Environmental Engineering Reference
In-Depth Information
performed. Use of enzyme for surface modification of SAMs on metal surfaces
could offer distinct advantages such as (1) development of methodologies of
attachment of organic moieties on SAMs after their assembly on metal surfaces,
which due to steric hindrance are difficult to achieve via chemical means; (2)
avoid multiple protection deprotection steps due to their high selectivity for a
given organic transformation; (3) possibly, avoid the use of organic solvents by
carrying out these reactions in bulk (solvent less), or aqueous medium; (4) use of
mild reaction conditions (room temperature to 708C) thus, ensuring structural
integrity of the SAMs formed; and (5) reported selectivity of enzyme reactions
may provide spatial and topographical ordering of the surface.
There are numerous reports of hydrolysis of lipid monolayers using different
lipases [94, 95]. Relatively few reports demonstrate lipase catalyzed esterifica-
tion synthesis on air/water monolayers [96, 97]. Specifically, Singh et al. have
reported use of lipase lipozyme for the synthesis of glycerol and fatty acid on
steric acid monolayers [96]. Singh et al. have also reported lipase-catalyzed
synthesis esterification of oleic acid with glycerol in monolayers [97]. Turner
et al. [98] have reported the hydrolysis of a phospholipid film which was
covalently attached via chemical methods to a silica surface. However, the
rigid structural ordering of the SAMs on the metal surface offers significant
bulk steric hindrance which may not be the case in the flexible lipid and air/
water monolayers as reported above. Breitinger's group have reported the
phosporolytic synthesis of
silica modified maltoheptaoside-alkoxysilane
anchor molecules [99].
Enzymatic, surface-initiated polymerizations of aliphatic polyesters was
reported for wider clinical use of aliphatic polyesters [100]. The hydroxyl-
terminated SAM acted as an initiation site for lipase B catalyzed ROP of
aliphatic polyesters, such as poly(e-caprolactone) and poly(p-dioxanone)
(Fig. 3.4). Another example of enzymatic SIP is the polymerization of
poly(3-hydroxybutyrate) (PHB), where PHB synthase, fused with a His-tag
at the N-terminus, was immobilized onto solid substrates through transition-
metal complexes, Ni (II)-NTA, and the immobilized PHB synthase catalyzed
the polymerization of 3-1-hydroxybutyryl-coenzyme A (3HB-CoA) to PHB
[101]. Loos et al. have reported the surface-initiated polymerization of
glucose-1-phosphate with potato phosphorylase as a catalyst on modified
silica particles [102].
Recently, Mahapatro et al. demonstrated the surface modification of func-
tional self-assembled monolayers on 316L stainless steel via lipase (Novozyme-
435) catalysis (Fig. 3.5) [103]. SAMs of 16-mercaptohexadecanoic acid
(-COOH SAM) and 11-mercapto-1-undecanol (-OHSAM) were formed on
316L SS, and lipase catalysis was used to attach therapeutic drugs - perphena-
zine and ibuprofen, respectively, on these SAMs. The reaction was carried out
in toluene at 608C for 5 h using Novozyme-435 as the biocatalyst. The FTIR,
XPS and contact angle measurements collectively concluded biocatalytic sur-
face modification of SAMs.
