# Binding of Arsenic by Common Functional Groups: An Experimental and Quantum-Mechanical Study
## 3 Results
### As(III)-Ligand Interactions
As expected, considering the high affinity of As(III) towards -SH groups, the stability of the species was higher with respect to simple -COOH or -NH\({}_{2}\) groups, and logK reached the value of 6.10 (for AsLH\({}_{3}\) species of _dmsa_). As will be shown below, quantum-mechanical calculations \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**L** & **Species (a)** & **log\(\beta\)** & **L** & **Species (a)** & **log\(\beta\)** & **L** & **Species (a)** & **log\(\beta\)** \\ \hline _mal_ & AsL & 1.44 \(\pm\) 0.01 (b) & _etan_ & AsLH & 12.22 \(\pm\) 0.05 (b) & _gly_ & AsLH & 10.40 \(\pm\) 0.08 (b) \\  & AsLH & 6.27 \(\pm\) 0.02 & _en_ & AsLH & 12.12 \(\pm\) 0.03 & _asp_ & AsLH & 10.79 \(\pm\) 0.02 \\ _tca_ & AsL & 1.39 \(\pm\) 0.04 & & AsLH\({}_{2}\) & 19.76 \(\pm\) 0.03 & & AsLH\({}_{2}\) & 15.39 \(\pm\) 0.03 \\  & AsLH & 7.22 \(\pm\) 0.02 & _dien_ & AsLH\({}_{2}\) & 20.84 \(\pm\) 0.04 & _lys_ & AsLH & 13.00 \(\pm\) 0.02 \\ _btc_ & AsLH & 7.54 \(\pm\) 0.02 & & AsLH\({}_{3}\) & 25.91 \(\pm\) 0.03 & & AsLH\({}_{2}\) & 21.85 \(\pm\) 0.04 \\  & AsLH\({}_{2}\) & 12.76 \(\pm\) 0.02 & _trien_ & AsLH\({}_{2}\) & 21.47 \(\pm\) 0.03 & _cys_ & AsL & 4.45 \(\pm\) 0.04 \\  & AsLH\({}_{3}\) & 17.05 \(\pm\) 0.01 & & AsLH\({}_{3}\) & 28.96 \(\pm\) 0.03 & & AsLH & 13.47 \(\pm\) 0.03 \\  & AsLH & & & AsLH\({}_{4}\) & 33.28 \(\pm\) 0.04 & & AsLH\({}_{2}\) & 21.89 \(\pm\) 0.04 \\ _mlt_ & AsL & 3.23 \(\pm\) 0.02 & _tetren_ & AsLH\({}_{4}\) & 34.43 \(\pm\) 0.02 & & & \\  & AsLH\({}_{2}\) & 13.34 \(\pm\) 0.03 & & AsLH\({}_{5}\) & 37.97 \(\pm\) 0.02 & & & \\ \hline \end{tabular} (a) As = As(III), (b) \(\pm\)standard deviation.  
\end{table} 
Table 1: Overall stability constants for As(III)–ligand systems in NaCl at \(I\) = 0.15 mol/L and T = 298.15 K.  
executed on a monothi ligand indicate that, similarly to the carboxylate, \(S^{-}\) directly bound to As(III) by the displacement of the OH group in As(OH)\({}_{3}\). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**L** & **Species (a)** & **nSH** & **nCOOH** & **nNH2** & **nS-** & **nCOOH** & **nNH3+** & **logK (b)** \\ \hline _mal_ & AsL & 0 & 2 & 0 & 0 & 2 & 0 & 1.44 \\  & AsLH & 0 & 2 & 0 & 0 & 1 & 0 & 1.05 \\ _ta_ & AsL & 0 & 3 & 0 & 0 & 3 & 0 & 1.39 \\  & AsLH & 0 & 3 & 0 & 0 & 2 & 0 & 1.40 \\  & AsLH\({}_{2}\) & 0 & 3 & 0 & 0 & 1 & 0 & 1.45 \\ _btc_ & AsLH & 0 & 4 & 0 & 0 & 3 & 0 & 1.33 \\  & AsLH\({}_{2}\) & 0 & 4 & 0 & 0 & 2 & 0 & 1.45 \\  & AsLH\({}_{3}\) & 0 & 4 & 0 & 0 & 1 & 0 & 1.66 \\ _mlt_ & AsL & 0 & 6 & 0 & 0 & 6 & 0 & 3.23 \\  & AsLH\({}_{2}\) & 0 & 6 & 0 & 0 & 5 & 0 & 2.30 \\ _etan_ & AsLH & 0 & 6 & 0 & 0 & 4 & 0 & 1.72 \\ _en_ & AsLH & 0 & 0 & 1 & 0 & 0 & 1 & 1.56 \\ _en_ & AsLH\({}_{2}\) & 0 & 0 & 2 & 0 & 0 & 1 & 2.18 \\ _dien_ & AsLH\({}_{2}\) & 0 & 0 & 2 & 0 & 0 & 2 & 2.72 \\  & AsLH\({}_{3}\) & 0 & 0 & 3 & 0 & 0 & 2 & 2.00 \\ _trien_ & AsLH\({}_{2}\) & 0 & 0 & 4 & 0 & 0 & 3 & 2.87 \\  & AsLH\({}_{3}\) & 0 & 0 & 4 & 0 & 0 & 2 & 2.68 \\  & AsLH\({}_{3}\) & 0 & 0 & 4 & 0 & 0 & 3 & 3.58 \\  & AsLH\({}_{4}\) & 0 & 0 & 4 & 0 & 0 & 4 & 3.85 \\ _tetren_ & AsLH\({}_{4}\) & 0 & 0 & 5 & 0 & 0 & 4 & 2.67 \\  & AsLH\({}_{5}\) & 0 & 0 & 5 & 0 & 0 & 5 & 3.52 \\ _gly_ & AsLH & 0 & 1 & 1 & 0 & 1 & 1 & 0.83 \\ _asp_ & AsLH & 0 & 2 & 1 & 0 & 2 & 1 & 1.16 \\  & AsLH\({}_{2}\) & 0 & 2 & 1 & 0 & 1 & 1 & 2.32 \\ _lys_ & AsLH & 0 & 1 & 2 & 0 & 1 & 1 & 1.94 \\  & AsLH\({}_{2}\) & 0 & 1 & 2 & 0 & 1 & 2 & 1.59 \\ _cys_ & AsL & 1 & 1 & 1 & 1 & 1 & 0 & 4.45 \\  & AsLH & 1 & 1 & 1 & 1 & 1 & 1 & 3.31 \\  & AsLH\({}_{2}\) & 1 & 1 & 1 & 0 & 1 & 1 & 3.59 \\ _tla_ & AsL & 1 & 1 & 0 & 1 & 1 & 0 & 3.33 \\  & AsLH & 1 & 1 & 0 & 0 & 1 & 0 & 2.09 \\ _tma_ & AsL & 1 & 2 & 0 & 1 & 2 & 0 & 4.41 \\  & AsLH & 1 & 2 & 0 & 0 & 2 & 0 & 3.25 \\  & AsLH\({}_{2}\) & 1 & 2 & 0 & 0 & 1 & 0 & 2.98 \\ _dmsa_ & AsLH & 2 & 2 & 0 & 1 & 2 & 0 & 5.58 \\  & AsLH\({}_{2}\) & 2 & 2 & 0 & 0 & 2 & 0 & 5.55 \\  & AsLH\({}_{3}\) & 2 & 2 & 0 & 0 & 1 & 0 & 6.10 \\ \hline \hline \end{tabular}
\end{table}