High Iodide Concentrations Research Articles

The kinetics of iodine disproportionation: a system of parallel second-order reactions sustained by a multi-species pre-equilibrium

Phosphate and borate buffers used commonly in the study of the disproportionation of iodine(0) into iodate (I(+5)) and iodide (I(−1)) catalyse the reaction. This offers significant advantages when the reaction is used to contain radio-iodine in a rupturing fission reactor, e.g., Three Mile Island. Here, such buffer catalysis has been investigated in solutions 0.20 mol l−1 in phosphate, borate, acetate or carbonate, with between 0–0.10 mol l−1 iodide. The reaction mechanism is modelled by spreadsheet, with parallel rate determining steps involving couplets such as HOI with I2OH−, all in pre-equilibrium with each other. At a given iodide concentration the kinetics are characterised by a peak in the graph of apparent rate constant versus pH. The peaks for hydroxide and each of the buffers except carbonate, coincided; carbonate displayed slightly anomalous behaviour at higher concentrations of iodide (0.10 mol l−1). The presence of a pKa in the pH domain occupied by the peak was not found to have any significant bearing on the result. The apparent rate constant for disproportionation increased linearly with phosphate concentration when the pH was that of the top of the peak. However, with the pH set on the shoulders of the peak catalysis increased initially, but then became saturated. It is not possible to ascribe, as in simpler systems, a single value to the catalytic activity of each buffer, which would apply across the entire reaction domain. In phosphate, a combination of parallel rate determining reactions involving I2OH−/IO−, I2OH−/HOI and HOI/IO− couplets was found to offer the best solution to the simultaneous fitting of the model to several sets of data. The reactivity of these couplets is investigated by means of molecular orbital theory.

Reaction–diffusion path planning in a hybrid chemical and cellular-automaton processor

To find the shortest collision-free path in a room containing obstacles we designed a chemical processor and coupled it with a cellular-automaton processor. In the chemical processor obstacles are represented by sites of high concentration of potassium iodide and a planar substrate is saturated with palladium chloride. Potassium iodide diffuses into the substrate and reacts with palladium chloride. A dark coloured precipitate of palladium iodide is formed almost everywhere except sites where two or more diffusion wavefronts collide. The less coloured sites are situated at the furthest distance from obstacles. Thus, the chemical processor develops a repulsive field, generated by obstacles. A snapshot of the chemical processor is inputted to a cellular automaton. The automaton behaves like a discrete excitable media; also, every cell of the automaton is supplied with a pointer that shows an origin of the cell’s excitation. The excitation spreads along the cells corresponding to precipitate depleted sites of the chemical processor. When the destination-site is excited, waves travel on the lattice and update the orientations of the pointers. Thus, the automaton constructs a spanning tree, made of pointers, that guides a traveler towards the destination point. Thus, the automaton medium generates an attractive field and combination of this attractive field with the repulsive field, generated by the chemical processor, provides us with a solution of the collision-free path problem.

Iodide Electron Transfer Kinetics in Dye-Sensitized Nanocrystalline TiO2 Films

Electron transfer kinetics plays a key role in determining the energy conversion efficiency of dye-sensitized photoelectrochemical solar cells. Photoinduced charge separation in such cells results in oxidation of the sensitizer dye. The resulting dye cation may be rereduced by recombination with injected electrons or by electron transfer from iodide ions in the redox electrolyte, often referred to as the regeneration reaction. In this paper, we employ transient absorption spectroscopy to investigate the kinetic competition between these two pathways in Ru(dcbpy)2(NCS)2-sensitized nanocrystalline film TiO2 electrodes immersed in a propylene carbonate electrolyte. The experiments monitored both the dye cation decay kinetics and the yield of product species, assigned to I2- radicals generated by electron transfer from iodide ions to the dye cation. The kinetic competition between the recombination and the regeneration processes is found to be dependent upon both the iodide concentration and the electrical bias applied to the dye-sensitized electrode. Similar regeneration kinetics were observed when Zn-tetra-p-carboxy-phenyl-porphyrin was used as sensitizer dye. In contrast to the recombination reaction, the rate of the dye cation regeneration reaction by iodide is found to be independent of applied bias. At high iodide concentrations, the cation regeneration reaction is sufficiently fast to compete successfully with the recombination reaction for all biases studied. When an intermediate iodide concentration is used, the acceleration of the recombination kinetics at negative biases results in a reduction in the dye cation lifetime and a loss of I2- yield. This bias dependence is found to be in good agreement with a numerical modeling of the data employing a continuous time random walk model for the charge recombination dynamics, assuming the iodide reaction to be first-order in iodide concentration. We conclude by discussing the implications of these observations for solar cell function.

Carbon forms in formation waters from the Pannonian Basin, Hungary

The amount of carbon in organic, inorganic and gas (CH 4 and CO 2) components, and the concentration of dissolved organics like humic substances, short-chain aliphatic acid anions (acetate and propionate), PAHs, phenols volatile with water vapor, alkylphenols, benzene, alkylbenzenes and oil were determined in groups of formation waters from different depths and locations in two adjacent subbasins located in the central part of the Pannonian Basin (southeast Hungary). The proportions of inorganic, organic and gas carbon to total carbon content of water, and the proportion of carbon content in the identified organic compounds to TOC were calculated. These proportions are characteristic of the location of water-bearing formations. The more aromatic character of organic matter together with the high ammonium and low iodide concentrations suggest a more terrestrial sedimentation in the Szeged area than in the Körös area, where the more aliphatic character with low ammonium and high iodide concentrations indicate a more aquatic paleoenvironment. In the Körös area, formation waters are highly depleted in 13C in the whole studied depth interval, compared to the Szeged area. The high negative δ 13C values of bicarbonate may be attributed to depletion of 13C in the sediment organic matter of aquatic origin, depletion of 13C in the atmospheric and soil CO 2 during the infiltration period before the last glacial, and a longer residence time of water.

Effect of speciation on the apparent diffusion coefficient in nonreactive porous systems

A combined theoretical and experimental study of the effect that concentration and ionic speciation have on the apparent diffusion coefficient is performed using a nonreactive porous material in a divided cell diffusion apparatus. Varying the ionic species concentration over two orders of magnitude changes the apparent diffusion coefficient by no more than 20% for the systems studied. By contrast, at fixed ionic concentration, varying the ionic species changes the initial apparent diffusion coefficient by a factor of two. Over longer periods of time, the apparent diffusion coefficient varies in time, increasing by a factor of ten or more. For one system, the macroscopic diffusion potential across the specimen induces a transient negative apparent diffusion coefficient; iodide ions are transported from regions of low iodide concentration to regions of high iodide concentration. The theoretical analysis shows that, in nonreactive porous systems, the behavior of all the concentrations and species studied can be completely characterized by an electro-diffusion system of equations that contain two time-independent constants: the porosity and the formation factor. The relationship between these results and the prediction of concrete performance in the field is discussed.

Software compensation improves the analysis of heterogeneous tumor samples stained for multiparameter DNA flow cytometry

Background: High concentrations of propidium iodide (PI), in combination with fluorescein isothiocyanate (FITC) and R-phycoerythrin (RPE) used for multiparameter DNA flow cytometry (FCM), cause spectral cross-talk into the green fluorescence channel (FL1). We have evaluated the use of post-acquisition software compensation (N-Color Compensation) in order to correct this spectral cross-talk caused by PI. Method: Cell mixtures were prepared consisting of keratin 8/18 FITC labeled, keratin 8/18 RPE labeled, and unlabeled MCF-7 breast carcinoma cells. DNA was stained with PI (100 μM). Post-acquisition software compensation was applied to correct the spectral cross-talk of PI fluorescence. Secondly, the distribution of the Ki-67 (FITC) protein during the cell cycle (PI) of SiHa cervical carcinoma cells (no software compensation) was compared to the Ki-67 expression pattern of SiHa cells, simultaneously stained for keratin 8 (RPE), after applying software compensation. Finally, software compensation was used to compare the relative levels of PCNA and p53 expression in two clinical ovarian cancer ascites specimens, stained for PCNA or p53 (FITC), keratin 8/18 (RPE), and DNA (PI), with a known p53 status (positive and negative, respectively). Results: The Ki-67 cell cycle-dependent pattern of a triply stained sample (Ki-67 (FITC), keratin 8 (RPE), and DNA (PI)) is restored after software compensation and the results are comparable to the Ki-67 distribution of a sample stained solely for Ki-67 and DNA. P53 expression could only be resolved after using software compensation in the p53 positive ovarian ascites (OA) sample. Conclusions: We conclude that software compensation is a robust and reliable post-acquisition method for the correction of RPE/PI spectral cross-talk, permitting better identification of weakly expressed proteins in heterogeneous clinical tumor samples stained for multiple cellular antigens and DNA using PI.

Regulation of the sodium iodide symporter by iodide in FRTL-5 cells.

The acute decrease in iodide organification in the thyroid in response to excess iodide is termed the acute Wolff-Chaikoff effect and normal organification resumes in spite of continued high plasma iodide concentrations (escape from the acute Wolff-Chaikoff effect). We have recently reported that large doses of iodide given to rats chronically decrease the sodium/iodide symporter (NIS) mRNA and protein, suggesting that escape is due to a decrease in NIS and subsequent iodide transport. We have now studied the effect of excess iodide on NIS in FRTL-5 cells to further explore the mechanisms whereby excess iodide decreases NIS. FRTL-5 cells were employed and were incubated in the presence or absence of various concentrations of iodide. NIS mRNA and protein and the turnover of NIS were assessed. NIS mRNA was measured by Northern analysis, NIS protein by Western analysis and NIS turnover by pulse-chase labeling experiments. Iodide (10(-) mol/l) had no effect on NIS mRNA in FRTL-5 cells at 24 and 48 h compared with cells cultured in the absence of iodide. However, excess iodide decreased NIS protein by 50% of control values at 24 h and by 70% at 48 h. This effect of iodide was dose dependent. Pulse-chase experiments demonstrated that there was no effect of iodide on new NIS protein synthesis and that the turnover of NIS protein in the presence of iodide was 27% faster than in the absence of added iodide. Excess iodide does not decrease NIS mRNA in FRTL-5 cells but does decrease NIS protein, suggesting that in this in vitro thyroid cell model iodide modulates NIS, at least in part, at a post-transcriptional level. This iodide-induced decrease in NIS protein appears to be due, at least partially, to an increase in NIS protein turnover.

Transforming growth factor-beta1 down-regulation of major histocompatibility complex class I in thyrocytes: coordinate regulation of two separate elements by thyroid-specific as well as ubiquitous transcription factors.

Transforming growth factor (TGF)-beta1-decreased major histocompatibility complex (MHC) class I gene expression in thyrocytes is transcriptional; it involves trans factors and cis elements important for hormone- as well as iodide-regulated thyroid growth and function. Thus, in rat FRTL-5 thyrocytes, TGF-beta1 regulates two elements within -203 bp of the transcription start site of the MHC class I 5'-flanking region: Enhancer A, -180 to -170 bp, and a downstream regulatory element (DRE), -127 to -90 bp, that contains a cAMP response element (CRE)-like sequence. TGF-beta1 reduces the interaction of a NF-kappaB p50/fra-2 heterodimer (MOD-1) with Enhancer A while increasing its interaction with a NF-kappaB p50/p65 heterodimer. Both reduced MOD-1 and increased p50/p65 suppresses class I expression. Decreased MOD-1 and increased p50/p65 have been separately associated with the ability of autoregulatory (high) concentrations of iodide to suppress thyrocyte growth and function, as well as MHC class I expression. TGF-beta1 has two effects on the downstream regulatory element (DRE). It increases DRE binding of a ubiquitously expressed Y-box protein, termed TSEP-1 (TSHR suppressor element binding protein-1) in rat thyroid cells; TSEP-1 has been shown separately to be an important suppressor of the TSH receptor (TSHR) in addition to MHC class I and class II expression. It also decreases the binding of a thyroid-specific trans factor, thyroid transcription factor-1 (TTF-1), to the DRE, reflecting the ability of TGF-beta1 to decrease TTF-1 RNA levels. TGF-beta1-decreased TTF-1 expression accounts in part for TGF-beta1-decreased thyroid growth and function, since decreased TTF-1 has been shown to decrease thyroglobulin, thyroperoxidase, sodium iodide symporter, and TSHR gene expression, coincident with decreased MHC class I. Finally, we show that TGF-beta1 increases c-jun RNA levels and induces the formation of new complexes involving c-jun, fra-2, ATF-1, and c-fos, which react with Enhancer A and the DRE. TGF-beta1 effects on c-jun may be a pivotal fulcrum in the hitherto unrecognized coordinate regulation of Enhancer A and the DRE.

Escape from the acute Wolff-Chaikoff effect is associated with a decrease in thyroid sodium/iodide symporter messenger ribonucleic acid and protein.

In 1948, Wolff and Chaikoff reported that organic binding of iodide in the thyroid was decreased when plasma iodide levels were elevated (acute Wolff-Chaikoff effect), and that adaptation or escape from the acute effect occurred in approximately 2 days, in the presence of continued high plasma iodide concentrations. We later demonstrated that the escape is attributable to a decrease in iodide transport into the thyroid, lowering the intrathyroidal iodine content below a critical inhibitory threshold and allowing organification of iodide to resume. We have now measured the rat thyroid sodium/iodide symporter (NIS) messenger RNA (mRNA) and protein levels, in response to both chronic and acute iodide excess, in an attempt to determine the mechanism responsible for the decreased iodide transport. Rats were given 0.05% NaI in their drinking water for 1 and 6 days in the chronic experiments, and a single 2000-microg dose of NaI i.p. in the acute experiments. Serum was collected for iodine and hormone measurements, and thyroids were frozen for subsequent measurement of NIS, TSH receptor, thyroid peroxidase (TPO), thyroglobulin, and cyclophilin mRNAs (by Northern blotting) as well as NIS protein (by Western blotting). Serum T4 and T3 concentrations were significantly decreased at 1 day in the chronic experiments and returned to normal at 6 days, and were unchanged in the acute experiments. Serum TSH levels were unchanged in both paradigms. Both NIS mRNA and protein were decreased at 1 and 6 days after chronic iodide ingestion. NIS mRNA was decreased at 6 and 24 h after acute iodide administration, whereas NIS protein was decreased only at 24 h. TPO mRNA was decreased at 6 days of chronic iodide ingestion and 24 h after acute iodide administration. There were no iodide-induced changes in TSH receptor and thyroglobulin mRNAs. These data suggest that iodide administration decreases both NIS mRNA and protein expression, by a mechanism that is likely to be, at least in part, transcriptional. Our findings support the hypothesis that the escape from the acute Wolff-Chaikoff effect is caused by a decrease in NIS, with a resultant decreased iodide transport into the thyroid. The observed decrease in TPO mRNA may contribute to the iodine-induced hypothyroidism that is common in patients with Hashimoto's thyroiditis.

Iodine and disinfection: theoretical study on mode of action, efficiency, stability, and analytical aspects in the aqueous system.

Although they have been in use for nearly 170 years, the mode of action of iodine-based disinfectants is not yet clearly understood, as is manifested, for example, in diverging judgements about the relevance of the individual iodine species. Although studies based on calculated equilibrium concentrations in pure iodine solutions have already been done, there is a lack of knowledge about iodine solutions in the presence of additional iodide which would be of intrinsic importance for disinfection practice. Therefore, a re-calculation was undertaken considering variations of this parameter in the pH range 0-14. The presented calculations concern fresh iodine solutions not affected by disproportionation (iodate formation) and provide information about the equilibrium concentrations of the species I, I2, I3, I5-, I6(2-), HOI, O1-, HI2O-, IO2- and H2OI+. Additional iodide and the pH value have a very pronounced influence on the individual equilibrium concentrations (several powers of ten); hence, conditions can be indicated where the number of species of virtual importance is drastically reduced. In the most common case with iodine in the presence of additional iodide at pH < 6, only I-, I2 and I3- play a role. In the absence of additional iodide, at pH 8-9 and at high dilution (c(I2) < 10(-5) M), on the other hand, HOI accounts for over 90% of the oxidation capacity. At high iodide concentration (e.g., Lugol's solution) the species I5- and I6(2-) make up 8.2% of the oxidation capacity. The iodine cation H2OI+, frequently quoted as an active agent in disinfection, is without any relevance under the conditions occurring in practice, as are IO- and HI2O- which become important only at pH > 10. The stability problem (i.e. rate of iodate formation) arising at pH > 6 can be reduced to hypoiodous acid, as manifested in the simple rate law d[IO3]/dt = 0.25 [HOI]3/[H+] which allows an estimation of stability under weakly alkaline conditions. The results of this study allow us to deduce general qualities of aqueous iodine solutions, such as reactivity, stability, and analytical aspects, and to estimate major disinfection-orientated properties such as microbicidal activity, irritation, and incorporation effects. Though the calculations consider primarily preparations devoid of polymeric organic compounds capable of complexing iodine species, the results can be largely transferred to iodophoric preparations.

Thyrotropin chronically regulates the pool of thyroperoxidase and its intracellular distribution: a quantitative confocal microscopic study.

The regulation of thyroperoxidase (TPO) expression and of its intracellular distribution was studied in porcine thyroid cells cultured on porous bottom filters. Cells were cultured for 18 days in the absence or in the presence of thyrotropin (TSH) and with or without iodide. Microsomes were purified and analyzed by electrophoresis. TPO was detected by immunoblotting with polyclonal anti-porcine TPO antibodies and quantified by scanning the bands. The amount of TPO was increased 2-fold by TSH. High concentrations of iodide (1-50 microM, added daily) decreased the level of TPO. Confocal microscopy served to determine the intracellular localization of TPO and its quantitative distribution. Intracellular and surface-located TPO was detected by fluorescein-labeled antibodies on saponin-treated cells. Quantitative confocal microscopy showed that TSH increased the total amount of TPO 2-fold as for immunoblotting. The highest amount of TPO was found in the perinuclear area and between the nucleus and the Golgi apparatus. Only 4% of TPO was present on the apical surface and about 1% on the basolateral membrane; the remainder (about 95%) was inside the cells. TSH did not change these relative contents. TSH modified the intracellular distribution of the enzyme, increasing the TPO pool from the perinuclear area to apical membrane. This domain could be a site of storage of TPO. Adding a physiological concentration of iodide (0.5 microM, daily) did not influence the intracellular distribution of TPO. We concluded that chronic TSH stimulation 1) increased 2-fold the pool of TPO but did not change the relative proportion of TPO inside the cells and on the apical surface, and 2) modified the intracellular distribution of vesicular TPO, the major part of which was accumulated in the perinuclear and cytoplasmic area under the subapical domain of the polarized cells.

Iodide suppression of major histocompatibility class I gene expression in thyroid cells involves enhancer A and the transcription factor NF-kappa B.

High concentrations of iodide can induce transient, clinical improvement in patients with autoimmune Graves' disease. Previous work has related this iodide action to the autoregulatory effect of iodide on the growth and function of the thyroid; more recently, we additionally related this to the ability of iodide to suppress major histocompatibility (MHC) class I RNA levels and antigen expression on thyrocytes. In this report, we describe a transcriptional mechanism involved in iodide suppression of class I gene expression, which is potentially relevant to the autoregulatory action of iodide. Transfection experiments in FRTL-5 cells show that iodide decreases class I promoter activity and that this effect can be ascribed to the ability of iodide to modulate the formation of two specific protein/DNA complexes with enhancer A, -180 to -170 bp, of the class 1 5'-flanking region. Thus, iodide decreases the formation of Mod-1, an enhancer A complex involving the p50 subunit of NF-kappa B and a c-fos family member, fra-2, which was previously shown to be important in the suppression of class I levels by hydrocortisone. Unlike hydrocortisone, iodide also increases the formation of a complex with enhancer A, which we show, in antibody shift experiments, is a heterodimer of the p50 and p65 subunits of NF-kappa B. The changes in these complexes are not duplicated by chloride and are related to the action of iodide on class I RNA levels by the following observations. First, FRTL-5 thyroid cells with an aged phenotype coincidentally lose the ability of iodide to decrease MHC class I RNA levels and to induce changes in either complex. Second, the effect of iodide on class I RNA levels and on enhancer A complex formation with Mod-1 and the p50/p65 heterodimer is inhibited by agents that block the inositol phosphate, Ca++, phospholipase A2, arachidonate signal transduction pathway: acetylsalicylate, indomethacin, and 5,8,11,14-eicosatetraynoic acid. Interestingly, iodide can also decrease formation of the Mod-1 complex and increase formation of the complex with the p50/p65 subunits of NF-kappa B when the NF-kappa B enhancer sequence from the Ig kappa light chain, rather than enhancer A, is used as probe; and both actions mimic the action of a phorbol ester. This suggests that iodide may regulate complex formation with NF-kappa B regulatory elements on multiple genes associated with growth and function, providing a potential mechanism relating the autoregulatory action of iodide on thyroid cells and its action on class I gene expression.

Relationship of Water Chemistry to Serum ThyroidHormones in Captive Sharks with Goitres

Captive whitetip reef sharks, Triaenodon obesus,at Sea Life Park (SLP) Hawaii, Waimanalo, Hawaii develop goitre, whereas, T. obesus at the Waikiki Aquarium (WAQ), Honolulu,Hawaii do not develop goitre. To determine theeffects of natural concentrations of iodine on thereduction of goitre, two sharks from SLP with goitrewere placed in an enclosed coastal lagoon with naturalseawater. Using ultrasound measurements the twogoitres were initially 11.4 cm and 14.6 cm in depthand after 3 months decreased to 4.7 cm and 5.7 cm. Radioimmunoassay analysis of the thyroid hormoneT3 sera concentrations were initially 0.22 ng/mland 0.33 ng/ml and increased to 1.84 ng/ml after beingplaced in the lagoon. Sera T4 were initially0.93 ng/ml and 0.99 ng/ml and increased dramaticallyto 17 ng/ml and 56 ng/ml. Over the six month samplingperiod, two resident sharks in the lagoon with normalthyroids had sera T3 concentrations from 0.89ng/ml to 1.1 ng/ml, and sera T4 concentrationsfrom 3.1 ng/ml to 7.9 ng/ml. The hypothyroidcondition in the SLP goitred-sharks is likely linkedto the low environmental iodide (<0.005 μM), andhigh nitrate (111 μM) of SLP water. The WAQwell-water facility was characterized by anoxic waterwith high iodide (0.60 μM), total iodine (1.90μM), and typical nitrate (24.6 μM)concentrations of interstitial groundwater. Thedifference of iodide concentration of SLP and WAQ tankwater (<0.005 μM versus 0.60 μM) wasdirectly related to the hydrogeology of the well-watersources. To avoid goitre in marine aquarium systems,we recommend maintaining iodide concentrations of atleast 0.15 μM.

The Iodine—Thiosulfate Reaction: a Pulse-Radiolysis Study and Spectrophotometric Evidence for the Intermediates I2S2O32- and IS203-.

Spectroscopic evidence for I2S2O32- and IS2O3-, postulated as intermediates in the iodine{thiosulfate reaction, has been obtained by using the technique of pulse radiolysis to oxidize iodide to I3- in the presence of thiosulfate. The spectra show blue shifts with respect to I3- and I2 respectively. The kinetics of the reaction over a range of concentrations different from those reported by Scheper and Margerum have also been studied and further evidence for their quantitative scheme has been obtained; a change predicted by their model, but not detected by them, in kinetic order in S2O32- at low thiosulfate and high iodide concentrations has been found.

Kinetics of disproportionation of hypoiodous acid at high pH, with an extrapolation to rainwater

V. W. Truesdale, J. Chem. Soc., Faraday Trans., 1997, 93, 1909 DOI: 10.1039/A700226B

In vivo and in vitro evidence for iodide regulation of major histocompatibility complex class I and class II expression in Graves' disease.

Increases in thyroid cell major histocompatibility complex (MHC) class I and class II expression have been suggested to be an important factor in the development or perpetuation of Graves' disease. It is hypothesized that elevations result in abnormal presentation of thyroid antigens to immune cells, and that iodide and/or methimazole (MMI) are effective therapeutic agents because, at least in part, of their suppression of MHC expression. In this report, we show that Graves' patients pretreated with iodide only 4 days before surgery have lower levels of MHC class I and class II RNA levels in their thyroid tissue than do patients with no iodide pretreatment (P < 0.001 and 0.03, respectively). Because patients in both groups are treated with MMI and because the change is independent of the amounts of MMI used to treat patients, the class I and class II changes cannot be ascribed to MMI. The iodide action to decrease MHC class I and class II RNA levels was duplicated using cultured human thyroid cells in vitro; the iodide effect was dependent on the iodide concentration, was not duplicated by chloride, was not associated with an alteration in cAMP levels or with a change in thyrotropin receptor RNA levels, and was evident in gamma-interferon-treated cells. The data suggest, therefore, that the therapeutic action of iodide in Graves' patients is associated with decreased MHC gene expression, that this action is a direct effect of high concentrations of iodide on the thyroid cells, and that altered MHC gene expression in the target tissue may well be associated with the development or perpetuation of Graves' disease.

Iodine speciation in the water column of the Rogoznica Lake (Eastern Adriatic Coast)

Specific concentration profiles of iodate, iodide and organo-iodine in the water column of the Rogoznica Lake, where both oxic and anoxic conditions occur, were observed. Iodate and iodide concentrations were determined directly in water samples by differential pulse voltammetry (DPV) and cathodic stripping square wave voltammetry (CSSWV), respectively. Concentrations of ‘labile’ and ‘stabile’ organo-iodine were determined by DPV in the samples pretreated with chlorine water and UV-irradiation (combined with hydrogen peroxide and followed by chlorine water addition), respectively. In this stratified water column (salinity and dissolved oxygen gradients) with pronounced biological productivity, high concentrations of iodide (up to 0.87 μM) and significant percentages of ‘labile’ and ‘stabile’ organo-iodine, up to 37% and 30% respectively, were found. The formation of ‘labile’ organo-iodine is primarily governed by chemical reactions with dissolved sulphur forms and organic compounds, as well as remineralization processes of ‘stabile’ organo-iodine.

Coulometric Study of Recovery Rates for Karl Fischer Titration of Water in Aldehydes and Ketones Using Rapidly Reacting Methanolic and 2-Methoxyethanolic Reagents

Factors itch influence the recovery of water with use of rapidly reaching imidazole-based methanolic or 2-methoxyethanolic Karl Fischer (KF) reagents were investigated coulometrically. Using cyclohexanone and benzaldehyde as model substances, it was found that, in addition to the well-known problems associated with low recoveries of water due to the bissulfite addition reaction, errors may also be caused by side reactions involving iodine. Such interferences are largest at the end point of a titration, where an excess of iodine is present, and will lead to an overcompensation when correcting the results for the endpoint drift. The extent of the sum of all the side reactions was found to decrease with the concentration of ioxide for all types of KF reagent investigated. The high reaction rates for the imidazole-based KF reagents, despite the high concentration of iodide, make it possible to use a very low end-point concentration of iodine. In this way, side reactions involving iodine can be further suppressed. However, for titrations carried out in 2-methoxyethanolic reagents, a relatively high concentration of iodine must be present at the end point in order to decrease the time needed for the reversal of the bisulfite addition reaction. For small amounts of water, i.e., less than 30 μg, a reagent based on metanol can be recommended, since the titrations are rapid and the recovery was found to be 100% for both cyclohexanone and benzaldehyde. For large amounts of water or slow titrations, the recoveries tend to decrease for all reagent mixtures investigated. One reason for this seems to be related to a change in stoichiometry for the KF reaction involved in the reversal of the bisulfite addition reaction

Mass-coupled chemical systems with computational properties

We simulate a pattern recognition device constructed from mass-coupled chemical reactors. Each reactor is an open system containing a bistable (iodate-arsenous acid) reaction. We store arbitrary patterns of high and low iodide concentrations in the network using a Hebb type rule. When the network is initialized with a pattern which is similar to a stored pattern, errors in the initial pattern are corrected and the similar stored pattern is recalled. When the network is initialized with a pattern which is not similar to a stored pattern, the network evolves to a homogeneous state which signals nonrecognition. The network is a programmable parallel computational device

Iodide as the mediator for the reductive reactions of peroxidases.

Lignin peroxidase H2 (LiPH2) from the white rot fungus Phanerochaete chrysosporium catalyzed the reduction of cytochrome c, nitro blue tetrazolium, ferric iron, molecular oxygen, and triiodide in a reaction mixture containing LiPH2, H2O2, EDTA, and iodide. Activity followed first order kinetics with respect to EDTA concentration. The reductive activity observed with LiPH2 using iodide as the mediator was comparable to that obtained using a variety of other free radical mediators such as veratryl alcohol, 1,4-dimethoxybenzene, and 1,2,3- and 1,2,4-trimethoxybenzene. EDTA-derived radicals were detected by ESR spin trapping upon incubation of LiPH2 with H2O2, iodide, and EDTA. Reduction activity was also observed using other peroxidases such as lactoperoxidase, horseradish peroxidase, and myeloperoxidase. For the reduction activity of LiPH2, it is proposed that the oxidation of EDTA is mediated by the iodide radical, and the reduction of various electron acceptors is mediated by EDTA radicals. The inhibition of reduction activity at higher concentrations of iodide might be due to the combination of iodide radicals to form I2 which forms a stable triiodide complex by reacting with excess iodide.