Sedimentation Coefficient Research Articles

Exploitation of nanocrystal suspension as an effective oral formulation for oxfendazole.

An oxfendazole (OFZ) nanocrystal suspension was prepared by acid-base neutralization and crystallization combined with ultrasonic dispersion to overcome the challenge of its poor oral bioavailability. The nanosuspensions were screened and optimized by single-factor experiments and an orthogonal design using size and appearance as indices. The morphology (differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD)) properties and pharmacokinetics of the best formulation were further developed. The results showed that the best cosolvent and stabilizer were malic acid and hydrogenated castor oil polyoxyethylene ether (HEL-40), respectively. Scanning electron microscopy demonstrated that the oxfendazole nanocrystals are irregular sheets with relative uniformity. The prepared nanocrystals have an average particle diameter of 431 ± 18nm, a polydispersity index (PDI) of 0.376 ± 0.128, a zeta potential of 2.30 ± 0.44mV, and a sedimentation coefficient of 0.993. The equilibrium solubility of nanocrystals in different solvents was significantly improved by 2.02-109.99-fold compared to OFZ crude. In 0.5% SDS-PBS (pH 2) and 0.5% SDS-PBS (pH 8) solution, oxfendazole nanocrystals were completely released within 5min, while the OFZ crude only released 60.26% and 28.31%, respectively. The pharmacokinetics showed that the Cmax, Tmax, and AUC0-∞ of OFZ nanosuspension and OFZ granules in rats after oral dosage at 50mg/kg were 4.23 and 13.63μg/mL, 2.04 and 1.67h, and 111.36 and 295.80μg*h/mL, respectively. The relative bioavailability of the oxfendazole nanosuspension was 265.61% compared to the OFZ granules. These results showed that the nanosuspension might be a promising oral formulation for the hardly soluble OFZ.

Prediction of long-term inter-seasonal variations of streamflow and sediment load by state-space model in the Loess Plateau of China

Streamflow and sediment load exporting from catchments usually show high inter-variability caused by climate variability and land surface changes. It is challenge to predict monthly or daily streamflow and sediment load using simply statistical methods. The state-space model is an effective tool for quantifying localized variations, and it only needs some easily obtained climate and land surface variables. However, there is no state-space model developed to predict the long-term variations of monthly streamflow, sediment load and suspended sediment concentration. In this study, fourteen main catchments in the Loess Plateau of China were chosen, and these catchments experienced abrupt reductions of annual streamflow (Q), specific sediment yield (SSY) and suspended sediment concentration (SSC) during the past five decades. The state-space model was developed to predict monthly Q, SSY and SSC during 1982–2011 by precipitation, potential evapotranspiration and normalized difference vegetation index. The results indicated that the monthly Q, SSY and SSC in summer season decreased significantly in nearly all the catchments (p < 0.01). The periodicity of monthly Q, SSY and SSC reduced, and especially the periodicity was not detected after 2003. The precipitation and previous Q were the two main state variables to estimate monthly Q with transition coefficients of 0.56 and 0.25, respectively, whereas Q and previous SSC were the most important state variables to estimate monthly SSY and SSC with transition coefficients of 0.50 and 0.34, respectively. The state-space model was satisfactory to simulate monthly Q, SSY and SSC with Nash-Sutcliffe model efficiency (NSE) over 0.85 in model calibration and validation. Furthermore, the model performance was best for predicting monthly Q, followed by predicting monthly SSY and SSC with the average NSE of 0.90, 0.89 and 0.87, respectively. The reductions of monthly streamflow and sediment load were mainly derived by soil and water conservation measures (SWCMs) and especially check-dams. The catchment runoff and sediment coefficient decreased significantly and linearly with the percentages of area affected by SWCMs (p < 0.01). This study indicates that the state-space model is a useful tool to predict streamflow and sediment load time series with the hydrological and land surface informations.

Analytical band centrifugation for the separation and quantification of empty and full AAV particles

Analytical band centrifugation (ABC) was first developed for the separation of macromolecules in centrifugation cells ~60 years ago. Since its development, ABC has been predominantly utilized to study macromolecular interactions or chemical reactions between two solutions in situ upon mixing. In this current study, we evaluated ABC separations on modern analytical ultracentrifugation (AUC) instruments for therapeutic adeno-associated viruses (AAVs). ABC provided sufficient separation between the genome-containing full AAV particle and the empty AAV capsid, which need to be controlled during the manufacturing process. Because ABC produces a physical separation, no complex algorithm or sophisticated software is needed to process the experimental raw data. ABC profiles, dubbed “centrifugrams”, can be analyzed with a similar approach as typically used for electrophoretic separations to produce relative percent area. Sedimentation coefficients (s) of analytes can also be determined from ABC. The relative area percent and s value obtained in ABC experiments were shown to be consistent with those determined by conventional sedimentation velocity AUC (SV-AUC). Additionally, the separation and quantification by ABC were found to be reproducible and did not appear to be sensitive to experimental variations of initial rotor temperature or cell misalignment. The robustness of the separation, ease of data processing, and universal applicability for analysis of different AAV serotypes make ABC a promising technique for routine analysis of empty and full AAV particle composition in therapeutic products.

Macroion molecule properties from slender body hydrodynamics

AbstractThe all‐atom molecular dynamics simulations were applied to determine physicochemical parameters for poly‐l‐lysine (a cationic macroion) and λ‐carrageenan (an anionic polysaccharide macroion) comprising the monomer length and the density. The molecule chain diameter for an equivalent cylinder was also calculated. These results were used for the interpretation of experimental data derived from dynamic viscosity measurements of macroion solutions enabling the intrinsic viscosity to be determined. It was confirmed that the molecules assume extended rod‐like conformations in dilute NaCl solutions. Considering the slender body hydrodynamics, the length to diameter parameter (aspect ratio) of the molecules was calculated as a function of their intrinsic viscosity. Using this parameter, the molar mass of macroions can be precisely calculated from a linear dependence derived in this work. The proportionality constant can be ab initio calculated using molecular dynamics modeling. It is confirmed that the formula yields reliable results for both anionic and cationic macroions. Except for the molar mass, the method can be used to predict the diffusion coefficient, the hydrodynamic diameter, the radius of gyration, and the sedimentation coefficients of macroion molecules in dilute electrolytes.

Direct Measurement of Sedimentation Coefficient Distributions in Multimodal Nanoparticle Mixtures.

Differential centrifugal sedimentation (DCS) is based on physical separation of nanoparticles in a centrifugal field prior to their analysis. It is suitable for resolving particle populations, which only slightly differ in size or density. Agglomeration presents a common problem in many natural and engineered processes. Reliable data on the agglomeration state are also crucial for hazard and risk assessment of nanomaterials and for grouping and read-across of nanoforms. Agglomeration results in polydisperse mixtures of nanoparticle clusters with multimodal distributions in size, density, and shape. These key parameters affect the sedimentation coefficient, which is the actual physical quantity measured in DCS, although the method is better known for particle sizing. The conversion into a particle size distribution is, however, based on the assumption of spherical shapes. The latter disregards the influence of the actual shape on the sedimentation rate. Sizes obtained in this way refer to equivalent diameters of spheres that sediment at the same velocity. This problem can be circumvented by focusing on the sedimentation coefficient distribution of complex nanoparticle mixtures. Knowledge of the latter is essential to implement and optimize preparative centrifugal routines, enabling precise and efficient sorting of complex nanoparticle mixtures. The determination of sedimentation coefficient distributions by DCS is demonstrated based on supracolloidal assemblies, which are often referred to as “colloidal molecules”. The DCS results are compared with sedimentation coefficients obtained from hydrodynamic bead-shell modeling. Furthermore, the practical implementation of the analytical findings into preparative centrifugal separations is explored.

Integrative effect of citrate on Cr(Ⅵ) and total Cr removal using a sulfate-reducing bacteria consortium

In controlling toxic Cr(Ⅵ) pollution, the sulfate-reducing bacteria (SRB) method—a bioresource technology—is considered more sustainable and stable than synthetic technologies; however, its mechanisms of metal removal are unclear. This study investigated the mechanism of the use of citrate as a carbon source in an SRB bioreactor for Cr(Ⅵ) removal by disassemble or simulation approach. We show that citrate can mask toxicity, whereby the IC50 value (inhibitory concentration affecting 50% of the test population) of citrate was higher than that of lactate, and that citrate can also protect water systems from oxidation. The anti-oxidation rate of citrate ranged from 76.00% to 90.92%; whereas for citrate‒Cr(Ⅲ), the oxidation rate was only 0.185%–0.587%. Citrate can up-regulate microbial genes and functions, causing acetate and sulfide (NaFeS2) accumulation. Acetate addition promoted Cr adsorption by sulfide (mainly NaFeS2) and promoted sulfide sedimentation. Moreover, in addition to Cr(Ⅵ) reduction and Cr(Ⅲ)‒sulfide generation, the addition of sulfide promoted sedimentation; the correlation coefficient between the sedimentation coefficient and the sulfur content was r = −0.88877 at p < 0.01. Therefore, citrate had a systemic radiative effect on every aspect of the SRB‒citrate system model for Cr(Ⅵ) removal. In addition to the reduction in the former simple model, an integrative effect (including adsorption, sedimentation, and metabolism) was combined with NaFeS2 for Cr removal, which was regulated by the SRB‒citrate system. Exploration and understanding of these mechanisms promote SRB‒citrate methods to be wider implications in practice.

Global multi-method analysis of interaction parameters for reversibly self-associating macromolecules at high concentrations

Weak macromolecular interactions assume a dominant role in the behavior of highly concentrated solutions, and are at the center of a variety of fields ranging from colloidal chemistry to cell biology, neurodegenerative diseases, and manufacturing of protein drugs. They are frequently measured in different biophysical techniques in the form of second virial coefficients, and nonideality coefficients of sedimentation and diffusion, which may be related mechanistically to macromolecular distance distributions in solution and interparticle potentials. A problem arises for proteins where reversible self-association often complicates the concentration-dependent behavior, such that grossly inconsistent coefficients are measured in experiments based on different techniques, confounding quantitative conclusions. Here we present a global multi-method analysis that synergistically bridges gaps in resolution and sensitivity of orthogonal techniques. We demonstrate the method with a panel of monoclonal antibodies exhibiting different degrees of self-association. We show how their concentration-dependent behavior, examined by static and dynamic light scattering and sedimentation velocity, can be jointly described in a self-consistent framework that separates nonideality coefficients from self-association properties, and thereby extends the quantitative interpretation of nonideality coefficients to probe dynamics in highly concentrated protein solutions.

Solution structure of deglycosylated human IgG1 shows the role of CH2 glycans in its conformation

The human immunoglobulin G (IgG) class is the most prevalent antibody in serum, with the IgG1 subclass being the most abundant. IgG1 is composed of two Fab regions connected to a Fc region through a 15-residue hinge peptide. Two glycan chains are conserved in the Fc region in IgG; however, their importance for the structure of intact IgG1 has remained unclear. Here, we subjected glycosylated and deglycosylated monoclonal human IgG1 (designated as A33) to a comparative multidisciplinary structural study of both forms. After deglycosylation using peptide:N-glycosidase F, analytical ultracentrifugation showed that IgG1 remained monomeric and the sedimentation coefficients s020,w of IgG1 decreased from 6.45 S by 0.16–0.27 S. This change was attributed to the reduction in mass after glycan removal. X-ray and neutron scattering revealed changes in the Guinier structural parameters after deglycosylation. Although the radius of gyration (RG) was unchanged, the cross-sectional radius of gyration (RXS-1) increased by 0.1 nm, and the commonly occurring distance peak M2 of the distance distribution curve P(r) increased by 0.4 nm. These changes revealed that the Fab-Fc separation in IgG1 was perturbed after deglycosylation. To explain these changes, atomistic scattering modeling based on Monte Carlo simulations resulted in 123,284 and 119,191 trial structures for glycosylated and deglycosylated IgG1 respectively. From these, 100 x-ray and neutron best-fit models were determined. For these, principal component analyses identified five groups of structural conformations that were different for glycosylated and deglycosylated IgG1. The Fc region in glycosylated IgG1 showed a restricted range of conformations relative to the Fab regions, whereas the Fc region in deglycosylated IgG1 showed a broader conformational spectrum. These more variable Fc conformations account for the loss of binding to the Fcγ receptor in deglycosylated IgG1.

Density Matching Multi-wavelength Analytical Ultracentrifugation to Measure Drug Loading of Lipid Nanoparticle Formulations.

Previous work suggested that lipid nanoparticle (LNP) formulations, encapsulating nucleic acids, display electron-dense morphology when examined by cryogenic-transmission electron microscopy (cryo-TEM). Critically, the employed cryo-TEM method cannot differentiate between loaded and empty LNP formulations. Clinically relevant formulations contain high lipid-to-nucleic acid ratios (10-25 (w/w)), and for systems that contain mRNA or DNA, it is anticipated that a substantial fraction of the LNP population does not contain a payload. Here, we present a method based on the global analysis of multi-wavelength sedimentation velocity analytical ultracentrifugation, using density matching with heavy water, that not only measures the standard sedimentation and diffusion coefficient distributions of LNP mixtures, but also reports the corresponding partial specific volume distributions and optically separates signal contributions from nucleic acid cargo and lipid shell. This makes it possible to reliably predict molar mass and anisotropy distributions, in particular, for systems that are heterogeneous in partial specific volume and have low to intermediate densities. Our method makes it possible to unambiguously measure the density of nanoparticles and is motivated by the need to characterize the extent to which lipid nanoparticles are loaded with nucleic acid cargoes. Since the densities of nucleic acids and lipids substantially differ, the measured density is directly proportional to the loading of nanoparticles. Hence, different loading levels will produce particles with variable density and partial specific volume. An UltraScan software module was developed to implement this approach for routine analysis.

Near-Atomic Structure of the 10S form of Myosin II: Implications for Inhibition, Activation and Disease

Myosin II is the molecular motor that powers contractility in muscle and nonmuscle cells. The two-headed molecule can exist in two conformations: compact (10S sedimentation coefficient) and extended (6S). The extended conformation assembles into filaments, which pull on actin to generate muscle contraction and cell motility. In the 10S structure, the tail is folded into three segments and the heads bend back and interact with each other and the tail, switching off ATPase activity, actin-activation and filament assembly. This energy-conserving, storage form can be activated by phosphorylation of its regulatory light chains (RLC) to form functional filaments as needed. We have solved the structure of smooth muscle 10S myosin to 4.3 Å resolution by cryo-EM, revealing near-atomic insights into its structure and inhibitory function (Yang et al., Nature, in press). The resulting refined atomic model shows clear secondary structure (α-helices, coiled-coil), with side-chain detail in some regions. The motor domains have the same (ADP.Pi) conformation, but their regulatory domains differ, allowing the two heads to meet asymmetrically. The coiled-coil shows considerable variations in pitch along its length. The regulatory domain backbone remains mostly helical as it joins the tail, with little apparent melting. The model reveals that the heads are prevented from binding to actin by steric clashes involving the tail and the other head, while their ATPase activity is impeded by constraints on movement of their converter domains. The positively charged N-terminal region of the RLC interacts with negative charge on the tail near the RLC phosphorylation site, suggesting a simple mechanism for activation. Disease-causing mutations in smooth and nonmuscle myosin II occur close to sites of head interaction with the tail, suggesting that interference with the 10S structure may underlie such diseases.

Shape and Sedimentation Coefficients of Supercoiled DNA Minicircles

Shape and Sedimentation Coefficients of Supercoiled DNA Minicircles

Calibrating analytical ultracentrifuges.

Analytical ultracentrifugation (AUC) is based on the concept of recording and analyzing macroscopic macromolecular redistribution that results from a centrifugal force acting on the mass of suspended macromolecules in solution. Since AUC rests on first principles, it can provide an absolute measurement of macromolecular mass, sedimentation and diffusion coefficients, and many other quantities, provided that the solvent density and viscosity are known, and provided that the instrument is properly calibrated. Unfortunately, a large benchmark study revealed that many instruments exhibit very significant systematic errors. This includes the magnification of the optical detection system used to determine migration distance, the measurement of sedimentation time, and the measurement of the solution temperature governing viscosity. We have previously developed reference materials, tools, and protocols to detect and correct for systematic measurement errors in the AUC by comparison with independently calibrated standards. This 'external calibration' resulted in greatly improved precision and consistency of parameters across laboratories. Here we detail the steps required for calibration of the different data dimensions in the AUC. We demonstrate the calibration of three different instruments with absorbance and interference optical detection, and use measurements of the sedimentation coefficient of NISTmAb monomer as a test of consistency. Whereas the measured uncorrected sedimentation coefficients span a wide range from 6.22 to 6.61 S, proper calibration resulted in a tenfold reduced standard deviation of sedimentation coefficients. The calibrated relative standard deviation and mean error of 0.2% and 0.07%, respectively, is comparable with statistical errors and side-by-side repeatability in a single instrument.

Measurement of the Translational Diffusion Coefficient and Hydrodynamic Radius of Proteins by Dynamic Light Scattering.

Diffusion is a fundamental process in biological systems that governs the molecular collisions driving biochemical reactions and membrane and transport. Measurement of the diffusion coefficient and application of the Stokes-Einstein equation produces the hydrodynamic radius, which is a commonly used gauge of particle size. Additionally, measurement of the diffusion coefficient and the sedimentation coefficient, and application of the Svedberg equation, yields the molecular weight, which is particularly useful in the characterization of very large macromolecules. Dynamic light scattering (DLS) is the most common method to measure the diffusion coefficient of macromolecules. We describe a procedure to perform DLS measurements on monomeric bovine serum albumin (BSA) purified by size-exclusion chromatography using the Zetasizer Nano S particle size analyzer. We compare several analytical methods in existing software programs to estimate the diffusion coefficient of BSA (extrapolated to water at 20°C at infinite dilution, ) and describe a statistical method to obtain 95% confidence limits of the precision of the estimates. We compare estimates to literature values obtained by diffusiometry, sedimentation velocity analytical ultracentrifugation, and other DLS instruments. The method of cumulant analysis in the program SEDFIT (www.analyticalultracentrifugation.com) produced the most precise estimate, 6.06 ± 0.07 F (1 F = 10-7 cm2 s-1), which was within the range of estimates obtained by diffusiometry or sedimentation velocity. This protocol is useful for DLS method validation and quality control.

Conformation of the von Willebrand factor/factor VIII complex in quasi-static flow

Von Willebrand factor (VWF) is a plasma glycoprotein that circulates noncovalently bound to blood coagulation factor VIII (fVIII). VWF is a population of multimers composed of a variable number of ∼280 kDa monomers that is activated in shear flow to bind collagen and platelet glycoprotein Ibα. Electron microscopy, atomic force microscopy, small-angle neutron scattering, and theoretical studies have produced a model in which the conformation of VWF under static conditions is a compact, globular “ball-of-yarn,” implying strong, attractive forces between monomers. We performed sedimentation velocity (SV) analytical ultracentrifugation measurements on unfractionated VWF/fVIII complexes. There was a 20% per mg/ml decrease in the weight-average sedimentation coefficient, sw, in contrast to the ∼1% per mg/ml decrease observed for compact globular proteins. SV and dynamic light scattering measurements were performed on VWF/fVIII complexes fractionated by size-exclusion chromatography to obtain sw values and z-average diffusion coefficients, Dz. Molecular weights estimated using these values in the Svedberg equation ranged from 1.7 to 4.1 MDa. Frictional ratios calculated from Dz and molecular weights ranged from 2.9 to 3.4, in contrast to values of 1.1–1.3 observed for globular proteins. The Mark–Houwink–Kuhn–Sakurada scaling relationships between sw, Dz and molecular weight, and , yielded estimates of 0.51 and –0.49 for as and aD, respectively, consistent with a random coil, in contrast to the as value of 0.65 observed for globular proteins. These results indicate that interactions between monomers are weak or nonexistent and that activation of VWF is intramonomeric.

Transport characteristics of non-uniform suspended sediment in the Jingjiang Reach after the Three Gorges Project operation

三峡工程运用后，坝下游荆江段来沙量大幅度减小，处于严重的不平衡输沙状态，次饱和水流冲刷河床使悬沙量沿程恢复.基于实测水沙资料，分析了三峡工程运用后荆江段非均匀悬沙恢复特点.提出了恢复效率的概念用以表征悬移质沿程恢复的程度，并根据实测水沙资料计算了荆江段1994-2017年非均匀悬沙的恢复效率.结果表明：三峡工程运用前，荆江段各粒径组悬沙恢复效率绝对值均接近0，故该时期内各粒径组泥沙冲淤幅度不大；三峡工程运用后，各粒径组悬沙恢复效率绝对值均明显增大，且粗沙（d>0.125 mm）恢复效率绝对值远大于细沙（d<0.125 mm），故粗沙恢复程度更高.这主要是由于荆江段床沙组成中粗沙部分含量大，而细沙含量小.最后建立了三峡水库蓄水后非均匀悬沙恢复效率与来水来沙条件（来沙系数）的关系，结果表明：各粒径组悬移质恢复效率均与来沙系数呈正相关关系，全沙、细沙和中沙的决定系数（R²）分别为0.89、0.67和0.69，相关性较高，故荆江段各粒径组悬移质泥沙恢复效率较大程度上受到来水来沙条件的影响.;The amount of suspended sediment entering the Jingjiang Reach of the middle Yangtze River has been greatly reduced owing to the operation of the Three Gorges Project (TGP), which caused the sediment transport of the reach at a severe non-equilibrium state, and the suspended sediment concentration recovered during the channel scour process. Therefore, the characteristics of non-equilibrium transport of non-uniform suspended sediment were analyzed based on the measured flow and sediment data. In addition, the recovery efficiency was proposed to represent the recovery speed for suspended sediment load, and the corresponding values were calculated annually from 1994 to 2017 based on the measured data of the Jingjiang Reach. Calculated results show that the suspended sediment recovery efficiency of all particle-size groups was very close to zero before the TGP operation, which means that the channel deformation was small during this period. However, the recovery efficiency of each particle-size group increased greatly after the operation of TGP, and the recovery efficiency of coarse sediment (d>0.125 mm) was much higher than that of fine sediment (d<0.125 mm). This is mainly because the content of coarse sediment in bed-material of Jingjiang Reach is large, while the content of fine sediment is relatively small. Finally, empirical relationship was developed between the recovery efficiency and incoming flow-sediment regime, which shows that the recovery efficiency of each group was negatively related to incoming sediment coefficient, with the correlation coefficient for the total, fine and coarse sediment being 0.89, 0.67 and 0.69, respectively. Therefore, it can be concluded that the recovery efficiency of suspended sediment was significantly affected by the incoming flow and sediment conditions.

Estimation of bivariate probability distributions of nanoparticle characteristics, based on univariate measurements

ABSTRACT The properties of complex particle systems typically depend on multivariate distributions of particle properties, like size and shape characteristics. Multidimensional particle property distributions can be a powerful tool to describe these systems. However, only few techniques exist which are able to simultaneously measure more than one property of individual particles in fast and efficient ways. It is shown how two-dimensional property spaces can be constructed by the combination of two univariate measurements to obtain bivariate particle size distributions. The proposed method is a general approach, which can be applied to a wide spectrum of particle systems and measurement devices. In this paper, the results of a case study are presented, which allow the estimation of bivariate distributions of length and diameter of nanorods, solely using univariate distributions of their particle mass and extinction-weighted sedimentation coefficient distributions. These quantities contain joint information about the particle lengths and diameters, which is used for the reconstruction. The method is validated in a simulation study in which the bivariate distribution to be reconstructed and the reconstruction parameters are varied. In addition, regularization techniques are introduced to reduce methodical errors. This approach can be transferred to other particle systems and measurement techniques, for which functional relationships between particle properties and measured quantities are well described.

Characterizing Drug-Polymer Interactions in Aqueous Solution with Analytical Ultracentrifugation.

We present a new approach for characterizing drug-polymer interactions in aqueous media, using sedimentation velocity analytical ultracentrifugation (AUC). We investigated the potential interaction of ketoconazole (KTZ), a poorly water-soluble drug, with polyacrylic acid (PAA) and a polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus) in aqueous buffers. The effect of the polymer on the sedimentation coefficient of the drug was the observable metric. The drug alone, when subjected to AUC, exhibited a very narrow sedimentation peak at 0.2 Svedberg (S), in agreement with the expectation for a monomeric drug with a molar mass < 1000 Dalton. Conversely, the neat polymers showed broad profiles with higher sedimentation coefficients, reflecting their larger more heterogeneous size distributions. The sedimentation profiles of the drug-polymer mixtures were expectedly different from the profile of the neat drug. With KTZ-Soluplus, a complete shift to faster sedimentation times (indicative of an interaction) was observed, while with KTZ-PAA, a split peak indicated the existence of the drug in both free and interacting states. The sedimentation profile of carbamazepine, a second model drug, in the presence of hydroxypropyl methyl cellulose acetate succinate (HPMCAS, another polymer) revealed multiple "populations" of drug-polymer species, very similar to the sedimentation profile of neat HPMCAS. The interactions probed by AUC were compared with the results from isothermal titration calorimetry. In vitro dissolution tests performed on amorphous solid dispersions prepared with the same drug-polymer pairs suggested that the interactions may play a role in prolonging drug supersaturation. The results show the possibility of characterizing drug-polymer interactions in aqueous solution with high hydrodynamic resolution, addressing a major challenge frequently encountered in the mechanistic investigations of the dissolution behavior of amorphous solid dispersions.

Probing the effect of aroma compounds on the hydrodynamic properties of mucin glycoproteins

Aroma compounds are diverse low molecular weight organic molecules responsible for the flavour of food, medicines or cosmetics. Natural and artificial aroma compounds are manufactured and used by the industry to enhance the flavour and fragrance of products. While the low concentrations of aroma compounds present in food may leave no effect on the structural integrity of the mucosa, the effect of concentrated aroma volatiles is not well understood. At high concentrations, like those found in some flavoured products such as e-cigarettes, some aroma compounds are suggested to elicit a certain degree of change in the mucin glycoprotein network, depending on their functional group. These effects are particularly associated with carbonyl compounds such as aldehydes and ketones, but also phenols which may interact with mucin and other glycoproteins through other interaction mechanisms. This study demonstrates the formation of such interactions in vitro through the use of molecular hydrodynamics. Sedimentation velocity studies reveal that the strength of the carbonyl compound interaction is influenced by compound hydrophobicity, in which the more reactive short chain compounds show the largest increase in mucin-aroma sedimentation coefficients. By contrast, the presence of groups that increases the steric hindrance of the carbonyl group, such as ketones, produced a milder effect. The interaction effects were further demonstrated for hexanal using size exclusion chromatography light scattering (SEC-MALS) and intrinsic viscosity. In addition, phenolic aroma compounds were identified to reduce the sedimentation coefficient of mucin, which is consistent with interactions in the non-glycosylated mucin region.

Study on the structure and formation mechanism of 15S globulin of soybeans

The structure and formation mechanism of 15S globulin of soybeans were investigated. After purification, 15S-rich fraction (75.6%) and 11S-rich fraction (94.3%) were obtained and further characterized with analytical ultracentrifugation (AUC) and transmission electron microscope (TEM). The results show that the molar masses of 11S and 15S are 313 kDa and 651 kDa, respectively, and the weight percentages of the monomer, dimer, and trimer in the TEM images are consistent with those of 11S, 15S, and 21S fractions measured by AUC, indicating that 15S and 21S are dimers and trimers of 11S monomer, respectively. The size of the 15S molecules is 21.1 nm × 10.4 nm, suggesting that two 11S molecules interact with each other from the side position. Moreover, the contents of subunits were determined by a combination of AUC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with the addition of 20 mM sodium dodecyl sulfate (SDS) and 10 mM 2-mercaptoethanol (2-ME). The content of the species with a sedimentation coefficient of 4.3 S in 15S-rich fraction, which is assigned as AB-SS-AB subunits, is significantly higher than that in 11S-rich fraction with the addition of SDS; this species disappears with the addition of 2-ME, demonstrating that AB-SS-AB subunits are formed by disulfide groups from two AB subunits. These disulfide groups may locate in a non-polar interior, which is not accessible to 2-ME when the protein remains its native structure.

Sedimentation Velocity Analytical Ultracentrifugation Analysis of Marketed Rituximab Drug Product Size Distribution.

Analytical methods suitable for intact drug products are often necessary to evaluate the equivalence in physicochemical properties between two drug products (DP) containing the same drug substance (DS), e.g., an innovator biologic drug and its proposed biosimilar. Analytical Ultracentrifugation (AUC) is a biophysics technique applied to the analysis of size and shape of biomolecules. However, the application of AUC to formulated monoclonal antibody (mAb) DP at high concentration has not been reported. A sedimentation velocity (SV) AUC procedure with a short-pathlength centerpiece was applied to two marketed rituximab DPs, Rituxan® (US) and Reditux® (India), without any buffer exchange or dilution. Detailed precision analysis was performed. Highly reproducible sedimentation coefficient values (S) and peak areas were obtained for the dominant (> 84%) monomeric rituximab peak. The minor mAb fragment peaks had large variation in both S values and peak areas (3-12%). The identification of oligomer peaks was only reproducible once the abundance was higher than 2%. SV-AUC provides an orthogonal characterization tool for protein size distribution, composition and assay, which could be informative for biosimilar drug developers who mostly only have access to formulated mAb. However, AUC needs thorough validation on its accuracy, precision and sensitivity.