Exceptional Stabilization Research Articles

Highly Stable Carboranyl Ligated Gold Nano-Catalysts for Regioselective Aromatic Bromination.

Achieving electronic/steric control and realizing selectivity regulation in nanocatalysis remains a formidable challenge, as the dynamic nature of metal-ligand interfaces, including dissolution (metal leaching) and structural reconstruction, poses significant obstacles. Herein, we disclose carboranyls (CBs) as unprecedented carbon-bonded functional ligands (Eads.CB-Au(111)=-2.90 eV) for gold nanoparticles (AuNPs), showcasing their exceptional stabilization capability that is attributed by strong Au-C bonds combined with B-H⋅⋅⋅Au interactions. The synthesized CB@AuNPs exhibit core(Aun)-satellite(CB2Au-) structure, showing high stability towards multiple stimuli (110 °C, pH=1-12, thiol etchants). In addition, different from conventional AuNP catalysts such as triphenylphosphine (PPh3) stabilized AuNPs, dissolution of catalytically active gold species was suppressed in CB@AuNPs under the reaction conditions. Leveraging these distinct features, CB@AuNPs realized outstanding p : o selectivities in aromatic bromination. Unbiased arenes including chlorobenzene (up to >30 : 1), bromobenzene (15 : 1) and phenyl acrylate were examined using CB@AuNPs as catalysts to afford highly-selective p-products. Both carboranyl ligands and carboranyl derived counterions are crucial for such regioselective transformation. This work has provided valuable insights for AuNPs in realizing diverse regioselective transformations.

Multiresponsive Behavior of the Pickering Emulsifier and Its Application for Collecting Small Oil Droplets in Water.

Responsive Pickering emulsions, with unique nanoparticle interfaces and sensitivity to external stimuli, significantly enhanced the stability and applicability of Pickering emulsions. Multifunctional composite material poly((2-(dimethylaminoethyl methacrylate)-b-(acrylate cyclodextrin))/Fe3O4 nanoparticles, namely P(DMAEMA-b-A-CD)/Fe3O4, with both multiresponsive characteristics and emulsifying capabilities had been designed to remove small oil droplets from water. Using the reversible addition-fragmentation chain transfer (RAFT) method, diblock polymers P(DMAEMA-b-A-CD) were grown in a controlled manner on the surface of Fe3O4. The Fe3O4 core showed responsiveness to a magnetic field, and the block copolymers prepared via the RAFT method demonstrated reactivity to both pH and CO2. The P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles exhibited the capability to form Pickering/Oxford emulsions with exceptional stabilization properties. It could be observed that the introduction of CO2, acid, and a magnetic field led to the breakage of the emulsion, while the emulsion could be restabilized by removing the CO2 and the magnetic field or by adding alkali. Measurements of interfacial tension, ζ-potential, and contact angle demonstrated that the emulsification/breakdown mechanisms associated with pH and CO2/N2 were related to the surface wettability of the nanoparticles. In addition, the emulsifier had an excellent cycling capacity with at least 10 cycles by CO2/N2. Additionally, P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles exhibited excellent stability in oil phases with large polarity differences and various real oil phases with different viscosities. Importantly, the P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles could serve as functional materials for efficiently separating small oil droplets from water through the application of a magnetic field. Therefore, P(DMAEMA-b-A-CD)/Fe3O4 nanoparticles held promising potential as materials with economic and commercial value for oil-water separation applications.

Promoted hydrogenation of CO2 to methanol over single-atom Cu sites with Na+-decorated microenvironment.

Although single-atom Cu sites exhibit high efficiency in CO2 hydrogenation to methanol, they are prone to forming Cu nanoparticles due to reduction and aggregation under reaction conditions, especially at high temperatures. Herein, single-atom Cu sites stabilized by adjacent Na+ ions have been successfully constructed within a metal-organic framework (MOF)-based catalyst, namely MOF-808-NaCu. It is found that the electrostatic interaction between the Na+ and Hδ- species plays a pivotal role in upholding the atomic dispersion of Cu in MOF-808-NaCu during CO2 hydrogenation, even at temperatures of up to 275°C. This exceptional stabilization effect endows the catalyst with excellent activity (306 g·kgcat-1·h-1), high selectivity to methanol (93%) and long-term stability at elevated reaction temperatures, far surpassing the counterpart in the absence of Na+ (denoted as MOF-808-Cu). This work develops an effective strategy for the fabrication of stable single-atom sites for advanced catalysis by creating an alkali-decorated microenvironment in close proximity.

Egg White Protein-Proanthocyanin Complexes Stabilized Emulsions: Investigation of Physical Stability, Digestion Kinetics, and Free Fatty Acid Release Dynamics.

Egg white proteins pose notable limitations in emulsion applications due to their inadequate wettability and interfacial instability. Polyphenol-driven alterations in proteins serve as an effective strategy for optimizing their properties. Herein, covalent and non-covalent complexes of egg white proteins-proanthocyanins were synthesized. The analysis of structural alterations, amino acid side chains and wettability was performed. The superior wettability (80.00° ± 2.23°) and rigid structure (2.95 GPa) of covalent complexes established favorable conditions for their utilization in emulsions. Furthermore, stability evaluation, digestion kinetics, free fatty acid (FFA) release kinetics, and correlation analysis were explored to unravel the impact of covalent and non-covalent modification on emulsion stability, dynamic digestion process, and interlinkages. Emulsion stabilized by covalent complex exhibited exceptional stabilization properties, and FFA release kinetics followed both first-order and Korsmeyer-Peppas models. This study offers valuable insights into the application of complexes of proteins-polyphenols in emulsion systems and introduces an innovative approach for analyzing the dynamics of the emulsion digestion process.

A high thermal stable pre‐oxidized polyacrylonitrile nanofiber separator for lithium‐ion battery

AbstractThe separator as a main part of lithium‐ion batteries (LIBs) acts as a primary factor that affects the safety property of the battery. The pre‐oxidized PAN (OPAN) separator as an alternative separator with high temperature resistance was developed through the electrospinning of PAN by thermal stabilization. The prepared OPAN separator showed an exceptional dimensional thermal stabilization, without obvious dimensional shrinkage after treated in the oven at 300°C for 30 min, which improves the safety of LIBs at high temperatures. The OPAN separator had a high porosity and excellent affinity to the electrolyte, along with 351.3% of electrolyte uptake. Furthermore, the ionic conductivity and the interfacial resistance of OPAN separator were 1.63 mS/cm and 881 Ω, better than 0.65 mS/cm and 1463 Ω of commercial Celgard 2400 separator. In addition, the LiFePO4/Li battery assembled with OPAN separator given an outstanding initial discharge specific capacity and coulomb efficiency of 152.1 mAh/g and 97.9% and shown an excellent capacity retention ability of 92.3% after 100 cycles. The battery assembled with OPAN separator exhibits more excellent rate performance than PAN and Celgard 2400 separators at a charge current density of 0.2–3.0 C. It is believed that this excellent separator with such remarkable performances and low cost can be a promising separator candidate for safe LIBs.

Cooperative Effect of Noncovalent Interactions on Tetrel Bonding in Halogenated Silanes.

Tetrel bond, a weak noncovalent interaction between the σ-hole of a Group IV element (silicon in our case) and the cloud of an electronegative element (oxygen in our case) is the focus of this work. The percentage strengthening of tetrel bond has been investigated by optimizing 16 binary complexes of halogenated silane and water of general formula SiXn H4-n -H2 O and 16 ternary complexes, of general formula NaX-SiXn H4-n -H2 O, where X=F, Cl, Br and I and n=1, 2, 3 and 4 at various levels of theory defined within the formalism of density functional theory (DFT). With the addition of NaX, tetrel bond between Si and O in SiXn H4-n -H2 O gets strengthened up to 49 %, owing to cooperativity effect exerted by hydrogen bonding between X and H in the ternary complex NaX-SiXn H4-n -H2 O. In the series of complexes studied here, overall stabilization due to cooperativity lies between 10 kJ/mol to 170 kJ/mol. This large extent of reinforcement due to cooperativity has never been showcased before. The exceptional stabilization and reinforcement owe its genesis to the transformation of the ternary complex into a cluster orchestrated by the H-bonding in most of the cases and covalent bonding in few of the cases.

Physicochemical properties and operational stability of Taguchi design-optimized Candida rugosa lipase supported on biogenic silica/magnetite/graphene oxide for ethyl valerate synthesis

Biobased ternary nanocomposites can stabilize enzymes for greater stability, catalytic activity and easy recovery. This study aimed to optimize biogenic silica/magnetite/graphene oxide nanocomposite supported Candida rugosa lipase (CRL/SiO2/Fe3O4/GO) for ethyl valerate (EV) synthesis and characterize the biocatalysts’ physicochemical properties and operational stability. CRL conjugated-oil palm leaves-derived biogenic SiO2/Fe3O4/GO nanocomposite showed a maximum immobilized protein of 44.13 ± 2.1 mg/g with a specific activity (534.87 ± 9.5 U/mg), than free CRL (≥700 U/mg). GL-A-SiO2/Fe3O4/GO exhibited the highest surface area (260.87 m2/g) alongside superior thermal stability in TGA/DTG. XRD revealed an amorphous SiO2 (crystallinity = 26.7%), while Fe3O4 existed as cubic spinel crystal (crystallinity = 90.2%). Taguchi Design-optimization found that CRL/SiO2/Fe3O4/GO best catalyzed the EV synthesis (90.4% in 3 h) at 40 ℃ using 3 mg/mL of biocatalyst, valeric acid/ethanol molar ratio of 1:2, in 10% (m/v) molecular sieves with stirring in heptane at 200 rpm. EV production was confirmed by FTIR- (C=O: 1738 cm−1 and C–O–C: 1174 cm−1) and GC–MS ([M]+m/z = 130, C7H14O2). CRL/SiO2/Fe3O4/GO’s reusability for 11 successive esterification cycles demonstrated the SiO2/Fe3O4/GO’s exceptional hyperactivation and stabilization properties on immobilized CRL. These findings conveyed the SiO2/Fe3O4/GO’s efficacy to alter CRL's physicochemical properties and operational stability for catalyzing higher yields EV.

Triggering Copper(II)-Mediated Base Pair Formation by Light.

Metal-mediated base pairs enable a site-specific incorporation of transition metal ions into nucleic acid structures. The resulting nucleic acid-metal complex conjugates are of interest in the context of functionalized nucleic acids, as they bear metal-based functionality. It is desirable to devise nucleic acids with an externally triggered metal-binding affinity, as this may allow regulating this functionality. Toward this end, a caged deoxyribonucleoside analog HNPP was devised for the site-specific binding of copper(II) ions upon irradiation by light, based on the ligand 3-hydroxy-2-methylpyridin-4(1H)-one (H) and the photocleavable 2-(2-nitrophenyl)propoxy protecting group (NPP). The formation of both H-Cu(II)-H homo base pairs and H-Cu(II)-X hetero base pairs (involving a second artificial deoxyribonucleoside X, based on imidazole-4-carboxylate) was achieved upon irradiation of DNA duplexes bearing the respective HNPP:HNPP or HNPP:X mispairs in the presence of copper(II) ions. The H-Cu(II)-X pair shows an exceptional DNA duplex stabilization of up to 43 °C upon its formation, exceeding that of the H-Cu(II)-H pair. It therefore represents one of the most stabilizing Cu(II)-mediated base pairs reported so far. Our findings expand the scope of light-triggered metal-mediated base pair formation by introducing a copper(II)-binding ligand.

Structures of hyperstable ancestral haloalkane dehalogenases show restricted conformational dynamics

Ancestral sequence reconstruction is a powerful method for inferring ancestors of modern enzymes and for studying structure–function relationships of enzymes. We have previously applied this approach to haloalkane dehalogenases (HLDs) from the subfamily HLD-II and obtained thermodynamically highly stabilized enzymes (ΔTm up to 24 °C), showing improved catalytic properties. Here we combined crystallographic structural analysis and computational molecular dynamics simulations to gain insight into the mechanisms by which ancestral HLDs became more robust enzymes with novel catalytic properties. Reconstructed ancestors exhibited similar structure topology as their descendants with the exception of a few loop deviations. Strikingly, molecular dynamics simulations revealed restricted conformational dynamics of ancestral enzymes, which prefer a single state, in contrast to modern enzymes adopting two different conformational states. The restricted dynamics can potentially be linked to their exceptional stabilization. The study provides molecular insights into protein stabilization due to ancestral sequence reconstruction, which is becoming a widely used approach for obtaining robust protein catalysts.

Design of highly stabilized nanocomposite inks based on biodegradable polymer-matrix and gold nanoparticles for Inkjet Printing

Nowadays there is a worldwide growing interest in the Inkjet Printing technology owing to its potentially high levels of geometrical complexity, personalization and resolution. There is also social concern about usage, disposal and accumulation of plastic materials. In this work, it is shown that sugar-based biodegradable polyurethane polymers exhibit outstanding properties as polymer-matrix for gold nanoparticles composites. These materials could reach exceptional stabilization levels, and demonstrated potential as novel robust inks for Inkjet based Printing. Furthermore, a physical comparison among different polymers is discussed based on stability and printability experiments to search for the best ink candidate. The University of Seville logo was printed by employing those inks, and the presence of gold was confirmed by ToF-SIMS. This approach has the potential to open new routes and applications for fabrication of enhanced biomedical nanometallic-sensors using stabilized AuNP.

Shedding Light on the Trehalose-Enabled Mucopermeation of Nanoparticles with Label-Free Raman Spectroscopy.

Nanoparticle-based drug delivery systems have attracted significant interest owing to their promise as tunable platforms that offer improved intracellular release of cargo therapeutics. However, significant challenges remain in maintaining the physiological stability of the mucosal matrix due to the nanoparticle-induced reduction in the matrix diffusivity and promotion of mucin aggregation. Such aggregation also adversely impacts the permeability of the nanoparticles, and thus, diminishes the efficacy of nanoparticle-based formulations. Here, an entirely complementary approach is proposed to the existing nanoparticle functionalization methods to address these challenges by using trehalose, a naturally occurring disaccharide that offers exceptional protein stabilization. Plasmon-enhanced Raman spectroscopy and far-red fluorescence emission of the plasmonic silver nanoparticulate clusters are harnessed to create a unique dual-functional, aggregating, and imaging agent that obviates the need of an additional reporter to investigate mucus-nanoparticle interactions. These spectroscopy-based density mapping tools uncover the mechanism of mucus-nanoparticle interactions and establish the protective role of trehalose microenvironment in minimizing the nanoparticle aggregation. Thus, in contrast to the prevailing belief, these results demonstrate that nonfunctionalized nanoparticles may rapidly penetrate through mucus barriers, and by leveraging the bioprotectant attributes of trehalose, an in vivo milieu for efficient mucosal drug delivery can be generated.

Pyridylphenylene dendrons immobilized on the surface of chemically modified magnetic silica as efficient stabilizing molecules of Pd species

Abstract Rigid pyridylphenylene dendrons were shown to successfully function as capping molecules for stabilization of both magnetite and Pd nanoparticles (NPs) to form hydrophobic, magnetically recoverable catalysts. However, syntheses in colloidal solutions require large amounts of dendrons and are difficult to scale up. Here, we developed a strategy for the nanocomposite formation by immobilization of the pyridylphenylene dendrons (D) on magnetic silica (Fe3O4-SiO2, MS) surface via the formation of ether or amide bonds, depending on the structure of flexible linkers on the MS surface and dendron focal groups. Both approaches allow attachment of small amounts of the dendrons with high surface coverage and impart amphiphilicity to the final composite. After the binding to the MS surface, the dendron pyridine moieties readily complex with Pd acetate, leading to a “cocktail” of Pd2+ and Pd0 species (the latter forming Pd NPs) due to partial reduction by composite functional groups. The MS-D-Pd nanocomposites were tested in the model Suzuki-Miyaura cross-coupling reaction of 4-Br-anisole and phenylboronic acid to evaluate their performance in hydrophilic conditions. MS-D-Pd demonstrated excellent performance, even at a very small amount of the catalyst, which is assigned to exceptional stabilization by dendritic ligands, allowing prevention of the metal leaching and preservation of catalytic properties upon magnetic separation. The immobilization of rigid hydrophobic dendrons on the hydrophilic magnetic support may allow one to extend the scope of catalytic reactions due to catalyst amphiphilicity.

The Nature of Stable Char Radicals: An ESR and DFT Study of Structural and Hydrogen Bonding Requirements.

Pyrolysis is a promising way to convert biomass into fuels and chemicals. This reaction is complex and inevitably involves a cascade of radical reactions that lead to char formation, in which some radicals become trapped and stabilized. Their nature is difficult to characterize, and in this respect computational chemistry can be a strong supplementary tool to electron spin resonance spectroscopy and other experimental methods. Here biomass char radicals and oxidation reactivity are studied experimentally, and density functional theory is used to predict the thermodynamic stability and g-values of carbon- and oxygen-centered radicals of polyaromatic char models including defect structures. Hydroxylated and especially certain dihydroxylated structures provide exceptional stabilization of oxygen-centered radicals. Hydrogen bonding plays a crucial role, and it is proposed that hydrogen atom transfer couples radical localizations. This is a new proposal on the structural requirements for stabilization of char radicals, which impacts our understanding of pyrolysis mechanisms and char reactivity.

Helical Folding of Hydroxy‐Substituted N‐Hetero‐ortho‐phenylenes Directed by Intramolecular Hydrogen Bonds

Derivatives of the ortho‐phenylene hexamer containing pyridine moieties and hydroxy groups were prepared through Negishi cross‐coupling reactions between bis(chloropyridyl)biphenyl and alkoxy‐substituted arylzinc reagents. X‐ray diffraction analysis revealed a closed helical folding directed by π–π stacking and hydrogen bonds. No broadening or coalescence of 1H NMR peaks was observed between 213 and 313 K, which indicates the high stability of the helical folding in CDCl3 solution. DFT calculations on the rotation of a single bond in the obtained compound indicated that the intramolecular hydrogen bonds led to exceptional stabilization of the closed helical folding. Right and left helices were separated by chiral column chromatography.

Aqueous ammonia abatement on Pt- and Ru-modified TiO2: Selectivity effects of the metal nanoparticles deposition method

A series of TiO2–based photocatalysts obtained by deposition of Pt nanoparticles (NPs) has been tested in the photocatalytic decomposition of aqueous ammonia under UVA irradiation. Two main deposition routes were employed, i.e. (i) the deposition of surfactant-stabilized preformed metal NPs and (ii) a modified version of the well-known deposition-precipitation technique, employing urea as precipitating agent. The effects that the deposition route and the amount of deposited metal have on both ammonia conversion (XNH3) and selectivity (SY) towards the different N-containing products (Y=N2, NO2−, NO3−) have been investigated systematically, in relation to the morphological distribution of NPs on TiO2, as evidenced by HR-TEM analysis. The combination of Pt (0.8wt.%) with a relatively low amount of Ru NPs (0.1wt.%) as co-catalysts, both deposited on TiO2 under optimized conditions, results in an exceptional stabilization of nitrite ions (SNO2−∼70%), from which N2, the most desired ammonia oxidation product, might subsequently be obtained catalytically.

A General Mechanism for Stabilizing the Small Sizes of Precious Metal Nanoparticles on Oxide Supports

We recently discovered that MgAl2O4 spinel (111) nanofacets optimally stabilize the small sizes of platinum nanoparticles even after severe high-temperature aging treatments. Here we report the thermal stabilities of other precious metals with various physical and chemical properties on the MgAl2O4 spinel (111) facets, providing important new insights into the stabilization mechanisms. Besides Pt, Rh, and Ir can also be successfully stabilized as small (1–3 nm) nanoparticles and even as single atomic species after extremely severe (800 °C, 1 week) oxidative aging. However, other metals either aggregate (Ru, Pd, Ag, and Au) or sublimate (Os), even during initial catalyst synthesis. On the basis of ab initio theoretical calculations and experimental observations, we rationalize that the exceptional stabilization originates from the epitaxially matched structure, i.e., lattice matching in geometry and the correspondingly strong electronic attractions at interfaces between the spinel (111) surface oxygens and epitaxial metals/metal oxides. On this basis, design principles for catalyst support oxide materials that are capable of stabilizing precious metals are proposed.

Interaction of spermine-alanine functionalized perylene bisimide dye aggregates with ds-DNA/RNA secondary structure

We report for the first time on the interaction of self-assembled perylene bisimide (PBI) dye aggregates with polynucleotides, revealing very high (nM) binding constants and exceptional thermal stabilization of double-stranded (ds)-DNA/RNA. Induced CD profiles of PBI dimer aggregates formed within DNA/RNA grooves show high sensitivity on the steric properties of the binding site, suggesting the applicability of such self-adjusting excitonically coupled PBI dimers for the sensing of the DNA/RNA secondary structure.

The Relationship between Lateral Ankle Sprain and Ankle Tendinitis in Ballet Dancers

The lateral ligament complex of the ankle is the most frequently injured structure in the body. Although most simple ankle sprains do not result in long-term disability, a significant number do not completely resolve, leading to residual symptoms that may persist for years. The most commonly reported symptoms, particularly among athletes, include instability, re-injury and tendinitis. Ballet dancers are a combination of artist and high-performance athlete; consequently, they are subjected to the same types of injuries as other athletes, including lateral ankle sprains and their sequelae. Furthermore, ballet dancers perform in unusual positions such as en pointe, which places the ankle in extreme plantar flexion, requiring stabilization by surrounding muscles. Dancers’ extraordinary performance demands place them at risk for other ankle injuries as well, including inflammation of several tendons, especially the peroneals. This report reviews the relevant literature to characterize the scope of lateral ankle sprains and sequelae, discuss the importance of the peroneal muscles in ankle stability, and explore a relationship between lateral ankle sprain and ankle tendinitis in ballet dancers. Informal interviews were conducted with physical therapists who specialize in treating ballet dancers, providing a clinical context for this report. An extensive review of the literature was conducted, including electronic databases, reference lists from papers, and relevant reference texts. Numerous studies have investigated ankle sprains and residual complaints; nearly all report that lateral ankle sprains commonly lead to chronic ankle instability. Studies exploring ankle stability have demonstrated that the peroneal muscles play a crucial role in ankle stabilization; EMC studies confirm they are the first to contract during ankle inversion stress. The dancers need for exceptional ankle stabilization may lead to peroneal overuse and tendinitis. Studies have linked peroneal pathology to a history of ankle sprain, but there is no dance medicine literature linking peroneal tendinitis to prior ankle sprains. A growing body of literature confirms myriad connections between lateral ankle sprains, residual instability, peroneal muscle increased activity, and tendinitis. It is our belief that ankle sprains lead to instability, particular en pointe, for which the peroneal muscles attempt to compensate. Their overuse for this static stabilizing function, as well as for dynamic dance movements, then leads to tendonitis. This knowledge may heighten awareness of the potential for developing tendonitis following ankle sprains, and lead to better rehabilitation of the injured ballet dancer.

Stabilization of Folded Peptide and Protein Structures via Distance Matching with a Long, Rigid Cross-Linker

Intramolecular cross-linking is predicted to stabilize the folded state of peptides and proteins most effectively if the cross-linker provides a rigid link that is well-matched in end-to-end distance with attachment sites in the peptide or protein. We describe a thiol-reactive sulfonated alkyne-based cross-linker that is demonstrably more effective than more flexible counterparts. Exceptional stabilization of helical structure in short peptides is obtained.

αArg-237 in Methylophilus methylotrophus (sp. W3A1) Electron-transferring Flavoprotein Affords ∼200-Millivolt Stabilization of the FAD Anionic Semiquinone and a Kinetic Block on Full Reduction to the Dihydroquinone

The midpoint reduction potentials of the FAD cofactor in wild-type Methylophilus methylotrophus (sp. W3A1) electron-transferring flavoprotein (ETF) and the alphaR237A mutant were determined by anaerobic redox titration. The FAD reduction potential of the oxidized-semiquinone couple in wild-type ETF (E'(1)) is +153 +/- 2 mV, indicating exceptional stabilization of the flavin anionic semiquinone species. Conversion to the dihydroquinone is incomplete (E'(2) < -250 mV), because of the presence of both kinetic and thermodynamic blocks on full reduction of the FAD. A structural model of ETF (Chohan, K. K., Scrutton, N. S., and Sutcliffe, M. J. (1998) Protein Pept. Lett. 5, 231-236) suggests that the guanidinium group of Arg-237, which is located over the si face of the flavin isoalloxazine ring, plays a key role in the exceptional stabilization of the anionic semiquinone in wild-type ETF. The major effect of exchanging alphaArg-237 for Ala in M. methylotrophus ETF is to engineer a remarkable approximately 200-mV destabilization of the flavin anionic semiquinone (E'(2) = -31 +/- 2 mV, and E'(1) = -43 +/- 2 mV). In addition, reduction to the FAD dihydroquinone in alphaR237A ETF is relatively facile, indicating that the kinetic block seen in wild-type ETF is substantially removed in the alphaR237A ETF. Thus, kinetic (as well as thermodynamic) considerations are important in populating the redox forms of the protein-bound flavin. Additionally, we show that electron transfer from trimethylamine dehydrogenase to alphaR237A ETF is severely compromised, because of impaired assembly of the electron transfer complex.