Living in a Cage Is a Restricted Privilege

Abstract

There exist molecules, whose shape is reminiscent of a cage, that are able to include either metal ions or anions or both. In contrast to what happens in the macroscopic world, where a kinetic barrier prevents the escaping of the guest from the cage, the inclusion-extrusion of an ion from a molecular cage is in most cases thermodynamically controlled and the ion can get in or out of the cage at will. This gives the basis for highly selective ion recognition processes by cage-shaped ligands or receptors for metal ions and anions. Nobody in everyday life would say that a cage (for birds or wild animals), even if nicely designed and splendidly decorated, was beautiful and appealing, due to the consciousness of its reprehensible function. This does not happen in chemistry and we admire the ingenuity and skilfulness of synthetic chemists for the design of cage-shaped polycyclic hosts, made for the inclusion of a variety of guests, but also capable of generating in the viewer emotion and gratification of aesthetical origin. We have tried to outline, in this chapter, the development of cages in metal coordination chemistry and in anion coordination chemistry, over the last 50 years.

[18F]Fluoropyridine‐losartan: A new approach toward human Positron Emission Tomography imaging of Angiotensin II Type 1 receptors

“…Interference from sodium chloride isotonic solutions was reported to produce broader spots with larger retention factor of Kryptofix® 2.2.2, due to the presumable formation of the cryptand‐sodium ion complex 31 . In fact, the feasibility of the complex formation was confirmed by X‐ray diffraction characterization of the crystalline salt 32 . Halvorsen et al reported a fast and simple TLC spot‐test method for the determination of tetrabutylammonium or Kryptofix® 2.2.2 in 18 F‐labeled radiopharmaceuticals, using iodoplatinate‐impregnated TLC plates 25 .…”

“…31 In fact, the feasibility of the complex formation was confirmed by X-ray diffraction characterization of the crystalline salt. 32 Halvorsen et al reported a fast and simple TLC spot-test method for the determination of tetrabutylammonium or Kryptofix ® 2.2.2 in 18 F-labeled radiopharmaceuticals, using iodoplatinate-impregnated TLC plates. 25 Following this procedure, we were able to analyze the residual Kryptofix ® 2.2.2 in [ 18 F]fluoropyridine-losartan formulations containing ascorbic acid.…”

An Introduction to the Mechanical Bond

“…It is well accepted that the beauty of a molecular structure is often associated with its shape in Euclidean geometry (topography), but here we recognize that beauty can be associated with topology as well. 233 have also engaged the beauty of molecular knots in a chapter in a monograph 32 on Beauty in Chemistry. We refer the reader to these articles for further discussion on topological beauty.…”

“…Following an introduction to the mechanical bond across a variety of different settings, communities, and length scales, we will preview the range of this book's contents in the context of molecular aesthetics (Section 1.3), before finally offering a perspective (Section 1.4) on the evolution of mechanostereochemistry. The discussion in Sections 1.1-1.3, which is driven by the concept of beauty in chemistry, 32 is expanded upon and borrowed from, in part, our review 33 of mechanical bonds in the context of beauty, with permission from the publisher (copyright 2012 Springer-Verlag).…”