Synkinesis

Biochemical reactions take place in the hydrophobic centers of membranes or enzyme clefts. Aqueous compartments of biological cells are usually taboo media for the formation of small molecular assemblies or covalent compounds. There is, however, one notable exception, namely the formation of inclusion 

Model building of deoxycholeic acid assemblies and x-ray studies of inclusion compound fibers (choleic acids) show that about eight deoxycholic acid molecules may entrap one palmitic acid molecule (Fig. 3.5.2). 

The extraordinary property of the deoxycholate micelles to absorb fatty 

Natural vesicles, in particular endosomes for the fransport of proteins and nucleotides through cell membranes, contain about 50 mol% cholesterol in a bilayer where the lipids closely resemble the mixtures foimd in egg lecithins. Typ- 

Cholesterol has, in general, the effect of making fluid membrane structures manageable and selective. Edge amphiphiles form charmels in vesicle membranes containing cholesterol. It has been shown that efficient pore formation for 

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Hemifacial spasm/postfacial nerve palsy synkinesis... 

Micelles are short-lived, ill-defined assemblies (see chapter 3) of 50-100 amphiphilic molecules in water. They can be target assemblies of synkineses if they answer a well-defined purpose. For example, one may design a system in which only two different molecules form a heterodimer within each micelle. In this case, the micelle could be a very simple SDS-micelle, but the components of the dimer must be carefully fitted to the micelle s size and lifetime. Synkinesis would concentrate on the structure of the dimer components rather than the micelle. Micelles may also be used in an irreversible light-induced charge... 

An electron donor or acceptor site is usually needed in organic synthons for covalent synthesis. The covalent connection of both leads to a new molecule in an essentially irreversible synthetic reaction. Organic synkinons for non-covalent synkinesis usually contain a hydrophilic and a hydrophobic part and/or proton donor or acceptor sites. Non-covalent connection of such amphiphiles leads to a molecular assembly in a reversible synkinetic reaction. Amphiphiles are not only surface active molecules ( surfactant, detergent ), but much more important, they create surfaces. This becomes particularly evident in microemulsions and in suspensions of vesicles and micellar fibres, but is also true in nanoholes and pores, on monolayer surfaces and for many other supramolecular structures. 

There are, for example synkinons for the synkinesis of micelles, vesicles, pores, fibres and planar mono- or multilayers. A given synkinon can also be applied for another synkinetic target if the conditions are changed or if the synkinon is chemically modified. The most simple example is stearic acid. At pH 9, it is relatively well-soluble in water and forms spherical micelles. If provided with a hydrogen bonding chiral centre in the hydrophobic chains (12-hydroxystearic acid), it does not only form spherical micelles in water but also assembles into helical fibres in toluene. At pH 4, stearic acid becomes water-insoluble but does not immediately crystallize out spherical vesicles form. A second type of synkinon, which produces perfectly unsymmetrical vesicle membranes, consists of bolaamphiphiles with two dififerent head groups on both ends of a hydrophobic core. Such bolaamphiphiles are also particularly suitable for the stepwise construction of planar multilayered assemblies. 

SDS micelles with dissolved thyminyloctyl w-ammonium salts form 1 1 complexes with N-6-acetyl-9-propyl adenines (Figure 3.9). The synkinesis of... 

Figure 4.27 Long-chain bolaamphiphiles with an electroneutral and a cationic head group form membranes around anionic polymers (here DMA) and colloids. Synkinesis of organic-inorganic composite materials in bulk aqueous media can thus be achieved. ...

The first and foremost rule for the synkinesis of supramolecular assemblies deduced is Molecular assemblies can only be prepared in pure form and analysed if they are reduced to mono- or bimolecular thinness. Multilayered assemblies will mostly be mixtures of differing assemblies containing molecules in many different environments. 

Figure 5.30 A molecular necklace prepared by synkinesis of poly (ethylene glycol) bis-amine and a-cyclodextrin. The molecular assembly was finally locked by capping with 2,4-dinitrofiuorobenzene.

Self-assembled monolayers can possess a chiral surface (see previous section) or well-defined holes on a molecular scale ( nanopores ). In the following section we indicate a recent methodology for the synkinesis of nanopores. Their use as receptor sites has as yet been extremely limited. This situation, however, is changing rapidly. 

Figure 6.19 Stepwise synkinesis of multilayer films from polymerizable, dicationic bolaamphiphiles and anionic polyelectrolytes. ...

The synkinesis of isolable organized monolayers by the LB technique is not restricted to amphiphiles. They can also be obtained from stiff polymers with multiple hydrocarbon side-chains ( hairy rods ) . Regular and stable bilayers were obtained consisting of stiff rods made of cellulose or silicon phthalo-cyanate chains which were separated by fluid alkane regions. Furthermore the... 

So far, we have described synkinesis only for molecular mono- and bilayer systems. 3D crystals are, in general, considered to constitute stable, chemically dead systems with no potential for the construction of reactive, supramolecular systems. There are, however, exceptions. First of all, the surface of crystals is, of course, as reactive as any other surface. Crystal engineering is considered here as the solid-state branch of synkinesis. Furthermore crystals with large cavities have recently been prepared. They contain inner surfaces which may have interesting receptor properties in co-crystallization and photochemical fixation processes, which constitute another type of planned synkinesis. Furthermore, spontaneous 3D crystallization may compete with the synkinesis of membranes and the molecular conformations and interactions in crystals are important standards for the study of membranes. The study of 3D crystal structures of amphiphiles is therefore mandatory as a basis for all structural work on molecular assemblies. 

The great diversity of concepts and synkinetic structures which have been realized within the last decade and which is partly represented in this volume, suggests that all kinds of membranes are accessible asymmetric, as thin as 2.0 nm, helical, porous, fluid or solid, chiral on the surface or in the centre, photoreactive etc. etc. This diversity will inevitably grow. A few obvious unsolved problems which need immediate attention can also be detailed e.g. synkinesis of solid micelles and vesicles from concave molecules with at least four hydrogen bonding sites, co-crystallization of porphyrins with solid membrane structures, and evaluation of nanopores as catalytic sites. Many more such target assemblies will undoubtedly be envisioned and successfully syn-kinetized. 

The other chapters then lead from the simple to the more complex molecular assemblies. Syntheses of simple synkinons are described at first. Micelles made of 10-100 molecules follow in chapter three. It is attempted to show how structurally ill-defined assemblies can be most useful to isolate single and pairs of molecules and that micelles may produce very dynamic reaction systems. A short introduction to covalent micelles, which actually are out of the scope of this book, as well as the discussion of rigid amphiphiles indicate where molecular assembly chemistry should aim at, namely the synkinesis of solid spherical assemblies. Chapter four dealing with vesicles concentrates on asymmetric monolayer membranes and the perforation of membranes with pores and transport systems. The regioselective dissolution of porphyrins and steroids, and some polymerization and photo reactions within vesicle membranes are also described in order to characterize dynamic assemblies. 

Muscle Spasms Hemifacial spasm Facial synkinesis Masticatory spasm... 

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