Hydroselenation of alkynes using NaBH4/BMIMBF4: easy access to vinyl selenides

A general and easy method for the synthesis of several vinyl selenides using NaBH₄ and BMIMBF₄ as a recyclable solvent is described. This efficient and improved method furnishes the corresponding vinyl chalcogenides preferentially with Z configuration. We also observed that when the same protocol was applied to phenyl acetylene, (E)-bis-phenylseleno styrene was obtained in good yield and with high selectivity.     

Comparison of slurry sampling and microwave-assisted digestion for calcium, magnesium, iron, copper and zinc determination in fish tissue samples by flame atomic absorption spectrometry

The development of a slurry sampling method for the determination of calcium, copper, iron, magnesium and zinc in fish tissue samples by flame atomic absorption spectrometry is described. In comparison with microwave-assisted digestion, the proposed method is simple, requires short time and eliminates total sample dissolution before analysis. Suspension medium was optimized for each analyte to obtain quantitative recoveries from fish tissue samples without matrix interferences. Nevertheless, iron recoveries higher than 46% were not found. Treatment of samples slurried in nitric acid by microwave irradiation for 15-30 s at 75-285 W permitted to achieve efficient recoveries for calcium, iron, magnesium and zinc. Further improvement in the matrix effects for iron determination was accomplished by the use of an additional step of short microwave-assisted suspension treatment. However, standard addition method was required for calcium and copper determination, being necessary hydrochloric acid as suspension medium for the last one. Although copper could not be determined in the certified reference material using microwave-assisted digestion, the accuracy of the slurry sampling method was verified for all the investigated analytes. Detection limits were 22.8 ± 8.0, 0.884 ± 0.092, 5.07 ± 0.76, 35.5 ± 0.7 and 1.17 ± 0.04 μg g⁻¹ for calcium, copper, iron, magnesium and zinc, respectively. The standard deviations obtained using slurry sampling method and microwave-assisted digestion were not significantly different, and the mean relative standard deviation of the over-all method (n = 3) of the slurry sampling method for different concentration levels was below 12%.     

Reaction kinetics of the selective liquid phase hydrogenation of styrene oxide to β-phenethyl alcohol

Liquid phase hydrogenation of styrene oxide using 1% Pd/C and NaOH as a promoter was found to give selectively β-phenethyl alcohol (PEA) under very mild conditions (313–333 K; 0.68–5.5 MPa). The kinetics of this system was investigated by collecting initial rate data in a batch slurry reactor. Rate of hydrogenation was found to decrease beyond a certain concentration of both hydrogen (>3 MPa) and styrene oxide (>0.5 kmol/m³). A Langmuir–Hinshelwood type rate equation has been proposed based on the initial rate data in the kinetic regime. The model predictions agree very well with the experimentally observed concentration–time data indicating the applicability of the proposed rate model.     

Synthesis and acid-base properties of (1H-benzimidazol-2-yl-methyl)phosphonate (Bimp2-). Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N-1)H and the phosphonate group

The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided.     

Two-step upflow anaerobic sludge bed system for sewage treatment under subtropical conditions with posttreatment in waste stabilization ponds

A pilot-scale sewage treatment system consisting of two upflow anaerobic sludge bed (UASB) reactors followed by five waste stabilization ponds (WSPs) in series was studied under subtropical conditions. The first UASB reactor started up in only 1 mo (stable operation, high chemical oxygen demand [COD] removal efficiency, low volatile fatty acids concentration in the effluent, alkalinity ratio above 0.7, biogas production above 0.1 Nm3/kg of CODremoved). Removal efficiencies up to 90% were obtained in the anaerobic steps at a hydraulic retention time of 6 + 4 h (80% removal in the first step). Fecal coliform removal in the whole system was 99.9999% (99.94% in anaerobic steps and 99.98% in WSPs). COD balances over UASB reactors are provided. A minimum set of data necessary to build COD balances is proposed. Intermittent sludge washout was detected in the reactors with the COD balances. Sludge washout from single-step UASB reactors should be monitored and minimized in order to ensure constant compliance with discharge standards, especially when no posttreatment is provided. The system combined high COD and fecal coliform removal efficiency with an extremely low effluent concentration, complying with discharge standards, and making it an attractive option for sewage treatment in subtropical regions.     

Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.     

Determination of triclosan in foodstuffs

A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese).     

Flexible square supramolecular rings with hydrogen-bonded bushing in solid-state oxalurate complexes: versatility of the oxalurate ligand in covalent and noncovalent binding

Isotypic pseudooctahedral complexes of Co, Ni, and Cu with two chelating oxalurate ligands and two water molecules, trans-[M(oxalurate)(2)(H(2)O)(2)], have been synthesized and isolated by a novel progressive crystallization technique. Diffraction analyses reveal that the three complexes form isotypic solid-state structures in which the molecular connectivity and complex network of noncovalent interactions are qualitatively identical throughout the series. The oxalurate groups form unbounded chains through two different self-recognition patterns-a typical DA-AD motif and an unusual DDA'-A'DD form (D = hydrogen bond donor, A' = double acceptor). The unsymmetrical oxalurate group possesses the topological properties necessary to form aggregates of higher symmetry, and the "M(oxalurate)(2)" fragments form a rhombic 2-D motif with hydrogen-bonded corners and with hydrogen-bond acceptors directed to the inside of the cyclic aggregate. The 2-D net is stacked to form a channeled 3-D structure, in which the coordinated aqua ligands form the principal interlayer interactions. The slanted channels are occupied by the axial waters and by waters of crystallization, which are hydrogen bonded to the channel walls to form an ordered bushing. The extensive 3-D hydrogen-bonded superstructure is flexible enough to accommodate the distortion produced by the Jahn-Teller effect in the copper compound without requiring a qualitative structural change. The bonds affected by Jahn-Teller distortion in the Cu complex [Cu-O = 2.3788(15) A] are significantly longer than their analogues in the Co and Ni complexes [Co-O = 2.175(2), Ni-O = 2.094(9) A].     

Quantum chemical aspects of the chelate effect in complexes

A typical “chelate” effect is demonstrated by means of all-electron ab initio LCGO SCF calculations on the [Li(HCONH₂)₂]⁺ complex in different geometrical arrangements. Energetic factors and the electronic structure of the complexes are discussed, showing the chelate effect to be connected with striking changes in bonding, density distribution and electronic energy.     

On Raman optical activity sign-switching between the ground and excited states leading to an unusual resonance ROA induced chirality

Raman optical activity (ROA) spectra recorded for a chiral naphthalene diimide derivative (nBu-NDI–BINAM) dissolved in a series of solvents exhibit strong solute to solvent induced chirality with: (1) dominating bands of solvents, (2) nBu-NDI–BINAM resonance ROA (RROA) bands which are barely visible, (3) monosignate RROA Solvent spectra with an unexpected sign concordant with that of the ECD band of the resonant electronic state, (4) bisignate RROA bands for a few solvents, and (5) superposition of non-resonant and resonant ROA bands of the chiral solvents. The unusual ROA enhancement was explained in terms of resonance energy transfer with resonant Raman emission. The surprising RROA sign-switching was found to be due to specific conformational equilibria where one solute conformer dominates in the ground and the other in the first excited singlet state, and, the signs of the related ECD bands of these two conformers are opposite.

Unusual solute to solvent induced chirality in ROA comes from specific conformer equilibria in the ground and the excited states.