Rate Constant Ka Research Articles

The fully reduced terminal oxidase bd-I isolated from Escherichia coli binds cyanide

Cytochrome bd-I from Escherichia coli belongs to the superfamily of prokaryotic bd-type oxygen reductases. It contains three hemes, b558, b595 and d, and couples oxidation of quinol by dioxygen with the generation of a proton-motive force. The enzyme exhibits resistance to various stressors and is considered as a target protein for next-generation antimicrobials. By using electronic absorption and MCD spectroscopy, this work shows that cyanide binds to heme d2+ in the isolated fully reduced cytochrome bd-I. Cyanide-induced difference absorption spectra display changes near the heme d2+ α-band, a minimum at 633 nm and a maximum around 600 nm, and a W-shaped response in the Soret region. Apparent dissociation constant (Kd) of the cyanide complex of heme d2+ is ∼0.052 M. Kinetics of cyanide binding is monophasic, indicating the presence of a single ligand binding site in the enzyme. Consistently, MCD data show that cyanide binds to heme d2+ but not to b5582+ or b5952+. This agrees with the published structural data that the enzyme's active site is not a di-heme site. The observed rate of binding (kobs) increases as the concentration of cyanide is increased, giving a second-order rate constant (kon) of ∼0.1 M−1 s−1.

Investigation of the Affinity of Aptamers for Bacteria by Surface Plasmon Resonance Imaging Using Nanosomes.

The cell-SELEX method enables efficient selection of aptamers that bind whole bacterial cells. However, after selection, it is difficult to determine their binding affinities using common screening methods because of the large size of the bacteria. Here we propose a simple surface plasmon resonance imaging method (SPRi) for aptamer characterization using bacterial membrane vesicles, called nanosomes, instead of whole cells. Nanosomes were obtained from membrane fragments after mechanical cell disruption in order to preserve the external surface epitopes of the bacterium used for their production. The study was conducted on Bacillus cereus (B. cereus), a Gram-positive bacterium commonly found in soil, rice, vegetables, and dairy products. Four aptamers and one negative control were initially grafted onto a biochip. The binding of B. cereus cells and nanosomes to immobilized aptamers was then compared. The use of nanosomes instead of cells provided a 30-fold amplification of the SPRi signal, thus allowing the selection of aptamers with higher affinities. Aptamer SP15 was found to be the most sensitive and selective for B. cereus ATCC14579 nanosomes. It was then truncated into three new sequences (SP15M, SP15S1, and SP15S2) to reduce its size while preserving the binding site. Fitting the results of the SPRi signal for B. cereus nanosomes showed a similar trend for SP15 and SP15M, and a slightly higher apparent association rate constant kon for SP15S2, which is the truncation with a high probability of a G-quadruplex structure. These observations were confirmed on nanosomes from B. cereus ATCC14579 grown in milk and from the clinical strain B. cereus J066. The developed method was validated using fluorescence microscopy on whole B. cereus cells and the SP15M aptamer labeled with a rhodamine. This study showed that nanosomes can successfully mimic the bacterial membrane with great potential for facilitating the screening of specific ligands for bacteria.

Evaluating the biomolecular interaction between delamanid/formulations and human serum albumin by fluorescence, CD spectroscopy and SPR: Effects on protein conformation, kinetic and thermodynamic parameters

Delamanid is an anti-tuberculosis drug used for the treatment of drug-resistant tuberculosis. Since delamanid has a high protein bound potential, even patients with low albumin levels should experience high and rapid delamanid clearance. However, the interaction between delamanid and albumin should be better controlled to optimize drug efficacy. This study was designed to evaluate the binding characteristics of delamanid to human serum albumin (HSA) using various methods: fluorescence spectroscopy, circular dichroism (CD), surface plasmon resonance (SPR), and molecular docking simulation. The fluorescence emission band without any shift indicated the interaction was not affected by the polarity of the fluorophore microenvironment. The reduction of fluorescence intensity at 344 nm was proportional to the increment of delamanid concentration as a fluorescence quencher. UV-absorbance measurement at the maximum wavelength (λmax, 280 nm) was evaluated using inner filter effect correction. The HSA conformation change was explained by the intermolecular energy transfer between delamanid and HSA during complex formation. The study, which was conducted at temperatures of 298 K, 303 K, and 310 K, revealed a static quenching mechanism that correlated with a decreased of bimolecular quenching rate constant (kq) and binding constant (Ka) at increased temperatures. The Ka was 1.75–3.16 × 104 M−1 with a specific binding site with stoichiometry 1:1. The negative enthalpy change, negative entropy change, and negative Gibbs free energy change demonstrated an exothermic-spontaneous reaction while van der Waals forces and hydrogen bonds played a vital role in the binding. The molecular displacement approach and molecular docking confirmed that the binding occurred mainly in subdomain IIA, which is a hydrophobic pocket of HSA, with a theoretical binding free energy of −9.33 kcal/mol. SPR exhibited a real time negative sensorgram that resulted from deviation of the reflex angle due to ligand delamanid-HSA complex forming. The binding occurred spontaneously after delamanid was presented to the HSA surface. The SPR mathematical fitting model revealed that the association rate constant (kon) was 2.62 × 108 s−1M−1 and the dissociation rate constant (koff) was 5.65 × 10−3 s−1. The complexes were performed with an association constant (KA) of 4.64 × 1010 M−1 and the dissociation constant (KD) of 2.15 × 10−11 M. The binding constant indicated high binding affinity and high stability of the complex in an equilibrium. Modified CD spectra revealed that conformation of the HSA structure was altered by the presence of delamanid during preparation of the proliposomes that led to the reduction of secondary structure stabilization. This was indicated by the percentage decrease of α-helix. These findings are beneficial to understanding delamanid-HSA binding characteristics as well as the drug administration regimen.

A Sensitive Technique Unravels the Kinetics of Activation and Trans-Cleavage of CRISPR-Cas Systems.

Activation of the CRISPR-Cas13a system requires the formation of a crRNA-Cas13a ribonucleoprotein (RNP) complex and the binding of an RNA activator to the RNP. These two binding processes play a crucial role in the performance of the CRISPR-Cas13a system. However, the binding kinetics remain poorly understood, and a main challenge is the lack of a sensitive method for real-time measurements of the dynamically formed active CRISPR-Cas13a enzyme. We describe here a new method to study the binding kinetics and report the rate constants (kon and koff) and dissociation constant (Kd) for the binding between Cas13a and its activator. The method is able to unravel and quantify the kinetics of binding and cleavage separately, on the basis of measuring the real-time trans-cleavage rates of the CRISPR-Cas system and obtaining the real-time concentrations of the active CRISPR-Cas ternary complex. We further discovered that once activated, the Cas13a system operates at a wide range of temperatures (7-37 °C) with fast trans-cleavage kinetics. The new method and findings are important for diverse applications of the Cas13a system, such as the demonstrated quantification of microRNA at ambient temperatures (e.g., 25 °C).

A Sensitive Technique Unravels the Kinetics of Activation and Trans‐Cleavage of CRISPR‐Cas Systems

AbstractActivation of the CRISPR‐Cas13a system requires the formation of a crRNA‐Cas13a ribonucleoprotein (RNP) complex and the binding of an RNA activator to the RNP. These two binding processes play a crucial role in the performance of the CRISPR‐Cas13a system. However, the binding kinetics remain poorly understood, and a main challenge is the lack of a sensitive method for real‐time measurements of the dynamically formed active CRISPR‐Cas13a enzyme. We describe here a new method to study the binding kinetics and report the rate constants (kon and koff) and dissociation constant (Kd) for the binding between Cas13a and its activator. The method is able to unravel and quantify the kinetics of binding and cleavage separately, on the basis of measuring the real‐time trans‐cleavage rates of the CRISPR‐Cas system and obtaining the real‐time concentrations of the active CRISPR‐Cas ternary complex. We further discovered that once activated, the Cas13a system operates at a wide range of temperatures (7–37 °C) with fast trans‐cleavage kinetics. The new method and findings are important for diverse applications of the Cas13a system, such as the demonstrated quantification of microRNA at ambient temperatures (e.g., 25 °C).

Kinetic modeling of the plasma pharmacokinetic profiles of ADAMTS13 fragment and its Fc-fusion counterpart in mice.

Introduction: Fusion of the fragment crystallizable (Fc) to protein therapeutics is commonly used to extend the circulation time by enhancing neonatal Fc-receptor (FcRn)-mediated endosomal recycling and slowing renal clearance. This study applied kinetic modeling to gain insights into the cellular processing contributing to the observed pharmacokinetic (PK) differences between the novel recombinant ADAMTS13 fragment (MDTCS) and its Fc-fusion protein (MDTCS-Fc). Methods: For MDTCS and MDTCS-Fc, their plasma PK profiles were obtained at two dose levels following intravenous administration of the respective proteins to mice. The plasma PK profiles of MDTCS were fitted to a kinetic model with three unknown protein-dependent parameters representing the fraction recycled (FR) and the rate constants for endocytosis (kup, for the uptake into the endosomes) and for the transfer from the plasma to the interstitial fluid (kpi). For MDTCS-Fc, the model was modified to include an additional parameter for binding to FcRn. Parameter optimization was done using the Cluster Gauss-Newton Method (CGNM), an algorithm that identifies multiple sets of approximate solutions ("accepted" parameter sets) to nonlinear least-squares problems. Results: As expected, the kinetic modeling results yielded the FR of MDTCS-Fc to be 2.8-fold greater than that of MDTCS (0.8497 and 0.3061, respectively). In addition, MDTCS-Fc was predicted to undergo endocytosis (the uptake into the endosomes) at a slower rate than MDTCS. Sensitivity analyses identified the association rate constant (kon) between MDTCS-Fc and FcRn as a potentially important factor influencing the plasma half-life in vivo. Discussion: Our analyses suggested that Fc fusion to MDTCS leads to changes in not only the FR but also the uptake into the endosomes, impacting the systemic plasma PK profiles. These findings may be used to develop recombinant protein therapeutics with extended circulation time.

EPLERENONE FLOATING MICROSPHERES: RADIOGRAPHIC AND PHARMACOKINETIC STUDIES IN RABBITS

Objective: The objective of the present investigation was to evaluate gastro-retentive performance and pharmacokinetic parameters of Eplerenone-optimized floating microspheres compared with formulated floating tablets. Methods: Microsphere contains antihypertensive drug Eplerenone as a core material encapsulated with the polymeric membrane for sustained drug release were prepared by solvent diffusion-evaporation technique. The prepared microspheres were evaluated for qualitative and quantitative parameters. The optimized formulation showed favorable in vitro floating and drug release profile. The gamma scintigraphy of the formulation was carried out in rabbit in order to determine the floating ability of the final formulation with barium sulfate. Prolonged gastric residence time of over 12 h was achieved in all the animals. Eplerenone-loaded optimized formulation was orally administered to rabbit and blood samples were used to determine pharmacokinetic parameter by using WinNonlin software 3.0 version. Results: Eplerenone floating microsphere, which are compared with pharmacokinetic parameters of the Floating tablet showed improved parameters of Cmax; similarly, time to reach peak plasma concentration (t-max) for Eplerenone Floating microspheres was 4 times increased against Floating tablet formulation. The area under the curve (AUC) for formulated floating tablet was found to be 9.69 µg/ml, whereas for floating microspheres it was 16.28 µg/ml, for formulated floated tablet absorption rate constant Ka was 1.61 h, elimination rate constant was 0.112 h and elimination half-life 6.2 h. The comparison of these data undoubtedly shows that the Cmax was not much valid, but AUC was increased to about 1.68 times in case of floating microspheres, absorption rate constant was found to be decrease 3.22 times when related to the floating microspheres, whereas Ke was found to be decrease 2.11 times when equated to floating microspheres, elimination half-life was increased by almost about two times. Conclusion: Eplerenone floating microsphere, which are compared with pharmacokinetic parameters of the floating tablets showed enhanced parameters of the formulated due to floating nature of the present designed formulation.

Revolutionizing the capture efficiency of ultrasensitive digital ELISA via an antibody oriented-immobilization strategy.

Bead-based digital ELISA, the most sensitive protein quantification method, has drawn much attention to exploring ultra-low abundance biomarkers in the life sciences and clinical applications. However, its major challenge refers to the low antigen capture efficiency in the immunoreaction process due to the low probability of collision between the deficient concentration of the analytes and the captured antibody-immobilized on the beads. Here, we achieved significantly improved reaction efficiency in the digital signal formation by fixing the orientation of antibodies and revealed the kinetic mechanism for the first time. A facile and fast antibody conjugation strategy that formed boronate ester complexes was designed to retain the uniform orientation of antibodies with controllable antibody density. Remarkably, the oriented immobilized antibody exhibited stronger antigen-binding capacity and faster antigen-binding speed compared to randomly immobilized antibodies, with capture efficiency increasing approximately 14-fold at 15 μg of antibody per 1 mg microbeads (0.035 antibody nm-2) under 0.5 h incubation. Combined with theoretical analysis, we verified that the improved capture efficiency of the oriented antibodies mainly originated from the considerable rise in the binding rate constant (kon) rather than the increase in antigen-binding sites, which further prominently decreased the limit of detection (LoD) in a shorter incubation time compared with the randomly immobilized antibody. In conclusion, the antibody oriented conjugation method effectively overcomes the low capture efficiency challenge of bead-based digital ELISA. It paves a promising way for further improving the digital immunoassay performance and promotes the early diagnosis of diseases by recognizing more ultra-low abundance significant biomarkers.

Altering Calcium Sensitivity in Heart Failure: A Crossroads of Disease Etiology and Therapeutic Innovation.

Heart failure (HF) presents a significant clinical challenge, with current treatments mainly easing symptoms without stopping disease progression. The targeting of calcium (Ca2+) regulation is emerging as a key area for innovative HF treatments that could significantly alter disease outcomes and enhance cardiac function. In this review, we aim to explore the implications of altered Ca2+ sensitivity, a key determinant of cardiac muscle force, in HF, including its roles during systole and diastole and its association with different HF types-HF with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). We further highlight the role of the two rate constants kon (Ca2+ binding to Troponin C) and koff (its dissociation) to fully comprehend how changes in Ca2+ sensitivity impact heart function. Additionally, we examine how increased Ca2+ sensitivity, while boosting systolic function, also presents diastolic risks, potentially leading to arrhythmias and sudden cardiac death. This suggests that strategies aimed at moderating myofilament Ca2+ sensitivity could revolutionize anti-arrhythmic approaches, reshaping the HF treatment landscape. In conclusion, we emphasize the need for precision in therapeutic approaches targeting Ca2+ sensitivity and call for comprehensive research into the complex interactions between Ca2+ regulation, myofilament sensitivity, and their clinical manifestations in HF.

Rapid and Label-Free Analysis of Antigen-Antibody Dynamic Binding of Tumor Markers Using Piezoelectric Quartz Crystal Biosensor.

Quantitative biomacromolecular diagnosis is rapidly developing in molecular oncology. In this study, we developed a continuous flow immunoassay device based on a piezoelectric (PZ) quartz crystal biosensor fabricated with whole-electrode occupation for the quantitative molecular diagnosis of tumor markers such as alpha-fetoprotein (AFP). Only one face of the crystal was in contact with the serum sample during the assays. First, the characteristics of AFP and anti-AFP binding kinetics, such as the optimal time for immune response, the average antigen binding rate, the kinetic constants and the optimal standard curve, were investigated. The overall immunoreaction time was only 12 min, the average antigen binding rate of AFP was 45.9 ng/min, the concentration range of AFP detection was 18.8-1100 ng/mL and the association rate constant (kon), dissociation rate constant (koff) and equilibrium dissociation constant (KD) were 5.58×104 M-1s-1,1.79×10-5 s-1 and 3.21×10-10 M, respectively. This sensing system was further validated by detecting AFP values from clinical serum samples, which were obtained from pregnant women, liver and lung cancer patients and those undergoing liver cancer screening. No cross-reactivity with lung cancer markers were found, and the detection results were in good agreement with the radioimmunoassay (RIA) results, with a relative deviation of no more than 3.7% and correlation coefficient r of 0.9998. Therefore, the developed immunoassay device has the potential to be used in large-scale screening for cancers, as well as in novel high-affinity binding drug development.

Photoinduced electron transfer in cytochrome bc1: Dynamics of rotation of the Iron-sulfur protein during bifurcated electron transfer from ubiquinol to cytochrome c1 and cytochrome bL

The electron transfer reactions within wild-type Rhodobacter sphaeroides cytochrome bc1 (cyt bc1) were studied using a binuclear ruthenium complex to rapidly photooxidize cyt c1. When cyt c1, the iron‑sulfur center Fe2S2, and cyt bH were reduced before the reaction, photooxidation of cyt c1 led to electron transfer from Fe2S2 to cyt c1 with a rate constant of ka = 80,000 s−1, followed by bifurcated reduction of both Fe2S2 and cyt bL by QH2 in the Qo site with a rate constant of k2 = 3000 s−1. The resulting Q then traveled from the Qo site to the Qi site and oxidized one equivalent each of cyt bL and cyt bH with a rate constant of k3 = 340 s−1. The rate constant ka was decreased in a nonlinear fashion by a factor of 53 as the viscosity was increased to 13.7. A mechanism that is consistent with the effect of viscosity involves rotational diffusion of the iron‑sulfur protein from the b state with reduced Fe2S2 close to cyt bL to one or more intermediate states, followed by rotation to the final c1 state with Fe2S2 close to cyt c1, and rapid electron transfer to cyt c1.

Study on the mechanism and kinetics of amine with steric hindrance absorbing CO2 in non-aqueous/aqueous solution

Several alkanolamines (1A2P, 2A1P, AMP, MAE, EAE, and IPAE) were selected to study the steric hindrance effect on reaction kinetics between amine and CO2 in ethanol and aqueous solutions. Pseudo first-order reaction rate constant k0 was measured by the stopped-flow apparatus. Zwitterion mechanism was applied to describe the reaction and the k0 was well fitted by the corresponding kinetic model with average absolute relative deviation (AARD) in a range of 1.08%-3.89%. Apparent second-order reaction rate constant KA revealed that the reaction rate is simultaneously controlled by steric hindrance and pKa of amines. Additional alkyl groups increase the steric hindrance of amines and accelerate the decomposition of zwitterions. As a result, the reaction rate decreases with stronger steric hindrance effect. The larger pKa is conducive to a better proton receiving of amine. This leads to an acceleration of the deprotonation reaction of zwitterion intermediate. In addition, the relative influence of steric hindrance and pKa on the reaction kinetics is also related to the solvent environment.

Passive immunization against COVID-19 by anti-SARS-CoV-2 spike IgG in commercially available immunoglobulin preparations in severe antibody deficiency

Passive immunization against COVID-19 by anti-SARS-CoV-2 spike IgG in commercially available immunoglobulin preparations in severe antibody deficiency

A Full Target-Mediated Drug Disposition (TMDD) Model to Explain the Changes in Recombinant Human Erythropoietin (rhEpo) Pharmacokinetics in Patients with Different Bone Marrow Integrity Following Hematopoietic Transplantation

Our aim was to build a mechanistic full target-mediated drug disposition (TMDD) model for rhEpo to better understand rhEpo disposition, Epo receptor (EpoR) synthesis, and degradation in hematopoietic transplant patients with four distinct bone marrow conditions. All PK data were analyzed simultaneously using the nonlinear mixed effect modeling approach with NONMEM. The final model was a two-compartmental full TMDD model, which adequately characterizes rhEpo PK in patients and provides insight into the dynamics of free EpoR, rhEpo-EpoR, and total EpoR. The model predicted association rate constant (kon), dissociation rate constant (koff), and internalization rate constant (kint) were 0.0276 pM−1h−1, 0.647 h−1, and 0.255h−1, respectively, which were supported by experimental data. Also, the EpoR degradation rate constant (kdeg) was estimated to be 0.461 h−1. EpoR production rate was estimated to be 37.5 pM/h for adults at pre-ablation baseline and 5.91 pM/h, and 4.19 pM/h in the early post-transplant post-engraftment, and late post-transplant full engraftment. Our model provides extensive information on the dynamics of free EpoR, total EpoR and rhEpo-EpoR, and proven to be more robust and can provide more physiologically relevant binding parameters than previous models.

The mitotic spindle protein CKAP2 potently increases formation and stability of microtubules.

Cells increase microtubule dynamics to make large rearrangements to their microtubule cytoskeleton during cell division. Changes in microtubule dynamics are essential for the formation and function of the mitotic spindle, and misregulation can lead to aneuploidy and cancer. Using in vitro reconstitution assays we show that the mitotic spindle protein Cytoskeleton-Associated Protein 2 (CKAP2) has a strong effect on nucleation of microtubules by lowering the critical tubulin concentration 100-fold. CKAP2 increases the apparent rate constant ka of microtubule growth by 50-fold and increases microtubule growth rates. In addition, CKAP2 strongly suppresses catastrophes. Our results identify CKAP2 as the most potent microtubule growth factor to date. These finding help explain CKAP2's role as an important spindle protein, proliferation marker, and oncogene.

Application of the Cu@PET Composite Track-Etched Membranes for Catalytic Removal of Cr(VI) Ions

This research examines the features of obtaining composite track-etched membranes based on copper microtubes using various compositions of a deposition solution and various types of reducing agents, such as formaldehyde (Cu_CHOH@PET), dimethylamine borane (Cu_DMAB@PET), glyoxylic acid (Cu_Gly@PET). The structure and composition of the membrane composites were studied by scanning elec-tron microscopy and X-ray phase analysis. It was shown that in the case of using dimethylamine borane as a reducing agent, the obtained composites consisted of copper(I) oxide (37.4 %) and copper(0) (62.6 %), in other cases single-component copper microtubes were obtained. The reduction reaction of chromium(VI) ions was used to evaluate the catalytic ability of prepared composites. It was found that the removal efficiency of chromium ions reached up to 95–97 % in the case of single-component composites; the presence of a cop-per(I) oxide phase in the structure of the Cu_DMAB@PET composites significantly reduced the activity of catalysts and under similar conditions, only 41% of the contaminant was removed from the reaction system. The degradation reaction of Cr(VI) was found to follow the Langmuir-Hinshelwood mechanism and a pseu-do-first-order kinetic model. The calculated value of the reaction rate constant ka for composites of the Cu_DMAB@PET composition (0.017 min–1) was more than 9 times less than that of composites obtained us-ing glyoxylic acid (0.156 min–1) and more than 15 times less than the ka value of Cu_CHOH@PET samples (0.249 min–1). Effect of temperatures on the catalytic ability of composites was studied in the temperature range of 10–38 °C. Some thermodynamic characteristics such as activation energy, enthalpy, and entropy of activation were calculated. It was found that the minimum value of the activation energy was obtained for the Cu_CHOH@PET samples.

Molecular insight into drugs binding to ctDNA: the fluorescence fast kinetic analysis of diclofenac and pentamidine

Diclofenac and pentamidine are renowned drugs able to bind DNA by groove-binding mechanisms. Even though the binding mechanism is known, accurate kinetic constants of the binary interaction have never been directly measured. The present work reports the study of the interaction between ctDNA and the two drugs, with very different molecular structure, by steady-state and stopped-flow fluorescence. From the stopped-flow kinetic measurements, we calculated the association and dissociation rate constants (kon and koff). The kinetic constants were then used to calculate the equilibrium dissociation binding constant (KD) and the values have been compared with what obtained from steady-state fluorescence.Graphical abstract

1088. A Whole-Body Quantitative System Pharmacology Physiologically-Based Pharmacokinetic (QSP/PBPK) Model to Support Dose Selection of ADG20: an Extended Half-Life Monoclonal Antibody Being Developed for the Treatment of Coronavirus Disease (COVID-19)

BackgroundADG20 is a fully human IgG1 monoclonal antibody engineered to have potent and broad neutralization against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other SARS-like CoVs with pandemic potential and an extended half-life. ADG20 is administered intramuscularly (IM). A QSP/PBPK model was constructed to support dose selection for a Phase 2/3 trial of ambulatory patients with mild to moderate COVID-19 (STAMP: NCT04805671).MethodsA QSP/PBPK model was used to simulate receptor occupancy (RO) and drug exposure in the upper airway (nasopharyngeal/oropharyngeal epithelial lining fluid [ELF] compartment). RO was linked to an existing viral dynamic model to enable the prediction of the natural time course of viral load and the effect of ADG20 on viral clearance and infectivity rate. RO was calculated using: 1) in vitro ADG20–SARS-CoV-2 binding kinetics (association rate constant (kon) of 1.52E+06 M-1•s1 and dissociation rate constant (koff) of 2.81E-04 s-1 from a Biacore assay; 2) time course of ADG20 concentrations in ELF; and 3) time course of viral load following ADG20 administration. Molar SARS-CoV-2 viral binding site capacity was calculated assuming 40 spike proteins per virion, 3 binding sites per spike, and an initial viral load of log 107 copies/mL for all patients. The QSP/PBPK model and a 2018 CDC reference body weight distribution (45–150 kg) were used to simulate 1000 concentration-time profiles for a range of candidate ADG20 regimens. ADG20 regimens were evaluated against 2 criteria: 1) ability to attain near complete ( >90%), and durable (28-day) SARS-CoV-2 RO in the ELF; and 2) ability to maintain ELF ADG20 concentrations relative to a concentration (0.5 mg/L) associated with 100% viral growth suppression in an in vitro post-infection assay.ResultsA single 300 mg IM ADG20 dose met the dose selection criteria in terms of RO (Figure A) and viral growth suppression (Figure B).ConclusionThese data support the evaluation of an ADG20 300 mg IM dose for the treatment of mild to moderate COVID-19. ADG20 is forecasted to attain near complete ( >90%) SARS-CoV-2 RO in the ELF and maintain ELF ADG20 concentrations above that associated with 100% viral growth suppression in vitro.Figure. QSP/PBPK model forecast of ADG20 300 mg IM in adults (A) Predicted RO expressed as percent occupancy with the dotted line representing the threshold for 90% RO. (B) Predicted median concentration of ADG20 relative to a concentration (0.5 mg/L) associated with 100% viral growth suppression as indicated by the dotted line; the shaded area represents the 90% prediction interval.Disclosures Evan D. Tarbell, PhD, Adagio Therapeutics, Inc. (Independent Contractor) Scott A. Van Wart, PhD, Adagio Therapeutics, Inc. (Independent Contractor) Laura M. Walker, PhD, Adagio Therapeutics, Inc. (Other Financial or Material Support, Laura M. Walker is an inventor on a patent application submitted by Adagio Therapeutics, Inc., describing the engineered SARS-CoV-2 antibody.) Andrew Santulli, PhD, Adagio Therapeutics, Inc. (Independent Contractor) Lynn E. Connolly, MD, PhD, Adagio Therapeutics, Inc. (Employee) Donald E Mager, PharmD, PhD, Adagio Therapeutics, Inc. (Independent Contractor) Paul G. Ambrose, PharmD, Adagio Therapeutics, Inc. (Employee)

Phosphorus removal from wastewater through struvite crystallization in a continuous fluidized-bed reactor: An improved comprehensive model

Promoting a wider application of struvite precipitation for nutrient recovery from wastewaters requires more efficient reactor designs, supported by models that integrate thermodynamic, kinetic and hydrodynamic behavior. The present work addresses the modeling of phosphorus recovery by struvite crystallization in fluidized-bed reactors, revealing discrepancies and errors in the literature and proposing corrections and improvements. A reduced thermodynamic model is presented. The potential of the struvite solubility constant was estimated to be 13.12 < pK < 13.30. Furthermore, a new strategy for a simple and quick estimation of the surface-area specific rate constant ka (1.70 dm/h ≤ ka ≤ 2.19 dm/h) was implemented. The technique involves operating the reactor with liquid in the transient regime as a completely stirred tank and solid-mixed bed in the pseudosteady state. Size distribution simulation results were obtained for different operational conditions using a one-dimensional perfect size classification model for the solid phase and a plug-flow model for the liquid phase.

Regulation of the Volume Flow Rate of Aqueous Methyl Blue Solution and the Wettability of CuO/ZnO Nanorods to Improve the Photodegradation Performance of Related Microfluidic Reactors.

Six CuO/ZnO nanorod (CuO/ZnONR)-based microfluidic reactors were constructed for different UV irradiation durations, with which an aqueous methylene blue (MB) solution was photodegraded at varied volume flow rate Q. Via numerical and experimental routes, the effects of the Q on the kinetic adsorption rate constant Ka and the initial rate constant KA of the CuO/ZnONR-based microfluidic reactors were discussed. Moreover, a reverse contacting angle (CA) trend of CuO/ZnONRs to the reaction constant K curve of corresponding CuO/ZnONR-based microfluidic reactor suggested that the CA of CuO/ZnONRs was another key influencing factor that affected greatly the photodegradation performance of the microfluidic reactors. The Q of the aqueous MB solution and the UV irradiation duration for the photodeposition of CuO/ZnONRs were optimized to be 125 μL/min and 1.0 h, the K of the CuO/ZnONR-based microfluidic reactors reached 4.84 min-1, and the related ΔKA/K was less than 6%. Similarly, these methods and results can be employed not only to enhance the mass transport and adsorption of specific species within other nanostructured matrix material-coated microchannels but also to enlarge the actual contacting surface areas between these microchannels and the related solution, which further improve the performance of other nanostructured catalyst-based microfluidic reactors, rGO microfluidic voltage generation, and a GOx/AuNW enzymatic glucose microfluidic sensor.