Imino Nitroxide Research Articles

Stereo sensitivity of exchange interactions in NiII and CuII heterospin complexes with 5-formylpyrrolyl-substituted nitroxides

5-Formylpyrrolyl-substituted nitronyl and imino nitroxide radicals HL1 and HL2 were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL1...HL1} pairs, the dominant interaction is the ferromagnetic exchange with J/kB = 8.8 K (Hamiltonian \(H = 2J\left( {\overrightarrow {{s_1}} \overrightarrow {{s_2}} } \right)\)). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L1)2], [Cu(L1)2], and [Ni(L2)2(MeOH)2]. In the complexes [Ni(L1)2] and [Cu(L1)2], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands.

Syntheses, structures, and magnetic characterizations of five Mn(II) and Co(II) complexes based on 2,6-Pyridyl-substituted nitronyl and imino nitroxide radical

The reaction of biradical 2,6-NITpy (1) (2,6-NITpy=2,6-bis (3′-oxide-1′-oxyl-4′,4′,5′,5′-tetramethylimidazolin-2′-yl) pyridine), 2-NIT-6-IMpy (2) (2-NIT-6-IMpy=2-(3′-oxide-1′-oxyl-4′,4′,5′,5′-tetramethylimidazolin-2′-yl)-6-(1′-oxyl-4′,4′,5′,5′-tetra-methylimidazolin-2′-yl) pyridine), or 2,6-IMpy (3) (2,6-IMpy=2,6-bis(1′-oxyl-4′,4′,5′,5′-tetra-methylimidazolin-2′-yl) pyridine) with M(hfac)2·XH2O (M=MnII, CoII) were investigated. These reactions were found to be related to the type of the metal ion employed. Interestingly, redox reactions involve in the synthesis process of the complexes. Structures of the five complexes were elucidated by X-ray analysis, and their magnetic properties were investigated in detail. The temperature dependence of χMT for all the five complexes at high temperature range exhibited antiferromagnetic interactions between the transition metal spin (MnII or CoII) and the nitroxide radical spin. At low temperature, the χMT curves exhibit different magnetic behaviors because of the different crystalline fields and intermolecular interactions.

First coordination compounds based on a bis(imino nitroxide) biradical and 4f metal ions: synthesis, crystal structures and magnetic properties.

The synthesis, crystal structures and magnetic properties of two families of heterospin complexes containing lanthanide ions and a bis(imino nitroxide) biradical (IPhIN = 1-iodo-3,5-bis(4',4',5',5'-tetramethyl-4',5'-dihydro-1H-imidazole-1'-oxyl)benzene) are reported: in [Ln2(hfac)6(IPhIN)(H2O)2] compounds, two lanthanide ions [Ln = Gd(III) (1) and Dy(III) (2)] are coordinated to the biradical, and in [Ln(hfac)3(IPhIN)(H2O)] compounds, one lanthanide ion (Ln = Tb(III) (3), Gd(III) (4) or Dy(III) (5)) is coordinated to the biradical. Ferromagnetic intramolecular magnetic interactions between Gd(III) and the biradical were found for 1 and 4, while intramolecular magnetic interactions between the radicals were ferro- and antiferromagnetic, respectively. Compound 2 shows a field induced slow relaxation of magnetization, which (under an external applied field of 2 kOe) exhibits an activation energy barrier of ΔE/kB = 27 K and a pre-exponential factor of 1.4 × 10(-8) s. To support the magnetic characterization of compound 3ab initio calculations were also performed.

A New Method for the Synthesis of Heterospin Complexes

The interaction of binuclear Co(II) pivalate [Сo2(H2O)Piv4(HPiv)4] with nitronyl nitroxide HL1 (2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) in organic solvents led to the formation of a pentanuclear heterospin complex [Co5(Piv)4L14L22]. A nontrivial peculiarity of the complex is the presence of both the starting nitronyl nitroxide L1 and its deoxygenated derivative imino nitroxide L2 (HL2: 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl) in its coordination sphere. Based on this, a new synthetic approach was developed, which suggests the use of both the starting radical and the product of its reduction in the reaction with the metal. The suggested approach is a new method for the synthesis of heterospin compounds, including those that cannot be obtained by other methods. It was shown that the reaction of Co(II) pivalate with a mixture of HL1 and HL2 can give a trinuclear heterospin complex [Co3(Piv)2L12L22]. The replacement of Co(II) by Ni(II) completely suppresses the reduction of HL1 into HL2, and Ni(II) pivalate does not react with HL1. The use of a known mixture of HL1 and HL2 in the reaction with [Ni2(H2O)Piv4(HPiv)4], however, led to the formation of a heterospin complex [Ni3L1L22(Piv)3(HPiv)3] also containing both nitronyl nitroxide and imino nitroxide.

An Azide-Functionalized Nitronyl Nitroxide Radical: Synthesis, Characterization and Staudinger–Bertozzi Ligation Reactivity

An azide-functionalized nitronyl nitroxide was synthesized and its reactivity towards the Staudinger–Bertozzi ligation was explored. Whereas a model reaction in solution showed the conversion of nitronyl nitroxide to an imino nitroxide radical, the same reaction at the interface of gold nanoparticles allowed for successful covalent incorporation of the nitronyl nitroxide radical onto the nanoparticles.

Synthesis, crystal structure and magnetism of two cobalt(II) complexes with imino and nitronyl nitroxides

Two new cobalt–radical complexes, namely [Co(IM-5-Br-2Py)2(N3)2]·MeOH (1) and [Co(NIT-5-Br-2Py)2(N3)2] (2) (IM-5-Br-2Py = 2-(5-bromo-2-pyridyl)-4,4,5,5-tetramethyl-limidazoline-1-oxyl, NIT-5-Br-2Py = 2-(5-bromo-2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized by magnetic and single-crystal X-ray diffraction studies. X-ray diffraction analysis indicates that both complexes possess mononuclear structures, in which two radical ligands coordinate to the Co(II) atom in chelating fashion and two azides act as terminal ligands. The magnetic properties for complexes 1 and 2 have been investigated in the temperature range 2–300 K. DC magnetic measurements show that the Co(II) atom of complex 1 interacts ferromagnetically with the directly bonding imino nitroxide, while the Co(II) atom strongly antiferromagnetically couples with the directly coordinated N–O group in complex 2.

Nitronyl Nitroxides as a Spin Probe in EPR Tomography In Vivo

Recently, new water- and blood-soluble nitronyl nitroxides, 2-(5-methyl-1H-imidazole-4-yl)-4,4,5,5-tetramethyl-4,5-dihydroimidazole-3-oxide-1-oxyl (NN1) and 2-(1H-imidazole-4-yl)-4,4,5,5-tetramethyl-4,5-dihydroimidazole-3-oxide-1-oxyl (NN2), (Fig. 1), were synthesized and used as contrast agents for MRI (Savelov et al. Dokl Academ Nauk 416(4): 493–495, 2007). Taking into account the high rate constants of NN’s reduction by ascorbic acid and other biologically relevant reductants, it is not clear which factors helped with the use of these nitroxides in vivo as a contrast reagent. Moreover, due to high solubility in an aqueous solution and low toxicity (Ovcharenko et al. in Dokl Academ Nauk 404(2):198–200, 2005, Eriksson et al. in Drug Metab Dispos 15(2):155–160, 1987, Afzal et al. in Polyhedron 22(14):1957–1964, 2003) of NNs, it seems possible to use them as a spin probe for NO in vivo with EPR tomography. In this paper, we studied reduction of NN1 and NN2 in model conditions (by ascorbic acid) and in vitro. In addition, the possibility of NN1 and NN2 to be used as paramagnetic probes for L-band EPR imaging in vivo was investigated. Nitric oxide (NO) expression in vivo leads to the decrease in concentrations of NN1, 2 upon the injection in a mouse body, that can be explained by the reaction of studied radicals with NO and fast transformation of the reaction products to diamagnetic species. Pharmacokinetics of NN1, 2 and limitations of their application as contrast agents in MRI are discussed also. Finally, the results of EPR tomography were compared with MRI data. It is shown that the fast reduction of the reaction product of NN with NO—imino nitroxides—is the main obstacle to use NN as a spin probe in vivo.

Synthesis, crystal structures, and magnetic properties of cobalt(II)-hexafluoro-acetylacetonate complexes with two new triazole-substituted nitronyl and imino nitroxide

Two new chelating radical ligands, NITphtrz (4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl-3-oxide) and IMphtrz (4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl), and their cobalt(II) complexes [Co(Hfac)2(NITphtrz)] (I) and [Co(Hfac)2(IMphtrz)] (II) (Hfac = hexafluoroacetylacetonate) have been prepared and characterized by IR, magnetic, and single-crystal X-ray analysis. The magnetic behaviors of the lignad NITphtrz and complex I have been discussed.

Synthesis, Crystal Structures, and Magnetic Properties of Cobalt(II)-Hexafluoro-Acetylacetonate Complexes with Two New Triazole-Substituted Nitronyl and Imino Nitroxide

Synthesis, Crystal Structures, and Magnetic Properties of Cobalt(II)-Hexafluoro-Acetylacetonate Complexes with Two New Triazole-Substituted Nitronyl and Imino Nitroxide

Nitronyl and imino nitroxide free radicals as precursors of magnetic phthalocyanine and porphyrin building blocks

Phthalonitrile and benzaldehyde bearing α-nitronyl and α-imino nitroxide free radicals have been synthesized as precursors of nitroxide substituted phthalocyanine and porphyrin macrocycle.

Crystal Structures and Magnetic Properties of Two New Cobalt(II) Complexes with Triazole-Substituted Nitronyl and Imino Nitroxide Radicals

Two new cobalt(II) complexes of formula [Co(hfac)2(NITphtrz) 1 and Co(hfac)2(IMphtrz) 2] have been prepared and characterized structurally [where NITphtrz = 4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl-3-oxide and IMphtrz = 4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl]. All of the complexes crystallize in an isomorphous triclinic space group P1- with the Co(II) ion octahedrally coordinated via the bidentate chelating mode. The magnetic measurements show that two complexes exhibit antiferromagnetic interactions between the metal ions and the nitroxide radicals.

Crystals of the CuII complex with nitronyl nitroxide and imino nitroxide exhibiting mechanical activity

As part of continuing studies of multispin compounds capable of exhibiting chemomechanical activity, a series of heterospin solids of the composition [Cu(hfac)2LxL′2−x], [Cu(hfac)2L′], [Cu2(Piv)4L′2]·0.5C6H14, and [Cu2(hfac)2(Piv)2L′2], where hfac is the hexafluoroacetylacetonate anion, L is 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, L′ is the imino nitroxide analog of L, viz., 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl, and Piv is the 2,2-dimethylpropionate anion, were synthesized and characterized. The packing of the synthesized crystals of the solid solutions [Cu(hfac)2LxL′2-x], where L predominates, is similar to that for [Cu(hfac)2L2], and these crystals are able to undergo chemomechanical motion. On the contrary, the crystals of [Cu(hfac)2LxL′2−x], where L′ predominates, have structural parameters similar to those of [Cu(hfac)2L′2] and do not exhibit thermally activated or photoactivated chemomechanical activity.

Theoretical Investigation of Stilbene as Photochromic Spin Coupler

Density functional theory (DFT) based calculations are used here to investigate the magnetic behavior, spectroscopic transitions, and possible photomagnetic properties of stilbene derivatives using photochromicity of cis- and trans-forms of the parent molecule. Nitronyl nitroxide (NN), iminonitroxide (IN), tetrathiafulvalene cation (TTF), and verdazyl (VER) are used as monoradical centers at the p, p' positions. The B3LYP functional with the usual broken symmetry approach and a sufficiently large basis set is chosen to obtain reliable estimates of the intramolecular exchange coupling constants (J). It is found that, with stilbene as a spacer, the coupling of TTF with NN, IN, and VER is always antiferromagnetic with J being generally large and negative. Although J values obtained for cis- and trans-forms are both negative, the difference in J values is quite large. Spectroscopic transition energies and corresponding oscillator strengths of cis- and trans-stilbene diradicals are estimated by time-dependent (TD)-DFT calculations using the same functional. Interestingly, the spectral features of the diradicals are similar to those of cis- and trans-stilbene, which suggests that stilbene diradicals would have good photoswitching properties. Finally, we show that, when these diradicals are placed in a matrix, photochromicity would be accompanied by a significant change in paramagnetic susceptibility.

Crystal structure of Synthesis and crystal structure of a new mercury(II) complex with imino nitroxide radical, C30H38Cl6Hg3N8O2

C30H38Cl6Hg3N8O2, triclinic, P1̄ (no. 2), a = 7.3649(5) Å, b = 11.4075(8) Å, c = 13.0120(9) Å, α = 100.454(1)°, β = 102.089(1)°, γ = 103.229(1)°, V = 1010.0 Å3, Z = 1, Rgt(F) = 0.0202, wRref(F2) = 0.0502, T = 291 K.

Discriminative EPR detection of NO and HNO by encapsulated nitronyl nitroxides

Nitric oxide, •NO, is one of the most important molecules in the biochemistry of living organisms. By contrast, nitroxyl, NO−, one-electron reduced analog of •NO which exists at physiological conditions in its protonated form, HNO, has been relatively overlooked. Recent data show that HNO might be produced endogenously and display unique biological effects. However, there is a lack of specific and quantitative methods of detection of endogenous HNO production. Here we present a new method for discriminative •NO and HNO detection by nitronyl nitroxides (NNs) using electron paramagnetic resonance (EPR). It was found that NNs react with •NO and HNO with similar rate constants of about 104 M− 1s− 1 but yield different products: imino nitroxides and the hydroxylamine of imino nitroxides, correspondingly. An EPR approach for discriminative •NO and HNO detection using liposome-encapsulated NNs was developed. The membrane barrier of liposomes protects NNs against reduction in biological systems while is permeable to both analytes, •NO and HNO. The sensitivity of this approach for the detection of the rates of •NO/HNO generation is about 1 nM/s. The application of encapsulated NNs for real-time discriminative •NO/HNO detection might become a valuable tool in nitric oxide-related studies.

Molecular System Based on Novel Photochromic Biindenylidenedione Derivative Demonstrating Photomodulation of Magnetism

AbstractStable nitronyl nitroxide radical and imino nitroxide radical were incorporated into the benzene rings of novel photochromic 7,7′‐dimethyl‐[2,2′‐bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione (1), leading to the synthesis of novel multifunctional compounds 4 and 5. The photochromic properties, ESR spectroscopy and magnetic properties of the title compounds were investigated. Compounds 4 and 5 possess visible photochromism upon photoirradiation, and their ESR signals undergo secular broadening after photoirradiation. The magnetic susceptibility measurement shows that the antiferromagnetic interaction of 4 and 5 becomes stronger after photoirradiation. In compounds 4 and 5 there are two kinds of spin centers after photoirradiation: one is nitroxide radical, and the other is photo‐generated radicals from two indanone moieties. Our results demonstrated that the colour and magnetic properties of compounds 4 and 5 could be modulated by photoirradiation.

The heart-protective mechanism of nitronyl nitroxide radicals on murine viral myocarditis induced by CVB3

Our previous researches showed that nitronyl nitroxyl derivatives, NNP and NNVP were good anti-oxidants and provided radioprotective effects in C6 cells. The objective of the present study is to investigate the possible antiviral effects and underlying pharmacological of the two nitronyl nitroxide radicals against CVB3 invitro and invivo. The results showed that NNP and NNVP were some of the most potent compounds in terms of their antiviral effects by protecting myocardial cells against oxidative damage of free radicals. Treatment with NNP or NNVP could decrease the intracellular ROS level invitro. They could lead to a significant decrease in activities of biochemical markers AST, CK and LDH in infected murine serum and could increase SOD and CAT activities and decreased MDA activities compared with infected control in vivo. NNP and NNVP could reduce NO production in infected mice by reacting with NO to produce the imino nitroxides which was confirmed by ESR spectrometry. In addition, NNP and NNVP could both decrease the mRNA expression of proinflammatory cytokines, TNF-α, IL-2 and IL-6. In conclusion, nitronyl nitroxide radicals NNP and NNVP were shown to have antiviral activities against CVB3 and they may represent potential therapeutic agents for viral myocarditis.

2-(4-Pyridyl)imino nitroxide-tetraphenylporphyrin zinc(II): A chemosensing ensemble for nicotine

2-(4-Pyridyl)imino nitroxide and tetraphenylporphyrin zinc(II) formed a stable complex by noncovalent bonding in a nonpolar solution. Nicotine displaced 2-(4-pyridyl)imino nitroxide when it was added to a solution of 2-(4-pyridyl)imino nitroxide-tetraphenylporphyrin zinc(II). The fluorescence intensity of tetraphenylporphyrin zinc(II) was altered by sequentially addition of 2-(4-pyridyl)imino nitroxide and nicotine. This was used to develop a new method for detection of nicotine.

A theoretical study on photomagnetic fluorescent protein chromophore coupled diradicals and their possible applications

We have designed and theoretically studied three different pairs of green fluorescent protein chromophores and their different homologue-based diradicals coupled with imino nitroxides. To begin with, the geometries of all these diradicals have been optimized at high spin (HS) state in the gas phase, in a water medium and in a blood plasma medium. The process of calculations is straightforward and well-established in the case of the gas phase. However, for calculations in water, we have adopted our own N-layer integrated molecular orbital and molecular mechanics (ONIOM) method. Similarly for the blood phase calculations, the polarized continuum model (PCM) method has been adopted. With these optimized geometries the magnetic exchange coupling constant (J) values are estimated for these diradicals in different media using the broken symmetry (BS) approach in an unrestricted DFT framework. In order to obtain the BS solutions in the ONIOM method, we have carried out ONIOM-BS, where the BS calculations are done for the inner high-level layer (diradical system) keeping the outer water layer at low level. In a similar fashion, a PCM-BS technique has also been adopted for the BS calculations in the PCM method. We have found that these diradicals have an ability to change their magnetic nature from antiferromagnetic in the trans form to ferromagnetic in the cis form upon irradiation of light with the appropriate wavelength. Using a time-dependent DFT (TDDFT) technique, the required wavelengths of light by which non-fluorescent dark trans diradicals turn into their corresponding bright fluorescent cis isomers are determined for each pair of diradicals for the gas and water media. This color change is indeed a signature of the change in magnetic state of the diradicals concerned. Here, we have also calculated the zero field splitting (ZFS) parameter (D), rhombic ZFS parameter (E) and ZFS magnitude (a2). From our calculations we ambitiously expect that if these diradicals are synthesized then they might be used as a successful, non-hazardous magnetic resonance imaging contrast agent (MRICA) in place of other metal-based contrast agents.

Tuning the sensitivity of fluorophore–nitroxide radicals

The synthesis of pyrene–pyrazole nitronyl and imino nitroxides is reported, along with characterization of the radicals by UV-Vis, PL and EPR techniques. The UV-Vis studies revealed that the nature of the spacer attached to the nitroxide plays a crucial role in the radical n–π* transition intensity. This finding forms the basis for the evaluation of these nitroxides as redox-probes. The results of these investigations confirmed the preliminary assumptions of the profound sensing properties of these radicals. In fact, it was demonstrated that the sensitivity of the newly synthesized probes far surpasses known literature analogues. Hence, the strategy described here opens new horizons for the targeted design of radical sensing materials.