Domoic acid at trace levels in lagoon waters: assessment of a method using internal standard quantification

Domoic acid (DA) is a neurotoxin produced by different algae, including pennate diatoms, principally from the genus Pseudo-nitzschia, and it is the main cause of amnesic shellfish poisoning. Determination of this toxin in seawater samples is fundamental to define the real contamination risks for aquatic species. We have developed two very sensitive instrumental methods using hydrophilic interaction liquid chromatography coupled using tandem mass spectrometry in positive and negative polarity modes. Instrumental detection limits were 9 pg mL^?1 for positive and 19 pg mL^?1 for negative ionisation. A procedural method based on solid-phase extraction for the determination of dissolved DA present in seawater has been developed, and an extraction procedure was employed for the determination of the toxin in the particulate fraction. DA quantification was performed using the internal standard method to account for signals fluctuations and random errors during sample treatment. To our knowledge, this is the first study to use this quantification method for DA determination. Trueness, extraction yield, matrix effects, repeatability and procedural detection limits were evaluated during method validation. Procedural detection limits of 0.3 pg mL^?1 (positive mode) and 0.6 pg mL^?1 (negative mode) were found for the dissolved fraction, and absolute limits of 0.4 pg (positive mode) and 6.0 pg (negative mode) for particulate samples were obtained. The most sensitive method in positive mode was applied to define DA occurrence in the Venice Lagoon. Trace concentrations of domoic acid ranging from 1.5 to 16.2 pg mL^?1 were found for the first time in the Venetian environment.

Amygdalar glutamatergic neuronal systems play a key role on the hibernating state of hamsters

Background  

Excitatory transmitting mechanisms are proving to play a critical role on neuronal homeostasis conditions of facultative hibernators such as the Syrian golden hamster. Indeed works have shown that the glutamatergic system of the main olfactory brain station (amygdala) is capable of controlling thermoregulatory responses, which are considered vital for the different hibernating states. In the present study the role of amygdalar glutamatergic circuits on non-hibernating (NHIB) and hibernating (HIB) hamsters were assessed on drinking stimuli and subsequently compared to expression variations of some glutamatergic subtype mRNA levels in limbic areas. For this study the two major glutamatergic antagonists and namely that of N-methyl-D-aspartate receptor (NMDAR), 3-(+)-2-carboxypiperazin-4-yl-propyl-1-phosphonate (CPP) plus that of the acid α-amine-3-hydroxy-5-metil-4-isoxazol-propionic receptor (AMPAR) site, cyano-7-nitro-quinoxaline-2,3-dione (CNQX) were infused into the basolateral amygdala nucleus. Attempts were made to establish the type of effects evoked by amygdalar glutamatergic cross-talking processes during drinking stimuli, a response that may corroborate their major role at least during some stages of this physiological activity in hibernators.     

Cadmium–halide and mixed cadmium–halide–dicyanamide polymers mediated by ancillary 2-aminoalkyl-pyridine ligands: Synthesis,X-ray single crystal structures and luminescence property

A series of mixed halide–dicyanamide and halide complexes of cadmium(II) mediated by 2-aminoalkyl-pyridine ligands [2-aminomethylpyridine (ampy) and 2-aminoethylpyridine (aepy)] have been synthesized. Five of them, [CdCl(dca)(aepy)]_n (1), [CdBr(dca)(ampy)]_n (2), [CdCl(dca)(ampy)]_n (3) (dca = dicyanamide); [CdI₂(aepy)]_n (4), and [CdI₂(ampy)]_n (5), (dca = dicyanamide) have been characterized by X-ray single crystal structure analysis. The structural determination shows that the compounds are 1D coordination polymers, with the exception of 3 that gives origin to a 2D sheet-like network. The ampy and aepy ligands (also with the occurrence of dca anions in 1–3) reveal to be useful ancillary fragments for the construction of unprecedented Cd–halide polymeric species. The crystal packing shows that the dimensionality of all compounds is enlarged to 2D, and 3D in the case of complex 3, through π–π interactions occurring between the pyridine rings. All the species exhibit interesting luminescence property in solution as well in solid state which is originated from ligand-centered π–π^∗ transitions. The fluorescence band maxima and fluorescence efficiency (in methanol) are found to be dependent not only on the pyridine ligand but also on the type of halide, and the co-ligand. Solid state luminescent study implies that π–π interactions occurring between pyridine rings are also important in controlling the fluorescence intensity. Amongst the synthesized complexes reported, complex 5 exhibits the highest fluorescence efficiency in methanol.     

New atropisomeric N-N ligands for CO/vinyl arene copolymerization reaction

New atropisomeric bidentate bipyridine-based ligands (3,3'-(ethylenedioxy)-2,2'-bipyridine 4; 3,3'-(propylenedioxy)-2,2'-bipyridine 4; 3,3'-(butylenedioxy)-2,2'-bipyridine 5) containing a bridge between the 3,3' positions of the aromatic rings have been prepared. Together with the previously reported analogous ligands ((R)-3,3'-(1-methylethylenedioxy)-2,2'-bipyridine) 1and ((S,S)-3,3'-(1,2-dimethylethylenedioxy)-2,2'-bipyridine) 2, they were used to synthesize the corresponding bis-chelated dicationic complexes [Pd(N-N)2][PF6]2. Crystal structures and comparison of the data obtained by X-ray analysis on four of these complexes is reported. These palladium compounds were used as precatalysts in the CO/styrene and CO/4-Me-styrene copolymerization reactions, where they showed that small variations in the ligand backbone remarkably affects the productivity of the catalytic system.     

Synthesis,crystal structure and thermal analysis of supramolecular architectures of copper(II)(2,2′-biimidazole) complexes using dicarboxylate as a coligand

Two new copper(II) complexes {[Cu(H₂biim)(H₂O)(suc)](H₂O)}_n (1) and {[Cu(H₂biim)₂(H₂O)][Cu(H₂biim)₂(glut)](glutH)(NO₃) · 2.5H₂O}_n (2) (H₂biim, 2,2′-biimidazole; suc, succinate dianion; glut, glutarate dianion) have been synthesized and characterized by single crystal X-ray diffraction study and thermal analysis. Complex 1 comprises of 1D zigzag coordination polymers, elongated along the crystallographic b-axis, connected through H-bonding and face-to-face π–π interactions to form a robust 3D network. Whereas complex 2 is built up of bischelated [Cu(II)(H₂biim)₂]²⁺ units, glutarate and nitrate anions and water molecules, held together through an extensive H-bonded system. The resulting 3D supramolecular architecture defines channels which are filled by lattice water molecules and disordered nitrate anions.     

Copper(II)-mediated oxidative transformation of vic-dioxime to furoxan: evidence for a copper(II)-dinitrosoalkene intermediate

The mononuclear copper(II) complex [Cu(H(2)L(1))(2)(H(2)O)](ClO(4))(2) (1) (where H(2)L(1) = 1,10-phenanthroline-5,6-dioxime) reacts with copper(II) perchlorate in acetonitrile at ambient conditions in the presence of triethylamine to afford a copper(II) complex, [Cu(L(3))(2)(H(2)O)](ClO(4))(2) (2a), of 1,10-phenanthroline furoxan. A similar complex [Cu(L(3))(2)Cl](ClO(4)) (2) is isolated from the reaction of H(2)L(1) with copper(II) chloride, triethylamine, and sodium perchlorate in acetonitrile. The two-electron oxidation of the vic-dioxime to furoxan is confirmed from the X-ray single crystal structure of 2. An intermediate species, showing an absorption band at 608 nm, is observed at -20 °C during the conversion of 1 to 2a. A similar blue intermediate is formed during the reaction of [Cu(HDMG)(2)] (H(2)DMG = dimethylglyoxime) with ceric ammonium nitrate, but H(2)DMG treated with ceric ammonium nitrate does not form any intermediate. This suggests the involvement of a copper(II) complex in the intermediate step. The intermediate species is also observed during the two-electron oxidation of other vic-dioximes. On the basis of the spectroscopic evidence and the nature of the final products, the intermediate is proposed to be a mononuclear copper(II) complex ligated by a vic-dioxime and a dinitrosoalkene. The dinitrosoalkene is generated upon two-electron oxidation of the dioxime. The transient blue color of the dioxime-copper(II)-dinitrosoalkene complex may be attributed to the ligand-to-ligand charge transfer transition. The intermediate species slowly decays to the corresponding two-electron oxidized form of vic-dioxime, i.e. furoxan and [Cu(CH(3)CN)(4)](ClO(4)). The formation of two isomeric furoxans derived from the reaction of an asymmetric vic-dioxime, hexane-2,3-dioxime, and copper(II) perchlorate supports the involvement of a dinitrosoalkene species in the intermediate step. In addition, the oxidation of 2,9-dimethyl-1,10-phenanthroline-5,6-dioxime (H(2)L(2)) to the corresponding furoxan and subsequent formation of a copper(I) complex [Cu(L(4))(2)](ClO(4)) (3) (where L(4) = 2,9-dimethyl-1,10-phenanthroline furoxan) are discussed.     

Synthesis, characterization and luminescence properties of polymeric cadmium(II) complexes with imidazole and its derivatives mediated by thiocyanate and dicyanamide anions

Three new polymeric complexes of cadmium(II) with imidazole and its derivatives [imidazole (Im), benzimidazole (Bim) and 1-methylimidazole (Mim)] mediated by thiocyanate and dicyanamide (dca) anions have been synthesized and characterized by X-ray single crystal structure analysis. The structure analyses reveal that complexes [Cd(SCN)₂(Bim)₂]_n (1) and [Cd(dca)₂(Im)₂]_n (2) are 1D coordination polymers, whereas complex [Cd(dca)₂(Mim)₂]_n (3) adopts a 2D network of (4, 4) topology and thereby suggests that the dimensionality of the coordination polymers are affected by the choice of the counter anions and by the organic ligands. All the species exhibit interesting luminescence property in methanol and in solid state originated from ligands-centered π-π* transitions. The π-π interactions occurring between organic rings (Im, Mim, and Bim) are observed to be important in controlling the fluorescence property of the species.     

1-(2-Picolyl)-substituted 1,2,3-triazole as novel chelating ligand for the preparation of ruthenium complexes with potential anticancer activity

The 1,4-disubstituted 1,2,3-triazole ligand prepared by click chemistry 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole (ppt) was investigated as novel chelating ligand for Ru(II) complexes with potential antitumor activity. The preparation and structural characterization, mainly by NMR spectroscopy in solution and by X-ray crystallography in the solid state, of four new Ru(II) complexes is reported: two isomeric Ru-dmso compounds, trans,cis-[RuCl(2)(dmso-S)(2)(ppt)] (1) and cis,cis-[RuCl(2)(dmso-S)(2)(ppt)] (2), and two half-sandwich Ru-[9]aneS(3) coordination compounds, [Ru([9]aneS(3))(dmso-S)(ppt)][CF(3)SO(3)](2) (3) and [Ru([9]aneS(3))Cl(ppt)][CF(3)SO(3)] (4). In all compounds ppt firmly binds to ruthenium in a bidentate fashion through the pyridyl nitrogen atom and the triazole N2, thus forming a puckered six-membered ring. The chemical behavior in aqueous solution of the water-soluble complexes 3 and 4 was studied by UV-Vis and NMR spectroscopy and compared to that of the previously described organometallic analogue [Ru(η(6)-p-cymene)Cl(ppt)][Cl] (5) in view of their potential antitumor activity. Compounds 3-5 were tested also in vitro for cytotoxic activity against two human cancer cell lines, one sensitive and one resistant to cisplatin, in comparison with cisplatin. Compound 4, the one that aquates faster, was found to be more cytotoxic than cisplatin against human lung squamose carcinoma cell line (A-549).     

New half sandwich-type Ru(II) coordination compounds characterized by the fac-Ru(dmso-S)3 fragment: influence of the face-capping group on the chemical behavior and in vitro anticancer activity

The Ru(II) complex fac-[RuCl(dmso-S)(3)(dmso-O)(2)][PF(6)] (P2) was found to be an excellent precursor for the facile preparation in high yield of half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N)(2)][PF(6)] (e.g. (N)(2) = 1,2-diaminoethane (en, 4), trans-1,2-diaminocyclohexane (dach, 5), or 2 NH(3) (6)). Neutral half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N-O)] where N-O is an anionic chelating ligand (e.g. N-O = picolinate (pic, 7)) are best prepared from the universal Ru(II)-dmso precursor cis-[RuCl(2)(dmso)(4)] (P1). These complexes, that were fully characterized in solution and in the solid state, are structurally similar to the anticancer organometallic compounds [Ru(η(6)-arene)(chel)Cl][PF(6)](n) but, in place of a face-capping arene, have the fac-Ru(dmso-S)(3) fragment. In contrast to what observed for the corresponding arene compounds, that rapidly hydrolyze the Cl ligand upon dissolution in water, compounds 4-6 are very stable and inert in aqueous solution. Probably their inertness is the reason why they showed no significant cytotoxicity against the MDA-MB-231 cancer cell line.