Several pieces of experimental evidence show that the water affinity of poly(N-isopropylacrylamide), PNIPAM, decreases with the increase of the degree of isotacticity. To give a rationale to such effect we carried out atomistic molecular dynamics simulations of PNIPAM 30-mers with content of meso dyads, m, of 45% and 59%, assuming a Bernoullian dyad distribution. The single chain behavior of these stereoisomers in water was modeled at 283 and 323 K, i.e., below and above the lower critical solution temperature, LCST. Simulation results show that the dyad composition has influence on size and conformation of the oligomer below the LCST, the isotactic-rich stereoisomer preferring conformations with lower radius of gyration. With reference to the cooperative hydration model of PNIPAM, we analyzed the organization and the dynamics of water in the surroundings of the polymer. Below the LCST the number of hydrogen bonds per water molecule in the first hydration shell and the water surface concentration around PNIPAM are affected by the meso/racemo dyad ratio, showing the higher hydrophobicity of the isotactic-rich system. Above the LCST the subtle effects leading to the modulation of conformation and hydration by means of tacticity are overtaken, and the chain collapse is observed for both systems up to a similar globular state. The comparison of simulation findings of the m 45% stereoisomer with available experimental results of atactic PNIPAM highlights additional molecular details of this macromolecule in aqueous environment. The characteristic time for motion of water molecules in the PNIPAM first hydration shell at 283 K is about 34 ps, in agreement with the experimental value.

Chiessi, E., Paradossi, G. (2016). Influence of Tacticity on Hydrophobicity of Poly(N-isopropylacrylamide): A Single Chain Molecular Dynamics Simulation Study. JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL, 120(15), 3765-3776 [10.1021/acs.jpcb.6b01339].

Influence of Tacticity on Hydrophobicity of Poly(N-isopropylacrylamide): A Single Chain Molecular Dynamics Simulation Study

CHIESSI, ESTER;PARADOSSI, GAIO
2016-03-31

Abstract

Several pieces of experimental evidence show that the water affinity of poly(N-isopropylacrylamide), PNIPAM, decreases with the increase of the degree of isotacticity. To give a rationale to such effect we carried out atomistic molecular dynamics simulations of PNIPAM 30-mers with content of meso dyads, m, of 45% and 59%, assuming a Bernoullian dyad distribution. The single chain behavior of these stereoisomers in water was modeled at 283 and 323 K, i.e., below and above the lower critical solution temperature, LCST. Simulation results show that the dyad composition has influence on size and conformation of the oligomer below the LCST, the isotactic-rich stereoisomer preferring conformations with lower radius of gyration. With reference to the cooperative hydration model of PNIPAM, we analyzed the organization and the dynamics of water in the surroundings of the polymer. Below the LCST the number of hydrogen bonds per water molecule in the first hydration shell and the water surface concentration around PNIPAM are affected by the meso/racemo dyad ratio, showing the higher hydrophobicity of the isotactic-rich system. Above the LCST the subtle effects leading to the modulation of conformation and hydration by means of tacticity are overtaken, and the chain collapse is observed for both systems up to a similar globular state. The comparison of simulation findings of the m 45% stereoisomer with available experimental results of atactic PNIPAM highlights additional molecular details of this macromolecule in aqueous environment. The characteristic time for motion of water molecules in the PNIPAM first hydration shell at 283 K is about 34 ps, in agreement with the experimental value.
31-mar-2016
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore CHIM/02 - CHIMICA FISICA
English
Con Impact Factor ISI
PNIPAM, water, hydrogen bond, stereoregularity, LCST, cooperative hydration
http://pubs.acs.org/doi/abs/10.1021/acs.jpcb.6b01339
Chiessi, E., Paradossi, G. (2016). Influence of Tacticity on Hydrophobicity of Poly(N-isopropylacrylamide): A Single Chain Molecular Dynamics Simulation Study. JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL, 120(15), 3765-3776 [10.1021/acs.jpcb.6b01339].
Chiessi, E; Paradossi, G
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/142887
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