Showing papers on "Iodide published in 1976"

The mechanism of action of the thioureylene antithyroid drugs.

Abstract: A model incubation system containing purified thyroid peroxidase (TPO) was used to study the mechanism of action of the thioureylene anti-thyroid drugs--propylthiouracil (PTU), methylmercapto imidazole (MMI) and carbimazole. Two general types of experiments were performed: a) measurement of the inhibitory effects of the drugs on TPO-catalyzed iodination and on TPO-catalyzed oxidation of guaiacol, and b) studies of the metabolism of PTU and MMI by the TPO model system. The major observations can be summarized as follows: 1) The thioureylene drugs are potent inhibitors of TPO-catalyzed iodination of protein and tyrosine. Their potency increases greatly as the concentration of I- decreases. 2) The thioureylene drugs are also potent inhibitors of TPO-catalyzed oxidation of guaiacol, a reaction that does not involve iodide. 3) MMI and PTU are readily oxidized in the model incubation system when iodide is present but not in the absence of iodide. The rate of oxidation increased as the iodide concentration was increased from 10 to 100 muM. 4) Oxidation of PTU and MMI by the model incubation system is inhibited by relatively slight increases in the concentration of PTU and MMI. These drugs are capable of inhibiting their own and each other's metabolism. 5) Inhibition of iodination is competitively antagonized by iodide at low drug concentrations, but not at higher drug concentrations. 6) Inhibition of iodination by MMI and PTU may be either reversible (low ratio of drug to iodide), or irreversible (higher ratio of drug to iodide). In reversible inhibition the iodination is inhibited for a period which may be as brief as 2 min or as long as 20 min, but thereafter, iodination begins, and there is escape from inhibition. During the lag-period there is extensive metabolism of the drug. In the case of irreversible inhibition of iodination is inhibited completely or almost completely for 60 min, and drug oxidation during this period is relatively low. 7) Irreversible inhibition may be transformed into reversible inhibition by increasing the concentration of TPO or the concentration of iodide. However, increasing the concentration of H2O2 or of tyrosine does not overcome irreversible inhibition. On the basis of these findings and of current views concerning the mechanism of enzymatic iodination, a scheme is proposed for the mechanism of inhibition by thioureylene drugs of TPO-catalyzed iodination of protein and tyrosine.

Effects of halides and bicarbonate on chloride transport in human red blood cells.

Abstract: Chloride self-exchange was determined by measuring the rate of 36Cl efflux from human red blood cells at pH 7.2 (0 degrees C) in the presence of fluoride, bromide, iodide, and bicarbonate. The chloride concentration was varied between 10--400 mM and the concentration of other halides and bicarbonate between 10--300 mM. Chloride equilibrium flux showed saturation kinetics. The half-saturation constant increased and the maximum flux decreased in the presence of halides and bicarbonate: the inhibition kinetics were both competitive and noncompetitive. The competitive and the noncompetitive effects increased proportionately in the sequence: fluoride less than bromide less than iodide. The inhibitory action of bicarbonate was predominantly competitive. The noncompetitive effect of chloride (chloride self-inhibition) on chloride transport was less dominant at high inhibitor concentrations. Similarly, the noncompetitive action of the inhibitors was less dominant at high chloride concentrations. The results can be described by a carrier model with two anion binding sites: a transport site, and a second site which modifies the maximum transport rate. Binding to both types of sites increases proportionately in the sequence: fluoride less than chloride less than bromide less than iodide.

The facile synthesis of lactones

Abstract: Direct lactonization of ω-hydroxy acids, HO(CH22)nCOOH with n=5, 7, 10, 11, 14, has been successfully carried out under mild conditions in good yields by the treatment with 1-methyl-2-chloropyridinium iodide in the presence of triethylamine. In the case of the acid with n=6, only lactide has been produced.

Crystal structure of the copper(I) iodide–pyridine (1/1 ) tetramer

Abstract: The crystal structure of the copper(I) iodide pyridine adduct has been determined by X-ray diffraction at 295 K and refined by least squares to R 0.057 for 2 710 ‘observed’ reflections. Crystals are orthorhombic, space group P212121, with a= 16.032(6), b= 15.510(2), and c= 11.756(3)A. The asymmetric unit is Cu4I4py4, based on the well-known tetrahedral tetrameric Cu4I4 unit, with Cu–N 2.04, Cu–I 2.70, and Cu–Cu 2.69 A; the latter distance is much shorter than in the analogous complexes formed with phosphine and arsine ligands.

On the mechanism of inhibition by iodine of the thyroid adenylate cyclase response to thyrotropic hormone.

Abstract: Rats maintained on a low-iodine diet were hypophysectomized, and their diet was then enriched with iodide. Cyclic AMP(cAMP) concentrations achieved in their thyroids following in vitro TSH stimulation were significantly lower than those in the thyroids of control animals that did not receive dietary iodide enrichment. The addition of 0.1% methimazole (MMI) or 1% KClO4, to the diet abolished this inhibitor effect of iodide. The administration of triiodothyronine in the diet did not reproduce the inhibitor effect of iodide. The effect of iodide in vitro on the thyroid cAMP response to TSH was then investigated using paired thyroid lobes obtained from intact rats fed a lowiodine diet. During a 15-min incubation period, concentrations of iodide up to 10−3M, together with TSH (125 mU/ml), did not affect the thyroid cAMP response to TSH. In contrast, the preincubation of the lobes in 5 × 10−5M Nal for 2 h preceding a final 15-min incubation in medium containing TSH alone resulted in final cAMP concentrations si...

Conversion of alkyl chlorides to bromides, selective reactions of mixed bromochloroalkanes, and halogen exchange.

Abstract: Primary alkyl chlorides are quantitatively converted to their corresponding bromides in the presence of ethyl bromide, N-methyl-2-pyrrolidinone, and a catalytic amount of metal bromide. A variety of chlorides can be converted. Selective functionalization at bromine of several primary bromochloroalkanes was studied in conjunction with the chloride-bromide conversion for multistep syntheses. Methods for halogen exchange between chloride, bromide, and iodide in the octyl halide series are presented.

Dry method for recycling iodine-loaded silver zeolite

Abstract: Fission product iodine is removed from a waste gas stream and stored by passing the gas stream through a bed of silver-exchanged zeolite until the zeolite is loaded with iodine, passing dry hydrogen gas through the bed to remove the iodine and regenerate the bed, and passing the hydrogen stream containing the hydrogen iodide thus formed through a lead-exchanged zeolite which adsorbs the radioactive iodine from the gas stream and permanently storing the lead-exchanged zeolite loaded with radioactive iodine.

The Reaction of Disodium Tetracarbonylferrate(–II) with Aldehydes

Abstract: Disodium tetracarbonylferrate (–II) is an efficient catalyst for the dismutation of aromatic aldehydes to esters, 2RCHO→RCOOCH2R. Aliphatic ones give aldol-condensation products upon treatment with the ferrate. A successive reaction of the ferrate with an aldehyde, RCHO, and then with alkyl iodide, R’I, gives an ester, R’COOCH2R, after protonation. The mechanisms of these reactions are discussed.

Kinetics of Thyroglobulin Iodination and of Hormone Synthesis Catalyzed by Thyroid Peroxidase

Abstract: The kinetics of tyrosine iodination and of thyroxine synthesis in thyroglobulin, different reactions catalyzed by the sane enzyme (thyroid peroxidase), have been compared. Thyroxine synthesis always began after a lag period of 3–5 min. This lag was constant whatever the rate of iodination; this rate of iodination was increased either by increasing the concentration of iodide or enzyme or by decreasing the concentration of thyroglobulin. Increasing the rate of iodination resulted in increasing the number of iodine atoms incorporated during the lag period. Thus the lag observed for thyroxine synthesis was constant and did not depend on the fact that free iodide or non-iodinated tyrosine residues of thyroglobulin were exhausted before thyroxine synthesis occurred. Finally, it appeared that, whatever the explanation of the lag, the enzyme catalyzes thyroid hormone synthesis at a slower rate than iodination. The existence of a lag also allowed us to prepare thyroglobulin samples with different iodine contents but without thyroid hormones. Thus iodination and thyroxine synthesis could be studied independently and the following results were obtained. 1 Iodotyrosine residues which can couple to form thyroxine are made considerably before coupling occurs. 2 H2O2 is required for coupling of these hormonogenic residues; thus the coupling reaction requires enzymic oxidation of the iodotyrosine residues. 3 In addition a strict requirement for iodide was needed for coupling: the requirement was dependent on the concentration of iodide. Thus iodide, a substrate of the iodination reaction, may also have other effects on the activity of thyroid peroxidase.

Iodide, thiocyanate and cyanide ions as capturing reagents in one-step copper-thiocholine method for cytochemical localization of cholinesterase activity.

Abstract: The necessity of the presence of iodide in Cu-ThCh reaction was investigated by following the precipitate formation "in vitro" and by evaluating the ultrastructural localization of the precipitate in sympathetic ganglion cells of the frog and in the end-plate regions of the rat diaphragm. It was found that thiocyanate or cyanide is the only anion that can be substituted for iodide as the capturing agent in precipitation. The optimal concentration in the preincubation and incubation media of any one of the three anions is from 2 to 5 mM. At a concentration below 1 mM precipitation "in vitro" is considerably delayed as a result of which in electron microscopy diffusion artefacts appear in tissue sections. The unconverted primary precipitate obtained in the presence of iodide had been used for ultrastructural localization of ChE activity and now this use has been extended to precipitates obtained in the presence of CN- or CNS-. Better-quality localization in the presence of either one of the latter anions suggests that they, and particularly CN-, should be substituted for I- in the one-step Cu-ThCh method for the cytochemistry of cholinesterases.

The oxidation of manganese(II) by chromium(VI) in the presence of oxalate ion

Abstract: The Oxidation of Manganese( 11) by Chromium( VI) in the Presence of Oxalate Ion Charles F Huber and C P Haight, Jr* Contribution f r o m the School of Chemical Sciences, University of Illinois Urbana, Illinois 61 801, Received August 11, 1975 Abstract: Manganese(I1) is oxidized quantitatively to M n ( C ~ 0 4 ) 3 ~ by - HCr04- in the presence of oxalate ion The reaction proceeds according to the rate law: rate = -d[Cr(VI)]/dt = k’[HCrO4-] [Mn(C204)22-] [C20d2-] [H+I2 The first-order de- pendence on a one-electron reductant is uncommon for chromate oxidations and has been found previously for reducing agents such as Mo(CN)s4- and Fe(CN)64- which form a bridge to Cr(V1) by expanding the coordination sphere of chromate This similarity and the observed rate law suggest an activated complex containing a doubly bridging oxalate ion, I This reaction provides a rational explanation for reported Mn(I1) catalyses of some Cr(V1) oxidations as opposed to the well-known inhibi- tion effect caused by Mn(I1) trapping of Cr(IV) intermediates Studies of Cr(V1) oxidations of oxalic acid abound in the The catalysis of the reaction by Mn(I1) was first observed by Dhar’ This runs contrary to the general effect of Mn(I1) on chromate oxidations-an inhibition caused by Mn(I1) capture of the Cr(1V) intermediate, which has been frequently used as a tool in studying the oxidation of other substra tes6 The interesting Mn(I1) catalyzed oxidation of oxalic acid has been studied by various workers Chakravarti and Ghosh2 found that the reaction order in oxalate decreased in the presence of Mn(I1) toward zero Bakore and Jain3 ob- tained similar results with respect to order in oxalate, and found a first-order dependence on Mn(II), with the rate con- stant varying with [HCr04-]065initial Both these studies fol- lowed the reaction by iodometric titration of the remaining oxidant, and under conditions of excess Cr(V1) over Mn(I1) Recently, Rocek and co-workers elucidated the uncatalyzed reaction of Cr(V1) as well as the reaction of the intermediates Cr(V) and Cr(1V) with oxalic acid5 They observed later that in the presence of Mn(I1) the decrease in absorbance a t the Cr(V1) 350 nm peak appeared to proceed in two stages (Figure l)’ The rate of decay in the second step corresponds to that observed by Taubeg for the decomposition of Mn(C204)33- Significantly, we have observed that solutions of this complex are capable of oxidizing iodide to 12 Since the earlier studies of Mn(I1) catalysis measured Cr(V1) iodometrically without realizing that Mn(II1) was present in significant concentra- tions, it is apparent that their data were wrongly considered and the reaction should be restudied spectrophotometrically W e report here the mechanism of the first step in the two-step process observed by Rocek 7 H + + HCr04- + 3 M n ( C ~ 0 4 ) 2 ~ - 3C204*- Cr3+ 3Mn(C204)33- 4 H 2 0 2Mr1(C104)3~- 2Mr1(C204)2~- C2042- + 2CO2 Experimental Section Reagent grade chemicals were used without further purification The concentration of the Mn(C104)2 stock solution was checked spectrophotometrically, following oxidation to M n 0 4 - using the method of Willard and G r e a t h o ~ s e ~ Measurements All kinetic and stoichiometric measurements were made by observing changes in absorbance due to the formation of Mn(C204)33- at 525 nm, where interference by Cr(V1) is negligible, using a Cary 14 spectrophotometer equipped with a water-circulating cell holder connected to a temperature bath All runs contained a large excess of an oxalate-acid oxalate buffer, to ensure that MnC204 would not reprecipitate LiC104 was added to maintain ionic strength at -06 M However, it is very difficult to maintain ionic strength in such concentrated solutions of divalent ions, and there is some doubt as to how much meaning the concept has in Journal of the American Chemical Society such situations A radiometer pH meter was used to measure hydrogen ion concentration Its calibration was checked against standard so- lutions of HC104 in a 06 M solution of LiC104 Half-lives obtained from the absorbance vs time curves were used to obtain pseudo-first-order rate constants, kobsd The reaction gen- erally obeyed good first-order kinetics for disappearance of Cr(V1) However, as pH increased, the relative rate of decay of Mn(II1) be- came high enough to interfere with observation of the production of Mn(II1) Above -pH 45, the interference became too great to obtain any value of half-lives No measurement was done at pH below 3 be- cause preliminary measurements indicated that the reaction would become too fast to measure accurately Actually it was discovered i n treating the data of Hasan and Rocek that the rate leveled off and then decreased at pH <3, so that our study might well have been extended to higher acidities Results Stoichiometry Observation a t 525 nm with excess Mn(I1) revealed formation of 3 mol of M n ( C ~ 0 4 ) 3 ~ for - each mole of Cr(V1) consumed It is known that M ~ I ( H ~ O will ) ~ not reduce Cr(V1) Therefore a Mn(I1)-oxalate complex must be the only reducing agent for chromium in this p H range HCr04- + 3Mn(C204)2*- + 3c2042- + 7 H + Cr3+ + 3Mr1(C204)3~- + 7 H 2 0 Kinetics Table I1 summarizes kinetic data based on kobsd for first-order decay in [Cr(VI)] Most data were obtained after the first or second half time Mn(I1) Dependence Two runs, not listed, contained an excess of Cr(V1) over Mn(I1) They showed a pseudo-first-order re- action indicating first-order dependence on Mn(I1) A series of runs with varying concentrations of excess Mn(I1) indicates that kobsd a [Mn(II)] (Figure 2) Hydrogen Ion and Oxalate Dependence Figure 3 shows kobsd vs [H+] for a series of runs with total oxalate concentration held constant It shows a dependence which varies from second to first order as [H+] increases Runs in which [OXIT varied indicated a dependence ranging from second to first order in oxalate Since the predominant Mn(I1) species present in these studies are MnC204 and M I I ( C * O ~ ) ~ this ~ - , suggests an ac- tivated state formed by reactions of HCr04-, Mn(C204)2*-, C2042-, and two H+ Assuming this, the following equation is obtained: kobsd = k’[Mn(C204)22-l [ C Z O ~ ~ [ H - ] + l 2 A simple derivation gives quantities: kobsd July 7, 1976 k&sd in terms of k‘ and known = k’K2Ka2[ M ~ ( I I ) ] T [ O X ] T ~ [ H ’ / + ( ] K a [H+] + K2Ka[OxlT)(Ka + [H+1)

Molecular motion, phase transitions, and disorder in the pyridinium halides

Abstract: The solid pyridinium chloride, bromide, and iodide salts were studied using 1H nuclear magnetic resonance and differential scanning calorimetry. Phase transitions were observed at 345 K for the chloride, 269 K for the bromide, and 247 K for the iodide. Well below each transition, the pyridinium ions are held rigidly in the crystal lattice, whereas above each transition the ions reorientate rapidly about an axis at right angles to the ring planes. From the temperature dependence of the spin–lattice relaxation times the high temperature phase reorientational activation energies were determined to be 1.55, 2.30, and 4.20 kcal/mol for the chloride, bromide, and iodide, respectively.

Reactions of trifluoromethyl iodide with methylgold(I) complexes. Preparation of trifluoromethyl-gold(I) and -gold(III) complexes

Abstract: Trifluoromethyl iodide reacts with [AuMeL] to give [AuMe2(CF3)L] and [AuIL](L = PMe3 or PMe2Ph), or [Au(CF3)L] and Mel (L = PPh3), or a mixture of these products (L = PMePh2). In some cases reaction of [AuMe(PMe3)] with CF3I gives [AuMe(CF3)I(PMe3)]. Evidence is presented that the reactions proceed, at least in part, by a free-radical chain mechanism.

Pharmacokinetics of a new skin wound cleanser

Abstract: Iodophors are effective germicidal agents that have prolonged antiseptic activity in contaminated wounds. A nontoxic surfactant, Pluronic F-68, has been used to formulate a safe and effective iodophor. The parameters necessary to regulate the activity of the iodophor were studied to develop a potent, yet safe bactericidal solution for use in human subjects. The parameters found to be most important were the pH of the solution and the concentration of sodium iodide. Lowering the pH of iodophors increased their stability and antiseptic activity. The free iodine in iodophor solutions prepared with a low pH is predominantly the highly biocidal diatomic iodine (I2). The concentration of iodide regulated the equilbrium of the dissolved iodine between its free and complexed form. Increasing the concentration of iodide in the iodophor lowered the amount of free iodine in solution and enhanced the concentration of the complexed iodide. It is the level of free iodine in an iodophor that determines its antiseptic activity. Low levels of free iodine yielded iodophors that had a slow bacterial kill rate but a prolonged duration of action. Manipulation of these variables permitted the generation of iodophors that varied considerably in their kill rates of bacteria and their duration of antibacterial activity. Iodophors tested in this study demonstrated a distinct superiority to noncomplexed iodine solutions (tincture and aqueous iodine solutions) as wound and skin cleansers.

The Release of Iodine from Iodide Salts by Gamma Radiolysis

Abstract: Gamma irradiation was found to release iodine in small amounts from powdered samples of cesium iodide and barium iodide, but not from zirconium iodides. The amount of iodine released was measured using silver foil detectors in sealed capsules that contained the salt. The amount of release was markedly affected by impurities, especially water, that were difficult to control; therefore, G values calculated were inaccurate but of the order of 10/sup -3/ atoms of iodine released for 100 eV of energy absorbed for CsI and BaI/sub 2/ near room temperature. The G values for the zirconium iodides were much smaller. The phenomenon of release of iodine from the ionic iodides by gamma radiation is discussed on the basis of published theories of the formation of defects in solids.

Thyroidal iodine metabolism during the development of the chick embryo.

Abstract: Stable iodine was measured in the thyroid gland of the chick embryo from day 9 to day 20 of incubation in order to evaluate quantitatively the functional development of the gland. Total iodine content increased progressively during incubation. From day 9 to day 17 of incubation, this increase resulted from the increases of pellet-bound iodine and of soluble iodine. Afterwards, it essentially paralleled the increase of the soluble thyroglobulinbound iodine which reflected the increase in both thyroglobulin content and the degree of iodination of the thyroglobulin. The total iodine, thyroglobulinbound iodine and thyroglobulin (TG) content, increased as power functions of time during incubation, with critical times on days 11 and 15. Their concentrations also increased during the whole incubation period, while the iodide concentration remained roughly constant (25 ng/mg) from day 13 to day 19. Only one iodoprotein, 19.5 S TG, was found, and its heterogeneity of iodination was demonstrated during the whole pe...

A convenient and general preparation of alkyl hydroperoxides and dialkyl peroxides

Abstract: Primary, secondary, and tertiary alkyl hydroperoxides and dialkyl peroxides can be prepared from the appropriate alkyl bromide or iodide and hydrogen peroxide or alkyl hydroperoxide in the presence of silver trifluoroacetate.

Process for the preparation of silver halide emulsions

Abstract: Emulsions having an improved sensitivity/grain ratio are obtained when a silver halide emulsion containing up to 20 mol % of AgI is prepared by the precipitation of a silver halide emulsion A containing up to 100 mol % of AgI and the addition of a silver halide emulsion B which contains up to 40 mol % of AgI, has an average grain size of at most 0.25 μm and is always more soluble in aqueous gelatine solution than emulsion A either due to its grain size or due to its iodide content, this being carried out in the presence of at least two compounds selected from imidazole, histidine (α-amino-β-imidazolyl-(5)-propionic acid) and other monocyclic, 5- or 6-membered heterocyclic compounds which have at least one ring nitrogen atom, are free from SH groups and form sparingly soluble silver salts in weak acid to neutral aqueous solutions, which salts redissolve at pH>9 when ammonia is added, one of the at least two compounds being imidazole or histidine and at least one other compound being a compound other than imidazole or histidine.

The Inhibitory Effect of Acute Administration of Excess Iodide on the Formation of Adenosine 3′,5′-Monophosphate Induced by Thyrotropin in Mouse Thyroid Lobes

Abstract: In a previous paper, we demonstrated that an inhibitory action of excess iodide on thyrotropin- induced thyroid hormone secretion occurs at a site subsequent to the generation of cyclic AMP. In the present study, however, we have found that thyroidal cyclic AMP formation induced by thyrotropin in vitro was markedly inhibited by the acute administration of excess iodide to mice fed a low iodine diet. In contrast, excess iodide failed to produce inhibition in animals fed a regular diet. In oitro stimulation by long-acting thyroid stimulator (LATS), prostaglandin E2, and 4-methylhistamine of cyclic AMP formation in mouse thyroid lobes was also significantly inhibited by the acute in vivo administration of excess iodide. The inhibition was completely relieved by the administration of methimazole prior to excess iodide. Furthermore, it has been shown that thyroid adenylate cyclase activity induced by thyrotropin was markedly depressed by excess iodide under similar experimental conditions. Therefore, it is sug...