WO1994004507A1 - Basket porphyrin oxygen carriers - Google Patents

Abstract

A dioxygen-binding complex of the 'picnic-basket' porphyrin type. The complex includes a phenylporphyrin structure, a metal M bound to the phenylporphyrin structure, where M is iron or cobalt, a strap structure attached to the phenylporphyrin structure and comprising a bridge linkage Y, where Y is X, X-CH2, or CH2-X-CH2, where X is O, S, S(=O), S(=O)2, NR, or +NRR', and R and R' are the same or different and are a hydrogen or a lower alkane, and a neutral, sigma-donating ligand, L, which binds to the metal on the open side of the phenylporphyrin structure. Use of the complex for extracting oxygen from a fluid and as a component in an oxygen sensor is also disclosed.

Description

BASKET PORPHYRIN OXYGEN CARRIERS

Portions of the research conducted in support of the present invention were sponsored by the National Institutes of Health, Grant No. GM17880.

1. Field of the Invention

The present invention relates to basket porphyrin compounds and their use as oxygen carriers.

2. References

Aldrichimica Acta 2_2:2 (1989).

Block, E. , Reactions of Orcranosulfur Compounds . A.T. Blomquist and H.H. Wasserman, eds., Academic Press, NY (1978) .

Borch, R.F., et al . , J. Am . Chem . Soc . 93 :12 (1971) .

Campbell, J. Org. Chem . 29:1830 (1964). Collman, J.P., et al., J. Am. Chem. Soc, 97:7185 (1975).

Collman, J.P., et al . , J . Am . Chem . Soc , 100:2761 (1978) .

Collman, J.P., et al., Proc. Nat. Acad. Sci., USA, 75:564 (1978) . Collman, J.P., et al., J. Am. Chem. Soc, 103:2450 (1981).

Collman, J.P. , et al., J. Am. Chem. Soc, 105:3052 (1983).

Collman, J.P., et a 1 . , Inorg . Chem . 22:1427-1432 (1983).

Collman, J.P., et al. (1988) J. Am. Chem. Soc. 110:3477-3486.

Elliott, CM. (1980) Anal. Chem. 52:666-668. Gilbert, E.E., Sulfonation and Related Reactions, ch. 2, Interscience Publishers, John Wiley & Sons, NY (1965) . Greenwald, R. , et al. , 2_8:1128 (1963). Harmon, R.E., et al . , J . Org. Chem . 34:11 (1969) .

Komatsu, T. , et al., J. Chem. Soc. Co mun. , 66 (1990) .

Lee, D.G., The Oxidation of Organic Compounds by Permanσenate Ion and Hexavalent Chromium, ch. 2, Open Court, LaSalle, IL (1980) .

Linard, J.E., et al., J. Am. Chem. Soc, 102:1896 (1980).

Lindsey, J. (1980) J. Org. Chem. 45:5215. Momenteau, M. , et al., J. Chem. Soc. Commun., 962 (1983).

Momenteau, M. , et al., J. Chem. Soc Commun., 341 (1982) .

Moroz, A.A. , et al . , Ruεεian Chem . Rev . 43:8 (1974) .

Sorrell, T.N. (1980) Inorg. Synth. 20:161-169. Suslick, K.S., J . Am . Chem . Soc , 105:3507 (1983).

Testaferri, L. , et al . , Syntheεiε pp. 751-755 (1983) .

Traylor, T.G., et al., J. Am. Chem. Soc, 103:5234 (1981). Traylor, T.G. , et al., J. Am. Chem. Soc, 107:604 (1985) .

Trost, B.M., et al . , Tetrahedron Letters 22:14 (1981) .

Uemori, Y. , and Kyuno, E. (198S) Inorg. Chem. 28:1690-1694.

3. Background of the Invention

A variety of synthetic porphyrins designed to mimic biological oxygen carriers have been proposed. Some examples include "capped" porphyrinε (see ref. 1 1975, 1981; Baldwin) , "bridged" porphyrins (Batter- sby, 1976, 1978) ; "picket fence" porphyrins (Collman, 1973, 1975), "pocket" porphyrins (Collman, 1981, 1983), "basket-handle" porphyrins (Momenteau, 1979, 1980, 1983, "gyroscope" porphyrins (Lecas, Boitrel) , "cyclophane" porphyrins (Diekmann, Traylor) , and "jelly-fish" type porphyrins (Uemori) .

Ideally, a synthetic oxygen carrier or binding compound should be easy to synthesize, have a high oxygen-binding affinity and yet be amenable to deoxygenation under selected conditions, be resistant to oxidative degradation, and be able to withstand heating without isomerization.

The development of metal porphyrins which have these qualities would have important commercial applications in a variety of areas, such as removal of oxygen from impure gases, oxygen-extraction from gases and liquids, and in oxygen sensors.

4. Summary of the Invention

The present invention includes, in one aspect, a dioxygen-binding complex of the form, when oxygenated:

where M is Fe or Co; L is a neutral, sigma- donating ligand; Y is X, X-CH₂, X-(CH₂)₂-X, or CH₂-X- CH₂, where X is 0, S, S(=0) , S(=0)₂, NR, or ⁺NRR' , and R and R' are the same or different and are a hydrogen or a lower alkane. The complex, in a toluene-soluble form, is characterized by a Pι₂(0₂) value, when measured in toluene containing 1,5-dicyclohexyl- imidazole, at 25°C, of less than about 40 Torr when M is Co, and less than about 0.5 Torr when M is Fe. The amidophenyl rings in the porphyrin skeletal structure may be unsubstituted or substituted, for example, with sulfonate groups, to enhance the water- solubility of the compound. Alternatively, a ring substituent may be used in anchoring the compound to a solid support.

Also forming part of the invention is a method for extracting oxygen from an oxygen-containing fluid. The method includes exposing an oxygen- containing fluid to an oxygen-binding complex of the type described above.

In one application, the method is designed for removing dioxygen in free form from an aqueous solution. The imidophenyl rings in the porphyrin skeletal structure of the oxygen-binding complex are substituted at one or more ring positions with substituents having terminal acid groups, preferably sulfonate groups, and the complex has an octanol/water partition coefficient less than 1.

In another application, the method is designed for extracting oxygen from an oxygen-containing gas mixture, where the oxygen-binding complex is attached to an oxygen-permeable membrane. The method includes exposing the gas to the membrane, on one side of the membrane, and applying a vacuum to the opposite side of the membrane, to draw off oxygen bound to the membrane via said complex.

Another application is designed for concentrating oxygen from an oxygen-containing fluid, where said complex is bound to a solid support.

After exposing the solid support to the fluid, the support is separated from the fluid and treated to remove bound oxygen.

These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.

Brief Description of the Drawings Fig. 1 shows a skeletal structure for oxygen- binding compounds of the present invention; Fig. 2 shows a reaction scheme used in synthesizing a porphyrin component for the oxygen- binding compounds of the present invention; Figs. 3A-3G show synthetic reaction schemes used in preparing a series of 'strap' structures for inclusion in the oxygen-binding compounds of the present invention;

Fig. 4 shows a reaction scheme for converting a 'strap' tetraester to a tetraacid chloride via a tetraacid.

Fig. 5 shows a reaction scheme used in sythesizing an un-metalated form of the oxygen- binding compounds of the present invention; Fig. 6 illustrates a synthesis of a water- soluble oxygen-binding compound of the present invention in an unmetalated form.

Fig. 7 shows a scheme for preparing an oxygenated form of an oxygen-binding compound of the present invention. Fig. 8 illustrates how an oxygen-binding compound of the invention can be modified in its strap region with a variety of chemical groups R.

Figs. 9A and 9B illustrate two types of covalent linkages of an oxygen-binding compound of the invention to a solid support.

Fig. 10 shows portions of a fiber-optic 0₂ sensor device utilizing the oxygen-binding compound of the invention.

Detailed Description of the Invention A skeletal structure (I) for a number of oxygen- binding compounds (also referred to herein as "picnic-basket porphyrins" or "porphyrin compounds") of the present invention is shown in Fig. 1. The oxygen-binding compounds of the invention generally comprise two main structural components: a 'phenylporphyrin' component (meso-α,α,α,α-tetrakis(o- aminophenyl)porphyrin) and a 'strap'component. The phenylporphyrin component contains four pyrrole nitrogen atoms for tightly binding metal ions. The 'strap' component includes two trivalent benzene rings linked to one another by a bridge linkage of variable length (one to four, and more preferably, one to three atoms) . Amide bonds connect the four carboxy groups of the strap to the four ortho-amino groups of the phenylporphyrin.

A reaction scheme described by Sorrell et al. (1980) for preparing a phenylporphyrin component of the present invention is shown in Fig. 2. Pyrrole

(IIB) is reacted with 2-nitrobenzaldehyde (IIA) to give jneso-tetrakis(o-nitrophenyl)porphyrin (III). This product in turn is reduced in the presence of SnCl₂ and HCl to give the tetraamino product as a mixture of four mutually interconvertable atropisomers. The α,α,α,α-atropisomer IV (in which all four amino groups reside on the same side of the porphyrin ring) can be enriched for and isolated in good yield by the method of Lindsey (1980) , although other isolation methods are known (Sorrell, 1980; and Elliott, 1980) . Details of the synthesis and isolation of meso-α,α,α,α:-tetrakis(o-aminophenyl)- porphyrin are given in Example 1. Figs. 3A-3G show synthetic schemes for preparing a number of 'strap' precursors to be incorporated into oxygen-binding compounds of the present invention. The straps include bridge linkages 'Y', which can be X, X-CH₂, X-(CH₂)₂-X, or CH₂-X-CH₂, where X is 0, S, S(=0), S(=0)₂, NR, or ⁺NRR' , and R and R' are the same or different and are a hydrogen or a lower alkane (i.e., an alkane having 1-4 carbon atoms) . In general, the straps are prepared first as tetraesters which are then converted via the tetracarboxylic acid to tetraacid chlorides for reaction with the phenylporphyrin of Fig. 2. In some cases, the strap can be prepared as a tetraacid, bypassing a tetraester species.

Fig. 3A shows a scheme for synthesizing a strap (VII) in which Y is 0CH₂CH,0 (Collman et al., 1988). The synthesis, detailed in Example 2A, involves the reaction of diethyl 5-hydroxyisophthalate (V) with 1,2-dibromoethane (VI). Fig. 3B shows a scheme for synthesizing a smaller, asymmetric strap where Y is CH₂0. The tetraester X is obtained from diethyl-5-bromomethylisophthalate (VII) and diethyl- 5-hydroxyisophthalate (IX) in high yield. Details of the synthesis are given in Example 2B. A reaction scheme for synthesizing a strap containing an oxygen atom linkage (XIV, Y = 0) is shown in Figure 3C. 3,5-Dimethylphenol XI and 1- bromo-3,5-dimethylbenzene XII are reacted in the presence of a copper catalyst to give the diarylether product XIII. The four methyl groups are then oxidized using KMn0₄ to give tetraacid XIV. Procedures for obtaining XIV are outlined in Example 2C. Fig. 3D illustrates a synthesis of a strap XVI (Y = CH₂OCH₂) by a method similiar to that used in Examples 2A and 2B.

Fig. 3E shows a reaction scheme for preparing a strap XX that contains a nitrogen atom in the bridge linkage (Y = CH₂N) . The scheme entails reacting 3,5-dicarbethoxybenzaldehyde XVII and diethyl 5- aminoisophthalate XVIII to form a Schiff base XIX, followed by reduction of the Schiff base with lithium cyanoborohydride to give tetraester XX. Procedures for obtaining XX are outlined in Example 2D. In addition, it should be appreciated that the amino nitrogen of the bridge can be alkylated using an alkylhalide or a mixture of alkylhalides to produce a tertiary or quaternary amine. A reaction scheme for preparing a strap containing an ethylene bridge is shown in Fig. 3F. The scheme involves the reaction of 3,5- dicarbethoxybenzaldehyde (XVII) with diethyl 5- bromomethylisophthalate in an ylide procedure that produces olefin XXI. Subsequent reduction with Wilkinson's catalyst (RhCl(PPh₃)₃) results in the desired product (XXII) . A synthetic protocol is given in Example 2E. Fig. 3G shows a reaction scheme for preparing a strap XXV (Y = S(=0)₂) that is one atom in length. l-bromo-3,5-dimethylbenzene XII and the sodium salt of 3,5-dimethyl-l-thiobenzene XXIII are reacted to give thioether XXIV, which is then oxidized to give the sulfone tetraacid XXV. A synthesis of XXV is outlined in Example 2F.

From the foregoing it should be readily apparent that a number of ^"different 'straps' having bridge linkages of different lengths and atom compositions can be prepared.

Figure 4 illustrates a general reaction scheme for converting a tetraester strap to a tetraacid chloride for subsequent reaction with the phenylporphyrin of Fig. 2 to give a picnic-basket porphyrin. The scheme is generally applicable to the various straps of the present invention and is illustrated in the Figure for the case where Y = CH₂0. As described in greater detail in Example 3, tetraester X is treated in a first step with concentrated aqueous sodium hydroxide in ethanol to precipitate the product tetraacid Xa as the sodium salt. The product is then dissolved in water and precipitated as the tetraacid Xa using 6 N HCl. In a second step, the resultant tetraacid is treated with thionyl chloride under reflux conditions to yield the tetraacid chloride XXVI. In cases where the strap is already produced as a tetraacid from monoaryl starting materials, only the second step (conversion of the tetraacid to the tetraacid chloride) is called for.

A general synthetic scheme for preparing a picnic-basket porphyrin according to the present invention is illustrated in Fig. 5 for the case where Y = CH₂0. Under dry conditions, α,α,α,Q.-tetra(o- aminophenyl)porphryin IV and tetraacid chloride XXVI are simultaneously added dropwise to a solution of CH₂C1₂ containing a small amount of triethylamine to trap HCl produced by the reaction. After completion of the addition, the reaction mixture is allowed to stir an additional 24 h at room temperature. The solution is then washed with saturated NaHC0₃ and saturated NaCl solutions, dried over Na₂S0₄, filtered, and evaporated to dryness. The residue is purified further by silica gel flash chromatrography, yielding purified picnic-basket porphyrin XXVII. Details of the above synthesis are provided in Example 4. For applications that require compounds of the present invention in water-soluble form, picnic- basket porphyrins prepared as above can be derivatized at one or more imidophenyl ring positions with substituents having terminal acid groups that impart water solubility to the porphyrin compound. Here, terminal acid groups are defined to include phosphonate, sulfonate, sulfinate, and carboxylate groups, which are attached either directly to the imidophenyl ring, or indirectly via 1 or 2 methylene groups. Preferably, the terminal acid groups are sulfonate groups.

Fig. 6 illustrates a reaction in which an unsubstituted porphyrin compound is treated with sulfuric acid to produce a sulfonated porphyrin derivative XXVIII containing sulfonate groups on the amidophenyl rings. A major site of sulfonation in each amidophenyl ring is the ring position para to the amido group. Details of a method of sulfonation are given in Example 5. A scheme for preparing oxygen-binding complexes of the present invention, in deoxygenated and oxygenated forms, is outlined in Fig. 7. The scheme includes three steps: metalation of the metal-free porphyrin XXVII to give a metal-porphyrin complex; addition of ligand L, which binds to the axial position of the metal on the "open" side of the heme (on the opposite side from the strap) to form a pentacoordinate, deoxygenated ligand-metal complex; and addition of oxygen, which binds to the axial position of the metal on the "inner" side of the heme (on the same side as the strap) to produce a hexacoordinate, oxygenated ligand-metal complex XXIX. Metalation (also termed "metal insertion") of the metal-free (unmetalated) porphyrin compound

(XXVII in the Figure) is accomplished by reaction with an iron or cobalt salt. As detailed further in Example 6, reaction of an unmetalated porphyrin compound with anhydrous FeBr₂ or CoBr₂ in an organic solvent under reflux conditions produces, after workup, the corresponding metal-porphyrin complex in high yield. Once bound to the porphyrin, the metal does not readily dissociate. However, the considerable sensitivity of iron-porphyrin complexes to oxidative degradation requires that metalation with iron be performed under scrupulously dry conditions, preferably in an inert-atmosphere box. A water-soluble porphyrin compound may also be metalated using the above conditions, but the compound must first be converted to a tetraalkylammonium salt or the like to be rendered soluble in the organic solvents above. Such conversion can be accomplished readily by use of a cation-exchange column. Following metalation, the resultant metalloporphyrin can be converted back to a water-soluble form by a second cation-exchange column (e.g. , using an exchange column (Na⁺ form) to produce the sodium salt of the metal-complex) . Irreversible oxidation of the metal in metalated porphyrin compounds to give oxidized derivatives that can no longer bind oxygen is a principle cause of degradation. The oxidation pathway involves the formation of a μ-peroxo-bridged metal-porphyrin dimer. Accordingly, it is desirable to construct a porphyrin complex so as to prevent the formation of a μ-peroxo-bridged dimer, while still allowing binding of dioxygen.

Accordingly, whereas the "inner" face of the metalloporphyrin is protected from dimer formation by steric encumbrance of the strap structure, protection of the "open" face of the porphyrin requires the presence of a neutral, sigma-donating ligand L, which can tightly bind the porphyrin metal on the "open" face of the porphyrin. Exemplary ligands include substituted as well as non-substituted nitrogen- containing aromatic heterocycles such as imidazole, pyridine, and pyrazine, and, less preferably, primary, secondary, and tertiary amines. Preferably, L is a 1,5-dialkylimidazole such as 1,5-dicyclo- hexylimidazole. Another preferred ligand is l- methylimidazole. Other substituted i idazoles can also be used, provided that at least one of the imidazole nitrogens remains unsubstituted. When the metalloporphyrin is free in solution, ligand is included in the solution typically in about a 100- to a 1000-fold excess, thereby minimizing the opportunity for oxygen to bind on the open face side of the metal. In solid phase, the ligand can be present in stoichiometric amounts, or is provided by the solid phase itself.

B. Oxygen-Binding Properties The oxygen-binding affinities of porphyrin complexes of the present invention can be measured by a UV-Vis spectrophoto etric titration method. Measurements are performed with the sample in the closed atmosphere, of defined volume, that is provided by a tonometer equipped with a cuvette and a septum. A solution containing the sample porphyrin complex is placed in the cuvette portion of the tonometer under an inert atmosphere, and then oxygen is introduced into the tomometer in a series of aliquots. After the addition of each aliquot, the tonometer is shaken to allow equilibration (for a few minutes) of oxygen with the sample solution, and then a UV-Vis spectrum of the sample is recorded. Measurement of the changing intensities of the absorbance peaks corresponding to the deoxygenated and oxygenated complexes allows the determination of the oxygen-binding affinity, as detailed in Example 7.

The oxygen-binding affinities of the Co(II) and Fe(II) complexes of two exemplary porphyrin compounds of the present invention are shown in Tables 1 and 2, in which the oxygen-binding affinities of prior art porphyrin compounds are included for comparison. Binding Affinity of Cobalt(II) Porphyrin Complexes

Table 1

0₂ Binding Affinity of Iron(II) Porphyrin Complexes

Table 2

The (*) in the lefthand column of Table 1 and 2 indicates a compound of the present invention. The (Ref) numbers in parentheses in the same column of these two tables indicate the literature citation for the compounds tested, as follows:

1. Collman, J.P., et al., Proc. Nat. Acad. Sci. , USA, 75:564

(1978).

2. Collman, J.P., et al., J. Am. Chem. Soc, 103:2450 (1981). 3. Collman, J.P. , et al., J. Am. Chem. Soc, 105:3052 (1983). 4. Traylor, T.G., et al., J. Am. Chem. Soc, 103:5234 (1981). 5. Traylor, T.G., et al., J. Am. Chem. Soc, 107:604 (1985). 6. Linard, J.E., et al., J. Am. Chem. Soc, 102:1896 (1980). 7. Collman, J.P. , et al., J. Am. Chem. Soc, 97:7185 (1975). 8. Momenteau, M. , et al., J. Chem. Soc Commun., 962 (1983). 9. Momenteau, M. , et al., J. Chem. Soc Commun., 341 (1982). 1100. Komatsu, T., et al., J. Chem. Soc Commun., 66 (1990). 11 Uemori, E., et al., Inorg. chem., 28:1690 (1989). 12 Suslick, K.S., J. Am. Chem. Soc, 105:3507 (1983). 13 Collman, J.P., et al., J. Am. Chem. Soc, 100:2761 (1978). As can be appreciated, the compounds of the present invention combine the unique features of (a) being thermal-resistant, in that they cannot be isomerized with heating and (b) having low P_1/2 (0₂) . This applies both to the Co and Fe complexes.

^C _' Applications

In one aspect, the invention includes a method for extracting oxygen from an oxygen-containing fluid. The method includes exposing an oxygen- containing fluid to the above-described oxygen- binding complex, producing the oxygenated form of the binding complex.

In one embodiment, the method is used in removing dioxygen in free form from an aqueous solution. In this embodiment, the oxygen-binding complex is derivatized, either at one or more of the imidophenyl rings in the porphyrin structure, or at a nitrogen atom in the strap in the structure, with chemical group(s) which result in good water solubility, preferably having an octanol/water partition coefficient of less than 1.

A water-soluble oxygen-binding compound suitable for use in an aqueous medium has been described above with respect to Fig. 6. The compound shown there contains one sulfonate group per imidophenyl ring in the skeletal structure of the binding compound. More generally, one or more of the rings are derivatized with substituents having free acid groups. Fig. 8 shows another approach to derivatizing the compound.

Here the compound contains a -N(H)-CH₂ strap, and allows for a variety of alkylated or acylated reactions at the strap amine, to produce a a desired R substituent on the strap, as indicated. Typically, the compound is complexed with Zn⁺², to protect the porphyrin amines, prior to the alkylation or acylation reactions.

In the present example, for use in producing a water-soluble derivative, the R group may be, for example, a long-chain polyethylene oxide (PEO) or a water-soluble polypeptide.

The water-soluble compound may be used to sequester molecular oxygen, for example, in an aqueous chemical solution or suspension in which oxidative reactions are to be limited.

In another general embodiment, the oxygen- binding compound is coupled to a solid support, for removing dioxygen from a fluid which is in contact with the support. Figs. 9A and 9B illustrate two general methods for attaching the compound to a support. In the method shown in Fig. 9A, the compound is anchored to the solid support, indicated at 50, by a linker 52 connected covalently to an amine group in the compound strap. Bifunctional linkers suitable for attaching the compound, e.g., through an amide linkage, to a solid support, e.g., through a carboxyl or OH group on the support, are well known. In the Fig. 9B embodiment, the compound is attached to a solid surface 56 via a ligand, such as an imidazole or pyridine ligand, using a suitable bifunctional reagent. Alternatively, the compound may be adsorbed to the surface by non-covalent attachment.

The solid support may be used for purifying an oxygen-containing gas, such as for removal of 0₂ from N₂, or for use in producing 0₂ in purified form. For example, the solid support may be formed on a shuttling structure which is operable between a collect position in which the solid support is in contact with an oxygen-containing fluid, such as air, and a release position, in which the bound oxygen is released from the support, e.g., by vacuum or heating. Alternatively, the support may be part of an electrode. Oxygen binding to the support occurs with the iron in the reduced state. To release bound oxygen, the metal is converted electrochemically to its oxidized state.

In a related embodiment, the method of the invention is used to extract 0₂ from a liquid or gaseous medium, by extraction of 0₂ through an oxygen-permeable polymeric membrane. Methods of forming porphyrin ring within an oxygen-permeable membrane are known (EPO 0464717 Al) . In a typical operation, the membrane is in contact with an oxygen- containing fluid on one side of the membrane, which may be a liquid from which 0₂ is to be extracted, or a gas containing 0₂ impurity, or a gas from which it is desired to obtain purified 0₂. Dioxygen in the fluid diffuses into the membrane and becomes bound to the oxygen-binding sites in the membrane. Molecular oxygen bound to the membrane can be removed from the sites, at the other side of the membrane, by applying a pressure differential across the membrane.

Fig. 10 shows an oxygen-sensor apparatus 60 constructed according to the invention. The apparatus includes an optical fiber probe 61 composed of a first fiber 62 having an end region which is prepared with a light-trans issive coating 65 of an oxygen-binding complex of claim 1, and a second fiber 64 which is adapted to receive light transmitted through the coating, when light is directed through the first fiber. As the coating in the probe is oxygenated, the spectral peak of the compound shifts.

The device further includes a light source or means 68 for producing a light in a selected wavelength between about 420 and 460 nm, and a sensor 70 for detecting light intensity directed from the distal end of fiber 64 back to a detection unit 72. Unit 72 is also designed to determine oxygen concentration, at the site of the fiber probe, from the time-dependent change in light intensity received by the sensor.

In a method for measuring oxygen pressure at a remote site, employing device 60, the probe is guided to a selected target site, i.e., a site within the vascular system of a patient. The time dependent change in spectral shift in light transmission is monitored to determine oxygen pressure at the site.

The following examples illustrate, but are not in any way intended to limit the scope of the invention.

EXAMPLES Reagents Iron dibromide (Strem) , cobalt dibro ide (Aldrich Chemical Co., Milwaukee, I) , and 1,5-dicyclohexylimidazole (Aldrich) were used as received. Solvents were distilled under a nitrogen atmosphere. Methylene chloride was distilled from P₂0₅. Methanol was dried and distilled from Mg(OMe),. Benzene, diethyl ether, tetrahydrofuran (THF) , and toluene were distilled from sodium benzophenone ketyl. Dry dimethylformamide was obtained by reduced pressure distillation from BaO. Thionyl chloride was distilled from triphenylphosphite. 2,6-Lutidine was stored over KOH and distilled from BaO. 1,2-Dimethylimidazole was distilled from KOH. Silica gel supplied by E. M. Science (Type 7736) was used for flash chromatography.

*H NMR Measurements

'H NMR spectra were obtained on a Nicolet NMC-300 or Varian XL-400 Spectrometer and referenced to the residual proton signals of the deuterated solvents. Fe(II) porphyrin NMR samples were prepared as follows. To an Fe(II) porphyrin, freshly prepared by metalation in a glovebox (0₂ < lppm) , CDC1₃ and 4-10 equivalents of imidazole were added, and the five-coordinate Fe(II) complexes were identified by their characteristic paramagnetic contact-shifted NMR spectra. These solutions were exposed to an atmosphere of 0₂ at room temperature, and spectra were obtained, also at room temperature. Amide protons of the porphyrins were identified by deuterium exchange with D₂0.

Example 1 Meεo- ,α, ,α-tetrakis(o-aminophenyl) orphyrin (IV) Compound IV was prepared by the method of Sorrell

(1980) as described below, except that the α,α,o_,α- atropisomer was isolated by the method of Lindsey (1980) . Quantities were scaled according to the amount of product desired. (i) Λfeso-tetrakis(2-nitrophenyl)porphyrin

(III). One hundred grams of 2-nitrobenzaldehyde (0.6 mole) were dissolved in 1700 L of glacial acetic acid in a 3-L three-neck round-bottom flask fitted with an efficient condenser and a dropping funnel. The solution was then heated just to its boiling point while being vigorously stirred with a magnetic stirring bar. Forty-six mL of pyrrole (47.6 g, 0.71 mole) were added dropwise to the solution at such a rate that the reaction did not become uncontrollable. The resultant black mixture was allowed to reflux for 30 minutes before being cooled in an ice bath to 35°C. (Tars form if the solution is cooled below this temperature.) During the cooling process, 250 mL of chloroform were slowly added to prevent the formation of tars. (The chloroform boils if the solution is too hot) . The purple crystalline product was filtered by suction, washed with five 100-mL portions of CHC1₃, and dried at 100°C overnight. Yield: 17.3-22.0 g (13.2-16.8%). UV-Vis (DMF) : 409, 518, 551, 594, and 652 nm.

(ii) meso-Tetrakis(2-aminophenyl)porphyrin (IV). A 3-L beaker was charged with 12.0 g (0.015 mole) of the product from the previous step and 600 mL of concentrated HCl (sp gr 1.18). To this was added a solution of 50 g (0.22 mole) of SnCl₂«H₂0 (reagent grade) dissolved in 50 mL of concentrated hydrochloric acid. The solution was stirred for 90 minutes at room temperature. The beaker was then placed in a hot water bath atop a hot plate-magnetic stirrer. The temperature of the bath was raised to 65°C in a 10-minute period and held between 65 and 70°C for 25 minutes. Good stirring was maintained during this time. (Heating above 75°C results in a low yield of impure product.) The beaker was then placed in an ice bath and swirled to bring the contents to room temperature. The solution was then neutralized by the slow addition (20-30 min) of about 600 mL of concentrated ammonium hydroxide. (Caution: This reaction is highly exothermic.) After cooling to room temperature, the highly basic solution (pH > 10) was stirred for at least 12 hours with 1 L of CHC1₃. The organic layer was separated and the aqueous phase was transferred to a 4-L separatory funnel. Water (1.5 L) was added and the solution was extracted with three 150-mL portions of CHC1₃. The combined extracts were washed with 1 L of dilute NH₄OH, which washings in turn were extracted with two 50-mL portions of chloroform. The combined organic portion was evaporated to 600 L on a rotary evaporator and then filtered by suction. The filtrate and washings were concentrated to 250 mL, 150 mL of 95% ethanol containing 10 mL of cone, aqueous NH₃ was added, and the solvent slowly evaporated until the remaining volume was about 200 mL. The sides of the flask were washed down with chloroform and 100 L of ethanol was added. The volume was then reduced to 75 mL, and the resulting crystals were filtered, washed with five 10-mL portions of 95% ethanol, and dried in an oven at 100°C for several hours. Yield: 6.6-8.1 g (65-80%) of a mixture of atropisomers. (iii) . α, ,α, atropisomer enrichment (Lindsey, 1980) .

Reagent-grade benzene (85 mL) and 36 g of silica gel were added to a 250-mL 3-neck round-bottom flask fitted with a nitrogen inlet and reflux condenser. This was immersed in an oil bath maintained at 75- 80°C, with magnetic stirring and a steady flow of benzene-saturated dry nitrogen gas. After 2 h, 1 g of the mixture of atropisomers was added to the flask. After an additional 20 h, the dark slurry was cooled to room temperature and then poured into a 53- mm diameter chromatography column. The residual undesired atropisomers were eluted with benzene- anhydrous ether (1:1) until the eluant became pale red in color (about 200 mL) , and then acetone-ether (1:1) was used to elute the α,α,α,α-atropisomer (IV). The column effluent was carefully monitored by TLC analysis (silica gel, benzene-ether (1:1)). The α,α,α,α-atropisomer eluted after elution of the α,α,α,β-atropisomer. ,H NMR (Me₂S0-d₆) δ 8.79 (s,8 H) , 7.69-6.97 (m,16 H) , 4.62 (s, 8 H) , -2.78 (s, 2 H) ; UV-Vis (DMF) : 648, 590, 553, 516, 415 nm.

Example 2 Syntheses of "straps" for incorporation into picnic-basket porphyrins 2A. Tetraester VII (Y = OCH₂CH₂0; Collman et al., 1988a)

(i) Diethyl 5-hydroxyisophthalate V. In a 500 mL three-neck round-bottom flask fitted with a magnetic stirrer, N₂ inlet, condenser, and gas dispersion tube was placed 25.0 g (0.137 mol) of 5- hydroxyisophthalic acid (Kodak) dissolved in 250 mL absolute ethanol. While the solution was stirred under a N₂ atmosphere, HCl gas was slowly bubbled into the solution through the gas dispersion tube for 10 min. The solution was stirred an additional 2 h and then poured into 1.5 L of water. The resultant white precipitate was collected by vacuum filtration, washed 3 times with 150 L of water, and dried under vacuum, m.p. 104-106°C. Yield: 31.0 g (95%).

(ii) Tetraester VII. In a 100 mL round-bottom flask under a N₂ atmosphere were stirred 9.50 g (40.0 mmol) of diethyl 5-hydroxyisophthalate V, 3.50 g (18.6 mmol) of 1,2-dibromoethane VI, and 10.0 g of K₂C0₃in 50 L of dry dimethylformamide (DMF) maintained at 60°C for 12 h. The reaction was monitored by TLC (Si0₂, 10:1 CH₂C1₂/Et₂0) . Six 1.0-g aliquots of 1,2-dibromoethane were added to the reaction mixture every 12 h over 3 days until TLC indicated the reaction was complete. Workup required pouring the reaction mixture into 400 L of water and stirring vigorously for 15 min, collecting the white precipitate by vacuum filtration, and washing 3 times with 10 mL of water. The precipitate, dissolved in 400 mL of CH₂C1₂, was washed 3 times with 100 L of 5% aqueous NaOH in a separatory funnel. The CH₂C1₂ solution was then dried over MgS0₄, filtered, and reduced by rotoevaporation to a white solid that was dried under vacuum. Yield: 5.7 g (57%).

2B. Tetraester X (Y = 0CH₂)

(i) Diethyl 5-methylisophthalate. 5-Methylisophthalic acid (34 g, 188.7 mmol) was placed in a 500 mL round-bottom flask fitted with a N₂ inlet, condensor, and gas dispersion tube. While stirring under a N₂ atmosphere, HCl was slowly bubbled into the solution through the gas dispersion tube for 20 minutes. The solution was stirred an additional 2 h and then poured into H₂0 (300 mL) . The mixture was extracted with CH₂C1₂ (2 x 150 mL) . The CH₂C1₂ layer was washed with H₂0 (3 x 150 mL) , dried over anhydrous Na₂S0₄, filtered, and evaporated to dryness under vacuum. The oily product was cooled in a freezer at -20°C overnight, and a yellowish solid was obtained. Yield: 36.6 g (82%). Η NMR (CDC1₃) : δ 8.47 (ε, 1H) , 8.03 (ε, 2H) , 4.39 (q, J = 7.1 Hz, 4H) , 2.44 (ε, 3H) , 1.40 (t, J = 7.1 Hz, 6H) . (ii) Diethyl 5-bromomethylisophthalate XIII. A 250 mL round-bottom flask was charged with diethyl-5-methylisophthalate (8 g, 33.9 mmol), N-bromosuccinimide (6 g, 33.7 mmol), benzoyl peroxide (50 mg) , and CC1₄ (100 mL) . The mixture was heated at reflux for 24 h, cooled to room temperature, and filtered. The filtrate was concentrated under reduced pressure to about 20 mL, and the crude product was precipitated upon cooling to -20°C. Purified product was obtained after recrystallization from 5% Et₂0/hexane (5.5g, 51.5%) . Η NMR (CDC1₃) : δ 8.61 (s, 1H) , 8.24 (s, 2H) , 4.55 (s, 2H) , 4.42 (q, J = 7.1, 4H) , 1.42 (t, J = 7.1, 6H) .

(iii) Tetraester X. Diethyl-5-bromomethyl- isophthalate VIII (5.12 g, 16.2 mmol), diethyl- 5-hydroxy-isophthalate IX (4.4 g, 18.5 mmol; see Example A) , K₂C0₃ (5 g) and dry DMF (50 mL) were placed in a 100 mL round-bottom flask under a N₂ atmosphere. The reaction mixture was stirred at room temperature. The reaction, monitored by TLC (Si0₂,

CH₂C1₂) , was complete after 12 h. The product mixture was poured into H₂0 (300 mL) and the aqueous solution extracted with CH₂C1₂ (2 x 150 mL) . The combined CH₂C1₂ layer was washed with saturated NaHC0₃ (100 mL) and 5% NaOH (50 mL) , dried over Na₂S0₄, filtered, and evaporated on a rotovap to give the product (7.41 g, 96.5%) . ^lE NMR (CDC1₃) : δ 8.67 (s, 1H) , 8.33 (ε, 3H) , 7.85 (s, 2H) , 5.22 (ε, 2H) , 4.42 (m, 8H) , 1.43(m, 12H) .

2C. Tetraacid XIV (Y = 0) This compound is prepared via the coupling of 3,5- dimethylphenol XI (Aldrich) with l-bromo-3,5- dimethylbenzene XII (Aldrich) to give diarylether XIII, followed by oxidation of the methyl groups to give tetraacid XIV. The coupling reaction is performed at an elevated temperature in the presence of K₂C0₃ and a catalytic amount of a copper catalyst such as CuCl, as described generally by Moroz et al. (1974) . Oxidation of the methyl groups is then accomplished using KMn0₄ (Lee, 1980) , giving the tetraacid.

2D. Tetraester XX (Y = CH₂N)

(i) 3,5-dicarbethoxybenzaldehyde XVII is prepared from diethyl 5-bromomethylisophthalate VIII (Example 2B) following the procedure of Kornblum et al. (1959) . Briefly, the bromide is added to an acetonitrile solution of silver tosylate (Aldrich) at 0-5°C (protected from light) and the mixture is allowed to come to room temperature overnight. The mixture is then added to ice water and extracted with ether. The resultant ethereal solution is evaporated and concentrated to dryness. The resultant benzyltosylate is then added to a fresh mixture of NaHC0₃ (20 g) DMSO (150 mL) heated at 150°C through which N₂ has been bubbling. After 3 minutes at 150°C, the reaction is rapidly cooled, and the benzaldehyde product XVII is purified by silica gel chromatography.

(ii) Diethyl 5-aminoisophthalate XVIII is prepared from the respective acid (Aldrich) by the esterification method in the first step of Example 2B.

(iii) The 3,5-dicarbethoxybenzaldehyde XVII and the diethyl 5-aminoisophthalate XVIII are then refluxed together in equimolar amounts overnight in absolute ethanol. The resultant Schiff base (XIX) is then purified by silica chromatography.

(iv) The Schiff base is converted to the product tetraester (XX) by the general method of Borch et al. (1971) . To 10 mmol of Schiff base in 25 L absolute methanol is added 4 mL of 5 N HCl followed by 6 mmol LiBH₃CN. The solution is stirred at 25°C for 72 hours, after which the methanol is evaporated to dryness. The residue is taken up in ether, washed with brine, and dried over MgS0₄, and then evaporated to dryness under reduced pressure. The crude product is purified by silica gel chromatography.

2E. Tetraester XXII (Y = CH₂CH₂)

(i) Olefin XXI is prepared from bromide VIII (Example 2B) and 3,5-dicarbethoxybenzaldehyde XVII (Example 2D) by the general ylide synthesis of Greenwald et al. (1963). Bromide VIII is reacted with PPh₃ to form the phosphonium salt. In a separate reaction flask, 25 mL DMSO is add to 0.05 moles NaH. The latter mixture is heated at 75-80°C for 45 minutes and then cooled in an ice bath. The phosphonium salt is then added (0.05 moles) as a DMSO solution (50 mL) . The resultant ylide is stirred for 10 minutes at 25°C after which aldehyde XVII is added, and the resultant mixture is stirred for 24 hours. The reaction mixture is poured into water and then extracted with ether. The resultant ethereal solution is then evaporated to dryness, and the residue is purified by silica gel chromatography to give purified olefin XXI.

(ii) The olefin • (0.012 moles) and Wilkinson's catalyst (Aldrich, 0.435 mmoleε) are dissolved in 200 mL ethanol under argon and the solution is then transferred to a medium-pressure hydrogenation apparatus. Hydrogenation is performed at 60°C and 60-80 psi for 8-12 hours. The ethanol is evaporated under reduced pressure, and the residue is dissolved in ether. The resultant ethereal solution is filtered through celite, and the filtrate is evaporated to dryness under reduced pressure to give the product, XXII.

2F. Tetraacid XXV (Y = S(=0)₂)

Diarylthioether XXIV is prepared from 1-bromo- 3,5-dimethylbenzene XII and the sodium salt of 3,5- dimethyl-1-thiobenzene XXIII by adaptation of a method from Testaferri et al. (1983) . A solution of XII (10 mmol) and XXIII (50 mmol) in DMF (30 mL) is stirred under nitrogen for 17 h at 100°C. The progress of the reaction is monitored by TLC. The mixture is cooled, poured into water (100 L) and extracted with ether (3 x 50 mL) . The organic layer is washed with water (2 x 50 mL) , dried with Na₂S0₄, and evaporated. The residue is chromatographed through a silica gel column using petroleum ether as eluent. The resultant diarylthioether is then oxidized to the sulfone-tetraacid XXV by KMn0₄ by the method described by Lee (1980) .

Example 3 Conversion of tetraester X to tetraacid chloride XXVI (i) Tetraacid Xa. Tetraester X (7.4 g, 15.7 mmol) was added to 95% EtOH (100 mL) in a 250 mL round-bottom flask fitted with a magnetic stirrer, heating mantle, and condenser. After the mixture was heated to 55°C, a solution of NaOH (5 g) in H₃0 (5 L) was added. The mixture was allowed to react for 12 h, cooled to room temperature, and filtered. The white precipitate was washed once with ethanol (25 mL) and then dissolved in H₂0 (300 mL) . The aqueous solution was treated with 6N HCl to precipitate the acid. The product was obtained by filtration, washed with H₂0 and dried at 80°C under a vacuum (5.6 g, 99.2%). -E NMR (D₂0/K₂C0₃) : 5 8.12 (s, 1H) , 7.94 (s, 2H) , 7.70 (S, 1H) , 7.49 (s, 2H) , 5.15 (s, 2H) . (ii) Tetraacid chloride XXVI. Tetraacid Xa (5 g, 13.9 mmol), thionyl chloride (20 mL) and a drop of DMF were added to a 50 mL round-bottom flask under a N₂ atmosphere. The mixture was heated at reflux for 6 h until all of the solid dissolved. The excess S0C1₂ was removed under vacuum to give the product as a light tan solid (5.2 g, 86.3%). Η NMR (CDC1₃) δ 8.87 (s, 1H) , 8.55 (s, 1H) , 8.52 (ε, 2H) , 8.02 (s, 2H) , 5.34 (ε, 2H) .

Example 4

Synthesis of picnic-basket porphyrin XXVII (Y = CH-,0)

Porphyrin XXVII was prepared from α,α, ,cc- tetra(o-aminophenyl)porphryin IV and tetraacid chloride XXVI. The reaction waε run under rigorouεly dry conditionε. All glassware was dried in an oven at 120°C and then cooled in the antechamber of a glove box. ,α,α,α-Tetra(o-aminophenyl)porphyrin IV (2.74 g, 4.1 mmol) was dissolved in CH₂C1₂ (200 mL) and stirred with 4 A molecular sieve pellets (Aldrich) (5 g) for 3 h in the glove box. The acid chloride XXVI (1.71 g, 4.1 mmol) was dissolved in CH₂C1₂ (200 mL) in a flask. A 2 L three-neck round-bottom flask containing triethylamine (5 L) and CH₂C1₂ (800 mL) was fitted with a N₂ inlet and two 250 L constant dropping funnels. The porphyrin and acid chloride solutions were transferred by cannula into respective funnels. At the same speed, the two reactants were added dropwise into the three-neck flask at 0°C under N₂ atmosphere over the course of 4 h. After the addition was complete, the solution was stirred an additional 24 h at room temperature. The CH₂C1₂ solution was reduced to 300 mL, washed once with saturated NaHC0₃ (100 L) and NaCl (100 L) solutions, dried over Na₂S0₄, filtered, and evaporated to dryness. The residue was dissolved in CH₂C1₂, loaded onto a silica gel flash column prepared from a CH₂C1₂ slurry, and eluted using 20% acetone/CH₂C1₂ to give the desired product (1.01 g, 25.8% yield).

-Η. NMR (CDC1₃) δ 9.02 ppm (s, 2H) , 8.98 (s, 2H) , 8.71 (m, 8H) , 8.26 (d, J = 8.1 Hz, 2H) , 8.17 (d, J = 8.0 Hz, 2H) , 7.87 ( , 4H) , 7.77 (m, 4H) , 6.62 (ε, 2H) , 6.09 (s, 2H) , 5.78 (s, 1H) , 5.57 (ε, 2H) D₂0- exchangable , 5 . 50 ( s , 2H) D₂0-exchangable , 5 . 34 ( s , 1H) , 4 . 52 ( ε , 2H) , -3 . 13 (ε , 2H) . UV-viε (CH₂C1₂) : 405 (shoulder) , 424 (Soret) , 518 , 550 (shoulder) , 590 , 644 nm.

Example 5

Sulfonation of picnic-basket porphyrins Picnic-basket porphyrin (3.25 mmol) iε mixed with 20 mL of cone, sulfuric acid, producing a blue- green mixture. This is transferred to a tall, 200 mL beaker and an additional 50 L of sulfuric acid is added. The resultant mixture iε stirred in a water bath maintained at 80-90°C for about 5 h and iε then allowed to sit, covered with a watch glaεε, at room temperature in a hood for another 50 h. After thiε time, the bright green solution is filtered through a frit to collect a small amount of residual starting material. The filtrate iε slowly diluted with 150 mL of water and then cooled in a refrigerator. Once cool, the resultant emerald green precipitate is filtered onto a 0.5 inch Celite pad in a large Buchner funnel. The filtrate is pale green and translucent. The pad material is then dried by suction and then vigorously stirred in 300 mL of acetone. Any clumps in the mixture are broken up manually. The resultant suspension is filtered again onto Celite and dried by suction. The dry Celite pad impregnated with the sulfonated product iε placed in a beaker and stirred with about 200 mL of 25% cone. ammonium hydroxide in methanol. The resultant red slurry is filtered through a frit to remove the Celite. The porphyrin product is washed from the Celite with a minimum of solvent. The resultant red filtrate is then mixed with 3 volumes of acetone to precipitate the porphyrin product which is then collected by vacuum filtration, washed with acetone, dried by suction, and dried under high vacuum to yield the purified, sulfonated product.

Example 6

Metal insertion into picnic-basket porphyrins A. Organic solvent-εoluble porphyrinε Iron Insertion. In a typical insertion reaction, picnic-basket porphyrin XXVII (40 mg) and 2,6-lutidine (0.2 mL) were added to a boiling solution of benzene and tetrahydrofuran (20 mL, 1:1) in a glove box. The oxygen concentration of the glove box was continually monitored and maintained at less than 1 ppm. Anhydrous FeBr₂ (100 mg) waε added and the reaction mixture was heated at reflux for about 30 min until the reaction was complete aε indicated by UV-viε spectroscopy (i.e., the disappearance of the 4 Q-bands of the metal-free porphyrin) . The solvents were evaporated under vacuum; the residue was redissolved in tetrahydrofuran/benzene (1:10) and loaded onto an alumina column (Activity 1 neutral A1₂0₃, manufactured by Woelm, 1 cm x 10 cm) . The product was eluted with methanol/tetrahydrofuran/benzene (1:1:10) and stored as a lyophilized solid. The metalated product was obtained in nearly quantitative yield.

Cobalt Insertion. In a typical insertion reaction, a solution of picnic-basket porphyrin (40 mg) , anhydrous CoCl₂ (100 mg) , and 2,6-lutidine (0.2 mL) in tetrahydrofuran (THF, 20 mL) was heated under reflux under a N₂ atmosphere. The reaction was monitored by UV-vis spectroscopy aε above and was complete after 2 h. The THF was removed under vacuum and the remaining solid waε dissolved in benzene (50 mL) . The benzene solution waε washed with dilute ammonia solution (3 x 30 mL) , dried with Na₂S0₄, filtered, and evaporated to dryness. The reεidue waε loaded on a silica gel column and the product was eluted with acetone/methylene chloride (1:5). The excesε solvents were removed to give quantitatively metalated product in 82-95% yield.

6.B. Water-soluble picnic-basket porphyrinε (e.g., made water-εoluble by εulfonic acid substituents) are prepared by the same general procedures outlined above, except that the picnic- basket porphyrin iε first converted to the tetrabutylammonium salt by cation-exchange chromatography to render the porphyrin soluble in THF or THF/benzene.

Example 7 Measurement of P₁₂ >₂)

Dioxygen affinities of metalated picnic-basket porphyrins were determined spectrophotometrically using a Hewlett-Packard 8452A diode array UV-Vis spectrometer equipped with a 7470A plotter. A closed atmosphere was attained using a 100 L tonometer (Ace Glass, Vineland, N.J.) equipped with a teflon-coated septum, a screw-seal, and a l cm cuvette. Spectra were recorded in the range 360-650 nm. The temperature of the cuvette was maintained at 25 ± 0.1 °C with a circulating liquid bath. Dioxygen binding affinities were measured by recording a series of absorbance spectra over a range of dioxygen concentrations and fitting the resultant data to an equation described further below. The equilibrium between the oxygenated and oxygen-free forms of the metalloporphyrin may be expressed as:

K

MP-B + O, => MP•B•O, where, 0₂ is the partial pressure of dioxygen (in Torr) , and K, which iε equal to the partial pressure at which 50% of the porphyrin molecules are oxygenated, is the equilibrium constant. The partial pressure (P_n(0₂)) after the addition of each dioxygen aliquot to the sample was derived from the partial pressure after addition of the previous aliquot by the equation:

P_n(0₂) = [(P_n.,(0₂) .(V-v)) + 760V] /V where V is the volume of the tonometer (not including the volume of the solution) , v iε the volume of the gas displaced by addition of the aliquot, and the pressure is held constant at 760 Torr. The relationship between P_n(0₂) and the equilibrium constant K can be expreεsed aε:

P„(0₂) = [M-Porph]_tot.l-Δe-(P_n(0₂)/ΔA) - 1/K

where [M-Porph],_ot is the total metalloporphyrin concentration, 1 is the pathlength of the cuvette in cm, Δe iε the difference in the molar extinction coefficientε between the oxygenated and deoxygenated formε, ΔA is the absorbance difference between the absorbance of the solution at the given P_n(0₂) value and in the absence of dioxygen. A plot of P_n(0₂) vs. P_n(0₂)/ΔA) provides a straight line with a y-intercept of -1/K.

In a general procedure, in an inert-atmosphere box, a metalated picnic-basket porphyrin was dissolved in toluene with a known excess of ligand L (generally 100 to 1000 times the concentration of the porphyrin) . The sample concentration waε selected to yield a maximum absorbance at the Soret band of about 1.2 absorbance units to ensure a linear responεe. After placing the εample in the tonometer and εealing, the tonometer waε removed from the inert- atmoεphere box and placed in the UV-Viε spectrophotometer, and the εample waε allowed to temperature-equilibrate.

Dioxygen (2% in nitrogen) waε added in known aliquots using a gas-tight syringe. An identical volume of gas waε removed from the tonometer before addition of the dioxygen aliquot to maintain constant pressure in the tonometer. After each addition of dioxygen, the sample waε shaken vigorously and then allowed to reach equilibrium before an absorbance spectrum was recorded. Thiε procedure waε repeated for each dioxygen aliquot. The range of oxygen partial preεεure used depended upon the oxygen- binding affinity of the particular porphyrin under study. Sets of spectra which showed isoεbestic points were used to calculate equilibrium constantε for oxygen-binding affinity. The absorbance values were taken from the Soret maximum. Line plots and least-squareε analyses were carried out using the program RS/1 (BBN Software Products Corporation) .

Although the invention has been described with respect to particular embodiments, it will be appreciated that various changeε and modificationε can be made without departing from the invention.

Claims

IT IS CLAIMED:

1. A dioxygen-binding complex of the form, when oxygenated:

where M is Fe or Co;

L is a neutral, sigma-donating ligand; Y is X, X-CH₂, or CH₂-X-CH₂, where X is O, S, S(=0), S(=0)₂, NR, or ⁺NRR', and R and R' are the same or different and are a hydrogen or a lower alkane; the complex, in a toluene-soluble form, is characterized by a P_ιn (0₂) value, when measured in toluene containing 1,5-dicyclohexylimidazole, at 25°C, of less than about 40 Torr when M is Co, and less than about 0.5 Torr when M is Fe.

The complex of claim 1, wherein Y is X-CH₂

The complex of claim 2, wherein Y is 0-CH₂ 4. The complex of claim 1, wherein imidophenyl rings in the porphyrin skeletal structure are substituted at one or more ring positions with sulfonate groups.

5. The complex of claim 4, wherein the complex is dissolved in an aqueous medium.

6. The complex of claim 1, bound to a εolid- phase support, via a covalent linkage between the solid support and an imidophenyl ring in the complex.

7. The complex of claim 1, bound to a solid- phase support, via a covalent linkage between ligand L and the solid support.

8. A method for extracting oxygen from an oxygen-containing fluid comprising: exposing an oxygen-containing fluid to the oxygen-binding complex of claim 1, with such in non- oxygenated form, and by said exposing, producing the oxygenated form of the complex.

9. The method of claim 8, wherein Y iε X-CH₂.

10. The method of claim 9, wherein Y iε 0-CH₂.

11. The method of claim 8, for use in removing dioxygen in free form from an aqueous solution, wherein imidophenyl rings in the porphyrin skeletal structure of the oxygen-binding complex are substituted at one or more ring poεitionε with sulfonate groups. 12. The method of claim 8, for extracting oxygen from an oxygen-containing gas mixture, wherein the oxygen-binding complex iε attached to an oxygen- permeable membrane, and εaid method includeε exposing the gas to the membrane, on one side of the membrane, and applying a vacuum to the opposite side of the membrane, to draw off oxygen bound to the membrane via said complex.

13. The method of claim 8, for concentrating oxygen from an oxygen containing fluid, wherein said complex is bound to a solid support, and which further includes, after exposing the complex to the fluid, separating the support from the fluid and treating the support to remove bound oxygen.

14. The method of claim 13, wherein said complex is bound to said support via a covalent linkage between the support and an imidophenyl ring in the complex.

15. The method of claim 13, wherein said complex iε bound to εaid support via a covalent linkage between the support and the ligand L in the complex.

16. A method of measuring the oxygen partial pressure in a liquid at a site which is accessible by an optical fiber, comprising directing to the site, an optical fiber pair which includeε a firεt fiber having an end region which iε prepared with a light-tranεmissive coating of an oxygen-binding complex of claim 1, and a second fiber which iε adapted to receive light tranεmitted through said coating, when light iε directed through the first fiber, directing light through said first fiber, at a wavelength between about 420-460 nm, measuring the intensity of light transmitted from the first through the second fiber, as a function of time, and by said measuring determining, the concentration of molecular oxygen at said site.

17. A device of measuring the oxygen partial pressure in a liquid at a site which is accessible by an optical fiber, comprising directing to the site, an optical fiber pair which includes a first fiber having an end region which is prepared with a light-transmissive coating of an oxygen-binding complex of claim 1, and a second fiber which is adapted to receive light transmitted through said coating, when light is directed through the first fiber, means for directing light through said first fiber, at a selected wavelength between about 420-460 nm, means for measuring the intensity of light transmitted from the first through the second fiber, as a function of time, and means for determining, from the measured light intensity, the concentration of molecular oxygen at said site.