Multi-residue screening of pesticides in vegetables,fruits and baby food by stir bar sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

The performance of stir bar sorptive extraction (SBSE) for the enrichment of pesticides from vegetables, fruits and baby food samples is discussed. After extraction with methanol, an aliquot is diluted with water and SBSE is performed for 60 min. By applying a new thermal desorption unit (TDU), fully automated and unattended desorption of 98 stir bars is feasible, making SBSE very cost-effective. The presence of pesticide residues is elucidated with the retention time locked gas chromatography–mass spectroscopy method (RTL-capillary GC–MS). With SBSE–RTL-capillary GC–MS operated in the scan mode, more than 300 pesticides can be monitored in vegetables, fruits and baby food. The multi-residue method (MRM) described provides detectabilities from the mg/kg (ppm) to the sub-μg/kg (ppb) level, thereby complying with the maximum residue levels (MRLs) set by regulatory organizations for pesticides in different matrices. Several examples, i.e. pesticide residues in lettuce, pears, grapes and baby food, illustrate the potential of SBSE–RTL-capillary GC–MS.     

Development of continuous surfactin production from potato process effluent by Bacillus subtilis in an airlift reactor

The biosurfactant surfactin has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin can be produced from an inexpensive low-solids (LS) potato process effluent with minimal amendments or pretreatments. Previous research has also shown that 95% or more of the surfactin in Bacillus subtilis cultures can be recovered by foam fractionation. In this work, we present the results of research to integrate surfactin production with foam fractionation. Experiments were performed in an airlift reactor, with continuous collection of the foam through a tube at the top of the column. Preliminary results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent may hamper continuous surfactin production.     

Ile, Leu, and Val methyl assignments of the 723-residue malate synthase G using a new labeling strategy and novel NMR methods

New NMR experiments are presented for the assignment of methyl (13)C and (1)H chemical shifts from Ile, Leu, and Val residues in high molecular weight proteins. The first class of pulse schemes transfers magnetization from the methyl group to the backbone amide spins for detection, while the second more sensitive class uses an "out-and-back" transfer scheme in which side-chain carbons or backbone carbonyls are correlated with methyl (13)C and (1)H spins. Both groups of experiments benefit from a new isotopic labeling scheme for protonation of Leu and Val methyl groups in large deuterated proteins. The approach makes use of alpha-ketoisovalerate that is (13)C-labeled and protonated in one of its methyl groups ((13)CH(3)), while the other methyl is (12)CD(3). The use of this biosynthetic precursor leads to production of Leu and Val residues that are (13)CH(3)-labeled at only a single methyl position. Although this labeling pattern effectively reduces by 2-fold the concentration of Leu and Val methyls in NMR samples, it ensures linearity of Val and Leu side-chain (13)C spin-systems, leading to higher sensitivity and, for certain classes of experiments, substantial simplification of NMR spectra. Very near complete assignments of the 276 Ile (delta 1 only), Leu, and Val methyl groups in the single-chain 723-residue enzyme malate synthase G (MSG, molecular tumbling time 37 +/- 2 ns at 37 degrees C) have been obtained using the proposed isotopic labeling strategy in combination with the new NMR experiments.     

[Re(η2-CS3)4]3−, a new trithiocarbonate-containing rhenium(V) dodecahedral anion

The mononuclear complex (NMe₄)₃[Re(²-CS₃)₄] has been prepared by adding CS₂ to ReS^– ₄ in a mixture of MeOH and NH₃. During the reaction, Re^VII is reduced to Re^V, the measured diamagnetism (X = –3.04 × 10^–4cm³mol^–1) of the complex showing that the two added electrons are coupled. (NMe₄)₃[Re(²-CS₃)₄] crystallizes in the space group Fddd, a = 11.985(4) Å, b = 23.001(11) Å, c = 47.463(19) Å, V = 13085(9) ų. The reaction of CS₂ results in the formation of trithiocarbonates bonded to the rhenium in a dodecahedral geometry.     

Mono- and dinuclear palladium(II) compounds containing nitrogen ligands. Crystal and molecular structure of [Pd(N,C-dmba)(NCO)(2,3-lut)] and [Pd(H2CCOMe)Cl(2,2′-bipy)]

The cyanate-bridged cyclopalladated compound [Pd(N,C-dmba)(-NCO)]₂ (1)(dmba = PhCH₂NMe₂) reacts in CH₂Cl₂ with 2,3-lutidine (2,3-lut), 3,4-lutidine (3,4-lut), 2,2-bipyridine (2,2-bipy) and 4,4-bipyridine (4,4-bipy), to give [Pd(N,C-dmba)(NCO)(2,3-lut)](2), [Pd(N,C-dmba)(NCO)(3,4-lut)](3), [{Pd(N,C-dmba)(NCO)}₂(-2,2-bipy)]· CH₂Cl₂ (4) and [{Pd(N,C-dmba)(NCO)}₂(-4,4-bipy)]· CH₂Cl₂ (5), respectively. The compounds were characterized by elemental analysis, i.r. and n.m.r. spectroscopy and also by t.g.a. The i.r. spectra of (2–5) display typical bands of monodentate N-bonded cyanate groups, whereas the n.m.r. data of (4) are consistent with the presence of a bridging 2,2-bipyridine ligand. Complex (4) decomposes slowly in acetone. One of the products formed, [Pd(H₂CCOMe)Cl(2,2-bipy)](6), was characterized by X-ray diffraction. As inferred from the t.g.a., the thermal stability decreases in the order:[{Pd(N,C-dmba)(NCO)}₂(-4,4-bipy)].CH₂Cl₂ (5) > [Pd(N,C-dmba)(2,3-lut)(NCO)](2)=[Pd(N,C-dmba)(3,4-lut)(NCO)](3) > [{Pd(N,C-dmba)(NCO)}₂(-2,2-bipy)]· CH₂Cl₂ (4). According to thermal analysis and X-ray diffraction patterns compounds (2–3) decompose into metallic palladium Pd(0), whereas (4–5) decompose with the formation of PdO. The X-ray crystal and molecular structure of [Pd(N,C-dmba)(NCO)(2,3-lut)](2) was determined. The lutidine unit is perpendicular to the coordination plane.     

Metallation reactions. XXXIV. Synthesis of 2‐(1‐hydroxy‐1‐arylethyl)‐1,3‐benzoxathiol‐3‐oxide derivatives

The reaction of benzoxathiole‐3‐oxide with lithiumdiisopropylamide in tetrahydrofuran gave an anion, which was reacted with various aryl‐methyl‐ketones to give 2‐(1‐hydroxy‐1‐arylethyl)‐1,3‐benzoxathiol‐3‐oxide derivatives. The reaction was carried out in different temperature conditions: at ‐88 °C the trans addition stereoisomers to the sulfoxide oxygen atom were the main products.     

1,4‐Di(isopropyl)‐1,4‐diazabutadien als Abfangreagenz für monomere Bruchstücke des Tetragalliumclusters Ga4[C(SiMe3)3]4 – Bildung eines ungesättigten GaN2C2‐Heterocyclus und eines Oxidationsprodukts mit Ga‐O‐O‐Ga‐Gruppe

1,4‐Di(isopropyl)‐1,4‐diazabutadiene as a Reagent for the Trapping of Monomeric Fragments of the Tetragalliumcluster Ga₄[C(SiMe₃)₃]₄ – Formation of an Unsaturated GaN₂C₂ Heterocycle and an Oxidation Product Containing a Ga‐O‐O‐Ga Group The tetrahedral tetragallium cluster Ga₄[C(SiMe₃)₃]₄ ( 1 ) dissociates upon dissolution to yield the monomeric fragments Ga‐R [R = C(SiMe₃)₃]. These monomers could be trapped now by the treatment of their solutions with 1,4‐di(isopropyl)‐1,4‐diazabutadiene. The product of the cycloaddition reaction ( 2 ) possesses a five‐membered GaN₂C₂ heterocycle with a coordinatively unsaturated gallium atom and an endocyclic C=C double bond. 2 is rather sensitive towards oxidation by traces of air. The contact with oxygen yielded a digallium peroxide [(C₂N₂iPr₂)RGa‐O‐O‐GaR(C₂N₂iPr₂)] ( 3 ) which was isolated in a very low yield only and which has a gallium atom attached to each oxygen atom of the inner peroxo group. Both chelating ligands of 3 possess an unpaired electron.     

Flavour analysis of Greek white wine by solid-phase microextraction-capillary gas chromatography-mass spectrometry

Solid-phase microextraction (SPME) was optimised for the qualitative determination of the volatile flavour compounds responsible for the aroma of Greek Boutari wine. Several factors influencing the equilibrium of the aroma compounds between the sample and the SPME fiber were taken into account, including the extraction time, the extraction temperature, the sampling mode (headspace and direct immersion or liquid SPME), and the presence of salt. Four different SPME fibers were used in this study. namely poly(dimethylsiloxane) (PDMS), poly(acrylate), carbowax-divinylbenzene and divinylbenzene-carboxen on poly(dimethylsiloxane). The best results were obtained using the PDMS fiber during headspace extraction at 25 degrees C for 30 min after saturating the samples with salt. The optimised SPME method was then applied to investigate the qualitative aroma composition of three other Greek wines, namely Zitsa, Limnos and Filoni.     

Solvolysis of 1,1-dimethyl-4-alkenyl chlorides: evidence for pi-participation

Tertiary 1,1-dimethyl-4-alkenyl chloride (1) solvolyzes with significantly reduced secondary beta-deuterium kinetic isotope effect (substrate with two trideuteromethyl groups) and has a lower entropy and enthalpy of activation than the referent saturated analogue 4 (k(H)/k(D) = 1.30 +/- 0.03 vs k(H)/k(D) = 1.79 +/- 0.01; Delta Delta H(++) = -9 kJ mol(-1), Delta Delta S(++) = -36 J mol(-1) K(-1), in 80% v/v aqueous ethanol), indicating participation of the double bond in the rate-determining step. Transition structure 1-TS computed at the MP2(fc)/6-31G(d) level of theory revealed that the reaction proceeds through a late transition state with considerably pronounced double bond participation and a substantially cleaved C-Cl bond. The doubly unsaturated compound 3 (1,1-dimethyl-4,8-alkadienyl chloride) solvolyzes with further reduction of the isotope effect, and a drastically lower entropy of activation (k(H)/k(D) = 1.14 +/- 0.01; DeltaS(++) = -152 +/- 12 J mol(-1) K(-1), in 80% v/v aqueous ethanol), suggesting that the solvolysis of 3 proceeds by way of extended pi-participation, i.e., the assistance of both double bonds in the rate-determining step.     

Medium calcium concentration determines keratin intermediate filament density and distribution in immortalized cultured thymic epithelial cells (TECs).

Isolation and culture of thymic epithelial cells (TECs) using conventional primary tissue culture techniques under conditions employing supplemented low calcium medium yielded an immortalized cell line derived from the LDA rat (Lewis [Rt1l] cross DA [Rt1a]) that could be manipulated in vitro. Thymi were harvested from 4-5-day-old neonates, enzymically digested using collagenase (1 mg/ml, 37 degrees C, 1 h) and cultured in low calcium WAJC404A medium containing cholera toxin (20 ng/ml), dexamethasone (10 nM), epidermal growth factor (10 ng/ml), insulin (10 mug/ml), transferrin (10 mug/ml), 2% calf serum, 2.5% Dulbecco's Modified Eagle's Medium (DMEM), and 1% antibiotic/antimycotic. TECs cultured in low calcium displayed round to spindle-shaped morphology, distinct intercellular spaces (even at confluence), and dense reticular-like keratin patterns. In high calcium (0.188 mM), TECs formed cobblestone-like confluent monolayers that were resistant to trypsinization (0.05%) and displayed keratin intermediate filaments concentrated at desmosomal junctions between contiguous cells. Changes in cultured TEC morphology were quantified by an analysis of desmosome/membrane relationships in high and low calcium media. Desmosomes were significantly increased in the high calcium medium. These studies may have value when considering the growth conditions of cultured primary cell lines like TECs.