Presence Of Azide Ion Research Articles

Carbon–oxygen bond cleavage: a new reaction mode for amides bonded through oxygen to cobalt(III)

Azide ion competition experiments and oxygen-17 and -18 studies have been used to determine the extent of cleavage of the coordinated oxygen–carbon bond when (amide- O)pentaamminecobalt(III) complexes were reacted in aqueous base. Base hydrolysis in the presence of azide ion at 22°C (0.10 M NaOH, 1.0 M NaN 3) of [(NH 3) 5CoOC(CH 3)NH 2] 2(S 2O 6) 3·3H 2O and [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O produced 12.5 and 13.0% azido complex respectively, as expected for tripositive complexes reacting solely by cobalt–ligand bond cleavage. However reaction of [(NH 3) 5CoOC(C 6H 5)NH 2] 2(S 2O 6) 3·3H 2O produced only 10.5% azido complex and this implied that 17% of the complex was reacting by carbon–oxygen bond cleavage. 17O NMR spectroscopy of the products of base hydrolysis of [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O in 22 atom% H 2 17O confirmed that it reacted largely by ligand substitution but the same experiment using [(NH 3) 5CoOC(CH 2F)NH 2] 2(S 2O 6) 3·3H 2O was inconclusive because of secondary hydrolysis of the liberated amide. Oxygen-18 analysis of coordinated water has demonstrated conclusively that for complexes of primary or secondary amides with electron-withdrawing substituents carbon–oxygen bond cleavage in aqueous base is a significant reaction: [(NH 3) 5CoOC(C 6H 5)NH 2] 2(S 2O 6) 3·3H 2O, 19%; [(NH 3) 5CoOC(CH 2F)NH 2] 2(S 2O 6) 3·3H 2O, 10%; and [(NH 3) 5Co(succinimido- O)](CF 3SO 3) 2·H 2O, 9%. The reaction was not detected when [(NH 3) 5CoOC(CH 3)NH 2] 2(S 2O 6) 3·3H 2O and [(NH 3) 5CoOC(CH 3)N(CH 3) 2](CF 3SO 3) 3·H 2O were dissolved in aqueous base as these amides are not electronically activated, nor was it detected for reaction of [(NH 3) 5CoOC(H)N(CH 3) 2](CF 3SO 3) 3·H 2O; this complex is activated towards addition by hydroxide ion (84% C–N cleavage) but lacks an ionisable proton on the amide nitrogen to facilitate proton transfer in the intermediate in the C–O bond rupture process.

Hydrolysis of (2-Deoxy-α-d-Glucopyranosyl)pyridinium Salts: The 2-Deoxyglucosyl Oxocarbenium Is Not Solvent-Equilibrated in Water

The hydrolysis reactions of four 2-deoxy-α-d-glucopyranosyl pyridinium salts exhibit first-order rate constants that are independent of pH in the range of 4.4−10.5 pH units. Derived second-order rate constants for the hydrolysis reactions of 2-deoxy-α-d-glucopyranosyl 4‘-bromoisoquinolinium tetrafluoroborate (4d) conducted in the presence of nucleophilic monoanions (μ = 2.0) including AcO-, Cl-, Br-, and N3- exhibit a Swain−Scott parameter (s) of 0.03 ± 0.10, indicating that these reactions show no sensitivity to the nature of the anion. In the presence of azide ion, a substantial quantity of the 2-deoxy-α-glucopyranosyl 4‘-bromoisoquinolinium salt hydrolysis product results from a post rate-limiting reaction of a cationic intermediate with azide. Analysis of the hydrolysis product ratios indicates that the 2-deoxyglucosyl oxocarbenium ion is not solvent-equilibrated in water. Furthermore, the reaction of solvent occurs about 2-fold faster with the cationic intermediate that is formed during solvolysis of...

Cathodic Electrogenerated Chemiluminescence of Luminol at Disposable Oxide-Covered Aluminum Electrodes

Luminol exhibits strong electrogenerated chemiluminescence during cathodic pulse polarization of oxide-covered aluminum electrodes in aqueous solution. This electrogenerated chemiluminescence can be enhanced by the presence of dissolved oxygen or by the addition of other coreactants such as hydrogen peroxide, peroxydisulfate, or peroxydiphosphate ions. However, luminol detection is most sensitive in the presence of azide ions, which not only enhance the electrogenerated chemiluminescence intensity but also decrease the intrinsic electroluminescence of the thin aluminum oxide film on the electrodes mainly producing the blank emission. The present method is based on tunnel emission of hot electrons into an aqueous electrolyte solution and allows the detection of luminol, isoluminol, and its derivatives below nanomolar concentration levels. The linear logarithmic calibration range covers several orders of magnitude of concentration of luminol or N-(6-aminohexyl)-N-ethylisoluminol. Therefore, the above-mentio...

Hot electron-induced time-resolved electrogenerated luminescence of Tb(III) ions at stationary oxide-covered aluminium electrodes

Injection of tunnel-emitted hot electrons from a pulse-polarised oxide-covered aluminium electrode into aqueous Tb(III) ion solution induces electrogenerated luminescence which comprises 5 D 4 → 7 F J transitions of Tb(III). The luminescence lifetime of a hydrated Tb(III) ion is ca. 500 μs while that of the main component of the cathodic intrinsic electrogenerated luminescence of the oxide film is only ca. 6 μs. This allows sensitive detection of Tb(III) ion on a time-resolved basis. Tb(III)-specific electrogenerated luminescence is enhanced by the presence of azide ions or coreactants like hydrogen peroxide and peroxodisulfate ions which produce highly oxidising radicals by one-electron reduction. The Tb(III)-specific electrogenerated luminescence is produced via several parallel mechanisms which usually involve oxidation state changes of Tb(III) that are difficult to produce in an aqueous medium. The cathodically produced primary species are tunnel-emitted hot electrons and F + centres of the oxide film. These primary species are capable of hard reductions and oxidations not normally encountered in the electrochemistry of aqueous solutions, and can probably produce hydrated electrons and hydroxyl radicals which are able to mediate reductions and oxidations in aqueous solution beyond the tunnelling distance from the oxide/electrolyte interface. The present electrogenerated luminescence is formed as a sum of the luminescence emitted by Tb(III) ions adsorbed at the oxide/electrolyte interface, partially incorporated in the oxide, and located in the solution at the close vicinity of the oxide/electrolyte interface.

Intramolecular Aza-Wittig Routes to Sydnoquinoxalines

3-(2-Azidophenyl)sydnone (5) was prepared directly from amine 3 by a novel process involving diazotization in the presence of azide ion. Reaction of the triphenylphosphine imide 7, derived from 5, with isocyanates or isothiocyanates gave the 4-aminosydno[3,4-a] quinoxalines 9 in moderate to good yield, presumably via aza-Wittig conversion to carbodiimide intermediates 8 and subsequent elecrophilic aromatic substitution at the sydnone ring 4-position.

A new approach to the stereospecific synthesis of branched-chain sugars

Darzens condensation of two readily available carbohydrate ketones with chloromethyl p-tolyl sulphone gave stereospecifically α,β-epoxy sulphones, in the presence of azide ion the latter afforded branched-chain functionalized azido-sugars.

Hydrolysis of p-Nitrophenyl Hexanoate in Hydrophobic Aggregate System

Abstract Hydrolysis of p-nitrophenyl hexanoate in the presence of azide ion (N3−) was accelerated by tetraheptylammonium bromide (1), which has four long alkyl chains. In contrast to 1, the other tetraalkylammonium salts which have shorter alkyl chains, (2)–(5), did not elevate the reactivity. p-Nitrophenyl acetate, less hydrophobic substrate, was not hydrolyzed so efficiently even in the presence of 1.

Base hydrolysis of mono-alkylsubstituted chloropentaamminecobalt(III) complexes

The preparation of the series ofcis- andtrans-[Co(NH3)4(RNH2)Cl]2+ complexes (withcis, R = Me orn-Pr andtrans, R = Me, Et,n-Pr,n-Bu ori-Bu) is described. The u.v-visible spectra indicate a decrease of the ligand field on increasing chain length. Infrared spectra show an enhanced Co-Cl bond strength compared to the pentaammine. Partial molar volumes of the complex cations do not reveal steric compression. From proton exchange studies in D2O it follows that [Co(NH3)5Cl]2+ and thecis- andtrans-[Co(NH3)4-(CH3NH2)C1]2+ complexes exchange the amine protons on the grouptrans to the chloro faster than those on thecis. A coordinated methylamine group exchanges its amine protons slower than a corresponding NH3 group in the parent pentaammine, but the methyl introduction accelerates the exchange of the other NH3 groups. The aquation of thetrans-alkylamine complexes (studied at 52° C) is acceleratedca. 10 times compared to the parent pentaammine, irrespective of the nature of the alkyl group. Thecis complexes do not show this acceleration of aquation. In base hydrolysis (studied at 25° C) thecis complexes are the most reactive (a factor 20 over the parent ion). Thecis/trans product ratio in base hydrolysis and the competition ratio in the presence of azide ions were calculated from the 500 MHz1H n.m.r. spectra, which display distinctly different alkyl resonances for each individual complex. Thecis ions react under stereochemical retention of configuration; thetrans compounds give 10±1%trans tocis rearrangement. The ionic strength (⩽4 mol dm−3) and the pH do not affect this result. The same product ratio is obtained in methanol-water and DMSO-water mixtures. Ammoniation in liquid ammonia gives the same ratios as in base hydrolysis, base-catalyzed solvolysis in neat methylamine gives stereochemical retention for both thecis- andtrans-methylamine ion. The product competition ratio (Co-N3)/(Co-OH2) for thecis compounds and the bulkier amines (R =n- andi-Bu), 15–25% at 1 mol dm−3N3−, isca. twice that of thetrans compounds and the pentaammine. The results are interpreted in the classical conjugate base mechanism, and discussed in the context of current ideas about stereochemistry of base hydrolysis.

Polarographic investigations on uranyl(Vl) complexes in dimethylsulfoxide. III. Halides and pseudohalides

The polarographic study of uranyl(IV)-halides complexes in DMS0 showed the formation of [UO2-F2] and [UO 2Cl] + stable species, while bromide and iodide ions do not form stable uranium(VI) complexes, in agreement with the “hard” character of uranyl ( VI) ion. The complexes formation between pseudohalides and uranium(VI) evidentiated the following species, stable enough to be polarographically revealed: [UO 2N 3 3] −, [UO 2CN) 2] and [UO 2(CN) 2]; on the contrary thiocyanate ion does not form sufficiently stable complex species in DMSO. Cyclic voltammetric tests were also performed to investtgate the anodic dissolution process of mercury in the presence of azide ion.

On the mechanism of the acridine orange sensitized photodynamic inactivation of lysozyme. I. Basic kinetics.

The kinetics of the photodynamic desactivation of lysozyme in presence of acridine orange as the sensitizer have been investigated in detail varying oxygen, protein, dye concentration, ionic strength and pH value. The kinetics can be approximately described as an over all pseudo-first-order rate process. Changing the solvent from water to D2O or by quenching experiments in presence of azide ions it could be shown that the desactivation of lysozyme is caused exclusively by singlet oxygen. The excited oxygen occurs via the triplet state of the dye with a rate constant considerably lower than that to be expected for a diffusionally controlled reaction. Singlet oxygen react chemically (desactivation, k=2.9 X 10(7) m(-1) sec(-1)) and physically (quenching process, k=4.1 X 10(8) m(-1) sec(-1)) with the enzyme. The kinetical analysis shows that additional chemical reaction between singlet oxygen and lysozyme would have only little influence on the kinetics of the desactivation as long as their products would be enzymatically active and their kinetical constants would be less than about 1 X 10(8) m(-1) sec(-1)).

Nuclear magnetic resonance titration curves of histidine ring protons. Human metmyoglobin and the effects of azide on human, horse, and sperm whale metmyoglobins.

Four titrating histidine ring C2 and C4 proton resonances are observed in 220 MHz proton NMR spectra of human metmyoglobin as a function of pH. Values of ionization constants determined from the NMR titration data using an equation describing a simple proton association-dissociation equilibrium are curves (1) 6.6, (2) 7.0, (3) 5.8, and (4) 7.4. Four histidine residues have also been found to be solvent-accessible in human metmyoglobin by carboxymethylation studies (Harris, C.M., and Hill, R.L. (1969) J. Biol. Chem. 244, 2195-2203). Two of the titration curves (3 and 4) deviate significantly from the chemical shift values normally observed for histidine C2 proton resonances. Curve 3, with a low pKa, is shifted downfield at high values of pH and also exhibits a second minor inflection with a pKa value of 8.8. On the other hand, the high pKa curve, 4, is shifted upfield at all values of pH. The characteristics of the NMR titration curves with the lowest and highest pKa values (3 and4) are very similar to curves observed previously with sperm whale and horse metmyoglobins (Cohen, J.S., Hagenmaier, H., Pollard, H., and Schechter, A.N. (1972) J. Mol. Biol. 71, 513-519). These results indicate that the histidine residues from which these curves are derived have unusual and characteristic environments in this series of homologous proteins. The NMR spectra of all three metmyoglobins are changed extensively as a result of azide ion binding, indicating conformational changes affecting the environments of several imidazole side chains. The presence of azide ion causes a selective downfield chemical shift for the low pKa curve and a selective upfield chemical shift for the high pKa curve in all three proteins. Azide also abolishes the second inflection seen in the low pKa curve at high pH. In addition to these effects, the presence of azide ion permits the observation of two additional titrating proton resonances for all three metmyoglobins. Increasing the azide to protein ratio at several fixed values of pH yields results which show that a slow exchange process is occurring with each of the metmyoglobins. In the azide titration studies the maximum changes in the NMR spectra occurred at approximately equimolar concentrations. The NMR results for these proteins in the absence and presence of azide ion are related to x-ray crystallographic studies of sperm whale metmyoglobin and the known alkylation properties of the histidine residues. Tentative assignments of the titrating resonances observed are suggested.

Is the concerted ene mechanism of the excited oxygen molecule reactions with olefins really eliminated. Photooxygenation and electrolysis in the presence of azide ions

Is the concerted ene mechanism of the excited oxygen molecule reactions with olefins really eliminated. Photooxygenation and electrolysis in the presence of azide ions