1,3-Dipolar [3+2] cycloaddition between azides and alkynes—an archetypal “click” chemistry—has been used increasingly for the functionalization of nucleic acids. Copper(I)-catalyzed 1,3-dipolar cycloaddition reactions between alkyne-tagged DNA molecules and azides work well, but they require optimization of multiple reagents, and Cu ions are known to mediate DNA cleavage. For many applications, it would be preferable to eliminate the Cu(I) catalyst from these reactions. Here we describe the solid-phase synthesis and characterization of 5’-dibenzocyclooctyne (DIBO)-modified oligonucleotides, using a new DIBO phosphoramidite, which react with azides via copper-free, strain-promoted alkyne-azide cycloaddition (SPAAC). We found that the DIBO group not only survived the standard acidic and oxidative reactions of solid-phase oligonucleotide synthesis SPOS, but that it also survived the thermal cycling and standard conditions of the polymerase chain reaction (PCR). As a result, PCR with DIBO-modified primers yielded “clickable” amplicons that could be tagged with azide-modified fluorophores or immobilized on azide-modified surfaces. Given its simplicity, SPAAC on DNA could streamline the bioconjugate chemistry of nucleic acids in a number of modern biotechnologies.

Characterization of platiness of kaolin pigments was derived from the divergence of measurements of their particle size distribution by two different techniques: sedimentation and light scattering. A numerical shape factor, which is related to the ratio of kaolin particle face diameter to its thickness, can be calculated to provide a quantitative measure of such platiness. Two sets of kaolin pigments were prepared from a Middle Georgia kaolin: delaminated and non-delaminated. Shape factors of delaminated samples were higher than those of non-delaminated ones. Maximum platiness was found between equivalent volume diameters of 1·0 and 2·0 μm. Examples are presented where properties of coated paper are correlated with the size and shape of kaolin pigments.

Diphenyland diethyl-silane react with an excess of octacarbonyldicobalt to give compounds of the formula R,SiCo,(CO),, ( R = Et, Ph). High resolution i.r. and mass spectra strongly suggest that these derivatives contain nonacarbonyltricobaltmethoxy-and tetracarbonylcobalt-groups directly bonded to silicon. The corresponding hydridotetracarbonylcobaltand heptacarbonyldicobalt-silicon compounds appear to be intermediates in the reactions.

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