Hemispherands binding

The hemispherands, spherands, calixarenes, and related derivatives. A number of hosts for which the pre-organization criterion is half met (the hemispherands) (Cram et al., 1982) or fully met (the spherands) (Cram, Kaneda, Helgeson Lein, 1979) have been synthesized. An example of each of these is given by (251) and (252), respectively. In (251), the three methoxyl groups are conformationally constrained whereas the remaining ether donors are not fixed but can either point in or out of the ring. This system binds well to alkali metal ions such as sodium and potassium as well as to alkylammonium ions. The crystal structure of the 1 1 adduct with the f-butyl ammonium cation indicates that two linear +N-H - 0... 

Why do you think corand 4.12 ([24]aneN602) is such an effective ATPase mimic given the discussion of the relatively low affinity for guest species such as alkali metal cations and halide anions set out in Chapters 3 and 4 Similarly, why was a hemispherand chosen as the central cation-binding core of enzyme mimic 12.16 as opposed to a spherand ... 

In addition to the spherands, Cram synthesized compounds in which at least half of the binding sites may be considered to be preorganized, the so-called hemispherands.6 In the parent molecule 2, the molecular cavity is composed of a rigid m-teranisyl moiety in which the oxygen binding sites are conformationally organized prior to complexation, and a flexible polyether... 

Other molecules include cryptophanes, for example, 24, hemispherands (an example is 25 " ), and podands The last-named are host compounds in which two or more arms come out of a central structure. Examples are 26 and 27 " and the latter molecule binds simple cations, such as Na, K, and Ca. Lariat ethers are compounds containing a crown ether ring with one or more side chains... 

In order to build better hosts which have preorganized binding sites. Cram and co-workers have prepared hemispherands [50] and spherands [51],... 

Similar to the hemispherands are the cryptahemispherands. Instead of a corand part, there is a cryptand part the rest of the host again is a highly preorganized spherand unit. Cryptahemi spherand 13 binds Na" as a seven-... 

Hemispberand A host derived from a spherand. Approximately half the binding sites in a hemispherand are pre organized in the manner of a spherand. 

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