Recent developments in metathesis of unsaturated fatty acids

Spurred by improvements in catalysts as well as new experimental designs, lipid researchers have attained some impressive new outcomes by applying olefin metathesis to fatty acid substrates. Monomers for polyamides, environmentally‐responsive coatings, and blends of biofuels are among the bio‐derived materials obtained. This reaction is a powerful way to reconfigure the C₁₈ skeleton into its component subunits such as alkenes or carboxylates, or to add functionality via a cross‐metathesis partner, thus continuing progress toward realizing the potential of plant oils as feedstocks for the biorefinery.     

Locked nucleic acids and intercalating nucleic acids in the design of easily denaturing nucleic acids: thermal stability studies

Intercalating nucleic acids (INA(R)s) with insertions of (R)-1-O-(1-pyrenylmethyl)glycerol were hybridized with locked nucleic acids (LNAs). INA/LNA duplexes were found to be less stable than the corresponding DNA/LNA duplexes when the INA monomer was inserted as a bulge close to the LNA monomers in the opposite strand. This property was used to make "quenched" complements that possess LNA in hairpins and in duplexes and are consequently more accessible for targeting native DNA. The duplex between a fully modified 13-mer LNA sequence and a complementary INA with six pyrene residues inserted after every second base as a bulge was found to be very unstable (Tm=30.1 degrees C) in comparison with the unmodified double-stranded DNA (Tm=48.7 degrees C) and the corresponding duplexes of LNA/DNA (Tm=81.6 degrees C) and INA/DNA (Tm=66.4 degrees C). A thermal melting experiment of a mixture of an LNA hairpin, with five LNA nucleotides in the stem, and its complementary DNA sequence gave a transition with an extremely low increase in optical density (hyperchromicity). When two INA monomers were inserted into the stem of the LNA hairpin, the same experiment resulted in a significant hyperchromicity comparable with the one obtained for the corresponding DNA/DNA duplex.     

Recent developments in graphene-based polymer composite membranes: Preparation,mass transfer mechanism,and applications

The shortage of water resources is a problem concerned by all countries in the world. In order to solve this problem of human survival, membrane separation technology promotes the development of water treatment field by virtue of its own advantages of high efficiency and low consumption. Membrane separation technology combined with nanomaterials has brought surprises to researchers. Graphene has unique structure and properties, making graphene and its derivatives have very good potential in water treatment and selective separation. Graphene-based materials combined with traditional polymer materials have great potential in the field of membrane separation technology. In this article, we first introduce the preparation methods and transport mechanism of graphene-based membranes, and then summarize the recent applications of graphene oxide/polymer composite membranes in water purification, gas separation, self-cleaning, and oil–water separation. It is expected to become the next generation of functional composite membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47761.     

Multidimensional mass spectrometry methods for the structural characterization of cyclic polymers

Several synthetic methods have been developed for the tailored preparation of cyclic macromolecules due to their unique physical and chemical properties. Unequivocal characterization of the macrocyclic architectures has remained challenging, however, because isomeric linear structures often exist, or the spectral features of linear vs. cyclic chains are similar. To address this problem, multidimensional mass spectrometry (MS) techniques have been evaluated for the separation and identification of polymeric macrocycles. Tandem mass spectrometry (MS²) is found to be ideally suitable for the differentiation of linear and cyclic architectures whose molecular ions exhibit distinct fragmentation characteristics. Conversely, differences in macromolecular sizes and shapes can be exploited to identify the correct architecture by ion mobility mass spectrometry (IM-MS). A third option, chromatographic separation (LC) before MS analysis, is available for the detection of cyclics in complex mixtures. The capabilities of these techniques and combinations thereof are demonstrated with specific covalent or supramolecular (co)polymers.     

Synthesis, mass spectrometry, and nuclear magnetic resonance characterization of Di-guerbet esters

Several Di-Guerbet esters (DGE) suitable for lubricant applications were synthesized from branched Guerbet alcohols and Guerbet acids. The mass spectra of DGE under electron-ionization and positive chemical-ionization (PCI) conditions were recorded. Gas chromatography-mass spectrometry, especially in PCI mode with methane as reagent gas, is an effective method for analyzing DGE. In methane positive chemical-ionization mass spectrometry, the DGE give molecular ion peaks. In both PCI and EI modes, some other characteristic ions including up to four McLafferty rearrangement products with high m/z are observed. Thus identification of both hydrocarbon moieties is possible. The DGE were also characterized by ¹H-and ¹³C nuclear magnetic resonance. Deceased.     

The mass spectrometry of iso and anteiso monoenoic fatty acids

The normal, iso, and anteiso Δ⁸- and Δ⁹-17:1 fatty acid methyl esters were synthesized and their electron impact-induced fragmentation was studied by mass spectrometry. The mass spectra of the preterminal branched monoenoic fatty acid methyl esters present characteristic fragment ions, now understood to be indicative of the position of the methyl group. These fragment ions are in the iso compound m/e 227 [M-55]⁺, m/e 195 [M-87]⁺, and m/e 177 [M-105]⁺, while in the anteiso compound these fragments are shifted by 14 mass units to m/e 213, m/e 181, and m/e 163. The 15-D-iso Δ⁸- and Δ⁹-17:1 methyl esters were synthesized because the characteristic fragment ions in the methyl branched compounds indicated a key role of the tertiary hydrogen atom in the rearrangement process. A fragmentation mechanism consisting of a double bond migration triggered by the tertiary hydrogen and an allylic cleavage assuming a displacement mechanism is proposed.     

Fast atom bombardment and tandem mass spectrometry for determing iso- and anteiso-fatty acids

Branched fatty acids can be distinguished from isomeric straight chain fatty acids by collisionally activating the (M-H)⁻ ions desorbed by using fast atom bombardment (FAB) mass spectrometry (MS). In particular, an acid with iso- fatty branching can be readily distinguished from one containing anteiso- branching; the latter undergoes loss of the elements of CH₄ and C₂H₆ but not C₃H₈. These decompositions are another example of remote charge site fragmentation. Mixtures of homologs and isomers can be investigated by using the combination of FAB and tandem mass spectrometry (MS-MS).     

Recent developments in the formation, characterization, and simulation of micron and nano-scale droplets of amorphous polymer blends and semi-crystalline polymers

Polymer micro- and nano-particles are fundamental to a number of modern technological applications, including polymer blends or alloys, biomaterials for drug delivery systems, electro-optic and luminescent devices, coatings, polymer powder impregnation of inorganic fibers in composites, and are also critical in polymer-supported heterogeneous catalysis. In this article, we review some of our recent progress in experimental and simulation methods for generating, characterizing, and modeling polymer micro- and nano-particles in a number of polymer and polymer blend systems. By using instrumentation developed for probing single fluorescent molecules in micron-sized liquid droplets, we have shown that polymer particles of nearly arbitrary size and composition can be made with a size dispersion that is ultimately limited by the chain length and number distribution within the droplets. Depending on the time scale for solvent evaporation—a tunable parameter in our experiments—phase separation of otherwise immiscible polymers can be avoided by confinement effects, producing homogeneous polymer blend micro- or nano-particles. These particles have tunable properties that can be controlled simply by adjusting the size of the particle, or the relative mass fractions of the polymer components in solution. Physical, optical, and mechanical properties of a variety of micro and nano-particles, differing in size and composition, have been examined using extensive classical molecular dynamics calculations in conjunction with experiments to gain deeper insights into fundamental nature of their structure, dynamics, and properties.     

煤矿阻化材料的研究进展

综述了近年来无机阻化剂、有机阻化剂、高分子阻化剂、复合阻化剂的研究进展,并介绍了各种阻化剂的优缺点;最后对其前景作了一定的展望。     

Recent developments in the toilet-bar market

During recent years consumers have shown an increasing willingness to purchase more expensive toilet soaps. Two types of toilet bars in particular, surfactant formula bars and antibacterial bars, have shown steady growth. Surfactant formula bars have gained acceptance because of their excellent lathering properties and the lack of soap scum, which eliminates the unsightly “bathtub ring.” Antibacterial bars have gained acceptance because of their ability to reduce the number of resident bacteria on the skin. This reduces the incidence of superficial cutaneous infection and slows down the development of objectionable body odors attributable to the bacterial decomposition of sweat.     

The expanding role of mass spectrometry in metabolite profiling and characterization

Mass spectrometry has a strong history in drug-metabolite analysis and has recently emerged as the foremost technology in endogenous metabolite research. The advantages of mass spectrometry include a wide dynamic range, the ability to observe a diverse number of molecular species, and reproducible quantitative analysis. These attributes are important in addressing the issue of metabolite profiling, as the dynamic range easily exceeds nine orders of magnitude in biofluids, and the diversity of species ranges from simple amino acids to lipids to complex carbohydrates. The goals of the application of mass spectrometry range from basic biochemistry to clinical biomarker discovery with challenges in generating a comprehensive profile, data analysis, and structurally characterizing physiologically important metabolites. The precedent for this work has already been set in neonatal screening, as blood samples from millions of neonates are tested routinely by mass spectrometry as a diagnostic tool for inborn errors of metabolism. In this review, we will discuss the background from which contemporary metabolite research emerged, the techniques involved in this exciting area, and the current and future applications of this field.     

Recent developments in chemical modification and characterization of natural fiber‐reinforced composites

A critical review of the literature on the various aspects of natural fibers and biocomposites with a particular reference to chemical modifications is presented in this paper. A notable disadvantage of natural fibers is their polarity which makes it incompatible with hydrophobic matrix. This incompatibility results in poor interfacial bonding between the fibers and the matrix. This in turn leads to impaired mechanical properties of the composites. This defect can be remedied by chemical modification of fibers so as to make it less hydrophilic. This paper reviews the latest trends in chemical modifications and characterizations of natural fibers. The structure and properties of natural fibers have been discussed. Common chemical modifications and their mechanisms have also been elaborated. The importance of chemical modifications and the resultant enhancement in the properties of the composites have also been reviewed. Recent investigations dealing with chemical modifications of natural fiber‐reinforced composites have also been cited. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

Analysis of fatty acids by mass spectrometry in the selected ion monitoring mode

GC/EI‐MS‐SIM (gas chromatography / electron ionisation – mass spectrometry with selected ion monitoring) can be easily applied to the determination of fatty acids as methyl esters (FAME). SIM masses should have a high relative abundance and for this reason we suggest m/z 74 and m/z 87 for saturated and monoenoic fatty acids as well as m/z 79 and m/z 81 for FAME with more than one double bond. The relevance and ratio of these fragment ions along with GC retention times enables a good identification of a FAME represented by a peak detected in the chromatograms. Compared to GC with a flame ionisation detector, this simple method provides a higher selectivity and better sensitivity. It also offers the possibilities of using a wide range of internal standards which enables the individual quantification of FAME instead of the determination of their contributions to the fatty acid pattern.     

Precise characterization of cuticular compounds in youngDrosophila by mass spectrometry

Cuticular hydrocarbons of youngDrosophila flies are singular with very long chains and complex diene mixtures. A precise characterization of these substances was carried out by epoxidation and analysis of the products by GC-MS with negative chemical ionization. InD. melanogaster, double bonds of dienes are more probable at carbon positions 11 or 13 and 21 or 23. InD. simulans, double bonds are shifted more towards the interior of the chain. Such a difference is also found among monoenes of both species. The analyses of monoenes and dienes confirm the similarity of cuticular compounds of young flies of both sexes in both species. A main cuticular compound ofD. erecta females, 9, 23-tritriacontadiene, is also presented.     

Recent developments in polypseudorotaxanes and polyrotaxanes

This review highlights developments since 2008 in the field of polypseudorotaxanes and polyrotaxanes. Progress in synthetic polyrotaxane chemistry has resulted in the preparation of numerous functionalized polymers for various applications in areas such as molecular machines, stimuli responsive materials, supramolecular gels and molecular sensors. This new genre of supramolecular polymers is advancing rapidly with several groups developing novel materials with unique characteristics.     

Recent advances in secondary lon mass spectrometry (SIMS) for polymer surface analysis

Since the first tentative applications of SIMS to study polymer surfaces around 1980 the field has developed very rapidly. The important experimental parameters which allow true ‘static’ SIMS analysis of polymers are now well established following systematic studies of ion beam damage cross-sections and the methodology of surface potential control is sufficiently understood to allow both positive and negative ion spectra to be routinely obtained from highly insulating materials. The principal advantage of SIMS over X-ray photoelectron spectroscopy (XPS or ESCA) comes from the molecular specificity inherent in a mass spectrometric technique. Several classes of polymers have been studied to establish fragmentation processes; in the case of acrylic polymers these studies have been extensive and detailed. From the technological point-of-view it is the ability to identify ‘small’ organic molecules on polymer surfaces which is most exploited. The information depth in typical systems has been established by correlation with angle-resolved XPS studies to be ～ å, this degree of surface sensitivity allows bulk-surface segregation effects in block copolymers to be followed as exemplified by studies of segmented poly (ether urethanes). Use can also be made of the isotope specificity of SIMS in derivatisation schemes or in polymerisation mechanism studies. Quantification of SIMS intensity data is now being explored. In the case of random methacrylate copolymers quantitative information on sequence statistics has been obtained. SIMS also has the potential for high spatial resolution analysis. The problems associated with unacceptable damage rates when working with sub-micron focussed beams have been studied and this has led to the development of the time-of-flight (TOF) imaging SIMS instrument. TOF SIMS is capable of accessing a mass range of an order of magnitude greater than the conventional quadrupole instrument and the application of both imaging and non-imaging TOF instrumentation to polymer surface analysis has recently commenced.     

Electrooxidation of biologically important hypoxanthine nucleosides and nucleotides at solid electrodes

The oxidation chemistry of hypoxanthine nucleosides and nucleotides viz., inosine, 2′-deoxyinosine, inosine-5′-monophosphate and inosine-5′-triphosphate has been studied in the pH range 2.1-11.1 at pyrolytic graphite electrode. In all the four compounds oxidation occurs in 6H⁺, 6e process at physiological pH (7.2) leading to the formation of allantoin as a major product. The products dimers and tetramers formed in the secondary electrode reactions depend on the nature of sugar molecule (ribose or deoxyribose) present and number of phosphate moieties attached to the sugar moiety. A comparison of redox chemistry and formation of electrooxidised products of inosine and its derivatives has been presented in this paper.