MOLECULAR PROBE FOR SELECTIVE DETECTION OF COPPER (II) IONS
20220144758 · 2022-05-12
Assignee
Inventors
Cpc classification
International classification
G01N21/25
PHYSICS
Abstract
Multifunctional dendritic molecular probes that selectively detect Cu.sup.2+ ions via potentiometric and fluorometric techniques with low detection limits are disclosed. The selective and reversible binding of the molecules with the Cu.sup.2+ ion was used to make solid-state microsensors by incorporating the molecular probes into the carbon-based membranes as an ionophore for Cu (II).
Claims
1. A compound having formula (I): ##STR00004## or a salt, an isomer, or tautomer thereof, wherein: R.sup.1, R.sup.2, and R.sup.6 are independently H, optionally substituted C1-C18 alkyl, C1-C18 optionally substituted C6-C18 aryl, or optionally substituted C5-C18 heteroaryl, and R.sup.3, R.sup.4, and R.sup.5 are C1-C18 alkyl optionally substituted with a C6-C18 aryl or a C5-C18 heteroaryl.
2. The compound of claim 1, wherein R.sup.3, R.sup.4, and R.sup.5 are independently optionally substituted benzyl.
3. The compound of claim 1, wherein R.sup.3, R.sup.4, and R.sup.5 are benzyl.
4. The compound of claim 1, wherein R.sup.1 and R.sup.2 are independently H, methyl, or ethyl.
5. The compound of claim 1, wherein R.sup.1 and R.sup.2 are methyl and R.sup.6 is H.
6. The compound of claim 1, wherein the compound is: ##STR00005##
7. A carbon-based membrane comprising a compound of claim 1 bound to the membrane.
8. The membrane of claim 7, wherein the compound is bound covalently or non-covalently.
9. A sensor comprising the membrane of claim 7.
10. The sensor of claim 9, wherein the sensor is a potentiometric, fluorimetric, or colorimetric sensor.
11. The sensor of claim 9, wherein the sensor is a potentiometric sensor with Cu.sup.2+ ion detection limit of about 3.5 μM and/or a fluorimetric sensor with Cu.sup.2+ ion detection limit of about 15 nM.
12. A Cu.sup.2+-selective electrode comprising a solid electron conductor in electrical contact with an ion-selective polymeric composition comprising a compound of claim 1.
13. The electrode of claim 12, wherein the solid electron conductor is a copper wire.
14. The electrode of claim 12, wherein the ion-selective polymeric composition further comprises: (a) tetraphenyl borate, tetrakis(4-chlorophenyl) borate, tetrakis [3,4-bis(trifluoromethyl) phenyl] borate, or a combination thereof, (b) polyvinyl chloride (PVC); (c) dioctyl sebacate (DOS), 1-nitro-2-(n-octyloxy) benzene (NPOE), or a combination thereof, and (d) carbon.
15. The electrode of claim 12, wherein the ion-selective polymeric composition further comprises tetraphenylborate, PVC, DOS, and Vulcan carbon powder.
16. A colorimetric device comprising a membrane impregnated with a compound of claim 1.
17. The colorimetric device of claim 16, wherein the membrane is a cellulose membrane.
Description
DESCRIPTION OF THE DRAWINGS
[0016] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee.
[0017] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.
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DETAILED DESCRIPTION
[0035] In one aspect, the disclosure provides a Cu (II) ionophore useful as a dual probe for potentiometry and fluorimetry. With this ionophore, Cu (II) ion concentration is quantitated using a single multifunctional molecule for both potentiometry and fluorometry, instead of two separate molecules for each method. Furthermore, by incorporating a strong hydrophobic fluorophore, such as a cinnamaldehyde derivative, into the dendron molecule, the Cu (II) ionophore is also useful as a fluoroionophore for Cu (II).
[0036] The disclosure provides a Cu (II) ionophore molecule that is selective against major transitional metal ions in addition to alkali and alkaline earth metal ions. The dendritic ionophore provides reversible binding with Cu (II) by using a dendritic moiety along with an attached cinnamaldehyde component resulting in a multifunctional dendritic molecular probe for the selective and sensitive detection of Cu (II). The dendritic molecular probe can act as an ionophore for potentiometric methods, and incorporation of a cinnamaldehyde moiety in the ionophore allows it to become a fluorescent molecular probe to detect Cu.sup.2+ ions. The selective and reversible binding of the molecule to Cu.sup.2+ was used to make a solid-state micro-ion selective electrode (ISE) by incorporating the multifunctional ionophore into the carbon-based membrane to detect Cu (II) with high selectivity and fast response time.
[0037] The inventors of the present disclosure recognized the need for improved compositions and methods for detecting Cu (II) ions. In embodiments, the present disclosure describes compounds and compositions useful as a molecular probe capable of selectively detecting Cu.sup.2+ ions via potentiometric, colorimetric, and fluorometric techniques with low detection limits.
[0038] In one aspect, the disclosure provides a compound of formula (I):
##STR00002##
[0039] or a salt, an isomer, or tautomer thereof, wherein:
[0040] R.sup.1, R.sup.2, and R.sup.6 are independently H, optionally substituted C1-C18 alkyl, optionally substituted C3-C18 alkenyl, optionally substituted C3-C18 alkynyl, optionally substituted C6-C18 aryl, or optionally substituted C5-C18 heteroaryl, and
[0041] R.sup.3, R.sup.4, and R.sup.5 are C1-C18 alkyl, C2-C18 alkenyl, or C2-C18 alkynyl, each of which is optionally substituted with a C6-C18 aryl or a C5-C18 heteroaryl.
[0042] As used herein, the terms “alkyl,” “alkenyl,” and “alkynyl” include straight-chain, branched-chain, and cyclic monovalent hydrocarbyl radicals, and combinations of these, which contain only C and H when they are unsubstituted. Examples include methyl, ethyl, isobutyl, cyclohexyl, cyclopentylethyl, 2-propenyl, 3-butynyl, and the like. The total number of carbon atoms in each such group is sometimes described herein, e.g., when the group can contain up to ten carbon atoms, it can be represented as 1-10C, as C1-C10, C.sub.1-C.sub.10, C.sub.1-10, C-C10, or C1-10.
[0043] The terms “heteroalkyl,” “heteroalkenyl,” and “heteroalkynyl,” as used herein, mean the corresponding hydrocarbons wherein one or more chain carbon atoms have been replaced by a heteroatom. Exemplary heteroatoms include N, O, S, and P. When heteroatoms are allowed to replace carbon atoms, for example, in heteroalkyl groups, the numbers describing the group, though still written as, for example, C3-C10, represents the sum of the number of carbon atoms in the cycle or chain and the number of such heteroatoms that are included as replacements for carbon atoms in the cycle or chain being described.
[0044] A single group can include more than one type of multiple bond, or more than one multiple bonds; such groups are included within the definition of the term “alkenyl” when they contain at least one carbon-carbon double bond, and are included within the term “alkynyl” when they contain at least one carbon-carbon triple bond.
[0045] “Aromatic” or “aryl” substituent or moiety refers to a monocyclic or fused bicyclic moiety having the well-known characteristics of aromaticity; examples include phenyl and naphthyl. Similarly, the terms “heteroaromatic” and “heteroaryl” refer to such monocyclic or fused bicyclic ring systems which contain as ring members one or more heteroatoms. Suitable heteroatoms include N, O, and S, inclusion of which permits aromaticity in 5-membered rings as well as 6-membered rings. When heteroatoms are allowed to replace carbon atoms, the numbers describing the group, though still written as, for example, C5-C10, represent the sum of the number of carbon atoms in the cycle or chain and the number of such heteroatoms that are included as replacements for carbon atoms in the cycle or chain being described. Typical heteroaromatic systems include monocyclic C5-C6 aromatic groups such as pyridyl, pyrimidyl, pyrazinyl, thienyl, furanyl, pyrrolyl, pyrazolyl, thiazolyl, oxazolyl, and imidazolyl, and fused bicyclic moieties formed by fusing one of these monocyclic groups with a phenyl ring or with any of the heteroaromatic monocyclic groups to form a C8-C10 bicyclic group such as indolyl, benzimidazolyl, indazolyl, benzotriazolyl, isoquinolyl, quinolyl, benzothiazolyl, benzofuranyl, pyrazolopyridyl, quinazolinyl, quinoxalinyl, cinnolinyl, and the like. Any monocyclic or fused ring bicyclic system which has the characteristics of aromaticity in terms of electron distribution throughout the ring system is included in this definition. It also includes bicyclic groups where at least the ring which is directly attached to the remainder of the molecule has the characteristics of aromaticity. Typically, the ring systems contain 5-12 ring member atoms. Preferably, the monocyclic heteroaryls contain 5-6 ring members, and the bicyclic heteroaryls contain 8-10 ring members.
[0046] The moieties described above can be optionally substituted with a variety of substituents. “Optionally substituted,” as used herein, indicates that the particular group being described may have one or more hydrogen substituents replaced by a non-hydrogen substituent, such as C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl, C5-C12 aryl, C1-C8 acyl, and heteroforms of these, each of which can itself be further substituted; other substituents include halogens (F, Cl, Br, I), OR, NR.sub.2, SR, SO.sub.2R, SO.sub.2NR.sub.2, NRSO.sub.2R, NRCONR.sub.2, NRC(O)OR, NRC(O)R, CN, C(O)OR, C(O)NR.sub.2, OC(O)R, C(O)R, and NO.sub.2, wherein each R is independently H, C1-C8 alkyl, C2-C8 heteroalkyl, C2-C8 alkenyl, C2-C8 heteroalkenyl, C2-C8 alkynyl, C2-C8 heteroalkynyl, C6-C10 aryl, C5-C10 heteroaryl, C7-C12 arylalkyl, or C6-C12 heteroarylalkyl, and each R is optionally substituted as described above for alkyl groups.
[0047] In some embodiments of formula (I), the aryl and heteroaryl substituents are optionally substituted with one or more halogens.
[0048] In some embodiments, R.sup.3, R.sup.4, and R.sup.5 are independently optionally substituted benzyl. In some embodiments, R.sup.3, R.sup.4, and R.sup.5 are independently benzyl.
[0049] In some embodiments, R.sup.1 and R.sup.2 are independently H, methyl, or ethyl. In some embodiments, R.sup.6 is H, methyl, or ethyl. In some embodiments, R.sup.6 is H. In some embodiments, R.sup.1 and R.sup.2 are methyl.
[0050] In certain embodiments, the compound is:
##STR00003##
[0051] The compounds of the disclosure selectively form a complex with a Cu.sup.2+ ion in the presence of other cations. Thus, the compounds of the disclosure can act as Cu (II) ionophore molecules that are selective against major transitional metal ions in addition to alkali and alkaline earth metal ions. In some embodiments, the compound and/or the sensor are selective over H.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+, Ca.sup.2+, Fe.sup.2+, Co.sup.2+, Zn.sup.2+, and Pb.sup.2+ ions. Without being bound by theory, the compounds reversibly bind with Cu (II), thus acting as multifunctional dendritic molecular probes for the selective and sensitive detection of Cu (II). In some embodiments, the compound's fluorescence is quenched upon complexing with a Cu.sup.2+ ion. In some embodiments, the compounds can act as an ionophore for potentiometric methods, as well as a fluorescent molecular probe to detect Cu.sup.2+ ions.
[0052] In another aspect, provided herein is a carbon-based membrane comprising a compound of formula (I) or formula (II). The compound can be incorporated into the membrane by any suitable means, for example, the compound can be bound covalently or non-covalently (e.g., by hydrophobic interactions).
[0053] In a further aspect, the disclosure provides a sensor comprising a membrane and/or a compound of the disclosure. The sensors of the disclosure can be used as potentiometric, fluorometric, or colorimetric sensors. In some embodiments, the sensor is a potentiometric sensor with a Cu.sup.2+ ion detection limit of about 3.5 μM or lower and/or a fluorometric sensor with a Cu.sup.2+ ion detection limit of about 15 nM or lower.
[0054] In certain embodiments, the disclosure provides a Cu (II) selective electrode, comprising a solid electron conductor in electrical contact with an ion-selective polymeric composition comprising a compound of formula (I) or formula (II) (e.g., a carbon-based membrane of the disclosure). Any suitable electron conductor can be used in the electrodes of the disclosure, for example, a copper or other electroconductive wire.
[0055] In some embodiments, the Cu (II) selective electrode is a solid-state microsensor (e.g., a sensor having a diameter of about 25 μm) prepared by incorporating a compound of the disclosure into a carbon-based membrane as an ionophore for Cu (II). In some embodiments, the Cu (II) selective electrode of the disclosure has a high selectivity and fast response time.
[0056] In some embodiments, the Cu (II) selective electrode has a broad linear range, e.g., about 10 μM to about 1 mM, and/or a Nernstian slope or a near Nernstian slope (e.g., of 30 mV/log [a.sub.Cu.sub.
[0057] In certain embodiments, the ion-selective composition or membrane of the sensors of the disclosure is prepared from a mixture that comprises: (a) tetraphenyl borate, tetrakis(4-chlorophenyl) borate, tetrakis[3,4-bis(trifluoromethyl) phenyl] borate, or a combination thereof; (b) polyvinyl chloride (PVC); (c) dioctyl sebacate (DOS), 1-nitro-2-(n-octyloxy) benzene (NPOE), or a combination thereof; (d) one or more compounds of formula (I) or formula (II), and (e) carbon. In certain of these embodiments, the ion-selective composition is prepared from a mixture comprising tetraphenylborate, PVC, DOS, Vulcan carbon powder, and one or more compounds of formula (I) or (II).
[0058] Representative Cu (II) selective membrane components of the disclosure can be used in the electrodes illustrated in
[0059] In some embodiments, the selectivity coefficients of this Cu.sup.2+ microsensor are log K.sub.Cu.sup.2+, .sub.A=−2.13, −3.80, −3.15, −3.42, −3.09, −2.55, −3.10, −3.00, and −2.21 for H.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+, Ca.sup.2+, Fe.sup.2+, Co.sup.2+, Zn.sup.2+, and Pb.sup.2+, respectively. The presence of hydrophobic dendritic moiety in the compounds of the disclosure makes them less prone to leaching from a hydrophobic membrane in an aqueous matrix, while the cinnamaldehyde component of the molecule helps in the detection of Cu.sup.2+ ions fluorometrically, as indicated by a change in fluorescence upon selective and reversible binding of the molecular probe to the Cu.sup.2+ ions. The strategic design of the molecular probe allows us to detect Cu.sup.2+ ions in drinking water by using the Cu (II) solid-state microsensor.
[0060] In another aspect, the disclosure provides a colorimetric device comprising a membrane impregnated with one or more compounds of formula (I) or (II). In some embodiments, the membrane is a cellulose membrane. In some embodiments, the colorimetric device is disposable. In some embodiments, the colorimetric device is a device that can be used for water testing (e.g., a test strip for testing tap water for the presence of Cu(II)).
[0061] The following is a description of representative Cu (II) ionophore compounds, their compositions (e.g., ionophore-containing membranes), and sensors (e.g., ion-selective electrodes) and their use in potentiometric, fluorometric, and colorimetric determination of Cu (II) ions.
[0062] Molecular Design of a Representative Cu (II) Ionophore and Fluorometric Characterization
[0063] The disclosed design for a representative molecular probe (Cu (II) ionophore compound of formula (II) shown in
[0064] To gain additional insights into the binding mode in the CMD-Cu.sup.2+ complex, the FT-IR spectra of the free CMD (1 mM) and CMD-Cu.sup.2+ (1:1) complex in methanol were obtained (
[0065] Potentiometric Characterization of a Representative Cu (II) Ionophore
[0066] The disclosed Cu (II) ionophore can be used as an ionophore for constructing a solid-state ISE for the detection of Cu (II) via potentiometry. A solid-state micro-ISE was constructed with the CMD as the ionophore, PVC as the binding polymer, a plasticizer, a hydrophobic anion, and Vulcan carbon, which gives a near Nernstian response of 30 mV/log [a.sub.Cu.sub.
TABLE-US-00001 TABLE 1 Composition and characterization of carbon-packed sensors, including slope, linear range, and detection limit (number of experiments = 6). Molar Linear Slope Plasticizer PVC VC ratio range (mV/log DL I (%) LA (%) (%) (%) (%) (LA:I) (M) [a.sub.Cu.sup.2+]) (μM) 6.9 KTCPB NPOE (30) 3 58.1 0.3 10.sup.−5-10.sup.−3 11.8 ± 4.2 13.8 ± 1.8 (2.0) 6.9 KTCPB NPOE (30) 3 56.8 0.6 10.sup.−5-10.sup.−3 12.5 ± 1.3 11.1 ± 0.8 (3.3) 6.9 KTCPB DOS (30) 3 56.8 0.2 10.sup.−5-10.sup.−3 14.8 ± 2.5 10.0 ± 3.3 (1.4) 6.9 KTCPB DOS (30) 3 56.8 0.6 10.sup.−5-10.sup.−3 17.2 ± 3.0 7.8 ± 2.2 (3.3) 10 KTCPB DOS (30) 3 53.5 0.4 10.sup.−5-10.sup.−3 16.0 ± 1.0 9.6 ± 0.9 (3.5) 10 KTCPB DOS (30) 3 52.5 0.6 10.sup.−5-10.sup.−3 19.4 ± 0.5 16.2 ± 2.5 (4.5) 10 NaTFPB DOS (30) 3 51.0 0.4 10.sup.−5-10.sup.−3 15.0 ± 3.6 334.1 ± 105.8 (6.0) 7 NaTPB DOS (30) 3 58.0 0.5 10.sup.−5-10.sup.−3 7.1 ± 2.8 54.2 ± 34.7 (2.0) 10 NaTPB DOS (30) 3 55.6 0.3 10.sup.−5-10.sup.−3 23.6 ± 7.2 3.0 ± 1.0 (1.4) 10 NaTPB DOS (30) 3 54.2 0.5 10.sup.−5-10.sup.−3 29.3 ± 2.9 3.5 ± 1.0 (2.8) I: ionophore; LA: lipophilic anion; PVC: polyvinyl chloride; VC: vinyl chloride; DL: detection limit; KTCPB: potassium tetrakis(4-chlorophenyl) borate; NaTFPB: sodium tetrakis [3,4-bis(trifluoromethyl) phenyl] borate; NaTPB: sodium tetraphenylborate; NPOE: 1-nitro-2-(n-octyloxy) benzene; DOS: dioctyl sebacate.
[0067] The effect of pH on the sensor was measured in the presence of 10.sup.−3 M CuCl.sub.2. The pH of the solution was adjusted by using either 0.1 M HCl or 0.1 M NaOH.
TABLE-US-00002 TABLE 2 Comparison table for the sensing performance between the ISEs made with CMD as ionophore vs. ISEs containing the commercially available Cu (II) ionophore I. Parameters CMD Cu (II) ionophore I Detection limit (μM) 3.5 0.14 Slope (mV/decade) 29.3 29 Response time (s) 1.5 9 pH range 3.5-6.0 3.2-5.5
[0068] Detection of Cu.sup.2+ in Tap Water
[0069] The Cu (II) micro-ISE was used to measure the amount of copper present in tap water collected from the main campus of Oregon State University (OSU). The CMD ionophore was also used as a fluorometric Cu (II) sensor to measure the amount of Cu.sup.2+ in the same tap water sample. Further, the results of the quantitative analysis were compared with those of inductively coupled plasma-optical emission spectrometry (ICP-OES) as a standard technique (Table 2). The calibration plot obtained with ICP-OES is shown in
TABLE-US-00003 TABLE 3 Water samples were collected, and the amount of Cu.sup.2+ was found in samples by using a Cu.sup.2+ ion-selective electrode (ISE) and atomic absorption spectroscopy (AAS) (number of experiments = 3). Water Sample ISE Fluorimetry ICP-OES Tap water 38.0 ± 1.7 μM 38.9 ± 0.9 μM 38.0 ± 0.9 μM (Gilbert Hall Addition at Oregon State University)
[0070] Paper-Based Colorimetric Cu.sup.2+ Sensor Using Cinnamaldehyde Modified Dendron Molecule (CMD)
[0071] Colorimetric detection of copper ion was investigated using cinnamaldehyde modified dendron molecule compound of formula (II) (CMD). The color change of CMD solutions was observed by dissolving 5 mg of CMD in 0.150 mL of DMF followed by the addition of 0.850 mL of aqueous Cu.sup.2+ ion (different concentrations from 1 μM to 1 mM). A distinct color change was observed from green to yellow to orange to red. Table 4 shows the results of the hydrogelation test with cinnamaldehyde modified dendron (CMD).
TABLE-US-00004 TABLE 4 Hydrogelation Test. Gelator DMF Other components Other Observed (mg) (mL) (mL) components Color 5 0.150 0.850 1 mM CuCl.sub.2 Green 5 0.150 0.850 10 mM CuCl.sub.2 Light yellow 5 0.150 0.850 100 mM CuCl.sub.2 Yellow 5 0.150 0.850 1 mM CuCl.sub.2 Light Orange 5 0.150 0.850 10 mM CuCl.sub.2 Orange 5 0.150 0.850 100 mM CuCl.sub.2 Light red 5 0.150 0.850 1M CuCl.sub.2 Red
[0072] The CMD molecule can be used to make a paper-based colorimetric device. The color change of CMD-containing paper by drop-casting 1.5 μL of 55 mM CMD (in DMF) on several Whatman #1 filter paper and on top of those drop-casted spots, 1.5 μL of different concentrations of aqueous solutions of Cu.sup.2+ ions (CuCl.sub.2) were drop-casted. A distinct color change was observed when different concentrations of copper ion was added. After the addition of copper to the CMD drop casted filter paper, the final color of the paper was photographed and analyzed using ImageJ software. Using ImageJ, the colored picture was split into Red, Green, and Blue channels, and the respective intensity value was analyzed and plotted against log[Cu.sup.2+ ] to obtain a calibration curve for Cu.sup.2+. Using this method, an unknown concentration of Cu.sup.2+ ion can be detected. [#1-9:0 μM (control experiment), 0.1 μM, 1 μM, 10 uM, 100 μM, 1 mM, 10 mM, 100 mM, 1 M]. Referring to
[0073] As used herein, the terms “Cu.sup.2+ ions” and “Cu (II) ions” are used interchangeably.
[0074] As used herein, the term “about” indicates that the subject value can be modified by plus or minus 5% and still fall within the disclosed embodiment.
[0075] All publications cited herein and the subject matter for which they are cited are hereby specifically incorporated by reference in their entireties.
[0076] The following examples are provided for the purpose of illustrating, not limiting, the invention. The examples demonstrate the design and synthesis of an exemplary molecular probe to detect Cu (II) by using both potentiometric and fluorometric methods. With the fluorometric technique, up to 15 nM Cu.sup.2+ could be detected, and the compound shows selectivity toward Cu.sup.2+ ions when tested against common metal ions such as H.sup.+, Na.sup.+, K.sup.+, Ca.sup.2+, Mg.sup.2+, and Zn.sup.2+. The molecular probe was used as an ionophore to develop a carbon-based solid-state micro-ISE to detect Cu (II) in a drinking water sample. The selectivity of the ionophore represents an improvement of at least one order of magnitude over the commercial ionophore and has a fast response time (1.5 s). With its improved selectivity and response time, this exemplary microsensor can be used to detect Cu (II) ions in micro-volumes, which also makes it compatible with scanning electrochemical microscopy (SECM).
EXAMPLES
[0077] The following examples describe the preparation of an exemplary Cu (II) ionophore compound useful as a dual probe for potentiometry and fluorimetry that allows quantification of Cu (II) ion concentration by using a single multifunctional molecule instead of two different molecules for potentiometry and fluorimetry separately.
[0078] Materials
[0079] All starting materials for the synthesis of cinnamaldehyde modified dendron (CMD) were obtained from Sigma-Aldrich. Vulcan carbon was obtained from Cabot Corporation. PVC was purchased from Aldrich. Tetramethyl silane was purchased from CIL. Potassium tetrakis(4-chlorophenyl) borate (KTCPB), sodium tetrakis [3,4-bis(trifluoromethyl) phenyl] borate (NaTFPB), and dioctyl sebacate (DOS) were purchased from TCI. 1-Nitro-2-(n-octyloxy) benzene (NPOE) was purchased from Alfa Aesar. An anion excluder, sodium tetraphenylborate (NaTPB), was obtained from Merck, and metal chlorides (M.sup.n+=Na.sup.+, K.sup.+, Mg.sup.2+, Ca.sup.2+, Cu.sup.2+, Fe.sup.2+, Co.sup.2+, Zn.sup.2+, and Pb.sup.2+) from TCI were used without any further purification. Deionized water (18 MΩ) was used to make aqueous solutions.
[0080] Instrumentation
[0081] Amperometric measurements were performed by using a CHI potentiostat (model #760 E, CHI, Austin, Tex., USA). A three-electrode system is comprising a working electrode, an Ag/AgCl reference electrode, and a Pt wire as the counter electrode were used. Potentiometric experiments were performed with a high-impedance unit (Lawson Labs, EMF 6) along with Ag/AgCl (1 M KCl) reference electrodes.
[0082] Ionophore Development Strategy
[0083] An ionophore should reversibly bind to the analyte with high selectivity and should be insoluble in aqueous solutions to use the ISE in water samples. Because hydrazide derivatives are known to bind Cu.sup.2+ ions, a benzo hydrazide-modified dendritic structure was developed, along with a cinnamaldehyde modification, to provide a multifunctional molecular probe for Cu.sup.2+ ions that is effective for both potentiometry and fluorimetry. The dendric molecular component in the molecule makes it hydrophobic, and the attached cinnamaldehyde moiety allows it to be a fluorescent molecular probe.
[0084] Synthesis of CMD
[0085] 3,4,5-Tris(benzyloxy)benzohydrazide (2 g, 0.0044 mol) and N,N-dimethyl cinnamaldehyde (1.0305 g, 0.0057 mol) were dissolved in a CHCl.sub.3 (15 mL) and MeOH (45 mL) mixture. The reagent mixtures were stirred at 65° C. for 36 h under N.sub.2 atmosphere. After 36 h, the reaction mixture was concentrated in vacuo and the compound purified by flash chromatography over silica gel as the stationary phase. The elution was performed with 15% MeOH in CHCl.sub.3 to give the pure product as a yellow solid (experimental yield 55%). .sup.1H NMR (700 MHz, DMSO-d.sub.6) δ: 2.97 (s, CH.sub.3, 6H), 5.03 (s, CH.sub.2, 2H), 5.21 (s, CH.sub.2, 4H), 6.85 (dd, J=8.2 Hz, CH, 1H), 6.92 (d, J=15.8 Hz, CH, 1H), 6.72-7.50 (m, ArH & PhH, 21H), 8.20 (d, J=9.2 Hz, CH═N, 1H), 11.47 (s, CONH, 1H) (
[0086] UV-Vis Spectroscopy
[0087] UV-Vis spectra of the ionophore (2×10.sup.−5 M) were obtained in a methanol solution. The UV-Vis absorption spectrum showed a characteristic peak of cinnamaldehyde centered at 387 nm. Job's plot was obtained to quantify the metal-to-ligand binding stoichiometry. Furthermore, the binding constant was acquired in a separate experiment by varying the stoichiometry between the metal and the ligand, and the Benesi-Hildebrand plot was obtained to calculate the binding constant from the slope of the plot.
[0088] Fluorescence Characterization and Quantifications of Cu (II)
[0089] The ionophore (2×10.sup.−5 M) showed strong fluorescence emission centered at 520 nm when excited at 387 nm. The fluorescence response was tested in the presence of different metal ions in a 1:1 mol equivalent ratio to find the selectivity of the molecular probe toward Cu.sup.2+. A calibration plot was obtained with varying concentrations of Cu.sup.2+ ions by using fluorescence intensity, which demonstrates the ability of the ionophore to act as a molecular fluorescence probe.
[0090] FT-IR Characterization
[0091] The FT-IR spectrum of the 10 mM of CMD and CMD with Cu.sup.2+ ions (1:1 mol ratio) was obtained using an FTIR spectrometer (PerkinElmer, Model: Spectrum II). The analyte solution was drop casted on a potassium bromide crystal optic disc (purchased from Alfa Aesar).
[0092] Fabrication of Cu.sup.2+ Microsensor
[0093] A borosilicate glass capillary (o.d. 1.5 mm, i.d. 0.86 mm) was first pulled with a pipette puller (Sutter Instruments, Novato, Calif., USA), and then polished to obtain an inner tip diameter of 25 μm (RG<2) to make a Cu.sup.2+ ion-selective microprobe. After optimization of the membrane components, the best ratio of the membrane components was determined. The ion-selective cocktail was prepared by mixing 10% ionophore, 2.8% tetraphenylborate, 3% PVC, 30% DOS, 54.2% Vulcan carbon powder, and 500 μL tetrahydrofuran (THF). The composition was mixed thoroughly with a glass rod on a watch glass until all THF evaporated. An extra 40.00% of DOS was further added to the membrane components to maintain consistency in a sensor paste. The pulled capillary was then backfilled with the sensor paste and pushed it to the pulled end with a Cu wire. To make electrical contact between the sensor paste and the inserted Cu wire, 5.00% Vulcan carbon in a DOS mixture was added to the pipette from the back-opening side. The Cu wire connection was secured by applying 10 min epoxy to the junction of the capillary end and the Cu wire. The sensor tip was polished with lens cleaning paper and cured overnight in 1 mM CuCl.sub.2 solution before the calibration of the Cu (II) microsensor.
[0094] Measurement Selectivity Coefficients
[0095] The selectivity coefficients against different metal ions were determined by the mixed solution (fixed interference) method. Background concentrations of 10.sup.−2 M solution for alkaline earth and transition metal cations and 10.sup.−1 M for alkali metal cations were used.
[0096] Drinking Water Sample Preparation
[0097] The water samples (tap water at Oregon State University, Corvallis, USA) were pretreated by filtering with Whatman #1 filter paper, and then the pH was adjusted to 5.5 by using 1 M HCl. The measurement was carried out three times by using both potentiometry and atomic absorption spectroscopy after the calibration.
[0098] While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.