Anions or Cations: Who Is in Charge of Inhibiting the Nickel(II) Promoted B- to Z-DNA Transition?

Various weakly binding cations and anions were studied at a concentration of 10 mM to ascertain their interaction with the nickel(II) promoted B- to Z-DNA transition of poly d(GC). These salts were ranked according to the decreasing amounts of nickel needed for the B- to Z-DNA transition and provided the following order:  NaCl ≈ Me4NCl > LiCl ≫ MgCl2 > no salt > NaBF4 ≈ NaNO3 ≈ NaClO4. Remarkably, it was found that going from sodium nitrate to sodium chloride increased the necessary amount of nickel to induce the transition to the left-handed helix of poly d(GC) by a factor of 10. This dramatic effect cannot be explained by the binding constant of nickel(II) to chloride to form the monocationic complex. We believe that this is the first reported example of the role of chloride anions, which appear to modulate the interaction of nickel(II) ions with the polyanionic DNA

Post-Protein-Binding Reactivity and Modifications of the <i>fac</i>-[Re(CO)₃]⁺ Core

The reactivity of the [Re­(CO)₃(H₂O)₂]⁺ complex coordinated to the His15 residue of HEW lysozyme is described. In the fully metalated protein (<b>Lys-1</b>), the Re ion retains its reactivity only toward selected ligands, while others induce a ligand-mediated demetalation of the enzyme. It is further shown that some of the complexes that may be “engineered” <i>on</i> the lysozyme do not react with the free protein even if present in solution in excess. The formation of stable metal adducts starting from <b>Lys-1</b> was confirmed by X-ray crystallography

The Synthesis of 1,2-Bis(1,5,9-triazacyclododecyl)ethane: A Showcase for the Importance of the Linker Length within Bis(alkylating) Reagents

The synthesis of 1,2-bis(1,5,9-triazacyclododecyl)ethane (1) showcases how different bis(alkylating) reagents change the reaction from an intra- to an intermolecular pathway. The isolation of the intermediate hexahydro-3a,6a-ethano-1H,4H,7H,9bH-9a-aza-3a,6a-diazoniaphenalene-3a,6a-diium (2) explained why initially the synthesis of 1 was not possible. Both isomers of 2 were found in solution. DFT calculations revealed that isomer 2a is 4.6 kcal/mol lower in energy than 2b. Synthesis of 1 was finally achieved by using oxalyl chloride

New Chiral Hypervalent Iodine Compounds in Asymmetric Synthesis

The synthesis of new chiral hypervalent iodine compounds 3 and their use in asymmetric oxidative functionalizations are described. The substituents in the chiral moiety and the stereoelectronic properties of the reagents 3, as well as the reaction conditions, have been optimized. Chiral hypervalent iodine compounds 3 have been investigated in the asymmetric dioxytosylation of styrene and in the α-oxytosylation of propiophenone as test reactions. X-ray structural analysis of some reagents shows an interaction between the chiral moiety and the iodine resulting in stereoselectivities up to 53% ee in the products

The Synthesis of 1,2-Bis(1,5,9-triazacyclododecyl)ethane: A Showcase for the Importance of the Linker Length within Bis(alkylating) Reagents

The synthesis of 1,2-bis(1,5,9-triazacyclododecyl)ethane (1) showcases how different bis(alkylating) reagents change the reaction from an intra- to an intermolecular pathway. The isolation of the intermediate hexahydro-3a,6a-ethano-1H,4H,7H,9bH-9a-aza-3a,6a-diazoniaphenalene-3a,6a-diium (2) explained why initially the synthesis of 1 was not possible. Both isomers of 2 were found in solution. DFT calculations revealed that isomer 2a is 4.6 kcal/mol lower in energy than 2b. Synthesis of 1 was finally achieved by using oxalyl chloride

Hydrolysis of β-Lactam Antibiotics Catalyzed by Dinuclear Zinc(II) Complexes: Functional Mimics of Metallo-β-lactamases

Three stable dinuclear zinc(II) complexes, [Zn2L1(μ-NO3)(NO3)2] and [Zn2L1(μ-OMe)(NO3)2], where L1 is 2,6-bis{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-methylphenolate, and [Zn2L2(NO3)3], where L2 is 2-{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-bromo-6-{[N‘-2-(2‘-pyridyl)ethyl]aminomethyl}phenolate, were synthesized and characterized in the solid state and in aqueous solution. These complexes catalyze the hydrolysis of penicillin G and nitrocefin, serving as functional synthetic analogues of the metallo-β-lactamases, bacterial enzymes responsible for antibiotic resistance. The mechanism of the hydrolysis was studied in detail for the catalyst precursor [Zn2L1(μ-NO3)(NO3)2], which converts into [Zn2L1(μ-OH)(NO3)n(sol)2-n](2-n)+ in the presence of water. The complex [Zn2L1(μ-OH)(NO3)2] (n = 2) was characterized in the solid state. Initial coordination of the substrate carboxylate group is followed by the rate-limiting nucleophilic attack of the bridging hydroxide at the β-lactam carbonyl group in aqueous solution. The product is formed upon fast protonation of the intermediate. Mononuclear complexes Zn(cyclen)(NO3)2 and Zn(bpta)(NO3)2 are as reactive in the β-lactam hydrolysis as the dinuclear complexes. Consequently, the second zinc ion is not required for catalytic activity

Hydrolysis of β-Lactam Antibiotics Catalyzed by Dinuclear Zinc(II) Complexes: Functional Mimics of Metallo-β-lactamases

Three stable dinuclear zinc(II) complexes, [Zn2L1(μ-NO3)(NO3)2] and [Zn2L1(μ-OMe)(NO3)2], where L1 is 2,6-bis{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-methylphenolate, and [Zn2L2(NO3)3], where L2 is 2-{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-bromo-6-{[N‘-2-(2‘-pyridyl)ethyl]aminomethyl}phenolate, were synthesized and characterized in the solid state and in aqueous solution. These complexes catalyze the hydrolysis of penicillin G and nitrocefin, serving as functional synthetic analogues of the metallo-β-lactamases, bacterial enzymes responsible for antibiotic resistance. The mechanism of the hydrolysis was studied in detail for the catalyst precursor [Zn2L1(μ-NO3)(NO3)2], which converts into [Zn2L1(μ-OH)(NO3)n(sol)2-n](2-n)+ in the presence of water. The complex [Zn2L1(μ-OH)(NO3)2] (n = 2) was characterized in the solid state. Initial coordination of the substrate carboxylate group is followed by the rate-limiting nucleophilic attack of the bridging hydroxide at the β-lactam carbonyl group in aqueous solution. The product is formed upon fast protonation of the intermediate. Mononuclear complexes Zn(cyclen)(NO3)2 and Zn(bpta)(NO3)2 are as reactive in the β-lactam hydrolysis as the dinuclear complexes. Consequently, the second zinc ion is not required for catalytic activity

The Synthesis of 1,2-Bis(1,5,9-triazacyclododecyl)ethane: A Showcase for the Importance of the Linker Length within Bis(alkylating) Reagents

The synthesis of 1,2-bis(1,5,9-triazacyclododecyl)ethane (1) showcases how different bis(alkylating) reagents change the reaction from an intra- to an intermolecular pathway. The isolation of the intermediate hexahydro-3a,6a-ethano-1H,4H,7H,9bH-9a-aza-3a,6a-diazoniaphenalene-3a,6a-diium (2) explained why initially the synthesis of 1 was not possible. Both isomers of 2 were found in solution. DFT calculations revealed that isomer 2a is 4.6 kcal/mol lower in energy than 2b. Synthesis of 1 was finally achieved by using oxalyl chloride

Hydrolysis of β-Lactam Antibiotics Catalyzed by Dinuclear Zinc(II) Complexes: Functional Mimics of Metallo-β-lactamases

Three stable dinuclear zinc(II) complexes, [Zn2L1(μ-NO3)(NO3)2] and [Zn2L1(μ-OMe)(NO3)2], where L1 is 2,6-bis{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-methylphenolate, and [Zn2L2(NO3)3], where L2 is 2-{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-bromo-6-{[N‘-2-(2‘-pyridyl)ethyl]aminomethyl}phenolate, were synthesized and characterized in the solid state and in aqueous solution. These complexes catalyze the hydrolysis of penicillin G and nitrocefin, serving as functional synthetic analogues of the metallo-β-lactamases, bacterial enzymes responsible for antibiotic resistance. The mechanism of the hydrolysis was studied in detail for the catalyst precursor [Zn2L1(μ-NO3)(NO3)2], which converts into [Zn2L1(μ-OH)(NO3)n(sol)2-n](2-n)+ in the presence of water. The complex [Zn2L1(μ-OH)(NO3)2] (n = 2) was characterized in the solid state. Initial coordination of the substrate carboxylate group is followed by the rate-limiting nucleophilic attack of the bridging hydroxide at the β-lactam carbonyl group in aqueous solution. The product is formed upon fast protonation of the intermediate. Mononuclear complexes Zn(cyclen)(NO3)2 and Zn(bpta)(NO3)2 are as reactive in the β-lactam hydrolysis as the dinuclear complexes. Consequently, the second zinc ion is not required for catalytic activity

The Synthesis of 1,2-Bis(1,5,9-triazacyclododecyl)ethane: A Showcase for the Importance of the Linker Length within Bis(alkylating) Reagents

The synthesis of 1,2-bis(1,5,9-triazacyclododecyl)ethane (1) showcases how different bis(alkylating) reagents change the reaction from an intra- to an intermolecular pathway. The isolation of the intermediate hexahydro-3a,6a-ethano-1H,4H,7H,9bH-9a-aza-3a,6a-diazoniaphenalene-3a,6a-diium (2) explained why initially the synthesis of 1 was not possible. Both isomers of 2 were found in solution. DFT calculations revealed that isomer 2a is 4.6 kcal/mol lower in energy than 2b. Synthesis of 1 was finally achieved by using oxalyl chloride