Acid-base behavior and Al3+ complex formation of synthesized 2,3-dihydroxyterephthalic acid (DHTPA) at pH 3 as a model compound of Inogashira fulvic acid (IFA)

Article abstract of DOI:10.1016/j.poly.2014.02.006

The interaction between the aluminum ion (Al³⁺) and Inogashira fulvic acid (IFA) at pH 3 was investigated using the calibration curve method for ²⁷Al NMR spectra. The average conditional stability constant (log K) can be calculated to be 2.00-2.04 (M^-1) (bidentate-monodentate) from the results of ²⁷Al NMR measurements. In addition, because IFA has various coordination sites, including COOH, phenolic and/or alcoholic OH groups, we attempted to synthesize 2,3-dihydroxyterephthalic acid (DHTPA) as a model compound with the functional groups of IFA for the investigation of the microscopic coordination mechanism between Al³⁺ and IFA by potentiometric titration and ²⁷Al NMR measurements. The pK _ai values of DHTPA could be determined successfully (pK_a1 = 2.3, pK_a2 = 3.4 and pK_a3 = 7.2; pK_a4 was not determined), and these values indicate that DHTPA can act as a powerful chelating ligand, even at pH 3. DHTPA can interact with Al³⁺, and it predominantly forms 1:1 and 2:1 Al-DHTPA complexes. The calculated average conditional formation constant (log K₁ and K₂) of each complex can be determined as 1.09 (1:1) and 4.81 (M^-1) (2:1). The results obtained showed that both the 1:1 and 2:1 Al-DHTPA complexes are formed and Al³⁺ interacts with IFA at pH3.

Full text of DOI:10.1016/j.poly.2014.02.006

Polyhedron 72 (2014) 135–139
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
3
+
Acid–base behavior and Al complex formation of synthesized
,3-dihydroxyterephthalic acid (DHTPA) at pH 3 as a model compound
of Inogashira fulvic acid (IFA)
2
Tsutomu Kurisaki a, , Mayumi Etou , Yoshihiro Okaue , Hisanobu Wakita , Takushi Yokoyama
⇑
b
b
a
b,
⇑
a
Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan, Fukuoka 814-0180, Japan
Department of Chemistry, Faculty of Science, Kyushu University, 6-10-1, Hakozaki, Higashi, Fukuoka 812-8581, Japan
b
a r t i c l e i n f o
a b s t r a c t
The interaction between the aluminum ion (Al3+) and Inogashira fulvic acid (IFA) at pH 3 was investigated
Article history:
Received 7 October 2013
Accepted 2 February 2014
Available online 13 February 2014
27
using the calibration curve method for Al NMR spectra. The average conditional stability constant
ꢀ1
27
(
logK) can be calculated to be 2.00–2.04 (M ) (bidentate–monodentate) from the results of Al NMR
measurements. In addition, because IFA has various coordination sites, including COOH, phenolic and/
or alcoholic OH groups, we attempted to synthesize 2,3-dihydroxyterephthalic acid (DHTPA) as a model
compound with the functional groups of IFA for the investigation of the microscopic coordination mech-
Keywords:
Inogashira fulvic acid
Al–DHTPA complex
Coordination mechanism
3+
27
anism between Al and IFA by potentiometric titration and Al NMR measurements. The pKai values of
DHTPA could be determined successfully (pKa1 = 2.3, pKa2 = 3.4 and pKa3 = 7.2; pKa4 was not determined),
and these values indicate that DHTPA can act as a powerful chelating ligand, even at pH 3. DHTPA can
interact with Al3 , and it predominantly forms 1:1 and 2:1 Al–DHTPA complexes. The calculated average
27
Al NMR
Complex formation
+
conditional formation constant (logK
1
and K
2
) of each complex can be determined as 1.09 (1:1) and 4.81
ꢀ1
(
M ) (2:1). The results obtained showed that both the 1:1 and 2:1 Al–DHTPA complexes are formed and
3
+
Al interacts with IFA at pH3.
Ó 2014 Published by Elsevier Ltd.
1
. Introduction
Humic substances (HS) are the most abundant natural organic
ical form. Organically coordinated Al, including the Al–FA complex,
is of great importance for reducing Al toxicity. Therefore, the inter-
action between Al and various FAs, especially Suwannee River FA,
has been studied extensively using various techniques [5–11]. In
this study, we focused on the interaction between Al and Ino-
gashira fulvic acid (IFA) using the calibration method for 27Al
NMR spectra. The structure and composition of FAs strongly de-
pend on the environment in which they are formed. FAs have var-
compounds formed by the decay of plant and animal biomass in
aquatic and terrestrial systems [1]. In particular, fulvic acid (FA),
which is a soluble fraction of HS at all pH values, is known to be
able to form metal–FA complexes with various metal ions in the
environment [2,3]. Complexation between FA and various metal
ions plays an important role in reducing the toxicity of metal ions
and the mobility of metal ions in natural waters. Aluminum (Al) is
known to interact with FA strongly, as is iron [2]. Generally, Al is
fixed as an oxide or aluminosilicate in nature, and these minerals
are insoluble at neutral pH and are barely released into the envi-
3+
a
ious coordination sites, which have wide pK values [12–14].
Therefore, it is difficult to obtain microscopic information about
the complexation between Al and FAs. We also tried to synthesize
a model compound with the functional groups of FAs. The major
functional groups of FAs that have complexing abilities with Al3+
are COOH, phenolic and/or alcoholic OH groups, and we attempted
to synthesize a model compound containing those groups.
3
+
ronment. However, Al is released as the aluminum ion (Al ) by soil
acidification, and it is easily transported in the aquatic environ-
ment [4]. The Al ion and its hydrolytic species have a toxic effect
on plants and animals, and the toxicity of Al depends on its chem-
3
+
In this study, we synthesized 2,3-dihydroxyterephthalic acid
(DHTPA, H L, Fig. 1), which has two COOH groups and two OH
4
groups, as a model compound with the functional groups of FAs.
The purpose of this study is as follows: (a) investigation of the acid
property of DHTPA; (b) the estimation of the conditional stability
constants of the Al–DHTPA complex using Al NMR and potentio-
metric titration methods. Moreover, we also estimated the
⇑
Corresponding authors. Tel.: +81 928716631 (T. Kurisaki). Tel.: +81 926423908
T. Yokoyama).
E-mail addresses: kurisaki@fukuoka-u.ac.jp (T. Kurisaki), yokoyamatakushi@
(
27
chem.kyushu-univ.jp (T. Yokoyama).
http://dx.doi.org/10.1016/j.poly.2014.02.006
0
277-5387/Ó 2014 Published by Elsevier Ltd.

1
36
T. Kurisaki et al. / Polyhedron 72 (2014) 135–139
3
+
COOH
OH
2.4. Preparation of a sample solution containing Al and each ligand
A sample solution was prepared by mixing the Al stock solution
and DHTPA or the IFA stock solution. The Al and DHTPA concen-
3
+
ꢀ3
OH
COOH
trations in the sample solution were fixed at 1.0 ꢂ 10
and
ꢀ4
3+
2
.0 ꢂ 10 M, respectively. In addition, the Al and IFA concentra-
ꢀ3
tions in the sample solution were fixed at 1.0 ꢂ 10 M and
3
Fig. 1. Structure of 2,3-dihydroxyterephthalic acid (DHTPA).
200 mg/dm , respectively. The pH was adjusted to pH 3 by adding
NaOH solution. The sample solution was allowed to stand for 24 h
before NMR measurements.
complex formation constant between Al3+ and Inogashira fulvic
acid (IFA). These complex formations were investigated at pH 3 be-
cause Al hydrolysis can be ignored under this condition.
. 27Al NMR measurements
3
The 27Al NMR spectra were recorded on a JEOL GX 400 spec-
trometer operating at 104.2 MHz (pulse delay, 0.4 s and 512 tran-
sients). The sample solutions were analyzed in 10 mm PTFF NMR
tubes. The NMR measurements were carried out at room
temperature.
2
. Experimental
2.1. Reagents
2 6
O)
]3+ in
For the determination of the concentration of Al[(H
the sample solutions at pH 3, a calibration curve was obtained as
follows. Al(NO solutions (pH 3) with different concentrations
were placed in 10 mm-diameter PTFE tubes. A sodium aluminate
3 3
All of the reagents used were of analytical grade. An Al(NO )
stock solution was prepared by dissolving Al(NO
HNO
3
)
3 2
ꢁ9H O in diluted
3 3
)
-
3
3
(0.1 mol dm (M)), and this solution was standardized by
EDTA titration. The synthetic method used for DHTPA is summa-
rized in the Supporting Information. IFA that was extracted from
Inogashira ando soil (Shizuoka prefecture, Japan) was commer-
cially obtained from the Japanese Humic Substances Society. IFA
was prepared by an IHSS (International Humic Substance Society)
method. The composition of the functional groups and the total
acidity is summarized in the Supporting Information (Table S-1).
The DHTPA and IFA stock solutions were prepared by dissolving
in water. All solutions were prepared with deionized-distilled
water.
ꢀ2
solution (1 ꢂ 10 M in 0.1 M NaOH solution) enclosed in a poly-
propylene tube of 5 mm in diameter was used as an external stan-
dard. The 5 mm polypropylene tube was inserted into the 10 mm
2
7
PTFE tube, and the Al NMR spectrum was measured. The ratios
3
+
ꢀ
4
]
of the peak intensities for [Al(H (0 ppm) and [Al(OH)
2
O)
6
]
(
80 ppm) were measured for the Al(NO ) solutions with different
3 3
concentrations. The calibration curve obtained is shown in the
Supporting Information (Fig. S1). For sample solutions, the ratio
was also measured by the same method, and the concentration
3
+
of free Al in the sample solutions was determined using a calibra-
tion curve.
2.2. Synthesis of DHTPA
4
. Results and discussion
To catechol (11 g, 0.1 mol), dissolved in 300 cm3 of methanol
(
under a nitrogen atmosphere), was added sodium hydroxide pel-
4.1. IFA system
lets (8 g, 0.2 mol) in one portion. The resulting solution was al-
lowed to sit overnight and was then evaporated in vacuo (105 °C,
3
+
To investigate the interaction between Al and IFA at pH 3, the
2
7
3+
3
2 h) to give a light tan, dry powder, which was further treated
Al NMR spectrum for the Al and IFA mixed solution at pH 3 was
with excess carbon dioxide (80 atm) at 185 °C (72 h) in a static,
stainless-steel bomb. The light tan solid product was acidified with
hot aqueous hydrochloric acid (6 N), filtered and washed with hot
water. The solid product was dissolved in hot aqueous sodium
hydroxide (pH 9), treated twice with charcoal, and then acidified
again with hydrochloric acid to obtain an almost white powder
measured. No specific peak due to the Al–IFA complex was ob-
2
7
served in the Al NMR spectrum (see Supporting Information,
Fig. S2). Because the IFA structure is complicated, the symmetry
3
+
of the Al combined with IFA may be considerably lowered. How-
ever, the peak intensity ratio ([0 ppm]/[80 ppm] = 1.46) of the sam-
ple solution containing IFA was lower than that ([0 ppm]/
ꢀ
1
3+
(
yield: 51.0%). Main IR peaks (KBr, cm ): 3500,
m
(OH, str); 1650
O): 7.28 (s, 2H, ArH);
ꢁH O: C, 44.44; H, 3.70.
[80 ppm] = 1.66) of the Al solution without IFA. This finding
1
3+
m
(C@O, str). H NMR chemical shifts (D
1.3 (s, 2H, OH). Anal. Calc. for C
Found: C, 45.34; H, 3.78%.
2
strongly indicates that a certain amount of Al can interact with
3
+
1
H
8 6
O
6
2
IFA. From the calibration curve, the free Al concentration and
3
+
the concentration of Al combined with IFA were estimated to
ꢀ
4
ꢀ4
be 8.83 ꢂ 10 and 1.17 ꢂ 10 M, respectively. The conditional
average stability constant for the Al–IFA complex, K , is defined
I
2.3. Potentiometry
by Eq. (1). The thermodynamic and spectroscopic studies on the
complexation equilibria of IFA in aqueous solution were investi-
gated by Miyajima and Mori [12]. They revealed that the average
degree of dissociation of IFA is around 0.33–0.46 (ionic strength
To determine the acid dissociation constant of DHTPA, a poten-
tiometric titration was carried out at 25 ± 0.1 °C under a current of
purified nitrogen gas using a pH meter (Orion 701A) with a glass
electrode (Orion No. 90-02) and a reference electrode (Orion No.
(
3
NaNO ): 0.01–1.00 M) by potentiometric titration. From this
value, we could calculate the concentration of the dissociated func-
tional group of IFA at pH 3. The total functional group concentra-
9
a
0-01). To determine the pK value of DHTPA, a DHTPA solution
ꢀ3
3
(
2 ꢂ 10 M in 0.1 M NaNO
3
, 40 cm ) was titrated against an NaOH
solution (1 ꢂ 10 M in 0.1 M NaNO ).
To investigate the interaction between Al and DHTPA at pH 3,
ꢀ3
tion of IFA was determined to be 1.44 ꢂ 10 M. In this study, we
ꢀ
2
3
assumed that the dissociated functional group of IFA combined
3+
3+
with Al was a monodentate or bidentate ligand.
ꢀ
2
an Al solution (2 ꢂ 10 M in 0.02 M NaNO
3
, pH 3) was titrated
, pH 3),
ꢀ3
Al þ IFA ꢀ Al ꢀ IFA
ð1Þ
ð2Þ
against a DHTPA solution (1 ꢂ 10 M in 0.02 M NaNO
3
+
and the change in the H concentration against the Al/DHTPA mo-
lar ratio was measured using the same system as described above.
K
I
¼ ½Al ꢀ IFAꢃ=½Alꢃfree½IFAꢃfree

T. Kurisaki et al. / Polyhedron 72 (2014) 135–139
137
Here, [Al]free represents the concentration of free Al3+ and
IFA]free is defined as the concentration of the free dissociated func-
[
ꢀ4
tional group of IFA ((1.20–1.32) ꢂ 10 M, bidentate–monoden-
tate). [IFA]free is defined as the difference of the total functional
ꢀ3
group concentration of IFA (1.44 ꢂ 10 M) and the concentration
of the Al–IFA complex. The logK value was calculated to be
.00–2.04 (bidentate–monodentate). Browne reported the condi-
I
2
3+
tional stability constants for Al binding Suwannee river fulvic
acid from pH 3.6–5.5 by potentiometric titration (logKorg = 3.2 at
pH 3.6) [6]. Lambert et al. also reported that the conditional stabil-
ity constants of Al /humic substance complexes ranged from 2.0
to 4.3, depending on the ratio of [Al]complex to dissolved organic car-
bon and the pH value [5]. In addition, Gerke also investigated the
3
+
conditional stability constants (K
0
) of humic-Al complexes at pH
= 4.00) [9]. Because in our experimental the pH is
, the amount of dissociated functional group of FA was lower than
value may be
slightly low. It has been reported that fulvic acid has several func-
tional groups whose pK values show a wide pH range. It is difficult
4
.0–6.0 (logK
0
3
that reported in previous studies. Thus, the logK
I
a
to determine the microscopic binding structure of Al–IFA com-
plexes, therefore we attempted to synthesize a model compound
with similar functional groups in FAs. Because the functional
groups of FAs that have complexing abilities with Al3 are COOH,
phenolic or alcoholic OH groups, we synthesized a model com-
pound containing those groups.
+
4.2. DHTPA system
To quantitatively express the acid dissociation constant for
DHTPA, it is necessary to determine the average degree of dissoci-
ation and pH at each point of the titration. Fig. 2(a) shows the titra-
tion curve for DHTPA. In this study, the data analysis was carried
out using the method described by Miyajima and Mori [12]. The
average degree of dissociation can be represented by Eq. (3).
Fig. 2. Titration curve for the DHTPA system (a) and the relationship between the
average degree of dissociation against total acid groups (a) and pK value (b).
a
þ
a
¼ fCNaOH
V
NaOH þ ½H ꢃðV
0
þ VNaOHÞg=n
A
ð3Þ
Here,
acid groups and n
determined by the end point of the titration. CNaOH indicates the
concentration of NaOH and VNaOH is the volume of the titrant. V
is the initial volume of the DHTPA solution. From the calculated
value and the pH determined by Eq. (3), the apparent acid disso-
ciation constant of DHTPA is defined as given in Eq. (4).
a
is an average degree of dissociation relative to the total
3+
To determine the complex formation between Al and DHTPA
A
is the amount of total acid groups, which was
27
at pH 3, the Al NMR spectrum for a sample solution containing
Al and DHTPA was measured. Because the amount of synthesized
DHTPA was very small and the solubility of DHTPA was relatively
low, all experiments were conducted under conditions where the
amount of Al exceeded that of DHTPA. No specific peak due to
an Al–DHTPA complex was observed in the NMR spectrum, such
as that observed for the Al–IFA complex (Supporting Information,
Fig. S3). However, the peak intensity ratio ([0 ppm]/
3+
0
a
3+
pK
a
¼ pH ꢀ logf
a
=ð1 ꢀ
a
Þg
ð4Þ
[
(
80 ppm] = 1.21) of the sample solution was lower than that
The pK is the apparent acid dissociate constant. Furthermore,
a
3
+
[0 ppm]/[80 ppm] = 1.66) of the Al solution without DHTPA. This
using the titration curve of DHTPA, Eqs. (3) and (4), a pK versus
plot was obtained (Fig. 2(b), close circle). Because DHTPA has
two OH groups and two COOH groups in the structure, the pK ver-
a
3
+
fact strongly indicates that a certain amount of Al can interact
a
3
+
with DHTPA, and the structure of Al in the complex is consider-
ably distorted (a decrease in symmetry). From the calibration curve
method, the molar ratio of [Al]free/[Al]complex is approximately 2.68.
Because detailed information about the complexation between
Al3+ and DHTPA could not be obtained by the NMR measurement,
the potentiometric titration of the Al–DHTPA system was
conducted. Fig. 3(a) shows the titration curve when an Al solu-
tion (pH 3) was titrated into a DHTPA solution (pH 3). In the titra-
tion experiment, the release of H was observed, which indicates
that displacement of H in DHTPA by Al occurred. Fig. 3(b) also
shows the relationship between the amount (moles) of Al added
and the amount (moles) of H released from DHTPA during the
titration experiment. There was a linear relationship between
these two variables until the Al/DHTPA molar ratio reached unity.
The slope of the line was approximately 0.62, which suggests that
a
sus
a
plot can be represented using individual pK
a
values (pKai) and
its fraction (f
i
) of each functional group.
X
pKai ¼ pH ꢀ logf
a
i
=ð1 ꢀ
a
i
Þg
a
¼
fia
i
ð5Þ
3+
The pKai values were estimated by the curve fitting method
using Eqs. (3)–(5). In Fig. 2(b), the closed and open circles represent
the experimental and calculated values, respectively. The experi-
mental and calculated results agreed well with each other. Because
DHTPA was oxidized above pH 9 during the titration experiment,
the data below pH 6 were used for the analysis. The acid dissocia-
tion constants of DHTPA obtained were as follows: pKa1 = 2.28,
pKa2 = 3.40 and pKa3 = 7.20. The COOH groups showed relatively
strong acid properties, which indicates that DHTPA can act as a
powerful chelating ligand for Al3+, even in acid aqueous solution.
+
+
3+
3+
+
+
3+
two H were released from DHTPA by combining with three Al

1
38
T. Kurisaki et al. / Polyhedron 72 (2014) 135–139
ꢀ
2ꢀ
AlH2L þ Al3þ ꢀ Al HL þ Hþ
þ
3þ
ions. Because H
3
L
(63 %) and H
2
L
(25 %) predominantly exist in
ð10Þ
2
the sample solution around pH 3, in this study we hypothesized
that these dissociated species would preferentially interact with
Al . Therefore, until the Al/DHTPA molar ratio reached unity, the
following two reactions predominantly occurred. Considering the
structure of DHTPA, it is possible that H
:1 Al-DHTPA and 2:1 Al
At equilibrium, the dominant structure of the Al–DHTPA com-
3
+
3
+
plex will be Al
modynamically stable, one Al in Al
chelate ring whose structure is similar to the salicylate complex
with Al [15]. On the other hand, another Al may form a mono-
dentate complex with a COO group (dissociated COOH group). Be-
cause the pKa4 value is approximately 15, the one OH group hardly
dissociates and the displacement of H by Al hardly occurs. The
proposed structures for AlH
Based on the above results, the change in the Al concentration
during the titration experiment can be calculated, and the distribu-
tion is represented in Fig. 3(c). Until Al/DHTPA reaches unity, com-
plexation predominantly occurs. From this distribution, when the
Al/DHTPA molar ratio is 5, the molar ratio of [Al]free/[Al]complex is
approximately 2.4. This value is quite similar to that from the
2
HL . Because the six-membered structure is ther-
3
+
3+
2
HL may form a stable
ꢀ
2ꢀ
3
L
2
and H L
can form
3
+
3+
1
2
-DHTPA complexes according to Eqs.
ꢀ
(
6) and (8).
ꢀ
þ Al3þ ꢀ AlH
þ
þ Hþ
+
3+
H
3
L
2
L
ð6Þ
+
3+
2
L and Al
2
HL are shown in Fig. 3(d).
þ
þ
ꢀ
3+
K
1
¼ ½AlH
2
L ꢃ½H ꢃ=½Alꢃfree½H
3
L ꢃ
ð7Þ
ð8Þ
ð9Þ
free
2
ꢀ
þ 2Al3þ ꢀ Al
HL þ Hþ
3þ
H
2
L
2
3
þ
þ
2
free
2ꢀꢃ
K
2
¼ ½Al
2
HL ꢃ½H ꢃ=½Alꢃ ½H
2
L
free
+
27
From the change in the H concentration during the titration,
the concentration of Al that interacts with DHTPA until Al/DHTPA
reached unity can be calculated. In addition, to determine
results of the Al NMR measurement ([Al]free/[Al]complex = 2.68).
Thus, the dominant complex species contained in the Al and
3
+
3+
2
7
DHTPA mixed solution, which was measured by Al NMR, is
ꢀ
3
2ꢀ
3+
[
H
3
L ]free and [H
2
L
]
free, we hypothesized that the concentration
Al
COOH and phenolic OH groups, and they have a wide range of
pK values. Our synthesized DHTPA has a COOH and phenolic OH
groups and these have a various pK values, which indicates that
2
HL . The natural FAs have various coordination sites, such as
+
of Al that is responsible for each reaction (Eqs. (6) and (8)) de-
ꢀ
2ꢀ
pends on the existing ratio of H
mental conditions. The calculated data are summarized in
Table 1. The calculated logK and logK values are 1.09 and 4.81,
respectively. In addition, until the range of the Al/DHTPA reached
unity, most of the DHTPA can interact with Al3 . Thus, with an
Al/DHTPA ratio above unity, the following reaction may occur
3
L
and H
2
L
under the experi-
a
a
DHTPA is a suitable model compound for the localized structure
of FA. Our results are quite useful for the fixation and detoxification
1
2
+
3+
of Al by natural organic compounds in nature. In addition, this
3
+
result is also useful to deduce the behavior of Al in the human
body. Recently, focus has been given to human exposure to Al
+
and some amount of H is released.
3
.1
.0
10
(
a)
(
b)
8
3
Al/DHTPA of 1
6
4
2
2
2
.9
.8
.7
:
:
Al + NaNO3
Al + DHTPA
2
y=0.6237x + 0.0014
10
0
2
4
6
8
10
0
20
30
40
50
0
0
0
.006
.004
.002
0
5
-
5
Amount of Al added / (x10 ) mole
(
c)
(d)
Al/DHTPA molar ratio
Free Al3+
Complexed Al3+
O
:
4
O
Al
C
:
O
C
OH
O
3
2
1
0
O
O
Al
:
molar ratio of
[
Al] /[Al]
free complex
Al
O
OH
C
O
COOH
L+
3+
AlH
2
Al HL
2
0
2
4
6
8
10
Al/DHTPA molar ratio
Fig. 3. Titration curve for the DHTPA and Al3+ system (a), the relationship between the amount of Al added and the amount of H+ released from DHTPA (b), the distribution
3+
3+
+
ꢀ3
3
of the Al concentration during the titration experiment (c) and the structures of the AlH
2
L
and Al
2
HL complexes (d). (a) s: DHTPA solution (1 ꢂ 10 mol/dm (M) in 0.02 M
3+
ꢀ2
3+
3+
ꢀ2
NaNO
3
, pH 3) titrated with Al solution (2 ꢂ 10 M in 0.02 M NaNO
3
, pH 3); h: NaNO
3
solution (0.02 M, pH 3) titrated with Al solution (2 ꢂ 10 M in 0.02 M NaNO
3
, pH
+
ꢀ6
3+
3
), (b) 4: Amount of H released/(ꢂ10 ) mole and (c) j: Concentration of free Al [Al]free, d: Concentration of complexed Al [Al]complex and N: Molar ratio of [Al]free
/
[
Al]complex.

T. Kurisaki et al. / Polyhedron 72 (2014) 135–139
139
Table 1
Concentrations of each fraction during the titration experiment
Al–DHTPA complex (logK
logK = 4.81).
= 1.09) and a 2:1 Al
2
–DHTPA complex
1
(
2
(Al/DHTPA molar ratio of 1).
Species
Concentration (M)
Appendix A. Supplementary data
Al3+
DHTPA(H
]
9.52 ꢂ 10
ꢀ4
[
[
[
[
total
ꢀ
4
4
L)]total
9.52 ꢂ 10
6.81 ꢂ 10
2.71 ꢂ 10
8.40 ꢂ 10
4.68 ꢂ 10
1.86 ꢂ 10
2.14 ꢂ 10
8.48 ꢂ 10
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2014.02.006.
ꢀ
ꢀ4
ꢀ4
ꢀ4
ꢀ4
ꢀ4
ꢀ4
ꢀ5
H
H
3
L ]initial
2
ꢀ
2
L
]
initial
Total [Al3+]complex
+
[
[
[
[
AlH
2
L ]
References
3
Al
2
HL +]
ꢀ
H
H
3
L ]free
[1] R. Sutton, G. Sposit, Environ. Sci. Technol. 39 (2005) 9009.
[2] K.M. Elkins, D.J. Nelson, J. Inorg. Biochem. 87 (2001) 81.
2
ꢀ
2
L
]
free
[
[
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and the interaction between Al3+ and some bioligands has been
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[
[
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investigated [16–19]. Because the most bio-ligands have a COOH
group and an OH group in their structures, our results regarding
DHTPA are useful for a discussion about the structural features of
Al complexes with bioligands.
[8] S.H. Sutheimer, S.E. Cabaniss, Geochem. Cosmochim. Acta 61 (1997) 1.
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[
[
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[
[
[
11] M. Yan, M.F. Benedetti, G.V. Korshin, Water Res. 47 (2013) 5439.
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5
. Conclusions
We have investigated the interaction between Al3+ and IFA at
[14] J.A. Leenheer, R.L. Wershaw, M.M. Reddy, Environ. Sci. Technol. 29 (1995) 399.
[
[
[
15] T. Yokoyama, H. Abe, T. Kurisaki, H. Wakita, Anal. Sci. 13 (1997) 425.
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pH 3, and the average conditional stability constant (logK) was cal-
culated to be 2.00–2.04. In addition, to investigate the microscopic
structure of the Al-IFA complex, we attempted to synthesize
DHTPA as a model compound with two COOH and two phenolic
OH groups. DHTPA can strongly interact with Al3 to form a 1:1
[18] X. Yang, Q. Zhang, L. Li, R. Shen, J. Inorg. Biochem. 101 (2007) 1242.
19] P. Rubini, A. Lakatos, D. Champmartin, T. Kiss, Coord. Chem. Rev. 228 (2002)
37.
[
1
+