Tweezers, molecular

Molecular Tweezers of Light Take the Measure of a Muscle Fiber s Force... 

Zimmermann, S.C. Rigid Molecular Tweezers as Hosts for the Complexation of Neutral Guests. 165, 71-102 (1993). 

A new chiral benzothiazine ligand 205 was synthesized by Harmata and co-workers <06JOC3650>. It could be converted into a chiral molecular receptor 207 in a simple way. This chiral species 207 could be used as a new class of chiral molecular tweezers. The synthesis of 205 commenced with the protection of the commercially available compound 202, which was then coupled with f7tj-sulfoximinc 77b using the one-pot, one-operation procedure <99AG(E)2419> affording enantiomerically pure benzothiazine 204. This was followed by deprotection to produce benzothiazine 205 in good yield. 

The reactions of titanocene derivatives TiX(C CsCR)Cp 2 (X = C1, C= CC=CR R = SiMe3, Et) or of cis-Pt(C=CC=CR)2(PR 3)2 with mononuclear metal complexes have given numerous products in which the diynyl ligand(s) are chelated to a low-valent metal via the internal C=C fragment(s). These cis-bis(diynyl) complexes are often referred to as molecular tweezers. 

A variety of molecules with a functional group located in a cleft have been synthesized (a) Zimmerman SC, Zeng Z, Wu W, Reichert DE (1991) J Am Chem Soc 113 183 ( Molecular tweezers ) (b) Rebek Jr J, (1990) Angew Chem 102 261 Int Ed Engl 29 245 (Oefts based on derivatives of Kemp s acid ). In both classes, a functional group is located in a slot. But the shielding is only from the top and from the bottom, not from the sides. 

Rigid Molecular Tweezers as Hosts for the Complexation of Neutral Guests... 

Mirkin and coworkers reported on catalytic molecular tweezers used in the asymmetric ring opening of cyclohexene oxide. In this case the early transition metal is the catalyst and rhodium functions as the structural inductor metal. The catalyst consists of two chromium salen complexes, the reaction is known to be bimetallic, and a switchable rhodium complex, using carbon monoxide as the switch. Indeed, when the salens are forced in dose proximity in the absence of CO the rate is twice as high and the effect is reversible [77]. 

Klarner et al. undertook detailed studies of the host/guest relationships between molecular tweezers formed from condensed hydrocarbon arenes and symmetrically and asymmetrically dendryl-substituted viologens - with a 4,4 -bi-pyridinium core acting as -electron acceptor and a Frechet-type dendron as 71-electron donor (Fig. 6.23). The strong fluorescence of the 1,3-dimethylenoxyben-zene units of the Frechet dendron is quenched as a result of the donor/acceptor interaction. Accordingly, in dichloromethane solution the 4,4 -bipyridinium core... 

Fig. 6.23 Uptake of a dendritic viologen-type guest molecule in the cavity of molecular tweezers (schematic according to...

Fig. 6.26 Molecular tweezers 1 as host compound and dicationic, dendritically substituted viologen guest compounds (3 and 4) of different generation numbers (according to Balzani, Klarner, Vogtle et al.)...

Molecular clips and tweezers are two closely related types of compound. Molecular tweezers represent a simple kind of receptor in which two guest-binding domains usually comprising flat,... 

Scheme 6.5 Conformational change in molecular tweezers 6.44 upon aromatic guest binding.29...

Figure 6.27 Optimised geometries of molecular tweezers 6.46 and 6.47. Tweezers 6.47 are ca.10 A wide at the tips but can close up upon guest binding.31...

Explain the incorporation of the methyl substituents in the Kemp s triacid based molecular tweezers shown in Scheme 6.6 in terms of the principle of preorganisation discussed in Chapter 1. 

Zimmerman, S. C., Rigid molecular tweezers as hosts for the complexation of neutral guests. Top. Curr. Chem. 1993, 165, 71-102. 

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