WO2002071057A1

WO2002071057A1 - Ionophore-based sensors

Info

Publication number: WO2002071057A1
Application number: PCT/US2002/006537
Authority: WO
Inventors: Jik Chin; Seok Jong Lee; Steven J. West
Original assignee: Thermo Orion Inc.
Priority date: 2001-03-05
Filing date: 2002-03-01
Publication date: 2002-09-12

Abstract

Disclosed are chemical sensors for the detection of ammonium ion. Also disclosed are ionophores designed for use in chemical sensors for the detection of ammonium ion. The ionophores contain a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs, inducing selectivity of said chemical sensors toward ammonium ion.

Description

PCT APPLICATION Docket No. 4518/00013

-IONOPHORE-BASED SENSORS

PRIORITY CLAIM

This application claims priority from two commonly owned pending Provisional Applications, Serial No. 60/273,700, filed 05 March 2001 and Serial No. 60/273,735 filed 05 March 2001, the disclosures of which are hereby incorporated herein by reference.

FIELD OF THE INVENTION

Disclosed are chemical sensors for the detection of ionic species, particularly the ammonium ion.. These sensors are based on ionophores containing a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs, inducing selectivity of said chemical sensors toward ammonium ion. Also disclosed are specific ionophores for chemical sensors used for the detection of ionic species, particularly the ammonium ion. The ionophores preferably containing a plurality of pyrazole rings.

BACKGROUND OF THE INVENTION

The following version of the Nernst-Nikolski equation is in general use for expression of the selectivity behavior of ISEs: £

where E is the measured potential of the ISE; E' is a constant depending on the reference electrode and other invariant features of the measurement cell; the term RT/F has its usual thermodynamic definition; α_t is the activity of the primary ion, "t", in other words the ISE's "target" ion; a, is the activity of any interfering ion "/; and K^*' ^∑J is the selectivity coefficient of the ISE toward the ion, i, relative to an interfering ion, j; and z and z, are the ionic charges of the ions i and j respectively.

For convenience, the selectivity coefficient is often expressed as a base- 10 logarithm. In the terms commonly employed in ISE technology, a more negative value for the logarithm of a selectivity coefficient indicates greater "preference" of the ISE for the primary ion, i.e., greater "discrimination" of the interfering ion. A value of zero indicates no preference or discrimination, and a positive value indicates preference for the interfering ion.

INFORMATION DISCLOSURE

For many years, the macrotetrolide antibiotic "nonactin", first described as an ionophore for ISEs by Scholer and Simon (Chimia 1970, 24, 372-4), has served as the workhorse ionophore in polymer membrane ammonium ISEs. Its structure is shown in Figure 1 and its selectivity towards ammonium compared to other common cations is shown in Table 1. A weakness of nonactin-based ISEs is the only modest discrimination of ammonium over potassium (logic ₊ ^₊ = -1.1 ).

Suzuki, et al. (Anal. Chem. 2000, 72, 2200-2205) have recently reported ammonium ISEs based on an ionophore they designate as TD19C6 (see, Figure 2). Improvement in the selectivity of the Suzuki ISE for ammonium ion over sodium ion when compared to nonactin-based ISEs is notable as shown in Table 1.

Kim, et al. (Anal. Chem. 2000, 72, 4683-4688) have recently reported ammonium ISEs based on ionophores they designate as derivatives of TDB18C6. Figure 3 illustrates one example. Selectivity of the Kim ISE for ammonium ion over sodium ion is further improved over Suzuki as shown in Table 1.

Λ l τ ,

Table 1. Selectivity Coefficients, log* NH_t 1*,

¹ Siswanta, D.; Hisamoto, H.; Tohma, H.; Yama oto, N.; Suzuki, K. Chem. Lett. 1994, 945.

² Suzuki, K.; Siswanta, D.; Otsuka, T.; Amano, T.; Ikeda, T.; Hisamoto, H.; Yoshihara, R.; Ohba, S. Anal. Chem. 2000, 72, 2200.

³ Kim, H. S.; Park, H. J.; Oh, H. J.; Koh, Y. K.; Choi, J. H.; Lee, D. H.; Cha, G. S.; Nam, H. Anal. Chem 2000, 72, 4683. SUMMARY OF THE INVENTION

In one embodiment, the present invention comprises polymer- membrane, ammonium-selective ISEs, or other chemical sensors, based on a new type of compound as ammonium-selective ionophore.

In another embodiment, the present invention is directed to ionophores designed especially for use in polymer-membrane, ammonium- selective ISEs, or other chemical sensors, based on a new type of compound as ammonium-selective ionophore.

Two preferred examples of this type of ionophore are depicted diagrammatically in Figure 4 and Figure 5 and are referred to as herein respectively as Compound 6 and Compound 11. A structure for the ammonium complex of Compound 6, as determined by X-ray crystallography, is shown in Figure 6. Compound 6 has the empirical formula C4oH4₃ 9. Compound 11 has the empirical formula C₃₃H₃6Ng.

Figure 6 shows that complexation with ammonium is accomplished through hydrogen bonding — the four hydrogen atoms of the ammonium ion hydrogen-bond to nitrogen atoms on "pyrazole" rings in the ionophores.

One preferred embodiment of the present invention is thus directed to chemical sensors for the detection of ammonium ion based on ionophores containing a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs, inducing selectivity of said chemical sensors toward ammonium ion.

Another preferred embodiment of the present invention is thus directed to the ionophores employed in chemical sensors for the detection of ammonium ion. As taught herein, these ionophores preferably containing a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs, inducing selectivity of said chemical sensors toward ammonium ion. Preferably, the number of pyrazole rings on the ionophore is four. More preferably, the ionophore has the structure shown in either Figure 4 or Figure 5. If desired, the ionophore may be a derivative of Compounds 6 or 11, which has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect the basicity of the pyrazole nitrogens and therefore modify the compound's ammonium- complexing properties.

If desired, the ionophore may be a derivative of Compounds 6 or 11, where the ionophore has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect size of the cavity into which the ammonium ion fits and therefore modify the compound's ammonium-complexing properties.

As described above, the ionophores of the present invention are designed for use in chemical sensors. One preferred chemical sensor using these ionophores is an electrochemical sensor, such as an ion selective electrode. One especially preferred ISE is used to detect the ammonium ion (NH₄ ⁺). Species other than the ammonium ion may likewise be detected using sensors according to this technology. For instance, another preferred chemical sensor is an optical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the chemical structure of the compound nonactin.

Figure 2 illustrates the chemical structure of the compound TD19C6.

Figure 3 illustrates the chemical structure of the compound TBD18C6.

Figure 4 illustrates the chemical structure of Compound 6, one of the preferred ionophores of the present invention. Figure 5 illustrates the chemical structure of Compound 11, one of the preferred ionophores of the present invention.

Figure 6 illustrates the chemical structure for the ammonium complex of Compound 6, as determined by X-ray crystallography.

Figure 7 illustrates the chemical structure of Compound 11, with labels added thereto identifying various functional portions of the structure.

Figure 8 illustrates one preferred synthetic scheme (Scheme 1) used to synthesize new ionophore receptors for the ammonium ion (NH₄ ⁺) .

Figure 9 illustrates another preferred synthetic scheme (Scheme 2) used to synthesize new ionophore receptors for the ammonium ion (NH₄ ⁺).

Figure 10 illustrates the formation of Compounds 7 and 12 from Compounds 6 and 11 respectively, as complexed with NH4PF6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, one embodiment of this invention is directed particularly to polymer-membrane ion-selective electrodes (ISEs) for ionic species, especially the ammonium ion (NH ⁺). The ammonium ISEs of the present application have improved selectivity over certain interfering cations compared to ISEs of prior art. This improved selectivity is conferred through the use of a newly developed type of ionophore. Methods for the synthesis of this type of ionophore and use in ISE membranes are taught in detail below..

Another preferred embodiment of this invention is directed particularly to ionophores which can be employed in polymer-membrane ion- selective electrodes (ISEs) for ionic species, especially the ammonium ion (NH₄ ⁺). The ammonium ISEs made using the ionophores of the present application have improved selectivity over certain interfering cations compared to ISEs of prior art. Methods for the synthesis of the new ionophores and the use thereof in ISE membranes are taught in detail below..

For the purpose of this detailed description, we will label certain parts of the molecular structure of Compound 6 and Compound 11. See, Figure 7.

As illustrated in Figure 7, these molecules both have four pyrazole rings labeled PI, P2, P3, and P4. PI, P2, and P3 are connected to the central benzene ring via a methylene group connected to the nitrogen labeled "Nl" on the pyrazole ring. PI and P2 have methyl substituents on the carbons labeled CI and C3. P3 has no methyl groups on CI and C3, but C3 is connected to a pyridine ring at a position adjacent to the pyridine nitrogen. Connected to the other adjacent carbon of the pyridine ring is the carbon labeled CI of the pyrazole ring labeled P4.

In Compound 11 , there are no substituents on P4 (except hydrogen atoms, not shown in the diagrams except on Nl). Compound 6 has a benzyl substituent on Nl of P4.

As labeled above and shown in Figure 7, the "N2" nitrogens of the four pyrazole rings are the sites to which the hydrogen atoms of an ammonium ion are bound in forming a complex with either Compound 6 or Compound 11.

In Figure 6 it can be seen that the ammonium ion sits in a cup- shaped cavity formed when pyrazole groups PI, P2, and P3 are oriented on the same side of the central benzene ring. P4, attached to P3 via the pyridine ring, wraps around to serve as a "lid" on the cup and thus the ammonium ion is completely enclosed by the ionophore.

It will be understood by those having ordinary skill in the chemical arts that many variations on the basic structures of Compound 6 and Compound 11 are possible that will not interfere with the ability of the compounds to complex ammonium ions, and in some cases may enhance complexation of ammonium compared to other ions. Thus one embodiment of the present invention includes derivatives of Compounds 6 and 11.

One parameter that may be expected to affect the complexation of ammonium and other ions is the basicity of the "N2" nitrogens in the pyrazole rings. Substituents, both directly on these rings and at other locations on the ionophore molecules, that have the properties of being "electron withdrawing" or "electron donating" might be expected to affect the basicity of these nitrogens and therefore the ammonium complexing properties of the molecules.

It will likewise be understood that insertion of "spacer" groups, such as methylene, when added to or removed from positions between the rings and elsewhere on the molecule may have the effect of optimizing the size of the cavity in which ammonium ion is enclosed and thereby enhance complexation of ammonium.

It will be noted that Compound 6 and Compound 11 differ in that a relatively bulky constituent, a benzyl group, which occupies the same position (N 1 of P4) in Compound 6 as a hydrogen atom in Compound 11 and yet, as shown in Table 1, both compounds can be used as ionophores in ammonium ISEs resulting in improved selectivity.

Likewise it will be recognized by those having ordinary skill in the chemical arts that these ionophores will likely be useful as components of other types of chemical sensors, for example, optical chemical sensors, although it is only their use in electrochemical sensors that is described here. Such alternative chemical sensor uses are likewise considered to be an embodiment of the present invention.

The present invention will be further illustrated with reference to the following examples which aid in the understanding of the present invention, but which are not to be construed as limitations thereof. All percentages reported herein, unless otherwise specified, are percent by weight. All temperatures are expressed in degrees Celsius.

Compound 6 and Compound 11 were incorporated into plasticized PVC membranes for evaluation as ammonium ISEs. Formulation of such membranes is well established technology. The subsequent ISEs were evaluated for selectivity towards ammonium ion relative to other common cations and the results appear in the Table 1. The selectivity constants were determined using the "fixed interference method", a technique well known to those versed in the art.

Example 1:

The following components were dissolved in 1.0 mL of tetrahydrofuran:

Compound 6 1.0 mg

Potassium tetrakis 4-chlorophenyl borate 0.5 mg

PVC 66 mg

2-Fluorophenyl-2-nitrophenyl ether 33 mg

Example 2:

The following components were dissolved in 1.0 mL of tetrahydrofuran:

Compound 11 1.0 mg

Potassium tetrakis 4-chlorophenyl borate 0.6 mg

PVC 66 mg

2-Fluorophenyl-2-nitrophenyl ether 33 mg

Those having ordinary skill in this field will understand the roles of these components in the order listed: ionophore to impart selectivity, inert anionic sites for charge balance, polymer as inert matrix, plasticizer to serve as hydrophobic membrane phase. With both membrane formulations, a rigid PVC tube with perforated end-cap served as the ISE body. The membrane solutions were deposited dropwise on the end-cap of the inverted tube while the perforations were blocked by a Teflon mandrill. After evaporation of the solvent (THF), the mandrill was removed. A 0.01 M solution of ammonium chloride was then placed in the ISE body and a silver-silver chloride wire inserted as internal reference. The ISEs were conditioned overnight in 0.01 M ammonium chloride in order to exchange the potassium ions from the borate salt with ammonium. Potential measurements were made using a pH meter and off- the-shelf reference electrode.

It will be recognized by those having ordinary skill in this art that many other means of formulating ISE membranes have been described in the literature and might also be employed to fabricate ISEs based on Compound 6, Compound 11, or their derivatives.

It will likewise be recognized that sensors that respond to ammonium ion can be configured for the sensing of ammonia. Examples and further references can be found in the following publication: West, S.J., et al. Anal. Chem. 1992, 64, 533-540.

It will likewise be recognized that modification of these molecules, as described above, may result in molecules that have useful selectivity toward ions other than ammonium and may therefore find use in chemical sensors for species other than ammonium. Note that in the publication cited in the previous paragraph, ionophores that were traditionally used for sodium sensing found utility in ammonia sensors.

The compounds described herein may be prepared by conventional synthetic techniques. Two especially preferred synthetic schemes are provided in Figures 8 and 9. Figure 10 shows the complexation reactions of Compounds 6 and 11 with NH PFβ to produce compounds 7 and 12 respectively. The following examples provide the current preferred methods for the formation of these compounds:

Synthetic Procedures:

Compound 1A l,3,5-Tris(benzyloxymethyl)-2,4,6-trimethylbenzene:

Sodium hydride (60% dispersion in mineral oil, 662 mg, 16.55 mmol) was added a solution of benzyl alcohol (1.56 mL. 15.06 mmol) in THF (10 mL) at 0°C. After being stirred for 10 minutes at 0°C, the mixture was raised to room temperature, followed by additional stirring for 30 minutes. A solution of l₎3,5-tris(bromomethyl)-2,4,6-trimethylbenzene¹ (1.0 g, 2.51 mmol) in THF (5 mL) was added by syringe and the mixture was stirred for 12h at room temperature. The mixture was quenched with brine (30 mL), extracted with ethyl acetate (2 x 30 mL), dried over M_gSθ4, filtered, and concentrated by rotary evaporator. The crude product was purified by flash column chromatography on silica gel (eluent: EtOAc/Hexane = 1: 19) to give the desired product (711 mg, 59%) as white solids: *H NMR (CDCb, 200 MHz) δ 7.46-7.41 (m, 15H), 4.65 (s, 12H), 2.46 (s, 9H); FAB-MS m/z 503.1 ([M+Na]⁺, calculated 503.2.

Compound IB l-Bromomethyl-3,5-bis(benzyloxmethyl)~2,4,6-trimethylbenzene:

Sodium hydride (2.2 equiv), benzyl alcohol (2 equiv), and 3,5-tris (bromomethyl) 2,4,6- trimethylbenzene (10.0 g, 25.1 mmol) were treated as described above. Flash column chromatography on silica gel (eluent, EtOAc:Hexane = 1: 19) to give l-bromomethyl-3,5-bis(benzyloxmethyl)-2,4,6- trimethylbenzene (6.1 g. 54%) as white solids: ^JH NMR (CDCb, 400 MHz) δ 7.45-7.35 (m, 10H), 4.64 and 4.60 (each s, 10H), 2.46 (s, 6H), 2.43 (s, 3H); ¹³C NMR (CDCb) δ 139.5, 138.6, 138.2, 133.3, 132.5, 128.7, 128.3, 128.0, 72.9, 67.1, 31.4, 16.1, 15.7; FAB-MS m/z 453.0 ([M+H]⁺, calculated 453.1. Compound 2:

A suspension of sodium hydride (60% dispersion in mineral oil, 64 mg, 1.60 mmol) in CH₃CN (6 mL) was treated with 2,6~bis(3- pyrazol) pyridine² (309 mg, 1.46 mmol). After being stirred for 30 minutes at room temperature, a solution of l-bromomethyl-3,5-bis(benzyloxymethyl)- 2,4,6-trimethylbenzene (600 mg, 1.33 mmol) in CH₃CN (3 mL) was added by cannula. After being stirred for 40 minutes, the mixture was quenched with aqueous ammonium chloride solution (10 mL), evaporated to remove CH₃CN solvent, and then extracted with dichloromethane (3 x 15 mL). The combined organic layers were dried over MgS0₄, filtered, and concentrated by rotary evaporator. The crude product was purified by flash column chromatography on silica gel (eluent, EtOAc:Hexane = 1: 1) to give the desired product, Compound 2 (411 mg. 53%) as white solids: ^!H NMR (CDCb, 400 MHz) δ 7.93 (dd, J=1.2, 7.6 Hz, IH), 7.77 (t, J=7.6 Hz, IH). 7.65 (d, J=2.0 Hz, IH), 7.57 (brd, IH), 7.39-7.25 (m, 10H), 7.03 (d, J=2.4 Hz, IH), 6.85 (d, J=2.4 Hz, IH), 6.77 (brs, IH), 5.46 (a, 2H), 4.60 (s, 4H), 4.57 (s, 4H), 2.41 (a, 3H), 2.33 (s, 6H); ¹³C NMR (CDCb) δ 152.2, 151.7, 139.7, 138.9, 138.4, 137.7, 133.6, 129.9, 129.5. 128.6, 128.3, 128.0, 119.3. 118.7. 104.5, 103.3, 94.6, 73.1, 67.1, 51.4, 16.2, 16.0; FAB-MS m/z 584.2 ([M+H]⁺), calculated 584.2.

Compound 3:

Sodium hydride (1.5 equiv), Compound 2 (240 mg, 0.41 mmol), and benzyl bromide (1.3 equiv) were treated as described above. Flash column chromatography on silica gel (eluent, EtOAc:Hexane = 1 :3 and 1:2) to give the desired product, Compound 3 (211 mg, 76%) as colorless syrups: Η NMR (CDCb, 400 MHz) δ 7.92-7.89 (m, 2H), 7.74 (t, 1=8.0 Hz, IH), 7.39- 7.23 (m, 16H), 7.05 (d, J=2.0 Hz, IH), 7.00 (d, J=2.4 Hz, IH), 6.91 (d, J=2.4 Hz, IH), 5.46 (s, 2H), 5.38 (s, 2H), 4.59 (s, 4H), 456 (s, 4H), 2.41 (s, 3H), 2.32 (s, 6H); ¹³C NMR (CDCb) δ 152.6, 152.5, 152.2, 152.1, 139.6, 138.9, 138.4, 137.2, 136.8. 133.5, 130.9, 129.7, 129.0, 128.7, 128.3, 128.0, 127.9, 118.7, 105.6, 104.5, 73.1, 61.1, 56.4, 51.4, 16.2, 16.0; FAB-MS m/z 674.2 ([M+H]⁺), calculated 674.3. Compound 4:

A solution of Compound 3 (150 mg, 0.22 mmol) in 8N HCI (5 mL) was refluxed for 2h. After cooling at room temperature, the solution was concentrated to remove the excess HCI, diluted with water (5 mL), basified to pH 9-10 with 4N NaOH, and extracted with dichloromethane (3 x 30 mL). The combined organic layers were dried over MgSθ4, filtered, and concentrated to give the desired product, Compound 4 (116 mg, 98%) as colorless oils: Η NMR (CDCb, 400 MHz) δ 7.92-7.88 (m, 2H), 7.73-7.69 (m, IH), 7.40-7.23 (m, 6H), 7.06-7.04 (m, 2H), 6.97-6.96 (m, IH), 5.44 (s, 2H), 5.36 (s, 2H), 4.66 (s, 4H), 2.50 (s, 3H), 2.41 (s, 6H); ¹³C NMR (CDCb) δ 152.6,

152.5, 152.1, 152.0, 139.0, 138.4, 137.2, 136.8, 133.7, 131.0, 130.8, 129.7. 129.0, 128.3, 127.9, 118.8, 118.7, 105.5. 104.8, 56.4, 51.2, 42.0, 16.1, 15.6; FAB-MS m/z 530.0 ([M+H]⁺), calculated 530.1.

Compound 5:

Sodium hydride (60% dispersion in mineral oil, 19 mg, 0.472 mmol) was added a solution of pyrazole (32 mg. 0.472 mmol) in THF (2 mL) at 0°C. After being stirred for 10 minutes at 0°C, the mixture was raised to room temperature, followed by additional stirring for 20 minutes. A solution of Compound 4 (50 mg, 0.094 mmol) in THF (1 mL) was added by syringe and the mixture was stirred overnight at room temperature. The mixture was quenched with water (5 mL), extracted with dichloromethane (2 x 10 mL), dried over MgSθ4, filtered, and concentrated to give the desired product, Compound 5 (55 mg, 99%): ^lH NMR (CDCb, 400 MHz) δ 7.93-7.86 (m, 2H), 7.74 (t, J=8.0 Hz, IH), 7.54 (d, J=2.0 Hz, 2H), 7.40 (d, J=2.4 Hz, IH), 7.35- 7.23 (m, 6H), 7.07 (d, J=2.0 Hz, 2H), 7.06-7.05 (m, 2H), 6.98 (d, J=2.4 Hz, IH), 6.21 (dd, J=2.0, 2.4 Hz, 2H), 5.51 (s, 2H), 5.45 (s, 4H), 5.39 (s, 2H), 2.38 (s, 6H), 2.36 (s, 3H); ¹³C NMR (CDCb) δ 152.0, 139.8, 139.7, 137.4, 136.7,

131.6, 131.2, 130.9, 129.5, 129.0, 128.3, 128.2, 127.9, 118.9, 118.8, 105.8, 105.6, 105.0, 56.5, 51.3, 50.9, 29.9, 16.6, 16.5. Compound 6:

Sodium hydride (5 equiv), 3,5-dimethyl pyrazole (5 equiv), and Compound 4 (68 mg, 0.128 mmol) were treated as described above in 98% yield (84 mg): ^JH NMR (CDCb, 400 MHz) δ 7.91-7.86 (m, 2H), 7.73 (t, J=7.6 Hz, IH), 7.39 (d, J =2.4 Hz, IH), 7.34-7.23 (m, 5H), 7.08 (d, J=2.0 Hz, IH) 7.04 (d, J=2.0 Hz, IH), 6.92 (d, J=2.0 Hz, IH), 5.76 (s, 2H), 5.49 (s, 2H), 5.39 (s, 2H), 5.22 (s, 4H), 2.31 (s, 3H), 2.29 (s, 6H), 2.15 (s, 6H), 2.11 (s, 6H) ¹³C NMR (CDCb) δ 147.4, 139.0, 138.8, 137.2, 132.1, 130.9, 130.2, 129.7, 129.0, 128.2, 127.9, 118.7, 105.5, 104.5. 56.4, 51.4, 48.4, 29.9, 16.9, 16.6, 13.8. 11.5; FAB-MS m/z 650.3 ([M+H]⁺, calculated 650.3.

Compound 7:

Colorless crystals of Compound 7 were obtained by recrystallizing stoichiometric amounts of Compound 6 (65 mg, 0.10 mmol) and NH4PF6 (16.3 mg, 0.10 mmol) from hot ethanol (3 mL) in 75% yield (~1 mg): Η NMR (CDCb-CD₃OD, 8:1), 400 MHz) 6 7.82 (t, J=8.4 Hz, IH), 7.70-7.64 (m, 3H), 7.54 (d, J=2.0 Hz, IH), 7.26-7.18 (m, 3H), 7.12-7.08 (m, 2H), 6.88 (d, J=2.0 Hz, IH), 6.83 (d, J=2.8 Hz, IH), 5.80 (s, 2H), 5.54 (s, 2H), 5.21 (s, 2H), 5.20 Cs, 4H), 4.09 (brs, 4H, NH₄), 2.47 (s, 3H), 2.36 (s, 6H), 2.10 (s, 6H), 1.69 (s, 6H).

Compound 8:

Sodium hydride (1.5 equiv), Compound 2 (125 mg, 0.21 mmol), and methoxybenzyl -chloride (MPMC1, 1.3 equiv) were treated as a same procedure of preparation of Compound 2, but using THF in place of CH3CN, to give the desired product, Compound 8 (135 mg, 90%) as colorless oils: 'H NMR, (CDCb, 400 MHz) δ 7.94-7.91 (m, 2H), 7.75 (t, J=8.0 Hz, IH), 7.41- 7.28 (m, 11H), 7.22 (d, J=8.4 Hz, 2H), 7.04 (d, J=2.4 Hz, IH), 7.02 (d, J=2.0 Hz, IH), 6.93 (d, J=2.4 Hz, IH), 6.88 (d, J=8.4 Hz, 2H), 5.48 (s, 2H). 5.32 (s, 2H), 4.61 (s, 4H), 4.58 (s, 4H), 3.79 (s, 3H), 2.43 (s, 3H), 2.34 (s, 6H); ¹³C NMR (CDCb) δ 159.7, 152.5, 152.4, 152.2, 139.6, 138.9, 138.4, 137.2, 133.5, 130.6, 129.7, 129.5, 128.7, 128.6, 128.3, 128.0, 118.7, 114.4, 105.4,

104.5, 73.1, 67.1, 56.0. 55.5, 51.4, 16.2, 16.0; FAB-MS m/z 704.3 ([M+H)⁺), calculated 704.3.

Compound 9:

A solution of Compound 8 (135 mg, 0.19 mmol) in 8N HCI (6 mL) was refluxed for 2h. After cooling at 0°C, the solution was basified to pH 9-10 with 4N NaOH and extracted with dichloromethane (3 x 25 mL). The combined organic layers were dried over MgS0 , filtered, and concentrated to give the desired product Compound 9 (105 mg, 99%) as white solids: ^XH NMR (CDCb, 400 MHz) δ 7.91-7.87 (m, 2H), 7.74 (t, J=8.0 Hz, IH), 7.35 (d, J=2.0 Hz, IH), 7.21 (d, J=8.4 Hz, 2H), 7.02-7.01 (m, 2H), 6.94 (d, J=2.8 Hz, IH), 6.87 (d, J=8.4 Hz, 2H), 5.47 (s, 2H), 5.31 (s, 2H), 4.70 (s, 4H), 3.78 (s, 3H), 2.53 (s, 3H), 2.43 (s, 6H); ¹³C NMR (CDCb) δ 159.7, 152.6, 152.3, 152.2, 152.0, 139.1, 138.4, 137.2, 133.7, 130.7, 130.6, 129.6, 129.5, 128.7, 118.8, 118.7, 114.4, 105.4, 104.8, 56.0, 55.5, 51.2, 41.9, 16.1, 15.7; FAB-MS m/z 560.1 ([M+H]⁺), calculated 560.1.

Compound 10:

Sodium hydride (5 equiv), 3,5-dimethyl pyrazole (5 equiv), and Compound 9 (105 mg, 0.19 mmol) were treated to the same procedure used for the preparation of Compound 5 to give the desired product, Compound 10 (128 mg, 99%) as colorless syrups: *H NMR (CDCb, 400 MHz) δ 7.91-7.87 (m, 2H), 7.73 (t, J=8.0 Hz, IH), 7.34 (d, J=2.0 Hz, IH), 7.21 (d, J=8.4 Hz, 2H), 7.06 (d, J=14.0 Hz, IH), 7.01 (d, J=2.0 Hz, IH), 6.92 (d, J=2.0 Hz, IH), 6.87 (d, J=8.4 Hz, 2H), 5.76 (s, 2H), 5.48 (s, 2H), 5.31 (s, 2H), 5.21 (s, 4H), 3.78 (s, 3H), 2.29 (brs, 9H), 2.15 (s, 6H), 2.10 (s, 6H); ¹³C NMR (CDCb) δ

159.6, 152.5, 152.4, 152.1, 147.4, 139.3, 139.1, 138.8, 137.2, 132.2, 130.6, 130.2, 129.7, 129.5, 128.7, 118.7, 118.6, 114.4, 105.5, 105.4. 104.6, 56.0, 55.5, 51.4, 48.5, 16.9, 16.7, 13.9, 11.5; FAB-MS m/z 680.3 ([M+H]⁺), calculated 680.3. Compound l l³:

To a solution of Compound 10 (75 mg, 0.11 mmol) in 5 mL of CH3CN- H2O (4: 1) was added eerie ammonium nitrate (242 mg, 0.44 mmol) and the reaction mixture was stirred at room temperature for 5h and then diluted with brine (10 mL). The reaction mixture was extracted with EtOAc (3 x 20 mL). The combined EtOAc layers were dried over MgS0₄ and concentrated. The crude product was purified by flash column chromatography on silica gel (eluent, MeOH:EtOAc, 1: 19) to give the desired product, Compound 11. (40 mg, 65%) as white solids: Η NMR (CDCb, 300 MHz) δ 7.87 (d, J=7.8 Hz, IH), 7.76 (t, J=7.8 Hz, IH), 7.64 (d, J=2.1 Hz, IH), 1.56 (d, J=7.8 Hz, IH), 7.17 (d, J=2.1 Hz, IH), 6.87 (d, J=2.1 Hz, IH), 6.77 (d, J=2.1 Hz, IH), 5.77 (s, 2H), 5.50 (s, 2H), 5.21 (s, 4H), 2.30 (s, 6H), 2.29 (s, 3H), 2.15 (s, 6H), 2.14 (s, 6H); ¹³C NMR (CDCb) δ 152.1, 151.7, 147.5, 139.4, 139.1, 138.8, 131.7, 132.1, 130.2, 129.9, 119.2, 118.7, 105.5, 104.5, 103.3, 51.4, 48.2, 16.8, 16.6, 13.8, 11.5; FAB-MS m/z 560.2 ([M+H]⁺), calculated 560.3.

Compound 12:

A mixture of Compound 11 (16 mg, 0.028 mmol) and NH₄PFe (4.6 mg, 0.028 mmol) in ethanol (2 mL) was stirred for 2h at room temperature, followed by concentration to give Compound 12, (quantitative yield) as white solids; Η NMR (CDCb, 400 MHz) δ 7.80-7.74 (m, 3H), 7.62-7.31 (m, 6H including 4H of NH₄), 6.81 (d, J=2.0 Hz, IH), 6.69 (d, J=2.4 Hz, IH), 5.77 (s, 2H), 5.51 (s, 2H), 5.11 and 5.05 (two peak, 4H), 2.34 (s, 6H), 2.32 (s, 3H), 2.14 (s, 6H), 1.79 (s, 6H).

The following references provide background information for the above examples. To the extent necessary, they are hereby incorporated herein by reference.

1. a) van der Made, A. W.; van der Made, R. H. J. Org. Chem., 1993, 58, 1262-1263, b) Zavada, J.; Pankova, M.; Holy, P.; Tichy, M. Synthesis, 1994, 1132. 2. a) Brumer, H.; Scheck, T. Chem Ber., 1992, 125, 701-709, b) Lin, Y.; Lang, Jr., S. A. J. Heterocyclic Chem., 1977, 14, 345

3. Burgess, K.; Liu, L. T.; Pal, B. J. Org. Chem., 1993, 58, 4758-4763.

The present invention has been described in detail, including the preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and/or improvements on this invention and still be within the scope and spirit of this invention as set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. Chemical sensors for the detection of ammonium ion based on ionophores containing a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs, inducing selectivity of said chemical sensors toward ammonium ion.

2. A chemical sensor as in Claim 1 where the number of pyrazole rings on the ionophore is four.

3. A chemical sensor as in Claim 1 where the ionophore has the structure shown in Figure 4.

4. A chemical sensor as in Claim 1 where the ionophore has the structure shown in Figure 5.

5. A chemical sensor as in Claim 1 where the ionophore has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect the basicity of the pyrazole nitrogens and therefore modify the compound's ammonium- complexing properties.

6. A chemical sensor as in Claim 1 where the ionophore has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect size of the cavity into which the ammonium ion fits and therefore modify the compound's ammonium-complexing properties.

7. A chemical sensor as in Claim 1 that is an electrochemical sensor.

8. A chemical sensor as in Claim 7 that is an ion-selective electrode.

9. A chemical sensor as in Claim 1 that is an optical sensor.

10. A chemical sensor as in Claim 1 that is configured to sense ammonia.

11. A chemical sensor as in Claim 1 that has useful selectivity toward a species other than ammonium.

12. An ionophore containing a plurality of pyrazole rings, so arranged that complexation of ammonium ion occurs.

13. An ionophore as in Claim 12, where the number of pyrazole rings on the ionophore is four.

14. An ionophore as in Claim 12, which has the structure shown in Figure 4.

15. An ionophore as in Claim 12, which has the structure shown in Figure 5.

16. An ionophore as in Claim 12, where the ionophore has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect the basicity of the pyrazole nitrogens and therefore modify the compound's ammonium- complexing properties.

17. An ionophore as in Claim 12, where the ionophore has a structure differing from those shown in Figure 4 or Figure 5 insofar as substituent groups are added or removed that affect size of the cavity into which the ammonium ion fits and therefore modify the compound's ammonium- complexing properties.