X-ray diffraction study of some mesogenic copper, nickel and vanadyl complexes

We present a comparative study of various metallomesogenic complexes, using X-ray diffraction methods. For a given ligand linked to different metal atoms (Cu, Ni, VO), the nature of this central atom influences mainly the magnetic susceptibilities of the mesophases. With different ligands, which keep the close neighbourhood of the metal atom unchanged, the apparent length of the mesogenic unit is longer for short ligands than for longer ones. This unexpected behaviour is qualitatively well explained by taking into account the global shape of the different complexes.     

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

Summary The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C₁₈. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s^–1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml^–1 for ONP, 5 ng ml^–1 for MNP, 4.3 ng ml^–1 for PNP and 7.9 ng ml^–1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.     

Enzymatic synthesis of 3-hydroxybutyramides and their conversion to optically active 1,3-aminoalcohols

3-Hydroxybutyramides are obtained in high optical yield from ethyl (±)-3-hydroxybutyrate and aliphatic amines when the reaction is catalyzed by Candida antartica lipase. The chemical reduction of these 3-hydroxybutyramides yields the corresponding 1,3 -aminoalcohols.     

Dihaloperhaloaryl(triphenylarsine)gold(III) Complexes

When C₆Cl₅AuAsPh₃ reacts with halogens, oxidation of the gold(I) complex and formation of X₂Au(C₆Cl₅)AsPh₃ (X = Cl, Br, I) take place. However, when C₆F₅AuAsPh₃ reacts with halogens, oxidation is only observed in the case of Cl₂, whilst I₂ (totally) and Br₂ (partially) split the AuC bond. This behaviour is contrary to that observed with C₆F₅AuPPh₃ and halogens, where the tendency to split the AuC bond decreases in the sequence Cl>B>I.     

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis

The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N(2) laser at 337.1 nm (3.65 J/cm(2)) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 microm is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.     

FIA-fluorimetric determination of adrenaline in pharmaceutical formulations by oxidation with molecular oxygen

The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h^–1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl^–1.     

Synthesis of monoacyl A-ring precursors of 1alpha,25-dihydroxyvitamin D3 through selective enzymatic hydrolysis

An efficient synthesis of monoacylated 1alpha,25-dihydroxyvitamin D3 A-ring precursors 15, 16, 18, and 19 has been described through an enzymatic hydrolysis process. Candida antarctica A lipase (CAL-A) hydrolyzes the C-5 acetate ester in trans stereoisomers 9 and 13, with complete and high selectivity, respectively. In the case of cis isomers 11 and 14, Chromobacterium viscosum lipase (CVL) is the enzyme of choice, exhibiting opposite selectivity for these two enantiomers. This lipase selectively catalyzes the hydrolysis at the C-3 acetate in diester 11 and at C-5 position in diester 14. It is noteworthy that through a hydrolysis reaction CAL-A and CVL allow the synthesis of the four A-ring monoacetylated precursors of 1alpha,25-dihydroxyvitamin D3, precursors which are complementary to those obtained by the enzymatic acylation process. In addition, with excellent yield CVL selectively hydrolyzes the C-3 chloroacetate ester instead of the C-5 acetate in diester 22, a key intermediate in the synthesis of new A-ring modified 1alpha,25-dihydroxyvitamin D3 analogues.     

Stability of tin etiopurpurin

Formulations of the tin etiopurpurin (SnET2) have been observed to undergo a spectral change on storage in dimethylformamide solution. This results in an alteration in the action spectrum, with enhanced photodynamic activity at lower wavelengths and decreased activity at 660 nm. On the basis of structural considerations, a reduced analog of SnET2 was prepared with an absorbance maximum at 640 nm. Formation of this product, termed SnET2H(2) relieves steric strain inherent in the parent molecule. Nuclear magnetic resonance, spectral and photodynamic data are consistent with the formation of SnET2H(2) during SnET2 storage. Slight modifications in the original synthesis are also reported, resulting in improved yields of intermediate products.     

Synthesis of luminescent gold(I) and gold(III) complexes with a triphosphine ligand

We have synthesized and characterized a series of trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine; X = Cl 1, Br 2, I 3, C(6)F(5) 4) and di- and trinuclear gold(III) complexes [[Au(C(6)F(5))(3)](n)(mu-triphos)] (n = 2 (5), 3 (6)). The crystal structure of 6 [[Au(C(6)F(5))(3)](3)(mu-triphos)] has been determined by X-ray diffraction studies, which show the triphosphine in a conformation resulting in very long gold-gold distances, probably associated with the steric requirements of the tris(pentafluorophenyl)gold(III) units. Complex 6 crystallizes in the triclinic space group P(-1) with a = 12.7746(16) A, b = 18.560(2) A, c = 21.750(3) A, alpha = 98.215(3) degrees, beta = 101.666(3) degrees, gamma = 96.640(3) degrees, and Z = 2. Chloride substitutions in complex 1 afford trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (X = Fmes (1,3,5-tris(trifluoromethyl)phenyl) 7, p-SC(6)H(4)Me 8, SCN 9) and [Au(3)Cl(3)(-)(n)()(S(2)CNR(2))(n)(mu-triphos)] (R = Me, n = 3 (10), 2 (12), 1 (14); R = CH(2)Ph, n = 3 (11), 2 (13), 1 (15)). The luminescence properties of these complexes in the solid state have been studied; at low temperature most of them are luminescent, including the gold(III) derivative 6, with the intensity and the emission maxima being clearly influenced by the nature and the number of the ligands bonded to the gold centers.