Bioaccumulation study of acrylates in algae (<Emphasis Type="Italic">Chlorella kessleri</Emphasis>) by Py-GC and Py-GC/MS

Acrylate monomers methylmethacrylate (MMA) and cyclohexylmethacrylate (CHMA) bioaccumulation has been determined in aquatic organism, algae (Chlorella kessleri). Algae were collected in amount of 0.4 mg and directly injected to the pyrolytical cell. In algae bodies accumulated monomers were analysed by pyrolysis gas chromatography (Py-GC) and pyrolysis gas chromatography coupled with mass spectrometry (Py-GC/MS). Traces of the accumulated monomers in algae body can be determined after 1-, 2-, 3-weeks of incubation. Maximum content of MMA was determined after 3-week of experiment, contrariwise in the case of CHMA after 2-week exposition. Relationship with pyrolysis temperature has also been studied.     

The potential of inductively coupled plasma-mass spectrometric detection for capillary electrophoretic analysis of pesticides

In this work, the potential of inductively coupled plasma-mass spectrometry (ICP-MS) coupled to capillary electrophoresis (CE) to determine organophosphorus pesticides (OPPs) is demonstrated. Element specific detection of (31)P with ICP-MS is performed for the detection of OPPs. Three common OPPs, including glyphosate, glufosinate, and aminomethylphosphonic acid (AMPA), were analyzed by CE-ICP-MS to demonstrate its applicability for the analysis of OPPs. The advantages of using ICP-MS with respect to other common detectors, such as flame photometric detection (FPD), for CE analysis of OPPs are shown. Additionally, different CE separation conditions were studied to achieve complete baseline separation of the pesticide compounds in short migration times. Two CE buffer systems were evaluated for the separation of OPPs using ICP-MS detection. A buffer solution containing 40 mmol.L(-1) ammonium acetate at pH 9.0 and an applied voltage of +20 kV were finally selected leading to a separation time of 10.0 min. Both migration time and area relative standard deviations (%RSD) were evaluated and their respective values were in the intervals of 1.1-3.3% and 2.7-5.3%. Detection limits obtained with the CE-ICP-MS system were in the range of 0.11-0.19 mg.L(-1) (as compound) yielding an enhancement of 130- to 230-fold with respect to FPD. The proposed methodology was finally applied for the determination of the OPPs mentioned above in natural river water samples.     

Low-valent cobalt complexes with three different pi acceptor ligands: experimental and DFT studies of the reduced and the low-lying excited states of (R-DAB)Co(NO)(CO), R-DAB = substituted 1,4-diaza-1,4-butadiene

The complexes (RN=CH-CH=NR)Co(NO)(CO) with R = isopropyl, 2,6-diisopropylphenyl, or p-tolyl are chemically and electrochemically reducible to radical anions at potentials which strongly depend on R. The DFT calculated structure for the neutral compound with R = iPr agrees with the experiment, and the computed structure of the anion radical reveals changes according to a reduction of the R-DAB ligand. EPR results confirm an (R-DAB)-based singly occupied molecular orbital in [(RNCHCHNR)Co(NO)(CO)](.-), with minor but detectable contributions from NO as supported by IR spectroelectrochemistry and as quantified by DFT spin density calculations. The calculations indicate increasingly stabilized CO, NO, and RNCHCHNR pi* acceptor orbitals, in that order. On the basis of TD-DFT (time-dependent density functional theory) calculations, the lowest-lying excited states are assigned to metal-to-(R-DAB) charge transfer transitions while bands due to the metal-to-nitrosyl charge transfer occur at higher energies but still in the visible region. Resonance Raman studies were used to probe these assignments.     

A molecular mechanics study of the effect of substitution in position 1 on the conformational space of the oxytocin/vasopressin ring

Summary The effect of the substitution in position 1 on the low-energy conformations of the oxytocin/vasopressin 20-membered ring was investigated by means of molecular mechanics. Three representative substitutions were considered: -mercapto-,-dimethyl)propionic acid (Dmp), (-mercapto-,-cyclopentamethylene)propionic acid (Cpp), both forming strong antagonists, and (,-dimethyl--mercapto)propionic acid (-Dmp), forming analogs of strongly reduced biological activity, with the -mercaptopropionic (Mpa) residue taken as reference. Both ECEPP/2 (rigid valence geometry) and AMBER (flexible valence geometry) force fields were employed in the calculations. Three basic types of backbone conformations were taken into account which are distinguished by the type of -turn at residues 3 and 4: 1/III, II, and I/III, all types containing one or two intra-annular hydrogen bonds. The allowed (ring-closed) disulfide-bridge conformations were searched by an algorithm formulated in terms of scanning the disulfide-bridge torsional angle C-S-S-C. The ECEPP/2 and AMBER energies of the obtained conformations were found to be in reasonable agreement. Two of the low-energy conformers of the [Mpa¹]-compound agreed very well with the cyclic part of the two conformers found in the crystal structure of [Mpa¹]-oxytocin. An analysis of the effect of -substitution on relative energies showed that the conformations with the N-C-CH₂-CH₂ (₁) and C-CH₂-CH₂-S (₁) angles of the first residue around (–100°, 60°) and (100°, –60°) are not affected; this in most cases implies a left-handed disulfide bridge. In the case of -substitution the allowed values of ₁ are close to ± 60°. This requirement, being in contradiction to the one concerning -substitution, could explain the very low biological activity of the -substituted analogs. The conformational preferences of substituted compounds can largely be explained by the analysis of local interactions within the first residue. Based on the selection of the conformations which are low in energy for both the reference and -substituted compounds, two distinct types of possible binding conformations were proposed, the first one being similar to the crystal conformer with a left-handed disulfide bridge, the second one having a right-handed bridge, but a geometry different from that of the crystal conformer with the right-handed bridge. The first type of disulfide-bridge arrangement is equally favorable for both I/III and II types of backbone structure, while the second one is allowed only for the II type of backbone. No conformation of the I/III type has a low enough energy to be considered as a possible binding conformation for all of the active compounds studied in this work.     

Ring-chain-transformations : Synthesis of ω-functionalized alkylthio-1,2,4-triazoles by reaction of cyclic S-analogous N-cyano or N-aroylcarbonimidoesters with hydrazines

Cyclic N-cyanocarbonimidodithioesters 4 or N-aroylcarbonimidothioic acid esters 10 react regioselectively with arylhydrazines and methylhydrazine by a ring chain transformation reaction forming ω-functionalized 3-alkylthio-1,2,4-triazoles 8 and 11 or 5-alkylthio-1,2,4-triazoles 9 .     

Synthesis of 3‐(Pyridin‐4‐Ylmethyl)‐4‐Substituted‐1,2,4‐Triazoline‐5‐Thione

The reaction of the hydrazide of pyridine‐4‐acetic acid with isothiocyanate gave thiosemicarbazide derivatives respectively. Further cyclization with 2% NaOH led to the formation of 4‐substituted 3‐(pyridin‐4‐ylmethyl)‐1,2,4‐triazoline‐5‐thione and 3‐(pyridin‐4‐ylmethyl)‐1,2,4‐triazoline‐5‐thione. The structures of all new products were confirmed by analytical and spectroscopic methods.     

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol⁻¹ over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale.     

Solubility of Solid 2-Methyl-1,3-butadiene (Isoprene) in Liquid Argon and Nitrogen at the Standard Boiling Points of the Solvents

The solubility of solid 2-methyl-1,3-butadiene (isoprene) in liquid argon at a temperature of 87.3 K and in liquid nitrogen at 77.4 K has been measured by the filtration method. The hydrocarbon contents in solutions were determined using gas chromatography. GC–MS was used to identify impurities in the solute. The experimental value of the mole fraction solubility of solid isoprene in liquid argon at 87.3 K is (1.41 ± 0.27) × 10^–6 and (1.56 ± 0.36) × 10^–7 in liquid nitrogen at 77.4 K. The Preston–Prausnitz method was used for calculation of the solubilities of solid hydrocarbon in liquid argon in the temperature range 84.0–110.0 K and in liquid nitrogen from 64.0 to 90.0 K. The solvent–solute interaction parameters l ₁₂ were also calculated. At 90.0 K liquid argon is a better solvent for isoprene than is liquid nitrogen. The experimental values of the solubilities of isoprene in liquid argon and nitrogen were compared with results obtained for selected unsaturated and aromatic hydrocarbons.     

Speciation of cationic selenium compounds in Brassica juncea leaves by strong cation-exchange chromatography with inductively coupled plasma mass spectrometry

Strong cation-exchange chromatography (SCX-HPLC) was used in conjunction with inductively coupled plasma mass spectrometry (ICP-MS) to investigate cationic selenium species present in leaf extract of wild-type Brassica juncea supplemented with selenite. Total amount of Se accumulated by the leaves was found to be 352 microg g(-1). Cation-exchange solid-phase extraction (SCX-SPE) was used to pre-concentrate the cationic species present in the leaf extract. Methylselenomethionine (MeSeMet) and dimethylselenoniumproprionate (DMSeP) were synthesized and characterized by electrospray quadrupole time-of-flight MS (ESI-QTOF-MS). Laboratory synthesized and commercially available standards were used in chromatographic studies to identify the Se species in the leaf extract through retention time comparisons and standard addition method. Major cationic selenium species identified in the present study were MeSeMet and methylselenocysteine (MeSeCys) while selenomethionine (SeMet) was found in minor quantities.     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).