Exploring DNA-interaction and molecular structure of ruthenium/1,2-bis-(diphenylphosphino)ethane)-based complex European Journal of Chemistry 14 (2) (2023) 193-201 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2023 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.14.2.193-201.2402 European Journal of Chemistry View Journal Online View Article Online Exploring DNA-interaction and molecular structure of ruthenium/1,2-bis-(diphenylphosphino)ethane)-based complex Victor Cardoso Campideli 1,†, Jerica Margely Montilla-Suárez 1,†, Tiago Almeida Silva 2, Dalila Chaves Sicupira 1, Katia Mara Oliveira 3 and Rodrigo Souza Correa 1,* 1 Departamento de Química, Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG, 35400-000, Brazil 2 Departamento de Química, Universidade Federal de Viçosa (UFV), Viçosa, MG, 36570-900, Brazil 3 Instituto de Química, Universidade de Brasília (UnB), Brasília, DF, 70910-900, Brazil * Corresponding author at: Departamento de Química, Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG, 35400-000, Brazil. † These authors contributed equally. e-mail: rodrigocorrea@ufop.edu.br (R.S. Correa). 10.5155/eurjchem.14.2.193-201.2402 Received: 24 December 2022 Received in revised form: 29 January 2023 Accepted: 11 February 2023 Published online: 30 June 2023 Printed: 30 June 2023 The mixture of cis and trans-[RuCl2(dppe)2] (dppe: 1,2-bis-(diphenylphosphino)ethane) was prepared and the interaction with CT-DNA was evaluated by several methods, including UV- vis DNA spectroscopic titration, viscosity, and electrochemical studies. Investigation suggests that [RuCl2(dppe)2] interacts moderately with CT-DNA. Interestingly, the cis- and trans-isomers interact differently with DNA, as proved by the square-wave voltammetry studies. Finally, the crystal structure of trans-[RuCl2(dppe)2]Cl was obtained from an electrochemical solution and studied in detail, which presents a distorted octahedral geometry and interatomic parameters different from those found in the trans- [RuCl2(dppe)2] complex. Crystal data for C52H48Cl4P4Ru: triclinic, space group P-1 (no. 2), a = 9.240(3) Å, b = 10.9290(18) Å, c = 11.993(3) Å, α = 78.707(11)°, β = 86.712(13)°, γ = 82.598(13)°, V = 1177.1(5) Å3, Z = 1, T = 293(2) K, μ(MoKα) = 0.732 mm-1, Dcalc = 1.467 g/cm3, 8434 reflections measured (6.934° ≤ 2Θ ≤ 51.986°), 4607 unique (Rint = 0.0973, Rsigma = 0.1171) which were used in all calculations. The final R1 was 0.0537 (I > 2σ(I)) and wR2 was 0.1347 (all data). Viscosity DNA interaction Crystal structure Ru/dppe complex UV-Vis spectroscopy Square-wave voltammetry Cite this: Eur. J. Chem. 2023, 14(2), 193-201 Journal website: www.eurjchem.com 1. Introduction Cancer is the replication of tumor cells (genetically modified) and can occur in several different ways in the human body. One of these disease treatments consists of the use of anticancer drugs, known as chemotherapeutic agents, in which one of the mechanisms of action is to interact with DNA altering its structure, leading to cell death, modulation of transcription, or interfering in replication to prevent the rapid proliferation of cancer cells in the body [1]. In recent years, many studies have been conducted based on metallodrug development based on the interaction of metal complexes with DNA, to understand the mechanism of action [2]. Since the discovery of cis-platin as a metallodrug in the late 1960s, scientists have been looking for new coordination compounds to fight cancer [3]. There are many platinum-based complexes with high biological activity. However, side effects and resistance have led many researchers to explore other non- platinum compounds, such as ruthenium, which has been widely studied in recent years [4,5]. DNA may be a target for anticancer metallodrugs and recent studies have used several compounds that interact with DNA as useful tools to visualise DNA damage [5,6]. Many assays are powerful tools for determining the mechanism of action of new molecules and can be crucial to the discovery of the next generation of DNA-binding anticancer metallodrugs. The covalent bond between metallodrug-DNA is an irreversible chemical bond that causes complete inhibition of DNA processes leading to cell death, as is suggested to occur with cis- platin [7]. On the other hand, the non-covalent bond is almost reversible or reversible, in which metallodrugs interact with DNA weakly or moderately. Generally, there are three main modes of non-covalent interactions, which include electrostatic interaction, groove binding, and intercalative binding [8-10]. To determine the type of metallodrug-DNA interactions, many techniques can be used, including cyclic voltammetry (CV) and square wave voltammetry (SWV) [11], nuclear magnetic resonance (NMR) [12], UV-visible and fluorescence titration studies [13], viscosity [14], circular dichroism (CD) and the Hoechst 33 258 staining assay [15], capillary electrophoresis (CE) [16] and atomic force microscopy (AFM) [17]. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.14.2.193-201.2402 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.14.2.193-201.2402 mailto:rodrigocorrea@ufop.edu.br http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.14.2.193-201.2402&domain=pdf&date_stamp=2023-06-30 194 Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 In recent years, there has been interest in the discovery and understanding of the cytotoxic activity of compounds based on ruthenium / phosphine and exploring their interaction with DNA as a possible target [18-20]. The complex studied in the present report is identified as [RuCl2(dppe)2], in which dppe is 1,2-bis-(diphenylphosphino)ethane and a mixture of cis and trans isomers of [RuCl2(dppe)2] has been used. The [RuCl2(dppe)2] complex was previously used as a precursor to obtain new active compounds [21,22]. In this study, the [RuCl2(dppe)2]/DNA interaction was investigated using viscosity, UV-vis DNA titration, and square-wave voltammetry. In addition, the crystal structure of trans-[RuCl2(dppe)2]Cl is reported. 2. Experimental 2.1. Synthesis of the cis-[RuCl2(DMSO)4] complex The cis-[RuCl2(DMSO)4] complex was synthesised by refluxing 0.5 g (2.41 mmol) of RuCl3.xH2O in dimethyl sulfoxide (DMSO) (5 mL) for 15 minutes. The reaction mixture was cooled to room temperature and acetone (20 mL) was added to form the yellow precipitate, which was washed with acetone and ethyl ether and vacuum-dried. 2.2. Synthesis of cis- and trans-[RuCl2(dppe)2] The mixture of cis- and trans-[RuCl2(dppe)2] complexes was obtained according to the methodology described by Bautista et al. [23]. For this, cis-[RuCl2(DMSO)4] 0.5 g (1.03 mmol) and 1,2- bis(diphenylphosphino)ethylene (dppe) 0.94 g (2.37 mmol) were added to 20 mL of dichloromethane. The reaction mixture was kept stirring for 5 hours and then the volume of the solution was reduced to approximately 3 mL. Subsequently, hexane was added to form a pale-yellow precipitate, which presents the mixture of complexes cis and trans-[RuCl2(dppe)2]. 2.3. UV-vis DNA spectroscopic titration The DNA solution was prepared by adding approximately 1.2 mg of CT-DNA (Calf Thymus) in approximately 1000 µL of tris-HCl buffer (4.5 mmol of Tris HCl, 0.5 mmol of Tris base and 50 mmol of NaCl) at a pH of 7.4. The exact concentration of CT- DNA was provided by spectroscopy in the UV-vis region. In a cuvette containing only a buffer solution (2000 μL), 80 μL of CT- DNA solution was added and the measurement was performed on the equipment. It is known that the molar absorptivity of CT- DNA at 260 nm is 6600 mol-1·cm-1·L. Therefore, knowing the absorbance and molar absorptivity at 260 nm and the optical path of the cuvette (b = 1 cm), the concentration of CT-DNA was determined using the Lambert-Beer law: 𝐴𝐴260 = 𝜀𝜀260 × 𝑏𝑏 × 𝑐𝑐 (1) Titrations were performed using two cuvettes: In cuvette I, corresponding to the blank, 1700 μL of tris buffer and 300 μL of DMSO were added, and in cuvette II, 1700 μL of tris buffer were added and 300 μL of the solution of the ruthenium complex in DMSO (in a concentration that does not exceed the Lambert- Beer Law). Then successive additions of 10 µL of CT-DNA were performed in the two cuvettes. The solutions were homo- genised for about half a minute and then the spectrum was recorded. The interaction constant (Kb) with DNA was determined based on the absorption maximum for each complex, using equation (2): [𝐷𝐷𝐷𝐷𝐷𝐷] �𝜀𝜀𝑎𝑎−𝜀𝜀𝑓𝑓� = [𝐷𝐷𝐷𝐷𝐷𝐷] �𝜀𝜀𝑏𝑏−𝜀𝜀𝑓𝑓� + 1 �𝐾𝐾𝑏𝑏�𝜀𝜀𝑏𝑏−𝜀𝜀𝑓𝑓�� (2) where: εa, εf, εb are the Aobsd/[Complex], the molar extinction coefficient of the free and bounded metal complexes, respect- tively. 2.4. DNA interaction by electrochemical studies The electrochemical characterization of the [RuCl2(dppe)2] complex was performed using a Potentiostat/Galvanostat Autolab model 302N, using a glass cell and a three-electrode system, in which platinum was used as the working and auxiliary electrode and Ag/AgCl (3.0 mol/L KCl) as the reference electrode. The [RuCl2(dppe)2] complex solution was prepared in dichloromethane (0.1 mol/L of tetrabutyl ammonium perchlorate (PTBA)) at a concentration of 2×10-4 mol/L. Cyclic voltammograms were recorded in the range of 0 to +1.6 V at different scan rates (10-100 mV/s). To assess the interaction of the [RuCl2(dppe)2] complex with CT-DNA, the square-wave voltammetry technique was used. A system of three electrodes was used, with the glassy carbon working electrode, Ag/AgCl (3.0 mol/L KCl) as a reference electrode and as the auxiliary electrode, a platinum plate. The [RuCl2(dppe)2] complex was prepared in a mixture of Tris-HCl buffer (4.5 mM Tris-HCl, 0.5 mM Tris-base and 0.1 mol/L NaCl, pH = 7.4) with 40% DMSO at a concentration of 1×10-4 M. First, the voltammetric profile of the complex was recorded and then successive 10 µL aliquots of a CT-DNA solution (4.67×10-3 M) were added to the complex solution. With each addition of CT- DNA, the system was shaken for a period of 5 min and then the voltammogram was recorded. 2.5. Viscosity To determine the changes that occur in the viscosity of a CT- DNA solution, solutions with different CT-DNA:metal complex molar ratios of 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared. Viscosity measurements were made using an Oswald viscometer in the thermostatic water bath at 25 ° C. Thus, keeping the concent- ration of CT-DNA constant (3.66×10-3 mol/L), a viscosity ratio η can be obtained from the following equation: 𝜂𝜂 = 𝑡𝑡−𝑡𝑡0 𝑡𝑡0 (3) where: t is the elution time of the solution CT-DNA:metal complex, and 𝑡𝑡0 is the elution time of free DNA. With the data obtained, it is possible to construct a graph of the relative viscosity vs. [DNA]/[complex], and to evaluate the possible changes in the viscosity of CT-DNA, in the presence of ruthenium complex. 2.6. X-ray crystallography study Single crystals of [RuCl2(dppe)2]Cl were obtained at room temperature by slow solvent evaporation of the electro- chemical solution. The X-ray diffraction experiment was carried out at room temperature on an Enraf-Nonius Kappa-CCD diffractometer using the MoKα radiation (λ = 0.71073 Å) monochromated with graphite. The crystal structure of trans- [RuCl2(dppe)2]Cl was solved by the direct method and refined using the SHELXS-97 and SHELXL-97 programmes (Table 1) [24], respectively. Absorption corrections were carried out using the Gaussian method, and all non-hydrogen atoms of trans-[RuCl2(dppe)2]Cl were located and refined with anisot- ropic thermal parameters. The C-H aromatic hydrogen atoms were added with C-H distance, fixed at 0.93 Å, and refined with fixed displacement parameters [Uiso(H) = 1.2 Ueq(Csp2)]. Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 195 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 Table 1. Crystal data and structure refinement for complex trans-[RuCl2(dppe)2]Cl. Empirical formula C52H48Cl4P4Ru Formula weight (g/mol) 1039.65 Temperature (K) 293(2) Crystal system Triclinic Space group P-1 a, (Å) 9.240(3) b, (Å) 10.9290(18) c, (Å) 11.993(3) α (°) 78.707(11) β (°) 86.712(13) γ (°) 82.598(13) Volume (Å3) 1177.1(5) Z 1 ρcalc (g/cm3) 1.467 μ (mm-1) 0.732 F(000) 532.0 Crystal size (mm3) 0.18 × 0.08 × 0.03 Radiation MoKα (λ = 0.71073) 2Θ range for data collection (°) 6.934 to 51.986 Index ranges -11 ≤ h ≤ 11, -13 ≤ k ≤ 13, -14 ≤ l ≤ 14 Reflections collected 8434 Independent reflections 4607 [Rint = 0.0973, Rsigma = 0.1171] Data/restraints/parameters 4607/0/277 Goodness-of-fit on F2 0.956 Final R indexes [I≥2σ (I)] R1 = 0.0537, wR2 = 0.1222 Final R indexes [all data] R1 = 0.0795, wR2 = 0.1347 Largest diff. peak/hole (e.Å-3) 0.73/-0.95 cis-[RuCl2(dppe)2] trans-[RuCl2(dppe)2] Figure 1. cis- and trans-isomers of complex [RuCl2(dppe)2]. Figure 2. Absorption spectrum in the UV-Vis region of the complex [RuCl2(dppe)2] (isomers cis / trans), in the concentration 1.5×10-3 mol/L, in the presence of successive additions of rates of CT-DNA (2.05×10-3 mol/L), in buffer Tris-HCl (pH = 7.4) and 10% of DMSO. The hydrogen of methylene groups of dppe was also set as isotropic with a thermal parameter 20% greater than the equivalent isotropic displacement parameter of the atom to which each one was bonded, and C-H bond lengths were fixed at 0.97 Å. For structure representation, the Mercury 4.0 programme was used [25]. 3. Results and discussion The mixture of trans- and cis-[RuCl2(dppe)2] complexes was obtained from the precursor cis-[RuCl2(DMSO)4] by replacing the four DMSO ligands with two diphosphine dppe (1,2-bis- (diphenylphosphino)ethane) ligands, as shown in Figure 1. The mixture of isomers was confirmed by 31P{1H} NMR, in which one singlet at δ 44 ppm is related to isomer trans and two triplets at δ 50.29 and 37.35 ppm (2JP-P = 19.6 Hz) belong to isomer cis. 3.1. UV-Vis DNA spectroscopic titration and viscosity First, spectrophotometric titrations were performed to evaluate the interaction of the [RuCl2(dppe)2] complex with CT- DNA. This technique is widely used to determine the complex- DNA affinity, in which the binding constant values (Kb) can indicate a high, moderate or weak interaction [26]. The UV-Vis spectrum for the [RuCl2(dppe)2] complex was investigated in the region between 200 and 600 nm. In Figure 2, it is possible to observe that the spectra of the mixture of cis- and trans- [RuCl2(dppe)2] complex decrease with CT-DNA addition, resulting in a hypochromism. 196 Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 Figure 3. Relative viscosity vs [DNA]/[complex], of thiazole orange and the complex [RuCl2(dppe)2] at a concentration 1.5×10-3 mol/L, in the presence of successive additions of CT-DNA ratios (3.66×10-3 mol/L), in Tris-HCl buffer (pH = 7.4) and DMSO. Figure 4. Cyclic voltammogram of the complex [RuCl2(dppe)2] (isomer cis e trans), in concentration 2×10-4 mol/L in 0.1 mol/L PTBA, in CH2Cl2. Scan rate = 50 mV/s. The initial spectrum (black) corresponds to the free complex (in the absence of DNA), while the other data were obtained after successive additions of 10 µL of CT-DNA to the complex solution. The Kb value was calculated from the absorp- tion band (λmax) at about 250 nm to the complex, and the Kb value is 3.9×104 M-1, revealing a moderate interaction compared with other metal complexes reported in the literature [27,28]. In addition, to better understand the interaction between the ruthenium complex and CT-DNA, viscosity measurements were performed. Intercalation and groove-binding interactions have been reported to contribute to an increase in viscosity, whereas covalent binding can cause a decrease in the relative viscosity of CT-DNA [29]. When the concentration of the ruthenium complex increases, the relative viscosity of CT-DNA decreases (Figure 3). For comparison, DNA viscosity was performed using a DNA intercalator, known as thiazole orange [30], which increases DNA viscosity in all molar additions studied. Therefore, a different curve profile for the ruthenium complex compared with thiazole orange may suggest that the complex does not act as a DNA intercalator. 3.2. Electrochemical and DNA interaction study by square wave voltammetry The complex [RuCl2(dppe)2] was characterized using cyclic voltammetry (Figure 4). This technique was used because of its sensitivity to redox processes. Cyclic voltammograms were investigated in the range of 0 to +1.6 V at different scan rates, and the recorded cyclic voltammograms in the scan rate range of 10-100 mV/s can be seen in Figure 5. In the cyclic voltammogram shown in Figure 4, the electrochemical profile of the [RuCl2(dppe)2] complex presents two oxidation processes Ru(II)/Ru(III) at +0.632 V and +0.926 V, referring to the cis- and trans-isomers of the [RuCl2(dppe)2] complex, respectively. The oxidation potential Ru(II)/Ru(III) for the cis isomer occurs in a more positive region (+0.926 V) when compared to the trans isomer (+0.632 V), indicating that in cis-configuration ruthenium is more deficient in electron density, requiring a higher potential for oxidation of the metal. The redox potential for the cis-isomer occurs at a higher potential than that of the trans-isomer as a result of the increase in the back-donation of ruthenium to the phosphorus atom in the cis-isomer. This behaviour occurs because phosphorus trans to phosphorus increases the trans cooperative effect, lowering the redox potential, which agrees with expected by Sullivan and Meyer [31]. From the cyclic voltammograms obtained at different scan rates, linear relationships between anodic peak current and the square root of the scan rate (Ip vs. v1/2 shown in Figure 5) were obtained for the oxidation peak of the cis and trans isomers, showing that both redox processes were controlled only by diffusion. The electrochemical response of the complex can change in the presence of DNA. Intercalation interactions lead to the potential shift to positive values as a result of the increase in the diffusion coefficient caused by the DNA molecule. Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 197 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 (a) (b) (c) Figure 5. (a) Cyclic voltammogram of the complex [RuCl2(dppe)2] (isomer cis and trans), at concentration 2×10-4 mol/L in 0.1 mol/L PTBA, in CH2Cl2 at different scan rates: (i) 10 mV/s; (ii) 20 mV/s; (iii) 30 mV/s; (iv) 40 mV/s; (v) 50 mV/s; (vi) 75 mV/s and (vii) 100 mV/s. (b, c) Graph of Ip vs. v1/2 obtained for the anodic peak of the isomer trans and isomer cis. On the contrary, electrostatic interactions promote a displa- cement of the potential to more negative values, since electrons are transferred from DNA to the complex. Covalent interactions, when new species are generated, lead to the appearance of new redox processes or the disappearance of existing processes. Interactions between the DNA grooves may not promote significant changes in potential values, but they do change the number of complexes available that can undergo redox reactions, as in other modes of interaction, affecting the intensity of electrochemical processes [13,32] Electrochemical study of the interaction with CT-DNA with the mixture of cis- and trans-[RuCl2(dppe)2] complexes was performed using SWV. This technique was used because of its high sensitivity to redox processes and reaction formation, which is greater than that of the cyclic voltammetry technique. Figure 6 shows the recorded voltammetric profile of the complex with successive 10 µL aliquots of a CT-DNA solution. After adding different concentrations of CT-DNA to the solution containing the mixture of cis and trans-[RuCl2(dppe)2] complexes (Figure 6), a significant current decrease was observed in the Ru(II)/Ru(III) redox process, indicating that complex/DNA interactions are occurring. In the cis-isomer (Figure 6), the current of the Ru(II)/Ru(III) redox process decreases and the potential does not change; this behaviour may indicate an interaction between the DNA grooves. On the other hand, analysing the Ru(II)/Ru(III) redox process for the trans-isomer after successive CT-DNA additions (Figure 6), it is possible to observe that the potential shifted to the most positive region and a subsequent increase in the peak current, in the case of the latest CT-DNA additions. This result indicates that the trans-isomer may be interacting with CT-DNA through intercalation or even through covalence, different from the behaviour observed in the cis-isomer of the [RuCl2(dppe)2] complex. To investigate whether the redox potential changes due to the dilution effect, we recorded a square-wave voltammogram of the complex adding only Tris-HCl buffer (without DNA), and no significant changes were observed. Thus, the peak current decrease occurs through DNA interaction. 3.3. Single crystal X-ray diffraction of complex trans- [RuCl2(dppe)2]Cl The electrochemical solution produced orange crystals after one week. The crystals were analysed by single crystal X- ray diffraction and resulted in the trans-[RuCl2(dppe)2]Cl complex (Figure 7). We highlight that in the crystal structure the metal center is in Ru3+ oxidation state, thus this is an unpublished structure, given that in the literature only the trans-[RuCl2(dppe)2] was reported and the metal center is Ru2+. The X-ray crystallographic studies confirm the presence of two dppe as bidentate ligands and two chlorido ligands in a trans-configuration. In the structure, the Ru atom is located on an inversion centre; thus, a half-molecule is observed in the asymmetric unit. The complex presents a slightly distorted octahedral geometry, as highlighted by the bond angles around the metal centres (Table 2). In the complex structure, the Cl1- Ru1-P1 (98.53(4)/81.47(4)°) and Cl1-Ru1-P2 (91.74(4)/ 88.26(4)°) bond angles are close to 90°, and the P1-Ru1-P2 (99.03(4)/80.97(4)°) bond angle is far from the expected value of 90° due to the tension of the five-membered chelate rings of the dppe ligand. The Cl1-Ru1-Cl2 bond angle adopting a trans- configuration is 180°. 198 Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 (a) (b) (c) Figure 6. (a) Square wave voltammograms obtained in buffer Tris-HCl (pH = 7.4)-40% (v/v) DMSO containing (i) [RuCl2(dppe)2] 100 µM; (ii) [RuCl2(dppe)2] 100 µM + DNA 15.5 µM; (iii) [RuCl2(dppe)2] 100 µM + CT-DNA 30.9 µM; (iv) cis-[RuCl2(dppe)2] 100 µM + CT-DNA 46.2 µM; (v) [RuCl2(dppe)2] 100 µM + CT-DNA 61.4 µM; (vi) [RuCl2(dppe)2] 100 µM + CT-DNA 76.5 µM; (vii) [RuCl2(dppe)2] 100 µM + CT-DNA 91.6 µM and (vii) [RuCl2(dppe)2] 100 µM + CT-DNA 180.0 µM. Parameters SWV: Frequency (f) = 20 Hz, Amplitude (A) = 50 mV, and potential increment (ΔEs) = 5 mV. (b) Graphs of peak potential versus concentration CT-DNA (Ep vs. [CT-DNA]) and (c) Peak current versus concentration CT-DNA (Ip vs. [CT-DNA]). Figure 7. Crystal structure of [RuCl2(dppe)2]Cl with ellipsoids drawn at 30% probability. Furthermore, it is observed that the bond lengths of Ru-P and Ru-Cl are in agreement with the values reported for Ru(III) complexes [33,34]. In the literature, four crystal structures containing the complex trans-[RuCl2(dppe)2] were reported. A solvent-free structure of trans-[RuCl2(dppe)2] [35] and three other crystalline forms containing one dichloromethane solvate [36], one chloroform solvate, and one tetrahydrofuran solvate [37]. When the structure of trans-[RuCl2(dppe)2]Cl is compared with trans-[RuCl2(dppe)2] [36], many differences can be observed. In trans-[RuCl2(dppe)2]Cl the Ru-Cl distance is 2.3310(12) Å, while the trans-[RuCl2(dppe)2] is slightly larger [2.436(1) Å], which is expected for a low-charged metal. On the other hand, the RuII-P bond distance for [RuCl2(dppe)2] is 2.369(1) Å [36] and 2.3811(13) Å [37], while in the structure reported here, the RuIII-P bond distance is also slightly larger [Ru1-P1 = 2.4587(11) and Ru1-P2 = 2.4374(11) Å], this aspect may be explained because, in the Ru(III) complex, the Ru-ligand back-donation decreases, thus, Ru-P bond is slightly weaker. Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 199 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 Table 2. Bond lengths and angles for trans-[RuCl2(dppe)2]Cl *. Bond lengths Atom Atom Length (Å) Atom Atom Length (Å) Ru1 P21 2.4374(11) C212 C213 1.390(6) Ru1 P2 2.4374(11) C111 C116 1.386(6) Ru1 P11 2.4586(11) C111 C112 1.398(6) Ru1 P1 2.4587(11) C126 C125 1.396(6) Ru1 Cl1 2.3310(12) C124 C125 1.369(7) Ru1 Cl11 2.3310(12) C124 C123 1.367(6) P2 C211 1.825(4) C122 C123 1.389(6) P2 C221 1.823(4) C226 C225 1.383(6) P2 C231 1.853(4) C116 C115 1.382(6) P1 C121 1.840(4) C213 C214 1.357(7) P1 C111 1.816(4) C216 C215 1.383(6) P1 C131 1.833(4) C112 C113 1.382(6) C211 C212 1.380(6) C215 C214 1.383(7) C211 C216 1.400(6) C114 C115 1.379(7) C221 C226 1.385(6) C114 C113 1.377(7) C221 C222 1.406(6) C225 C224 1.371(8) C231 C131 1.524(5) C223 C224 1.372(8) C121 C126 1.381(5) C223 C222 1.379(6) C121 C122 1.384(6) Bond angles Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) P21 Ru1 P2 180.0 C226 C221 C222 118.2(4) P21 Ru1 P1 99.03(4) C222 C221 P2 121.6(3) P2 Ru1 P1 80.97(4) C131 C231 P2 110.7(3) P2 Ru1 P11 99.03(4) C126 C121 P1 122.8(3) P21 Ru1 P11 80.97(4) C126 C121 C122 119.0(4) P11 Ru1 P1 180.0 C122 C121 P1 117.9(3) Cl1 Ru1 P21 91.74(4) C211 C212 C213 120.5(4) Cl11 Ru1 P2 91.74(4) C116 C111 P1 119.2(3) Cl1 Ru1 P2 88.26(4) C116 C111 C112 118.3(4) Cl11 Ru1 P21 88.26(4) C112 C111 P1 122.4(3) Cl11 Ru1 P11 81.47(4) C231 C131 P1 107.0(3) Cl1 Ru1 P11 98.53(4) C121 C126 C125 120.2(4) Cl1 Ru1 P1 81.47(4) C123 C124 C125 120.4(4) Cl11 Ru1 P1 98.53(4) C121 C122 C123 120.5(4) Cl11 Ru1 Cl1 180.0 C225 C226 C221 121.3(5) C211 P2 Ru1 118.35(13) C115 C116 C111 121.5(4) C211 P2 C231 103.6(2) C124 C125 C126 119.9(4) C221 P2 Ru1 118.74(15) C124 C123 C122 119.9(5) C221 P2 C211 102.89(19) C214 C213 C212 120.6(5) C221 P2 C231 103.56(18) C215 C216 C211 121.1(5) C231 P2 Ru1 107.79(13) C113 C112 C111 120.0(5) C121 P1 Ru1 124.86(13) C216 C215 C214 119.2(5) C111 P1 Ru1 117.70(14) C113 C114 C115 120.0(4) C111 P1 C121 102.02(18) C114 C115 C116 119.5(5) C111 P1 C131 107.09(19) C224 C225 C226 119.5(5) C131 P1 Ru1 103.19(14) C224 C223 C222 120.5(5) C131 P1 C121 99.5(2) C225 C224 C223 120.5(4) C212 C211 P2 121.6(3) C223 C222 C221 119.9(4) C212 C211 C216 118.2(4) C213 C214 C215 120.5(5) C216 C211 P2 120.2(3) C114 C113 C112 120.7(5) 6 C221 P2 120.2(3) * Symmetry code: 1 -x, 2-y, -z. Figure 8. C-H···Cl- hydrogen bonding and Cl-···Cl- halogen bond, stabilizing the crystal structure of the complex trans-[RuCl2(dppe)2]Cl. 200 Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 The crystal structure of trans-[RuCl2(dppe)2]Cl presents non-classical C-H···Cl1s hydrogen bonding, keeping the counter-ion caged (Figure 8). The C-H···Cl intermolecular contacts are around 2.8 Å. Furthermore, the complex presents an intermolecular Cl···Cl halogen bond at 3.123 Å, which is consistent with values reported elsewhere [38]. 4. Conclusions In summary, the interaction with DNA of cis and trans isomers of the complex [RuCl2(dppe)2] was investigated. UV-Vis and viscosity analysis showed that the cis- and trans-isomer mixtures exhibit moderate interaction with DNA. Interestingly, DNA interaction by square wave voltammetric indicates that the interaction of cis-isomer may occur by DNA grooves, while the complex trans-[RuCl2(dppe)2] probably interacts with DNA by intercalation or by covalence. Finally, the crystal structure of the trans-[RuCl2(dppe)2]Cl complex was presented and compared with the trans-[RuCl2(dppe)2] complex. This study contributes to a better understanding of complex/DNA interaction, mainly, allowing identification of two different DNA interaction modes by using square wave voltammograms. Acknowledgements We would like to thank Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nı́vel Superior (CAPES), and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) for the financial support. Jerica Margely Montilla-Suárez thanks the Universidade Federal de Ouro Preto for master’s fellowship. The authors thank Professor Javier Ellena for crystallographic facilities and Professor Alzir A. Batista for providing the ruthenium salt. Supporting information CCDC-2232620 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam. ac.uk/structures/, or by e-mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could appear to influence the work reported in this paper. Sample availability: Samples of the compound are available from the author. CRediT authorship contribution statement Conceptualization: Victor Cardoso Campideli, Jerica Margely Montilla-Suárez, Rodrigo Souza Corrêa; Methodology: Victor Cardoso Campideli, Jerica Margely Montilla-Suárez, Tiago Almeida Silva, Dalila Chaves Sicupira, Katia Mara Oliveira, Rodrigo Souza Correa; Software: Katia Mara Oliveira, Rodrigo Souza Correa; Validation: Tiago Almeida Silva, Dalila Chaves Sicupira, Katia Mara Oliveira, Rodrigo Souza Correa; Formal Analysis: Victor Cardoso Campideli, Jerica Margely Montilla-Suárez, Katia Mara Oliveira; Investigation: Victor Cardoso Campideli, Jerica Margely Montilla-Suárez, Tiago Almeida Silva; Resources: Dalila Chaves Sicupira, Katia Mara Oliveira, Rodrigo Souza Correa; Data Curation: Victor Cardoso Campideli, Jerica Margely Montilla- Suárez, Katia Mara Oliveira; Writing - Original Draft: Victor Cardoso Campideli, Jerica Margely Montilla-Suárez, Katia Mara Oliveira, Rodrigo Souza Correa; Writing - Review and Editing: Katia Mara Oliveira, Rodrigo Souza Correa; Visualization: Katia Mara Oliveira, Rodrigo Souza Correa; Funding acquisition: Rodrigo Souza Correa; Supervision: Katia Mara Oliveira, Rodrigo Souza Correa; Project Administration: Dalila Chaves Sicupira, Katia Mara Oliveira, Rodrigo Souza Correa. Funding This research was funded by Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG APQ-01674-18) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 311302/2020-3). ORCID and Email Victor Cardoso Campideli victor.campideli@aluno.ufop.edu.br https://orcid.org/0000-0001-6262-2268 Jerica Margely Montilla-Suárez jerica.suarez@aluno.ufop.edu.br https://orcid.org/0000-0001-6898-6652 Tiago Almeida Silva tiago.a.silva@ufv.br https://orcid.org/0000-0002-7202-789X Dalila Chaves Sicupira dalila@ufop.edu.br https://orcid.org/0000-0003-2552-6845 Katia Mara Oliveira katia.oliveira@unb.br https://orcid.org/0000-0003-4749-0281 Rodrigo Souza Correa rodrigocorrea@ufop.edu.br https://orcid.org/0000-0003-2783-0816 References [1]. Cross, D.; Burmester, J. K. Gene therapy for cancer treatment: past, present and future. Clin. Med. Res. 2006, 4, 218–227. [2]. Kumar, L. S.; Prasad, K. S.; Revanasiddappa, H. D. 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Ru(II)-Naphthoquinone mailto:data_request@ccdc.cam.ac.uk mailto:victor.campideli@aluno.ufop.edu.br https://orcid.org/0000-0001-6262-2268 mailto:jerica.suarez@aluno.ufop.edu.br https://orcid.org/0000-0001-6898-6652 mailto:tiago.a.silva@ufv.br https://orcid.org/0000-0002-7202-789X mailto:dalila@ufop.edu.br https://orcid.org/0000-0003-2552-6845 mailto:katia.oliveira@unb.br https://orcid.org/0000-0003-4749-0281 mailto:rodrigocorrea@ufop.edu.br https://orcid.org/0000-0003-2783-0816 Campideli et al. / European Journal of Chemistry 14 (2) (2023) 193-201 201 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.2.193-201.2402 complexes with high selectivity for triple-negative breast cancer. Dalton Trans. 2020, 49, 16193–16203. [20]. Carvalho, D. E. L.; Oliveira, K. M.; Bomfim, L. M.; Soares, M. B. P.; Bezerra, D. P.; Batista, A. A.; Correa, R. S. Nucleobase derivatives as building blocks to form Ru(II)-based complexes with high cytotoxicity. ACS Omega 2020, 5, 122–130. 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This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Synthesis of the cis-[RuCl2(DMSO)4] complex 2.2. Synthesis of cis- and trans-[RuCl2(dppe)2] 2.3. UV-vis DNA spectroscopic titration 2.4. DNA interaction by electrochemical studies 2.5. Viscosity 2.6. X-ray crystallography study 3. Results and discussion 3.1. UV-Vis DNA spectroscopic titration and viscosity 3.2. Electrochemical and DNA interaction study by square wave voltammetry 3.3. Single crystal X-ray diffraction of complex trans-[RuCl2(dppe)2]Cl 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement Funding ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: