Click chemistry in materials synthesis. III. Metal‐adhesive polymers from Cu(I)‐catalyzed azide–alkyne cycloaddition

1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007     

Polytriazoles as copper(I)-stabilizing ligands in catalysis

Polytriazolylamines were synthesized by the copper(I)-catalyzed ligation of azides and alkynes. The C3-symmetric derivative, TBTA, was shown to be a powerful stabilizing ligand for copper(I), protecting it from oxidation and disproportionation, while enhancing its catalytic activity.     

Characterization of NIST food-matrix standard reference materials for their vitamin C content

The vitamin C concentrations in three food-matrix Standard Reference Materials (SRMs) from the National Institute of Standards and Technology (NIST) have been determined by liquid chromatography (LC) with absorbance detection. These materials (SRM 1549a Whole Milk Powder, SRM 1849a Infant/Adult Nutritional Formula, and SRM 3233 Fortified Breakfast Cereal) have been characterized to support analytical measurements made by food processors that are required to provide information about their products’ vitamin C content on the labels of products distributed in the United States. The SRMs are primarily intended for use in validating analytical methods for the determination of selected vitamins, elements, fatty acids, and other nutrients in these materials and in similar matrixes. They can also be used for quality assurance in the characterization of test samples or in-house control materials, and for establishing measurement traceability. Within-day precision of the LC method used to measure vitamin C in the food-matrix SRMs characterized in this study ranged from 2.7 % to 6.5 %.     

Mechanisms of tetrazole formation by addition of azide to nitriles

It is well-known that azide salts can engage nitriles at elevated temperatures to yield tetrazoles; however, there is continued debate as to the mechanism of the reaction. Density functional theory calculations with the hybrid functional B3LYP have been performed to study different mechanisms of tetrazole formation, including concerted cycloaddition and stepwise addition of neutral or anionic azide species. The calculations presented here suggest a previously unsuspected nitrile activation step en route to an imidoyl azide, which then cyclizes to give the tetrazole. The activation barriers are found to correlate strongly with the electron-withdrawing potential of the substituent on the nitrile.     

Preparation and characterization of standard reference material 1849 infant/adult nutritional formula

Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST.