Heterodimerizers solutions

To see whether water could be activated and added to Jt-systems other than alkynes, the metal-catalyzed hydrolysis of nitriles was studied [20]. For this purpose novel homodimeric and heterodimeric bis(acetylacetonato)ruthenium(ii) complexes bearing the 6-diphenylphosphino-N-pivaloyl-2-aminopyridine (10a) and 3-diphenylphosphinoisoquinolone (Ila) ligands were prepared. The molecular structures of these precatalyst were studied in solution and also in the solid state and revealed some unusual hydrogen-bonding patterns, in particular for the heterodimeric system in which the acetylacetonato ligand is involved (Scheme 2.7). 

On the other hand, there are examples of exclusive heterodimerization. Both tetra-aryl- and tetra-tosylureas readily form homodimers when they are dissolved alone in an apolar solvent. However, heterodimers are the only detectable species in a solution containing both compounds in a 1 1 ratio. An example of this selective heterodimerization [41] is demonstrated by the NMR-spectra in Figure 5.4. Only when one of these tetra-ureas is present in excess can signals for its homodimer be seen by NM R. This early observation by Rebek and Castellano [42] is especially important for the template syntheses described below. Other examples of exclusive formation of heterodimers will be discussed later. 

All proton NMR spectra were recorded on a Varian Unity 600 at 25 C. 6 to 10 mg of the disulfide linked c-Myc-Max heterodimeric LZ were dissolved in 0.5 mL of potassium phosphate buffer (50 mM, 10% DiO / 90% H2O and pH 4.7) containing 100 mM KCl and ImM 2,2-dimethyl-2-silapentane-5-sulfonic acid (DSS) to yield solutions ranging from 0.75 to 1.25 mM. Proton resonances were assigned from two-dimensional double quantum filtered correlation spectroscopy (DQF-COSY (21)), two-dimensional total correlation spectrocopy (TOCSY mixing time = 50 ms (22)) and two-dimensional nuclear Overhauser enhancement spectrocopy (NOESY mixing times = 150 and 200 ms (23)) experiments. Sequential assignment of the proton resonances was performed as described by Wuthrich (24). 

Lavigne P, Crump MP, Gagne SM et al (1998) Insights into the mechanism of heterodimerization from the 1H-NMR solution structure of the c-Myc-Max heterodimeric leucine zipper. J Mol Biol 281 165-181... 

Reinhoudt and co-workers (51) targeted O2 and prepared water-soluble models of heme-protein active sites. These were self-assembling, heterodimeric capsules of cationic Co(II) porphyrin (27) and tetrasulfonato calix[4]arene (28) (Fig. 12). A millipore VMWP membrane, loaded with an aqueous solution of 27 (2 mA/), 28 (6mM), and 1-methyl imidazole (20 mM), showed a facilitated transport of O2. The facilitation factor of 1.15 and the O2/N2 selectivity of... 

Olefin Cross Metathesis. Olefin cross metathesis (CM) represents a valuable alternative to traditional carbon-carbon double bond forming reactions however, its practical utilization is sometimes limited by the generation of multiple homodimerization products (4 and 5) when reacting 1 and 2 to obtain the desired heterodimerization product 3 in solution phase (Scheme 6.1a). A solid support can induce chemoselectivity in CM reactions, as the immobilization of one olefin as 6 can effectively prevent its homodimerization (Scheme 6.1b). Moreover, the soluble olefin 2 can be added in excess to drive the reaction to completion. While the soluble olefin is capable of... 

Rebek and co-workers also prepared hybrid dimeric capsules based on resorcin [4]arene 15 and tetraimide cavitand 12 (Fig. 32.7) [39, 40]. In CDCI3 solution, mixtures of resorcinarene 15 and cavitand 12 at different molar ratios produced three different containers in varying amounts the two homocapsular assemblies (156 12 12) and the heterodimeric assembly (12 15) [39]. Interestingly, in the... 

The calix[4]arene-based ligand syntones 129-133 with either aryl urea or sulfonylurea fragments on the upper rims in their cone-conformation gave small hydrogen-bonded capsules 338-342 by Scheme 3.24, while their heterodimeric capsules have been exclusively formed when both aryl- and sulfonylureas-containing syntones are present in solution [25]. All these homo- and het-erodi- and tetrameric capsules are able to reversibly encapsulate suitable guests in organic media. 

Simultaneous, multiple ester formation was employed to assemble larger multitopic assemblies. For example, self-assembled molecular capsules via boronate esterification have been demonstrated. Two calix[3]arenes, one having the upper rim functionalized with diols, the other functionalized with boronic acids, were combined in the presence of a templating agent to form the heterodimeric capsule (Fig. 25). Extensive NMR analysis was performed to show that the two calixarenes in solution by themselves do not interact. It is only when tetramethyl ammonium acetate is added that the capsule forms. NMR diffusion studies have further demonstrated that the ammonium cation is included within the cavity. In addition, reversible decomposition-reconstruction of the capsule was observed in response to pH. 

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