Mediated S-Nitrosylation of Bisulfide Ion - ACS Publications

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Formation of [RuIII(edta)(SNO)]2− in RuIII(edta)-Mediated S‑Nitrosylation of Bisulfide Ion Debabrata Chatterjee,*,† Papiya Sarkar,† Maria Oszajca,‡ and Rudi van Eldik*,‡,§ †

Chemistry and Biomimetics Group, CSIR-Central Mechanical Engineering Research Institute, M.G. Avenue, Durgapur 713209, India Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland § Department of Chemistry and Pharmacy, University of Erlangen-Nuremberg, Egerlandstr. 1, 91058 Erlangen, Germany ‡

S Supporting Information *

ABSTRACT: The reaction of hydrogen sulfide (H2S) and nitric oxide (NO) is of great physiological significance in human organisms. Our present studies show that RuIII(edta) (edta4− = ethylenediaminetetraacetate) mediates the S-nitrosylation of bisulfide ion (HS−) using NO to form [RuIII(edta)(SNO)]2−, the first-ever example of a ruthenium complex containing thionitrite (SNO−) in aqueous solution. The reaction product [RuIII(edta)(SNO)]2− was characterized by IR, electron paramagnetic resonance, and electrospray ionization mass spectroscopy. Our studies further show that formation of the putative thionitrous acid coordinated to RuIII(edta) does not occur via the reaction of [RuIII(edta)NO]− with HS−.

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INTRODUCTION

Materials. The starting complex K[RuIII(Hedta)Cl]·2H2O was prepared as reported in the literature8 and characterized.8 The complex K[Ru I I I (Hedta)Cl] immediately transforms into [RuIII(Hedta)(H2O)] when dissolved in water.9,10 All reagents used were of the highest grade commercially available. Doubly distilled H2O was used to prepare all the solutions. Solutions of sodium bisulfide were prepared strictly under anaerobic conditions, and their concentration was determined by iodometric titration.2 The reaction of RuIII(edta) with HS− was performed by mixing the aqueous solution of RuIII(edta) and NaHS (in phosphate buffer). All experimental solutions were prepared strictly under Ar atmosphere. Gas-tight Hamilton syringes were used to transfer these solutions throughout the studies. Solution of NO was prepared by saturating phosphate buffer solution (0.1 M) with NO gas (Canister of 99.5% pure NO gas was procured from Eurasian Associates). Instrumentation. UV−vis absorption spectral studies were performed using a Varian Model Cary 100 spectrophotometer. Spectra were recorded with A Mettler Toledo (ReactIR 45) spectrometer equipped with a DiComp AgX fiber probe, diamond ATR element, and an MCT detector was used to record in situ IR spectra of the reaction mixture. Raman spectroscopy was performed with a Trivista 555 spectrograph (Princeton Instruments) and using 413.1 nm excitation from a Kr+ laser (Coherent, Sabre Innova SBRC-DBW-K). EPR data were taken using an X-band (9.1 GHz) JEOL JES-FA 200 spectrometer. ESI-MS measurements were recorded by a Q-TOF MS (Waters, USA) in the negative ion ESI mode. The flow rate was 300 μL h−1. N2 was used as drying gas. The applied capillary voltage was 3000 V. The pH of the buffer solution was measured with a Mettler Delta 350 pH meter. Phosphate buffers (0.1 M) were used to control the pH of the experimental solutions.

While nitric oxide (NO) regulates many physiological functions,1 current reports reveal that hydrogen sulfide (H2S), an odious toxin, can also function as a key signaling molecule offering a variety of beneficial effects to our bodies.2 Both NO and H2S have emerged as major redox controllers of many features of cellular and physiological functions within a number of organ systems.3 However, mechanistic understanding of the NO−H2S chemical interactions and subsequent biological effects, as well as their roles in regulating several biological functions under ailment, is still elusive.4 The formation of the Snitrosothiol, HSNO (via trans-nitrosation of S-nitrosoglutathione and H2S in aqueous solution), and its characterization has been reported recently by Filipovic et al.5 In very recent work the same group reported the heme-iron mediated transformation of H2S to HSNO in the presence of nitrite.6 We were inspired by the ability of a metal complex to mediate the formation of HSNO in the reaction of H2S and nitrite ion (NO2−)6 and set out to examine the ability of the RuIII(edta) complex (edta4− = ethylenediaminetetraacetate) toward transformation of H2S to HSNO in the presence of NO. The ability of the RuIII(edta) complex to mediate S-nitrosylation of biological thiols (cysteine, glutathione)7 led to a successful platform for the present work. This communication describes our success with the discovery of a complex, [RuIII(edta)(SNO)]2−, that results from the reaction of [{RuIII(edta)S}2]4− with nitric oxide (NO) in anaerobic aqueous solution at pH 8.2. By using UV−vis, IR, electron paramagnetic resonance (EPR), and electrospray ionization mass spectrometry (ESI-MS) techniques we demonstrated the formation of [RuIII(edta)(SNO)]2− in aqueous medium. © XXXX American Chemical Society

EXPERIMENTAL SECTION

Received: March 10, 2016

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DOI: 10.1021/acs.inorgchem.6b00615 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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from [RuIII(edta)(H2O)]−, could not produce the S-bonded [RuIII(edta)(TU)]− complex (λmax = 466 nm; εmax = 1960 ± 20 M−1 cm−1).9 We assign the peak at m/z = 845.84 to {[(edta)RuIIISSRuIII(edta)]4− + 3H+}. Simulation of the isotopic distribution for {[(edta)RuIIISSRuIII(edta)]4− + 3H+} and comparison of the calculated molecular weight (845.89) with that obtained experimentally are in excellent agreement as seen in Figure 2.

RESULTS AND DISCUSSION The ESI-MS spectrum recorded for the solution containing the RuIII(edta) complex showed a characteristic signal for [RuIII(edta)]− at m/z = 390.2 (see Figure S1 in the Supporting Information). To take the advantage of the lability of the RuIII(edta) complex toward substitution,11 HS− was subjected to react with the RuIII(edta) complex at pH 8.2 (phosphate buffer). Considering pKa values (pKa1 = 7.02 and pKa2 ≈ 17.1)12,13 related to the proton dissociation equilibria of H2S, it is presumed that at pH > 8.0 the presence of H2S and S2− in the solution is insignificant. Under aerobic conditions, addition of a solution of NaHS in phosphate buffer (pH 8.2) to a pale yellow solution of [RuIII(edta)(OH)]2− resulted in a rapid change in color from pale yellow to bluish-green. The overall spectral changes recorded just after mixing of the solution of RuIII(edta) with that of NaHS at pH 8.2 are shown in Figure 1.

Figure 2. ESI-MS spectra of [(edta)RuIIISSRuIII(edta)]4− (a) obtained experimentally and (b) simulated.

Addition of a phosphate buffer solution saturated with NO to the argon-purged green solution of [(edta)Ru I I I SSRuIII(edta)]4− under anaerobic conditions resulted in the rapid disappearance of the green color. The observed spectral changes (Figure 3) are ascribed to the formation of

Figure 1. Spectral changes that occurred upon mixing of the solutions of RuIII(edta) and HS− at pH 8.2 (phosphate buffer). [RuIII] = 0.1 mM, [HS−] = 0.25 mM.

The spectral features shown in Figure 1 are very similar to that of a disulfur bridged complex [(NH3)5RuSSRu(NH3)5]4+ reported long ago by Taube and co-workers.14 A very similar spectral pattern observed in the present case is indicative of the formation of the “edta” analogue of the disulfur bridged ruthenium complex reported earlier.14 The dinuclear complex [(edta)RuIIISSRuIII(edta)]4− was subjected to Raman spectral studies for further characterization in comparison to [(NH3)5RuSSRu(NH3)5]4+.14 The Raman spectrum of [(edta)RuIIISSRuIII(edta)]4− showed a band at 525 cm−l (see Figure S2 in the Supporting Information) characteristic of the S−S stretching. This is quite comparable to the band (519 cm−1) reported for [(NH3)5RuSSRu(NH3)5]4+.14 The identification of the green compound as a disulfur bridged [(edta)RuIIISSRuIII(edta)]4− entity by Raman spectroscopy has been well-supported by ESI-MS studies. The recorded spectra of the green solution of [(edta)RuIIISSRuIII(edta)]4− shows an intense signal at m/z = 845.84 (see Figure S3 in the Supporting Information). When mixed with NaHS, no peak for [RuIII(edta)]− (at m/z = 390.2) was detected in the spectrum (see Figure S3), suggesting that no free [RuIII(edta)]− is present in the green solution. Further examination of the green reaction mixture confirmed the absence of RuIII(edta) complex in the solution, since addition of a solution of thiourea (TU), a potential nucleophile that readily substitutes the aqua-molecule

Figure 3. Spectra of (a) [(edta)RuIIISSRuIII(edta)]4− and (b) recorded immediately after mixing with the solution of NO in phosphate buffer.

[RuIII(edta)(SNO)]2−. The basis for this description is the results from the ESI-MS studies, which unambiguously support the formation of [RuIII(edta)(SNO)]2− in the reaction mixture. The peak at m/z = 845.84 corresponding to [(edta)RuIIISSRuIII(edta)]4− disappeared, and a new peak appeared at m/z 452.98 in the mass spectrum (see Figure S4 in the Supporting Information) of the resultant solution obtained by mixing the NO solution (in phosphate buffer) with the green solution of [(edta)RuIIISSRuIII(edta)]4−. The signal at m/z = 452.98 is assigned to {[RuIII(edta)(SNO)]2− + H+}. The calculated molecular weight (m/z = 452.94) is indeed very close to the experimentally obtained value (m/z = 452.98) as seen in Figure 4. The excellent agreement between the experimental and simulated spectra (Figure 4) undoubtedly establishes the B

DOI: 10.1021/acs.inorgchem.6b00615 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Scheme 1. Pictorial Representation of the RuIII(edta)Mediated Nitrosylation of HS− by NO

Figure 4. ESI-MS spectra of [RuIII(edta)(SNO)]2− (a) obtained experimentally and (b) simulated.

formation of [RuIII(edta)(SNO)]2−. Formation of [RuIII(edta)(SNO)]2− was further characterized by FTIR spectral measurements in solution. A new peak found at 1530 cm−1 in the IR spectrum (see Figure S5 in the Supporting Information) is assigned to the νNO vibration of RuSNO, which was not seen in the IR spectrum of the green solution of [(edta)RuIIISSRuIII(edta)]4− or [RuIII(edta)(OH)]2−. It may be noted here that the value of the νNO vibration (1530 cm−1) observed in the present case is in good agreement with the value reported (1596 cm−1) for HSNO in the gas phase.15 The solution of [Ru(edta)(SNO)]2− so produced in the reaction of [(edta)RuIIISSRuIII(edta)]4− with NO was further subjected to EPR studies. The EPR spectrum (Figure 5) of the

(NO)R]2− (RSH = cysteine, glutathione) was reported earlier by us.7 However, the capability of RuIII(edta) to impart stability to the bond between the coordinated S atom and NO, a πaccepting molecule as observed in the present case with regard to the formation of [RuIII(edta)SNO]2−, a first-ever example of a RuIII−S-NO species, is indeed unique. To test this special ability of RuIII(edta), we performed the reaction of the green complex [(edta)RuIIISSRuIII(edta)]4− with cyanide ion (CN−), another π-accepting species, and found that by mixing with CN−, the green solution of [(edta)RuIIISSRuIII(edta)]4− turned red (overall spectral changes are shown in Figure S6 in the Supporting Information). The formation of the [RuIII(edta)SCN)]2− species in the reaction system was supported by the spectral data (λmax = 450 nm; εmax = 1010 ± 50 M−1 cm−1).9 It is worth mentioning here that a similar observation in regard to the formation of [RuIII(NH3)5SCN]2+ in the reaction of [Ru(NH3)5SSRu(NH3)5]4+ and CN− was reported by Taube and co-workers.14 Having demonstrated the nitrosylation of the S atom of HS− coordinated to the ruthenium(III) center in the present case, we turned our attention to examine the reaction of coordinated NO with HS−. The strong affinity of the RuIII(edta) complex toward NO binding and its pharmaceutical importance are welldocumented in the literature.18a RuIII(edta) binds NO very rapidly (k ≈ 1 × 107 M−1 s−1)18b to produce [RuIII(edta)(NO)]−, which is stable under an inert atmosphere. We prepared [RuIII(edta)(NO)] − (by reacting [RuIII(edta)(OH)]2− with dissolved NO in phosphate buffer (at pH 8.2) and performed ESI-MS studies. The recorded spectrum for [RuIII(edta)(NO)]− revealed a sharp signal at m/z = 420.1 (see Figure S7 in the Supporting Information), which we assigned to [RuIII(edta)(NO)]−. EPR studies on the [RuIII(edta)(NO)]− complex were performed, and the absence of any EPR signals (Figure S8 in the Supporting Information) reaffirmed the fact that [RuIII(edta)(NO)]− indeed exists as [RuII(edta)(NO+)]− in solution.19 The EPR spectrum (Figure S8 in the Supporting Information) remained featureless even after addition of HS− (in excess) to the solution of [RuII(edta)(NO+)]−. ESI-MS studies of the resultant solution did not reveal any signal supporting the formation of [RuIII(edta)(SNO)]2 but confirmed the formation of a disulfur bridged complex in the reaction system via multistep reactions (see Figure S9 in the Supporting Information).

Figure 5. EPR spectrum of [RuIII(edta)(SNO)]2− in H2O at room temperature.

[Ru(edta)(SNO)]2− yielded g components at 2.576 (g1), 2.321 (g2), and 1.790 (g3) characteristics of a low spin (half integer, S = 1/2) d5 system with gav {= 1/3(g1 + g2 + g3)} value of 2.229. The g values are well in the range reported for related ruthenium(III) complexes,16 including RuIII(edta) molecule.17 The above findings are schematically summarized in Scheme 1. The complex [RuIII(edta)(OH)]2− reacts with HS− giving rise to the disulfur bridged dinuclear complex, [(edta)RuIIISSRuIII(edta)]4− (eq 1). Formation of thionitrite (SNO−) coordinated to ruthenium(III) occurs in the reaction as outlined in eq 2. Under anaerobic conditions NO reacts with the coordinated S atom of the sulfido complex [(edta)RuIIISSRuIII(edta)]4− to produce the S-nitrosylated product complex [RuIII(edta)SNO]2− in the reaction system. Interaction of NO with the coordinated S atom of the RuIII−SR moiety resulting in the formation of the S-nitrosylated product [RuIII(edta)SC

DOI: 10.1021/acs.inorgchem.6b00615 Inorg. Chem. XXXX, XXX, XXX−XXX

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(6) Miljkovic, J. L.; Kenkel, I.; Ivanović-Burmazovic, I.; Filipovic, M. R. Angew. Chem., Int. Ed. 2013, 52, 12061. (7) Chatterjee, D.; Jaiswal, N.; Schmeisser, M.; van Eldik, R. Dalton Trans. 2014, 43, 18042. (8) Diamantis, A. A.; Dubrawski, J. V. Inorg. Chem. 1981, 20, 1142. (9) Matsubara, T.; Creutz, C. Inorg. Chem. 1979, 18, 1956. (10) Bajaj, H. C.; van Eldik, R. Inorg. Chem. 1988, 27, 4052. (11) Chatterjee, D. Coord. Chem. Rev. 1998, 168, 273. (12) Perrin, D. D. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution, 2nd ed.; Pergamon Press: Oxford, U.K., 1982. (13) Meyer, B.; Ward, K.; Koshlap, K.; Peter, L. Inorg. Chem. 1983, 22, 2345. (14) Brulet, C. R.; Isied, S. S.; Taube, H. J. Am. Chem. Soc. 1973, 95, 4758. (15) Nonella, M.; Huber, J. R.; Ha, T.-K. J. Phys. Chem. 1987, 91, 5203. (16) Kadish, K. M.; Nguyen, M.; Van Caemelbecke, E.; Bear, J. L. Inorg. Chem. 2006, 45, 5996. (17) Khan, M. M. T.; Chatterjee, D.; Merchant, R. R.; Paul, P.; Abdi, S. H. R.; Srinivas, D.; Siddiqui, M. R. H.; Moiz, M. M.; Bhadbhade, M. M.; Venkatasubramanian, K. Inorg. Chem. 1992, 31, 2711. (18) (a) Chatterjee, D.; Mitra, A.; De, G. S. Platinum Met. Rev. 2006, 50, 2. (b) Davies, N. A.; Wilson, M. T.; Slade, E.; Fricker, S. P.; Murrer, B. A.; Powell, N. A.; Henderson, G. R. Chem. Commun. 1997, 47. (19) (a) Wanat, A.; Schneppensieper, T.; Karocki, A.; Stochel, G.; van Eldik, R. J. Chem. Soc., Dalton Trans. 2002, 941. (b) Zanichelli, P. G.; Miotto, A. M.; Estrela, H. F. G.; Soares, F. R.; Grassi-Kassisse, D. M.; Spadari-Bratfisch, R. C.; Castellano, E. E.; Roncaroli, F.; Parise, A. R.; Olabe, J. A.; de Brito, A. R. M. S.; Franco, D. W. J. Inorg. Biochem. 2004, 98, 1921. (20) Filipovic, M. R.; Eberhardt, M.; Prokopovic, V.; Mijuskovic, A.; Orescanin-Dusic, Z.; Reeh, P.; Ivanovic-Burmazovic, I. J. Med. Chem. 2013, 56, 1499. (21) Quiroga, S. L.; Almaraz, A. E.; Amorebieta, V. T.; Perissinotti, L. L.; Olabe, J. A. Chem. - Eur. J. 2011, 17, 4145.

CONCLUSIONS In summary, this report includes evidence for the formation of [RuIII(edta)(SNO)]2−, which is unprecedented for the ruthenium system. This study thus opens the way to use transition metals other than iron20,21 for S-nitrosylation of sulfide using NO. The above findings further suggest that the formation of the Ru-HSNO in resemblance to Fe-HSNO6,20,21 is not possible in the reaction of [Ru(edta)NO]− with HS−.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00615. Characterization data including ESI-MS, EPR, Raman, UV−vis, rapid scan, and IR spectra. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. (D.C.) *E-mail: [email protected]. (R.v.E.) Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS P.S. thanks the CSIR, New Delhi, for a junior research fellowship (CSIR-JRF). REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00615 Inorg. Chem. XXXX, XXX, XXX−XXX