Headspace solvent microextraction of trihalomethane compounds into a single drop

Headspace solvent microextraction (HSME) into a single drop is developed for the determination of six trihalomethanes, CH2Cl2, CHCl3, C4H9Cl, CCl4, C2HCl3, and C2Cl4, in aqueous solution. A drop of benzyl alcohol containing bromoform, as an internal standard, is used for extraction. The analytes are extracted by suspending a 3-microL drop directly from the needle of a microsyringe. The needle passes through the septum of a vessel, and the needle tip appears above the surface of the solution. After the prescribed extraction time, the drop is drawn back into the syringe. The syringe is then removed, and its content is injected directly into a gas chromatography column for analysis. The main parameters affecting the HSME process, such as stirring speed, microdrop volume, sample solution temperature, microsyringe needle temperature, sample volume, solution pH, extracting solvent, and ionic strength of the solution, are studied. Also, the linear range and precision of the method are examined.     

Simultaneous determination of cobalt, nickel and palladium in micellar media using partial least square regression and direct orthogonal signal correction

A simple, novel and sensitive spectrophotometric method was described for the simultaneous determination of cobalt, nickel and palladium. The method is based on the complex formation of Co, Ni and Pd with 1-(2-pyridylazo)-2-naphtol (PAN) in Tween-80 micellar media. All factors affecting on the sensitivity were optimized and the linear dynamic range for determination of Co, Ni and Pd was found. The experimental calibration matrix was designed by measuring the absorbance over the range of 520-700 nm for 21 samples of 0.10-1.0, 0.050-0.50 and 0.050-4.0 microg ml(-1) of Co, Ni and Pd, respectively. The partial least square (PLS) modeling based on singular value decomposition (SVD) was used for the multivariate calibration of the spectrophotometric data. The direct orthogonal signal correction was used for pre-processing of data matrices and the prediction results of model, with and without using direct orthogonal signal correction, were statistically compared. The effects of various anions and cations on selectivity of the method were investigated. The proposed method was successfully applied to the determination of Co, Ni and Pd in water and alloy samples.     

Complexation of palladium cyanide with imidazolidine-2-thione and its derivatives

Summary Pd(CN)₂ reacts with imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione(Diaz), 1,3-diazipnane-2-thione (Diap) and their derivatives to yield complexes of stoichiometry [PdL₂(CN)₂] or [PdL(CN)₂] (L = Imt, Diaz or Diap and L = Imt having N-Me, Et or Pr substituents), which were characterized by elemental analysis, i.r., ¹H and ¹³C n.m.r. spectroscopy. Both mono- and bis ligand complexes are thought to be square planar with the monoligand binding to metal via sulphur (bridging) and the bis ligand via the monodentate thione group. The ¹³C enriched Pd(¹³CN)₂ complex was prepared and the ¹³C n.m.r. recorded. The C-2 resonance of ¹³C n.m.r. of Imt, Diaz or Diap complexes of the copper(I), silver(I), gold(I) and palladium(II) were compared.     

Fine-tuning water exchange on Gd(III) poly(amino carboxylates) by modulation of steric crowding

In the objective of optimizing water exchange rate on stable, nine-coordinate, monohydrated Gd(III) poly(amino carboxylate) complexes, we have prepared monopropionate derivatives of DOTA4- (DO3A-Nprop4-) and DTPA5- (DTTA-Nprop5-). A novel ligand, EPTPA-BAA(3-), the bisamylamide derivative of ethylenepropylenetriamine-pentaacetate (EPTPA5-) was also synthesized. A variable temperature 17O NMR study has been performed on their Gd(III) complexes, which, for [Gd(DTTA-Nprop)(H2O)]2- and [Gd(EPTPA-BAA)(H2O)] has been combined with multiple field EPR and NMRD measurements. The water exchange rates, k(ex)(298), are 8.0 x 10(7) s(-1), 6.1 x 10(7) s(-1) and 5.7 x 10(7) s(-1) for [Gd(DTTA-Nprop)(H2O)]2-, [Gd(DO3A-Nprop)(H2O)]- and [Gd(EPTPA-BAA)(H2O)], respectively, all in the narrow optimal range to attain maximum proton relaxivities, provided the other parameters (electronic relaxation and rotation) are also optimized. The substitution of an acetate with a propionate arm in DTPA5- or DOTA4- induces increased steric compression around the water binding site and thus leads to an accelerated water exchange on the Gd(III) complex. The k(ex) values on the propionate complexes are, however, lower than those obtained for [Gd(EPTPA)(H2O)]2- and [Gd(TRITA)(H2O)]- which contain one additional CH(2) unit in the amine backbone as compared to the parent [Gd(DTPA)(H2O)]2- and [Gd(DOTA)(H2O)]-. In addition to their optimal water exchange rate, [Gd(DTTA-Nprop)(H2O)]2- has, and [Gd(DO3A-Nprop)(H2O)]- is expected to have sufficient thermodynamic stability. These properties together make them prime candidates for the development of high relaxivity, macromolecular MRI contrast agents.     

Crystal Structure of a New Ammonium Potassium Selenomolybdate Compound K3.31(NH4)0.69[Se2Mo5O21]·2H2O

An inorganic compound formulated as K_3.31(NH₄)_0.69[Se₂Mo₅O₂₁]·2H₂O has been synthesized by conventional solution method and characterized by scanning electron microscopy, IR, UV-Vis spectroscopies behaviors. The structure of the title compound has been determined from a single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2₁/n, with a?=?9.9371(2) ?, b?=?23.3545(2) ?, c?=?10.5179(2) ?, β?=?114.12(3)°, V?=?2227.7(5) ?³ and Z?=?4. It was revealed that the Strandberg-type polyoxoselenomolybdate cluster can be considered as a ring formed by five distorted edge- and corner-sharing MoO₆ octahedra, capped on both poles by a selenate pyramids sharing three vertices with the ring molybdenum centers. The Strandberg clusters are connected with ammonium ions and water molecules through hydrogen-bonding interactions which ensure the cohesion of the structure into a three-dimensional network.     

Electronic and Structural Properties of Neutral, Anionic, and Cationic Rh x Cu4−x (x = 0–4) Small Clusters: A DFT Study

In this study, electronic structure, stability, and tendency to exchange electron of neutral, anionic, and cationic Rh _x Cu_4?x (x = 0–4) small clusters were investigated by density functional theory calculations. For neutral small clusters, it was found that the most stable structures of Rh₄, Rh₃Cu and Rh₂Cu₂ have distorted tetrahedral shape while the most stable structures of RhCu₃ and Cu₄ have quasi-planer shape. Adding charges to the clusters, caused shapes of the most stable structures undergo variations. Stabilities of the neutral, anionic, and cationic clusters decrease linearly with increasing the copper content. In addition, calculated chemical harnesses indicated that the small cluster with 75 % copper content has the least chemical hardness. Interestingly, prevailing number of electronegative (Rh) and electropositive (Cu) atoms in the anionic and cationic clusters coincides with high dipole moment in these species that occur at 25 and 75 % copper respectively.     

Selective Oxidative Cleavage of Benzylic Carbon-Nitrogen Double Bonds Under Non-Aqueous Condition with Tetrakis(pyridine)-Silver Dichromate [(Py)2Ag]2 Cr2O7

Carbonyl derivatives of phenylhydrazine, 2-nitrophenylhydrazine, 2, 4-dinitrophenazine, semicarbozone, and hydroxylamine are converted to their corresponding carbonyl compounds with tetrakis(pyridine)silver dichromate in benzene. Selectivity is also observed for benzylic C = N cleavage.     

The Influence of Ripeness on the Phenolic Content,Antioxidant and Antimicrobial Activities of Pumpkins (Cucurbita moschata Duchesne)

Cucurbita moschata Duchesne (Cucurbitaceae) is a plant food highly appreciated for the content of nutrients and bioactive compounds, including polyphenols and carotenoids, which contribute to its antioxidant and antimicrobial capacities. The purpose of this study was to identify phenolic acids and flavonoids of Cucurbita moschata Duchesne using high-performance liquid chromatography–diode array detection–electrospray ionization tandem mass spectrometry (HPLC–DAD–ESI-MS) at different ripening stages (young, mature, ripened) and determine its antioxidant and antimicrobial activities. According to the results, phenolic acids and flavonoids were dependent on the maturity stage. The mature fruits contain the highest total phenolic and flavonoids contents (97.4 mg GAE. 100 g⁻¹ and 28.6 mg QE. 100 g⁻¹).A total of 33 compounds were identified. Syringic acid was the most abundant compound (37%), followed by cinnamic acid (12%) and protocatechuic acid (11%). Polyphenol extract of the mature fruits showed the highest antioxidant activity when measured by DPPH (0.065 μmol TE/g) and ABTS (0.074 μmol TE/g) assays. In the antimicrobial assay, the second stage of ripening had the highest antibacterial activity. Staphylococcus aureus was the most sensitive strain with an inhibition zone of 12 mm and a MIC of 0.75 mg L⁻¹. The lowest inhibition zone was obtained with Salmonella typhimurium (5 mm), and the MIC value was 10 mg L⁻¹.     

DFT computational study towards investigating Cladribine anticancer drug adsorption on the graphene and functionalized graphene

Structural Chemistry - Density functional theory calculations at the M06-2X/6-31G** level have been carried out to examine the adsorption behavior of Cladribine drug on the graphene and graphene...