bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring Systems
Authors: Döring Steve , Kotov Vasily V. , Erker Gerhard , Kehr Gerald , Bergander Klaus , Kataeva Olga , Fröhlich Roland 
Published: April 2003

AbstractTreatment of the substituted (diarylphosphanyl)methyl group‐4 metallocene complexes [(C5H4−CR1R2−PAr2)2ZrCl2] (2: R1/R2 = CH3/CH3, H/CH3, H/aryl) with Li[B(C6F5)4] in dichloromethane solution results in chloride ligand abstraction (with LiCl precipitation) to yield the complexes [(C5H4−CR1R2−PAr2)2Zr−Cl+] (5), with both phosphanyl groups internally coordinated to the metal centre. Three possible diastereoisomers are observed in the case of 5c (R1 = H; R2 = CH3), while bulkier R2 substituents give higher selectivities. The thermally induced (reversible) cleavage of the Zr−phosphane linkage results in dynamic NMR behaviour. Gibbs activation energies of ΔG≠(298 K) = 14.8 ± 0.5 and 14.5 ± 0.5 kcal/mol were obtained for these intramolecular equilibration processes in the complexes trans‐5d (R1 = H; R2 = Ph) and trans‐5e (R1 = H; R2 = ferrocenyl), respectively. Treatment of the substituted (dimethylamino)methyl metallocene complexes [(C5H4−CR1R2−NMe2)2ZrCl2] (6a, 6b) with Li[B(C6F5)4] proceeds analogously to yield the cation systems [{C5H4−C(CH3)2−NMe2}2ZrCl+] (12a) and [{C5H4−CH(CH3)−NMe2}2ZrCl+] (12b, three possible diastereoisomers). Both complexes have their pairs of amino groups coordinated to the metal centre. The complexes exhibit dynamic NMR spectra. Selective equilibration of the diastereotopic N(CH3)A(CH3)B resonances of complex 12a is observed [ΔG≠(233 K) = 11.5 ± 0.2 kcal/mol], whereas the adjacent C(CH3)A(CH3)B methyl groups remain diastereotopic. The dynamic equilibration of the latter was observed at a markedly higher temperature [ΔG≠(333 K) = 17.3 ± 0.2 kcal/mol]. Treatment of [{C5H4−C(CH3)2−NMe2}CpZrCl2] (10) with Li[B(C6F5)4] resulted in the formation of complex [{C5H4−C(CH3)2−NMe2}CpZr−Cl+] (11), which shows the internal −N(CH3)A(CH)B equilibration proceeding with a markedly higher activation barrier [ΔG≠(333 K) = 17.6 ± 0.2 kcal/mol] than in 12a, and a stereochemical memory effect indicative of solvent coordination to the metal centre of the resulting highly electrophilic chlorozirconocene cation intermediate. Complex 11 was characterised by an X‐ray crystal structure analysis, which shows the internal Zr←amine coordination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
SiO2‐CaO Vitreous Films Deposited onto Ti6Al4V Substrates
Authors: Izquierdo‐Barba Isabel , Asenjo Agustina , Esquivias Luis , Vallet‐Regí María 
Published: April 2003

AbstractA sol‐gel dipping method has been utilised to deposit SiO2‐CaO films onto Ti6Al4V alloy substrates. These layers were prepared by the dip‐coating technique from a series of precursor solutions with different concentrations of glassy xSiO2‐(1 − x)CaO (x = 0.8 mol) diluted with absolute ethanol. The characterisation of the films by a variety of techniques reveals differences in the textural properties and in the films’ thicknesses depending on the sol concentration in the precursor solution. Concentrated precursor solutions yield porous layers with a higher thickness and surface roughness than those obtained from the dilute ones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Ruthenium‐Catalysed Selective Transetherification of Substituted Vinyl Ethers To Form Acetals and Aldehydes
Authors: Saoud Mustapha , Romerosa Antonio , Mañas Carpio Sonia , Gonsalvi Luca , Peruzzini Maurizio 
Published: April 2003

AbstractThe water‐soluble ruthenium allenylidene complex [{RuCl(μ‐Cl)(C=C=CPh2)(TPPMS)2}2]Na4 catalyses the selective transformation of substituted linear and cyclic vinyl ethers with MeOH, under mild non acidic conditions, to give acetals, while aldehydes and ketones are obtained in a CHCl3/H2O mixture, which allows for easy recycling of the catalyst. NMR studies showed that the reaction follows a transetherification mechanism rather than simple acid‐catalysed hydrolysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Oligomerisation of Ethylene to Linear α‐Olefins by new Cs‐ and C1‐Symmetric [2,6‐Bis(imino)pyridyl]iron and ‐cobalt Dichloride Complexes
Authors: Bianchini Claudio , Mantovani Giuseppe , Meli Andrea , Migliacci Fabio , Zanobini Fabrizio , Laschi Franco , Sommazzi Anna 
Published: April 2003

AbstractA new family of Cs‐ and C1‐symmetric 2,6‐bis(imino)pyridyl ligands has been synthesised. These ligands, which differ from their known counterparts in the contemporaneous presence of alkyl and aryl substituent at the ketimine nitrogen atoms, form stable, five‐coordinate complexes with FeCl2 and CoCl2. All ligands and catalysts have been fully characterised both in the solid state and in solution. A single‐crystal X‐ray analysis of [CoCl2{2‐[CMe=N−(2,6‐dimethylphenyl)]‐6‐(CMe=N−C6H11)C5H3N}]·H2O shows the metal centre to adopt a highly distorted square‐pyramidal geometry. In combination with methylaluminoxane (MAO), both iron and cobalt compounds act as effective and selective (> 99%) catalysts for the oligomerisation of ethylene to a Schulz−Flory distribution of α‐olefins, with the α factor ranging from 0.61 to 0.91. The iron catalysts exhibit TOFs as high as 7·105 mol C2H4 (mol of cat × h)−1 and are much more active than their cobalt analogues. Experiments at different ethylene pressures with the iron catalysts showed that both the propagation rate and the chain transfer rate are first order in ethylene pressure. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)
Mn and Fe K‐edge XAS Spectra of Manganese and Iron Nitrido Compounds
Authors: Niewa Rainer , Hu Zhiwei , Kniep Rüdiger 
Published: April 2003

AbstractWe performed a Mn K‐edge XAFS study of a number of highly moisture‐sensitive nitridomanganates with manganese in different oxidation states and in various surroundings: Li2[(Li1−xMnIx)N] [x = 0.75(1)], Li24[MnIIIN3]3N2, and Li7[MnVN4]. For reference purposes Mn, MnO and θ‐Mn6N5+x [x = 0.26(1)] were measured. The energy positions of the pre‐edge maxima are almost independent of the electronic state of Mn, while the intensity is sensitive to the geometric arrangement of the coordination of Mn. The main‐edge is sensitive to the oxidation state − a clear shift to higher energies with increasing oxidation state can be seen. This shift is smaller than the shift observed for the corresponding oxides, due to the lower electronegativity of nitrogen compared to oxygen, and corresponds to a higher covalency of the Mn−N bond. Similar results can be taken from the Fe K‐edges of Li2[(Li1−xFeIx)N] with x = 0.20(1) and Li3[FeIIIN2] in comparison to metallic Fe, FeIISO4·7H2O and α‐FeIII2O3. The results are consistent with the presence of an unusual oxidation state (+1) for the transition metals in the phases of the general composition Li2[(Li1−xMx)N]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Characterization of (PTU)I2 (PTU = 6‐n‐propyl‐2‐thiouracil) and (CMBZT)I2 (CMBZT = 5‐chloro‐2‐mercaptobenzothiazole) and Possible Implications for the Mechanism of Action of Anti‐Thyroid Drugs
Authors: Antoniadis Constantinos D. , Corban Ghada J. , Hadjikakou Sotiris K. , Hadjiliadis Nick , Kubicki Maciej , Warner Stephanie , Butler Ian S. 
Published: April 2003

AbstractDirect reaction of 6‐n‐propyl‐2‐thiouracil (PTU), a widely used anti‐thyroid drug against hyperthyroidism (Graves’ disease), or 5‐chloro‐2‐mercaptobenzothiazole (CMBZTH) with iodine in a molar ratio of 1:1 resulted in the formation of the charge‐transfer (CT) complexes [(PTU)I2] (1) or [(CMBZT)I2] (2). All reactions were carried out in dichloromethane and water solutions. Compounds 1 and 2 were characterized by elemental analyses, FT‐Raman, FT‐IR, UV/Vis and 1H NMR spectroscopy. The crystal structures of both complexes were determined by X‐ray diffraction at 120(1) K (1) and 293(2) K (2). The charge‐transfer nature of the bonds in the adducts 1 and 2 was verified by the lengthening of the I−I bond lengths as compared to the S−I bond lengths and by the characteristic CT bands observed in the UV spectra of the complexes. Compound 1 [(C7H10N2OS)I2] [monoclinic with space group P21/c and a = 9.8501(7), b = 10.3101(7), c = 12.0287(8) Å, β = 99.707(6)°, Z = 4] consists of a propylthiouracil ligand bonded with an iodine atom through sulfur. Extended intermolecular N−H···O contacts link the molecules forming a supramolecular assembly. Compound 2 {(C7H4ClNS2)I2} [orthorhombic, space group P212121, a = 4.1650(10), b = 9.691(2), c = 28.471(6) Å, Z = 4] consists of a 5‐chloro‐2‐mercaptobenzothiazole ligand bonded with an iodine atom through sulfur. An extended intermolecular linkage via I···H−N bonds leads to the formation of an extended structure. Attempts to draw conclusions on the behavior of a thioamide — when used as an anti‐thyroidal drug — towards iodine have been made. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Human Telomeric Sequence (T2AG3)n is Efficiently Cross‐Linked by AN1 Binding to the Platinum of a trans‐Pt(NH3)2 Chelate of an Antisense Oligo‐2′‐O‐Methylribonucleotide
Authors: Perrier Sandrine , Seela Frank , Schwartz Annie , Leng Marc , Chottard Jean‐Claude 
Published: April 2003

AbstractIn order to irreversibly cross‐link an antisense oligonucleotide to the human telomeric sequence (T2AG3)n, the inter‐strand bridging rearrangement described by Leng et al. was investigated on (21‐mer antisense) (20‐mer target) duplexes: (G*NG*)(TA) ⇄ (G*NG)(TA*), G*NG* being a trans‐[Pt(NH3)2{1,3‐(GNG)‐N7‐G,N7‐G}] chelate with N = U or T. Three different duplexes were studied, confirming first that for a DNA target strand the rearrangement was faster with a platinated oligo‐2′‐O‐methylribonucleotide than with a deoxy oligonucleotide as antisense strand. Second, a telomeric DNA target strand was cross‐linked faster than an all‐purine oligonucleotide containing a single TA doublet. Accordingly, the half time of formation of the cross‐linked hybrid duplex [2′‐OMe‐r(CCCUAACCCG*UGACCCUAACCC)]·[d(T2AG3)2(TTA*G3)(T2AG3)] is one minute, compared with the nine days required for the complete formation of the bridged d(CTCCTG*TGTCTC)·d(GAGATA*AGGAG) duplex. The NMR analysis of the latter showed that the platinum cross‐link involves the A*N1 moiety as ligand. The timescale difference between the two reactions raised the question of an eventual kinetic cross‐link which might isomerize to the final one observed. This question was addressed using 1‐deazaadenine in the TA doublet of the three target strands of this work. No cross‐linking reaction was observed, proving that AN1 is the bridging atom in all the cases studied so far. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Use of essential oils as media for the enantioselective esterification of the monoterpene perillyl alcohol catalyzed by lipase
Authors: Skouridou Vasso , Stamatis Haralambos , Kolisis Fragiskos N. 
Published: April 2003

AbstractThe synthesis of perillyl alcohol esters by direct esterification catalyzed by immobilized lipase from Candida antarctica (Novozyme 435) was studied. For this purpose, fatty acids with a chain length from 3‐16 were used. The reactions were carried out in mixtures of α‐pinene and myrcene as well as in pure organic solvents. It was found that the esterification rates increased from 3.7‐6.9 mM/min when using decreasing concentrations of myrcene in α‐pinene (100‐0%). Higher rates and conversions were obtained with decanoic acid as the acyl donor (6.9 mM/min, 81.5%), while lower conversions were obtained with fatty acids of shorter (propionic acid, 5.6%) or longer (hexadecanoic acid, 62.5%) carbon chain. In addition, it was found that the effect of the water activity depended on the chain length of the acyl donor and the composition of the solvent mixture. Also, esterification rates increased from 1.8‐6.9 mM/min with increasing hydrophobicity of the solvent (logP from 0.9‐4.8) of the organic solvent used. Finally, it was found that Candida antarctica lipase presented a preference in the esterification of (S)‐(—)‐ and (R)‐(+)‐perillyl alcohol in favor of the (R)‐(+) enantiomer. The enantioselectivity was found increased with increasing logP, whereas the water activity of the reaction mixture did not affect the enantioselectivity significantly.
Effects of dietary fish oil and oxidized cholesterol on the concentration of 7β‐hydroxycholesterol in liver, plasma, low density lipoproteins and erythrocytes of rats at various vitamin E supply
Authors: Ringseis Robert , Eder Klaus 
Published: April 2003

AbstractTwo experiments with rats were carried out to investigate the effect of dietary fish oil and oxidized cholesterol on the concentration of 7β‐hydroxycholesterol, an oxysterol of mainly nonenzymatic origin, in liver, plasma, low density lipoproteins and erythrocytes of rats at different vitamin E supply. In Experiment 1, four groups of rats received diets with coconut oil or salmon oil (100 g/kg diet) and vitamin E concentrations of 40 or 240 mg α‐tocopherol equivalents/kg. In Experiment 2, eight groups of rats received diets supplemented with pure or oxidized cholesterol (5 g/kg), coconut oil or salmon oil (100 g/kg diet) and vitamin E concentrations of 40 or 240 mg α‐tocopherol equivalents/ kg. Rats fed the salmon oil diets had significantly higher concentrations of 7β‐hydroxycholesterol in liver, plasma, low density lipoproteins and erythrocytes than rats fed coconut oil diets. Rats fed the diets supplemented with oxidized cholesterol had significantly higher concentrations of 7β‐hydroxycholesterol in all the samples analyzed than rats fed pure cholesterol. Increasing the dietary vitamin E concentration from 40 to 240 mg α‐tocopherol equivalents/kg diet reduced the concentration of 7β‐hydroxycholesterol in plasma; the concentrations of 7β‐hydroxycholesterol in liver, low density lipoproteins and erythrocytes were not influenced by the dietary vitamin E concentration. The study suggests that diets with fish oil or oxidized cholesterol are critical with respect to the formation of 7β‐hydroxycholesterol.
Chemical and physical properties of a sunflower oil with high levels of oleic and palmitic acids
Authors: Guinda Ángeles , Dobarganes M. Carmen , Ruiz‐Mendez M. Victoria , Mancha Manuel 
Published: April 2003

AbstractHigh‐oleic high‐palmitic sunflower oil (HOHPSO) has been obtained from field‐grown mutant sunflower seeds CAS‐12. The fatty acid and triacylglycerol compositions, the thermo‐oxidative stability and the physical properties of the HOHPSO were determined and compared with those of the conventional and high oleic sunflower oils and those of a liquid fraction of palm oil (olein). The major fatty acids of the HOHPSO were monoenes (57.7% oleic, 7.3% palmitoleic) and palmitic (27, 8%), while the content of linoleic acid was low (2.3%). The saturated fatty acids were almost absent from the sn‐2 position and, thus, the major triacylglycerol (TAG) molecular species were those with one or two saturated fatty acids at the sn‐1, 3 positions and oleic acid at the sn‐2 position (mainly POO and POP). Total polar compounds and their distribution in oxidised TAG monomers and TAG polymers were determined after 10 h at 180 °C. The HOHPSO showed enhanced thermal stability, producing half the amount of total polar compounds, and much less TAG polymers, as the palm olein. The stability index (Rancimat) of the HOHPSO was unusually high (19 h at 120 °C). The thermal properties of the HOHPSO (determined from the differential scanning calorimetry thermograms) were different from those of the palm olein. The HOHPSO presents lower solid fat con‐tents than the palm olein above 15 °C and hence remains liquid at common working temperatures.
Adsorptive fouling of inorganic membranes during microfiltration of vegetable oils
Authors: Hafidi Abdellatif , Pioch Daniel , Ajana Hamid 
Published: April 2003

Abstracta The objective of the present paper is to contribute to a better understanding of the fouling phenomenon occurring during microfiltration of crude vegetable oil. To assess the role some oil components play in the fouling, the latter was monitored by the evolution of fluxes during the microfiltration of different model oils. Resistances to mass transfer were discussed to estimate the contribution of different phenomena and to compare hydrophilic and hydrophobic membrane materials. A drastic flux decline was obtained when filtering crude sunflower oil through different types of alumina membranes. Purified sunflower oil, with or without added free fatty acids, did not show any important fouling during crossflow microfiltration, suggesting that neither triglycerides nor free fatty acids are involved in the phenomenon to a large extent. By way of contrast, addition of phospholipids to the purified oil caused a drastic flux drop similar to that observed for the crude oil. The presence of small amounts of phospholipids increased the resistance to about 60 to 130% compared to that of the purified oil. The reason is most likely a fast adsorption occurring in the first instants during membrane wetting. Overall the fouling phenomenon is probably due to the fact that the phospholipids form supramolecular structures at the surface of the membrane.
Quality parameters evolution during biodiesel oxidation using Rancimat test
Authors: Lacoste Florence , Lagardere Lionel 
Published: April 2003

AbstractA study was carried out in order to evaluate the evolution of peroxide value, anisidine value, kinematic viscosity at 40 °C, ester and linolenic acid content, UV absorbency, acid value, polymer and tocopherol content during the oxidation of fatty acid methyl ester (FAME) using the Rancimat test chosen by CEN for measuring oxidation stability of FAME (pr EN 14112). The oxidation curves obtained during Rancimat test were compared with those obtained by the variation of oxidation parameters mentioned above, against the time. All quality parameters studied present visible variation along Rancimat test except UV 270 nm. At the end of Rancimat induction period, the seven samples tested do not meet FAME or oils and fats specifications such as kinematic viscosity, acid value, ester content or peroxide value. Rancimat induction period is well correlated to induction period given by quality parameters (0.963<R2<0.999), but Rancimat induction period is almost 10% higher than induction period given by quality parameters. Main conclusion is that induction period determined by conductivity is well correlated to degradation of quality parameters along Rancimat test.
Determination of trans double bonds in polyunsaturated fatty acid methyl esters from their electron impact mass spectra
Authors: Mjøs Svein Are , Pettersen Jan 
Published: April 2003

AbstractThe geometrical isomers of unsaturated fatty acid methyl esters were analysed by gas chromatography — electron impact mass spectrometry. Distinct differences in the electron impact mass spectra of methylene‐interrupted tri‐ and tetra‐unsaturated fatty acid methyl esters were observed. The differences were particularly related to the geometry of the central double bond in trienes or the two central double bonds in tetraenes. Trans geometry in these positions led to a significant decrease of m/z 79 [C6H7]+, which is the base peak in the all‐cis isomers. Disappearance or significant reductions of ions that are used for the determination of double bond positions in the corresponding cis isomers were also observed in the same spectra. The observed differences may be of help in the identification of double bond geometry in fatty acid isomers.
Oxidation of mixtures of triolein and trilinolein at elevated temperatures
Authors: Kamal‐Eldin Afaf , Velasco Joaquín , Dobarganes Carmen 
Published: April 2003

AbstractThe aim of this study was to investigate how triolein and trilinolein are oxidised at elevated temperatures (60‐220 °C) in mixtures with octadecane, used as a saturated diluent. The percentages of triolein/trilinolein and octadecane and the oxidation conditions (temperature and time) were chosen according to a statistical central composite design. Heating was performed in a Rancimat equipment. The extent of oxidation was assessed by measuring the peroxide value by titration against potassium iodide, total polar compounds by solid‐phase extraction, triacylglycerol polymers by high‐performance size‐exclusion chromatography, and the losses of triolein and trilinolein by gasliquid chromatography. The results indicated that maximum peroxide values were obtained at intermediate temperatures while the formation of polar compounds and polymers were only significant at temperatures above 140 °C. Interestingly, under the conditions used, concentration of octadecane was not significant in spite of the wide temperature range selected. Finally, independently of the concentration of triolein and trilinolein in the sample, at temperatures below 140 °C only losses of trilinolein were observed.
Proposed mechanisms of cholesterol‐lowering action of plant sterols
Authors: Trautwein Elke A. , Duchateau Guus S. M. J. E. , Lin Yuguang , Mel'nikov Sergey M. , Molhuizen Henri O. F. , Ntanios Fady Y. 
Published: April 2003

AbstractPlant sterols (or phytosterols) are naturally occurring compounds structurally related to cholesterol with different side chain configurations. To date, numerous studies have shown that dietary intake of plant sterols either in their free form or as fatty acid esters is effective at lowering plasma total and low density lipoprotein cholesterol. The main mechanism responsible for the cholesterol‐lowering effect of free and esterified plant sterols is the inhibition of intestinal cholesterol absorption. Several sites within the intestinal tract have been suggested where this inhibition might take place. Different mechanisms, such as competition with cholesterol for solubilisation in dietary mixed micelles, co‐crystallisation with cholesterol to form insoluble mixed crystals, and interference with the hydrolysis process by lipases and cholesterol esterases are believed to contribute to the lowering of serum cholesterol concentrations by plant sterols. There is also emerging evidence that plant sterols interfere with transport‐mediated processes of cholesterol uptake. The consequence of all these actions, although their individual contribution on the overall effect remains to be established, is that intestinal cholesterol absorption is reduced, while more cholesterol is excreted in the faeces.The aim of this review is to summarise the current understanding concerning the mechanism of action by which plant sterols affect cholesterol metabolism and thus exert their cholesterol‐lowering effect. The review will focus on the gut, e.g. on the physico‐chemical effects at the gastric‐duodenal level, on absorptive site effects, and on intra‐cellular trafficking, i.e. effects at the epithelial cell level.
Simple multifractal cascade model for air pollutant concentration (APC) time series
Authors: Lee Chung‐Kung , Ho Ding‐Shun , Yu Chung‐Chin , Wang Cheng‐Cai , Hsiao Yun‐Hua 
Published: April 2003

AbstractA simple two‐scale Cantor set with unequal scales and weights was presented for the APC time series. The validity of this multifractal cascade model was examined with a one‐year length of hourly average CO, NO, NO2, O3, PM10 and SO2 observations. This model fits remarkably well the entire spectrum of scaling exponents for the examined APC time series. It was found that the multifractal characteristics of the examined APC time series were closely related to both scale and weight parameters. Moreover, the weight parameter could be used to distinguish the degree of right‐skewness of APC frequency distribution. However, the relationship between the long‐range dependence and model parameters still requires further investigation. Some problems concerning the applicability of multifractal models on air pollution are also discussed. Copyright © 2003 John Wiley & Sons, Ltd.