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1.
UV sensitivity of the vegetative and reproductive tissues of two Antarctic brown macroalgae was compared. Photosynthesis as well as the content and localization of phenolic substances were determined. Responses to UV radiation were quantified as chlorophyll fluorescence (Fv/Fm). Ascoseira mirabilis showed high UV tolerance, while in Cystosphaera jacquinotii Fv/Fm decreased by 15–21%, the receptacles being more tolerant than the vegetative blades. The phlorotannin contents showed an opposite pattern: the soluble fraction dominated in C. jacquinotii while in A. mirabilis the insoluble fraction was more abundant. Soluble phlorotannins were higher in the reproductive than in vegetative tissues in both species. Images of tissue cross‐sections under violet‐blue light excitation confirmed a high allocation of phenolic compounds (as blue autofluorescence) in C. jacquinotii, both in reproductive and vegetative blades. The allocation and proportions of the soluble and insoluble phlorotannins could be related with the observed UV tolerance of the vegetative and reproductive tissues.  相似文献   
2.
The increasing use and production of nanomaterials have led to growing concern over the release of new pollutants to the environment. Fullerenes have been a subject of intense research, both because of their unique chemistry and because of technological applications. The development of analytical methods to quantify the fullerenes in complex sample matrices is a crucial step in the study of their occurrence and exposure, and thus in risk assessment. This paper reports the development and optimisation of a method combining liquid chromatography with ion-trap mass spectrometry (LC-ITMS) for analysis of the fullerene C(60). Under the optimised chromatogram conditions, a C(18) analytical column had good selectivity for fullerenes C(60) and C(70), with retention times of 3.0 and 4.1 min, respectively. Mass spectrometric detection was tested and optimised using three common ionisation techniques-atmospheric-pressure chemical ionisation (APCI), atmospheric-pressure photoionisation (APPI), and electrospray ionisation (ESI). The molecular ion was most abundant for C (60) (-) (m/z=720) in APCI and APPI, whereas adduct ions were formed with the molecular ion in ESI. Finally, the performance of the three ionisation techniques examined was compared by use of five validation criteria. The instrument detection limit (8 ng mL(-1)), quantification limit (27 ng mL(-1)), detection sensitivity (90.2 ng mL(-1)), linear range (8-1,000 ng mL(-1)), and repeatability (15 %) of APPI make it the most promising ionisation technique for fullerene C(60) analysis.  相似文献   
3.
Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu2+ and Ni2+) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [CuI(ref)(A)]+. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
4.
Ethene was copolymerized (1) with 1,5‐hexadiene with rac‐ethylenebis(indenyl)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) with 1,7‐octadiene with bis(n‐butylcyclopentadienyl)zirconium dichloride/MAO and rac‐ethylenebis(indenyl)hafnium dichloride (Et[Ind]2HfCl2)/MAO used as catalysts at 80 °C in toluene. The copolymer microstructure and the influence of diene incorporation on the rheological properties were examined. Ethene and 1,5‐hexadiene formed a copolymer in which a major fraction of the 1,5‐hexadiene was incorporated into rings and a small fraction formed 1‐butenyl branches. The copolymerization of ethene with 1,7‐octadiene resulted in a higher selectivity toward branch formation. Some of the branches formed long‐chain‐branching (LCB) structures. The ring formation selectivity increased with decreasing ethene concentration in the polymerization reactor. Melt rheological properties of the diene copolymers resembled those of metallocene‐catalyzed LCB homopolyethenes and depended on the vinyl content, the catalyst, and the polymerization conditions. At high diene contents, all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind]2HfCl2, where only 0.2 mol % 1,7‐octadiene in the copolymer was required to achieve significantly modified rheological properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3805–3817, 2001  相似文献   
5.
The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density.  相似文献   
6.
Five differently substituted 1-(2-benzothiazolyl)-3,5-diphenyl formazans were studied by laser desorption ionization (LDI) and matrix assisted laser desorption/ionization (MALDI) mass spectrometry. The best explanation of the results is that the formazan molecules are photoionized to molecular radical ions, which then further react by ion-molecule reactions. Supporting this proposal was the abundant formation of [M − H]+ ions under LDI. These ions are not observed at all under either electron or chemical ionization. Under MALDI, the extent of the oxidation process is clearly dependent on the ability of the matrix to act as a reducing agent. With transition metals the formazans formed singly charged 1:2 metal:formazan complexes. The most stable electronic configuration of the complex determined the oxidation state of the metal regardless of its initial oxidation state. In some cases, this process also demanded a gas-phase reduction of the formazan. The ionization efficiency and affinity for complex formation depended on the substituent at the 3-phenyl group; both were increased by an electron donating substituent. The formazans were also tested as potential matrices for MALDI. Reasonable results were observed for several groups of compounds; however, only the piperazine ligands produced higher quality spectra with formazans than with common commercial matrices.  相似文献   
7.
Parameter study of electrospinning of polyamide-6   总被引:2,自引:0,他引:2  
Importance of different solution and process parameters were evaluated in multi-nozzle electrospinning of polyamide-6. We were interested in how those parameters affect firstly on fibre diameters and fibre diameter distribution and secondly on production rate and disturbances of the process. The trial series was planned using orthogonal experimental design. Altogether eight parameters having three or two levels each were chosen for this study. The chosen solution parameters were polymer grade, viscosity of solution, salt content and solvent grade and process parameters, voltage, distance, nozzle size and feeding pressure of solution. This study was performed using continuous electrospinning equipment consisting of multiple nozzles and horizontal electric field. Literature findings about the influences of certain variables are often contradictory. These contradictions and their possible causes were discussed.  相似文献   
8.
The electron impact induced fragmentations of nine 2,2-disubstituted 1,3-oxathiolanes have been studied by means of exact mass measurement and metastable ion analysis. The ring cleavage almost always takes place so that the C(2)? S and C(5)? O bonds are broken, leading to the most stable products. The nature of the substituents determines the primary fragmentations of molecular ions. Ring cleavage is important only if both substituents are alkyl groups or if the carbon attaching to the ring has an alkyl character. The loss of the substituent becomes the most favourable process if it is attached to the ring through the electron-deficient carbon atom.  相似文献   
9.
Ammonia, isobutane and methane chemical ionization mass spectra have been measured for some substituted cis-1,3-cyclopentane dicarboxylic acids and their derivatives. The relative proton affinities of the different functional groups determine the protonation site in the molecule and thereby greatly affect the fragmentation. Intramolecular catalysis clearly facilitates the elimination of water in cases where functional groups can interact with each other.  相似文献   
10.
The international joint project HYCREF (Contract No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogeneous and stable reference materials of water, soil, and waste contaminated with mineral oil hydrocarbons and to certify the mineral oil content by gas chromatographic methods. The results of a feasibility study for the preparation of three soil reference materials are discussed in this paper, and for the preparation of three waste reference materials in the second part (Koch et al., Accred Qual Assur submitted for publication). The soil materials were selected to represent different soil types and contamination levels. The project plan set three requirements for these reference materials: uncertainty in the mineral oil content resulting from the certification exercise <5%, a sample inhomogeneity of <3% and a minimum long-term stability of 5 years. For the most part, these requirements were met within this project.  相似文献   
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