Biomedical Engineering Reference
In-Depth Information
chain, so can the scavenging ef ect on superoxide anion increase when DS
increases from 0.28 to 0.41. Although with further increase in DS to 0.54,
the electron cloud density of active hydroxyl and amino groups increases,
the content of active amino groups decreases, and thus the electron-donat-
ing activity decreases. Nevertheless, carboxymethylated chitosan (no car-
boxymethyl position specii ed) was used with the intention of protecting
the chondrocytes from induced apoptosis: in fact it restored the level of
mitochondrial membrane potential, down-regulated the NO synthase
expression and scavenged reactive oxygen species in chondrocytes [299].
Another carboxylated derivative, succinyl chitosan, identii ed as inhibi-
tor of free radical mediated oxidation of cellular biomolecules [300]. High
MW O-carboxymethyl chitosan at the maximum concentration of 40 mg/
ml did not show any scavenging activity against the O
2
-
, but low MW
O-carboxymethyl chitosan (1.1-4.35 kDa) showed very modest activity,
indicative of the importance of the molecular size and free functions [301].
Quaternised carboxymethyl chitosan had better HO
scavenging activity
than that of carboxymethyl chitosan, as a result of the positive charge on
the quaternised chitosan [302].
Huang,
et al.
, synthesised two chitooligosaccharides derivatives, succi-
nyl chitosan and chitosan-N-2-hydroxypropyl trimethyl ammonium chlo-
ride by introducing carboxyl (-COCH
2
CH
2
COO¯) and quaternised amino
-CH
2
CH(OH)CH
2
N(CH
3
)
3
+
groups to the amino position with dif erent
substitution degrees for the purpose of altering the total amount of hydro-
gen atoms capable of reacting with radicals, and modifying their metal ion
chelating ability [303]. Scavenging of carbon-centered and nitrogen-cen-
tered radicals was directly af ected by the amount of abstractable hydro-
gen atoms in oligosaccharide molecules. In contrast, structure-activity
relationships revealed that chelation of Fe
2+
ions indirectly contributed for
their observed HO
scavenging activity apart from hydrogen abstraction.
Xie,
et al.
, reported that water-soluble chitosan derivatives prepared by
grat copolymerisation of maleic acid sodium onto hydroxyporpyl chito-
san and carboxymethyl chitosan sodium, showed radical scavenging activ-
ity against HO
and O
2
-
which could be related to the contents of active
hydroxyl and amino groups in the polymer chains [278, 304]. h e antioxi-
dant activity of eugenol grat ed or gallic acid conjugated, l avonoid grat ed
chitosan, 2-(4(or2)-hydroxyl-5-chloride-1,3-benzene-di-sulfanimide)-
chitosan or sulfanilamide derivative of chitosan is accredited to additional
-OH groups and disruption of intramolecular hydrogen bonds between
amine and hydroxyl groups [305-309].
Chitosan substituted at N with 1,3,5-thiadiazine-2-thione residue dis-
played superior activity than chitosan because the substituted group
