Further Metal-containing Systems

289 Transition Metals in Supramolecular Chemistry, ed. J.P. Sauvage, Wiley, New York, 1999. 

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Electrode potentials are relative values because they are defined as the EMF of cells containing a reference electrode. A number of authors have attempted to define and measure absolute electrode potentials with respect to a universal reference system that does not contain a further metal-electrolyte interface. It has been demonstrated by J. E. B. Randles, A. N. Frumkin and B. B. Damaskin, and by S. Trasatti that a suitable reference system is an electron in a vacuum or in an inert gas at a suitable distance from the surface of the electrolyte (i.e. under similar conditions as those for measuring the contact potential of the metal-electrolyte system). In this way a reference system is obtained that is identical with that employed in solid-state physics for measuring the electronic energy of the bulk of a phase. 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

In order to achieve improved nanofabrication performance, novel functional block copolymer systems are strongly desired. Many researchers have recognized this, and novel functional systems such as metal-containing block copolymer systems have significantly simplified and improved nanofabrication processes. The combination of top-down microscale patterns with the bottom-up nanopatterns are attractive for integrating functional nanostructures into multipurpose on-chip devices. However, in order to use these materials in real-time applications, further development is still needed. More ground-shaking discoveries are needed and are also fully expected. 

Apart from ATRP, the concept of dual initiation was also applied to other (controlled) polymerization techniques. Nitroxide-mediated living free radical polymerization (LFRP) is one example reported by van As et al. and has the advantage that no further metal catalyst is required [43], Employing initiator NMP-1, a PCL macroinitiator was obtained and subsequent polymerization of styrene produced a block copolymer (Scheme 4). With this system, it was for the first time possible to successfully conduct a one-pot chemoenzymatic cascade polymerization from a mixture containing NMP-1, CL, and styrene. Since the activation temperature of NMP is around 100 °C, no radical polymerization will occur at the reaction temperature of the enzymatic ROP. The two reactions could thus be thermally separated by first carrying out the enzymatic polymerization at low temperature and then raising the temperature to around 100 °C to initiate the NMP. Moreover, it was shown that this approach is compatible with the stereoselective polymerization of 4-MeCL for the synthesis of chiral block copolymers. 

Although some of the concepts established for metal/ oxide systems are also valid for non-oxide ceramics, there are other concepts which are specific to these kinds of ceramics, owing to their predominantly covalent (SiC, BN, AIN) or metallic (TiC, TiN, WC) character. These materials seldom can be obtained as the high-purity monocrystalline specimens desirable for fundamental wetting studies. Usually, they are sintered materials with impurity contents higher than 0.1% and they often contain open porosity. Further difficulties arise from the high oxidization tendency of many of them, the presence of an oxide layer dramatically changing their wettability by liquid metals. 

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