Partial Specific Adiabatic Compressibility Research Articles

Characterization of the ergometric properties of commercial bioactive dairy peptides

The thermodynamic properties of bioactive peptides provide insights into their functional behavior and their biological efficacy. We conducted precise analyses of the density, the ultrasonic velocity and the relative attenuation of serial dilutions of three commercial dairy peptides prepared by enzymatic methods. From these we determined the partial specific volume and the partial specific adiabatic compressibility coefficient for the peptides. At concentrations greater than ~2.5 ​mg ​mL−1, the apparent values for specific volume and adiabatic compressibility were constant, differing between the three peptides at ±3% for specific volume and ±70% for compressibility. Both specific volume and adiabatic compressibility were highly dependent on concentration, indicating the importance of precise low concentration measurements to obtain correct values for these thermodynamic parameters. From these parameters it was apparent that restructuring of water molecules around the peptides (and their associated counterions) led to compact solutes that were also incompressible. These thermodynamic analyses are critical for understanding how the properties and the beneficial effects of bioactive peptides are influenced by their chemical environment.

Fractionation of Acacia seyal gum by ion exchange chromatography

Acacia gum is a complex gum exudate from trees of selected Acacia species (i.e. A. senegal and A. seyal). It is a continuum of molecular species showing diverse, sugar and protein composition, molar mass and charge density. Numerous studies have been conducted on several aspects of Acacia senegal gum (Asen), including its fractionation. Acacia seyal gum (Asey) has been less studied, although it has recently been gaining importance. Certain gum characteristics, such as the protein and polysaccharide composition and the molecular parameters, play a key role in the Acacia gums functionality and, hence, in their uses by food, pharmaceutical or materials industries. Our main objective is to obtain a fraction from Asey gum with high molar mass and high protein content, allowing future research works and industrial applications. Asey gum has been separated by ion exchange chromatography (IEC) into two different fractions, IEC-F1 and IEC-F2, which have been thoroughly characterized. Thus, we have succeeded to recover a protein-rich fraction with high molar mass and high intrinsic viscosity, the fraction IEC-F1. The Mark-Houwink-Sakurada analysis further indicated that fraction IEC-F1 presents more anisotropic conformation compared to fraction IEC-F2. From the partial specific volume (vs°) and the partial specific adiabatic compressibility (βs°) coefficients, a more flexible and less hydrated structure in the fraction IEC-F1 compared to Asey gum was suggested.

Recovery, structure and physicochemical properties of an aggregate-rich fraction from Acacia senegal gum

Acacia senegal gum (Asen) is a natural exudate of Acacia trees species largely used in food as well as other industries. This natural product appears as a continuum of molecular species which shows diverse sugar and protein composition, molar masses and charge density. The presence of larger macromolecules, or aggregates, has been demonstrated to have a great influence on the Acacia gum characteristics. The present work is designed to recover and characterize one protein-rich fraction presenting a high aggregate content. With this fraction we will open the door to future works with the aim to acquire a deeper knowledge about the origin and the role of the aggregates from Asen gum. Our methodology is based on the well-known ion exchange chromatography, using DEAE Sephacel gel as stationary phase. We have separated Asen into two different fractions (fraction IEC-F1 and fraction IEC-F2), being both of them confirmed as arabinogalactan-proteins (AGP) by Yariv detection. Fraction IEC-F1 has been thoroughly characterized (sugar and amino acid composition, molar mass distribution, weight-average molar mass, number-average molar mass, polydispersity index, intrinsic viscosity, radius of gyration, Mark-Houwink-Sakurada analysis, hydrodynamic radius, partial specific volume and partial specific adiabatic compressibility). From amino acid data, we have estimated that fraction IEC-F1 theoretically corresponds to about 70% of HICF3 and 30% of HICF2, respectively the second and the third fractions separated by hydrophobic interaction chromatography (HIC) and largely described in literature. The obtained information indicates that fraction IEC-F1 appears as a fraction highly rich in aggregates.

Flexibility and Hydration of Amphiphilic Hyperbranched Arabinogalactan-Protein from Plant Exudate: A Volumetric Perspective

Plant Acacia gum exudates are composed by glycosylated hydroxyproline-rich proteins, which have a high proportion of heavily branched neutral and charged sugars in the polysaccharide moiety. These hyperbranched arabinogalactan-proteins (AGP) display a complexity arising from its composition, architecture, and conformation, but also from its polydispersity and capacity to form supramolecular assemblies. Flexibility and hydration partly determined colloidal and interfacial properties of AGPs. In the present article, these parameters were estimated based on measurements of density and sound velocity and the determination of volumetric parameters, e.g., partial specific volume (vs°) and coefficient of partial specific adiabatic compressibility coefficient (βs°). Measurements were done with Acacia senegal, Acacia seyal, and fractions from the former separated according to their hydrophobicity by Hydrophobic Interaction Chromatography, i.e., HIC-F1, HIC-F2, and HIC-F3. Both gums presented close values of vs° and βs°. However, data on fractions suggested a less hydrated and more flexible structure of HIC-F3, in contrast to a less flexible and more hydrated structure of HIC-F2, and especially HIC-F1. The differences between the macromolecular fractions of A. senegal are significantly related to the fraction composition, protein/polysaccharide ratio, and type of amino acids and sugars, with a polysaccharide moiety mainly contributing to the global hydrophilicity and a protein part mainly contributing to the global hydrophobicity. These properties form the basis of hydration ability and flexibility of hyperbranched AGP from Acacia gums.

Effect of pH and Glucose on the Stability of α-lactalbumin

The objective of this study is to understand the influence of pH and effect of cosolvent (glucose) on the stabilization of bovine α-lactalbumin by using ultrasonic techniques. Values of density, ultrasonic velocity and viscosity were measured for bovine α-lactalbumin (5 mg/ml) dissolved in phosphate buffer (pH 2, 5, 7, 9 and 12) solutions mixed with and without the cosolvent at 30 °C. These measurements were used to calculate few thermo-acoustical parameters such as adiabatic compressibility, intermolecular free length, acoustic impedance, relaxation time, relative association constant, the partial apparent specific volume and the partial apparent specific adiabatic compressibility for the said systems. The obtained results revealed a strong comparison between the effects of acidic and alkaline pH values on protein denaturation, i.e., the acidic pH are instantaneous and are of less magnitude whereas alkaline pH are slower but sharper. Further the present study supports the fact that the presence of glucose stabilizes α-lactalbumin against denaturation due to pH variation, which may be due to the strengthening of non-covalent interactions and the steric exclusion effect.

Impact of cosolvent (glucose) on the stabilization of ovalbumin

Proteins are stabilized by glucose against denaturation due to extremes of pH. This was studied by means of density, ultrasonic velocity, viscosity and surface tension measurements in the ovalbumin (5 mg/ml) dissolved in phosphate buffer (pH 2, 5, 7, 9 and 12). Few thermo-acoustical parameters such as adiabatic compressibility, intermolecular free length, acoustic impedance, the partial apparent specific volume and the partial apparent specific adiabatic compressibility were calculated for the said systems. Obtained results suggest that the stabilization of ovalbumin occurs in the presence of glucose through strengthening of hydrophobic interactions supported by other non-covalent interactions and the steric exclusion effect of the cosolvent molecules.

Solvent effects on the molecular structures of crude gliadins as revealed by density and ultrasound velocity measurements

Gliadins were extracted from hard red spring wheat flour with 70% (v/v) aqueous ethanol and lyophilized. These crude gliadins were dissolved in 70% (v/v) aqueous ethanol or 4 mM acetic acid with or without ultrasonication. Precise measurements of the density and ultrasound velocity of the solutions were made at 20 °C. For non-sonicated solutions, crude gliadins solubilized in ethanol had a slightly larger partial specific volume (0.76 cm 3 g −1), and a larger partial specific adiabatic compressibility coefficient (15 × 10 −11 Pa −1) compared to those solubilized in acid (0.739 cm 3 g −1, 3.1 × 10 −11 Pa −1, respectively). Larger values are consistent with the existence of complexes formed by gliadins and lipids in aqueous ethanol solutions. Utrasonication had no effect on these protein–lipid complexes based on measurements of density, but it did alter the compressibility of gliadins in dilute acid (making them almost twice as compressible). Novel insights into gluten protein properties can be gained from compressibility measurements of solutions using ultrasonic resonators when coupled with measurements of protein specific volume.

Compressibilities and Volume Fluctuations of Archaeal Tetraether Liposomes

Bipolar tetraether lipids (BTLs) are abundant in crenarchaeota, which thrive in both thermophilic and nonthermophilic environments, with wide-ranging growth temperatures (4–108°C). BTL liposomes can serve as membrane models to explore the role of BTLs in the thermal stability of the plasma membrane of crenarchaeota. In this study, we focus on the liposomes made of the polar lipid fraction E (PLFE). PLFE is one of the main BTLs isolated from the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius. Using molecular acoustics (ultrasound velocimetry and densimetry), pressure perturbation calorimetry, and differential scanning calorimetry, we have determined partial specific adiabatic and isothermal compressibility, their respective compressibility coefficients, partial specific volume, and relative volume fluctuations of PLFE large unilamellar vesicles (LUVs) over a wide range of temperatures (20–85°C). The results are compared with those obtained from liposomes made of dipalmitoyl-L- α-phosphatidylcholine (DPPC), a conventional monopolar diester lipid. We found that, in the entire temperature range examined, compressibilities of PLFE LUVs are low, comparable to those found in gel state of DPPC. Relative volume fluctuations of PLFE LUVs at any given temperature examined are 1.6–2.2 times more damped than those found in DPPC LUVs. Both compressibilities and relative volume fluctuations in PLFE LUVs are much less temperature-sensitive than those in DPPC liposomes. The isothermal compressibility coefficient ( β T lipid) of PLFE LUVs changes from 3.59 × 10 −10 Pa −1 at 25°C to 4.08 × 10 −10 Pa −1 at 78°C. Volume fluctuations of PLFE LUVs change only 0.25% from 30°C to 80°C. The highly damped volume fluctuations and their low temperature sensitivity, echo that PLFE liposomes are rigid and tightly packed. To our knowledge, the data provide a deeper understanding of lipid packing in PLFE liposomes than has been previously reported, as well as a molecular explanation for the low solute permeation and limited membrane lateral motion. The obtained results may help to establish new strategies for rational design of stable BTL-based liposomes for drug/vaccine delivery.

Amyloid Protofibril is Highly Voluminous and Compressible

We report here results of the first direct measurement of partial volume and compressibility changes of a protein as it forms an amyloid protofibril. We use a high precision density meter and an ultrasonic velocity meter on a solution of intrinsically denatured, disulfide-deficient variant of hen lysozyme, and follow the time-dependent changes in volume and compressibility, as the protein spontaneously forms a protofibril. We have found a large increase in partial specific volume with time from 0.684 to 0.724 mL x g-1 (Deltanu = 0.040 mL x g-1 corresponding to 570 mL x (mol monomer)-1) and in partial specific adiabatic compressibility coefficient from -7.48 x 10(-12) to +1.35 x 10(-12) cm2 x dyn-1 (Deltabetas = 8.83 x 10(-12) x cm2 x dyn-1) as the monomer transforms into a protofibril. The results demonstrate that the protofibril is a highly voluminous and compressible entity, disclosing a cavity-rich, fluctuating nature for the amyloid protofibril. The volume and compressibility changes occur in two phases, the faster one preceding the major development of the beta-structure in the protofibril as monitored by CD.

Specific volume and adiabatic compressibility measurements of native and aggregated recombinant human interleukin‐1 receptor antagonist: Density differences enable pressure‐modulated refolding

High hydrostatic pressures have been used to dissociate non-native protein aggregates and foster refolding to the native conformation. In this study, partial specific volume and adiabatic compressibility measurements were used to examine the volumetric contributions to pressure-modulated refolding. The thermodynamics of pressure-modulated refolding from non-native aggregates of recombinant human interleukin-1 receptor antagonist (IL-1ra) were determined by partial specific volume and adiabatic compressibility measurements. Aggregates of IL-1ra formed at elevated temperatures (55 degrees C) were found to be less dense than native IL-1ra and refolded at 31 degrees C under 1,500 bar pressure with a yield of 57%. Partial specific adiabatic compressibility measurements suggest that the formation of solvent-free cavities within the interior of IL-1ra aggregates cause the apparent increase in specific volume. Dense, pressure-stable aggregates could be formed at 2,000 bar which could not be refolded with additional high pressure treatment, demonstrating that aggregate formation conditions and structure dictate pressure-modulated refolding yields.

Acoustic analysis of bound rubber formed in silica/SBR compounds

The compressibility of the bound rubber around the silica particle was evaluated by an acoustic technique. The density and the longitudinal wave velocity of a silica/SBR compound were measured as a function of the silica content. The density increased linearly with the filler content. The longitudinal wave velocity was almost constant within the experimental error. The mass ratio of the bound rubber to the silica in the silica/SBR compounds was 1.08 ± 0.03 kg kg −1 which was measured by a thermal gravimetric analysis (TGA). The partial specific adiabatic compressibility of the silica was estimated as (0.1 ± 0.5) × 10 −10 Pa −1 on the basis of a three states model. The adiabatic compressibility of the bound rubbers in the silica/SBR compounds was (4.6 ± 0.5) × 10 −10 Pa −1. The compressibility was almost the same as that of the SBR, and the value was twice larger than the compressibility of the bound rubber formed in a CB/SBR composite.

High‐pressure studies of aggregation of recombinant human interleukin‐1 receptor antagonist: Thermodynamics, kinetics, and application to accelerated formulation studies

Recombinant human interleukin-1 receptor antagonist (IL-1ra) in aqueous solutions unfolds and aggregates when subjected to hydrostatic pressures greater than about 180 MPa. This study examined the mechanism and thermodynamics of pressure-induced unfolding and aggregation of IL-1ra. The activation free energy for growth of aggregates (DeltaG-/+(aggregation)) was found to be 37 +/- 3 kJ/mol, whereas the activation volume (DeltaV-/+(aggregation)) was -120 +/- 20 mL/mol. These values compare closely with equilibrium values for denaturation: The free energy for denaturation, DeltaG(denaturation), was 20 +/- 5 kJ/mol, whereas the partial specific volume change for denaturation, DeltaV(denaturation), was -110 +/- 30 mL/mol. When IL-1ra begins to denature at pressures near 140 MPa, cysteines that are normally buried in the native state become exposed. Under oxidizing conditions, this results in the formation of covalently cross-linked aggregates containing nonnative, intermolecular disulfide bonds. The apparent activation free energy for nucleation of aggregates, DeltaG-/+(nuc), was 42 +/- 4 kJ/mol, and the activation volume for nucleation, DeltaV-/+(nuc),was -175 +/- 37 mL/mol, suggesting that a highly solvent-exposed conformation is needed for nucleation. We hypothesize that the large specific volume of IL-1ra, 0.752 +/- 0.004 mL/g, coupled with its relatively low conformational stability, leads to its susceptibility to denaturation at relatively low pressures. The positive partial specific adiabatic compressibility of IL-1ra, 4.5 +/- 0.7 +/- 10(-12) cm2/dyn, suggests that a significant component of the DeltaV(denaturation) is attributable to the elimination of solvent-free cavities. Lastly, we propose that hydrostatic pressure is a useful variable to conduct accelerated formulation studies of therapeutic proteins.

Acoustic analysis of composite soft materials III: Compressibility of boundary layers around particles of mica and calcium carbonate

AbstractThe velocities of longitudinal, transverse, and leaky surface skimming compressional waves (LSSCW) of polyvinylchloride composite materials were measured as a function of the particle concentration. The mica and calcium carbonate (CC) particles were used as additives. The longitudinal and transverse velocities for the PVC/mica composite increased with the concentration of the mica. In the case of the PVC/CC composite, the transverse velocity increased with the concentration of the CC particle, but the longitudinal velocity was independent of the concentration. The LSSCW velocity for the polyvinylchloride matrix did not change in each composite. The partial specific volume and the partial specific adiabatic compressibility of each particle dispersed in polyvinylchloride were evaluated from sound velocity and density data. The compressibility of the boundary layer around the particles was estimated. The thickness of the boundary layer around the mica particle was estimated. For the PVC/CC composite, on the other hand, a softer phase than the PVC matrix was formed around the CC particle because the compressibility of the boundary layer was larger than that of the PVC matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1385–1392, 2005

Acoustic Analysis of Composite Soft Materials IV. Evaluation of Compressibility of Bound Rubber in Carbon Black Filled SBR

A carbon black (CB) filled styrene-butadiene rubber (SBR) compound was investigated by acoustic techniques, scanning acoustic microscopy and longitudinal wave velocitometry.The CB agglomerates of larger than 5 µm dispersed in the compound mixed by two-roll mill were observed as black spots in acoustic micrographs. On the other hand, the CB agglomerates in the compound mixed by oil-pressure kneader were not observed in the acoustic micrograph, since the particle size of the agglomerates was less than 5 µm.The density and the longitudinal wave velocity of the compound were measured as a function of the weight percentage of the CB. The density and the velocity increased linearly with the content of the CB. The mass ratio of the bound rubber to the CB in the unvulcanized sample was determined by using toluene extraction and thermo gravimetric analysis. The partial specific adiabatic compressibility of the CB was estimated as (−0.5±0.5)×10−10 Pa−1 on the basis of the three states model. The adiabatic compressibility of the bound rubber was (2.2±0.5)×10−10 Pa−1, and it is half of that of the SBR matrix.

Partial specific volume and adiabatic compressibility of G-actin depend on the bound nucleotide.

We determined the partial specific volume and partial specific adiabatic compressibility of either ATP- or ADP-bound monomeric actin in the presence of Ca(2+) by measuring the density of and sound velocity in a monomeric actin solution at 18 degrees C. The partial specific volume of ATP-bound monomeric actin, equal to 0.744 cm(3)/g, which is exceptionally high among globular proteins, was reduced to 0.727 cm(3)/g when the tightly bound ATP was replaced with ADP. Associated with this, the adiabatic compressibility of ATP-bound monomeric actin, equal to 8.8 x 10(-12) cm(2)/dyne, decreased to 5.8 x 10(-12) cm(2)/dyne, which is a common value for globular proteins. These results suggested that an extraordinarily soft global conformation of ATP-bound monomeric actin is packed into a compact mass associated with the hydrolysis of bound ATP. When monomeric actin was limitedly proteolyzed at subdomain 2 with subtilisin, the nucleotide-dependent flexibility of the global conformation of monomeric actin was lost.

Acoustic analysis of composite soft materials. I. Characterization of the core and boundary layer from compressibility of core/shell particles dispersed in poly(vinyl chloride)

The sound velocity of butyl acrylate rubber particles modified by poly(methyl methacrylate) in poly(vinyl chloride) was measured as a function of particle concentration. A model for estimating the adiabatic compressibility of the particle and the boundary layer was proposed. From the model, the partial specific adiabatic compressibility of the particles and the rubber core were evaluated. The adiabatic compressibility of the rubber core was estimated as 3.82 × 10−10 Pa−1. The adiabatic compressibility of the poly(methyl methacrylate) shell is discussed based on the modified model. The study indicates that the shell, including the boundary layer between butyl rubber and poly(methyl methacrylate), is perturbed by the butyl acrylate molecules and is so soft as to be comparable to the rubber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2089–2094, 2001

Stabilisation of ovalbumin by maltose

Sugars stabilise proteins against extremes of pH and heat denaturation. This was studied by means of density, ultrasonic velocity and viscosity measurements of the following systems (i) ovalbumin–phosphate buffer (pH 2.4, 5.2, 7.0 and 8.9) and (ii) ovalbumin–maltose–phosphate buffer (pH 2.4, 5.2, 7.0 and 8.9) systems as functions of concentration and temperature. The partial specific volumes ( ν ̄ 0 ), partial specific adiabatic compressibility ( β ̄ s ), intrinsic viscosity, [ η] and shape factor, ν, were calculated for the said systems. The results obtained from such studies suggest that the stabilisation of ovalbumin occurs in the presence of maltose through strengthening of hydrophobic interactions.

Acoustic analysis of composite soft materials. I. Characterization of the core and boundary layer from compressibility of core/shell particles dispersed in poly(vinyl chloride)

AbstractThe sound velocity of butyl acrylate rubber particles modified by poly(methyl methacrylate) in poly(vinyl chloride) was measured as a function of particle concentration. A model for estimating the adiabatic compressibility of the particle and the boundary layer was proposed. From the model, the partial specific adiabatic compressibility of the particles and the rubber core were evaluated. The adiabatic compressibility of the rubber core was estimated as 3.82 × 10−10 Pa−1. The adiabatic compressibility of the poly(methyl methacrylate) shell is discussed based on the modified model. The study indicates that the shell, including the boundary layer between butyl rubber and poly(methyl methacrylate), is perturbed by the butyl acrylate molecules and is so soft as to be comparable to the rubber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2089–2094, 2001

Volumetric and spectroscopic characterizations of the native and acid-induced denatured states of staphylococcal nuclease

We have characterized the acid-induced denaturation of staphylococcal nuclease (SNase) at different urea concentrations by a combination of ultrasonic velocimetry, high precision densimetry, and CD spectroscopy. Our CD spectroscopic results suggest that, at low salt and acidic pH, the protein is unfolded with disrupted secondary and tertiary structures. Furthermore, as judged by far UV CD spectra, the protein is further unfolded at acidic pH upon the addition of urea up to the concentration of 1.5 M. The midpoint of the transition shifts to more neutral pH values and the cooperativity of the transition decreases as the acid-induced denaturation of SNase occurs at higher urea concentrations. We find that the change in volume, Δν, accompanying the acid-induced denaturation of SNase increases from −0.013 cm3 g−1 (−218 cm3 mol−1) in the absence of urea to 0.011 cm3 g−1 (185 cm3 mol−1) at 1.5 M urea. At all urea concentrations, the partial specific adiabatic compressibility, k°s, of the protein decreases upon its unfolding with the values of Δk°s equal to −6.3×10−6 (−0.106 cm3 mol−1 bar−1), −4.5×10−6 (−0.076 cm3 mol−1 bar−1), −4.6×10−6 (−0.077 cm3 mol−1 bar−1), and −3.8×10−6 (−0.064 cm3 mol−1 bar−1) cm3 g−1 bar−1 at urea concentrations of 0, 0.5, 1.0, and 1.5 M, respectively. In general, our volumetric results suggest that the acid-induced denatured state of SNase is only partially unfolded with the solvent-exposed surface area equal to 70–80 % of that expected for the fully extended conformation.

Compressibility and specific volume of actin decrease upon G to F transformation

We measured the densities as well as the sound velocities in solutions of G-actin, F-actin and the reconstituted thin filament. Using the data obtained, we determined their partial specific volumes and partial specific adiabatic compressibilities. The objectives were to investigate the volume change of actin upon polymerization and to detect the conformational change associated with the Ca 2+-binding to the reconstituted thin filament. The partial specific volume and the partial specific adiabatic compressibility of G-actin were 0.749 cm 3/g and 9.3 · 10 −12 cm 2/dyne, respectively. The results suggest that G-actin is a rather soft protein compared with other globular proteins. The partial specific volumes of F-actin were in a range of 0.63–0.66 cm 3/g depending on the solvent conditions. The partial specific adiabatic compressibilities of F-actin were negative (−(7–13) · 10 −12 cm 3/dyne). These data indicate that the amount of hydration may increase by several times upon polymerization assuming that the size of the cavity remains constant. We detected little difference between the partial specific adiabatic compressibility of the reconstituted thin filament in a Ca 2+-bound state and that in a Ca 2+-unbound state. This suggests that the Ca 2+ binding affected not the subunit itself but the inter-subunit junction.