Composition of essential oils of four <Emphasis Type="Italic">Hedychium</Emphasis>species from Vietnam

Background

Vietnam is a country blessed with many medicinal plants widely used as food and for medicinal purposes, and they contain a host of active substances that contribute to health. However, the analysis of chemical constituents of these plant species has not been subject of literature discussion.

Results

In this study, the chemical compositions of essential oils of four Hedychium species, obtained by hydrodistillation, were determined by means of gas chromatography-flame ionization detector (GC-FID) and gas chromatography–mass spectrometry (GC-MS) techniques. Individually, α-pinene (52.5%) and β-pinene (31.8%) were present in the leaf oil of Hedychium stenopetalum Lodd., while linalool (45.2%), (E)-nerolidol (8.7%) and α-pinene (5.0%) were identified in the root. The leaf of Hedychium coronarium J. König was characterized by α-pinene (20.0%), linalool (15.8%), 1,8-cineole (10.7%), α-pinene (10.1%) and α-terpineol (8.6%); while α-pinene (23.6%), α-humulene (17.1%) and β-caryophyllene (13.0%) were identified in the root. Hedychium flavum Roxb., gave oil whose major compounds were α-pinene (22.5%), α-humulene (15.7%) and β-caryophyllene (10.4%) in the leaf; α-humulene (18.9%), β-caryophyllene (11.8%) and α-pinene (11.2%) in the stem, as well as α-pinene (21.8%), linalool (17.5%) and 1,8-cineole (13.5%) in the root. The main constituents of Hedychium ellipticum Buch.-Ham. ex Smith were (E)-nerolidol (15.9%), α-pinene (11.8%) and bornyl acetate (9.2%) in the leaf with 1,8-cineole (40.8%), α-pinene (18.3%) and α-pinene (11.0%) occurring in the root.

Conclusions

Ubiquitous monoterpenes and sesquiterpenes were identified as characteristic markers for Hedychium species. This work is of great importance for the evaluation of Hedychium essential oils grown in Vietnam.

     

Syntheses of the first N-mono- and N,N'-dipolyfluoroalkyl-4,4'-bipyridinium compounds

Reactions of 4,4'-bipyridine (1) with excess of polyfluoroalkyl iodides (2a-d) at 100-110 degrees C, under neat conditions, led to the formation of monoquaternary salts (3a-d) in > 90% yields. Salts 3a-d were metathesized with LiN(SO2CF3)2 either in water or water/acetone mixtures to form ionic liquids (4a-d), respectively, in > 88% yields. When 1 was reacted with 2.5 equivalent of 2a-c in DMF at 110 degrees C, the diquaternary salts 5a-c were formed in > 85% yields. Alternatively, 5a-c were also synthesized by heating a mixture of 3a-c and 2a-c (1.25 equivalent) in DMF. The metathesis reaction of 5a-c with LiN(SO2CF3)2 produced dicationic ionic liquids (6a-c) in > 86% yield.     

Analytical characteristics and determination of major novel brominated flame retardants (NBFRs) in indoor dust

A new method was developed and optimized for the detection of major “novel” brominated flame retardants (NBFRs), which included decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), tetrabromobisphenol A-bis(2,3-dibromopropylether) (TBBPA-DBPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate (TBPH) and hexachlorocyclopentadienyl-dibromocyclooctane (HCDBCO). Several solid phase sorbents were tested, and finally, a two-step cleanup procedure was established. The first step on activated silica was used to fractionate the dust extracts, while the second step on acidified silica (silica gel impregnated with sulphuric acid 44% w/w) and on Florisil®, respectively, was essential for advanced cleanup. High recoveries for NBFRs (range, 75–94%) were achieved. Analysis was performed by gas chromatography coupled with mass spectrometry in electron capture negative ionization using a DB-5ms (15 m?×?0.25 mm?×?0.1 μm) capillary column. Quantification of DBDPE, BTBPE and TBBPA-DBPE was based on ion m/z 79, while characteristic ions were used for quantification of TBB (m/z 359), HCDBCO (m/z 310) and TBPH (m/z 384). The method provided good repeatability; within- and between-day precision were ≤14% for all NBFRs. Method limits of quantification ranged between 1 and 20 ng g^?1; dust and NBFRs were not detected in blanks. The method was further applied to indoor dust (n?=?21) collected from e-waste facilities in Thailand. Except for HCDBCO, all NBFRs were detected in the e-waste dust with concentrations up to 44,000 and 22,600 ng g^?1 DBDPE and BTBPE, respectively. The dust profile was dominated by DBDPE (50%)?>?BTBPE (45%)?>?TBBPA-DBPE (3%)?>?TBPH (1.9%)?>?TBB (0.1%). Significant correlations (p?相似文献   

Synthesis of optically active 2-alkoxy-2H-pyran-3(6H)-ones. Their use as dienophiles in Diels-Alder cycloadditions.

Optically active 2-alkoxy-2H-pyran-3(6H)-ones (4a-d) were synthesized in one step by the tin(IV) chloride-promoted glycosylation and rearrangement of the 2-acetoxy-3,4-di-O-acetyl-D-xylal (3) prepared from D-xylose (1). The absolute configuration of the new stereocenter at C-2 was determined by chemical transformation of the dihydropyranones 4a and 4b into the known alkyl pentopyranosides (7a and 7b, respectively). Also, from (1)H NMR experiments using a chiral ytterbium shift reagent, the enantiomeric excesses for 4a (>86%) and 4b (>77%) were established. Enantiomerically pure 4c and 4d were obtained by reaction of 3 with chiral 2-octanol (R and S, respectively). Dihydropyranones 4a-d were employed as dienophiles in Diels-Alder cycloadditions with 2,3-dimethylbutadiene and butadiene. Under thermal conditions, only moderate yields (approximately 50%) of cycloadducts 9a-c and 10a were respectively obtained with good diastereofacial selectivity (>80%). Optimized Lewis acid promoted cycloadditions led to 9a-d and 10a,c in higher yields (approximately 80%) and with higher diastereoselectivities (>94%). The major products were formed by approach of the dienes from the less hindered face of the dihydropyranones, and the minor products (such as 11a) were formed by addition from the opposite side. Furthermore, cycloadduct 9a was stable in an alkaline solution, whereas 11a underwent epimerization under the same conditions.     

Bridged tetraquaternary salts from N,N'-polyfluoroalkyl-4,4'-bipyridine

4,4'-Bipyridine (1) with excess of polyfluoroalkyl bromide or iodides 2a-d at 100-110 degrees C without solvent gave the monoquaternary salts 3a-d in >90% yields. However, 1 with 2.5 equiv of 2a-c in DMF at 110 degrees C resulted in the diquaternary salts 5a-c in >85% yields. In DMF, 5a-c were obtained in comparable yields when a molar excess of 2a-c reacted with 3a-c. 1,4-Dibromobutane with 3a,b in DMF at 100 degrees C led to the tetraquaternary salts 7a,b in approximately 85% yields. In water or acetone/water as a solvent, salts 3a-d and 5a-c were metathesized with LiN(SO(2)CF(3))(2) and KSO(3)CF(3) to produce monoquaternary ionic liquids 4a-h in >88% yields and diquaternary ionic liquids 6a-f in >86% yields, respectively. Tetraquaternary ionic liquids 8a,b were obtained when LiN(SO(2)CF(3))(2) was reacted with salts 7a,b. These compounds were stable to 340 degrees C as determined by DSC. They are the first N-mono-, N,N'-di-, and N,N,N',N'-tetra-4,4'-polyfluoroalkylbipyridinium quaternary salts and ionic liquids.     

Source Apportionment Research of Fine Particulate Matter in the Atmosphere by PAHs

Haze weather frequently occurs in many cities in China. Polycyclic aromatic hydrocarbons(PAHs) in fine particulate matter(PM_2.5) can adversely affect the environment and human health. In this paper, PM_2.5 samples were collected at nine sites in a city in northeastern China from September 2013 to October 2014. Sixteen USEPA(US Evironment Protection Agency) priority PAHs in PM_2.5 were analyzed to determine their spatial and temporal distribution characteristics. The source apportionment of PAHs was conducted with the Positive Matrix Factorization(PMF) model. The results indicate that the concentrations of total PAHs(T-PAHs) in PM_2.5 are within the range of 0.26 to 72.48 ng/m³. The seasonal variation of T-PAHs is winter >spring >autumn >summer, and the space distribution of PAHs is JZP >DP >BFH >LP >EESA >IPT >CP >HZMC >JYP. In all types of PAHs, three-ring and five-ring PAHs are significantly prominent(62%) in the heating period due to petrogenic sources and traffic emissions. Middle- and high-ring PAHs in the non-heating period are caused by coal combustion and vehicle exhaust, which accounts for 77% of the total emissions. The source apportionment results obtained by the diagnostic ratio of PAHs reflect that coal burning, traffic and other sources have a distinct influence on PAH emissions in this city. Six factors are defined by PMF v5.0, namely, coke oven emissions(7.7%), biomass burning(44.3%), petrogenic sources(10.7%), coal combustion(10.4%), gasoline engine emissions(16.7%), and diesel engine emissions(10.3%). The results indicate that the PAHs in PM_2.5 in the city are primarily caused by combustion processes and vehicle exhaust.     

Preparation of Optically Enriched Secondary Alkyllithium and Alkylcopper Reagents—Synthesis of (−)‐Lardolure and Siphonarienal

Optically enriched secondary alkyl iodides were converted into secondary alkyllithium and secondary alkylcopper compounds with very high retention of configuration. Quenching with various electrophiles, including chiral epoxides, provided a range of chiral molecules with high enantiomeric purity (>90 % ee). This method has been applied in an iterative fashion in the total synthesis of (?)‐lardolure in 13 steps and 5.4 % overall yield (>99 % ee, dr>99:1) and siphonarienal in 15 steps and 5.6 % overall yield (>99 % ee, dr>99:1) starting from commercially available ethyl (R)‐3‐hydroxybutyrate (>99 % ee).     

Atom Transfer Radical Polymerization of Methyl Methacrylate High Efficiently Initiated by Azo-containing Iniferter

Two novel azo-containing iniferters, (4,4′-(diazene-1,2-diyl) bis(4,1-phenylene) bis(2-(diethylca-rbamothioylthio)-2-methylpropanoate (BDCMP) and 4-((4-bromophenyl)diazenyl)phenyl-2-(diethylcarbamothioylthio)-2-methylpropanoate (PDCMP) were synthesized and used successfully as the initiators for atom transfer radical polymerization of methyl methacrylate (MMA). The kinetic plots were first order and the molecular weights of the polymers with narrow molecular weight distributions increased with the monomer conversions. Furthermore, the results showed that the apparent initiation efficiencies (f was close to 0.90 defined as M _n(th)/M _n(GPC)) of BDCMP and PDCMP were both higher than that (f was lower than 0.5) of 2-N,N-(diethylamino)dithiocarboyl-isobutyrate (EDCIB), which was reported previously by us (14 Zhang, W., Zhu, X. L., Cheng, Z. P. and Zhu, J. 2007. J. Appl. Polym. Sci., 106: 230–7. [Crossref] , [Google Scholar]). The obtained mono- and bi-functional PMMAs containing azo and N,N-diethyldithiocarbamate (DC) groups were confirmed by ¹H-NMR and ultraviolet absorption spectra, respectively. The block copolymer, poly (methyl methacrylate)-b-polystyrene (PMMA-b-PS), was also successfully prepared via the ATRP chain-extension experiment using the obtained PMMA as a macroinitiator.     

Threonine aldolases—an emerging tool for organic synthesis

In a systematic study, 21 ring-substituted benzaldehydes were reacted with glycine under catalysis with a l-threonine aldolase (lTA) from Pseudomonas putida and a d-threonine aldolase (dTA) from Alcaligenes xylosoxidans to form the corresponding β-hydroxy-α-amino acids 1-18. dTA proved to be highly selective with ee's >99% (d) and de's up to 99% (syn). Two thiamphenicol precursors were synthesized utilizing dTA on a preparative scale. lTA-catalyzed reactions led to ee's >99% (l) but low to moderate de's (20-50%, syn).     

Silicon-carbon unsaturated compounds. 73. Photolysis of cis- and trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane in the presence of tert-butyl alcohol and acetone

Irradiation of cis-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1a) in the presence of tert-butyl alcohol in hexane with a low-pressure mercury lamp bearing a Vycor filter proceeded with high stereospecificity to give cis-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2a), in 33% isolated yield, together with a 15% yield of 1-[(tert-butoxy)methylphenylsilyl]-4-(methylphenylsilyl)butane (3). The photolysis of trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1b) with tert-butyl alcohol under the same conditions gave stereospecifically trans-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2b) in 41% isolated yield, along with a 12% yield of 3. Similar photolysis of 1a and 1b with tert-butyl alcohol-d₁ produced 2a and 2b, respectively, in addition to 1-[(tert-butoxy)(monodeuteriomethyl)(phenyl)silyl]-4-(methylphenylsilyl)butane. When 1a and 1b were photolyzed with acetone in a hexane solution, cis- and trans-2,3-benzo-1-isopropoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (4a and 4b) were obtained in 25% and 23% isolated yield. In both photolyses, 1-(hydroxymethylphenylsilyl)-4-(methylphenylsilyl)butane (5) was also isolated in 4% and 5% yield, respectively. The photolysis of 1a with acetone-d₆ under the same conditions gave 4a-d₆ and 5-d₁ in 18% and 4% yields.     

Asymmetric Synthesis of 3-Substituted 4-Oxoesters Using the SAMP-/RAMP-Hydrazone Method

Based on aldehydes 1a—f or ketone 1g, 3-substituted 4-oxo esters 6a—g were synthesized in three steps in moderate to good overall yield (12—50%) and in excellent enantiomeric excesses (ee >90—>95%) by an Umpolung-strategy employing the SAMP-/RAMP-hydrazone method. The key step in the synthesis is the highly diastereoselective alkylation of lithiated SAMP-hydrazones 3a—g (chiral d²-nucleophiles) with tert-butyl bromoacetate (4) (a²-electrophile) to furnish the alkylated 3-hydrazono tert-butylesters 5a—g in good yields (58—91%) and in excellent diastereomeric excesses (de >90—>98%). Regeneration of the carbonyl functionality by cleavage of the hydrazones 5a—g was accomplished either by acidic hydrolysis or ozonolysis to give the acid labile and oxidation-sensitive 3-substituted 4-oxo esters 6a—g in moderate yields (19—63%) and in excellent enantiomeric excesses (ee >90—>95%). The absolute configuration of compounds 6a—g were assigned by conversion of 4-oxo esters (S)-6d and (R)-6e into their corresponding known 3-substituted λ-butyrolactones (S)-7d and (R)-7e.     

GC and GC-MS Studies on the Essential Oil and Thiophenes from Tagetes patula L.

The production and the composition of the compounds (mono-, sesquiterpenes and acetylenic thiophenes) obtained by the steam distillation of Tagetes patula L. have been investigated. The volatile oil was produced by steam distillation. GC was carried out on three types of stationary phase using flame ionization and mass selective detection. Percentage data were calculated by the area normalization method with very good repeatability (RSD below 5%). Oils from flower-heads were rich in β-caryophyllene (53.5%) and the leaves contained terpinolene in high concentration (21.1%). The main volatile component of the hairy roots and intact roots was 5-(3-buten-1-ynyl)-2,2'-bithienyl (BBT) yielding 28.5% and 44.0% in the oils. Three new minor constituents were identified as α-gurjunene, β-caryophyllene and (E)-β-farnesene. A flash chromatographic method was developed for the isolation of thiophenes from a solvent extract of intact roots. The collected fractions were screened by TLC and analyzed by GC-MS. Three thiophene fractions were obtained containing BBT, 5-(4-acetoxy-1-butynyl)-2,2'-bithienyl (BBTOAc) and 5-(4-hydroxy-1-butynyl)-2,2'-bithienyl (BBTOH).     

Poly(vinylpyrrolidone)-modified graphite carbon nanofibers as promising supports for PtRu catalysts in direct methanol fuel cells

Carbon nanomaterials, including herringbone graphite carbon nanofibers (GNFH), multiwalled carbon nanotubes (MWCNT), and carbon black, were surface-modified by a new poly(vinylpyrrolidone) (PVP) grafting process as well as by the conventional acid-oxidation (AO) process, and characterized by FTIR, TGA, Raman, HRTEM, XRD, and XPS measurements. Pt nanoparticles of 1.8 nm were evenly deposited on all PVP-grafted carbon nanomaterials. The effects of the two surface modification processes on the dispersion, average Pt nanoparticle sizes, the electrocatalytic performance, and electrical conductivities of Pt-carbon nanocomposites in direct methanol oxidation were systematically studied and compared. It was found that the PVP-grafted carbon nanomaterials have much less loss in the electric conductivity and thus better electrocatalytic performance, 17-463% higher, than their corresponding acid oxidation-treated nanocomposites. The electrocatalytic performance of the Pt-carbon nanocomposites decreases in the following order: Pt-PVP-GNFH > Pt-PVP-MWCNTarc > Pt-AO-MWCNTarc > Pt-PVP-MWCNTCVD > Pt-AO-MWCNTCVD > Pt-XC-72R > Pt-AO-GNFH, with the Pt-PVP-GNFH nanocomposite having approximately 270% higher performance than that of the Pt-Vulcan XC-72R nanocomposite. In addition, PtRu-PVP-GNFH shows even better (50% higher) electrocatalytic activity than the Pt-PVP-GNFH nanocomposite at a 0.6 V applied voltage.     

Metallocenes with Cp Ring-Fused to Chalcogen Heterocycles: Synthesis and Polymerization Results

Abstract

Substituted metallocene ligands containing cyclopentadiene ring fused to either selenophene or benzo[b]tellurophene were prepared following methods previously developed for analogs containing sulfur. 5-Methyl-4,5-dihydro-cyclopenta[b]-selenophen-6-one ( 2 ) and 3-Methyl-3,4-dihydro-benzo[b]cyclopenta[d]telluraphen-2-one ( 7 ) (major isomers) were prepared by polyphosphoric acid catalyzed Friedel-Crafts acylation/Nazarov cyclization of methacrylic acid onto selenophene and respectively benzo[b]tellurophene. Following reduction of the ketone to alcohol, then dehydration, the chalcogen-containing cyclopentadiene olefins were prepared. The olefins were deprotonated with n-butyllithium followed by either bridging with dichlorodimethylsilane, deprotonation and metallation, or deprotonation and direct metallation. In this manner, isomeric mixtures of –rac/-meso dimethylsilanediylbis(η⁵-5-Methyl-cyclopenta[b]selenophen-yl)zirconium dichloride ( 5 ) Bis(η^5?2-methyl-cyclopenta[b][1 Brintzinger, H. H., Fischer, D., Mülhaupt, R., Rieger, B. and Waymouth, R. 1995. Angew. Chem., 107: 1255[Crossref] , [Google Scholar]]benzotelluraphen-yl)zirconium dichloride ( 9 ) were prepared and characterized. Complexes formed active olefin polymerization catalyst when activated with methylalumoxane. Polymerization results with ethylene and propylene are included.     

Air Assisted Dispersive Liquid–Liquid Microextraction (AA-DLLME) Using Hydrophilic–Hydrophobic Deep Eutectic Solvents for the Isolation of Monosaccharides and Amino Acids from Kelp

Abstract

Air assisted dispersive liquid–liquid microextraction (AA-DLLME) using hydrophilic–hydrophobic deep eutectic solvents (DES) was developed for the simultaneous isolation of monosaccharides and amino acids with wide ranges of polarities from kelp using high performance liquid chromatography (HPLC). A response surface methodology (RSM) on a Box–Behnken design (BBD) model was employed to identify the optimal extraction parameters. Air assisted dispersive liquid-phase microextraction performed using the optimum deep eutectic solvent system, five push–pull cycles, a ratio of solid to liquid equal to 3?mg·mL^?1, 10% (w/v) NaCl, and a centrifugation time of 6?min provided the best analytical performance. The optimal extracted concentrations of d-(+)-galactose, l-(-)-fucose, dl-tyrosine, and dl-valine in kelp were 16.7?±?0.2, 8.6?±?0.2, 2.6?±?0.1, and 1.6?±?0.1?mg·g^?1, respectively. The method recoveries for d-(+)-galactose, l-(-)-fucose, dl-tyrosine, and dl-tyrosine were from 87 to 102%, 84 to 103%, 87 to 104%, and 85 to 103%. The relative standard deviations (RSDs) (n?=?4) for the intra-day and inter-day determinations were <6.17%.     

Magnetic nanoparticles modified with polydimethylsiloxane and multi-walled carbon nanotubes for solid-phase extraction of fluoroquinolones

We have surface-functionalized magnetic particles (MPs) with polydimethylsiloxane and multi-walled carbon nanotubes in a two-step reaction. The MPs were applied to solid-phase extraction of the fluoroquinolones ofloxacin, norfloxacin, ciprofloxacin, enrofloxacin prior to their determination by capillary liquid chromatography. The effects of sample pH, adsorption time, type of eluent, desorption time and desorption temperature were investigated. Under the optimum conditions, the extraction efficiencies are in the range from 81.5?% to 94.1?%, with relative standard deviations (RSDs) of <7.6?%. The detection limits vary from 0.24 to 0.48?ng?mL^?1. The method was applied to the analysis of spiked mineral water and honey. The recoveries for the fluoroquinolones in the real samples range from 84.0?% to 112?%, with RSDs ranging from 2.9?% to 7.8?%.

用半制备高效液相色谱法制备少量的阿苯达唑亚砜单一对映体

涂敷直链淀粉-三(3,5-二甲基苯基氨基甲酸酯)(ADMPC)于自制的球形氨丙基硅胶上,制备了手性固定相。用高效液相色谱法(HPLC)在正相条件下,用该固定相在分析柱上直接拆分了广谱驱虫药物阿苯达唑亚砜外消旋体(Albendazole Sulfoxide,ABZSO)。然后,将分析色谱方法扩展到了半制备色谱,进行该药物的半制备分离,考察了不同进样量对半制备色谱的参数的影响。在最大进样量下,83h制备了各约1g的阿苯达唑亚砜的两种单一对映体。( )ABZSO的产率大于98．0％,纯度大于99．9％;(-)ABZSO的产率大于94．0％,纯度大于99．0％。     

Free Radical Ring-Opening Polymerization of 4-n-Hexyl- and 4-n-Decyl-2-methylene-1,3-dioxolanes

Two alkyl-substituted cyclic ketene acetals, 4-n-hexyl-2-methylene-1,3-dioxolane (4) and 4-n-decyl-2-methylene-1,3-dioxolane (6), were shown to undergo free radical ring-opening polymerization with the introduction of an ester group into the backbone of an addition polymer. The spontaneous polymerization of 4 (presumable by an ionic mechanism) produced a polymer containing no ring-opened units; furthermore 4 and 6 could be stabilized with respect to spontaneous polymerization by the addition of small amounts of pyridine. On the other hand, the polymerization of 4 in a 50% (by weight) benzene solution at 110°C with di-tertbutyl peroxide as the catalyst gave quantitative ring opening to give a polyester containing both possible isomeric ring-opened units. Bulk polymerization of 4 at 60°C at 53% conversion gave 50% ring opening which was divided 31% to 19% between cleavage to give the intermediate secondary free radical and the intermediate primary radical. Copolymerization of 4 with equimolar quantities of styrene at 110°C gave at 56% conversion a copolymer consisting of 67% styrene units, 22% ester-containing units resulting from cleavage to form a secondary radical, 7% of the isomeric ester-containing units, and 4% nonring-opened units. Polymerization studies with monomer 6 gave results very similar to those obtained with 4.     

Study of tanshinone IIA tissue distribution in rat by liquid chromatography-tandem mass spectrometry method

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for determining tanshinone IIA in rat tissues. After a single step liquid-liquid extraction with diethyl ether, tanshinone IIA and loratadine (internal standard) was subjected to LC/MS/MS analysis using positive electro-spray ionization under selected reaction monitoring mode. Chromatographic separation of tanshinone IIA and loratadine was achieved on a Hypersil BDS C(18) column (i.d. 2.1 x 50 mm, 5 microm) with a mobile phase consisting of methanol-1% formic acid (90:10, v/v) at a flow rate of 300 microL/min. The intra-day and inter-day precision of the method were less than 10.2 and 12.4%, respectively. The intra-day and inter-day accuracies ranged from 99.7 to 109.7%. The lowest limit of quantification for tanshinone IIA was 1 ng/mL. The method was applied to a tanshinone IIA tissue distribution study after an oral dose of 60 mg/kg to rats. Tanshinone IIA tissue concentrations decreased in the order of stomach > small intestine > lung > liver > fat > muscle > kidneys > spleen > heart > plasma > brain > testes. Tanshinone IIA still could be detected in most of the tissues at 20 h post-dosing. These results indicate that the LC/MS/MS method was rapid and sensitive to quantify tanshinone IIA in different rat tissues.     

Thermal degradation in a trimodal poly(dimethylsiloxane) network studied by (1)H multiple quantum NMR

Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation. For the domains with low , a broadening in the distribution was observed with aging time. For the domain with high , increases in both the mean and the width in were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 degrees C. Degraded samples also were analyzed by traditional solid-state (1)H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement.