Chemistry Reference
In-Depth Information
O
C
O
-
HC
CH
H
Me
H
C
N
N
N
OS
2+
Fe
2+
N
N
N
Me
C
C
Me
-
H
H
HC
CH
C
H
XVI
Me
XVII
SCHEME 5.3
Ferrocene.and.osmium.bipyridyl.
OEt
EtO
Ph
N
OEt
EtO
N
-
N
N
-
N
Co
2+
N
N
Co
2+
Ph
Ph
-
N
N
OEt
EtO
N
-
N
N
OEt
EtO
Ph
XVIII
XIX
SCHEME 5.4
Co-tetraphenylporphyrin.and.cobalt.phthalocyanine.
The. simplest. way. from. an. analytical. point. of. view. would. be. a. direct. electrochemical. recon-
stitution.of.the.enzyme.(Figure.5.4,.pathway.“E”)..The.main.problem.for.this.was.already.briely.
sketched,.and.lies.in.the.fact.that.the.active.center.is.usually.buried.in.the.protein.shell..To.circum-
vent.the.problem,.it.is.attempted.to.“wire”.the.active.center.with.the.electrode.surface.(see.Figure.
5.6).. Sensors. with. an. underlying. concept. of. direct. electron. transfer. are. sometimes. called. third-
generation.sensors.
The. oldest. approach. of. wiring. is. the. use. of. redox. polymers. (Figure. 5.6,. part. “A”).. The. elec-
trons. are. shuttled. via. redox. groups. bound. to. a. polymeric. backbone. into. the. active. center. of. the.
enzyme.. Useful. redox. groups. are. ferrocene. and. Os-bipyridine. complexes. (Scheme. 5.3).. Other.
assays.have.been.developed.recently.and.rely.mainly.on.a.conductive.“wire”.(carbon.nanotubes).or.
gold.nanoparticles.attached.to.the.coenzyme.(FAD.in.case.of.oxidases).[1912,1913]..The.attachment.
is. attained. normally. via. covalent. bonding. (CNT). or. sulide. sorption. (AuNP).. The. apoenzyme. is.
reconstituted.with.the.modiied.FAD.where.the.nanosized.material.acts.as.a.wire..Apart.from.the.
three.“generations”.of.oxidase-based.sensors.another.detection.pathway.is.open.if.the.product.of.
the.enzymatic.reaction.is.electroactive..This.is.often.the.case.with.phenols.and.polyphenols.in.com-
bination.with.polyphenol.oxidase,.which.produces.quinoid.structures.that.can.be.reduced.again.
Search WWH ::
Custom Search