Modulation of ionization and structural properties of weak polyelectrolytes due to 1D, 2D, and 3D confinement

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

On the origin and consequences of high DMAEMA reactivity ratio in ATRP copolymerization with MMA: An experimental and theoretical study#

“…Despite our monomers being polar, the impact of solvation on those interaction modalities in our case is unlikely to be more than weak, as the employed solvent is toluene ( ); it was thus decided to neglect the use of continuous model solvents. We already provided evidences supporting this idea in a work were cationic metallocenic complexes catalyzed olefin polymerization, and preliminary calculations on a few cases indicated this to be correct also for radical polymerizations in absence of chemically specific interactions such as normal or charged hydrogen bonds …”

“…These indicated the presence of a higher DMAEMA concentration at the chain beginning (Fig. ) compared to the average copolymer composition, a finding that has a direct relevance to both the theoretical foundations of the polymers designed for the discussed drug delivery applications and the analysis of the release kinetics from vesicles . Wishing to obtain copolymers of more uniform composition along a chain, a possible approach emerges from the modeling results in Section Rationalization, which suggest a difference between MMA and DMAEMA partition coefficients due to the complexation of the latter.…”

“…We already provided evidences supporting this idea in a work were cationic metallocenic complexes catalyzed olefin polymerization, 26,27 and preliminary calculations on a few cases indicated this to be correct also for radical polymerizations in absence of chemically specific interactions such as normal or charged hydrogen bonds. 4,5,28,29 What may instead be more problematic in using continuous solvent models in the task we set to accomplish, it is their limited ability in correctly estimating the change in system entropy upon formation of the TSs from dissociated reactants. Such issue descends from the fact that reaction field models are not able to correctly describe the molecularity of the true solvent, which has to be displaced from the first solvation shell of each species for the reactive collision to take place.…”

“…5) compared to the average copolymer composition, a finding that has a direct relevance to both the theoretical foundations of the polymers designed for the discussed drug delivery applications 6,7 and the analysis of the release kinetics from vesicles. 28,29 Wishing to obtain copolymers of more uniform composition along a chain, a possible approach emerges from the modeling results in Section Rationalization, which suggest a difference between MMA and DMAEMA partition coefficients due to the complexation of the latter. Thus, one may favor (disfavor) even more the partition of MMA (DMAEMA) from the bulk to the regions surrounding the growing polymer by appropriately choosing the reaction solvent, which impacts on the stability of the complex between DMAEMA and CuBr.…”

Modulation of Polyelectrolyte Adsorption on Nanoparticles and Nanochannels by Surface Curvature

“…[1][2][3][4][5][6][7] The interaction of a single polyelectrolyte chain with surfaces of different curvatures have been the subject of recent investigations. [8][9][10][11][12][13] The adsorption of polyelectrolytes from solution to form a film on planar and convex surfaces has been also extensively studied in literature and it is relatively well understood. [14][15][16][17][18][19][20][21][22] However, the adsorption of polyelectrolytes from solution on concave surfaces is still poorly investigated.…”