Larger Linked Systems

Di- and polytopic host-guest systems have provided a convenient starting point for the construction of larger assemblies and many systems of this type are now known. For example, in an early study Kimura et synthesised the catecholamine complex 17. The crown ether unit of this ditopic host was known to be an effective receptor for primary alkyl ammonium salts, whereas the partially protonated form of the hexamine ring had been documented to bind anionic substrates (such as car-boxy lates) or electron-donor substrates (such as catechols). Accordingly, this host forms stable 1 1 complexes with zwitterionic guests such as amino acids, pep- 

Kimura, H. Fujioka and M. Kodama, J. Chem. Soc., Chem. Commun., 1986, 1158. 

Whitesides et al. have prepared a series of large self-assembled structures containing multiple host-guest interactions. These assemblies were built around primary interactions between cyanuric acid (CA) and melamine (M) derivatives as illustrated by 18 (and were designated CA-M) where CA contains similar hydrogen 

Further members of the series having, for example, double-decker (19) and tripledecker (20) structures have been prepared together with other examples incorpo- 

A related aggregate based on hub(MMM)3 , incorporating nine melamine centres, has been reported. In this case, hub(MMM)3 associates with nine neo-hexylisocyanurates to yield an aggregate containing ten molecules that are arranged in three parallel rosettes. The structure is stabilised by 54 hydrogen bonds. 

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Automation System A system based on a computer technology with input devices (e.g., sensors), output devices (e.g., actuators), and communication links (e.g., telemetry and cable networks) that are collectively designed to perform a specific function or group of functions (e.g., control, protection or monitoring). Automation systems may be linked into larger integrated systems. [Defined for this book.]... 

A bromine-initiated method for the preparation of sulfonate-linked aziridines has been developed <2001TL1037>. Treatment of the sulfonamide with r-butylhypochlorite generates the intermediate Wchloramine salt. Reaction of the chloramine with phenyltrimethylammonium bromide (PTAB) provides the sulfonamide-linked aziridine. This method does not provide any improvement in yield relative to either the copper- or rhodium-catalyzed reaction systems. It does however work for the preparation of the bicyclo[5.1.0] system as both the copper- and rhodium-catalyzed reactions give C-H insertion products in this attempt to prepare the larger ring system (entry 6). 

Figure 1.44 Allowed values cp and ip angles for 0-glycosidic link of cellobiose (a) or maltose (b). In (a) black squares or circles indicate positions of observed conformational angles in cellobiose or cellobiose units found in larger polysaccharide systems. In (b) black triangle or circles indicate position of observed conformational angles in maltose or maltose units found in a larger polysaccharide systems (adapted from Rees Smith, 1995, Figs. 7 5).

In small domestic systems, the electricity will be converted to a single AC voltage. In larger industrial systems, the fuel ceU wiU be linked to a three-phase supply, as discussed in Section 10.3.2. 

The resistivity of epoxy resins to radiation increases with cross-link density. However, highly cross-linked systems are brittle and less suited for cryogenic applications. A dose of 5 x lO Gy (5 x 10 rad) is admissible for very brittle epoxy resins and 10 Gy (10 rad) for flexible resins. Thermoplastics with atoms larger than C, H, O, N, such as fluorine in PTFE, exhibit a large cross section to slow neutrons and are not stable to radioactivity (33). Pol3dmides, eg, Kerimid 601, are more resistant than epoxy resins (34). 

Molecules larger than those considered so far are fonned by linking together several smaller components. A new kind of dynamics typical of these systems is already seen in a molecule such as C2Hg, in which there is hindered rotation of the two methyl groups. Systems with hindered internal rotation have been studied in great... 

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