EPR Studies Research Articles

Amine‐Free, Directing‐Group‐Free and Redox‐Neutral α‐Alkylation of Saturated Cyclic Ketones

AbstractThe activation of the α‐C−H bond of ketones typically requires an amine and a directing group to guide the reaction selectivity in amine‐catalysis carbonyl chemistry. For an α‐C−H bond activation of ketone, directing groups are also required to control the reaction selectivity. Reported herein is the first α‐alkylation of cyclic ketones in the absence of an amine catalyst and directing group. 1H NMR, XPS, EPR studies and DFT calculations indicate that an α‐carbon radical intermediate is formed through direct and selective activation of the inert α‐C−H bond of ketones chelating on the surface of colloidal quantum dots (QDs). Such an interaction is essential for weakening the C−H bond, as exemplified, using CdSe QDs as the sole photocatalyst to execute α‐C−H alkylation of cyclic ketones under visible‐light irradiation. Without an amine catalyst and directing group, the high step‐ and atom‐economy transformation under redox‐neutral condition opens a new way for α‐C−H functionalization of ketones in carbonyl chemistry.

Amine-Free, Directing-Group-Free and Redox-Neutral α-Alkylation of Saturated Cyclic Ketones.

The activation of the α-C-H bond of ketones typically requires an amine and a directing group to guide the reaction selectivity in amine-catalysis carbonyl chemistry. For an α-C-H bond activation of ketone, directing groups are also required to control the reaction selectivity. Reported herein is the first α-alkylation of cyclic ketones in the absence of an amine catalyst and directing group. 1 H NMR, XPS, EPR studies and DFT calculations indicate that an α-carbon radical intermediate is formed through direct and selective activation of the inert α-C-H bond of ketones chelating on the surface of colloidal quantum dots (QDs). Such an interaction is essential for weakening the C-H bond, as exemplified, using CdSe QDs as the sole photocatalyst to execute α-C-H alkylation of cyclic ketones under visible-light irradiation. Without an amine catalyst and directing group, the high step- and atom-economy transformation under redox-neutral condition opens a new way for α-C-H functionalization of ketones in carbonyl chemistry.

Investigation of Photoelectrocatalytic and Magnetic Properties of Sr2YbRu1-xTaxO6 (x = 0, 0.25, 0.5, 0.75, and 1).

We report the effect of substitution of Ru by Ta in Sr2YbRuO6 on its magnetic and photoelectrocatalytic properties. The powder X-ray diffraction data, was satisfactorily refined in the monoclinic space group, P21/n. The DC magnetization studies indicated that Sr2YbRuO6 shows antiferromagnetic interaction through Yb-O-Ru orbital ordering, with the highest Weiss temperature, among Sr2YbRu1-xTaxO6 (x = 0, 0.25, 0.5, and 0.75) which have values of -148, -125, -118, and -102 K, respectively. The difference in observed and theoretical magnetic moments was found to increase as x increases. It was also observed that with the increase of Ta concentration in Sr2YbRu1-xTaxO6, the band gap increased almost linearly, from 1.78(1) eV (x = 0) to 2.08(1) (x = 0.75), and thereafter a sharp increase 2.65(1) eV (x = 1) was observed, with the lowering of energy level of valence band, along with disruption in orbital ordering as x increases. The photoelectrocatalytic oxygen evolution reaction (OER) studies carried out on the series yield a maximum photocurrent density of 17 μA/cm2 and photoresponse current of 5.5 μA/cm2 at 0.8 V at an onset potential at 0.29 V vs Ag/AgCl for Sr2YbRuO6. The XPS analysis showed Ta and Ru to be in +5/+4 oxidation states, with the highest concentration of Ru4+ ion observed for Sr2YbRuO6. The presence of oxygen vacancies was confirmed by XPS as well as EPR studies.

Magnetic Anisotropy Transfer from Mono‐ to Polymetallic Complexes

AbstractThe reaction of multi‐bidentate oxamate‐based copper(II) complexes with the [Ni(iPrtacn)Cl2] complex (iPrtacn:1,4,7‐triisopropyl‐1,4,7‐triazacyclononane) has been investigated. X‐ray diffraction studies reveal that for all compounds the oxamato κO,κΟ’ bidentate coordination site replaces the two chloride ions in [Ni(iPrtacn)Cl2] to form trimetallic {CuNi2} (1–3), hexametallic {Cu2Ni4} (4) and enneametallic {Cu3Ni6} (5) complexes. The investigation of the magnetic properties shows that Cu−Ni interactions through the oxamato bridge are in the expected range (−111 cm−1, −68 cm−1). For 1–3, both the sign and strength of the magnetic couplings are computed independently from DFT calculations, and these estimates broadly agree with the experiments. The magnetization measurements and EPR studies reveal that 1–3 are anisotropic: a significant portion of the large anisotropy of the [Ni(iPrtacn)Cl2] complex is retained, resulting in a D value for the S=3/2 ground state of 5 cm−1 on average. This is no longer the case for 4 and 5 where the anisotropy of the Ni(II) complexes is diluted due to the high nuclearity of the final edifices. These results show that it is possible to obtain trimetallic complexes with a high anisotropy and a high spin value for the ground state by a judicious choice of the interacting metal ions.

Influence of Bi co-catalyst particle size on the photocatalytic activity of BiOI microflowers in Bi/BiOI junctions – A mechanistic study of charge carrier behaviour

Herein, we investigate the effect of Bi particle size in BiOI/Bi junctions on their photocatalytic function towards NO gas. BiOI microflowers (BiOI) and BiOI microflowers decorated with micron-sized Bi particles (BiOI/Bi MPs) were produced by a solvothermal method. BiOI decorated with nano-sized Bi particles (BiOI/Bi NPs) were produced by a reduction process. All samples were physically characterised by XRD, FT-IR, SEM, HR-TEM coupled with EDX analysis, DR-UV–visible and PL spectroscopy and functionally characterised by photocatalytic testing towards NO gas, TAS and EPR spectroscopy.Their photocatalytic activity towards NO gas was measured following ISO protocol (ISO 22197–1:2016). The best performing BiOI-based sample was BiOI/Bi NPs, showing NO and NOx conversion efficiencies of ∼33 and ∼11% under UVA light, and ∼26 and ∼8.1% under visible light, respectively. The BiOI and BiOI/Bi MPs samples showed significantly lower activities, displaying overall NOx conversion efficiencies of ∼3.5 and ∼0.8% under UVA light, respectively. Importantly, the best performing BiOI/Bi NPs samples showed visible light activity that was at least 6 times higher than that of a commercial TiO2 benchmark (CristalACTiVTM PC-S7). TAS measurements showed that charge carriers were significantly longer lived in the BiOI/Bi NPs sample (t50% from 10 μs of ∼90 μs) than the BiOI and BiOI/Bi MPs samples (t50% from 10 μs of ∼50 μs). This was attributed to the significant degree of interfacial contact formed between Bi and BiOI in the BiOI/Bi NPs sample, which enhanced charge carrier separation. EPR studies showed that this interfacial contact between BiOI and Bi likely promoted the formation of VO, which may have contributed to enhancement seen in photocatalytic activity in the BiOI/Bi junction.

Cyclo-matrix Poly(cyclotriphosphazene-co-kaempferol) Microspheres: Synthesis, Characterization, EPR Study and Their Controlled Drug Release Application

Cyclo-matrix Poly(cyclotriphosphazene-co-kaempferol) Microspheres: Synthesis, Characterization, EPR Study and Their Controlled Drug Release Application

Structural and Physicochemical Properties of Carbon Nitride Nanoparticles via Precursor Thermal Treatment: Effect on Methyl Orange Photocatalytic Discoloration

In this work, we synthesized and characterized carbon nitride (CN) nanoparticles obtained by the thermal treatment (550 °C) of urea, melamine, dicyandiamine, and dicyandiamine-barbituric acid in an open reactor and evaluated the effect of different precursors on the photocatalytic performance. CNs obtained from melamine, dicyandiamine, and dicyandiamine-barbituric acid were 3D melon-type structures. On the other hand, CN obtained from urea was a 2D microporous, amorphous structure whose melon or graphitic arrangement could not be determined. The presence of structural defective states (mainly C radicals) was corroborated by EPR studies of the solids. The photocatalytic activity of CN powders for methyl orange (MO) discoloration was investigated using 350 nm and simulated solar light (SSL) irradiation. MO removal efficiencies were correlated with the particle’s energy gap, specific surface area, degree of crystallinity, and C radical defects produced upon irradiation. Moreover, the obtained conduction and valence band potentials in the range of −0.60 and + 2.14 V vs NHE (pH = 7), respectively, evidence CN capacity to oxidize water to hydroxyl radicals (HO•) and reduce O2 to superoxide radical anions (O2•–). The formation of both radicals upon SSL irradiation of CN suspensions was confirmed by EPR experiments. The largest specific surface area, the highest charge carrier density, and the amount of C radical defects observed for CN obtained from urea (CNu) account for their highest photocatalytic performance. However, the estimated CNu photonic efficiency of ca. 8% still indicates a deficient separation/migration efficiency of photoinduced charge carriers. Despite CNu performance being higher than those of other CNs obtained from the thermal treatment of simple precursors, further environmentally friendly strategies are still needed to overcome the intrinsic disadvantages of CN before it may be employed in technological applications. A discussion on probable CN mechanisms forming reactive species and leading to MO decolorization is given.

EPR studies and radiation shielding properties of silver aluminum phosphate glasses

EPR studies and radiation shielding properties of silver aluminum phosphate glasses

Synthesis and Characterization of Face-to-Face Arylsulfanyl and Phenoxyl Radicals Embedded in Mesoporous Silicas

Recent applications of bi-, oligo-, or polyradicals to spin sciences have generated considerable interest in the design of new bi-/oligoradical organic molecules. Nevertheless, studies of physicochemical properties open shell systems are generally based on stable homonuclear organic radicals, which represent only a small portion of the existing radicals. In this context, diazene precursors of heteroatomic radicals were incorporated into the SBA-15 silica framework. Photolysis at 360 nm of the diazene moiety resulted in the formation of two face-to-face oxygen- and sulfur-centered radicals. These systems were characterized by X-, Q-, and W-band EPR spectroscopy by comparing them to silicas functionalized with either face-to-face sulfur-centered radicals or face-to-face oxygen-centered radicals. These EPR studies allowed measuring their half-life as well as their relaxation times (T1 and T2). The properties of silicas functionalized with sulfur- and oxygen-centered radicals fall between those measured for the two reference systems functionalized with only sulfur- or oxygen-centered radicals. These nanostructured silicas functionalized by two radicals of different nature are new potential candidates as a polarizing agent for DNP NMR.

Effect of strontium loading on the structural and thermodynamic properties of Ca10-xSrx(PO4)6F2(x= 2, 4, 6, 8) solid solutions for radioactive waste immobilization

Fluorapatite is being contemplated as a potential host for the incorporation of fluoride bearing radioactive nuclear waste. Ca10(PO4)6F2 and Sr10(PO4)6F2 are two fluorapatites which are studied extensively for the purpose of radioactive waste immobilization. Here, in this work a series of solid solutions having compositions Ca10-xSrx(PO4)6F2(x = 2, 4, 6 and 8) were synthesized by solid state chemistry route. The detailed structural properties of these solid solutions were analysed by powder XRD, FTIR and Raman spectroscopy. Rietveld refinement was used to determine the structural changes as well as micro-structural strain in these compositions. At lower loading of Sr2+, there is a preference on site occupation of Sr2+ between two crystallographic Ca2+ sites as evidenced by Rietveld refinement. The calculated average strain values in the calcium rich compositions (x = 2 and 4) are higher than the strontium rich compositions (x = 6 and 8). Thermo-physical properties such as heat capacity and thermal expansion of Ca10-xSrx(PO4)6F2 (x = 2, 4, 6, 8) solid solutions were experimentally measured for the first time.Heat capacity values follow the usual solid solution behaviour. Electron beam irradiation studies show that these substituted solutions are resistant to phase degradation up to 1000 kGy as revealed by powder XRD. Moreover, combined FTIR, Raman and EPR studies confirmed that higher strontium content is detrimental to the fluorapatite through surface modification. This study further gives insight into design of better matrix in terms of 90Sr loading capacity and stability.

An Intramolecular Radical C–N Coupling by N-Iodosuccinimide

AbstractA useful method for the formation of benzimidazole-fused phenanthridines through an intramolecular coupling of unactivated C(sp2)–H and N(sp3)–H bonds using N-iodosuccinimide (NIS) in trifluoroethanol (TFE) is presented. The synthesis of benzo[4,5]imidazo[1,2-f]phenanthridines from 2-([1,1′-biphenyl]-2-yl)-1H-benzo[d]imidazole derivatives is mild, efficient, and sustainable, with high yields and minimal waste generation. The control experiments and EPR studies were aimed at rationalizing the radical pathway of the reaction. Specifically, the use of 1,1-diphenylethylene, TEMPO, BHT, and DMPO as a free-radical spin-trapping reagent in EPR studies, allowed us to conceive a radical pathway. The gram-scale synthesis further supported the practical utility of the methodology for the field of synthetic chemistry.

NMR and EPR study of the interaction of tris(3-hydroxy-4-pyridinonato) Ga(III) complexes with liposomes that mimic plant membranes

We performed an NMR and EPR study of the interaction of four [Ga(3,4-HPO)3] chelates with liposomes derived from a soybean extract (SEL) and simpler formulations using POPC (100%) and POPE:POPC (50%). Parent [Fe(3,4-HPO)3] chelates are eligible to prevent Iron Deficiency Chlorosis and we took advantage of the likenesses of the ions Fe (III) and Ga (III), and the fact their metal ion complexes are isostructural, to perform a combined NMR and EPR study to get information about the permeation properties of the complexes.The results demonstrate the presence of liposomes loaded with Ga-chelates and that the distribution of complexes alongside the bilayer is dependent on their structure. Two compounds, [Ga(mpp)3] and [Ga(etpp)3], have a higher affinity for the polar region of the liposome bilayer thus suggesting that their structure facilitates their permanence at the root-rhizosphere interface. Chelates [Ga(dmpp)3] and [Ga(mrb13)3] interact with all types of protons of the lipid bilayer thus implying that they travel all along the bilayer structure indicating their higher permeation properties through soybean membranes.The results obtained for compound, [Ga(mrb13)3], which has been included in this work but was not yet tested in plant supplementation experiments, encourage its testing in in vivo plant studies once this study revealed that it interacts strongly with the model membranes. If the results of the future experiments in plants are positive and consistent with the present membrane-interaction studies the latter could constitute a good screening test for future compounds thus saving reagents and time.

Designing of 3D Architecture Flower-like Mn-Promoted MgO and Its Application for CO2 Adsorption and CO2-Assisted Aerobic Oxidation of Alkylbenzenes.

Sustainable chemistry research prioritizes reducing atmospheric carbon dioxide, and one logical solution is to develop adsorbents suitable for carbon capture and utilization. In this work, a new family of three-dimensional (3D) flower-like Mn-promoted MgO was synthesized by the coprecipitation method and used as an adsorbent for CO2 capture and a catalyst for CO2 utilization. The scanning electron microscopy (SEM) analysis of the samples shows a 3D architecture composed of thin nanosheets. The X-ray diffraction (XRD) analysis confirms the presence of the MgO with a cubic structure, while X-ray photoelectron spectroscopy (XPS) reveals the existence of Mn particles as a combination of Mn3+ and Mn4+ ions on MgO. N2 adsorption-desorption experiments highlight the beneficial contribution of Mn particles to surface area enhancement and reveal the existence of mesopores. Furthermore, the designed 3D Mn-doped MgO as an adsorbent demonstrates its capability to improve the ability of MgO to adsorb CO2 (from 0.28 mmol/g for pure MgO to 0.74 mmol/g) in ambient conditions and it is regenerable up to 9 cycles with a slight variation after the third cycle. Moreover, Mn-doped MgO shows good catalyst activity for the oxidation of ethylbenzene derivatives to carbonyl compounds in the presence of CO2 and O2. Mn-15/MgO shows excellent catalytic behavior with a conversion of 97.4 and 100% selectivity. Also, it is regenerable with an insignificant decrease in conversion (∼11.63%) after seven cycles, while the selectivity of acetophenone remains stable. The analyses of the recycled sample suggest that the chemical compositions of Mn and Mg influence the catalytic activity of those Mn-promoted MgO materials. The role of CO2 gas in the aerobic oxidation of ethylbenzene to acetophenone has also been proved. Finally, the control experiments and EPR studies reveal that the reaction takes place through the formation of radicals.

Dynamic EPR Studies of the Formation of Catalytically Active Centres in Multicomponent Hydrogenation Systems

The formation of catalytically active nano-sized cobalt-containing structures in multicomponent hydrogenation systems based on Co(acac)2 complex and various cocatalysts, namely, AlEt3, AlEt2(OEt), Li-n-Bu, and (PhCH2)MgCl, has been studied for the first time in detail using dynamic EPR spectroscopy. It is shown that after mixing the initial components, paramagnetic structures are formed, which include a fragment containing Co(0) with the electronic configuration 3d9, as well as a fragment bearing an aluminium, lithium, or magnesium atom, depending on the nature of the used cocatalyst. Such bimetallic paramagnetic sites are stabilized by acetylacetonate ligands. In addition, the paramagnetic complex contains the arene molecule(s), and the cobalt atom is bonded with the atom of the corresponding non-transition through the alkyl group of the co-catalyst, in particular through the carbon atom in the α-position with respect to the atom of the non-transition element. Due to the high reactivity of the described intermediates, they, under the conditions of hydrogenation catalysis, are transformed into nano-sized cobalt-containing structures that act as carriers of the catalytically active sites. Furthermore, because of the high reactivity and paramagnetism, such intermediates can be detected only by the EPR technique. The paper describes the whole experimental way of interpreting the EPR signals corresponding to the intermediates, precursors of catalytically active structures. In addition, a possible mathematical model based on the obtained experimental EPR data is presented.

Do Rutin and Quercetin Retain Their Structure and Radical Scavenging Activity after Exposure to Radiation?

The influence of ionizing radiation on the physicochemical properties of quercetin and rutin in the solid state was studied. Quercetin and rutin were irradiated with the standard recommended radiation dose (25 kGy) according to EN 522 standard. The samples were irradiated by electron beam radiation. EPR studies indicate the formation of a small number of free radicals due to irradiation. Moreover, some radicals recombined with the mean lifetime of 1200 and 93 h, and a stable radical concentration reached only 0.29 and 0.90 ppm for quercetin and rutin, respectively. The performed spectroscopic study (FT-IR) confirmed the radiostability of the flavonoids tested. Chromatographic tests (HPLC, HPLC-MS) showed that irradiation of quercetin and rutin with a 25 kGy dose did not change the physicochemical properties of the tested compounds. Degradation products were not observed. The antioxidant activities were determined by the 2,2-diphenyl-1-pycrylhydrazyl (DPPH) free radical scavenging activity assay, ABTS Radical Scavenging Assay (ABTS), Ferric Reducing Antioxidant Power Assay (FRAP), Cupric Ion Reducing Antioxidant Capacity Assay (CUPRAC). The conducted research confirmed that exposure to ionizing radiation does not change the chemical structure of tested flavonoids and their antioxidant properties.

Controllably solar-driven C‒C coupling organic synthesis integrated with H2 production over P-doped g-C3N4 with NiS nanoparticles modification

The development of mild and environmental method for direct transformation of aromatic alcohol into hydrobenzoin via controlled C‒C coupling is a highly attractive but challenging goal. In this paper, a P-doped g-C3N4 photocatalyst with NiS nanoparticles modification is first reported to apply the visible-light-driven C‒C coupling of aromatic alcohol into hydrobenzoin, as well as integrating with the production of clean H2 fuel. The synergistic effect of doped P atoms and formed type-II heterojunction between PCN and NiS improves the light absorption ability of g-C3N4 and greatly suppresses the charge recombination. Optimized 2.0% NiS/PCN composite achieves the complete conversion of aromatic alcohol within 6 h reaction time, as far as we known, which is the highest efficiency so far for aromatic alcohol conversion via photocatalytic strategy. Hydrobenzoin is controllably formed with 68% selectivity, together with a highly-efficient H2 production rate of 994.8 μmol·g−1·h−1. In-situ EPR studies reveal a preferential activation of C‒H bond than O‒H bond in aromatic alcohol by photoexcited holes, forming C6H5ĊH2OH radicals for subsequent coupling. The residual protons interact with photoexcited electrons to generate H2. Our study not only offers an efficient g-C3N4-based photocatalyst for the synthesis of hydrobenzoin under mild conditions, but also opens up a new avenue for manipulating the activation of C‒H or O‒H bonds for high selectivity of hydrobenzoin product.

A multicomponent lithium aluminum zinc germanate glass influenced by copper ions in its dielectric and spectroscopic characteristics

Multi component Li2O–Al2O3– ZnO–GeO2 glasses doped with CuO ranging from 0 to 1.0 mol% were prepared by the conventional melt quenching technique. Spectroscopic (optical absorption, IR, and EPR) and dielectric properties of the prepared glasses were examined. The EPR and optical absorption studies indicate that low-concentration CuO samples contain both Cu2+ and Cu + ions. CuO concentrations up to 0.6 mol% increased the level of disorder in the glass network, as indicated by IR studies. The dielectric study reveals the influence of copper valance states on the structural aspect of the samples. It has been shown from all these studies that the copper ions can be present in Cu3+ state in these glasses as well as Cu2+ and Cu+ states and thus participate in glass network formation. A quantitative analysis of the dielectric properties of the glasses has indicated that when the CuO concentration exceeds 0.6 mol%, the insulating strength increases. As a result, aluminum ions have been found to be tetrahedrally coordinated instead of octahedral. CuO concentrations above 0.6 mol% in the glass matrix significantly alter the physical properties of these glasses. The reduction of Cu2+ ions to Cu + ions has significantly effected the spectroscopic and dielectric investigations.

Copper(I) Photocatalyzed Bromonitroalkylation of Olefins: Evidence for Highly Efficient Inner-Sphere Pathways.

We report the visible light-mediated copper-catalyzed vicinal difunctionalization of olefins utilizing bromonitroalkanes as ATRA reagents. This protocol is characterized by high yields and fast reaction times under environmentally benign reaction conditions with exceptional scope, allowing the rapid functionalization of both activated and unactivated olefins. Moreover, late-stage functionnalization of biologically active molecules and upscaling to gram quantities is demonstrated, which offers manifold possibilities for further transformations, e.g. access to nitro- and aminocyclopropanes. Besides the synthetic utility of the title transformation, this study undergirds the exclusive role of copper in photoredox catalysis showing its ability to stabilize and interact with radical intermediates in its coordination sphere. EPR studies suggest that such interactions can even outperform a highly favorable cyclization of transient to persistent radicals contrasting iridium-based photocatalysts.

Experimental Determination of an Isolated trans‐Dinitrosyl Manganese(II) Heme Analogue

AbstractThe lack of direct proof in either natural or synthetic systems for trans‐dinitrosyl hemes, a key intermediate in the reactions of heme proteins (e.g. soluble guanylate cyclase (sGC), cytochrome c′ and So H‐NOX) with nitric oxide (NO), has hampered understanding of the exact reaction mechanisms, such as the formation of the five‐coordinate heme complex with NO at the proximal side (5c NOP). Herein, we report the first isolation of a dinitrosyl metalloporphyrin complex, the six‐coordinate, low‐spin {Mn(NO)2}7 species [Mn(TPP)(NO)2] (TPP2−=meso‐tetraphenylporphyrin dianion). The complex shows distinct features, such as an elongated axial bond (1.877(9) vs. 1.641(5) Å), a higher NO stretching bond position (1760 vs. 1735 cm−1) and an isotropic resonance at g = 2.0, in sharp contrast to those of five‐coordinate mononitrosyl analogues. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and EPR studies provided deep insight into the reaction processes, demonstrating different responses of porphyrinates to NO.

Experimental Determination of an Isolated trans-Dinitrosyl Manganese(II) Heme Analogue.

The lack of direct proof in either natural or synthetic systems for trans-dinitrosyl hemes, a key intermediate in the reactions of heme proteins (e.g. soluble guanylate cyclase (sGC), cytochrome c' and So H-NOX) with nitric oxide (NO), has hampered understanding of the exact reaction mechanisms, such as the formation of the five-coordinate heme complex with NO at the proximal side (5c NOP ). Herein, we report the first isolation of a dinitrosyl metalloporphyrin complex, the six-coordinate, low-spin {Mn(NO)2 }7 species [Mn(TPP)(NO)2 ] (TPP2- =meso-tetraphenylporphyrin dianion). The complex shows distinct features, such as an elongated axial bond (1.877(9) vs. 1.641(5) Å), a higher NO stretching bond position (1760 vs. 1735 cm-1 ) and an isotropic resonance at g = 2.0, in sharp contrast to those of five-coordinate mononitrosyl analogues. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and EPR studies provided deep insight into the reaction processes, demonstrating different responses of porphyrinates to NO.