Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2002-05-09
2004-01-13
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S403040, C526S161000, C546S002000, C548S101000
Reexamination Certificate
active
06676816
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to transition metal complexes with (pyridyl)imidazole ligands. In addition, the invention relates to the preparation of the transition metal complexes and to the use of the transition metal complexes as redox mediators.
BACKGROUND OF THE INVENTION
Enzyme-based electrochemical sensors are widely used in the detection of analytes in clinical, environmental, agricultural and biotechnological applications. Analytes that can be measured in clinical assays of fluids of the human body include, for example, glucose, lactate, cholesterol, bilirubin and amino acids. Levels of these analytes in biological fluids, such as blood, are important for the diagnosis and the monitoring of diseases.
Electrochemical assays are typically performed in cells with two or three electrodes, including at least one measuring or working electrode and one reference electrode. In three electrode systems, the third electrode is a counter-electrode. In two electrode systems, the reference electrode also serves as the counter-electrode. The electrodes are connected through a circuit, such as a potentiostat. The measuring or working electrode is a non-corroding carbon or metal conductor. Upon passage of a current through the working electrode, a redox enzyme is electrooxidized or electroreduced. The enzyme is specific to the analyte to be detected, or to a product of the analyte. The turnover rate of the enzyme is typically related (preferably, but not necessarily, linearly) to the concentration of the analyte itself, or to its product, in the test solution.
The electrooxidation or electroreduction of the enzyme is often facilitated by the presence of a redox mediator in the solution or on the electrode. The redox mediator assists in the electrical communication between the working electrode and the enzyme. The redox mediator can be dissolved in the fluid to be analyzed, which is in electrolytic contact with the electrodes, or can be applied within a coating on the working electrode in electrolytic contact with the analyzed solution. The coating is preferably not soluble in water, though it may swell in water. Useful devices can be made, for example, by coating an electrode with a film that includes a redox mediator and an enzyme where the enzyme is catalytically specific to the desired analyte, or its product. In contrast to a coated redox mediator, a diffusional redox mediator, which can be soluble or insoluble in water, functions by shuttling electrons between, for example, the enzyme and the electrode. In any case, when the substrate of the enzyme is electrooxidized, the redox mediator transports electrons from the substrate-reduced enzyme to the electrode; and when the substrate is electroreduced, the redox mediator transports electrons from the electrode to the substrate-oxidized enzyme.
Recent enzyme-based electrochemical sensors have employed a number of different redox mediators such as monomeric ferrocenes, quinoid compounds including quinines (e.g., benzoquinones), nickel cyclamates, and ruthenium amines. For the most part, these redox mediators have one or more of the following limitations: the solubility of the redox mediators in the test solutions is low, their chemical, light, thermal, and/or pH stability is poor, or they do not exchange electrons rapidly enough with the enzyme or the electrode or both. Some mediators with advantageous properties are difficult to synthesize. Additionally, the redox potentials of some of these reported redox mediators are so oxidizing that at the potential at which the reduced mediator is electrooxidized on the electrode, solution components other than the analyte are also electrooxidized. Some other of these reported redox mediators are so reducing that solution components, such as, for example, dissolved oxygen, are also rapidly electroreduced. As a result, the sensor utilizing the mediator is not sufficiently specific.
SUMMARY OF THE INVENTION
The present invention is directed to novel transition metal complexes. The present invention is also directed to the use of the complexes as redox mediators. The preferred redox mediators typically exchange electrons rapidly with enzymes and electrodes, are stable, can be readily synthesized, and have a redox potential that is tailored for the electrooxidation of analytes, such as glucose for example.
One embodiment of the invention is a transition metal complex having the general formula set forth below.
In this general formula, M is cobalt, iron, ruthenium, osmium, or vanadium; c is an integer selected from −1 to −5, 0, or +1 to +5 indicating a positive, neutral, or negative charge; X represents at least one counter ion; d is an integer from 0 to 5 representing the number of counter ions, X; L and L′ are independently selected from the group consisting of:
and L
1
and L
2
are other ligands. In the formula for L and L′, R′
1
, is a substituted or an unsubstituted alkyl, alkenyl, or aryl group. Generally, R′
3
, R′
4
, R
a
, R
b
, R
c
, and R
d
are independently —H, —F, —Cl, —Br, —I, —NO
2
, —CN, —CO
2
H, —SO
3
H, —NHNH
2
, —SH, —OH, —NH
2
, or substituted or unsubstituted alkoxycarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, alkoxy, alkylamino, dialkylamino, alkanoylamino, arylcarboxamido, hydrazino, alkylhydrazino, hydroxylamino, alkoxylamino, alkylthio, alkenyl, aryl, or alkyl.
The transition metal complexes of the present invention are effectively employed as redox mediators in electrochemical sensors, given their very fast kinetics. More particularly, when a transition metal complex of this invention is so employed, rapid electron exchange between the transition metal complex and the enzyme and/or the working electrode in the sensor device occurs. This electron exchange is sufficiently rapid to facilitate the transfer of electrons to the working electrode that might otherwise be transferred to another electron scavenger in the system. The fast kinetics of the mediator is generally enhanced when L
2
of a mediator of the formula provided above is a negatively charged ligand.
The transition metal complexes of the present invention are also quite stable. For example, when such a complex is used as a mediator in an electrochemical sensor, the chemical stability is generally such that the predominant reactions in which the mediator participates are the electron-transfer reaction between the mediator and the enzyme and the electrochemical redox reaction at the working electrode. The chemical stability may be enhanced when a mediator of the formula provided above, wherein L
2
is a negatively charged ligand, has a “bulky” chemical ligand, L
1
, that shields the redox center, M, and thereby reduces undesirable chemical reactivity beyond the desired electrochemical activity.
The electrochemical stability of the transition metal complexes of the present invention is also quite desirable. For example, when such a complex is used as a mediator in an electrochemical sensor, the mediator is able to operate in a range of redox potentials at which electrochemical activity of common interfering species is minimized and good kinetic activity of the mediator is maintained.
Thus, the present invention provides novel transition metal complexes that are particularly useful as redox mediators in electrochemical sensing applications. The advantageous properties and characteristics of the transition metal complexes of the present invention make them ideal candidates for use in the electrochemical sensing of glucose, an application of particular importance in the treatment of diabetes in human populations.
DETAILED DESCRIPTION
When used herein, the definitions set forth below in quotations define the stated term.
The term “alkyl” includes linear or branched, saturated aliphatic hydrocarbons. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl and the like. Unless otherwise noted, the term “alkyl” includes both alkyl and cycloalkyl groups.
The term “alkoxy” describes an alkyl group joined to the remain
Heller Adam
Mao Fei
Olsen Kaj K.
Parsons Hsue & de Runtz LLP
TheraSense Inc.
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