Number Of Monomer Units Research Articles

Book 1. Biopolymer conjugates industrial applications Chapter 1. Biopolymeric conjugation with thermoplastics and applications

Abstract Biopolymers are natural polymers manufactured chemically or generated from biological materials. Biopolymers are a renewable and biodegradable resource. They can be found in various applications in food, manufacturing, packaging, and biomedical engineering industries. Biopolymers are attractive materials due to biocompatibility, biodegradability, natural abundance, and specific properties such as non-toxicity. Biopolymers can be classed on a variety of scales, including origin, the number of monomeric units, the basis of degradability, and heat response. Biopolymers have a wide range of uses due to their unique characteristics and topologies. Biopolymers are reinforced with diverse elements to improve their intended characteristics and practical applications. There is a conjugation of biopolymer with thermoplastic materials. Thermoplastic or thermoset plastic is a form of plastic polymer material that can be molded at a high temperature and solidifies upon cooling. Polylactic acid, polycarbonate, polyethylene, polypropylene, polyvinyl alcohol, and polyester are among the many thermoplastics. These thermoplastics were combined with biopolymers to increase their physical, mechanical, and thermal qualities. The works that investigated the conjugation of thermoplastic materials to biopolymers were discussed in this chapter.

Deterministic approximation for the nucleation-growth type model of nanoparticle formation: A validation against stochastic simulations

A deterministic approximation method is introduced here for a complicated kinetic model that describes nanoparticle formation with nucleation and growth steps. The model starts from monomer units, some of which combine in a nucleation reaction, and the number of monomer units (n) in a kinetically effective nucleus is an unbounded integer parameter in the model. The growth steps are second-order processes between a particle and a monomer unit, the rate constant of which depends on the size of the growing nanoparticle in a way that is given in a kernel function. Four different kernels are considered: diffusion kernel (size independence), Brownian kernel (direct proportionality to the linear size), surface kernel (direct proportionality to the surface), mass kernel (direct proportionality to the volume or mass). Aggregation or coagulation are not part of the model. The approximation method works well for all four kernels and all integer values of n, and yields analytical formulas for the average and the most important moments (zeroth, first, and the one that is relevant for the kernel function) of the nanoparticle size distribution at every stage of the process. The approximation is validated against stochastic simulations using the Gillespie algorithm within the framework of the continuous time discrete state approach to stochastic kinetics. The comparison shows that the obtained analytical formulas are applicable for all practically important cases of the model and provide a way to interpret the dependence of average nanoparticle size on the ratio of the rate constants of nucleation and particle growth.

A Computational Study of the Dissociation of CaS Nanoclusters in the Extracellular Fluid of Cancer Cells: the Effect of pH in the Structure and Stability of Protonated CaS Nanoclusters

The acidic pH found in the extracellular fluid of many cancer tumors is an important difference from the slightly basic pH found in the corresponding benign cells. Contrary to common anti‐cancer drugs that have significant side effects in healthy cells, calcium sulfide (CaS) nanoclusters have shown to induce apoptosis selectively in human lung, skin, and breast cancer cell lines in vitro. We hypothesize that CaS nanostructures selectively dissociate in the characteristic acidic extracellular environments of cancer cells into free Ca2+ ions and sulfides such as H2S, HS‐ and S2‐, which can be proved via bench and computational experiments. Theoretical calculations at the DFT/B3LYP/DGVZVP level of theory of bare and protonated (CaS)n clusters (n = 1 to 4) were performed to address this hypothesis using the Gaussian 16W and GaussView 6.0.16 programs by varying the number of protons in a CaS cluster to assess cluster stability and reaction pathways in both acidic and neutral media. The total cluster energy decreases with the number of monomer units (n) in the (CaS)n clusters. The CaS monomer and dimer are more stable in water than in their corresponding standard state by about 336kJ/mol and 390kJ/mol, respectively. A single protonation of a sulfur atom in the solvated monomer results in an increase in the Ca‐S bond length from 2.55Å to 2.73Å, indicative of increasing drive to dissociate. It requires protonation of a sulfur atom by two hydrogen atoms to dissociate the cluster into free Ca2+ and H2S. Water facilitates the dissociation of the clusters when the sulfur atom is bonded by two protons. The products of the reaction of the solvated (CaSH2)2+ is more stable than the corresponding gas phase cluster ion by a significant 1479 kJ/mole. These results are consistent with the dissociation of CaS clusters to free Ca2+ and H2S in acidic media like the one found in the extracellular fluid of malignant tumors. Ca2+ ions are known to cause cell damage in cytosolic concentrations higher than 500nM. The biochemistry of H2S is still under study by several groups worldwide but it is generally accepted that it can be genotoxic and induce apoptosis. Therefore, CaS nanoclusters are promising drugs to selectively inhibit malignant tumor growth with little impact on benign tissue. The results are discussed in terms of the basic requirements of a (CaS)n‐based formulation for cancer treatment.

Root and Rhizosphere Processes under Drought: Digging Deeper to Enhance Ecosystem Resilience

Root and Rhizosphere Processes under Drought: Digging Deeper to Enhance Ecosystem Resilience

Electrochemical, in silico and time-resolved EPR behaviour of semiconductive π-conjugated poly(p-phenyleneethynylenevinylene)s (PPEV)

A series of poly(p-phenyleneethynylenevinylene)s (PPEV), synthesized by step-growth polymerization of 1,4-dialkoxybenzene and 9,9-bis(2’-ethylhexyl)fluorene-diethynyl monomers and featuring aryl-(E)-enyne repeating units were investigated by experimental and computational techniques with respect to their conjugative and conductive properties. HOMO-LUMO band gaps in the range 2.64–2.79 eV were determined by cyclic voltammetry and UV–vis spectroscopy. In agreement with these data, conductivity measurements performed on thin films drop cast from dichloromethane solutions exhibit values in the range 10-4–10-3 S cm-1 depending on the identity of the repeat units and on the length of alkyl chains. A p-type doping of the materials was achieved through exposure of the films to iodine vapor with a relevant increase of conductivity up to 7-folds compared to the undoped polymers. The cationic hole resulting by electron transfer from one PPEV to the electron acceptor PCBM was observed in situ by TREPR spectroscopy. In addition, DFT calculations performed on well-defined oligomeric models of the PPEVs provide HOMO-LUMO band gaps in agreement with the experimental values and disclose the dependence on both the length and type of conformers in the polymeric chain. Plots of the calculated band gaps versus 1/n, with n the number of monomer units, show a linear trend and predict that the maximum values of conductivity of the materials are reached with n as low as ≥ 6–7, which correspond to the average degrees of polymerization achievable by the synthetic procedure.

Going Beyond the Carothers, Flory and Stockmayer Equation by Including Cyclization Reactions and Mobility Constraints.

A challenge in the field of polymer network synthesis by a step-growth mechanism is the quantification of the relative importance of inter- vs. intramolecular reactions. Here we use a matrix-based kinetic Monte Carlo (kMC) framework to demonstrate that the variation of the chain length distribution and its averages (e.g., number average chain length xn), are largely affected by intramolecular reactions, as mostly ignored in theoretical studies. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex xn profile with possible plateau formation may arise. The joint consideration of stoichiometric and non-stoichiometric conditions allows the validation of hypotheses for both the intrinsic and apparent reactivities of inter- and intramolecular reactions. The kMC framework is also utilized for reverse engineering purposes, aiming at the identification of advanced (pseudo-)analytical equations, dimensionless numbers and mechanistic insights. We highlight that assuming average molecules by equally distributing A and B FGs is unsuited, and the number of AB intramolecular combinations is affected by the number of monomer units in the molecules, specifically at high FG conversions. In the absence of mobility constraints, dimensionless numbers can be considered to map the time variation of the fraction of intramolecular reactions, but still, a complex solution results, making a kMC approach overall most elegant.

Step‐Growth Polymerized Systems of Type “A1+A2+A3”: A Method to Calculate the Bivariate (Molecular Size) × (Path Length) Distribution

AbstractStep‐growth polymerizing systems of type “A1+A2+A3” are considered. The monomers bear one (A1), two (A2), or three (A3) identical reactive sites. In the reactor vessel, at a given degree of conversion, a wide range of polymeric molecules has formed, differing in both molecular size and in branching structure, determined by the laws of probability. In a slice of the molecular size distribution, all polymeric molecules have the same size (i.e., are built up by the same number of monomeric units), but differ in number and position of branching points (A3's). A method is presented to calculate the path length distribution for each such slice. Here, path length is the number of chemical bonds in the path connecting two monomeric units in the molecule. The shape and moments of this distribution may help rheologists and polymer manufacturers in improving the properties of their products. The system “A1+A2+A3” is the most simple representative of the more general step‐growth polymerizing systems of type “Afi,” and of type “AfiBgi.” Extension of this calculation method to these for the chemical industry more relevant systems is intended.

Methodology for Determination of the Key Parameters of Conjugated Polymer Electrodeposition, Based on a Combination of Spectroelectrochemistry and Electrochemical Quartz Crystal Microbalance

Methodology based on a combination of experimental data obtained by in situ methods of spectroelectrochemistry and electrochemical quartz crystal microbalance has been proposed for determination of the key parameters of the conjugated polymer deposition on the electrode surface via monomer electrooxidation. These parameters are: the current efficiency of the process, the charge spent per an oxidized monomer molecule, the number of monomer units inside the deposited film, and the average number of valence bonds per one monomer unit inside the film. Besides, the electrochemical quartz crystal microbalance method applied to the discharge process of the electropolymerized film allows determining the average charging (oxidation) degree of the monomer unit at the polymerization potential and the degree of the solvent participation in the polymer’s redox transitions. The applicability of the proposed approach has been demonstrated by example of magnesium polyporphine films obtained by oxidation of unsubstituted magnesium porphine on inert electrode in acetonitrile solution at a low potential.

A Simple and Direct Route to High-Performance Acrylamido-Based Kinetic Gas Hydrate Inhibitors from Poly(acrylic acid)

(Meth)acrylamido-based polymers are used commercially in kinetic hydrate inhibitor formulations to prevent gas hydrate formation in upstream oil and gas flow lines. The monomers used to make these polymers are relatively expensive. We have now synthesized a series of acrylamido-based polymers directly from low molecular weight poly(acrylic acid) (PAA) in a high-yield process, avoiding the use of expensive monomers. Cloud points of the polymers made from PAA were similar to the homopolymers made from the acrylamido monomers, indicating a good conversion from the acid to the amide group. Slow constant-cooling KHI screening tests were carried out on the new polymers in a series of steel rocking cells using a structure II-forming natural gas mixture. Poly(N-isopropylacrylamide), poly(N-(n-propyl) acrylamide), and polyacryloylpyrrolidine prepared directly from PAA all gave an excellent KHI performance, comparable to the homopolymers made from the acrylamido monomers. This direct synthesis method also allows for a very controlled comparison of the activity of the acrylamido functional groups because every polymer can be derived from the same PAA starting material. Thus, the number of monomer units in each homopolymer is kept constant. Conversion of the poly(methacrylic acid) or poly(methyl methacrylate) by the reaction with amines to give the methacrylamido polymers was not successful, probably due to the steric effect of the backbone methyl groups.

Magnetic field influence on asphaltene aggregation monitored by diffusion NMR spectroscopy: Is aggregation reversible at high magnetic fields?

We have shown that asphaltene self-association induces temperature gradients and convection currents and it is necessary to suppress these effects to obtain accurate data by DOSY NMR techniques. An interesting finding of this investigation is that aggregation process has been found to be affected by the magnetic field. The obtained results have shown for the first time a significant increase in diffusion coefficients of aggregates upon the increase in the magnetic field strength indicating higher molecular mobility of the present species and possible degradation of aggregates. We have shown that changes in diffusion coefficients are not a consequence of relaxation or viscosity effects. It is not yet clear what the reason for such behavior is and whether this effect is intrinsic. Traces of paramagnetic metals present in asphaltene samples may play a role in this process but this hypothesis is yet to be explored. Furthermore, this study has revealed a similar concentration range in which the Middle East crude oil asphaltenes aggregate being in agreement with previous results. Aggregates form different molecular weight species with different composition and number of monomer units. Ongoing experiments will throw more light on the magnetic field dependent asphaltene aggregation. This may have an impact on developing strategies for resolving asphaltene precipitation issues.

Molecular-Level "Observations" of the Behavior of Gold Nanoparticles in Aqueous Solution and Interacting with a Lipid Bilayer Membrane.

We use coarse-grained molecular dynamics simulations to "observe" details of interactions between ligand-covered gold nanoparticles and a lipid bilayer model membrane. In molecular dynamics simulations, one puts the individual atoms and groups of atoms of the physical system to be "observed" into a simulation box, specifies the forms of the potential energies of interactions between them (ultimately quantum based), and lets them individually move classically according to Newton's equations of motion, based on the forces arising from the assumed potential energy forms. The atoms that are chemically bonded to each other stay chemically bonded, following known potentials (force fields) that permit internal degrees of freedom (internal rotation, torsion, vibrations), and the interactions between nonbonded atoms are simplified to Lennard-Jones forms (in our case) and coulombic (where electrical charges are present) in which the parameters are previously optimized to reproduce thermodynamic properties or are based on quantum electronic calculations. The system is started out at a reasonable set of coordinates for all atoms or groups of atoms, and then permitted to develop according to the equations of motion, one small step (usually 10 fs time step) at a time, for millions of steps until the system is at a quasi-equilibrium (usually reached after hundreds of nanoseconds). We then let the system play out its motions further for many nanoseconds to observe the behavior, periodically taking snapshots (saving all positions and energies), and post-processing the snapshots to obtain various average descriptions of the system. Alkanethiols of various lengths serve as examples of hydrophobic ligands and methyl-terminated PEG with various numbers of monomer units serve as examples of hydrophilic ligands. Spherical gold particles of various diameters as well as gold nanorods form the core to which ligands are attached. The nanoparticles are characterized at the molecular level, especially the distributions of ligand configurations and their dependence on ligand length, and surface coverage. Self-assembly of the bilayer from an isotropic solution and observation of membrane properties that correspond well to experimental values validate the simulations. The mechanism of permeation of a gold NP coated with either a hydrophobic or a hydrophilic ligand, and its dependence on surface coverage, ligand length, core diameter, and core shape, is investigated. Lipid response such as lipid flip-flops, lipid extraction, and changes in order parameter of the lipid tails are examined in detail. The mechanism of permeation of a PEGylated nanorod is shown to occur by tilting, lying down, rotating, and straightening up. The nature of the information provided by molecular dynamics simulations permits understanding of the detailed behavior of gold nanoparticles interacting with lipid membranes which in turn helps to understand why some known systems work better than others and aids the design of new particles and improvement of methods for preparing existing ones.

Regression Analysis for Nucleation-Elongation Model of Supramolecular Assembly: How To Determine Nucleus Size.

Nucleation-elongation is known to give satisfactory descriptions of many supramolecular polymerization systems in thermal equilibrium. Its key feature is the necessity to form a "nucleus" consisting of a certain number of monomer units before being able to grow into a longer polymer chain. The size of the nucleus has significant implications for the understanding of the supramolecular polymerization mechanism. Here we investigate how experiments can give information on the nucleus size by regression analysis of various types of measurements. The measurements of free monomer concentrations, diffusion coefficients, and calorimetric response as functions of concentration or temperature are considered. The nucleation-elongation model with a general value for the nucleus size is used to provide mathematical expressions for these experimental observables. Numerical experiments are performed where experimental errors are simulated by computer-generated random numbers, and it is investigated whether least-squares fitting analyses can give the correct values of the nucleus size in the presence of experimental errors. It is recommended that the calorimetric measurements such as differential scanning calorimetry (DSC) or isothermal titration calorimetry (ITC) be performed under various conditions to correctly determine the nucleus size experimentally.

Obtaining the Dielectric Constant of Polymers from Doubly Charged Species in Ion-Mobility Mass Spectrometry

Ion-mobility mass spectrometry of doubly charged polyethylene glycol (PEG) is performed after electrospray-ionization time-of-flight mass spectrometry and the dependency of the effective collision cross-section, CCSeff, on the number of monomer units, n, is evaluated with the help of molecular dynamics simulations. Assuming a balance between elastic and Coulomb forces inside short and asymmetric doubly charged chains, a method is developed for evaluating the dielectric constant, e, which is found to be 7.87 for PEG for n = 14–28. From the same experiment at higher chain lengths, the characteristic ratio Cn of 4.30 for PEG (n ≥ 63) can be evaluated according to an earlier reported method, which is demonstrated here to also work with doubly charged species. The proposed method enables an extremely swift and precise measurement both of e and Cn of polymer that is free of solvent or impurities from one single experiment.

Quantum-classical calculations of X-ray photoelectron spectra of polymers-Polymethyl methacrylate revisited.

In this work, we apply quantum mechanics/molecular mechanics (QM/MM) approach to predict core-electron binding energies and chemical shifts of polymers, obtainable via X-ray photoelectron spectroscopy(XPS), using polymethyl methacrylate as a demonstration example. The results indicate that standard parametrizations of the quantum part (basis sets, level of correlation) and the molecular mechanics parts (decomposed charges, polarizabilities, and capping technique) are sufficient for the QM/MM model to be predictive for XPS of polymers. It is found that the polymer environment produces contributions to the XPS binding energies that are close to monotonous with the number of monomer units, totally amounting to approximately an eV decrease in binding energies. In most of the cases, the order of the shifts is maintained, and even the relative size of the differential shifts is largely preserved. The coupling of the internal core-hole relaxation to the polymer environment is found to be weak in each case, amounting only to one or two tenths of an eV. The main polymeric effect is actually well estimated already at the frozen orbital level of theory, which in turn implies a substantial computational simplification. These conclusions are best represented by the cases where the ionized monomer and its immediate surrounding are treated quantum mechanically. If the QM region includes only a single monomer, a couple of anomalies are spotted, which are referred to the QM/MM interface itself and to the neglect of a possible charge transfer.

The molecular structural features controlling stickiness in cooked rice, a major palatability determinant

The stickiness of cooked rice is important for eating quality and consumer acceptance. The first molecular understanding of stickiness is obtained from leaching and molecular structural characteristics during cooking. Starch is a highly branched glucose polymer. We find (i) the molecular size of leached amylopectin is 30 times smaller than that of native amylopectin while (ii) that of leached amylose is 5 times smaller than that of native amylose, (iii) the chain-length distribution (CLD: the number of monomer units in a chain on the branched polymer) of leached amylopectin is similar to native amylopectin while (iv) the CLD of leached amylose is much narrower than that of the native amylose, and (v) mainly amylopectin, not amylose, leaches out of the granule and rice kernel during cooking. Stickiness is found to increase with decreasing amylose content in the whole grain, and, in the leachate, with increasing total amount of amylopectin, the proportion of short amylopectin chains, and amylopectin molecular size. Molecular adhesion mechanisms are put forward to explain this result. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability by quantifying the components and molecular structure of leached starch.

Correlation between the shape of the ion mobility signals and the stepwise folding process of polylactide ions.

In the field of polymer characterization, the use of ion mobility mass spectrometry (IMMS) remains mainly devoted to the temporal separation of cationized oligomers according to their charge states, molecular masses and macromolecular architectures in order to probe the presence of different structures. When analyzing multiply charged polymer ions by IMMS, the most striking feature is the observation of breaking points in the evolution of the average collision cross sections with the number of monomer units. Those breaking points are associated to the folding of the polymer chain around the cationizing agents. Here, we scrutinize the shape of the arrival time distribution (ATD) of polylactide ions and associate the broadening as well as the loss of symmetry of the ATD signals to the coexistence of different populations of ions attributed to the transition from opened to folded stable structures. The observation of distinct distributions reveals the absence of folded/extended structure interconversion on the ion mobility time scale (1-10ms) and then on the lifetime of ions within the mass spectrometer at room temperature. In order to obtain information on the possible interconversion between the different observed populations upon ion activation, we performed IM-IM-MS experiments (tandem ion mobility measurements). To do so, mobility-selected ions were activated by collisions before a second mobility measurement. Interestingly, the conversion by collisional activation from a globular structure into a (partially) extended structure, i.e. the gas phase unfolding of the ions, was not observed in the energetic regime available with the used experimental setup. The absence of folded/extended interconversion, even upon collisional activation, points to the fact that the polylactide ions are 'frozen' in their specific 3D structure during the desolvation/ionization electrospray processes. Copyright © 2017 John Wiley & Sons, Ltd.

Isotropic-to-nematic transition in melt of polydisperse semi-flexible homopolymers

ABSTRACTThe isotropic-to-nematic phase transition in a melt of semi-flexible homopolymers with length polydispersity have been considered within the Landau–de Gennes approach. The number of monomer units in chain is assumed to be a random variable distributed by the Schulz–Zimm distribution; the stiffness of macromolecules has been taken into account within discrete worm-like chain model. It was found that increase of polydispersity yields the increase of the temperature of the isotropic–nematic transition.

Thermo-responsive oligomeric poly(tetrabutylphosphonium styrenesulfonate)s as draw solutes for forward osmosis (FO) applications

A series of oligomeric poly(tetrabutylphosphonium styrenesulfonate)s (PSSP#, where # is the number of monomer units in the oligomer) were prepared from tetrabutylphosphonium styrenesulfonate (SSP) as a monomer for application as a draw solute in a forward osmosis (FO) system. Although the water permeation flux values in the FO system using the oligomeric PSSP as a draw solute were slightly smaller than those using the monomeric SSP, the reverse solute flux values using the PSSPs were found to be much smaller than those using the SSP, indicating that the oligomers are more efficient draw solute materials in the FO system than the low molecular weight monomer. For example, when 20wt.% of the PSSP5 aqueous solution is used as the draw solution, the water permeation flux and reverse solute flux values are 14.50 LMH and 0.14 gMH, respectively, and when 20wt.% of the SSP aqueous solution is used, they are 16.28 LMH and 0.53 gMH, respectively. Since PSSPs have a lower critical solution temperature (LCST), the PSSP in water could be simply separated by heating to above the LCST without any other separation process. Moreover, it was found that the PSSPs have excellent bactericidal property above 99.9% against Escherichia coli (ATCC 8739).

Fractional Brownian modeled linear polymer chains with one dimensional Metropolis Monte Carlo simulation

The scaling expression for fractional Brownian modeled linear polymer chains was obtained both theoretically and numerically. Through the probability distribution of fractional Brownian paths, the scaling was found out to be 〈R2〉 ~ N2H, where R is the end-to-end distance of the polymer chain, N is the number of monomer units and H is the Hurst parameter. Numerical data was generated through the use of Monte Carlo simulation implementing the Metropolis algorithm. Results show good agreement between numerical and theoretical scaling constants after some parameter optimization. The probability distribution confirmed the Gaussian nature of fractional Brownian motion and the behavior is not affected by varying values of the Hurst parameter and of the number of monomer units.

Numerical solution of mixed continuous–discrete population balance models for depolymerization of branched polymers

A simulation technique to describe the depolymerization of branched polymers via bivariate population balance modeling was developed. The polymers were characterized by two internal coordinates: the number of monomer units and branching bonds. Three commonly used mechanisms for depolymerization (random chain, end chain, and random debranching scission) were applied and formulated such that only physically possible polymers were created. The mechanisms and the population balance equation were formulated in a mixed continuous–discrete manner. The population balance equation was solved using the Direct Quadrature Method of Moments (DQMOM). With this algorithm, the time evolution of the distribution with respect to the internal coordinate was computed. In addition, the algorithm was validated through comparison with Monte Carlo simulations. Notably, the accuracy of the mixed continuous–discrete formulation was significantly higher that of the continuous formulation. However, DQMOM was found to be unsuitable for describing the temporal evolution of the distribution for random scission.