Proper and improper hydrogen bonds in metalloorganic crystal architecture: experimental evidence in [CoCp(2)](+) and [FeCp(2)](+) salts

The [FeCp2]+ and [CoCp2]+ salts are the first examples of metalloorganic complexes where the proton donor eta5-Cp shows both "proper" and "improper" hydrogen bonds when it is involved in intermolecular bonding with different anionic proton acceptors. Blue or red shift of the C-H stretching frequency is the clear experimental evidence.     

A modified wigner function set for the smoluchowski operator representation in anisotropic liquids

The set of non-orthogonal functions D^j_pq(Ω)^P1/2(Ω), in which the Wigner rotation functions are multiplied by the equilibrium orientational distribution, is shown to provide a convenient basis for the solution of the rotational diffusion problem in anisotropic liquids,in the entire range of orientational ordering.     

Copper(II) complexes with substituted thiosemicarbazones of alpha-ketoglutaric acid: synthesis, X-ray structures, DNA binding studies, and nuclease and biological activity

New alpha-ketoglutaric acid thiosemicarbazone (H(3)ct) derivatives and their copper complexes were synthesized and characterized by analytical and spectroscopic (IR and NMR) methods. For two of the ligands, Me-H(3)ct and Allyl-H(3)ct, and for a complex, [Cu(Me-Hct)(OH(2))](n) x 2nH(2)O, the X-ray structures were also determined. In the latter the copper atom shows a 4 + 1 pyramidal coordination, a water oxygen appears in the apical position, and three of the basal positions are occupied by the SNO tridentate ligand and the fourth by a carboxylic oxygen of an adjacent molecule that gives rise to a polymeric chain. DNA binding constants were determined, and studies of thermal denaturation profiles and nuclease activity were also performed. Tests in vitro on human leukemia cell line U937 were carried out on cell growth inhibition, cell cycle, and apoptosis induction.     

Electrochemical behavior of 3-amino-pyridine, 2,3-diamino-pyridine and 2,6-diamino-pyridine in aqueous solutions

The electrochemical behavior of 3-amino-pyridine, 2,3-diamino-pyridine and 2,6-diaminopyridine has been investigated in the pH range 0.7–13 at platinum and carbon paste solid electrodes with periodical renewal of the diffusion layer. Electrolysis at controlled potential of 3-amino-pyridine and 2,3-diamino-pyridine have been carried out in the pH range 0.7–13. The formation, among the oxidation products of 3-amino-pyridine, in alkaline solutions, of 3,3′-azopyridine has been pointed out and the percentages of this compound at changing pH were reported.     

Electrochemical behavior of mesidine in aqueous solutions

The electrochemical oxidation of mesidine has been investigated in the pH range 0.7–11 at a platinum electrode with periodical renewal of the diffusion layer and at a stationary carbon paste electrode. A E_1/2/pH relation for the platinum electrode has been derived in the pH range 0–7. It has been indicated that the only oxidation products of mesidine are 2,6-dimethylbenzoquinone-4-(2′,4′,6′-trimethyl)-anil at pH <8 and 2,4,6,2′,4′,6′-hexamethylazoxybenzene at pH>8. Oxidation mechanisms consistent with the kinetic parameters and the oxidation products are discussed.     

Correction for Inner Filter Effects in Fluorescence Spectroscopy

A method is proposed for correcting experimental fluorescence readings for inner filter effects, i.e. the absorption of the exciting light and/or the absorption of the emitted radiation, which cause the non-linearity between fluorescence intensity and fluorophor concentration. Basically the method consists of measuring the fluorescence intensity at two different points along the diagonal in the cell. Unlike similar methods proposed in the literature, the two points are corrected simultaneously for both absorption of excitation and of emission radiation without the necessity of reading the optical density of the solution, and with a very simple data elaboration.     

Rapid determination of dissolved silica in natural waters

A method is described for the simple and rapid determination of soluble silica in natural waters, based on the well-known molybdenum blue complex. Soluble silica reacts with an excess of ammonium molybdate at pH 1.5–2 to form silicomolybdate. Citrate/tartrate addition reduces phosphate and arsenate interference, if present. An acid solution if iron(II) and fluoride ions is used as reductant. Absorbance is read at 828 nm. The solution is stable at least 2 hr. Traces of silica are determinable down to 10 μg SiO₂ liter^?1 with an error of ± 3%. The analysis time is about 10 min. The effect caused by several other ions has been determined.     

Synthesis of some substituted pyrido[1,2-a]pyrimidin-4-ones and 1,8-naphthyridines

The substituted 4H-pyrido[1, 2-a]pyrimidin-4-ones (I) were obtained by the condensation of substituted 2-aminopyridines with δ-ketocarboxylic esters in PPA. Some of the derivatives I were transformed into the corresponding 1, 8-naphthyridines II and III.     

Metal-Salen Schiff base complexes in catalysis: practical aspects

Schiff base ligands are considered "privileged ligands" because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.