Simultaneous determination of bufadienolides and phenolic compounds in sea squill (Drimia maritima (L.) Stearn) by HPLC-DAD-MSn as a means to differentiate individual plant parts and developmental stages

Mediterranean sea squill (Drimia maritima (L.) Stearn) is used in the production of medicinal products. Current HPLC methods comprise tedious sample clean-up and have been merely focused on the analysis of cardiac glycosides, whereas a thorough characterization of D. maritima considering both the latter compound class and more hydrophilic secondary metabolites in one HPLC run has not been performed so far. Consequently, a novel HPLC-DAD-MSⁿ method has been developed allowing the simultaneous determination of both cardiac glycosides and phenolic compounds, which is characterized by simplified sample preparation. This method was applied to characterize sea squill, revealing a complex profile of its extractive compounds derived from the two classes. Furthermore, the potential of the method reported here to quantitate the predominant compounds, i.e., dihydroquercetin derivatives and bufadienolides, was demonstrated. The occurrence of phenolic compounds, not described for sea squill so far, and of characteristic compounds specific to individual plant parts or vegetation stages was further addressed. The data revealed that classification of various vegetation phases based on quantitative evaluation of bufadienolides and dihydroquercetin derivatives applying principal component analysis (PCA) appears possible. Thus, the methodology presented here forms the basis for future routine application in quality control of raw materials and pharmaceutical preparations derived from sea squill. This will allow systematic comparison of different plant parts, vegetation stages and origins based on an extended sample set. Figure

Red sea squill with inflorescence and cross-section of a fresh bulb     

Optimization of dispersive liquid-liquid microextraction of copper (II) by atomic absorption spectrometry as its oxinate chelate: application to determination of copper in different water samples

In this study a dispersive liquid-liquid microextraction (DLLME) method based on the dispersion of an extraction solvent into aqueous phase in the presence of a dispersive solvent was investigated for the preconcentration of Cu(2+) ions. 8-Hydroxy quinoline was used as a chelating agent prior to extraction. Flame atomic absorption spectrometry using an acetylene-air flame was used for quantitation of the analyte after preconcentration. The effect of various experimental parameters on the extraction was investigated using two optimization methods, one variable at a time and central composite design. The experimental design was performed at five levels of the operating parameters. Nearly the same results for optimization were obtained using both methods: sample size 5 mL; volume of dispersive solvent 1.5 mL; dispersive solvent methanol; extracting solvent chloroform; extracting solvent volume 250 microL; 8-hydroxy quinoline concentration and salt amount do not affect significantly the extraction. Under the optimum conditions the calibration graph was linear over the range 50-2000 muicro L(-1). The relative standard deviation was 5.1% for six repeated determinations at a concentration of 500 microg L(-1). The limit of detection (S/N=3) was 3 microg L(-1).     

Analysis and validation of the phosphorylated metabolites of two anti-human immunodeficiency virus nucleotides (stavudine and didanosine) by pressure-assisted CE-ESI-MS/MS in cell extracts: sensitivity enhancement by the use of perfluorinated acids and alcohols as coaxial sheath-liquid make-up constituents

A CE method utilizing triple quadrupole electrospray (ES) MS (MS/MS) detection was developed and validated for the simultaneous measurement of nucleoside 5'-triphosphate and 5'-monophosphate anabolites of the anti-HIV (human immunodeficiency virus) didanosine (ddAMP, ddATP) and stavudine (d4TMP, d4TTP), among a pool of 14 endogenous 5'-mono-, di-, and triphosphate nucleosides. These compounds were spiked and extracted from peripheral blood mononuclear cells (PBMCs) which are the sites of HIV replication and drug action. An acetic acid/ammonia buffer (pH 10, ionic strength of 40 mM) was selected as running electrolyte, and the separation was performed by the simultaneous application of a CE voltage of +30 kV and an overimposed pressure of 28 mbar (0.4 psi). The application of pressure assistance was needed to provide stable ES conditions for successful coupling. The coupling was carried out with a modified sheath-flow interface, with one uninterrupted capillary (80 cmx 50 microm id; 192 microm od) in a dimension that fits into the ESI needle to get a stable ion spray. Some CE-MS parameters such as overimposed pressure, sheath-liquid composition, sheath-liquid and sheath-gas flow rates, ES voltage, and the CE capillary position were optimized in order to obtain an optimal sensitivity. The use of perfluorinated alcohols and acids in the coaxial sheath-liquid make-up (2,2,2-trifluoroethanol + 0.2 mM tridecafluoroheptanoic acid) appeared to provide the best MS sensitivity and improve the stability of spray. The linearity of the CE-MS and CE-MS/MS methods was checked under these conditions. Validation parameters such as accuracy, intraday and interday precision, and LOQs were determined in CE-MS/MS mode. Finally, the quantitation of d4T-TP and ddA-TP was validated in this CE-MS/MS system.     

Structural characterization and formation kinetics of sitting-atop (SAT) complexes of some porphyrins with copper(II) ion in aqueous acetonitrile relevant to porphyrin metalation mechanism. Structures of aquacopper(II) and cu(II)-SAT complexes as determined by XAFS spectroscopy

The formation of the sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin (H(2)tpp), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (H(2)t(4-Clp)p), 5,10,15,20-tetramesitylporphyrin (H(2)tmp), and 2,3,7,8,12,13,17,18-octaethylporphyrin (H(2)oep) with the Cu(II) ion was spectrophotometrically confirmed in aqueous acetonitrile (AN), and the formation rates were determined as a function of the water concentration (C(W)). The decrease in the conditional first-order rate constants with the increasing C(W) was reproduced by taking into consideration the contribution of [Cu(H(2)O)(an)(5)](2+) in addition to [Cu(an)(6)](2+) to form the Cu(II)-SAT complexes. The second-order rate constants for the reaction of [Cu(an)(6)](2+) and [Cu(H(2)O)(an)(5)](2+) at 298 K were respectively determined as follows: (4.1 +/- 0.2) x 10(5) and (3.6 +/- 0.2) x 10(4) M(-1) s(-1) for H(2)tpp, (1.15 +/- 0.06) x 10(5) M(-1) s(-1) and negligible for H(2)t(4-Clp)p, and (4.8 +/- 0.3) x 10(3) and (1.3 +/- 0.3) x 10(2) M(-1) s(-1) for H(2)tmp. Since the reaction of H(2)oep was too fast to observe the reaction trace due to the dead time of 2 ms for the present stopped-flow technique, the rate constant was estimated to be greater than 1.5 x 10(6) M(-1) s(-1). According to the structure of the Cu(II)-SAT complexes determined by the fluorescent XAFS measurements, two pyrrolenine nitrogens of the meso-substituted porphyrins (H(2)tpp and H(2)tmp) bind to the Cu(II) ion with a Cu-N(pyr) distance of ca. 2.04 A, while those of the beta-pyrrole-substituted porphyrin (H(2)oep) coordinate with the corresponding bond distance of 1.97 A. The shorter distance of H(2)oep is ascribed to the flexibility of the porphyrin ring, and the much greater rate for the formation of the Cu(II)-SAT complex of H(2)oep than those for the meso-substituted porphyrins is interpreted as due to a small energetic loss at the porphyrin deformation step during the formation of the Cu(II)-SAT complex. The overall formation constants, beta(n), of [Cu(H(2)O)(n)()(an)(6)(-)(n)](2+) for the water addition in aqueous AN were spectrophotometrically determined at 298 K as follows: log(beta(1)/M(-1)) = 1.19 +/- 0.18, log(beta(2)/M(-2)) = 1.86 +/- 0.35, and log(beta(3)/M(-3)) = 2.12 +/- 0.57. The structure parameters around the Cu(II) ion in [Cu(H(2)O)(n)(an)(6-n)](2+) were determined using XAFS spectroscopy.     

Taurine as a ligand. An investigation of Ag(I)- and Cd(II)-taurine complex equilibria by direct and competitive techniques, and use of the Ag(I)-taurine complex electrode to assess taurine in solution

The behaviour of taurine as a ligand (L) towards silver(I) and cadmium(II) was studied at 25 degrees C and in 1 mol dm(-3) NaClO(4), as a constant ionic medium. Experimental data, obtained for both cations from electromotive force measurements performed by using silver and cadmium amalgam and glass electrodes, were explained by assuming the formation of the AgL, AgL(2), CdL, and CdL(2) complexes. The taurine protonation constant and stability constants of the above complexes were determined. The cadmium(II)-taurine system was investigated by determining the free concentration of taurine from the Ag electrode potential and the knowledge of equilibria existing between silver(I) and taurine. Experimental data obtained from this approach were explained by assuming the presence of the above species with very close stability constant values. The success of this method supports the possibility of using the Ag/Ag-taurine, taurine electrode to measure the free concentration of taurine in its solutions.     

Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol,chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.     

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3)

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.     

Cumulated double bond systems as ligands : X. N-sulfinylaniline complexes of rhodium(I) and iridium(I) of the type [MCl(PR3)2L] in which L is coordinated via the π-NS and via the sulfur atom respectively; crystal and molecular structure of [RhCl(P-i-Pr3)2(4-MeC6H4NSO)]; determination of the 1J(103Rh15N) by 15N NMR spectroscopy

Each of the compounds [MCl(Pr₃)₂(ArylNSO)] (M = Rh^I, Ir^I; R = i-Pr, Cy: Aryl = C₆H₅, 4-MeC₆H₄, 4-ClC₆H₄, 2,4,6-Me₃C₆H₂ appears to exist as two isomers both in the solid state and in solution. The molecular and single crystal structure of one of the isomers of [RhCl(P-i-Pr)₃)₂(4-Me₆H₄NSO)] shows that the N-sulfinylaniline ligand is in the cis-configuration and coordinated to the rhodium atom via the sulfur-atom. The ligand lies in a plane which includes the rhodium atom and is in agreement with the Rh-S distance of 2.10 Å. IR results of the compounds (solid and solutions), ²¹P NMR data and ¹⁵N NMR of a ¹⁵N labelled compound, which yielded a ¹⁰³Rh¹⁵N coupling constant of 15.5 Hz, show that in the second isomer the N-sulfinylaniline ligand is probably bonded to the metal atom via the π-NS bond.The ratio of the metal-π-NS bonded isomer and the metal-S bonded isomer decreases in the order Aryl = 4-ClC₆H₄ > C₆H₅ > 4-MeC₆H₄; R = i-Pr > Cy and M = Rh > Ir. The interconversion of the two isomers is intramolecular and becomes observable on the ³¹P NMR time scale at about 40° C for M = Rh.In the case of [Ir(P-i-Pr₃)₂(4-MeC₆H₄NSO)], cyclometallation of the sul- finylaniline is observed via the ortho-carbon atom, whereas cyclometallation via P-i-Pr₃ is observed when the ortho-positions are blocked by methyl groups, e.g. when L = 2,4,6-Me₃C₆H₂NSO.     

A very simple synthesis of K3[Re(NO)(CN)5] · 2 H2O directly from [ReO4]−: Existence of two structural isomers in aqueous medium as indicated by13C N.m.r. spectroscopy

Summary Perrhenate(VII) was reductively nitrosylated using an excess of CN^–, OH^– and NH₂OH · HCl, and from the reaction mixture K₃[Re(NO)(CN)₅] · 2H₂O has been isolated. Its aqueous solution behaves as a 31 electrolyte and its¹³C n.m.r. spectrum in D₂O solution suggests that the complex molecule forms two types of isomeric structure arising from the two different modes of intramolecular hydrogen (deuterium) bonding of the two lattice water (D₂O in the bulk solvent) molecules.     

Chains of [RE6] octahedra coupled by (NCN) links in the network structure of RE2Cl(CN2)N. Synthesis and structure of two novel rare earth chloride carbodiimide nitrides with structures related to the RE2Cl3 type

Solid state metathesis reactions between RECl(3) (RE = La, Ce) and Li(2)CN(2) at 800 degrees C have led to the discovery of the rare earth chloride carbodiimide nitrides La(2)Cl(CN(2))N (1) and Ce(2)Cl(CN(2))N (2), respectively. Single crystal X-ray diffraction analyses revealed that 1 and 2 crystallize isotypic in an orthorhombic system (Cmmm, Z = 4, a = 13.3914(8) A, b = 9.6345(7) A, c = 3.9568(2) A for 1 and a = 13.340(1) A, b = 9.5267(8) A, c = 3.9402(5) A for 2). The crystal structures of 1 and 2 contain linear chains of edge-sharing octahedra built from rare earth metal atoms. Similar to [M(6)X(8)] type clusters, the [RE(6)] octahedra are capped by eight nitrogen atoms above their faces, of which four are from N(3-) ions and the other four are from (CN(2))(2-) ions. The chains are interconnected by bridging (CN(2))(2-) to form a three-dimensional network with Cl(-) ions in linear channels. Compounds 1 and 2 are surprisingly stable toward air and water. They have been characterized by thermal analysis, infrared spectroscopy, and magnetic susceptibility studies.     

Bis(3,5-dimethylpyrazol-1-yl)acetate bound to titania and complexed to molybdenum dioxido as a bidentate N,N′-ligand. Direct comparison with a bipyridyl analog in a photocatalytic arylalkane oxidation by O2

Bis(3,5-dimethylpyrazol-1-yl)acetate, well known as a tridentate N,N,O ligand, was bound to MoO₂Cl₂ in a bidentate N,N manner by anchoring covalently, at first, the ligand onto a titanium oxide surface, followed by its complexation with the molybdenum dioxo entity. It was fully characterized by ¹³CPMAS NMR and FT-IR spectroscopy. The tethered complex was directly compared with an analogous bipyridyl species in the catalytic ethylbenzene oxidation by O₂ at room temperature, atmospheric pressure, and under visible light. The bis(pyrazol-1-yl) catalyst exhibited a significant initial higher oxygen atom transfer (OAT) capability, well in accord with its electron donating property. It was, unfortunately, hampered by a premature leaching phenomenon, totally absent in the comparable bipyridyl system.     

Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol, chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.