Meso-scale Simulations of Poly(N-isopropylacrylamide) Grafted Architectures

2014 ◽  
Vol 1619 ◽  
Author(s):  
Sanket A. Deshmukh ◽  
Ganesh Kamath ◽  
Derrick C. Mancini ◽  
Subramanian K.R.S. Sankaranarayanan ◽  
Wei Jiang
Keyword(s):  
Conformational Dynamics ◽  
Md Simulations ◽  
Polymer Chains ◽  
Effect Of Temperature ◽  
Solution Temperature ◽  
Radius Of Gyration ◽  
Core Particle ◽  
Thermosensitive Polymer ◽  
Critical Solution Temperature ◽  
Different Diameters

ABSTRACTPoly(N-isopropylacrylamide) (PNIPAM) is a thermosensitive polymer that is well-known for its behavior at a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water, and above this temperature, polymer chains collapse and transform into a globule state. The conformational dynamics of single chains of polymer in a solution is known to be different from those of grafted structures that comprise of an ensemble of such single chains. In this study, we have carried out MD simulations of a mesoscopic nanostructure of PNIPAM polymer chains consisting of 60 monomer units grafted onto gold nanoparticles of different diameters, to study the effect of temperature and core particle size on the polymer conformations. Additionally, we have also studied the effect of grafting density on the coil-to-globule transition exhibited by PNIPAM through the LCST. The systems investigated consisted of ∼3 and ∼6 million atoms. Simulations were carried out below and above the LCST of PNIPAM, at 275K and 325K. Simulation trajectories were analyzed for radius of gyration of PNIPAM chains.

Effect of Methanol/Water Mixtures on the Lower Critical Solution Temperature of Poly(N-isopropylacrylamide)

2014 ◽  
Vol 1622 ◽  
pp. 25-30 ◽  
Author(s):  
Sanket A. Deshmukh ◽  
Ganesh Kamath ◽  
Derrick C. Mancini ◽  
Subramanian K.R.S. Sankaranarayanan
Keyword(s):  
Mole Fraction ◽  
Lower Critical Solution Temperature ◽  
Md Simulations ◽  
Polymer Chains ◽  
Solution Temperature ◽  
Radius Of Gyration ◽  
Solvation Dynamics ◽  
Water Mixture ◽  
Critical Solution Temperature ◽  
Lcst Behavior

ABSTRACTPoly(N-isopropylacrylamide) (PNIPAM) is a thermo-sensitive polymer that exhibits a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water and above this temperature polymer chains collapse prior to aggregation. In the presence of methanol, electron paramagnetic resonance (EPR) spectroscopy suggests that, LCST of PNIPAM is depressed up to certain mole fraction of methanol (0.35 mole fraction) and it is speculated that addition of methanol affects the PNIPAM-water interactions. Above 0.35 mole fraction of methanol, LCST gets elevated to temperatures above ∼305 K (32°C) and cannot be detected up to 373 K (100 °C). The atomistic origin of this co-solvency effect on the LCST behavior is not completely understood. In the present study, we have used molecular dynamics (MD) simulations to investigate the effect of methanol-water mixtures on conformational transitions and the LCST of PNIPAM. We employ two different force fields i.e. polymer consistent force-field (PCFF) and CHARMM to study solvation dynamics and the PNIPAM LCST phase transition in various methanol-water mixture compositions (0.018, 0.09, 0.27, 0.5, and 0.98 mole fractions). Simulations are conducted at fully atomistic level for three different temperatures (260, 278, and 310 K) and radius of gyration (Rg) of PNIPAM chains was computed for determination of LCST behavior of PNIPAM.

Effect of Ionic Strength on the Aggregation Propensity of Aβ1-42 Peptide: An In-silico Study

2020 ◽  
Vol 14 (3) ◽  
pp. 216-226
Author(s):  
Priyanka Borah ◽  
Venkata S.K. Mattaparthi
Keyword(s):  
Diffusion Coefficient ◽  
Ionic Strength ◽  
Marked Effect ◽  
Computational Study ◽  
Conformational Dynamics ◽  
Rapid Change ◽  
Md Simulations ◽  
Radius Of Gyration ◽  
Aggregation Propensity ◽  
In Silico Study

Background: Aggregation of misfolded proteins under stress conditions in the cell might lead to several neurodegenerative disorders. Amyloid-beta (Aβ1-42) peptide, the causative agent of Alzheimer’s disease, has the propensity to fold into β-sheets under stress, forming aggregated amyloid plaques. This is influenced by factors such as pH, temperature, metal ions, mutation of residues, and ionic strength of the solution. There are several studies that have highlighted the importance of ionic strength in affecting the folding and aggregation propensity of Aβ1-42 peptide. Objective: To understand the effect of ionic strength of the solution on the aggregation propensity of Aβ1-42 peptide, using computational approaches. Materials and Methods: In this study, Molecular Dynamics (MD) simulations were performed on Aβ1-42 peptide monomer placed in (i) 0 M, (ii) 0.15 M, and (iii) 0.30 M concentration of NaCl solution. To prepare the input files for the MD simulations, we have used the Amberff99SB force field. The conformational dynamics of Aβ1-42 peptide monomer in different ionic strengths of the solutions were illustrated from the analysis of the corresponding MD trajectory using the CPPtraj tool. Results: From the MD trajectory analysis, we observe that with an increase in the ionic strength of the solution, Aβ1-42 peptide monomer shows a lesser tendency to undergo aggregation. From RMSD and SASA analysis, we noticed that Aβ1-42 peptide monomer undergoes a rapid change in conformation with an increase in the ionic strength of the solution. In addition, from the radius of gyration (Rg) analysis, we observed Aβ1-42 peptide monomer to be more compact at moderate ionic strength of the solution. Aβ1-42 peptide was also found to hold its helical secondary structure at moderate and higher ionic strengths of the solution. The diffusion coefficient of Aβ1-42 peptide monomer was also found to vary with the ionic strength of the solution. We observed a relatively higher diffusion coefficient value for Aβ1-42 peptide at moderate ionic strength of the solution. Conclusion: Our findings from this computational study highlight the marked effect of ionic strength of the solution on the conformational dynamics and aggregation propensity of Aβ1-42 peptide monomer.

scholarly journals Effects of the Hydrophilic–Lipophilic Balance of Alternating Peptides on Self-Assembly and Thermo-Responsive Behaviors

2019 ◽  
Vol 20 (18) ◽  
pp. 4604 ◽  
Author(s):  
Ihsan ◽  
Nargis ◽  
Koyama
Keyword(s):  
Aqueous Solutions ◽  
Self Assembly ◽  
Polymer Chains ◽  
Systematic Evaluation ◽  
Solution Temperature ◽  
Critical Solution Temperature ◽  
Hydrophilic Lipophilic Balance ◽  
Upper Critical Solution Temperature ◽  
Cloud Points ◽  
Micellization Behavior

A series of N-substituted poly(Gly–alter–Val) peptides were successfully synthesized for the systematic evaluation of the micellization behavior of alternating peptides. Three-component polymerization employing an aldehyde, a primary ammonium chloride, and potassium isocyanoacetate afforded four alternating peptides in excellent yields. We investigated the dependence of the hydrophilic–lipophilic balance of alternating peptides on the micellization behavior. All the aqueous solutions of alternating peptides exhibited upper critical solution temperature (UCST) behaviors, strongly indicating that the alternating binary pattern would mainly contribute to the UCST behaviors. The cloud points of alternating peptides shifted to higher temperatures as the side chains became more hydrophilic, which is opposite to the trend of typical surfactants. Such unusual micellization behaviors appeared to be dependent on the quasi-stable structure of single polymer chains formed in water.

scholarly journals Thermally responsive polymeric hydrogel brushes: synthesis, physical properties and use for the culture of chondrocytes

2006 ◽  
Vol 4 (12) ◽  
pp. 117-126 ◽  
Author(s):  
John Collett ◽  
Aileen Crawford ◽  
Paul V Hatton ◽  
Mark Geoghegan ◽  
Stephen Rimmer
Keyword(s):  
Crosslink Density ◽  
Cell Attachment ◽  
Viable Cell ◽  
Contact Angles ◽  
Polymer Chains ◽  
Solution Temperature ◽  
Critical Solution Temperature ◽  
Thermally Responsive ◽  
Isopropyl Acrylamide ◽  
Responsive Polymer

Hydrogel brushes are materials composed of a water-swollen network, which contains polymer chains that are grafted with another polymer. Using a thermally responsive polymer, poly( N -isopropyl acrylamide) (polyNIPAM), as the graft component we are able to maintain the critical solution temperature ( T crit ), independent of the overall composition of the material, at approximately 32°C. The change in swelling at T crit is a function of the amount of polyNIPAM in the system. However, there is a much smaller change in the surface contact angles at T crit . PolyNIPAM-based materials have generated considerable interest, as ‘smart’ substrates for the culture of cells and here, we show the utility of hydrogel brushes in cell culture. Chondrocytes attached to the hydrogel brushes and yielded viable cell cultures. Moreover, the chondrocytes could be released from the hydrogel brushes without the use of proteases by reducing the temperature of the cultures to below T crit to induce a change in the conformation of the polyNIPAM chain at T crit . The importance of the crosslink hydrogel component is illustrated by significant changes in cell attachment/cell viability as the crosslink density is changed.

scholarly journals Constrained thermoresponsive polymers – new insights into fundamentals and applications

2021 ◽  
Vol 17 ◽  
pp. 2123-2163
Author(s):  
Patricia Flemming ◽  
Alexander S Münch ◽  
Andreas Fery ◽  
Petra Uhlmann
Keyword(s):  
Phase Transition ◽  
Current Knowledge ◽  
Polymer Chains ◽  
Switching Behavior ◽  
Solution Temperature ◽  
Miscibility Gap ◽  
Underlying Structure ◽  
Thermoresponsive Polymers ◽  
Critical Solution Temperature ◽  
Stimuli Responsive Polymers

In the last decades, numerous stimuli-responsive polymers have been developed and investigated regarding their switching properties. In particular, thermoresponsive polymers, which form a miscibility gap with the ambient solvent with a lower or upper critical demixing point depending on the temperature, have been intensively studied in solution. For the application of such polymers in novel sensors, drug delivery systems or as multifunctional coatings, they typically have to be transferred into specific arrangements, such as micelles, polymer films or grafted nanoparticles. However, it turns out that the thermodynamic concept for the phase transition of free polymer chains fails, when thermoresponsive polymers are assembled into such sterically confined architectures. Whereas many published studies focus on synthetic aspects as well as individual applications of thermoresponsive polymers, the underlying structure–property relationships governing the thermoresponse of sterically constrained assemblies, are still poorly understood. Furthermore, the clear majority of publications deals with polymers that exhibit a lower critical solution temperature (LCST) behavior, with PNIPAAM as their main representative. In contrast, for polymer arrangements with an upper critical solution temperature (UCST), there is only limited knowledge about preparation, application and precise physical understanding of the phase transition. This review article provides an overview about the current knowledge of thermoresponsive polymers with limited mobility focusing on UCST behavior and the possibilities for influencing their thermoresponsive switching characteristics. It comprises star polymers, micelles as well as polymer chains grafted to flat substrates and particulate inorganic surfaces. The elaboration of the physicochemical interplay between the architecture of the polymer assembly and the resulting thermoresponsive switching behavior will be in the foreground of this consideration.

scholarly journals Structure and Dynamics of Highly Attractive Polymer Nanocomposites in the Semi-Dilute Regime: The Role of Interfacial Domains and Bridging Chains

Polymers ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2749
Author(s):  
Emmanuel N. Skountzos ◽  
Katerina S. Karadima ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Dynamic Properties ◽  
Mass Density ◽  
Polymer Nanocomposite ◽  
Md Simulations ◽  
Polymer Chains ◽  
Hydroxyl Groups ◽  
Single Chain ◽  
Adsorbed Polymer ◽  
End Distance ◽  
Different Diameters

Detailed molecular dynamics (MD) simulations are employed to study how the presence of adsorbed domains and nanoparticle bridging chains affect the structural, conformational, thermodynamic, and dynamic properties of attractive polymer nanocomposite melts in the semi-dilute regime. As a model system we have chosen an unentangled poly(ethylene glycol) (PEG) matrix containing amorphous spherical silica nanoparticles with different diameters and at different concentrations. Emphasis is placed on properties such as the polymer mass density profile around nanoparticles, the compressibility of the system, the mean squared end-to-end distance of PEG chains, their orientational and diffusive dynamics, the single chain form factor, and the scattering functions. Our analysis reveals a significant impact of the adsorbed, interfacial polymer on the microscopic dynamic and conformational properties of the nanocomposite, especially under conditions favoring higher surface-to-volume ratios (e.g., for small nanoparticle sizes at fixed nanoparticle loading, or for higher silica concentrations). Simultaneously, adsorbed polymer chains adopt graft-like conformations, a feature that allows them to considerably extend away from the nanoparticle surface to form bridges with other nanoparticles. These bridges drive the formation of a nanoparticle network whose strength (number of tie chains per nanoparticle) increases substantially with increasing concentration of the polymer matrix in nanoparticles, or with decreasing nanoparticle size at fixed nanoparticle concentration. The presence of hydroxyl groups at the ends of PEG chains plays a key role in the formation of the network. If hydroxyl groups are substituted by methoxy ones, the simulations reveal that the number of bridging chains per nanoparticle decreases dramatically, thus the network formed is less dense and less strong mechanically, and has a smaller impact on the properties of the nanocomposite. Our simulations predict further that the isothermal compressibility and thermal expansion coefficient of PEG-silica nanocomposites are significantly lower than those of pure PEG, with their values decreasing practically linear with increasing concentration of the nanocomposite in nanoparticles.

A Nanostructured Thermosensitive Smart Surface With Integrated Microheater for Wettability Control

2008 ◽  
Author(s):  
Ghanashyam Londe ◽  
Anindarupa Chunder ◽  
Lei Zhai ◽  
Hyoung J. Cho
Keyword(s):  
Glass Substrate ◽  
Large Scale ◽  
Solution Temperature ◽  
Response Analysis ◽  
Thermosensitive Polymer ◽  
Critical Solution Temperature ◽  
Lab On Chip ◽  
Time Response Analysis ◽  
On Chip ◽  
Smart Surface

This paper describes the design and fabrication of a switchable thermosensitive polymer with an integrated microheater as a smart surface platform for wettabilty control. The thermoresponsive surface is synthesized on a glass substrate using the polymer poly(N-isopropylacrylamide) (PNIPAAm) which can change its wettability when subjected to change in temperature. PNIPAAm is hydrophilic when the surface temperature is less than the lower critical solution temperature (LCST) range of about 28–33 °C and is hydrophobic above the LCST range. The PNIPAAm surface is heated by spiral gold microheaters which are fabricated on the lower side of the glass substrate. The contact angle change with change in temperature is tested using a standard goniometer. Time response analysis of the surface is presented. This smart surface can be used as an active or adaptive component for microflow regulation and can be potentially integrated into large scale lab-on-chip (LOC) systems.

scholarly journals Atomistic simulation for coil-to-globule transition of poly(2-dimethylaminoethyl methacrylate)

Soft Matter ◽  
2015 ◽  
Vol 11 (12) ◽  
pp. 2423-2433 ◽  
Author(s):  
Sa Hoon Min ◽  
Sang Kyu Kwak ◽  
Byeong-Su Kim
Keyword(s):  
Molecular Dynamics ◽  
Aqueous Solution ◽  
Lower Critical Solution Temperature ◽  
Atomistic Simulation ◽  
Md Simulations ◽  
Solution Temperature ◽  
Critical Solution Temperature ◽  
Dimethylaminoethyl Methacrylate

We investigate the coil-to-globule transition of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) in the aqueous solution through the lower critical solution temperature (LCST) by atomistic molecular dynamics (MD) simulations.

Color Transition Properties of Water Dispersible Polydiacetylene Particles Conjugated with the Thermosensitive Polymer

2017 ◽  
Vol 863 ◽  
pp. 38-43
Author(s):  
Izumi Harano ◽  
Chigusa Okano ◽  
Yuriko Takayama ◽  
Eri Nasuno ◽  
Ken-ichi Iimura ◽  
...  
Keyword(s):  
Color Change ◽  
Uv Light ◽  
Aqueous Media ◽  
Polymerization Reaction ◽  
Solution Temperature ◽  
Thermosensitive Polymer ◽  
Critical Solution Temperature ◽  
Color Transition ◽  
Water Dispersible ◽  
System A

An assembly of diacetylene molecules is necessary to progress a topochemical reaction as UV-irradiated polymerization. In this study, we attempt to regularly assemble 10, 12- pentacosadiynoic acid (PCDA) by freezing the solution, followed by lyophilization. Dried PCDA assembly was easily dispersed in aqueous solution by sonication. Irradiation of UV light can promote polymerization reaction of PCDA judging from a color change of the solution into blue. A color transition of the polyPCDA-dispersed solution from blue to red was observed at approximately 56°C due to distortion of its π-conjugated system. A color transition temperature could be controlled by hybridization with thermosensitive hydroxypropyl cellulose, of which lower critical solution temperature appears around 38-39°C. By synchronizing to coli-globule transition of HPC in aqueous media, blue-red transition response of water-dispersed polyPCDA could be induced by changing conformation of surrounded polymer.

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