Currents in narrow pores

Details Currents in narrow pores Currents in narrow pores

1995-11-17

1998-04-07

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

2102572, 21050027, 204600, 204450, B01D 1100

Patent

active

057360502

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for controlling the permeability to ions or uncharged molecules of a synthetic membrane, and to switching and sensor devices which use this effect.
The characteristic feature of ion channels in biological membranes is that when an electric potential is applied across the membrane, the resultant date most explanations of this phenomenon have been based on the notion that conducting and non-conducting states represent "open" and "closed" configurations of the channel, and that the transition between them results from the physical movement of part of the channel structure,--the
The applicants have found that current fluctuations typical of those observed with biological channels can be observed with purely synthetic membrane filters that may be devoid of any added lipid or protein. Two other features of biological ion channels are ion selectivity and when current across synthetic membrane filters is measured. It is believed that the results may be interpreted in terms of the special properties of ion conductance through water that is confined near an interface; they may be observed whenever the contribution of bulk conductance is minimal, such as in a narrow pore having a high surface to volume ratio.
Flow of electrolytes or non-electrolytes through pores in biological membranes that are induced by agents as varied as certain haemolytic viruses, bacterial or animal toxins, immune molecules or detergents at sub-lytic concentration show properties that are remarkably similar from agent to agent. These include inhibition by divalent cations, with relative efficacy Zn.sup.2+ >Ca.sup.2+ >Mg.sup.2+ and, when the agents are incorporated into planar lipid bilayers with an applied voltage across them, fluctuations in current typical of "single channel" openings and closings of endogenous ion channels; in several of these systems protons also inhibit flow (with relative efficacy H.sup.+ >Zn.sup.2+).
The applicants have studied flow (i.e. current) of non-electrolytes and electrolytes through purely synthetic membrane filters and find the same effect of divalent cations and protons, provided the membrane pores are narrow enough. It is concluded that these effects are features of flow along any liquid--solid interface, that can be observed wherever the contribution of bulk is minimised (as in the case of very narrow pores).
The word "pore" in the context of the present invention is intended to include a hole through a membrane or the space between two apposed surfaces that may be two solids or two lipid monolayers.
For simplicity the term "membrane" is used in the present description, but it is to be understood that, unless otherwise specified, this term encompasses films or sheets of any shape and thickness and whose thickness may or may not be uniform, and also encompasses the combination of two solids or two lipid monolayers whose relative configuration forms at least one pore as defined above.
The possible applications of a switching device based on synthetic organic materials are wide ranging. Some are listed below:
(1) a switched pore can control the transfer of particular solvent and solute molecules across an otherwise impermeable membrane which has applications in chemical engineering.
(2) a pore that may be switched from low to high conductance can also serve as a sensitive detector of particular conditions such as pH and ionic strength or even an elevation in the concentration of a particular solute molecule. Such a detector may have a very high gain (or amplification) in that the concentration change required to switch the pore conductance may be very much smaller than the detected flow through the pore when it is opened. Applications of this effect include chemical and medical monitoring of solutions with the rapid detection of changes in specific constituents of the solution.
(3) A pore is switched from high to low conductance by the particular conditions that prevail within the pore or in the immediate vicinity of its two ends. Thus by special preparation

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