Chemistry Commons^™

Synthesis And Characterization Of Pbs Quantum Sheets Through Lamellar Assembly, And Updates To The Cdse Quantum Wire Synthesis, Paul James Morrison

Arts & Sciences Graduate Student Theses and Dissertations

This dissertation reports the novel synthesis of PbS quantum plates (QPs) via a reaction executed at low temperatures. The PbS QPs are grown in a template-assisted mechanism, with the first excitonic peak observed in the visible region of light at ~620 nm (2.0 eV), at an energy radically different than the band gap of bulk PbS (~3000 nm, 0.42eV). The large energy shift is due to the extremely thin dimension of these nanoplates, which is determined to be ~1 nm in thickness. Thickness measurements are made in a powder X-ray diffractometer (XRD) at low angles (between 2-15º 2θ). These measurements …

Study Of Ii-Vi Colloidal Semiconductor Magic-Size Nanoclusters And Crystalline Quantum Platelets, Yuanyuan Wang

Arts & Sciences Graduate Student Theses and Dissertations

The main objective of this project is to prepare and isolate the smallest, discrete, magic-size nanoclusters of cadmium selenide (CdSe) and to grow crystalline, wurtzite CdSe quantum platelets (QPs) at room temperature. The achievement of these goals enables us to provide a general synthesis of II-VI semiconductor magic-size nanoclusters and low-temperature routes to well-passivated nanocrystals having a range of compositions and morphologies.The magic-size nanocluster (CdSe)13 is grown in a lamellar-bilayer soft template at room temperature. The results described in this thesis strongly suggest that [(CdSe)13(n-octylamine)13] is the most thermodynamically stable nanocluster and serves as a key intermediate in the formation …

Polyol Synthesis Of Silver Nanowires By Heterogeneous Nucleation And Mechanistic Aspects Influencing Its Length And Diameter, Waynie M. Schuette

Arts & Sciences Graduate Student Theses and Dissertations

Various additives are employed in the polyol synthesis of silver nanowires (Ag NWs), which are typically halide salts such as NaCl. A variety of mechanistic roles have been suggested for these additives. My research showed that the early addition of NaCl in the polyol synthesis of Ag NWs from AgNO3 in ethylene glycol results in the rapid formation of AgCl nanocubes, which induce the heterogeneous nucleation of metallic Ag upon their surfaces. Ag NWs subsequently grow from these nucleation sites. The conclusions are supported by studies using ex-situ generated AgCl nanocubes.Additionally, the final mean silver nanowire diameter is found to …

Kinetic Analysis And Inhibition Studies Of Iron-Dependent Histone Demethylases, Barbara Gordon Cascella

Arts & Sciences Graduate Student Theses and Dissertations

The research presented herein focuses on the kinetics and inhibition of the KDM4 subfamily of Jumonji C (JmjC) domain-containing histone demethylases (HDMs). Belonging to the larger class of alpha-ketoglutarate (alpha-KG)-dependent, non-heme iron monooxygenases, the JmjC-HDMs remove methyl groups from mono-, di-, and tri-methylated histone lysine residues through an Fe(IV)-oxo-catalyzed hydroxylation reaction. JmjC-HDMs have been found to play integral roles in the maintenance of genomic integrity as well as in the regulation of transcription. Three KDM4 members were studied: the mixed H3K9/H3K36 demethylases KDM4A and KDM4C, and the pure H3K9 demethylase KDM4E. KDM4C is a hypoxia-inducible factor 1 (HIF-1) target gene …

Cationic Metallocene-Containing Polymers: From Synthesis To Applications, Jiuyang Zhang

Theses and Dissertations

Metallopolymers, with the combination of metals and polymeric framworks, have attracted a lot of attention during the past decades. The development of metallopolymers has been largely driven by the desire to combine the synthetic efficiency and versatility of an organic polymer framework with the unique redox, responsive and catalytic properties of inorganic metals. Among different kinds of metallopolymers, metallocene-containing polymers， have been widely utilized for applications ranging from electrochemical sensors to templates for advanced inorganic catalysts to battery materials, due to their unique physicochemical properties. In the first part of my thesis, we showed controlled/living polymerization strategies to prepare well-defined …

Toward The Combinatorial Development Of Hydrophobic-Tagged Antifolate-Directed Degradation Of Human Thymidylate Synthase, Daniel J. Menasco

Theses and Dissertations

Direct post-translational control over a protein of interest (POI) can be exploited by manipulating the cells protein quality-control systems responsible for either intracellular turnover through ubiquitination (POI half-life) or repairing and degrading misfolded proteins.1 In an effort to target and degrade a high value POI we selected the enzyme human thymidylate synthase (TS) for post-translational degradation through ligand-directed ubiquitination and hydrophobic tagging. Thymidylate synthase catalyzes the reductive methylation of 2’-deoxyuridine monophosphate (dUMP) to 2’-deoxythymidine monophosphate (dTMP). As the de novo source of dTMP the regulation of intracellular TS is strictly controlled by ubiquitinindependent proteasomal degradation mediated by an internal TS-degron …

Universal Two-Electron Correlation Operator On Excited States, Bryan Thomas Nichols

Theses and Dissertations

Excited states of chemical systems are extremely important in understanding spectra, chemical phenomena, as well as how a particular compound behaves in reactions. Computationally, excited states are normally very expensive to calculate. The difficulty in calculating these states with wavefunction based methods can be mainly attributed to the calculation of large multi-determinant wavefunctions. One reason to use a complicated multi-determinant wavefunction is to include some of the effects of correlation energy. The quantity of correlation energy can most simply be defined as the reduction in energy caused by any two or more electrons trying to avoid each other. The most …

Surface Functionalization Of Inorganic Substrates With Polymeric Ligands Using Raft Polymerization, Anand Viswanath

Theses and Dissertations

This work focused on using polymers to modify the surface of various inorganic substrates, ranging from TiO2, ITO, CDSe and CdS nanostructures to micron sized silica particles. The synthesis of the polymers using the RAFT technique and the characterization of the functionalized substrates were analyzed in detail to provide insights into their use for various applications. In the first part of this work, novel phosphate based RAFT agents and phosphate containing polymers, including poly(methyl methacrylate) (PMMA), poly(glycidyl methacrylate) (PGMA) and poly(dimethyl siloxane) (PDMS) were synthesized. Alkyne functionalized PGMA was used to click to ITO surfaces in a grafting-to method, and …

Mono-N-Acyl-2,6-Diaminopimelic Acid Derivatives: Analysis By Electromigration And Spectroscopic Methods And Examination Of Enzyme Inhibitory Activity, Jan Hlaváček, Miloslava Vítovcová, Petra Sázelová, Jan Pícha, Václav Vaněk, Miloš Buděšínský, Jiří Jiráček, Danuta M. Gillner, Richard C. Holz, Ivan Mikšík, Václav Kašička

Chemistry Faculty Research and Publications

Thirteen mono-N-acyl derivatives of 2,6-diaminopimelic acid (DAP)—new potential inhibitors of the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE; EC 3.5.1.18)—were analyzed and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies and two capillary electromigration methods: capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). Structural features of DAP derivatives were characterized by IR and NMR spectroscopies, whereas CZE and MEKC were applied to evaluate their purity and to investigate their electromigration properties. Effective electrophoretic mobilities of these compounds were determined by CZE in acidic and alkaline background electrolytes (BGEs) and by MEKC in acidic and alkaline BGEs …

Structural Studies And Reactions Of Rhenium And Rhenium-Gold Metal Carbonyl Complexes, Yuen Onn Wong

Theses and Dissertations

The six-membered heavy atom heterocycles [Re2(CO)8(μ-H)(μ-SbPh2)]2, 2.1 and Pd[Re2(CO)8(μ-H)(μ-SbPh2)]2, 2.3, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re2(CO)8(μ-H)(μ-SbPh2). The palladium atom that lies in the center of the heterocycle 2.3 was removed to yield 2.1. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd2Re4(μ-Ph)(CO)16(μ4-SbPh)(μ3-SbPh2)(μ-H)2, 2.2, was also formed in these reactions of palladium with Re2(CO)8(μ-H)(μ-SbPh2). Thermolysis of 2.1 at 85 °C yielded Re3(CO)12(μ-SbPh2)(μ-H)2, 2.4 (2.9% yield), Re3(CO)12(μ-SbPh2)2(μ-H), 2.5 (25.1% yield), and Re3(CO)13(μ-SbPh)(μ-H), 2.6 (14.6% yield). The electronic structure of 2.1 and 2.3 …

Synthesis And Characterization Of Polymer (Sulfonated Poly-Ether-Ether-Ketone) Based Nanocomposite (H-Boron Nitride) Membrane For Hydrogen Storage, Naresh Muthu, S. Rajashabala, R. Kannan

Chemistry and Biochemistry Faculty Publications

The development of light weight and compact hydrogen storage materials is still prerequisite to fuel-cell technology to be fully competitive. The present experimental study reports the hydrogen storage capability of sulfonated poly-ether-ether-ketone (SPEEK)-hexagonal boron nitride (h-BN) (SPEEK-h-BN) nanocomposite membranes. The nanocomposite membranes are prepared by considering various amount of h-BN (0, 1, 3 and 5 wt. %) by phase inversion technique. The degree of sulfonation of the PEEK (SPEEK) is found to be 65% by Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy. Hydrogen adsorption studies have been carried out using a Seiverts-like hydrogenation setup. The membranes are characterized …

Thermomechanical Performance Assessment Of Bio-Based Pu Adhesives Derived From Castor Oil, Anand Patel

Electronic Theses & Dissertations

Thermomechanical Performance Assessment of Bio-based PU Adhesives Derived from Castor Oil

An Abstract of the Thesis by

Anand V. Patel

Adhesives play a critical role in binding diverse materials, thereby promoting structural integrity and functional versatility across numerous daily applications. A significant challenge remains in developing polyurethane adhesives that exhibit exceptional bonding strength, as many are derived from petroleum products. To reduce dependence on non-renewable resources and offer sustainable and affordable alternatives, vegetable oils are being utilized to create a range of polyurethane adhesives. These oils are preferred due to their low toxicity, cost-effectiveness, and reduced environmental impact. This research …

Colloidal And Biological Properties Of Triscationic Amphiphiles With One Or Two Tails, John N. Marafino

Masters Theses, 2010-2019

The decline in the development of novel antimicrobials, combined with the misusage and over prescription of antibiotics, has contributed to the increasing prevalence of antimicrobial-resistant infections. Thus development of effective novel disinfectants could reduce the transmission of pathogens and decrease the risk of infection by antibiotic resistant organisms. The antimicrobial activity of amphiphiles, compounds with hydrophobic and hydrophilic regions, was first reported in 1935, and has influenced the synthesis of amphiphiles with variations in structure. In this study, three series of amphiphiles were synthesized by two subsequent Menshutkin reactions. Each amphiphile contains one or two hydrocarbon tails ranging from 8 …

New 4-Aminoquinoline Compounds To Reverse Drug Resistance In P. Falciparum Malaria, And A Survey Of Early European Antimalarial Treatments, Katherine May Liebman

Dissertations and Theses

Intermittent fevers caused by Plasmodium parasites have been known for millennia, and have caused untold human suffering. Today, millions of people are afflicted by malaria each year, and hundreds of thousands die. Historically, the most successful synthetic antimalarial drug was chloroquine, as it was safe, inexpensive, and highly efficacious. However, plasmodial resistance to chloroquine now greatly limits its utility. Previously in our laboratories it has been shown that attachment of a "reversal agent moiety" to the side chain of chloroquine can result in the restoration of activity against chloroquine-resistant strains of P. falciparum malaria. In the first part of the …

Electrochemical Synthesis Of Nanostructured Noble Metal Films For Biosensing, Jay Kishan Bhattarai

Dissertations

Nanostructures of noble metals (Au and Ag) are of interest because of their important intrinsic properties. Noble metals by themselves are conductive, physically robust, chemically inert, and strongly bind to thiols. However, when the nanostructures are formed, they in addition possess high surface area and unique optical properties tunable by adjusting the shape and size. All of these properties make nanostructures of noble metals suitable candidates to be used as a transducer for biosensing. Individual nanostructures might be easier to prepare but difficult to handle to be used as a transducer. Therefore, we prepared and analyzed nanostructured films/coating of noble …

Getting Down To The Fundamentals Of Hydrogen Bonding: Anharmonic Vibrational Frequencies Of (Hf)2 And (H2o)2 From Ab Initio Electronic Structure Computations, J. Coleman Howard, Jessica L. Gray, Amanda J. Hardwick, Linh T. Nguyen, Gregory S. Tschumper

Chemistry Faculty Research & Creative Works

This work presents a systematic investigation into the basis set convergence of harmonic vibrational frequencies of (H₂O)₂ and (HF)₂ computed with second-order Møller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles method with perturbative connected triples, CCSD(T), while employing correlation-consistent basis sets as large as aug-cc-pV6Z. The harmonic vibrational frequencies presented here are expected to lie within a few cm^-1 of the complete basis set (CBS) limit. For these important hydrogen-bonding prototype systems, a basis set of at least quadruple-ζ quality augmented with diffuse functions is required to obtain harmonic vibrational frequencies within 10 …

Reaction Rates Of Amino Acids With Derivatives Of The Anticancer Drug Cisplatin, Celia Jess Whelan

Mahurin Honors College Capstone Experience/Thesis Projects

We are studying reactions of cisplatin derivatives, which differ in both size and shape, with various amino acids. When reaction with DNA occurs, apoptosis is observed, ideally leading to termination of the cancer. Due to the affinity of cisplatin for sulfur-containing amino acids, reaction with proteins may occur prior to access to the DNA, producing a large array of products, which could potentially be toxic to the human body. Both the size and shape of the platinum complexes often affect the reactions with protein targets more so than with DNA targets. By performing reactions of specific amino acids targets with …

Coordination Nature Of 4-Mercaptoaniline To Sn(Ii) Ion: Formation Of A One Dimensional Coordination Polymer And Its Decomposition To A Mono Nuclear Sn(Iv) Complex, Eon S. Burkett, Tasneem A. Siddiquee

Chemistry Faculty Research

The coordination of the bifunctional ligand 4-mercaptoaniline with aqueo us tin(II) metal ion was studied. A coordination polymer was synthesized when an aqueous solution of SnCl2 was treated with 4-MA. The crystalline material is stable under atmospheric conditions retaining its oxidation state. However, when submerged in a solution saturated with oxygen, the compound oxidizes to a mononuclear tin(IV) complex. Both the compounds were characterized by single crystal X-ray diffraction studies. Although the structure of the tin(IV) complex was previously reported, crystal structure of this compound was redetermined.

Antifungal Amphiphilic Aminoglycoside K20: Bioactivities And Mechanism Of Action, Sanjib K. Shrestha, Cheng-Wei Tom Chang, Nicole Meissner, John Oblad, Jaya P. Shrestha, Kevin N. Sorensen, Michelle M. Grilley, Jon Y. Takemoto

Chemistry and Biochemistry Faculty Publications

K20 is a novel amphiphilic antifungal aminoglycoside that is synthetically derived from the antibiotic kanamycin A. Reported here are investigations of K20′s antimicrobial activities, cytotoxicity, and fungicidal mechanism of action. In vitro growth inhibitory activities against a variety of human and plant pathogenic yeasts, filamentous fungi, and bacteria were determined using microbroth dilution assays and time-kill curve analyses, and hemolytic and animal cell cytotoxic activities were determined. Effects on Cryptococcus neoformans H-99 infectivity were determined with a preventive murine lung infection model. The antifungal mechanism of action was studied using intact fungal cells, yeast lipid mutants, and small unilamellar lipid …

Molecular Dynamics Study Of The Opening Mechanism For Dna Polymerase I, Carol A. Parish, Bill R. Miller Iii, Eugene Y. Wu

Chemistry Faculty Publications

During DNA replication, DNA polymerases follow an induced fit mechanism in order to rapidly distinguish between correct and incorrect dNTP substrates. The dynamics of this process are crucial to the overall effectiveness of catalysis. Although Xray crystal structures of DNA polymerase I with substrate dNTPs have revealed key structural states along the catalytic pathway, solution fluorescence studies indicate that those key states are populated in the absence of substrate. Herein, we report the first atomistic simulations showing the conformational changes between the closed, open, and ajar conformations of DNA polymerase I in the binary (enzyme:DNA) state to better understand its …

Analysis Of Drug Interactions With Lipoproteins By High Performance Affinity Chromatography, Matthew R. Sobansky

Department of Chemistry: Dissertations, Theses, and Student Research

High density lipoprotein (HDL), low density lipoprotein (LDL), and very low density lipoprotein (VLDL) are lipoproteins previously shown to bind many basic and neutral hydrophobic drugs in serum. These interactions impact the distribution, delivery, metabolism, and excretion of drugs and are important in determining drug activity, pharmacokinetics, and toxicity in the human body. Information about drug-lipoprotein interactions and the strength of these interactions can be useful in determining the distribution of drugs following administration.

The research presented in this dissertation uses high performance affinity chromatography (HPAC) and packed columns to study binding of the drug propranolol to immobilized lipoproteins such …

Optical Characterization And Distribution Of Chromophoric Dissolved Organic Matter (Cdom) In Soil Porewater From A Salt Marsh Ecosystem, Catherine D. Clark, Paige Aiona, Jason K. Keller, Warren J. De Bruyn

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

To characterize chromophoric dissolved organic matter (CDOM) in marsh porewaters and its contribution as a carbon source, optical properties (absorbance, fluorescence indices, 3-dimensional excitation-emission matrices [EEMs]) of soil porewater and surface water were measured in a southern Californian salt marsh. Absorption coefficients and fluorescence intensities were higher in porewater than in overlying surface waters, consistent with higher CDOM concentration at depth. Humic-type peaks A and C were observed in EEMs in all samples, and peak M was observed in surface waters and shallow porewater to -5 cm depth. Fluorescence:absorbance (flu:abs) ratios and spectral slopes (S) decreased across the surface interface, …

Microchip Thermal Gradient Gas Chromatography, Anzi Wang

Theses and Dissertations

Although the airbath oven is a reliable heating method for gas chromatography (GC), resistive heating is needed for higher analytical throughput and on-site chemical analysis because of size, heating rate and power requirements. In the last thirty years, a variety of resistive heating methods were developed and implemented for both benchtop and portable GC systems. Although fast heating rates and low power consumption have been achieved, losses in column efficiency and resolution, complex construction processes and difficulties experienced in recovering damaged columns have also become problematic for routine use of resistively heated columns. To solve these problems, a new resistively …

Association Of G-Quadruplex Forming Sequences With Human Mtdna Deletion Breakpoints, D. W. Dong, F. Pereira, Steven Paul Barrett , '13, J. E. Kolesar, K. Cao, J. Damas, Liliya A. Yatsunyk, F. B. Johnson, B. A. Kaufman

Chemistry & Biochemistry Faculty Works

Background: Mitochondrial DNA (mtDNA) deletions cause disease and accumulate during aging, yet our understanding of the molecular mechanisms underlying their formation remains rudimentary. Guanine-quadruplex (GQ) DNA structures are associated with nuclear DNA instability in cancer; recent evidence indicates they can also form in mitochondrial nucleic acids, suggesting that these non-B DNA structures could be associated with mtDNA deletions. Currently, the multiple types of GQ sequences and their association with human mtDNA stability are unknown. Results: Here, we show an association between human mtDNA deletion breakpoint locations (sites where DNA ends rejoin after deletion of a section) and sequences with G-quadruplex …

Rnase L Contributes To Experimentally Induced Type 1 Diabetes Onset In Mice, Chun Zeng, Xin Yi, Danny Zipris, Hongli Liu, Lin Zhang, Qiaoyun Zheng, Krishnamurthy Malathi, Ge Jin, Aimin Zhou

Chemistry Faculty Publications

The cause of type 1 diabetes continues to be a focus of investigation. Studies have revealed that interferon α (IFNα) in pancreatic islets after viral infection or treatment with double-stranded RNA (dsRNA), a mimic of viral infection, is associated with the onset of type 1 diabetes. However, how IFNα contributes to the onset of type 1 diabetes is obscure. In this study, we found that 2-5A-dependent RNase L (RNase L), an IFNα-inducible enzyme that functions in the antiviral and antiproliferative activities of IFN, played an important role in dsRNA-induced onset of type 1 diabetes. Using RNase L-deficient, rat insulin promoter-B7.1 …

Fabrication, Characterization, Optimization And Application Development Of Novel Thin-Layer Chromatography Plates, Supriya Singh Kanyal

Theses and Dissertations

This dissertation describes advances in the microfabrication of thin layer chromatography (TLC) plates. These plates are prepared by the patterning of carbon nanotube (CNT) forests on substrates, followed by their infiltration with an inorganic material. This document is divided into ten sections or chapters. Chapter 1 reviews the basics of conventional TLC technology. This technology has not changed substantially in decades. This chapter also mentions some of the downsides of the conventional approach, which include unwanted interactions of the binder in the plates with the analytes, relatively slow development times, and only moderately high efficiencies. Chapter 2 focuses primarily on …

Comparison Of Upper Tropospheric Carbon Monoxide From Mopitt, Ace-Fts, And Hippo-Qcls, Sara Martínez-Alonzo, Merritt N. Deeter, Helen M. Worden, John C. Gille, Louisa K. Emmons, Laura L. Pan, Mijeong Park, Gloria L. Manney, Peter F. Bernath, Chris D. Boone

Chemistry & Biochemistry Faculty Publications

Products from the Measurements Of Pollution In The Troposphere (MOPITT) instrument are regularly validated using in situ airborne measurements. However, few of these measurements reach into the upper troposphere, thus hindering MOPITT validation in that region. Here we evaluate upper tropospheric (~500 hPa to the tropopause) MOPITT CO profiles by comparing them to satellite Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) retrievals and to measurements from the High-performance Instrumented Airborne Platform for Environmental Research Pole to Pole Observations (HIPPO) Quantum Cascade Laser Spectrometer (QCLS). Direct comparison of colocated v5 MOPITT thermal infrared-only retrievals, v3.0 ACE-FTS retrievals, and HIPPO-QCLS measurements shows …

Continuous Polymer Reactor Design, David Sujay Kingsley

Dissertations

Twin screw extruders can be used as continuous polymer reactors to process polymers, which are conventionally made through batch reactors. Batch processes have certain undesirable qualities such as improper mixing and the inability to precisely control the reaction, which leads to variation between batches and potential exotherms. The work presented in this dissertation investigates the use of continuous polymer reactor designs to efficiently process renewable sourced thermoplastic polyurethanes (TPU), and prepreg epoxy matrix prepolymers.

The overall goal of this research is to highlight the modularity of twin screw extruders as continuous polymer reactors to synthesize the relevant polymers. Chapter I …

Physicochemical Characterization Of Novel 1,1 0-Phenanthrolines, Dominic Millheim

Masters Theses

1,10-Phenanthroline is a well-known and often-used ligand with a variety of interesting properties and applications to both organic and inorganic chemistry. Interest in novel 1,10-phenanthrolines substituted at the 5- and 6- position has grown recently due to their interesting fluorometric and spectroscopic properties. They have been evaluated recently for applications including chemical sensors, chemical indicators, pharmacological targets and bioactive reagents.

1,10-Phenanthroline, an epoxidated synthetic intermediate, and a novel 5,6- disubstituted aminoalcohol derivative were studied to determine the degree of influence that iterative physical and chemical transformations have on the donor properties of the N-C-C-N pocket. Multiple analytical techniques including potentiometry …

Distinct Conformational Behaviors Of Four Mammalian Dual-Flavin Reductases (Cytochrome P450 Reductase, Methionine Synthase Reductase, Neuronal Nitric Oxide Synthase, Endothelial Nitric Oxide Synthase) Determine Their Unique Catalytic Profiles, Mohammad Mahfuzul Haque, Mekki Bayachou, Jesus Tejero, Claire T. Kenney, Naw M. Pearl, Sang-Choul Im, Lucy Waskell, Dennis J. Stuehr

Chemistry Faculty Publications

Multidomain enzymes often rely on large conformational motions to function. However, the conformational setpoints, rates of domain motions and relationships between these parameters and catalytic activity are not well understood. To address this, we determined and compared the conformational setpoints and the rates of conformational switching between closed unreactive and open reactive states in four mammalian diflavin NADPH oxidoreductases that catalyze important biological electron transfer reactions: cytochrome P450 reductase, methionine synthase reductase and endothelial and neuronal nitric oxide synthase. We used stopped-flow spectroscopy, single turnover methods and a kinetic model that relates electron flux through each enzyme to its conformational …