Environmental Engineering Reference
In-Depth Information
The ternary complexes of
Cu
2
+
, Ni
2
+
, Co
2
+
and Zn
2
+
with resorcinol as
primary ligand and with some biologically important aliphatic dicarboxylic
acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic) as secondary
ligands in aqueous solution at 25 °C and
I
=
0.1 mol dm
−
3
NaNO
3
show very
high conditional stability constants, such as
log
10
β
MAR
=
13. 05
−
16. 48
for
Cu
2
+
, 11.72-13.32 for Ni
2
+
, 10.01-11.29 for Zn
2
+
, and 8.78-10.01 for Co
2
+
,
compared to those of the respective binary complexes (2.29-7.30, 2.29-6.10,
2.33-5.80 and 2.19-5.80, respectively, ranges including both log
10
K
1
and log
10
K
2
) (Table
2
) (Radalla
2010
). The ternary complexes between vanadium(III)-
picolinic acid (or dipicolinic acid) and the amino acids cysteine, histidine, aspar-
tic acid and glutamic acid have been examined in aqueous solution at 25 °C
and 3.0 mol
·
dm
−
3
KCl as ionic medium (Table
2
) (Rosas et al.
2010
; Shiozawa
et al.
2011
). The results show that the stability constants range from
−
1.96-4.8
for three ternary complexes of aspartic acid, 0.74-2.26 for three ternary com-
plexes of glutamic acid, 1.71-8.69 for four ternary complexes of cysteine, and
−
0.35-10.22 for histidine (Rosas et al.
2010
)
.
For dipicolinic acid as a primary
ligand, the stability constants range from
−
5.98 to 8.17 for five ternary com-
plexes of aspartic acid,
−
6.2 to 10.59 for five ternary complexes of glutamic
acid,
−
1.54 to 13.91 for four ternary complexes of cysteine, and
−
9.7 to 14.1
for five ternary complexes of histidine (Shiozawa et al.
2011
). The significantly
high values of the stability constants of ternary complexes are similar to those
of DOM in natural surface waters or hydrophobic acids extracted from surface
waters (
K
1
=
8-15; Table
1
) (Midorikawa and Tanoue
1998
; Sunda and Hanson
1987
,
1991
; Sunda and Ferguson
1983
; Moffett et al.
1990
; Coale and Bruland
1988
,
1990
; van Den Berg
1984
; Midorikawa and Tanoue
1996
). Therefore, for-
mation of ternary complexes could be vital to understand the M-DOM compl-
exation in natural waters. The results of a species distribution obtained for the
Cu
2
+
+
malonic acid
+
resorcinol system shows that the formation of MA starts
at pH < 3, reaches a maximum concentration (70 % total Cu
2
+
) at pH 4.2 and
decreases to a minimum when MAR becomes predominant. The maximum con-
centrations of MA
2
and MR are less than 5 % of total Cu
2
+
in solution (Radalla
2010
).
These results suggest the following hypotheses (Radalla
2010
): (i) Stabilities of
ternary complexes with respect to the aliphatic dicarboxylic acids follow the order:
adipic > succinic > malic > malonic > maleic > tartaric > oxalic; this behavior
can be explained in terms of the decrease in basicity of the aliphatic dicarboxylic
acids in the same direction. (ii) The complex stability of the ternary complexes
with respect to the metal ion present follows the Irving-Williams series (Irving and
Williams
1948
). (iii) The stabilities of the ternary complexes are higher than for
the 1:1 binary complexes of the corresponding aliphatic dicarboxylic acid or res-
orcinol for all systems studied; this behavior can be attributed to some coopera-
tive interaction in the ternary complex between the carboxylic acid and resorcinol,
such as H-bond formation. Finally, it is vital to examine the formation of ternary
complexes of metal ions with fulvic acids and tryptophan in aqueous media, under
laboratory conditions. This should be the focus for future studies.
