Synthesis, characterization and slow release properties of O-naphthylacetyl chitosan

Article abstract of DOI:10.1016/j.carbpol.2012.01.076

O-naphthylacetyl chitosan (NA-chitosan) was first prepared via protecting the amino groups with phthalic anhydride, followed by reaction with 1-naphthylacetyl chloride. The intermediates were hydrolyzed with anhydrous hydrazine to obtain final product. The derivatives of each step were characterized with Fourier transform infrared spectroscopy (FT-IR) and ¹³C solid state nuclear magnetic resonance (NMR). Results showed NA-chitosan had both naphthylacetyl and amino groups in the main chain of the polysaccharide. Elemental analysis showed that the substitution degree of hydroxyl was 0.4. Thermogravimetric analysis (TGA, DTG) of NA-chitosan was observed with much lower decomposition peak at 283°C than that of chitosan at 300°C. The release of 1-naphthylacetic acid was dependent on both pH values and the medium temperature, and at pH 12.0, 60°C the release period could last for 55 days.

Full text of DOI:10.1016/j.carbpol.2012.01.076

Carbohydrate Polymers 88 (2012) 1189–1194
Contents lists available at SciVerse ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Synthesis, characterization and slow release properties
of O-naphthylacetyl chitosan
b
a
a
a,∗
a,∗∗
Shuming Tao , Ran Pang , Chao Chen , Xueqin Ren , Shuwen Hu
a
Department of Environmental Sciences & Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193 PR China
Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193 PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
O-naphthylacetyl chitosan (NA-chitosan) was first prepared via protecting the amino groups with
phthalic anhydride, followed by reaction with 1-naphthylacetyl chloride. The intermediates were
hydrolyzed with anhydrous hydrazine to obtain final product. The derivatives of each step were character-
Received 28 November 2011
Received in revised form 3 January 2012
Accepted 24 January 2012
Available online 1 February 2012
13
ized with Fourier transform infrared spectroscopy (FT-IR) and C solid state nuclear magnetic resonance
(NMR). Results showed NA-chitosan had both naphthylacetyl and amino groups in the main chain of the
polysaccharide. Elemental analysis showed that the substitution degree of hydroxyl was 0.4. Thermo-
gravimetric analysis (TGA, DTG) of NA-chitosan was observed with much lower decomposition peak at
Keywords:
Chitosan
◦
◦
2
83 C than that of chitosan at 300 C. The release of 1-naphthylacetic acid was dependent on both pH
1
-Naphthylacetic acid
◦
values and the medium temperature, and at pH 12.0, 60 C the release period could last for 55 days.
Slow release
©
2012 Elsevier Ltd. All rights reserved.
1
. Introduction
(Fernández-Pérez, Villafranca-Sánchez, Flores-Céspedes, Pérez-
García, & Daza-Fernández, 2010; Thérien-Aubin, Baille, Zhu, &
Marchessault, 2005; Muzzarelli, 2009a; Zhang, Jin, Liu, & Du, 2001).
Unfortunately, natural polymers often have low reactivity with the
bioactive compound due to the poor solubility in common solvents.
Many attempts have tried to improve the reactivity between the
carrier and the bioactive compound which mainly include creating
new, highly reactive functional groups both in the carrier and in the
bioactive agent, or finding specific activators to get a direct reaction
(Jantas & Delczyk, 2005; Martin, Sánchez-Chaves, & Arranz, 1999;
Sánchez-Chaves, Rodríguez, & Arranz, 1997).
Among the natural polymers, chitosan is an amino polysaccha-
ride possessing unique properties, multidimensional structures,
highly sophisticated functions and wide applications in biomed-
ical, agricultural, and other industrial areas (Muzzarelli et al.,
2012; Sogias, Williams, & Khutoryanskiy, 2008). Due to the abun-
dant hydroxyl groups and highly reactive amino groups, it offers
great opportunity for chemical modification, such as acylation, N-
phthaloylation, alkylation, graft copolymerization and so on, which
affords a wide range of derivatives used in food and nutrition
products, drugs and pharmaceuticals industry, materials science
and agricultural practice (Kumar, Muzzarelli, Muzzarelli, Sashiwa,
& Domb, 2004; Muzzarelli, 2009b; Pillai, Paul, & Sharma, 2009;
Sashiwa & Aiba, 2004).
Slow/controlled release polymers have been widely investi-
gated in the industry, agriculture and daily life productions for the
release of active substances such as nutrients, pesticides, drugs and
aromatics (Fernández-Pérez, Villafranca-Sánchez, Flores-Céspedes,
&
Daza-Fernández, 2011; Herrmann, 2007; Shaviv, 2000).
Slow/controlled release formulations regulate the supply of active
ingredients, allowing a slower and continuous delivery to the envi-
ronment. Therefore, they reduce the loss caused by leaching and
evaporation, maintaining the concentration between the limit of
toxicity and the effectiveness (Johnston, Such, & Caruso, 2009; Tree-
udom, Wanichwecharungruang, Seemork, & Arayachukeat, 2011).
1
-Naphthylacetic acid (NAA), one of the well known plant
growth regulators (PGRs) which belongs to the auxin family, is
a rooting agent and used for the vegetative propagation from
stem and leaf cutting of plants. Literatures shows various kinds
of slow or controlled release polymers containing NAA were
synthesized which were based on both synthetic and natural
polymers (Arranz & Sánchez-Chaves, 1995; Jantas & Delczyk,
2
005; Jantas, 2007; Manolova, Ignatova, Rashkov, Sepulchre, &
Spassky, 1997). Natural polymers such as starch, cellulose, chi-
tosan, sodium alginate, lignin and there derivatives are more
promising than synthetic polymers on food and biomedical appli-
cations due to their better biodegradability and biocompatibility
To our knowledge, no previous report is available on the
slow release of 1-naphthylacetic acid (NAA) based on chitosan.
In the present work, a novel O-naphthylacetyl chitosan (NA-
chitosan) was prepared by reacting the amino groups with phthalic
anhydride, followed by reaction with 1-naphthylacetyl chloride
and hydrolysis under anhydrous hydrazine. The structure of
∗
Corresponding author. Tel.: +86 010 62733407; fax: +86 010 62731016.
Corresponding author. Tel.: +86 010 62731255; fax: +86 010 62731016.
E-mail addresses: renxueqin@cau.edu.cn (X. Ren), shuwenhu@cau.edu.cn (S. Hu).
∗
∗
0
144-8617/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbpol.2012.01.076

1
190
S. Tao et al. / Carbohydrate Polymers 88 (2012) 1189–1194
◦
Scheme 1. Synthetic route of O-naphthylacetyl chitosan. Reagents and conditions: (1) phthalic anhydride, DMF/water, 120 C, 8 h; (2) 1-naphthylacetyl chloride, DMF/LiCl,
triethylamine, 24 h; (3) anhydrous hydrazine, absolute alcohol, 12 h.
NA-chitosan was characterized and its slow release property was
also investigated.
stirred with 200 mL methanol at room temperature for 1 h fol-
lowed by another filtration. This process was repeated for 3 times
to remove all of excess phthalic anhydride. The resulting precipi-
◦
2
. Materials and methods
tate was dried under vacuum at 80 C overnight yields a total 10.5 g
product as of pale tan powder (Scheme 1, product 1).
2
.1. Materials
Thionyl chloride (15 mL) was added to 11.52 g 1-naphthylacetic
acid in a 100 mL two-necked round bottom flask with a mag-
netic stirrer. The reaction proceeded at 50 C for 12 h, and then
◦
Chitosan was purchased from Golden-Shell Biochemical Co.,
Ltd. (Taizhou, China) with the deacetylation degree at 90% and
was used without further purification. All other chemicals were
purchased from Sinopharm Chemical Reagent Co., Ltd (Shang-
hai, China). N,N-dimethylformamide (DMF) was treated by stirring
evaporated with a rotary evaporator to remove excess thionyl chlo-
◦
ride. The resulting orange oil was vacuum distilled (b.p. 152 C at
3
0.54 × 10 Pa) and pure 1-naphthylacetyl chloride was obtained as
a yellowish oil (Ignatova, Manolova, & Rashkov, 1998).
with CaH2 (50 g/L) overnight, followed by vacuum distillation at
0.5 g N-phthaloyl chitosan was dissolved in 100 mL DMF con-
taining 10% (wt%) LiCl, 2 g 1-naphthylacetyl chloride was added
dropwise over 30 min. The mixture was intensively stirred using a
magnetic stirrer for 24 h at room temperature. After the reaction,
the mixture was filtrated by 100 mesh nylon net to remove insol-
uble substances, and then the bronzy liquid was transferred into a
beaker with 100 mL methanol. The reddish brown precipitate was
collected by filtration, washed three times with 100 mL methanol
and 200 mL distilled water respectively and dried under vacuum to
get 1.5 g product as N-phthaloyl-O-naphthylacetyl chitosan (PNA-
chitosan) (Scheme 1, product 2).
40 mL absolute alcohol was blended with 0.5 g PNA-chitosan
powder in a 100 mL two-necked round bottom flask with a con-
denser and a magnetic stirrer, and then added with 1.25 mL
anhydrous hydrazine. After reflux for 12 h and filtration of the
formed O-naphthylacetyl chitosan (NA-chitosan), the product was
washed with 30 mL methanol for 3 times and dried under vacuum
to get a yellowish powder (Scheme 1, product 3).
3
2
0 mmHg (2.7 × 10 Pa). Hydrazine was dried by refluxing it with
an equal amount of KOH pellets for 3 h, and then distilled from fresh
NaOH in a flow of dry N . Thionyl chloride was distilled at normal
2
pressure prior to use. Phthalic anhydride and 1-naphthylacetic acid
were of analytical grade and used without further treatments.
2.2. Synthesis of O-naphthylacetyl chitosan (Scheme 1)
The three-step synthetic route is illustrated in Scheme 1. Chi-
tosan was converted into N-phthaloyl chitosan based on previously
reported method (Kurita, Ikeda, Yoshida, Shimojoh, & Harata,
2
002). A total 7.0 g (42.4 mmol) chitosan was stirred with 19.0 g
(
(
128.27 mmol) phthalic anhydride in 140 mL DMF containing 5%
vol%) distilled water. The mixture was heated at 120 C under
◦
nitrogen for 8 h. After the reaction, the resulting pale tan mixture
was cooled to room temperature and poured into ice water. The
precipitate was collected by filtration, then the precipitate was

S. Tao et al. / Carbohydrate Polymers 88 (2012) 1189–1194
1191
2.3. Analytical methods
FT-IR spectra were recorded on a Nicolet NEXUS-470 Spec-
trometer (Thermo Fisher Scientific, USA) from KBr pellets at room
temperature. About 2 mg of the samples was ground thoroughly
with KBr and pellets were prepared using a hydraulic press under
2
a pressure of 600 kg/cm . All spectra were recorded with an accu-
−
1
mulation number of 32 scans and a resolution of 8 cm
.
1
3
Solid-state
C
cross-polarization magic angle spinning
(
CP/MAS) NMR spectra were taken by a BRUKER DMX 300 (Bruker,
◦
13
Germany) at 25 C using a 7 mm probe with
C frequency
of 100.40 MHz at total suppression of sidebands (TOSS) and
TOSS dipolar-dephased for non-quaternary carbon suppression
(
TOSDL-NQS) mode.
C, H, N elemental composition of chitosan and its derivatives was
determined using a Vario EL III instrument (Elementar, Germany).
The solubility of chitosan and its derivates was evaluated
in organic solvent such as dimethyl sulfoxide (DMSO), N,N-
dimethylformamide (DMF), chloroform, toluene, and 1% aqueous
Fig. 1. FT-IR spectra of (a) chitosan; (b) N-phthaloyl chitosan; (c) N-phthaloyl-O-
naphthylacetyl chitosan; (d) O-naphthylacetyl chitosan.
◦
acetic acid solution at the concentration of 10 mg/mL at 25 C.
Thermogravimetric analysis (TGA, DTG) was carried out with a
TGA Q50 (TA Instruments, USA). All analysis was performed with
a 5 mg sample in an open aluminum pans under nitrogen atmo-
sphere, and the gas flow rate was 40 mL/min. Then the sample was
and absorptions at 1778, 1712 and 721 cm 1 due to phthalimido
−
and aromatic groups in phthaloyl groups disappeared completely.
−
1
Meanwhile, the peaks at 1738 and 781 cm
which represented
◦
heated at constant rates of 10 C/min during the analysis and the
O-naphthalene ester were still considerably sharp. The above data
indicated that NA-chitosan had been successfully prepared.
To further validate the structure, the solid-state 13C NMR spectra
of the products were obtained. In the TOSS mode, chitosan showed
typical chemical shift at 104.23 (C1), 86.00 (C4), 75.24 (C5, C3),
◦
final temperature was up to 600 C.
The NAA release from NA-chitosan tests was carried out in fresh
buffer solutions at pH 4.0 (0.05 M NaOH, 0.288 M CH COOH), pH
3
9
.2 (0.147 M NaHCO , 0.0178 M Na CO ), pH 12.0 (0.01 M NaOH).
3 2 3
A 10 cm long dialysis bag with 10 mg NA-chitosan was placed in
conical bottle containing 100 mL buffer solution and incubated at
61.45 (C6), 58.47 (C2), 23.46 ppm (CH ) (data not shown) (Gartner
et al., 2011). Compared to chitosan, signals of phth, phenylene and
phth C O in N-phthaloyl chitosan were observed at 123.53, 131.42,
3
◦ ◦ ◦
2
0 C, 40 C, and 60 C. Periodically, 2.5 mL sample was withdrawn
and analyzed by UV at 281 nm. The residue was checked by FT-IR
to confirm the structure.
135.82 and 168.83 ppm (Fig. 2a ) which were consistent with the
1
previous literature (Kurita et al., 2002). Fig. 2b shows much broad
1
and strong peaks at 126 ppm, and the peak at 168 ppm is less sharp
than Fig. 2a , and it can be explained by bonding of naphthylacetic
1
3
. Results and discussion
acid, the ratio of aromatic in the main chain was increased, and
the signal of phth C O was overlapped by signals of C O from
Even chitosan is an attractive biomacromolecule, the poor
COOCH C H . After the deprotection of amino groups as shown
2 10 9
solubility in common solvents restricts its further application.
Chemoselective N-phthaloylation of chitosan not only provides
protected functional groups but also improves its solubility. In
our case (Scheme 1), dissolution of 0.5 g N-phthaloyl chitosan in
in Fig. 2c , the signal of pyranose in NA-chitosan is significantly
stronger due to the decrease of aromatic in the main chain.
1
In the TOSDL-NQS mode, peaks due to CH and CH should dis-
2
appear because of the short relaxation times. As expected, peaks
between 20 and 100 ppm belonging to the pyranose were disap-
1
00 mL DMF containing 10% (wt%) LiCl enabled the acylation reac-
tions occurred in homogeneous mixtures under mild conditions.
Removal of the phthaloyl group from PNA-chitosan can be finished
efficiently and conveniently by treating with anhydrous hydrazine.
FT-IR studies were carried out to confirm the structures as
shown in Fig. 1. Compared the spectra of chitosan (curve a) with N-
peared in TOSDL-NQS mode (Fig. 2a , b , c ) compared with cures
2 2 2
in TOSS mode (Fig. 2a , b , c ). Only two peaks at 169.19 and
1
1
1
131.36 ppm ascribable to the carbonyl and C1, C2 of phthaloyl could
be observed in N-phthaloyl chitosan (Fig. 2a ). After the esterifica-
2
tion between N-phthaloyl chitosan and 1-naphthylacetyl chloride
−
1
phthaloyl chitosan (curve b), the peaks at 1659 and 1599 cm were
attributed to carbonyl stretching vibration. N H bending vibra-
tion in chitosan disappeared after the N-phthaloylation. The twin
(Fig. 2b ), peaks at about 169 and 130 were much stronger than
2
N-phthaloyl chitosan (Fig. 2a ) mainly due to the bulk groups of
2
naphthyl C5, C6 and the ester groups of O C O. As discussed
previously in the TOSS mode, these peaks were weak again after
using anhydrous hydrazine to remove the protective groups as to
NA-chitosan.
−1
absorptions at 1778 and 1712 cm were characteristic of imide
C O stretching vibration, and a relatively high intense peak at
−
21 cm corresponded to CH bending vibration in phthalic ring
2
1
7
demonstrated that the N-phthaloylation reaction was successful. In
Carbon, hydrogen, nitrogen elements composition of
chitosan and chitosan derivatives are given below: chi-
tosan, Calc for (C H11NO4)0.9(C H13NO5)0.1·0.56H O, Found:
−
1
the case of PNA-chitosan (curve c), two new peaks at 1744 cm and
−1
7
81 cm were assigned to the stretching vibration of ester groups
6
8
2
in COOCH C10H9 and CH2 bending vibration in the naphthyl
C, 43.68; N, 7.97; H, 7.27. N-phthaloyl chitosan, Calc for
2
ring (Hussein, Zainal, Yahaya, & Foo, 2002; Jantas, 2007). In the
(C14H13NO6)0.9(C H13NO5)0.1·0.65H O, Found: C, 54.79; N, 4.82;
8
2
−1
meantime, the broad band around 3443 cm ascribed to stretching
vibration of inter- and intra-molecular hydrogen bond from NH2
and OH of chitosan molecules was either absented or decreased in
the chitosan derivatives. After the deprotection of N-phthaloyl, the
resultingNA-chitosan(curved) revealeda characteristicabsorption
H, 5.00. PNA-chitosan, Calc for (C38
H
29
NO ) (C
H
NO7)
,
8
0.9 32 29
0.1
Found: C, 73.15; N, 2.15; H, 4.85. NA-chitosan, Calc for
(C18H19NO5)0.4(C20H21NO6)0.1 (C H11NO4)0.5, Found: C, 58.40;
6
N, 6.12; H, 5.91. PNA-chitosan showed a high degree of substi-
tution and the hydroxyl groups (1 primary hydroxyl at C6 and
1 secondary hydroxyl at C3) were fully substituted. It could be
−1
at 1592 cm corresponding to N H bending vibration in chitosan,

1
192
S. Tao et al. / Carbohydrate Polymers 88 (2012) 1189–1194
Fig. 2. Solid-state 13C cross-polarization magic angle spinning NMR spectra in total suppression of sidebands mode (a1) N-phthaloyl chitosan; (b1) N-phthaloyl-O-
naphthylacetyl chitosan; (c1) O-naphthylacetyl chitosan; in total suppression of sidebands dipolar-dephased for non-quaternary carbon suppression mode (a2) N-phthaloyl
chitosan; (b2) N-phthaloyl-O-naphthylacetyl chitosan; (c2) O-naphthylacetyl chitosan.
validated from the FT-IR studies, in Fig. 1, curve c, there are no
improved, which could be soluble in halogenated hydrocarbons,
aromatic, and polar solvents such as chloroform, toluene, tetrahy-
drofuran, dimethyl sulfoxide and N,N-dimethylformamide. That
was mainly because the hydroxyl and amino groups in the main
chain of chitosan were mostly substituted by the bulk benzene and
naphthalene groups. After the deprotection, the solubility of NA-
chitosan was limited, but it was still highly swollen in dimethyl
sulfoxide and N,N-dimethylformamide.
−1
absorption around 3443 cm ascribed to stretching vibration of
inter- and intra-molecular hydrogen bond from NH2 and OH
of chitosan molecules. As to NA-chitosan, it could be calculated
as (C18H19NO5)0.4(C20H21NO6)0.1 (C H11NO4)0.5. The substitution
6
degree of hydroxyl was about 0.4, which mainly causing naphtha-
lene ester partly hydrolyzed in the alkaline environment when the
deprotection of N-phthaloyl proceeded.
The solubility of chitosan derivatives is shown in Table 1. Orig-
inal chitosan dissolved only in aqueous AcOH, and the resulting
chitosan derivatives exhibited an enhanced affinity for organic
solvents, thus the solubility of PNA-chitosan was significantly
TGA and DTG curves of chitosan and chitosan derivatives are
shown in Fig. 3. It showed chitosan had a significant stage of
weight losing started at about 280 C and reached a maximum with
◦
weight loss of 52% due to the decomposition of chitosan, and at
◦
about 100 C, a weight loss about 1.8% was corresponded to water
evaporation in materials. The chitosan had a faster decomposition
Table 1
◦
◦
◦
between 250 C and 350 C and reached the maximum at 300 C
which was consistent with the literature (Ma, Yang, Kennedy, &
Nie, 2009). The N-phthaloyl chitosan showed higher initial decom-
Solubility of chitosan and chitosan derivatives.
Sample
Solvents
DMSO
◦
DMF
CHCl3
Toluene
1% HAc
position temperature started at about 350 C and decomposition
◦
◦
peak at 409 C than chitosan. It reached a maximum at 423 C with
weight loss of 88.0%. Compared to chitosan, PNA-chitosan showed
Chitosan
−
±
+
±
−
±
+
±
−
−
+
−
−
−
+
−
+
N-phthaloyl chitosan
PNA-chitosan
NA-chitosan
−
−
−
◦
a mild speed of decomposition during the temperature of 180 C
and 480 C. It had a decomposition peak at 345 C and the total
weight loss reached 77.4% from 285 C to 389 C. Regarding the
◦
◦
◦ ◦
+
Soluble; ± partially soluble or highly swelled; – insoluble.

S. Tao et al. / Carbohydrate Polymers 88 (2012) 1189–1194
1193
Fig. 3. (a) TGA thermograms of chitosan and chitosan derivatives and (b) DTG curves
for chitosan and chitosan derivatives.
Fig. 4. The release behavior of NAA after heterogeneous hydrolysis at different con-
◦
ditions: (a) under various pH values, 40 C and (b) at various temperatures, pH
NA-chitosan, there were three degradation stages: the first stage
started at about 25–75 C with a weight loss of 2.6% ascribed to the
9.2.
◦
volatile low molecular products and water; the second degradation
◦
stage was at about 125–175 C, which could be explained as the sol-
1
995). The slow release of NAA from some isomeric hexyl 1-
naphthylacetates made it possible to employ these esters every
years, which significantly reduced the cost of distribution and
relieved the environmental stress (Dolci, Navissano, Gay, Eynard,
◦
vent of DMF; the third degradation stage was at about 200–400 C
and reached a maximum at 342 C with weight loss of 63.4%. It was
clear that the thermal stability decreased in this order: N-phthaloyl
chitosan > chitosan > PNA-chitosan > NA-chitosan.
◦
2
&
Rangone, 1999). As to NA-chitosan, the release period sustained
To study the active ingredient release, polymeric derivatives
were hydrolyzed heterogeneously. Commonly, the release behav-
ior of bioactive agents from polymer-bioactive compound adducts
depends on a number of factors, including the sample form,
the hydrophilic character of the compound, the pH value of the
medium, and the incubation temperature (Arranz & Sánchez-
Chaves, 1995). The NAA release behavior of the NA-chitosan under
different pH values of the media at 40 C was investigated. It could
be found (Fig. 4a) that at pH 12.0, the cumulative release rate was
significantly higher than that of pH 4.0 and pH 9.2, mainly due to
◦
up to 2 months at pH 12.0 in 40 C, indicating its supply dura-
tion could be even longer under milder conditions. The persistent
release of NAA provided a consecutive biological activity on crops.
The presence of amino groups in NA-chitosan maintained the vari-
ous unique functions of chitosan, and it may lead to great potential
in biological functions such as antifungal activity (Kumar et al.,
2
004; Liu, Du, Wang, & Sun, 2004), and it could be exploited in
◦
chitosan-based seed coatings and other crop protection applica-
tions (Muzzarelli et al., 2012).
−
the greater availability of OH . This was consistent with the results
described in prior study (Ignatova et al., 1998). Release data at pH
◦ ◦ ◦
9
.2 of the compound adducts at 20 C, 40 C, and 60 C are shown
in Fig. 4b. As incubation temperature increased, the hydrolysis rate
was even higher.
The FT-IR spectra of the residue samples from the heterogeneous
hydrolysis at different release periods were carried out to monitor
the structural changes of the NA-chitosan. Fig. 5 reveals that the
−
1
typical absorption intensity of NA-chitosan at 1738 and 781 cm
representing O-naphthalene ester are weakened. As the hydroly-
sis time increased to 55 days, these peaks were almost invisible.
−1
Meanwhile, the peaks at 1659 and 1599 cm attributed to CH
and NH stretching vibration in chitosan were becoming stronger
2
which indicated that NA-chitosan turned out to be chitosan again.
From the data above, NA-chitosan displayed clearly slow release
properties of NAA. The low molecular weight bioactive compound
(
NAA) was released from the polymer upon the hydrolysis of the
Fig. 5. FT-IR spectra of (a) O-naphthylacetyl chitosan; (b), (c), (d) represent the
spectra of the residues after the heterogeneous hydrolysis at pH 12.0 at 60 C for 15
days, 35 days, 55 days, respectively.
ester groups, which was demonstrated in former literatures as
well (Eynard, Gay, Occelli, Dolci, & Martini, 1986; Tsatsakis et al.,
◦

1
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S. Tao et al. / Carbohydrate Polymers 88 (2012) 1189–1194
4
. Conclusions
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and amino groups in the main chain of the polysaccharide. N-
phthaloyl chitosan provided a reactive intermediate of chitosan
which facilitated the immobilization of bioactive agrochemical
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O-naphthylacetyl chitosan (PNA-chitosan) could be easily carried
out after treatment with anhydrous hydrazine. The release of NAA
linked to chitosan was strongly dependent on both pH value and
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1
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Acknowledgements
This work was supported by Chinese National Scientific Founda-
tion (20875100 & 21175150); The New Century Excellent Talents
in Universities (NCET-07-0810), by Ministry of Education of China;
National Key Technology R & D Program (2011BAD11B02), by Min-
istry of Science & Technology of China; The Innovative Group Grant
of NSFC (30821003), by Ministry of Education of China.
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