Molecular acid - base-controlled

Fig. 17 (a) Seif-assembly of the triply threaded supramolecular system 14 j13H36+ and the subsequent synthesis of the triply interlocked species 15H39+. (b, c) Operation of I5H39+ as an acid-base controlled molecular elevator [78-80]... 

Selectivity in catalytic oxidation/reduction and acid-base reactions has been a long-term challenge in the catalysis field. While it has been recognized that the control of molecular activation and reaction intermediates is critical in achieving high selectivity, this issue has not been adequately addressed and is a serious challenge to the field. 

Oxidation. Oxidative studies are designed to reveal the primary oxidative degradation products due to oxidation. Oxidative degradants in drug substances and drug products normally are the result of reaction with molecular oxygen. As in the case of acid/base hydrolysis, appropriate controls are necessary. 

These interactions may usefully be described as an acid-base type interaction, in which the cyclopropane ring acts as a base (electron donor) and the proton or cationic center acts as the acid (electron acceptor). One of the factors that controls the basicity of a hydrocarbon is the energy of the highest occupied molecular orbital (HOMO).60 The 6-31 G HOMO energies of some cycloalkanes and cycloalkenes are given in Table 4.61... 

Figure 13.11 Structure formula of 10H39+ and its operation as a molecular elevator controlled by acid-base inputs.

Figure 6.7 A chemically controllable molecular shuttle. The macrocydic ring can be switched between the two stations of the dumbbell-shaped component by acid-base inputs.

There has been a resurgence of interest in proton-coupled redox reactions because of their importance in catalysis, molecular electronics and biological systems. For example, thin films of materials that undergo coupled electron and proton transfer reactions are attractive model systems for developing catalysts that function by hydrogen atom and hydride transfer mechanisms [4]. In the field of molecular electronics, protonation provides the possibility that electrons may be trapped in a particular redox site, thus giving rise to molecular switches [5]. In biological systems, the kinetics and thermodynamics of redox reactions are often controlled by enzyme-mediated acid-base reactions. 

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