Concentration and temperature dependence of viscosity in lysozyme aqueous solutions

Flow Activation Energy of High-Concentration Monoclonal Antibody Solutions and Protein-Protein Interactions Influenced by NaCl and Sucrose

The solution viscosity and protein-protein interactions (PPIs) as a function of temperature (4-40 °C) were measured at a series of protein concentrations for a monoclonal antibody (mAb) with different formulation conditions, which include NaCl and sucrose. The flow activation energy (Eη) was extracted from the temperature dependence of solution viscosity using the Arrhenius equation. PPIs were quantified via the protein diffusion interaction parameter (kD) measured by dynamic light scattering, together with the osmotic second virial coefficient and the structure factor obtained through small-angle X-ray scattering. Both viscosity and PPIs were found to vary with the formulation conditions. Adding NaCl introduces an attractive interaction but leads to a significant reduction in the viscosity. However, adding sucrose enhances an overall repulsive effect and leads to a slight decrease in viscosity. Thus, the averaged (attractive or repulsive) PPI information is not a good indicator of viscosity at high protein concentrations for the mAb studied here. Instead, a correlation based on the temperature dependence of viscosity (i.e., Eη) and the temperature sensitivity in PPIs was observed for this specific mAb. When kD is more sensitive to the temperature variation, it corresponds to a larger value of Eη and thus a higher viscosity in concentrated protein solutions. When kD is less sensitive to temperature change, it corresponds to a smaller value of Eη and thus a lower viscosity at high protein concentrations. Rather than the absolute value of PPIs at a given temperature, our results show that the temperature sensitivity of PPIs may be a more useful metric for predicting issues with high viscosity of concentrated solutions. In addition, we also demonstrate that caution is required in choosing a proper protein concentration range to extract kD. In some excipient conditions studied here, the appropriate protein concentration range needs to be less than 4 mg/mL, remarkably lower than the typical concentration range used in the literature.

Classical and Nonclassical Nucleation Mechanisms of Insulin Crystals

Although the Classical Nucleation Theory (CNT) is the most consensual theory to explain protein nucleation mechanisms, experimental observations during the shear-induced assays suggest that the CNT does not always describe the insulin nucleation process. This is the case at intermediate precipitant (ZnCl2) solution concentrations (2.3 mM) and high-temperature values (20 and 40 °C) as well as at low precipitant solution concentrations (1.6 mM) and low-temperature values (5 °C). In this work, crystallization events following the CNT registered at high precipitant solution concentrations (3.1 and 4.7 mM) are typically described by a Newtonian response. On the other hand, crystallization events following a nonclassical nucleation pathway seem to involve the formation of a metastable intermediate state before crystal formation and are described by a transition from Newtonian to shear-thinning responses. A dominant shear-thinning behavior (shear viscosity values ranging more than 6 orders of magnitude) is found during aggregation/agglomeration events. The rheological analysis is complemented with different characterization techniques (Dynamic Light Scattering, Energy-Dispersive Spectroscopy, Circular Dichroism, and Differential Scanning Calorimetry) to understand the insulin behavior in solution, especially during the occurrence of aggregation/agglomeration events. To the best of our knowledge, the current work is the first study describing nonclassical nucleation mechanisms during shear-induced crystallization experiments, which reveals the potential of the interdisciplinary approach herein described and opens a window for a clear understanding of protein nucleation mechanisms.

Droplet-based microfluidic platform for viscosity measurement over extended concentration range

Rheology of concentrated protein solutions is crucial for the understanding of macromolecular crowding dynamics as well as the formulation of protein therapeutics. The cost and scarcity of most protein samples prevents wide-scale rheological studies as conventional viscosity measurement methods require large sample volume. There is a growing need for a precise and robust viscosity measurement tool that minimizes consumption and simplifies the handling of highly concentrated protein solutions. This objective is achieved by combining microfluidics and microrheology: we developed a specific microsystem to study the viscosity of aqueous solutions at high concentrations. The PDMS chip allows in situ production, storing and monitoring of water-in-oil nanoliter droplets. We perform precise viscosity measurements inside individual droplets by particle-tracking microrheology of fluorescent probes. Pervaporation of water through a PDMS membrane induces aqueous droplet shrinking, concentrating the sample up to 150 times, thus allowing viscosity measurements along an extended concentration range in just one experiment. The methodology is precisely validated by studying the viscosity of sucrose solutions. Two model proteins are also studied with sample consumption reduced to as little as 1 μL of diluted solution, showcasing the viability of our approach for the study of biopharmaceuticals.

Biomolecular response to hour-long ultralow field microwave radiation: An effective coarse-grained model simulation

Various electronic devices, which we commonly use, radiate microwaves. Such external perturbation influences the functionality of biomolecules. In an ultralow field, the cumulative response of a molecule is expected only over a time scale of hours. To study the structural dynamics of biomolecules over hours, we adopt a simple methodology for constructing the coarse-grained structure of the protein molecule and solve the Langevin equation under different working potentials. In this approach, each amino acid residue of a biomolecule is mapped onto a number of beads, a few for the backbone, and few for the side chain, depending on the complexity of its chemical structure. We choose the force field in such a way that the dynamics of the protein molecule in the presence of ultralow radiation field of microvolt/nm could be followed over the time frame of 2 h. We apply the model to describe a biomolecule, hen egg white lysozyme, and simulate its structural evolution under ultralow strength electromagnetic radiation. The simulation revealed the finer structural details, like the extent of exposure of bioactive residues and the state of the secondary structures of the molecule, further confirmed from spectroscopic measurements [details are available in Phys. Rev. E 97, 052416 (2018)10.1103/PhysRevE.97.052416 and briefly described here]. Though tested for a specific system, the model is quite general. We believe that it harnesses the potential in studying the structural dynamics of any biopolymer under external perturbation over an extended time scale.

Characterization and Modeling of Reversible Antibody Self-Association Provide Insights into Behavior, Prediction, and Correction

Reversible antibody self-association, while having major developability and therapeutic implications, is not fully understood or readily predictable and correctable. For a strongly self-associating humanized mAb variant, resulting in unacceptable viscosity, the monovalent affinity of self-interaction was measured in the low μM range, typical of many specific and biologically relevant protein-protein interactions. A face-to-face interaction model extending across both the heavy-chain (HC) and light-chain (LC) Complementary Determining Regions (CDRs) was apparent from biochemical and mutagenesis approaches as well as computational modeling. Light scattering experiments involving individual mAb, Fc, Fab, and Fab'2 domains revealed that Fabs self-interact to form dimers, while bivalent mAb/Fab'2 forms lead to significant oligomerization. Site-directed mutagenesis of aromatic residues identified by homology model patch analysis and self-docking dramatically affected self-association, demonstrating the utility of these predictive approaches, while revealing a highly specific and tunable nature of self-binding modulated by single point mutations. Mutagenesis at these same key HC/LC CDR positions that affect self-interaction also typically abolished target binding with notable exceptions, clearly demonstrating the difficulties yet possibility of correcting self-association through engineering. Clear correlations were also observed between different methods used to assess self-interaction, such as Dynamic Light Scattering (DLS) and Affinity-Capture Self-Interaction Nanoparticle Spectroscopy (AC-SINS). Our findings advance our understanding of therapeutic protein and antibody self-association and offer insights into its prediction, evaluation and corrective mitigation to aid therapeutic development.

Temperature Dependence of Protein Solution Viscosity and Protein-Protein Interactions: Insights into the Origins of High-Viscosity Protein Solutions

Protein solution viscosity (η) as a function of temperature was measured at a series of protein concentrations under a range of formulation conditions for two monoclonal antibodies (MAbs) and a globular protein (aCgn). Based on theoretical arguments, a strong temperature dependence for protein-protein interactions (PPI) indicates highly anisotropic, short-ranged attractions that could lead to higher solution viscosities. The semi-empirical Ross-Minton model was used to determine the apparent intrinsic viscosity, shape, and "crowding" factors for each protein as a function of temperature and formulation conditions. The apparent intrinsic viscosity was independent of temperature for aCgn, while a slight decrease with increasing temperature was observed for the MAbs. The temperature dependence of solution viscosity was analyzed using the Andrade-Eyring equation to determine the effective activation energy of viscous flow (E_a,η). While E_a,η values were different for each protein, they were independent of formulation conditions for a given protein. PPI were quantified via the osmotic second virial coefficient (B₂₂) and the protein diffusion interaction parameter (k_D) as a function of temperature under the same formulation conditions as the viscosity measurements. Net interactions ranged from strongly attractive to repulsive by changing formulation pH and ionic strength for each protein. Overall, larger activation energies for PPI corresponded to larger activation energies for η, and those were predictive of the highest η values at higher protein concentrations.

An Empirical Quantitative Model Describing Simultaneously Temperature and Concentration Effects on Protein Solution Viscosity

The viscosity of high-concentration protein solutions can lead to a range of challenges in drug product manufacturing and administration. Accurately modeling the viscosity of biologics solutions in response to changes in the formulation and surrounding environment is of significant interest and remains a challenge. Here, we show a practical method of modeling the viscosity of a therapeutic solution in response to changes in temperature and protein concentration. Our viscosity model consists of a Ross-Minton model of concentration dependence and a modified Arrhenius temperature dependence. We measured the viscosity as a function of concentration and temperature of 4 therapeutic antibodies in a range of potential clinical formulations. With these data, our model shows surprising generality, proving effective with different types of antibodies, formulations, and a range of more than 2 orders of magnitude in viscosity. Our approach is built on existing theory but provides a practical approach to modeling the viscosity of formulated drug product over the range of process-relevant concentrations and temperatures to better mitigate challenges in the drug manufacturing process.

Microwave-radiation-induced molecular structural rearrangement of hen egg-white lysozyme

We have investigated the nonthermal effect of 10 GHz/22 dBm microwave radiation on hen egg-white lysozyme (HEWL) over different irradiation times, ranging from 2 min to 1 h. To ensure a control over the radiation parameters, a pair of microwave rectangular waveguides is used to irradiate the samples. Optical spectroscopic measurements, which include UV-visible absorption spectroscopy, Raman spectroscopy, and far UV CD spectroscopy, reveal the exposure of the buried tryptophan (Trp) residues of the native molecule between 15 and 30 min of radiation. The higher duration of the perturbation leads to a compact structure of the protein and Trp residues are buried again. Interestingly, we do not find any change in the secondary structure of the protein even for 1 h duration of radiation. The relaxation dynamics of the irradiated molecules also has been discussed. We have shown that the molecules relax to their native configuration in 7-8 h after the radiation field is turned off. The structural rearrangement over the above timescale has further been probed by a model calculation, based on a modified Langevin equation. Our coarse-grained simulation approach utilizes the mean of atomic positions and net atomic charge of each amino acid of native HEWL to mimic the initial conformation of the molecule. The modified positions of the residues are then calculated for the given force fields. The simulation results reveal the nonmonotonous change in overall size of the molecule, as observed experimentally. The radiation parameters used in our experiments are very similar to those of some of the electronic devices we often come across. Thus, we believe that the results of our studies on a simple protein structure may help us in understanding the effect of radiation on complex biological systems as well.

GRPY: An Accurate Bead Method for Calculation of Hydrodynamic Properties of Rigid Biomacromolecules

Two main problems that arise in the context of hydrodynamic bead modeling are an inaccurate treatment of bead overlaps and the necessity of using volume corrections when calculating intrinsic viscosity. We present a formalism based on the generalized Rotne-Prager-Yamakawa approximation that successfully addresses both of these issues. The generalized Rotne-Prager-Yamakawa method is shown to be highly effective for the calculation of transport properties of rigid biomolecules represented as assemblies of spherical beads of different sizes, both overlapping and nonoverlapping. We test the method on simple molecular shapes as well as real protein structures and compare its performance with other computational approaches.

Delivery Considerations of Highly Viscous Polymeric Fluids Mimicking Concentrated Biopharmaceuticals: Assessment of Injectability via Measurement of Total Work Done "WT"

An account is given of the recent development of the highly viscous complex biopharmaceuticals in relation to syringeability and injectability. The specific objective of this study is to establish a convenient method to examine problem of the injectability for the needle-syringe-formulation system when complex formulations with diverse viscosities are used. This work presents the inter-relationship between needle size, syringe volume, viscosity, and injectability of polymeric solutions having typical viscosities encountered in concentrated biologics, by applying a constant probe crosshead speed on the plunger-syringe needle assembly and continuously recording the force-distance profiles. A computerized texture analyzer was used to accurately capture, display, and store force, displacement, and time data. The force-distance curve and area under the curve are determined, and total work done for complete extrusion of the syringe content was calculated automatically by applying an established Matlab program. Various concentrations (i.e., 0.5-4% w/v of polymeric fluids/dispersions) of polyethylene oxide (PEO) and hydroxypropyl methylcellulose (HPMC) with viscosity ranges of 5-100 cP mimicking concentrated monoclonal antibody solutions and complex biopharmaceutical formulations are investigated. Results indicate that calculated values of total work done to completely extrude the syringe content are the most appropriate parameter that describes viscosity-injection force of dispersed formulations. Additionally, the rheological properties of HPMC and PEO fluids in the context of syringeability and injectability are discussed.

Challenges in Predicting Protein-Protein Interactions from Measurements of Molecular Diffusivity

Dynamic light scattering can be used to measure the diffusivity of a protein within a formulation. The dependence of molecular diffusivity on protein concentration (traditionally expressed in terms of the interaction parameter k_D) is often used to infer whether protein-protein interactions are repulsive or attractive, resulting in solutions that are colloidally stable or unstable, respectively. However, a number of factors unrelated to intermolecular forces can also impact protein diffusion, complicating this interpretation. Here, we investigate the influence of multicomponent diffusion in a ternary protein-salt-water system on protein diffusion and k_D in the context of Nernst-Planck theory. This analysis demonstrates that large changes in protein diffusivity with protein concentration can result even for hard-sphere systems in the absence of protein-protein interactions. In addition, we show that dynamic light scattering measurements of diffusivity made at low ionic strength cannot be reliably used to detect protein conformational changes. We recommend comparing experimentally determined k_D values to theoretically predicted excluded-volume contributions, which will allow a more accurate assessment of protein-protein interactions.

Theoretical and Experimental Investigation of the Translational Diffusion of Proteins in the Vicinity of Temperature-Induced Unfolding Transition

Translational diffusion is the most fundamental form of transport in chemical and biological systems. The diffusion coefficient is highly sensitive to changes in the size of the diffusing species; hence, it provides important information on the variety of macromolecular processes, such as self-assembly or folding-unfolding. Here, we investigate the behavior of the diffusion coefficient of a macromolecule in the vicinity of heat-induced transition from folded to unfolded state. We derive the equation that describes the diffusion coefficient of the macromolecule in the vicinity of the transition and use it to fit the experimental data from pulsed-field-gradient nuclear magnetic resonance (PFG NMR) experiments acquired for two globular proteins, lysozyme and RNase A, undergoing temperature-induced unfolding. A very good qualitative agreement between the theoretically derived diffusion coefficient and experimental data is observed.

Parallel temperature-dependent microrheological measurements in a microfluidic chip

Microfluidic stickers are used as a sample environment to measure the microrheology of monoclonal antibody (mAb) protein solutions. A Peltier-based microscope stage is implemented and validated, and is capable of controlling the sample temperature over the range 0.9-40 °C. The design accounts for heat transfer to and from the objective, controls the sample environment humidity to mitigate condensation, and provides adequate damping to reduce vibration from the cooling system. A concentrated sucrose solution is used as a standard sample to provide an in situ temperature measurement by the Stokes-Einstein-Sutherland relation. By combining microfluidic stickers and microrheology, 72 temperature-concentration viscosity measurements of mAb solutions can be made in 1 day, a significant increase in throughput over conventional rheometry.

Intrinsic Viscosity of Proteins and Platonic Solids by Boundary Element Methods

The boundary element (BE) method is used to implement a very precise computation of the intrinsic viscosity for rigid molecules of arbitrary shape. The formulation, included in our program BEST, is tested against the analytical Simha formula for ellipsoids of revolution, and the results are essentially numerically exact. Previously unavailable, very precise results for a series of Platonic solids are also presented. The formulation includes the optional determination of the center of viscosity; however, for globular proteins, the difference compared to the computation based on the centroid is insignificant. The main application is to a series of 30 proteins ranging in molecular weight from 12 to 465 kD. The computation starts from the crystal structure as obtained from the Protein Data Bank, and a hydration thickness of 1.1 Å obtained in previous work with BEST was used. The results (extrapolated to an infinite number of triangular boundary elements) for the proteins are separated into two groups:  monomeric and multimeric proteins. The agreement with experimental measurements of the intrinsic viscosity in the case of monomeric proteins is excellent and within experimental error of 5%, demonstrating that the solution and crystal structure are hydrodynamically equivalent. However, for some multimeric proteins, we observe strong systematic deviations around -20%, which we interpret as a systematic deviation of the solution structure from the crystal structure. A possible description of the structural change is deduced by using simple ellipsoid model parameters. A method to obtain intrinsic viscosity values for proteins to 1-2% accuracy (better than experimental error) on the basis of a single BE computation (avoiding the need for an extrapolation on the number of surface triangles) is also presented.

Sensing glucose concentrations at GHz frequencies with a fully embedded Biomicro-electromechanical system (BioMEMS)

The progressive scaling in semiconductor technology allows for advanced miniaturization of intelligent systems like implantable biosensors for low-molecular weight analytes. A most relevant application would be the monitoring of glucose in diabetic patients, since no commercial solution is available yet for the continuous and drift-free monitoring of blood sugar levels. We report on a biosensor chip that operates via the binding competition of glucose and dextran to concanavalin A. The sensor is prepared as a fully embedded micro-electromechanical system and operates at GHz frequencies. Glucose concentrations derive from the assay viscosity as determined by the deflection of a 50 nm TiN actuator beam excited by quasi-electrostatic attraction. The GHz detection scheme does not rely on the resonant oscillation of the actuator and safely operates in fluidic environments. This property favorably combines with additional characteristics-(i) measurement times of less than a second, (ii) usage of biocompatible TiN for bio-milieu exposed parts, and (iii) small volume of less than 1 mm3-to qualify the sensor chip as key component in a continuous glucose monitor for the interstitial tissue.

Study of Bovine Serum Albumin Solubility in Aqueous Solutions by Intrinsic Viscosity Measurements

The behavior of bovine serum albumin (BSA) in water is scarcely studied, and the thermodynamic properties arising from the experimental measurements have not been reported. Intrinsic viscosity measurements are very useful in assessing the interaction between the solute and solvent. This work discussed in a simple determination of the enthalpy of BSA in aqueous solution when the concentration ranges from 0.2 to 36.71% wt. and the temperature from 35 to 40°C. The relationship between the concentration and intrinsic viscosity is determined according to the method of Huggins. The temperature increase reduces the ratio between inherent viscosity and concentration (ηi/c). This is reflected in the Van't Hoff curve. Furthermore, this work proposes hydrodynamic cohesion value as an indicator of the degree of affinity of protein with water and thermodynamic implications in conformational changes.

High-dose monoclonal antibodies via the subcutaneous route: challenges and technical solutions, an industry perspective

This review summarizes the various challenges in product development involved in subcutaneous administration of high-dose monoclonal antibodies and attempts to provide an industry perspective of some of the available technologies and potential avenues to overcome these challenges.

A comparison of the activation energy of viscous flow for hen egg-white lysozyme obtained on the basis of different models of viscosity for glass-forming liquids

The paper presents the results of viscosity determinations on aqueous solutions of hen egg-white lysozyme at a wide range of concentrations and at temperatures ranging from 5°C to 55°C. On the basis of these measurements and different models of viscosity for glass-forming liquids, the activation energy of viscous flow for solutions and the studied protein, at different temperatures, was calculated. The analysis of the results obtained shows that the activation energy monotonically decreases with increasing temperature both for solutions and the studied protein. The numerical values of the activation energy for lysozyme, calculated on the basis of discussed models, are very similar in the range of temperatures from 5°C to 35°C.

Rheological and syringeability properties of highly concentrated human polyclonal immunoglobulin solutions

This study of highly concentrated polyvalent immunoglobulin solutions, IgG, aimed at analyzing the relationships between protein concentration and aggregation on the one hand and viscosity on the other hand. Viscosity variations as a function of IgG concentration showed two well-defined behaviours: a Newtonian behaviour for low-concentrated solutions and a shear-thinning behaviour for highly concentrated ones. The viscosity data fitted very well with the Mooney model, suggesting the absence of intermolecular interactions in the IgG solutions that behaved like a non-interacting suspension of hard particles. The polyclonal nature of IgG seems to prevent intermolecular interaction. The shape factor, determined from Mooney fitting, revealed a non-spherical shape of the polyclonal IgG molecules. The rheological properties were also correlated with the injection force (F) through hypodermic needles by syringeability tests. Here, F was mainly affected by three parameters: the solution viscosity, the injection flow rate, and the needle characteristics. In fact, syringeability tests showed that F increased with IgG concentration and flow rate and decreased with the internal diameter of the needle. A zone for optimal injection conditions was then identified taking into account the different affecting parameters and mainly a maximum force for manual injection, which was fixed at 30N.

Viscoelastic characterization of high concentration antibody formulations using quartz crystal microbalance with dissipation monitoring

With increasing protein concentrations, therapeutic protein formulations are increasingly demonstrating significant deviations from ideal dilute solution behavior due to protein-protein interactions. These interactions lead to unique biophysical challenges in the administration of biopharmaceuticals including high apparent viscosity and viscoelasticity as well as challenges in maintaining the physical stability of proteins in solution. Here, we describe a straightforward analytical method to calculate the complex modulus and viscosity of high concentration protein solutions from measurements made using quartz crystal microbalance with dissipation monitoring (QCM-D). Further, this methodology was used to investigate the dependence of the storage and loss moduli (G' and G'', respectively) of a humanized monoclonal antibody solution on solution pH. Unlike recent reports, the effect of protein deposition onto the surface of the quartz sensor crystal was measured and explicitly accounted for during analysis when determining the solution's complex modulus. It was found that the ratio G''/G' was significantly greater than unity for all solutions investigated, but demonstrated a distinct maximum at pH 5.5 indicating that the solution exhibited the greatest liquid-like behavior at this pH. In addition, measurements were made at higher frequencies, which were found to be more sensitive to the changes in pH than those made at lower frequencies. It was also found that the viscoelastic ratio was relatively insensitive to the frequency of measurement at lower pH, but showed greater dependence on frequency as pH increased. The characterization of the rheological properties of high concentration antibody solutions provides insight into protein-protein interactions, and the methodology presented here demonstrates a straightforward way to determine the viscoelastic properties using ultrasonic rheology without the drawbacks of numerical fitting.

Protein binding onto surfactant-based synthetic vesicles

Synthetic vesicles were prepared by mixing anionic and cationic surfactants, aqueous sodium dodecylsulfate with didodecyltrimethylammonium or cetyltrimethylammonium bromide. The overall surfactant content and the (anionic/cationic) mole ratios allow one to obtain negatively charged vesicles. In the phase diagram, the vesicular region is located between a solution phase, a lamellar liquid crystalline dispersion, and a precipitate area. Characterization of the vesicles was performed by electrophoretic mobility, NMR, TEM, and DLS and we determined their uni-lamellar character, size, stability, and charge density. Negatively charged vesicular dispersions, made of sodium dodecylsulfate/didodecyltrimethylammonium bromide or sodium dodecylsulfate/cetyltrimethylammonium bromide, were mixed with lysozyme, to form lipoplexes. Depending on the protein/vesicle charge ratio, binding, surface saturation, and lipoplexes flocculation, or precipitation, occurs. The free protein in excess remains in solution, after binding saturation. The systems were investigated by thermodynamic (surface tension and solution calorimetry), DLS, CD, TEM, 1H NMR, transport properties, electrophoretic mobility, and dielectric relaxation. The latter two methods give information on the vesicle charge neutralization by adsorbed protein. Binding is concomitant to modifications in the double layer thickness of vesicles and in the surface charge density of the resulting lipoplexes. This is also confirmed by developing the electrophoretic mobility results in terms of a Langmuir-like adsorption isotherm. Charges in excess with respect to the amount required to neutralize the vesicle surface promote lipoplexes clustering and/or flocculation. Protein-vesicle interactions were observed by DLS, indicating changes in particle size (and in their distribution functions) upon addition of LYSO. According to CD, the bound protein retains its native conformation, at least in the SDS/CTAB vesicular system. In fact, changes in the alpha-helix and beta-sheet conformations are moderate, if any. Calorimetric methods indicate that the maximum heat effect for LYSO binding occurs at charge neutralization. They also indicate that enthalpic are by far the dominant contributions to the system stability. Accordingly, energy effects associated with charge neutralization and double-layer contributions are much higher than counterion exchange and dehydration terms.

Some Properties of Lysozyme−Lithium Perfluorononanoate Complexes

Mixtures containing lysozyme, LYSO, and a fully fluorinated surfactant, lithium perfluorononanoate, LiPFN, were investigated in a wide range of concentrations and mole ratios. To ensure consistency to the data, a comparison was made, when possible, with the more conventional SDS as surfactant. Molecular solutions, precipitates, and micellar phases have been observed. The region of existence for each phase depends on the LiPFN/LYSO mole ratios, r, and was determined by different experimental methods. Optical absorbance, CD, 19F NMR, viscosity, electrical conductivity, and dielectric relaxation methods were used. Some methods give information on the protein conformation, others on the state of the surfactant or on the collective system properties, respectively. Addition of LiPFN gives rise to a solution, a poly phase dispersion (at low surfactant to protein ratios) and to a micelle-mediated redissolution of the precipitates. Concomitant to the above macroscopic properties, peculiar effects in the state of LYSO are observed. Low amounts of surfactant reduce significantly the amount of alpha-helix in favor of the beta-sheet conformation of the protein. The former is almost completely regained once micelle-assisted redissolution of the complex occurs. The tertiary structure of the protein, conversely, is lost at low surfactant content and never recovered. Such evidence suggests the occurrence of a molten globule conformation for LYSO in micellar media.

Predictive modeling of protein adsorption along the bed height by taking into account the axial nonuniform liquid dispersion and particle classification in expanded beds

Expanded bed adsorption (EBA) is a special chromatography technique with perfect classification of adsorbent particles in the column, thus the performance of protein adsorption in expanded beds is particular, obviously nonuniform and complex along the column. Detailed description of the complex adsorption kinetics of proteins in expanded bed is essential for better analyzing of adsorptive mechanisms, the design of chromatographic processes and the optimization of operation parameters of EBA processes. In this work, a theoretical model for the prediction of protein adsorption kinetics in expanded beds was developed by taking into account the classified distribution of adsorbent particles along the bed height, the nonuniform behaviors of axial liquid dispersion, the axial variation of local bed voidage as well as the axial changes of target component mass transfer. The model was solved using the implicit finite difference scheme combining with the orthogonal collocation method, and then applied to predict the breakthrough behaviors of bovine serum albumin (BSA) on Streamline DEAE and lysozyme on Streamline SP along the bed height in expanded beds under various conditions. In addition, the experiments of front adsorption of BSA on Streamline DEAE at different axial column positions were carried out to reveal the adsorption kinetics of BSA along the bed height in a 20 mm I.D. expanded bed, and the influences of liquid velocity and feed concentration on the breakthrough behaviors were also analyzed. The breakthrough behaviors predicted by the present model were compared with the experimental data obtained in this work and in the literature published. The agreement between the prediction and the experimental breakthrough curves is satisfied.

Determination of some hydrodynamic parameters of ovine serum albumin solutions using viscometric measurements

The influence of protein concentration and temperature on the viscosity of ovine serum albumin (OSA) solutions was studied. The Mooney equation and a modified Arrhenius formula were used to described the viscosity-concentration and viscosity-temperature dependence of the solutions, respectively. The effective specific volume, the activation energy and entropy of viscous flow for hydrated OSA were calculated. The axial ratio and the dimensions of the main semi-axes of hydrated OSA were established. At low concentration limit, the temperature dependence of the intrinsic viscosity and Huggins coefficient is presented. Comparison of some hydrodynamic parameters obtained for different proteins has been made.

A comparison of solution conformation and hydrodynamic properties of equine, porcine and rabbit serum albumin using viscometric measurements

This paper presents the results of viscosity determinations on aqueous solutions of equine, porcine and rabbit serum albumin over a wide range of concentrations and at temperatures ranging from 5 degrees C to (42-45) degrees C. The results are compared with human and bovine serum albumin previously studied. Viscosity-temperature dependence is discussed on the basis of the modified Arrhenius formula. The effective specific volume, the activation energy and entropy of viscous flow for all investigated albumins are compared. Viscosity-concentration dependence, in turn, is discussed on the basis of Mooney equation. Based on the assumption that theoretical and experimental values of Simha factor--at high temperature limit--are equal to each other, the hydrodynamic volume of the studied albumins has been calculated. The numerical values of a self-crowding factor were also obtained. At low concentration limit, the numerical values of the intrinsic viscosity and of Huggins coefficient were compared.

Microsecond freeze-hyperquenching: development of a new ultrafast micro-mixing and sampling technology and application to enzyme catalysis

A novel freeze-quench instrument with a characteristic <<dead-time>> of 137 +/- 18 micros is reported. The prototype has several key features that distinguish it from conventional freeze-quench devices and provide a significant improvement in time resolution: (a) high operating pressures (up to 400 bar) result in a sample flow with high linear rates (up to 200 m s(-1)); (b) tangential micro-mixer with an operating volume of approximately 1 nl yields short mixing times (up to 20 micros); (c) fast transport between the mixer and the cryomedium results in short reaction times: the ageing solution exits the mixer as a free-flowing jet, and the chemical reaction occurs "in-flight" on the way to the cryomedium; (d) a small jet diameter (approximately 20 microm) and a high jet velocity (approximately 200 m s(-1)) provide high sample-cooling rates, resulting in a short cryofixation time (up to 30 micros). The dynamic range of the freeze-quench device is between 130 micros and 15 ms. The novel tangential micro-mixer efficiently mixes viscous aqueous solutions, showing more than 95% mixing at eta < or = 4 (equivalent to protein concentrations up to 250 mg ml(-1)), which makes it an excellent tool for the preparation of pre-steady state samples of concentrated protein solutions for spectroscopic structure analysis. The novel freeze-quench device is characterized using the reaction of binding of azide to metmyoglobin from horse heart. Reaction samples are analyzed using 77 K optical absorbance spectroscopy, and X-band EPR spectroscopy. A simple procedure of spectral analysis is reported that allows (a) to perform a quantitative analysis of the reaction kinetics and (b) to identify and characterize novel reaction intermediates. The reduction of dioxygen by the bo3-type quinol oxidase from Escherichia coli is assayed using the MHQ technique. In these pilot experiments, low-temperature optical absorbance measurements show the rapid oxidation of heme o3 in the first 137 micros of the reaction, accompanied by the formation of an oxo-ferryl species. X-band EPR spectroscopy shows that a short-living radical intermediate is formed during the oxidation of heme o3. The radical decays within approximately 1 ms concomitant with the oxidation of heme b, and can be attributed to the PM reaction intermediate converting to the oxoferryl intermediate F. The general field of application of the freeze-quench methodology is discussed.

On the hydrodynamics and temperature dependence of the solution conformation of human serum albumin from viscometry approach

The paper presents the results of viscosity determinations on aqueous solutions of human serum albumin (HSA) at a wide range of concentrations and at temperatures ranging from 5 to 45 degrees C. On the basis of a modified Arrhenius formula and Mooney's equation, the viscosity-temperature and viscosity-concentration dependence of the solutions are discussed. The effective specific volume, the activation energy and entropy of viscous flow for hydrated HSA were calculated. Different models of HSA molecule are discussed and the best one-from the hydrodynamic point of view-was established. At low concentration limit, such rheological quantities as the intrinsic viscosity and Huggins coefficient were obtained. Using the dimensionless parameter [eta]c, the existence of three characteristic ranges of concentrations: diluted, semi-diluted and concentrated, was shown.

Viscosity analysis of the temperature dependence of the solution conformation of ovalbumin

The viscosity of ovalbumin aqueous solutions was studied as a function of temperature and of protein concentration. Viscosity-temperature dependence was discussed on the basis of the modified Arrhenius formula at temperatures ranging from 5 to 55 degrees C. The activation energy of viscous flow for hydrated and unhydrated ovalbumin was calculated. Viscosity-concentration dependence, in turn, was discussed on the basis of Mooney equation. It has been shown that the shape parameter S decreases with increasing temperature, and self-crowding factor K does not depend on temperature. At low concentration limit the numerical values of the intrinsic viscosity and of Huggins coefficient were calculated. A master curve relating the specific viscosity etasp to the reduced concentration c[eta], over the whole range of temperature, was obtained and the three ranges of concentrations: diluted, semi-diluted and concentrated, are discussed. It has been proved that the Mark-Houvink-Kuhn-Sakurada (MHKS) exponent for ovalbumin does not depend on temperature.

A comparative study on viscosity of human, bovine and pig IgG immunoglobulins in aqueous solutions

This paper presents the results of viscosity determinations on aqueous solutions of human, bovine and pig IgG immunoglobulins over a wide range of concentrations and at temperatures ranging from 5 degrees C to 55 degrees C. On the basis of the generalized Arrhenius formula, the viscosity temperature and the viscosity concentration dependence of the solutions are discussed. By applying an asymptotic form of the generalized Arrhenius formula, such rheological quantities as the intrinsic viscosity and Huggins coefficient were calculated.

Co-operating ATP sites in the multiple drug resistance transporter Mdr1

The ATPase activity of the multiple drug resistance transporter Mdr1 (P-glycoprotein, gp170) depended on the concentration of ATP with both positive and negative co-operativity both in the absence and in the presence of verapamil. Four co-operating binding sites for ATP were required to adequately model the experimental findings. The activation energy for the ATPase activity increased from approximately 385 kJ x mol-1 at 10 microM ATP to 512 kJ x mol-1 at 1600 microM, while changes in verapamil concentration had little effect. This indicates that the reaction mechanism of ATP hydrolysis depends on ATP concentration and is further evidence for co-operation of ATP binding sites. Free ATP in higher concentration was inhibitory; however, this inhibition could be reduced by complexing the ATP with Mg2+. Free Mg2+ had little effect on Mdr1 apart from complexing ATP.