The Reduction of CS2N3 − Ion In Acidic Solution

Abstract

The electrochemical behaviour of 1, 2, 3, 4-thiatriazol-5-thiolate CS₂N₃ ^? ion in acidic solutions has been investigated. A cathodic wave has been detected, (E_1/2 =?1.05V versus S.C.E., M=1.0M (NaC10₄) and NaCS₂N₃ 1.00 × 10^?3M). The characteristics of this wave have been investigated by D.C., A.C. polarography and controlled potential electrolysis. A mechanism which involves the interaction of CS₂N₃ ^? with mercury and cyclic regeneration of mercury has been proposed. The reduction of CS₂N₃ ^? by amalgamated zinc has been also investigated and the results correlated with the pseudo-halide electrochemical reduction.     

Structure de Modeles de Polyesters 2.-Determination de la Purete optique par RMN 13C et H de Dibenzoyloxy 1,2 Propane,l,3 Butane et 3-Methyl 1,4 Butane a l'Aide de Reactifs chiraux

Abstract

The enantiomeric purity of a series of polyester model compounds has been assayed by NMR spectroscopy, using chiral lantha-nide shift reagents. The dependencc of proton and ¹³ C NMR spectra on concentration and temperature has been investigated.     

Halogen-Free Room-Temperature Brønsted Acidic Ionic Liquid [Hmim]+ HSO4 − as a Recyclable Green “Dual Reagent” Catalysis for the Synthesis of Triarylmethanes (TRAMs)

Abstract

The halogen-free Brønsted acidic ionic liquid methylimidazolium hydrogen sulfate ([Hmim]⁺ HSO₄ ^?) acts as a very efficient catalyst for the one-pot, two-component Baeyer condensation of a variety of aromatic aldehydes with dimethyl or diethyl aniline at room temperature. This “green” reagent behaves as both catalyst and solvent; that is, it exhibits “dual-reagent catalysis.” The room-temperature acidic ionic liquid could be recycled several times with almost no loss in the yield of the reaction. This is the first report of the Baeyer synthesis with a halogen-free ionic liquid.     

Role of Acid-Base Equilibria in the Reduction of Selenious(IV) Acid

ABSTRACT

Electroanalytical methods have been widely used for determination of Se(IV), but the nature of the reduction processes involved is not well understood. Polarographic reduction occurs in three waves (i₁, i₂, and i₃) the height of which changes with pH. We proved that in wave i₁, H₃SeO₃ ⁺ is reduced, in i₂ H₂SeO₃, and in i₃ HSeO₃ ^-. SeO₃ ^2? is not reducible. All reductions involve a transfer of six electrons and yield selenides. Limiting currents are controlled by the rate of protonation. As proton donors, in addition to H₃O⁺, the acid forms of the buffer present also act. Limiting currents increase markedly with increasing concentration of the buffer. Tenfold increase in buffer concentration can result in up to 200% increase in limiting current.     

Construction of Extended and Polymeric 1,3-Dithiolane and Tetrathiafulvalene Derivatives using Cycloaddition of Bun 3PßCS2

Abstract

Cycloaddition of the adduct between Buⁿ ₃P and CS₂ to strained double bonds such as in norbornene gives novel zwitterionic products such as 5. The compound 5 reacts with acetylenic dipolarophiles by cycloaddition accompanied by loss of Buⁿ ₃P to give dihydro-TTF derivatives. The corresponding reaction also occurs for norbornadiene and by using this a range of new extended sulfur-rich structures and substituted TTFs have been obtained.     

Synthesis and evaluation of multitopic bisbenzothiazolyl calix[4]arenes for ionic toxicants

Abstract

Two new benzothiazolyl calix[4]arene-based multitopic molecular receptors L-1 and L-2 have been synthesised and evaluated for recognition of ionic toxicants. The receptors selectively interact with copper, silver and fluoride ion toxicants as assessed through UV-visible, NMR and colorimetric techniques. The stability of L-1:Cu⁺² and L-2:Cu⁺² complexes was found to be higher than that of complexes formed with Ag⁺ and F^– complexes in the presence of trifluoroacetic acid. Superiority of L-1 over L-2 for analysis of identified toxicants has been determined by measurement of binding constants.     

Is the 1 J PSe Coupling Constant a Reliable Probe for the Basicity of Phosphines? A 31P NMR Study

Abstract

The influence of different heteroaryl and functionalized aryl substituents on the electron-donating ability and basicity of the phosphorus atoms in heteroaryl phosphines and diphosphines has been determined by the use of the direct ¹J_PSe coupling constants of the corresponding selenides. The generality of the use of ³¹P–⁷⁷Se spin–spin coupling constants as probe for the basicity of phosphines is discussed as well as the scope and limits of this concept.

GRAPHICAL ABSTRACT      

The rhodium complex of a tris(bipyridine) ligand—Its electrochemical behaviour and function as mediator for the regeneration of NADH from NAD+

The tris-bipyridine ligand3a and its stoichiometric Rh³⁺ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at –620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)₃]³⁺. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD⁺. The preparative electrolysis of the Rh³⁺ complex of3a in the presence of NAD⁺ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)₃]³⁺ was not observed.     

Perimedine-linked rhodamine dye in visual sensing of Al3+, Fe3+ and Fe2+ ions in aqueous organic medium under different experimental conditions

ABSTRACT

Perimedine labelled rhodamine dye 1 has been designed and synthesised. Metal ion binding studies of 1 have been performed in CH₃CN/H₂O (3:1, v/v, 10 mM Tris-HCl buffer, pH = 6.90). Compound 1 senses multiple metal ions such as Al³⁺, Fe³⁺ and Fe²⁺ by exhibiting turn on fluorescence and colour change (colourless to pink) under different experimental conditions. Concentration variation distinguishes Al³⁺ from Fe³⁺ ion. At low concentration (c = 1 x 10^?4 M), only Al³⁺ ion can exhibit turn on fluorescence with sharp colour change. Sensing of Fe²⁺ ion through turn on fluorescence and colour change has been possible via in situ oxidation by following Fenton’s reaction.     

UNUSUAL DOWNFIELD DEUTERIUM ISOTOPE SHIFT EFFECT ON THE 31P CHEMICAL SHIFTS OF DIALKYL BENZYLPHOSPHONATES

Abstract

A surprising linear downfield effect on the ³¹P chemical shift of a benzylphosphonate of deuterium substitution on the benzyl carbon has been noted. Its potential usefulness in mechanistic studies is suggested.     

Tris(dialkylamino)phosphine Chalcogenide Complexes of Tin(IV) Chloride: A Multinuclear (31P, 77Se,and 119Sn) NMR Characterization

Abstract

Four octahedral complexes of the type SnCl₄.2L [L = (R₂N)₃P(E): E = Se; R = Me(1), Et(2) and E = S; R = Me(3), Et(4)] have been studied in solution by multinuclear (³¹P, ⁷⁷Se, and ¹¹⁹Sn) NMR spectroscopy. ³¹P and ⁷⁷Se NMR data were informative of changes associated with complex formation. The solution structure of the complexes was confirmed by their ¹¹⁹Sn NMR spectra that showed two triplet features for each complex, attributed to a mixture of the expected cis and trans isomers. The triplet signal is due to the coupling with two equivalent phosphorus atoms, consistent with an octahedral geometry around the tin center. In addition, density functional theory (DFT)/B3LYP calculations have been carried out to support the interpretations of NMR data. The results are discussed and compared with those reported for related complexes.

GRAPHICAL ABSTRACT      

Etude Polarographique De La Marcellomycine

Abstract

Polarographic study of marcellomycine.

d.c., a.c. and d.p. polarography and cyclic voltammetric techniques were used to investigate the electrochemical properties of marcellomycine. These are found to be quite similar to those of aclacinomycine or carminomycine, the main reversible two-electron wave being attributed tot he reduction of the quinonic structure. The molecule undergoes a degradation process starting in acidic medium and giving rise to the formation of two small irreversible waves at more negative potentials. This process is time, illumination and pH dependent. Important adsorption phenomena interfere in the investigated pH range but are lowered in very acidic medium. Quantitative measurements have been carried out at pH 1 and 6 in a 10^?3 to 10^?5 M concentration range using d.c. polarography. d.p. technique allows determinations in a restricted 10^?5 to 10^?4 M range. A detection limit of 1 · 10^?5 M has been fixed at pH 1.     

REVIEW: SPECTROSCOPIC STUDIES OF OXOVANADIUM COORDINATION COMPOUNDS

Abstract

In this review we present selected examples of our studies of oxovanadium(IV) and oxovanadium(V) complexes relevant for the bioinorganic chemistry of vanadium. Some of the investigated complexes are good models for different steps of vanadium metabolism or for a better understanding of the structural and electronic peculiarities of the coordination spheres of these oxocations in biomolecules. The investigated systems include ligands such as nucleotides, carbohydrates, phosphates, amino acids, oxine derivatives, porphine-like cores and other simple organic and inorganic ligands. All these complexes have been systematically investigated by means of vibrational (infrared and Raman) and electronic spectroscopy and, in some cases, also by thermal and electrochemical behavior. The potentialities and possibilities of the spectroscopic methodologies are illustrated and discussed and some general trends, useful for the structural characterization of these and similar systems, are emphasized.     

Extraction and Spectrophotometric Determination of Manganese(VII) with N1-Hydroxy-N1,N2-Diphenylbenzamidine

Abstract

Spectrophotometric determination of manganese(VII) at 614 nm after its extraction with N¹ -hydroxy-N¹,N²-diphenylbenzamidine into amyl alcohol at pH 7–8 is described. Beer's law was obeyed for 0.1–10 μg ml^?1 Mn(VII). The effects of experimental variables and of several diverse ions on the determination of manganese(VII) have been studied. The method has been applied to the determination of manganese in steels and in water extracts of a commercial tea and is found to be simple, precise and highly selective.     

TRANSITION METAL COMPLEXES OF AMINOPHOSPHONIC ACID ANALOGUES OF METHIONINE AND ALANINE IN AQUEOUS SOLUTION

Abstract

The stoichiometrics and stability constants of the nickel(II), copper(II) and zinc(II) complexes of l-amino-3-methylthiopropanephosphonic acid (MetP) and 1-amino-ethanephosphonic acid (a-AlaP) have been determined pH-metrically at 25°C at an ionic strength of 0.2 mol dm^?3 (KC1). From the stability data and the absorption spectra of the complexes it has been established that simple aminophosphonic acids coordinate to the nickel(II) and copper(II) ions forming chelate complexes in which the metal binding mode is bidentate with the {NH₂, PO₃ ^2-} donor set. ³¹P and ¹H NMR measurements showed that MetP and α-AlaP exhibit similar properties in the presence of zinc(II) ions, but the ligand reacts to form a cyclic phosphonoamidate in neutral and slightly alkaline solution in the Zn(II)-α-AlaP system and at slightly acidic conditions in the Zn(II)-MetP system. This difference reveals that the latter ligand at pH > 7 prefers Zn(II) coordination involving all possible (amino, phosphonate and thioether sulfur) donor groups.     

SPECTROPHOTOMETRIC STUDY OF THE THERMODYNAMICS OF COMPLEXATION OF LITHIUM AND SODIUM IONS WITH DIBENZO-24-CROWN-8 IN BINARY DIMETHYLFORMAMIDE-ACETONITRILE MIXTURES USING MUREXIDE AS A METALLOCHROMIC INDICATOR

Abstract

Complexation of Li⁺ and Na⁺ with dibenzo-24-crown-8 has been studied in dimethylformamide-acetonitrile mixtures by means of a competitive spectrophotometric technique using murexide as metal ion indicator. Stabilities of the resulting 1:1 complexes were investigated at various temperatures and enthalpies and entropies of complexation were determined from the temperature dependence of the formation constants. Sodium forms a more stable complex with the crown ether than lithium. There is an inverse linear relationship between log K_f and the mole fraction of DMF in the solvent mixtures. The ΔH°-TΔS° plot of all thermodynamic data, obtained for both crown complexes in different solvent mixtures, shows a fairly good linear correlation, indicating the existence of an enthalpy-entropy compensation effect in complexation.     

电解液对全铅单液流电池电极性能的影响

研究Pb(II)和H+离子浓度对全铅单液流电池正、负电极在复合石墨基体上电化学行为的影响.结果表明,PbO2正极和Pb负极的电极过程受电化学和扩散混合控制.Pb(II)氧化沉积成PbO2时出现成核环,铅负极成核过电位小,充放电电压差远小于PbO2正极,电池极化主要来自PbO2正极.增加H+浓度有利于降低PbO2正极和Pb负极的极化,但析氧、析氢副反应和腐蚀加重.增大Pb(II)浓度有利于抑制析氧,但PbO2正极充电电压升高,充放电电压差增大.Pb(II)浓度较低时,充放电过程中PbO2沉积层少许脱落,充电电压进一步降低且更趋平稳.为此,电解液中HBF4浓度以2 mol L-1为宜,Pb(II)浓度应在0.9 mol L-1以上.     

Synthesis of SE- and TE-Containing Amino Acids: Useful Probes for Structural Studies of Proteins

ABSTRACT

The synthesis of (l)-Se-cystine, (l)-[⁷⁷Se]-cystine and (l)-Te-cystine in 4 steps from commercially available 2(S)-[(tert-butoxycarbonyl)amino]-3-hydroxy-propionate has been accomplished. [4-¹³C]Te-Met has been synthesized in a one pot reaction.     

Gas Chromatography of δ1-Tetrahydrocannabinol

Abstract

Quantitative gas chromatography of small amounts of δ¹ - tetrahydrocannabinol has been demonstrated on a variety of silicone columns. Retention data in the form of methylene unit values were obtained on these columns.