Radical-based Reactions Research Articles

Copper‐biomolecule complexes in the gas phase. The ternary way

This review deals with copper complexes of a variety of organic and bioorganic molecules that have been produced as gas-phase ions by electrospray and other ionization methods and studied experimentally by mass spectrometry and theoretically by ab initio and density functional theory computations. Ternary complexes of Cu((II)) allow one to modify the oxidation state and coordination sphere of the copper ion and thus induce novel fragmentations that involve redox and radical-based reactions. Structure elucidation, distinction, and quantitation of leucine and isoleucine isomers in peptides, distinction of enantiomers in chiral compounds, and sensitive detection of antibiotics are some of the highlights of mass spectrometry of ternary copper complexes. Binary copper complexes are mainly represented by Cu((I)) species in which the copper ion displays the properties of a weak Lewis acid.

Review of vinyl graft copolymerization featuring recent advances toward controlled radical-based reactions and illustrated with chitin/chitosan trunk polymers.

Review of vinyl graft copolymerization featuring recent advances toward controlled radical-based reactions and illustrated with chitin/chitosan trunk polymers.

Crystallographic investigations of ribonucleotide reductase

Introduction Ribonucleotide reductase catalyses the de novo production of deoxyribonucleotides. The enzyme reduces all the four main ribonucleotides to the corresponding deoxyribonucleotides. In higher organisms and in Eschmkhziz coli. this takes place at the diphosphate level I 1 1. Kibonucleotide reductase from E. coZi is a multisubunit alpL enzyme, where the two homodinieric proteins are denoted R1 and R2. The larger a L subunit I i l contains the binding sites for the substrate and for allosteric effectors, and also the redox-active cysteine residues [ 1 J. Subunit R1 has a molecular mass of 2 x 86 k1)a and each subunit contains 76 1 residues. K 1 carries two types of allosteric-effector sites: an overall activity site and a substrate-specificity site. ATP works as a general effector for eilzynie activity. The substrate-specificity effectors regulates the enzyme, so that suitable proportions of the different deoxyribonucleotides are produced. The smaller pL protein, denoted R2, contains the dinuclear ferric centre, and a stable free tyrosyl radical that is necessary for the enzymic activity [ 21. l'he K2 protein has a molecular mass of 2x43,s k l h , and each subunit contains 375 amino acids. K 2 was shown to contain a tyrosyl radical a long time ago, and the radical was shown to be localized over the tyrosine ring. From sequence comparisons, the radical tyrosine was suggested to be Tyr', which was later confirmed by site-directed mutagenesis 13). 7'he radical is generated in close cooperation with a binuclear iron centre by molecular oxygen. T h e ribonucleotide subunit K 2 was the first enzyme for which a stable free protein radical was ch;iracterized [ 21. Since then, a number of enzymes have been shown to use amino acids as 'built in' redox cofactors in radical-based reactions (see other papers in this colloquium). 'l'he radical tyrosyl122 is essential for the activity of the enzyme, and was therefore thought to participate in the enzymic reaction by creating an intermediate substrate radical, thereby activating the substrate for further reduction by a pair of thiols [4]. The tyrosyl radical is not consumed in the substrate-reduction cycle and the radical transfer between Tyr' and the substrate must be reversible in such a scheme. The tyrosyl radical can be scavenged by different nucleotide analogues binding at the active site, which demonstrates the feasibility of a radical transfer from Tyr* to the substrate. There is, however, no evidence yet for a radical transfer in the other direction, from the substrate to Tyr'.