Even-numbered Chains Research Articles

Sphingolipid profiling reveals differential functions of sphingolipid biosynthesis isozymes of Caenorhabditis elegans

Multiple isozymes are encoded in the Caenorhabditis elegans genome for the various sphingolipid biosynthesis reactions, but the contributions of individual isozymes are characterized only in part. We developed a simple but effective reversed-phase liquid chromatography-tandem mass spectrometry (RPLC-MS/MS) method that enables simultaneous identification and quantification of ceramides (Cer), glucosylceramides (GlcCer), and sphingomyelins (SM) from the same MS run. Validating this sphingolipid profiling method, we show that nearly all 47 quantifiable sphingolipid species found in young adult worms were reduced upon RNA interference (RNAi) of sptl-1 or elo-5, which are both required for synthesis of the id17:1 sphingoid base. We also confirm that HYL-1 and HYL-2, but not LAGR-1, constitute the major ceramide synthase activity with different preference for fatty acid substrates, and that CGT-3, but not CGT-1 and CGT-2, plays a major role in producing GlcCers. Deletion of sms-5 hardly affected SM levels. RNAi of sms-1, sms-2, and sms-3 all lowered the abundance of certain SMs with an odd-numbered N-acyl chains (mostly C21 and C23, with or without hydroxylation). Unexpectedly, sms-2 RNAi and sms-3 RNAi elevated a subset of SM species containing even-numbered N-acyls. This suggests that sphingolipids containing even-numbered N-acyls could be regulated separately, sometimes in opposite directions, from those containing odd-numbered N-acyls, which are presumably monomethyl branched chain fatty acyls. We also find that ceramide levels are kept in balance with those of GlcCers and SMs. These findings underscore the effectiveness of this RPLC-MS/MS method in studies of C. elegans sphingolipid biology.

XFEL Microcrystallography of Self-Assembling Silver n-Alkanethiolates.

New synthetic hybrid materials and their increasing complexity have placed growing demands on crystal growth for single-crystal X-ray diffraction analysis. Unfortunately, not all chemical systems are conducive to the isolation of single crystals for traditional characterization. Here, small-molecule serial femtosecond crystallography (smSFX) at atomic resolution (0.833 Å) is employed to characterize microcrystalline silver n-alkanethiolates with various alkyl chain lengths at X-ray free electron laser facilities, resolving long-standing controversies regarding the atomic connectivity and odd-even effects of layer stacking. smSFX provides high-quality crystal structures directly from the powder of the true unknowns, a capability that is particularly useful for systems having notoriously small or defective crystals. We present crystal structures of silver n-butanethiolate (C4), silver n-hexanethiolate (C6), and silver n-nonanethiolate (C9). We show that an odd-even effect originates from the orientation of the terminal methyl group and its role in packing efficiency. We also propose a secondary odd-even effect involving multiple mosaic blocks in the crystals containing even-numbered chains, identified by selected-area electron diffraction measurements. We conclude with a discussion of the merits of the synthetic preparation for the preparation of microdiffraction specimens and compare the long-range order in these crystals to that of self-assembled monolayers.

The lipidomic correlates of epigenetic aging across the adult lifespan: A population-based study.

Lipid signaling is involved in longevity regulation, but which specific lipid molecular species affect human biological aging remains largely unknown. We investigated the relation between complex lipids and DNA methylation-based metrics of biological aging among 4181 participants (mean age 55.1 years (range 30.0-95.0)) from the Rhineland Study, an ongoing population-based cohort study in Bonn, Germany. The absolute concentration of 14 lipid classes, covering 964 molecular species and 267 fatty acid composites, was measured by Metabolon Complex Lipid Panel. DNA methylation-based metrics of biological aging (AgeAccelPheno and AgeAccelGrim) were calculated based on published algorithms. Epigenome-wide association analyses (EWAS) of biological aging-associated lipids and pathway analysis were performed to gain biological insights into the mechanisms underlying the effects of lipidomics on biological aging. We found that higher levels of molecular species belonging to neutral lipids, phosphatidylethanolamines, phosphatidylinositols, and dihydroceramides were associated with faster biological aging, whereas higher levels of lysophosphatidylcholine, hexosylceramide, and lactosylceramide species were associated with slower biological aging. Ceramide, phosphatidylcholine, and lysophosphatidylethanolamine species with odd-numbered fatty acid tail lengths were associated with slower biological aging, whereas those with even-numbered chain lengths were associated with faster biological aging. EWAS combined with functional pathway analysis revealed several complex lipids associated with biological aging as important regulators of known longevity and aging-related pathways.

Mechanisms for the structural dependent transformation of 6:2 and 8:2 polyfluoroalkyl phosphate diesters in wheat (Triticum aestivum L.)

Polyfluoroalkyl phosphate esters (PAPs) are widely used and detected in various environmental media and organisms, but little is known about their behaviors in plants. In this study, the uptake, translocation and transformation of 6:2 and 8:2 diPAP in wheat using hydroponic experiments were investigated. 6:2 diPAP was more easily taken up by roots and translocated to shoots than 8:2 diPAP. Their phase I metabolites were fluorotelomer saturated carboxylates (FTCAs), fluorotelomer unsaturated carboxylates (FTUCAs) and perfluoroalkyl carboxylic acids (PFCAs). PFCAs with even-numbered chain length were the primary phase I terminal metabolites suggesting that they were mainly generated through β-oxidation. Cysteine and sulfate conjugates were the primary phase II transformation metabolites. The higher levels and ratios of phase II metabolites in the 6:2 diPAP exposure group indicated that the phase I metabolites of 6:2 diPAP were more susceptible to phase II transformation than that of 8:2 diPAP, which was confirmed by density functional theory calculation. Enzyme activity analyses and in vitro experiments demonstrated that cytochrome P450 and alcohol dehydrogenase actively participated in the phase Ⅰ transformation of diPAPs. Gene expression analyses showed that glutathione S-transferase (GST) was involved in the phase Ⅱ transformation, and the subfamily GSTU2 played a dominant role.

Genomics of carbon atomic chains

To realise the technological potential of subnanometer graphene junctions, there is a need to understand how their electronic and spintronic properties are controlled by the carbon chains bridging their gaps. Motivated by the recent experimental efforts to form in-situ all-carbon junctions using graphene electrodes connected to carbon chains, here we systematically study a wide variety of such structures. We find that although a wide range of transport properties are possible, the junctions can be divided into a small number of categories, according to their qualitative transport properties. For example, we find that junctions bridged by even-numbered chains of carbon atoms tend to have a lower conductance than those bridged by odd-numbered atomic chains. We also find that junctions with ferromagnetically aligned electrode surface edges have a higher transmission than anti-ferromagnetically aligned ones, because ferromagnetic alignment tends to increase the transmission of one of the spin carriers. We also examine the effect of terminal rings, electrode terminal edges and the effect of saturation of edges with hydrogen on transport properties of all-carbon junctions. Just like genomics, our findings provide a complete set of information to construct junctions formed by carbon chains with desired properties for spintronic applications.

SnOct2-catalyzed and alcohol-initiated ROPs of L-lactide – About the influence of initiators on chemical reactions in the melt and the solid state

SnOct2 (Sn(II) 2-ethylhexanoate) catalyzed ROPs of L-lactide were performed in bulk with eight different alcohols as initiators. The time was varied between 1 h and 24 h for all initiators. For two initiators the temperature was also lowered to 115 °C. Even-numbered chains were predominantly formed in all polymerizations at short times, but the rate of transesterification (e.g. even/odd equilibration) and the molecular weight distribution were found to depend significantly on the nature of the initiator. Observed transesterification reactions also continued in solid poly(L-lactide), and with the most active initiator, almost total equilibration was achieved even at 130 °C. This means that all chains including those of the crystallites were involved in transesterification reactions proceeding across the flat surfaces of the crystallites. The more or less equilibrated crystalline polylactides were characterized by DSC and SAXS measurements with regard to their melting temperature (Tm), crystallinity and crystal thickness.

Alkyl chain regulation: distinctive odd–even effects of mechano-luminescence and room-temperature phosphorescence in alkyl substituted carbazole amide derivatives

A series of carbazole amide derivatives with different lengths from methyl to octyl (CAC-N, N = 1–8). Compounds with even-numbered alkyl chains exhibit mechanoluminescence (ML) property, however, no ML is observed in the odd-numbered counterparts.

Effect of the anti-inflammatory drug diclofenac on lipid composition of bacterial strain Raoultella sp. KDF8.

The strain Raoultella sp. KDF8 was cultivated on three sources of carbon and energy, glycerol, ethanol and diclofenac, for periods of time ranging from 24 to 72h. Using thin-layer chromatography, nine classes of phospholipids were detected and the amount of phosphatidylethanolamine (PtdEtn) decreased with increasing cultivation time. Conversely, the ratio of phospholipids having three or four acyls (acyl-phosphatidylglycerol (APtdGro), N-acyl-PtdEtn (NAPtdEtn) and cardiolipin (Ptd2Gro) increased during cultivation. GC-MS analysis showed that the percentage of fatty acids containing a cyclopropane ring increased almost tenfold whereas the amount of fatty acids bearing even-numbered chains dropped to less than one-third after 24h and 72h in cultures on glycerol and diclofenac, respectively. Shotgun analysis showed significant changes in the representation of molecular species of phospholipids. For instance, there was a 36-fold change in the ratio of 16:1/16:1/16:1-APtdGro to c17:0/c17:0/c17:0-APtdGro and a 12-fold ratio change for 16:1/16:1/16:1-NAPtdEtn to c17:0/c17:0/c17:0-NAPtdEtn; the Ptd2Gro ratio of 16:1 to c17:0 acids equalled 1750. Our results show that the bacteria overcome destabilization of the inner cytoplasmic cell membrane and a bacterial outer membrane by altering the geometric arrangement of acyl chains, i.e. switching from monounsaturated to cyclopropane fatty acids (16:1 versus c17:0).

Even–Odd Alkyl Chain-Length Alternation Regulates Oligothiophene Crystal Structure

Alkyl chains of varied length and steric bulk are generally appended to π-conjugated chromophores to increase solubility. These alkyl chains also regulate many aspects of the solid-state packing and, in turn, resultant electronic and optical properties of organic semiconductors, yet there remains little understanding as to how these moieties govern such characteristics. Here, we report on a series of (2,5-bis(3-alkylthiophen-2-yl) thieno[3,2-b]thiophenes) (BTTT) monomers where the single-crystal packing configurations and melting points alternate as a function of whether the alkyl side chains have an even or odd number of carbon atoms. When the alkyl chains contain an even number of carbon atoms, the molecules predominantly crystallize with the BTTT units of the stacked lamellae aligned in the same direction. In contrast, when the number of carbon atoms is odd, alternating lamellae are twisted with respect to their neighbors, i.e. the BTTT moieties in one layer are aligned in an orthogonal-like fashion to those in its neighboring lamellae, and the crystal melting points tend to be higher than those with the even-numbered alkyl chains. With density functional theory calculations and geometric analyses, the variations in crystal structure and thus the differences in physical properties are rationalized by an oscillating interlayer interaction that is a function of alkyl side chain atom count and length. This study characterizes an extreme case of an organic semiconductor crystal packing alternation to highlight the effect of even–odd assembly as an underutilized and under-reported handle for tuning the molecular packing of organic semiconductor materials.

The influence of coupling between chains on the conductivity of atomic carbon chains

This work presents a theoretical investigation on the electronic properties of double atomic carbon chains bridging graphene electrodes with density functional theory in combination with non-equilibrium Green's function. The influence of strain on the conductance of atomic carbon chains is significant. However, the coupling effect between adjacent chains dominates the intrinsic transport of double atomic carbon chains. For the coupled double atomic chains, the electron conductance of even-numbered atomic chains is significantly enhanced, while the electron conductance of odd-numbered atomic chains decreases to a certain degree, and the dependence of the conductance of double atomic chains on electrode configuration is stronger than the corresponding single atomic chain. More intriguingly, the coupled double atomic chains exhibit excellent spin-filtering properties with antiparallel spins on two electrodes. The current spin polarization stems from the coupling-induced changes of electron density and band offset reaches 100%. The coupled double atomic carbon chains have great potential application in spintronic devices and carbon-based field-effect transistors.

Cyclic poly(l-lactide)s via simultaneous ROP and polycondensation (ROPPOC) catalyzed by dibutyltin phenoxides

Starting from dibutyltin oxide, four catalysts were synthesized, namely the dibutyltin bisphenoxides of phenol (SnPh), 4-chlorophenol (SnCP), 4-hydroxybenzonitrile (SnCN) and pentafluorophenol (SnOPF). With the first three catalysts polymerizations of l-lactide at 160 °C in bulk yielded large fraction of linear chains having phenylester end groups at short reaction times. At longer times the fraction of cycles considerably increased at the expense of the linear chains, when SnCN was used as catalyst. With SnOPF only cyclic polylactides were obtained at low Lac/Cat ratios (<400) with weight average molecular weights (Mw) up to 90 000 Da, whereas for high Lac/Cat ratios mixtures of cyclic and linear chains were found. Polymerizations in solution enabled variation of the molecular weight. Polymerizations of meso-lactide at temperatures down to 60 °C mainly yielded even-numbered linear chains supporting the postulated ROPPOC mechanism.

Compound-Specific δ13C of n-Alkanes: Clean-Up Methods Appraisal and Application to Recent Sediments of a Highly Contaminated Bay

Different clean-up methods to determine isotopic composition of n-alkanes were tested. Sources of organic matter in Guanabara Bay were re-examined through the δ13C of individual n-alkanes in surface sediment samples. The n-alkanes were efficiently isolated without significant losses of the compounds of interest. The δ13C of n-alkanes (n-C17 to n-C35) ranged between -34.0 and -26.4‰. More depleted δ13C values associated to higher carbon preference index (CPI > 4) suggest prevalence of biogenic n-alkanes from terrestrial origin in the inner stations influenced by inputs from mangrove areas. Small isotopic differences between odd and even-numbered chains and 13C-enrichment in long-chain homologues indicate a petrogenic hydrocarbons contribution. Higher concentrations of short-chain compounds associated to a more 13C-enriched total organic carbon (TOC) were found near the most intense sewage discharges. Results show that δ13C of n-alkanes can be applied to a highly degraded system as the Guanabara Bay and help improve the characterization of the organic matter.

Moving beyond the ubiquitous: the diversity and biosynthesis of specialty compounds in plant cuticular waxes

Cuticular waxes coat aerial plant surfaces to protect tissues against biotic and abiotic stress. The waxes are complex mixtures of fatty-acid-derived lipids formed on modular biosynthetic pathways, with varying chain lengths and oxygen functional groups. The waxes of most plant species contain C26–C32 alcohols, aldehydes, alkanes, and fatty acids together with their alkyl esters, and comparisons between diverse wax mixtures have revealed matching chain length distributions between some of these compound classes. Based on such patterns, the biosynthetic pathways leading to the ubiquitous wax constituents were hypothesized early on, and most of these pathway hypotheses have since been confirmed by biochemical and molecular genetic studies in model species. However, the most abundant wax compounds on many species, including many important crop species, contain secondary functional groups and thus their biosynthesis differs at least in part from the ubiquitous wax compounds with which they co-occur. Here, we survey the chemical structures of these species-specific specialty wax compounds based on a comprehensive CAS SciFinder search and then review relevant reports on wax compositions to help develop and refine hypotheses for their biosynthesis. Across the plant kingdom, specialty wax compounds with one, two, and three secondary functional groups have been identified, with most studies focusing on Angiosperms. Where multiple specialty wax compounds were reported, they frequently occurred as homologous series and/or mixtures of isomers. Among these, it is now possible to recognize series of homologs with predominantly odd- or even-numbered chain lengths, and mixtures of isomers with functional groups on adjacent or on alternating carbon atoms. Using these characteristic molecular geometries of the co-occurring specialty compounds, they can be categorized and, based on the common structural patterns, mechanisms of biosynthesis may be predicted. It seems highly likely that mixtures of isomers with secondary functions on adjacent carbons arise from oxidation catalyzed by P450 enzymes, while mixtures of isomers with alternating group positions are formed by malonate condensation reactions mediated by polyketide synthase or ketoacyl-CoA synthase enzymes, or else by the head-to-head condensation of long-chain acyls. Though it is possible that some enzymes leading to ubiquitous compounds also participate in specialty wax compound biosynthesis, comparisons between co-occurring ubiquitous and specialty wax compounds strongly suggest that, at least in some species, dedicated specialty wax compound machinery exists. This seems particularly true for the diverse species in which specialty wax compounds, most notably nonacosan-10-ol, hentriacontan-16-one (palmitone), and very-long-chain β-diketones, accumulate to high concentrations.

Switching of spins and entanglement in surface-supported antiferromagnetic chains

Previous experimental studies discovered universal growth of chains and nanowires of various chemical elements on a corrugated molecular network of Cu3N on the Cu(110). Herein, performing combined ab initio and quantum Hamiltonian studies we demonstrate that such chains can be used for a fast spin switching and entanglement generation by locally applied magnetic pulses. As an example, we show that in antiferromagnetic Co chains a strong entanglement between ends of chains occurs during spin switching. A novel parity effect in spin dynamics is reported. Even-numbered chains are found to exhibit significantly faster spin switching than odd-numbered counterparts. Moreover, at certain parameters of the system the dimerization effect in the spin dynamics of the chains was found. Our studies give a clear evidence that tailoring spin dynamics and entanglement can be achieved by magnetic fields and by tuning exchange interactions in supported chains.

Interesting odd-even rules of spin-filtering and magnetoresistance effects in a single-molecule spintronic device

By using nonequilibrium Green's functions in combination with the density functional theory, the spin transport properties of a single-molecule spintronic device are investigated. The computational results show that when the magnetic configuration of the device is set as parallel, the perfect spin-filtering effect can be observed. Especially, this perfect spin-filtering effect is independent of the number of carbon atoms in the carbon chain. However, when the magnetic configuration is set in antiparallel, the spin-filtering effect displays a strong odd-even oscillatory characteristic, namely, the spin-filtering efficiencies of odd-numbered chain systems have a higher values than even-numbered chain systems. Moreover, the magnetoresistance effect can also be observed in this single-molecule spintronic device. In contrast to the odd-even oscillatory characteristic of the spin-filtering effect in the antiparallel magnetic configuration, high magnetoresistance ratios belong to even-numbered chain systems while low magnetoresistance ratios belong to odd-numbered chain systems. The mechanisms are suggested for these interesting phenomena.

The electron transport properties of zigzag graphene nanoribbons with upright standing linear carbon chains

Abstract The electron transport properties of zigzag graphene nanoribbons (ZGNRs) with upright standing carbon chains are investigated by using first-principles calculations. The calculated results show a significant odd-even dependence. The currents of even-numbered chain configurations are small because a suppression emerges around the Fermi energy in the transmission spectra under a finite bias. However the I − V curves of odd-numbered chain structures display metallic properties with a big transmission peak in the transmission spectra, indicating the high conductance. These properties offer an interesting method by modifying the odd-even parity of the carbon chains to tune the electron transport properties of ZGNRS.

Stability of conductance oscillations in carbon atomic chains**Project supported by the National Natural Science Foundation of China (Grant Nos. 11304079, 11404094, and 51201059), the Priority Scientific and Technological Project of Henan Province, China (Grant No. 14A140027), the School Fund (Grant No. 2012BS055), and the Plan of Natural Science Fundamental Research of Henan University of Technology, China (Grant No. 2014JCYJ15).

The conductance stabilities of carbon atomic chains (CACs) with different lengths are investigated by performing theoretical calculations using the nonequilibrium Green’s function method combined with density functional theory. Regular even–odd conductance oscillation is observed as a function of the wire length. This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads. The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel, whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance toward higher energies is observed as the number of carbon atoms increases. The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads. Results show that the current–voltage evolution of CACs can be affected by the chain length. The differential and second derivatives of the conductance are also provided.

Parity effect in the ground state localization of antiferromagnetic chains coupled to a ferromagnet.

We investigate the ground states of antiferromagnetic Mn nanochains on Ni(110) by spin-polarized scanning tunneling microscopy in combination with theory. While the ferrimagnetic linear trimer experimentally shows the predicted collinear classical ground state, no magnetic contrast was observed for dimers and tetramers where noncollinear structures were expected based on abinitio theory. This striking observation can be explained by zero-point energy motion for even-numbered chains derived within a classical equation of motion leading to nonclassical ground states. Thus, depending on the parity of the chain length, the system shows a classical or a quantum behavior.

Rectifying performance and negative differential resistance behavior in graphite-chain-nanoribbon junctions

Electronic transport properties of graphite-nanoribbon conjunctions bridged by carbon atomic chains have been investigated. The first-principles calculations show that their I-V characteristics display odd-even effects. Specifically, current in odd-numbered chains is carried by resonances originating from the hybridization of the surface of the graphite electrode, chain and nanoribbon states, while even-numbered chains are mediated by tunneling between the graphite electrode and chain states. The rectifying performance in our models was found to be a result of asymmetric distortions of conducting resonances of the graphite electrode and chain states. It was also found that odd-numbered chains exhibit NDR behaviors caused by depressed chain states.

High Performance Dye-Sensitized Solar Cells with Alkylpyridinium Iodide Salts in Electrolytes

Pyridinium iodide salts, which are competitive to the conventional imidazolium iodide salts, have been used for dye-sensitized solar cells as iodide sources and ionic conductivities. Pyridinium iodide series are easy to prepare and less expensive than the imidazolium series salts. In this research, quite comparable efficiencies were obtained from electrolytes with pyridinium iodide salts. For the experiments, pyridinium salts with a few different alkyl chains are applied. When a pyridinium head is modified to picolinium, which has a methyl group on the pyridinium head, a noticeable V(oc) drop has been observed. However, the length of the alkyl chains on the pyridinium head does not affect V(oc) effectively. The odd-numbered alkyl chains showed slightly lower V(oc) compared to that of the even-numbered alkyl chains. Finally, the performances of the cells with pyridinium salts are compared to those of the conventional cells with imidazolium salts.