Nitric oxide plays an important role in several physiological processes. This study investigates model ruthenium ammine coordination compounds to control NO bioavailability: cis-[RuCl(NO)(NH3)4]+ (1+), cis-[RuCl(NO)(NH3)4]2+ (12+), cis-[RuCl(NO)(NH3)4]3+ (13+), trans-[RuCl(NO)(NH3)4]+ (2+), trans-[RuCl(NO)(NH3)4]2+ (22+), trans-[RuCl(NO)(NH3)4]3+ (23+), [Ru(NO)(NH3)5]+ (3+), [Ru(NO)(NH3)5]2+ (32+), and [Ru(NO)(NH3)5]3+ (33+). We employed natural population analysis (NPA) atomic charges (qNPA) and the LUMO to identify the main reduction sites in the complexes 1, 2 and 3. For example, in the transformations 12+ → 1+, 22+ → 2+, and 33+ → 32+, the main reduction site was a NO π* orbital, which accounted for the lower electron density of the Ru-NO bond critical point (BCP) in 1+, 2+, and 32+ than 12+, 22+, and 33+, respectively, as shown by the quantum theory of atoms in molecules (QTAIM). The QTAIM method indicated that the electron density was larger in Ru-NO BCP due to the Cl negative cis- and trans-influence in 12+ and 22+, respectively, as compared with the NH3 influence in 33+. Compared to trans-Cl-Ru-NO in 22+, the interacting quantum atoms method demonstrated that cis-Cl-Ru-NO in 12+ displayed (i) a larger repulsive electrostatic energy, which agreed with qNPA, and (ii) a less negative exchange-correlation energy between Ru and the NO nitrogen atom, which agreed with topological analyses performed by the QTAIM method. Thus, the combination of topological and energy decomposition analyses allowed the mechanism behind the Ru-NO bond to be revealed regarding the influence of the total charge and the relative position of the ligands.

Objectives Vascular smooth muscle cell (VSMC) migration and proliferation at sites of vascular injury are both critical steps in the development of intimal hyperplasia (IH). Local delivery of nitric oxide (NO) largely prevents these events. Among the NO donors, tetraazamacrocyclic nitrosyl complexes, such as trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclamNO), gained attention for their features, which include the possibility of being embedded in solid matrices, and ability to participate in a nitrite/NO catalytic conversion cycle. Methods Methods used to evaluate cyclamNO activity: safety margin by NR and MTT; cell proliferation by 3H-thymidine incorporation and proliferating cell nuclear antigen (PCNA) expression; antimigratory properties by transwell and wound healing; prevention of cell phenotypic switching under platelet-derived growth factor type BB (PDGF-BB) stimuli by analysis of alpha smooth muscle actin (α-SMA) expression. Key findings Cell proliferation and migration induced by PDGF-BB were significantly inhibited by cyclamNO. The ~60% reduction on expression of contractile protein α-SMA induced by PDGF-BB revealed VSMC phenotypic switching which is significantly prevented by cyclamNO. Compared to the NO donor sodium nitroprusside, cyclamNO showed to be significantly less cytotoxic. Conclusions With great potential to maintain VSMC functionality and prevent IH-associated events, cyclamNO might be a promissory drug for several applications in cardiovascular medicine, as in stents.

•The versatility of tetraazamacrocycles, as cyclam, in ruthenium chemistry.•Tetraazamacrocyle isomerization and/or oxidative dehydrogenation in ruthenium complexes.•Chemical, photochemical, and biological aspects of tetraazamacrocycle ruthenium complexes.•Structure and density functional theory calculations of tetraazamacrocycle ruthenium complexes.•Spectral properties of tetraazamacrocycle ruthenium complexes.

Macrocyclic ligands are relevant because of the properties they impart to transition metal complexes, such as enhanced thermodynamic stability and slowed substitution kinetic behavior. Here, we address issues not previously reviewed, revisit others, present new results, and review and discuss the results obtained in the last decade for ruthenium(II/III) complexes with tetraazamacrocycles (mac) such as cyclam (1,4,8,11-tetraazacyclotetradecane), [RuL1L2(mac)]q+ with emphasis on nitrosyls. Topics include synthesis, macrocycle functionalization, structure, spectroscopy, photochemistry, reactivity, density functional theory calculations, and biological properties. [RuL1L2(mac)]q+ complexes exhibit a rich chemistry, sometimes unusual, which depends on macrocycle ring size, the presence of N- or C-pendant groups, metal oxidation state, electronic structure, and the nature of L1 and L2. These same features can be used to tune the properties of the complexes leading to potential applications in diverse fields.

Background: Ruthenium (Ru) tetraamines are being increasingly used as nitric oxide (NO) carriers. In this context, pharmacological studies have become highly relevant to better understand the mechanism of action involved.Objective: To evaluate the vascular response of the tetraamines trans-[RuII(NH3)(4)(Py)(NO)](3+), trans-[RuII(Cl)(NO)(cyclan)](PF6)(2), and trans-[RuII(NH3)(4)(4-acPy)(NO)](3+).Methods: Aortic rings were contracted with noradrenaline (10(-6) M). After voltage stabilization, a single concentration (10(-6) M) of the compounds was added to the assay medium. The responses were recorded during 120 min. Vascular integrity was assessed functionally using acetylcholine at 10(-6) M and sodium nitroprusside at 10(-6) M as well as by histological examination.Results: Histological analysis confirmed the presence or absence of endothelial cells in those tissues. All tetraamine complexes altered the contractile response induced by norepinephrine, resulting in increased tone followed by relaxation. In rings with endothelium, the inhibition of endothelial NO caused a reduction of the contractile effect caused by pyridine NO. No significant responses were observed in rings with endothelium after treatment with cyclan NO. In contrast, in rings without endothelium, the inhibition of guanylate cyclase significantly reduced the contractile response caused by the pyridine NO and cyclan NO complexes, and both complexes caused a relaxing effect.Conclusion: The results indicate that the vascular effect of the evaluated complexes involved a decrease in the vascular tone induced by norepinephrine (10(-6) M) at the end of the incubation period in aortic rings with and without endothelium, indicating the slow release of NO from these complexes and suggesting that the ligands promoted chemical stability to the molecule. Moreover, we demonstrated that the association of Ru with NO is more stable when the ligands pyridine and cyclan are used in the formulation of the compound.

Surface coating of metallic materials using the sol-gel technique is a suitable approach to obtain hybrid materials with improved properties for biomedical applications. In this study, an AISI 316L stainless steel surface was coated with ormosils prepared from tetraethylsiloxane and 3-glycidoxypropyltrimethoxysilane or polydimethylsiloxane. The characterization of structural and surface properties was performed by several techniques. Surface microstructure, morphology, and energy are dependent on organosilane type and content. Chemical stability of coatings was investigated by static immersion tests in phosphate buffer solution at 37 °C, and silicon leaching after 21 days was found to be in the range of ∼200−300 μg L−1. Mechanical adhesion was found to be within 1.0 and 3.7 N cm−1. The interaction of the samples and materials in the cardiovascular environment was investigated through cellular behavior. Biological assays were performed with slides to avoid any cytotoxic effects on human endothelial cells (HUVEC) and rabbit arterial smooth muscle cells (RASM). No significant alterations were observed after 24 h in the viability of RASM and HUVEC cells exposed to different coatings. No increase of HUVEC or RASM migration was observed after 24 h as evaluated by transwell migration assay. The hybrid materials showed suitable properties for potential application as biomaterials in cardiovascular environment as well as for incorporation of bioactive species with the aim to prepare drug-eluting stents.

In some pathologic circumstances (e.g., septicemia) nitric oxide (NO) synthesis is higher and it is implicated in lowering of the blood pressure that usually is less responsive to conventional therapy with adrenaline and vasopressin. Thus, new specific therapeutic approaches using high affinity NO scavengers are of great relevance. Accordingly, some new ruthenium compounds with this putative property were synthesized. The aim of this work was to evaluate the NO scavenging activity of those compounds. Aorta rings obtained from the thoracic aorta of adult male Wistar rats were suspended under 60% of maximal tension in an organ bath, containing 15 mL of Krebs-Henseleit solution (36.5 ± 0.1ºC, pH 7.2-7.4, gassed with 95% O2:5% CO2). After 60 min stabilization period, maximum contraction of aortic rings was obtained in response to noradrenaline. After that, acetylcholine was added in order to obtain maximal relaxation. Cumulative concentration-response curves were obtained to the compounds: trans-[Ru(NH3)4(SO4)(4-picoline)](BF4) (Ru-pic); trans-[Ru(NH3)4 (SO4) (nicotinamida)](BF4) (Ru-ina); trans-[Ru(NH3)4(SO4) (isonicotina mide)] (BF4) (Ru-isn); [Ru(NH3)5Cl]Cl2 (Ru-Cl); [Ru(edta)Cl] (Ru-EDTA); cis-[Ru(NH3)4oxalato](TFMS)3 (Ru-cis-Ox); cis-[Ru(NH3)4(H2O)2 (TFMS)3 (Ru-cis-aquo) and trans[Ru(NH3)5(H2O)(TFMS)3 (Ru-trans-aquo). The same procedure was performed in the presence of L-NAME, an inhibitor of nitric oxide synthase. Control rings were not exposed to any ruthenium compound. The mean ± sem of the tension developed by the tissues following exposition to noradrenaline was 1.94 ± 0.17 gf. Acetylcholine reduced the developed tension to 0.17 ± 0.04 gf. In the presence of the all Ru-compounds, the developed tensions (gf) were: 1.68 ± 0.19 (Ru-pic; n=5); 1.43 ± 0.15 (Ru-isn; n=5); 1.47 ± 0.16 (Ru-ina; n=5); 1.74 ± 0.13 (Ru-EDTA; n=5); 2.93 ± 0.24 (Ru-Cl; n=5); 2.85 ± 0.07 (Ru-cis-Ox; n=5); 3.08 ± 0.15 (Ru-cis-aquo; n=5); 3.12 ± 0.12 (Ru-trans-aquo; n=5); [p<0.05 compared to control, Student t test]. All the analyzed compounds were able to cancel the effect of acetylcholine and had similar potencies (pD2; mean ± sem): 5.60 ± 0.18 (Ru-pic); 5.34 ± 0.25 (Ru-isn); 5.40 ± 0.27 (Ru-ina); 5.48 ± 0.23 (Ru-Cl); 6.45 ± 0.39 (Ru-EDTA); 5.19 ± 0.30 (Ru-cis-Ox); 5.59 ± 0.24 (Ru-cis-aquo); 5.03 ± 0.37 (Ru-trans-aquo). None of the effects of acetylcholine or compounds were observed when they were tested in the presence of L-NAME. The data suggested that all compounds were able to scavenge NO in rat aortic rings and to restore the vascular tone.

Electron spin resonance (ESR) spectra of irradiated gum Arabic with doses between 0.5 and 5 kGy were studied. A linear relationship between the absorbed dose and the intensities of the ESR spectra was observed. ESR spectra of irradiated gum Arabic showed a decay of relative concentrations of free radicals originated by radiation and the production of at least two species of free radicals with half-times: 3.3 and 125.4 h. The results of spectral simulations for these radical groups were giso=2.0046; A=1.2 mT and gx=gy=2.0062, gz=2.0025. Hydration and dehydration of irradiated gum Arabic returns the ESR spectrum to its initial state before irradiation. The results show that ESR can be used as simple and reliable method to detect irradiated gum Arabic up to 60 days after initial radiation with doses on the order of 5 kGy.

The syntheses and properties of trans-[Ru(NH3)4(L)(NO)](BF4)3 (L=isonicotinic acid (inaH) (I) or ina-Tat48–60 (II)) are described. Tat48–60, a cell penetrating peptide fragment of the Tat regulatory protein of the HIV virus, was linked to the ruthenium nitrosyl through inaH. I and II release NO after reduction forming trans-[Ru(NH3)4(L)(H2O)]3+. The IC50 values against B16-F10 melanoma cells of I and II (21μmolL−1 and 23μmolL−1, respectively) are close to that of the commercially available cisplatin (33μmolL−1) and smaller than similar complexes. The cytotoxicity is assigned to the NO released from I and II.

The immobilization and characterization of trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclam=1,4,8,11-tetraazacyclotetradecane), and [Ru(NO)(Hedta)] (Hedta=ethylenediaminetetraacetic acid) entrapped in poly(d,l-lactic-co-glycolic) acid (PLGA) nanoparticles (NP) using the double emulsification process is described. Scanning electron microscopy and dynamic light scattering revealed that the particles are spherical in shape, have a size distribution between 220 and 840 nm of diameter, and have a tendency to aggregate confirmed by a zeta potential between -3.2 and +3.5 mV. Using this method the loading efficiency was 26% for trans-[Ru(NO)Cl(cyclam)](PF6)2 and 32% for [Ru(NO)(Hedta)]. The release of the complexes from the NPs shows that cyclam-NP and Hedta-NP exhibited a two-phase exponential association release pattern, which was characterized by an initial complex burst during the first 24 h, followed by a slower release phase complex profile, due to a few pores observed in surface of nanoparticles using atomic force microscopy. The in vitro cytotoxic activity of the nitrosyl complexes in solution and incorporated in PLGA nanoparticles on melanoma cancer cells (cell line B16-F10) was investigated. The lower cytotoxicity of trans-[RuCl(cyclam)(NO)]2+ (12.4±2.6%) and [Ru(NO)(Hedta)] (4.0±2.7%) in solution compared to that of trans-[Ru(NO)(NH3)4py]3+ (46.1±6.4%) is consistent with the rate constant release of NO of these complexes (k-NO=6.2×10(-4) s(-1), 2.0×10(-3) s(-1), and 6.0×10(-2) s(-1), respectively); the cytotoxicities are also inhibited in the presence of the NO scavenger carboxy-PTIO. The phototoxicity of these complexes is due to NO release, which lead to 53.8±6.2% of cell death in the presence of trans-[Ru(NO)Cl(cyclam)](PF6)2 and 22.3±5.1% in the presence of [Ru(NO)(Hedta)]. The PLGA nanoparticles loaded with trans-[Ru(NO)Cl(cyclam)](PF6)2 and [Ru(NO)(Hedta)] exerted in vitro a reduced activity against melanoma cells when compared to the activity of complex in solution (nonentrapped in nanoparticles). Blank PLGA nanoparticles did not exhibit cytotoxicity. In the presence of light and of ruthenium nitrosyl complexes or cyclam-NP and Hedta-NP, B16-F10 cells displayed a considerable damage of the surface with rupture of the plasma membrane. This behavior is an indicative of the efficiency of the DDS to deliver the NO from the entrapped complex when photoinduced.

Rhodenal, a turn-on fluorescent sensor for iron, derived from rhodamine-B, was synthesized and characterized. Its electronic absorption spectrum in ethanol has bands at 410 (ε=500cm−1mol−1L), 316 (ε=14×103cm−1mol−1L), and 272nm (ε=32×103 cm−1mol−1L), and it is pH sensitive with two pKa values (1.2 and 2.8). It reacts promptly with Fe3+, with a pesudo-first order rate constant of 1×103s−1, with an equilibrium constant of 1.3×106mol−1L, forming a violet complex (λmax=540nm) with a fluorescent emission at 582nm, with a higher sensitivity and selectivity compared to those of Fe2+, Ba2+, Al3+, K+, Ca2+, Ni2+, Co2+, Cd2+, Cr3+, Hg2+, Mg2+, Mn2+, Na+, or Cu2+. Biological assays with B16-F10 showed high permeability of plasma membrane to rhodenal and, according to confocal microscopy results, the fluorescent source originated from within the cell revealed iron pools within cytoplasmic and nuclear sub-compartments, making rhodenal a very good prospective Fe3+ sensor, in aqueous solution and especially for biological iron pool detection.

Nitric oxide plays an important role in various biological processes, such as neurotransmission, blood pressure control, immunological responses, and antioxidant action. The control of its local concentration, which is crucial for obtaining the desired effect, can be achieved with exogenous NO-carriers. Coordination compounds, in particular ruthenium(III) and (II) amines, are good NO-captors and -deliverers. The chemical and photochemical properties of several ruthenium amine complexes as NO-carriers in vitro and in vivo have been reviewed. These nitrosyl complexes can stimulate mice hippocampus slices, promote the lowering of blood pressure in several in vitro and in vivo models, and control Trypanosoma cruzi and Leishmania major infections, and they are also effective against tumor cells in different models of cancer. These complexes can be activated chemically or photochemically, and the observed biological effects can be attributed to the presence of NO in the compound. Their efficiencies are explained on the basis of the [RuIINO+]3+/[RuIINO0]2+ reduction potential, the specific rate constant for NO liberation from the [RuNO]2+ moiety, and the quantum yield of NO release.

Ruthenium complexes including nitrosyl or nitrite complexes are particularly interesting because they can not only scavenge but also release nitric oxide in a controlled manner, regulating the NO-level in vivo. The judicious choice of ligands attached to the [RuNO] core has been shown to be a suitable strategy to modulate NO reactivity in these complexes. In order to understand the influence of different equatorial ligands on the electronic structure of the Ru-NO chemical bonding, and thus on the reactivity of the coordinated NO, we propose an investigation of the nature of the Ru-NO chemical bond by means of energy decomposition analysis (EDA), considering tetraamine and tetraazamacrocycles as equatorial ligands, prior to and after the reduction of the {RuNO}(6) moiety by one electron. This investigation provides a deep insight into the Ru-NO bonding situation, which is fundamental in designing new ruthenium nitrosyl complexes with potential biological applications.