## 3 Results and Discussion
### Structure Elucidation of the Au Complex by NMR  
In comparison with the \({}^{1}\)H NMR spectrum of 2,4-DTu, the \({}^{1}\)H NMR spectrum of the gold complex showed 7 singlets at 10.81 ppm, 11.00 ppm, 12.27 ppm, 12.43 ppm, 12.88 ppm, 13.62 ppm, and 14.13 ppm. Additionally, there were 8 signals at 5.45 ppm, 5.81 ppm, 6.51 ppm, 7.10 ppm, 7.27 ppm, 7.39 ppm, 7.76 ppm, and 8.31 ppm. As can be seen, the \({}^{1}\)H NMR spectrum of the gold complex contains more signals than the \({}^{1}\)H NMR spectrum of the ligand only. Moreover, the HSQC spectrum showed the following 9 signal correlations: (5.44 ppm-99.94 ppm), (5.81 ppm-104.91 ppm), (6.51 ppm-116.83 ppm), (7.10 ppm-116.00 ppm), (7.26 ppm-137.92 ppm), (7.39 ppm-115.50 ppm), (7.39 ppm-142.04 ppm), (7.76 ppm-140.73 ppm), and (8.31 ppm-156.48 ppm). Consequently, it can be assumed that 2,4-dithiouracil could possibly undergo desulfurization [41] by the influence of the NaOH used during the synthesis of the Au complex causing the replacement of one of the sulfur atoms or both of them with oxygen, thus obtaining 2-thiouracil and uracil in the reaction mixture. The pairs of signals (5.44 ppm-99.94 ppm) and (5.81 ppm-104.91 ppm) were assigned correspondingly to the protons and carbons, H-5 and C-5, in the respective structures of uracil and 2-thiouracil. There was a multiplet at 7.39 ppm with an area of 3.48 in the \({}^{1}\)H NMR spectrum where there were presumably four signals located closely to each other. Therefore, two of these signals at 7.39 ppm were assigned to the protons (H-6) in the structures of the obtained uracil and 2-thiouracil for which the corresponding HSQC correlations (7.39 ppm-142.04 ppm) were found. The signals at 10.81 ppm and 11.00 ppm as well as at 12.27 ppm and 12.43 ppm were assigned, respectively, to the NH-1 and NH-3 protons in uracil and 2-thiouracil. The \({}^{1}\)H NMR spectral data for the Au complex are given in Table 4.  
The signal assignments made for uracil and 2-thiouracil were in good agreement with the \({}^{1}\)H and \({}^{13}\)C NMR data provided in the Chemical Book spectral database ([[https://www.chemicalbook.com/SpectrumEN_66-22-8_1](https://www.chemicalbook.com/SpectrumEN_66-22-8_1) HNMR.htm]([https://www.chemicalbook.com/SpectrumEN_66-22-8_1](https://www.chemicalbook.com/SpectrumEN_66-22-8_1) HNMR.htm) (accessed on 22 July 2024)) for uracil, as well as with the signal assignments for 2-thiouracil presented in a previous paper [31] concerning the synthesis of new Au, Cu, and Pd complexes with 2-thiouracil. In accordance with the assignments presented for the ligand in Table 3, the signals at 6.51 ppm, 7.26 ppm, 12.88 ppm, and 13.62 ppm in the \({}^{1}\)H NMR spectra of the Au complex clearly showed the presence of uncoordinated 2,4-dithiouracil. However, the other HSQC correlations (7.10 ppm-116.00 ppm), (7.39 ppm-115.50 ppm), (7.76 ppm-140.73 ppm), and (8.31 ppm-156.48 ppm) were associated with the presence of some tautomeric forms of 2,4-dithiouracil and 2-thiouracil that could participate as ligands in the Au complex containing deprotonated nitrogen atoms. Thus, it can be hypothesized that not only under the alkaline \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Atom** & \(\delta\) **(\({}^{3}\)C) ppm** & **DEPT-135** & \(\delta\) **(\({}^{1}\)H) ppm** & **Multiplicity (J, Hz)** & **\({}^{1}\)H-\({}^{1}\)H COSY** & **HMDC** \\ \hline
1 (NH) & & & 12.90 & s & & \\ \hline
2 (C=S) & 172.87 & C & & & & \\ \hline
3 (NH) & & & 13.64 & s & & \\ \hline
4 (C=S) & 187.81 & C & & & & \\ \hline
5 & 117.16 & CH & 6.50 & d (7.1) & 6 & 4, 6 \\ \hline
6 & 136.69 & CH & 7.27 & d (7.1) & 5 & 2, 4, 5 \\ \hline \end{tabular}  
\({}^{a}\) In DMSO-\(d\)6 solution. All these assignments were in agreement with COSY, HMQC, and HMBC spectra.  
\end{table} 
Table 3: \({}^{1}\)H and \({}^{13}\)C NMR spectral data and \({}^{1}\)H-\({}^{1}\)H COSY and HMBC correlations for 2,4-dithiouracil [600.13 MHz (\({}^{1}\)H) and 150.903 MHz (\({}^{13}\)C)] \({}^{a}\).