Low Molecular Weight Salts Research Articles

Properties of cross-linked copolymers of polypropylene glycol maleate with acrylic acid obtained at various concentrations of the RAFT agent

The initial polypropylene glycol maleate has been obtained by the polycondensation reaction of maleic anhydride and propylene glycol. The molecular weight of the synthesized unsaturated polyester resin has been determined. The copolymers under study have been obtained by radical copolymerization of p-PGM. The possibility of synthesizing new polymers based on p-PGM with acrylic acid in the presence of a RAFT agent has been shown. The effect of RAFT agent concentration on the network density and product yield has been studied. It has been found that the yield of the cross-linked polymer decreases, its swelling capacity increases, and the yield of the linear polymer increases with an increase in the RAFT agent concentration. The effect of organic solvents, pH, and low-molecular-weight salts on the swelling degree of the synthesized copolymers has been investigated. The research results demonstrate that the susceptibility of polymer hydrogels to organic solvents and changes in pH, and low molecular weight salts, is affected by the amount of RAFT agent in the polymer. The synthesized objects have been characterized by infrared spectroscopy. Scanning electron microscopy has estimated the polymer surface morphology and pore sizes

Influence of Low Molecular Weight Salts on the Viscosity of Aqueous-Buffer Bovine Serum Albumin Solutions.

Pharmaceutical design of protein formulations aims at maximum efficiency (protein concentration) and minimum viscosity. Therefore, it is important to know the nature of protein-protein interactions and their influence on viscosity. In this work, we investigated the dependence of the viscosity of BSA in an aqueous 20 mM acetate buffer at pH = 4.3 on protein concentration and on temperature (5–45 °C). The viscosity of the solution increased with protein concentration and was 230% higher than the viscosity of the protein-free formulation at 160 mg/mL. The viscosity decreased by almost 60% in the temperature range from 5 to 45 °C. The agreement of the modified Arrhenius theory with experiment was quantitative, whereas a hard-sphere model provided only a qualitative description of the experimental results. We also investigated the viscosity of a 100 mg/mL BSA solution as a function of the concentration of added low molecular weight salts (LiCl, NaCl, KCl, RbCl, CsCl, NaBr, NaI) in the range of salt concentrations up to 1.75 mol/L. In addition, the particle size and zeta potential of BSA-salt mixtures were determined for solutions containing 0.5 mol/L salt. The trends with respect to the different anions followed a direct Hofmeister series (Cl− > Br− > I−), whereas for cations in the case of viscosity the indirect Hofmeister series was observed (Li+ > Na+ > K+ > Rb+ > Cs+), but the values of particle sizes and zeta potential did not show cation-specific effects. Since the protein is positively charged at pH = 4.3, anions are more attracted to the protein surface and shield its charge, while the interaction with cations is less pronounced. We hypothesize that salt surface charge shielding reduces protein colloidal stability and promotes protein aggregate formation.

Mechanistic differences in the effects of sucrose and sucralose on the phase stability of lysozyme solutions

The effect of two disaccharide analogues, sucrose and sucralose, on the phase stability of aqueous lysozyme solutions has been addressed from a mechanistic viewpoint by a combination of experiment and molecular dynamics (MD) simulations. The influence of the added low molecular weight salts (NaBr, NaI and NaNO3) was considered as well. The cloud-point temperature measurements revealed a larger stabilizing effect of sucralose. Upon increasing sugar concentration, the protein solutions became more stable and differences in the effect of sucralose and sucrose amplified. It was confirmed that the addition of either of the two sugars imposed no secondary structure changes of the lysozyme. Enthalpies of lysozyme-sugar mixing were exothermic and a larger effect was recorded for sucralose. MD simulations indicated that acidic, basic and polar amino acid residues play predominant roles in the sugar-protein interactions, mainly through hydrogen bonding. Such sugar mediated protein-protein interactions are thought to be responsible for the biopreserative nature of sugars. Our observations hint at mechanistic differences in sugar-lysozyme interactions: while sucrose does not interact directly with the protein's surface for the most part (in line with the preferential hydration hypothesis), sucralose forms hydrogen bonds with acidic, basic and polar amino acid residues at the lysozyme's surface (in line with the water replacement hypothesis).

Loading of doxorubicin into surface-attached stimuli-responsive microgels and its subsequent release under different conditions

This study highlights the use of chargeable stimuli-responsive microgels for modification of rather hydrophobic model surfaces and reveals the optimal conditions, which are to be applied for enhanced microgel adsorption onto such surfaces. The highly efficient surface modification is achieved when the microgel is adsorbed in its uncharged and sufficiently dehydrated (hydrophobized) state. After subsequent charging, the adsorbed microgels can be loaded with a bioactive payload of opposite charge, wherein a negatively charged microgel acts as a capacious container hosting a considerable amount of a positively charged drug (doxorubicin). The loaded doxorubicin can be gradually eluted through washing, this process being facilitated if the eluent contains a low molecular weight salt, thereby manifesting that binding of the drug to the microgel is of pronounced electrostatic nature. Furthermore, the release of doxorubicin from the surface-attached microgels can also be induced by linear synthetic polyelectrolytes, which could be, as shown for the first time in this work, any polyions, both cationic and anionic ones. Hence, polycations compete with the drug for binding to the surface-attached anionic microgel, while polyanions compete with the microgel for binding of doxorubicin. Such competitive interactions in ternary systems (microgel - drug - linear polyion) result in displacement of doxorubicin from the surface-attached microgels, regardless of whether the polymer-competitor is oppositely or even (rather peculiarly) similarly charged with respect to the microgel. Thus, this study illustrates means, which can be used to control escape of bioactive payloads from oppositely charged microgels, and this knowledge can be exploited for development of uptake and release systems for various applications (e.g., in medicine or agriculture) and prognosis of their functioning in complex aqueous environments, which can contain inter alia various (bio)macromolecular species.

Viscoelastic Solutions of Wormlike Micelles of a Cationic Surfactant and a Stiff-Chain Anionic Polyelectrolyte

The phase behavior and rheological properties of the mixtures of wormlike micelles of the cationic surfactant erucyl-bis(hydroxyethyl) methyl ammonium chloride and oppositely charged stiff-chain polyelectrolyte xanthan are studied. It is shown that, in the presence of an excess of a low molecular weight salt, which suppresses complex formation between the surfactant and the polymer, mixing allows a synergistic increase in the elastic modulus of the system to be achieved, which may be due to the formation of entanglements between polymer chains and wormlike micelles.

Cationic electrolyte copolymers of diallyldimethylammonium chloride with carboxybetaine 2-(diallyl(methyl) ammonio) acetate of various compositions in water solutions of different ionic strengths

Random copolymers of diallyldimethylammonium chloride (DADMAC) and carboxybetaine 2-(diallyl(methyl)ammonio) acetate (DAMA) with different compositions (10%/90%), (50%/50%) and (70%/30%), as well as poly(DAMA) and poly(DADMAC) homopolymers, were synthesized. Molecular characteristics of poly(DADMAC–co–DAMA) copolymers and homopolymers were determined in water solutions in the presence of 0.1 M NaOH and a low molecular weight salt (NaCl in various concentrations) by viscometery, dynamic and static light scattering. Dependences of several important conformational parameters, such as swelling coefficient α, the Huggins constant kH, and the second virial coefficient A2, on copolymer composition (charge asymmetry) and NaCl concentration in solution were analyzed. It was shown that growth of charge asymmetry leads to sharp increase in copolymer size.

Brine Recycling from Industrial Textile Wastewater Treated by Ozone. By-Products Accumulation. Part 1: Multi Recycling Loop

The “reactive” dyeing of textiles requires an application of low-molecular-weight salts (LMWS), such as NaCl or Na2SO4, as necessary auxiliary agents. LMWS acts only as a remediation factor and remains in the dyeing effluents constitute brine. The main goal of the presented study was to investigate the application of ozone technology for industrial textile wastewater highly polluted by LMWS. The study was divided into two parts. In Part 1, by-products accumulated during multi-recycling of the same wastewater was investigated. While Part 2 was devoted to the scaling up of ozonation process, Part 1 concerns the efficiency of textile wastewater ozonation carried out as a repeatable process. The sequence of wastewater treatment and textile dyeing was repeated four times in a closed loop using the same process water. Although the wastewater decolorization was efficient in the subsequent ozonation cycles, some adverse effects, such as an increase in chemical oxygen demand (COD) and self-buffering at pH 9.5–10.0, were suggested the accumulation of by-products. The preliminary detection of by-products by thin layer chromatography (TLC) revealed phenol and naphthol derivatives as the transformation products (TPs) of ozonation. Dyeing of cotton using purified wastewater (brine) resulted in very good DECMC color matching parameters (under 1.16), but only in the first recycling loop, and then the TPs affected the process.

Brine Recycling from Industrial Textile Wastewater Treated by Ozone. By-Products Accumulation. Part 2: Scaling-Up

Extremely high volumes of salty wastewater are produced by textile manufacturers daily. Therefore, brine recycling from the wastewater should be regarded as a crucial issue within the textile industry. Ozonation was used in this two-part study as a purification method for industrial textile wastewater polluted by low-molecular-weight salts (LMWS). Part 1 revealed the accumulation of ozonation by-products in a multi-recycling system. The objective of Part 2 was the scaling-up of the process and the investigation of the occurrence of by-products. It was found that ozonation works well in an alkaline reaction medium, which was characteristic of the wastewater from a dye house; an almost complete color removal was achieved within 30 min of treatment. The brine that was produced from the wastewater treated by ozonation in a 20 L bubble column reactor was recycled successfully. Dyeing of cotton with five types of reactive dyes in various shades resulted in very good values of DECMC, which is the normative color matching parameter, and were between 0.15 and 1.2. The color fastness obtained for upcycled fabrics were satisfactory, and not worse than standard values. Although accumulation of the side products was detected in Part 1, the fabric discharges produced in the scaled-up process were free from carcinogenic amines and heavy metals. The study indicated that ozonation can be applied in the industry as a method for textile wastewater recycling.

Effect of Cephtriaxone and Cephtasidim Antibiotics on Enzymatic Hydrolysis of Chitosan-Based Pellicular Materials

Enzymatic hydrolysis of chitosan-based films supplemented with cephtasidim and cephtriaxone antibiotics on a substrate saturated with water, diluted acetic acid, or Ringer-Locke physiological saline was studied. Supplementation with antibiotics having the chemical structure of low molecular weight salts reduced the rate of enzymatic hydrolysis of chitosan regardless of the medium used. The decrease was related to the suppression of polyelectrolyte swelling of the polycation rather than enzyme inhibition. The addition of antibiotics to chitosan films can apparently be considered an approach to directed reduction of the film enzymatic hydrolysis rates, which may contribute to an increase in film lifetime on the wound surface.

Calorimetric studies of interactions between low molecular weight salts and bovine serum albumin in water at pH values below and above the isoionic point

Isothermal titration calorimetry was used to determine the temperature and salt concentration dependence of the enthalpy of mixing, ΔmixH, of bovine serum albumin (BSA) in aqueous buffer solutions with several low molecular weight salts. Three buffers were used: acetate (pH=4.0), MOPS (7.2), and borate (9.2). Since the isoionic point of BSA is at pI ≈ 4.7, the net charge of BSA in acetate buffer was positive (≈ +20), while in the other two buffer solutions it was negative (≈−15 in MOPS and ≈−25 in borate). The majority of the recorded heat effects were exothermic, while only at pH=9.2 a weak endothermic effect upon mixing BSA with LiCl, NaCl, and KCl was observed. For all buffer solutions the absolute values of ΔmixH of sodium salts followed the order: NaCl < NaBr < NaNO3< NaI < NaSCN, which is the reverse Hofmeister series for anions. The magnitude of the effects was the largest in acetate buffer and decreased with an increasing pH value of the solution. While the effect of varying the anion of the added salts was strongly pronounced at all pH values, the effect of the cation (LiCl, NaCl, KCl, RbCl and CsCl salts) was weak. The most interesting feature of the results obtained for pH >pI was the fact that ΔmixH were considerably more sensitive to the anion (co-ion to the net BSA charge) than to the cation species. This indicated that anions interacted quite strongly with the BSA even at pH values where the net charge of the protein was negative. We showed that ΔmixH at high addition of salts correlated well with the enthalpy of hydration of the corresponding salt anion. This finding suggested, consistently with some previous studies, that a part of the exothermic contribution to ΔmixH originated from the hydration changes upon the protein–salt interaction. Theoretical analysis, based on the primitive model of highly asymmetric electrolyte solutions solved within the mean spherical approximation, was used to estimate Coulomb effects upon mixing.

Supramolecular Hydro- and Ionogels: A Study of Their Properties and Antibacterial Activity.

Diimidazolium-based organic salts, bearing peptides or amino acids as anions have been synthesised and tested for their gelling ability in biocompatible solvents. These low molecular weight salts were successfully used as gelators in phosphate buffered saline (PBS) solution and ionic liquids. Then, the properties of the obtained soft materials were analysed in terms of melting temperature and gel strength as accounted for by rheological investigations. The gel-phase formation was studied by using UV/Vis and resonance light scattering measurements, whereas the morphology of the soft materials was analysed by using polarised optical microscopy and scanning electron microscopy. To get information about the organisation of the gelator in the gelatinous matrix, X-ray diffraction measurements were performed both on the neat gelators and their gels. The results collected show that the properties of the gel phases, like the thermal stability, the self-repairing ability, the resistance to flow as well as the morphology, are dependent on the nature of the anion. Furthermore, bioassays revealed that the obtained diimidazolium organic salts possessed antimicrobial activity, against gram-negative and gram-positive tester strains. In particular and noteworthy, the diimidazolium organic salts exert a bactericidal capability, which was retained even if they are included in the gel phase. Thus, a novel kind of bioactive soft material was obtained that could be fruitfully employed as a non-covalent coating exerting antibacterial capability.

Self-Assembly of Lecithin and Bile Salt in the Presence of Inorganic Salt in Water: Mesoscale Computer Simulation.

The influence of inorganic salt on the structure of lecithin/bile salt mixtures in aqueous solution is studied by means of dissipative particle dynamics simulations. We propose a coarse-grained model of phosphatidylcholine and two types of bile salts (sodium cholate and sodium deoxycholate) and also take into account the presence of low molecular weight salt. This model allows us to study the system on rather large time and length scales (up to about ∼20 μs and 50 nm) and to reveal mechanisms of experimentally observed increasing viscosity upon increasing the low molecular weight salt concentration in this system. We show that increasing the low molecular weight salt concentration induces the growth of cylinder-like micelles formed in lecithin/bile salt mixtures in water. These wormlike micelles can entangle into transient networks displaying perceptible viscoelastic properties. Computer simulation results are in good qualitative agreement with experimental observations.

Microgels enable capacious uptake and controlled release of architecturally complex macromolecular species

This study highlights the use of microgels as containers of high capacity for uptake and triggered release of multi-functional guests. As a model guest, heteroarm star-shaped copolymers (miktoarm stars) are chosen, as their certain arms could carry different active moieties, while other arms could act as “stickers” to the microgel host. Electrostatic attraction is used as a binding principle, wherein positively charged bis-hydrophilic miktoarm stars interact with negatively charged microgels. Functioning of microgels as containers with high capacity offers the possibility to construct promising stimuli-responsive uptake and release systems. Hence, aqueous mixtures of these oppositely charged polymeric components, the microgels and the miktoarm stars, were investigated in dependence on their initial charge ratio (icr = [cationic charges]/[anionic charges]) and on the concentration of a low molecular weight salt. The miktoarm stars are able to penetrate into the microgels to compensate their negatively charged groups. The amount of the miktoarm stars bound to the microgels can be controlled via ionic strength of the system, with limiting cases from quantitative binding to no binding. Then, such a microgel-based polyelectrolyte complex consists of one microgel and more than 1000 miktoarm stars. Furthermore, a jump-wise increase of ionic strength in solutions of the complexes triggers the complete release of the miktoarm stars from the microgel, and the system stays always colloidally stable. Thus, microgel-based polylectrolyte complexes provide opportunities for many important applications, especially in targeted/controlled delivery.

Morphological structure of Gluconacetobacter xylinus cellulose and cellulose-based organic-inorganic composite materials

Scanning electron microscopy, ultra-small-angle neutron scattering (USANS), small-angle neutron and X-ray scattering (SANS and SAXS), as well as low-temperature nitrogen adsorption, were used in the studies of micro- and mesostructure of polymer matrix prepared from air-dry preliminarily disintegrated cellulose nano-gel film (synthesized by Gluconacetobacter xylinus) and the composites based on this bacterial cellulose. The composites included ZrO2 nanoparticles, Tb3+ in the form of low molecular weight salt and of metal-polymer complex with poly(vinylpyrrolydone)-poly(methacryloyl-o-aminobenzoic acid) copolymer. The combined analysis of the data obtained allowed revealing three levels of fractal organization in mesostructure of G. xylinus cellulose and its composites. It was shown that both the composition and an aggregation state of dopants have a significant impact on the structural characteristics of the organic-inorganic composites. The composites containing Tb3+ ions demonstrate efficient luminescence; its intensity is an order of magnitude higher in the case of the composites with the metal-polymer complex. It was found that there is the optimal content of ZrO2 nanoparticles in composites resulting in increased Tb3+ luminescence.

Copolymers of diallyldimethylammonium chloride and 2-(diallyl(methyl) ammonio) acetate: Effect of composition and ionic strength on conformational properties

Copolymerization of diallyldimethylammonium chloride (DADMAC) with 2-(diallyl(methyl) ammonio) acetate (DAMA) was studied. A homologous series of random copolymers (poly(DADMAC-co-DAMA)) with the DADMAC:DAMA ratio equal to 3:7 was investigated by dynamic and static light scattering, viscometry, and flow birefringence in 0.1M NaOH solutions with the addition of NaCl (up to 1M). The Mark-Kuhn-Houwink equations were obtained. It was established that decrease in the concentration of low molecular weight salt leads to sharp increase in thermodynamic quality of solvents, and, therefore, in swelling of the macromolecules. Equilibrium rigidity of the studied copolymer was determined as 5nm. Conformational behavior of poly(DADMAC) (polyelectrolyte), poly(DAMA) (polyzwitterion) and poly(DADMAC-co-DAMA) with the DADMAC:DAMA ratio equal to 3:7 was investigated in solutions at different ionic strength values. It was established that at NaCl concentrations below 0.1M, copolymer exhibits properties typical of polyelectrolyte, and at higher NaCl concentrations it exhibits properties typical of polyzwitterion. Detailed consideration of contributions of optical effects of micro- and macroform to the observed flow birefringence in copolymer solutions allowed us to estimate optical characteristics of copolymer macromolecules. It was established that in salt-free aqueous solution, poly(DADMAC-co-DAMA) macromolecular coils swell isotropically.

Hydrophobic interaction and patch charge attraction in α-Al2O3 dispersions under the influence of adsorbed low molecular-weight polyacrylic acid sodium salt and poly(methacrylic acid) sodium salt: yield stress and AFM force study

Maximum yield stress data showed that low molecular-weight (Mw) (∼7 kDa) poly(methacrylic acid) sodium salt (PMA-Na) additive at low surface coverage displayed significant patch charge attraction in contrast to polyacrylic acid sodium salt (PAA-Na) additive of similar Mw and surface coverage. Intramolecular hydrophobic interaction between CH3 groups in the polymer molecule during adsorption produced a much more compact patch with a higher negative charge density giving rise to the stronger patch charge attraction. At high surface coverage, intermolecular hydrophobic interaction between CH3 groups on the adsorbed layer of the interacting particles was not observed from maximum yield stress data. Such interaction was, however, observed in AFM force-distance characterization data for interaction between spherical alumina particles and sapphire plates coated with PMA-Na in retraction mode. The compression of the adsorbed layers at contact during the approach mode was postulated to deform and breakup the intramolecular interaction between the CH3 groups and promoted intermolecular interaction between these groups in the layer coating the particle and plate. This resulted in a strong adhesion force seen in the retraction mode after contact at low pH near the point of zero charge.

Effect of added salt on swelling dynamics of ultrathin films of strong polyelectrolytes

Solvent mass uptake and swelling dynamics of spin coated poly(sodium-4-styrenesulfonate) (NaPSS) films containing different concentration of externally added monovalent salt ions have been performed in presence of water vapor to study the effect of low molecular weight salt ions on the swelling dynamics of charged polymeric chains in confined geometry. Diffusion coefficient of the water molecules within the NaPSS films, as obtained from the solvent mass uptake study, is found to be independent of salt concentration. Swelling dynamics of the chains in presence of water vapor has been studied in-situ using X-ray reflectivity technique. The actual salt concentration and the distribution of salt ions within the films were examined using X-ray Photoelectron Spectroscopy (XPS). The diffusion coefficients of the NaPSS chains show a salt concentration independent behavior and are of same order as that of salt free NaPSS chains. Whereas, the fraction of charged monomers, that determines the strength of the repulsive interaction between the polymer segments, increases with salt concentration when the later becomes comparable to that of already present counterions in the system. The Na and Cl ions show clear tendency to be redistributed within the films instead of forming NaCl salt. The negative Cl ions migrate towards the top surface whereas the positive sodium ions accumulate on the substrate. Counterion condensation process of the polyelectrolyte chains gets inhibited by the internal electric field produced between the top Cl− layer and the bottom Na+ layer which increases the effective charge of the polyelectrolyte chains.

Разработка буровых растворов на основе полисахаридов и природных минералов

The technology of oil well drilling in complex geological conditions by applying the drilling muds based on the polysaccharides – gellan, xanthan and their mixture which potentially possess a good flocculation properties and the ability to reversible sol-gel transition in dependence of temperature and concentration of low molecular weight cations in water has been justified in this work. For the preparation of drilling muds, gellan and xanthan were used, these polymers were obtained from biomass by an aerobic fermentation using microorganisms Sphingomonas elodea and Xanthomonas campestris. Bentonite was used as a natural mineral. Physical and chemical characteristics of aqueous and aqueous-salt solutions of natural polysaccharide gellan including: density, intrinsic and effective viscosity, static shear stress, dynamic shear stress, sedimentation stability and other parameters were determined while varying polymer compositions and concentrations, ionic strength of the solution, nature of low molecular weight salts, concentration of dispersion phase, pH of the medium and temperature.

Ubiquitous distribution of salts and proteins in spider glue enhances spider silk adhesion.

Modern orb-weaving spiders use micron-sized glue droplets on their viscid silk to retain prey in webs. A combination of low molecular weight salts and proteins makes the glue viscoelastic and humidity responsive in a way not easily achieved by synthetic adhesives. Optically, the glue droplet shows a heterogeneous structure, but the spatial arrangement of its chemical components is poorly understood. Here, we use optical and confocal Raman microscopy to show that salts and proteins are present ubiquitously throughout the droplet. The distribution of adhesive proteins in the peripheral region explains the superior prey capture performance of orb webs as it enables the entire surface area of the glue droplet to act as a site for prey capture. The presence of salts throughout the droplet explains the recent Solid-State NMR results that show salts directly facilitate protein mobility. Understanding the function of individual glue components and the role of the droplet's macro-structure can help in designing better synthetic adhesives for humid environments.

Viscoelasticity of smart fluids based on wormlike surfactant micelles and oppositely charged magnetic particles.

Novel viscoelastic smart suspensions based on cationic wormlike micelles (WLMs) of erucylbis(hydroxyethyl)methylammonium chloride and oppositely charged submicron magnetite particles in the presence of added low molecular weight salt were prepared and investigated. The suspensions demonstrate remarkable stability against sedimentation, which can be due to the incorporation of particles into the network of entangled WLMs by linking to energetically unfavorable micellar end-caps. Added particles enhance significantly the viscosity, the plateau modulus, and the relaxation time of the system, acting as additional multifunctional physical cross-links in the micellar network. The increase of plateau modulus stops when the concentration of particles reaches ca. 1.5 wt %, indicating that all micellar end-caps available in the system are linked to the particles. Further addition of particles may lead just to the redistribution of micellar ends between the particles without creation of new elastically active chains. The increase of rheological characteristics by added particles is more pronounced in suspensions with a smaller content of low molecular weight salt KCl when the WLMs are shorter in length and therefore contain a larger amount of end-caps responsible for the interaction with the particles. Magnetite particles not only enhance the rheological characteristics but also impart magnetoresponsive properties to the suspension. Upon application of magnetic field, the liquidlike system transforms into a solidlike one, demonstrating a constant value of storage modulus in all frequency range and the appearance of yield stress, which is due to the formation of field-aligned chainlike aggregates of particles opposing the flow. A combination of responsive properties inherent to both the matrix and the particles makes these smart fluids very competitive with other magnetic soft matter materials for various applications.