Supramolecular assemblies, host-guest

Andersen UN, Seeber G, Fiedler D, Raymond KN, lin D, Harris D (2006) Characterization of self-assembled supramolecular [Ga4L4] host-guest complexes by electrospray ionization mass spectrometry. J Am Soc Mass Spectrom 17(3) 292-296... 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

This entry to supramolecular chemistry allows one, at the same time, to develop a host-guest chemistry because the space inside the cucurbituril barrel is sufficient to confine small "guesf molecules. This is illustrated with the crystallization of the supramolecular adduct [W3S4(H20)8Cl](pyH ccuc) Cl4a 5.5 H2O with a pyridinium cation inside the cucurbituril cavity [48]. The introduction of guest molecules may vary the net charge on the assembly and consequently the whole packing in the solid state. 

Goshe, A.J., Steele, I.M., Ceccarelli, C., Rheingold, A.L. and Bosnich, B. (2002) Supramolecular chemistry and self-assembly special feature supramolecular recognition on the kinetic lability of thermodynamically stable host-guest association complexes. Proceedings of the... 

Host-guest systems made from dendritic materials have potential in the areas of membrane transport and drug delivery [68, 84, 85]. In a recent report [136] Tomalia and coworkers investigated structural aspects of a series of PAM AM bolaamphiphiles (e.g., 50) with a hydrophobic diamino do decane core unit. Fluorescence emission of added dye (nile red) was significantly enhanced in an aqueous medium in the presence of 50 unlike the cases when 51 and 52 were added (Fig. 23). Addition of anion surfactants to this mixture generated supramolecular assemblies which enhanced their ability (ca.by 10-fold) to accommodate nile red (53). Further increase in emission was noted by decreasing the pH from the normal value of 11 for PAMAM dendrimers to 7. At lower pH values the... 

Siderophore-ionophore supramolecular assembly formation via host-guest complexation of the pendant protonated amine arm of ferrioxamine B has been confirmed by X-ray crystallography (Fig. 28) (203). The stability and selectivity of this interaction as a function of ionophore structure, metal ion identity, and counter anion identity were determined by liquid-liquid extraction, isothermal calorimetry, and MS (204 -211). Second-sphere host-guest complexation constants fall in the range 103— 106M-1 in CHC13 and methanol depending on ionophore structure. 

Fig. 28. Host-guest complex formed between ferrioxamine B (4) and 18-crown-6 crown ether an ionophore-siderophore supramolecular assembly.

Keywords Supramolecular Chemistry m Host-Guest Chemistry m Self-Assembly... 

Keywords Constrictive Binding m Crown Ethers m Hemicarcerands a Host-Guest Chemistry a Noncovalent Interactions aRotaxanes a Self-Assembly a Slippage a Supramolecular Chemistry... 

Indeed, we anticipate that the Platonic and Archimedean solids may be used for the construction of hosts which conform to those solids not yet realized and additional members of each family, where supramolecular synthesis, via self-assembly, will play a major role in their design, ushering in an era of spherical host-guest chemistry. 

Noncovalent interactions play a special role in synthetic procedures used to assemble various types of supramolecular species. These syntheses rely on the stabilization provided by non-covalent interactions between recognition sites incorporated within precursors. Various types of non-covalent interactions can be used as a recognition motif utilized to guide the synthesis.Targeted synthesis of macro- and supramolecular structures of various sizes, shapes, and functionality has now become possible. Supramolecular chemistry offers incredible applications in various fields such as medicinal chemistry (drug delivery systems),host-guest chemistry,catalysis,and molecular electronics. ... 

As described above, cavitand 13 is able to extract efficiently silver(I) ion. For a guest to host ratio G/H>2 a new species was formed and recovered in quantitative yield and was identified as the 2 4 complex 132-(AgPic)4. The X-ray crystal structure of the 132-(AgPic)4 complex showed a supramolecular assembly made of two cavitands linked by their upper rim with four silver cations through P=S...Ag...S=P coordination (Fig. 9) [70]. 

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. 

Pluth, M.D. and Raymond, K.N. (2007) Reversible guest exchange mechanisms in supramolecular host-guest assemblies. Chem. Soc. Rev, 36 (2), 161-171. 

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