Ion Concentration of External Solution as a Characteristic of Micro- and Nanogel Ionic Reservoirs
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- 作者：Sergey Kazakov ; Marian Kaholek ; Irina Gazaryan ; Boris Krasnikov ; Korki Miller ; Kalle Levon
- 刊名：Journal of Physical Chemistry B
- 出版年：2006
- 出版时间：August 10, 2006
- 年：2006
- 卷：110
- 期：31
- 页码：15107 - 15116
- 全文大小：304K
- 年卷期：v.110,no.31(August 10, 2006)
- ISSN：1520-5207
文摘
Ion-sensitive hydrogel is regarded as an ionic reservoir, i.e., a system capable of changing the external pH orionic strength by accumulating or releasing ions. The concept of a hydrogel ionic reservoir was demonstratedfor hydrogel particles of three different size ranges: macrogel (1000-6000 
m), microgel (~20-200 m),and nanogel (~0.2 m). Ion sensitivity of poly(N-isopropylacrylamide-co-1-vinylimidazole) (PNIPA-VI)microgels with imidazolyl (ionizable) groups was confirmed by the pH dependence of their volume, whilenanogels were characterized by dynamic light scattering. On the contrary, the volume of poly(N-isopropylacrylamide) (PNIPA) microgels without ionizable groups was pH independent in the whole rangeof pH from 10 to 2. Four distinct regions of pH-behavior were observed for PNIPA-VI hydrogel micro- andnanoparticles using potentiometric titration of their suspensions. Time-resolved measurements of ionconcentrations in the suspension of hydrogel particles revealed a substantial difference in kinetics of pHequilibration for (i) ion-sensitive hydrogels (PNIPA-VI) vs hydrogels without ionizable groups (PNIPA) and(ii) PNIPA-VI hydrogels of different sizes. On the basis of the experimental observations, a two-step mechanismaffecting the kinetics of proton uptake into the hydrogel particles with ionizable groups was proposed: (1)fast binding of ions to the immediate surface of each particle and (2) a slower successive diffusion of boundsites into the next inner layer of polymer network. In accord with the mechanism proposed, a quasi-chemicalkinetic model of pH relaxation to equilibrium was developed to fit the experimental data for the time courseof proton uptake by macro-, micro-, and nanogels into two exponentials with the characteristic times of 
1and 2. We believe the same kinetic model will be pertinent to describe phenomenological and molecularmechanisms controlling proton transport in/out bacteria, cells, organelles, drug delivery vehicles, and othernatural or artificial multifunctional ionic containers. The approach can be easily extended for the other ions(e.g., Na+, K+, and Ca2+).
m), microgel (~20-200 m),and nanogel (~0.2 m). Ion sensitivity of poly(N-isopropylacrylamide-co-1-vinylimidazole) (PNIPA-VI)microgels with imidazolyl (ionizable) groups was confirmed by the pH dependence of their volume, whilenanogels were characterized by dynamic light scattering. On the contrary, the volume of poly(N-isopropylacrylamide) (PNIPA) microgels without ionizable groups was pH independent in the whole rangeof pH from 10 to 2. Four distinct regions of pH-behavior were observed for PNIPA-VI hydrogel micro- andnanoparticles using potentiometric titration of their suspensions. Time-resolved measurements of ionconcentrations in the suspension of hydrogel particles revealed a substantial difference in kinetics of pHequilibration for (i) ion-sensitive hydrogels (PNIPA-VI) vs hydrogels without ionizable groups (PNIPA) and(ii) PNIPA-VI hydrogels of different sizes. On the basis of the experimental observations, a two-step mechanismaffecting the kinetics of proton uptake into the hydrogel particles with ionizable groups was proposed: (1)fast binding of ions to the immediate surface of each particle and (2) a slower successive diffusion of boundsites into the next inner layer of polymer network. In accord with the mechanism proposed, a quasi-chemicalkinetic model of pH relaxation to equilibrium was developed to fit the experimental data for the time courseof proton uptake by macro-, micro-, and nanogels into two exponentials with the characteristic times of 1and 2. We believe the same kinetic model will be pertinent to describe phenomenological and molecularmechanisms controlling proton transport in/out bacteria, cells, organelles, drug delivery vehicles, and othernatural or artificial multifunctional ionic containers. The approach can be easily extended for the other ions(e.g., Na+, K+, and Ca2+).