Viscosity B-coefficients and standard partial molar volumes of amino acids, and their roles in interpreting the protein (enzyme) stabilization

Influence of artificial sweeteners sodium saccharin and acesulfame potassium on the hydration properties, taste behavior and solubility of caffeine

Caffeine is the most widely used psychoactive compound, due to its bitterness it is often paired with sweeteners, a role that is increasingly being filled by artificial sweeteners to to their higher sweetness and low caloric value. This study investigates how sodium saccharin and acesulfame potassium influence the hydration, taste, and solubility of caffeine through solubility, volumetric, acoustic, and viscosimetric analyses. Based on the gathered data we calculated: solubility of caffeine and accompanying thermodynamic parameters, molar volumes, Masson's slope (Sv), expansibility (Eфo), Hepler's coefficient, hydration numbers, compressibilities and Jones-Dole coefficient B, among others. The results indicate that both sweeteners slightly reduce caffeine's bitterness, significantly enhance its water solubility, and increase water orderliness, though their effects on hydration differ. The increase of solubility is most pronounced with sodium saccharin, over twofold, while with acesulfame potassium caffeine is over 1.5 times more soluble.

Interference of potassium chloride and diammonium hydrogen phosphate on volumetric, viscometric and spectroscopic properties of aqueous nicotinamide

Understanding how vitamins and fertilizers interact in aquatic environments is crucial for managing water quality, protecting aquatic life, and promoting sustainable agricultural practices. The molecular interactions between nicotinamide (NA) and two fertilizers, potassium chloride (KCl) and diammonium hydrogen phosphate (DAP), were examined by density (ρ) and viscosity (η) measurements in order to investigate and analyze the solvation behavior that occurs in the ternary solutions (NA + KCl/DAP + water). All of these investigations were conducted at temperatures ranging from 293.15 to 313.15 K and experimental pressures P = 101 kPa. The volumetric characteristics such as apparent molar volume (V ϕ), partial molar volume (V 0 ϕ) and partial molar expansibility (E 0 ϕ) were analyzed. The Jones-Dole equation was used to link experimentally observed viscosity values with solution molarity, yielding viscosity coefficients A F and B J, temperature derivatives of E 0 ϕ (∂E 0 ϕ/∂T) P and B J (∂B J/∂T) have been used to determine the structure-building/breaking properties of the solute. The free energy of activation for viscous flow per mole of solvent (Δμ 0# 1) and per mole of solute (Δμ 0# 2), as well as the entropy and enthalpy of activation per mole of solvent (ΔS 0# 2 and ΔH 0# 2 respectively) were also evaluated. The results show that ion-ion and ion-hydrophilic interactions are dominant in the systems under investigation. The novelty of studying vitamins and fertilizers in aquatic environments lies in the potential to uncover new interactions and mechanisms, leading to more effective environmental management strategies, innovative agricultural practices, and improved understanding of aquatic ecosystem dynamics.

Surface tension measurement and calculation of model biomolecular condensates

The surface tension of liquid-like protein-rich biomolecular condensates is an emerging physical principle governing the mesoscopic interior organisation of biological cells. In this study, we present a method to evaluate the surface tension of model biomolecular condensates, through straighforward sessile drop measurements of capillary lengths and condensate densities. Our approach bypasses the need for characterizing condensate viscosities, which was required in previously reported techniques. We demonstrate this method using model condensates comprising two mutants of the intrinsically disordered protein Ddx4N. Notably, we uncover a detrimental impact of increased protein net charge on the surface tension of Ddx4N condensates. Furthermore, we explore the application of Scheutjens-Fleer theory, calculating condensate surface tensions through a self-consistent mean-field framework using Flory-Huggins interaction parameters. This relatively simple theory provides semi-quantitative accuracy in predicting Ddx4N condensate surface tensions and enables the evaluation of molecular organisation at condensate surfaces. Our findings shed light on the molecular details of fluid-fluid interfaces in biomolecular condensates.

Exploration of Diverse Interactions of l-Methionine in Aqueous Ionic Liquid Solutions: Insights from Experimental and Theoretical Studies

Here, we have investigated some physicochemical parameters to understand the molecular interactions by means of density (ρ) measurement, measurement of viscosity (η), refractive index(n _D) measurement, and conductance and surface tension measurements between two significant aqueous ionic liquid solutions: benzyl trimethyl ammonium chloride (BTMAC) and benzyl triethyl ammonium chloride (BTEAC) in an aqueous l-methionine (amino acid) solution. The apparent molar volume (Φ_v), coefficient of viscosity (B), and molar refraction (R _M) have been used to analyze the molecular interaction behavior associated in the solution at various concentrations and various temperatures. With the help of some important equations such as the Masson equation, the Jones-Doles equation, and the Lorentz-Lorenz equation, very significant parameters, namely, limiting apparent molar volumes (Φ_v ⁰ ), coefficient of viscosity (B), and limiting molar refraction (R _M ⁰), respectively, are obtained. These parameters along with specific conductance (κ) and surface tension (σ) are very much helpful to reveal the solute-solvent interactions by varying the concentration of solute molecules and temperature in the solution. Analyses of Δμ₁ ^0#, Δμ₂ ^0#, TΔS ₂ ^0#, ΔH ₂ ^0#, and thermodynamic data provide us valuable information about the interactions. We note that l-Met in 0.005 molality BTEAC ionic liquid at 308.15 K shows maximum solute-solvent interaction, while l-Met in 0.001 molality BTMAC aqueous solution of ionic liquid at 298.15 K shows the minimum one. Spectroscopic techniques such as Fourier transform infrared (FTIR), ¹H-NMR, and UV-vis also provide supportive information about the interactions between the ionic liquid and l-methionine in aqueous medium. Furthermore, adsorption energy, reduced density gradient (RDG), and molecular electrostatic potential (MESP) maps obtained by the application of density functional theory (DFT) have been used to determine the type of interactions, which are concordant with the experimental observations.

Conductometric and Fluorescence Probe Analysis to Investigate the Interaction between Bioactive Peptide and Bile Salts: A Micellar State Study

The present work deals with the micellar state study of sodium cholate and sodium deoxycholate in the aqueous solution of a bioactive peptide, namely glycyl dipeptide, having different concentrations through conductivity and fluorescence methods at different temperatures. The data obtained from conductivity is plotted against the concentration of Bile salts, and CMC (critical micelle concentration) values are calculated. The results realized have been elucidated with reference to Glycyl dipeptide-bile salts hydrophobic/hydrophilic interactions existing in solution. In addition, the CMC values converted to mole fraction (Xcmc) values have been used to evaluate the standard thermodynamic factors of micellization viz., enthalpy H, free energy ΔGm0, and entropy (ΔSm0) which extract information regarding thermodynamic feasibility of micellar state, energy alteration, and the assorted interactions established in the existing (bile salts-water-glycyl dipeptide) system. Furthermore, the pyrene fluorescence spectrum has also been utilized to study the change in micro polarity induced by the interactions of bile salts with glycyl dipeptide and the aggregation action of bile salts. The decrease in modification in the ratio of intensities of first and third peaks i.e., (I1/I3) for the pyrene molecules in aqueous bile salts solution by the addition of dipeptide, demonstrates that the micelle polarity is affected by glycyl dipeptide. This ratio has also been utilized to determine CMC values for the studied system, and the results have been found to be in good correlation with observations made in conductivity studies.

Can Jones-Dole's B-Coefficient be a Consistent Structure-Making/Breaking Marker? Rigorous Molecular-Based Analysis and Critical Assessment of Its Marker Uniqueness

We analyzed the consistency, or lack thereof, of the conjectured connection between the sign of Jones-Dole's B-coefficient, or its isobaric-temperature derivative, and the structure-making/breaking ability of a solute in a dilute solution. We sought to shed light on some crucial issues, including (i) whether Jones-Dole's B-coefficient contains any embedded microstructural information, (ii) whether we can either assign any definite foundation to the widely used assumption about the sign of the B-coefficient and its structure-making/breaking trend or provide a rational justification for its use as a structure-making/breaking marker, and (iii) whether we actually need Jones-Dole's B-coefficient and its isobaric-temperature derivative as markers for the interpretation of structure-making/breaking trends. Thus, we first addressed the fundamental (statistical mechanical) microscopic to (thermodynamic) macroscopic foundations of a rigorous approach to the structure-making/breaking ability of a solute, regardless of the type of solvent or nature of the solute-solvent intermolecular interaction asymmetries, and its exact relationships to the resulting solution thermodynamics. Then, we derived the required conditions for the signs of the B-coefficient and/or its isobaric-temperature derivative to describe either a structure-making or a structure-breaking event, according to the actual solute-induced perturbation of the solvent microstructure, and consequently, tested the rationale underlying the B-based conjectured structure-making/breaking markers. Moreover, we invoked a well-known transition-state (TS) interpretation of the B-coefficient to connect it explicitly to the derived molecular-based structure-making/breaking signature and to find under which TS conditions the signs of the B-coefficient and its temperature derivative could describe the actual solute-induced perturbation of the solvent microstructure. We illustrated the actual structure-making/breaking behavior for a series of aqueous solutes over a wide range of solute-solvent intermolecular interaction asymmetries and compared their behavior against that predicted by Jones-Dole's based markers. This comparison, supported by rigorous thermodynamic arguments, highlighted the lack of uniqueness (or one-to-one correspondence) in the response of the B-based markers to the solute-solvent intermolecular interaction asymmetry, and therefore, their inadequacy as structure-making/breaking descriptors. Finally, we discuss the findings and provide a cautionary outlook on the use of the viscosity-based structural markers.

Fast and slow EQCM response of zwitterionic weak electrolytes to changes in the electrode potential: a pH-mediated mechanism

Using a fast electrochemical quartz crystal microbalance (EQCM), zwitterionic electrolytes were studied with regard to changes of resonance frequency and resonance bandwidth after the electrode potential was switched. In addition to a fast change of frequency (within milliseconds), a further, slower process with opposite direction is observed. Both the fast and the slow process change sign when the pH is varied across the isoelectric point (pI). The fast process can be attributed to double layer recharging. Its characteristic time is slightly larger than the charge response time (the RC-time) as inferred from electrochemical impedance spectroscopy (EIS). With regard to the slow process, amino acids with moderate concentration behave markedly different from concentrated solutions of proteins. For amino acids, the slow process is larger in amplitude than the fast process and the QCM response is Sauerbrey-like. The shift in half bandwidth is smaller than the shift in frequency and the overtone-normalized frequency shifts agree between overtones (-Δf/n ≈ const. with n the overtone order). This can be explained with a viscosity change in the diffuse double layer. Independent measurements show that the viscosities of these electrolytes are higher than the average in a pH range around the pI. Presumably, the slow process reflects a rearrangement of molecules after the net charge on the molecule has increased or decreased, changing the degree of dipolar coupling and, in consequence, the viscosity. For concentrated solutions of bovine serum albumin (BSA), the QCM response does not follow Sauerbrey behaviour, which can be explained with viscoelasticity and viscoelastic dispersion. The slow process lets the frequency and the bandwidth relax towards a baseline, which is the same for jumps to more positive and to more negative potentials. Presumably, the slow process in this case is caused by a reorientation of molecules inside the Helmholtz layer, such that they screen the electric field more efficiently than immediately after the voltage jump.

Solubility Parameters of Amino Acids on Liquid-Liquid Phase Separation and Aggregation of Proteins

The solution properties of amino acids determine the folding, aggregation, and liquid–liquid phase separation (LLPS) behaviors of proteins. Various indices of amino acids, such as solubility, hydropathy, and conformational parameter, describe the behaviors of protein folding and solubility both in vitro and in vivo. However, understanding the propensity of LLPS and aggregation is difficult due to the multiple interactions among different amino acids. Here, the solubilities of aromatic amino acids (SAs) were investigated in solution containing 20 types of amino acids as amino acid solvents. The parameters of SAs in amino acid solvents (PSASs) were varied and dependent on the type of the solvent. Specifically, Tyr and Trp had the highest positive values while Glu and Asp had the lowest. The PSAS values represent soluble and insoluble interactions, which collectively are the driving force underlying the formation of droplets and aggregates. Interestingly, the PSAS of a soluble solvent reflected the affinity between amino acids and aromatic rings, while that of an insoluble solvent reflected the affinity between amino acids and water. These findings suggest that the PSAS can distinguish amino acids that contribute to droplet and aggregate formation, and provide a deeper understanding of LLPS and aggregation of proteins.

Volumetric, acoustic, viscometric, calorimetric and spectroscopic studies to elucidate the effects of citrate and tartrate based food preservatives on the solvation behaviors of acidic amino acids at different temperatures

The effects of trisodium citrate (TSC) and disodium tartrate (DST) based food preservatives on the hydration behaviors of the amino acids l-aspartic acid (ASP) and l-glutamic acid (GLU) have been studied using thermodynamic, transport, calorimetric and spectroscopic studies. The volumetric, acoustic and viscosity data suggest that hydrophilic-ionic/hydrophilic interactions are predominant in these systems. The calculated parameters are worthwhile for exploring the solutes as structure-breakers, and the solutes undergo pairwise interactions with the co-solutes. The sweetness of both amino acids decreases in the presence of the preservatives. The hydration number and solvation data suggest that these solutes are more hydrated in water. The dominance of dehydration effects in relation to TSC is observed from the positive enthalpy changes in calorimetry studies and the negative chemical shifts in 1H NMR studies.

Drug Delivery Systems: Study of Inclusion Complex Formation between Methylxanthines and Cyclodextrins and Their Thermodynamic and Transport Properties

This paper presents an analysis of the molecular mechanisms involved in the formation of inclusion complexes together with some structural interpretation of drug–carrier molecule interactions in aqueous multicomponent systems comprising methylxanthines and cyclodextrins. The determination of apparent partial molar volumes (φV) from experimental density measurements, both for binary and ternary aqueous solutions of cyclodextrins and methylxanthines, was performed at low concentration range to be consistent with their therapeutic uses in the drug-releasing field. The estimation of the equilibrium constant for inclusion complexes of 1:1 stoichiometry was done through the mathematical modelling of this apparent molar property. The examination of the volume changes offered information about the driving forces for the insertion of the xanthine into the cyclodextrin molecule. The analysis on the volumes of transfer, ΔφV,c, and the viscosity B-coefficients of transfer, ΔB, for the xanthine from water to the different aqueous solutions of cyclodextrin allowed evaluating the possible interactions between aqueous solutes and/or solute–solvent interactions occurring in the solution. Mutual diffusion coefficients for binary, and ternary mixtures composed by xanthine, cyclodextrin, and water were measured with the Taylor dispersion technique. The behavior diffusion of these multicomponent systems and the coupled flows occurring in the solution were analyzed in order to understand the probable interactions between cyclodextrin–xanthine by estimating their association constants and leading to clearer insight of these systems structure. The measurements were performed at the standard (298.15 ± 0.01) K and physiological (310.15 ± 0.01) K temperatures.

Volumetric Investigations on Molecular Interactions of Glycine/l-alanine in Aqueous Citric Acid Solutions at Different Temperatures

Apparent molar volumes \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\phi_{V})$$\end{document}(ϕV) of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg⁻¹ were determined from density measurements at temperatures T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\phi_V^{\text{o}})$$\end{document}(ϕVo) and their corresponding partial molar volumes of transfer \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\Delta_{\text{tr}} \phi_{V} )$$\end{document}(ΔtrϕV) have been calculated from the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi_{V}$$\end{document}ϕV data. The negative \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta_{\text{tr}} \phi_{V}$$\end{document}ΔtrϕV values obtained for glycine/l-alanine from water to aqueous CA solutions indicate the dominance of hydrophilic–hydrophobic/hydrophobic–hydrophilic and hydrophobic–hydrophobic interactions over ion/hydrophilic–dipolar interactions. Further, pair and triplet interaction coefficients, i.e.\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(V_{\text{AB}} )\;{\text{and}}\; (V_{\text{ABB}} )$$\end{document}(VAB)and(VABB) along with hydration number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(n_{\text{H}} )$$\end{document}(nH) have also been calculated. The effect of temperature on the volumetric properties of glycine/l-alanine in water and in aqueous CA solutions has been determined from the limiting partial molar expansibilities \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\partial \phi_{V}^{\text{o}} /\partial T)_{p}$$\end{document}(∂ϕVo/∂T)p and their second-order derivative \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\partial^{2} \phi_{V}^{\text{o}} /\partial T^{2} )_{{P}}$$\end{document}(∂2ϕVo/∂T2)P. The apparent specific volumes \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\nu_{\phi} )$$\end{document}(νϕ) for glycine and l-alanine tend to approach sweet taste behavior both in the presence of water and in aqueous CA solutions. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\nu_{\phi}$$\end{document}νϕ values for glycine/l-alanine increase with increase in concentration of CA at all temperatures studied. This reveals that CA helps in enhancing the sweet taste behavior of glycine/l-alanine which also supports the dominance of hydrophobic–hydrophobic interactions.

Gating-induced large aqueous volumetric remodeling and aspartate tolerance in the voltage sensor domain of Shaker K+ channels

Neurons encode electrical signals with critically tuned voltage-gated ion channels and enzymes. Dedicated voltage sensor domains (VSDs) in these membrane proteins activate coordinately with an unresolved structural change. Such change conveys the transmembrane translocation of four positively charged arginine side chains, the voltage-sensing residues (VSRs; R1-R4). Countercharges and lipid phosphohead groups likely stabilize these VSRs within the low-dielectric core of the protein. However, the role of hydration, a sign-independent charge stabilizer, remains unclear. We replaced all VSRs and their neighboring residues with negatively charged aspartates in a voltage-gated potassium channel. The ensuing mild functional effects indicate that hydration is also important in VSR stabilization. The voltage dependency of the VSR aspartate variants approached the expected arithmetic summation of charges at VSR positions, as if negative and positive side chains faced similar pathways. In contrast, aspartates introduced between R2 and R3 did not affect voltage dependence as if the side chains moved outside the electric field or together with it, undergoing a large displacement and volumetric remodeling. Accordingly, VSR performed osmotic work at both internal and external aqueous interfaces. Individual VSR contributions to volumetric works approached arithmetical additivity but were largely dissimilar. While R1 and R4 displaced small volumes, R2 and R3 volumetric works were massive and vectorially opposed, favoring large aqueous remodeling during VSD activation. These diverse volumetric works are, at least for R2 and R3, not compatible with VSR translocation across a unique stationary charge transfer center. Instead, VSRs may follow separated pathways across a fluctuating low-dielectric septum.

Insights into the role of electrostatics in temperature adaptation: a comparative study of psychrophilic, mesophilic, and thermophilic subtilisin-like serine proteases

To investigate the role of electrostatics in different temperature adaptations, we performed a comparative study on subtilisin-like serine proteases from psychrophilic Vibrio sp. PA-44 (VPR), mesophilic Engyodontium album (Tritirachium album) (PRK), and thermophilic Thermus aquaticus (AQN) using multiple-replica molecular dynamics (MD) simulations combined with continuum electrostatics calculations. The results reveal that although salt bridges are not a crucial factor in determining the overall thermostability of these three proteases, they on average provide the greatest, moderate, and least electrostatic stabilization to AQN, PRK, and VPR, respectively, at the respective organism growth temperatures. Most salt bridges in AQN are effectively stabilizing and thus contribute to maintaining the overall structural stability at 343 K, while nearly half of the salt bridges in VPR interconvert between being stabilizing and being destabilizing, likely aiding in enhancing the local conformational flexibility at 283 K. The individual salt bridges, salt-bridge networks, and calcium ions contribute differentially to local stability and flexibility of these three enzyme structures, depending on their spatial distributions and electrostatic strengths. The shared negatively charged surface potential at the active center of the three enzymes may provide the active-center flexibility necessary for nucleophilic attack and proton transfer. The differences in distributions of the electro-negative, electro-positive, and electro-neutral potentials, particularly over the back surfaces of the three proteases, may modulate/affect not only protein solubility and thermostability but also structural stability and flexibility/rigidity. These results demonstrate that electrostatics contributes to both heat and cold adaptation of subtilisin-like serine proteases through fine-tuning, either globally or locally, the structural stability and conformational flexibility/rigidity, thus providing a foundation for further engineering and mutagenesis studies.

Differently charged surface patches contribute to temperature adaptation of subtilisin-like serine proteases through affecting/modulating the protein solubility and thermostability and the structural flexibility/rigidity/stability.