Properties Of Aqueous Solutions Research Articles

Impact of physicochemical properties on stabilities of aqueous solutions of potassium 1-fluorobenzoyltrifluoroborate salt

Physicochemical properties of aqueous solutions of potassium 4-fluorobenzoyl-trifluoroborate salt have been studied to know the effect of concentrations and time on its stabilities because these properties are essential to predict and control chemical reactions and, to develop new substances with innovative applications. Here, pH, refractive index, density, conductivity and molar refractivity have been evaluated during 92 days and, the Ka and pKa for all solutions have been calculated. Salt concentrations and time show effects on the densities, pH and conductivities of the solutions while the refractive indexes and molar refractivity remain practically constant during the time studied. The infrared, Raman and UV–vis spectra of acid in gas phase and aqueous solution have been predicted by using hybrid B3LYP/6-311++G** calculations. Intra-molecular halogen OH…F interactions predicted for the acid in both media probably explain the decreasing observed in the conductivity values. Full vibrational assignments of acid and its scaled force constants in both media are reported. The decreasing observed in the f(νBF3) force constants of the three species in both media suggest that the trifluoroborate group plays an important role in the properties of salt. The predicted UV spectrum of acid in aqueous solution compared with the experimental of salt suggest that the anion, acid and salt species are present in aqueous solution, as evidenced by the physicochemical properties. Hence, the presence of three species in solution justify the variations observed in the pH, density, conductivity, force constants and positions of IR and Raman bands related to OH and BF3 groups.

Electrical conductivity based algorithm for precise application of liquid nitrogenous fertilizers

Precise application of nitrogenous fertilizers mainly urea ammonium nitrate (UAN) and granular urea (both pure and neem-coated) in aqueous form, is critically important for basal and foliar applications. The physicochemical properties of aqueous solution of these nitrogenous fertilizers plays important role in design of any liquid fertilizer application system. The study was carried out during 2019–20 at ICAR-Indian Agricultural Research Institute, New Delhi with an aim to develop algorithms for use in sensors-based systems for real time monitoring of available N concentration in the fertilizer solution before its application. The physicochemical properties like pH, electrical conductivity (EC), specific gravity (SG), dynamic viscosity (DV), surface tension (ST) and percentage light absorbance (LA) of urea ammonium nitrate (UAN-28%), pure urea, and neem coated urea in diluted form (pre-selected N-concentrations i.e. 0.78, 0.9, 1.08, 1.33, 1.75, 2.54 and 4.67% corresponding to the dilution ratios of 1:35, 1:30, 1:25, 1:20, 1:15, 1:10 and 1:05) were measured and analyzed for their significance with N-concentration. Electrical conductivity (EC) alone showed a significant relationship with N-concentrations. Prediction models were developed for diluted UAN and granular urea fertilizers based on the EC and N-concentrations. The regression models in terms of EC to predict N-concentration had coefficients of determination (R2) of 0.998, 0.998, and 0.999 for diluted UAN, pure urea, and neem coated urea with water, respectively showed a great potential for their sensor based precise application. The controlled application of diluted liquid fertilizers with water can be achieved through sensing relevant physicochemical property.

Structural and dynamic behaviour of concentrated aqueous solutions of (poly)ethylene glycols: Insight into the impact of hydrophobicity, hydrogen bonding and chain length

Understanding the delicate interplay between hydrophobicity/hydrophilicity, hydrogen bonding ability and solute size in modulating the chemico-physical properties of aqueous solutions with increasing solute concentration is a challenging task. Here, we focus on how bulk properties, such as diffusion and aggregation behaviour, are affected by the different hydration patterns observed for differently concentrated aqueous solutions of (poly)ethylene glycols, and their corresponding methoxyethers, of various lengths. Using a combined experimental and computational approach, we analyse solutions of ethylene glycol (EG), dimethoxyethane (DME), polyethylene glycol with 4 repeating units capped with either hydroxyl (PEG200) or methoxyl (PEG250DME) tails, and polyethylene glycol with 9 repeating units (PEG400). By disentangling the contributions of hydrophobicity, hydrogen bonding ability, and chain length, we observe that for the smaller solutes electristriction and hydrophobic hydration are the main phenomena occurring. Instead, as the solute becomes larger, these effects give way to the non-trivial conformational flexibility that can either favour or disfavour intermolecular interactions which lead to the formation of water-rich regions excluded from the solute.

Effect of triazolium-based ionic liquid (1, 4-dimethyl- 4H-1, 2, 4-triazolium iodide) on volumetric and ultrasonic properties of binary aqueous solutions of benzamide/benzylamine: experimental and computational study

ABSTRACT In the current investigation, effect of triazolium-based ionic liquid 1, 4-Dimethyl- 4 H-1,2,4-triazolium iodide (DMTI) on volumetric and ultrasonic properties of binary aqueous solutions of benzamide/benzylamine is analysed at four equidistant temperatures and atmospheric pressure. Molecular interactions of DMTI in binary aqueous solutions of benzylamine/benzamide are also interpreted using density (ρ) and speed of sound (u) data along with FT-IR measurements. Different volumetric and ultrasonic parameters were also computed by employing the experimental values of density (ρ) and speed of sound (u), and are further used to elucidate various kinds of interactions in the ternary system. Volumetric and acoustic transfer parameters were further used for the computation of interaction coefficients (pair and triplet). To analyse the outcomes of the estimated parameters, spectroscopic and density-functional theory (DFT) investigations have also been carried out.

Electrokinetic properties of NaCl solution via molecular dynamics simulations with scaled-charge electrolytes.

Scaling ionic charges has become an alternative to polarizable force fields for representing indirect charge transfer effects in molecular simulations. In our work, we apply molecular dynamics simulations to investigate the properties of NaCl aqueous solutions in homogeneous and confined media. We compare classical integer- and scaled-charge force fields for the ions. In the bulk, we validate the force fields by computing equilibrium and transport properties and comparing them with experimental data. Integer-charge ions overestimate dielectric saturation and ionic association. Both force fields present an excess in ion-ion correlation, which leads to a deviation in the ionic conductivity at higher ionic strengths. Negatively charged quartz is used to simulate the confinement effect. Electrostatic interactions dominate counter-ion adsorption. Full-charge ions have stronger and more defined adsorption planes. We obtain the electroosmotic mobility of the solution by combining the shear plane location from non-equilibrium simulations with the ionic distribution from equilibrium simulations. From the Helmholtz-Smoluchowski equation, the zeta potential and the streaming potential coupling coefficient are computed. From an atomic-scale perspective, our molecular dynamics simulations corroborate the hypothesis of maximum packing of the Stern layer, which results in a stable and non-zero zeta potential at high salinity. The scaled-charge model representation of both properties is in excellent qualitative and quantitative agreement with experimental data. With our work, we demonstrate how useful and precise simple scaled-charge models for electrolytes can be to represent complex systems, such as the electrical double layer.

Solution studies, synthesis and antibacterial activity of Ga(III) complexes with bis-kojate derivatives

Given the recognized major problem of microbial drug resistance for human health, new metal-based drugs have been currently explored for their antimicrobial properties, including gallium-based compounds as potential metallophores that could perturb Fe’s interactions with proteins. Herein we have designed and synthesized two bis-kojate ligands (named L4 and L6) and studied their Ga(III) complexes for their physico-chemical and biological properties. In particular a detailed study of their complexation properties in aqueous solution, showed equilibrium models with formation of quite stable dinuclear 2:3 metal:ligand complexes, though with different stability. Solid state complexes were also prepared and characterized and complementary DFT studies indicated that [Ga2(L4)3] complex, with higher stability, seems to adopt a three-ligand bridging conformation, while that for L6 adopt a one ligand bridging conformation. Preliminary investigation of the antibacterial activity of these gallium complexes showed antipseudomonal activity, which appeared higher for the complex with L4, a feature of potential interest for the scientific community.

Effect of Additive (1-Butyl-1-methyl Pyrrolidinium Tetrafluoroborate) on Volumetric, Acoustic and Conductance Properties of Binary Aqueous Solutions of Benzylamine at T = (288.15, 298.15, 308.15, 318.15) K

Effect of additive, 1-butyl-1-methyl pyrrolidinium tetrafluoroborate [BmPyrr+][BF4–] on the volumetric, acoustic and conductance properties of binary aqueous solution of benzylamine has been analyzed at equidistant temperature range using different techniques. Using density and speed of sound data, volumetric and acoustic parameters like apparent and partial molar volumes (Vφ and Vφ0), apparent and partial molar isentropic compressions (Kφ,S and K0φ,S), partial molar volume of transfer and partial molar isentropic compression of transfer (ΔVφ0 and ΔK0φ,S) have been calculated. Conductance parameters like molar conductance (Λm), limiting molar conductance (Λ°m) and activation energy are also calculated using conductance data. All these parameters were used to analyze various types of interactions present in the system. Furthermore, density functional theory (DFT) calculations were conducted for comprehensive understanding of structural variations of ion pairs affecting their physical properties. The hydrogen bond formation in the mixture components was examined by using IR spectrum. Both DFT and Hartee-Fock (HF) methods were used to analyze the results. In addition, the DFT/B3LYP-D3 calculations were also carried out to gather data on the molecular geometry, interactions and other molecular characteristics of the ionic liquid under study.

Magnetic surface-imprinted polymer microspheres coupled with HPLC-MS/MS for sensitive detection of amphetamine-type drugs in water

Magnetic surface imprinted polymer microspheres (Fe3O4@MIPs) were successfully synthesized via Pickering emulsion polymerization, utilizing N-Methylphenethylamine as a surrogate template for amphetamine-type drugs. Fe3O4@MIPs not only possessed excellent dispersibility and enough magnetic properties in aqueous solutions, but also displayed good selectivity towards six amphetamines, with an imprinting factor ranging from 1.8 to 2.6. The adsorption kinetics closely aligned with the pseudo-second-order model, and the adsorption efficiency exceeds 80 % for each amphetamine at equilibrium. Fe3O4@MIPs were then employed as the efficient adsorbents for the extraction of amphetamine drugs. Extraction parameters, including sample pH, the mass of adsorbent, and the type and volume of eluting solvent, were carefully optimized. In combination with the high performance liquid chromatography tandem triple quadrupole mass spectrometry (HPLC-MS/MS), a selective magnetic solid-phase extraction (MISPE) method utilizing Fe3O4@MIPs was developed for the detection of six amphetamines in water samples. The limits of detection and limits of quantitation were determined to be 5.2∼23 ng L−1 and 17∼77 ng L−1, respectively. Recoveries for the six target drugs from lake water and sewage samples fell within the range of 87.2∼110 %. Additionally, the MISPE-HPLC-MS/MS method exhibited excellent repeatability, with a precision below 8.5 % at two spiking levels. The prepared Fe3O4@MIPs possessed the advantages of high selectivity, straightforward preparation, facile separation and good reusability, and was highly suitable for the efficient extraction of amphetamine-type substances in complex environmental water.

Review of the Low-Temperature Acoustic Properties of Water, Aqueous Solutions, Lipids, and Soft Biological Tissues.

Existing data on the acoustic properties of low-temperature biological materials is limited and widely dispersed across fields. This makes it difficult to employ this information in the development of ultrasound applications in the medical field, such as cryosurgery and rewarming of cryopreserved tissues. In this review, the low-temperature acoustic properties of biological materials, and the measurement methods used to acquire them were collected from a range of scientific fields. The measurements were reviewed from the acoustic setup to thermal methodologies for samples preparation, temperature monitoring, and system insulation. The collected data contain the longitudinal and shear velocity, and attenuation coefficient of biological soft tissues and biologically relevant substances-water, aqueous solutions, and lipids-in the temperature range down to -50 °C and in the frequency range from 108 kHz to 25 MHz. The multiple reflection method (MRM) was found to be the preferred method for low-temperature samples, with a buffer rod inserted between the transducer and sample to avoid direct contact. Longitudinal velocity changes are observed through the phase transition zone, which is sharp in pure water, and occurs more slowly and at lower temperatures with added solutes. Lipids show longer transition zones with smaller sound velocity changes; with the longitudinal velocity changes observed during phase transition in tissues lying between these two extremes. More general conclusions on the shear velocity and attenuation coefficient at low-temperatures are restricted by the limited data. This review enhance knowledge guiding for further development of ultrasound applications in low-temperature biomedical fields, and may help to increase the precision and standardization of low-temperature acoustic property measurements.

Albumin-mediated molecular competition of supramolecular photosensitizers for NIR-II imaging-guided phototherapy

Heptamethine cyanines (Cy7) typically exhibit strong near-infrared (NIR) fluorescence signals when in monodisperse states, but their distinctive π-conjugated structure leads to limited solubility in aqueous solutions, ultimately resulting in inherent fluorescence self-quenching. Enhancing the fluorescence quantum yield of these agents within aqueous environments, in order to achieve high-resolution biological imaging, presents a significant challenge. Herein, a benzothiazole-based Cy7-derivative (Cy7-BTH) is developed, exhibiting unique H-aggregation properties in aqueous solutions. Bovine serum albumin (BSA) binds to Cy7-BTH (BSA@Cy7-BTH) to modulate its molecular stacking and energy transfer, boosting its fluorescence accompanied by bright NIR-II tail emission. The competitive binding alters the planarity of Cy7-BTH, restricting its intramolecular rotation, and simutaneously changes the conformation of BSA, leading to BSA@Cy7-BTH aggregation to form hierarchical-structured nanoparticles. Notably, the BSA@Cy7-BTH nanoparticles significantly enhanced photothermal response of Cy7-BTH while maintaining its controlled reactive oxygen species (ROS) generation, offering NIR-II imaging-guided surgical removal of primary tumors, and simultaneously inhibiting cancer cell metastasis by synergistic PDT/PTT dissection of metastatic tumor cells in sentinel lymph nodes (SLNs). This study provides an innovative but facile strategy for their potential clinical applications by precisely regulating the intermolecular competitive interactions of NIR theranostic agents.

ABSORPTION AND LUMINESCENCE PROPERTIES OF ACID AND SALT FORMS OF MONONUCLEOTIDES, THEIR COMPONENTS AND COMPLEXES WITH D-MANNITOL AT ROOM TEMPERATURE

Aim. The aim of this work was to analyze and compare spectral properties of aqueous nucleotide solutions in conditions close to biological systems. We studied the absorption and luminescence (Ex and Em fluorescence and Em phosphorescence) of monoribonucleotides, their disodium salts, bases and nucleosides, and mixes with D-mannitol dissolved in water at room temperature. Methods. There were measured absorbance spectra using a Specord 210plus instrument and fluorescence excitation and emission and phosphorescence spectra using Horiba Fluoro Max 4+ instruments. Results. There were obtained the absorption, excitation, and luminescence spectra of aqueous solutions 1 mg/ml of nucleotides, their components, and mixtures with mannitol (in ratio 1:4). We observed a change in the ratio between the peaks of the spectra of acidic and salt forms of nucleotides. Conclusions. The observations confirmed that nucleotides, nucleosides, and nucleic acid bases exhibit luminescence at room temperature, which might be useful information for further research in this area. In addition, a comparative analysis of the spectra showed possible interactions between nucleotide molecules and mannitol.

Quasi-intrinsic thiobase derivatives as potential targeted photosensitizers in two-photon photodynamic therapy

In this study, a set of potential quasi-intrinsic photosensitizers for two-photon photodynamic therapy (PDT) are proposed based on the unnatural 2-amino-8-(1′-β-ᴅ-2′-deoxyribofuranosyl)-imidazo[1,2-ɑ]-1,3,5-triazin-4(8H)-one (P), which is paired with the 6-amino-5-nitro-3-(1′-β-ᴅ-2′-deoxyribofuranosyl)-2(1H)-pyridone (Z) and can specifically recognize breast and liver cancer cells. Herein, the effects of sulfur substitution and electron-donating/electron-withdrawing groups on the photophysical properties in aqueous solution are systematically investigated. The one- and two-photon absorption spectra evidence that the modifications could result in red-shifted absorption wavelength and large two-photon absorption cross-section, which contributes to selective excitation and provides effective PDT for deep-seated tissues. To ensure the efficient triplet state population, the singlet–triplet energy gaps and spin–orbit coupling constants were examined, which is responsible for a rapid intersystem crossing rate. Furthermore, these thiobase derivatives are characterized by the long-lived T1 state and the large energy gap for radiationless transition to ensure the generation of cytotoxic singlet oxygen.

Weak Magnetic Fields Regulate the Ability of High Dilutions of Water to Enhance ROS Production by Neutrophils

The influence of magnetic fields on the physico–chemical properties of water and aqueous solutions is well known. We have previously shown that weak combined magnetic fields with a 60 µT static component and a 100 nT (at 12.6 Hz) variable component are able to activate neutrophils, both directly and indirectly, through water pre-incubated in these fields. The ability to influence the activity of neutrophils was retained in serial dilutions of water, but only when a mechanical effect (shaking) was applied at each dilution step. Here, we confirm that combined magnetic fields are required for the formation of the stimulatory activity of water on ROS production by neutrophils. For the first time, we determined the threshold values of a constant magnetic field (at least 350–550 nT) necessary to maintain this activity in a series of successive dilutions. Additionally, the biophysical properties of various dilutions appeared to be not identical. This confirms that the number of technological steps (successive dilutions with physical influence) is a key factor that determines the activity of highly diluted samples.

Micellization, aggregation, interaction, and solubilization behaviors of mixed solutions of cationic gemini and nonionic surfactants

AbstractThe micellization properties of mixed aqueous solutions of a cationic gemini surfactant (CGS) and Triton X‐100, a conventional non‐ionic surfactant, with various mole fractions, were determined by measuring the surface tension at different temperatures. Various theoretical models were used to analyze the behavior of this mixed system. The interactions between CGS and Triton X‐100 were determined to be non‐ideal and synergistic. The calculated interaction parameters (βM) have negative values at all temperatures and for all mole fractions, showing attractive interactions. It was found that increasing the mole fraction of Triton X‐100 significantly increased the synergistic effect (more negative values). Micellar aggregation number (Nagg) values of pure surfactants and their mixtures in different ratios were obtained with the steady‐state fluorescence quenching method. Furthermore, the molar solubilization ratio of Sudan III organic dye in all surfactants aqueous systems was obtained using UV–Visible spectrophotometry. At concentrations above critical micelle concentration, the solubility of Sudan III in water was substantially increased linearly for all systems and it was observed that the enhancement was even more significant for mixed surfactant systems.

Protective action of water-soluble fullerene adducts on the example of an adduct with l-arginine

We present radioprotective, antiglycating, and photoprotective properties of a water-soluble C60 fullerene derivative with l-arginine (C60-Arg) and composite films based on collagen containing C60-Arg. The synthesis of these materials is described. The identification of the synthesised materials was carried out using modern physicochemical methods of analysis. The physicochemical properties of aqueous solutions of C60-Arg, such as, particle size distribution, zeta potentials, distribution coefficient in the octan-1-ol–water system were measured. The computer simulation of the process of C60-Arg association in aqueous and isotonic solutions was carried out using Molecular Dynamics. Composite films based on collagen containing C60-Arg demonstrate significant improvement in mechanical properties, cell adhesion, and cell proliferation when the nano-modifier is added. This shows high potential for the use of the C60-Arg adduct in biomedicine.

Competition between indigo carmine and water in the formation of dynamics behavior at different temperatures

We apply molecular dynamics methods to determine the impact of temperature on the structural and dynamic properties of aqueous solution of indigo carmine at temperatures between 300 and 323 К. We report that indigo carmine motion changes from the sub-diffuse to the diffuse regime at t = 100 ps, while water molecules continue to move in the slowed sub-diffuse regime. We demonstrate that the determining factor in the change of the structural and dynamic properties of the aqueous solution of indigo carmine at temperatures between 300 and 323 K is the change in the local structure of water and that the presence of indigo carmine leads to the decrease in temperatures at which a slowed motion of solution components is observed.

Alkali hydroxide (LiOH, NaOH, KOH) in water: Structural and vibrational properties, including neutron scattering results.

Structural and vibrational properties of aqueous solutions of alkali hydroxides (LiOH, NaOH, and KOH) are computed using quantum molecular dynamics simulations for solute concentrations ranging between 1 and 10M. Element-resolved partial radial distribution functions, neutron and x-ray structure factors, and angular distribution functions are computed for the three hydroxide solutions as a function of concentration. The vibrational spectra and frequency-dependent conductivity are computed from the Fourier transforms of velocity autocorrelation and current autocorrelation functions. Our results for the structure are validated with the available neutron data for 17M concentration of NaOH in water [Semrouni et al., Phys. Chem. Chem. Phys. 21, 6828 (2019)]. We found that the larger ionic radius [rLi+<rNa+<rK+] and higher concentration disturb the hydrogen-bond network of water, resulting in more disordered cationic hydration shell. Our abinitio simulation data for solute concentrations ranging between 1 and 10M can be used to guide future elastic and inelastic neutron-scattering experiments.

Donor-Acceptor Assembly of Amphiphilic Molecules Based on 9,10-Distyrylanthracene Derivatives with Terminal Naphthalene Groups.

Amphiphilic rod-coil compounds have excellent photophysical properties and can be assembled into supramolecular nanostructures of different sizes in water or polar solvents. Herein, we synthesized the amphiphilic compounds 2N-DSA, 4N-DSA, and 6N-DSA with 9,10-distyrylanthracene (DSA) as the core and a naphthalene unit as the terminal group that connected DSA through a tetraethylene glycol chain. These compounds have excellent aggregation-induced emission (AIE) properties in aqueous solution and are assembled into worm-like fragments or different sizes of spherical assemblies, defending the volume ratio of the rod to coil segments. Notably, the donor-acceptor interaction between DSA and electron- deficient compounds 2,4,6-trinitrophenol (TNP), 2,4,5,7-tetranitrofluorenone (TNF), and tetraethylene glycol dinitrobenzoate (TGDNB) forms a charge transfer complex, which can be used as a nanoreactor to improve the yield of the Suzuki coupling reaction about 8-10 times. The experimental results reveal that the synergy effect of the donor-acceptor, intermolecular π-π stacking, and hydrophobic-hydrophilic interactions significantly influences the morphology of aggregates and the efficiency of the nanoreactor.

Self-assembling and foaming properties of nonionic, cardanol-based surfactants in aqueous solutions

Surfactants from renewable sources have gained attention due to their potential as substituents for petroleum-based chemicals. In this sense, surfactants based on cardanol, a compound abundant in the cashew nutshell liquid, have been proposed as suitable candidates for this purpose. However, their application is hindered by the lack of quantitative and reliable information about their bulk and surface properties in aqueous solutions. In this work, for the first time, three nonionic, cardanol-derived surfactants (7EO, 9EO, and 12EO), with different number of ethylene oxide (EO) units in the polar headgroup, had their foaming performances analyzed and correlated with their respective surface (equilibrium and dynamic surface tension and surface viscoelasticity) and bulk (cloud points, critical micelle concentration, micelle diameter, and viscosity) properties. Depending on the EO number, different scenarios were seen. Solutions containing the 7EO surfactant were below the cloud point at room temperature and presented antifoaming properties. Aqueous solutions of 9EO and 12EO displayed foamability comparable to solutions prepared with a traditionally employed anionic surfactant (sodium dodecyl sulfate, SDS) at the same concentrations. The surfactant 12EO presented a rapid surface adsorption, thus favoring the formation of large amounts of foam during aeration. Furthermore, solutions of 9EO resulted in foams that were considerably more stable than the ones formed by SDS. Such an enhanced stability was attributed to the presence of elongated micelles, formed at the vicinity of the cloud point, that increased solution viscosity and delayed the liquid drainage in the foams. This surfactant also promoted the formation of highly viscoelastic surface films that contributed to foam stabilization. The obtained results suggest that these surfactants can be used in the formulation of new products with a more sustainable character and with improved properties. Moreover, they indicate the important interchange among bulk aggregates, surface properties and foam stability in aqueous surfactant systems.

Concentration Dependence of Elastic and Viscoelastic Properties of Aqueous Solutions of Ficoll and Bovine Serum Albumin by Brillouin Light Scattering Spectroscopy.

The cellular environment is crowded with macromolecules of different shapes and sizes. The effect of this macromolecular crowding has been studied in a variety of synthetic crowding environments: two popular examples are the compact colloid-like Ficoll macromolecule and the globular protein bovine serum albumin (BSA). Recent studies have indicated that a significant component of bound or surface-associated water in these crowders reduces the available free volume. In this work, Brillouin light scattering experiments were performed on aqueous solutions of Ficoll 70 and Ficoll 400 with concentrations ranging from 1 to 35 wt % and BSA with concentrations of 1 to 27 wt %. From the dependence of spectral peak parameters on polymer concentration, we determined fundamental solution properties: hypersound velocity, adiabatic bulk modulus and compressibility, apparent viscosity, and hypersound attenuation. The existing theory that ignores intermolecular interactions can capture only the observed linear trends in the frequency shift up to a threshold concentration, beyond which a quadratic term accounting for intermolecular interactions is necessary. This likely indicates a transition from the dilute to semidilute regime. In the Ficoll solutions (but not BSA), we see evidence for a central mode, which is indicative of relaxation in the hydration shell of Ficoll.