Structure and dynamics of water surrounding the poly(methacrylic acid): A molecular dynamics study

Abstract

All-atom molecular dynamics simulations are used to study a single chain of poly(methacrylic acid) in aqueous solutions at various degrees of charge density. Through a combination of analysis on the radial distribution functions of water and snapshots of the equilibrated structure, we observe that local arrangements of water molecules, surrounding the functional groups of COO- and COOH in the chain, behave differently and correlated well to the resulting chain conformation behavior. In general, due to strong attractive interactions between water and charged COO- via the formation of hydrogen bonds, water molecules tend to form shell-like layers around the COO- groups. Furthermore, water molecules often act as a bridging agent between two neighboring COO- groups. These bridged water molecules are observed to stabilize the rodlike chain conformation that the highly charged chain reveals, as they significantly limit torsional and bending degrees of the backbone monomers. In addition, they display different dynamic properties from the bulk water. Both the resulting oxygen and hydrogen spectra are greatly shifted due to the presence of strong H-bonded interactions.

The x-ray absorption spectroscopy model of solvation about sulfur in aqueous L-cysteine

“…76,77 If present, the waters within this array will exchange with waters in the bulk solvent, but at some rate much slower than the bulk exchange rate. 94 If this picture is accurate, the solvation region around sulfur will include slow-exchange water molecules that can contribute some back-scattering intensity to the sulfur K-edge spectrum.…”

“…Similar water molecule networks have been reported for other dissolved aqueous amino acids. [73][74][75][76][77] Such a network would constitute an extended stable shell of water molecules about cysteine. Any durably located bridging network of hydrogen-bonded water molecules with a S Cys -O w1 -O w2 angle of 150…”

Molecular dynamics study of the effects of calcium ions on the conformational properties of comb-like poly(acrylic acid-co-methyl allyl polyoxyethylene ether)

“…behavior of salts and the dynamics of water [27][28][29][30][31][32][33]. For example, Molnar [27] studied the mechanism of ''like-charge attraction'' by the fully atomistic molecular dynamics simulations and found that the interaction of calcium ions with single chains of poly(acrylic acid)(PAA) strongly influenced the original sodium ion distribution and shielded polyanions from approaching each other, which was contrary to the assumption that precipitation is initially induced by intermolecular Ca 2+ bridging.…”

“…Various all-atom computer simulations have been used to study the interaction of salts ions with the -COO À functional groups of the polycarboxylate-type superplasticizers and found that Ca 2+ ions bridging was responsible for the conformational collapse [28,31]. However, only single polyelectrolyte chain in salt solution was usually selected as the model, and therefore only intramolecular Ca 2+ bridging was observed.…”

“…The conformational properties of the superplasticizers were dominated by various anions (OH À , SO 4 2À ) and cations (Na + , K + , Ca 2+ ) [6,7]. To study the effects of the ions, especially the cations, on the conformation of superplasticizers, many studies have been done, including experiments [8][9][10][11][12][13][14][15] and computational simulations [16][17][18][19][20][21][22][23]. For experimental studies, it has been shown that many factors, such as the charge density of the polymers, the pH value of the solution, the ionic species and the ionic strength, would have a comprehensive influence on the conformations of polyelectrolyte in the solution [24][25][26].…”