Supramolecular Anchoring

Fig-1 Schematic presentation of supramolecular anchoring of catalysts to dendritic... 

Fig. 7 The concept of supramolecular anchoring of catalysts to dendritic binding sites immobilized on silica (A) and the binding motif based on hydrogen bonding (HB) that has been used...

The properties of photochromic molecules such as DHI 7 and related compounds are dependent not only on structure but to a large extent also on their environment. Clear differences are to be expected if solution or solid phases of photochromic molecules are compared, i.e. (1) containing supramolecular anchor groups, (2) in liquid crystalline phases, or (3) polymer-containing photochromic systems. It is necessary to use the appropriate spectral methods for the detection of different properties. In addition to normal methods, photoacoustic spectroscopy (PAS), polarized light, and others may be applied. 

Abstract Artificial metalloenzymes can be created by incorporating an active metal catalyst precursor in a macromolecular host. When considering such artificial metalloenzymes, the first point to address is how to localize the active metal moiety within the protein scaffold. Although a covalent anchoring strategy may seem most attractive at first, supramolecular anchoring strategy has proven most successful thus far. 

Figure 10.9 Ligands used for artificial metalloenzymes designed for supramolecular anchoring to SAV.

A supramolecular assembly of macromolecules bearing antenna dendron has been reported. Pyrazole-anchored PBE dendrons were synthesized to examine the coordination behavior to transition-metal cations (Cu, Au, Ag) [31]. Self-assembled metallacycles were found. The Cu-metallacycle further formed luminescent fibers about 1 pm in diameter. The luminescence (605 nm) occurred by the excitation of the dendron (280 nm) and the excitation spectrum was coincident with the absorption spectrum of the dendron, suggesting the antenna effect. Interestingly, the luminescence of the Cu-metallacycle fiber disappeared when the fiber was dissociated into the individual metallacycles in C2H2. 

Besides the preparation of glyconanotube conjugates by supramolecular interactions, another synthetic pathway commonly used involved covalent attachment of the saccharidic units on the CNT scaffolds. The progress recently recorded concerning the derivatization of unfunctionalized CNTs, allowing introduction of suitable anchoring functions at their surface, are the basis of this synthetic alternative.255... 

Ribaudo F, van Leeuwen PWNM, Reek JNH (2006) Supramolecular Dendritic Catalysis Noncovalent Catalyst Anchoring to Fimctionalized Dendrimers. 20 39-59 Richmond TG (1999) Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds. 3 243-269... 

Precedence for remote electron transfer like that observed in the Ti02-Ru (II)-L-Os(II) triads exists. In previous work, a supramolecular approach for designing a molecular sensitizer with controlled orientation of the component units on the semiconductor surfaces was reported (Fig. 9). The binuclear compound is based on a fac-Re(I)(dcbH2)(CO)3 surface anchoring unit and a —Ru(II)(bpy)2 chromophore linked through an ambidentate cyanide ligand [24]. Due to the facial... 

Supramolecular chemistry also provides new tools for catalyst anchoring. We have shown that catalysts can be noncovalently attached to various soluble and insoluble supports, affording recyclable catalysts. Interestingly, the reversible nature of the noncovalent bond gives rise to new opportunities. In the first instance, we foresee an important role for supramolecular bidentate ligands in combinatorial catalysis - but as a consequence of the entirely new properties many new applications are envisioned. We look forward to new developments and results in this exciting emerging area of supramolecular catalysis. 

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