A revised worm‐like chain model for elasticity of polypeptide chains

The elasticity of polypeptide chains is usually characterized by the worm‐like chain model that was proposed first to describe the elasticity of double‐stranded DNA. However, the molecular dynamics simulation data on the elasticity of the polypeptide chains are deviated significantly away from the theoretical data obtained based on the worm‐like chain model. Here, we provide a revised worm‐like chain model by considering entropic, enthalpic, and hydrophobic effects and the effect of the compressing force applied to the polypeptide chains. The theoretical data obtained based on the revised model are in good agreement with the molecular dynamics simulation data. Additionally, we reveal that, besides the positive‐force regime in the elasticity of polypeptide chains, the negative‐force regime also plays important roles in the biological functions of proteins. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 297–307     

In situ adsorption studies of a 14-amino acid leucine-lysine peptide onto hydrophobic polystyrene and hydrophilic silica surfaces using quartz crystal microbalance, atomic force microscopy, and sum frequency generation vibrational spectroscopy

The adsorption of a 14-amino acid amphiphilic peptide, LK14, which is composed of leucine (L, nonpolar) and lysine (K, charged), on hydrophobic polystyrene (PS) and hydrophilic silica (SiO2) was investigated in situ by quartz crystal microbalance (QCM), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. The LK14 peptide, adsorbed from a pH 7.4 phosphate-buffered saline (PBS) solution, displayed very different coverage, surface roughness and friction, topography, and surface-induced orientation when adsorbed onto PS versus SiO2 surfaces. Real-time QCM adsorption data revealed that the peptide adsorbed onto hydrophobic PS through a fast (t < 2 min) process, while a much slower (t > 30 min) multistep adsorption and rearrangement occurred on the hydrophilic SiO2. AFM measurements showed different surface morphologies and friction coefficients for LK14 adsorbed on the two surfaces. Surface-specific SFG spectra indicate very different ordering of the adsorbed peptide on hydrophobic PS as compared to hydrophilic SiO2. At the LK14 solution/PS interface, CH resonances corresponding to the hydrophobic leucine side chains are evident. Conversely, only NH modes are observed at the peptide solution/SiO2 interface, indicating a different average molecular orientation on this hydrophilic surface. The surface-dependent difference in the molecular-scale peptide interaction at the solution/hydrophobic solid versus solution/hydrophilic solid interfaces (measured by SFG) is manifested as significantly different macromolecular-level adsorption properties on the two surfaces (determined via AFM and QCM experiments).     

Spatiotemporal Resolved Live Cell Membrane Tracking through Photo-click Reactions Enriched in Lipid Phase

A set of photo-switchable monopeptides derived from cis-β-dibenzodiazocine-l -alanine (cis-DBDAA) have been designed and synthesized, which are capable of photo-click reacting with diaryltetrazoles or diarylsydnones in a hydrophobic phospholipid bilayer environment. The DBDAA monopeptides include both a hydrophobic tail on C-terminal, providing high affinity toward lipid membrane, and a modularized functional moiety on N-terminal, enabling rapid optimization of the self-assembly strength to form multifunctional supramolecules. With the cis-DBDAA monopeptides photo-switched into trans-configuration, we were able to disrupt the supramolecular assembly through an efficient photo-click reaction across the lipid bilayer of liposomes. We reveal that the performance of the photo-click reactions between the monopeptides and photo-generated nitrile imine intermediates is significantly enhanced by enrichment of both reactants in the hydrophobic membrane lamel of liposomes. Enrichment of the DBDAA monopeptide in lipid phase serves as a convenient method to introduce bioorthogonal chemical handles on live cell membranes, which enables fluorescence labelling of single cell's membrane with high spatiotemporal resolution to facilitate the studies on cell membrane dynamics.     

Tuning Surface Wettability of Poly(3‐sulfopropyl methacrylate) Brushes by Cationic Surfactant‐Driven Interactions

In this communication, polyanionic poly(potassium 3‐sulfopropyl methacrylate) (PSPM) brushes were switched from hydrophilic to hydrophobic by exchange of the counter cations. First, poly(potassium 3‐sulfopropyl methacrylate) brushes were grown by means of atom transfer radical polymerization (ATRP) from thiol monolayers of initiating ω‐mercaptoundecyl bromoisobutyrate and mixed monolayers of thiol initiator and 1‐undecanothiol (blank thiol) attached to gold surfaces. The kinetics of the polymerization reaction were followed by means of the quartz microbalance technique with dissipation (QCM‐D). The collapse of PSPM brushes in the presence of cationic surfactants like quaternary ammonium salts (tetraethylammonium bromide, hexadecyltrimethylammonium bromide) and imidazolium salts (1‐dodecyl‐3‐methylimidazolium bromide, 1H,1H,2H,2H‐perfluoro‐1‐decyl‐3‐methylimidazolium bromide) was shown by QCM‐D. Water contact angle measurements proved that the wettability of the surface could be tuned reversibly from hydrophilic values (<30 °) to hydrophobic ones (>85 °).

     

Surface properties and enzymatic degradation of end-capped poly(l-lactide)

Surface properties and enzymatic degradation of poly(l-lactide) (PLLA) end-capped with hydrophobic dodecyl and dodecanoyl groups were investigated by means of advancing contact angle (θ_a) measurement, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The θ_a values of end-capped PLLA films were larger than those of non-end-capped PLLA films, suggesting that the hydrophobic dodecyl and dodecanoyl groups were segregated on the film surface. The weight changes of end-capped PLLA thin films during enzymatic degradation in the presence of proteinase K were monitored by using a QCM technique. The relatively fast weight loss of PLLA film occurred during first few hours of degradation, followed by a decrease in the erosion rate. The erosion rate of PLLA films at the initial stage of degradation was dependent on the chain-end structure of PLLA molecules, and the value decreased with an increase in the amount of hydrophobic functional groups. The surface morphologies of PLLA thin films before and after degradation were characterized by AFM. After the enzymatic degradation, the surface of non-end-capped PLLA films was blemished homogeneously. In contrast, the end-capped PLLA thin films were degraded heterogeneously by the enzyme, and many hollows were formed on the film surface. From these results, it has been concluded that the introduction of hydrophobic functional groups at the chain-ends of PLLA molecules depressed the erosion rate at the initial stage of enzymatic degradation.     

Kinetics of CO2 nanobubble formation at the solid/water interface

The kinetics of adsorption of CO(2) molecules dissolved in aqueous solution onto a hydrophobised silica surface were investigated using a quartz crystal microbalance (QCM). The results of this investigation were compared with those obtained earlier from tapping mode atomic force microscopy (TMAFM) under the same experimental conditions (J. Yang, J. Duan, D. Fornasiero, J. Ralston, J. Phys. Chem. B., 2003, 107(25), 6139-6147; ref. 1). The QCM results represent the early stage of CO(2) gas adsorption (<20 min), before CO(2) gas bubbles adsorbed on the surface can be directly observed by TMAFM. The QCM results confirmed our observation from TMAFM imaging: that CO(2) gas molecules present in solution only adsorb on silica when its surface is hydrophobic. More importantly, the results showed that gas adsorption/bubble growth undergoes two consecutive kinetic processes: a slow and a fast adsorption process.     

The effect of methyl group on the mechanical properties of hydrophobic association hydrogel

Hydrophobic association hydrogels were fabricated via micellar copolymerization of acrylamide and hydrophobic monomers lauryl (meth)acrylate (LA or LMA) in an aqueous solution of sodium dodecyl sulfate. The effect of methyl groups of hydrophobic monomers on the crosslinking network structure and mechanical behavior of the gels was investigated on the basis of rubber elastic theory. It was found that the LMA-gel exhibited higher effective crosslink density and elastic modulus. The methyl groups of hydrophobic monomers limited the flexibility of the methacrylate backbone in the association domain, which resulted in the increment of chains constraints. With the increase of stretch rate, the dissipated energy of LMA-gel increased more highly than that of LA-gel. In addition, the methyl group hindered the movement of polymer chains, leading to the lower recovery efficiency of dissipated energy for LMA-gel. In contract, the LA-gel exhibited a rapid response to external force, and possessed better elasticity and self-recovery property. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1505–1512     

Exothermic nonreversing process in the phase transition of poly(N‐isopropylacrylamide) studied with stochastic temperature‐modulated DSC

Exothermic nonreversing process is predicted to present in the phase transition of poly(N‐isopropylacrylamide) (PNIPAM). By employing TOPEM‐DSC, exothermic nonreversing heat flow peak is observed for the first time, and it usually appears under nonquasi‐static conditions. The exothermic nonreversing heat flow is proved to be from the formation of hydrogen bonds by the comparative studies on the phase transition of poly(N,N‐diethylacrylamide) (PDEAM) and cyclic heating and cooling of PDEAM and PNIPAM. Further TOPEM‐DSC studies on the phase transition of poly(NIPAM‐co‐DEAM) and poly(NIPAM‐co‐AAm) prove that hydrophobic force rather than hydrogen bonding is the main driving force for the phase transition, and hydrophobic force is also the driving force for the formation of inter‐ and intrachain hydrogen bonding. However, the phase transition driven by only hydrophobic force is a slow process. The combined action of hydrogen bonding and hydrophobic force makes the phase transition occur much faster. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1869–1877     

Effect of Hydrodynamic Forces on meso‐(4‐Sulfonatophenyl)‐Substituted Porphyrin J‐Aggregate Nanoparticles: Elasticity,Plasticity and Breaking

The J aggregates of 4‐sulfonatophenyl meso‐substituted porphyrins are non‐covalent polymers obtained by self‐assembly that form nanoparticles of different morphologies. In the case of high aspect‐ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small‐angle X‐ray scattering measurements in a disk‐plate rotational cell, and cone–plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles.     

Thermoelasticity of networks in swelling equilibrium

A theoretical analysis of the thermoelastic behavior of polymeric networks in swelling equilibrium with excess diluent, using both the kinetic theory of elasticity and the Flory-Huggins theory of mixing, is presented. Our calculations are restricted to the special case of diluents composed of a single constituent. The results are used to obtain the ratio of the energy component of the force f_e to the total force f of rubber networks swollen in excess n-decane, and we find f_e/f to be 0.17, which compares favorably with the value 0.18 reported for the unswollen network. Furthermore, f_e/f is independent of elongation, in accordance with theory. The kinetic theory of elasticity is reasonably well obeyed in this highly swollen system although there remains a small contribution to the force from the C₂ term of the Mooney-Rivlin phenomenological elasticity equation. It is not believed that this has an appreciable effect on f_e/f.     

Uniformly Oriented Zeolite ZSM‐5 Membranes with Tunable Wettability on a Porous Ceramic

Facile fabrication of well‐intergrown, oriented zeolite membranes with tunable chemical properties on commercially proven substrates is crucial to broadening their applications for separation and catalysis. Rationally determined electrostatic adsorption can enable the direct attachment of a b‐oriented silicalite‐1 monolayer on a commercial porous ceramic substrate. Homoepitaxially oriented, well‐intergrown zeolite ZSM‐5 membranes with a tunable composition of Si/Al=25–∞ were obtained by secondary growth of the monolayer. Intercrystallite defects can be eliminated by using Na⁺ as the mineralizer to promote lateral crystal growth and suppress surface nucleation in the direction of the straight channels, as evidenced by atomic force microscopy measurements. Water permeation testing shows tunable wettability from hydrophobic to highly hydrophilic, giving the potential for a wide range of applications.     

Fast Water Relaxation through One‐Dimensional Channels by Rapid Energy Transfer

Water in carbon nanotubes is surrounded by hydrophobic carbon surfaces and shows anomalous structural and fast transport properties. However, the dynamics of water in hydrophobic nanospaces is only phenomenologically understood. In this study, water dynamics in hydrophobic carbon nanotubes is evaluated based on water relaxation using nuclear magnetic resonance spectroscopy and molecular dynamics simulations. Extremely fast relaxation (0.001 s) of water confined in carbon nanotubes of 1 nm in diameter on average is observed; the relaxation times of water confined in carbon nanotubes with an average diameter of 2 nm (0.40 s) is similar to that of bulk water (0.44 s). The extremely fast relaxation time of water confined in carbon nanotubes with an average diameter of 1 nm is a result of frequent energy transfer between water and carbon surfaces. Water relaxation in carbon nanotubes of average diameter 2 nm is slow because of the limited number of collisions between water molecules. The dynamics of interfacial water can therefore be controlled by varying the size of the hydrophobic nanospace.     

New cut angle quartz crystal microbalance with low frequency-temperature coefficients in an aqueous phase

In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (dF/dT) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of dF/dT is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low dF/dT values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its dF/dT value is close to zero at ca. 25 °C and its averaged value of |dF/dT| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle.     

Hydrodynamic Effects in Soft‐matter Self‐assembly: The Case of J‐Aggregates of Amphiphilic Porphyrins

Chiral J‐aggregates of achiral amphiphilic porphyrins (4‐sulfonatophenyl and aryl meso‐substituted porphyrins) show several effects under the hydrodynamic forces of common stirring. These effects can be classified as pure mechanic (e. g. elasticity, plasticity and breaking of the self‐assembly non‐covalent bonding) and chemically selective as detected in the formation/growth of the nanoparticles. Diastereoselective, enantioselective and, depending on the sign of chiral shear forces, even enantiospecific selections have been described. Some types of these effects have been reported in other type of J‐aggregates. Reversible and irreversible structural effects have been studied by atomic force imaging. The determination of the optical polarization properties (linear and circular) of their solutions is best done using Mueller matrix polarimetry methods.     

QCM study of microbiological activity during long-term exposure to atmosphere—aluminium colonisation by <Emphasis Type="Italic">Aspergillus Niger</Emphasis>

The study demonstrated a possibility to sense the activity of microorganisms on metals in situ under atmosphere conditions using a quartz crystal microbalance (QCM) as a sensitive mass change detector. Other innovative aspects of the QCM application include long-term monitoring (over month), taking count of the influence of atmospheric pressure and application of Al-glued foil electrodes. The research subject was aluminium colonisation by Aspergillus niger Tiegh., a filamentous ascomycete fungus. The difference between the QCM data for abiotic and biotic samples reflected microbiological activity, which resulted in exponential mass gain during exposure. The increase in mass was due to various phenomena, i.e. development of biomass, secretion of metabolites, water uptake by the colony and microbially induced corrosion. The glued foil method demonstrated a possibility to expand the scope of the QCM studies from evaporated, sputtered or electroplated materials to those, from which thin foils may be produced. Dedicated to Professor Dr. Algirdas Vaškelis on the occasion of his 70th birthday.     

A Quartz Crystal Microbalance (QCM) Study of Single-Strand DNA Hybridization and Hydrolytic Cleavage

The use of a quartz crystal microbalance (QCM) for monitoring in situ the immobilization of single-strand DNA marked with mercaptol group at the 5′-end on the surface of a gold-filled 7.995 MHz AT-cut quartz crystal by Au-S bond with the self-assembly technique is reported. The hybridization of ssDNA with complementary 10-mer ODN and 8-mer ODN is described. The QCM was also employed to analyze DNA cleavage by cerium(IV) ions under moderate conditions. The results showed that the QCM, which is capable of sensitive measurement, was able to investigate the immobilization, hybridization, and cleavage of ssDNA in situ. The cerium(IV) ions produced no cleavage in double-strand DNA; they were, however, able to hydrolyze single-strand DNA. Thus, the hydrolytic cleavage of ssDNA at a specific site could be ensured by protective hybridization.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 877–880.Original English Text Copyright © 2005 by Zhu, Gao, Shen, Yang, Yuan.The text was submitted by the authors in English.     

Water cluster growth in hydrophobic solid nanospaces

The growth mechanism of water clusters in carbon nanopores is clearly elucidated by in situ small-angle X-ray scattering (SAXS) studies and grand canonical Monte Carlo (GCMC) simulations at 293-313 K. Water molecules are isolated from each other in hydrophobic nanopores below relative pressures (P/P(0)) of 0.5. Water molecules associate with each other to form clusters of about 0.6 nm in size at P/P(0)=0.6, accompanied by a remarkable aggregation of these clusters. The complete filling of carbon nanopores finishes at about P/P(0)=0.8. The correlation length analysis of SAXS profiles leads to the proposal of a growth mechanism for these water clusters and the presence of the critical cluster size of 0.6 nm leads to extremely stable clusters of water molecules in hydrophobic nanopores. Once a cluster of the critical size is formed in hydrophobic nanopores, the predominant water adsorption begins to fill carbon nanopores.     

Characterization of New Titanium Oxide Polymer Hybrid Membranes for Biofilm Formation

Abstract

Presently, there is great need to create new matrices for diverse applications particularly in the fields of biotechnology and food industry. Here, we report on the synthesis of new matrices based on a mixture of polymer cellulose acetate butyrate/copolymer polyacrylonitrile acrylamide/TiO₂. The characterization of the new matrices was performed using IR spectroscopy, QCM technology, and SEM. The tests revealed that when we use our polymers as carriers, there is a limit for the concentration of titanium of 5%. Further increasing of Ti concentration leads to precipitation processes. The QCM analyses show that a low concentration of Ti(OBu)₄ does not influence the viscosity of the matrices obtained, but their elasticity changes significantly. The membranes obtained were successfully applied for biofilm formation of Yeast strain Saccharomyces cerevisiae.     

A quartz crystal microbalance study of the removal of solid organic soils from a hard surface in aqueous surfactant solution

A quartz crystal microbalance (QCM) has been employed to monitor the removal of two model solid organic soils, dotriacontane and tripalmitin, from the hard surface of the QCM crystal in aqueous surfactant solutions of octa-ethyleneglycol mono n-dodecyl ether (C₁₂E₈). We have investigated the effect of varying the thickness of the soil coating on soil removal and the effect of soaking the soil in high-purity water for an extended period of time before adding surfactant. The QCM results support the view that net soil removal is preceded by a stage of water and surfactant penetration into the soil. The rate of penetration and rate of removal depends on the soil type. Water and surfactant take longer to penetrate dotriacontane compared to tripalmitin coatings. The removal process also occurs over a longer period of time in the case of dotriacontane coatings. The percentage of material removed is less for dotriacontane, compared to tripalmitin coatings. The initial coating thickness on the hard surface does not appear to govern the final percentage of soil removed, at least in the thickness range accessible to the QCM (approximately ≤800 nm). Immersing the soil coated surfaces in water for a relatively long time, hastens the onset of the removal stage after surfactant is added but does not significantly influence the rate and extent of removal from the hard surface.