What is the impact of reducing the space available to molecules onto their properties is a fundamental question for capillary systems, molecular biology and transport, protein and material sciences. Possibly influenced by space restriction, ionization degree has rarely been studied for confined polyelectrolytes; Monte Carlo titrations and coarse-grained models are thus used to investigate structural and ionization changes induced on a single polyelectrolyte chain by confinement into slit (1D), cylindrical (2D), or spherical (3D) cavities. Four polyelectrolyte models differing in chain stiffness and the possible formation of charged hydrogen bonds (c-H-bonds) are studied. Low pH effective ionization constants (pK(a)) of confined chains are lower than for the free species if c-H-bonds can be formed. This is especially evident for 3D-confined stiff chains, a finding rationalized by the impact of global compression onto chain conformations. If no c-H-bonds are allowed, chain ionization is largely unaffected by 1D or 2D confinement, while it is depressed by 3D. Chain confinement Helmholtz energy (Delta A(conf)) was computed as a function of both pH and confining width (W) to gauge the impact of ionization-induced stiffening onto Delta A(conf) versus W behavior, the partition coefficient K(pH; W) governing absorption, and the average number of c-H-bond formed.
Modulation of ionization and structural properties of weak polyelectrolytes due to 1D, 2D, and 3D confinement
MELLA, MASSIMO;IZZO, Lorella
2017-01-01
Abstract
What is the impact of reducing the space available to molecules onto their properties is a fundamental question for capillary systems, molecular biology and transport, protein and material sciences. Possibly influenced by space restriction, ionization degree has rarely been studied for confined polyelectrolytes; Monte Carlo titrations and coarse-grained models are thus used to investigate structural and ionization changes induced on a single polyelectrolyte chain by confinement into slit (1D), cylindrical (2D), or spherical (3D) cavities. Four polyelectrolyte models differing in chain stiffness and the possible formation of charged hydrogen bonds (c-H-bonds) are studied. Low pH effective ionization constants (pK(a)) of confined chains are lower than for the free species if c-H-bonds can be formed. This is especially evident for 3D-confined stiff chains, a finding rationalized by the impact of global compression onto chain conformations. If no c-H-bonds are allowed, chain ionization is largely unaffected by 1D or 2D confinement, while it is depressed by 3D. Chain confinement Helmholtz energy (Delta A(conf)) was computed as a function of both pH and confining width (W) to gauge the impact of ionization-induced stiffening onto Delta A(conf) versus W behavior, the partition coefficient K(pH; W) governing absorption, and the average number of c-H-bond formed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
