Guest chemicals

Cyclo- dextrin Guest Chemical composition" Space group Ref. 

The concept of photostimulated phase separation can be applied to construct chemical-induced phase transition systems, which change the conformation reversibly in response to special chemicals. For the systems, host molecules are used as the receptor groups instead of photoisomerizable chromophores. Host molecules, such as crown ethers or cyclodextrins, are known to change the property by capturing guest chemicals in their cavity [16]. We employed benzo[l 8]crown-6 as the receptor molecule and incorporated it into the pendant groups of PNIPAM. 

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],... 

Most uses of the CDxs involve host/guest chemistry. They mainly form inclusion complexes with a variety of molecules (largely organic compounds). Many applications have been encountered, from modifications in the physical-chemical properties of guests to changes in the guest chemical activity. ... 

Examples of the hydroquinone inclusion compounds (91,93) are those formed with HCl, H2S, SO2, CH OH, HCOOH, CH CN (but not with C2H 0H, CH COOH or any other nitrile), benzene, thiophene, CH, noble gases, and other substances that can fit and remain inside the 0.4 nm cavities of the host crystals. That is, clathration of hydroquinone is essentially physical in nature, not chemical. A less than stoichiometric ratio of the guest may result, indicating that not all void spaces are occupied during formation of the framework. Hydroquinone clathrates are very stable at atmospheric pressure and room temperature. Thermodynamic studies suggest them to be entropic in nature (88). 

Inclusion compounds open up a wide area of applications (1,2,17—28). An important aspect in this connection is the specific microenvironment created by the host enclosure of the guest which exerts an influence on the physical, spectroscopic, chemical, and other properties of the guest. 

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

Chemical transformations at the macroeyclic chromophorc of expanded porphyrins are still not known. The complexation behavior of expanded porphyrins is very different from that of nonexpanded porphinoid macrocycles. The coordination hole of the expanded porphyrins is often too big for the complexation of a single metal ion, so in fact two metal ions can be chelated. With some expanded porphyrins, anion binding is observable, a striking difference to the nonexpanded porphyrins. The complexation behavior and the host-guest chemistry of expanded porphyrins is a rapidly growing field of research. The work in this field has been reviewed. Ie f... 

Under near-equilibrium conditions the shape of this curve is related to two contributions, the compositional dependence of the configurational entropy of the guest ions, and the contribution to the chemical potential from the electron gas [31]. 

The primary question is the rate at which the mobile guest species can be added to, or deleted from, the host microstructure. In many situations the critical problem is the transport within a particular phase under the influence of gradients in chemical composition, rather than kinetic phenomena at the electrolyte/electrode interface. In this case, the governing parameter is the chemical diffusion coefficient of the mobile species, which relates to transport in a chemical concentration gradient. 

Parts of this paper were prepared at the Department of Chemical Engineering, Massachusetts Institute of Technology, where the author was a guest in the academic year 1964-1965. 

Figure 34 Chemical formula of y-cyclodextrin consisting of eight glucose molecules with adamantane as the guest entrapped within its hydrophobic cavity. Structures of a- and P-cyclodextrins will be similar but made up of six and seven (n = 6, 7) glucoses,...

---