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Copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry is widely used and has demonstrated particular utility for bio-orthogonal conjugation reactions. Here we describe a one-pot, heterogeneous bioconjugation and purification method for selectively activated CuAAC. A Cu(II) precursor, with either the neutral ligand 1,10-phenanthroline-5,6-dione or the anionic ligand 4,7-diphenyl-1,10-phenanthroline-disulfonic acid, is converted to the active Cu(I) species within an ion-exchange matrix using zinc amalgam as the reducing agent. The Cu(I) complexes are then layered on top of a size-exclusion matrix within a commercial microcentrifuge spin column; passing a mixture of an ethynyl-labeled biomolecule and an azide-bearing ligand through the column results in clean and efficient coupling. The methodology is demonstrated by glycosylating a DNA oligonucleotide as well as by labeling a membrane-penetrating peptide (octa-arginine) with a coumarin dye.

Geometrical data for 52 instances of the C--N~N substructure have been retrieved from the Cambridge Structural Database. A scatterplot of the N----N bond length (range 1.078-1.146,~,) versus the C--N bond length (range 1.278-1.450A) shows a strong negative correlation (linear correlation coefficient=-0.846): a decrease in N~N triple-bond character is directly correlated with increasing double-bond character of C--N. Three discrete chemical subgroups can be identified in the dataset: benzenediazonium compounds, adiazoketones and diazoalkanes with mean N----N/C--N bond lengths of 1.093 (2)/1.394 (6), 1.115 (3)/1.328 (5) and 1.133 (3)/ 1.301 (8),~, respectively. AbstractPrimary diffraction data for this paper [Yashima, Sasaki, Kakihana, Yamaguchi, Arasi & Yashimura (1994). Acta Cryst. B50, 663-672] have been deposited with the IUCr (Reference: OH0040). Copies may be obtained through The Managing Editor, International Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England.All relevant information is given in the Abstract.

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