Viscous and dielectric properties of α-tocopherol and α-tocopherol acetate

This article presents the results of the shear viscosity and the dielectric relaxation measurements performed for α-tocopherol and α-tocopherol acetate, two principal compounds from the vitamin E group. The temperature dependence of the viscosity and dielectric relaxation time of the compounds can be very well reproduced with the Vogel–Fulcher–Tammann equation. It was found that for both tocopherols, the viscosity and the relaxation time attain their infinite high value (solid-like state) at the temperature of ～60 K below the transition to the glass state.     

Development and validation of HPLC method for the determination of α-tocopherol in human erythrocytes for clinical applications

In this work, a simple isocratic reversed-phase HPLC method for determination of alpha-tocopherol in human erythrocytes has been developed and validated. After separation of plasma the erythrocytes were washed three times with 0.9% sodium chloride containing 0.01% butylated hydroxytoluene (BHT) as antioxidant and then were diluted 1:1 (v/v) with the same solution. In the liquid-liquid extraction (LLE) procedure, 2500 microL of n-hexane was added to 500 microL of erythrocytes. After 2 min this mixture was deproteinized by addition of cool ethanol (500 microL, 5 min) denatured with 5% methanol containing alpha-tocopherol acetate (20 micromol L(-1)), as internal standard, and then extracted for 5 min by vortex mixing. After centrifugation (10 min, 1600xg) an aliquot (2000 microL) of the clean extract was separated and evaporated under nitrogen. The residue was dissolved in 400 microL methanol and analysed by reversed-phase HPLC on a 4.6 mmx150 mm, 5 microm Pecosphere C18 column; the mobile phase was 100% methanol, flow rate 1.2 mL min(-1). The volume injected was 100 microL and detection was by diode-array detector at a wavelength of 295 nm. The extraction recovery of alpha-tocopherol from human erythrocytes was 100.0+/-2.0%. The detection limit was 0.1 micromol L(-1) and a linear calibration plot was obtained in the concentration range 0.5-20.0 micromol L(-1). Within determination precision was 5.2% RSD (n=10), between determination precision was 6.1% RSD (n=10). The method was applied successfully in a clinical study of patients with acute pancreatitis and for determination of the reference values in the healthy Czech population.     

Simultaneous determination of retinol acetate, retinol palmitate, cholecalciferol, α-tocopherol acetate and alphacalcidol in capsules by non-aqueous reversed-phase HPLC and column backflushing

Summary A very simple non-aqueous reversed-phase HPLC method has been developed for analysis of retinol acetate, retinol palmitate, cholecalciferol, α-tocopherol acetate and alphacalcidol in capsules without the need for saponification. A reversed-phase (LiChrospher C8, 4.6 mm i.d.) column is used with acetonitrile-methanol, 95∶5 (v/v) as mobile phase at flow rate of 1 mL min⁻¹. Sample treatment consists only in dilution of the capsule contents withn-hexane and methanol. This method is suitable for routine quantification in the industrial quality-assurance laboratory.     

Comparison of the photochemical behaviors of α-tocopherol and its acetate in organic and aqueous micellar solutions

Photoionization is known to take place when α-tocopherol (TOH) is excited to the S(1) state in a polar medium. It has been previously suggested that TO(?) is formed only as a result of proton release by TOH(?+), a process that is expected to occur, in a protic solvent, on the subnanosecond time scale. Recent redeterminations of the molar absorption coefficients of e(aq)(–) (Hare J. Phys. Chem. A 2010, 114, 1766) and of TOH(?+) and TO(?) (Naqvi J. Phys. Chem. A 2010, 114, 10795) have paved the way for testing the above suggestion, even if subnanosecond time resolution is not available, since it implies the equality of [e(aq)(–)](0) and [TO(?)](0), where [···](0) denotes the concentration of the enclosed species immediately after a nanosecond laser pulse. Nanosecond pump-probe spectroscopy of TOH in aqueous micellar solution (AMS) and two organic solvents with similar polarities (acetonitrile and methanol) has revealed that prompt formation of TO(?) through dissociation (TOH + hν → TO(?) + H(?)) is not negligible even in AMS. In acetonitrile, TOH(?+) and TO(?) are formed with comparable yields, and the former converts quantitatively into TO(?) within 15 μs. In methanol, TO(?) was observed, but no evidence was found for electron ejection from TOH. Only one photoproduct, namely TO(?), could be detected when α-tocopherol acetate (TOAc) was excited to the S(1) state in several polar and nonpolar solvents; TOAc has been found to be a more efficient energy degrader than TOH.     

Solid phase extraction with electrospun nanofibers for determination of retinol and α-tocopherol in plasma

A novel packed-fiber solid phase extraction procedure based on electrospun nanofibers for simultaneous determination of vitamins A (retinol) and E (α-tocopherol) in human plasma has been developed. Parameters affecting extraction efficiency were investigated in detail. The limit of detection is 0.01 μg mL^?1 for retinol, and 0.3 μg mL^?1 for α-tocopherol. The linear range is from 0.05 to 2.0 μg mL^?1 for retinol, and from 0.5 to 30 μg mL^?1 for α-tocopherol. The precision (RSD) is <6%, and the relative recovery >90%. The method was applied to analysis of retinol and α-tocopherol in human plasma with satisfactory results.     

Effects of α-tocopherol and its acetate on the hydrolytic activity of phospholipase D in egg yolk phosphatidylcholine bilayers

Effects of -tocopherol (Toc) and -tocopherol acetate (TocA) on the hydrolysis activity of phospholipase D (fromStreptomyces chromofuscus) were studied in small unilamellar vesicles (SUV) of egg yolk phosphatidylcholine (PC). Choline produced in the reaction was monitored by use of a choline oxidase — oxygen electrode. Addition of 18 mol% Toc into SUV (2 mM PC) brought about a twofold rate of choline production. On the other hand, the effect of 18 mol% TocA in SUV was very small. The apparent maximum velocity,V _max(app), increased by addition of Toc in SUV. The apparent Michaelis constant,K _m(app), was unchanged by addition of Toc and TocA in SUV. The Toc and TocA molecules did not have significant effects when PC was solubilized in the micelles of heptaethylene glycol dodecyl ether. The effects of Toc and TocA are, therefore, not due to specific ones on the enzyme itself, but rather upon the bilayer-organization of the substrate. Measurements of spreading pressure showed complete miscibility of PC and Toc, and limited mutual solubility of PC and TocA, suggesting stronger attractive interactions between Toc and PC than those between TocA and PC in the bilayers.     

Comparison of a novel ultra-performance liquid chromatographic method for determination of retinol and α-tocopherol in human serum with conventional HPLC using monolithic and particulate columns

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.     

Rapid and cost-effective LC–MS/MS method for determination of hydroxycitric acid in plasma: Application in the determination of pharmacokinetics in commercial Garcinia preparations

Garcinia cambogia is one of the most commonly used anti-obesity dietary supplements, and hydroxycitric acid (HCA) is a major constituent in the commercial preparations of Garcinia. High doses of HCA are often consumed without much awareness of its pharmacokinetic and toxicokinetic parameters, and therefore, a complete understanding of its effects is lacking. The first step in understanding these parameters is the availability of a reliable bioanalytical method. Here, we present the first report on a UPLC–MS/MS method for analysis of HCA in rat plasma after a simplified and cost-effective protein precipitation. Chromatographic separation of the analytes in the supernatant was achieved using hydrophilic interaction liquid chromatography, where mass parameters were optimized and a rapid 5-min quantitative assay was developed. The method was highly sensitive, accurate, precise and linear in the concentration range of 10.5–5000 ng/mL (validated according to the United States Food and Drug Administration guidelines). Further, the method was successfully used to describe the pharmacokinetic profile of HCA in rat plasma after the administration of pure HCA and commercial Garcinia preparations.     

Bromination of α-tocopherol methano-dimer and ethano-dimer

Bromination of the ethano-dimer of α-tocopherol (6) afforded pyrano-spirodimer of α-tocopherol (7) quantitatively, while the methano-dimer of α-tocopherol (10) produced a mixture of products, including the furano-spirodimer 11, pyrano-spirodimer 7, and 5-bromo-γ-tocopherol (12), the latter two formed in an unusual dealkylative fragmentation step. The mechanisms were studied by a combination of trapping reactions as well as kinetic and computational studies.     

Application of solvent extraction and synchronous spectrofluorimetry to the determination of the formation constant for a 1:1 complex of carbazole withβ-cyclodextrin in water-dimethyl sulfoxide medium

Extraction of carbazole in heptane was performed at 25±1°C with an aqueous dimethyl sulfoxide (DMSO) medium containing -cyclodextrin (CD) at consecutive concentrations in the range of 0–10 mM. The fluorescence intensity of carbazole remaining in the heptane phase was measured by synchronous scanning fluorimetry. The apparent formation constant (K _f) for a 1:1 carbazole: CD inclusion complex in water-DMSO medium was determined by using a linear plot of the distribution ratio calculated from the fluorescence intensities vs. the -CD concentration. The values thus obtained ranged from 477 M^–1 in a 10% v/v DMSO medium to 12.1 M^–1 in a 60% v/v medium. Good linear relationships were observed between logK _f and the DMSO concentration ([DMSO]), and also between logK _f and the logarithm of the distribution coefficient (K _d) for carbazole. The formation constant in 100% water was estimated to be approximately 1.0×10³ M^–1 on the basis of the logK _f vs. [DMSO] and the logK _f vs. logK _d correlations.     

New water-soluble forms of α-tocopherol: preparation and study of antioxidant activity in vitro

Water-soluble forms of α-tocopherol (vitamin E) possessing antioxidant activity in vitro were obtained by encapsulating in N-vinylpyrrolidone with triethylene glycol dimethacrylate polymer particles and were characterized by various physicochemical methods. Quantum-chemical modeling of a structure of α-tocopherol with the copolymer moiety and its theoretical absorption spectra modeling were carried out.     

LC–MS/MS method for the determination of erianin in rat plasma: Application to a pharmacokinetic study

Erianin is one of the bibenzyl ingredients isolated from Dctidrobium chrysotoxum Lindl. In recent years, erianin has attracted attention owing to its antitumor activity. In this study, an LC–MS/MS method was established to measure erianin in rat plasma. Gigantol was used as the internal standard. A Waters Acquity UPLC BEH C₁₈ column was employed for chromatographic separation. The mobile phase consisted of water containing 0.1% formic acid and acetonitrile with a gradient elution at the flow rate of 0.4 ml/min. Selective reaction monitoring mode was used for quantitative analysis of erianin in positive electrospray ionization. In the concentration range of 0.1–1200 ng/ml, erianin in rat plasma was linear with correlation coefficient >0.999. The lowest limit of quantification was 0.1 ng/ml. The intra- and inter-day RSDs were <9.69%, while the RE was in the range of −8.59–11.24%. The mean recovery was >85.37%. Erianin was stable in rat plasma after storage under certain conditions. The validated method was demonstrated to be selective, sensitive and reliable, and has been successfully applied to pharmacokinetic study of erianin in rat plasma. Erianin was rapidly eliminated from rat plasma with a short half-life (〜1.5 h) and low oral bioavailability (8.7%).     

Application of a simple and sensitive GC–MS method for determination of morphine in the hair of opium abusers

Thirty hair samples were collected from male opioid abusers for whom the presence of morphine in their urine samples was confirmed by thin layer chromatography (TLC). The hair samples were decontaminated by washing with isopropanol, deionized water, and isopropanol, dried at room temperature, and cut into small pieces. Samples of the latter (30 mg ) were digested by incubation in a mixture of methanol–trifluoroacetic acid (9:1) for 18 h at 45 °C and sonicated to improve the extraction process. The methanolic phase was evaporated to dryness under a stream of nitrogen at 50 °C. The sample was derivatized by addition of N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) and 1% trimethyliodosilane (TMIS) at 70 °C for 20 min, with sonication. Derivatized samples (1 L) were injected into a gas chromatograph–mass spectrometer (GC–MS) system fitted with a capillary column; the Finnigan MS was operated in SIM mode. Naltrexone was used as internal standard (IS). The masses of the ions selected for morphine and naltrexone were 429 and 557, respectively. The limit of quantitation was set at 0.03 ng mg^–1 hair. By using the above procedure we detected morphine in all the samples examined, in the concentration range 0.26–10.31 ng mg^–1 hair.     

Retention and selectivity of basic drugs on solid-phase extraction sorbents: Application to direct determination of β-blockers in urine

Seven solid phase sorbent materials with reversed-phase, mixed-mode interactions (ion-exchange and reversed-phase), and molecularly imprinted polymers (MIP), namely Oasis HLB, Oasis MAX, Oasis MCX, Bond Elute Plexa, Bond Elute Plexa PAX, Bond Elute Plexa PCX, and SupelMIP sorbents, were investigated. The present study was focused on the retention and elution of pharmaceutically active substances based on several analyte-sorbent interaction properties. Basic drugs, such as β-blockers (i.e., atenolol, pindolol, acebutolol, metoprolol, labetalol, and propranolol) were selected as the model compounds for this study. These compounds are frequently encountered in anti-doping tests. The extraction efficiencies of the individual sorbents were compared based on the recovery of known amounts of the targeted analytes in a metered elution volume (500 μL) in three separate elution fractions. The elution efficiency of the total amount of the target analytes on various sorbents was not appreciably influenced by the volume of eluent required for complete elution. Based on the small matrix effects and clear baseline, SupelMIP was the most suitable sorbent for urine analysis. The relative analyte recoveries of the SPE-HPLC procedure proved satisfactory for the range from 94 % to 105 %, with an RSD ranging from 2 % to 4 %. The regression equations for all of the targeted compounds exhibited excellent linearity (r ² ?>?0.9991) over the range of 10 to 1000 ng mL^–1. The limits of detection and quantification for the selected β-blocker compounds in urine were in the ranges of 0.6 to 2.0 ng mL^–1 and 2.0 to 6.7 ng mL^–1, respectively.     

The Application of the Trichloroacetimidate Method to the Synthesis of α-D-Gluco- and α-D-Galactopyranosides

Abstract

The trichloroacetimidate method has been applied to the construction of α-d-galacto- and α-d-glucopyranosides. The readily available β-trichloroacetimidates of 2,3,4,6-tetra-O-benzyl-d-galacto- and glucopyranose (1-β and 3-β, respectively) have been employed in glycosidations with several monosaccharides (either A, B, C or D) under varying experimental conditions. With the galactose derivative 1-β as a donor and each of the monosaccharides A-D as acceptors, the corresponding disaccharides 1A-1D, were obtained in high yield and with good α-stereoselectivity when employing diethyl ether as solvent and either trimethylsilyl- or tert-butyldimethylsilyl trifluoro-methane sulphonate as catalyst. Glycosidations with the glucose derivative 3-β, as donor, and with the monosaccharide acceptors A, B or D, gave the corresponding disaccharides 3A, 3B and 3D, in high yield but with somewhat lower α-diastereoselectivity than observed with the galactose derivative 1-β. The stereochemical outcome of the reactions is rationalised in terms of possible reaction mechanisms.     

Hydrochloride method for the determination of monomer in the polycondensation of esters of α-amino acids

Summary A method is proposed for determining the monomer in the polycondensation of esters of-amino acids. The accuracy of the method was to within 1–1.5%.     

A simplified and reliable LC–tandem mass spectrometry method for determination of ulipristal acetate in human plasma and its application to a pharmacokinetic study in healthy Chinese volunteers

In this study, a simplified, sensitive and reliable LC–tandem mass spectrometry method was established and validated for the quantification of ulipristal acetate (UPA) in human plasma and for the investigation of pharmacokinetic profile of UPA following a single oral administration of ella (UPA 30-mg tablet) in healthy Chinese volunteers. Plasma samples were analyzed after being processed by protein precipitation with methanol. Chromatographic separation was performed on a Kinetex EVO C₁₈ column (2.1 × 50 mm, 2.6 μm) using gradient elution with a mobile phase composed of methanol and water containing 2 mm ammonium acetate and 0.3% formic acid at a flow rate of 0.3 mL/min. The chromatographic running time was 4.0 min per sample. The MS detection was performed via an LC system with the positive ion electrospray ionization interface in multiple reaction monitoring mode using the transition of m/z 476.2 → 134.1 for UPA and m/z 479.3 → 416.2 for UPA-d3 [internal standard (IS)], respectively. UPA and IS were monitored without severe interference from the biological matrices. The method was linear over the wide concentration range of 0.300–300 ng/mL. The intra- and inter-day precision and accuracy were well within the limits required for bioanalytical assays. The method was first used to describe the pharmacokinetic characteristic of UPA after a single oral administration of ella in healthy Chinese volunteers. Based on a between-study comparison, there were statistically significant differences (p < .05) between Chinese and Caucasian volunteers for the systemic exposure of UPA, suggesting that race seems to significantly impact the systemic exposure of UPA.     

The Preparation of α-Phosphonovinylzirconocenes and their Application in the Stereospecific Synthesis of α-Halo-l-alkenylphosphonates

Hydrozirconation of 1-alkylnylphosphonates gives the organozirconium(Ⅳ) complexes 2 in syn-addition way.Complexs 2 was trapped with NCS,NBS or I2 to afford stereodifined α-halo-1-alkenylphosphonates in moderate to high yields.     

Synthesis and antioxidant properties of novel α-tocopherol glycoconjugates

Glycoconjugates of α-tocopherol (1), synthesized using click chemistry between α-tocopherol-azide and glyco-alkynes are solids, have enhanced water solubility and exhibit radical-scavenging activities comparable to 1, as determined by DPPH and lipid peroxidation assay methods.     

Determination of α-tocopherol in Cosmetic Products by Chronopotentiometry

Abstract

In the present study, a rapid chronopotentiometric method was developed for the determination of α-tocopherol in various cosmetic products. Determination of α-tocopherol is based on its irreverse oxidation by constant current at the planar glassy carbon electrode. The influence of the most important experimental parameters of chronopotentiometry was investigated. After optimization, an appropriate procedure for the sample preparation was developed. Under the defined experimental conditions, a detection limit of 7.5 mg L^?1 of α-tocopherol was obtained. The accuracy of the defined method was confirmed by means of recovery assay. The developed method was successfully applied to quantitation of α-tocopherol in various cosmetic products.