Paradoxes and paradigms: observations on pyrohydrolysis,oxygen bomb combustion,and alkaline carbonate fusion,most frequently used decomposition methods for subsequent determination of fluorine and accompanying thermochemistry

Pyrohydrolysis, oxygen bomb combustion, and alkaline carbonate fusion are the most frequently used methods for decomposition of fluorine containing materials. The efficiency of these methods was proven by the determination of fluorine content in certified reference materials of clay and vegetation. Possible reactions proceeding during decomposition were suggested and accompanying thermochemistry discussed. The Gibbs energies were estimated to establish if suggested reactions are thermodynamically favorable or not. In addition, linear relationships between the enthalpies of formation of metal fluorides and the balanced values of the enthalpies of formation of the plausible reaction products (metal tungstates, metal oxides, or metal carbonates), electronegativity of metals, and number of fluorine atoms in metal fluorides were established. These equations were suggested for the estimation of the enthalpies of formation of metal tungstates, metal oxides, or metal carbonates, for which experimental data are not available.     

Structural diversity of isothiocyanato Cd(II) and Zn(II) Girard’s T hydrazone complexes in solution and solid state: effect of H-bonding on coordination number and supramolecular assembly of Cd(II) complex in solid state

The isothiocyanato Zn(II) complex (1) and mixed isothiocyanato/thiocyanato Cd(II) complex (2) with the condensation product of 2-acetylpyridine and trimethylammoniumacetohydrazide chloride (Girard’s T reagent) (HLCl) were investigated both experimentally and theoretically. The crystal structures of both complexes showed tridentate N₂O coordination of hydrazine ligand. In complex 1 square-pyramidal coordination surrounding of Zn(II) consists of deprotonated hydrazone ligand and two isothiocyanato ligands, while in octahedral Cd(II) complex ligand is coordinated without deprotonation as a positively charged species and coordination geometry is completed with two N-coordinated and one S-coordinated NCS^? anions. NMR spectroscopy and molar conductivity results for Cd(II) and Zn(II) complexes indicated their instability in solution. DFT calculations were performed to explain coordination preference and stability of complexes 1 and 2 in solid state and in solution. The obtained Cd(II) complex is the first reported mononuclear pseudohalide/halide Cd(II) complex with quinoline-/pyridine-based hydrazone ligands possessing octahedral geometry in solid state. In this complex, H-bonding has significant impact on coordination number and supramolecular assembly in solid state.     

A Non‐Heme Iron Photocatalyst for Light‐Driven Aerobic Oxidation of Methanol

Non‐heme (L)Fe^III and (L)Fe^III‐O‐Fe^III(L) complexes (L=1,1‐di(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)ethan‐1‐amine) underwent reduction under irradiation to the Fe^II state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge‐transfer excitation of a Fe^III?μ‐O?Fe^III complex to generate [(L)Fe^IV=O]²⁺ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)Fe^II. Under aerobic conditions, irradiation accelerates reoxidation from the Fe^II to the Fe^III state with O₂, thus closing the cycle of methanol oxidation to methanal.     

Phytochemical analysis of Saponaria officinalis L. shoots and flowers essential oils

Phytochemical analysis by GC and GC/MS of the essential oil samples obtained from fresh shoots and flowers of Saponaria officinalis L. allowed the identification of 96 components in total, comprising 94.7% and 86.0% of the total oils compositions, respectively. Regarding the shoots essential oil, the major of 87 identified volatile compounds were phytol (14.1%), tricosane-6,8-dione (13.4%), patchouli alcohol (7.9%) and tricosane (7.2%), whereas patchouli alcohol (20.0%), heneicosane (11.5%) and tricosane (8.4%) were dominant among the 66 volatiles in the flower oil. Nonterpenoid compounds had the highest contribution in S. officinalis shoots essential oil (53.7%), while in the flower oil, constituents were almost evenly distributed between the oxygenated sesquiterpenoid (41.2%) and nonterpenoid compounds (39.5%).     

Metal contents in tench otoliths: relationships to the aquatic environment

A monitoring of the quality of waters was attempted determining metal accumulation in target organs as otoliths of freshwater fish. Tenchs of age ranging between 2 and 10 years were sampled in three different canals receiving wastewater from industrial, agricultural and urban activities. Metal contents were determined in both lapilli and asterisci otoliths, using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Analytical data are reported for minor metals and for some trace metals. Al, Fe and Zn have contents depending on the environment where the fish has lived, while Na, K, Ca and Sr contents are insensitive to the different aquatic habitat. Considering the two types of otolith separately, lapilli display a different affinity for trace metals (Al, Fe and Zn), while in asterisci this affinity is matched only for zinc. The high affinity of zinc for both types of otoliths suggests using this metal for discriminating the fresh waters by checking its accumulation in otoliths, as well as correlating this accumulation with age of the fish: a negative power curve equation is proposed. Since highest concentrations are found in individuals of 2-3 yr., it is advisable to use this fish for such environmental studies.     

The signal-to-noise ratio as the measure for the quantification of lysophospholipids by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

The subject of this report is the determination of lysophospholipids; lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine and lysophosphatidic acid, by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). The mean signal-to-noise ratio (S/N) was used for the first time as a measure of lysophospholipid concentration. Two different sample preparation procedures were applied, the 'standard' procedure and the 'premix' in order to check to what extent these methods influence the results of the lysophospholipid quantification. Results can be summarised as follows: (a) All classes of lysophospholipids can be easily and sensitively analysed by MALDI-TOF MS. The smallest detectable amount of lysophospholipids was 0.09 pmol on the sample plate. That is about two orders of magnitude lower than the amount detectable by standard chromatographic methods. (b) The mean S/N of all peaks detected in the positive ion mass spectra can be used as a measure of the lysophospholipid concentration. Whereas the S/N for neutral lysophospholipids correlated with the applied concentrations only when the samples were analysed as 'premix', the sample preparation and application procedure did not influence the quantification of acidic lysophospholipids. The standard deviations were not higher than 10% of the mean value. (c) All spectra were additionally analysed in the presence of CsCl. The addition of caesium ions makes the peak identification unambiguous in phospholipid mixtures, but the Cs adducts of lysophospholipids do not properly reflect their concentration and, therefore, they were not useful for quantification. (d) The applicability of the method was demonstrated on the organic extract of human neutrophils.     

Abatement of waste-water biorefractory organics via electro-oxidative treatment

The electrochemical oxidation of coumaric acid, a biorefractory compound present in several industrial waste waters, has been investigated by use of Pt-Ti anodes and at electrolyte concentration (0.02 N NaCl or Na2SO4) low enough to allow direct dischargeability of the waste water into superficial water basins according to the Italian law (DL 152/11-5-99). Particularly, the role of the electrolyte over the conversion rate has been assessed. The obtained results show that the oxidation process should take place both at the electrode surface and in the bulk of the solution, via electrochemically-generated oxidising species (H2O2, persulfates, Cl2, NaClO). The faster coumaric acid abatement rates were found with chloride based electrolytes, which, however, lead to the formation of non-biodegradable small-molecular-weight chlorinated hydrocarbons.     

Study of the Lipophilicity and Retention Behavior of Some s-Triazine Derivatives on Aminoplast and Cellulose

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of four groups of s-triazine derivatives (15 compounds) has been studied on aminoplast and cellulose...     

The kinetics of water desorption from porous glasses

The kinetics of water desorption from porous glasses silica gel and porous aluminosilicates were followed through the TG and DTG methods. In all cases only one thermodesorption peak appeared. The kinetic parameters were determined by standard nonisothermal methods. The activation energy is constant and independent of the coverage degree and pore diameter in the system porous glass-water. The functionE(θ) were determined for the silica gel and porous aluminosilicatesE=E ₀+a exp (-bθ). The parametersE ₀,a andb depend on the SiO₂/Al₂O₃ ratio and on the distribution of active centers on the surface.     

Transition metal complexes with thiosemicarbazide-based ligands,Part II,Synthesis and characterisation of nickel(II), cobalt(II), manganese(II) and zinc(II) complexes with the pentadentate ligand, 2,6-diacetylpyridine bis(S-methylisothiosemicarbazone)

Summary The reaction of warm alcoholic solutions of acetates of Co^II, Mn^II, Zn^II and Ni^II with 2, 6-diacetylpyridine andS-methylisothiosemicarbazide hydrogen iodide yielded the complexes: [Co(H₂L)I₂]·H₂O, [Mn(H₂L)(MeOH)₂]I₂, [Zn(H₂L)(MeOH)I]I and [Ni(HL)]I, (H₂L=the pentadentate pentaaza-ligand 2, 6-diacetylpyridine bis(S-methylisothiosemicarbazone)). The reaction of methanolic solutions of [Ni(HL)]I and NH₄NCS or LiOAc.2H₂O, give [Ni(HL)]NCS and NiL, respectively. For the complexes of Co^II, Mn^II and Zn^II, a pentagonal bipyramidal configuration is proposed, with H₂L in the equatorial plane and two unidentate ligands (I and/or MeOH) in the axial positions. The complexes [Ni(HL)]X (X=I or NCS) and NiL probably have monomeric five- and dimeric six-coordinate structures, respectively, in which only the chelate ligand is involved in coordination.