798
K. M. G. Mostofa et al.
Em = 220–230/322–336 nm) in aqueous solution (Zhang et al. 2010). Note that
the fluorescence properties of EPS are similar to those of tryptophan, with higher
fluorescence intensity at peak T UV -region than at peak T-region and similar Ex/
Em maxima.
The conditional stability constants (log 10 K) for the complexation of some
standard organic and inorganic ligands with metal ions are identified in aqueous
solution as 3–6 for Cu 2+ -carboxylic or HO group; 2.8 for Cu 2+ -amine (NH 2 );
4.4 for Cu 2+ -ethanol amine; 6.6 for Cu 2+ -glycine (NH 2 –CH 2 –COOH or NH 3
+ –
CH 2 –COO − ); 8.5 for Cu 2+ -ethylene diamine (NH 2 –CH 2 –CH 2 –NH 2 ); 7.2 for
Cu 2+ - aspartic acid [HOOC–CH(NH 2 )–CH 2 –COOH]; 9.4 for Cu 2+ - iminodiaacetic acid (HOOC–CH 2 –NH 2 –CH 2 –COOH); 8.3 for Cu 2+ - diaminopropanol;
11.4 for Cu 2+ - ethylenediamine-N-acetic acid; 13.0 for Cu 2+ -diethylenetriamine;
6.27 and 11.76 for Eu 3+ -5-sulfosalicylic acid; 6.4 and 11.99 for Cm 3+ -5sulfosalicylic acid; 8.06 and 15.34 for Am 3+ -5-sulfosalicylic acid; 8.56 and
17.51 for Pu 3+ -5-sulfosalicylic acid; 59.65 and 14.06 for Th 4+ - catechol; 48.51
and 64.86 for Th 4+ -hydroquinone; and 16.98, 46.46, and 59.65 for Th 4+ - resorcinol (Table 1) (Nair and Chander 1983; Martin and Prados 1974; Thakur et al.
2006; Smith 1974). The stability constants of various standard organic substances
are similar to those of allochthonous and autochthonous DOM in natural waters,
indicating that carboxylic, phenolic and amino group-containing carboxylic acid
bound in allochthonous and autochthonous DOM may form complexes with
metal ions in aqueous solution.
The binary complexes of Cu 2+ , Ni 2+ , Co 2+ and Zn 2+ with resorcinol and
some biologically important aliphatic dicarboxylic acids (adipic, succinic,
malic, malonic, maleic, tartaric and oxalic) in aqueous solution at 25 °C and
I = 0.1 mol dm −3 NaNO 3 suggest the following hypotheses (Radalla 2010): (i)
Stability of the 1:1 binary complexes for all investigated ligands is higher than that
of the corresponding 1:2 ones. (ii) Normal 1:1 and 1:2 complexes of resorcinol are
formed with all of the metal ions studied. (iii) The order of stability constants of
the 1:1 complexes of all investigated ligands with respect to the divalent transition
metal ions follows the Irving-Williams series (Zn < Cu > Ni > Co) (Irving and
Williams 1948). (iv) Stability of the 1:1 metal-complexes of aliphatic dicarboxylic
acids follows their basicity (pK a1 + pK a2 ), where K a1 and K a2 are the first and second dissociation constants, respectively.
Experimental studies show that photoinduced degradation can decrease the
conditional stability constants of M-DOM complexes in stream waters (log
K 1 = 4.9 to 4.1) and in wetland waters (log K 1 = 8.02 and log K 2 = 6.1 to
7.61 and 5.85, respectively), whilst their values are increased in river DOM (log
K 1 = 7.59 and log K 2 = 5.83 to 7.63 and 5.88, respectively) and in lake DOM
(log K 1 = 16.3 to 16.8). The values remain the same (log K 1 = 13.5) before
and after irradiation of estuarine waters (Wu et al. 2004a; Brooks et al. 2007;
Sander et al. 2005; Shank et al. 2006). The decomposition of the functional
groups in DOM is susceptible to decrease the stability constants of the M-DOM
complexes in natural waters. In contrast, the increase in stability constants of
the M-DOM complexes is likely caused by the formation of new photoproducts
K. M. G. Mostofa et al.
Em = 220–230/322–336 nm) in aqueous solution (Zhang et al. 2010). Note that
the fluorescence properties of EPS are similar to those of tryptophan, with higher
fluorescence intensity at peak T UV -region than at peak T-region and similar Ex/
Em maxima.
The conditional stability constants (log 10 K) for the complexation of some
standard organic and inorganic ligands with metal ions are identified in aqueous
solution as 3–6 for Cu 2+ -carboxylic or HO group; 2.8 for Cu 2+ -amine (NH 2 );
4.4 for Cu 2+ -ethanol amine; 6.6 for Cu 2+ -glycine (NH 2 –CH 2 –COOH or NH 3
+ –
CH 2 –COO − ); 8.5 for Cu 2+ -ethylene diamine (NH 2 –CH 2 –CH 2 –NH 2 ); 7.2 for
Cu 2+ - aspartic acid [HOOC–CH(NH 2 )–CH 2 –COOH]; 9.4 for Cu 2+ - iminodiaacetic acid (HOOC–CH 2 –NH 2 –CH 2 –COOH); 8.3 for Cu 2+ - diaminopropanol;
11.4 for Cu 2+ - ethylenediamine-N-acetic acid; 13.0 for Cu 2+ -diethylenetriamine;
6.27 and 11.76 for Eu 3+ -5-sulfosalicylic acid; 6.4 and 11.99 for Cm 3+ -5sulfosalicylic acid; 8.06 and 15.34 for Am 3+ -5-sulfosalicylic acid; 8.56 and
17.51 for Pu 3+ -5-sulfosalicylic acid; 59.65 and 14.06 for Th 4+ - catechol; 48.51
and 64.86 for Th 4+ -hydroquinone; and 16.98, 46.46, and 59.65 for Th 4+ - resorcinol (Table 1) (Nair and Chander 1983; Martin and Prados 1974; Thakur et al.
2006; Smith 1974). The stability constants of various standard organic substances
are similar to those of allochthonous and autochthonous DOM in natural waters,
indicating that carboxylic, phenolic and amino group-containing carboxylic acid
bound in allochthonous and autochthonous DOM may form complexes with
metal ions in aqueous solution.
The binary complexes of Cu 2+ , Ni 2+ , Co 2+ and Zn 2+ with resorcinol and
some biologically important aliphatic dicarboxylic acids (adipic, succinic,
malic, malonic, maleic, tartaric and oxalic) in aqueous solution at 25 °C and
I = 0.1 mol dm −3 NaNO 3 suggest the following hypotheses (Radalla 2010): (i)
Stability of the 1:1 binary complexes for all investigated ligands is higher than that
of the corresponding 1:2 ones. (ii) Normal 1:1 and 1:2 complexes of resorcinol are
formed with all of the metal ions studied. (iii) The order of stability constants of
the 1:1 complexes of all investigated ligands with respect to the divalent transition
metal ions follows the Irving-Williams series (Zn < Cu > Ni > Co) (Irving and
Williams 1948). (iv) Stability of the 1:1 metal-complexes of aliphatic dicarboxylic
acids follows their basicity (pK a1 + pK a2 ), where K a1 and K a2 are the first and second dissociation constants, respectively.
Experimental studies show that photoinduced degradation can decrease the
conditional stability constants of M-DOM complexes in stream waters (log
K 1 = 4.9 to 4.1) and in wetland waters (log K 1 = 8.02 and log K 2 = 6.1 to
7.61 and 5.85, respectively), whilst their values are increased in river DOM (log
K 1 = 7.59 and log K 2 = 5.83 to 7.63 and 5.88, respectively) and in lake DOM
(log K 1 = 16.3 to 16.8). The values remain the same (log K 1 = 13.5) before
and after irradiation of estuarine waters (Wu et al. 2004a; Brooks et al. 2007;
Sander et al. 2005; Shank et al. 2006). The decomposition of the functional
groups in DOM is susceptible to decrease the stability constants of the M-DOM
complexes in natural waters. In contrast, the increase in stability constants of
the M-DOM complexes is likely caused by the formation of new photoproducts