Continuous Ultrasound-Assisted Leaching of Phenoxyacid Herbicides in Soil and Sediment with in-situ Sample Treatment

Summary Ultrasound, water and Na₂EDTA·2H₂O have been used for continuous leaching with in-situ sample treatment of acid herbicides (namely, bentazone, 2,4-D, trichlopyr, 2,4,5-T and 2,4,5-Tp) from different types of soil (namely, clayey, slimy, sandy, organic and limy) and one sediment. The subsequent steps for quantitation of the leached analytes (namely, preconcentration, individual chromatographic separation and UV detection) were performed using a flow injection manifold that permits automation of the overall process. The main factors contributing to the leaching efficiency—namely, ultrasound radiation amplitude, probe position, percentage of duty cycle of ultrasound exposure, extractant flow-rate and temperature of the water bath in which the extraction cell is immersed—were optimized by means of a central composite design. Also, the kinetics of the leaching step with Na₂EDTA·2H₂O was studied. In all cases, the recoveries of the target analytes were higher than 92%. The detection and quantification limits were 10 and 30 ng g^–1, respectively, for all analytes, but trichlopyr (detection and quantification limits 5 and 12 ng g^–1, respectively). The relative standard deviations for repeatability range between 2.8–5.3%.     

Preparation and characterization of molybdenum and tungsten compounds with diazabutadiene ligands constructed from amino esters and glyoxal: Crystal structures of meso and C2-symmetric isomers of Mo(CO)4(dab-asp(OMe)-OMe)

The title compounds were prepared by heating solutions of ester protected amino acids (H-l-Ala-OEt, H-β-Ala-OEt, H-l-Val-OMe, GABA-OMe, H-l-Asp(OMe)-OMe) and glyoxal in the presence of M(CO)₄(pip)₂ (M=Mo, W). The resulting novel complexes, M(CO)₄(dab-xxx-OR) (dab=diazabutadiene), contain an N,N′-diimine ligand and were characterized by ¹H- and ¹³C-NMR, IR, and UV-vis measurements. The low energy band in the visible portion of the electronic spectrum is assigned to a MLCT transition and exhibits solvatochromism. The valine, alanine and aspartic ester derivatives have C₂ symmetry resulting from the C₂ symmetry of the ligand. The reaction of the alanine and aspartic amino esters in the presence of NEt₃ produces diastereomeric mixtures caused by racemization at the amino acid α-carbon. Racemization is not observed during the formation of the valine derivatives. The crystal structures of (R,S)-Mo(CO)₄(dab-asp(OMe)-OMe) (5-RS), and (S,S)-Mo(CO)₄(dab-asp(OMe)-OMe) (5-SS), were determined. The structure of 5-RS confirms that racemization at the α-carbon occurred. 5-SS has C₂ symmetry.     

The Stereostructure of Porphyra‐334: An Experimental and Calculational NMR Investigation. Evidence for an Efficient ‘Proton Sponge’

The mycosporine‐like amino acid (MAA) porphyra‐334 ( 1 ) is subjected to extensive ¹H‐ and ¹³C‐NMR analysis as well as to density‐functional‐theory (DFT) calculations. All ¹H‐ and ¹³C‐NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500‐MHz standard COSY, HMQC, and HMBC experiments, as well as by one‐dimensional (DPFGSE‐NOE) and two‐dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D₂O solution. DFT Calculations yield ¹³C‐NMR chemical shifts which are in good agreement for species 6 which is the imino N‐protonated form of 1 . An exceptionally high proton affinity of 265.7 kcal/mol is calculated for 1 , indicating that 1 may behave as a very powerful ‘proton sponge’ of comparable strength as synthetic systems studied so far. Predictions of ¹³C‐NMR chemical shifts by the ‘NMRPredict’ software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine‐glycine 16 . This supports the assumption that 1 is biochemically derived from 3,3‐O‐didehydroquinic acid ( 17 ). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study.     

4-Aminobicyclo[2.2.2]octan-2-ones and -ols <Emphasis Type="Italic">via</Emphasis> Enamine Intermediates

Summary. The synthesis of new bicyclo[2.2.2]octane derivatives is described and their structures were established by NMR experiments. All compounds were tested in in vitro assays for their activities against causative organisms of malaria and African sleeping sickness and compared to those of former synthesized compounds.     

Synthesis of pure stereoisomers of benzo[b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activity

Several benzo[b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-(tert-butoxycarbonyl)-β-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N,N-bis-(tert-butoxycarbonyl)-(Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh₃)₄, Na₂CO₃, DME/H₂O] with several boronic benzo[b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl₂(PPh₃)₂. A model dipeptide was prepared coupling a benzo[b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the β, β-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria (B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.     

Acid and redox properties of mixed oxides prepared by calcination of chromate-containing layered double hydroxides

Layered double hydroxides (LDHs) with Mg and Al in the layers and carbonate, nitrate or chloride in the interlayer, or with Zn and Al in the layers and chloride in the interlayer, have been prepared by coprecipitation, and have been used as precursors to prepare chromate-containing LDHs. All these systems, as well as those obtained upon their calcination up to 800 °C, have been characterised by powder X-ray diffraction, FT-IR and vis-UV spectroscopies, temperature-programmed reduction (TPR), nitrogen adsorption at −196 °C for surface texture and porosity assessment, and FT-IR monitoring of pyridine adsorption for surface acidity determination. The results obtained show that the crystallinity of the chromate-containing LDH depends on the precursor used. The layered structure of the Mg, Al systems is stabilised up to 400 °C upon incorporation of chromate; however, the Zn,Al-chromate samples collapse between 200 and 300 °C, with simultaneous formation of ZnO. Calcination of the samples above 400 °C gives rise to a reduction of Cr(VI) to Cr(III), as concluded from vis-UV spectroscopic studies. The TPR profiles show that chromate in ZnAl hydrotalcite is more easily reduced than that incorporated in the magnesium ones. Moderately strong surface Lewis acid sites exist in all samples calcined below 500 °C.     

Aromaticity in azlactone anions and its significance for the Erlenmeyer synthesis

Azlactone anions—the key intermediates in the classical Erlenmeyer synthesis of amino acids—apparently possess aromatic stabilization, as indicated by the relative rate of base catalyzed deuterium exchange in the following analogs: 1-methyl-2-phenyl-5(4H)-imidazolone > 2-phenyl-5(4H)-oxazolone (azlactone) > 3,3-dimethyl-2-phenyl-4(3H)-pyrrolone. This is paralleled by the relative rate of condensation of these compounds with hexadeuteroacetone. Reported pK_a data also suggest that the azlactone products of the Erlenmeyer synthesis are analogs of the fulvenes.     

Analysis of amino acids in individual human erythrocytes by capillary electrophoresis with electroporation for intracellular derivatization and laser-induced fluorescence detection

A method for monitoring amino acids in single erythrocytes is described. For intracellular derivatization, reagent fluorescein isothiocyanate (FITC) was introduced into living cells by electroporation. For an 8 microm erythrocyte, the analytes were diluted by a factor of only 1.6. After completion of the derivatization reaction, a single cell was injected into the separation capillary tip and lysed there. The derivatized amino acids were separated by capillary electrophoresis, followed by laser-induced fluorescence detection. Nine amino acids were quantitatively determined, with amounts of amino acids ranging from 3.8-32 amol/single cell.     

Determination of amino acid enantiomers in orange juices by chiral phase capillary gas chromatography

Summary The configurations of free amino acids (AAs) in orange juice beverages (commercial products of satisfactory and unsatisfactory quality), an orange juice concentrate (bulk product suspected of being adulterated), and in an orange juice that has been contaminated by addition ofLactobacillus plantarum as a model for microbial spoilage, were determined, after derivatization, by means of gas-liquid chromatography (GC) using fused-silica capillary columns coated with Chirasil-L-Val or Chirasil-D-Val as stationary phases. AAs were isolated from juices by treatment with Dowex WX8 ion-exchanger and were investigated, by GC, as theirN(O)-pentafluoropropionylorN(O)-trifluoroacetyl 1-propyl esters. It was found that the high quality orange juice beverage contained L-AAs exclusively whereas this juice, after fermentation withLactobacillus, contained free D-Ala (32.7%), D-Val (62.3%), D-Phe (20.0%), D-Glu (24.3%), D-Ser (2.6%), D-Asp (0.8%), and significant amounts of D-Pro [% D=100 D/(D+L)]. D-Ala (8.8%) and D-Ser (4.2%) were found in a sensory and analytically unsatisfactory orange juice beverage, whilst D-Ala (27.5%) and D-Ser (14.3%) were detected in the orange juice concentrate suspected of being adulterated.Although capillary GC on chiral stationary phases is regarded as being highly suitable for the determination of AA enantiomers in fruit juice beverages, detection of D-AAs is currently not considered as conclusive proof of fruit juice adulteration caused by addition of AA racemates since a non-microbial origin of D-AAs in the respective juice, or an original occurrence of D-AAs, in either the free, substituted, or peptide-bonded form in the fruits, cannot be excluded with certainty.Presented in part at the Deutscher Lebensmittelchemikertag, Sept. 18–21, 1990, Frankfurt and at the 14. Jahrestagung Deutscher Lebensmitteltechnologen, Nov. 15–17, 1990, Düsseldorf.     

Capillary gas chromatographic analysis of amino acids in geological environments with electron capture detection

Studies have been performed on the analysis of 21 amino acids using a fused-silica open tubular (FSOT) capillary column, and electron-capture detection (ECD) or flame-ionization detection (FID). It was shown with the N(O)-heptafluorobutyryl (HFB) amino acid isobutyl esters that the ECD response was several hundred times more sensitive than the FID response. The relative standard deviation (RSD) of retention relative to norleucine is determined with the ECD. RSD values for all N(O)-HFB amino acid isobutyl esters are relatively small (≦ 0.5%). This method has been successfully applied to trace analysis of most of the amino acids from fossil brachiopods and black shales.