Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-01-12
2002-04-30
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S064000, C210S656000
Reexamination Certificate
active
06380276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with polymer-metal ion composites and methods for reversibly binding target compounds using such composites. More particularly, the invention pertains to stable composites comprising an amorphous polymer matrix having a plurality of channels with metal ion-ligand complexes immobilized therein. The metal complexes include a metal ion, preferably an ion of a transition metal, having a ligand bonded to the metal ion and the polymer matrix. The metal complexes are dispersed within the polymer matrix so that the metal ions are preferably at least about 8 Å apart. The composites are formed by polymerizing a polymeric moiety with a metal-ion ligand complex template in the presence of a solvent. The template preferably further includes a spacer ligand which is selected based upon its size or properties and which can be removed after polymerization to yield a composite having a particular chemical and/or physical environment around the metal sites. In the methods of the invention, the composites are contacted with a target compound under conditions for binding the compound. The composites and methods are particularly useful for reversibly binding compounds selected from the group consisting of oxygen, carbon monoxide, carbon dioxide, compounds having an atom of P, S, or N, and mixtures thereof.
2. Description of the Prior Art
The function of metal ions in biomolecules is controlled by two interrelated structural features: the structure of the metal ion coordination sphere which includes the geometric relationship of metal-bound ligands; and the molecular architecture of the metal binding site that controls the secondary coordination sphere (or microenvironment) about the metal ion. While the role of the former is well known in directing the activity of metalloproteins, the importance of the latter cannot be overlooked. Microenvironments about the metal ion active sites which are induced by the protein structure regulate several properties, including hydrophobicity, polarity, electrostatics, solvation, and the dielectric constant. Furthermore, the morphology of the metal active site in metalloproteins can govern the accessibility of substrates by the metal ions. Protein-created microenvironments thus have a significant role in controlling the reactivity of the metal ions.
The effects of the microenvironment on the functions of metal ions in proteins is illustrated by the diverse activity of heme-containing proteins. (Dawson, J. H.,
Science
, Vol. 240, p. 433, (1988); Ortiz de Montellano, P. R.,
Acc. Chem. Res
., Vol. 20, p. 289, (1987)). In hemoglobin and myoglobin, the steric constraints and hydrogen bonding capacity of the distal side of the heme pocket has a significant effect on the oxygen binding properties of these proteins. (Suslick, K. S. et al.,
J. Chem. Educ
., Vol. 62, p. 974, (1985)). In the oxygenases and peroxidases, the functions of enzymes are affected greatly by the various protein environments that house the catalytic iron heme moieties. For example, cytochrome p
450
(a monooxygenase) and chloroperoxidase (which halogenates substrates) have identical heme active sites with axially bound thiolates, yet their functions are vastly different. (Dawson, J. H.,
Science
, Vol. 240, p. 433, (1988)).
Protein structure also controls other properties necessary for metal ions to fiction in biomolecules. In most cases, the active sites are located within the interior of the proteins, isolated from each other to prevent undesirable interactions. For example, in human hemoglobin the four heme dioxygen binding sites are isolated from each other by the globin, and the closest distance between heme sites is 25 Å. (Perutz, M. F. et al.,
Acc. Chem. Res
., Vol 20, p. 309, (1987)). This is imperative for reversible O
2
binding because if the heme sites were allowed physical contact, either by intra or intermolecular pathways, the four-electron auto-oxidation of O
2
would occur, leading to thermodynamically stable &mgr;-oxo bridge iron species. In hemoglobin, like many metal ion-containing proteins, access by external ligands to the metal sites is provided by channels that connect the active sites to the surface of the proteins. The channel structure, while providing a means of entry into the active sites, can also aid in orienting substrates as they approach the metal ion as well as assist in the selection of substrates.
In the past, there has been great interest in developing synthetic systems that mimic the structural, physical, and functional properties of the metal ion sites found in proteins. (Ibers, J. A. et al.,
Science
, Vol. 209, p. 223, (1980); Karlin, K. D.
Science
, Vol. 261, p. 701, (1993)). One approach to examine the role of microenvironments in the functions of metal ions within proteins is to simulate various architectural features in low molecular weight systems. (Karlin, K. D.,
Science
, Vol. 261, p. 701, (1993)). Design features found in proteins have been incorporated into organic ligand systems to help direct the chemistry at the metal centers in solution. The reversible binding of O
2
to synthetic iron porphyrin is one example where the design of organic ligands can dictate the reaction chemistry at a distant metal site. (Suslick, K. S. et al.,
J Chem Educ
., Vol. 62, p. 974, (1985); Momenteau, M. et al.,
Chem. Rev
., Vol. 94, p. 659, (1994)). The picket-fence iron porphyrin of Collman was the first synthetic heme to reversibly bind O
2
in solution at room temperature by preventing the intermolecular iron oxygen interactions that lead to M-oxo bridge iron species. (Collman, J. P.,
Acc. Chem. Res
., Vol. 10, p.265, (1977)). A variety of other porphyrins and non-porphyrin ligands have since been designed containing cavity motifs that, when metallated with iron, are capable of forming Fe—O
2
adducts. (Suslick, K. S. et al.,
J. Chem Educ
., Vol. 62, p. 974, (1985); Momenteau, M. et al.,
Chem. Rev
., Vol. 94, p. 659, (1994); Jones, R. D. et al.,
Chem. Rev
., Vol. 79, p. 139, (1979); Busch, D. H. et al.,
Chem. Rev
., Vol. 94, p. 585, (1994)). In addition, other notable examples where ligand design has aided in mimicking biological function in synthetic systems include: the specific recognition of metal ions; (Cram, D. J.,
Angew. Chem., Int. Ed. Engl
., Vol. 27, p. 1009, (1988); Lehn, J. M.,
Angew. Chem., Int. Ed. Engl
., Vol.27, p. 89, (1988); Pedersen, C. J.,
Angew. Chem., Int. Ed. Engl
., Vol. 27, p. 1021, (1988)) the acceleration of the rates of chemical reactions; (Breslow, R.,
Science, Vol.
218, p. 532, (1982)) and in artificial receptors that show strong and selective binding of organic substrates (Hamilton, A. J.,
Chem. Educ
. Vol.67, p.821, (1990); Diederich, F. J.,
Chem. Educ
. Vol. 67, p. 813, (1990); Tjivikua, T. et al.,
J. Am. Chem. Soc
. Vol. 112, p. 1250, (1990); Webb, T. H. et al.,
J Am. Chem. Soc
., Vol 113, p. 8554, (1991)). Finally, template copolymerization methods have been used extensively to generate systems that selectively bind analytes. Wutff, G.,
Angew. Chem., Int. Ed. Engl
., Vol. 34, p. 1812 (1995); Mosbach, K., Trends Biotech., Vol. 19, p. 9 (1994); Shea, K. J.,
Trends Poly. Sci
., Vol. 2, p. 166 (1994). In most cases, these molecular systems use a combination of morphological control of a binding cavity and weak bonding interactions to guide the recognition process.
Another approach simulating the site isolation properties of metalloproteins is to attach synthetic metal complexes onto the surface of solid supports. For example, embedding the diethyl ester of heme in a hydrophobic matrix of polystyrene and 1-(2 phenylethyl)-imidazole permits the Fe(II) sites of the heme to reversibly bind O
2
(Wang, J. H.,
J. Am. Chem. Soc
., Vol. 80, p. 3168, (1958); Wang, J. H.,
Acc. Chem. Res
., Vol. 3, p. 90, (1970)). It has also been reported that crosslinked polystyrene containing attached imidazole ligands can coordinate Fe(II) tetraphenylporphyrin (Fe
II
TPP). (Collman, J. P. et al.,
J. Am. Chem. Soc
., Vol. 95,
Borovik Andrew
Krebs John
Sharma Anjal
Foelak Morton
Hovey Williams Timmons & Collins
The University of Kansas
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