Ian O. Sutherland

The formation of complexes by asymmetrical tricyclic hosts

Abstract The five asymmetrical tricyclic hosts (9, a-c) and (10, a and b) were synthesised from the mono-protected diaza crown others (7a) and (7c). These hosts form 1:1 complexes with bis-alkylammonium cations H3N+CH2nN+H3. A detailed examination of the complexes of host (10a), using H NMR spectroscopy, shows that in most cases complexation involves a single conformation of the host molecule. Competition experiments show that the selectivity of complexation by this host involves at least two different conformations of the -CH2(CH2OCH2)2CH2- bridge. Complexes formed by the analogous host (10b) involve, to a major extent, a single conformation (17a) of the host molecule.

Stereospecific synthesis of exo- and endo-1,3-dimethyl-2,9-dioxabicyclo-[3.3.1]-nonane

Abstract The title compounds may be synthesised in an enantioselective and diastereospecific manner from (±)-4-hydroxynona-2,8-diene using the Sharpless asymmetric epoxidation as the key step in the reaction sequence.

Self-replication in a Diels–Alder reaction

The Diels–Alder reaction between ene 1 and diene 2 at 23 and 40 n°C shows sigmoidal characteristics for the formation of product 3 and na response to added 3 that indicates that it is an efficient catalyst for nthe reaction.

Cation binding by a crown-capped porphyrin

Abstract The crown ether capped metalloporphyrins (6) form complexes with metal cations; complex formation may be detected by fluorescence quenching for (6, M=ZnII or CuII) and paramagnetic guest cations or, in some cases, by FAB mass spectrometry. Complexation with alkyl ammonium cations was also examined using absorption spectrometry.

Face to face porphyrins as synthetic host molecules

Abstract The bis-zincporphyrins 9 and 11 were prepared from the bis-(3′-hydroxyphenyl)-porphyrin 6. Both bis-zincporphyrins formed complexes in CHCl3 with a variety of amines and showed a strong preference for diamines, such as H2N(CH2)nNH2 and 4,4′-dipyridyl. The limited degree of chain length recognition for the diamine guests by both hosts is associated with conformational flexibility of both host and guest but the rigid guest, 4,4′-dipyridyl, is selectively complexed through operation of the chelate effect.

Chromoionophores with high lithium and sodium selectivity

Abstract The new phenolic cryptand reagents 2a and 2b are readily prepared and have very high selectivity for Li + and Na + respectively.

Chelation effects in the binding of bidentate ligands by a face-to-face zinc porphyrin

The face-to-face zinc porphyrin (2) is a selective host for 4,4′- bipyridyl as compared with the diamines H2N(CH2)nNH2. This selectivety arises from a much higher chelation factor (14M) for the bipyridyl guest as compared with the very low factors (M) for the diamines. These results are discussed in terms of host and guest structures and compared with other host–guest systems.

Molecular Recognition by Macropolycyclic Hosts

The formation of complexes between crown ethers and aklylammonium cations may, to some extent, be modelled using standard molecular mechanics methods and an appropriate charge distribution scheme. Monocyclic crown ethers may be developed to give chromoionophores suitable for use in optical fibre based ion sensors. The incorporation of two crown ether systems into polycyclic host molecules which show highly selective complexation of guest bis-alkylammonium cations is described. The scope of these ditopic receptors may be extended by using metalloporphyrins in place of one or both of the crown ether binding sites.

The synthesis of phenolic cryptands–efficient acid catalysis in a molecular cavity

The reaction of 1,3-bisbromomethyl-2-methoxy benzene with diaza-15-crown-5 or diaza-18-crown-6 in acetonitrile gives the phenolic cryptands 6a and 6c; it is shown that the formation of 6a involves the methoxy cryptand salt 9 which undergoes efficient demethylation by bromide anion as a result of acid catalysis within the cavity of the cryptand system.

A chromogenic reagent for calcium. The importance of ion-pairing in cation selection

The chromoionophore 2 has been synthesised from the corresponding diaza 18-crown-6 in two steps in good overall yield, and the reagent 2 extracts calcium cations from aqueous solutions in the pH range 7–9 with moderately high selectivity as compared with sodium and with high selectivity as compared with other cations of biological interest; the series of apparently similar reagents 2, 3 and 4 shows very wide variation in Na+/Ca2+ selectivity.