Dinuclear, tetranuclear and polymeric complexes in copper(II) perchlorate/pyridine-2,6-diamidoxime chemistry: synthetic, structural and magnetic studies

The initial use of pyridine-2,6-diamidoxime (pdamoH(2)) in metal cluster and polymer chemistry is described. Depending on the reaction conditions employed, the Cu(ClO(4))(2)·6H(2)O/pdamoH(2) system has provided access to the dinuclear compound [Cu(2)(pdamoH)(2)(ClO(4))(2)(MeOH)(2)] (1), the chain-like polymer [Cu(2)(pdamoH)(2)](n)(ClO(4))(2n) (2) and to the tetranuclear cluster [Cu(4)(pdamo)(2)(pdamoH)(2)](ClO(4))(2) (3). Single-crystal, X-ray crystallography reveals different coordination modes for the pdamoH(-) ligand in each compound, providing the first evidence for the flexibility and versatility of the anionic forms of pdamoH(2). Variable-temperature magnetic susceptibility studies indicate very strong antiferromagnetic coupling in the three complexes, attributable to the double oximato bridges which link the Cu(II) spin carriers.     

Differential ESI-MS behaviour of highly similar metallothioneins

ESI-MS can only be accepted as a quantification method when using standards with a high resemblance to the analyte(s). Unfortunately, this is usually not applicable to metallothioneins (MTs), a superfamily of singular metal-binding cysteine-rich proteins, present in all living organisms, since the absence of suitable reference material due to the high diversity among metal-MT species precludes their quantification by molecular mass spectrometry. Even thus, it is widely assumed that the intensities of the ESI-MS peaks of similar species are directly correlated with their relative concentration in the sample, and this has been extended to the determination of different MT proteins coexisting in a sample.Practically all organisms contain several MT isoforms, some of them exhibiting highly similar sequences, with conserved coordinating Cys residues. For the current analysis, we used as a model system the MT isoforms of two terrestrial snails (Helix pomatia and Cornu aspersum). Hence, distinct samples were prepared by mixing, at different molar ratios, the recombinant HpCuMT and HpCdMT isoforms from H. pomatia, or the recombinant CaCuMT, CaCdMT and CaCdCuMT isoforms from C. aspersum, and they were analyzed by ESI-MS both at neutral pH (for Zn-loaded MT forms) and at acidic pH (for the corresponding apo-forms). The results here presented reveal that the ESI-MS peak intensity of a single MT species strongly depends on its sensitivity to be ionized, and thus, on the presence or absence of metal ions bound. Furthermore, our data demonstrate that very similar MT isoforms of the same organism with similar pI (ranging from 7.9 to 8.3) can show a clear different sensitivity to ES ionization, something that cannot be readily predicted only by consideration of their amino acid content. In conclusion, even in this optimum case, deductions about quantity features of MT samples drawn from ESI-MS measurements should be carefully considered.     

Exit Times from Equilateral Triangles

In this paper we obtain a closed form expression of the expected exit time of a Brownian motion from equilateral triangles. We consider first the analogous problem for a symmetric random walk on the triangular lattice and show that it is equivalent to the ruin problem of an appropriate three player game. A suitable scaling of this random walk allows us to exhibit explicitly the relation between the respective exit times. This gives us the solution of the related Poisson equation.     

Synthesis, structure, redox properties, and catalytic activity of new ruthenium complexes containing neutral or anionic and facial or meridional ligands: an evaluation of electronic and geometrical effects

The synthesis of a family of new Ru complexes containing meridional or facial tridentate ligands with the general formula [Ru(II)(T)(D)(X)](n+) [T = 2,2':6',2' '-terpyridine or tripyrazolylmethane; D = 4,4'-dibenzyl-4,4',5,5'-tetrahydro-2,2'-bioxazole (S,S-box-C) or 2-[((1'S)-1'-(hydroxymethyl)-2'-phenyl)ethylcarboxamide]-(4S)-4-benzyl-4,5-dihydrooxazole (S,S-box-O); X = Cl, H(2)O, MeCN or pyridine] has been described. All complexes have been spectroscopically characterized in solution through (1)H NMR and UV-vis techniques. Furthermore, all of the chloro complexes presented here have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic S,S-box-C ligands undergo a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic oxazolinic ligands S,S-box-O, which are also strongly attached to the metal center and produce a strong sigma-donation effect over the Ru metal center. The redox properties of all complexes have also been studied by means of cyclic voltammetry, strongly reflecting the nature of the ligands; both effects, geometrical (facial vs meridional) and electronic (neutral vs anionic), can be unveiled and rationalized. Finally, the reactivity of the Ru-OH(2) complexes has been tested with regard to the epoxidation of trans-stilbene, and it has been shown that, in this particular case, the reactivity is practically not dependent on the redox potentials of the catalyst but, in sharp contrast, it is strongly dependent on the geometry of the tridentate ligands.     

Fluoroquinolones in soils: Assessment of extraction methods

The extraction of six fluoroquinolones from agricultural soils with different physicochemical characteristics (pH, texture and organic carbon content) has been investigated. Different solvents, consisting of hydroorganic mixtures, have been tested, and basic buffer solutions, with either acetonitrile or acetone, have proved to be suitable extraction solvents. Conventional mechanical shaking and microwave-assisted extraction techniques have been evaluated, and mechanical shaking has been selected. Recovery rates from freshly spiked (overnight) soils ranged from 65 to 90%, depending on the quinolone. No relevant dependence on soil characteristics has been observed. The effect of ageing on the extraction behaviour of fluoroquinolones has also been considered. In comparison with freshly spiked soils, extractions from residues aged for some months have resulted in about 20–25% lower recovery rates.     

Use of proficiency testing materials for the calculation of detection and quantification limits in the analysis of organochlorine compounds in human serum

A method for the calculation of the limits of detection (LD) and quantification (LQ) for the analysis of organochlorine compounds in serum is described. The method is based on the analysis of proficiency testing materials, an external quality assessment for selected pollutants, and the study of the signal/noise ratio of chromatograms obtained from GC-ECD injection. This method provides representative results for matrix effects, instrumental variability and extraction recoveries in the analysis of serum samples.     

Straightforward preparation of enantiopure 3-amino-4,4-dimethylpyrrolidin-2-one and its derivatives

An easy access to both enantiomers of 3-amino- and 3-(dimethylamino)-4,4-dimethylpyrrolidin-2-one from rac-pantolactam using (R)-α-methylbenzylamine as a chiral auxiliary is described.     

Studying the interactions of a platinum(II) 9-aminoacridine complex with proteins and oligonucleotides by ESI-TOF MS

The interaction of a novel Pt complex, [Pt(dmba)(N9-9AA)(PPh(3))](+)1 (dmba = N,N-dimethylbenzylamine-κN,κC; 9AA = 9-aminoacridine), which exhibits anti-tumor activity, with certain key proteins has been monitored by ESI-MS. Also, the interaction of 1 with a designed double-stranded oligonucleotide containing the GG motif has been followed by mass spectrometry as well as by fluorimetry. The results obtained show the low interaction of 1 with the considered proteins and the absence of covalent interaction with the oligonucleotides, but the fluorimetric data confirm the π-π interaction of 1 with the double-stranded DNA, which is probably the reason of the previously reported activity of 1 in several tumor cell lines.     

Ranks of q-Ary 1-Perfect Codes

The rank of a q-ary code C of length n, r(C), isthe dimension of the subspace spanned by C. We establish the existence of q-ary 1-perfectcodes of length for m 4 and r(C)= n – m + s for each s {1,,m}. This is a generalization of the binary case proved by Etzion and Vardy in[4].     

Thermodynamic properties of the dissociation of several α-oxooximes

The changes in free energy, enthalpy and entropy for the dissociation of several -oxooximes (phenylglyoxal aldoxime, glyoxylanilide oxime,N-ethyl-glyoxylanilide oxime and 1-phenyl-1,2-propanedione-2-oxime) have been determined in water-ethanol medium (50% v/v) at 0.5M ionic strength (NaNO₃) and 25 °C. The changes in dissociation free energy were calculated from the pK _a values determined by glass-electrode potentiometry, and refined by using the programs MINIGLASS and SUPERQUAD. The dissociation enthalpies were determined by direct thermometric titration, and refined by using the programs MINITERM and MULTITERM.