Noncovalent interaction, donor-acceptor

D. Noncovalently Linked Donor-Acceptor Pairings via Hydrogen-Bonding Interaction. 313... 

D. NONCOVALENTLY LINKED DONOR-ACCEPTOR PAIRINGS VIA HYDROGEN-BONDING INTERACTION... 

As in the molecular case (Dl), the definition (D2) allows the supramolecular unit(s) to be determined by an operational NBO search of a given electron distribution ir(fi, r2,..., Fjv ) 12. Given the NBO molecular units of the distribution, we can search the intermolecular interactions (e.g., the table of perturbative donor-acceptor stabilizations) to determine the connecting noncovalent bonds that satisfy the required thermal threshold, and thereby determine the contiguously bonded supramolecular unit(s) by (D2). 

Fig. 18 Different representations of the same donor-acceptor [2]catenane. Line drawings (a) and condensed structural formulas (b) were the order of the day until the modem era of MIMs gave way to structural diagrams (c) and crystal structures (d). Graphical representations, also called cartoons (e), can be a helpful compromise between these representations when attempting to emphasize the topology, noncovalent bonding interactions, shape, beauty, or function of a MIM...

The formation of a hydrogen bond between the amide proton and one carbonyl oxygen of NQ was indicated in the Ec + —NQ /M" complex to stabilize the complex (see above). Electron-transfer reactions were believed to be regulated through such noncovalent interactions that play an important role in biological ET systems, where electron donors and acceptors are usually bound to proteins at a fixed distance (123-127). Eor example, in the bacterial photosynthetic reaction center (bRC) from Rhodobacter Rb) sphaeroides, an electron is transferred from... 

In the context of the foregoing discussion, the hydrogen-bonded donor-acceptor supramolecules of Figure 1 meld the constructs of both inter- and intramolecular electron transfer. From the standpoint of intermolecular electron transfer, these systems represent a preformed precursor complex held together by noncovalent interactions from the standpoint of intramolecular electron transfer, these systems provide a fixed-distance donor-acceptor pair in which charge transport occurs along a noncovalent pathway. 

The formation of the donor acceptor complexes of Figure 1 occurs by self-assembly , which is defined as the noncovalent interaction of two or more molecular subunits to form an aggregate whose novel structure and properties are determined by the natures and positioning of the components [27 32]. The construction of complex, multicomponent aggregates requires intermolecular interactions that are directional and/or selective. The selectivity, particularly in asymmetric and multiply-bonded systems, allows for considerable influence over the association process by careful use of complementary components. With directionality, it is possible to control the separation and, in some cases, the relative orientation between donor-acceptor subunits. 

System 1 is a benchmark in D—[H]—A electron-transfer studies because it provides the first direct experimental validation to the hypothesis that donor-acceptor coupling is affected by the presence and nature of the noncovalent interaction. Comparison of 1 with Wasielewski s covalently linked model system 2 [71], which... 

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