Solid-phase extraction and sample stacking-micellar electrokinetic capillary chromatography for the determination of multiresidues of herbicides and metabolites

Micellar electrokinetic capillary chromatography (MEKC) with diode array detection was used for the separation of 13 compounds (eight herbicides widely used in agriculture: metribuzin, lenacil, ethofumesate, atrazine, terbutryn, isoproturon, chlorotoluron and linuron, and five of their principal degradation products; namely, deethylatrazine, 2-hydroxyatrazine, deethyl-2-hydroxyatrazine, deisopropylatrazine and 3-chloro-4-methylphenylurea). Peak separation for the 13 analytes was not successful when a single surfactant system was employed, neither sodium dodecyl sulfate (SDS) nor dioctyl sulfosuccinate (DOSS) sodium salt. However, a mixture of these herbicides was successfully separated using a mixed micellar system involving SDS–DOSS in less than 14 min. An application study of an on-line concentration technique for MEKC was carried out to enhance sensitivity. The optimized on-line stacking procedure consisted simply of the addition of 50 mM of sodium chloride to the injection sample, the stacking effect being more intensive as analyte polarity increased. When this stacking procedure was combined with an off-line sample preconcentration step, based on solid-phase extraction, analytes could be detected in the ppb range. The whole method was applied to ultra-high-quality and natural waters. Linear relationships between the analytical signal and the initial analyte concentration were found to be independent of the type of water, except for the more polar analytes for which small differences were observed.     

Organocatalytic ring expansion of beta-lactams to gamma-lactams through a novel N1-C4 bond cleavage. direct synthesis of enantiopure succinimide derivatives

Tetrabutylammonium cyanide (20 mol %) catalyzes ring expansion of 4-(arylimino)methylazetidin-2-ones 2 to 5-aryliminopyrrolidin-2-ones 3 through a novel N1-C4 bond cleavage of the beta-lactam nucleus. New, efficient one-pot protocols to enantiopure succinimide derivatives 3 and 4 from beta-lactam aldehydes 1 have also been developed. [reaction: see text]     

The solubilization of alcohols in micellar solutions

The specific conductivities of dodecyldimethylbenzylammonium bromide (C12BBr) have been determined in aqueous butanol and aqueous benzyl alcohol solutions in the temperature range of 5-40°C. From these data the temperature dependent critical micelle concentration (cmc) was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The thermal properties such as standard Gibbs free energy, enthalpy and entropy of solubilization of alcohols in the micelles were estimated for the phase separation model. The change in heat capacity upon solubilization of alcohol in the micelle has been estimated form the above properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of cationic carbonyl complexes of manganese(I) with bidentate ligands

Summary Bidentate ligands can readily replace acetone in thefac-[Mn(CO)₃(chel)(OCMe₂)]⁺ complexes or the perchlorate group fromfac-[Mn(CO)₃(chel)(OClO₃)] yieldingfac-[Mn(CO)₃(chel)(L-L)]⁺ or [{fac-Mn(CO)₃(chel)}₂(L-L)]²⁺ [chel = 1,10-phenanthroline (phen), 2,2-bipyridine (bipy), 1,2-bis(diphenylphosphine)ethane (dpe); L-L = bis(diphenylphosphine)methane (dpm), dpe, 1,4-bis(diphenylphosphine)butane (dpb), succinonitrile (suc), and glutaronitrile (glu)]. Some of these mononuclear complexes are precursors for binuclear complexes which are linked by bridging phosphines or nitriles.     

Determination of lead in natural waters using flow injection with on-line preconcentration and flame AAS detection

A rapid and sensitive method has been developed for the determination of lead in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with silica gel treated with a mixture of Aliquat 336 and nitroso-R-salt. The lead is retained at pH 5.5. The preconcentrated lead is directly eluted from the column to the nebulizer-burner system using 150 L of 0.1 mol/L hydrochloric acid. The optimum preconcentration conditions are given and the retention efficiency achieved is higher than 80%. The enrichment factor is 37 and 100 for sample volumes of 5 and 30 mL, respectively. The limits of detection are 10.0, 6.0 and 4.0 ng/mL when 5, 10 and 30 mL of water is preconcentrated.     

Direct capillary electrophoretic determination of three chemotherapeutic drugs in human urine

Summary Capillary zone electrophoresis (CZE) has been used for direct determination of 6-thioguanine, methotrexate, and 5-fluorouracil in human urine, by use of a fused-silica capillary (60.2 cm×75 μm i.d.). Separation was performed after hydrodynamic injection for 7 s; the separation potential and capillary temperature were 25 kV and 35°C, respectively. A 45mm borate buffer solution (pH 9.2) was used as separation electrolyte. Under these conditions the analysis takes approximately 10 min and interday precision of migration times and corrected peak areas is satisfactory. A linear response over the concentration range 3.0–20.0 mg L¹ was observed for the three chemotherapeutic drugs in diluted human urine. Detection limits (s/n=3) for 6-thioguanine and methotrexate were approximately 1.60 mg L¹ in diluted human urine; that for fluorouracil was 2.60 mg L¹. A 2-ml volume of human urine was diluted with 2-mL of water and introduced directly into the electrophoresis system. CZE was shown to be a good method with regard to simplicity, satisfactory precision, and sensitivity. This method resulted in especially excellent recoveries for determination of methotrexate in all the different urine samples analysed (n=10).     

Evaluation of surface- and ground-water pollution due to herbicides in agricultural areas of Zamora and Salamanca (Spain)

The pollution of agricultural land due to herbicides was assessed in the Guare?a and Almar river basins, situated in the provinces of Zamora and Salamanca (Spain). A set of fifteen herbicides, including triazines, ureas, amides and others, was selected owing to their frequency of use, the amounts used, their toxicity and their persistence in the environment. Solid-phase extraction with polymeric cartridges, followed by HPLC with diode-array detection, were used to monitor the herbicides. This technique was chosen owing to the wide range of functionality and polarity of the analytes under study. The detection limits obtained were in the 0.004-0.025 microg/l range (lambda=220 nm). Surface and ground waters, taken from different locations in the basins, were analyzed over a 6-month period. The presence of six out of the fifteen herbicides monitored--chlortoluron, atrazine, terbutryn, alachlor, diflufenican and fluazifop-butyl--was detected in several samples at levels ranging from the detection limit to 1.2 microg/l. The relationship of these herbicides to the agricultural activities of the zone is discussed.     

Preparation of new monoanionic "scorpionate" ligands: synthesis and structural characterization of titanium(IV) complexes bearing this class of ligand

The preparation of new "scorpionate" ligands in the form of the lithium derivatives [(Li(bdmpzdta)(H(2)O))(4)] (1) [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], [Li(bdphpza)(H(2)O)(THF)] (2) [bdphpza = bis(3,5-diphenylpyrazol-1-yl)acetate], and [Li(bdphpzdta)(H(2)O)(THF)] (3) [bdphpzdta = bis(3,5-diphenylpyrazol-1-yl)dithioacetate] has been carried out. Furthermore, a series of titanium complexes has been prepared by reaction of TiCl(4)(THF)(2) with the lithium reagents [(Li(bdmpza)(H(2)O))(4)] (4) [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] and 1. Under the appropriate experimental conditions neutral complexes, namely [TiCl(3)(kappa(3)-bdmpza)] (5), [TiCl(3)(kappa(3)-bdmpzdta)] (6), and [TiCl(2)(kappa(2)-bdmpzdta)(2)] (7), and cationic complexes, namely [TiCl(2)(THF)(kappa(3)-bdmpza)]Cl (8) and [TiCl(2)(THF)(kappa(3)-bdmpzdta)]Cl (9), were isolated. Complexes 8 and 9 undergo an interesting nucleophilic THF ring-opening reaction to give the corresponding alkoxide-containing species [TiCl(2)(kappa(3)-bdmpza)(O(CH(2))(4)Cl)] (10) and [TiCl(2)(kappa(3)-bdmpzdta)(O(CH(2))(4)Cl)] (11). A family of alkoxide-containing complexes of general formulas [TiCl(2)(kappa(3)-bdmpza)(OR)] [R = Me (12); R = Et (14); R = (i)Pr (16); R = (t)Bu (18)] and [TiCl(2)(kappa(3)-bdmpzdta)(OR)] [R = Me (13); R = Et (15); R = (i)Pr (17)] was also prepared. The structures of these complexes have been determined by spectroscopic methods, and in addition, the X-ray crystal structures of 3, 7, 10, and 11 were also established.     

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.     

Role of anions on the crystal structures of copper(II) and zinc(II) complexes of a tunable butterfly cyclophane macrocycle

Three crystal structures of a ditopic cyclophane ligand (L) in which two 1,5,8,12-tetraamine molecules have been attached through methylene spacers to the ortho positions of a benzene ring are reported. The first one (1) corresponds to the tetraprotonated free macrocycle (H4L4+) having two tetrachlorozincate(II) counteranions (C24H54O2N8Cl8Zn2, a = 9.1890(2) A, b = 14.0120(3) A, c = 15.3180(3) A, alpha = 89.2320(7) degrees , beta = 82.0740(6) degrees , gamma = 83.017(1) degrees , Z = 2.00, triclinic, P); the second one (2) is of a binuclear Cu2+ complex having coordinated chloride anions and perchlorate counteranions (C24H58O14N8Cl4Cu2 a = 9.9380(2) A, b = 30.2470(6) A, c = 53.143(1) A, orthorhombic, F2dd, Z = 18), and the third one (3) corresponds to an analogous Zn2+ complex that has been crystallized using triflate as counteranion (C26H(51.2)O(6.6)N8Cl2F6S2Zn2 a = 8.472(5) A, b = 9.310(5), c = 13.745(5) A, alpha = 84.262(5) degrees , beta = 77.490(5) degrees , gamma = 73.557(5) degrees , triclinic, P, Z = 2). The analysis of the crystallographic data clearly shows that the conformation of the macrocycle and, in consequence, the overall architecture of the crystals are controlled by the anions present in the moiety, pi-pi-stacking associations, and hydrogen bonding interactions. The protonation and stability constants for the formation of the Cu2+ and Zn2+ complexes in aqueous solution have been determined potentiometrically in 0.15 mol dm(-3) NaClO4 at 298.1 K. Intramolecular hydrogen bonding defines the protonation behavior of the compound. Positive cooperativity is observed in the formation of the Cu2+ complexes.