Position Of Bond Research Articles

Thermochromic and highly tunable color emitting bis-tolane based liquid crystal materials for temperature sensing devices

The luminescent compounds based on the D-π-A system consisting of substituted pyrrole as acceptor, π conjugated bis-tolane and -OMe, -N(CH3)2, -N(Ph)2 at termini acting as donors have been synthesized. On heating, all the compounds exhibited distinct mesomorphic behavior depending upon donating groups and substituents at the acceptor unit. These luminescent liquid crystals exhibited emission from blue, green to reddish orange with high quantum efficiency in solid as well in solutions state. We discovered the rarely reported three membered ring interactions between the Br at alpha position of pyrrole and acetylene bond and their impact on luminescence efficiency via single crystal structure of 2Br–CN–N(CH3)2 and 2Br–CN–N(Ph)2. Furthermore, the thermochromic behavior of these LLCs compounds has been explored, especially CN–N(Ph)2, its reddish orange emission changed to blue at 240 °C–250 °C in pure state, while in dimethyl silicone polymer (PDMS) film, it switched to blue at 200 °C and completely vanished at 240 °C. These simple and highly emissive compounds display outstanding thermochromic properties above 200 °C, thus will be potentiality valuable for high temperature sensing devices.

Graphical Transition Moment Decomposition and Conceptual Density Functional Theory Approaches to Study the Fundamental and Lower-Level Overtone Absorption Intensities of Some OH Stretching Vibrations.

The investigation of electron density migrations caused by molecular structure changes is of central importance in various fields of chemistry. To address this topic in general and to study absorption intensities of vibrations, we analyze sensitive dipole moment functions (DMFs) of a molecule by combining the linear response function of conceptual DFT and bond dipoles separated by the quantum theory of atoms in molecules with a graphical transition moment decomposition scheme. The fundamental intensities of OH stretching vibrations depend strongly on the substituents but only weakly on the molecular conformations. Interestingly, in some alcohols, completely opposite trends have been observed for the lower-level overtone intensities: a weak substituent dependence but a stronger conformation dependence. It is well known that the formation of a hydrogen-bonded complex increases the OH stretching fundamental intensity, but less well known is the decrease in their overtone intensities. To investigate these characteristics comprehensively, we calculated their intensities (Δv = 1, 2, and 3) for conformers of ethanol and trifluoroethanol (TFE) and hydrogen-bonded phenol (PhOH) systems via the DFT method in the local mode model for the OH stretching coordinate ΔR. Their first and second derivatives of the electron density with respect to ΔR were calculated and interpreted using their bond moments. For ethanol and TFE, the OH, CC, and CH bond moments were found to make an important contribution to the molecular DMF derivatives parallel to the OH bond. The OH bond contributes only to the first derivative of DMF, and its conformational dependence is determined by the magnitude of the charge polarization of each structure. The electron density derivatives in the CC bond region were largely maintained during the internal rotation; thus, their conformation-dependent contributions were expressed by a geometrical factor of the CC bond direction. The CH bond at the antiperiplanar position of the OH bond was found to make a remarkably large contribution to the second derivative of DMF in the gauche conformer. The importance of electron density migration on substituents was also identified in the hydrogen-bonded phenol, in which the π-electron density change on the aromatic ring was clearly shown. This migration creates the DMF derivatives both perpendicular and parallel to the OH bond and strongly affects the absorption intensities. In all the cases, some bond moments on the substituents contribute to the first and second DMF derivatives in a structure-dependent manner, thus explaining their stereoelectronic effects.

The Formation of Methyl Ketones during Lipid Oxidation at Elevated Temperatures.

Lipid oxidation and the resulting volatile organic compounds are the main reasons for a loss of food quality. In addition to typical compounds, such as alkanes, aldehydes and alcohols, methyl ketones like heptan-2-one, are repeatedly described as aroma-active substances in various foods. However, it is not yet clear from which precursors methyl ketones are formed and what influence amino compounds have on the formation mechanism. In this study, the formation of methyl ketones in selected food-relevant fats and oils, as well as in model systems with linoleic acid or pure secondary degradation products (alka-2,4-dienals, alken-2-als, hexanal, and 2-butyloct-2-enal), has been investigated. Elevated temperatures were chosen for simulating processing conditions such as baking, frying, or deep-frying. Up to seven methyl ketones in milk fat, vegetable oils, and selected model systems have been determined using static headspace gas chromatography-mass spectrometry (GC-MS). This study showed that methyl ketones are tertiary lipid oxidation products, as they are derived from secondary degradation products such as deca-2,4-dienal and oct-2-enal. The study further showed that the position of the double bond in the precursor compound determines the chain length of the methyl ketone and that amino compounds promote the formation of methyl ketones to a different degree. These compounds influence the profile of the products formed. As food naturally contains lipids as well as amino compounds, the proposed pathways are relevant for the formation of aroma-active methyl ketones in food.

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.

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.

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.

Long-term Investors, Demand Shifts, and Yields

I use detailed data on bond and derivative positions of pension funds and insurance companies (P&Is) in the Netherlands to study demand shifts and their causal effect on yields. In particular, I exploit a reform in the regulatory discount curve that makes liabilities more sensitive to changes in the 20-year interest rate but less so to longer maturity rates. Following the reform, P&Is reduced their longest maturity holdings but increased those with maturities close to 20 years. The aggregate demand shift caused a steepening of the long-end of the yield curve with a decrease in the 20-year yield of 10 basis points and an increase in the 30-year yield of 20 basis points. Similar effects on yields appear in a large panel of European countries after EU insurance regulation implemented the same reform. My findings have important policy implications, as they indicate that the regulatory framework of long-term investors directly affects the governments’ cost of borrowing.

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.

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.

Transformation of oil and hexadecane in soil by microbial preparations and earthworms

This study focuses on the effect of earthworms, oil-decomposing microbial preparation Destroil, and their combination on the destruction of oil in contaminated soil. The earthworms Eisenia andrei Bouché, 1972 accelerated the transformation of oil and hexadecane by microbiological preparations Destroil and Devouroil. The use of the combination of biological product and earthworms resulted in: (1) maximum reduction in the content of oil and hexadecane in the soil samples under study; (2) reduction of the phytotoxicity of oil-contaminated soil; (3) improvement in the agrophysical properties of soils in comparison with the action of these biodegradants separately. The transformation of oil hydrocarbons was monitored using NMR and IR spectroscopy. The biological oxidation process was accompanied by the accumulation of unsaturated triglycerides of variable structure. The chain length of the acid residue of triglycerides varied within the C11-C22 carbon atoms. In this case, the number of carbon atoms in the chain was most often -C18. The position of the double bonds was stochastic. At the same time, they were all removed from the carboxyl group by more than 4 carbon atoms. Stimulation of the processes of complex biotransformation of hexadecane under the action of the drug Devouroil and earthworms was manifested with the introduction of a biological product at concentrations of 32 × 1010 cells/kg and 64 × 1010 cells/kg. A further increase in the number of cells of the biological product Devouroil with the combined use of the biological product and worms led to a leveling of the stimulating effect of earthworms on the transformation processes of this hydrocarbon. At the same time, the phytotoxicity of the studied samples decreased.

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.

ЛІПІДНИЙ ОБМІН В ОРГАНІЗМІ РИБ ЗА ДІЇ ЧИННИКІВ ОТОЧУЮЧОГО ВОДНОГО СЕРЕДОВИЩА

Lipids are a heterogeneous group of chemical compounds that are found in all animal and plant organisms and combine based on common properties. The physiological role of lipids in fish is extremely important and diverse. They perform a number of functions, including energetical, structural, regulatory and others.
 The authors analyzed the data in the domestic and foreign literature on the structural and functional importance of lipids in fish. The role of lipids in the processes of adaptation of aquatic organisms to adverse factors of the aquatic environment (temperature, salinity, chemical pollution) by changing the ratio of certain classes of lipids, their fatty acid composition and spatial orientation of fatty acid "tails" in biological membranes. The regulatory role of lipids in the functioning of membrane enzymes is analyzed.
 The authors argue that to find the causes of reduced productivity of fish in a polluted aquatic environment, it is necessary to study bodily changes in lipid metabolism, which are one of the main structural and metabolic compounds, responsible for the formation of adaptive reactions.
 By adaptation to low temperatures the inclusion of polyene fatty acids in the membrane lipids increases and also increases desaturation. Caused by changes in the temperature of the adjustment in the composition of membrane lipids are aimed at maintaining the mobility of membranes. By adaptation to the temperature factor the level of saturated or unsaturated fatty acids, the ratio of the main classes of phospholipids and cholesterol, asymmetry in the distribution of proteins and lipids in the cell membrane may change.
 The effects of hydrostatic pressure and salinity of water on lipid metabolism in fish are analyzed. It has been established that phase transitions are largely determined by the same properties of membrane lipids as with temperature change. First of all, it is the degree of saturation of fatty acids, the length of their chain, the position of the double bond and the number of hydrocarbon atoms (pair or not pair). It is shown that in the organs and tissues or fish, involved in the processes of osmoregulation, during adaptation to salt water the lipid content increases.
 Under the influence of toxic factors in different species of fish a general adaptation strategy is traced, which consists of increasing the content of those lipid fractions, that maintain the energy status of fish for excretion and neutralization of toxicants, reducing the permeability of biological cell membranes to limit the entry of toxicants into fish organism.

Kinetics and degradation mechanism of atmospheric isoprene (2‐methyl‐1, 3‐butadiene (C5H8)) with chlorine radical and its derivatives—A theoretical study

AbstractIsoprene (2‐methyl‐1, 3‐butadiene (C5H8)) is one of the most prominent and abundant non‐methane hydrocarbon existing in the lower level of the troposphere. In this work, possible reaction mechanism of chlorine (Cl) radical initiated isoprene and its subsequent reactions are investigated using quantum chemical methods at M06‐2X/CCSD(T)/6‐311+G* level of theory. The calculated thermodynamic result shows that the reaction of isoprene with the Cl radical at the terminal CC bond position plays an important role to predict the end products. The calculated rate coefficient for the reaction between isoprene and Cl radicals (Cl addition at C1, C3, C4 and C5 positions) is found to be 4.89 × 10−11, 6.91 × 10−10, 1.63 × 10−10 and 8.12 × 10−10 cm3/molecule/s at 298 K. The branching ratio and atmospheric lifetime have been calculated from the reaction rate coefficient values of isoprene + Cl. The reaction force analysis predicts Cl radical addition at the terminal CC bond position plays a dominant role by structural rearrangement. The kinetic and thermodynamic results reveal that the electrophilic addition of Cl radical to the terminal carbon atom plays the dominant role in the marine boundary. Further, the subsequent reaction of Cl‐isoprene adduct radical helps for the development of ozone layer during daytime.

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.

Countercurrent chromatographic fractionation followed by gas chromatography/mass spectrometry identification of alkylresorcinols in rye

Alkylresorcinols (5-alkyl-1,3-dihydroxybenzenes, ARs) are bioactive phenolic lipid compounds which are particularly abundant in rye and partly other cereals. In this study on ARs, whole rye grain extracts were gained with cyclohexane/ethyl acetate (46/54, w/w). Silylated extracts were used to develop a gas chromatography with mass spectrometry method in the selected ion monitoring mode (GC/MS-SIM) for the sensitive detection of conventional ARs along with keto-substituted (oxo-AR) and ring-methylated ARs (mAR) with 5-alkyl chain lengths of 14 to 27 carbon atoms and 0 to 4 double bonds in one run. Analysis was performed by countercurrent chromatographic (CCC) fractionation using the solvent system n-hexane/ethyl acetate/methanol/water (9/1/9/1, v/v/v/v). Subsequent GC/MS-(SIM) analysis of 80 silylated CCC fractions enabled the detection of 74 ARs in the sample. The CCC elution of the ARs followed the equivalent chain length (ECL) rule in which one double bond compensated the effect of two (additional) carbon atoms. Novel or rarely reported ARs were detected in virtually all classes, i.e. saturated AR (AR14:0), even-numbered monounsaturated AR isomers (AR16:1-AR26:1), triunsaturated ARs (AR25:3), oxo-ARs (AR17:0 oxo, AR19:1 oxo, AR21:2 oxo, AR23:2 oxo) and odd-numbered methyl-ARs (mAR15:0-mAR23:0). Positions of the double bonds of monounsaturated ARs and oxo-ARs were determined with the help of dimethyl disulfide (DMDS) derivatives.Graphical abstract

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.

Mass spectrometry distinguishing C=C location and cis/trans isomers: A strategy initiated by water radical cations

We present an approach for the elucidation of C=C bond position and cis/trans isomers, which is achieved by the reaction of ambient water radical cations and double bonds, followed by the fragmentation of epoxide radical cations to generate diagnostic ions in tandem mass spectrometry. Hexenol double bond positional isomers and cis/trans isomers which exhibit different properties and biological functions are characterized as a proof of concept. The merits of the approach include the simplicity of experimental setup, rapid derivatization (within seconds), the obviation of organic solvents, as well as easy spectral interpretation.

Isomer-specific speciation behaviors probed from premixed flames fueled by acetone and propanal

Chemical structures of low-pressure premixed flames respectively fueled by two C3 carbonyl isomers, acetone and propanal, at different equivalence ratios (1.0 and 1.5) were experimentally investigated in this work. Detailed speciation information was obtained by employing molecular-beam mass spectrometry with tunable synchrotron photoionization. A detailed kinetic model including the chemistry of acetone and propanal was developed and tested with the current flame speciation measurements. By combining experimental observations and modeling interpretations, comparisons were made regarding fuel-specific reaction pathways and the resulting different species pools. Some fuel-specific intermediates were detected and quantified in this work, such as ketene in acetone flames and methylketene in propanal flames. Particularly, the quantitative speciation measurements of ketene, an important primary intermediate of acetone, were satisfactorily predicted by the current model, which included an updated ketene sub-mechanism. Major efforts in this work were devoted to gaining some insights into the effects of the carbonyl position in fuel molecules on the speciation behaviors under premixed flame conditions. Carbonyl functionalities in the two C3 carbonyl compounds are tightly bonded and preferably preserved in CO. Due to the different position of the CO bond in the two isomers, the oxidation of propanal leads to abundant ethyl as a chain carrier, while the acetone consumption easily results in a significant amount of methyl, an inhibitor on the fuel reactivity. As a result, higher reactivity of propanal was observed. More importantly, the different fuel consumption patterns also influence the speciation behaviors. Specifically, the larger concentration of benzene precursors such as allyl, was observed in the propanal flames. Besides, typical oxygenated emissions formaldehyde and acetaldehyde had more remarkable concentrations in acetone and propanal flames, respectively.