Combination of sorption properties of polydimethylsiloxane and solid‐phase extraction sorbents in a single composite material for the passive sampling of polar and apolar pesticides in water

Passive sampling techniques have been developed as an alternative method for in situ integrative monitoring of trace levels of neutral pesticides in environmental waters. The objective of this work was to develop a new receiving phase for pesticides with a wide range of polarities in a single step. We describe the development of three new composite silicone rubbers, combining polydimethylsiloxane mechanical and sorption properties with solid‐phase extraction sorbents, prepared as a receiving phase for passive sampling. A composite silicone rubber composed of polydimethylsiloxane/poly(divinylbenzene‐co‐N‐vinylpyrrolidone) was selected by batch experiments for its high sorption properties for pesticides with octanol‐water partition coefficients ranging from 2.3 to 5.5. We named this composite material “Polar/Apolar Composite Silicone Rubber”. A structural study by scanning electron microscopy confirmed the homogeneous dispersion of the sorbent particles and the encapsulation of particles within the polydimethylsiloxane matrix. We also demonstrate that this composite material is resistant to common solvents used for the back‐extraction of analytes and has a maximal resistance temperature of 350°C. Therefore, the characteristics of the “Polar/Apolar Composite Silicone Rubber” meet most of the criteria for use as a receiving phase for the passive sampling of pesticides.     

A disymmetric terpyridine based ligand for the formation of luminescent di-aquo lanthanide complexes

The synthesis of ligand H3 based on a disymmetrically substituted terpyridine core functionalised by a carboxylic acid in the 6-position and a bis(carboxymethyl)aminomethyl function in the 6'-position is described. The coordination behaviour of this heptadentate (4N/3O) ligand with lanthanide cations (Ln=Eu, Gd and Tb) was studied in solution showing the formation of complexes with [Ln] stoichiometry. Complexes with general formula [Ln(H2O)2] were isolated from neutral water solutions containing equimolar amounts of cations and ligands, and the complexes were characterized in the solid state (elemental analysis, IR) and in solution (mass spectrometry). The photo-physical properties of the luminescent complexes of Eu and Tb were studied in water solution by means of absorption, steady state and time-resolved emission spectroscopies. Evolution of the luminescence lifetimes of the Eu and Tb complexes in H2O and D2O reveals the presence of two water molecules coordinated in the first coordination sphere of the cations. Despite this important hydration number, the overall luminescence quantum yields of the complexes remained elevated, especially in the case of Tb (Phi=22.0 and 6.5% respectively for Tb and Eu). Upon crystallisation the Gd complex formed dimeric species in which two gadolinium atoms are each heptacoordinated by one ligand, the coordination sphere being completed by a single water molecule and a bridging carboxylate function, pointing to different behaviours in the solid and liquid states.     

Multiple-frequency EPR spectra of two aqueous Gd3+ polyamino polypyridine carboxylate complexes: a study of high field effects

In the search for highly efficient magnetic resonance imaging contrast agents, polyamino polypyridine carboxylate complexes of Gd3+ have shown unusual properties with both very rapid and very slow electron spin relaxation in solution observed by electron paramagnetic resonance. Since the relationship between the molecular structure and the electron spin properties remains quite obscure at this point, detailed studies of such complexes may offer useful clues for the design of Gd3+ compounds with tailored electronic features. Furthermore, the availability of very high-frequency EPR spectrometers based on quasi-optical components provides us with an opportunity to test the existing relaxation theories at increasingly high magnetic fields and observation frequencies. We present a detailed EPR study of two gadolinium polyamino polypyridine carboxylate complexes, [Gd(tpaen)]- and [Gd(bpatcn)(H2O)], in liquid aqueous solutions at multiple temperatures and frequencies between 9.5 and 325 GHz. We analyze the results using the model of random zero-field splitting modulations through Brownian rotation and molecular deformations. We consider the effect of concentration on the line width, as well as the possible existence of an additional g-tensor modulation relaxation mechanism and its possible impact on future experiments. We use (17)O NMR to characterize the water exchange rate on [Gd(bpatcn)(H2O)] and find it to be slow (approximately 0.6 x 10(6) s-1).     

Carbenoid Pathways in Copper‐Catalyzed Intramolecular Cyclopropanations of Phenyliodonium Ylides

The enantioselectivity of the copper‐catalyzed intramolecular cyclopropanation of allyl diazomalonates and the corresponding phenyliodonium ylides was investigated with a series of chiral, non‐racemic ligands. The reaction of 6b in the presence of the bis[dihydrooxazole] ligand Xa in refluxing 1,2‐dichloroethane proceeded to 8b with an enantiomer excess (ee) of up to 72% under optimized conditions. In contrast, 8b resulting from reaction of ylide 7b with the same ligand, but in CH₂Cl₂ at 0°, had an ee of only 30%. With other ligands, diazomalonate 6b reacted with a lower enantioselectivity than ylide 7b , however. The intramolecular cyclopropanation of the acetoacetate‐derived phenyliodonium ylide 15b afforded 16b with 68% ee with ligand Xa , but the corresponding diazo compound was unreactive when exposed to chiral copper catalysts. The observation of asymmetric induction in the Cu‐catalyzed reactions of the ylides 7 and 15 is consistent with a carbenoid mechanism; however, the discrepancy of the enantioselectivities observed between diazomalonate 6b and ylide 7b suggests a competing unselective pathway for cyclopropanation outside of the coordination sphere of copper.     

Spiro[4.4]nonatetraene and its Positive and Negative Radical Ions: Molectronic Structure Investigations

The electronic structure of spiro[4.4]nonatetraene 1 as well as that of its radical anion and cation were studied by different spectroscopies. The electron‐energy‐loss spectrum in the gas phase revealed the lowest triplet state at 2.98 eV and a group of three overlapping triplet states in the 4.5 – 5.0 eV range, as well as a number of valence and Rydberg singlet excited states. Electron‐impact excitation functions of pure vibrational and triplet states identified various states of the negative ion, in particular the ground state with an attachment energy of 0.8 eV, an excited state corresponding to a temporary electron attachment to the 2b₁ MO at an attachment energy of 2.7 eV, and a core excited state at 4.0 eV. Electronic‐absorption spectroscopy in cryogenic matrices revealed several states of the positive ion, in particular a richly structured first band at 1.27 eV, and the first electronic transition of the radical anion. Vibrations of the ground state of the cation were probed by IR spectroscopy in a cryogenic matrix. The results are discussed on the basis of density‐functional and CASSCF/CASPT2 quantum‐chemical calculations. In their various forms, the calculations successfully rationalized the triplet and the singlet (valence and Rydberg) excitation energies of the neutral molecule, the excitation energies of the radical cation, its IR spectrum, the vibrations excited in the first electronic absorption band, and the energies of the ground and the first excited states of the anion. The difference of the anion excitation energies in the gas and condensed phases was rationalized by a calculation of the Jahn‐Teller distortion of the anion ground state. Contrary to expectations based on a single‐configuration model for the electronic states of 1 , it is found that the gap between the first two excited states is different in the singlet and the triplet manifold. This finding can be traced to the different importance of configuration interaction in the two multiplicity manifolds.     

Triphenylphosphinoxid (L) als Solvens und Ligand für Metallphthalocyaninate; Synthese und Struktur von [{Li(L)}2(μ‐pc)], [Li(L)4][Lipc] · Solvat, [Mg(L)pc] · Solvat und [Zn(L)pc] · Solvat

Triphenylphosphine Oxide (L) as Solvent and Ligand for Metallophthalocyaninates; Synthesis and Structure of [{Li(L)}₂(μ‐pc)], [Li(L)₄][Lipc] · Solvate, [Mg(L)pc] · Solvate, and [Zn(L)pc] · Solvate Triphenylphosphine oxide (L) coordinates to metallophthalocyaninates of Li, Mg and Zn at 300 °C. After purification and recrystallization in different solvents the very soluble and stable title compounds have been isolated and structurally characterized. In [{Li(L)}₂(μ‐pc)], the Li atom lies in a distorted tetragonal pyramid of four isoindole N atoms (N_i) at a distance varying between 2.163(5) and 2.301(5) Å, and an O atom at 1.863(5) Å. In [Li(L)₄] · [Lipc] · S, the Li atom of the cation coordinates four O atoms in a distorted tetrahedral arrangement at a distance varying from 1.887(9) to 1.953(9) Å, while the Li atom of the anion is in a quasi quadratic planar geometry of four N_i atoms (1.951(9)–1.977(9) Å) with the Li atom being displaced by 0.15 Å out of the (N_i)₄ plane. The structural data of the distorted tetragonal pyramidale Mg(N_i)₄O moiety in [Mg(L)pc] and the solvates [Mg(L)pc] · S (S = CH₂Cl₂, thf, 2py) generally do not vary significantly: Mg–N_i/2.035(3) –2.061(3) Å, Mg–O/1.955(2)–2.000(3) Å. The Mg atom is displaced by ca. 0.52 Å out of the (N_i)₄ plane towards the O atom and the Mg–O–P moiety is bent (ca. 153°). [Zn(L)pc] · S crystallizes as a mixed crystal of equal parts of the conformer with a bent (155.1(3)°) and that of a quasi linear Zn–O–P moiety (174.2(3)°). Structural data of the Zn(N_i)₄O moiety: (Zn–N_i)_av: 2.024/2.013 Å; Zn–O: 2.050(4)/2.081(4) Å; Zn–(N_i)₄: 0.40/0.33 Å. In the crystal, the Mg and Zn derivates aggregate in double layers forming pairs. The pc ligands in the triclinic complexes with good overlap of the neighbouring pc ligands are in a waving conformation, while those in the monoclinic complexes with weak overlap are in a concave conformation.     

Voltammetric Detection of Lead(II) Using Amide‐Cyclam‐ Functionalized Silica‐Modified Carbon Paste Electrodes

2‐(4,8,11‐Triscarbamoylmethyl‐1,4,8,11‐tetraazacyclotetradec‐1‐yl)acetamide (TETAM) derivatives bearing 1, 2, or 4 silylated arms have been synthesized and grafted to the surface of silica gel and ordered mesoporous silica samples. The resulting organic‐inorganic hybrids have been incorporated into carbon paste electrodes and applied to the preconcentration electroanalysis of Pb(II). The attractive recognition properties of these cyclam derivatives functionalized with amide pendent groups toward Pb(II) species and the highly porous structure of the adsorbents can be exploited for the selective and sensitive detection of the target analyte. Various parameters affecting the preconcentration and detection steps have been discussed with respect to the composition and pH of both accumulation and detection media, the nature of the adsorbent (number of silylated groups linking the macrocycle to silica, texture of materials), the accumulation time, and the presence of interfering cations. Under optimal conditions and for 2 min accumulation at open‐circuit, the voltammetric response increased linearly with the Pb(II) concentration in a range extending from 2×10^?7 to 10^?5 M, while a longer accumulation time of 15 min afforded a linear calibration curve between 10^?8 and 10^?7 M with a detection limit of 2.7×10^?9 M which is well below the European regulatory limit of lead in consumption water.     

Electrochemical transduction on self-assembled monolayers: are covalent links essential?

Electrochemical transduction without covalent links between redox and complexant units in a complexing self-assembled monolayer has been established. The results demonstrate that transduction depends on the crown ether/ferrocene ratio and appears to be tunable.     

Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.