## 3 Results and Discussion
### Structure Elucidation of the Cu Complex by NMR  
In contrast with the \({}^{1}\)H NMR spectrum of the Au complex, there were no signals for the NH-1 and NH-3 protons of 2,4-dithiouracil in the \({}^{1}\)H NMR spectrum of the Cu complex (see Table 5). On the other hand, there were singlets at 10.80 ppm, 11.00 ppm,  
Figure 2: \({}^{13}\)C CP MAS NMR spectrum of Au complex (**A**); \({}^{13}\)C CPPI MAS NMR spectrum of Au complex (**B**); \({}^{13}\)C CP MAS NMR spectrum of the 2,4-DTiu (**C**). 12.26 ppm, and 12.43 ppm, similar to those found in the \({}^{1}\)H NMR spectrum of the Au complex for 2-thiouracil and uracil, indicating again that 2,4-dithiouracil most probably underwent desulfurization [41] under the alkaline conditions of the synthesis of the Cu complex due to the used NaOH. Also, the HSQC correlations (5.45 ppm-99.78 ppm) and (5.81 ppm-105.03 ppm) were close to the ones observed in the HSQC spectrum of the Au complex for the protons and carbons (H-5 and C-5) in uracil and 2-thiouracil, respectively. In this case, there was a multiplet at 7.39 ppm with an area of 3.27, probably consisting of three proton signals. Additionally, the HSQC spectrum showed the following correlations: (7.40 ppm-115.27 ppm) and (7.38 ppm-141.85 ppm), where the signals at 7.38 and 141.85 can be assigned to the protons and carbons, H-6 and C-6, in the structures of the uncoordinated ligands, i.e., uracil and 2-thiouracil. Thus, for the ligands coordinated with Cu, one signal was left at 7.40 ppm, one signal at 7.28 ppm, and two signals at 8.33 ppm in the \({}^{1}\)H NMR spectrum. Based on the HSQC correlations (7.40 ppm-115.27 ppm) and (7.28 ppm-115.48 ppm), the pairs of the chemical shifts (7.28 ppm and 7.40 ppm) and (115.27 ppm and 115.48 ppm) were assigned to the signals of the protons and carbons (H-5 and C-5), whereas the signals at 8.33 ppm and 156.26 ppm were for the protons and carbons, H-6 and C-6, of the coordinated ligands. The HSQC correlations (7.40 ppm-115.27 ppm) and (8.33 ppm-156.26 ppm) were very close to the HSQC correlations (7.39 ppm-115.50 ppm) and (8.31 ppm-156.48 ppm) observed in the HSQC spectrum of the Au complex. Thus, it can be assumed there is one ligand that would be common for both complexes, i.e., a coordinated 2-thiouracil with the following chemical shifts for its protons and carbons (H-5, H-6, C-5 and C-6)--7.40 ppm, 8.33 ppm, 115.27 ppm, and 156.26 ppm, respectively. Thus, the other pairs of signals (7.28 ppm and 115.48 ppm) and (8.33 and 156.26 ppm) probably corresponded to the protons and carbons H-5, C-5, H-6, and C-6, respectively, in the coordinated uracil. Both ligands would probably be coordinated bidentately with Cu-uracil with both its oxygen atoms and the thiouracil ligand with its sulfur and oxygen atoms (Figure 3). As can be seen from the HSQC spectrum, there were no additional signals that could be observed for the protons and carbons of 2,4-dithiouracil. Figure 3: A possible structure and coordination binding sites in the Cu complex. If Z\({}_{1}\) = H\({}_{2}\)O or DMSO-h\({}_{6}\), then Z\({}_{2}\) = H\({}_{2}\)O or DMSO-h\({}_{6}\). \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Atom** & **2-Tu b** & **U b** & **2-Tu.U.Cu c** \\ \hline
1 & 12.26, s & 10.80, s & \\
2 & & & \\
3 & 12.43, s & 11.00, s & \\
4 & & & \\
5 & 5.81, d (7.3 Hz) & 5.45, d (8.2 Hz) & 7.28, d (5.5 Hz) (U) \\  & & & 7.40 d, m (2-Tu) \\
6 & 7.38 d, m & 7.38 d, m & 8.33, m (U) \\  & & & 8.33, m (2-Tu) \\ \hline \hline \end{tabular}  
* In DMSO-d\({}_{6}\) solution. All these assignments were in agreement with the HSQC spectrum. b The corresponding assignments concern the uncoordinated ligands—2-thiouracil (2-Tu), uracil (U). c Spectral data suggest that 2-Tu and U are ligands in our complex. d This chemical shift was assigned from the HSQC spectrum.  
\end{table} 
Table 5: \({}^{1}\)H NMR spectral data for the Cu complex [500.13 MHz (\({}^{1}\)H)] a.