Biomedical subjects

Richard H. Fish

Publications and source records attributed to Richard H. Fish.

3 recordsLinked to original sources

PubMed1999

Biomimetic Oxidation Studies. 11. Alkane Functionalization in Aqueous Solution Utilizing in Situ Formed [Fe(2)O(eta(1)-H(2)O)(eta(1)-OAc)(TPA)(2)](3+), as an MMO Model Precatalyst, Embedded in Surface-Derivatized Silica and Contained in Micelles.

The biomimetic, methane monooxygenase enzyme (MMO) precatalyst, [Fe(2)O(eta(1)-H(2)O)(eta(1)-OAc)(TPA)(2)](3+) (TPA = tris[(2-pyridyl)methyl]amine), 1, formed in situ at pH 4.2 from [Fe(2)O(&mgr;-OAc)(TPA)(2)](3+), 2, was embedded in an amorphous silicate surface modified by a combination of hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide). The resulting catalytic assembly was found to be a biomimetic model for the MMO active site within a hydrophobic macroenvironment, allowing alkane functionalization with tert-butyl hydroperoxide (TBHP)/O(2) in an aqueous reaction medium (pH 4.2). For example, cyclohexane was oxidized to a mixture of cyclohexanone, cyclohexanol, and cyclohexyl-tert-butyl peroxide, in a ratio of approximately 3:1:2. The balance between poly(ethylene oxide) and poly(propylene oxide), tethered on the silica surface, was crucial for maximizing the catalytic activity. The silica-based catalytic assembly showed reactivity somewhat higher in comparison to an aqueous micelle system utilizing the surfactant, cetyltrimethylammonium hydrogen sulfate at its critical micelle concentration, in which functionalization of cyclohexane with TBHP/O(2) in the presence of 1 was also studied at pH 4.2 and was found to provide similar products: cyclohexanol, cyclohexanone, and cyclohexyl-tert-butyl peroxide, in a ratio of approximately 2:3:1. Moreover, the mechanism for both the silica-based catalytic assembly and the aqueous micelle system was found to occur via the Haber-Weiss process, in which redox chemistry between 1 and TBHP provides both the t-BuO(*)() and t-BuOO(*)()( )()radicals. The t-BuO(*)()( )()radical initiates the C-H functionalization reaction to form the carbon radical, followed by O(2) trapping, to provide cyclohexyl hydroperoxide, which produces the cyclohexanol and cyclohexanone in the presence of 1, whereas the coupling product emanates from t-BuOO(*)() and cyclohexyl radicals. A discussion concerning both approaches for alkane functionalization in water will be presented.

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PubMed1998

A New, Aqueous (1)H NMR Shift Reagent Based on Host-Guest Molecular Recognition Principles for Organic Compound Structural Analysis: Non-covalent pi-pi and Hydrophobic Interactions Using a Supramolecular Host, [CpRh(2'-deoxyadenosine)](3)(OTf)(3).

We have discovered that the supramolecular host [CpRh(2'-deoxyadenosine)](3)(OTf)(3) (1, Cp = eta(5)-C(5)Me(5), OTf = CF(3)SO(3)(-)) has utility as a new, aqueous (1)H NMR shift reagent, via a host-guest molecular recognition process that occurs by non-covalent pi-pi and hydrophobic interactions, with a wide variety of H(2)O-soluble organic substrates. These organic compound guests that we present, to illustrate the utility of host 1 as a novel, aqueous (1)H NMR shift reagent, encompass examples such as aromatic carboxylic acids, phenylacetic acid (G1), 1-naphthoic acid (G2), and 2-naphthoic acid (G3), an aliphatic carboxylic acid, cyclohexylacetic acid (G4), as well as biological compounds, a di- and a tetrapeptide containing terminal L-tryptophan (Trp) or L-phenylalanine (Phe) groups, L-Trp-L-Phe (G5) and L-Trp-L-Met-L-Asp-L-Phe amide (G6) in the pH range 5-10. A discussion of the molecular recognition parameters that effect the (1)H NMR shifts of the organic guests and a comparison with the water-soluble lanthanide shift reagents (LSRs) will be presented to demonstrate the usefulness of this aqueous molecular receptor as an aid for organic compound structural analysis.

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PubMed1996

Synthesis and Structural Studies of Metal Complexes of the Biological Ligand 2-Quinaldic Acid: Utilization of the Polymer Pendant Analog PS-2-QA for Selective Aluminum Ion Removal from Aqueous Solution.

The synthetic reactions of quinaldic acid (2-QA, 1), a ligand with potential implications in Al(3+) ion biological transport and in pharmaceutical applications and of use for the removal and recovery of Al(3+) ions from environmental waste sites, were studied with tri- and divalent metal ions that encompass Al(3+), Fe(3+), Ga(3+), Zn(2+), Ni(2+), Mn(2+), and Co(2+). The Al(3+), Fe(3+), and Ga(3+) metal ion complexes, 2-4, of 1 were characterized by FT-IR, FAB/MS, NMR, and elemental analysis and provided the following structural formula with 1 of 2-QA(4)M(2)(&mgr;-OH)(2).S, where S = H(2)O or pyridine. In the case of the Ga(3+ )analog, 4.Py, the unequivocal &mgr;-OH dimer structure was determined by single-crystal X-ray analysis [space group, P1; a = 13.387(3) Å; b = 14.016(2) Å; c = 14.549(2) Å; alpha = 87.74(2) degrees; beta = 73.44(2) degrees; gamma = 82.61(2) degrees; Z = 2; volume = 2592.6 Å(3)]. A description of the X-ray crystal structure of 2-QA(4)Ga(2)(&mgr;-OH)(2).4 pyridine, 4.Py, will also be presented. The corresponding bis(2-QA) metal complexes of Zn(2+), Ni(2+), Mn(2+), and Co(2+), 5-8, were also studied and all provided a formula of 2-QA(2)M.1.5 H(2)O, which were also characterized by many of the above-mentioned spectroscopic techniques. The polymer-supported (PS) version of 1, PS-2-QA, bonded to modified, macroporous 6% cross-linked polystyrene-divinylbenzene beads, was synthesized by an electrophilic substitution reaction on the aromatic ring of a 2-QA derivative, ethyl 2-quinaldate, with the chloromethylated precursor, PS-CH(2)Cl, followed by subsequent ester hydroysis to the free PS-2-QA ligand. The PS-2-QA ligand was found to selectively remove Al(3+) ions from aqueous acidic solution (pH = 3-5) in the presence of other divalent metal ions, namely, Cu(2+), Zn(2+), Ni(2+), Mn(2+), and Co(2+) as well as a trivalent metal ion, Cr(3+).

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