Macromolecules In Aqueous Solution Research Articles

Phase Behaviors of Charged Macromolecules in Aqueous Solutions

AbstractCompared to the charge–charge interaction, the role of the dipole‐dipole interaction has long been ignored in the phase behaviors of charged macromolecules in solutions. Charged macromolecules in solutions exhibit rich phase behaviors due to their complexity and they have been studied extensively. Phase separation can happen for charged macromolecules in the presence of monovalent salt, multivalent salt, and oppositely charged polymers, surfactants, etc., and for more advanced charged macromolecules such as polyzwitterions and polyampholytes, the phase diagram is even richer. In this perspective, the unacknowledged role of dipole‐dipole interaction in the phase behaviors of charged macromolecular solutions will be introduced. Dipolar polymers can form complex, self‐regulating structures which can be employed in various fields from drug‐delivery systems to next‐generation polymers. More importantly, it will shed light on how some of the life's basic and coherent structures such as biomolecular condensates and membrane‐less organelles are assembled and built by charged biomacromolecules such as DNA, RNA, and proteins.

Interchain Hydrodynamic Interaction and Internal Friction of Polyelectrolytes.

Polyelectrolytes (PE) are polymeric macromolecules in aqueous solutions characterized by their chain topology and intrinsic charge in a neutralizing fluid. Structure and dynamics are related to several characteristic screening length scales determined by electrostatic, excluded volume, and hydrodynamic interactions. We examine PE dynamics in dilute to semidilute conditions using dynamic light scattering, neutron spinecho spectroscopy, and pulse field gradient NMR spectroscopy. We connect macroscopic diffusion to segmental chain dynamics, revealing a decoupling of local chain dynamics from interchain interactions. Collective diffusion is described within a colloidal picture, including electrostatic and hydrodynamic interactions. Chain dynamics is characterized by the classical Zimm model of a neutral chain retarded by internal friction. We observe that hydrodynamic interactions are not fully screened between chains and that the internal friction within the chain increases with an increase in ion condensation on the chain.

Remodeling of Biomembranes and Vesicles by Adhesion of Condensate Droplets.

Condensate droplets are formed in aqueous solutions of macromolecules that undergo phase separation into two liquid phases. A well-studied example are solutions of the two polymers PEG and dextran which have been used for a long time in biochemical analysis and biotechnology. More recently, phase separation has also been observed in living cells where it leads to membrane-less or droplet-like organelles. In the latter case, the condensate droplets are enriched in certain types of proteins. Generic features of condensate droplets can be studied in simple binary mixtures, using molecular dynamics simulations. In this review, I address the interactions of condensate droplets with biomimetic and biological membranes. When a condensate droplet adheres to such a membrane, the membrane forms a contact line with the droplet and acquires a very high curvature close to this line. The contact angles along the contact line can be observed via light microscopy, lead to a classification of the possible adhesion morphologies, and determine the affinity contrast between the two coexisting liquid phases and the membrane. The remodeling processes generated by condensate droplets include wetting transitions, formation of membrane nanotubes as well as complete engulfment and endocytosis of the droplets by the membranes.

Studying of the temperature influence on stability of fibrinogen macromolecules in aqueous solution: A literature mini-review

A review of the literature, multiple authors in order to systematize information on the effect of temperature in the range of 25-42 ° C on blood proteins, to conduct further studies of the effect of temperature on the stability of fibrinogen molecules in aqueous solution. Study of works on the determination of conformation and stability of protein molecules in the temperature range of living organisms.

Does It Bind? A Method to Determine the Affinity of Calcium and Magnesium Ions for Polymers Using 1H NMR Spectroscopy.

The binding of calcium and magnesium ions (M2+) by polymers and other macromolecules in aqueous solution is ubiquitous across chemistry and biology. At present, it is difficult to assess the binding affinity of macromolecules for M2+ without recourse to potentiometric titrations and/or isothermal titration calorimetry. Both of these techniques require specialized equipment, and the measurements can be difficult to perform and interpret. Here, we present a new method based on 1H NMR chemical shift imaging (CSI) that enables the binding affinity of polymers to be assessed in a single experiment on standard high-field NMR equipment. In our method, M2+ acetate salt is weighed into a standard 5 mm NMR tube and a solution of polymer layered on top. Dissolution and diffusion of the salt carry the M2+ and acetate ions up through the solution. The concentrations of acetate, [Ac], and free (unbound) M2+, [M2+]f, are measured at different positions along the sample by CSI. Binding of M2+ to the polymer reduces [M2+]f and hinders the upward diffusion of M2+. A discrepancy is thus observed between [Ac] and [M2+]f from which the binding affinity of the polymer can be assessed. For systems which form insoluble complexes with M2+, such as sodium polyacrylate or carboxylate-functionalized nanocellulose (CNC), we can determine the concentration of M2+ at which the polymer will precipitate. We can also predict [M2+]f when a solution of polymer is mixed homogeneously with M2+ salt. We assess the binding properties of sodium polyacrylate, alginate, polystyrene sulfonate, CNC, polyethyleneimine, ethylenediamenetetraacetic acid, and maleate.

Weakly hydrated anions bind to polymers but not monomers in aqueous solutions.

Weakly hydrated anions help to solubilize hydrophobic macromolecules in aqueous solutions, but small molecules comprising the same chemical constituents precipitate out when exposed to these ions. Here, this apparent contradiction is resolved by systematically investigating the interactions of NaSCN with polyethylene oxide oligomers and polymers of varying molecular weight. A combination of spectroscopic and computational results reveals that SCN- accumulates near the surface of polymers, but is excluded from monomers. This occurs because SCN- preferentially binds to the centre of macromolecular chains, where the local water hydrogen-bonding network is disrupted. These findings suggest a link between ion-specific effects and theories addressing how hydrophobic hydration is modulated by the size and shape of a hydrophobic entity.

Comprehensive physical visualisation of the chain conformation and solution property of carboxymethylated konjac glucomannan: Comparison of charged and uncharged polyelectrolytes

The present work deals with a comprehensive molecular characterization and delineation of solution property of a series of charged and uncharged carboxymethylated konjac glucomannan (CMKGM) with different molecular weights (Mw, 1.57 × 105–7.33 × 105) and degrees of substitution (DS, 0.19–1.63) by using various rheological models and solution scaling theory. CMKGM macromolecules in aqueous solutions are found to adopt semi-flexible chain conformation and show a tendency close to rigid chains with decreasing Mw and increasing DS. For uncharged CMKGM solutions, the Huggins–Kraemer, Heller, Fuoss and Wolf approaches can achieve equally excellent fitting results for the determination of intrinsic viscosity [η], whereas for charged CMKGM solutions, only the Huggins–Kraemer and Wolf plots are valid. In accordance with the physical scaling law, a scaling relationship exists between rheological parameters and concentration c for salt and salt-free aqueous solutions of CMKGM. The relationship of specific viscosity ηsp ~ c[η] and ηsp ~ c ~ Mw is derived for CMKGM in a high ionic strength environment (NaCl 0.15 M) by using the Kulicke-Keniewske approach. The constitutive models of the linear Maxwell model and two kinds of non-linear PTT and Giesekus models have also been applied to quantitatively describe the rheological properties of CMKGM entangled solutions under either dynamic or steady shear flow.

Studying the physics of charged macromolecules by single molecule fluorescence spectroscopy.

It is well documented that conventional methods such as dynamic light scattering have encountered difficulties in characterizing charged macromolecules and, therefore, it is desirable that new methods and techniques are introduced. With the ultra-high sensitivity, single molecule fluorescence spectroscopy has successfully lowered the detection limit considerably and enabled measurement under extreme dilution conditions-around the concentration of 10-9M-at which the effect of inter-chain electrostatic repulsion is suppressed. Furthermore, the excellent spatial and temporal resolution as well as the capacity of molecular recognition of these methods help in obtaining rich information of charged macromolecules. This paper summarizes the applications of single molecule fluorescence spectroscopy, especially fluorescence correlation spectroscopy and photon counting histogram, in the studies on charged macromolecules in aqueous solutions and plenty of new information has been revealed on the molecular conformation, counterion distribution, and a few important governing factors. The powerfulness and effectiveness of single molecule fluorescence spectroscopy make it promising in the investigations of charged macromolecules.

Interfacial solvation can explain attraction between like-charged objects in aqueous solution.

Over the past few decades, the experimental literature has consistently reported observations of attraction between like-charged colloidal particles and macromolecules in aqueous solution. Examples include nucleic acids and colloidal particles in the bulk solution and under confinement, and biological liquid-liquid phase separation. This observation is at odds with the intuitive expectation of an interparticle repulsion that decays monotonically with distance. Although attraction between like-charged particles can be rationalized theoretically in the strong-coupling regime, e.g., in the presence of multivalent counterions, recurring accounts of long-range attraction in aqueous solution containing monovalent ions at low ionic strength have posed an open conundrum. Here, we show that the behavior of molecular water at an interface-traditionally disregarded in the continuum electrostatics picture-provides a mechanism to explain the attraction between like-charged objects in a broad spectrum of experiments. This basic principle will have important ramifications in the ongoing quest to better understand intermolecular interactions in solution.

Macromolecular sizes of serum albumins in its aqueous solutions

Changes in the structure and sizes of human and bovine serum albumins as well as polyvinyl alcohol macromolecules in aqueous solutions depending on temperature, concentration, and acid-base balance (pH) of the solutions are discussed. It is taken into consideration that the change in the hydrodynamic radius of a macromolecule is one of the indicators of structural phase transformations of globular proteins. The methods of the macromolecular radii determination from the shear viscosity and the self-diffusion of macromolecules in solutions are discussed. The hydrodynamic radius values of albumin and polyvinyl alcohol macromolecules obtained by the above methods are thoroughly compared. Consideration of these questions provides us with important information on the nature of the binding of water molecules with protein macromolecules.

Association of Carboxymethyl Chitin Macromolecules in Aqueous Solution

The processes of association of 6-O-carboxymethyl chitin macromolecules (in salt and mixed forms) in aqueous solution are studied by dynamic light scattering. It is shown that the solution of 6‑O‑carboxymethyl chitin in the salt form contains two types of particles: small particles (9–16 nm) corresponding to the size of single macromolecules and larger (150–177 nm) associates. In the solution of the mixed form of 6-O-carboxymethyl chitin, only associated particles are present (80–800 nm). Using FTIR spectroscopy, it is shown that the association of 6-O-carboxymethyl chitin macromolecules in the aqueous solution is due to the formation of both hydrogen bonds and ion pairs between the functional groups of the polymer.

Viscometric Determination of the Conformations and Sizes of Polyethylene Glycol Macromolecules in Aqueous Solutions

The kinematic viscosities of solutions of polyethylene glycol (PEG) of different molecular weights (1000, 1500, 3000, 4000, and 6000) are studied at 293.15–323.15 K in the 0–5 g/dL range of concentrations. Parameters are calculated according to the obtained data: characteristic viscosity, the Huggins constant, parameter α in the Kuhn–Mark–Houwink equation, characteristic viscosity in a θ solvent, the coefficient of swelling of the macromolecular coil in solution, root-mean-square distance of PEG macromolecular chain, and the length of Kuhn segments. It is found that the macromolecular coil is partially permeable for the surrounding liquid (water) and opens slightly. It was shown that the PEG molecules shrink as the temperature is raised, as is typical of flexible chain polymers.

Time correlation functions and kinetic coefficients in systems with molecular or chemical exchange

We develop a kinetic theory for systems with molecular or chemical exchange. In such systems, particles can successively reside in two different dynamical states with the inter-state transition. A prominent example of the molecular exchange (ME) is aqueous solutions of macromolecules (proteins, DNA) or metal ions, where a water molecule can move freely in a bulk of the solution or perform a constrained motion in a bound state. This may be the surface of the macromolecule or the ion's hydration shell. Another example, which refers to the chemical exchange (CE), is a molecule in a solution, that reversibly alternates its conformation — different conformations imply different rotational and translational motion. We consider the case of Poissonian exchange between states and general, non-Poissonian exchange and derive general relations for time correlation functions and kinetic coefficients. The application of the theory is illustrated by computation of time correlation functions and kinetic coefficients for translational and rotational motion of particles in systems with exchange.

Hydrodynamic behavior of chitosan hydrochloride macromolecules in aqueous solutions of D- and l-ascorbic acid

The hydrodynamic behavior of chitosan hydrochloride macromolecules in aqueous solutions of D- and l-ascorbic acid in a temperature range 25–45°C was studied by capillary viscometry. The intrinsic viscosity, the Huggins constant, and the temperature coefficient of viscosity were estimated. The effect of the ionic strength of the solvent mixture, predetermined by varying the acid concentration or introducing NaCl, on the hydrodynamic volume of macromolecules and their manifestation of polyelectrolyte properties was revealed. It was established that an increased temperature had led to the macromolecular coils getting more compact and the thermodynamic quality of the water-acid medium as a polymer solvent getting poorer. Despite the close values of pH and ionic strength of the aqueous solutions of D- and l-ascorbic acid, chitosan hydrochloride in the d-ascorbic acid solution is characterized by larger macromolecules and the polymer interaction with the solvent mixture components is energetically more favorable. It is suggested that the conformational state of chitosan hydrochloride is affected not so much by the macrochain stiffness as by the isomeric form of ascorbic acid. A comparison was made of the viscometric parameters of the aqueous solution of the aminopolysaccharide in ascorbic acid with its traditional solvent media, namely: water, acetic and hydrochloric acids, and sodium acetate buffer.

Binary Mixtures of Ionic Liquids in Aqueous Solution: Towards an Understanding of their Salting-In/Salting-Out Phenomena.

The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. In order to expand the knowledge on the salting-in/-out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water in presence of other IL/salts were conducted at 298.15 K at atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, in a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow to better understand the ILs impact when designing liquid-liquid separation processes.

Decomposition of carboxymethyl cellulose based on nano-knife principle

The traditional degradation of organic pollutants is based on the sacrifice of chemical or biological reagents. In this study, a purely physical technique was developed to break the chemical bonds and consequently decompose macromolecules in aqueous solution. Assisted with a high-speed mechanical blade, refined quartz sand grains with particularly sharp nano-scale edges can act as ‘nano-knives’, which are able to cut the long chain of carboxymethyl cellulose (CMC, as a model molecule). High performance size exclusion chromatography measurements evidenced that the original CMC molecules (41,000 Da) were decomposed into a series of smaller molecules (460, 1000, 2200, 21,000, 27,000 and 31,000 Da). Consequently, the initial viscosity of the CMC solution (2 g/L) rapidly decreased by approximately 50% after 3 min treatment by the nano-knife materials along with the mechanical blade. Fourier transform infrared (FTIR) spectra indicated that the original functional groups were still present and new functional groups were not produced after shearing. The intensity of the main functional group β-1-4-glycosidic bond (wavenumber 1062 cm−1) was observed to markedly decrease after shearing. These results indicated that the long-chain CMC was cleaved into short-chain CMC. A degradation mechanism was proposed whereby the cutting force generated by the rapid motion of the nano-knives may be responsible for the breakage of β-1-4-glycosidic bonds in the macromolecular cellulose backbone. These results provide support for a potentially more affordable and environment-friendly strategy for physical-based decomposition of recalcitrant organic pollutants from aqueous solution without the need of chemical or biological reagents.

Coacervates and coaggregates: Liquid–liquid and liquid–solid phase transitions by native and unfolded protein complexes

Coacervates are self-assemblies formed by oppositely charged macromolecules in aqueous solution. Although coacervates usually take a homogeneous spherical shape with flowability, they have the potential to adopt unexpected macroscopic structures. In this study, we investigated the influence of the interaction mode and morphology on unfolded proteins constituting coacervates and coaggregates using ovalbumin (OVA) and lysozyme (LYZ) as the model systems. The unfolded proteins were prepared via heating at 80 °C and then incubated at ambient temperature. OVA and LYZ formed complexes at pH values between their respective isoelectric points in both their native and unfolded states. The unfolded proteins were more prone to form complexes than the native proteins due to hydrophobic interactions rather than electrostatic attraction. Interestingly, native OVA and LYZ formed liquid-like coacervates with spherical shapes, whereas unfolded OVA and LYZ formed solid-like coaggregates with amorphous structures. Understanding the difference between coacervates and coaggregates will provide fundamental information regarding differences between the amorphous aggregation and liquid–liquid phase separation of proteins.

Behavior of Aqueous Solutions of Thermosensitive Starlike Polyalkyloxazolines with Different Arm Structures

The behavior of aqueous solutions of starlike polyalkyloxazolines with a calix[8]arene core is investigated by light scattering and turbidimetry. Polyethyloxazoline, the gradient copolymer of ethyloxazoline and isopropyloxazoline, and the block copolymers of polyethyloxazoline and polyisopropyloxazoline are used as arms. Using the methods of molecular hydrodynamics and optics, it is shown that the arms of the studied stars are strongly folded in organic solvents. It is found that the structure of arms affects the processes of self-organization and aggregation of their macromolecules in aqueous solutions. At room temperature, the dimensions of aggregates and their fraction in solutions depend on the position of ethyloxazoline and isopropyloxazoline units with respect to the calixarene core. Introducing ethyloxazoline units into macromolecules is accompanied by an increase in both the phase-separation temperature and the width of this interval relative to the corresponding characteristics of the star with polyisopropyloxazoline arms. For stars with copolymer arms, the temperatures of the end of phase transition differ insignificantly. Differences in the behavior of the studied arms are due to the fact that the dehydration temperature for polyethyloxazoline is noticeably higher than that for polyisopropyloxazoline.

A Study of the Effect of a Protein on the Structure of Water in Solution Using Terahertz Time-Domain Spectroscopy.

Terahertz time-domain spectroscopy (THz-TDS) was used to determine the spectra (range = 1.2-120 cm-1) of aqueous solutions of bovine serum albumin (BSA) at pH range 2.5-10. Under each of the selected pH, BSA molecules exist in a different conformation, compared to other pH values. The spectra were used to calculate the functions of the dielectric permittivity of BSA solutions. Dielectric functions of the aqueous phase of BSA solutions were calculated based on the Bruggeman model, without the contribution of BSA itself. Fitting of the dielectric functions was performed using a model which includes three water spectral bands: two relaxation bands with relaxation times of about 8.28 and 0.3 ps and a vibrational band with a maximum of about 180 cm-1. The parameters of these bands were determined through fitting and physical interpretation at the molecular level can be provided for each of them. A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule. At the same time, the structure of more distant layers of the hydration shells is destroyed, with an increased formation of free water molecules. Some differences are observed in the effect of different BSA conformations on the aqueous phase of solution. The proposed approach can be generalized and applied for studying of a wide class of biological macromolecules in aqueous solutions.

Effects of Monomer Feed Amounts on Solution Properties and Solution Morphologies for a Comb-like Ter-polymer

ABSTRACTAn acrylamide(AM)-based ter-polymer (PAAB) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS) and p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VBE, polymerization degree: 24) was synthesized by an aqueous free-radical copolymerization. In order to obtain a PAAB polymer with both good thickening properties and surface and interfacial properties in brine solutions for enhanced oil recovery (EOR), the influences of the NaAMPS and VBE feed amounts on the intrinsic and apparent viscosities and the surface and interfacial tensions of the PAAB polymer in aqueous solutions were investigated. The optimum NaAMPS feed amount was 9 mol%; an excessive feed amount interfered with the aggregations of the PAAB macro-molecules in aqueous solutions and on the surfaces of aqueous solutions and the interfaces between aqueous solutions and kerosene. In addition, for this NaAMPS feed concentration, the PAAB polymer showed the highest apparent viscosities and the lowest surface and interfacial tensions in 5 g L−1 NaCl for a VBE feed amount of 1.1 mol%. The mechanism giving rise to the solution properties for this polymer was examined. For this purpose, the effect of the polymer concentration on the supra-molecular structures of the PAAB polymer in water and in 5 g/L NaCl, were investigated by ultraviolet spectral analysis using pyrene as a probe. A transmission electron microscope (TEM) was also used to observe the morphologies of the associated structures in aqueous solutions to explore the correlation between the solution properties and solution structures for PAAB; expanded polymer chain bundles were formed at a polymer concentration of 0. 4 g L−1, higher than the critical micelle concentration (0. 3 g L−1).