Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “solvent reduction”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Electrochemical stability of LiMF6 (M = P, As, Sb) in tetrahydrofuran and sulfolane

The electrochemical stability of LiSbF6 and LiPF6 in aprotic organic solvents has been investigated. Electrochemical studies, conductivity measurements, and open-circuit stability tests were conducted on LiSbF6 in tetrahydrofuran and sulfolane. Cyclic voltammetric studies of SbF6(-) were compared with those of AsF6(-) and PF6(-) anions. Sb(V) was reduced to Sb(III), and then to Sb(0). AsF6(-) was reduced to AsF3, while no reduction of PF6(-) was observed. The reduction products of AsF6(-) and SbF6(-) passivated the glassy carbon electrode, presumably due to LiF precipitation. Peak potentials were observed to shift in the positive direction as a function of concentration. This was accounted for on the basis of a follow-up chemical reaction.

Nanjundiah, C.↗
DOE OSTI2021

Principle in developing novel fluorinated sulfone electrolyte for high voltage lithium-ion batteries

A new class of fluorinated sulfones, β-fluorinated sulfones, were designed and synthesized as electrolyte solvents for high voltage lithium-ion batteries. While the oxidation potential of β-fluorinated sulfones is slightly lower than that of α-fluorinated sulfones, it is still significantly higher than the oxidation potential of regular sulfones, which already possess fairly high anodic stability. However, β-fluorinated sulfones exhibit a significant decrease in reduction potential compared to α-fluorinated sulfones, rendering them more stable towards graphite anodes. Moreover, the reduced lithium solvating power of β-fluorinated sulfones compared to regular sulfones mitigates the transition metal dissolution of cathodes. Taken together, these middle ground properties of β-fluorinated sulfone-based electrolytes enable the very stable long-term cycling of graphite||LiNi 0.6 Co 0.2 Mn 0.2 O 2 full cells. Finally, the outstanding performance of β-fluorinated sulfones designed by applying the “golden middle way” paves a new path for the development of an effective electrolyte system.

25 ENERGY STORAGE↗
NASA NTRS2003

Effects of Fiber Reinforcement Architecture on the Hygrothermal-Mechanical Performance of Polyimide Matrix Composites for Aeropropulsion Applications

A lightweight sandwich support structure, for the combustor chamber of a new generation liquid propellant rocket engine, was designed and fabricated using a polymer matrix composite (PMC) facesheet on a Ti honeycomb core. The PMC facesheet consisted of high stiffness carbon fiber, M40JB, and high temperature Polyimides, such as PMR-II-50 and HFPE-II-52. Six different fiber architectures; four harness satin (4HS) woven fabric, uni-tape, woven-uni hybrid, stitched woven fabric, stitched uni-tape and triaxial braided structures have been investigated for optimum stiffness-thickness-weight-hygrothermal performance design criteria for the hygrothermal-mechanical propulsion service exposure conditions including rapid heating up to 200 F/sec, maximum operating temperature of 600 F, internal pressure up to 100 psi. One of the specific objectives in this study is to improve composite blistering resistance in z-direction at minimum expense of in-plane mechanical properties. An extensive property-performance database including dry-wet mechanical properties at various temperatures, thermal-physical properties, such as blistering onset condition was generated for fiber architecture down-selection and design guidelines. Various optimized process methods such as vacuum bag compression molding, solvent assistant resin transfer molding (SaRTM), resin film infusion (RFI) and autoclaving were utilized for PMC panel fabrication depending on the architecture type. In the case of stitched woven fabric architecture, the stitch pattern in terms of stitch density and yarn size was optimized based on both in-plane mechanical properties and blistering performance. Potential reduction of the in-plane properties transverse to the line of stitching was also evaluated. Efforts have been made to correlate the experimental results with theoretical micro-mechanics predictions. Changes in deformation mechanism and failure sequences in terms of fiber architecture will be discussed.

Shin, E. Eugene↗
DOE OSTI2020

Ion-Conducting Thermoresponsive Films Based on Polymer-Grafted Cellulose Nanocrystals

Mechanically robust, thermo-responsive, ion-conducting nanocomposite films are prepared from poly(2-phenylethyl methacrylate) grafted cellulose nanocrystals (MxG-CNC-g-PPMA). One-component nanocomposite films of the polymer grafted nanoparticle (PGN) MxG-CNC-g-PPMA are imbibed with 30 wt% imidazolium-based ionic liquid, to produce flexible ion-conducting films. These films with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (MxG-CNC-g-PPMA/[H]) not only displays remarkable improvements in toughness (>25 times) and tensile strength (>70 times) relative to the corresponding nanocomposites consisting of the ionic liquid imbibed in the two component CNC/PPMA nanocomposite, but also shows higher ionic conductivity than the corresponding neat PPMA with the same wt.% of ionic liquid. Notably, the one-component film containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (MxG-CNC-g-PPMA/[E]) exhibits temperature responsive ionic conduction. The ionic conductivity decreases at around 60°C as a consequence of the lower critical solution temperature (LCST) phase transition of the grafted polymer in the ionic liquid, which leads to phase separation. Moreover, holding the MxG-CNC-g-PPMA/[E] film at room temperature for 24 hours returns the film to its original homogenous state. These materials exhibit properties relevant to thermal cutoff safety devices (e.g., thermal fuse) where a reduction in conductivity above a critical temperature is needed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Towards Understanding of Cracking during Drying of Thick Aqueous-Processed LiNi 0.8 Mn 0.1 Co 0.1 O 2 Cathodes

Replacing N-methyl-2-pyrrolidone (NMP) with water for processing of lithium-ion battery (LIB) electrodes has both cost and environmental benefits, which include reduced drying time, lower dryer capital cost, elimination of NMP recovery capital equipment, and no release of volatile organic compounds (VOCs) into the environment. However, aqueous-processed thick cathodes (≳4 mAh/cm 2 ) typically exhibit detrimental cracking during drying that is not observed for the NMP-based counterpart. The reasons for cracking of these water-based thick electrodes are still not well understood due to the complex nature of the colloidal dispersions used in the LIB electrode processing steps. In this work, the contributions of various factors responsible for cracking are discussed. We show that eliminating hydrogen evolution due to corrosion of the aluminum current collector eliminated the majority of the cracks regardless of the coating thickness, identifying the gas evolution as the primary reason for electrode cracking. Some secondary cracks and pinhole-type defects remained after addressing the aluminum current collector corrosion, which are thought to be caused by an inferior binding network formed by carbon black and binder in aqueous-processed cathodes compared to those processed with NMP. The thick aqueous processed cathodes are not able to sufficiently withstand the drying stresses without crack formation. We demonstrate reduction of these secondary defects by either improving the binding network or by reducing the drying stress. The former was achieved by replacing carbon black with vapor grown graphite tubes (VGGTs) that caused a more efficient utilization of the emulsion binder. Here, the latter was achieved by adding a small amount of IPA as a co-solvent that has been shown to reduce capillary stresses.

25 ENERGY STORAGE↗
DOE OSTI2026

Electrochemical Deconstruction of Ortho-Phthalate Plasticizers and Recovery of Plasticizing Moieties

Electrochemical methods for the direct reduction of alkyl esters have been understudied but provide a potential advantage for addressing specific waste streams given that such strategies often require only a minimal chemical profile. One such waste stream that could benefit from electrochemical remediation is poly(vinyl chloride) (PVC) plastics. PVC recycling often faces challenges due to the complexity of such waste. Solvent-based recycling methods pose several advantages for addressing post-use PVC; however, such methods are complicated by the high amounts of toxic legacy plasticizers (ortho-phthalates) present in PVC. A potential solution to addressing such phthalates is to address them electrochemically, coupled with recovery of the resulting valuable products. Presented herein is an optimized electrochemical method for ester activation that is leveraged to separate and recover the aromatic and alkyl components of ortho-phthalate plasticizers. The resulting aliphatic alcohols may be reused to prepare other non-toxic plasticizers. This electro-degradation method is demonstrated on six phthalates that have been identified to pose health concerns in addition to plasticizers recovered from commercial samples of PVC.

di-(2-ethylhexyl) phthalate↗
DOE OSTI2024

Rotating cylinder electrode in reactive CO 2 capture: Identifying active C species via transport, VLE models and kinetics

Here, this article explores technical challenges and potential methodologies for understanding electrochemical Reactive CO 2 Capture (RCC) mechanisms. RCC offers potential energy cost advantages by directly converting captured CO 2 into fuels and chemicals, unlike traditional carbon capture and utilization (CCU) processes that require sequential capture, concentration, and compression. However, direct conversion of captured CO 2 introduces complexity due to additional equilibrium buffer reactions, making it challenging to identify active species for reduction in electrochemical studies. This article discusses methods to integrate transport, thermodynamics, and kinetics concepts to identify active carbon sources in RCC. Vapor‐Liquid Equilibrium (VLE) and transport models are validated against experimental results obtained in a gastight rotating cylinder electrode reactor and are shown as useful tools for studying RCC in heterogeneous electrocatalysts across different capture agents, solvents, and temperatures. This article establishes an experimental framework for advancing research in electrochemical RCC.

Electrocatalysis↗
NASA NTRS2012

Aqueously Dispersed Silver Nanoparticle-Decorated Boron Nitride Nanosheets for Reusable, Thermal Oxidation-Resistant Surface Enhanced Raman Spectroscopy (SERS) Devices

The impurity-free aqueous dispersions of boron nitride nanosheets (BNNS) allowed the facile preparation of silver (Ag) nanoparticle-decorated BNNS by chemical reduction of an Ag salt with hydrazine in the presence of BNNS. The resultant Ag-BNNS nanohybrids remained dispersed in water, allowing convenient subsequent solution processing. By using substrate transfer techniques, Ag-BNNS nanohybrid thin film coatings on quartz substrates were prepared and evaluated as reusable surface enhanced Raman spectroscopy (SERS) sensors that were robust against repeated solvent washing. In addition, because of the unique thermal oxidation-resistant properties of the BNNS, the sensor devices may be readily recycled by short-duration high temperature air oxidation to remove residual analyte molecules in repeated runs. The limiting factor associated with the thermal oxidation recycling process was the Ostwald ripening effect of Ag nanostructures.

Lin, Yi↗
DOE OSTI2025

Differentiating Ligand Tailoring and Cation Incorporation as Strategies for Tuning Heterobimetallic Cerium Complexes

Tuning of redox-active complexes featuring metals with high coordination numbers by incorporation of secondary redox-inactive cations has received far less attention than it deserves. Here, appending moderate steric bulk to a tripodal ligand framework has been tested for its influence on secondary-cation-driven structural and electrochemical tuning of cerium, a lanthanide that tends to adopt high coordination numbers. A quasi -C 3 -symmetric cerium(III) complex denoted [Ce] has been prepared that features pendant benzyloxy groups, and this work demonstrates that this species offers a site capable of binding single Na + or Ca 2+ ions. Electrochemical and UV-visible spectroscopic studies reveal equilibrium binding affinity of [Ce] for Na + in acetonitrile solvent, contrasting with tight binding of all cations in all other previously studied systems of this type. The modulated cation binding can be attributed to the bulky benzyloxy groups, which impact the thermodynamics of cation binding but do not impede the formation of cerium centers with coordination number 8 upon binding of either Na + or Ca2 + . Finally, the Ce(IV/III) reduction potential was found to be tunable under the equilibrium binding conditions, highlighting the potentially significant role that controlled structural changes can play in modulating the solution properties of heterobimetallic complexes.

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

Insights into solvent and surface charge effects on Volmer step kinetics on Pt (111)

Abstract The mechanism of pH-dependent hydrogen oxidation and evolution kinetics is still a matter of significant debate. To make progress, we study the Volmer step kinetics on platinum (111) using classical molecular dynamics simulations with an embedded Anderson-Newns Hamiltonian for the redox process and constant potential electrodes. We investigate how negative electrode electrostatic potential affects Volmer step kinetics. We find that the redox solvent reorganization energy is insensitive to changes in interfacial field strength. The negatively charged surface attracts adsorbed H as well as H + , increasing hydrogen binding energy, but also trapping H + in the double layer. While more negative electrostatic potential in the double layer accelerates the oxidation charge transfer, it becomes difficult for the proton to move to the bulk. Conversely, reduction becomes more difficult because the transition state occurs farther from equilibrium solvation polarization. Our results help to clarify how the charged surface plays a role in hydrogen electrocatalysis kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Understanding the Active Site Structures and Achieving Catalytic Activity Tuning of Atomically Dispersed FeN 4 Sites for Oxygen Reduction Reaction

Atomically dispersed Fe–—N—C catalysts with high oxygen reduction reaction (ORR) activity have attracted great attention since the last decade. Due to comparable ORR activity and low material cost, they are promising platinum group metal (PGM)-free catalysts that can replace the commercialized Pt/C materials; furthermore, it can facilitate the efficiency of the fuel cell technologies and mitigate dependence on fossil fuels. Great advancements have been made to experimentally optimize the synthesis approach of the Fe–—N—C catalysts, enhance the ORR activity, and improve the catalyst stability. Similarly, recent theoretical studies also provide enriched understanding of the active site structures, properties, and reaction mechanisms. In this review, discussions are made upon utilizing combined experimental and computational spectroscopy to reveal the active site structures, employing mechanistic studies to investigate reaction thermodynamics and kinetics, as well as developing scaling relationships to assist the design and development of future PGM-free catalyst materials. Furthermore, recent advances in studying Fe–—N—C catalysts utilizing electrified surface models and explicit solvation models are also discussed. Not only can these aspects improve the accuracy of theoretical simulation and predictions but also deepen the understanding of the catalyst properties and reaction mechanisms under the effect of surface charges and solvent molecules.

Fe single-atom catalysts↗
DOE OSTI2022

Integration of a high oxygen permeability ionomer into polymer electrolyte membrane fuel cell cathodes for high efficiency and power density

In this work, we present a study on the integration of a high oxygen permeability ionomer (HOPI) with high durability carbon supported platinum (Pt/C) catalysts to prepare cathode catalyst layers (CCLs) for polymer electrolyte membrane fuel cells (PEMFCs). A key motivation is the production of PEMFCs with high efficiency and durability for heavy-duty fuel cell vehicles. Our results from integrating a pre-commercial HOPI with robust, state-of-the-art catalysts with medium and low surface area carbon supports show significant increases in specific activities (67% increase over the standard commercial ionomer) at low current densities and reduced oxygen (O 2 ) transport resistances (R O2 ’s) at high current densities, enabling both higher efficiency and peak power density. The reduction in the R O2 with the HOPI is most significant at low relative humidity (RH), due to its more rigid backbone structure resisting compaction at lower water contents. In our ink optimization analysis, we show that the HOPI in this study achieves its peak performance with an ionomer to carbon ratio (I/C) of 0.6 and a moderately alcohol-rich ink solvent when fabricating catalyst layers by the decal method with an automatic wet film coater.

08 HYDROGEN↗
DOE OSTI2022

Elucidating the mechanism of photochemical CO 2 reduction to CO using a cyanide-bridged di-manganese complex

The complex, [{[Mn(bpy)(CO) 3 ] 2 }(μ-CN)] + (Mn 2 CN + ), has previously been shown to photochemically reduce CO 2 to CO. The detailed mechanism behind its reactivity was not elucidated. In this work, the photoevolution of this reaction is studied in acetonitrile (MeCN) using IR and UV-vis spectroscopy. Samples were excited into the Mn I → π* bpy metal-to-ligand charge transfer (MLCT) absorption band triggering CO loss, and rapid MeCN solvent ligation at the open coordination site. It is concluded that this process occurs selectively at the Mn axial ligation site that is trans to the C-end of the bridging cyanide. Upon further photolysis, the metal–metal bonded dimeric species, [(CO) 3 (bpy)Mn–Mn(bpy)(CO) 3 ] (Mn–Mn) is observed to form under anaerobic conditions. The presence of this dimeric species coincides with the observation of CO production. When oxygen is present, CO 2 photoreduction does not occur, which is attributed to the inability of Mn 2 CN + to convert to the metal–metal bonded dimer. Photolysis experiments, where the Mn–Mn dimer is formed photochemically under argon first and then exposed to CO 2 , reveal that it is the radical species, [Mn(bpy)(CO) 3 ˙] (Mn˙), that interacts with the CO 2 . Since the presence of Mn–Mn and light is required for CO production, [Mn(bpy)(CO) 3 ˙] is proposed to be a photochemical reagent for the transformation of CO 2 to CO.

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

Striking stability of a mixed-valence thallium(III)-thallium(I) complex in some solvents

At the dissolution of solid anhydrous thallium(III) trifluoromethanesulfonate, Tl(CF 3 SO 3 ) 3 , or thallium(III) trifluoroacetate, Tl(CF 3 COO) 3 , in dimethylsulfoxide (dmso) or N,N,N’,N’-tetramethylurea (tmu), intensely red-colored complexes are formed. This red thallium complex is stable for years in dmso, while it is reduced fairly rapidly to thallium(I) in tmu with a half-life time of an hour. At the dissolution of Tl(CF 3 SO 3 ) 3 in N,N-dimethylpropyleneurea (dmpu) an immediate reduction to thallium(I) takes place. A stable colorless aqueous thallium(III) solution is obtained at the dissolution in acidic water. Stable dmso solutions and solid dmso solvates of thallium(III) perchlorate, nitrate and trifluormethanesulfonate can be prepared by adding dmso to concentrated acidic aqueous thallium(III) solutions. These experimental observations conclude that the pure solids Tl(CF 3 SO 3 ) 3 and Tl(CF 3 COO) 3 play an essential role in the formation of the red-colored thallium complexes. 205 Tl NMR data show that the red thallium complex contains equal amounts of thallium(III) and thallium(I). The structure of the red thallium complex in dmso, as determined by EXAFS, has Tl–O bond distances of 2.216(3) and 2.80(2) Å, which are in very close agreement with the bond distances obtained in the pure dmso solvates of the thallium(III) and thallium(I) ions, respectively, and a Tl···Tl distance of 3.49(1) Å bridged by oxygen atoms. From the EXAFS data it is impossible to distinguish if dmso molecules and/or trifluoromethanesulfonate ions act as bridges. DFT calculations could eliminate some structures due to the irrelevant structural parameters or the energetics of the proposed reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

How do super concentrated electrolytes push the Li-ion batteries and supercapacitors beyond their thermodynamic and electrochemical limits?

Increasing the energy density of energy storage devices is currently the key target of many battery and supercapacitor research activities. For both types of devices, the electrochemical stability window (ESW) determines the effective energy density of the device. ESWs are defined by the effective oxidation and reduction potentials of the electrolyte, which are controlled by many various factors, including the HOMO/LUMO (highest/lowest unoccupied molecular orbital) energies of the electrolyte molecules, the nature of the electrode/electrolyte interphases, and other physicochemical properties. The concentration of the electrolyte would affect the HOMO/ LUMO levels thus also change the ESW. A higher concentration of salt induces specific arrangements among the anion, cation, and solvent molecules of an electrolyte, altering the bulk behavior of the electrolyte, resulting in drastic change in the electrode interfaces. These uniquely modified physicochemical properties extend the ESW in several different ways, including the enhancement in the kinetic stability of the electrodes, as well as the thermodynamic and Nernst shifts of the oxidation/reduction potentials of the electrolyte. For organic electrolytes, it is the reduced amount of free solvent molecules that plays the key role in such changes; whereas for aqueous electrolytes, it is the scarcity of free water molecules and the reduced water activity that control the key properties of the electrolyte. Here, we focus on elucidating the fundamental structural changes occurring within an electrolyte system with increasing salt concentrations. The underlying mechanisms which not only facilitates the extension of the ESW, but also enables higher rate capabilities and mitigates aluminum dissolution for batteries with organic electrolytes, are meticulously explained. Further, we thoroughly discuss the importance of high-voltage stability in aqueous battery systems by exploiting the changed properties observed with higher concentrations of salts. To finish, high-voltage supercapacitors enabled by superconcentrated electrolytes are also explored.

25 ENERGY STORAGE↗
DOE OSTI2022

Melt-Spun PAN Precursor for Cost-Effective Carbon Fibers in High Pressure Compressed Gas Tankage

The objective of this program was to synthesize melt-spinnable polyacrylonitrile (PAN) precursor that will lead to carbon fiber 25% less expensive than carbon fiber produced from conventional PAN precursor when produced in large volumes. The carbon fiber produced from this precursor needs to achieve ≥ 700 ksi tensile strength with this cost reduction to replace the incumbent fiber. In this program, the technology for producing precursor and then converted carbon fiber (CF) capable of meeting the 700 ksi target was to be demonstrated at a small scale in tows, containing ≥ 100 filaments. If this program moved on to a “Phase 2”, the processes would be scaled up to produce and test Type IV compressed gas storage tanks capable of meeting the 700-bar ultimate targeted FOA performance level. Precursor fiber production typically contributes a large fraction (~50%) to finished CF manufactured cost. Presently, all high strength CFs are manufactured from solution spun PAN precursor, accomplished at low temperatures using large amounts of environmentally unfriendly solvents that impart major impact to line speed and costs involved with handling and reclaiming the solvents and associated “waste streams” required in spinning and extracting those solvents. PAN melt spinning was demonstrated by the company BASF in CF precursor production and used in production of some other acrylic fibers, but significant production challenges remain for meeting the established CF metrics. Melt spinning requires use of plasticizers to suppress the melt temperature of the predominantly PAN formulation to a point sufficiently below the temperature of significant cross-linking. Fortunately, BASF and this team’s earlier work had demonstrated acrylic formulations melt spun with combinations of plasticizing solvents at much lower solvent levels. This project team made significant progress in understanding technical issues and identifying formulation pathways in earlier work in this area where >250ksi strength was achieved. The goal of this program was to pursue a more comprehensive approach with a larger, more diverse team having greater equipment design and overall production capabilities to push rapidly beyond the science to resolve remaining “engineering” issues associated with establishing stable, continuous processes for precursor fiber leading to enhanced, cost-effective CF and composite tank production.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Enhanced Electrolyte Transport and Kinetics Mitigate Graphite Exfoliation and Li Plating in Fast–Charging Li–Ion Batteries

Despite significant progress in energy retention, lithium-ion batteries (LIBs) face untenable reductions in cycle life under extreme fast-charging (XFC) conditions, which primarily originate from a variety of kinetic limitations between the graphite anode and the electrolyte. Through quantitative Li + loss accounting and comprehensive materials analyses, it is directly observed that the operation of LIB pouch cells at 4 C||C/3 (charging||discharging) results in Li plating, disadvantageous solid-electrolyte-interphase formation, and solvent co-intercalation leading to interstitial decomposition within graphite layers. It is found that these failure modes originate from the insufficient properties of conventional electrolytes, where employing a designed ester-based electrolyte improved the capacity retention of these cells from 55.9% to 88.2% after 500 cycles when operated at the aforementioned conditions. These metrics are the result of effective mitigation of the aforementioned failure modes due to superior Li + transport and desolvation characteristics demonstrated through both experimental and computational characterization. Finally, this work reveals the vital nature of electrolyte design to XFC performance.

25 ENERGY STORAGE↗
DOE OSTI2022

Changes in active-site geometry on X-ray photoreduction of a lytic polysaccharide monooxygenase active-site copper and saccharide binding

The recently discovered lytic polysaccharide monooxygenases (LPMOs) are Cu-containing enzymes capable of degrading polysaccharide substrates oxidatively. The generally accepted first step in the LPMO reaction is the reduction of the active-site metal ion from Cu 2+ to Cu + . Here we have used a systematic diffraction data collection method to monitor structural changes in two AA9 LPMOs, one from Lentinus similis (LsAA9_A) and one from Thermoascus auranti­acus (TaAA9_A), as the active-site Cu is photoreduced in the X-ray beam. For LsAA9_A, the protein produced in two different recombinant systems was crystallized to probe the effect of post-translational modifications and different crystallization conditions on the active site and metal photoreduction. We can recommend that crystallographic studies of AA9 LPMOs wishing to address the Cu 2+ form use a total X-ray dose below 3 × 10 4 Gy, while the Cu + form can be attained using 1 × 10 6 Gy. In all cases, we observe the transition from a hexa­coordinated Cu site with two solvent-facing ligands to a T-shaped geometry with no exogenous ligands, and a clear increase of the θ 2 parameter and a decrease of the θ 3 parameter by averages of 9.2° and 8.4°, respectively, but also a slight increase in θ T . Thus, the θ 2 and θ 3 parameters are helpful diagnostics for the oxidation state of the metal in a His-brace protein. On binding of cello-oligosaccharides to LsAA9_A, regardless of the production source, the θ T parameter increases, making the Cu site less planar, while the active-site Tyr—Cu distance decreases reproducibly for the Cu 2+ form. Thus, the θ T increase found on copper reduction may bring LsAA9_A closer to an oligosaccharide-bound state and contribute to the observed higher affinity of reduced LsAA9_A for cellulosic substrates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗