Essential oil of <Emphasis Type="Italic">Laurus nobilis</Emphasis> from Montenegro

Steam distilled oil from the shoots, separated leaves, and stem, as well as from the flower of laurel (Laurus nobilis), grown in Montenegro, were analyzed by GC and GC/MS. The yield of essential oil was as follow: 1.4% in young shoots, 1.5% in the separated leaves, and 0.7% in separated stems. The main constituents of all investigated oils were 1,8-cineole, methyleugenol, and α-terpinyl acetate. Besides, α-pinene, β-pinene, sabinene, and linalool were also present. It was interesting and important for commercial samples of laurel essential oil that there was no significant difference among the essential oil obtained from young shoots and those obtained from leaves and stem. The main constituents of the flower oil were 1,8-cineole (15.7%), β-caryophyllene (9.5%), γ-muurolene (7.1%), α-terpinyl acetate (6.5%), and methyleugenol (3.9%). Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 337–339, July–August, 2007.     

Suggestions on the Contribution of Methyl Eugenol and Eugenol to Bay Laurel (Laurus nobilis L.) Essential Oil Preservative Activity through Radical Scavenging

The present study examined the radical scavenging potential of the two benzene derivatives found in the bay laurel essential oil (EO), namely methyl eugenol (MEug) and eugenol (Eug), theoretically and experimentally to make suggestions on their contribution to the EO preservative activity through such a mechanism. Calculation of appropriate molecular indices widely used to characterize chain-breaking antioxidants was carried out in the gas and liquid phases (n-hexane, n-octanol, methanol, water). Experimental evidence was based on the DPPH^• scavenging assay applied to pure compounds and a set of bay laurel EOs chemically characterized with GC-MS/FID. Theoretical calculations suggested that the preservative properties of both compounds could be exerted through a radical scavenging mechanism via hydrogen atom donation. Eug was predicted to be of superior efficiency in line with experimental findings. Pearson correlation and partial least square regression analyses of the EO antioxidant activity values vs. % composition of individual volatiles indicated the positive contribution of both compounds to the radical scavenging activity of bay laurel EOs. Eug, despite its low content in bay laurel EOs, was found to influence the most the radical scavenging activity of the latter.     

The Composition of the Essential Oil of Stachys iberica Subsp. Stenostachya Growing In Turkey

The water distilled essential oil from dried aerial parts ofStachys ibericasubsp.stenostachya(Lamiaceae) was analyzed by GC/MS. Seventy-one compounds were characterized representing 96% of the oil. The main constituents were found as linalyl acetate (42.2%), linalool (18.9%), geranyl acetate (8.2%), and -terpineol (5.3%).     

N-(15,16-Dihydroxylinoleoyl)-glutamine and N-(15,16-epoxylinoleoyl)-glutamine isolated from oral secretions of lepidopteran larvae

N-(15,16-Dihydroxylinoleoyl)-glutamine (1) and N-(15,16-epoxylinoleoyl)-glutamine (2) and were identified in the regurgitant of lepidopteran larvae (Spodoptera exigua and Spodoptera frugiperda) by LC-MS. After methanolysis and derivatisation with MSTFA, the positions of the hydroxy groups of 1 were identified by GC-MS. The structures of both conjugates were confirmed by synthesis.     

Electronic and steric effects of ligands as control elements for rhodium-catalyzed asymmetric hydrogenation

Electronic and steric effects in the rhodium diphosphinite catalyzed asymmetric hydrogenation were investigated. A series of electronically and sterically modified (S)-BINOL and (S)-H₈-BINOL ligands was synthesized and effects on the catalytic performance were studied. Phosphinite basicity was varied by using p-CH₃O, p-CH₃, p-H, p-CF₃, 3,5-(CH₃)₂, 3,5-(CF₃)₂ substituents on the diphenylphosphine moieties. In the hydrogenation of dimethyl itaconate and methyl (Z)-α-acetamido cinnamate an increase in enantioselectivity and activity was observed with increasing phosphine basicity.     

Comparison of the acute toxicity of tributyltin and copper to veliger larvae of Nassarius reticulatus (L.)

The ban on the use of tributyltin (TBT) is promoting an increasing use of copper as an active biocide in antifouling paints, with consequent rising levels of this metal in the environment. This study assesses the acute toxicity of copper and tributyltin to the larvae of the mollusc gastropod Nassarius reticulatus. Recently hatched veligers were exposed to nominal TBT‐Sn concentrations of 0.9, 1.4, 1.9, 2.8, 3.8, 4.7 and 5.6 µg l^?1 and nominal copper concentrations of 9.4, 23.4, 46.9, 70.3, 93.8, 117.2, 140.6 and 164.1 µg l^?1 for up to 96 h, under static conditions (17 ± 1 °C and 33 ± 1 psu). The percentage of larval mortality was determined for each organometal/metal concentration and exposure time (1, 24, 48, 72 and 96 h). Both TBT and copper had a highly significant effect on larvae survival (p < 0.001) for all times of exposure, except for the first hour in the particular case of TBT. The lowest observed effect concentration for TBT‐Sn decreased over time from 3.8 µg l^?1 at 24 h to 1.9 µg l^?1 at 96 h, whereas for copper it remained constant over time (46.9 µg l^?1). The median lethal concentration (LC₅₀) for TBT‐Sn decreased from 4.87 µg l^?1 at 24 h to 1.78 µg l^?1 at 96 h, and the LC₅₀ for copper decreased from 83.08 µg l^?1 at 24 h to 58.84 µg l^?1 at 96 h. TBT is far more toxic to N. reticulatus larvae than copper. However, owing to the higher copper environmental concentrations, the risk factors of the two biocides may approach each other. This stresses the need to find adequate substitutes for organotin biocides in future antifouling paints. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimating molecular masses of petroleum-derived fractions: High mass (>2000 u) materials in maltenes and asphaltenes from Maya crude oil

Molecular mass ranges and average masses of fractions from a heavy Mexican crude oil (Maya) have been studied, using mainly size exclusion chromatography (SEC) and laser desorption-mass spectrometry (LD-MS). Method development focused on the use of planar chromatography and size exclusion chromatography (SEC), to isolate narrow bands of material from solubility-separated fractions of the crude oil. The procedure provides a planar chromatography based method for studying mass ranges in complex hydrocarbon mixtures. It allows the calculation of ‘best estimate’ values for number and mass-averages. These can then be used in average structural parameter (ASP) calculations, for studying structural features of the samples. The method is applicable to both coal and petroleum-derived samples. The molecular mass estimates arrived at in this work for petroleum-derived samples are considerably higher than those reported by other workers for similar samples. The results presented here provide strong evidence for the presence of ions approaching m/z 10,000 in the Maya asphaltene. The maltene fraction was found to contain a small amount of ions with mass (m/z) in excess of 2000.     

Study and validity of 13C stable carbon isotopic ratio analysis by mass spectrometry and 2H site-specific natural isotopic fractionation by nuclear magnetic resonance isotopic measurements to characterize and control the authenticity of honey

Honey samples were analyzed by stable carbon isotopic ratio analysis by mass spectrometry (SCIRA-MS) and site-specific natural isotopic fractionation measured by nuclear magnetic resonance (SNIF-NMR) to first determine their potentials for characterizing the substance and then to combat adulteration. Honey samples from several geographic and botanical origins were analyzed. The δ¹³C parameter was not significant for characterizing an origin, while the (D/H)_I ratio could be used to differentiate certain single-flower varieties. Application of the official control method of adding a C₄ syrup (AOAC official method 998.12) to our authentic samples revealed anomalies resulting from SCIRA indices that were more negative than −1‰ (permil). A filtration step was added to the experimental procedure and provided results that were compliant with the natural origin of our honey samples. In addition, spiking with a C₄ syrup could be detected starting at 9-10%. The use of SNIF-NMR is limited by the detection of a syrup spike starting only at 20%, which is far from satisfying.     

A new equation to reproduce the enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from water to aqueous methanol mixtures at 298 K

The enthalpies of transfer of formamide (Form) N-methylformamide (NMF) and N,N-dimethylformamide (DMF) from water to aqueous methanol mixtures are reported and analysed in terms of the new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using the new solvation theory to reproduce the enthalpies of transfer shows excellent agreement between the experimental and calculated data over the entire range of solvent compositions. The analyses show that the solvation of DMF is random in the aqueous methanol mixtures while Form and NMF are preferentially solvated by methanol. It is also found that the interaction of the solutes is stronger with methanol than with water.     

Enthalpies of transfer of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide mixtures at 298.15 K

Previous studies have established that the extended coordination model of solvation can satisfactorily account for the variation in the transfer enthalpies of solutes in mixed-solvent systems. The model parameter relating to the solute-induced disruption of the solvent structure shows a marked dependence on the nature of the mixed solvent. In the present paper we report the transfer enthalpies of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide (DMSO) systems. Analysis of these in terms of the extended coordination model confirms both the model's ability to account for the experimental data, and the variability of the structural disruption parameter. The solvation parameters recovered from the analyses indicate that the net effect of acetonitrile on the solvent structure is a breaking of solvent-solvent bonds. The extent of bond breaking of the solvent increases from MeOH to EtOH.     

Oxidative status of human low density lipoprotein isolated by anion-exchange high-performance liquid chromatography--assessment by total hydroxyoctadecadienoic acid, 7-hydroxycholesterol, and 8-iso-prostaglandin F(2alpha)

This study aims to measure the oxidative status of LDL from human plasma (n=26) as assessed by biomarkers for lipid peroxidation, total hydroxyoctadecadienoic acid (tHODE), 7alpha- and 7beta-hydroxycholesterol (t7-OHCh), and 8-iso-prostaglandin F(2alpha) (t8-iso-PGF(2alpha)) after subfractionation of LDL with an anion-exchange HPLC (AE-HPLC). LDL was separated and quantified by AE-HPLC as LDL-1, LDL-2, and LDL-3 in the order of the anionic charge of the LDL particles. The concentrations of tHODE, t7-OHCh, and t8-iso-PGF(2alpha) in both plasma and LDL subfractions were assessed after reduction and saponification. In this method, the free and ester forms of hydroperoxides, ketones, and hydroxides of linoleic acid and cholesterol are measured as tHODE and t7-OHCh, respectively. It was found that tHODE significantly correlated with the proportion of LDL-2 and LDL-3 as well as with the concentration of malondialdehyde-modified LDL in plasma. Further, by the analyses of LDL subfractions, the concentrations of tHODE, t8-iso-PGF(2alpha), and t7-OHCh in LDL-3 were found to be significantly higher than those in LDL-1 and LDL-2. These results clearly indicate that the extent of oxidation increases in the order of LDL-1相似文献   

Regioselective addition of Ti enolates to conjugated enones: New insights into the mechanism based on experimental and DFT investigation

The regioselective addition mechanism of the Ti(IV) enolates derived from α-diazo-β-keto carbonyl compounds and α-diazo-β-keto phosphonates to conjugated enones has been studied on the basis of a hypothetical bridging chloride-controlled theory, by density functional theory (DFT), and experimentally. The DFT results indicate that, for the Ti(IV) enolate 3 derived from α-diazo-β-keto carbonyl compounds, the free energy of the bridging chloride-controlled 1,2-addition transition state is 2.4 kcal/mol higher than that of 1,4-addition, and the calculated enthalpies of 1,2-addition is 4.36 kcal/mol more than that of 1,4-addition. For the Ti(IV) enolate 4 derived from α-diazo-β-keto phosphonates, in contrary, the free energy of the bridging chloride-controlled 1,2-addition transition state is 1.1 kcal/mol lower than that of 1,4-addition, and the calculated enthalpy of 1,2-addition is 3.46 kcal/mol less than that of 1,4-addition. Our findings demonstrate that the nucleophilic addition of these Ti(IV) enolates to conjugated enones was carried out not only kinetically but also irreversibly for the first time.     

Fine structures of 8-G-1-(arylethynylselanyl)naphthalenes (G = H, Cl, Br): Factors to control the linear alignment of five GSe–CC–CAr atoms in crystals and the behavior in solution

8-G-1-(p-YC₆H₄CCSe)C₁₀H₆ [2 (G = Cl) and 3 (G = Br): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f) and NO₂ (g)] have been prepared and the NMR spectra measured, in addition to 1 (G = H). Structures have been determined by X-ray crystallographic analysis for 2b, 2e and 2g, which are all type B (B), where the Se–C_sp bond is placed in the naphthyl plane in B. The type is classified as A if the Se–C_sp bond is perpendicular to the naphthyl plane. Structures around the p-YC₆H₄ (Ar) group are pd (perpendicular) for Y = OMe (2b) and Cl (2e) and pl (planar) for Y = NO₂ (2g), where the Se–C_Nap bond is placed in the aryl plane in pl and perpendicular to the plane in pd. The 1b (A: pd) structure changes dramatically on going to 2b (B: pd) with G = Cl at the 8-position. The effect is called the G-dependence in 2. The G-dependence arises from the energy lowering effect of the n_p(Cl)σ^*(Se–C_sp) 3c–4e interaction. Structures are both (B: pd) for 1e and 2e and both (B: pl) for 1g and 2g. One may realize that the structures are unchanged by G = Cl in place of G = H for Y = Cl and NO₂ at a first glance. However, the B structures in 2e and 2g must be much more stabilized by the G-dependence of the n_p(Cl)σ^*(Se–C_sp) 3c–4e interaction or the GSe–C_sp–C_sp–C_sp2 5c–6e type interaction. The structures of 2 and 3 are examined in solution based on the NMR parameters. The results show that 2 and 3 behave very similarly to each other and the structures are predominantly B, with some equilibrium between pd and pl around the aryl groups in solution. Quantum chemical calculations support the observations.     

The stir-frying can reduce hepatorenal toxicity of Fructus Tribuli by inactivating β-glucosidase and inhibiting the conversion of furostanol saponins to spirostanol saponins

The purpose of this study was to illustrate the mechanism of “enzyme inactivation and toxicity reduction” of Fructus Tribuli (FT) after being heating processed. Ultra-high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) was used to quantitatively analyze the contents of four steroidal saponins in crude Fructus Tribuli (CFT) and stir-fried Fructus Tribuli (SFT) under different storage times at room temperature. The enzyme activity of β-D-glucosidase in CFT and SFT were determined and calculated by ultraviolet–visible spectrometry (UV-VIS spectrometry). In addition, the enzyme hydrolysates of FOT and tribuluside A were qualitatively analyzed by ultra-high-performance liquid chromatography coupled with quadruple-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS). The hepatorenal toxicity of spirostanol saponins in FT were further confirmed by in vivo and in vitro experiment. This study confirmed that “enzyme inactivation and toxicity reduction” was one of the reasons why the stir-frying can reduce hepatorenal toxicity of FT, and further enriched the exploration on the mechanism of processing toxicity reduction.