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Hemocyanins are large multi-subunit copper proteins that transport oxygen in many arthropods and molluscs. Comparison of the amino acid sequence data for seven different subunits of arthropod hemocyanins from crustaceans and chelicerates shows many highly conserved residues and extensive regions of near identity. This correspondence can be matched closely with the three domain structure established by x-ray crystallography for spiny lobster hemocyanin. The degree of identity is particularly striking in the second domain of the subunit that contains the six histidines which ligate the two oxygen-binding copper atoms. The polypeptide architecture of spiny lobster hemocyanin appears to be the same in all arthropods. This structure must therefore be at least as old as the estimated time of divergence of crustaceans and chelicerates, about 540 to 600 million years ago.

Also, two minor isomers were detected 6 3.07 (dt, J = 10, 2.5 Hz) and 6 3.31 (dm, J = I O Hz) in a 95.1:2.6:2.3 ratio. (la,2cr,3a)-N-Methyl-6-isopropylidene-3-propy~-4-cyclohexen~l,2dicarboximide: 'H NMR (CDC13, 200 MHz) 6 0.95 (t, J = 7.2 Hz, 3 H), 1.43-1.89 (m, 4 H), 1.91 (s, 3 H), 2.00 (s, 3 H), 2.29 (m, 1 H), 2.79 ,925,905, 840,790,735 cm-l; MS, m / e 364, 320, 308, 211. (la,2cr,3a)-N-Methyl-S-( tert -butyldimethylsiloxy)-6-isopropylidene-3-propyl-4-cyclohexene-l,2-carboximide: IH NMR (CDC13, 200 MHz) 1.30-1.86 (m. 4 H), 1.96 (s, 3 H), 2.13 (m, 1 H), 2.86 (s, 3 H), 3.06 (dd,

8-Cyclodextrins bearing two or seven aminomethyl groups in the 6-position (compounds la,b) are shown to act as polytopic receptors for nucleotides. la discriminates the guest compounds on the basis of nucleobase nature, sugar type (oxy-or deoxyriboses), and position of the phosphate groups (3' or 5'). For the first time such selectivity toward different moieties of nucleotides is realized by one artificial receptor simultaneously and in water as a solvent. lb, although considerably less selective, exhibits very high sensitivities with binding constants of up to 3 X 106 M-1. Comparison between complexes with inorganic phosphates, ribose phosphates, riboses, and nucleotides allows quantification of the different binding contributions: up to 20 kJ/mol for ionic interactions (as a function of the number of salt bridges) and 10-13 kJ/mol for the ribose unit. The nucleobases, although discriminated, are shown to contribute repulsive rather than attractive forces to complex formation. Complexation-induced NMR chemical shifts and intermolecular NOES allow insight into the supramolecular structures. These results are in line with molecular mechanics simulations (CHARMm) which also show that the strong electrostatic interactions with l b draw the substrate further away from the secondary interaction sites and thus lower the selectivity. The sugar moiety is shown by NOE to rest in the cyclodextrin cavity. This complexation, in contrast to usual expectations, is stronger for the more hydrophilic ribose derivatives in comparison to the deoxy compounds. Selective broadening of some proton signals is ascribed, on the basis of T1 measurements, to complex dissociation processes rather than slow tumbling effects. IntroductionThe selective complexation of nucleotides and nucleosides by synthetic host compounds has been the focus of an increasing number of publication^.^^^ These studies can make essential contributions toward the understanding of noncovalent interactions involving nucleic acids, as well as toward the development of new diagnostic tools. Most of the reported synthetic hosts rely on complexation through hydrogen bonding with a nucleobase. Consequently, many of these systems, with a few exception^,^ were studied in lipophilic solvents. In aqueous solutions, the major

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