Presence Of Thiocyanate Ions Research Articles

Molecular pharmacology of the AMPA agonist, ( S)-2-amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid [( S)-APPA] and the AMPA antagonist, ( R)-APPA

The heterocyclic analogue of ( S)-glutamic acid, ( S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid [( S)-AMPA] is a potent and selective AMPA receptor agonist, whereas the enantiomeric compound, ( R)-AMPA, is virtually inactive. We have previously characterized ( RS)-2-amino-3-(3-hydroxy-5-phenyl-4-isoxazolyl)propionic acid [( RS)-APPA] as a partial AMPA receptor agonist showing about 60% of the efficacy of ( RS)-AMPA. This partial agonism produced by ( RS)-APPA is, however, only apparent, since resolution of ( RS)-APPA has now been shown to provide the full AMPA receptor agonist, ( S)-APPA, whereas ( R)-APPA is a non-N- methyl- d-aspartic acid (non-NMDA) receptor antagonist showing preferential AMPA blocking effects. In agreement with classical theories for competitive interaction between agonists and antagonists, the efficacy of depolarizations produced by ( S)-APPA in the rat cortical wedge preparation was shown to be progressively reduced with increasing molar ratios of ( R)-APPA/( S)-APPA. These compounds and the competitive antagonists ( RS)-2-amino-3-(3-carboxymethoxy-5-methyl-4-isoxazolyl)propionic acid [( RS)-AMOA], 6-cyano-7-nitroquinoxalin-2,3-dione (CNQX) and 6-nitro-7-sulfamoylbenzo( f)quinoxalin-2,3-dione (NBQX) were also tested in [ 3H]AMPA and [ 3H]CNQX binding systems, the latter ligand being used in the absence or presence of thiocyanate ions. On the basis of these studies it is suggested that ( RS)-AMPA and the AMPA agonist ( S)-APPA interact with a high-affinity receptor conformation, whereas the competitive antagonists ( RS)-AMOA and ( R)-APPA, derived from these agonists, preferentially bind to a low-affinity AMPA receptor conformation. The competitive antagonists, CNQX and NBQX which are structurally unrelated to ( RS)-AMPA or ( RS)-APPA, do not seem to discriminate between these two AMPA receptor conformations. The modified [ 3H]CNQX binding assay containing thiocyanate ions was shown to provide receptor affinity data for AMPA receptor agonists as well as antagonists, which correlate with the potencies of these compounds in the cortical wedge preparation. Using autoradiographic techniques, ( S)- and ( R)-APPA were shown to exhibit significantly different absolute potencies as inhibitors of [ 3H]AMPA binding in a number of regions of the rat brain.

Kainate binding to the AMPA receptor in rat brain.

Displacement of [3H]AMPA and [3H]CNQX by kainate was measured in membranes and solubilized fractions from rat brain. In soluble fractions, plots of [3H]AMPA and [3H]CNQX binding displaced by kainate resulted in one-site fits with Ki values in the range of 1-3 microM. In membranes, plots of [3H]AMPA binding displaced by kainate resulted in graphs which were better fit by two-site regression analysis than by a one-site fit. The Ki value for the high-affinity component of these two-site fits was 3-9 microM and the low-affinity component Ki was in the range of 70-120 microM; similar values were determined for kainate displacement of [3H]CNQX. The presence of thiocyanate ions had no effect on kainate displacement of [3H]CNQX. Since the affinity for kainate of the presumed synaptic AMPA receptor is in the range of EC50 values for kainate determined from physiological studies, these data contribute further evidence for the idea that kainate binding to synaptic AMPA receptors may be responsible for many of kainate's physiological effects.

Extraction Spectrophotometric Determination of Molybdenum(V) with N1-(o-Chlorophenyl)-N1-hydroxy-N2-(o-methylphenyl)benzamidine Hydrochloride and Thiocyanate

Abstract A highly selective method has been developed for the extraction and spectrophotometric determination of molybdenum(V) using N1-(o-chlorophenyl)-N1-hydroxy-N2-(o-methylphenyl)benzamidine hydrochloride and thiocyanate. The reagent reacts with molybdenum(V) in the presence of thiocyanate ion and forms orange red complex in strongly acidic medium. Which can be extracted with benzene. The extract shows a sharp maximum at 470 nm, having molar absorption coefficient 3770 cm3 mol−1 cm−1. The system obeys Beer’s law from 3 to 22 ppm. A large number of metal ions associated with matrix of Mo, such as Ni, Co, Cu, V, Nb, Ti, Zn, etc. do not interfere with the determination. The applicability of the method has been tested with various alloys. The stoichiometry of mixed complex is found to be 1 : 2 : 2 (metal : reagent : thiocyanate).

Studies on the adsorption behaviour of trace amounts of cerium on manganese dioxide from aqueous solutions in the presence of complexing agents

Adsorption behaviour of trace amounts of cerium on manganese dioxide has been studied as a function of pH (1–10) in the presence of EDTA, oxalate, citrate, tartrate, cyanide and thiocyanate ions. The influence of their concentration on the adsorption has also been investigated. Maximum adsorption of cerium has been noticed at pH≥6. Under specific conditions, adsorption of other metal ions has been measured for comparison. Low distribution coefficients are obtained for Cs(I) and Hg(II) in the presence of oxalate, and for Cr(III) in the presence of thiocyanate ions. Based on these data, separation of cesium, chromium and mercury from rare earths and cerium scavenging in natural water or in waste water treatment can be achieved.

The Bound Ligand Effect in the Complexation Kinetics of Some Anionogallium(III) Complexes

Abstract The formation rate of some anionogallium(III) complexes (GaA) with 4,5-dihydroxy-1,3-benzenedisulfonate (H2L2−) in the presence of thiocyanate ion has been studied spectrophotometrically by a stopped-flow technique. The rate law is expressed as d[GaL−]/dt=kGa[Ga3+[H2L2−]+kGaOH[GaOH2+][H2L2−]+kGa(OH)2[Ga(OH)2+][H2L2−]+kGaNCS[GaNCS2+][H2L2−], with kGa=101.23 M−1 s−1 (M=mol dm−3), kGaOH=103.36 M−1 s−1, kGa(OH)2=104.37 M−1 s−1, and kGaNCS=103.90 M−1 s−1 at 25 °C and I=0.50M. The enhanced reactivity of GaA as compared to that of Ga3+ is attributable to the labilizing effect of the bound ligand A on the rate of loss of coordinated water molecules at GaA. Together with the additional formation rate constants of monoisothiocyanato- and monooxalatogallium(III) with 2-hydroxy-2,4,6-cycloheptatrien-1-one, this labilizing effect is quantitatively discussed in terms of the electron-donating ability of the ligand.

The effect of thiocyanate ions on the corrosion of copper in perchloric acid

The effect of thiocyanate ions on the corrosion of copper in 0.1 M HClO 4 was investigated in the presence of various concentrations of thiocyanate ions using weight loss and polarization methods. The corrosion rate decreased markedly in the presence of thiocyanate ions and maximum percentage protection (93.7%) was obtained at 10 −3 M thiocyanate ions. The drift of the corrosion potential in the less noble direction and the increase in the anodic Tafel slope are consistent with the inhibition by thiocyanate ions of both the anodic and the cathodic reactions of the corrosion process. The variation in the corrosion rate with the concentration of thiocyanate ions is attributed to the specific adsorption of thiocyanate ions and precipitation of cuprous thiocyanate on the copper surface.

Thiocyanate ion formation in rapeseed meals.

Meal prepared from unheated rapeseed (Brassica napus cv. Zephyr) showed the presence of t,iocyanate ion, while meal from heated seed of the same cultivar did not show detectable amounts. Unheated seed meal on autolysis, and heated seed meal on incubation with thioglucosidase, yielded increased amounts of thiocyanate ion. Various commercial rapeseed meals showed the presence of t,iocyanate ion only after enzyme incubation. Low glucosinolate, cv. Bronowski, and higher glucosinolate, cv. Zephyr on enzymic incubation yielded comparable amounts of thiocyanate ion, suggesting that the precursor responsible in the two varieties was the same and present in similar quantities. No formation of thiocyanate ion was observed on incubation of sinigrin with thioglucosidase. Rats dosed with heated meal, containing intact glucosinolate, showed a slight increase of thiocyanate ion in the urine as compared with control rats dosed with water, while a relatively large increase followed dosing with sinigrin. Rats dosed with meal containing free thiocyanate ion excreted the ingested thiocyanate ion almost quantitatively.

Contribution a l'etude des effets catalytiques exerces par les composes soufres a l'electrode a gouttes de mercure. Cas de la thiouree

The influence of thiourea and some of its N-alkyl-derivatives on the reduction of various metallic cations (Ni 2+, Co 2+, Co 2+) has been studied in neutral medium at the dropping mercury electrode. The polarographic curves exhibit kinetic prewaves reaching a 2 − e amplitude at high concentration. In addition fairly large extra-currents can be detected at verynegative potentials. By resorting to classical and pulse polarography and to macro-electrolysis, it has been demonstrated that these currents are related to both the electroreduction of thiourea with production of sulphide and cyanide ions and catalytic discharge of water itself. The reaction mechanism is discussed in terms of the structure of the organic compound and the properties of the electrode metal surface, in connection with similar phenomena observed in the presence of thiocyanate ion (reduction of the thione group) and sulfur proteins (catalytic hydrogen evolution).

Reactions of µ-hydroxo-dicobalt(III) complexes. Part VIII. Kinetic studies of the bridge cleavage of the µ-hydroxo-bis[penta-amminecobalt(III)] complex

The kinetics of bridge cleavage of the µ-hydroxo-bis[penta-amminecobalt(III)] complex, (NH3)5Co·OH·Co(NH3)55+[equation (i)] have been studied in aqueous perchloric acid solutions, I= 2·0M(LiClO4), at 15–30 °C. (NH3)5Co·OH·Co(NH3)55++ H++ H2O → 2Co(NH3)5H2O3+(i) For the range of hydrogen-ion concentration investigated (10–4–2·0M), first-order rate constants, kobs, show the dependdence (ii) on [H+]. kobs=k1[H+]+k2(ii) At 25 ° C: k1=(5·37 ± 0·07)× 10–3 l mol–1 s–1, ΔH1‡= 12·0 ± 0·8 kcal mol–1, ΔS1‡=–28·7 ± 2·7 cal K–1 mol–1; and k2=(7·58 ± 0·10)× 10–3 s–1, ΔH2‡= 20·1 ± 0·70 kcal mol–1, ΔS2‡=–1·0 ± 2·2 cal K–1 mol–1. In the presence of thiocyanate ions (0·06–0·80M), Kobs, can be expressed as in (iii), where a and bare ca. 15% smaller than k1 and k2 due to ion-pairing. kobs=a[H+]+b+c[H+][NCS–](iii) At 25 °C and I= 2·0M(LiClO4) : c= 0·137 ± 0·003 I2 mol–2 s–1, ΔHc‡= 10·9 ± 0·6 kcal mol–1, and ΔSc‡=–25·8 ± 2·2 cal K–1 mol–1. The thiocyanate-dependent path yields equal amounts of the complexes Co(NH3)5NCS2+ and Co(NH3)5H2O3+ as primary products.

Catalytic polarographic current of nickel(II) in acetonitrile in the presence of thiocyanate ions

The effect of thiocyanate ion on the electrode reaction of nickel(II) in acetonitrile solution was investigated by d.c. polarography, i-t curve analysis, a.c. polarography and controlled potential electrolysis. In the presence of thiocyanate ion, nickel(II) exhibited a catalytic pre-wave in LiClO 4 , NaClO 4 and NH 4 ClO 4 supporting electrolytes, and a catalytic maximum wave in Me 4 NClO 4 , Et 4 NClO 4 and n-Bu 4 NClO 4 . The maximum wave usually separated into two maxima. The characteristics of these maxima were studied as a function of concentration of nickel(II), LiSCN and n-Bu 4 NClO 4 . A mechanism which involves adsorption equilibria between bulk and adsorbed thiocyanate and quaternary ammonium ions, the cyclic regeneration of adsorbed thiocyanate ion for the pre-wave and the catalytic reduction of thiocyanate ion with the electroreduced active metallic nickel for the maximum wave has been presented. The characteristics of the two maxima are discussed on the basis of the difference in character of the adsorption process of thiocyanate and quaternary ammonium ions.

Catalytic polarographic current of nickel(II) in acetonitrile in the presence of thiocyanate ions

The effect of thiocyanate ion on the electrode reaction of nickel(II) in acetonitrile solution was investigated by d.c. polarography, i-t curve analysis, a.c. polarography and controlled potential electrolysis. In the presence of thiocyanate ion, nickel(II) exhibited a catalytic pre-wave in LiClO4, NaClO4 and NH4ClO4 supporting electrolytes, and a catalytic maximum wave in Me4NClO4, Et4NClO4 and n-Bu4NClO4. The maximum wave usually separated into two maxima. The characteristics of these maxima were studied as a function of concentration of nickel(II), LiSCN and n-Bu4NClO4. A mechanism which involves adsorption equilibria between bulk and adsorbed thiocyanate and quaternary ammonium ions, the cyclic regeneration of adsorbed thiocyanate ion for the pre-wave and the catalytic reduction of thiocyanate ion with the electroreduced active metallic nickel for the maximum wave has been presented. The characteristics of the two maxima are discussed on the basis of the difference in character of the adsorption process of thiocyanate and quaternary ammonium ions.

Interactions of polymers and cationic surfactants with thiocyanate as counterions

The interactions of deodecylammonium ions with nonionic polymers such as polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyvinylalcohol-acetate copolymer (PVA-Ac) were strengthened by changing the counterion from chloride to thioeyanate. For example, whereas the specific viscosity of a PVP solution underwent little change by addition of dodecylammonium chloride, addition of dodecylammonium thiocyanate (DASCN) decreased it at low concentrations and raised it remarkably at high concentrations. Such a viscosity change by DASCN is of a different type from that by sodium dodecylsulfate (NaDS) and may be attributed to a concurrent binding of the dodecylammonium ion with SCN− to the hydrophobic parts of the polymers. Therefore, the mechanism of binding of DASCN to the polymers is different from that of NaDS, whose dodecylsulfate ion is itself bound directly to many nonionie polymers. The binding of DASCN to the polymers was also exhibited by the higher solubilization power of the mixed solutions of DASCN wih the polymers than that of the DASCN solution alone for an oil-soluble dye Yellow OB. The binding of the dodecylammonium cation to PVP with the aid of the inorganic counterion was in the order of SCN− > I− > Br− > CI−, and as for small organic anions such as ethylsulfate, butyrate, and caproate the effect was very poor or insignificant. Dodeeylpyridinium thiocyanate did not show an interaction with PVP and PEO, but interacted strongly with hydrophobie PVA-Ac. The polymer-cationic interaction in the presence of thiocyanate ion thus depends specifically on the polymer and cationic head group of the surfactant.

Le chlorure de triphényltétrazolium en tant que reactif en chimie analytique—III: Titrage volumétrique du zinc

Zinc(II) is titrated with triphenyltetrazolium chloride in the presence of thiocyanate ions. A light yellow, amorphous precipitate of [TT] 2[Zn(CNS) 4] is formed. Under the same conditions cobalt(II) forms a blue compound, [TT] 2[Co(CNS) 4], whose solubility product is greater than that of [TT] 2[Zn(CNS) 4]. This difference between the solubility products allows cobalt(II) to be used as indicator in the titration of zinc(II). Nitrobenzene is employed as a common solvent for the two compounds. At the end-point the nitrobenzene changes colour from light yellow to green.

Influence de la cinétique des réactions chimiques sur les courbes de polarisation : Application à l'étude des complexes thiocyanés du titane(iv) et du titane(III)

The electrochemical oxidation-reduction of the system titanium(IV) — titanium(III) is slow at dropping mercury electrode in perchloric acid or hydrochloric acid, but becomes rapid in the presence of thiocyanate ions. On the basis of polarization curves, interpreted according to a preliminary theoretical study, the authors conclude that the rapid electrochemical reaction is the following: TiOH.SCN +2 + H + + e ⇌ TiSCN +2 + H 2O An application of the findings to the polarographic determination of titanium is given.

Sedimentation and optical rotation behavior of bovine plasma albumin at low pH in the presence of various anions. Effect of charge on molecular expansion

In order to clarify the role of net molecular charge in the expansion of plasma albumin at low pH, sedimentation and optical rotation measurements were carried out in the presence of anions differing widely in their extent of binding to BPA. Thus it was possible to vary the net charge on the protein molecule independent of the extent of binding of protons. It was demonstrated as a first approximation that the extent of expansion, as determined from both sedimentation and rotation measurements, is a function of the net charge on the molecule. Quantitatively, however, specific rotation and molecular size do not always change in a parallel manner, nor are they affected in the same way by changes in ionic strength. Changes in specific rotation may be attributed to partial breakdown of the secondary (possibly helical) structure as a result of intrachain charge repulsion, while interchain repulsion (changes in tertiary structure) are held responsible for a large part of the change observed in viscosity and sedimentation constant. Conversion of the native albumin molecule to “expandable” form appeared to be accompanied by a moderate increase in molecular radius in the presence of chloride ion. On the other hand, this isomerization can occur without increase in radius in the presence of thiocyanate ion. No significant change in optical rotation accompanies formation of the “expandable” molecule.