Position Of Double Bond Research Articles

Pharmacokinetic studies of ginsenosides Rk1 and Rg5 in rats by UFLC–MS/MS

A rapid ultra-fast liquid chromatography tandem mass spectrometry method was developed and validated to determine ginsenosides Rk1 and Rg5, a pair of isomers, in rat plasma, which was successfully applied to their pharmacokinetic studies. Two ginsenosides were given to male Sprague-Dawley rats via intragastrical and intravenous routes, respectively, and the impact of double bond position on the pharmacokinetic features of the two ginsenosides was elucidated in rats. Ginsenoside Rg3 was used as internal standard and ethyl acetate was applied to extract analytes and internal standard. Chromatographic separation was carried out on a reverse-phase UPLC HSS T3 column (100 × 2.1 mm, 1.8 μm). The flow rate was set to 0.4 ml/min. The fragmentation transition was m/z 765.4 → m/z 101.1 for two ginsenosides. The mobile phases were composed of 0.1% formic acid aqueous solution and acetonitrile. The linear range was 2-1,000 ng/ml for the two ginsenosides. Intra- and inter-day precisions were <11.67%, and accuracy fluctuated from -7.44 to 6.78%. The extraction recovery, matrix effect and stability were within acceptable levels. After treatment with ginsenosides Rk1 and Rg5, some differences were found in their pharmacokinetic profiles in rats. The maximum plasma drug concentration and the area under the plasma drug concentration-time curve of ginsenoside Rg5 were about 5 times bigger than those of ginsenoside Rk1 after oral administration, and 3 times higher after intravenous administration. The oral bioavailabilities of ginsenosides Rk1 and Rg5 were 0.67 and 0.97%, respectively. The results indicated that ∆20(22) -ginsenosides showed better pharmacokinetic features than ∆20(21) -ginsenosides with the same glycosylation.

Simultaneous determination of short-chain fatty alcohols in aged oil and biodiesels by stable isotope labeling assisted liquid chromatography-mass spectrometry

Short-chain fatty alcohols (SCFAs) are one of the reactants for the production of biodiesels. The SCFA residues at the trace level have a significant impact on biodiesel quality. However, the analysis of SCFAs in aged biodiesels has not been reported so far, which is probably due to the unavailability of an appropriate analytical method for the simultaneous determination of SCFAs. Herein, we developed a novel analytical approach with high sensitivity and selectivity for the simultaneous identification and determination of SCFAs in seed oil and biodiesel samples during the simulated real-time aging by stable isotope labeling assisted liquid chromatography-mass spectrometry (SIL-LC-MS). A pair of isotope labeling reagents, pyridine (Py) and [2H5]pyridine ([2H5]Py), were used to label SCFAs in biodiesels and standards, respectively. The [2H5]Py labeled SCFAs were used as internal standards to compensate for the detection of variances. The simultaneous determination of SCFAs was performed by LC-MS with an improved detection selectivity and sensitivity. The limits of detection (LODs) values were ranged from 0.2 to 0.5 ng mL−1 for the investigated SCFAs. Good linearity was observed in the studied ranges (R2 > 0.99) and good precision with relative standard deviations (RSDs) was in the range of 4.9–18.1%. Average recoveries were obtained in the range of 80.3%–115.4%. The matrix effects were in the range of 70.0–104.3%. The validated SIL-LC-MS method was applied to the simultaneous quantitative analysis of SCFAs in seed oil and biodiesel samples and the LC-MS analysis could be done within 3 min. The formation mechanism of SCFAs in aged oil and biodiesel samples was also investigated by this method. The results suggest that SCFAs were formed and their composition changed during the simulated real-time aging of long-chain fatty acid (LCFA), long-chain fatty acid methyl ester (FAME), seed oil, and biodiesels. Moreover, we found that the formation of 1-pentanol and 1-hexanol was associated with the number and position of double bonds in LCFAs and FAMEs.

Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst.

The catalytic transposition of double bonds holds promise as an ideal route to alkenes of value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, normally requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst selectively produces either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on noncovalent modifications.

Preliminary Identification of the Sex Pheromones of the Citrus Fruit Borer (Citripestis sagittiferella Moore) Inhabiting the Mekong Delta of Vietnam

Abstract Citripestis sagittiferella is one of the most harmful pest insects of pomelo in the Mekong Delta of Vietnam. In order to utilize sex pheromone as tool for population monitoring by which supplies information for timing control, the sex pheromone of C. sagittiferella was preliminarily identified then tested under field condition. Fruits infected C. sagittiferella larvae were collected from pomelo orchards in Vinh Long and Hau Giang provinces and brought to Can Tho University laboratory for rearing to extract the pheromone. The analysis was conducted by GC-EAD, GC-MS and the double bond position was affirmed by analysis of its DMDS adduct. GC-EAD analysis resulted in three EAG-responses, namely component I (Comp. I), Comp. II and Comp. III. Mass spectra with diagnostic ions at m/z 61, 194 and 192 ([M-60]+ ions) indicated that they were unsaturated 14 carbons (C14) straight chain acetates. Reference to the synthetic standards by both GC-EAD and GC-MS analysis confirmed that the three pheromone components were (E)-11-tetradecenyl acetate (E11-14:OAc), (Z)-11-tetradecenyl acetate (Z11-14:OAc) and (9Z,11E)-9,11-tetradecadienyl acetate (Z9, E11-14:OAc), respectively. Unfortunately, lures prepared from mixtures of synthetic E11-14:OAc, Z11-14:OAc and E9, Z11-14:OAc at several mixing ratios showed no attraction to C. sagittiferella males in field tests.

One-Pot Extractive Transesterification of Fatty Acids Followed by DMOX Derivatization for Location of Double Bonds Using GC-EI-MS.

Fatty acids are an essential structural and energy storage component of cells and hence there is much interest in their metabolism, requiring identification and quantification with readily available instrumentation, such as GC-MS. Fatty acid methyl esters (FAMEs) can be generated and extracted directly from biological tissue, in a one-pot process, and following high resolution GC, their respective chain length, degrees of unsaturation, and other functionalities can be readily identified using EI-MS. Defining the positions of the double bonds in the alkyl chain requires conversion of the FAMEs into their respective dimethyloxazoline (DMOX) derivatives. Following EI, this derivative allows charge retention on the heterocycle, and concomitant charge remote fragmentation of the alkyl chain to yield key double bond position identifying ions. The protocols described herein have been applied to the identification and quantification of fatty acids harvested from microalgae grown to produce biofuels and to the screening of salt tolerant Arabidopsis mutants.

Lipid Analysis by Gas Chromatography and Gas Chromatography-Mass Spectrometry.

Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) represent powerful tools for the quantitative and structural analysis of plant lipids. Here, we outline protocols for the isolation, separation, and derivatization of plant lipids for subsequent GC and GC-MS analysis. Plant lipids are extracted with organic solvents and separated according to their polarity by thin-layer chromatography or solid phase extraction. As most lipids are not volatile, the analytes are derivatized by transmethylation or trimethylsilylation to enable the transition of the molecules into the gas phase. After separation on the polymer matrix of the GC column, the analytes are detected by flame ionization or mass spectrometry. This chapter includes methods suitable for the analysis of lipid-bound or free fatty acids, long chain alcohols, and monoacylglycerols and for the determination of double bond positions in fatty acids.

The allosteric inhibition of glycine transporter 2 by bioactive lipid analgesics is controlled by penetration into a deep lipid cavity

The role of lipids in modulating membrane protein function is an emerging and rapidly growing area of research. The rational design of lipids that target membrane proteins for the treatment of pathological conditions is a novel extension in this field and provides a step forward in our understanding of membrane transporters. Bioactive lipids show considerable promise as analgesics for the treatment of chronic pain and bind to a high-affinity allosteric-binding site on the human glycine transporter 2 (GlyT2 or SLC6A5). Here, we use a combination of medicinal chemistry, electrophysiology, and computational modeling to develop a rational structure–activity relationship for lipid inhibitors and demonstrate the key role of the lipid tail interactions for GlyT2 inhibition. Specifically, we examine how lipid inhibitor head group stereochemistry, tail length, and double-bond position promote enhanced inhibition. Overall, the l-stereoisomer is generally a better inhibitor than the d-stereoisomer, longer tail length correlates with greater potency, and the position of the double bond influences the activity of the inhibitor. We propose that the binding of the lipid inhibitor deep into the allosteric-binding pocket is critical for inhibition. Furthermore, this provides insight into the mechanism of inhibition of GlyT2 and highlights how lipids can modulate the activity of membrane proteins by binding to cavities between helices. The principles identified in this work have broader implications for the development of a larger class of compounds that could target SLC6 transporters for disease treatment.

Omega-3 versus Omega-6 fatty acid availability is controlled by hydrophobic site geometries of phospholipase A2s

Human phospholipase A2s (PLA2) constitute a superfamily of enzymes that hydrolyze the sn-2 acyl-chain of glycerophospholipids, producing lysophospholipids and free fatty acids. Each PLA2 enzyme type contributes to specific biological functions based on its expression, subcellular localization, and substrate specificity. Among the PLA2 superfamily, the cytosolic cPLA2 enzymes, calcium-independent iPLA2 enzymes, and secreted sPLA2 enzymes are implicated in many diseases, but a central issue is the preference for double-bond positions in polyunsaturated fatty acids (PUFAs) occupying the sn-2 position of membrane phospholipids. We demonstrate that each PLA2 has a unique preference between the specific omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and the omega-6 arachidonic acid (AA), which are the precursors of most proinflammatory and anti-inflammatory or resolving eicosanoids and related oxylipins. Surprisingly, we discovered that human cPLA2 selectively prefers AA, whereas iPLA2 prefers EPA, and sPLA2 prefers DHA as substrate. We determined the optimal binding of each phospholipid substrate in the active site of each PLA2 to explain these specificities. To investigate this, we utilized recently developed lipidomics-based LC-MS/MS and GC/MS assays to determine the sn-2 acyl chain specificity in mixtures of phospholipids. We performed μs timescale molecular dynamics (MD) simulations to reveal unique active site properties, especially how the precise hydrophobic cavity accommodation of the sn-2 acyl chain contributes to the stability of substrate binding and the specificity of each PLA2 for AA, EPA, or DHA. This study provides the first comprehensive picture of the unique substrate selectivity of each PLA2 for omega-3 and omega-6 fatty acids.

Access to a Phthalazine Derivative Through an Angular cis-Quinacridone.

Intramolecular electrophilic cyclization of a bisanthranilate afforded an angular cis-quinacridone compound, which condensed with hydrazine to give a phthalazine derivative. A [2+2+2] cyclization reaction occurred at the C-N double bond position of phthalazine when reacted with dimethyl acetylenedicarboxylate. The structures of these novel compounds were confirmed by crystallographic analysis. The phthalazine derivative decomposes back to quinacridone at ambient condition in the dark and as a solid with a half lifetime of about 22 months.

Action of phytosterols on thermally induced trans fatty acids in peanut oil

The effects of six phytosterols on thermally induced trans fatty acids (TFAs) in peanut oil were investigated. Peanut oil, triolein, trilinolein and trilinolenin heated at 180 °C for 12 and 24 h with or without phytosterols were analyzed by GC-FID. The atomic net charge distribution, frontier molecular orbital energy (FMOE), and bond dissociation energy (BDE) of six phytosterols were calculated by density functional theory. Results showed that six phytosterols inhibited the formation of trans oleic acid, trans linoleic acids, trans linolenic acids, and total TFAs. The anti-isomerization effects of phytosterols were mainly associated with hydroxyl site activities, which were affected by the double bond position in the main skeleton of cyclopentane tetrahydrophenanthrene and the number of double bonds on the C17 branch chain. The FMOE difference and BDE of phytosterol molecules were closely related to their anti-isomerization rates. The anti-isomerization mechanisms of phytosterols on TFAs in peanut oil were proposed.

Synthesis of Macrocyclic β‐Peptidomimetics by Ring‐Closing Metathesis

AbstractThe synthesis of a series of conformationally constrained peptidomimetics containing a 9‐to‐13‐atom‐membered ring by ring‐closing metathesis (RCM) is described. The second‐generation Grubbs catalyst proved to be the most effective in producing the desired cyclic β‐peptidomimetics with moderate to good yields. Reaction characteristics such as the influence of alkene chain length in the precursors, position of double bond and ring size of products were also discussed.

Electrospray ionization with higher-energy collision dissociation tandem mass spectrometry toward characterization of ceramides as [M + Li]+ ions: Mechanisms of fragmentation and structural identification

Ceramide is a huge lipid family consisting of diversified structures in which various modifications are seen in the fatty acyl chain and the long chain base (LCB). In this contribution, a higher collision energy (HCD) linear ion-trap mass spectrometric method (LIT MSn) was applied to study the mechanisms underlying the fragmentation processes of ceramide molecules in 12 subclasses, which were desorbed by ESI as the [M + Li]+ ions. Multiple sets of fragment ions reflecting the fatty acyl chain and LCB were observed in the HCD MS2 spectra for all the ceramide classes, resulting in unambiguous definition of the ceramide structures, including the chain length and the modification (α-hydroxy-, β-hydroxy-, ω-hydroxy-FA) of the fatty acyl moiety, and the types of LCB (sphingosine, phytosphigosine, 6-hydroxy-sphingosine). Thereby, this approach permits differentiation of isomeric structures and ceramide species in the biological specimen can be unveiled in detail. By application of sequential MS3, the double bond position along the fatty acyl chain of the molecule can be located, and a complete structural characterization of ceramides can be achieved.

Understanding the Mechanism and Selectivities of the Reaction of Meta-Chloroperbenzoic Acid and Dibromocarbene with β-Himachalene: A DFT Study

This study was performed to understand the site selectivity in the reaction between β-himachalene and meta-chloroperbenzoic acid (m-CPBA) in the first step followed by the addition of dibromocarbene (CBr2) to the main monoepoxidation product Pα formed in the first reaction. Calculations were performed using the Becke three-parameter hybrid exchange functional and the Lee–Yang–Parr correlation functional (B3LYP) with the 6-311 + G (d, p) basis set. Transition states were located by QST2, and their highlighting was validated by the existence of only one imaginary frequency in the Hessian matrix. The action of m-CPBA on β-himachalene was analyzed on the two double bonds of β-himachalene whose theoretical calculations show that the attack affects the most substituted double bond on α side containing hydrogen of ring junction. The obtained Pα product thereafter treated with dibromocarbene leads via an exothermic reaction to the six-membered ring double bond position of α-monoepoxide. The major products Pαα are kinetically and thermodynamically favored with a high stereoselectivity in perfect correlation with the experimental observations.

Enhancement of one- and two-photon absorption and visualization of intramolecular charge transfer of pyrenyl-contained derivatives.

To further improve the pyrenyl-contained derivatives two-photon absorption (TPA) and third-order nonlinear optical (NLO) properties, three steps of optimization are employed based on experimental molecule PCVS-B: heteroatomic substitution, exchanging the position of double bonds and adding a branch. The contributions of π electrons to localized orbital locators and Mayer bond orders (LOL-π and IABπ) show that the second step can enhance the chemical interaction between pyrenyl and the branched-chain. Two visual methods of charge density difference (CDD) and transition density matrix (TDM) are combined to intuitively analyze the intramolecular charge transfer (ICT) process of one (two) photon absorption; results show that both following two steps can increase the degree of ICT on the conjugated plane of the pyrenyl. The sum over state (SOS) model was used to find out the dominant two-photon transition process. The difference between the dipole moments obtained by the McRae equation is applied to the three-state model, revealing the inherent law of the second static hyperpolarizability.

Resolving the Complexity of Spatial Lipidomics Using MALDI TIMS Imaging Mass Spectrometry.

Lipids are a structurally diverse class of molecules with important biological functions including cellular signaling and energy storage. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) allows for direct mapping of biomolecules in tissues. Fully characterizing the structural diversity of lipids remains a challenge due to the presence of isobaric and isomeric species, which greatly complicates data interpretation when only m/z information is available. Integrating ion mobility separations aids in deconvoluting these complex mixtures and addressing the challenges of lipid IMS. Here, we demonstrate that a MALDI quadrupole time-of-flight (Q-TOF) mass spectrometer with trapped ion mobility spectrometry (TIMS) enables a >250% increase in the peak capacity during IMS experiments. MALDI TIMS-MS separation of lipid isomer standards, including sn backbone isomers, acyl chain isomers, and double-bond position and stereoisomers, is demonstrated. As a proof of concept, in situ separation and imaging of lipid isomers with distinct spatial distributions were performed using tissue sections from a whole-body mouse pup.

Sex pheromone analysis and effective attraction of males of the cabbage webworm, Hellula undalis, inhabiting the Mekong Delta of Vietnam

Abstract Hellula undalis is a harmful insect pest of green mustard in the Mekong Delta of Vietnam. In order to establish a tool for a sustainable pest control program, the sex pheromone of H. undalis inhabiting the Mekong Delta was examined. GC-EAD and GC–MS analyses of pheromone gland extracts from the virgin females elucidated three new components, (Z)-11-tetradecenyl acetate (Z11-14:OAc), (Z)-11-hexadecenal (Z11-16:Ald), and (11E,13E)-11,13-hexadecadien-1-ol, in addition to the known pheromone component (11E,13E)-11,13-hexadecadienal (E11,E13-16:Ald). Double bond positions of the two monoenyl components were determined by GC–MS analysis of the pheromone extract treated with dimethyl disulfide. On the other hand, GC–MS analysis of the female body extract detected the unsaturated hydrocarbon (3Z,6Z,9Z)-3,6,9-tricosatriene (Z3,Z6,Z9-23:H). Field examinations of their synthetic compounds indicated the significant role of E11,E13-16:Ald as a major component and a clear synergistic effect of the two monoenyl compounds as a minor component. Although the 3:3:7 mixture of Z11-14:OAc, E11-16:Ald, and E11,E13-16:Ald captured the largest number of males among the tested mixtures, the activity was still quite a bit lower than that of virgin females. However, the 3:3:7:1 mixture, which was prepared by adding a small amount of Z3,Z6,Z9-23:H to the 3:3:7 ternary lure, succeeded in attracting males more powerfully than the females did. This strong synergistic effect was not observed when the triene was added to unmixed E11,E13-16:Ald, indicating important roles of not only the triene but also the two monoenyl compounds as natural pheromone components.

Positional determination of the carbon\u2013carbon double bonds in unsaturated fatty acids mediated by solvent plasmatization using LC\u2013MS

Fatty acids (FAs) are the central components of life: they constitute biological membranes in the form of lipid, act as signaling molecules, and are used as energy sources. FAs are classified according to their chain lengths and the number and position of carbon–carbon double bond, and their physiological character is largely defined by these structural properties. Determination of the precise structural properties is crucial for characterizing FAs, but pinpointing the exact position of carbon–carbon double bond in FA molecules is challenging. Herein, a new analytical method is reported for determining the double bond position of mono- and poly-unsaturated FAs using liquid chromatography-mass spectrometry (LC–MS) coupled with solvent plasmatization. With the aid of plasma on ESI capillary, epoxidation or peroxidation of carbon–carbon double bond in FAs is facilitated. Subsequently, molecular fragmentation occurs at or beside the epoxidized or peroxidized double bond via collision-induced dissociation (CID), and the position of the double bond is elucidated. In this method, FAs are separated by LC, modified by plasma, fragmented via CID, and detected using a time-of-flight mass spectrometer in a seamless manner such that the FA composition in a mixture can be determined. Our method enables thorough characterization of FA species by distinguishing multiple isomers, and therefore can uncover the true diversity of FAs for their application in food, health, and medical sciences.

Combining Mass Spectrometry with Paternò-Büchi Reaction to Determine Double-Bond Positions in Lipids at the Single-Cell Level.

Single cell MS (SCMS) techniques are under rapid development for molecular analysis of individual cells among heterogeneous populations. Lipids are basic cellular constituents playing essential functions in energy storage and the cellular signaling processes of cells. Unsaturated lipids are characterized with one or multiple carbon-carbon double (C═C) bonds, and they are critical for cell functions and human diseases. Characterizing unsaturated lipids in single cells allows for better understanding of metabolomic biomarkers and therapeutic targets of rare cells (e.g., cancer stem cells); however, these studies remain challenging. We developed a new technique using a micropipette needle, in which Paternò-Büchi (PB) reactions at C═C bond can be induced, to determine locations of C═C bonds in unsaturated lipids at the single-cell level. The micropipette needle is produced by combining a pulled glass capillary needle with a fused silica capillary. Cell lysis solvent and PB reagent (acetone or benzophenone) are delivered into the micropipette needle (tip size ≈ 15 um) through a fused silica capillary. The capillary needle plays multiple functions (i.e., single cell sampling probe, cell lysis container, microreactor, and nano-ESI emitter) in the experiments. Both regular (no reaction) and reactive (with PB reaction) SCMS analyses of the same cell can be achieved. C═C bond locations were determined from MS scan and MS/MS of PB products assisted by Python programs. This technique can potentially be used for other reactive SCMS studies to enhance molecular analysis for broad ranges of single cells.

Double bond localization in unsaturated rhamnolipid precursors 3-(3-hydroxyalkanoyloxy)alkanoic acids by liquid chromatography\u2013mass spectrometry applying online Patern\xf2\u2013B\xfcchi reaction

Lipids are biomolecules with a broad variety of chemical structures, which renders them essential not only for various biological functions but also interestingly for biotechnological applications. Rhamnolipids are microbial glycolipids with surface-active properties and are widely used biosurfactants. They are composed of one or two l-rhamnoses and up to three hydroxy fatty acids. Their biosynthetic precursors are 3-hydroxy(alkanoyloxy)alkanoic acids (HAAs). The latter are also present in cell supernatants as complex mixtures and are extensively studied for their potential to replace synthetically derived surfactants. The carbon chain lengths of HAAs determine their physical properties, such as their abilities to foam and emulsify, and their critical micelle concentration. Despite growing biotechnological interest, methods for structural elucidation are limited and often rely on hydrolysis and analysis of free hydroxy fatty acids losing the connectivity information. Therefore, a high-performance liquid chromatography-mass spectrometry method was developed for comprehensive structural characterization of intact HAAs. Information is provided on chain length and number of double bonds in each hydroxy fatty acid and their linkage by tandem mass spectrometry (MS/MS). Post-column photochemical derivatization by online Paternὸ–Büchi reaction and MS/MS fragmentation experiments generated diagnostic fragments allowing structural characterization down to the double bond position level. Furthermore, the presented experiments demonstrate a powerful approach for structure elucidation of complex lipids by tailored fragmentation.

Influence of the double bond position in combustion chemistry of methyl butene isomers: A shock tube and laser absorption study

AbstractShock tube experiments have been carried out on 2‐methyl‐1‐butene (2M1B), 2‐methyl‐2‐butene (2M2B), and 3‐methyl‐1‐butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time‐histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350‐1630 K and pressures of 8.3‐10.5 atm with stoichiometric mixtures of 0.075% fuel in O2/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time‐resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C3H3 + O2 = CH2CO + HCO reaction are suggested based on the current investigation.