Double Bond Length Research Articles

Quantitative Mapping of Triacylglycerol Chain Length and Saturation Using Broadband CARS Microscopy

Lipid droplets (LDs), present in many cell types, are highly dynamic organelles that store neutral lipids, primarily triacylglycerols (TAGs). With the discovery of new LD functions (e.g., in immune response, protein clearage, and occurrence with disease), new methods to study LD chemical composition in situ are necessary. We present an approach for in situ, quantitative TAG analysis using label-free, coherent Raman microscopy that allows deciphering LD TAG composition in different biochemically complex samples with submicrometer spatial resolution. Employing a set of standard TAGs, we generate a spectral training matrix capturing the variation caused in Raman-like spectra by TAG backbone, chain length, and number of double bonds per chain, as well as the presence of proteins or other diluting molecules. Comparing our fitting approach to gas chromatography measurements for mixtures of standard TAGs and food oils, we find the root mean-square error for the prediction of TAG chemistry to be 0.69 CH2 and 0.15 #C=C. When progressing to more complex samples such as oil emulsions and LDs in various eukaryotic cells, we find good agreement with bulk gas chromatography measurements. For differentiated adipocytes, we find a significant increase in the number of double bonds in small LDs (below 2 μm in diameter) compared to large LDs (above 2 μm in diameter). Coupled with a relatively limited sample preparation requirement, this approach should enable rapid and accurate TAG LD analysis for a variety of cell biology and technological applications.

Endocannabinoids Facilitate the Opening of the M-Channel

The M-channel is a neuronal ion channel complex that is important for stabilizing neurons at subthreshold potential, limiting continuous neuronal firing. The M-channel belongs to the KV7 channel family and is formed mainly by KV7.2/KV7.3 heteromultimers. The physiological importance of the M-channel is evident by channel mutations that have been linked to an inherited form of juvenile epilepsy. We have previously described that polyunsaturated fatty acids activate the M-channel and thereby dampen neuronal excitability. Several members within the large family of endocannabinoids are structurally related to polyunsaturated fatty acids. We therefore hypothesize that endocannabinoids may modulate the activity of the M-channel. To test that hypothesis, we studied the effect of different endocannabinoids on the human KV7.2/KV7.3 channel expressed in Xenopus oocytes, using two-electrode voltage clamp. We found that specific compounds belonging to the endocannabinoid family activate the M-channel by shifting the voltage dependence of channel opening towards negative voltages and increasing the maximal conductance. In particular, N-Arachidonoyl L-serine (ARA-S) had a large activating effect, with significant effects from 0.3 μM. In contrast, some of the most commonly known endocannabinoids, e.g. 2-Arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide), did not activate the M-channel. From a systematic comparison of compounds with distinct chemical properties, we conclude that a negative charge of the head group is crucial for the activating effect, whereas the specific length and number of double bonds of the acyl tail is less important. Altogether, these findings suggest that specific members within the family of endocannabinoids may signal non-canonically via the M-channel. Understanding which endocannabinoids target the M-channel is of importance for interpretation of endocannabinoid effects on neuronal excitability and may be utilized for future development of pharmaceutical agents.

A Novel Strategy for Targeted Lipidomics Based on LC-Tandem-MS Parameters Prediction, Quantification, and Multiple Statistical Data Mining: Evaluation of Lysophosphatidylcholines as Potential Cancer Biomarkers.

Lipid quantification is the ultimate goal in lipidomics studies challenged by the availability of standard compounds. A novel strategy for targeted lipidomics based on LC-MS/MS parameters prediction and multivariate statistical analysis was developed for the quantitation of lysophosphatidylcholines (LPCs) in this study. Multiple linear regression models were established with the acyl chain length and number of double bonds after the prediction correlation coefficients ( R2pred) were evaluated. Then related analytical parameters including collision energy, declustering potential, retention time, and response factor were successfully predicted for any given LPC. With this "model-prediction" strategy, sensitivity, accuracy, and coverage of targeted lipidomics were improved significantly, and 60 LPCs were determined simultaneously in plasma for the first time. An integrated evaluation method for multi-indexes, logistic regression-ROC analysis was also proposed after biomarkers were identified by Student's t test, univariate ROC curve, and PLS-DA. Then the developed workflow was successfully used to discover and evaluate multi-LPCs indexes (a set of LPCs biomarkers with the best discriminating ability) for differentiating lung, breast, colorectal, and gastric cancer from controls, and among different types of cancer. Finally, the multi-LPCs index for lung cancer was compared with the plasma before and after treatment to test its utility. The novel targeted lipidomics methodology for LPCs was expected to provide a new insight into quantitative lipidomics and further clinical application.

Combustion and emissions characteristics of date pit methyl ester in a single cylinder direct injection diesel engine

Current biofuels for diesel engines are largely derived from food crops and there is significant concern, recognised by legislation, that such fuels do not result in net reductions of greenhouse gas emissions when considering the entirety of the production to usage lifecycle. A potential alternative approach is to utilise the lipid content of organic waste streams arising from food crop cultivation for the manufacture of sustainable diesel fuels. This paper therefore presents experimental studies carried out on a modern direct injection diesel engine supplied with a biodiesel (fatty acid methyl esters) produced from waste date pits to determine the combustion and emissions characteristics of an alternative fuel produced from a food residue. Date pit methyl esters were tested relative to both rapeseed and soybean methyl esters, unblended and as blends with a reference fossil diesel, alongside reference fossil diesel and a commercially available fossil diesel from Oman, at constant injection timing and constant ignition timing at a constant engine speed of 1200 rpm. Gas chromatograph analysis of the methyl esters fatty acid composition found a significantly shorter mean alkyl moiety chain length and lower number of double bonds in the case of the date pit esters than either the rapeseed or soybean biodiesel. All of the methyl esters exhibited a similar duration of ignition delay less than that displayed by a reference fossil diesel, but with a higher premixed burn fraction and peak heat release rate in the case of date pit methyl esters relative to those of rapeseed and soybean. Exhaust emissions of NOx were found to be lowest for the unblended date pit methyl esters, suggesting a greater influence of adiabatic flame temperature on rates of thermal NOx production than global in-cylinder temperatures in the case of the unblended methyl esters. Relative to the reference fossil diesel and Oman diesel, all of the methyl esters tested resulted in low particulate matter emissions.

ω-6 and ω-9 polyunsaturated fatty acids with double bonds near the carboxyl head have the highest affinity and largest effects on the cardiac IKs potassium channel.

AimThe IK s channel is important for termination of the cardiac action potential. Hundreds of loss‐of‐function mutations in the IK s channel reduce the K+ current and, thereby, delay the repolarization of the action potential, causing Long QT Syndrome. Long QT predisposes individuals to Torsades de Pointes which can lead to ventricular fibrillation and sudden death. Polyunsaturated fatty acids (PUFAs) are potential therapeutics for Long QT Syndrome, as they affect IK s channels. However, it is unclear which properties of PUFAs are essential for their effects on IK s channels.MethodsTo understand how PUFAs influence IK s channel activity, we measured effects on IK s current by two‐electrode voltage clamp while changing different properties of the hydrocarbon tail.ResultsThere was no, or weak, correlation between the tail length or number of double bonds in the tail and the effects on or apparent binding affinity for IK s channels. However, we found a strong correlation between the positions of the double bonds relative to the head group and effects on IK s channels.ConclusionPolyunsaturated fatty acids with double bonds closer to the head group had higher apparent affinity for IK s channels and increased IK s current more; shifting the bonds further away from the head group reduced apparent binding affinity for and effects on the IK s current. Interestingly, we found that ω‐6 and ω‐9 PUFAs, with the first double bond closer to the head group, left‐shifted the voltage dependence of activation the most. These results allow for informed design of new therapeutics targeting IK s channels in Long QT Syndrome.

Solvent, structural, quantum chemical study and antioxidative activity of symmetrical 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides

15 symmetric 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides were synthesized in this work. Their structures were characterized using IR, 1H and 13C NMR, and UV–Vis spectroscopy. DFT calculations indicated that s-trans/s-trans conformation prevail in all compounds. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear solvation-free energy relationships (LSER), i.e., Kamlet–Taft and Catalan models. A linear free energy relationship (LFER) in the form of single substituent parameter equations (SSP) was used to postulate quantitative structure–property relations of substituent effect on NMR data. TD-DFT results showed dependence of electronic transition on the substituent effects. The push–pull character of these compounds was analyzed by differences in 13C chemical shift of the ethylenic double bond in 2- and 6-positions of cross-conjugated with pyridinum central ring. Also, the quotient of the occupations for the bonding π and anti-bonding π* orbitals of this bond was considered. Good correlations of the selected parameter between double bond lengths with π*/π and 13C chemical shift differences of the bridging group proved them to be adequate descriptor of push–pull character. Synthesized compounds were screened for the antioxidant activity, using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical methods, and results demonstrated moderate antioxidant potential.

Mechanism of Long-Chain Free Fatty Acid Protonation at the Membrane-Water Interface

Long-chain free fatty acids (FFAs) play an important role in several physiological and pathological processes such as lipid fusion, adjustments of membrane permeability and fluidity, and the regulation of enzyme and protein activities. FFA-facilitated membrane proton transport (flip-flop) and FFA-dependent proton transport by membrane proteins (e.g., mitochondrial uncoupling proteins) are governed by the difference between FFA’s intrinsic pKa value and the pH in the immediate membrane vicinity. Thus far, a quantitative understanding of the process has been hampered, because the pKa value shifts upon moving the FFA from the aqueous solution into the membrane. For the same FFA, pKa values between 5 and 10.5 were reported. Here, we systematically evaluated the dependence of pKa values on chain length and number of double bonds by measuring the ζ-potential of liposomes reconstituted with FFA at different pH values. The experimentally obtained intrinsic pKa values (6.25, 6.93, and 7.28 for DOPC membranes) increased with FFA chain length (C16, C18, and C20), indicating that the hydrophobic energy of transfer into the bilayer is an important pKa determinant. The observed pKa decrease in DOPC with increasing number of FFA double bonds (7.28, 6.49, 6.16, and 6.13 for C20:0, C20:1, C20:2, and C20:4, respectively) is in line with a decrease in transfer energy. Molecular dynamic simulations revealed that the ionized carboxylic group of the FFAs occupied a fixed position in the bilayer independent of chain length, underlining the importance of Born energy. We conclude that pKa is determined by the interplay between the energetic costs for 1) burying the charged moiety into the lipid bilayer and 2) transferring the hydrophobic protonated FFA into the bilayer.

Neutral noble gas compound with a xenon-metal double bond: A theoretical study of F2XeWF2

The noble gas compound containing a double bond of xenon and transition metal atoms (i.e. F2XeWF2) is predicted by using quantum-chemical calculations. At the MP2 level of theory, the predicted XeW bond length of 2.45 Å is comparable to the corresponding standard double bond length of 2.55 Å (i.e. the sum of double bond radii of Xe and W atoms). Natural bond orbital analysis indicates that the XeW double bond consists of a σ-bond and a π-bond, which is also supported by Atoms in Molecules (AIM) analysis.

IR spectroscopy as a source of data on bond strengths

The aim of this work is the estimation of double bond strength, namely CO bonds in ketones and aldehydes and CC bonds in various compounds. By the breaking of these bonds one or both fragments formed are carbenes, for which experimental data on the enthalpies of formation (ΔHf298) are scarce. Thus for the estimation of ΔHf298 of the corresponding carbenes, the empirical equations were proposed based on different approximations. In addition, a quantum chemical calculations of the ΔHf298 values of carbenes were performed, and the data obtained were compared with experimental values and the results of earlier calculations.Equations for the calculation of CO bond strengths of different ketones and aldehydes from the corresponding stretching frequencies ν(CO) were derived. Using the proposed equations, the strengths of CO bonds of 25 ketones and 12 conjugated aldehydes, as well as CC bonds of 13 hydrocarbons and 7 conjugated aldehydes were estimated for the first time. Linear correlations of CC and CO bond strengths with the bond lengths were established, and the equations permitting the estimation of the double bond strengths and lengths with acceptable accuracy were obtained. Also, the strength of central CC bond of stilbene was calculated for the first time. The uncertainty of the strengths of double bonds obtained may be regarded as accurate ±10–15 kJ/mol.

The 3-hydroxyacyl-CoA dehydratases HACD1 and HACD2 exhibit functional redundancy and are active in a wide range of fatty acid elongation pathways

Differences among fatty acids (FAs) in chain length and number of double bonds create lipid diversity. FA elongation proceeds via a four-step reaction cycle, in which the 3-hydroxyacyl-CoA dehydratases (HACDs) HACD1-4 catalyze the third step. However, the contribution of each HACD to 3-hydroxyacyl-CoA dehydratase activity in certain tissues or in different FA elongation pathways remains unclear. HACD1 is specifically expressed in muscles and is a myopathy-causative gene. Here, we generated Hacd1 KO mice and observed that these mice had reduced body and skeletal muscle weights. In skeletal muscle, HACD1 mRNA expression was by far the highest among the HACDs However, we observed only an ∼40% reduction in HACD activity and no changes in membrane lipid composition in Hacd1-KO skeletal muscle, suggesting that some HACD activities are redundant. Moreover, when expressed in yeast, both HACD1 and HACD2 participated in saturated and monounsaturated FA elongation pathways. Disruption of HACD2 in the haploid human cell line HAP1 significantly reduced FA elongation activities toward both saturated and unsaturated FAs, and HACD1 HACD2 double disruption resulted in a further reduction. Overexpressed HACD3 exhibited weak activity in saturated and monounsaturated FA elongation pathways, and no activity was detected for HACD4. We therefore conclude that HACD1 and HACD2 exhibit redundant activities in a wide range of FA elongation pathways, including those for saturated to polyunsaturated FAs, with HACD2 being the major 3-hydroxyacyl-CoA dehydratase. Our findings are important for furthering the understanding of the molecular mechanisms in FA elongation and diversity.

Computational modeling of strained alkenes: Choosing the right computational model

AbstractThe applicability of 12 different quantum chemical calculation methods, including density functional theory (DFT) and ab initio methods, for describing strained alkenes and modeling their gas‐phase basicities (GB), hydrogenation enthalpies, and double bond geometries was studied for a series of systematically defined compounds R1R2C = CR3R4. The calculated values were compared to experimental data that had been compiled from literature for several compounds within the series. The closest relationship between the computational results and experimental data occurred with the G2MP2 ab initio method. The best DFT method for GB values was M062X and for hydrogenation enthalpies PBEPBE. At the same time, the relative effects of compound structure variations on the calculated values were similar among all 12 of the calculation methods tested. The double bond length was relatively insensitive to the sizes of the R substituents in R1R2C = CR3R4, but the torsion angles changed significantly in response to structural changes to the compounds when none of the groups R1–R4 was hydrogen.

Stability and in vitro release behaviour of encapsulated omega fatty acid-rich oils in lentil protein isolate-based microcapsules

The objective of this study was to investigate the use of a lentil protein isolate-based microcapsule design as a platform for entrapping different types of omega fatty acid-rich oil (e.g. canola, fish and flaxseed oils) and to characterise differences in the physical properties (e.g. moisture content, water activity, colour, wettability, particle size, surface oil and entrapment efficiency), storage stability and in vitro release behaviour of the entrapped oils. All microcapsules displayed similar physical properties regardless of the core material. Free fatty acid content, peroxide value, 2-thiobarbituric acid reactive substances and accelerated oxidation test were investigated between the free and encapsulated oils to determine protective effects from microencapsulation and found the wall material provided the greatest protective effect to the fish oils relative to the others. Based on an in vitro release assay, it was proposed that different intrinsic properties of fatty acids (e.g. polarity, conformation, chain length and number of double bonds) led to different release properties under simulated conditions. For instance, more encapsulated canola oil (∼8.9%) was released within simulated gastric fluid, whereas more encapsulated fish oil (∼73.4%) was released within simulated gastrointestinal fluids. Overall, the capsule design used in this study could be potentially used as a universal platform to deliver more healthy oils.

Development and application of sub-2-μm particle CO2 -based chromatography coupled to mass spectrometry for comprehensive analysis of lipids in cottonseed extracts.

Refined cottonseed oil has widespread applications in the food and chemical industries. Although the major lipids comprising cottonseed oil (triacylglycerols) are well known, there are many diverse lipid species in cotton seeds that occur at much lower levels and have important nutritional or anti-nutritional properties. The lipid technical samples were prepared in chloroform. The biological samples were extracted using a mixture of isopropanol/chloroform/H2 O (2:1:0.45). The data were collected using high and low collision energy with simultaneous data collection on a time-of-flight (TOF) mass spectrometer which allowed the characterization of lipids by precursor and product ion alignment. The supercritical fluid chromatography methodology is flexible and can be altered to provide greater retention and separation. The comprehensive method was used to screen seed lipid extracts from several cotton genotypes using multivariate statistical analysis. Method variables influencing the peak integrity and chromatographic separation for a mixture of lipids with different degrees of polarity were explored. The experiments were designed to understand the chromatographic behavior of lipids in a controlled setting using a variety of lipid extracts. Influences of acyl chain length and numbers of double bonds were investigated using single moiety standards. The methodology parameters were examined using single moiety lipid standards and standard mixtures. The method conditions were applied to biological lipid extracts, and adjustments were investigated to manipulate the chromatography. Insights from these method variable manipulations will help to frame the development of targeted lipid profiling and screening protocols. Copyright © 2017 John Wiley & Sons, Ltd.

Protonation of Long Chain Fatty Acids at the Membrane-Water Interface

Long-chain free fatty acids (FA) play an important role in several physiological and pathological processes such as lipid fusion, alteration of membrane permeability and fluidity, as well as regulation of enzyme and protein activity. FA-facilitated membrane proton transport (flip-flop) and FA-dependent proteinaceous proton transport (as in the case of mitochondrial uncoupling proteins) are governed by the difference between FA's pK and the pH in the immediate membrane vicinity1,2. So far, a quantitative understanding of the process is hampered by the shift in the pK value of carboxylic groups that occurs upon moving the FA from the aqueous solutions into the membrane. Its molecular origin is not understood, conceivably because the reported pKa values for the same FA are scattered between 5 and 10.5. Here we systematically obtained the dependence of apparent pKa values on chain length, number and position of double bonds by measuring the zeta-potential of liposomes reconstituted with FA at different pH. pKa ranged from 6.4 to 7.6. Combining the zeta potential measurements with molecular dynamic simulations, we found that pK is determined by the interplay between the energetic costs for burying a charged moiety into the bilayer and the hydrophobic interactions between the free and lipid-bound fatty acid chains.1. Pohl, E. E., Voltchenko, A. M. & Rupprecht, A. Flip-flop of hydroxy fatty acids across the membrane as monitored by proton-sensitive microelectrodes. Biochim.Biophys.Acta 1778, 1292-1297 (2008).2. Rupprecht, A. et al. Role of the transmembrane potential in the membrane proton leak. Biophys.J. 98, 1503-1511 (2010).

New insights into the photochemistry of carotenoid spheroidenone in light-harvesting complex 2 from the purple bacterium Rhodobacter sphaeroides

Light-harvesting complex 2 (LH2) from the semi-aerobically grown purple phototrophic bacterium Rhodobacter sphaeroides was studied using optical (static and time-resolved) and resonance Raman spectroscopies. This antenna complex comprises bacteriochlorophyll (BChl) a and the carotenoid spheroidenone, a ketolated derivative of spheroidene. The results indicate that the spheroidenone-LH2 complex contains two spectral forms of the carotenoid: (1) a minor, “blue” form with an S2 (11Bu+) spectral origin band at 522 nm, shifted from the position in organic media simply by the high polarizability of the binding site, and (2) the major, “red” form with the origin band at 562 nm that is associated with a pool of pigments that more strongly interact with protein residues, most likely via hydrogen bonding. Application of targeted modeling of excited-state decay pathways after carotenoid excitation suggests that the high (92%) carotenoid-to-BChl energy transfer efficiency in this LH2 system, relative to LH2 complexes binding carotenoids with comparable double-bond conjugation lengths, derives mainly from resonance energy transfer from spheroidenone S2 (11Bu+) state to BChl a via the Qx state of the latter, accounting for 60% of the total transfer. The elevated S2 (11Bu+) → Qx transfer efficiency is apparently associated with substantially decreased energy gap (increased spectral overlap) between the virtual S2 (11Bu+) → S0 (11Ag−) carotenoid emission and Qx absorption of BChl a. This reduced energetic gap is the ultimate consequence of strong carotenoid–protein interactions, including the inferred hydrogen bonding.

Infrared Spectra and Density Functional Calculations for Singlet CH2═SiX2 and Triplet HC-SiX3 and XC-SiX3 Intermediates in Reactions of Laser-Ablated Silicon Atoms with Di-, Tri-, and Tetrahalomethanes.

Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC-SiX3 and XC-SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C-Si bond in the silene is a true double bond, the C-Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si-X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C-Si bond lengths in these carbenes (1.782 Å for HC-SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 Å for CHF2-SiF) and the double-bond length in the silene (1.704 Å for CHF═SiF2). The silicon s(2)p(2) and titanium s(2)d(2) electron configurations produce similar primary products, but the methylidyne with Ti has a bond to carbon stronger than that of the halosilyl carbene.

Poly(diol fumarates); A new class of tunable antimicrobial polymers

Event Abstract Back to Event Poly(diol fumarates); A new class of tunable antimicrobial polymers Alexander M. Tatara1, Emma Watson1*, Tejus Satish1, Dimitrios P. Kontoyiannis2* and Antonios G. Mikos1* 1 Rice University, Bioengineering, United States 2 University of Texas MD Anderson Cancer Center, Infectious Diseases, United States Introduction: Due to the tremendous healthcare burden of device-related infections, novel biomaterials and strategies for prevention of pathogenic device colonization are warranted. There is in vitro and clinical evidence that diols, or carbon chains featuring two alcohol groups, have inherent antimicrobial properties[1],[2]. These molecules have been demonstrated to have a broad spectrum of efficiency, including inhibition of both bacterial and fungal pathogens[2]. This antimicrobial effect can be modulated by the length of the diol carbon chain[1]. Therefore, we have designed a novel class of diol-based, unsaturated, aliphatic polyesters that biodegrade into monomers capable of mitigating infection (Fig. 1). This new class of polymers, the poly(diol fumarates) (PDFs), can be crosslinked to form networks of scaffolds with antimicrobial degradation products. Both the diol carbon length as well as degree of available double bonds are tunable, resulting in a highly controllable class of antimicrobial polymers. In this work, we first investigated the effects of diol carbon length on synthesis and polymer physicochemical properties. We next measured the effects of double bond density on PDF physicochemical properties. Lastly, PDFs were crosslinked into a network structure to create scaffolds that were evaluated for swelling and mechanical properties as a function of diol length and crosslinking density. Materials and Methods: PDFs were synthesized by a condensation reaction between equimolar concentrations of diol (hexanediol, octanediol, or decanediol) and dicarboxylic acid (fumaric acid and/or succinic acid). A multifactorial design approach was taken to create 15 unique formulations of PDF (Table 1). The resulting polymers were characterized, based on altering diol carbon length and amount of double bonds, via proton-nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry, and rheology to confirm synthesis, measure chain length, characterize transition temperatures, and evaluate polymer viscosities, respectively. Scaffolds of crosslinked PDF networks were fabricated by mixing the polymers with crosslinker (n-vinyl-2-pyrrolidinone, 1:1 mass ratio) and photoinitiator (Irgacure 819, 0.3 wt%)[3]. The effects of different diols and availability of double bonds on the resulting Fourier Transform Infrared spectra, swelling ratios, and compressive properties of these networks were measured as previously described[3]. For compressive testing, a mixture of PDF, crosslinker, and photoiniator was poured into cylindrical molds (3 mm in diameter, 6 mm in height), exposed to blue light for 160 seconds to initiate crosslinking, and then compressed at a crosshead speed of 1 mm/min[3]. Results and Discussion: The PDFs were successfully synthesized from a variety of diols with different densities of double bonds, dependent on the ratio of fumaric acid to succinic acid. Analysis is ongoing, but preliminary data indicate significant differences in physicochemical properties of polymers and networks formed by PDFs (Fig. 2). Conclusion: PDFs are a new class of biodegradable unsaturated aliphatic polyesters. Different PDFs can be synthesized with a variety of diols and tunable physicochemical properties. Due to its flexibility, this new class of polymers has potential for a variety of anti-infection applications. Barrow Scholars Program; Armed Forces Institute of Regenerative Medicine II (Award No. W81XWH-14-2-0004); John S. Dunn Foundation; Baylor College of Medicine Medical Scientist Training Program (NIH T32 GM007330); Frances King Black Endowment for Cancer Research

Preparation and crystal structure of U3Fe2C5: An original uranium–iron carbide

The U3Fe2C5 compound was prepared from the elements by arc-melting, followed by an heat-treatment in an induction furnace, at 1250°C for 1h and 1300°C for 2h. The crystal structure of this phase was determined by direct methods from single crystal X-ray diffraction data. U3Fe2C5 crystallizes in an original tetragonal crystal structure, with space group I4/mmm, a=3.4980(3)Å and c=19.8380(15)Å as lattice constants and two formula units per cell. This new type structure is characterized by the simultaneous presence of isolated and pairs of carbon atoms, the interatomic distances in the pairs being similar to a typical carbon–carbon double bond length found in a molecule. U3Fe2C5 is closely related to UC and UFeC2, and can be seen as build from two (distorted) UFeC2 unit cells and a UC layer.

Functional characteristics of spirilloxanthin and keto-bearing Analogues in light-harvesting LH2 complexes from Rhodobacter sphaeroides with a genetically modified carotenoid synthesis pathway

Light-harvesting 2 (LH2) complexes from a genetically modified strain of the purple photosynthetic bacterium Rhodobacter (Rba.) sphaeroides were studied using static and ultrafast optical methods and resonance Raman spectroscopy. Carotenoid synthesis in the Rba. sphaeroides strain was engineered to redirect carotenoid production away from spheroidene into the spirilloxanthin synthesis pathway. The strain assembles LH2 antennas with substantial amounts of spirilloxanthin (total double-bond conjugation length N=13) if grown anaerobically and of keto-bearing long-chain analogs [2-ketoanhydrorhodovibrin (N=13), 2-ketospirilloxanthin (N=14) and 2,2′-diketospirilloxanthin (N=15)] if grown semi-aerobically (with ratios that depend on growth conditions). We present the photophysical, electronic, and vibrational properties of these carotenoids, both isolated in organic media and assembled within LH2 complexes. Measurements of excited-state energy transfer to the array of excitonically coupled bacteriochlorophyll a molecules (B850) show that the mean lifetime of the first singlet excited state (S1) of the long-chain (N≥13) carotenoids does not change appreciably between organic media and the protein environment. In each case, the S1 state appears to lie lower in energy than that of B850. The energy-transfer yield is ~0.4 in LH2 (from the strain grown aerobically or semi-aerobically), which is less than half that achieved for LH2 that contains short-chain (N≤11) analogues. Collectively, the results suggest that the S1 excited state of the long-chain (N≥13) carotenoids participates little if at all in carotenoid-to-BChl a energy transfer, which occurs predominantly via the carotenoid S2 excited state in these antennas.

Enhanced oleate uptake and lipotoxicity associated with laurate

Free fatty acids have been reported to induce cell death (lipotoxicity), but the effects depend on the carbon chain length and number of double bonds. Medium-chain saturated fatty acids (MC-SFAs), such as laurate, have less lipotoxicity than long-chain saturated fatty acids (LC-SFAs), such as palmitate. Monounsaturated fatty acids, such as oleate, have also been reported not only to exert cytotoxic effects, but also to reduce the lipotoxicity of LC-SFA. However the interaction between MC-SFA and oleate with respect to cell death is unclear. In this report, we found that lipotoxicity was enhanced by a combination of laurate and oleate relative to either fatty acid alone. The possible mechanisms involved were examined by measuring the production of reactive oxygen species, mitochondrial depolarization, caspase-3 activity, and lipid droplet formation. Although the stress signals and cell death pathways were distinct among different cell types, we found a common phenomenon of enhanced lipid droplet formation in all cells tested. Using fluorescent- or radioisotope-labeled fatty acids, we found that oleate, but not laurate, increased the uptake of fluorescent-labeled fatty acids, and the combinatory effect was more efficient than with oleate alone. We also found that laurate increased oleate uptake, but the effect of oleate on laurate uptake varied among cell types. These results suggest that laurate enhances the influx rate of oleate, the increased intracellular concentration of which not only enhances lipid storage, but also induces cell death by lipotoxic stress responses, which vary according to cell type.