), in self-assembled hollow compounds. Pd(II)-linked coordination hosts (cage, bowl, or tube) are found to strictly control the oligomerization of 7 (R = 2-naphthyl) in such a way that their optimal guests are produced in their cavities. Thus, within coordination tube 1, one molecule of 7 is accommodated and subsequently hydrolyzed to give silanetriol RSi(OH)3 (4). Under ordinary aqueous conditions, this reactive compound undergoes rapid polycondensation (so-called sol-gel condensation) leading to Si-O networks. Within the cavity of 1, however, 4 remains very stable and the polycondensation is completely suppressed. On the other hand, coordination bowl 2 and cage 3 give its dimers RSi(OH)2OSi(OH)2R (5) and cyclic trimers [RSi(OH)O]3 (6), respectively. X-ray crystallographic studies clearly show that the cavity size and the shape of 1, 2, and 3 nicely fit with those of 4, 5, and 6, respectively, demonstrating that the cavities strictly direct the oligomerizaion reaction of 7.

Characterization of encapsulating supramolecules by using CSI-MS with ionization-promoting reagents.

Guanidine nitrate, DMF, DMA, and DMSO are proven to be efficient ionization-promoting reagents in coldspray ionization mass spectrometry (CSI-MS) for the self-assembled cage Pt compound 1 in aqueous solution. These reagents made it possible to characterize the structures of encapsulated guest molecules in the cage. Detailed structure determinations of the cage compound encapsulating various kinds of guest molecules by using positive CSI-MS with ionization-promoting reagents are described.