Host-guest chemistry characterization

Electronic spectroscopy has significantly contributed to the characterization of zeolites and of molecules adsorbed on their internal surface. A comprehensive review of UV-VIS spectroscopic investigations on zeolitic systems is too wide a scope to cover in this article. Instead different topics of application will be surveyed illustrated by selected examples taking into special account more recent work. As in zeolite science it has become fashionable to speak of host/guest chemistry, so first the host and later the guest will be discussed. 

Soon after crown ethers came on the scene as the first synthetic host molecules capable of binding guests, cryptands followed, and soon thereafter, the spherands. The preorganization of these three classes of molecules follows the order of their invention, as does overall binding affinity, i.e., crownsNobel Laureate, was the creator of the family of hosts that he named spherands. The spherand story began shortly after the genesis of supramolecular chemistry, and it demonstrates how quickly the field matured, as complex syntheses and methods of characterization enhanced the rapid sophistication of host-guest chemistry. 

The formation of clathrate inclusion compounds in which guest species are enclosed by channels or cages that occur in a given host lattice was first discovered in the middle of the past century Since then a large number of clathrates and solvates, found mostly by chance as by-products of research in other areas, have been characterized ". These multicomponent systems attracted however relatively little attention, and a systematic development of their chemistry was very slow. The rapid advancement of host-guest chemistry in the last two decades, since the pioneering work of Pedersen on crown ethers provided a turning point in this respect. Initially,... 

Cahxarenes are one of the most interesting scaffolds for molecular recognition in host guest chemistry. The versatihty of calixarene macrocycles includes modification of their upper and lower rims, different conformation behavior, and hydrophobic cavity for the inclusion of guest molecules. The conformational preference of calixarene derivatives depends on the substitution at the upper and lower rim. Numerous attractive receptors have been developed for the detection of various guest molecules. The molecular recognition can be characterized by various... 

This handbook serves as a companion volume to Zeolite Science and Technology, which was published in 2003. The scope and philosophy of the two books is much the same because they share the same publisher and coeditors. Because both volumes are strong on the basics and fundamentals, they are handbooks rather than simple monographs on the most recent applications, which tend to become outdated quickly. It has been our intent to focus keenly on the fundamental properties of the materials. Advances made in recent years concerning synthesis, characterization, host-guest chemistry, and modern applications are included. The permanent intracrystalline porosity feature ties these layered materials together for adsorptive and catalytic applications, among others. 

Dynamic combinatorial chemistry (DCC) is marvelously effective at discovering receptors for a broad array of analytes. The nature of the internal competition experiment ensures (normally) that the most effective binder for the analyte of interest is amplified for subsequent identification and characterization. In the context of a host-guest assembly, the issue of stereochemistry can be manifested in a number of scenarios. These include various permutations of chiral or achiral guests, along with achiral, enan-tiopure, or racemic dynamic library components. 

Fendler JH (1982) Membrane mimetic chemistry characterizations and applications of micelles, microemulsions, monolayers, bilayers, vesicles, host-guest systems, and polyions. Wiley, New York... 

Studies on molecular recognition by artificial receptors are thus one of the most important approaches to such characterization in relation to supramolecular chemistry [4]. Functional simulation of intracellular receptors in aqueous media has been actively carried out with attention to various noncovalent host-guest interactions, such as hydrophobic, electrostatic, hydrogen-bonding, charge-transfer, and van der Waals modes [5-10]. On the other hand, molecular recognition by artificial cell-surface receptors embedded in supramolecular assemblies has been scarcely studied up to the present time, except for channel-linked receptors [11-13]. 

Like the currently popular area, called nanoscience , the field of supramolecular chemistry has rather hazy boundaries. Indeed, both areas now share much common ground in terms of the types of systems that are considered. From the beginning, electrochemistry, which provides a powerful complement to spectroscopic techniques, has played an important role in characterizing such systems and this very useful book goes considerably beyond the volume on this same topic by Kaifer and Gomez-Kaifer that was published about 10 years ago. Some of the classic supramolecular chemistry topics such as rotaxanes, catenanes, host-guest interactions, dendrimers, and self-assembled monolayers remain, but now with important extensions into the realms of fullerenes, carbon nanotubes, and biomolecules, like DNA. 

Jerry L. Atwood is Curator s Professor of Chemistry at the University of Missouri-Columbia. His research has focused on supramolecular chemistry. His research group has synthesized and examined a broad array of host-guest chemical systems (e.g., liquid clathrates, macromolecular hosts). A principal method for characterization of these systems has been single crystal X-ray structure determination [41-43],... 

Chapter 9 (Biological Applications—Supramolecular Chemistry). Independent of their easily observed photochromic behavior, characterized by their absorption spectra, photochromic compounds are interesting models for supramolecular chemistry involving selective host-guest recognition. This is especially true for biological applications. 

SFB 624 in Bonn proposed a definition for template-assisted reactions [265] which states that a template steers a reaction through spatial pre-organization of the reactants via a suitably defined pattern of non-covalent, covalent, or coordinative-reversible bonds. It acts as an entropic sink such that thermochemical criteria can be used to characterize the template-mediated process. Template-mediated reactions may revolve several times but high turn over numbers are not necessarily required. Also, the template does not necessarily need to be recovered once the reaction took place. In this work, we elaborate on this non-formal description, which aims to embrace as many chemical processes involving templates and host-guest interactions as possible. Our aim is to arrive at a more formal basis utilizing well-established thermochemical concepts. The classical thermochemical approach of physical chemistry to chemical reactions may provide an option to define transferable concepts for the plethora of template-assisted processes. 

J. H. Fendler, Membrane Mimetic Chemistry Characterization and Applications of Micelles, Microemulsions. Monolayers, Bilayers. Vesicles, Host-Guest Systems and Polyanions, Wiley-Interscience, New York, 1982. 

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