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Azapeptides, peptide analogues in which the alpha-carbon of one or more of the amino acid residues is replaced with a nitrogen atom, exhibit propensity for adopting beta-turn conformations. A general protocol for the synthesis of azapeptides without racemization on solid phase has now been developed by introducing the aza-amino acid residue as an N-Boc-aza(1)-dipeptide. This approach has been validated by the synthesis of six N-Boc-aza(1)-dipeptides and their subsequent introduction into analogues of the C-terminal peptide fragment of the human calcitonin gene-related peptide (hCGRP). By performing an aza-amino acid scan of such antagonist peptides, a set of aza-hCGRP analogues was synthesized to examine the relationship between turn secondary structure and biological activity.

Compounds with strong thermodynamic affinity for carbon dioxide (CO(2)) have been designed and synthesized that dissolve in CO(2), then associate to form gels. Upon removal of the CO(2), these gels produced free-standing foams with cells with an average diameter smaller than 1 micrometer and a bulk density reduction of 97 percent relative to the parent material.

Scheme 1. Proposed reactions of Mn ions and tmtacn ligands in zeolite Y. Reaction a: In the chelation reaction, the Mn" ion leaves an all-zeolite coordination, for example on a six-membered ring, to form a mononuclear [ M n " ( t m t a~n ) ]~~ chelate complex. Reaction b: The interaction of [Mn"(tmta~n)]~'-NaY with H,O, in a wateriacetone medium leads to intrazeolite formation of Mnii'-MniV dinuclear complexes or other dimerization products (X = 0'-, OH-, or other oxygen bridges).

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