Search results for "table"

A New Building Block for Organometallic–Inorganic Hybrid Polymers: The Mixed Group 15/16 Element Ligand Complex [Cp* 2 Mo 2 (μ,η 2:2 ‐PSe) 2 (μ‐Se)] …

2010

The synthesis and spectroscopic characterization of [Cp*2Mo2P2Se3] (1; Cp* = C5Me5) and its use as a molecular building block in the formation of copper(I) halide polymers is described. The reaction of 1 in CH2Cl2 with 2 equiv. of CuBr and CuI in CH3CN under diffusion conditions gave [(Cp*2Mo2P2Se3)2(CuBr)2] (2) and [(Cp*2Mo2P2Se3)(CuX)3(CH3CN)]n (X = I; 3/4), respectively. The structure of 2 is distinguished by a central Cu2Br2 ring coordinated on each side by a tripledecker complex through one of its P atoms. A 2D network is formed by weak interactions between Se atoms of neighboring molecules. Compound [(Cp*2Mo2P2Se3)(CuI)3(CH3CN)]n exists in two isomeric forms 3 and 4. The crystal struc…

Selenium Partitioning and Stable Isotope Ratios in Urban Topsoils

2011

oxides. Th e δ82/76 Se values of total Se in the topsoils were close to the bulk Earth composition with an average δ82/76 Se value of −0.03 ± SD 0.38‰ suggesting that there was no or little Se isotope fractionation in soil. We attribute the small isotope fractionation to the low bioavailability of Se as a consequence of the presence of Fe oxides (adsorbing the dominating Se(IV) forms strongly), organic matter, and SO 4 2− (prevents biouptake of the Se(IV) forms) in the study soils. Small Se isotope fractionations of −0.59 to −0.35‰ in mainly forest soils and of 0.26 to 0.45‰ in mainly alluvial soils were presumably caused by soil/plant-recycling and Se contamination by river water, respecti…

The role of the transfer group in the intramolecular [5+2] cycloadditions of substituted β-hydroxy-γ-pyrones: a DFT analysis

2005

The intramolecular [5+2] cycloaddition reactions of a series of 3-OR (R=SiMe3, H, CHO, Me) substituted β-hydroxy-γ-pyrones bearing tethered alkenes were studied using DFT methods at the B3LYP/6–31G* level. The role of the transfer R group was analyzed considering two alternative channels: (i) in channel a the process is initialized by the transfer of the R group with formation of an oxidopyrylium ylide intermediate, which is followed of an intramolecular [5+2] cycloaddition; (ii) in channel b, the process is initialized by the intramolecular [5+2] cycloaddition on the γ-pyrone followed by the transfer of the R group. Copyright © 2005 John Wiley & Sons, Ltd.

Digestion and absorption of polyunsaturated fatty acids

1991

Polyunsaturated fatty acids play an important part in the structure and function of cellular membranes and are precursors of lipid mediators which play a key role in cardiovascular and inflammatory diseases. Dietary sources of essential fatty acids are vegetable oils for either linoleic or alpha-linolenic acids, and sea fish oils for eicosapentaenoic and docosahexaenoic acids. Because of the specificity of the pancreatic lipid hydrolases, triglyceride fatty acid distribution is an essential parameter in the digestibility of fats. The efficiency of the intestinal uptake depends on the hydrolysis and especially on their micellarization. n-3 polyunsaturated fatty acid ethyl ester digestion is …

Time–carbonyl groups equivalence in photo-oxidative aging of virgin/recycled polymer blends

2004

AbstractThe photo-oxidation behaviour of polymers is strongly dependent on the initial amount of carbonyl groups along the chains. The growing use of recycled post-consumer polymers coming from products used outdoors and then photo-oxidised, both pure and blended with the same virgin polymer, gives rise to an unpredictable behaviour of weathering resistance of products made with these materials. The present work shows that the carbonyl group–exposure time curves can be shifted along the time axis to give a single generalised master plot. It is then possible to predict the formation of the new carbonyl groups by knowing only the initial amount of the same carbonyl groups. The same shift fact…

Determination of zirconium traces in polymers by ICP-IDMS - a powerful and fast method for routine testing of zirconium residues in polyolefins

1999

Zirconium trace analyses play an important role for polyolefins produced by modern catalytic processes with zirconium metallocenes. A reliable and fast routine testing method by inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) was therefore developed, which allows the determination of zirconium in polymers down to the low ng/g level. With respect to its precision, accuracy, and time-consumption this method is suitable for routine testing of production processes. A spike solution, enriched in the stable isotope 91Zr, was prepared and used for the isotope dilution procedure, which has the advantage of being an internal “one point” calibration method. The polyolefin sam…

Revisiting delta-6 desaturase regulation by C18 unsaturated fatty acids, depending on the nutritional status.

2009

Dietary polyunsaturated fatty acids (PUFA) play a key role in regulating delta-6 desaturase (D6D), the key enzyme for long-chain PUFA biosynthesis. Nevertheless, the extent of their effects on this enzyme remains controversial and difficult to assess. It has been generally admitted that C18 unsaturated fatty acids (UFAs) regulate negatively delta-6 desaturase (D6D). This inhibition has been evidenced in regard to a high glucose/fat free (HG/FF) diet used in reference. However, several nutritional investigations did not evidence any inhibition of desaturases when feeding fatty acids. Because the choice of the basal diet appeared to be of primary importance in such experiments, our goal was t…

ChemInform Abstract: Comparative Lipase-Catalyzed Hydrolysis of Ethylene Glycol Derived Esters. The 2-Methoxyethyl Ester as a Protective Group in Pep…

2010

and variability in Posidonia oceanica associated with seasonality and plant fraction

2003

Abstract The carbon and nitrogen isotopic compositions of fractions of the seagrass Posidonia oceanica (L.) Delile in a Mediterranean shallow environment (Stagnone di Marsala, western Sicily) were investigated seasonally throughout 1998. The stable isotope ratios of seagrass leaves (intermediate and adult), rhizomes, leaf litter and aegagropiles were compared over 1 year in order to distinguish between seasonal and plant part variability. Significant differences in the isotopic composition tested using ANOVA were observed as a function of both plant fraction and season. There was an overall trend towards less discrimination against 13 C in summer (average δ 13 C ∼ −10‰) than in winter (aver…

Water-Blown Polyisocyanurate Foams From Vegetable Oil Polyols

2008

Polyols with the hydroxyl value OHV from 290 to 318 mg KOH/g are synthesized from rapeseed, sunflower seed, flaxseed, or coconut oils by the way of their: (1) transesterification with triethanolamine or (2) amidization with diethanolamine. The influence of water as the blowing agent on the storage stability of the polyol premix system is assessed from values of the polyol premix system pH, acid value, and variations in such parameters as cream and gel time. Water-blown polyisocyanurate (PIR) foams (150 · II × 300; II—isocyanate index) characterized by good mechanical characteristics, dimensional stability at 70°C and at relative humidity RH = 95% as well as by a very low water absorbance, …