Isolation,identification and synthesis of the sex pheromone of the citrus mealybug,Planococcus citri (risso)

The sex attractant pheromone of the citrus mealybug, $\text{Planococcus citri}$ (Risso), has been Identified as (1$\text{R}$-$\text{cis}$)-(+)-2,2-dimethyl-3-(1-methylethenyl)cyclobutanemethanol acetate (VI).     

Room-temperature synthesis and conductivity of the pyrochlore type Dy2(Ti1−yZry)2O7 (0?y?1) solid solution

Different compositions in a solid solution of general formula Dy₂(Ti_1−yZr_y)₂O₇, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y?0.4, which, as observed in the similar Y₂(Ti_1−yZr_y)₂O₇, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y>0.6, reaching a maximum value of ∼5×10⁻³ for Dy₂Zr₂O₇ at 900 °C.     

INTERACTION OF THE PEPTIDE HORMONE ADRENOCORTICOTROPIC ACTH(l-24), WITH A MEMBRANE MODEL SYSTEM: A FLUORESCENCE STUDY*

The peptide hormone adrenocorticotropin and a related peptide were studied in solution and in interaction with a model system of membranes (small unilamellar vesicles of dipalmitoylphosphatidylcholine and 17% dimyristoylphosphatidylglycerol) via fluorescence spectroscopy. In aqueous solution, intramolecular distances between the fluorescent residues R(Tyr²-Trp⁹) = 9.2 Å and R(Trp⁹-Tyr²³) 18 Å were obtained, in agreement with molecular models. Interaction of the peptide with the negatively charged membrane is evident from the alteration of the Trp photophysical parameters (quantum yield, fluorescence spectra and anisotropy), with a partition constant between the lipidic and aqueous phase of Kp =1–2 times 10³. The existence of two populations of Trp in the membrane, which are distinctly accessed by acrylamide, was concluded from the tryptophan fluorescence quenching study; the two fractions are located near the membrane interface as inferred from its fluorescence quenching by the 5-doxylstearate and 16-doxylstearate lipophilic quenchers. This result is further supported by energy transfer experiments to the 3-(9-anthroyloxyl)stearic acid and 12-(9-anthroyloxyl)stearic acid probes.     

Dehydration and crystallization process in sol-gel zirconia

Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry (DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO_2-x(OH)_2x·yH₂O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of 3-amino-1,2,4-triazole (amitrole) in environmental waters by capillary electrophoresis

3-Amino-1,2,4-triazole (amitrole) is a widely used pesticide, with many difficulties to be analyzed at the regulatory level in drinking water, because its high solubility in water. This paper describes a simple and fast method for the simultaneous determination of amitrole and atrazin-2-hydroxy, principal degradation product of s-triazines, by capillary zone electrophoresis. Separation and determination of these herbicides in water samples was performed in 0.02 mol l⁻¹ phosphate buffer at pH 3.2. The method allows determination of the amitrole and atrazin-2-hydroxy in water samples in concentration lower than 100 μg l⁻¹. The detection limits using a previous preconcentration step of amitrole in Alberche River (Comunidad Autónoma de Madrid, Spain) and drinking water spiked samples was of 4 μg l⁻¹.     

Applicability of the WKB method in asymmetric double wells with degenerate and nondegenerate minima

To test the applicability of the WKB semiclassical approximation to correctly describe the tunneling frequencies and energy levels in asymmetric double wells, we have considered the cases where the asymmetry comes from the nondegeneracy of the two minima and when it comes from the asymmetry in the shape of the barrier between both minima. To do this, we compare the tunneling frequencies and energy levels obtained through the WKB method for symmetric and asymmetric cases with exact results obtained by a basis set procedure. Our results show that the semiclassical WKB approximation has to be used with caution for asymmetric double wells. © 1994 by John Wiley & Sons, Inc.     

Microwaves in organic synthesis. Thermal and non-thermal microwave effects

Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur by conventional heating and even modifications of selectivity (chemo-, regio- and stereoselectivity). The effect of microwave irradiation in organic synthesis is a combination of thermal effects, arising from the heating rate, superheating or "hot spots" and the selective absorption of radiation by polar substances. Such phenomena are not usually accessible by classical heating and the existence of non-thermal effects of highly polarizing radiation--the "specific microwave effect"--is still a controversial topic. An overview of the thermal effects and the current state of non-thermal microwave effects is presented in this critical review along with a view on how these phenomena can be effectively used in organic synthesis.     

The dependence of 10Dq upon the metal–ligand distance,R, for transition-metal complexes. What is its microscopic origin?

Experimental results on 3d O_h complexes in insulators reveal that 10Dq α R^?n, where R is the metal–ligand distance and n is close to five. This strong dependence determines the Huang–Rhys factor, S(A_1g), associated to the symmetric A_1g mode of the first excited state of complexes like MnX and CrX (X = halide) and makes it possible to measure R changes down to ∽ 10^?3 Å. This work is devoted to understanding, within a molecular orbital framework, the microscopic origin of such a dependence, which is related to the corresponding one displayed by the transferred spin densities fσ, f_s, and fπ. The analysis is focused on MnF. As a main result, it is shown that though fσ ? f_s the interaction between d(e_g) orbitals and 2s orbitals of F^? is not only primarily responsible for the R dependence of 10Dq but also makes a significant contribution to the 10Dq value itself. The present work thus shows that the significant dependence of 10Dq upon R is ultimately related to the strong dependence of f_s and the isotropic superhyperfine constant A_s upon R displayed by the experimental results of several 3d impurities. © John Wiley & Sons, Inc.     

Towards a better understanding of the cisplatin mode of action

We have studied how platinum(II) complexes [Pt(dien)Cl]Cl, [Pt(en)Cl2] and cisplatin react with hybrid molecules that contain sulfur and nitrogen ligands, in particular Phac-Met-linker-p5'dG (Phac = phenylacetyl), Phac-His-linker-p5'dG, Phac-His-Met-linker-p5'dG and Phac-His-Gly-Met-linker-p5'dCATGGCT. The progress of the reactions was monitored by HPLC, and by [1H,15N]-HSQC NMR when 15N-cisplatin was used. The products were isolated and characterised by using enzymatic and chemical reactions and spectroscopic techniques (UV and/or NMR spectroscopy, electrospray or MALDI-TOF mass spectrometry). The combined use of digestion with proteases and reaction with hydrogen peroxide followed by mass spectrometric analysis indicated the platinum coordination positions on the peptide moiety of the largest hybrid. Monofunctional Pt-S adducts were transformed into Pt-N complexes in which Pt-N7 bonds were formed preferentially. Most of the chelates isolated had Pt-S bonds, and, in the case of cisplatin complexes, loss of the ammine trans to sulfur gave rise to the formation of tricoordinate species with platinum-mediated peptide-nucleotide cross-links. 1,2-Intrachain platinum GpG adducts were only obtained in very small amounts (1-4%).     

Kinetic fluorimetric determination of nanogram amounts of manganese, based on its catalysis of the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone with hydrogen peroxide

A kinetic method is described for the determination of trace amounts of manganese(II), based on its catalytic effect on the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide. The reaction is followed by measuring the rate of change of fluorescence (lambda(ex) 365 and lambda(em) 440 nm). The calibration is linear over the manganese range 2-9 ng ml with a precision of +/-1%. The proposed method suffers from few interferences.