Metal Analyses in Environmental and Pharmaceutical Samples by Capillary Electrophoresis with Methyl 3‐Amino‐3‐(pyridin‐3‐yl)propanoate Dihydrochloride as a New Ion‐Pairing Reagent

Separation and determination of some common metal ions was achieved with methyl 3‐amino‐3‐(pyridin‐3‐yl)propanoate dihydrochloride (MAPP) as an ion‐pairing reagent and pyridine as a detectable counter‐ion for indirect UV detection at 254 nm. The effects of the complexing reagent and chromophore concentrations, applied voltage, and organic solvent content on the separation were investigated. The optimized separation was carried out in a running electrolyte containing 16 mM MAPP and 20 mM pyridine at pH 4.0 and was successfully applied to the qualitative and quantitative analysis of Li⁺, Na⁺, Mg²⁺, Ca²⁺, Ba²⁺, Ni²⁺, and Zn²⁺ in pharmaceutical vitamin preparations and various water samples.     

Solvent Extraction and Spectrophotometric Determination of Uranium Using α-Benzoin Oxime as Chelating Agent

Solvent extraction of uranium by a chloroform solution of α-benzoin oxime was studied and the formation of uranium-α-benzoin oxime complex described. The uranium-α-benzoin oxime complex has two maximum absorbance at 350 nm and 427 nm. A constant absorbance was obtained for 1 × 10^?3 M uranium when the concentration of α-benzoin oxime was higher than 1.2 × 10^?2 M. Ions of Ag⁺, Fe³⁺, V⁵⁺, Cu²⁺, and W⁶⁺ were found to have interference. A solution containing 0.1–10 mg uranium at pH 1.6–6.8 was extracted with 1 × 10^?3 M ?2 × 10^?3 M α-benzoin oxime solution in chloroform. With single extraction, the maximum amount of uranium passing into organic layer was at least 98%. Under this condition the presence of diverse ions except V⁵⁺ does not significantly interfere the extraction of uranium.     

Syntheses,and Crystal Structures of Indium Complexes with η2‐Piperidinyldithiocarbamate and η2‐Pyridine‐2‐Thionate Containing Ligands: Structures of [In(η2‐S2CNC5H10)3] and [In(η2‐pyS)3]

The η²‐thio‐indium complexes [In(η²‐thio)₃] (thio = S₂CNC₅H₁₀, 2 ; SNC₄H₄, (pyridine‐2‐thionate, pyS, 3 ) and [In(η²‐pyS)₂(η²‐acac)], 4 , (acac: acetylacetonate) are prepared by reacting the tris(η²‐acac)indium complex [In(η²‐acac)₃], 1 with HS₂CNC₅H₁₀, pySH, and pySH with ratios of 1:3, 1:3, and 1:2 in dichloromethane at room temperature, respectively. All of these complexes are identified by spectroscopic methods and complexes 2 and 3 are determined by single‐crystal X‐ray diffraction. Crystal data for 2 : space group, C2/c with a = 13.5489(8) Å, b = 12.1821(7) Å, c = 16.0893(10) Å, β = 101.654(1)°, V = 2600.9(3) ų, and Z = 4. The structure was refined to R = 0.033 and Rw = 0.086; Crystal data for 3 : space group, P2₁ with a = 8.8064 (6) Å, b = 11.7047 (8) Å, c = 9.4046 (7) Å, β = 114.78 (1)°, V = 880.13(11) ų, and Z = 2. The structure was refined to R = 0.030 and Rw = 0.061. The geometry around the metal atom of the two complexes is a trigonal prismatic coordination. The piperidinyldithiocarbamate and pyridine‐2‐thionate ligands, respectively, coordinate to the indium metal center through the two sulfur atoms and one sulfur and one nitrogen atoms, respectively. The short C‐N bond length in the range of 1.322(4)–1.381(6) Å in 2 and C‐S bond length in the range of 1.715(2)–1.753(6) Å in 2 and 3 , respectively, indicate considerable partial double bond character.     

Anomalies in the molecular ion region in the electron impact mass spectra of α- and β-hydroxyesters

In the electron impact mass spectra of some alkyl α- and β-hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M^+· and the presence of the [M + 1]⁺ ion instead is observed. This phenomenon is especially characteristic of C₃? C₆ glycolates and diethyl malate, and is due to chemical auto-ionization—ion-molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M ? 2]^+·, [M ?1]⁺ and M^+· ions in the mass spectra of other β- and α-hydroxyesters is discussed.     

Catalytic Adsorptive Stripping Voltammetric Determination of Cobalt and Nickel as Their α‐Furil Dioxime Complexes

The exploitation of the catalytic‐adsorptive effect in the Co(II)‐dioxime‐nitrite systems provides a significant increase of the Co adsorptive stripping voltammetric response and subsequently the influence of the interfering elements such as Ni and Zn is strongly diminished. The purpose of the present paper was to study voltammetric properties of Co and Ni in a supporting electrolyte containing ammonia buffer, α‐furil dioxime in the absence and in the presence of nitrite, by differential pulse polarography and adsorptive stripping voltammetry. Results of detailed studies aimed at optimizing the analytical parameters for simultaneous catalytic adsorptive stripping voltammetric determination of Co and Ni in the form of complexes with α‐furil dioxime in the presence of Zn matrix are presented. In the supporting electrolyte of composition 0.1 M NH₄Cl, 0.5 M NH₃, 4×10^?5 M αFD, 0.5 M NaNO₂ the linearity range amounts from 0.03 to 2.4 μg/L for Co and from 0.3 to 9 μg/L for Ni for 20 s of accumulation. The method enables the determination of Co and Ni in the presence of a great excess of Zn with the detection limit equal to 0.02 μg/L Co and 0.2 μg/L Ni obtained for a 20 s accumulation time.     

Potentiometric investigation of the silver(I) complexes of a series of sulphur-containing α,ω-diamines

The composition and the stability constants of the complexes formed between Ag(I) and ligands of the type where n,m = 2,2; 2,3; 2,4; 3,3; 3,4; 4,4, have been determined by a pH/pM-metric method at 25°C in a 0.5 M (K)NO₃ medium. The determination of the stability constants proceeded by a combination of a graphical method and a least squares minimization procedure. The complex formation is discussed in comparison with silver complexes formed with S-containing mono-amines and in terms of the Taft σ*-parameters for the substituents. Below pH = 4, the protonated complexes AgLH₂³⁺ and AgL₂H₄⁵⁺ are formed and the thioethergroup is the only coordinating centre. In neutral and alkaline medium there was evidence for the species AgLH²⁺, Ag₂L₂H₂⁴⁺, Ag₂L₂H³⁺, Ag₂L₂²⁺, AgL₂H₃⁴⁺, AgL₂H²⁺, AgL₂ + and Ag₂L²⁺ in which Ag⁺? S and Ag⁺? NH₂ bonds are involved. It is shown that in the Ag₂L₂²⁺ and Ag₂L²⁺ complexes the ligands effectively coordinate through all available donor centres.     

Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

H NMR of the α,α′-bipyridine and o-phenanthroline adducts of n-butyltin trichloride

¹H NMR spectra of the α,α′-bipyridine adduct of n-BuSnCl₃ indicated the non-equivalence of the two pyridine rings. In particular the signals of the proton on the carbon atom adjacent to the two nitrogen atoms were widely separated. Similar spectral behavior was observed in the o-phenanthroline adduct. These adducts therefore are concluded to have the n-butyl group lying on the N---Sn---N plane of the hexacoordinated complexes. The configurational rearrangement of these adducts was markedly accelerated in the presence of excess n-BuSnCl₃.     

Magnetic and EPR Studies of α-, β-, and γ-Fe2WO6 Phases at Low Temperatures

The polymorphic modifications α-, β-, and γ-Fe₂WO₆ of the iron tungstate system were studied by means of magnetic susceptibility and EPR measurements at low temperatures. Both methods revealed a significant paramagnetic contribution, probably resulting from local distortions of the antiferromagnetic bulk structure induced by a disturbed cation ordering or the presence of Fe²⁺ ions. The magnetic susceptibility revealed a peak at 260 K for all samples which can be related with an AF phase transition. The EPR spectra comprised the contribution of various isolated paramagnetic iron centers, one arising from high-spin Fe³⁺ ions in rhombic crystal field symmetry with E/D ≈ 1/3 and D ≈ 0.22 cm^-1, an anisotropic EPR signal consistent with an S= 3/2 ground state with large zero-field splitting, and a dominant component in the g ≈ 2 region presumably arising from an S = 1/2; spin state. The latter spectra were tentatively attributed to the formation of multi-iron clusters, one of them invoking the presence of Fe²⁺ ions as well. For the βFe₂WO₆ phase an additional EPR spectrum was observed, which probably results from high-spin Fe³⁺ ions in a weak crystal field.     

4,4′‐Thio­dipyridinium tetra­chloro­copper(II)

The title compound, (C₁₀H₁₀N₂S)[CuCl₄], was obtained by the reaction of cupric chloride with pyridine‐4‐thiol in a mixture of aceto­nitrile and tetra­hydro­furan, suggesting that the desulfurization and coupling reactions of pyridine‐4‐thiol occurred in the presence of the Cu²⁺ ion. X‐ray diffraction analysis reveals the presence of one 4,4′‐thio­dipyridinium cation, H₂bps²⁺, and one [CuCl₄]²⁻ anion. The cations interact with the anions via N—H⋯Cl hydrogen‐bonding interactions to form a closed `chair' conformation.     

Efficient asymmetric addition of diethylzinc to aldehydes using C2‐novel chiral pyridine β‐amino alcohols as chiral ligands

A series of novel C₂‐symmetric chiral pyridine β‐amino alcohol ligands have been synthesized from 2,6‐pyridine dicarboxaldehyde, m‐phthalaldehyde and chiral β‐amino alcohols through a two‐step reaction. All their structures were characterized by ¹H NMR, ¹³C NMR and IR. Their enantioselective induction behaviors were examined under different conditions such as the structure of the ligands, reaction temperature, solvent, reaction time and catalytic amount. The results show that the corresponding chiral secondary alcohols can be obtained with high yields and moderate to good enantiomeric excess. The best result, up to 89% ee, was obtained when the ligand 3c (2S,2′R)‐2,2′‐((pyridine‐2,6‐diylbis(methylene))bisazanediyl))bis(4‐methyl‐1,1‐diphenylpentan‐1‐ol) was used in toluene at room temperature. The ligand 3g (2S,2′R)‐2,2′‐((1,3‐phenylenebis(methylene))bis(azanediyl))bis(4‐methyl‐1,1‐diphenylpentan‐1‐ol) was prepared in which the pyridine ring was replaced by the benzene ring compared to 3c in order to illustrate the unique role of the N atom in the pyridine ring in the inductive reaction. The results indicate that the coordination of the N atom of the pyridine ring is essential in the asymmetric induction reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Resonance Raman spectra of metalloporphyrins. On the methine-bridge vibrations of ferric octaethylporphyrins and its α′, β′, γ′, and δ′ deutero derivatives

Raman spectra of Fe³⁺ and Pd²⁺ octaethylporphyrin (OEP) and their α′, β′, γ′, and δ′ deutero derivatives were measured with the 5145, 4880 and 4765 Å lines of an Ar ion laser. Raman bands due to methine-bridge stretching vibrations were assigned and their vibrational amplitudes were calculated from the observed frequency shifts on deuterium substitution of methine-bridge hydrogens. These vibrations correspond to the spin-state sensitive Raman bands of heme proteins. On the basis of symmetry considerations and the observed polarizations, vibrational assignments of other Raman bands were made.     

Chemical ionization and collisional activation spectra of α,β-unsaturated nitriles

A study of the chemical ionization (CI) and collisional activation (CA) spectra of a number of α, β-unsaturated nitriles has revealed that the even-electron ions such as [MH]⁺ and [MNH₄]⁺ produced under chemical ionization undergo decomposition by radical losses also. This results in the formation of M ⁺˙ ions from both [MH]⁺ and [MNH₄]⁺ ions. In the halogenated molecules losses of X˙ and HX compete with losses of H˙ and HCN. Elimination of X˙ from [MH]⁺ is highly favoured in the bromoderivative. The dinitriles undergo a substitution reaction in which one of the CN groups is replaced with a hydrogen radical and the resulting mononitrile is ionized leading to [M ? CN + 2H]⁺ under CI(CH₄) or [M ? CN + H + NH₄] and [M ? CN + H + N₂H₇]⁺ under CI(NH₃) conditions.     

Synthese und Eigenschaften von Sr3Mo1.5Zn0.5O7‐δ, einer Phase mit perowskitverwandter Schichtstruktur

Synthesis and Properties of the Layered Perovskite Phase Sr₃Mo_1.5Zn_0.5O_7‐δ The new layered perovskite phase Sr₃Mo_1.5Zn_0.5O_7‐δ was synthesized by solid state reaction using a Zn/ZnO oxygen buffer. The crystal structure was refined from X‐ray powder pattern by the Rietveld method. The compound crystallizes tetragonal in the space group I4/mmm (no. 139) with the lattice parameters a = 3.9631(3) Å, c = 20.583(1) Å. An oxygen deficiency corresponding to δ ≈ 0.25 was determinated, indicating the presence of molybdenum in mixed valence (Mo⁴⁺ and Mo⁶⁺).     

Metal Complexes with Biologically Important Ligands. CLXVI Tetracarbonyl Complexes of Chromium(0) and Molybdenum(0) with Schiff Bases from Pyridine‐2‐carboxaldehyde and α‐Amino Acid Esters as N,N‐Chelate Ligands

The complexes [M(CO)₄(pyridyl‐CH=N‐CHRCO₂R′)] (M = Cr, Mo; R = H, CH₃, CH(CH₃)₂, CH₂CH(CH₃)₂) were obtained by reaction of the Schiff bases from pyridine‐2‐carboxaldehyde and glycine, L‐alanine, L‐valine or L‐leucine esters with the norbornadiene complexes [M(CO)₄(nbd)] and were characterized by IR, ¹H and ¹³C NMR and UV‐vis spectra. The deeply colored complexes exhibit solvatochromism.     

Complexation and aromatization of α,β-unsaturated cyclic ketones by Ru(H2O)6 and (Bz)Ru(H2O)3: molecular structure of (η-Tosylate)(η-hydroxycyclopentadienyl)Ru and of (η-Tosylate)(η-1,4-dihydroxy-2,3,5,6-tetramethylbenzene)Ru

Ruaq²⁺(OTs)₂ complexes in aqueous solution to unsaturated cyclic ketones. These aromatized on heating to π-arene Ru complexes. Thus, with cyclohexonone the main product was Ru(η⁶-phenol)₂²⁺, 4, along with some Ru(η⁶-phenol)(η⁶-OTs)⁺, 6. Similarly gave cyclopentenone in the presence of various arenes Ru(η⁵-hydroxycyclopentadienyl)(η⁶-arene)⁺. Duruquinone complexed to Ruaq²⁺ as a monoprotanated hydroquinolate in Ru(η⁶-2,3,5,6-tetramethyl-1,4-hydroquinone)(η⁶-OTs), 14. Ru(η⁵-cyclopentadienyl)(η⁶-OTs), 8, and 14 were characterized by single crystal x-ray structure analyses, data see Table 1. Whereas both ligands in 8 are planar, the 1,4-hydroquinone ligand in 14 shows distinct bending of the COH groups.     

Hydrogen bonding in two benzene‐1,2‐diaminium pyridine‐2‐carboxylate salts and a cocrystal of benzene‐1,2‐diamine and benzoic acid

The isostructural salts benzene‐1,2‐diaminium bis(pyridine‐2‐carboxylate), 0.5C₆H₁₀N₂²⁺·C₆H₄NO₂^?, (1), and 4,5‐dimethylbenzene‐1,2‐diaminium bis(pyridine‐2‐carboxylate), 0.5C₈H₁₄N₂²⁺·C₆H₄NO₂^?, (2), and the 1:2 benzene‐1,2‐diamine–benzoic acid cocrystal, 0.5C₆H₈N₂·C₇H₆O₂, (3), are reported. All of the compounds exhibit extensive N—H…O hydrogen bonding that results in interconnected rings. O—H…N hydrogen bonding is observed in (3). Additional π–π and C—H…π interactions are found in each compound. Hirshfeld and fingerprint plot analyses reveal the primary intermolecular interactions and density functional theory was used to calculate their strengths. Salt formation by (1) and (2), and cocrystallization by (3) are rationalized by examining pK_a differences. The R₂²(9) hydrogen‐bonding motif is common to each of these structures.     

Formation of [M − H]+ ions in electron impact mass spectra of nitrosocarbonyl compounds α- and γ-nitrosocarbonyl compounds

The presence of the [M + H]⁺ ions and the absence of the monomer molecular ions M^+· in the mass spectra of some tertiary α- and γ-nitrosocarbonyl compounds is reported. This effect is caused by the rearrangement of the mobile hydrogen in the α-carbonyl position in the fragmentation pattern of the dimer molecular ions 2M^+·.     

Regulation of α‐Chymotrypsin Catalysis by Ferric Porphyrins and Cyclodextrins

Positively charged α‐chymotrypsin (ChT) formed a 1:1 complex with negatively charged 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphyrinato iron(III) (FeTPPS) in phosphate buffer at pH 7.4 through electrostatic interaction. In spite of the large binding constant (K=4.8×10⁵ M ^?1), FeTPPS could not completely inhibit the catalysis of ChT in the hydrolysis of the model substrate, N‐succinyl‐L ‐phenylalanine p‐nitroanilide (SPNA). The degree of inhibition (60 %) was saturated at 1.6 equivalents of FeTPPS, which indicates that covering of the active site of ChT by FeTPPS was insufficient. The enzymatic activity lowered by FeTPPS was entirely recovered for the freshly prepared sample when the porphyrin on the protein surface was detached by per‐O‐methylated β‐cyclodextrin (TMe‐β‐CD), which formed a stable 1:2 inclusion complex with FeTPPS (K₁=1.26×10⁶ M ^?1, K₂=6.3×10⁴ M ^?1). FeTPPS gradually induced irreversible denaturation of ChT, and the denatured ChT further lost its catalytic ability. No repairing effect of TMe‐β‐CD was observed with irreversibly denatured ChT. A new reversible inhibitor, 5,10,15,20‐tetrakis[4‐(3,5‐dicarboxyphenylmethoxy)phenyl]porphyrinato iron(III) (FeP8M), was then designed, and its inhibitory behavior was examined. FeP8M formed very stable 1:1 and 1:2 FeP8M/ChT complexes with ChT, the K₁ and K₂ values being 2.0×10⁸ and 1.0×10⁶ M ^?1, respectively. FeP8M effectively inhibited the ChT‐catalyzed hydrolysis of SPNA (maximum degree of inhibition=85 %), and the activity of ChT was recovered by per‐O‐methylated γ‐cyclodextrin. No irreversible denaturation of ChT occurred upon binding with FeP8M. The kinetic data support the observation that, for nonincubated samples, both inhibitors did not cause significant conformational change in ChT and inhibited the ChT activity by covering the active site of the enzyme.     

Design of a New Non‐enzymatic Sensor Based on a Substituted A2BO4+δ Perovskite for the Voltammetric Detection of Glucose

Instant determination of glucose levels is necessary to monitor the treatment of diabetes. The next generation of electrochemical sensors aims to eliminate the use of enzymes because of their lack of stability and the complex procedure to immobilize them on the electrode. In this paper Pr_1.92Ba_0.08Ni0.₉₅Zn_0.05O_4+δ perovskite, a A₂BO_4+δ type, was tested, for the first time for non enzymatic detection of glucose. It was synthesized by a sol‐gel method. The obtained crystallized powder was structurally characterized by XRD, morphologically characterized by SEM and EDX and electrochemically characterized. A monoclinic crystallographic system was formed. The presence of Pr₂O₃ during synthesis and calcination is in agreement with the formation of defects in the crystalline network and the disproportionation of Ni^III sites into Ni^II and Ni^IV, due to the substitution of Pr by Ba. The oxido‐reduction of Ni^II sites is observed by cyclic voltammetry. The electrocatalytic oxidation of glucose through the electrooxidized Ni^II site was observed on a gold electrode, at 481 mV. The analytical performance of this glucose sensor is good in comparison to previously published ABO₃ perovskite modified electrodes, in terms of dynamic range (1.5 μM–7000 μM) and detection limit (0.5 μM). Its application to human serum shows that there is no interference for glucose detection.