Linear Polymers In Solution Research Articles

Polymers of the candidalysin peptide become membrane pores.

C. albicans infection requires the action of the virulence factor candidalysin (CL), which damages the plasma membrane of target human cells (Moyes Nature 2016). However, the molecular mechanism that CL uses to permeabilize membranes was unknown. We have employed complementary biophysical, modeling, microscopy, and cell biology methods to reveal that CL forms membrane pores using a unique molecular mechanism (Russell eLife 2022). Unexpectedly, we observed that CL readily assembles into linear polymers in solution. We propose that the basic structural unit in polymer formation is a CL oligomer, which is sequentially added into a string configuration that can close into a loop. Our data indicate that CL loops spontaneously insert into the membrane to become membrane pores. We identified a CL mutation (G4W) that inhibited the formation of polymers in solution and prevented formation of pores in synthetic lipid membrane systems. Studies in epithelial cells showed that G4W CL failed to activate the danger response signaling pathway, a hallmark of the pathogenic effect of CL. These results indicate that CL polymerization in solution is a necessary step for the damage of cellular membranes. Analysis of thousands of CL pores by atomic force microscopy revealed co-existence of simple depressions and complex pores decorated with protrusions. Imaging and modeling indicate that the two types of pores are formed by CL oligomers assembled into alternate orientations. We propose that this structural rearrangement represents a maturation mechanism that stabilizes pore formation . The data show that CL uses a previously unknown mechanism to damage membranes, whereby pre-assembly of CL loops in solution directly leads to formation of membrane pores. Our investigation not only unravels a new paradigm for the formation of membrane pores, but additionally identifies CL polymerization as a novel therapeutic target to treat candidiasis.

Predicting Phase Behavior of Linear Polymers in Solution Using Machine Learning

Predicting Phase Behavior of Linear Polymers in Solution Using Machine Learning

Spatial Demixing of Ring and Chain Polymers in Pressure-Driven Flow

We investigate mixtures of ring and linear polymers in solution at various number ratios, ranging from pure chains to pure rings, and at densities around the overlap concentration. In bulk and at r...

Fractionation and DOSY NMR as Analytical Tools: From Model Polymers to a Technical Lignin

One key challenge hindering the valorization of lignin is its structural complexity. Artificial lignin-like materials provide a stepping stone between the simplicity of model compounds and the complexity of lignin. Here, we report an optimized synthesis of an all-G β-O-4 polymer 1 designed to model softwood lignin. After acetylation, the polymer Ac-1(V) was fractionated using a protocol that involved only volatile organic solvents, which left no insoluble residue. Using diffusion ordered spectroscopy NMR in combination with gel permeation chromatography, it was revealed that this fractionated material behaved like a flexible linear polymer in solution (average α > 0.5). Acetylated kraft lignin was subsequently processed using the same fractionation protocol. By comparison with the model polymer, we propose that the acetylated kraft lignin is composed of two classes of materials that exhibit contrasting physical properties. One is comparable to the acetylated all-G β-O-4 polymer Ac-1, and the second has a significantly different macromolecular structure.

Simulating dynamic crossover behavior of semiflexible linear polymers in solution and in the melt

We present a molecular dynamics study of the dynamic scaling behavior of linear polymers in solution and in the melt when their character changes from fully flexible to semiflexible. The stiffness of the chains is determined by a bending potential. It is shown that the relaxation times tau(p) characterizing the internal dynamics of the polymer chains as well as the mean square mode amplitudes <chi(p)(2)> exhibit a clear crossover from Rouse to bending modes with increasing mode number p. For small mode numbers p the well-known p(-2) Rouse behavior is observed, whereas large mode numbers exhibit the p(-4) scaling, typical of the bending modes of semiflexible chains. We study the extension and the onset of the region where the crossover from p(-2) to p(-4) behavior occurs. With increasing stiffness of the chains we observe a shift of the crossover domain to smaller p-values. We also investigate the effect of chain stiffness on the monomer dynamics, based on their mean square displacements. Finally, we compare our results to previous simulations, where the scaling behavior of semiflexible chains was studied and which were restricted to a smaller range of persistence lengths l(p) and p values.

A Novel Self-Assembled, Self-Healing, Ordered Biomaterial

Geometrically-ordered biomaterials are beneficial to tissue engineering and to studies of cell mechanics. In addition, techniques to produce microscale and nanoscale ordered objects can be applied to solve engineering problems in industrial settings. We present a magnetically self-assembled two-dimensional crystal of thrombin-coated superparamagnetic microbeads formed on a liquid-air interface. The thrombin-coated beads catalyzed the cleavage of fibrinogen in solution to form fibrin fibers that self-assembled into a nanometer-scale fibrin network whose fibers have been shown to follow the ordering of the scaffolding bead crystal (Alsberg, et al. (2006) Tissue Engineering. 12, 3247.). Computer simulations and analysis of confocal fluorescence microscopic images reveal the mechanism by which the system self-assembles to its geometrically-ordered form. We demonstrate that the process of self-assembly is dependent on the lattice geometry, but not on the details of fibrin biology. We formulate a set of rules that are required for ordering: (i) The monomers must be adherent to the scaffold beads, (ii) The monomers must be able to polymerize into a linear polymer in solution, (iii) Growing polymer fibers must be able to diffuse about a pivot at their point of attachment to the beads and (iv) Interactions between the monomers, polymers, and fibers, other than polymerization must be minimal. We demonstrate a microrheological system for measuring the time-dependent dynamics of formation of the fibrin network. The crystalline order of the magnetic microbeads allows us to sample the forming network's viscoelastic properties at regularly spaced intervals. Using the magnetic interactions between the beads as a force transducer, we demonstrate the effects of mechanically perturbing the forming gel, showing that broken connections in the network are repaired. Taken together, the results suggest that the process is generalizable, and that the resulting system is self-healing during the formation of the lattice.

A macromolecule in a solvent: Adaptive resolution molecular dynamics simulation

The authors report adaptive resolution molecular dynamics simulations of a flexible linear polymer in solution. The solvent, i.e., a liquid of tetrahedral molecules, is represented within a certain radius from the polymer's center of mass with a high level of detail, while a lower coarse-grained resolution is used for the more distant solvent. The high resolution sphere moves with the polymer and freely exchanges molecules with the low resolution region through a transition regime. The solvent molecules change their resolution and number of degrees of freedom on the fly. The authors show that their approach correctly reproduces the static and dynamic properties of the polymer chain and surrounding solvent.

Swelling behavior of polystyrene networks in some aliphatic esters and linear polystyrene solutions

Polystyrene networks were synthesized by free radical polymerization of styrene in the presence of dibenzoyl peroxide as an initiator, divinylbenzene as a crosslinker at 50 °C in toluene under nitrogen atmosphere. The swelling behavior of the synthesized polystyrene networks were studied at different temperatures in methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, tert-butyl acetate, and isopentyl acetate. Equations were given for the variation of the polymer-solvent interaction parameter, χ12, as a function of reciprocal absolute temperature in the temperature range from 25 to 75 °C. Polystyrene networks were swollen in linear polystyrene solutions in toluene of different concentrations. Linear polystyrene samples were almost monodisperse and of high molecular weight. The equilibrium swelling degrees were evaluated using the Flory-Rehner theory. The relation of volume swelling ratio, qv, to the volume fraction of the linear polymer in solution, φ, was evaluated and characterized by interaction parameter of crosslinked polystyrene with linear polystyrene, χ23. The parameter χ23 was found around zero as expected from mixtures of similar chemical structures by extrapolating the values of χ23 at tested concentrations to zero solvent concentration.

Phase Separation of a Model Binary Polymer Solution in an External Field

The phase separation of a simple binary mixture of incompatible linear polymers in solution is investigated using an extension of the sedimentation equilibrium method, whereby the osmotic pressure of the mixture is extracted from the density profiles of the inhomogeneous mixture in a gravitational field. In Monte Carlo simulations the field can be tuned to induce significant inhomogeneity, while keeping the density profiles sufficiently smooth for the macroscopic condition of hydrostatic equilibrium to remain applicable. The method is applied here for a simplified model of ideal but mutually avoiding polymers, which readily phase separate at relatively low densities. The Monte Carlo data are interpreted with the help of an approximate bulk phase diagram calculated from a simple, second-order virial coefficient theory. By derivation of effective potentials between polymer centers of mass, the binary mixture of polymers is coarse-grained to a "soft colloid" picture reminiscent of the Widom-Rowlinson model for incompatible atomic mixtures. This approach significantly speeds up the simulations and accurately reproduces the behavior of the full monomer resolved model.

Eight‐arm star polystyrene in methylcyclohexane: Cloud‐point curves, critical lines, and coexisting densities and viscosities

AbstractWe measured the cloud‐point curves of eight‐arm star polystyrene (sPS) in methylcyclohexane (MCH) for polymer samples of three total molecular masses [weight‐average molecular weight (Mw) × 10−3= 77, 215, or 268]. We found a downward shift of 5–15 K in the critical temperature (Tc) of the star polymer solutions with respect to linear polystyrene (PS) solutions of the sameMw. The shift inTcbecame smaller asMwincreased. The critical volume fraction for eight‐arm sPS in MCH was equal within experimental uncertainty (10–40%) to that of linear PS in MCH. For sPS ofMw= 77,000 in MCH, we studied the mass density (ρ) as a function of temperature (T). As for linear polymers in solution, the difference in ρ between coexisting phases (Δρ) could be described overt= (Tc−T)/Tcfor 1.1 × 10−4&lt;t&lt; 4.7 × 10−3with the Ising value of the exponent β in the expression Δρ =Btβ. Both ρ(T) aboveTcand the average value of ρ belowTcwere linear functions of temperature; no singular corrections were observed. The measurements of the shear viscosity (η) nearTcfor sPS (Mw= 74,000) in MCH indicated a strong critical anomaly in η, but the data were not precise enough for a quantitative analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 129–145, 2004

Photo-Cross-Linkable PNIPAAm Copolymers. 2. Effects of Constraint on Temperature and pH-Responsive Hydrogel Layers

Photo-cross-linkable co- and terpolymers of N-isopropylacrylamide, 2-(dimethylmaleimido)-N-ethyl-acrylamide as the photosensitive component, and 3-acryloylaminopropionic acid or N-(2-(dimethylamino)ethyl)acrylamide as ionizable comonomers were prepared by free radical polymerization. Aqueous solutions of the linear un-cross-linked co- and terpolymers showed lower critical solution temperature behavior. The phase transition temperature, which was detected by differential scanning calorimetry, ranged from 23.1 to 39.2 °C depending on the pH of the solution and the composition of the polymer. Surface plasmon resonance and optical waveguide spectroscopy were used to obtain information about the swelling behavior of hydrogel films of the photo-cross-linked polymers, giving a measurement of film thickness and refractive index. The transition temperatures of the cross-linked polymer gels showed similar trends to those of the corresponding linear polymers in solution, and the gels were shown to be both temperature- and pH-responsive, with the transition temperature ranging from 25.3 to 44.9 °C for films having a 200 nm dry film thickness. However, the swelling behavior of the cross-linked gels was found to vary as a function of dry film thickness, and three samples were selected for a more detailed study of how film thickness affects the transition temperature and swelling ratio of hydrogel films. Dry film thicknesses ranged from 9 nm to 2.3 μm, and the swelling behavior of the films fell into two distinct regimes separated by a critical thickness, which ranged from 280 to 500 nm. In the thin-film regime, the transition temperature of the films was independent of film thickness, but the refractive index of the films in the collapsed state decreased as film thickness decreased, indicating that these films are not able to fully collapse. In the thick-film regime, the swelling ratio of the films was independent of film thickness, but the transition temperature decreased as much as 2.6 °C as the film thickness increased. This was explained by the constraint imposed on the film by the presence of a fixed substrate, with the length scale of this constraint related to the critical thickness. In these films, the ionizable comonomers were found to have little effect on the swelling ratio, which is determined primarily by cross-linking density in the swollen state and by film thickness in the collapsed state.

Molecular Weight Dependence of Hydrodynamic and Thermodynamic Properties for Well-Defined Linear Polymers in Solution

Data on hydrodynamic and thermodynamic properties of several well-defined, linear flexible polymer chains in thermodynamically good solvents and theta solvents are tabulated and critically evaluated. The polymers considered are 1,4-polybutadiene, 1,4-polyisoprene, polyisobutylene, polystyrene, and poly(α-methylstyrene). Extensive data, obtained as a function of molecular weight, are evaluated for the intrinsic viscosity, radius of gyration, hydrodynamic radius, and second virial coefficient. The resulting power law relationships between the measured properties and polymer molecular weight are reported.

Integral equation theory of polymers: Translational invariance approximation and properties of an isolated linear polymer in solution

In this paper, we continue investigations on the solution methods for the generalized Percus–Yevick equations for the pair correlation functions of polymers, which were formulated in the previous papers of this series [J. Chem. Phys. 99, 4084, 4103 (1993)]. Previously, they were reduced to recursive integral equations and solved numerically. In this paper, a translational invariance approximation is used to reduce the number of integral equations to solve. In this approximation, only N integral equations out of N2 integral equations are required for a polymer consisting of N beads (monomers). The behavior of an isolated polymer is studied with three different potential models, a soft sphere, a hard sphere, and a Lennard-Jones potential. The main motivation for considering these three potential models is in testing the idea of universality commonly believed to hold for some properties of polymers. We find that the universality holds for the power law exponent for the expansion factor of polymers at high temperatures. The end-to-end distance distribution functions, intermediate distribution functions, chemical potentials, the density distributions, and various expansion factors of the polymer chain are computed from the solutions of the integral equations in the case of coiled, ideal, and collapsed states of the polymer. The expansion factors in the collapsed regime are found to obey power laws with respect to the length of the polymer and [B(T)−B(θ̄)], where B(T) is the second virial coefficient and θ̄ is a modified θ temperature. The values of these exponents approach those from the known theories of polymer collapse as the chain length becomes long and the ratio of bond length to bead radius becomes large.

Polymer statistics

Abstract A new method of simulating the equilibrium shape of linear polymers in solution is presented, based on the analytical output of the statistical mechanical treatment of polymers using the pair approximation of the cluster variation method (CVM). The reported simulation has the following features: it can form a simulation of the equilibrium state of a polymer system by one sweep of the field; therefore it is fast, even if the size of the system is large. Although the average length of polymers in the system is specified by a parameter in the CVM calculation, the analytical output describes a system composed of different-length polymers. The average end-to-end distance is measured as a function of the length l, and gives the length dependence lv with v=0.52 for the phase separation case and 0.59 for the athermal case. The result indicates the capability of the simulation to distinguish between the different configurations taken by the polymers under different solvent conditions.

Characterization Of The Binding of Inorganic Polymers To Oxide Surfaces By NMR and NMR/MAS Spectroscopy

ABSTRACTSolution and solid state Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy have been used to monitor the 31P signal of cyclic phosphazenes and associated linear polymers in solution and of these materials bound to alumina in stabilized dispersions. The differences between the simple solution experiments and the suspensions are being studied to determine the viability of NMR techniques to probe the chemical interactions between inorganic polymer dispersants and alumina particles. It has been observed in colloidal suspensions that the adsorption of phosphazenes onto an aluminum oxide surface causes a broadening of the 31P signal in solution NMR. This broadening is dependant on the amount of solid to polymer concentration, the amount of solids loading, the solvent polarity and the phosphazene substituent under investigation [1]. Conversely, the solid MAS experiments show a narrowing of the 31P signal upon adsorption of the phosphazene to alumina.

Carbon‐13 spin‐lattice relaxation study of linear polymers in solution

AbstractProton‐decoupled, partially relaxed, Fourier‐transform NMR of 13C in natural abundance was used to determine spin‐lattice relaxation times of individual carbons of polyisobutylene, polyacrylonitrile, poly(vinyl chloride), and poly(vinyl alcohol) in solution. It is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the excess spin energy from equilibration of all the 13C, even of quaternary carbons, in the polymers dealt with here is transferred to the lattice mainly through 13C‐1H dipolar interactions. It is shown that the segmental motions responsible for the spin‐lattice relaxation of the polymer skeleton in solution can be described by the isotropic model within a good approximation, except for poly(vinyl alcohol) at low temperature. The activation energies of skeletal and internal methyl motions are estimated from the temperature dependence of the correlation time. Differences in the 13C line widths for individual carbons of polyisobutylene are discussed briefly.

Molecular Theories of Rubberlike Elasticity and Polymer Viscoelasticity

Abstract The foundation for nearly all the molecular theories of the physical properties of polymers was laid in 1934 when Guth and Mark and Kuhn first recognized the role of configurational entropy of polymer chains. By virtue of ability of their segments to rotate with respect to each other along the chain backbone, macromolecules are capable of assuming a myriad of conformations. It is this long, flexible chain nature of polymer molecules that provides us a link in interpreting the macroscopic physical properties in terms of microscopic molecular dynamics. In this review we shall demonstrate the utilization of conformational statistics in the formulation of molecular theories for two important aspects of the mechanical properties of polymers. The first part deals with the equilibrium elastic response of a crosslinked rubberlike network. A simplified derivation will be given on the basis of the entropic approach. Some of the underlying assumptions will then be examined, and the contribution of internal energy to rubber elasticity scrutinized. The second part describes the transient viscoelastic properties of linear polymers in solution and in bulk. Limitations of the model will be assessed and its applications to experimental data explored. It should be pointed out that a number of reviews are available in the literature both for elasticity and viscoelasticity of polymers. The present work is not an exhaustive review of these fields, but rather concentrates on the more recent developments not previously discussed. The emphasis will be placed upon polymers in the bulk state, although solution properties will be mentioned where appropriate.

High‐resolution NMR of crosslinked polymers: Effects of crosslinked density and solvent interaction

AbstractMeasurements have been made of the dependence of nuclear magnetic resonance bandwidths of polymers on the degree of crosslinking. Poly(methyl methacrylates) and poly(hexadecyl acrylates) were studied. Three regions of behavior are apparent: (1) in lightly crosslinked materials, bandwidths are quite insensitive to the degree of crosslinking, and the networks behave almost as linear polymers in solution; (2) in moderately crosslinked material, bandwidths are significantly affected by the degree of crosslinking; and (3) in highly crosslinked materials, bandwidths are extremely sensitive to crosslink density, and the polymer peaks become so broad that they disappear almost completely. These results indicate that segmental motion of a polymer in solution is not a function solely of its molecular weight, and that a certain degree of crosslinking is required to restrict polymer motion at the segmental level. The solvent (benzene) peak is always a singlet in swollen poly(methyl methacrylate) systems with swelling ratios up to 6.4 (regions 1 and 2, above) but as the swelling ratio further decreases to 3.5 (region 3), the solvent peak splits into a doublet; this phenomenon may indicate the existence of two different arrangements of solvent molecules in the swollen network, for which interchange is not sufficiently rapid to produce a single line.

Behavior of linear polymers in solution

Behavior of linear polymers in solution