A Monte Carlo Study of Weak Polyampholytes: Stiffness and Primary Structure Influences on Titration Curves and Chain Conformations
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- 作者：Serge Ulrich ; Marianne Seijo ; Serge Stoll
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：July 26, 2007
- 年：2007
- 卷：111
- 期：29
- 页码：8459 - 8467
- 全文大小：616K
- 年卷期：v.111,no.29(July 26, 2007)
- ISSN：1520-5207
文摘
The conformation and titration curves of weak polyampholytes are examined using Monte Carlo simulationswith screened Coulomb potentials in the Grand Canonical ensemble. Two different types of monomers areconsidered. Depending on the solution pH, monomers A are weak acidic sites that can either be negativelycharged or uncharged (as carboxylic groups), whereas monomers B are weak basic sites that can either bepositively charged or uncharged (as amino groups). The influence of the chain stiffness, primary structure,and ionic concentration on the acid/base properties of the polyampholyte chains are systematically investigated.By adjusting the pH values, titration curves and then the fractions of positively and negatively ionized chargedmonomers are calculated. Stiffness influence is estimated by comparing two models of chain: a fully flexibleand a rod-like polyampholyte. Different primary structures such as statistical (diblock, octablock, and alternating)and random polyampholytes are also considered. We demonstrate that the primary structure plays importantroles in the acid/base properties as well as the charge distribution along the polymer backbone of a statisticalrod-like polyampholyte. When flexible polyampholytes are considered, polyampholyte conformations promotethe attractive electrostatic interactions between positively and negatively charged monomers, hence leadingto more or less compact conformations and acid/base properties relatively different in comparison to therod-like polyampholytes. Various conformations such as extended, globular, and pearl-necklace conformationsare found in good agreement with the literature by adjusting the interaction parameter between monomersand monomer stoichiometry.