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X-ray absorption spectroscopy (XAS) is a powerful tool for examining changes of the electronic and molecular structure following light-induced excitation of a molecule. Specifically, this method can be applied to investigate the ground (GS, RuNO) and metastable states (MS1, RuON and MS2, Ruη2(NO)) of the nitrosyl ligand (NO), which differ in their coordination mode to the metal. In this work, we report for the first time experimental and theoretical (DFT) Ru L3,2-edge XA spectra for the octahedral complex trans-[RuNOPy4F](ClO4)2 (1, Py = pyridine) in both ground and metastable states. The transition from GS to MS1 using 420 nm light excitation leads to a significant downshift of the 2p â†’ LUMO(+1) peaks by about 0.5-0.8 eV, attributed to the destabilisation of 2p orbitals and stabilization of LUMO(+1). Subsequent irradiation of MS1 at 920 nm produces isomer MS2, for which even greater stabilization of LUMO occurs, though without a significant change in 2p energy. The change in 2p energy is attributed to a variation in the charge on the Ru atom after NO isomerization, while LUMO(+1) stabilization is related to changes in the Ru(NO) bond length and the composition of this orbital.

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The reaction of [RuNO(Py)2Cl2OH] with bipyridine in water-ethanol media results in trans-(NO, OH)-[RuNO(Py)(Bpy)ClOH]+ with an acceptable yield (60-70%) as hexafluorophosphate salt. Further treatment of the hydroxy-complex with concentrated HF quantitatively leads to trans-(NO, F)-[RuNO(Py)(Bpy)ClF]+. Despite the chirality of both coordination spheres, the hexafluorophosphate salts crystallized as racemates. A NO-linkage isomerism study of the obtained complexes was performed at 80 K with different excitation wavelengths (405, 450, 488 nm). The most favorable wavelengths for the MS1 isomer (Ru-ON) formation were 405 and 450 nm, where the linkage isomer populations were 17% and 1% for [RuNO(Py)(Bpy)ClOH]PF6 and [RuNO(Py)(Bpy)ClF]PF6. The shift of the excitation wavelength to the green (488 nm) sharply decreased the MS1 population. The IR-spectral signatures of MS1 were registered. Reverse-transformation Ru-ON (MS1)-Ru-NO (GS) was investigated for [RuNO(Py)(Bpy)ClOH]PF6 using IR and DSC techniques that made it possible to determine the kinetic parameters (Ea and k0) and decay temperature.

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Photoinduced linkage isomers (PLI) of the NO ligand in transition-metal nitrosyl compounds can be identified by vibrational spectroscopy due to the large shifts of the (NO) stretching vibration. We present a detailed experimental and theoretical study of the prototypical compound K2[RuCl5NO], where (NO) shifts by ≈150 cm-1 when going from the N-bound (κN) ground state (GS) to the oxygen-bound (κO) metastable linkage isomer MS1, and by ≈360 cm-1 when going to the side-on (κ2N,O) metastable linkage isomer MS2. We show that the experimentally observed N-O stretching modes of the GS, MS1, and MS2 exhibit strong coupling with the Ru-N and Ru-O stretching modes, which can be decoupled using the local mode vibrational theory formalism. From the resulting decoupled pure two-atomic harmonic oscillators the local force constants are determined, which all follow the same quadratic behavior on the wavenumber. A Bader charge analysis shows that the total charge on the NO ligand is not correlated to the observed frequency shift of (NO).

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Two ruthenium nitrosyl complexes of Na[RuNOCl4L] with nitronyl nitroxide radicals coordinated to ruthenium with N-donor pyridine rings were prepared and described. The crystal structure of both complexes is 1D or 2D polymeric, due to the additional coordination of sodium cation by bridging the chloride ligands or oxygen atoms of nitroxides. Partially, the oligomeric forms remain in the solutions of the complexes in acetonitrile. The magnetic measurements in the solid state demonstrate the presence of antiferromagnetic interactions through the exchange channels, with the distance between paramagnetic centers equal to 3.1-3.9 Å. The electrochemical behavior of the prepared complexes was investigated in acetonitrile solutions.

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The first examples of Bi(III) and Sb(III) halide compounds combined with a photoswitchable ruthenium nitrosyl unit are reported. The structures of [RuNOPy4Br]4[Sb2Br8][Sb3Br12]2 (1) and (H3O)[RuNOPy4Br]4[Bi2Br9]3·3H2O (2) were determined by X-ray diffraction, and exhibit three different structural types of group 15 halometalates. Low-temperature IR-spectroscopy measurements reveal that the irradiation of 1 at 365 nm switches a stable Ru-NO (GS) unit to a metastable Ru-ON (MS1) linkage. Moreover, the light excitation of 2 at 365 or 405 nm induces the additional formation of a side-bond isomer Ru-η2-(NO) (MS2). The reverse reactions MS1/MS2 → GS can be induced by red-infrared light irradiation or by heating at temperatures >200 K. The obtained synthetic and spectroscopic data open the way for the preparation of hybrid halide complexes with a variety of photoswitchable complexes (NO2, SO2, N2, etc.), and give an insight into the behavior of light-induced species embedded in polynuclear halides.

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1H NMR measurements are reported for the CD2Cl2/CDCl3 solutions of the Co(II) calix[4]arenetetraphosphineoxide complex (I). Temperature dependences of the 1H NMR spectra of I have been analyzed using the line shape analysis, taking into account the temperature variation of paramagnetic chemical shifts, within the frame of the dynamic NMR method. Conformational dynamics of the 2:1 Co(II) calix[4]arene complexes was conditioned by the pinched cone ↔pinched cone interconversion of I (with activation Gibbs energy ΔG≠(298K) = 40 ± 3 kJ/mol. Due to substantial temperature dependence of paramagnetic shifts, complex I can be used as model compound for designing an NMR thermosensor reagent for local temperature monitoring.

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The complexes [Co(NH3)6][Ir(C2O4)3] and [Ir(NH3)6][Co(C2O4)3]·H2O have previously been synthesized and their thermal properties studied. The [Ir(NH3)6][Ir(C2O4)3] and [Co(NH3)6][Co(C2O4)3]·3H2O complexes considered here are the end members in a series of possible isostructural solid solutions based on the complex salts in the Co-Ir system. Their crystal structures and thermal properties are described in detail, including temperature-dependent in situ X-ray diffraction. During the thermolysis of these compounds, layered metal nanoparticles are formed. Close attention is paid to the details of the [Co(NH3)6][Ir(C2O4)3] synthesis. It has been shown that the formation of this complex salt is temperature dependent; upon heating, a new phase of the K3[Co(NH3)6][Ir(C2O4)3]2·6H2O salt is formed, which incorporates the initial iridium compound into the crystal structure of the double complex salt. The target [Co(NH3)6][Ir(C2O4)3] product is obtained if the synthesis is carried out at room temperature.

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A light-induced linkage NO isomer (MS1) in trans-[Ru(15NO)(py)419F](ClO4)2 is detected and measured for the first time by solid-state MAS NMR. Chemical shift tensors of 15N and 19F, along with nJ(15N-19F) spin-spin couplings and T1 relaxation times of MS1, are compared with the ground state (GS) at temperatures T < 250 K. Isotropic chemical shifts (15N and 19F) are well resolved for two crystallographically independent cations (A and B) [Ru(15NO)(py)419F]2+, allowing to define separately both populations of MS1 isomers and thermal decay rates for two structural sites. The relaxation times T1 of 19F in the case of GS (30/38.6 s for sites A/B) and MS1 (11.6/11.8 s for sites A/B) indicate that both isomers are diamagnetic, which is the first experimental evidence of diamagnetic properties of MS1 in ruthenium nitrosyl. After light irradiation (λ = 420 nm), the NO ligand rotates by nearly 180° from F-Ru-N-O to F-Ru-O-N, whereby the isotropic chemical shifts of δiso(15N) increase and those of δiso(19F) decrease. The nJ(15N-19F) couplings increase from 2J(15N-Ru-19F)GS = 71 Hz to 3J(15N-O-Ru-19F)MS1 = 105 Hz. These results are interpreted on the basis of DFT-CASTEP calculations including Bader-, Mulliken-, and Hirshfeld-charge density distributions of both states.

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The stability of a photoactivated isonitrosyl state was boosted by confining a pre-designed bicarboxylate ligand with a ruthenium nitrosyl fragment in a 2D metal-organic framework. The novel Zn/Ru-based MOF, {Zn[RuNO(H2O)(inic)2(OH)2]2}·12H2O (inic = isonicotinate), was obtained with enhanced isonitrosyl stability by 30 K (up to 200 K) compared to the related ruthenium-only complex.

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ABSTARCTThe development of new anti-influenza drugs remains an active area, and efforts in this direction will likely continue far into the future. In this paper, we present the results of a theoretical study explaining the mechanisms behind the antiviral activity of camphor derivatives. These include camphecene and a number of its analogues. The compounds tested can inhibit hemagglutinin (HA) by binding to it at two possible sites. Moreover, the binding site located at the site of proteolysis is the most important. Serial passaging of influenza in the presence of camphecene leads to the formation of mutation-associated resistance. Specifically, camphecene causes a significant mutation in HA (V615L). This substitution likely reduces the affinity of the compound for the binding site due to steric restriction of the positioning of camphecene in the binding cavity. Molecular dynamics (MD) simulation results show that the mutant HA is a more stable structure in terms of thermodynamics. In other words, launching conformational rearrangements preceding the transition from pre- to post-fusion requires more energy than in wild type HA. This may well explain the lower virulence seen with the camphecene-resistant strain.

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The synthetic approaches for the preparation of trans(NO,OH)-cis(NO2,NO2)-[RuNO(L)2(NO2)2OH], where L = ethyl nicotinate (I) and methyl nicotinate (II), are reported. The structures of the complexes are characterized by X-ray diffraction and analyzed by Hirshfeld surface analysis. Both compounds show a nitric oxide release reaction under 445 or 532 nm irradiation of dimethyl sulfoxide (DMSO) solutions, which is studied by combined ultraviolet-visible- (UV-vis), infrared- (IR), and electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations. The charge transfer from the OH-Ru-NO chain and nitrite ligands to the antibonding orbitals of Ru-NO is responsible for the photo-cleavage of the ruthenium-nitrosyl bond. The elimination of NO leads to a side reaction, namely the protonation of the parent hydroxyl compound. The cytotoxicity and photo-induced cytotoxicity investigations of both compounds on the breast adenocarcinoma cell line MCF-7 reveal that (I) and (II) are cytotoxic with IC50 values of 27.5 ± 2.8 µM and 23.3 ± 0.3 µM, respectively. Moreover, (I) shows an increase of the toxicity after light irradiation by 7 times (IC50 = 4.1 ± 0.1), which makes it a prominent target for deeper biological investigations.

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Photoinduced NO-linkage isomers were investigated in the solid state of labelled trans-[Ru(14/15NO)(py4)F](ClO4)2 complex by combined IR-spectroscopy and DFT calculations. Based on the experimental data and the DFT calculations of this isotopically labelled 14/15NO nitrosyl compound, we present a complete assignment of the vibrational bands of three nitrosyl linkage isomers in a range from 4000 to 200 cm-1. The calculated IR-spectra match well with the experimental data allowing reliable assignment of the vibrational bands. The structural change from the Ru-NO (GS) to the Ru-ON (MS1) and Ru-η2-(NO) (MS2) linkage configuration leads to the downshift of the ν(NO) and ν(Ru-(NO)) bands, and a corresponding increase of the energy of the ν(Ru-F) band. The shift of the bands corresponds to the change of the Ru-(NO) and Ru-F bond lengths: increase of the Ru-(NO) bond length leads to the decrease of the energy of the ν(Ru-(NO)) band; decrease of the Ru-F bond length leads to the increase of the energy of the ν(Ru-F) band. These observations can be extrapolated to the family of related nitrosyl complexes and therefore be used for the qualitative prediction of the Ru-(NO) and Ru-Ltrans-to-NO bond lengths of different linkage isomers in the framework of one complex. While the formation of linkage isomers is a reversible process, long-time irradiation sometimes induces irreversible reactions such as the release of NO. Here, we show that the photolysis of trans-[Ru(14/15NO)(py4)F](ClO4)2 in KBr pellets may lead to the release of nitrous oxide N2O, conceivably through the formation of a {Ru-(κ2-ONNO)} intermediate.

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Two new complexes trans-(H3O)[RuNO(NH3)4F](NO3)1.5F1.5·0.5H2O (I) and trans-[RuNO(NH3)4F](ClO4)Cl (II) are synthesized and characterized by single crystal X-ray diffraction. The complexes crystallized in the centrosymmetric space groups I4/m and P21/n due to specific intermolecular interactions; the strongest ones are represented by N-HO contacts. The irradiation of the complexes in the blue-light range induces the formation of Ru-ON isomers (MS1), determined by IR spectroscopy and differential scanning calorimetry (DSC). The subsequent excitation of MS1 by infrared light induces the formation of Ru-(η2-(NO)) (MS2) isomers, confirmed by the same techniques. Using combined IR and DSC analysis, the activation barriers (Ea) and frequency factors (lg k0) of the MS1 → GS and MS2 → GS reactions are determined. According to the kinetic parameters, the calculated lifetimes (k-1) of MS1 at 300 K are 33 and 178 min for I and II, respectively. To the best of our knowledge, the thermal stability of MS1 in II is the highest among known related complexes. The thermal stability of MS2 was found to be lower (the lifetimes are 0.12 and 0.02 s at 300 K for I and II, respectively), which is characteristic of these states. The high thermal stability of MS1 can be applied for the design of photochromic materials and to generally facilitate the investigation of the states.

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In this work we have demonstrated that the ruthenium nitrosyl complex [RuNO(ß-Pic)2(NO2)2OH] is suitable for investigation of the inactivation of DNA repair enzymes in vitro. Photoinduced inhibition of DNA glycosylases such as E. coli Endo III, plant NtROS1, mammalian mNEIL1 and hNEIL2 occurs to an extent of ≥90% after irradiation with the ruthenium complex. The photophysical and photochemical processes of [RuNO(ß-Pic)2(NO2)2OH] were investigated using stationary and time-resolved spectroscopy, and mass spectrometry. A possible mechanism of the photo-processes was proposed from the combined spectroscopic study and DTF calculations, which reveal that the photolysis is multistage. The primary and secondary photolysis stages are the photo-induced cleavage of the Ru-NO bond with the formation of a free nitric oxide and RuIII complex followed by ligand exchange with solvent. For E. coli Endo III, covalent interaction with the photolysis product was confirmed by UV-vis and mass spectrometric methods.

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The conditions for the photogeneration of NO linkage isomers at room temperature are studied. By pulsed laser irradiation in the blue spectral range, the long-lived Ru-ON isomer can be generated at room temperature, which is crucial for potential applications, such as holography and data storage. By using static and time-resolved spectroscopy (UV/Vis and IR), we give evidence that the liftime of the Ru-(η2 -(NO)) isomer is a decisive parameter for the formation of the Ru-ON isomer at high temperature owing to a two-step isomerization mechanism Ru-NO→Ru-(η2 -(NO))→Ru-ON. Furthermore, we report the low-temperature structures for each isomer, which were revealed by photocrystallography.

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The complex trans-[RuNO(NH3)4F]SiF6 was synthesized in quantitative yield and the structure was characterized by X-ray diffraction and spectroscopic methods. The complex crystallizes in the non-centrosymmetric space group Pn. Hirshfeld surface analysis revealed that the dominant intermolecular interactions are of types H...F and F...O, which are likely to be responsible for the packing of the molecules in a non-centrosymmetric structure. Irradiation with blue light leads to the formation of Ru-ON (metastable state MS1) and Ru-η2-(NO) (metastable state MS2) bond isomers, as shown by IR and UV-Vis spectroscopy. The structural features of the MS1 isomer were elucidated by photocrystallography. The complex exhibits exceptionally good thermal stability of the metastable state MS1, such that it can be populated by light at 290-300 K, which is important for potential applications. The second harmonic (SH) emission can be generated by femtosecond-pulsed irradiation of the complex. The generated SH is rather efficient and stable under long-term exposure. Finally, since both metastable states and harmonic generation can be generated at room temperature, an attempt to drive the SH response by photoisomerization of the nitrosyl ligand was made and is discussed.

RESUMEN

The properties of Ru-ON states were studied in cis-[RuNO(NH3)2(NO2)2OH] under illumination. The structure contains two nonequivalent complexes, and the metastable state was generated for both molecules with 19(1) and 31(1)% populations. The MS1 thermal decay occurs as a one-step process at about 240 K according to differential scanning calorimetry (DSC). For the first-order reaction, the frequency factor and activation energy for the decay process were determined as 2.0(2) × 10(13) s(-1) and 68.3(4) kJ mol(-1), respectively. Also, the simultaneous metastable state decay observed via DSC was in agreement with IR spectroscopy.