PHOTOLYTIC REARRANGEMENT OF METRONIDAZOLE TO 1-HYDROXYETHYL-2-METHYL-4-HYDROXYIMINO-5-OXO-IMIDAZOLE AND THE FORMATION OF COPPER COMPLEXES OF THESE COMPOUNDS

Abstract— A labile intermediate in the photolytic rearrangement of the antibacterial drug, metronidazole, was identified by isolating the product of photolysis of metronidazole benzoate in methanol. The intermediate, 1-hydroxyethyl-2-methyl-4-hydroxyimino-5-oxo-imidazole, was shown to act as a bidentate chelating agent for copper(II) ions, whereas metronidazole forms a weak monodentate complex. The intermediate may be relevant to the bioactivation mechanism of metronidazole.     

Radiation degradation of copolymers of methyl methacrylate and 3-oximino-2-butanone methacrylate

Copolymers of methyl methacrylate and 3-oximino-2-butanone methacrylate (OM) were investigated as deep-UV and e-beam resists. Their increased sensitivity relative to PMMA (up to 50 times) was correlated with the radiation chemical yields of the volatile products and main chain scissions. The degradation of these copolymers, activated by the 3-oximino-2-butanone entity, is discussed in terms of energy absorption mechanisms and the subsequent scission reactions.     

Metal to ligand group transfer reactions : II. Reactions of some π-allylrhodium(I) complexes with trifluoroacetic acid and alkyl,acyl and trimethyltin halides

Rh(π-C₃H₅)(PF₃)₃ (I), reacts with trifluoroacetic acid to form propene and [Rh(CF₃COO)(PF₃)₂]₂ (II). I reacts with t-butyl bromide to give [RhBr(PF₃)₂]₂ and a mixture of propene and 2-methyl-1-propene and with n-propyl bromide to give propene and [RhBr(PF₃)₂]₂. Rh(π-C₃H₅)(PPh₃)₂ (III), and t-butyl bromide yield propene and 2-methyl-1-propene. In these reactions a mechanism involving β-hydrogen abstraction and hydrogen migration via the metal to carbon is proposed. When III reacts with Me₃SnCl the Me₃Sn—moiety migrates intact to the π-allyl group. I reacts with acetyl chloride to give propene, [RhCl(PF₃)₂]₂ and the carbonyl rhodium complex Rh₂Cl₂(PF₃)₃(CO). II does not apparently undergo phosphine ligand exchange unlike the analogous halogeno-bridged dimers.     

The crystal structure of a Di(tetramethylammonium)-bis[R,R-tartrato(2-)]-cis-dioxomolybdate(VI), (NMe4)2[MoO2(C4H4O6)2] · EtOH · 1.5 H2O,with comments on tartrate coordination

Summary In the salt (NMe₄[MoO₂(H₂tart)₂] · EtOH · 1.5 H₂O (H₄tart = R,R-(+)-tartaric acid) the tartrato-ligands are linked to molybdenum through a carboxyl oxygen and the vicinal deprotonated hydroxyl oxygen atom, with carboxyl oxygentrans to terminal oxygen of the MoO₂ cis-dioxo core. The configuration about Mo is A. The C-C-C-C torsion angles of the ligands are almost 180°. This enables inter-ligand H-bonding from the uncoordinated hydroxyl groups. The five skeletal atoms from the uncoordinated section of a ligand are nearly co-planar. The probable strong preference fortrans coordination of carboxyl must limit the range of dissolved molybdenum(VI)-tartrate species.     

Anodic stripping voltammetry of sulphide at a nickel film: towards the development of a reagentless sensor

The determination of sulphide at an electrochemically generated nickel oxide layer at glassy carbon and screen-printed electrodes in acidic media has been examined and appraised. The NiO layer was found to produce a stripping-like signal to sulphide and gave a linear peak current response from 20 to 90 μM. The response was further enhanced by repetitive cycling allowing accumulation of nickel sulphide at the electrode surface such that lower micromolar levels of sulphide (i.e. 5 μM) can be determined. The response at the NiO layer to sulphide is shown to be reproducible over a period of 24 h, thereby offering the development of a disposable amperometric sensor for sulphide.     

Reactions of methylniobium(V) and methyltantalum(V) chlorides with carbodiimides

The chlorides Me_xMCl_5-x, M = Nb, Ta, x = 1, 2, 3 react with carbodiimides RNCNR (R = isopropyl, cyclohexyl, p-tolyl) to give products of the types MCl₄[NR-C(Me)=NR], MeMCl₃[NR-C(Me)=NR], MCl₃[NR-C(Me)=NR]₂, Me₂MCl₂[NR-C(Me)=NR], MeMCl₂[NR-C(Me)=NR]₂, which cóntain bidentate acetamidine groups arising from insertion of the carbodiimide into the metal-carbon bond. The products have been characterised by elemental analysis IR and proton NMR spectra.     

Channel flow cell studies on the evaluation of surface pretreatments using phosphoric acid or polymaleic acid for calcite stone protection

The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment.     

Aerobic alcohol oxidation catalyzed by a new, oxygen-bridged heterometallic compound [PPh4][Ru(N)Me2(μ2-O)2Pd((−)-sparteine)]

The reaction between the new hydroxy compound [PPh₄][Ru(N)(OH)₂Me₂] and Pd(OSiMe₃)₂((−)-sparteine) produces (Me₃Si)₂O, H₂O and a new heterobimetallic compound [PPh₄][Ru(N)Me₂(μ₂-O)₂Pd((−)-sparteine)] in good yield. The Ru/Pd bimetallic compound catalyzes the oxidation of aryl and allyl alcohols to the corresponding carbonyl compound in air and the rearrangement of allylic alcohols unsaturated aldehydes. It also oxidizes PPh₃ to O-PPh₃ under O₂.     

The equilibrium properties and folding kinetics of an all-atom Go model of the Trp-cage

The ultrafast-folding 20-residue Trp-cage protein is quickly becoming a new benchmark for molecular dynamics studies. Already several all-atom simulations have probed its equilibrium and kinetic properties. In this work an all-atom Go model is used to accurately represent the side-chain packing and native atomic contacts of the Trp-cage. The model reproduces the hallmark thermodynamics cooperativity of small proteins. Folding simulations observe that in the fast-folding dominant pathway, partial alpha-helical structure forms before hydrophobic core collapse. In the slow-folding secondary pathway, partial core collapse occurs before helical structure. The slow-folding rate of the secondary pathway is attributed to the loss of side-chain rotational freedom, due to the early core collapse, which impedes the helix formation. A major finding is the observation of a low-temperature kinetic intermediate stabilized by a salt bridge between residues Asp-9 and Arg-16. Similar observations [R. Zhou, Proc. Natl. Acad. Sci. U.S.A. 100, 13280 (2003)] were reported in a recent study using an all-atom model of the Trp-cage in explicit water, in which the salt-bridge stabilized intermediate was hypothesized to be the origin of the ultrafast-folding mechanism. A theoretical mutation that eliminates the Asp-9-Arg-16 salt bridge, but leaves the residues intact, is performed. Folding simulations of the mutant Trp-cage observe a two-state free-energy landscape with no kinetic intermediate and a significant decrease in the folding rate, in support of the hypothesis.