Addition Of Bromide Ions Research Articles

Photochemical reactions of dissolved organic matter and bromide ions facilitate abiotic formation of manganese oxide solids

Manganese (Mn) oxide solids are ubiquitous in nature, acting as both electron donors and acceptors in diverse redox reactions in the environment. Reactions of Mn(III/IV) oxides with dissolved natural organic matter (DOM) are commonly described as reductive dissolutions that generate Mn2+(aq). In this study, we investigated the role of photochemical reactions of DOM in Mn2+(aq) oxidation and the resulting formation of Mn oxide solids. During the photolysis of DOM, reactive intermediates can be generated, including excited triplet state DOM (3DOM*), hydroxyl radicals (•OH), superoxide radicals (O2•−), hydrogen peroxide, and singlet oxygen. Among these, we found that O2•− radicals were mainly responsible for Mn oxidation. The solution pH controlled the formation of Mn oxide solids by affecting both Mn2+ oxidation by O2•− during photolysis of DOM and reductive dissolutions of Mn oxide solids by DOM. Further, with the addition of bromide ions (Br−), reactions between 3DOM* and Br−, together with reactions between •OH and Br−, can form reactive bromide radicals. The formed Br radicals also promoted Mn oxide formation. In DOM with more aromatic functional groups, more Mn2+ was oxidized to Mn oxide solids. This enhanced oxidation could be the result of promoted pathways from charge-transfer state DOM (DOM•+/•−) to O2•−. These new observations advance our understanding of natural Mn2+ oxidation and Mn(III/IV) oxide formation and highlight the underappreciated oxidative roles of DOM in the oxidation of metal ions in surface water illuminated by sunlight.

Phase Regulation Strategy of Perovskite Nanocrystals from 1D Orthomorphic NH4PbI3 to 3D Cubic (NH4)0.5Cs0.5Pb(I0.5Br0.5)3 Phase Enhances Photoluminescence

AbstractThis work reports this first synthesis of 1D orthomorphic NH4PbI3 perovskite nanocrystals (NCs) considering the role of inorganic ammonium ions at the nanoscale. The addition of bromide ions at the halogen site did not improve the photoluminescence properties. Furthermore, the 3D cubic phase of (NH4)0.5Cs0.5Pb(I0.5Br0.5)3 NCs with bright photoluminescence was synthesized by adding Cs ions into the crystal lattice of (NH4)Pb(I0.5Br0.5)3. Moreover, the photophysical properties of different phase structures were studied using femtosecond transient absorption (FTA) spectroscopy. The ultrafast trap state capture process is a key factor in the change of photoluminescence properties and the cubic phase may be the best structure for photoluminescence. These results suggest that the ammonium ion perovskite (AIP) nanocrystals could be potential materials for optoelectronic applications through A‐site cation substitution.

Phase Regulation Strategy of Perovskite Nanocrystals from 1D Orthomorphic NH4 PbI3 to 3D Cubic (NH4 )0.5 Cs0.5 Pb(I0.5 Br0.5 )3 Phase Enhances Photoluminescence.

This work reports this first synthesis of 1D orthomorphic NH4 PbI3 perovskite nanocrystals (NCs) considering the role of inorganic ammonium ions at the nanoscale. The addition of bromide ions at the halogen site did not improve the photoluminescence properties. Furthermore, the 3D cubic phase of (NH4 )0.5 Cs0.5 Pb(I0.5 Br0.5 )3 NCs with bright photoluminescence was synthesized by adding Cs ions into the crystal lattice of (NH4 )Pb(I0.5 Br0.5 )3 . Moreover, the photophysical properties of different phase structures were studied using femtosecond transient absorption (FTA) spectroscopy. The ultrafast trap state capture process is a key factor in the change of photoluminescence properties and the cubic phase may be the best structure for photoluminescence. These results suggest that the ammonium ion perovskite (AIP) nanocrystals could be potential materials for optoelectronic applications through A-site cation substitution.

Behind the role of bromide ions in the synthesis of ultrathin silver nanowires

The bromide-mediated polyol method has been widely used to synthesize ultrathin silver nanowires, however, the reason why the addition of bromide ions can reduce the diameter of silver nanowires is unclear. To elucidate this mechanism, we have conducted a series of experiments in which the amount of halide ions is kept constant while the ratio of Cl− to Br− ions is varied, to investigate how the halide ions influence the morphology of AgNWs. Based on these experiments and previous studies, we propose herein that the bromide ions fulfill three roles: (i) facilitating the formation of AgBr cubes as nucleation events, (ii) limiting the lateral growth of AgNWs and (iii) enabling the formation of more stable AgBr complexes. Our current study should be useful for enabling size-controlled synthesis of silver nanowires via the bromide-mediated polyol method.

Broad-spectrum antimicrobial photocatalysis mediated by titanium dioxide and UVA is potentiated by addition of bromide ion via formation of hypobromite

Antimicrobial photocatalysis involves the UVA excitation of titanium dioxide (TiO2) nanoparticles (particularly the anatase form) to produce reactive oxygen species (ROS) that kill microbial cells. For the first time we report that the addition of sodium bromide to photoactivated TiO2 (P25) potentiates the killing of Gram-positive, Gram-negative bacteria and fungi by up to three logs. The potentiation increased with increasing bromide concentration in the range of 0–10mM. The mechanism of potentiation is probably due to generation of both short and long-lived oxidized bromine species including hypobromite as shown by the following observations. There is some antimicrobial activity remaining in solution after switching off the light, that lasts for 30min but not 2h, and oxidizes 3,3′,5,5′-tetramethylbenzidine. N-acetyl tyrosine ethyl ester was brominated in a light dose-dependent manner, however no bromine or tribromide ion could be detected by spectrophotometry or LC–MS. The mechanism appears to have elements in common with the antimicrobial system (myeloperoxidase+hydrogen peroxide+bromide).

Simulation for radiolytic products of seawater: effects of seawater constituents, dilution rate, and dose rate

Radiolysis calculations of simulated seawater were conducted using reported data on chemical yields and chemical reaction sets to predict the effects of seawater constituents on water radiolysis. Hydrogen, oxygen, and hydrogen peroxide were continuously produced from simulated seawater during γ-ray irradiation. The concentration of H2 exceeded its saturation concentration before it reached the steady-state concentration. The production behavior of these molecules was significantly promoted by the addition of bromide ions (Br−) because of the high reactivity of Br− with the hydroxyl radical, an effective hydrogen scavenger. It is also shown that the concentrations of these molecules were effectively suppressed by diluting seawater constituents by less than 1%.

Spectral characteristics of water clusters in the interaction with ozone molecules and bromide ions

The molecular dynamics method is used to study the interaction of the (Br−) i (H2O)50 − i clusters in a medium of water vapor with ozone molecules. The clusters absorb O3 molecules and retain them, along with Br− ions, for a 25-ps-long calculation procedure. The presence of bromide ions results in significant increases in the values of the real and imaginary parts of the relative permittivity. The addition of bromide ions causes a significant increase in the integrated IR radiation absorption intensities and in the radiant power emitted by the clusters. The addition of Br− ions only slightly affects the intensity of the Raman spectra until the number of Br− reaches six, when a dramatic decrease of the integrated intensity of this spectrum occurs. Bromide ions absorbed by water clusters produce a much more lasting impact on the ozone molecules trapped by the cluster than chlorine ions do, all other things being equal.

Electrostatic Pushing Effect: A Prospective Strategy for Enhanced Drug Delivery

Contrary to the expected quenching, unprecedented and remarkable enhancement is observed in the fluorescence of an anionic fluorophore, 8-anilino-1-naphthalene sulfonate, with the addition of bromide ion in cationic cetyltrimethylammonium bromide micellar medium. Electrostatic pushing effect of the halide ion on the anionic fluorophore that forces the probe to penetrate further into the micellar interior has been assigned to be responsible for the novel observation. Experiments with other probes and surfactants propose that the electrostatic pushing effect is rather a general phenomenon. While applying to the ionic drugs in real biosystems, potential application of the unorthodox effect remains in enhancing the solubilization of the drugs into the active target region leading to a radical enhancement in the drug efficacy.

Reactivity at the film/solution interface of ex situ prepared bismuth film electrodes: A scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM) investigation

Bismuth film electrodes (BiFEs) prepared ex situ with and without complexing bromide ions in the modification solution were investigated using scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM). A feedback mode of the SECM was employed to examine the conductivity and reactivity of a series of thin bismuth films deposited onto disk glassy carbon substrate electrodes (GCEs) of 3 mm in diameter. A platinum micro-electrode ( ϕ = 25 μm) was used as the SECM tip, and current against tip/substrate distance was recorded in solutions containing either Ru(NH 3) 6 3+ or Fe(CN) 6 4− species as redox mediators. With both redox mediators positive feedback approach curves were recorded, which indicated that the bismuth film deposition protocol associated with the addition of bromide ions in the modification solution did not compromise the conductivity of the bismuth film in comparison with that prepared without bromide. However, at the former Bi film a slight kinetic hindering was observed in recycling Ru(NH 3) 6 3+, suggesting a different surface potential. On the other hand, the approach curves recorded by using Fe(CN) 6 4− showed that both types of the aforementioned bismuth films exhibited local reactivity with the oxidised form of the redox mediator, and that bismuth film obtained with bromide ions exhibited slightly lower reactivity. The use of SECM in the scanning operation mode allowed us to ascertain that the bismuth deposits were uniformly distributed across the whole surface of the glassy carbon substrate electrode. Comparative AFM measurements corroborated the above findings and additionally revealed a denser growth of smaller bismuth crystals over the surface of the substrate electrode in the presence of bromide ions, while the crystals were bigger but sparser in the absence of bromide ions in the modification solution.

Transformation of Pyrene in Aqueous Chlorination in the Presence and Absence of Bromide Ion: Kinetics, Products, and Their Aryl Hydrocarbon Receptor-Mediated Activities

To assess the endocrine-disrupting activity stemming from the presence of pyrene in drinking water, the kinetics of chlorination of pyrene was investigated at room temperature, the products of its aqueous chlorination with and without bromide ion were identified, and their aryl hydrocarbon receptor (AhR)-mediated activities were determined. It was found that the presence of bromide ion greatly promoted the reaction rate of chlorination of pyrene accompanied with the formation of brominated products. While the main product was 1-Cl-pyrene without the addition of bromide ion, di-Br-pyrene and 1-Br-pyrene became the main products in the presence of bromide ion. GC-MS and NMR analysis identified three structures of dibromopyrene in chlorination with the addition of bromide ion as 1,3-di-Br-pyrene, 1,6-di-Br-pyrene, and 1,8-di-Br-pyrene, and their molar ratio was determined to be approximately 0.3:1:1. Finally, 1-Br-pyrene, 1,3-di-Br-pyrene, a mixture of 1,6-di-Br-pyrene and 1,8-di-Br-pyrene (di-Br-pyrene), 1-Cl-pyrene, and a mixture of 1,6-di-Cl-pyrene and 1,8-di-Cl-pyrene (di-Cl-pyrene) were fractionated by HPLC, and their AhR-mediated activities were assessed by a yeast assay. It was found that the effective molar concentrations (or mass concentration) showing half-maximal transcriptional response, EC50, for pyrene, 1-Br-pyrene, 1-Cl-pyrene, di-Cl-pyrene, and di-Br-pyrene were 5632 (1.14), 3089 (0.86), 1942 (0.46), 597.2 (0.21), and 147.3 (0.04) nM (mg/L), respectively.

Evaluation of Kojic Acid for Determining Heme and Nonheme Haloperoxidase Activities Spectrofluorometrically

Heme‐containing haloperoxidases (heme haloperoxidases) catalyze peroxide‐dependent oxidation of halide ions to hypohalite ions. Nonheme haloperoxidases catalyze peroxidation of alkyl acids to peroxyacids that subsequently oxidize halide ions to hypohalite ions. Hypohalite ions react with kojic acid spontaneously with concomitant production of fluorescence. This reaction was examined for suitability in assaying heme and nonheme haloperoxidase activities spectrofluorometrically. Heme haloperoxidases were assayed directly from hypohalite generation whereas nonheme enzymes were assayed by coupling peroxyacid formation to bromide ion oxidation. Peroxidation of kojic acid by chloroperoxidase and myeloperoxidase did not require halide ions and was not increased upon their addition, demonstrating that haloperoxidase activity was not distinguished from the classical peroxidase‐like activity of these enzymes. Addition of bromide ions to specimens of nonheme haloperoxidase, however, resulted in increased rates of fluorescence generation, indicative of the presence of distinct peroxidase and haloperoxidase enzymes. The heme poison sodium azide inhibited chloroperoxidase, myeloperoxidase, and horseradish peroxidase activities totally but inhibited only a portion of nonheme haloperoxidase activity, verifying that the last specimen was contaminated with heme‐containing peroxidase. Results show the utility of kojic acid for fluorometrically measuring haloperoxidase activity, particularly that of the nonheme enzyme.

Kinetics and mechanism of the oxidation of some neutral and acidic α-amino acids by tetrabutylammonium tribromide

The oxidation of eleven amino acids by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid results in the formation of the corresponding carbonyl compounds and ammonia. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with some of the amino acids while others exhibit second-order dependence. It failed to induce polymerization of acrylonitrile. The effect of solvent composition indicate that the rate of reaction increases with increase in the polarity of the medium. Addition of tetrabutylammonium chloride has no effect on the rate of oxidation. Addition of bromide ion causes decrease in the oxidation rate but only to a limiting value. The reaction is susceptible to both polar and steric effects of the substituents. A suitable mechanism has been proposed

Inhibition of chemical oscillations by bromide ion in the Briggs-Rauscher reaction

The addition of bromide ions to the component solutions of the Briggs– Rauscher oscillating system produces a variety of phenomena, depending on the sequence of the addition and on the initial bromide concentration. If the addition is made some minutes after the mixing of H2O2 and acidic IO3− and before adding malonic acid and Mn2+ ions, the oscillations last for five or six cycles, then suddenly ceases. If the addition is made immediately after the mixing of H2O2 and acidic IO3− and before adding malonic acid and Mn2+ ions, the oscillations do not start at all. The addition of bromide ions to an actively oscillating BR reaction causes a rapid suppression of the oscillations. Our observations may be accounted for by a mechanism involving the IBr species. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 641–646, 1998

Denitrosation of N-acetyl-N 1-nitrosotryptophan in acid solution

The denitrosation of DL-N-acetyl-N1-nitrosotryptophan has been studied kinetically in water in the acid range 4 × 10–2–1M-H2SO4 and also at lower acidities in buffer solutions pH 2–6. The reaction gave DL-N-acetyltryptophan and nitrous acid quantitatively and was not significantly reversible under these conditions. First-order behaviour was found for both the nitrosamine and acid in the sulphuric acid reactions, and the reaction was also acid-catalysed in the pH region 2–6. The reaction rate constant was unaffected by the addition of N-acetyltryptophan. In 0.04M-H2SO4 the rate constant was unchanged by the addition of bromide ion, thiocyanate ion, iodide ion, and thiourea, and the kinetic solvent isotope effect kH2O/kD2O was 1.3 at 0.7M-H2SO4 and 1.1 at 0.1M- H2SO4. However at pH 6 catalysis was observed by chloride, bromide, thiocyanate, azide, and iodide ion with increasing efficiency along this sequence. As the concentration of the nucleophile was increased the reaction rate constant tended to become independent of the nucleophile concentration. Thus N-acetyl-N1-nitrosotryptophan behaves as a typical nitrosamine at very low acidities around pH 6, whereas at higher acidities it shows a pattern of behaviour reminiscent of that shown by nitrosamides. The pH–rate profile for denitrosation shows clearly that there are two pathways associated with the acid-catalysed reaction, one predominant at around pH 4–7 and the other at acidities greater than pH 1. The former is associated with nucleophilic catalysis and the latter is not. The results are discussed in terms of two possible sites of protonation of the substrate (at O and C-3), and the changing effective rate limiting step, as the nucleophile concentration is changed. N-Acetyl-N1-nitrosotryptophan can be used to nitrosate (or diazotise) other species such as 4-nitroaniline, but only in the absence of a nitrous acid trap, indicating that this nitrosamine is not a direct nitrosating agent towards amines under these conditions. A minor photochemical decomposition pathway has been established for N-acetyl-N1-nitrosotryptophan at pH 6, but it was not examined in detail.

Response of the Belousov–Zhabotinskii oscillating reaction to addition of either bromide or cerium(IV) ions

When the Belousov–Zhabotinskii oscillating reaction is perturbed by rapid addition of bromide ions, the oscillations disappear but then recover. The time taken for this recovery depends on the extent of concentration perturbation, but the new frequency and amplitude of oscillation closely resemble the frequency and amplitude before perturbation. These observations show that this oscillating chemical reaction follows a limit cycle type of behaviour. A similar pattern is observed when solutions containing cerium(IV) ions are rapidly added to the oscillating reaction, although there is a more marked change in frequency and amplitude. The experimental results are compared with the results obtained from a numerical analysis of the effects of similar perturbations on the oscillations for two model schemes of oscillating reactions.

Mechanistic studies of the decomposition of halonitrobenzene anion radicals

Summary The electrochemical reduction of several halonitrobenzenes has been studied in dimethylformamide (DMF), acetonitrile (AN), and dimethyl sulfoxide (DMSO). The initial reduction is a one-electron process which yields the corresponding anion radical. Dissociation of the anion radicals to give a neutral nitrophenyl radical and halide ion occurs quite rapidly for o-bromonitrobenzene and the three isomers of iodonitrobenzene. Nitrobenzene is then formed as a result of an abstraction of a hydrogen atom from either the solvent or the supporting electrolyte by the nitrophenyl radical. The stability of the anion radicals in the three solvent systems decreases in the order: DMSO > AN > DMF. The order of the rates of the decomposition of the anion radicals is the same in all three solvents: o-iodo-> o-bromo- ≫ p-iodo- > m-iodonitrobenzene. The addition of iodide ion significantly decreases the decomposition rates of all iodonitrobenzene anion radicals. The addition of bromide ion has little or no effect on either the stability of the anion radical of o-bromonitrobenzene or the anion radicals of the iodonitrobenzenes.

Organometallic compounds : V. Kinetics of phenyl-tin cleavage by a chelating agent

The kinetics of tin-phenyl cleavage of diphenyltin dichloride by 8-quinolinol (HOx) in dimethyl sulfoxide have been determined at 178–192. The rate of formation of the product, Cl 2Sn(Ox) 2, is given by the expression, rate  k obs [(C 6H 5) 2SnCl 2], where k obs  k 1 ÷ k 2 [ HOx] 2. The two-term expression reflects a dissociative mechanism and a mechanism which involves formation and decomposition of C 6H 5SnCl 2. 2HOx. A mass-law retardation effect is demonstrated by the addition of chloride ion, though the addition of bromide ion causes no alteration in the rate. It appears that the second mechanism consists of a nucleophilic attack by 8-quinolinol followed by activation of electrophilic proton and incipient phenyl carbanion through coordination.