Flexible Polymeric Chains Research Articles

Design of Dendritic Foldamers as Catalysts for Organic Synthesis

Background:: Multistranded foldamers mimic biopolymer architecture, through the assembly and folding of intrinsically flexible polymeric chains attached to polyol core have been synthesised here. The synthesised dendritic motifs possess helical cavities with properly arranged active sites. As these cavities are large enough to accommodate guest molecules, their application as synthetic foldamer catalyst were investigated in Knoevenagel and Mannich reactions. Methods:: It is presumed to be the potentiality of dendritic foldamers to form reverse micelle in the interior of helical motif containing many reactive sites. Results:: Inside the dendritic foldamer, the substrates are adequately concentrated, work together in cooperation for ligand-binding, and stabilize the transition state as in enzymes that helps to accelerate the reaction rate many times greater than in bulk solution. Conclusion:: An unrivalled reaction rate and high yield of products were obtained within a short time in both Knoevenagel and Mannich reactions by using dendritic foldamers as catalysts.

Surface hydrophobization of hydrogels via interface dynamics-induced network reconfiguration

Effective and easy regulation of hydrogel surface properties without changing the overall chemical composition is important for their diverse applications but remains challenging to achieve. We report a generalizable strategy to reconfigure hydrogel surface networks based on hydrogel–substrate interface dynamics for manipulation of hydrogel surface wettability and bioadhesion. We show that the grafting of hydrophobic yet flexible polymeric chains on mold substrates can significantly elevate the content of hydrophobic polymer backbones and reduce the presence of polar groups in hydrogel surface networks, thereby transforming the otherwise hydrophilic hydrogel surface into a hydrophobic surface. Experimental results show that the grafted highly dynamic hydrophobic chains achieved with optimal grafting density, chain length, and chain structure are critical for such substantial hydrogel surface network reconfiguration. Molecular dynamics simulations further reveal the atomistic details of the hydrogel network reconfiguration induced by the dynamic interface interactions. The hydrogels prepared using our strategy show substantially enhanced bioadhesion and transdermal delivery compared with the hydrogels of the same chemical composition but fabricated via the conventional method. Our findings provide important insights into the dynamic hydrogel–substrate interactions and are instrumental to the preparation of hydrogels with custom surface properties.

Phthalide cardo chain extended imine skeletal linked maleimido end capped nanotitania reinforced novel polybenzoxazine (nTiO2/PBZ) hybrid nanocomposites

A new class of nanotitania reinforced polybenzoxazine (nTiO2/PBZ) hybrid nanocomposites was synthesized using newly designed phthalide cardo chain extended imine skeletal linked maleimido end capped polybenzoxazine (PHM-PBZ) and nTiO2 through in-situ sol-gel method. The formation of hybrid nanocomposites was confirmed by NMR and FT-IR spectra. The structurally stable nTiO2 present in the nTiO2/PBZ hybrids accounted their exceptional thermal stability and good char yield. The restricted motion of flexible polymeric chain resulted from the inclusion of nTiO2 in the PBZ system increased the glass transition temperature ( T g) to a higher percentage than that of neat PBZ system. With the successive enhancement in the incorporation of nTiO2, the synthesized nanocomposites exhibited better thermal stability, higher flame retardancy and lesser water absorption behaviour than the of neat PBZ. The sequential increments in the loading level of nTiO2 onto the PBZ matrices caused the lower value of dielectric constant than that of neat PBZ. The homogeneity and successful dispersion of the nTiO2 fillers in the PBZ matrix were ascertained from the strong fluorescent emissions observed in the wavelength range of 300–550 nm through optical studies. Scanning electron microscope and transmission electron microscopic micrographs evidenced the successful incorporation of nTiO2 as can be seen from the different morphology at the nanoscale level in the PBZ matrix. This kind of structurally designed nTiO2/PBZ nanocomposites may find multifaceted applications in the form of adhesives, encapsulants, matrices and sealants and in the fields of automobile and microelectronics applications for better performance and longevity.

In vitro mucoadhesive properties of hydrophilic polymers: Effects of contact time, disk shape, and molecular weight

AbstractThis study aimed to investigate the effects of various factors, including contact time, disk shape, and polymer molecular weight, on the in vitro mucoadhesive properties of disks prepared using hydrophilic polymers. Mucoadhesive performance was evaluated by measuring the peak detachment force and work of adhesion values using tensile tests. The mucoadhesive force and work of adhesion values increased with increasing contact time between the polymeric disks and mucin gel layer until 60 s. Increased mucoadhesive performances were typically observed when the disks comprised high‐molecular‐weight polymers, which indicates the increase in the entanglement. Increasing the thicknesses of the disks allowed the disks to absorb more water and thereby have more flexible polymeric chains, enhancing the mucoadhesive capacity. The proportional increase in the mucoadhesive force and work values were observed with increasing the surface areas of the disks. In conclusion, this study comprehensively demonstrated the effects of various experimental factors on mucoadhesion.

Effect of silver nanoparticles combined with antibiotics on different phylogenetic groups of Escherichia coli

Silver nanoparticles (Ag-NPs) can attach to flexible polymeric chains of antibiotics, hence it can be used in combination with antibiotics against resistant bacteria. In this study, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and MBC/MIC ratio of Ag-NPs and antibiotics (gentamicin, tetracycline, erythromycin, ciprofloxacin, nalidixic acid, cefixime, cephalexin, amoxicillin, ampicillin, and penicillin) were quantified against 50 Escherichia coli isolates (25 human urinary tract infection and 25 avian colibacillosis). All isolates had been assigned as four phylogenetic groups A, B1, B2, and D. The results showed that the majority of the human and broiler isolates belonged to phylogenetic groups A and B2. MBC/MIC ratio of Ag-NPs in combination with antibiotics was assessed. It was found that the MIC of the majority of broiler isolates to Ag-NPs was equal to or greater than 50 µg/ml. To conclude, as combination of penicillin with Ag-NPs and ciprofloxacin with Ag-NPs exhibited profound impact against isolates, the combinations might be used against multidrug resistant bacteria.

Combined efficacy of silver nanoparticles and commercial antibiotics on different phylogenetic groups of Escherichia coli

Silver nanoparticles (Ag-NPs) can attach to flexible polymeric chains of antibiotics, hence it can be used in combination with antibiotics against resistant bacteria. In this study, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and MBC/MIC ratio of Ag-NPs and antibiotics (gentamicin, tetracycline, erythromycin, ciprofloxacin, nalidixic acid, cefixime, cephalexin, amoxicillin, ampicillin, and penicillin) were quantified against 50 Escherichia coli isolates (25 human urinary tract infection and 25 avian colibacillosis). All isolates had been assigned as four phylogenetic groups A, B1, B2, and D. The results showed that the majority of the human and broiler isolates belonged to phylogenetic groups A and B2. MBC/MIC ratio of Ag-NPs in combination with antibiotics was assessed. It was found that the MIC of the majority of broiler isolates to Ag-NPs was equal to or greater than 50 μg/ml. To conclude, a combination of penicillin and ciprofloxacin with Ag-NPs exhibited profound impact against isolates, the combinations might be applicable for treating multidrug-resistant bacteria.

Structural features of polymeric silicon glycerolate hydrogels

Structural features of polymeric silicon glycerolate hydrogels based on tetrafunctional silicon glycerolates were investigated using model process, namely, hydrolytic transformation of difunctional silicon glycerolates, by IR and 1H NMR spectroscopy, elemental analysis, atomic emission spectrometry. The possibility of forming a polymer network containing Si—O—Si and Si—OCH2CH(OH)CH2O—Si fragments was demonstrated. The molecular weight of the sub-chains in the network was calculated using Flory—Rehner approach based on the mechanical properties of the swollen network of flexible polymeric chains.

Rupture of polymers by chain scission

One of the distinguishing features of elastomeric materials, which consist of a network of flexible polymeric chains, is that the deformation response is dominated by changes in entropy. Accordingly, most classical theories of rubber-like elasticity consider only the entropy and neglect any changes in internal energy. On the other hand, the fracture of strongly cross-linked elastomers is essentially energy dominated, as argued in the well-known Lake–Thomas model for the toughness of elastomers. However, a single model unifying these two phenomena is still lacking. We provide a rational yet simple model for deformation and fracture of cross-linked polymers, based on two ingredients: (i) a non-Gaussian statistical mechanics model of polymer chains that accounts for the increase in energy due to the deformation of molecular bonds; (ii) a chain scission criterion based on the bond deformation energy attaining a critical value. Using this model, we can estimate the rupture stretch of elastomeric materials from fundamental quantities describing the polymer network. We use this model to relate the flaw sensitivity of elastomers to an intrinsic material length scale related to the network structure.

Features of silicon- and titanium-polyethylene glycol precursors in sol-gel synthesis of new hydrogels.

The formation of organic/inorganic hydrogels based on silicon and titanium polyethylene glycolates, new biocompatible water-soluble precursors in sol-gel processing, was investigated. The influence of different factors on the gelation process, such as excess of PEG, water molar content, pH of medium, electrolyte additives, was investigated in comparison with silicon- and titanium-glycerol precursors. The specific features of gelation for each type of precursor were revealed. It has been determined that titanium polyethylene glycolates synthesized and used in the excess of PEG formed transparent polymeric hydrogels resistant to syneresis under certain conditions. The titanium polyethylene glycolates synthesized without excess of PEG formed turbid heterogeneous colloidal gels. In the case of silicon polyethylene glycolates the hydrogels obtained were polymeric. Dynamic light scattering was used to confirm the polymeric or colloidal type of gelation. The solid and liquid phases of polymeric silicon- and titanium-polyethylene glycol hydrogels were separated by exhaustive extraction. The solid phase was characterized by combined thermal analysis with simultaneous quadruple mass spectrometry, XRD, IR spectroscopy, and liquid phase-atomic emission spectroscopy. The structural features of polymeric gels were investigated by SEM and TEM methods. The cross-linking density of polymeric hydrogels was evaluated using Flory-Rehner theory based on the mechanical properties of swollen networks of flexible polymeric chains.

Mechanism of structural networking in hydrogels based on silicon and titanium glycerolates

Formation of organic/inorganic hydrogels based on silicon– and titanium–glycerol precursors synthesized by transesterification of alkoxy derivatives in excess of glycerol was investigated. The precursors in excess of glycerol and obtained gels were studied by chemical and physical methods including gelation kinetics, IR spectroscopy, XRD, dynamic and electrophoretic light scattering, mechanical deformation, which disclosed the basic difference in the gelation mechanism and structure of network in the hydrogels. Due to this difference, the gelation time of silicon– and titanium–glycerol precursors depended on pH or electrolyte addition in an opposite way. In the wide pH range, silicon–glycerol hydrogel was a polymeric single-phase system formed by the polymeric network homogeneously swollen in liquid water/glycerol medium. Flory–Rehner theory applied to the elastic modulus of these gels gave 40–180 monomer base units in the subchains of the network depending on water content in the gel. The mechanism of networking was three-dimensional polycondensation promoted by the electrically charged functional groups attached to the flexible polymeric chains. Electrolyte solutions provided the gelation according to Hofmeister series. Titanium–glycerol hydrogels were heterogeneous colloid systems at pH > 1.5 and single-phase polymeric gels at lower pH. Electrolyte solutions provided the gelation according to Schultze–Hardy rule.

A Simulation Model of Biofilms with Autonomous Cells, 2 ‐ Explicit Representation of the Extracellular Polymeric Substance

AbstractBiofilms are complex colonies of bacteria that grow in contact with a wall, often in the presence of a water flow. In the current work, biofilm colony growth is investigated using a two‐dimensional lattice Monte–Carlo algorithm based on the bond‐fluctuation algorithm (BFA). One of the distinguishing characteristics of biofilms, the synthesis and physical properties of the extracellular polymeric substance (EPS) in which the cells are embedded, is explicitly taken into account. Cells are modeled as autonomous closed loops with well‐defined mechanical and biological properties, while the EPS is modeled as flexible polymeric chain synthesized by the cells during their growth. By tuning the structural, energy, biological, and morphologic parameters of the model, the cell shapes as well as the growth and maturation of various types of biofilm colonies (including colonies with multiple species) can be controlled.magnified image

High‐Frequency Dynamical Behavior of Poly(ethylene glycol)+H2O Mixtures by Brillouin Spectroscopy

AbstractBrillouin spectroscopy has been used to examine high‐frequency dynamical behavior of aqueous solutions of poly(ethylene glycol) (Mw ≈ 400g/mol) at 298K in the entire concentration region. It was found that a relaxation process takes place in the experimental frequency window that significantly affects the shape of experimentally recorded spectrum of the density fluctuations (dynamical structure factor). The process detected was attributed to segmental motion of the flexible polymeric chain. The full spectrum analysis of Brillouin spectra has been performed taking advantage of the relaxation function previously used in describing a single relaxation process in dielectric examination of water solutions of PEG 400. The proposed data processing procedure permits a qualitative reproduction of concentration dependencies of the hypersonic wave velocity and absorption measured. The shapes of the concentration dependencies of the relaxation times obtained from the Brillouin and the dielectric spectroscopies are in good agreement over a very broad concentration range, although their absolute values are scaled by the factor of 3. This result indicate that the two processes revealed independently by dielectric and Brillouin spectroscopies, apparently separated in time‐scale, are just the same relaxation process.

Structural Features ofmeso-Tetrakis(4-carboxyphenyl)porphyrin Interacting with Amino-Terminated Poly(propylene oxide)

The neutralization reaction between the meso-tetrakis(4-carboxyphenyl)porphyrin (TPPC) and O-(2-aminopropyl)-O‘-(2-methoxyethyl)poly(propylene glycol) (Jeffamine M-600) in 1:4 stoichiometric ratio affords a stable supramolecular adduct (TPPC@Jeffamine). This species has been characterized in aqueous and chloroform solution through a series of spectroscopic techniques, including 1H and 13C NMR spectroscopy, UV/vis absorption, steady-state and time-resolved fluorescence emission, time-resolved fluorescence anisotropy, and resonance light scattering. All the experimental findings point to a different structural arrangement of the porphyrin chromophores within the supramolecular adduct depending on the quality of the solvent. In aqueous solution, the TPPC@Jeffamine contains mainly monomeric porphyrins while the flexible polymeric chains are folded and entangled to give larger aggregates. An insight into the structure of the basic building unit is given by SAXS measurements which, assuming a core−shell model, ...

Elastic Bounded Diffusion. Dynamics of Ferrocene-Labeled Poly(ethylene glycol) Chains Terminally Attached to the Outermost Monolayer of Successively Self-Assembled Monolayers of Immunoglobulins

A model of elastic bounded diffusion is presented for the quantitative analysis of the dynamics of redox probes borne by the loose ends of linear and flexible polymeric chains terminally grafted to building blocks of a self-assembled construction. Experimentally, poly(ethylene glycol) chains bearing a ferrocene probe were terminally attached at the last one of a series of immunoglobulins monolayers successively self-assembled on top of a glassy carbon electrode. In cyclic voltammetry, the creation of a concentration gradient provoked a diffusion-like displacement of the ferrocene probe counterbalanced by the springlike elasticity of the terminally attached polymeric chain. The morphology and the intensity of the signal depend markedly on the distance separating the terminal attachment from the electrode surface and on the potential scan rate. The observed changes are qualitatively and quantitatively justified by the model. Both the diffusion and the elasticity can be quantitatively characterized.

The nematic dumbbell model

Flexible polymeric chains (Kuhn chains) made up of nematogenic moieties are considered here. The simplest approach to the dynamics of such a system, in both the isotropic and the nematic phases, is that of modeling the chain as an elastic dumbbell where the ‘‘spring’’ law also accounts for the nematic interaction. The constitutive equation of this ‘‘nematic dumbbell model’’ is thereby derived. The rheological predictions so obtained are qualitatively compared with the most prominent features of LCP rheology as well as with previous theoretical results.

Local orientational motions in flexible polymeric chains

Effects of chain connectivity, viscous resistance of the environment, and internal barriers to conformational transitions are studied in relation to local orientational motions in flexible chains. Calcu- lations are performed according to the dynamic rotational isomeric states scheme. Only a single transition over a bond at a time is assumed. That such single bond rotations are indeed possible in a sequence of 20 bonds without significant distortion of the tails is shown by the present analysis. The increase in the fric- tional resistance to motion with the size of the mobile sequence is investigated for polyethylene at 300 K. The latter, referred to as the size effect, is included in the treatment through consideration of the total path traveled by each of the moving atoms. Orientational autocorrelation functions for a bond at the end of an N bond mobile sequence are evaluated in the presence and absence of the size effect. Two different correlation times, emphasizing short and long time motions, are defined. Dependence of the correlation times on the length of the mobile sequence is evaluated.

Anisotropy of a flexible polymeric chain in a nematic field : neutron scattering versus magnetic resonance

Flexible polymeric chains are dissolved in a nematic liquid crystal; the effect of the nematic field is probed through s.a.n.s. and 2H n.m.r. The orientational order for the segments of perdeuterated polystyrene (Mw = 2 100), dissolved in p-ethoxybenzilidene p-n butylaniline, is obtained from 2H n.m.r. spectra : this parameter has the same temperature dependence as the order parameter of the solvent. Yet s.a.n.s. experiments do not show an anisotropy of the overall dimensions of the same macromolecules dissolved in p-azoxy-anisole. This apparent conflict is resolved when the anisotropy of the radius of gyration is calculated as a function of the spherical harmonics which describe the averaged orientation of the segments.