Showing papers by "J. Fraser Stoddart published in 1990"

From Enzyme Mimics to Molecular Self-Assembly Processes

Abstract: Publisher Summary This chapter discusses that the development of enzyme mimics and analogues is traced from those systems inspired by one of nature's gifts—the cyclodextrins—through to some of the many wholly synthetic examples that have been realized in the wake of the accidental discovery of the crown ethers. It has been suggested that a second generation of such man-made compounds, which are larger in terms of molecular weight, emerges from a new synthetic strategy that relies on the self-assembly, molecule-by-molecule, of supramolecular and polymolecular structures. The commonly recognized features of enzymes need not necessarily all be shared by artificial enzymes. The chapter discusses that enzyme mimics have many advantages—including much greater stabilities to reaction conditions—over enzymes. They can also be modified structurally to satisfy a given set of requirements.

A New Mode of Metal Encapsulation

Abstract: All ten oxygen atoms of the acyclic oligomer 1 c participate in the coordination of Ba2⊕ in the “scorpion” complex 1c · Ba(SCN)2 · Me2CO. The eleventh coordination site is occupied by the acetone molecule. A further characteristic of the complex are strong OHċN hydrogen bonds to the thiocyanate counterion. The ligands 1 also exhibit a high selectivity for cations with ionic radii of 1.2–1.3 A, which could be explained with the help of molecular modeling studies. (Figure Presented.) Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany

Complexation and Molecular Recognition of Neutral and Anionic Substrates in the Solid and Solution States by Bisparaquat(1,4)Cyclophane

Abstract: The bisparaquat(l,4)cyclophane O4+, which can be synthesized in two steps from bipyridine and para-xylylene dibromide, is soluble as its tetrakis(hexafluorophosphate) in organic solvents such as acetonitrile and as its tetrachloride in water. In acetonitrile, O4+·4PF6− forms weak 1:1 inclusion complexes with 1,2−, 1,3−, and 1,4-dimethoxybenzene whereas, in water, 04+·4Cl− binds hydroquinol as well as its dimethyl ether. X-Ray crystallography shows that the bisparaquat(1,4)cyclophane tetracation O4+ forms crystalline 1:1 inclusion complexes with 1,2− and 1,4-dimethoxybenzenes in which the π-electron rich diphenol ethers are sited inside the channels of the π-electron deficient bipyridinium rings of the tetracation O4+ separated, as before, by layers of anions and neutral molecules in continuous hollow stacks of a zeolitic nature.