Synthesis, Structures, and Electrochemistry of Gold(III) Ethylenediamine Complexes and Interactions with Guanosine 5‘-Monophosphate

Abstract

Abstract[Au(en)Cl 2 ]Cl·2H 2 O has been synthesized and its structure has been solved for the first time by the single crystal X-ray diffraction method. The complex has square planar geometry about the Au(III) and the anionic Cl − is located in the apical position and at a distance of 3.3033(10) Å compared to 2.2811 (9) 3+ . 1 H, 13 C, and 31 P NMR reveal that in aqueous solution [Au(en)Cl 2 ] + bonds to guanosine 5'-monophosphate, 5'-GMP, (1:1 mole ratio) via N7, although the stability is not very high. NMR data also indicate that N7-O6 or N7-phosphate 5'-GMP chelation, as found in some Au(III)-nucleotide complexes, is not present. The Au(III) complex undergoes hydrolysis at pH > 2.5−3.0 and, therefore N1 coordination to 5'-GMP is not observed. No direct coordination between 5'-GMP and [Au(en) 2 ]Cl 3 is observed. KeywordsGold(III); guanosine 5'-monophosphate; NMR; cyclic voltammetry; X-ray structure Gold(III) complexes are isoelectronic and generally isostructural to platinum(II) complexes, and therefore it is anticipated that they will have similar activity to the Pt(II) antitumor drugs.1-5 However, compared to the corresponding Pt(II) complexes, Au(III) complexes have not been well explored chemically or electrochemically, possibly because few gold(III) complexes have been shown to be sufficiently stable in aqueous solution.6,7Ethylenediamine (en) is a common chelating ligand that is widely used in transition metal complexes. Its gold complexes have been known since 1931,8-10 Methods and Materials MaterialsNaAuCl 4 ·2H 2 O, ethylenediamine, D 2 O, and dmso-d 6 were purchased from Aldrich Chemical Co. and used as received. H 2 (5'-GMP) and Na 2 (5'-GMP) were purchased from Sigma and used as received. All solutions other than those for NMR measurements were prepared using deionized water that was purified with a Barnstead NANOpure cartridge system (18 MΩ). Nucleotide Stock Solutions-Na 2 (5'-GMP) or H 2 (5'-GMP) was dissolved in H 2 O or D 2 O and the concentration of the nucleotide was determined by UV spectroscopy (λ max 252 nm; ε = 1.37 × 10 4 M −1 cm −1 ; pH 7). The required amount of Au(III) compound was added to the 5'-GMP solution. Syntheses MethodsThermogravimetric Analysis-Measurements were made on a Shimadzu TGA-50 analyzer under N 2 atmosphere with a flow rate of 20 mL min −1 in a Pt cell. Samples weighed 3−7 mg. The temperature increased at 20 °C min −1 from room temperature to 900°C .NMR-Spectra were obtained in D 2 O on a Varian Inova 500 MHz in D 2 O. The temperature dependent 1 H studies were referenced to internal tetramethylammonium ion at 3.185 ppm and the spectra at 26 °C were referenced to the HOD line at 4.800 ppm (The TMA + resonance is very near that of ethylenediamine and can overlap at times). 31 P spectra were referenced to external 85 % H 3 PO 4 and 13 C spectra to DSS. pD = pH (meter reading) + 0.40.Electrochemical Measurements-A CHI 832 workstation (CH Instruments, Inc.) was used to collect electrochemical data. Experiments were performed at room temperature (20 ± 1 °C) in ...

A spectroscopic and electrochemical investigation of the oxidation pathway of glycyl-d,l-methionine and its N-acetyl derivative induced by gold(III)

“…The Au(III)-Au(0) reduction was also evident from the presence of metallic gold on the electrode surface. In the cyclic voltammogram, no [AuCl 2 ] -complex could be detected due to the fact that the chlorido ligand is not a π-acceptor which could stabilize this complex [48]. On the reverse sweep, a definite oxidation wave I′ at 1.02 V was observed (Fig.…”

A study of [Au(ethylenediamine)Cl2]Cl interaction with L-methionine and DL-seleno-methionine by1H and13C NMR spectroscopy

“…Figure 2 shows the 1 H NMR spectra for Met reaction with HAuCl 4 at pD = 3.8. Higher pH causes the hydrolysis of [Au(en)Cl 2 ]Cl complex [16]. Downfield shifts were observed in H5, H3 and H2 after ligation to gold metal center.…”

“…Ethylenediamine (en) is the most common chelating ligand and its gold complexes have been known since 1931 [16]. The crystal structure of [Au(en)Cl 2 ]Cl has a square planar geometry about gold(III) and the anionic Cl − ion is located in the equatorial positions [16].…”

“…The crystal structure of [Au(en)Cl 2 ]Cl has a square planar geometry about gold(III) and the anionic Cl − ion is located in the equatorial positions [16]. The interest in this complex is due to the fact that similar complexes have shown significant cytotoxic effects [1].…”

Electrochemical monitoring of the oxidative coupling of alkynes catalyzed by triphenylphosphine gold complexes

“…Similar responses were obtained for complexes 2 and 3. This electrochemistry separates from those reported for gold complexes with dithiolate and dithiolene ligands [21,22] and porphyrins [23,24], among others [25].…”