Decapeptide Agonists of Human C5a: The Relationship between Conformation and Spasmogenic and Platelet Aggregatory Activities

A series of decapeptide analogues corresponding to the C-terminal region of human C5a anaphylatoxin (C5a) was synthesized with residue substitutions to restrict conformational flexibility in the C-terminus. These conformationally constrained peptides behaved as agonists of C5a in spasmogenic assays (smooth muscle contraction in human fetal artery, guinea pig ileum, and guinea pig lung parenchyma) as well as guinea pig platelet aggregation. There were significant correlations in the potencies of these peptides between the various assays. A structure-function analysis led to the identification of a preferred backbone conformation that correlated with the expression of these biological responses. These backbone structural motifs were consistent with a helix-like conformation for residues 65-69, an elongated structure for residues 70-71, and a β-turn of either type II or type V for residues (71)72-74. The most potent of these agonists expressed almost 5% if the potency of natural C5a

Bent carbon surface moieties as active sites on carbon catalysts for phosgene synthesis

Active sites in carbon-catalyzed phosgene synthesis from gaseous CO and Cl2 have been identified using C60 fullerene as a model catalyst. The carbon atoms distorted from sp2 coordination in non-planar carbon units are concluded to generate active Cl2. Experiments and density functional theory calculations indicate the formation of a surface-bound [C60⋯Cl2] chlorine species with radical character as key intermediate during phosgene formation. It reacts rapidly with physisorbed CO in a two-step Eley-Rideal-type mechanism