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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Manganese Mediated Formic Acid Dehydrogenation

A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand tBu PNNOP ( tBu PNNOP=2,6–(di– tert –butylphosphinito)(di– tert –butylphosphinamine)pyridine) (1) and the catalyst is readily prepared with MnBrCO 5 to form [( tBu PNNOP)Mn(CO) 2 ][Br] (2). Dehydrohalogenation of 2 generated the neutral five coordinate complex ( tBu PNNOP)Mn(CO) 2 (3). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h –1 , rivaling many noble metal systems. The parent chelate, tBu PONOP ( tBu PONOP=2,6–bis(di– tert –butylphosphinito)pyridine) or tBu PNNNP ( tBu PNNNP=2,6–bis (di– tert –butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [( tBu PONOP)Mn(CO) 2 ][Br] (4) and [( tBu PNNNP)Mn(CO) 2 ][Br] (5). In conclusion, FA dehydrogenation with the hybrid–ligand supported 2 exhibits superior catalysis to 4 and 5.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Catalytic Transformation of Positional Nitrophenol Isomers on Highly Active Ag/Linde‐Type A4 Zeolite: A Comparative Analysis

Abstract The catalytic transformation of ortho‐( o‐ NP), meta‐( m‐ NP) and para‐nitrophenols ( p‐ NP) by Ag nanoparticles (Ag‐NPs) stabilised on zeolite A4 (ZA4) is presented for the first time. The catalysts are prepared by microwave‐assisted synthesis (Ag/ZA4‐MW) or ion exchange (Ag/ZA4‐IE). The results indicate that the nitrophenol reduction rate depends on the molecule structure and the presence of low‐coordinated metallic Ag‐NPs (∼2 nm and sub nanometric species). Meanwhile, the reactivity tendency depends on the synthesis methodology ( m‐ NP> p‐ NP> o‐ NP and o‐ NP> m‐ NP> p‐ NP for Ag/ZA4‐MW and Ag/ZA4‐IE, respectively). The turnover frequency (TOF) values estimated for nitrophenols reduction are superior for Ag/ZA4‐MW catalyst by several orders of magnitude compared with those obtained for Ag/ZA4‐IE catalyst. In addition, the catalyst exhibits remarkable catalytic stability for the reduction of p‐ NP even after the fifth consecutive catalytic run. The presently prepared catalysts are characterised by superior catalytic activity for the reduction of nitroaromatic compounds than similar Ag‐based materials reported in the literature.

Horta‐Fraijo, Patricia↗
DOE OSTI2021

Photochemical CO 2 Reduction Using Rhenium(I) Tricarbonyl Complexes with Bipyridyl-Type Ligands with and without Second Coordination Sphere Effects

In this study, the effect of phenyl, phenol, aniline, amino, and CF 3 substituents of the 2,2'-bipyridine ligand in fac-ReCl(L)(CO) 3 (L=2,2'-bipyridine derivative) catalysts on photochemical CO 2 reduction in dimethylacetamide is examined, in order to understand the structure-function relationships and to compare the catalytic activities with the previously published electrochemical results. All complexes including ReCl(bpy)(CO) 3 have similar excited-state lifetimes and emission spectra, but complex 1 with the Ph-NH 2 moiety exhibits a significantly larger molar absorption coefficient for its metal-to-ligand charge transfer (MLCT) band. All complexes we tested produce CO with only a negligible amount of H 2 and formate in self-sensitized systems in the presence of triethanolamine (TEOA) and in some cases, BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole). The presence of the Ph-NH 2 moiety (complex 1) has a beneficial effect on both electrochemical and photochemical activity, allowing a turnover number (TON) of 32 and 120 for photochemical CO production (without and with BIH, respectively). In the case of the Ph-OH group in the second coordination sphere (complexes 4 and 6), these complexes are active for photochemical CO 2 reduction, despite the formation of a stable 6-coordinate Re-OPh intermediate via reductive deprotonation as previously observed under electrochemical conditions. Overall, BIH accelerates the rate of formation of the one-electron reduced species (OERS) of the Re catalysts and allows higher turnover frequency (TOF) and TON for CO formation. The X-ray structures of complexes 1 and 4 were determined to have distorted octahedral Re centres, and show π-π stacking interactions with neighboring molecules as well as intramolecular hydrogen bonds to the internal chloride ligands. The unusually high absorptivity of the MLCT absorption of complex 1 has been explained by TD-DFT calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Non-Oxidative Dehydrogenation Pathways for the Conversion of C 2 -C 4 Alcohols to Carbonyl Compounds

Gold nanoparticles (NPs) supported on hydrotalcite (Au/HT) are highly active and selective catalysts for the continuous, gas-phase, non-oxidative dehydrogenation of bioderived C 2 -C 4 alcohols. Here, a sharp increase in turn over frequency (TOF) is noted when the size of Au NPs is less than 5 nm relating to the strong synergy between metallic Au NPs and the acid-base groups on the support surface. It is demonstrated that catalytic activity depends critically on Au NP size, support composition, and support pretreatments. A reaction pathway elucidated from kinetic isotope effects suggests that the abstraction of β-H by Au NPs (C-H activation) is the rate-determining step in the dehydrogenation of bioderived C 2 -C 4 alcohols.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Electrochemical Water Oxidation by a Catalyst-Modified Metal-Organic Framework Thin Film

Water oxidation, a key component in artificial photosynthesis, requires high overpotentials and exhibits slow reaction kinetics that necessitates the use of stable and efficient heterogeneous water-oxidation catalysts (WOCs). Here, we report the synthesis of UiO-67 metal–organic framework (MOF) thin films doped with [Ru(tpy)(dcbpy)OH2]2+ (tpy=2,2':6',2''-terpyridine, dcbpy=5,5'-dicarboxy-2,2'-bipyridine) on conducting surfaces and their propensity for electrochemical water oxidation. The electrocatalyst oxidized water with a turnover frequency (TOF) of (0.2±0.1) s-1 at 1.71 V versus the normal hydrogen electrode (NHE) in buffered solution (pH~7) and exhibited structural and electrochemical stability. The electroactive sites were distributed throughout the MOF thin film on the basis of scan-ratedependent voltammetry studies. This work demonstrates a promising way to immobilize large concentrations of electroactive WOCs into a highly robust MOF scaffold and paves the way for future photoelectrochemical water-splitting systems.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Iridium Complexes with Proton-Responsive Azole-Type Ligands as Effective Catalysts for CO 2 Hydrogenation

Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity towards CO 2 hydrogenation in 2.0 M KHCO 3 aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO 2 /H 2 (1:1) have been reported as an alternative to photo- and electrochemical CO 2 reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4 and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generating pendent-bases in basic media, recorded high initial TOF values of 1300 h -1 , 1550 h -1 and 2000 h -1 , respectively. Here, spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in the high catalytic performance in basic media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

N,N,O Pincer Ligand with a Deprotonatable Site That Promotes Redox-Leveling, High Mn Oxidation States, and a Mn 2 O 2 Dimer Competent for Catalytic Oxygen Evolution

The new complex [Mn(bipyalk)(H 2 O)(µ-O)] 2 (OTf) 2 {bipyalk = 2-([2,2'-bipyridin]-6-yl)propan-2-olate} catalyzes oxygen evolution with a TOF of 0.0055 s –1 when driven by the sacrificial oxidant KHSO 5 in water. It is proposed on the basis of EPR experiments that the catalyst proceeds through a Mn V (µ-O) 2 Mn V =O intermediate supported by the highly donating tertiary alkoxide moiety of the ligand. The Mn(IV,IV) dimer can also be formed electrochemically from its precursor, Mn(bipyalkH)Cl 2 . A related series of bis-ligated monomers of the type [Mn n (bipyalkH x )(bipyalkH y )](PF 6 ) 2 is also reported, where the dication features Mn II , Mn III , and Mn IV oxidation states and corresponding protonation states. Electrochemical data on this series underscore the importance of proton loss at the alcohol/alkoxide moiety during oxidation to maintain low overpotentials required for catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis, Characterization, and HER Activity of Pendant Diamine Derivatives of NiATSM

A pair of bis-thiosemicarbazonato-Ni(II) complexes with pendant polyamines, (N,N'-(dimethylethylenediaminothiosemi-carbazonato)-4-(methylthiosemi-carbazonato)butane-2,3-diimine)-nickel(II) (1) and (N,N'-bis(dimethylethyl-enediaminothiosemi-carbazonato)butane-2,3-diimine)-nickel(II) (3), have been synthesized. Methylation at the terminal amines yields the cationic derivatives 2 and 4. All complexes are fully characterized by spectroscopic, electrochemical, and single-crystal X-ray diffraction methods. Single crystal X-ray diffraction studies on all four Ni(II) complexes confirm a square planar Ni(II) framework with no significant changes in the coordination environment as a function of the pendant groups. Spectroscopic studies are consistent with a similar electronic structure in all complexes. However, electrochemical investigations reveal significant cathodic shifts in the Ni(II)L/Ni(II)L ·– and Ni(II)L ·– /Ni(I)L ·2– reduction potentials of the methylated vs. non-methylated species. The HER activity of all four nickel complexes were evaluated in acetonitrile with glacial acetic acid. The 3 complex was shown to have the highest activity with a TOF of 6.3 × 10 3 s -1 , an overpotential of 0.56 V, and faradaic efficiency of 100%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Comparative study on the novel umami‐active peptides of the whole soybeans and the defatted soybeans fermented soy sauce

Abstract BACKGROUND Two kinds of soy sauce produced via fermentation of the whole soybeans and the defatted soybeans (soy sauce termed ‘SSS’ and ‘SSD’, respectively) were subjected to the treatment using aqueous ethanol solutions with high concentrations. Then tasty peptides were separated from SSS and SSD by sensory guided fractionation, using macroporous resin and reverse‐phase high‐performance liquid chromatography (RP‐HPLC), and identified by ultra‐performance liquid chromatography quadrupole time‐of‐flight tandem mass spectrometry (UPLC‐Q‐TOF‐MS/MS). Results The result showed that umami‐active fractions and ≤ 3 kDa peptides were mainly concentrated in the supernatants resulted from the treatment with 60% ethanol and the precipitates resulted from the treatment with 80% ethanol. The contents of ammonia nitrogen, non‐salt solids, bitter amino acids, amino acids in peptides and the proportion of ≤ 3 kDa peptides in SSS were higher than those in SSD. Sixteen and fourteen tasty peptides were separated from SSS and SSD, among them five dipeptides (γ‐Glu‐Glu, Glu‐Glu, γ‐Glu‐Cys, γ‐Glu‐Leu, Glu‐Leu and Ile‐Glu) with a glutamic acid residue were identified both in SSS and SSD, which have been reported as umami/kokumi‐active peptides in soy sauce. Several peptides identified from SSS (Thr‐Gly‐Cys, Gly‐Leu‐Glu, Val‐Glu‐Ala‐Leu and Gly‐Gly‐Gly‐Glu) and SSD (Asp‐Arg, Asp‐Ala‐Glu, Glu‐Val‐Cys and Gly‐Gly‐Gly‐Glu) are tasty and/or umami‐active peptides but have not been reported as tasty peptides in the past. Conclusion Most of the peptides separated from SSD and SSS could impart an umami‐enhancing effect on soy sauce, and the marginally more kokumi and bitterness hydrophobic peptides were found in SSS than SSD. © 2020 Society of Chemical Industry

Zhu, Xiping↗
DOE OSTI2021

Oxidation of an iso-paraffinic alcohol-to-jet fuel and n-heptane mixture: an experimental and modelling study

Oxidation of ATJ/n-heptane blends was studied over a wide range of test conditions, using single pulse shock tubes. Test conditions were designed to study the effect of pressure (4 and 50 bar), and fuel loading (~100-1400 ppm) on the oxidation of the blends across a wide range of temperatures (800-1300 K). These effects were observed by measuring concentrations of intermediate species formed using in-line Gas Chromatography (GC) and GCxGC TOF-MS. Results showed that increasing the initial fuel load does not have a significant impact on the results. However, increasing the pressure shifts the mixture reactivity to a lower temperature by about 150 K and causes the fuel to be oxidized instead of decomposing pyrolytically as at lower pressures. Additional experiments for pure ATJ and pure n-heptane were performed at conditions matching the ATJ/n-heptane 50 bar experiments to analyze the differences between the pure and mixed fuels. Speciation measurements were compared against predictions from a detailed kinetic model. The ability of the kinetic model to capture the effects of varying experimental test conditions on the evolution of intermediate species is discussed and kinetic analyses have been conducted to identify the important reaction pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High-efficiency single-junction p-i-n GaAs solar cell on roll-to-roll epi-ready flexible metal foils for low-cost photovoltaics

We demonstrate the fabrication and characterization of high-efficiency, single-junction p-i-n GaAs solar cells, on flexible metal foil with epi-ready buffer via roll-to-roll fabrication. Single-junction p-i-n GaAs solar cells were fabricated using metal–organic chemical vapor deposition (MOCVD). Furthermore, an efficiency greater than 13% was obtained at 1 sun, which is the highest reported efficiency on GaAs photovoltaics directly deposited on metal tapes. This exceeds our previously reported study showcasing 11.5% efficiency on single-junction p-n solar cell structure. Improved morphology of p-i-n structure compared with p-n is explained by atomic force microscopy (AFM), scanning electron microscopy (SEM), and helium ion microscopy (HIM) measurements. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis showed reduced Zn diffusion in p-i-n cell compared with the p-n cell. We attribute the improvement in efficiency of p-i-n cells on flexible metal tapes to the quality of the junction, surface morphology, controlled diffusion of species within the active layers, and increase in absorption due to the optimized intrinsic layer thickness.

14 SOLAR ENERGY↗
DOE OSTI2012

Enhanced control of end-group composition in poly(3-hexylthiophene)s prepared by GRIM

The ability to prepare well-defined semiconducting polymers is essential for understanding the link between structure and function in organic photovoltaic devices. A general method for enhanced control of the degree of functionality of end-functionalized poly(3-hexylthiophene)s (P3HT) prepared by Grignard Metathesis (GRIM) polymerization has been developed. In the absence of additives, the degree of functionality of end-functional P3HTs prepared by quenching of the GRIM polymerization with a Grignard reagent is dependent on the Grignard reagent utilized. In this study, additives such as styrene and 1-pentene are shown to alter the end-group composition of tolyl-functionalized P3HTs as determined by MALDI-TOF MS. In particular, when quenching the GRIM polymerization with tolylmagnesium bromide a modest decrease in the difunctional product is observed, and the yield of the monofunctional product increases significantly. Temperature and lithium chloride (LiCl) addition also play impactful roles. Monofunctional P3HT is found to be the major product (65%) when the functionalization is done in the presence of LiCl and styrene at 0oC, whereas in the absence of additives the monofunctional product is present at only 20%.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Using C₆₀⁺ Sputtering to Improve Detection Limit of Nitrogen in Zinc Oxide

C₆₀⁺ sputtering was firstly used to determine depth profile of nitrogen in zinc oxide materials by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Compared to traditional Cs+ sputtering depth profiling, the C₆₀⁺ sputtering provides over 200 times of effective signal intensity and the detection limit is about 10 times better. In addition, our X-ray photoelectron spectroscopy (XPS) results show that sputtering zinc oxide materials by 10 keV C₆₀⁺ leads to very weak carbon deposition at bottom of the sputter crater.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Programmable Chemical Gradient Patterns by Soft Grayscale Lithography

A method for fabricating chemical gradients on planar and nonplanar substrates using grayscale lithography is reported. Compliant grayscale amplitude masks are fabricated using a vacuum-assisted microfluidic filling protocol that employs dilutions of a carbon-black-containing polydimethylsiloxane emulsion (bPDMS) within traditional clear PDMS (cPDMS) to create planar, fully self-supporting mask elements. The mask is then placed over a surface functionalized with a hydrophobic coumarin-based photocleavable monolayer, which exposes a polar group upon irradiation. The mask serves to modulate the intensity of incident UV light, thereby controlling the density of molecules cleaved. The resulting molecular-level grayscale patterns are characterized by condensation microscopy and imaging mode time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Due to the inherent flexibility of this technique, the photofuse as well as the gradient patterns can be designed for a wide range of applications; in this paper two proof-of-concept demonstrations are shown. The first utilizes the ability to control the resulting contact angle of the surface for the fabrication of a passive pressure-sensitive microfluidic gating system. The second is a model surface modification process that utilizes the functional groups deprotected during the photocleavage to pattern the deposition of moieties with complementary chemistry. The spatial layout, resolution, and concentration of these covalently linked molecules follow the gradient pattern created by the grayscale mask during exposure. Furthermore, the programmable chemical gradient fabrication scheme presented in this work allows explicit engineering of both surface properties that dictate nonspecific interactions (surface energy, charge, etc.) and functional chemistry necessary for covalent bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Covalent Triazine-Based Frameworks with Ru-tda Based Catalyst Anchored via Coordination Bond for Photoinduced Water Oxidation

Light-induced water splitting (hν-WS) for the production of hydrogen as a solar fuel is considered a promising sustainable strategy for the replacement of fossil fuels. An efficient system for hν-WS involves a photoactive material that, upon shining light, is capable of separating and transferring charges to catalysts for the hydrogen and oxygen evolution processes. Covalent triazine-based frameworks (CTFs) represent an interesting class of 2D organic light-absorbing materials that have recently emerged thanks to their tunable structural, optical and morphological properties. Typically, catalysts (Cat) are metallic nanoparticles generated in situ after photoelectroreduction of metal precursors or directly drop-casted on top of the CTF material to generate Cat-CTF assemblies. Here, in this work, the synthesis, characterization and photocatalytic performance of a novel hybrid material, Ru-CTF, is reported, based on a CTF structure featuring dangling pyridyl groups that allow the Ru-tda (tda is [2,2':6',2'“-terpyridine]-6,6'”-dicarboxylic acid) water oxidation catalyst (WOC) unit to coordinate via covalent bond. The Ru-CTF molecular hybrid material can carry out the light-induced water oxidation reaction efficiently at neutral pH, reaching values of maximum TOF of 17 h -1 and TONs in the range of 220 using sodium persulfate as a sacrificial electron acceptor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Noncovalent Immobilization of Pentamethylcyclopentadienyl Iridium Complexes on Ordered Mesoporous Carbon for Electrocatalytic Water Oxidation

The attachment of molecular catalysts to conductive supports for the preparation of solid-state anodes is important for the development of devices for electrocatalytic water oxidation. The preparation and characterization of three molecular cyclopentadienyl iridium(III) complexes, Cp*Ir(1-pyrenyl(2-pyridyl)ethanolate-κO,κN)Cl (1) (Cp* = pentamethylcyclopentadienyl), Cp*Ir(diphenyl(2-pyridyl)methanolate-κO,κN)Cl (2), and [Cp*Ir(4-(1-pyrenyl)-2,2'-bipyridine)Cl]Cl (3), as precursors for electrochemical water oxidation catalysts, are reported. These complexes contain aromatic groups that can be attached via noncovalent π-stacking to ordered mesoporous carbon (OMC). The resulting iridium-based OMC materials (Ir-1, Ir-2, and Ir-3) were tested for electrocatalytic water oxidation leading to turnover frequencies (TOFs) of 0.9–1.6 s -1 at an overpotential of 300 mV under acidic conditions. The stability of the materials is demonstrated by electrochemical cycling and X-ray absorption spectroscopy analysis before and after catalysis. Theoretical studies on the interactions between the molecular complexes and the OMC support provide insight onto the noncovalent binding and are in agreement with the experimental loadings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Impact of Salt Chemistry and Interlayer Architecture on Solid Electrolyte Interphase Composition and Performance

Reversible lithium metal anodes require interphases that are chemically stable, mechanically robust, and compatible with scalable processing. Here, we use slot-die-coated, salt-rich PEO interlayers to design SEI nanolayers on Cu current collectors and isolate how salt anion chemistry controls interphase composition and lithium plating/stripping behavior in architectures relevant to Li plating and anode-free cells. Mesoscale modeling shows that dendrite initiation at SEI defects is governed by a tradeoff among interphase thickness, ionic conductivity, and stiffness through defect-driven current focusing, motivating controlled formation from thin precursor layers. Using UHV-transferred XPS and ToF-SIMS depth profiling after controlled Li deposition, we find that fluorinated sulfonylimide salts (LiTFSI, LiFSI) form mixed inorganic/organic interphases containing LiF and PEO-derived alkoxides, with LiFSI producing a more LiF-dominant Li-facing surface than LiTFSI under identical conditions. In contrast, LiNO 3 -containing interlayers yield a comparatively thick nitrate-derived interphase that reduces upon Li contact to an N-rich inorganic layer (Li–N/N 3− , LiN x O y ). In Cu| |Li cells, these designed interlayers reduce interfacial resistance and improve Coulombic efficiency (CE) and critical current density (CCD) relative to uncoated controls, with LiFSI- and LiNO 3 -based interlayers providing the highest CE/CCD. Overall, the results demonstrate a manufacturing-relevant approach to engineer SEI nanolayers by salt chemistry, providing pathways to improve reversible lithium metal anodes while reducing reliance on LiTFSI.

anion chemistry↗
DOE OSTI2019

Linum Lignan and Associated Biochemical Pathways in Human Health and Plant Defense

This chapter primarily addresses formation of the plant-protecting and human health-protecting lignans found in flax seed coat tissue. Yet, the fundamentals of how plants in general biochemically produce their protective seed coats (protecting the embryo until germination) is very poorly understood at the molecular level, in spite of its massive evolutionary importance. Flax is no exception. Herein, we address the natural product molecular species produced from the “mixed” biochemical pathways to both the flax seed lignans and other metabolite classes associated with same, as well as what is known about their localization in situ and their biosynthesis (proteins and enzymes involved). The biosynthetic pathway known to this point to the plant defense lignans in leaf and stem tissue is also discussed. Discovery of the biochemical steps leading to flax seed coat lignan biosynthesis, with a particular emphasis on the genes, dirigent proteins (DPs), downstream pinoresinol lariciresinol reductases, and secoisolariciresinol dehydrogenase, is described. Advances made thus far from X-ray structural biology investigations, as well as MALDI TOF MS/MS and Ion Mobility metabolite imaging, of these biochemical processes to the lignan components in situ are also summarized. While the predominant health-protecting flax seed coat lignans are secoisolariciresinol glucoside (SDG) derived, they are essentially not present as such in this tissue. Instead, SDG exists in covalently linked form to other “mixed” biochemical pathway metabolites, of which there are currently 8 other distinct natural product entities known to be involved. The biosynthesis of other components, such as herbacetin diglucoside and hydroxymethyl glutaric acid, is also briefly discussed. What is known about the macromolecular structure of these lignan-containing mixed biochemical pathway metabolites to date during seed coat maturation is briefly summarized. Flaxseed, however, also contains other lignans, such as pinoresinol, isolariciresinol and matairesinol, albeit in tiny amount, which are released on alkali (base) treatment of flax seed or preparations thereof. The lignan yatein which, by comparison, accumulates in flax leaf and stem tissue appears to be involved in plant defense. What is known about its biochemical pathway and function is summarized. Interestingly, flax DPs are encoded by a 44-membered multi-gene family, of which only a few are of known biochemical/physiological function. Future research is urgently needed to ascertain the in vivo functions of this DP family, including probing the evolutionary ramifications of same and their relevance to successful evolutionary transition of aquatic plants to terrestrial vascular plant form.

dirigent proteins, lignin, Linum, flax, structure ↗