Chemistry Reference
In-Depth Information
2.2.3
Pyridoxamine-Surfactant Systems
Surfactants provide interesting systems in bioorganic chemistry. The specific micro-
environments produced by surfactant micelles in aqueous media are effective for si-
mulation of catalytic functions in the hydrophobic active sites of enzymes. This has
inspired several groups to study various pyridoxamine-surfactant systems for transa-
minase enzyme mimics. The first work was reported by Kondo et al. [22], who found
that N-dodecylpyridoxal chloride forms a Schiff base with hydrophobic
-amino acids,
such as tryptophan, phenylalanine, phenylglycine, and S-benzylcysteine, in the catio-
nic micelle of hexadecyltrimethylammonium chloride. The formation constants were
large, and the resulting Schiff bases underwent transamination to give the correspond-
ing
a
a
-keto acids effectively, even in the absence of metal ions in aqueous media at
30.0
C.
Murakami et al. studied alternative pyridoxamine-surfactant systems [23]. These
authors synthesized hydrophobic pyridoxamine derivatives (
30
and
31
) and peptide
lipid molecules (
32
-
35
). Catalyst
30
or
31
and the peptide lipids formed bilayer mem-
branes in water, which showed transamination reactivity in the presence of metal ions
such as Cu(
II
). It was proposed that the pyridoxamine moiety was placed in the so-
called hydrogen-belt domain interposed between the polar surface region and the hy-
drophobic domain that is composed of double-chain segments within the bilayer as-
sembly. The basic group (such as imidazole) in the peptide lipid molecules could cat-
alyze the proton transfer involved in the transamination reaction. In addition, marked
substrate discrimination by these bilayer membrane systems was performed through
hydrophobic interactions between substrates and the catalytic site.
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