Evaluation of microextraction by packed sorbent,liquid–liquid microextraction and derivatization pretreatment of diet‐derived phenolic acids in plasma by gas chromatography with triple quadrupole mass spectrometry

Miniaturized sample pretreatments for the analysis of phenolic metabolites in plasma, involving protein precipitation, enzymatic deconjugation, extraction procedures, and different derivatization reactions were systematically evaluated. The analyses were conducted by gas chromatography with mass spectrometry for the evaluation of 40 diet‐derived phenolic compounds. Enzyme purification was necessary for the phenolic deconjugation before extraction. Trimethylsilanization reagent and two different tetrabutylammonium salts for derivatization reactions were compared. The optimum reaction conditions were 50 μL of trimethylsilanization reagent at 90°C for 30 min, while tetrabutylammonium salts were associated with loss of sensitivity due to rapid activation of the inert gas chromatograph liner. Phenolic acids extractions from plasma were optimized. Optimal microextraction by packed sorbent performance was achieved using an octadecylsilyl packed bed and better recoveries for less polar compounds, such as methoxylated derivatives, were observed. Despite the low recovery for many analytes, repeatability using an automated extraction procedure in the gas chromatograph inlet was 2.5%. Instead, using liquid–liquid microextraction, better recoveries (80–110%) for all analytes were observed at the expense of repeatability (3.8–18.4%). The phenolic compounds in gerbil plasma samples, collected before and 4 h after the administration of a calafate extract, were analyzed with the optimized methodology.     

Synthesis of Hindered Phenolic Esters over Ion-Exchange Resins

The esterification of 3,5-di-tert-butyl-4-hydroxybenzoic acid with 1-hexadecanol over a series of ion-exchange resins was investigated, in which resin D072 exhibited excellent catalytic performance. The influence of water on the reaction was also investigated, and it was found that water could improve the selectivity and increase the yield of the target product. Treatment of resins with aqueous sodium hydroxide could improve the selectivity of the target product but remarkably decreased the conversion of 3,5-di-tert-butyl-4-hydroxybenzoic acid. This result indicated that strong Brønsted acid sites played an important role in the reaction. Furthermore, D072 was efficiently recycled four runs by simple treatment with mineral acid. Finally, a series of hindered phenolic esters were successfully synthesized under the optimal reaction conditions. Therefore, a simple and versatile method for the synthesis of hindered phenolic esters has been established over ion-exchange resins and the target products were obtained in good yields.     

Formation of double helix self-assembled monolayers of ethynylhelicene oligomer disulfides on gold surfaces

Optically active ethynylhelicene pentamers and hexamers linked by disulfide bonds were synthesized. They formed self-assembled monolayers (SAMs) with double helix structure on gold surfaces, which were analyzed by infrared reflection-absorption spectroscopy (IR-RAS), quartz crystal microbalance (QCM), surface plasmon resonance (SPR), and circular dichroism (CD). Double helix SAMs could be formed on gold surfaces either from double helices or random coils in solution. The double helices on the surface were more stable than in solution. This result suggested the presence of strong intercomplex interactions between double helix complexes on the surface.     

氢键介质的芳酰胺折叠体:从构象控制到功能演化

根据芳环上酰胺和氢键受体位置的不同,氢键介质的芳酰胺和酰肼折叠体可以产生折叠、螺旋、"之"字型、直线型及其他扩展型的构象.由于氢键具有较高的稳定性及芳酰胺固有的平面性特征,这一系列的芳酰胺寡聚体拥有较高的可预测的构象.芳酰胺骨架本身可以通过简单的酰胺键偶合反应构筑,而不同的官能团也可以选择性地引入到特定的骨架内部或其侧...     

Tautomerization in gas-phase ion chemistry of isomeric C-8 deoxyguanosine adducts from phenol-induced DNA damage

Collision-induced dissociation (CID) of 8-(4'-hydroxyphenyl)-2'-deoxyguanosine and 8-(2'-hydroxyphenyl)-2'-deoxyguanosine was investigated using sequential tandem mass spectrometry. These adducts represent biomarkers of DNA damage linked to phenolic radicals and were investigated to gain insight into the effects of chemical structure of a C-8 modification on fragmentation pathways of modified 2'-deoxyguanosine (dG). CID in MS(2) of the deprotonated molecules of both the isomers generated the same product ion having the same m/z values. CID in MS(3) of the product ion at m/z 242 and CID in MS(4) experiments carried out on the selected product ions at m/z 225 and m/z 218 afford distinct fragmentation patterns. The conformational properties of isomeric product ions from CID showed that the ortho-isomers possess the unique ability to tautomerize through an intramolecular proton transfer between the phenolic OH group and the imine nitrogen (N7). Tautomerization of ortho-isomers to their keto-tautomers led to differences in their system of conjugated double bonds compared with either their enol-tautomer or the para-isomer. The charge redistribution through the N-7 site on the imidazole ring is a critical step in guanosine adduct fragmentation which is disrupted by the formation of the keto-tautomer. For this reason, different reaction pathways are observed for 8-(4'-hydroxyphenyl)-2'-deoxyguanosine and 8-(2'-hydroxyphenyl)-2'-deoxyguanosine. We present herein the dissociation and the gas-phase ion-molecule reactions for highly conjugated ions involved in the CID ion chemistry of the investigated adducts. These will be useful for those using tandem mass spectrometry for structural elucidation of C-8 modified dG adducts. This study demonstrates that the modification at the C-8 site of dG has the potential to significantly alter the reactivity of adducts. We also show the ability of tandem mass spectrometry to completely differentiate between the isomeric dG adducts investigated.     

Essential Oils of Seven Lamiaceae Plants and Their Antioxidant Capacity

Oxidative stress has been reported as a cause of many diseases like Parkinson′s, Alzheimer′s, cardiovascular disease, and diabetes. Oxidative stress can also lead to cancer formation by promoting tumor development and progression. Antioxidants derived from Lamiaceae plants play an important role in natural medicine, pharmacology, cosmetology, and aromatherapy. Herein, we examine the antioxidative capacity of essential oils from seven aromatic Lamiaceae plants against the synthetic radicals DPPH and ABTS. Among the essential oils analyzed, the most robust scavenging capacities were found in mixtures of volatile compounds from thyme and savory. The scavenging activity of tested EOs against the ABTS radical was clearly higher than activity towards DPPH. Analysis of essential oils with weaker antioxidant activity has shown that volatile compounds from marjoram, sage, and hyssop were more active than EOs from lavender and mint. It can be suggested that the potent antioxidant capacity of thyme (Thymus vulgaris) and savory (Satyreja hortensis) are related to a high level of phenolic constituents, such as thymol and carvacrol. On the other hand, the elevated antioxidative power of marjoram, sage, and hyssop essential oils may also be due to their terpinene, o-cymene, terpinolene, and terpinen-4-ol constituents. Although non-phenolic components are less active than thymol or carvacrol, they may affect antioxidant capacity synergistically.     

Polyphenols from Certain Fruiting Plants Growing in Uzbekistan

The qualitative and quantitative compositions of phenolic compounds from certain species of fruiting plants of the Elaeagnaceae, Rosaceae, and Rosasaceae families were studied.     

Hydroxyl chain‐end functionalization of polymeric organolithium compounds with oxetane

Hydroxyl chain‐end functionalizations of polymeric organolithium compounds with oxetane (trimethylene oxide) were studied in benzene at 25 °C. Functionalizations of poly(styryl)lithium and polystyrene‐oligo‐butadienyllithium proceed efficiently to form the corresponding ω‐hydroxypropyl‐functionalized polymers in 98 and 97% isolated yields, respectively. No nonfunctional polymer (≤1–2%) was detected by thin layer chromatography (TLC) analysis for either polymer. All functionalized polymers were characterized by ¹³C and ¹H NMR analyses; no evidence for oxetane oligomerization at the chain end was observed. The MALDI‐TOF mass spectrum of ω‐hydroxypropylpolystyrene was consistent with the expected structure without any detectable oligomerization of oxetane. A small, but detectable series of peaks corresponding to nonfunctional polystyrene was also observed in the MALDI‐TOF mass spectrum. The functionalization of the adduct of 1,1‐diphenylethylene and PSLi produced the corresponding ω‐hydroxypropyl‐functionalized polymer in only 86% isolated yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2684–2693, 2006     

Preparation of telechelic oligomers by thermal degradation of propylene copolymers

The reactive end groups of nonvolatile oligomers obtained by controlled thermal degradation of poly(propylene-ran-ethylene) and poly(propylene-ran-1-butene) were determined by ¹H and ¹³C NMR spectroscopy. The molar ratio of unsaturated to saturated end groups was found to be about 9:1. The average number of unsaturated end groups per molecule was between 1.6 and 1.8, indicating that 60–80 mol% of the oligomer molecules were telechelic, having two terminal unsaturated end groups. These oligomers had a lower polydispersity than the raw material, despite their lower molecular weight and melting temperature. Although the end groups resulting from each monomer unit could be detected by ¹³C NMR, the end group composition differed from that of the main chains of the raw materials. The end group composition was satisfactorily explained by the differences in bond dissociation energy and activation energy of elementary reactions that occurred during thermal degradation, based on the monomer composition of the raw materials.