Quantitative determination of sulfonamide in meat by liquid chromatography-electrospray-mass spectrometry

This paper describes a newly developed liquid chromatography–electrospray-mass spectrometry (LC–ES-MS) method for the quantitative determination of nine commonly used sulfonamides (sulfadiazine, sulfapyridine, sulfamerazine, sulfamethazine, sulfamonomethoxine, sulfisoxazole, sulfadimethoxine, sulfaquinoaline and sulfaphenazole) in meat. [M+H]⁺ and [M+Na]⁺ were the two major ions detected in positive ion mode. Selective ion monitoring was employed for quantitative determination. Satisfactory linearity, 0.1–10 μg ml⁻¹, of each compound was obtained. Blank meat samples were fortified at levels between 50 and 500 μg kg⁻¹. [Phenyl-¹³C6]sulfamethazine was used as internal standard. Sulfonamides were isolated from meat with a solvent extraction procedure and then determined by LC–ES-MS. The limits of detection were below 10 μg kg⁻¹. The application of this newly developed method was demonstrated by analyzing various beef, pork and chicken samples from local markets.     

Studies on adducts of rhodium(II) tetraacetate and rhodium(II) tetratrifluoroacetate with some amines in CDCl3 solution using H, C and N NMR

¹H, ¹³C and ¹⁵N NMR spectroscopy has been applied for investigation of amine adducts with rhodium(II) tetraacetate dimer and rhodium(II) tetratrifluoroacetate dimer in CDCl₃ solution. Subsequent formation of two adducts, 1:1 and 2:1, was proved by NMR and VIS titration experiments, and by NMR measurements at reduced temperatures, from 233 to 273 K. The adduct formation shift, defined as Δδ=δ_adduct−δ_ligand and characterizing complexation reaction, varies from ca. 0 to +1.6 ppm for ¹H, from ca. −10 to +6 ppm for ¹³C and from −4.4 to −39 ppm for ¹⁵N NMR. Formation of N–Rh bond slows the inversiof on the nitrogen atom and generates, in the case of N-methyl-(1-phenylethyl)-amine, a nitrogenous chiral center in the molecule. VIS spectra of amine-dirhodium salt mixture contain two bands in the 532–597 nm spectral range, assigned to 1:1- and 2:1-adducts.     

Monodentate and bidentate trifluoroacetato ligands in bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato)thallium(III)—a new dynamic 4:3 piano stool seven-coordinate geometry

The crystal structure of bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato) thallium(III), Tl(N---Me---tpp)(CF₃CO₂)₂ (2), was established and the coordination sphere around the Tl³⁺ ion is described as 4:3 tetragonal base–trigonal base piano stool seven-coordinate geometry in which the two cis CF₃CO₂ ⁻ groups occupy two apical sites. The plane of the three pyrrole nitrogen atoms [i.e. N(2), N(3) and N(4)] strongly bonded to Tl³⁺ is adopted as the reference plane 3N. The pyrrole N(1) ring bearing the methyl group [i.e. C(45)H₃] is the most deviated one from the 3N plane making a dihedral angle of 23.3° whereas smaller angles of 9.9, 2.7 and 4.7° occur with pyrroles N(2), N(3), and N(4), respectively. Because of the larger size of the thallium(III) ion, Tl is considerably out of the 3N plane; its displacement of 1.02 Å is in the same direction as that of the two apical CF₃CO₂ ⁻ ligands. The intermolecular trifluoroacetate exchange process for 2 in CD₂Cl₂ solvent is examined through ¹⁹F and ¹³C NMR temperature-dependent measurements. In the slow-exchange region, the CF₃ and carbonyl (CO) carbons of the CF₃CO₂ ⁻ groups in 2 are separately located at δ 114.3 [¹J(C–F)=290 Hz, ³J(Tl–C)=411 Hz] and 155.1 [²J(C–F)=37 Hz, ²J(Tl–C)=204 Hz], respectively, at −106 °C. In the same slow-exchange region, the fluorine atoms of 2, Tl(N---Me---tpp)(CF₃CO₂)⁺ and the free CF₃CO₂ ⁻ are located at δ −73.76 [⁴J(Tl–F)=44 Hz], −73.30 [⁴J(Tl–F)=22 Hz], and −76.15 ppm at −97 °C, respectively.     

One-electron oxidation of mitomycin C and its corresponding peroxyl radicals. A steady-state and pulse radiolysis study

The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G_i (-MMC) = 3.0 and at 364 nm G_i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH₃) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10⁹ dm³ mol⁻¹ s⁻¹. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm³ mol⁻¹ cm^t-1), 410 nm (ε = 1450 dm³ mol⁻¹ cm⁻¹) and 505 nm ( ε = 5420 dm³ mol⁻¹ cm⁻¹). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ₁ = (0.85 ± 0.1) × 10³ s⁻¹, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 10⁸ dm³ mol^-1 s⁻¹. Around 410 nm the kinetics are rather mixed and could not be resolved.

The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a G_i (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH₃) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N₂O and 20% O₂. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm³ mol⁻¹ cm⁻¹), 410 nm (ε = 2900 dm³ mol⁻¹ cm⁻¹) and 520 nm (ε = 5500 dm³ mol⁻¹ cm⁻¹). The O₂-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O₂) = 5 × 10⁷ dm³ mol⁻¹ s⁻¹, around 480 nm κ = 1.6 × 10⁸ dm³ mol⁻¹ s⁻¹ and at 510 nm and above, κ = 3 × 10⁸ dm³ mol⁻¹ s⁻¹. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ₁ = 1.5 × 10³ s⁻¹ and at 500 nm and above, κ = 7.0 × 10³ s⁻¹.

The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients.     

Cu2(bipy)2V6O17: A new type of layered inorganic–organic hybrid copper(II) vanadate

Hydrothermal reaction of copper(II) acetate, 2,2′-bipyridine (bipy) and NH₄VO₃ at 170 °C lead to a new layered polyoxovanadate with organically covalent-bonded copper(II) complex, Cu₂(bipy)₂V₆O₁₇ (1). Cu₂(bipy)₂V₆O₁₇ (1) is a new copper(II) vanadium(V) oxide featuring a new layered architecture, in which the V₂O₇ dimeric units and the cyclic tetranuclear V₄O₁₂ cluster units are interconnected via corner sharing into a unique one-dimensional {V₆O₁₇}⁴⁻ anionic chain, such chains are further bridged by {Cu(bipy)}²⁺ complex cations into a 010 organic–inorganic hybrid layer.     

Studies on beta-type reaction and kinetics of lanthanides with p-bromochloroarsenazo

The reaction behaviour of the β-type chelates of lanthanide ions (Ln³⁺) with p-bromochloroarsenazo (4-CAsA-pB) in 0.01 mol l⁻¹ HClO₄ solution has been studied systematically by a spectrophotometric method. All the lanthanide ions can form β-type chelates with p-bromochloroarsenazo. The maximum absorption wavelength is in the range 727–731 nm, the molar absorptivities are about 6.0 × 10⁴ – 9.0 × 10⁴ cm² mol⁻¹, the composition ratio of Ln³⁺ ions with 4-CAsA-pB is 1:2 and the actual combining ratio is 2:4. The optimum acidity range (ΔpH value) of the formation of β-type chelates has been obtained. Kinetic parameters, such as the reaction order and rate constants, have also been studied and a formation mechanism for the β-type chelates has been proposed.     

H NMR Spectra and electronic structure of binuclear niobocene and titanocene containing fulvalene ligands

¹H NMR spectra of binuclear metallocene hydride complexes, (η⁵ : η⁵-C₁₀H₈)(C₅H₅)₂M₂(μ-H)₂ (M = Nb, 20°C and Ti, (−60 to +25°C), were studied. The Nb complex is diamagnetic and gives a high resolution spectrum. The coordination of bridging hydride H atoms provides Nb atoms with complete 18 electron configuration. In its ground state, the Ti complex is also diamagnetic (the spectrum at −60°C agrees to that) in spite of only 17 electron configuration of each Ti atom. However, the population of the excited triplet state in the case of the Ti complex is appreciable at temperatures higher than −30°C, the proton resonance lines being shifted downfield and significantly broadened as compared with the spectrum at −60°C.     

Reactivity and electronic property of decaphenylmetallocenes of Mo and W atoms

The perphenylmetallocene complexes (η⁵-C₅Ph₅)₂W (1), [(η⁵-C₅Ph₅)₂W]⁺I₃⁻ (1⁺I₃), (η⁵-C₅Ph₅)₂Mo (2) and [(η⁵-C₅Ph₅)₂Mo]⁺I₃⁻ (2⁺I₃) have been prepared. Hydrogenation of 1 in THF produces (η⁵-C₅Ph₅)₂WH₂ (4), while (η⁵-C₅Ph₅)₂WHCl (3) is afforded in 1,2-dichloroethane solvent. Carbonylation of 1 produces (η⁵-C₅Ph₅)₂W(CO) (5). Treatment of 1 with the strong acid CF₃SO₃H leads to the dicationic species [(η⁵-C₅Ph₅)₂W]⁺²[CF₃SO₃]⁻₂ (1⁺²Tf₂) after crystallization. The structures of 2⁺I₃ and 1⁺²Tf₂ have been determined by an X-ray diffraction study. The magnetic susceptibility study indicates a ³E_2g ground-state for 1 and 2, and a ⁴A_2g ground-state for 1⁺ and 2⁺.     

Highly stereoselective reduction of methyl ketone complexes of the chiral Lewis acid [(η-C5H5)Re(NO)(PPh3)] by K(s-C4H9)3BH; synthesis of optically active secondary alcohols and derivatives

Reaction of optically active ketone complexes (+)-(R)-[(η⁵-C₅H₅)Re(NO)-(PPh₃)(η¹-O=C(R)(CH₃)]⁺ BF₄⁻ (R = CH₂CH₃, CH(CH₃)₂m C(CH₃)₃, C₆H₅) with K(s-C₄H₉)₃BH gives alkoxide complexes (+)-(RS)-(η⁵-C₅H₅)Re(NO)(PPh₃)-(OCH(R)CH₃) (73–90%) in 80–98% de. The alkoxide ligand is then converted to Mosher esters (93–99%) of 79–98% de.     

Bis(η-pentamethylcyclopentadienyl)-and(ηcyclopentadienyl) (η-pentamethylcyclopentadienyl)-platinium dications: Pt(IV) metallocenes

Reaction of [Pt₂(η⁵-C₅Me₅)₂(η-Br)₃]³⁺(Br⁻)₃ with C₅R₅H (R = H,Me) in the presence of AgBF₄ gives the first platinocenium dications, [Pt(η⁵-C₅Me₅)(η⁵-C₅R₅)]²⁺(BF₄⁻ )₂. On electrochemical reduction, [pt(η⁵-C₅Me₅)₂]²⁺ yields [Pt(η⁴-C₅Me₅H)(η²-C₅Me₅)]+ BF₄⁻. kw]Cyclopentadienyl; Metallocenes; Platinum; Electrochemistry     

Speciation analysis of arsenic and selenium compounds in environmental and biological samples by ion chromatography-inductively coupled plasma dynamic reaction cell mass spectrometer

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic and selenium. The arsenic and selenium species studied included arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), selenite [Se(IV)] and selenate [Se(VI)]. Gradient elution using (NH₄)₂CO₃ and methanol at pH 9 allowed the chromatographic separation of all species in less than 12 min. Effluents from the IC column were delivered to the nebulization system of ICP-DRC-MS for the determination of arsenic and selenium. The potentially interfering ³⁸Ar⁴⁰Ar⁺ and ⁴⁰Ar⁴⁰Ar⁺ at the selenium masses m/z 78 and 80 were reduced in intensity by approximately 3 orders of magnitude by using 0.6 mL min⁻¹ CH₄ as reactive cell gas in the DRC while an Rpq value of 0.3 was used. Meanwhile, arsenic was determined as the adduct ion ⁷⁵As¹²CHH⁺ at m/z 89, which is more sensitive than ⁷⁵As. The limits of detection for arsenic and selenium were in the range of 0.002–0.01 ng mL⁻¹ and 0.01–0.02 ng mL⁻¹, respectively, based on peak height. The relative standard deviation of the peak areas for five injections of 5 ng mL⁻¹ As and Se mixture was in the range of 2–4%. The concentrations of arsenic and selenium species have been determined in urine samples collected locally. The major As and Se species in urines were AsB, DMA and probably selenosugar at concentration of 20–40, 15–19 and 17–31 ng mL⁻¹, respectively. The recoveries were in the range of 94–105% for all the determinations. This method has also been applied to determine various arsenic compounds in two fish samples. In this study, a simple and rapid microwave-assisted extraction method was used for the extraction of arsenic compounds from fish. The arsenic species were quantitatively leached with an 80% v/v methanol solution in a focused microwave field during a period of 5 min.     

Rapid determination of aluminum by UV-vis diffuse reflectance spectroscopy with application of suitable adsorbents

Diffuse reflectance spectroscopy (DRS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of aluminum. In this analytical technique, the analyte in samples are extracted onto a solid sorbent matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface. Alternatively, colored aluminum complexes formed in solution can also be immobilized onto adsorbent surface and be measured by DRS technique. Octadecyl silica disk, methyltrioctylammonium chloride–naphthalene and MCM-41 were examined as adsorbents. Eriochrome cyanine R and quinalizarin were used as coloring reagents. Optimal sorption conditions were found for each system of analyte–reagent–adsorbent. The concentration of analyte is determined using the appropriate form of the Kubelka–Munk function. We obtained for each of the aluminium–reagent–adsorbent system a calibration curve by plotting the absorbance versus the log 10²[Al³⁺] μg ml⁻¹. The linear dynamic range extends over two orders of magnitude within 0.01–15 μg ml⁻¹ with little differences in the range and in the correlation coefficients among the adsorbents. We consider that for a rapid determination of aluminum a spot-test-DRS combination with a detection limit of 1.0 × 10⁻² μg ml⁻¹ is the more facile and preferred technique.     

Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions

The reactions of the diruthenium carbonyl complexes [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]X (X=BF₄⁻ (1a) or PF₆⁻ (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes [Ru₂(μ-dppm)₂(μ-CO)₂(η²-(L,L))₂]X_n ((L,L)=acetate (O₂CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ either migrates within the same complex or into a different one, or is simply replaced. The reaction of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ (1) with 2,2′-bipyridine produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)₂] (2), [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-bpy)]⁺ (3), and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-bpy)₂]²⁺ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO₂H–Et₃N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et₃N produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-acac)] (5) and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-acac)₂] (6). Compound 2 can also react with acetylacetone–Et₃N to produce 6. Surprisingly [Ru₂(μ-dppm)₂(μ-CO)₂(η²-quin)₂] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et₃N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum.     

Preparation and characterization of ruthenium(II), rhodium(III) and iridium(III) complexes of isocyanide bearing the azo group

Reactions of [(η⁶-arene)RuCl₂]₂ (1) (η⁶-arene=p-cymene (1a), 1,3,5-Me₃C₆H₃ (1b), 1,2,3-Me₃C₆H₃ (1c) 1,2,3,4-Me₄C₆H₂(1d), 1,2,3,5-Me₄C₆H₂ (1e) and C₆Me₆ (1f)) or [Cp*MCl₂]₂ (M=Rh (2), Ir (3); Cp*=C₅Me₅) with 4-isocyanoazobenzene (RNC) and 4,4′-diisocyanoazobenzene (CN–R–NC) gave mononuclear and dinuclear complexes, [(η⁶-arene)Ru(CNC₆H₄N=NC₆H₅)Cl₂] (4a–f), [Cp*M(CNC₆H₄N=NC₆H₅)Cl₂] (5: M=Rh; 6: M=Ir)_, [{(η⁶-arene)RuCl₂}₂{μ-CNC₆H₄N=NC₆H₄NC}] (8a–f) and [(Cp*MCl₂)₂(μ-CNC₆H₄N=NC₆H₄NC)}] (9: M=Rh; 10: M=Ir)_, respectively. It was confirmed by X-ray analyses of 4a and 5 that these complexes have trans-forms for the ---N=N--- moieties. Reaction of [Cp*Rh(dppf)(MeCN)](PF₆)₂ (dppf=1,1′-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC₆H₄N=NC₆H₅)](PF₆)₂ (7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF₃SO₃), giving a rectangular tetranuclear complex 11b, [{(η⁶-1,3,5-Me₃C₆H₃)Ru(μ-Cl}₄(μ-CNC₆H₄N=NC₆H₄NC)₂](CF₃SO₃)₄ bridged by four Cl atoms and two μ-diisocyanoazobenzene ligands. Photochemical reactions of the ruthenium complexes (4 and 8) led to the decomposition of the complexes, whereas those of 5, 7, 9 and 10 underwent a trans-to-cis isomerization. In the electrochemical reactions the reductive waves about −1.50 V for 4 and −1.44 V for 8 are due to the reduction of azo group, [---N=N---]→[---N=N---]²⁻. The irreversible oxidative waves at ca. 0.87 V for the 4 and at ca. 0.85 V for 8 came from the oxidation of Ru(II)→Ru(III).     

Analysis of pesticides in fruit, vegetables and cereals using methanolic extraction and detection by liquid chromatography–tandem mass spectrometry

A method for analysing carbamates and other relatively polar pesticides by LC–MS–MS with electrospray ionisation has been developed. The method is based on extraction by ultrasonication using a methanolic ammonium acetate–acetic acid buffer. After centrifugation the samples are filtered in Miniprep filter HPLC vials and detected by LC–MS–MS. To compensate for variations in the MS response [¹³C₆]-carbaryl was used as internal standard and matrix-matched pesticide solutions were used as external standards for the quantification. The method has been validated for the matrices apple, avocado, carrot, lettuce, orange, potato and wheat at the spiking levels—0.02; 0.04 and 0.20 mg kg⁻¹. Recoveries were generally in the range 70–120%. Results from participation in three intercomparisons proved the accuracy of the method. As the analytical procedure does not include any concentration or cleanup steps, it is easy and fast to perform, making it applicable for routine analysis in large pesticide monitoring programmes.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

Structures of propionaldehyde, butyraldehyde, and pivalaldehyde complexes of the chiral rhenium fragment [(η-C5H5)Re(NO)(PPh3)]

The crystal structures of propionaldehyde complex (RS,SR)-(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₃)]⁺ PF₆⁻ (1b⁺ PF₆^s−; monoclinic, P2₁/c (No. 14), a = 10.166 (1) Å, b = 18.316(1) Å, c = 14.872(2) Å, β = 100.51(1)°, Z = 4) and butyraldehyde complex (RS,SR)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₂CH₃)]⁺ PF₆⁻ (1c⁺PF₆⁻; monoclinic, P2₁/a (No. 14), a = 14.851(1) Å, b = 18.623(3) Å, c = 10.026(2) Å, β = 102.95(1)°, Z = 4) have been determined at 22°C and −125°C, respectively. These exhibit C O bond lengths (1.35(1), 1.338(5) Å) that are intermediate between those of propionaldehyde (1.209(4) Å) and 1-propanol (1.41 Å). Other geometric features are analyzed. Reaction of [(η⁵-C₅H₅)Re(NO)(PPh₃)(ClCH₂Cl)]⁺ BF₄⁻ and pivalaldehyde gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHC(CH₃)₃)]⁺BF₄⁻ (81%), the spectroscopic properties of which establish a π C O binding mode.     

Formation, solution structure and reactivity of alkylperoxo complexes of titanium

A detailed in situ ¹³C and ¹H NMR spectroscopic characterization of the following families of alkylperoxo complexes of titanium is presented: Ti(η²-OOtBu)_n(OiPr)_4−n, where n = 1–4; binuclear complexes [(iPrO)₃Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)] and [(η²-OOtBu)(iPrO)₂Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)]; complexes with β-diketonato ligands: Ti(LL)₂(OEt)(η²-OOtBu), Ti(LL)₂(OiPr)(η²-OOtBu), Ti(LL)₂(η²-OOtBu)₂, Ti(LL)₂(OtBu)(η¹-OOtBu), where HLL = acetylacetone, dipivaloylmethane. These alkylperoxo complexes could not be isolated due to their instability and were studied in situ at low temperatures. Whereas the side-on (η²) coordination mode of tert-butylperoxo ligand is generally preferable, the end-on (η¹) coordination caused by spatial hindrance from surrounding bulky ligands is found in two cases. The quantitative data on the reactivity of alkylperoxo complexes found towards sulfides and alkenes were obtained. The system TiO(acac)₂/tBuOOH in C₆H₆ was reinvestigated using ¹³C and ¹H NMR spectroscopy. The structure of the complex Ti(acac)₂{CH₃C(O)(OOtBu)COO} actually formed in this system was elucidated. Four types of titanium(IV) alkylperoxo complexes were detected in the Sharpless–Katsuki catalytic system using ¹³C NMR spectroscopy.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.