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1.
Oxidation thermal parameters on samples of polypropylene (PP) stabilized with hydroxytyrosol were determined. For comparison
purposes, α-tocopherol and a synthetic phenolic commercial antioxidant (Irganox 1076), were also analyzed. Oxidation induction
time (OIt) and oxidation induction temperature (OIT) were determined by differential scanning calorimetry (DSC). The addition
of hydroxytyrosol 0.1 mass% to PP was enough to obtain efficient stabilization during processing. Certain decrease in stabilizing
properties of natural antioxidants was observed for compression moulded materials at high temperatures. However, these samples
were still efficiently stabilized in comparison to the pure material. Hydroxytyrosol showed good performance as polypropylene
antioxidant and it might be considered as promising alternative to the use of phenolic synthetic compounds. 相似文献
2.
P. Bracco 《Polymer Degradation and Stability》2007,92(12):2155-2162
Ultra-high molecular weight polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility of adding synthetic Vitamin E to medical grade UHMWPE is currently under investigation.In the present work, medical grade UHMWPE was blended with 0.05, 0.1 or 0.5 w/w% of α-tocopherol and consolidated by compression moulding. Small blocks of reference UHMWPE and of each blend were then gamma irradiated to 30 or 100 kGy. FTIR spectroscopy was used to monitor changes in both the polymer and the additive. Thin sections of virgin and α-tocopherol doped UHMWPE irradiated and unirradiated were aged in a ventilated oven at 90 °C and the kinetic of oxidation was followed by FTIR. In addition, CL-imaging curves were recorded at 180 °C on both irradiated and unirradiated samples.Phenol loss is observed in all the α-tocopherol doped samples upon irradiation. Hypotheses on the rearrangements of the additive structure include the formation of quinonoid products. Nevertheless, all the additive-containing samples exhibit better oxidation resistance compared to the virgin material, indicating stabilizing activity of the α-tocopherol derivatives. 相似文献
3.
I. Sziklai-László D. Majchrzak I. Elmadfa M. á. Cser 《Journal of Radioanalytical and Nuclear Chemistry》2009,279(2):585-590
The metabolic roles of vitamin E and selenium are closely related, and to a very great extent, each can compensate for the
deficiency of the other. The aim of the study was to determine and compare the Se and vitamin E (α- and γ-tocopherol) contents
of breast milk and commercially available infant formulas in Hungary. The Se content was measured by instrumental neutron
activation analysis (INAA), while the α-, and γ-tocopherol concentrations were determined by high performance liquid chromatography
(HPLC). The mean Se concentration was 17.4±2.8 μg/L in transitional and 13.8±2.3 μg/L in mature milk. It was found that, all
of the starter (ST), the follow-on (FO) and the specialized formulas (SF) had lower Se content than breast milk. Transitional
breast milk resulted in a higher Se intake (14 μg/day) than mature milk (11 μg/day). The daily Se intakes in Hungarian infants
were within the Recommended Dietary Allowance (RDA) range. The natural vitamin E contents of human milk were similar during
the early and late lactation. Mature breast milk had 3.30±1.13 mg/L α-TE concentration and this was significantly higher than
that of in ST (1.98±1.57), and FO (1.77±0.78), or in SF ready to feed preparations (1.03±0.74). The present study suggests
that the formulas for the optimal development of young infants, should contain concentrations of these antioxidants on a level
which is comparable to that of the human milk. 相似文献
4.
L. A. Zhuravleva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(7):1130-1134
The results from developing a kinetic model for testing water-soluble antioxidants by examining the micelle formation and
oxidation kinetics of water-emulsion ethyl oleate and methyl linoleate substrates are presented. The optimum composition of
the system, the catalyst, and the emulsifying agent are selected. The model is tested using standard, synthetic, and natural
antioxidants. Criteria for evaluating the antioxidant’s efficiency are proposed. A more complex mechanism for the action of
ionol is presented, along with the possibility of using it as an external standard. The high antioxidant activity of capoten
and the manifestation of antioxidant properties by α-tocopherol under selected conditions are demonstrated. 相似文献
5.
A new potential source of natural vitamin E from thirteen samples of Corylus avellana L. leaves was screened: the major Italian cultivar — Tonda romana (collected from Latium and Sardinia localities); ten local
genotypes from Sardinia — Moro seme, Suconcale, Moro, Sarda grossa, Sarda grossa seme, Sarda schiacciata, Coccoredda, Sarda
lunga, Sarda piccola and Sarda tardiva; wild genotype — Selvatico from Latium. The determination was performed after optimizing
the high-efficiency pressurized liquid extraction (PLE) conditions of α-tocopherol from Italian hazelnut tree green leaves.
Moro from Sardinia showed the highest content of α-tocopherol (237.4±0.3 μg/g d.w). Leaves of this genotype may be considered
as a potential new source for natural α-tocopherol.
__________
Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 538–540, November–December, 2005. 相似文献
6.
N. T. Berberova L. B. Kirillova Yu. T. Pimenov E. R. Milaeva A. I. Prokofev 《Russian Journal of Electrochemistry》2000,36(7):752-755
The influence of electrochemical characteristics of antioxidants (dl-α-tocopherol, 2,6-dialkyl substituted phenols) on the oleic acid oxidation by oxygen of air is studied at 65°C. The stability
of the antioxidant radical cations, which form in the first oxidation step, is presumed to be connected with their antioxidant
activity. The formation of stable paramagnetic intermediates is confirmed by the example ofdl-α-tocopherol and its acetate, using ESR spectroscopy. Different reactivity of the antioxidants with respect to a single-electron
oxidant, spatially hindered o-quinone, is studied 相似文献
7.
González-Martín I Hernández-Hierro JM Bustamante-Rangel M Barros-Ferreiro N 《Analytical and bioanalytical chemistry》2006,386(5):1553-1558
The vitamin E (α- and (β+γ)-tocopherol) contents present in alfalfa (fresh or dehydrated) were analysed using near-infrared
spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe. The range of vitamin E was 0.55–5.16 mg/100 g
for α-tocopherol and 0.07–0.48 for (β+γ)-tocopherol. The regression method employed was modified partial least squares (MPLS).
The equations developed using the fibre-optic probe for 69 samples of alfalfa (dehydrated and fresh) to determine the content
of vitamin E in feeds had multiple correlation coefficients (RSQs) and prediction corrected standard errors (SEP (C)) of 0.946
and 0.321 mg/100 g for α-tocopherol and 0.956 and 0.022 mg/100 g for (β+γ)-tocopherol. The predicted values of vitamin E in
feeds using NIRS technology applying the fibre-optic probe directly on the sample with neither previous treatment nor manipulation
are comparable to those obtained using the chemical method, which included alkaline hydrolysis and hexane extraction of the
vitamin from the unsaponifiable fraction before chromatographic determination. 相似文献
8.
Wimut Sermsri Purim Jarujamrus Juwadee Shiowatana Atitaya Siripinyanond 《Analytical and bioanalytical chemistry》2010,396(8):3079-3085
Flow field-flow fractionation (FlFFF) was used for size characterization of gold nanoparticles. The measured particle sizes
obtained from FlFFF for the commercial 10 nm gold nanoparticle standard and the gold nanoparticles synthesized in the laboratory
were in good agreement with those measured by transmission electron microscopy (TEM). Further, the capability of α-tocopherol
to induce enlargement of gold nanoparticles by catalysis of the reduction of AuCl4− by citrate was observed by monitoring the changes in particle size of gold nanoparticles using FlFFF. The effects of α-tocopherol
and incubation time on enlargement of the gold nanoparticles were examined. Higher concentrations of α-tocopherol resulted
in larger nanoparticles. At fixed α-tocopherol concentration, larger nanoparticles were formed at longer incubation times. 相似文献
9.
F Granado-Lorencio C Herrero-Barbudo I Blanco-Navarro B Pérez-Sacristán 《Analytical and bioanalytical chemistry》2010,397(3):1389-1393
Our aim was to assess the suitability of ultra-high performance liquid chromatography (UHPLC) for the simultaneous determination
of biomarkers of vitamins A (retinol, retinyl esters), E (α- and γ-tocopherol), D (25-OH-vitamin D), and the major carotenoids
in human serum to be used in clinical practice. UHPLC analysis was performed on HSS T3 column (2.1 × 100 mm; 1.8 μm) using
gradient elution and UV–VIS detection. The system allows the simultaneous determination of retinol, retinyl palmitate, 25-OH-vitamin
D, α- and γ-tocopherol, lutein plus zeaxanthin, α-carotene, β-carotene, α- and β-cryptoxanthin and lycopene. The method showed
a good linearity over the physiological range with an adequate accuracy in samples from quality control programs. Suitability
of the method in clinical practice was tested by analyzing samples (n = 286) from patients. In conclusion, UHPLC constitutes a reliable approach for nutrient/biomarker profiling allowing the
rapid, simultaneous and low-cost determination of vitamins A, E, and D (including vitamers and ester forms) and the major
carotenoids in clinical practice. 相似文献
10.
Perla Relkin Jin-Mi Jung Michel Ollivon 《Journal of Thermal Analysis and Calorimetry》2009,98(1):13-18
Fat fractions composed by different proportions of low (LMT) or high (HMT) melting temperature triacylglycerols were used,
alone or in mixture with α-tocopherol for the preparation of oil-in-water protein stabilised nano-emulsions. Addition of α-tocopherol
to the LMT or HMT fat fractions was accompanied by different changes in the emulsion characteristics such as fat droplet size
distributions, under-cooling and polymorphic transitions, in parallel with different extent of α-tocopherol degradation reactions.
Our results showed higher immobilisation pattern of α-tocopherol molecules and higher protection against degradation when
incorporated in higher size fat droplets, which presented 2Lα → 2Lβ′ polymorphic transitions under cooling and re-heating cycles. 相似文献
11.
A critical analysis is presented of the use of an overall single rate reaction equation instead of the true rate equation
corresponding to a complex process consisting of two consecutive reactions. In accordance with this approximation, which is
often used in the kinetic analysis of systems in which several reactions take place, the overall process is described by apparent
activation parameters (the apparent activation energy Eap and the apparent pre-exponential factor Aap) and an apparent conversion function.
The theoretical isotherms (α=α(t), where α is the conversion degree and t is time) were simulated for a system in which two
consecutive reactions occur. In this case, the apparent activation parameters depend on (a) the considered range of temperature;
and (b) the temperature for a given conversion degree. It is shown that the apparent activation parameters are correlated
by the compensation effect relationship: ln Aap = α* + β*Eap where α* and β* are the linear regression parameters.
The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those
for which these parameters were evaluated is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Mingliang Xin Yujie Ma Kai Xu Mingcai Chen 《Journal of Thermal Analysis and Calorimetry》2013,114(3):1167-1175
A study on the efficiency of bio-based compound as stabilizer for linear low density polyethylene (LLDPE) is reported. A water extract from Ampelopsis grossedentata (Dihydromyricetin) is used. Its stabilizing activity is compared with two commercial phenolic antioxidants: methyl gallate (MG) and Irganox 1010. Based on the measurement of the oxidation onset temperature (OOT) of LLDPE/antioxidant samples, it is found that the antioxidant ability of the three kinds of antioxidants is in the following order: DMY > 1010 > MG. The antioxidant ability and thermal decomposition activation energy (E a) of antioxidants are further examined by thermal gravimetric analysis. The effects of water extraction on the migration resistance of LLDPE/antioxidants are also evaluated by monitoring the OOT change, demonstrating that DMY retained high stability against migration. 相似文献
13.
A critical analysis of the use of an overall single rate reaction equation instead of the true rate equation corresponding
to a complex process consisting in two consecutive reactions is presented. In accordance with this approximation, often used
in the kinetic analysis of the system in which several reactions take place, the overall process is described by the apparent
activation parameters (the apparent activation energy, E
ap, and the apparent pre-exponential factor, A
ap) and the apparent conversion function.
The theoretical isotherms (α=α(t), where a is the conversion degree and t is the time) have been simulated for a system in which two consecutive reactions occur. In this case, the apparent activation
parameters depends on: (a) the considered range of the temperature; (b) the temperature, for a given conversion degree. It
is shown that the apparent activation parameters are corrrelated by the compensation effect relationship: lnA
ap=α*+β*E
ap where α* and β* are the parameters of the linear regression.
The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those
for which these parameters were evaluated, is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
S. Al-Malaika H. Ashley S. Issenhuth 《Journal of polymer science. Part A, Polymer chemistry》1994,32(16):3099-3113
The antioxidant role of α-tocopherol (vitamin E) in low-density polyethylene (LDPE), and the nature of its transformation products formed during extrusion of the polymer are investigated. The melt stabilizing effectiveness of α-tocopherol was found to be very high, higher than that of the commercial hindered phenol antioxidants, Irganox 1076 and 1010, after single and multiple extrusion. The high antioxidant activity of α-tocopherol as a melt stabilizer is due, at least in part, to its transformation products. The importance of the processing history and the parent antioxidant concentration on the transformation products is discussed. Transformation products of α-tocopherol were analyzed after each of the four extrusion passes of the polymer. These were fractionated, analyzed, and characterized by HPLC and spectroscopy, respectively. The main products formed are diastereoisomers of dimers and trimers, as well as aldehydes; the relative concentration of each was shown to depend on processing severity (number of extrusion passes) and the initial concentration of α-tocopherol. The dihydroxydimer was found to be formed at a high concentration relative to the other products and proportional with the initial concentration of tocopherol. Based on both the identity and distribution of transformation products, a mechanism is proposed for the melt stabilization effect of α-tocopherol in LDPE. © 1994 John Wiley & Sons, Inc. 相似文献
15.
G. K. Ziyatdinova E. R. Giniyatova H. C. Budnikov 《Journal of Analytical Chemistry》2012,67(5):467-473
As established, α-tocopherol is electrochemically active on glassy carbon electrode in the available range of anodic potentials
in acetonitrile and its aqueous mixtures. However, an increase in the water percentage up to 50% and beyond leads to a substantial
decrease and then the total disappearance of the analytical signal. A scheme of electrode reaction responsible for the signal
formation is proposed. The effect of surfactants on the oxidation of α-tocopherol in aqueous acetonitrile is estimated. As
found, surfactants (N-dodecylpyridinium bromide, Triton X-100 and N-cetylpyridinium bromide) enhance the current of α-tocopherol oxidation. The surfactants reduce the detection limit and extend
the analytical range. Analytical methods for the voltammetric quantification of α-tocopherol in drugs in the presence of surfactants
are elaborated and may be recommended for the control of pharmaceuticals. 相似文献
16.
17.
M. G. Perevozkina N. M. Storozhok A. P. Krysin V. E. Borisenko 《Russian Chemical Bulletin》2006,55(8):1380-1387
In a model system of initiated oxidation of methyl oleate, the antioxidant activities of 3-hydroxy-2-ethyl-6-methylpyridinesuccinate
(mexidol) and bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl] disulfide (SO-4) were studied and compared with those of α-tocopherol and 1-hydroxy-2,6-di-tert-butyl-4-methylbenzene (dibunol). A linear pattern of dependence of the inhibitory effect on the concentration of compounds
was established. The ability of antioxidants to decompose hydroperoxides and inhibit their accumulation was revealed. The
combined inhibitory effects of SO-4 with mexidol, α-tocopherol, and phospholipids were described for the first time. The rate
constant for disproportionation of the SO-4 phenoxyl radicals, k
9 = 0.90·103 L mol−1 s−1, was determined by steady-state photolysis. The rate constant k
10
eff for the reactions of SO-4 phenoxyl radicals with lipids characterized by different unsaturation degrees were determined for
methyl oleate, linolic and arachidonic acids containing one, two, and four multiple bonds, and phospholiopids containing polyunsaturated
fatty acids.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1330–1337, August, 2006. 相似文献
18.
The use of hydroxytyrosol (3,4-dihydroxy-phenylethanol) as a potential alternative to synthetic compounds in the melt stabilization of polyolefins is considered. Hydroxytyrosol was found to play a role in enhancing the oxidative stability of olive oil, and a similar reduction in polyolefins’ thermo-oxidative degradation during processing is expectable. Rheological tests (melt flow index and viscosity vs. shear rate) showed the good antioxidant performance of hydroxytyrosol during polypropylene processing as was also demonstrated by the increase in apparent activation energies and oxidation induction parameters after addition to polypropylene (0.1 wt%). Results were compared to those obtained for a commercial synthetic phenolic antioxidant and for a natural compound widely used in polymer stabilization (α-tocopherol). The main conclusion of this work is the good performance of hydroxytyrosol in polypropylene stabilization during processing and consequently the possibility of its use in formulations with improved resistance to oxidative degradation. 相似文献
19.
The enthalpies, activation energies, and rate constants for the reactions of 15 phenoxyl radicals derived from natural bioantioxidants
with hydroperoxides, C-H bonds of linoleic acid, SH-groups of l-cysteine, and O-H bonds of α-tocopherol (60 reactions) were calculated. The activation energies were calculated using the
model of intersecting parabolas. The interatomic distances in the reaction sites of the transition states of the studied reactions
were calculated. The factors affecting the reactivity of these radicals are discussed. The activation energy of the reaction
of oxygen with the O-H bond of the 1,2-dihydroxybenezene semiquinone radical was estimated. 相似文献
20.
Citová I Havlíková L Urbánek L Solichová D Nováková L Solich P 《Analytical and bioanalytical chemistry》2007,388(3):675-681
Retinol and α-tocopherol are biologically active compounds often monitored in blood samples because of their evident importance
in human metabolism. In this study a novel ultra-performance liquid chromatographic (UPLC) method used for determination of
both vitamins in human serum has been compared with conventional HPLC with particulate and monolithic C18 columns. In UPLC a sub-two-micron particle-hybrid C18 stationary phase was used for separation, in contrast with a five-micron-particle packed column and a monolithic column with
a highly porous structure. Methanol, at flow rates of 0.48, 1.5, and 2.5 mL min−1, respectively, was used as mobile phase for isocratic elution of the compounds in the three methods. Detection was performed
at 325 nm and 290 nm, the absorption maxima of retinol and α-tocopherol, respectively. Analysis time, sensitivity, mobile-phase
consumption, validation data, and cost were critically compared for these different chromatographic systems. Although cost
and mobile-phase consumption seem to make UPLC the method of choice, use of the monolithic column resulted in almost the same
separation and performance with a slightly shorter analysis time. These methods are alternatives and, in routine laboratory
practice, more economical means of analysis of large numbers of biological samples than use of a traditional particulate column. 相似文献