Nitroxide radicals. Controlled release from and transport through biomimetic and hollow fibre membranes

Lvovich

2010

Langmuir

Earlier we have shown that many important properties of ionic aqueous channels in biological membranes can be imitated using simple biomimetic membranes. These membranes are composed of mixed cellulose ester-based filters, impregnated with isopropyl myristate or other esters of fatty acids, and can be used for high-throughput drug screening. If the membrane separates two aqueous solutions, combination of relatively hydrophilic polymer support with immobilized carboxylic groups results in the formation of thin aqueous layers covering inner surface of the pores, while the pore volume is filled by lipid-like substances. Because of these aqueous layers biomimetic membranes even without proteins have a cation/anion ion selectivity and specific (per unit of thickness) electrical properties, which are similar to typical properties of biological membranes. Here we describe frequency-dependent impedance of the isopropyl myristate-impregnated biomimetic membranes in the 4-electrode arrangement and present the results as Bode and Nyquist diagrams. When the membranes are placed in deionized water, it is possible to observe three different dispersion processes in the frequency range 0.1 Hz to 30 kHz. Only one dispersion is observed in 5 mM KH(2)PO(4) solution. It is suggested that these three dispersion features are determined by (a) conductivity in aqueous structures/channels, formed near the internal walls of the filter pores at high frequencies, (b) dielectric properties of the whole membrane at medium frequencies, determined by polymer support, aqueous layers and impregnating oil, and, finally, (c) by the processes in hydrated liquid crystal structures formed in pores by impregnating oil in contact with water at low frequencies.

Section: Discussionmentioning

confidence: 96%

“…Water/oil interface transfer kinetics is an important but still not well studied phenomenon, complicated by ionization, unstirred layers, etc. To understand the process better we can use the data from . In this case the mass transfer coefficient of a noncharged nitroxide radical through the oil/water interface is ∼10 −4 cm/s.…”

Section: Discussionmentioning

confidence: 99%

Biomimetic Membranes with Aqueous Nano Chanels but without Proteins: Impedance of Impregnated Cellulose Ester Filters

Lvovich

2010

Langmuir

“…2 Still, this assumption cannot be always correct. Recently we have demonstrated that the interface resistance plays essential role for exit of nitroxide radicals from biomimetic membrane 26 and for transport of H + and electrons through electroconductive polyaniline membranes. 27 If the membrane is very thin (common situation in biology) and transport through the membrane is fast, the assumption of low interface resistance cannot be valid anymore, and more accurate description should be based on the equivalent circuit with diodes, describing the changes of standard chemical potential through the interface.…”

Section: Discussionmentioning

confidence: 99%

Role of Standard Chemical Potential in Transport through Anisotropic Media and Asymmetrical Membranes

Zhang

2003

J. Phys. Chem. B

Description of mass transport in a media or through a membrane usually is based on the assumption that a standard chemical potential µ 0 of a substance is constant and does not change with the distance in the media or membrane. This common assumption is not valid for asymmetrical or nonhomogeneous membranes. More accurate analysis of the transport, given in this paper, is based on one of the major principles of linear thermodynamics, according to which any flux is proportional to the gradient of electrochemical potential µ. It also takes care of possible changes of standard chemical potential µ 0 in asymmetrical media or membrane. It is demonstrated that an asymmetrical media, but not a membrane separating two similar phases, can act as a diffusion-based diode. Still, even with the membranes, if both the standard chemical potential and activity gradients are negative, the flux is increased and the time lag is decreased. Time lag, which is usually used to calculate a diffusion coefficient, can be much less than the one on the basis of the Einstein-Barrer equation. Asymmetry also allows additional improvement of membrane selectivity. Transport through both the membrane interface and the inner part of asymmetrical membrane far from equilibrium even for nonelectrolytes can be described by equivalent circuit, which has three diodes, with one of them looking to the opposite direction. The developed model and equivalent circuit are reduced to the common concepts if the asymmetry of the membrane decreases.

“…In other words, using simple oil-impregnated filters, it is possible to imitate the transport of gases, nonelectrolytes and ions because our membrane is based on the same fundamental principles, which determine barrier properties of biomembranes. In terms of material science, we can say that the barrier properties both of biomembranes and impregnated filters are formed by liquid crystals or similar structures, which was confirmed by nitroxide spin probes and DSC [ 62 , 64 ]. The ordering of impregnating oils is distorted by nitrocellulose polymer chains penetrating through the membrane.…”

Section: Introductionmentioning

confidence: 99%

Biomimetic Membranes without Proteins but with Aqueous Nanochannels and Facilitated Transport. Minireview

2021

Membr. Membr. Technol.

Imitation of biological membranes and aqueous channels attracts more and more attention. In this review, we mention both the early and very recent papers in this area. Still, we concentrate our attention on less known biomimetic membranes, which are commercial nitrocellulose ultrafilters, impregnated by esters of fatty acids. Pores in filters are filled with lipid-like oils, but aqueous nanochannels are spontaneously formed on the inner pore surfaces with carboxylic groups fixed on nitrocellulose. This combination imitates the most fundamental barrier properties of biological membranes, including specific (per unit thickness) permeability of respiratory gases, transport of nonelectrolytes, water, and ions, cation/anion selectivity, electric impedance, etc. The activation energy for water transport in nanochannels is similar to that in aquaporin. In the presence of fatty acids and other carriers, it is possible to observe facilitated and coupled active counter transport of different metal cations in exchange to H + and without any transmembrane pressure, voltage or ATP. When quinones are dissolved in oils, light-sensitive co-transport of electrons and H + through oil is possible. In this case, redox-active substances are separated by the membrane. They are not mixed, but they still react. Small biomimetic membranes can be used as electrochemical drug sensors in drug detection and screening, medium size membranes—for smart transdermal drug -delivery, and large membranes—for industrial separation and purification. For example, after small modifications, they can be used for metal recovery, including radioactive strontium removal from nuclear waste accumulated and stored since the Cold War.