Dumbbell-shaped molecules

The x-ray structure of free calmodulin was determined by the group of Charles Bugg, University of Alabama. It is a dumbbell-shaped molecule... 

Clipping. The clipping method relies on the synthesis of the rotaxane by formation of the macrocycle (host) in the presence of a dumbbell shaped molecule. The partial macrocycle undergoes a ring closing reaction around the dumbbell shaped molecule, thereby forming the rotaxane. 

This stiffness also has an influence on the shape of the dendrimers, when different core building units are employed. The biphenyl core 9 leads to the dumbbell shaped molecule whose most stable conformers show a twist between 20° and 60° around the central biphenyl unit. 2, based on the tetrahedral core 4, with a diabolo-like molecular shape which resembles the shape of the core very well. Due to the large number of benzene rings around the central methane unit, the branches are hindered in their rotation (Scheme 4), lowering the internal mobility of the molecule compared to 15. 

Scheme 4.29. Cascade construction of dumbbell shaped molecules that form stacked aggregates in aqueous environments.

The application of this template to the clipping of acyclic dumbbell-shaped molecules to form rotaxanes [14] has received less intensive scrutiny but involves a similar synthetic scheme and conditions. A few representative examples of [2]rot-axanes synthesized in this manner (16-20) are shown in Figure 10.2 [15c, 18-21]. The use of a 1,5-dihydroxynaphthalene core in these cases usually results in higher yields of the desired interlocked products [18,21]. 

Schmittel M, Kalsani V, Mai P, Bats JW (2006) The HETTAP approach self-assembly and metal ion sensing of dumbbell-shaped molecules and clip molecules. Inorg Chem 45 6370... 

Fig. 81 Dumbbell-shaped molecules based on oligobiphenylene fragments...

Several macrocyclic compounds have been prepared using Wittig reactions including tetraepoxyannulenes, which utilized the ylide derived from phos-phonium salt (57), and rotaxanes, molecules in which one or more macrocyclic components are trapped around a rod section of a dumbbell-shaped molecule, obtained by treating terephthaldehyde derivatives with dibenzylic bis(triphenyl-phosphonium)-stoppered [2]rotaxane (58). Aromatic triesters have been obtained by the (ethoxycarbonylmethylene)triphenylphosphorane-catalysedcyclo-trimerisation of ethyl propynoate. ... 

The simplest rotaxanes are molecules made from a macrocycle threaded onto a dumbbell-shaped molecule consisting of an axle bearing bulky end groups (or stoppers) to prevent macrocycle unthreading. The name rotaxane was coined in 1967 by Schill and Zollenkopf [3] and supplanted the term hooplane proposed the same year by Harrison and Harrison [4]. As a matter of fact, these authors described quite simultaneously two very different rotaxane syntheses. 

Apart from this n-vector model allowing for a -component order parameter, there is also the need to consider order parameters of tensorial character. This happens, for example, when we consider the adsorption of molecules such as N2 on grafoil. For describing the orientational ordering of these dumbbell-shaped molecules, the relevant molecular degree of freedom which matters is their electric quadrupole moment tensor,... 

The prototype EF hand protein, calmodulin, is found in all eukaryotic cells and may exist as an individual monomeric protein or as a subunit of a multimeric protein. A dumbbell-shaped molecule, calmodulin contains four Ca -blndlng sites with a Kq of 10 M. The binding of Ca " to calmodulin causes a conformational change that permits Ca /calmodulln to bind various target proteins, thereby switching their activity on or off (Figure 3-28). Calmodulin and similar EF hand proteins thus function as switch proteins, acting in concert with Ca to modulate the activity of other proteins. 

Rotaxane is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule that is threaded through a macrocycle. The name... 

FIGURE 2.15 Molecular structure of amphiphilic dumbbell-shaped molecule 14 and representation of the reversible interconversion of helical fibers into nanocapsules. Reprinted with permission from Reference 55. Copyright 2006 John Wiley Sons, Inc. 

Rotaxanes (see Rotaxanes—Self-Assembled Links, Self-Processes) are interlocked structures in which one or more (polyrotaxanes) cyclic components are threaded by a dumbbell-shaped molecule (the axle). In pseudorotaxanes, the two components can dissociate but with a considerable kinetic barrier. The formation of pseudorotaxanes generally... 

Recently, a third process has been identified which constitutes an example of strict self-assembly.The so-called slippage approach to rotaxane synthesis Figure 5) is based upon size complementarity between the macrocyclic polyether, BPP34C10, containing two 7i-electron rich recognition sites and the stoppers comprised of suitable tetra-arylmethane groups at the ends of dumbbell-shaped molecules incorporating at least one 4,4 -bipyridinium unit. ... 

During the late sixties the structurally more complex nogalamycin (10) [72] was isolated and characterized. This anthracycline is unique as two carbohydrate groups (nogalose and aminoglucose) are linked to the opposite ends of the tetracyclic aglycon, yielding a dumbbell shaped molecule. As a consequence, one of the bulky... 

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