Determination of polycyclic aromatic hydrocarbons in honey by matrix solid-phase dispersion and gas chromatography/mass spectrometry

A multiresidue method was developed for the de termination of 16 polycyclic aromatic hydrocarbons (PAHs) in unifloral and multifloral honeys. The analytical procedure is based on the matrix solid-phase dispersion of honey on a mixture of Florisil and anhydrous sodium sulfate in small glass columns and extraction with hexane-ethyl acetate (90 + 10, v/v) with assisted sonication. The PAH residues are determined by gas chromatography with mass spectrometric detection using selected-ion monitoring. Average recoveries for all the PAHs studied were in the range of almost 80 to 101%, with relative standard deviations of 6 to 15%. The limits of detection ranged from 0.04 to 2.9 microg/kg. The simultaneous extraction and cleanup of samples makes this method simple and rapid, with low consumption of organic solvents     

Interference of ruthenium red analogues at photosystem II of spinach thylakoids

The effect of ruthenium red analogues on several thylakoid photosynthetic activities has been investigated. RR, RV, RRPh1, RRPh2 and Ph inhibit ATP synthesis and electron flow from water to MV (basal, phosphorylating and uncoupled) as their concentration increases, thus, they act as a Hill reaction inhibitor. They inhibit uncoupled electron transport through PSII from water to DCPIP and partially from DPC to DCPIP. However, these compounds do not affect uncoupled PSI electron transport from DCPIP to MV. Therefore, the target of interaction is at the level of OEC and the span P(680) to Q(A) for RR, RRPh1 and RRPh2. Chlorophyll a fluorescence studies corroborate the already found interference sites and may affect the disconnection between chlorophyll molecules within the LHCII and/or between antennae and RCs, or decreases the exciton to reach the RC and inhibition of PSII occurs. RRPh2 is six times more active than RR. Finally, Ph inhibits electron flow interacting at the level of Q(B).     

Preparation of an eight-membered sesquiterpene lactone resulting from sequential Gif System GoAgg(III) and MCPBA oxidation of (+)-10beta,14-dihydroxy-allo-aromadendrane

Studies aimed at a comparison of chemical, biomimetic (Gif system GoAgg(III))and enzymatic (CHMO) transformations of natural (+)-10beta,14-dihydroxy-allo-aromadendrane have led to preparation of an eight-member sesquiterpene lactone.     

Flow injection analysis: Rayleigh light scattering technique for total protein determination

A novel flow injection analysis (FIA) method with Rayleigh light scattering (RLS) detection was developed for the determination of total protein concentrations. This method is based on the weak intensity of RLS of bromothymol blue (BB) (3',3"-dibromothymolsulfonephthalein) which can be enhanced by the addition of protein in weakly acidic solution. A common spectrofluorimeter was used as a detector. It was proved that the application of this method to quantify the total proteins in real samples by using bovine serum albumin was possible. The RLS signal was detected at lambda(ex)= lambda(em)=572 nm. The linear range was 7.0-70.0 microg mL(-1), the detection limit was 3.75 microg mL(-1), the reproducibility was 5.5% (n=7), and the sample throughput was 26 h(-1).     

Atmospheric degradation of 2-butanol, 2-methyl-2-butanol, and 2,3-dimethyl-2-butanol: OH kinetics and UV absorption cross sections

The absolute rate coefficients for the reactions of hydroxyl radical (OH) with 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)) were measured as a function of temperature (263-354 K) and pressure (41-193 Torr of He, Ar, and N(2)) by the pulsed laser photolysis/laser-induced fluorescence technique. This work represents the first absolute determination of k(1)(-)k(3) and their temperature dependence. No pressure dependence of the rate coefficients was observed in the range studied. Thus, k(i)(298 K) values (x10(-12) cm(3) molecule(-1) s(-1) with an uncertainty of +/-2sigma) were averaged over the pressure range studied yielding 8.77 +/- 1.46, 3.64 +/- 0.60, and 9.01 +/- 1.00 for 2-butanol (k(1)), 2-methyl-2-butanol (k(2)), and 2,3-dimethyl-2-butanol (k(3)), respectively. k(1) and k(3) exhibit a slightly negative temperature dependence over the temperature range studied. In contrast, the rate coefficient for the reaction of OH with 2-methyl-2-butanol (k(2)) did not show any temperature dependence. Some deviation of the conventional Arrhenius behavior was clearly observed for k(3). In this case, the best fit to our data was found to be described by the three-parameter expression k(T) = A + B exp(-C/T). The UV absorption cross sections of 2-butanol, 2-methyl-2-butanol, and 2,3-dimethyl-2-butanol have also been measured at room temperature between 208 and 230 nm. The values reported constitute the first determination of the UV cross sections of those alcohols. Our results are compared with previous studies, when possible, and are discussed in terms of the H-abstraction by OH radicals. The atmospheric implications of these reactions and the photochemistry of these alcohols are also discussed.     

Rhodium-catalyzed hydroformylation of C6 alkenes and alkene mixtures - a comparative study in homogeneous and aqueous-biphasic media using PPh3, TPPTS and TPPMS ligands

The complexes RhH(CO)L₃, where L = PPh₃, P(m-C₆H₄SO₃Na)₃ (TPPTS), and (C₆H₅)₂P(m-C₆H₄SO₃Na) (TPPMS) were used as catalyst precursors for a comparative study of the catalytic hydroformylation of several C6 alkenes and alkene mixtures under moderate reaction conditions in homogeneous (PPh₃) and aqueous-biphasic (TPPTS, TPPMS) media. The biphasic systems are efficient for the hydroformylation of hex-1-ene, 2,3-dimethyl-1-butene, styrene, cyclohexene, and mixtures thereof, in water/n-heptane at 80 °C. The main problem associated with these catalysts is their tendency to promote alkene isomerization if the effective syngas concentration in the liquid phases is low, but this side-reaction can be suppressed by using higher CO/H₂ pressures (54 atm). The selectivity of both water-soluble catalysts for linear products of hex-1-ene and for branched products of styrene is modest in comparison with the homogeneous system, which may limit their utility for classical oxo uses, but this is not a disadvantage for other interesting applications related to the hydroformylation of alkene mixtures and particularly to naphtha upgrading where linear and branched products are equally useful. The catalysts can be recycled without significant loss of activity and are resistant to the presence of benzothiophene in the mixture.     

Reductive elimination reaction of rhenium complexes trans-(η-C5Me5)Re(CO)2(chloroaryl)Cl

Thermal reaction of the chloroaryl-chloride complexes trans-(η⁵-C₅Me₅)Re(CO)₂(Ar^Cl)Cl (Ar^Cl = 3-ClC₆H₄, 3-ClC₆H₃(4-Me) and 3,5-Cl₂C₆H₃) in acetonitrile did not interconvert to the cis isomer, instead the complex ReCl(CO)₂(NCMe)₃ and the corresponding 5-Ar^Cl-1,2,3,4,5-pentamethylcyclopentadiene were formed. Similar reductive elimination products were obtained when the starting rhenium complexes were reacted with trimethylphosphite in toluene.     

A sensitive spectrophotometric method for lead determination by flow injection analysis with on-line preconcentration

A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l⁻¹, a detection limit of 5.0 ng ml⁻¹ and a sample throughput of 15 h⁻¹. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES.     

Influence of aromatic substituents on metal(II)salen catalysed, asymmetric synthesis of α-methyl α-amino acids

The influence of substituents on both the aromatic rings of the catalyst, and the benzylidene unit of the substrate are investigated in the (salen)copper(II) catalysed asymmetric benzylation of alanine derivatives. Catalysts with electron-donating, and electron-withdrawing substituents of various sizes and at various locations on the aromatic rings of the salen ligand were prepared, but all exhibited inferior enantioselectivity to the parent (salen)copper(II) complex. In contrast, the introduction of halogenated substituents onto the aromatic ring of the N-benzylidene alanine methyl ester substrate was found to enhance the enantioselectivity of the alkylation with a para-chloro substituent giving optimal results. A new procedure for the preparation of the catalysts which avoids the need for chromatography on sephadex LH20 is reported, and the optimal catalyst obtained in this way was found to be a cobalt(salen) complex.     

1,3-Dichloro-2-butene: a useful precursor for the 2-butene-1,3-dianion and its corresponding 1,3-dipolar synthon

The reaction of 1,3-dicloro-2-butene (1; 5:1 Z:E-mixture) with lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 1% molar) in the presence of different electrophiles [EtCHO, PrⁱCHO, Bu^tCHO, c-C₆H₁₁CHO, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO, (c-C₃H₅)₂CO, Me₃SiCl] in THF at temperatures ranging between −78 and −50°C gives, after hydrolysis with water, the corresponding products 2 in different Z:E-ratios depending on the electrophile used. Treatment of some diols 2 with hydrochloric acid gives dienic alcohols 3 or substituted dihydropyrans 4, depending on the structure of the starting diol. Finally, the same dichlorinated starting material is transformed into the corresponding allylic amines derived from morpholine and benzyl methyl amine and submitted to the same DTBB-catalysed lithiation as above, so after reaction with different electrophiles [Bu^tCHO, c-C₆H₁₁CHO, Me₂CO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO, Me₃SiCl] and final hydrolysis with water, compounds 7 are isolated having a Z-configuration. A mechanistic explanation for this behaviour is given.