Archive of "What's New in Chemistry"

Bergmann and Raymond at UCB have synthesized a supramolecular complex with remarkable properties. The make a ligand from two moles of 2,3-dihydroxybenzoic acid and one mole of 1,5-diaminonapthalene, using an amide bond. The adjacent hydroxyl groups deprotonate to form a ligand for metals such as Ga(III), Al(III), and Fe(III), but because the two benzene rings are so remote, each forms a bond to a separate metal. In fact, four metal ions are involved, in a tetrahedral arrangement, generating a complex with the stoichiometry of ML₆^-12. This material has a hole in the center of the tetrahedron capable of encapsulating a material of 300-500 cubic Angstoms. Because of the high charge on the molecule, positive ions are especially attracted to the interior. This affinity generates a way to stabilize protonated materials sufficiently to allow acid catalyzed hydrolysis in basic solutions! Science 2007, 316, 85-88.

How amino acids arose on earth is a question chemists have asked for some time. It is known that chondrite meterorites contain amino acids, and one suggestion is that amino acids formed in the interstellar media might have been splashed onto the earth. A recent paper by Snow et. al. has explored the synthesis of amino acids by the gas phase reaction of protonated hydroxylamine with propionic acid to produce alpha and beta-alanine by both calculational and experimental methods. The formation of the beta form is favored both kinetically and thermodynamically. The calculated transition state for NH₂ insertion into the methyl C-H bond of the carboxylic acid involves strong hydrogen bonding between the hydroxylamine cation and the carbonyl oxygen of the acid. This is apparently stronger in the seven membered ring in the case of beta insertion than in the six membered ring of the alpha insertion. J. Amer. Chem. Soc., 2007, 129, 9910-9917.

In a recent paper by Mirkin and co-workers at Northwestern, it is reported that DNA fragments attached to gold nanoparticles can be used to detect aqueous Hg²⁺ in the micromolar concentration range. Gold nanoparticles exhibit absorption characteristics that are sensitive to the aggregation of the nanoparticles. The researchers made two kinds of DNA substituted nanoparticles. In the first, the DNA sequence was C₁₀T₁₀TT₁₀ and in the second it was C₁₀A₁₀TA₁₀. When these two kinds of particles are mixed, they bind to each other, leading to an aggregation of nanoparticles. The presence of mercuric ion enhances this binding because of selective coordination to the T/T mismatch. Hence the absorption characteristics of the gold nanoparticles are changed by the presence of mercuric ion, thereby generating an efficient sensor for mercuric ion. Angewandte Chemie, International Edition 2007, 46, 4093-4096.