Molecular and electronic structure of square-planar nickel II, nickel III and nickel III pi-cation radical complexes with a tetradentate o-phenylenedioxamidate redox-active ligand

The molecular and electronic structures of the electron transfer series of four-coordinate square-planar nickel complexes with the ligand o-phenylenebis(N'-methyloxamidate), [NiL]z (z = 2-, 1-, 0), have been evaluated by DFT and TDDFT calculations, and most of their experimentally available structural and spectroscopic properties (X. Ottenwaelder et al., Dalton Trans., 2005, DOI: 10.1039/b502478a) have been reasonably reproduced at the B3LYP level of theory. The anionic species [NiL]2- and [NiL]- are genuine low-spin nickel II and nickel III complexes with diamagnetic singlet (S = 0) and paramagnetic doublet (S = 1/2) states, respectively. The nickel III complex presents shorter Ni-N(amidate) bond distances (1.85-1.90 A) than the parent nickel II complex (1.88-1.93 A) and characteristic LMCT bands in the NIR region (lambda max = 794 and 829 nm) while the analogous MLCT bands for the nickel(II) complex are in the UV region (lambda max = 346 and 349 nm). The neutral species [NiL] is a nickel III o-benzosemiquinonediimine pi-cation radical complex with a diamagnetic singlet (S = 0) and a paramagnetic triplet (S = 1) states fairly close in energy but fundamentally different in orbital configuration. The singlet metal-radical ground state results from the antiferromagnetic coupling between the 3d(yz) orbital of the Ni III ion (S(M) = 1/2) and the pi(b) orbital of the benzosemiquinone-type radical ligand (S(L) = 1/2), which have a large overlap and thus strong covalent bonding. The triplet metal-radical excited state involves the ferromagnetic coupling between the Ni III 3d(zx) orbital and the benzosemiquinone-type pi(b) orbital, which are orthogonal to each other. The singlet and triplet states of the nickel III pi-cation radical complex possess characteristic quinoid-type short-long-short alternating sequence of C-C bonds in the benzene ring, as well as intense MLCT transitions in the VIS (lambda max = 664 nm) and NIR (lambda max = 884 nm) regions, respectively.     

Magnetic anisotropy of a high-spin octanuclear nickel(II) complex with a meso-helicate core

The octanickel(II) cluster 2b has been synthesized from the novel ferromagnetically coupled dinickel(II) metallacryptand 1b assembled from the m-phenylene-bis(oxamate) ligand. Complex 2b exhibits a dimer-of-tetramers structure, with two oxamate-bridged propeller-shaped tetranuclear units connected through three meta-substituted phenylenediamidate bridges, giving a metallacryptand core of the meso-helicate type. Complex 2b behaves as a ferromagnetically coupled dimer of two S=2 Ni(II)4 units with appreciable magnetic anisotropy.     

An experimental and theoretical study of the 13C and 31P chemical shielding tensors in solid O-phosphorylated amino acids

A series of l and dl forms of O-phosphorylated amino acids (serine, threonine, tyrosine) have been studied by using solid-state multinuclear NMR spectroscopy and ab initio calculations. Principal elements of the (13)C and (31)P chemical shielding tensors have been measured and discussed in relation to zwitterionic structures and intermolecular contacts. DFT calculations have been compared with experimental data showing their ability to reproduce experimentally obtained tensor values in this challenging class of compounds. The changes of orientation of (31)P chemical shielding tensor with respect to the molecular frame in the presence of hydrogen bonds have been revealed and discussed on the ground of theoretical calculations. The measurements of internuclear P...P distances, based on Zeeman magnetization exchange between (31)P spins with differing chemical shielding tensor orientations, were exploited for a clear distinction between enantiomers and racemates.     

Polynuclear and 1-D derivatives of 1,3-bis(dimethylamino)-2-propanolato ligand. Structure and magnetic characterization

Several new Cu(II) derivatives of the 1,3-bis(dimethylamino)-2-propanolato (bdmap) ligand with formula [Cu(2)(bdmap)(acac)(NH(3))(3)(MeOH)](ClO(4))(2), [Cu(2)(bdmap)(NO(2))(3)(H(2)O)](4) and [Cu(2)(bdmap)(OH)(ox)(0.5)(H(2)O)(2)](n)(ClO(4))(n)xnH(2)O were synthesized and characterized both structurally and magnetically. Dinuclear compound crystallizes in the monoclinic system, space group P2(1)/c, octanuclear compound crystallizes in the triclinic space group P1 and the 1-D alternating system crystallizes in the monoclinic system, space group P2/n. Magnetic analysis indicates strong antiferromagnetic coupling for all derivatives, mainly due to the interaction through the alkoxo O-atom of the bdmap ligand. The effect on the magnetic behaviour of the additional bridging ligands is analysed.     

Comparison of methanol and acetonitrile as solvents for the separation of sertindole and its major metabolites by capillary zone electrophoresis

Sertindole (1-[2-[4-[5-chloro-1-(4-fluorophenyl)-1H-indol-3-yl]-1-piperidinyl]ethyl]-2-imidazolidinone), an atypical antipsychotic drug, was separated by capillary electrophoresis from its two main metabolites norsertindole and dehydrosertindole. The low solubility of the analytes in water (octanol-water partition coefficient is about 10(5)) is overcome by the use of methanol (MeOH) and acetonitrile (ACN) as solvents for the background electrolyte (BGE). Mobilities were measured in BGEs with defined pH in a broad range. It was found that in MeOH the mobility of the analytes is mainly governed by acid-base equilibria, whereas in ACN other reactions like ion pairing and homo-conjugation play a pronounced role and lead to a complex pattern of the mobility as function of the pH. However, separation can be obtained in less than 10 min in both solvent systems.     

HepG2 human hepatocarcinoma cells: an experimental model for photosensitization by endogenous porphyrins

Endogenous protoporphyurin IX (PpIX) synthesis after δ-aminolaevulinic acid (ALA) administration occurs in cancer cells in vivo; PpIX, which has a short half-life, may thus constitute a good alternative to haematoporphyrin derivative (HPD) (or Photofrin). This study assesses the ability of the human hepatocarcinoma cell line HepG2 to synthesize PpIX in vitro from exogenous ALA, and compares ALA-induced toxicity and phototoxicity with the photodynamic therapy (PDT) effects of HPD on this cell line.

ALA induced a dose-dependent dark toxicity, with 79% and 66% cell survival for 50 and 100 μg ml⁻¹ ALA respectively after 3 h incubation; the same treatment, followed by laser irradiation (λ = 632 nm, 25 J cm⁻²), induced a dose-dependent phototoxicity, with 54% and 19% cell survival 24 h after PDT. Whatever the incubation time with ALA, a 3 h delay before light exposure was found to be optimal to reach a maximum phototoxicity.

HPD induced a slight dose-dependent toxicity in HepG2 cells and a dose- and time-dependent phototoxicity ten times greater than that of ALA-PpIX PDT. After 3 h incubation of 2.5 and 5 μg ml⁻¹ HPD, followed by laser irradiation (λ = 632 nm, 25 J cm⁻²), cell survival was 59% and 24% respectively at 24 h.

Photoproducts induced by light irradiation of porphyrins absorb light in the red spectral region at longer wavelengths than the original porphyrins. The possible enhancement of PDT effects after HepG2 cell incubation with ALA or HPD was investigated by irradiating cells successively with red light (λ = 632 nm) and light (λ = 650 nm). The total fluence was kept constant at 25 J cm⁻². For both HPD and ALA-PpIX PDT, phototoxicity was lower when cells were irradiated for increased periods with λ = 650 nm light than with λ = 632 nm light alone. This suggests that any photoproducts involved either have a short life or are poorly photoreactive.

Not all cell lines can synthesize PpIX after ALA incubation. HepG2 cells, which can synthesize enzymes and precursors of endogenous porphyrin synthesis, represent a good in vitro model for experiments using ALA-PpIX PDT. In addition, ALA-PpIX PDT may represent a new, specific treatment for hepatocarcinomas.     

Determination of volatile alkyl sulfides in wastewater by headspace solid-phase microextraction followed by gas chromatography-mass spectrometry

An analytical procedure based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to mass spectrometry in the electron impact mode has been developed for the determination of low-molecular-mass sulfides and disulfides in wastewater. Parameters affecting to the extraction of these volatile alkyl sulfides (VASs) with the SPME, such as the extraction temperature, sample volume, pH and the NaCl addition to the matrix, have been optimised using a polydimethylsiloxane-Carboxen fibre. The linear dynamic range was close to three orders of magnitude for all the studied compounds. Detection limits of 4 ng l(-1) for dimethyl sulfide, 0.7 ng l(-1) for ethylmethyl sulfide, 5 ng l(-1) for diethyl sulfide and 1 ng l(-1) for dimethyl disulfide were achieved, with a relative standard deviation between 4 and 6%. The developed analytical methodology was applied to determine those VASs in different wastewaters.     

Simulation of the photodissociation of Ar 3 +

A simulation of the photodissociation of Ar ₃ ⁺ is performed in the range 200–650nm. The approach relies on Diatomic in Molecules electronic modelling, Molecular Dynamics and the Hemiquantal method. The results are used to interpret the experimental abundance of slow ions in terms of the various absorption bands. Kinetic energy distributions of all fragments are analysed at 530 and 280nm for two internal energies. The time evolution of the cluster is discussed and a concerted one-step mechanism emerges involving charge fluctuations. The simulation only yields fast-fast and fastslow photoneutral-photoneutral coincidences.