Abstract
A new Ag(I) coordination complex, Ag(C11H10N2O)2·NO3 (C11H10N2O = 4-(2-hydroxyphenyl)-2-methylpyrimidine) is successfully synthesized and characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. This complex features a three-dimensional framework consisting of hydrogen bonds, π–π stacking interactions, coordination interactions, and electrostatic interactions. Moreover, the thermal stability and non-isothermal thermal decomposition reaction kinetics of the complex are well investigated by the methods of Kissinger and Ozawa. Finally, the antitumor ability of the complex is evaluated against human lung cancer cells (NCI-H460), human hepatocellular cancer cells (HepG2), and human breast cancer cells (MCF7). The complex exhibits potent antitumor activities against HepG2 and MCF7 cancer cells.
Keywords
Presented here is a new Ag(I) coordination framework, namely Ag(C11H10N2O)2⋅NO3 (1, C11H10N2O = 4-(2-hydroxyphenyl)-2-methylpyrimidine). Complex 1 features three-dimensional (3D) network structure in which Ag ions and ligands are linked by Ag–N coordinate bonds, hydrogen bonds, π–π stacking interactions and electrostatic interactions. The thermal decomposition activation energy of complex 1 is 261.83kJ•mol-1 (Ozawa’s method). Complex 1 shows better vitro antitumor effect than carboplatin against human hepatocellular cancer cells HepG2 and human breast cancer cells MCF7.
Introduction
Nitrogen-containing heterocyclic compounds are very important organic frameworks and are widely present in natural products, synthetic drugs, and naturally occurring peptides. 1 Due to their excellent electronic, catalytic, and biological properties, nitrogen-containing heterocyclic compounds have been widely applied in many fields, such as in the study of physiologically active molecules 2 and the preparation of functional materials, 3 and have been involved in catalysis 4 and coordination chemistry. 5 Pyrimidines are important heterocyclic compounds because they possess highly valuable skeletons that are widely found in many biologically active compounds and pharmaceuticals. 6 A number of pyrimidine derivatives exhibit good biological activities, including antibacterial, 7 antiviral, 8 anticancer,9,10 anticonvulsant, 11 antioxidant, 12 and anti-inflammatory activities. 13 However, pyrimidine heterocyclic compounds containing two N atoms have strong coordination ability, and easily form π–π stacking and hydrogen bonding. Hence, they form complexes with novel structures and unique properties when they are self-assembled with metal ions.14,15
Silver ions have strong broad-spectrum antibacterial and bacteriostatic effects. Clinically, silver salts can be used to treat chronic ulcers, large skin burns, and prevent neonatal conjunctivitis and other bacterial infections. 16 It has been reported that silver complexes have useful antibacterial activity against Staphylococcus aureus (Gram-positive), Pseudomonas aeruginosa (Gram-negative), Escherichia coli, and other pathogenic bacteria,17,18 and they have antiproliferative activity against human colorectal cancer cells (HTC 116) and human leukemia cells (HL 60). 19
Based on the above research, this paper hopes to combine pyrimidines and silver ion into the same molecule by synthesizing coordination complex, so we synthesized 4-(2-hydroxyphenyl)-2-methylpyrimidine, and it was used to self-assemble with Ag(I) ions under solvothermal conditions. Gratifyingly, we obtained a new coordination complex, namely, Ag(C11H10N2O)2·NO3 (
Results and discussion
Synthesis of complex 1
1-(2-Hydroxyphenyl)ethan-1-one reacts with N,N-dimethylformamide dimethyl acetal (DMF-DMA) to afford the intermediate enaminone (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one (Scheme 1). The latter reacts with acetamidine hydrochloride under alkaline condition to afford ligand 4-(2-hydroxyphenyl)-2-methylpyrimidine. Finally, the complex

Synthesis of the 4-(2-hydroxyphenyl)-2-methylpyrimidine ligand.
Crystal structure description
The X-ray crystallographic data of complex
Crystallographic data for complex 1.
Selected bond angles (°) and bond lengths (Å) of 1.
Symmetry codes: (a) 1 − x, y, z.

Molecular structure of complex
The crystal-packing analysis demonstrated that there are three hydrogen bonds in complex
Hydrogen-bonding parameters in complex 1.
Symmetry codes: (i) 1 − x, 1 − y, −1/2 + z; (ii) 3/2 − x, 3/2 − y, 1/2 + z.

One-dimensional chain structures in complex

Two-dimensional layers in complex
The crystal analysis further demonstrates that face-to-face π–π stacking interactions are observed between neighboring antiparallel ligand skeletons (Figure 4). The benzene ring of the ligand at the (x, y, z) position has π–π stacking interactions with the pyrimidine ring of the adjacent ligand at the (3/2 − x, 1/2 + y, z) position (centroid-to-centroid distance (Cg2–Cg1iii, Cg1 and Cg2 represent the ring centroids of the benzene and pyrimidine rings, respectively) of 3.536(2) Å and a vertical distance from Cg2 to the pyrimidine ring of 3.3940(15) Å). The pyrimidine ring of the ligand at the (x, y, z) position has π–π stacking interactions with the benzene ring of the adjacent ligand at the (3/2 − x, −1/2 + y, z) position (centroid-to-centroid distance (Cg1–Cg2iV) of 3.423(4) Å and a vertical distance from Cg1 to the benzene ring of 3.352(13) Å). These parameters agree well with classical π–π stacking interaction data.
21
The ligands are linked by π–π stacking interactions to form one-dimensional chains along the b-axis. These chains are further linked by coordination interactions into a 2D layer along the ab plane. Hydrogen bonds, π–π stacking interactions, coordination interactions, and electrostatic interactions assemble complex

π–π stacking interactions in complex

Packing diagram of complex
Thermal stability
Differential scanning calorimetry (DSC) was employed to evaluate the thermal stability of complex

DSC curves of complex
Kinetics of non-isothermal thermal decomposition
In order to study the thermal decomposition reaction kinetics of complex
Calculated parameters for complex
According to the peak temperature at different heating rates, the Kissinger
22
and Ozawa
23
methods were used to fit the calculations. The values of ln(β/Tp) and lnβ were plotted against 1000/Tp, respectively, and linear regression analysis was conducted. The thermal decomposition activation energy E of complex
In vitro antitumor activity
The in vitro antitumor activity of complex
The in vitro antitumor activity of complex
In vitro inhibitory activity of complex
Conclusion
A 3D network complex Ag(C11H10N2O)2·NO3 based on Ag(I) and 4-(2-hydroxyphenyl)-2-methylpyrimidine has been successfully prepared. The single-crystal structures show that the title complex exhibits a 3D network structure in which Ag ions and ligands are linked by Ag–N coordinate bonds, hydrogen bonds, π–π stacking interactions, and electrostatic interactions. In addition, we have studied the thermal stability and non-isothermal thermal decomposition kinetics of the title complex. The results indicate that its decomposition is only a thermal process. The decomposition peak temperatures are 234.8, 236.1, 239.5, and 241.9 °C at heating rates of 8, 10, 15, and 20 °C min−1, respectively. The thermal decomposition activation energy of the title complex is 266.81 kJ mol−1 (the Kissinger method). The results of the in vitro antitumor activity show that the inhibition effect of the title complex against HepG2 and MCF7 cancer cells is better than that of carboplatin.
Experimental
Reagents were purchased from commercial sources and used as received, unless mentioned otherwise. Reactions were monitored by thin-layer chromatography (TLC) using UV light to visualize the course of the reaction. Purification of the reaction products was carried out by recrystallization. Chemical yields refer to those of pure isolated substances. Elemental analyses were recorded on a PerkinElmer 240C Elemental Analyzer. Infrared spectra were measured on a Nicolet 6700 FTIR spectrometer in the range of 400–4000 cm−1 as KBr pellets. Single-crystal X-ray diffraction was carried out with an Oxford Xcalibur E diffractometer. The thermal behavior (DSC) was studied under an N2 flow with a DSC-Q100 TA instrument.
4-(2-Hydroxyphenyl)-2-methylpyrimidine
The mixture of 1-(2-hydroxyphenyl)ethan-1-one (204 mg, 1.5 mmol) and DMF-DMA (536 mg, 4.5 mmol) was refluxed in N,N-dimethylformamide (50 mL) at 80 °C for 1.5 h. The reaction progress was monitored by TLC. After cooling to room temperature, the reaction mixture was poured into saturated NaCl solution (100 mL), and a yellow precipitate appeared. The precipitate was filtered and washed with saturated NaCl solution. The yellow precipitate was recrystallized form ethyl acetate to give (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one. 24 (E)-3-(dimethylamino)-1-(2-hydroxy-phenyl)prop-2-en-1-one: 85% yield; yellow solid; m.p. = 127~128 °C; ESI-HRMS calcd for C11H13NO2 [M + H]+: 191.0952; found: 191.0964.
To a mixture of (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one (191 mg, 1 mmol) and acetamidine hydrochloride (142 mg, 1.5 mmol) in methanol (30 mL) was added NaOH (120 mg, 3 mmol). The reaction mixture was stirred at 80 °C for 12 h and the progress of the reaction was monitored by TLC. Upon completion, the solvent was removed under reduced pressure. The residue was taken up in ice water (30 mL), the pH adjusted to neutrality with a solution of 5% HCl, and then extracted with ethyl acetate. The organic layer was washed with water and then dried over anhydrous sodium sulfate. Finally, the solvent was removed to afford the crude product which was purified by column chromatography using hexane/ethyl acetate (5/1, v/v) as the eluent to give pure 4-(2-hydroxyphenyl)-2-methylpyrimidine. 25 4-(2-Hydroxyphenyl)-2-methylpyrimidine: 85% yield; pale yellow solid; m.p. = 181~183 °C; IR (cm−1, KBr) ν: 3053, 1575, 1496, 1468, 1445, 1402, 1301, 1227, 859, 773, 752; 1H NMR (400 MHz, CDCl3): δ 13.84 (s, 1H), 8.62 (d, J = 4.9 Hz, 1H), 7.71 (d, J = 7.9 Hz, 1H), 7.53 (d, J = 5.0 Hz, 1H), 7.31 (t, J = 7.6 Hz, 1H), 6.95 (d, J = 8.3 Hz, 1H), 6.85 (t, J =7.5 Hz, 1H), 2.70 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 165.83, 164.51, 161.25, 157.86, 133.59, 126.89, 119.17, 119.01, 116.66, 112.09, 25.79; ESI-HRMS calcd for C11H10N2O [M + H]+: 187.0871; found 187.0861; anal calcd for C11H10N2O (187.08): C, 70.95; N, 15.04; H, 5.41; found: C, 71.17; N, 15.18; H, 5.62.
Ag(C11H10N2O)2·NO3 (1)
A mixture of 4-(2-hydroxyphenyl)-2-methylpyrimidine (558 mg, 3 mmol), AgNO3 (255 mg, 1.5 mmol), ethanol (5 mL), and H2O (3 mL) was placed in a 15-mL Teflon liner. The resulting mixture was stirred for 30 min at room temperature, and then the mixture was sealed in a Parr autoclave and kept at 100 °C for 2 days. After being slowly cooled to the room temperature, yellow prism-shaped crystals of
X-ray single-crystal structure determination
A suitable single crystal of
In vitro determination of the antitumor activity
The compounds to be tested were dissolved in DMSO and further diluted to different concentrations with culture medium. The tumor cells NCI-H460, HepG2, and MCF7 were inoculated in 96-well plates with 5 × 104 cells per well. After incubation for 12 h, different concentrations of test compounds were added to the 96-well plate, with the concentration of each compound being 2, 4, 8, 16, 32, and 40 μmol/L, respectively. The final concentration of DMSO in the culture medium should be controlled and less than 0.01%, while no drugs were added to the blank control group, only containing culture medium. Each concentration of the drug and control groups was tested with three multiple wells. After 12 h, cell-counting MTT was used to determine the viability of the NCI-H460, HepG2, and MCF7 cells, and 10 μL of a 5-mg/mL MTT solution was added to each well plate followed by incubation for 12 h at 37 °C. The absorbance of each well was recorded with an automatic microplate reader at 490 nm. The inhibition rate was calculated according to the absorbance value, and the IC50 value was calculated according to the inhibition rate.
Supplemental Material
sj-docx-1-chl-10.1177_17475198221103541 – Supplemental material for Synthesis, characterization, thermal behavior, and antitumor activities of an Ag(I) complex based on 4-(2-hydroxyphenyl)-2-methylpyrimidine
Supplemental material, sj-docx-1-chl-10.1177_17475198221103541 for Synthesis, characterization, thermal behavior, and antitumor activities of an Ag(I) complex based on 4-(2-hydroxyphenyl)-2-methylpyrimidine by Wu-Wu Li, Min-Yan Zheng, Yong-Hui Shang, Jin-Qiong Xu, Zun-Ting Zhang, Hao-Nan Zheng, Xiao-Peng Li, A-Tong Weng, Ling-Ying Feng and Lu Liu in Journal of Chemical Research
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the Scientific Research Program Funded by Shaanxi Provincial Education Department (no. 19JK0767), the Natural Science Basic Research Plan Funded by Shaanxi Province of China (no. 2020JM1543), the Scientific Research Project Funded by Xianyang Normal University (nos XSYK21041 and XSKY19046), the University Students Research and Innovation Training Program of Ministry of Education (no. S202010722009), the Qing–Lan Talents Project Funded by Xianyang Normal University (no. XSYQL201904), and the Seventh Batch of College Student Innovation and Entrepreneurship Base Team of Xianyang Normal University (no. XSYC202118).
References
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