Supramolecular assemblies structural characterization

In this context it is interesting to note that archaea, which possess S-layers as exclusive cell wall components outside the cytoplasmic membrane (Fig. 14), exist under extreme environmental conditions (e.g., high temperatures, hydrostatic pressure, and salt concentrations, low pH values). Thus, it is obvious one should study the effect of proteinaceous S-layer lattices on the fluidity, integrity, structure, and stability of lipid membranes. This section focuses on the generation and characterization of composite structures that mimic the supramolecular assembly of archaeal cell envelope structures composed of a cytoplasmic membrane and a closely associated S-layer. In this biomimetic structure, either a tetraether... 

Reference [33] describes recent progress on cyanine probes that bind noncova-lently to DNA, with a special emphasis on the relationship between the dye structure and the DNA binding mode. Some of the featured dyes form well-defined helical aggregates using DNA as a template. This reference also includes spectroscopic data for characterizing these supramolecular assemblies as well as the monomeric complexes. 

The nanometer- to micrometer-scale dimensions of supramolecular assemblies present many challenges to rigorous compositional and structural characterization. Development of adequate structure-property relationships for these complex hierarchical systems will require improved measurement methods and techniques. The following areas constitute critical thrusts in instrument development. 

Arsenic dithiocarbamates, As(S2CNR2)3 (R = Bu, CH2Ph),399 and toluene-3,4-dithiolato arsenic and bismuth dithiocarbamato derivatives, (MeC6H3S2) M(S2CNR2) (M = As, Bi R = Me, Et, CH2CH2)400 have been structurally characterized and the supramolecular self-assembly in Sb(III) dithiocarbamates has been carefully examined.401... 

The past decade has seen a dramatic improvement in the strategies and instrumentation available to characterize the structures of interfacial supramolecular assemblies. Current thrusts are towards in situ techniques that probe the structure of the interfacial supramolecular assembly with increasingly fine spatial and time resolution. The objective of this field is to assemble reaction centers around which the environment is purposefully structured at the molecular level, but extends over supramolecular domains. The properties of the assembly are controlled not only by the properties of the molecular building blocks but especially by the interface. Therefore, the focus is on both the interfacial and bulk properties of monolayers and thin films. Issues that need to be addressed include the film thickness, structural homogeneity and long-range order, as well as the electrochemical and... 

To further explore the environment inside such hexameric hosts, Atwood and coworkers performed structural characterization and spectrofluorometric studies of the capsule-bound fluorescent probe molecule pyrene butyric acid (PBA) 52 [71]. Single-crystal X-ray diffraction studies on 52 (50b)6 show not only that encapsulated guests interact with the host walls in the solid state, but also that the n surfaces of the guest molecules are well separated from one another within the capsule. The spectroscopic studies in solution corroborated this finding and revealed an average of 1.5 molecules of 52 per capsule. The assembly remains intact over four weeks in the solution phase, suggesting that the carboxylic acid groups and the polyaromatic nature of 52 do not destabilize the overall supramolecular assembly. 

Calixarene-based M5 [calix[4]arene sulfonates] vH20 (M = Na x= 12) K (v = 8) Rb (x = 5) Cs (x = 4J) have been used to construct supramolecular assemblies. They have been structurally characterized, and exist as bilayers of anionic truncated pyramids in the cone configuration ... 

The book describes the wealth of membrane structures realized by chemists mainly within the last two decades - micelles, vesicles, fibres, and surface monolayers - from the point of view of supramolecular chemistry. It puts new emphasis on "synkinetic" procedures for the preparation of non-covalent assemblies as well as their structural characterization by electron microscopy, solid state NMR spectroscopy, and comparison to X-ray crystal structures. 

This chapter deals with structurally characterized tin(II) and tin(IV) compounds containing either unusual bonds to tin atoms or unique geometric arrangements around the tin center. While we emphasize molecular compounds, selected examples of supramolecular assemblies featuring unusual structural traits are also discussed. Strictly inorganic compounds will not be considered, as they are amply described elsewhere. ... 

Crystallography does not help directly in synkinetic chemistry, since the molecular conformations in three-dimensional crystals are invariably different and in general much more simple than in supramolecular assemblies. Packing forces usually flatten out bends in molecules, which are all-important in highly hydrated and curved assemblies. Crystals should, however, be used as references for the interpretation of solid-state C-NMR spectra, which do not provide directly any information about conformations. Equally useful are crystal structures of cocrystals of two different compounds. They make it possible to identify and characterize the major molecular interactions (Dunitz, 1979 Luger, 1980 Cluster et al., 1994), which are presumably also present in heterodimers and assembhes in water. 

In the case of ort/io-disubstituted aldehydes, one obtains extremely dense n stacks with Soret band absorptions at 370 nm, whereas meta-disubstituted analogs give a lateral packing characterized by 450-nm Soret bands (Fig. 6.3.1). Such covalent porphyrin oligomers are useful references in structure elucidation of corresponding supramolecular assemblies, where one cannot hope for a... 

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