The risk of mixing dilute hydrogen peroxide and acetone solutions

The curious cases of tetrahydrosalen-type ligands interacting with Ni(II): structures and ligand-based oxidation reactions

This work centers around the nickel complexes derived from two tetrahydrosalen-type proligands: N,N'-bis(2-hydroxybenzyl)-o-phenylenediamine (H2salophan) and N,N'-bis(2-hydroxy-3-methylbenzyl)-o-phenylenediamine (H2salophan_Me). The reaction of H2salophan with Ni(OAc)2·4H2O generates a dinuclear complex Ni2(Hsalophan)2(OAc)2 or Na[Ni2(salophan)2(OAc)] when NaOH is added to assist ligand deprotonation. The reaction of H2salophan_Me with Ni(OAc)2·4H2O, however, yields a mononuclear complex Ni(Hsalophan_Me)2. Unlike the corresponding salen-type nickel complexes, these tetrahydrosalen-type complexes are paramagentic and air sensitive (in solution). Oxidation by O2 or peroxides results in dehydrogenation of the ligand backbone to form the salen-type complexes.

Diverse and unexpected outcomes from oxidation of the platinum(II) anticancer agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] by hydrogen peroxide

Oxidation of the anti-tumour agent [Pt{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)], 1 (py = pyridine) with hydrogen peroxide under a variety of conditions yields a range of organoenamineamidoplatinum(II) compounds [Pt{(p-BrC₆F₄)NCH=C(X)NEt₂}Cl(py)] (X = H, Cl, Br) as well as species with shared occupancy involving H, Cl and Br. Thus, oxidation of the -CH₂-CH₂- backbone (dehydrogenation) occurs, often accompanied by substitution. Oxidation of 1 with H₂O₂ in acetone yielded 1:1 co-crystallized [Pt{(p-BrC₆F₄)NCH=CHNEt₂}Cl(py)], 1H and [Pt{(p-BrC₆F₄)NCH=C(Cl)NEt₂}Cl(py)], 1Cl. The former was obtained pure in low yield from the oxidation of 1 with (NH₄)₂[Ce(NO₃)₆] in acetone, and the latter was obtained from 1 and H₂O₂ in CH₂Cl₂ at near reflux. From the latter reaction under vigorous refluxing [Pt{(p-BrC₆F₄)NCH=C(Br)NEt₂}Cl(py)], 1Br was isolated. In refluxing acetonitrile, oxidation of 1 with H₂O₂ yielded [Pt{(p-BrC₆F₄)NCH=C(H₀.₂₅Br_0.75)NEt₂}Cl(py)], 1H_0.25Br_0.75, in which the alkene is mainly substituted by Br in a dual occupancy. Treatment of 1 with H₂O₂ and tetrabutylammonium hydroxide in acetone at room temperature formed [Pt{(p-HC₆F₄)NCH₂CH₂NEt₂}Cl(py)], 2. Oxidation of [Pt{(p-HC₆F₄)NCH₂CH₂NEt₂}Br(py)], 3 with H₂O₂ in boiling acetonitrile gave the ligand oxidation product [Pt{(p-HC₆F₄)NCH=C(Br)NEt₂}Br(py)], 3Br. All major products were identified by X-ray crystallography as well as by ¹H and ¹⁹F NMR spectra. In cases of mixed crystals or dual occupancy compounds, the ¹⁹F and ¹H NMR spectra showed dissociation into the components in the solution in the same proportions as in isolated crystalline material.

Synthesis of bis-Phosphate Iminoaltritol Enantiomers and Structural Characterization with Adenine Phosphoribosyltransferase

Phosphoribosyl transferases (PRTs) are essential in nucleotide synthesis and salvage, amino acid, and vitamin synthesis. Transition state analysis of several PRTs has demonstrated ribocation-like transition states with a partial positive charge residing on the pentose ring. Core chemistry for synthesis of transition state analogues related to the 5-phospho-α-d-ribosyl 1-pyrophosphate (PRPP) reactant of these enzymes could be developed by stereospecific placement of bis-phosphate groups on an iminoaltritol ring. Cationic character is provided by the imino group and the bis-phosphates anchor both the 1- and 5-phosphate binding sites. We provide a facile synthetic path to these molecules. Cyclic-nitrone redox methodology was applied to the stereocontrolled synthesis of three stereoisomers of a selectively monoprotected diol relevant to the synthesis of transition-state analogue inhibitors. These polyhydroxylated pyrrolidine natural product analogues were bis-phosphorylated to generate analogues of the ribocationic form of 5-phosphoribosyl 1-phosphate. A safe, high yielding synthesis of the key intermediate represents a new route to these transition state mimics. An enantiomeric pair of iminoaltritol bis-phosphates (L-DIAB and D-DIAB) was prepared and shown to display inhibition of Plasmodium falciparum orotate phosphoribosyltransferase and Saccharomyces cerevisiae adenine phosphoribosyltransferase (ScAPRT). Crystallographic inhibitor binding analysis of L- and D-DIAB bound to the catalytic sites of ScAPRT demonstrates accommodation of both enantiomers by altered ring geometry and bis-phosphate catalytic site contacts.

Highly efficient detection of hydrogen peroxide in solution and in the vapor phase via fluorescence quenching

Herein we report the highly efficient and sensitive detection of hydrogen peroxide in both aqueous solution and in the vapor phase via fluorescence quenching (turn-off mechanism) of the amplified fluorescent conjugated polymer-titanium complex induced by hydrogen peroxide. Inter- and intra-polymer energy migration leads to extremely high sensitivity.