Theoretical analysis of resonant raman scattering: Simulations of lineshapes and excitation profiles

The steady-state response of a three-level system in the presence of a strong laser field is described with the density operator formalism, in order to derive an analytical expression for the intensity of resonance Raman scattering. The Liouville equation for the density operator is written in quantum form for both the molecular system and the radiation field, making use of the dipole and rotating-wave approximations for the matter-radiation interaction, and of the Markov approximation for the molecular decays. The equation is solved exactly for the laser field, and in perturbative way for the generated field. The results account for power broadening of the generated line. Rabi intensity-dip of the generated signal, and for the excitation profiles in the Franck-Condom approximation.     

Direct measurement of gas solubility and diffusivity in poly(vinylidene fluoride) with a high-pressure microbalance

We present solubility and diffusion data for the gases methane and carbon dioxide in the polymer poly(vinylidene fluoride). The polymer was cut from extruded piping intended for use in offshore oil and gas applications. Measurements were carried out using a purpose-built high-pressure microbalance. These properties were determined in the temperature range 80-120 °C and in the pressure range 50-150 bar for methane and 20-40 bar for carbon dioxide. In general, good agreement was obtained for similar measurements reported in the literature. Solubility follows a Henry’s law (linear) dependence with pressure. Diffusion coefficients for each of the gases in the polymer were also measured using the balance. Activation energies for diffusion and heats of solution for the two gases in the polymer were also determined.     

Production and energetic use of biogas from energy crops and wastes in Germany

The production of biogas for reducing fossil CO₂ emissions is one of the key strategic issues of the German government and has resulted in the development of new process techniques and new technologies for the energetic use of biogas. Progress has been made in cultivating energy crops for biogas production, in using new reactor systems for anaerobic digestion, and in applying more efficient technologies for combined heat and power production. Recently, integration of fuel cells within the anaerobic digestion process was started, and new technologies for biogas upgrading and conversion to hydrogen were tested. This article describes the trends in Germany for achieving more efficient energy production.     

Determination of methylmercury in environmental samples using static headspace gas chromatography and atomic fluorescence detection after aqueous phase ethylation

A rapid and automated method for the determination of monomethylmercury (MMHg) in environmental samples was developed using headspace gas chromatography with atomic fluorescence detection in combination with aqueous phase ethylation. Sample preparation steps were optimized for sediments, biological samples, and water samples using certified reference materials and real samples with a broad range of MMHg concentrations. Different extraction procedures were compared for both sediments and biological samples. The methods were applied in the intercomparison exercises for the certification of MMHg in sediments (IAEA 405) and in Oyster tissue (BCR 710) and the results were accepted for certification. The detection limits for MMHg are 0.002 ng Hg/g for sediments and biological samples and 0.01 ng Hg/L for water samples. The method was tested for methylation artifacts; no artifact was observed in the sediment samples and CRMs tested.     

Traditional medicine in Syria: folk medicine in Aleppo governorate

The use of Traditional Arabic Medicine (TAM) for various diseases has been popular but scarcely studied in Syria. In the present study, we carried out ethnobotanical and ethnopharmacological research on the plants traditionally used to cure various diseases in northern Syria. The information was collected from the city and villages of the Aleppo governorate "Mohaafazah" in the north of Syria, collecting data directly on the basis of a detailed survey of inhabitants and herbalists. In this survey, we found that hundreds of plant species are still in use in TAM for the treatment of various diseases. We selected the most common 100 species, used in the treatment of more than 25 diseases. Among these plants, 53 are used for treating gastrointestinal disorders, 38 for respiratory system diseases, including asthma, bronchitis and cough, 34 for skin diseases, 21 for diabetes, 17 for kidney and urinary disorders, 16 for cardiac disorders, 14 for infertility and sexual impotency, 13 for treating liver diseases, 13 for several types of cancer, 9 for enhancing breast milk excretion, 8 for weight loss, 5 for reducing cholesterol, and three for weight gain. Plants were collected and identified: scientific Latin names, local names, the used parts of the plant, the herbal preparations and the local medical uses are described. Scientific literature concerning the activity of the investigated species is also reported and discussed according to their traditional uses.     

Simultaneous determination of copper and lead in ethanol fuel by anodic stripping voltammetry

The presence of trace metals in car fuels plays an important role in the engine maintenance. In addition, these metals contribute for the environmental contamination in big cities and their control is necessary. Square Wave Stripping Voltammetry (SWSV) is a very sensitive technique for elemental trace determination and was applied for ethanol fuel analysis. The first studies were done searching for the best conditions for copper determination in alcoholic medium, utilizing gold electrodes. During these studies, the possibility of the simultaneous determination of copper and lead in the same experiment was observed. Two procedures for the analysis of these metals were adopted: The direct quantification of metals in alcohol–water mixtures and a second way that involves the evaporation of the organic solvent and re-suspension of the ions with water+electrolyte. Good recovery values were obtained for synthetic samples spiked with known amounts of metals. The results obtained for the two methods were in good agreement. The detection limits for copper and lead in 75% ethanol–water ratio solution were calculated as 120 and 235 ng l⁻¹, respectively, for 15-min deposition time.     

Treatment of Anomalous Vapor Diffusion in Polymers

The mechanics of thermally-activated gaseous diffusion in polymers have long been studied for development of theoretical understanding of the interactive forces responsible for the non-linear nature of diffusion and the resultant enthalpic changes in the polymer. Methodologies and calculations have been developed in this work for treatment of experimental data for elimination of thickness-related anomalies in water vapor diffusion and for delineation of pressure effects. Linearized data for different polymer thicknesses and the attendant internal thermal effects have been generated by using calculated single molecule diffusion values. Equally linear data are obtained for different pressures by the use of a graphical method from which identical diffusion values are obtained, independent of material thickness and external pressure. True comparisons and classification of polymers as to their diffusivities are thus possible for development of barrier materials for food and drug packaging and for protective encapsulation of electronic devices. Results will be reported for three structurally different polymers. This revised version was published online in July 2006 with corrections to the Cover Date.     

微波萃取毛细管电泳等离子体原子发射光谱法分析银杏中的元素形态

以微波萃取提取银杏叶与银杏果中的水溶液。采用毛细管电泳-电感耦合等离子体原子发射光谱法(CE-ICP-AES),对银杏叶与银杏果水提取液中的Ca、Mg、Zn、Cu等元素的形态进行了研究,并对这些元素在银杏叶和银杏果中的含量及其水提取液中的提取率做了对比研究。     

A pilot study for the preparation of a new Reference Material based on antarctic krill

The preparation of new Certified Reference Materials (CRMs) of antarctic matrices forms the backbone of an ongoing project in the framework of the Italian National Program for Antarctic Research. The first CRM of this kind (MURST-ISS-A1 Antarctic Marine Sediment) is already available. The second phase focuses on the certification of antarctic krill, a small shrimp extremely abundant in the Southern Ocean. The total mass of krill available for this purpose is approximately 44 kg and results from the combination of three different catches (Ross Sea, Marguerite Bay and Livingston Island, respectively). The quantification of the following elements in the raw mass appears to be affordable by current analytical techniques, values being in the range of (in μg/g) 0.11–0.30 for As, 0.03–0.12 for Cd, 0.06–0.23 for Cr, 6.1–21 for Cu, 5.7–7.6 for Fe, 0.005–0.008 for Hg, 0.7–1.2 for Mn, 0.013– 0.077 for Ni, 0.04–0.57 for Pb and 12–16 for Zn. On the other hand, the average values ascertained in freeze-dried krill are as a rule one order of magnitude higher, i.e., (in μg/g), 3.2 for As, 0.6 for Cd, 1.8 for Cr, 75 for Cu, 61 for Fe, 0.025 for Hg, 4.6 for Mn, 0.7 for Ni, 2.1 for Pb and 81 for Zn. Information on the pretreatment of krill and details on the planned certification campaign are also given. Received: 10 June 1997 / Revised: 24 September 1997 / Accepted: 28 September 1997     

Phase system selectivity and two-dimensional separations in liquid column chromatography

Correlations between the separation selectivity in aqueous and non-aqueous reversed-phase systems and in normal-phase LC systems were investigated for samples containing different numbers of two repeat structural elements. Such samples are best separated in "orthogonal" two-dimensional chromatographic systems, showing selectivity for one type of the repeat structural element only in the first dimension and for the other structural element only in the second dimension. The number of resolved compounds improves as the degree of orthogonality of the separation systems increases with decreasing correlation between the selectivities for the sample structural distribution in the two dimensions. Orthogonal systems with non-correlated selectivities for each repeat structural element provide the highest number of separated peaks and regular arrangement of the peaks over the two-dimensional retention space according to the individual structural element distribution and the best use of the available peak capacity. Fully orthogonal systems are difficult to find in practice. Partially orthogonal system with correlated selectivities for one structural type distribution, but with one system non-distinguishing the distribution for the other structural element are still useful for the two-dimensional separations. The correlations between the selectivities for repeat regular structural increments were employed to evaluate the suitability of phase systems for two-dimensional HPLC separations. The selectivity correlation in various reversed-phase and normal-phase systems was evaluated for two sample types: (1) Various RP columns show significantly inversely correlated selectivities for acyl lengths and numbers of double bonds distribution, but the differences in the double bond selectivity can be used for practical separations of triacylglycerols with the same equivalent carbon numbers. (2) Synthetic EO-PO block (co)oligomers with two-dimensional distribution of oxyethylene and oxypropylene monomer units were separated according to the two distribution types using on-line two-dimensional reversed-phase-normal-phase LC with a C18 column in the first dimension and an aminopropyl silica column in the second dimension.     

Simultaneous determination of sulphadiazine and trimethoprim in plasma and tissues of cultured fish for residual and pharmacokinetic studies.

Clean-up and high-performance liquid chromatographic methods for the simultaneous determination of sulphadiazine and trimethoprim in fish plasma and tissues have been developed. The average recovery of sulphadiazine varied from 74% in liver to 92% in plasma, whereas that of trimethoprim varied from 60% in liver to 97% in plasma. The sample pretreatment procedures were simple, selective and robust, having a limit of quantification of 250 ng/ml for trimethoprim and 50 ng/ml for sulphadiazine in plasma, 15 ng/g for sulphadiazine and 80 ng/g for trimethoprim in muscle, and 30 ng/g for sulphadiazine and 160 ng/g for trimethoprim in liver. The assay was tested on plasma from Atlantic salmon treated with Tribrissen.     

Normal Coordinate Analysis for Polymer Systems: Capabilities and New Opportunities

Normal coordinate analysis is an important tool in studying the structure, dynamics, and physical properties of polymer systems. In this article the capabilities of normal coordinate analysis (NCA) are explored in some detail. The use of the eigenvalues and eigenvectors from NCA is catalogued for a wide variety of purposes: for assigning or interpreting polymer spectra, for structural determination, for constructing force fields, for computing heat capacity and other thermodynamic properties, and for computing other physical properties. Examples are given for crystals, melts, and amorphous systems. Also described are methods for characterizing the normal mode vectors that are especially useful for larger systems, in which a large amount of data must be analyzed or where visualization or animation fails. Finally, a recently developed method for eliminating negative eigenvalues in systems with tens of thousands of atoms, trajectory averaging, is presented. Also described are several advances in numerical linear algebra for speeding up the diagonalization phase and for computing physical properties without requiring full diagonalization of the Hessian matrix.     

Evaluation of the kinetic data for intramolecular 1,x-hydrogen shifts in alkyl radicals and structure/reactivity predictions from the carbocyclic model for the transition state

Experimental and computational kinetic data for the intramolecular 1,x-hydrogen shift in alkyl radicals are compiled in Arrhenius format for x = 2-5. Significant experimental disparity remains, especially for x = 2 and 3. Experimental data for radicals with tert centers or bearing spectator substituents are lacking for all x, and none exist for x = 6. The common use of the strain energy of the unsubstituted (x+1)-carbocycle to coarsely model the activation energy for the 1,x-shift is extended to explore more subtle differences in progressively methyl-substituted systems by use of molecular mechanics estimates of differences in strain between radicals and carbocycles. For x = 5 and 6, a sterically driven increase in E is predicted for shifts in the tert --> tert class that apparently runs counter to the behavior of bimolecular hydrogen transfers. In contrast, a sterically driven decrease in E is predicted to result from spectator methyl groups for the prim --> prim reaction class for all x. There is no experimental basis to test these predictions; fragmentary computational evidence lends some support to the second but is ambiguous concerning the first. Possible deficiencies in the use of carbocycles as transition state models are discussed.     

New cleft-like molecules and macrocycles from phosphonate substituted spirobisindanol

We have synthetized medium-sized cyclophanes and macrocycles containing phosphonic groups, directly linked to the aromatic rings of the phanes or as pendant arms,for use as specific receptors for the selective complexation of neutral guests or for complexing lanthanides, as luminescent sensors and for diagnostic bioassays in medicine.Furthermore, because it would be of great interest for biochemistry as well as for pharmacological studies to dispose of preorganized rigid chiral hosts for biorelevant molecules we designed inter alia, some new chiral macrocycles capable of a triple binding mode and we used them for constructing macrocycles that could also be of interest for chiral recognition and chiral separations. Thus, in this paper we shall review the salient aspects of some macrocycles synthetized in our laboratory, all possessing the phosphonate moiety and a spirobisindanol scaffold and able to act as complexing agents for cations and organic substrates. In particular, we shall describe their NMR characterization, their stereochemistry in solution and in the solid state, and their use as chiral receptors for biorelevant molecules. Chiral HPLC resolution of some of them is also reported.     

Need for food reference material in Latin America

Summary Even if some Latin American countries still need to extend their capacity for food quality control, many do have good control laboratories and high quality research institutions. That makes the need for reference material in Latin America similar to that of other parts of the world.The region has special problems related to mail and shipment delays, and to the lack of information on available reference material. It is recommended that additional reference material being made available for vitamins in food, for polar and non-polar organophosphorus pesticides in vegetables, for organophosphorus pesticide and veterinary drugs in meat etc.Reference material should simulate real samples as closely as possible; reference samples for water should contain phthalates which in environmental samples interfere with organochlorines and reference material for organophosphates in vegetables should contain metabolites and degradation products.It is also recommended that commercial standards for trace metals should have the production date and the guaranteed stability printed on the label. Information on reference material should be included in the methods published by AOAC, AOCS and similar publications.     

Rapid and sensitive detection of auxins and flavonoids in plant samples by high-performance liquid chromatography coupled with tandem mass spectrometry

Simultaneous determination of indole-3-acetic acid and methyl indole-3-acetic acid ester in small amounts of plant tissue is essential for elucidating their mutual transformation mechanism and the in vivo function of methyl indole-3-acetic acid ester. Rapid quantification of flavonoids in the same sample is important for clarifying their roles in the transport of auxins and other phytohormones. Herein, we describe a simple method for the simultaneous determination of indole-3-acetic acid and its methyl ester in the roots of the Arabidopsis thaliana seedlings and a protocol for the rapid extraction and quantification of quercetin and kaempferol in these seedlings. High-performance liquid chromatography coupled with electrospray ionization time-of-flight tandem mass spectrometry was used for the detection of all the compounds. Negative data for indole-3-acetic acid and positive data for methyl indole-3-acetic acid ester were collected in two successive files with a single injection of the extracted sample. Under optimized conditions, the limit of detection for the four compounds was 2 ng/mL for indole-3-acetic acid, 0.5 ng/mL for methyl indole-3-acetic acid ester, 5 ng/mL for quercetin, and 1 ng/mL for kaempferol, respectively. Because of the high sensitivity of the assay, only 2-10 mg of the plant material was required to obtain quantitative results.     

Anharmonic effects in ammonium nitrate and hydroxylammonium nitrate clusters

The covalent and ionic clusters of ammonium nitrate and hydroxyl ammonium nitrate are characterized using density functional theory and second-order vibrational perturbation theory. The most stable structures are covalent acid-base pairs for the monomers and ionic acid-base pairs for the dimers. The hydrogen-bonding distances are greater in the ionic dimers than in the covalent monomers, and the stretching frequencies are significantly different in the covalent and ionic clusters. The anharmonicity of the potential energy surfaces is found to influence the geometries, frequencies, and nuclear magnetic shielding constants for these systems. The inclusion of anharmonic effects significantly decreases many of the calculated vibrational frequencies in these clusters and improves the agreement of the calculated frequencies with the experimental data available for the isolated neutral species. The calculations of nuclear magnetic shielding constants for all nuclei in these clusters illustrate that quantitatively accurate predictions of nuclear magnetic shieldings for comparison to experimental data require the inclusion of anharmonic effects. These calculations of geometries, frequencies, and shielding constants provide insight into the significance of anharmonic effects in ionic materials and provide data that will be useful for the parametrization of molecular mechanical force fields for ionic liquids. Anharmonic effects will be particularly important for the study of proton transfer reactions in ionic materials.     

Research and development activities on polymer for the 21st century in korea

The polymer industries have been expanded steadily from the beginning of 1970's. Accordingly, the production capacity of commodity plastics reached 5.37 million tons in 1993, which ranked fourth in the world. The market for the engineering plastics is not fully matured yet, but the recent annual increasing rate was higher than 20% for demand and 40% for production. A state of the art for research and development activities on polymer for 21st century in Korea will be briefly reviewed in terms of technology evolution, polymers for electronic industry, for environment, and for energy saving.     

Simultaneous determination of benzene and toluene in the blood using head-space gas chromatography

A head-space method for the simultaneous determination of benzene and toluene in blood using a gas chromatograph equipped with a photoionization detector was developed. Internal standards for benzene and toluene were fluorobenzene and o-xylene, respectively, and the detection limit was 5 nmol/l for both solvents. This method is sensitive enough for needs of biological monitoring of benzene and toluene in exposed workers. With automation it offers a possibility for routine measurements. An application of the method in monitoring exposed workers in the industry is presented.     

Theoretical and experimental investigation of the energetics of cis-trans proline isomerization in peptide models

The energetics of cis-trans proline isomerization in small peptide models have been investigated using the hybrid density functional theory method B3LYP with a 6-31+G* basis set. The molecules studied are models for the phospho-Ser/Thr-Pro substrate for Pin-1, a peptidyl-prolyl isomerase (PPIase) involved in cell division. Pin-1 requires phosphorylation of a Ser or Thr residue adjacent to a Pro residue in the substrate and catalyzes cis-trans isomerization about the proline amide bond. The dihedral angle that would correspond to the reaction coordinate for isomerization of the omega peptide bond was investigated for several small models. Relaxed potential energy scans for this dihedral angle in N-methylacetamide, 1, N,N-dimethylacetamide, 2, acetylpyrrolidine, 3 and acetylproline, 4, were carried out in 20 degrees steps using the B3LYP/6-31+G* level of theory. In addition, similar scans were carried out for 1-4 protonated on the acetylamide carbonyl oxygen. Optimized structures for 1-4 protonated on the amide nitrogen were also obtained at B3LYP/6-31+G*. Relative proton affinities were determined for each site at various angles along the reaction coordinate for isomerization. The relative proton affinities were anchored to experimental gas phase proton affinities, which were taken from the literature for 1 and 2, or determined in an electrospray ionization-quadrupole ion trap instrument using the extended kinetic method for 3 and 4. Proton affinities of 925 +/- 10 and 911 +/- 12 kJ/mol were determined for 3 and 4, respectively. These studies suggest that the nitrogen atom in these amides becomes the most basic site in the molecule at a dihedral angle of ca. 130 degrees . In addition, the nitrogen atoms in 2-4 are predicted to attain basicities in the range 920-950 kJ/mol, making them basic enough to be the preferred site for hydrogen bonding in the Pin-1 active site, in support of the proposed mechanism for PPIases.