ClO2, the so-called "ideal biocide", could also be applied as an antiseptic if it was understood why the solution killing microbes rapidly does not cause any harm to humans or to animals. Our aim was ...to find the source of that selectivity by studying its reaction-diffusion mechanism both theoretically and experimentally.
ClO2 permeation measurements through protein membranes were performed and the time delay of ClO2 transport due to reaction and diffusion was determined. To calculate ClO2 penetration depths and estimate bacterial killing times, approximate solutions of the reaction-diffusion equation were derived. In these calculations evaporation rates of ClO2 were also measured and taken into account.
The rate law of the reaction-diffusion model predicts that the killing time is proportional to the square of the characteristic size (e.g. diameter) of a body, thus, small ones will be killed extremely fast. For example, the killing time for a bacterium is on the order of milliseconds in a 300 ppm ClO2 solution. Thus, a few minutes of contact time (limited by the volatility of ClO2) is quite enough to kill all bacteria, but short enough to keep ClO2 penetration into the living tissues of a greater organism safely below 0.1 mm, minimizing cytotoxic effects when applying it as an antiseptic. Additional properties of ClO2, advantageous for an antiseptic, are also discussed. Most importantly, that bacteria are not able to develop resistance against ClO2 as it reacts with biological thiols which play a vital role in all living organisms.
Selectivity of ClO2 between humans and bacteria is based not on their different biochemistry, but on their different size. We hope initiating clinical applications of this promising local antiseptic.
The bromate–aniline oscillatory reaction was discovered 4 decades ago, but neither the detailed mechanism nor the key products or intermediates of the reaction were described. We report herein a ...detailed study of this reaction, which yielded new insights. We found that oscillatory oxidation of aniline by acidic bromate proceeds, to a significant extent, via a novel reaction pathway with the periodic release of carbon dioxide. Several products were isolated, and their structures, not described so far, were justified on the basis of MS and NMR. One of the main products of the reaction associated with the CO2 release route can be assigned to 2,2-dibromo-5-(phenylimino)cyclopent-3-en-1-one. A number of known compounds produced in the studied reaction, including unexpected brominated 1-phenylpyrroles and 1-phenylmaleimides, were identified by comparison with standards. A mechanism is suggested to explain the appearance of the detected compounds, based on coupling of the anilino radical with the produced 1,4-benzoquinone. We assume that the radical adduct reacts with bromine to form a cyclopropanone intermediate that undergoes a Favorskii-type rearrangement. Further oxidation and bromination steps including decarboxylation lead to the found brominated phenyliminocyclopentenones. The detected derivatives of 1-phenylpyrrole could be produced by a one-electron oxidation of a proposed intermediate 2-phenylamino-5-bromocyclopenta-1,3-dien-1-ol followed by β-scission with the abstraction of carbon monoxide. Such a mechanism is known from the combustion chemistry of cyclopentadiene. The proposed mechanism of this reaction provides a framework for understanding the observed oscillatory kinetics.
This work studies the effect of salt contamination in weak acid-base diodes by numerical modeling. In a positive salt effect some salt is added to the alkaline reservoir, while the negative salt ...effect appears as a suppression of the positive one by contaminating also the acidic side of the diode. First, the positive and negative salt effects were investigated for weak electrolytes and they were found to be similar to those in a traditional strong acid-base diode. Next, positive and negative salt effects were studied when the ions of the contaminating salt were different from that of the weak electrolytes.
In the positive salt effect it was found that at a certain critical concentration of the added salt the current increases sharply in a nonlinear fashion. In a negative salt effect it was found that the diode current responds strongly even for small changes in the salt concentration on the acidic side. The sensitivity of a weak acid-base diode was found to be similar to that of a strong one, thus it can be also applied as a sensitive detector of nonhydrogen cations in an acidic medium. Furthermore, weak electrolytes provide milder conditions for the non-reactive parts of the diode, and their potential profiles can also be more suitable for ion detectors.
•COMSOL's relaxation algorithm used for modeling strong acid-base diodes was developed to simulate weak acid-base diodes.•Nonlinear phenomena called positive and negative salt effects in weak acid-base diodes were found and studied numerically.•Impact of foreign ions (which are not present in the uncontaminated weak electrolytes) was investigated.•With weak electrolytes setups (parameter sets) were found, which are advantageous for an ion-sensing application.
An empirical mesh adaption algorithm is introduced for modeling one-dimensional reaction-diffusion systems with large moving gradients. Our new algorithm is based on the revelation, that in ...reaction-diffusion systems the high moving concentration gradients appear nearby to the region where the rate of reaction is maximal, thus the local reaction rate can be used to control the mesh adaption. We found, that the main advantage of such a method is its simplicity and easy implementation. As an example we study an acid-base diode, where large moving gradients appear. The mathematical model of the diode contains several parabolic PDEs, coupled with one elliptic PDE. An r-refinement technique is used and attached to the commercial finite element solver COMSOL. We investigated the time-dependent salt effects of the diode with our developed algorithm. Our mesh adaption method is advantageous for modeling of any reaction-diffusion systems with localized high concentration gradients.
Adaptive FEM; Moving mesh; Reaction-diffusion systems; Acid-base diode; COMSOL Multiphysics
Background
Chlorine dioxide (ClO2) is an inorganic, potent biocide and is available in highly purified aqueous solution. It can be administered as an oral antiseptic in this form.
Objectives
Our aim ...is to determine the level of inflammatory markers and cytochrome genes expressed by enterocytes exposed to different concentrations of hyperpure chlorine dioxide solution.
Methods
Porcine jejunal enterocyte cell (IPEC‐J2) cultures were treated with the aqueous solution of hyper‐pure chlorine dioxide of various concentrations. We determined the alterations in mRNA levels of inflammatory mediators, such as IL6, CXCL8/IL8, TNF, HSPA6 (Hsp70), CAT and PTGS2 (COX2); furthermore, the expression of three cytochrome genes (CYP1A1, CYP1A2, CYP3A29) were analysed by quantitative PCR method.
Results
The highest applied ClO2 concentration reduced the expression of all three investigated CYP genes. The gene expression of PTGS2 and CAT were not altered by most concentrations of ClO2. The expression of IL8 gene was reduced by all applied concentrations of ClO2. TNF mRNA level was also decreased by most ClO2 concentrations used.
Conclusions
Different concentrations of chlorine dioxide exhibited immunomodulatory activity and caused altered transcription of CYP450 genes in porcine enterocytes. Further studies are needed to determine the appropriate ClO2 concentration for oral use in animals.
HOI versus HOIO Selectivity of a Molten-type AgI Electrode Holló, Gábor; Kály-Kullai, Kristóf; Lawson, Thuy B ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
07/2014, Letnik:
118, Številka:
26
Journal Article
Recenzirano
AgI electrode is often applied not only to determine iodine concentration but also to follow oscillations in the weakly acidic medium of the Bray–Liebhafsky and Briggs–Rauscher reactions where it ...partly follows the hypoiodous acid (HOI) concentration. It is known that HOI attacks its matrix in the corrosion reaction: AgI + HOI + H+ ⇆ Ag+ + I2 + H2O and the AgI electrode measures the silver ion concentration produced in that reaction. The signal of the electrode can be the basis of sensitive and selective HOI concentration measurements only supposing that an analogous corrosive reaction between AgI and iodous acid (HOIO) can be neglected. To prove that assumption, the authors calibrated a molten-type AgI electrode for I–, Ag+, HOI, and HOIO in 1 M sulfuric acid and measured the electrode potential in the disproportionation of HOIO, which is relatively slow in that medium. Measured and simulated electrode potential versus time diagrams showed good agreement, assuming that the electrode potential is determined by the HOI concentration exclusively and the contribution of HOIO is negligible. An independent and more direct experiment was also performed giving the same result. HOIO was produced with a new improved recipe. Conclusion: an AgI electrode can be applied to measure the HOI concentration selectively above the so-called solubility limit potential.
An application of the so-called acid-base diode would be the sensitive detection of nonhydrogen cations in an acidic medium based on salt-effects. For diode purposes different connecting elements ...between the acidic and aqueous reservoirs of the diode were developed, namely a polyvinyl alcohol (PVA) hydrogel cylinder, and a polyvinyl butyral (PVB) membrane. During the measurement of the voltage – current characteristic (VCC) of the diode, it was found, that in the case of PVA gel cylinder an overshoot (a local maximum followed by a local minimum) appeared in the time vs. current curve, while the diode was switched between modes (open or closed), that is the direction of the applied voltage was reversed. The overshoot did not appear in PVB membrane.The existence of overshoots was studied by numerical simulations. The time response of the diode with different hypothetic connecting elements was investigated, when the diode was switched between modes via changing the polarity of applied voltage. We found that larger diffusion coefficients of hydrogen and hydroxide ions explain the appearance of overshoots. By examining the concentration and potential profiles a qualitative explanation of this phenomenon was given.
With Fenton-type experiments, it is shown that the intense CO2/CO evolution in the Briggs−Rauscher (BR) reaction is due to decarboxylation/decarbonylation of organic free radicals. The metal ion ...applied in the Fenton-type experiments was Fe2+ or Ti3+ or Mn2+ combined with H2O2 or S2O8 2− as a peroxide, whereas the organic substrate was malonic acid (MA) or a 1:1 mixture of MA and iodomalonic acid (IMA). Experiments with a complete BR system applying MA or the MA/IMA mixture indicate that practically all CO2 and CO comes from IMA. The decarboxylation/decarbonylation mechanisms of various iodomalonyl radicals can be analogous to that of the bromomalonyl radicals studied already in the Belousov−Zhabotinsky (BZ) reaction. It is found that an intense CO2/CO evolution requires the simultaneous presence of H2O2, IO3 −, Mn2+, and IMA. It is suggested that the critical first step of this complex reaction takes place in the coordination sphere of Mn2+. That first step can initiate a chain reaction where organic and hydroperoxyl radicals are the chain carriers. A chain reaction was already found in a BZ oscillator as well. Therefore, the analogies between the BR and BZ oscillators are due to the fact that in both mechanisms, free radicals and, in most cases, also transition-metal complexes play an important role.
Pt is a common redox electrode used to follow oscillations qualitatively in the Briggs–Rauscher (BR) and the Bray–Liebhafsky (BL) reactions from the time of their discovery. Although the potential ...oscillations of the electrode reflect the temporal pattern of the reaction properly, there is no general agreement as to how that potential is determined by the components of the reaction mixture. In this article, first we investigate how iodine species in different oxidation states affect the potential of a Pt electrode. It was found that I(+3) and I(+5) species do not affect the potential; only I–, I2, and HOI may have an influence. Although the latter three species are always present simultaneously as participants of the rapid iodine hydrolysis equilibrium, it was found that below and above the so-called hydrolysis limit potential (HLP, where the iodide and HOI concentrations are equal) the actual potential determining redox couple is different. Below the HLP, it is the traditional I2/I– redox couple, but above the HLP, it is the HOI/I2 redox pair that determines the potential of a Pt electrode. That change in the potential control mechanism was proven experimentally by exchange current measurements. In addition, from the potential response of the Pt electrode below and above the HLP, it was possible to calculate the equilibrium constant of the iodine hydrolysis as K°H = (4.97 ± 0.20) × 10–13 M2, in rather good agreement with earlier measurements. We also studied the perturbing effect of H2O2 on the previously mentioned potentials. The concentration of H2O2 was 0.66 M, as in the BR reaction studied here. It was found that below the HLP, the perturbing effect of H2O2 was minimal but above the HLP, H2O2 shifted the mixed potential considerably down toward the HLP. In our experiments with the BR reaction, the potential oscillations of the Pt electrode crossed the HLP, indicating that from time to time the HOI concentration exceeds that of the iodide. We can conclude that although the perturbing effect of H2O2 prevents the calculation of concentrations from Pt potentials above the HLP, I–/I21/2 ratios can be calculated as a good approximation from Pt potentials below the HLP.
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