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Developing novel luminescent materials with ideal properties is an endless project, urged by growing requirements of advances in energy saving, healthy lighting and environmental friendliness. Herein, a series of ScCaOBO 3 :Ce 3+ ,Mn 2+ phosphors with excellent luminescence properties were synthesized by the high temperature solid state method. X-ray diffraction was applied to analyse the phase composition of the obtained phosphors. The morphology and dopant distribution were observed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The Rietveld refinements and luminescence spectra indicate that Ce 3+ preferentially occupies the Sc 3+ site and produces a blue emission band at around 460 nm, which originates from the characteristic 5d-4f transitions, while Mn 2+ preferentially occupies the Ca 2+ site and emits red light due to its characteristic 4 T 1 ( 4 G)- 6 A 1 ( 6 S) transitions. Upon excitation at 354 nm, both Ce 3+ and Mn 2+ emissions can be obtained and further investigations evidenced that the broad and intense light emission of Mn 2+ located in the red spectral region is the result of energy transfer from Ce 3+ to Mn 2+ . Theoretical calculations reveal that the energy transfer process from Ce 3+ to Mn 2+ is of the resonance type and is governed by electric dipole-dipole interactions. Since the ScCaOBO 3 :Ce 3+ ,Mn 2+ phosphors are capable of producing broadband emissions that widely cover the blue and red spectral regions, the introduction of a green light-emitting phosphor CMA:Tb 3+ can conveniently generate high quality white light. Therefore, a white light-emitting diode device with extremely high color rendering indices, R a = 93.7 and R 9 = 91.9, was successfully obtained.

High valent metal-oxo intermediates are versatile oxidants known to facilitate both oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactions in nature. In addition to performing essential yet challenging biological reactions, these intermediates are known for their selectivity in favoring the formation of one oxidation product. To understand the basis for this selectivity, we explore the role of equatorial ligand field perturbations in Mn IV -oxo complexes on chemoselectivity in cyclohexene oxidation. We also examine reactions of Mn IV -oxo complexes with cyclohexene- d 10 , cyclooctene, and styrene. Within this series, the product distribution in olefin oxidation is highly dependent on the coordination environment of the Mn IV -oxo unit. While Mn IV -oxo complexes with sterically encumbered, and slightly tilted, MnO units favor CC epoxidation products in cyclohexene oxidation, a less encumbered analogue prefers to cleave allylic C-H bonds, resulting in cyclohexenol and cyclohexenone formation. These conclusions are drawn from GC-MS product analysis of the reaction mixture, changes in the UV-vis absorption spectra, and kinetic analyses. DFT computations establish a trend in thermodynamic properties of the Mn IV -oxo complexes and their reactivity towards olefin oxidation on the basis of the MnO bond dissociation free energy (BDFE). The most reactive Mn IV -oxo adduct from this series oxidizes cyclohexene- d 10 , cyclooctene, and styrene to give corresponding epoxides as the only detected products. Collectively, these results suggest that the chemoselectivity obtained in oxidation of olefins is controlled by both the coordination environment around the MnO unit, which modulates the MnO BDFE, and the BDFEs of the allylic C-H bond of the olefins.

In this paper, Cu(II), Mn(II) and Zn(II) complexes with N , N , N -trimethyl-2-oxo-2-(2-(1-(thiazol-2-yl)ethylidene)hydrazinyl)ethan-1-aminium chloride (HL1Cl) were synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis and DFT calculations. In all three complexes, a ligand (L1) is coordinated in a deprotonated formally neutral zwitterionic form via NNO donor set atoms. Cu(II) and Zn(II) form mononuclear penta-coordinated complexes [CuL1(N 3 )(CH 3 OH)]BF 4 and [ZnL1(N 3 ) 2 ], respectively, while Mn(II) forms a binuclear [Mn 2 L1 2 (μ- 1,1 -N 3 ) 2 (N 3 ) 2 ]·2CH 3 OH complex, with unusual distorted trigonal-prismatic geometry around the metal centers. The antimicrobial activity of these complexes was tested against a panel of Gram-negative and Gram-positive bacteria, two yeasts and one fungal strain. The binuclear Mn(II) complex showed antifungal activity of similar intensity to amphotericin B. Based on the results of the brine shrimp test and DPPH radical scavenging activity, the most active Cu(II) and Mn(II) complexes were selected for evaluation of cytotoxic activity against five malignant cancer cell lines (HeLa, A375, MCF7, PC-3 and A549) and one normal cell line HaCaT. Both complexes showed significant activity. It should be pointed out that the activity of the Mn(II) complex against the MCF7 breast cancer cell line is only slightly weaker than that of cisplatin, but with selectivity to the tumor cell line in comparison to normal HaCaT cells, which is non-existent in the case of cisplatin.

The binding ability of lectins has gained attention owing to the carbohydrate-specific interactions of these proteins. Such interactions can be applied to diverse fields of biotechnology, including the detection, isolation, and concentration of biological target molecules. The physiological aspects of the lectin concanavalin A (ConA) have been intensively studied through structural and functional investigations. X-ray crystallography studies have proven that ConA has two β-sheets and a short α-helix and that it exists in the form of a metalloprotein containing Mn 2+ and Ca 2+ . These heterometals are coordinated with side chains located in a metal-coordinated domain (MCD), and they affect the structural environment in the carbohydrate-binding domain (CBD), which interacts with carbohydrates through hydrogen bonds. Recent studies have shown that ConA can regulate biophysical interactions with glycoproteins in virus envelopes because it specifically interacts with diverse polysaccharides through its CBD (Tyr, Asn, Asp, and Arg residues positioned next to the MCD). Owing to their protein-protein interaction abilities, ConA can form diverse self-assembled complexes including monomers, dimers, trimers, and tetramers, thus affording unique results in different applications. In this regard, herein, we present a review of the structural modifications in ConA through metal-ion coordination and their effect on complex formation. In recent approaches, ConA has been applied for viral protein detection, on the basis of the interactions of ConA. These aspects indicate that lectins should be thoroughly investigated with respect to their biophysical interactions, for avoiding unexpected changes in their interaction abilities.

A general interest in harnessing the oxidizing power of dioxygen (O 2 ) continues to motivate research efforts on bioinspired and biomimetic complexes to better understand how metalloenzymes mediate these reactions. The ubiquity of Fe- and Cu-based enzymes attracts significant attention and has resulted in many noteworthy developments for abiotic systems interested in direct O 2 reduction and small molecule activation. However, despite the existence of Mn-based metalloenzymes with important O 2 -dependent activity, there has been comparatively less focus on the development of these analogues relative to Fe- and Cu-systems. In this Perspective , we summarize important contributions to the development of bioinspired mononuclear Mn complexes for O 2 activation and studies on their reactivity, emphasizing important design parameters in the primary and secondary coordination spheres and outlining mechanistic trends.

Several organic salts based on the combination of two different choline derivative cations and MnCl3-, GdCl4- and TbCl4- as anions were immobilized in mesoporous silica nanoparticles (MSNs) by a two-step synthetic method. Firstly, MSNs were functionalized with choline derivative cations with chloride anions and then the metals were incorporated by the reaction of the chloride with the respective metal chloride salts. These nanomaterials were fully characterized by different characterization techniques such as 1H-NMR, FT-IR, elemental analysis, TEM, TGA, N2 adsorption, XRD and DLS. These characterization data were important to confirm the successful functionalization of the nanomaterials and to access their textural properties and colloidal stability. The final materials were also characterized by ICP-MS that indicated the metal contents. The cytotoxicity profile was evaluated in four different cell lines (3T3, 293T, HepG2 and Caco-2), which shows some relevant differences between the metal organic salts and their immobilized analogues.

[FeFe]-hydrogenase (H 2 ase) catalyzes hydrogen evolution reactions (HERs), with an excellent performance that rivals that of platinum, the active site of which is built with crucial structural features required for efficient H-H bond formation. Herein, we report a mononuclear manganese complex (1) that contains a square pyramid coordination sphere and an intramolecular aniline as the proton relay, consistent with the crucial features of the active site in H 2 ase. Benefitting from these features, complex 1 electrocatalyzes the HER with a turnover frequency (TOF) exceeding 10 000 s -1 at -1.45 V (versus the ferrocenium/ferrocene couple) using anilinium tetrafluoroborate as a proton source. This work provides the first Mn-based functional model of H 2 ase, serving as a new paradigm for a high performance, low cost, environmentally benign hydrogen production electrocatalyst.

A new Ni(ii) complex [NiL] (complex 1) of an asymmetrically di-condensed N 2 O 3 donor Schiff base ligand, N-salicylidene-N'-3-methoxysalicylidene-1,3-propanediamine (H 2 L), has been synthesized and utilized for the synthesis of three heterometallic complexes, [(NiL) 2 Mn(NCS) 2 (CH 3 OH) 2 ]·CH 3 OH (2) [(NiL) 2 Mn(N(CN) 2 ) 2 (CH 3 OH) 2 ]·CH 3 OH (3) and [(NiL) 2 Mn 2 (N 3 ) 2 (μ 1,1 -N 3 ) 2 (CH 3 OH) 2 ] (4). Single crystal X-ray diffraction analyses show that complexes 2 and 3 have linear trinuclear structures where two tridentate O 3 donor (NiL) units are coordinated to the central octahedral Mn(ii) centre, whereas complex 4 has a centrosymmetric tetranuclear structure where two binuclear (NiL)Mn units are linked via two phenoxido and two μ 1,1 -N 3 bridges. Among the heterometallic complexes (2-4), only 4 is active towards the catalytic oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone. The turnover number for the aerobic oxidation of 3,5-DTBC is 935 h -1 . ESI-mass spectra have been recorded to scrutinize the mechanistic pathway of this catalytic reaction. Variable temperature magnetic susceptibility measurements suggest that complexes 2-4 are antiferromagnetically coupled with coupling constants (J) of -4.84 and -5.23 cm -1 for complexes 2 and 3, respectively and J 1 = -2.20 cm -1 , J 2 = 1.13 cm -1 and J 3 = -1.12 cm -1 for complex 4. DFT calculations have been used to rationalize the magnetic super-exchange in complexes 2-4, by computing the theoretical coupling constants and analyzing the spin density plots.

A one-pot synthetic route has been developed for the assembly of peptide Mn(i)-carbonyl bioconjugates. It allows the installation of a variety of chelating agents at the late stage, and after just one purification step the TAT-MnCO complexes can be obtained. The resulting bioconjugates showed different and tunable CO releasing kinetics upon visible light activation.

Two classes of heterogenized biomimetic catalysts were prepared and characterized for hydrocarbon oxidations: (1) by covalent anchorage of the three Mn(iii) meso-tetrakis(2-, 3-, or 4-pyridyl)porphyrin isomers by in situ alkylation with chloropropyl-functionalized silica gel (Sil-Cl) to yield Sil-Cl/MnPY (Y = 1, 2, 3) materials, and (2) by electrostatic immobilization of the three Mn(iii) meso-tetrakis(N-methylpyridinium-2, 3, or 4-yl)porphyrin isomers (MnPY, Y = 4, 5, 6) on non-modified silica gel (SiO2) to yield SiO2/MnPY (Y = 4, 5, 6) materials. Silica gel used was of column chromatography grade and Mn porphyrin loadings were deliberately kept at a low level (0.3% w/w). These resulting materials were explored as catalysts for iodosylbenzene (PhIO) oxidation of cyclohexane, n-heptane, and adamantane to yield the corresponding alcohols and ketones; the oxidation of cyclohexanol to cyclohexanone was also investigated. The heterogenized catalysts exhibited higher efficiency and selectivity than the corresponding Mn porphyrins under homogeneous conditions. Recycling studies were consistent with low leaching/destruction of the supported Mn porphyrins. The Sil-Cl/MnPY catalysts were more efficient and more selective than SiO2/MnPY ones; alcohol selectivity may be associated with hydrophobic silica surface modification reminiscent of biological cytochrome P450 oxidations. The use of widespread, column chromatography, amorphous silica yielded Sil-Cl/MnPY or SiO2/MnPY catalysts considerably more efficient than the corresponding, previously reported materials with mesoporous Santa Barbara Amorphous No 15 (SBA-15) silica. Among the materials studied, in situ derivatization of Mn(iii) 2-N-pyridylporphyrin by covalent immobilization on Sil-Cl to yield Sil-Cl/MnP1 showed the best catalytic performance with high stability against oxidative destruction and reusability/recyclability.

This paper describes the synthesis and structural characterization of four new manganese(iii) complexes (1-4) derived from N3O donor Schiff base ligands and their biomimetic catalytic activities related to catechol oxidase and phenoxazinone synthase. X-ray crystallography reveals that the Schiff bases coordinate the metal centre in a tridentate fashion, leaving the pendant tertiary amine nitrogen atom either protonated or free to balance the charge of the system, and these pendant triamines participate in strong hydrogen bonding interactions in the solid state. The hydrogen bonding ability of the pendant triamines at the second coordination sphere plays a crucial role in the substrate recognition and the stability of the complex-substrate intermediates. The effect of substitution at the phenolate ring towards the redox potential of the metal centre and the catalytic activity of these complexes has been observed. Detailed kinetic studies further disclose the deuterium kinetic isotope effect in which the transfer of the proton along the hydrogen bond from the substrates to the pendant triamine group at the secondary coordination sphere occurs at the key step in the catalytic reaction. The present reactivity nicely resembles the biochemical reactivities in the natural system in which a concerted electron and proton transfer to different species is usually observed. Remarkably, although some sort of influence of the secondary coordination sphere on catalytic activity has been reported mimicking the function of these metalloenzymes, such a direct participation of the secondary coordination sphere, particularly in modelling phenoxazinone synthase, has not been observed to date.

Five new heterometallic Cu(ii)-Mn(ii) discrete trinuclear complexes, [(CuL)2Mn(CH3COO)2] (1), [(CuL)2Mn(NO3)2] (2), [(CuL)2Mn(C6H5COO)(H2O)]Cl (3), [(CuL)2Mn((p-OH)C6H5COO)(H2O)]ClO4 (4) and [(CuL)2Mn(HCOO)(H2O)]ClO4 (5), have been synthesized using a metalloligand, CuL derived from an N2O2 donor Schiff base, H2L (N,N'-bis(α-methylsalicylidene)-1,3-propanediamine). Single-crystal structural analyses reveal that all five complexes have a common [(CuL)2Mn] core, where two terminal metalloligands, CuL, are connected to the central metal ion, Mn(ii), via double phenoxido bridges. Among the complexes, 1 and 2 possess linear structures where the terminal Cu(ii) atoms are bridged to the central Mn(ii) atoms by acetate and nitrate ions, respectively along with the double phenoxido bridges, whereas 3, 4 and 5 have bent structures in which the respective anionic coligands, benzoate, p-hydroxybenzoate and formate ions are coordinated only to central Mn(ii) in monodentate fashion along with a water molecule that completes its hexa-coordinated geometry. Among the complexes, 1, 3, 4 and 5 show quite high bio-mimicking catecholase-like activity for the aerial oxidation of 3,5-di-tert-butylcatechol with turnover numbers (Kcat) of 139 h-1, 439 h-1, 348 h-1 and 730 h-1, respectively, whereas complex 2 is practically inactive towards this reaction. The presence of the coordinated water molecule to Mn(ii) in the bent complexes, 3-5, appears to be responsible for their high catalytic activity and the difference in their activity may be attributed to steric crowding due to the anionic coligand, whereas the inactivity of 2 seems to be associated with the low basicity of the nitrate ion. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 1-5 are antiferromagnetically coupled with the exchange coupling constants (J) = -8.54 cm-1, -11.50 cm-1, -19.83 cm-1, -10.65 cm-1 and -10.27 cm-1 for 1, 2, 3, 4 and 5 respectively as is expected from the Cu-O-Mn bridging angles.

Oxygen atom transfer (OAT) reactions employing transition metal-oxo species have tremendous significance in homogeneous catalysis for industrial use. Understanding the structural and mechanistic aspects of OAT reactions using high-valent metal-oxo species is of great importance to fine-tune their reactivity. Herein we examine the reactivity of a non-heme high-valent oxo-manganese(iv) complex, [Mn IV H 3 buea(O)] - towards a variety of substrates such as PPh 2 Me, PPhMe 2 , PCy 3 , PPh 3 , and PMe 3 using density functional theory as well as ab initio CASSCF/NEVPT2 methods. We have initially explored the structure and bonding of [Mn IV H 3 buea(O)] - and its congener [Mn IV H 3 buea(S)] - . Our calculations affirm an S = 3/2 ground state of the catalyst with the S = 5/2 and S = 1/2 excited states predicted to be too high lying in energy to participate in the reaction mechanism. Our ab initio CASSCF/NEVPT2 calculations, however, reveal a strong multi-reference character for the ground S = 3/2 state with many low-lying quartets mixing significantly with the ground state. This opens up various reaction channels, and the admixed wave-function evolves during the reaction with the excited triplet dominating the ground state wave-function at the reactant complex. Our calculations predict the following pattern of reactivity, PCy 3 < PMe 3 < PPh 3 < PPhMe 2 < PPh 2 Me for the OAT reaction with the Mn IV [double bond, length as m-dash]O species which correlates well with the experimental observations. Detailed electronic structure analysis of the transitions states reveal that these substrates react via an unusual low-energy δ-type pathway where a spin-up electron from the substrate is transferred to the δ* x 2 -y 2 orbital of the Mn IV [double bond, length as m-dash]O facilitated by its multi-reference character. The unusual reactivity observed here has implications in understanding the reactivity of [Mn4Ca] species in photosystem II.

An amino acid containing octanuclear heterometallic {[MnCa] 2 } cluster has been synthesized, alongside a structurally-related trigonal prismatic [MnCa] 2+ cage.

Two series of photoinduced tricarbonyl manganese(i) compounds were prepared from the reaction of [MnBr(CO)3(2-C(H)[double bond, length as m-dash]O)] (2-C(H)[double bond, length as m-dash]O: quinoline-2-carboxaldehyde and pyridine-2-carboxaldehyde) and para-substituted aniline derivatives (X = OH, OCH3, Cl and NO2). Different electron-donating and electron-withdrawing substituents were introduced in the para-position of the phenyl ring to investigate their influence on the stability of the compounds in the dark and the photophysical properties upon illumination at 525 nm. When kept in the dark, the aerated solutions of the complexes in dimethyl sulfoxide (DMSO) and CH2Cl2 were stable. In the solution, the complexes bearing electron-withdrawing substituents, exchange their bromo ligands with DMSO solvent molecules, as evidenced from infrared and UV/Vis studies as well as time-dependent density functional theory (TDDFT) calculations. The complexes were assessed for their cytotoxicity, both in the dark and upon exposure to a 525 nm LED, against the human hepatocarcinoma cell line (HepG2). A marked reduction in the viability of HepG2 cells treated with the complex functionalized with quinoline and methoxy substituent was observed after illumination in a dose-dependent manner, with an IC50 value of 7.1 μM, making it the most phototoxic compound in our study.

Herein, we report the synthesis, characterization, crystal structure, density functional theory calculations, and water-oxidizing activity of a pivalate Mn-Ca cluster. All of the manganese atoms in the cluster are Mn(iv) ions and have a distorted MnO6 octahedral geometry. Three Mn(iv) ions together with a Ca(ii) ion and four-oxido groups form a cubic Mn3CaO4 unit which is similar to the Mn3CaO4 cluster in the water-oxidizing complex of Photosystem II. Using scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, extended X-ray absorption spectroscopy, chronoamperometry, and electrochemical methods, a conversion into nano-sized Mn-oxide is observed for the cluster in the water-oxidation reaction.

A series of solid solution CaAl12-xGaxO19:Mn4+ phosphors were prepared via a high-temperature solid-state reaction. Their structural properties were characterized by X-ray diffraction (XRD) and the luminescence was investigated via photoluminescence spectra. The obtained CaAl12-xGaxO19:Mn4+ phosphor has a strong broad excitation band in the range of 250-550 nm, which can be easily excited by the UV, NUV and blue light, and a broad emission band centered at 655 nm between 600 nm and 800 nm due to the 2Eg → 4A2g transition of the Mn4+ ion. The PL spectra indicate that the intensity of CaAl12O19:Mn4+ can be enhanced when the Ga3+ concentration equals 1. Furthermore, the element mapping, optical properties, thermal stability, fluorescence lifetime and CIE chromaticity reveal that the CaAl12-xGaxO19:Mn4+ phosphors can be considered as potential candidates in indoor plant cultivation.

A new, facile Cu(ii) template method has been employed for the unsymmetrical dicondensation of 1,2-ethylenediamine with salicylaldehyde and o-vanillin. The mononuclear complex, [CuL] (1), thus obtained, has been used as an O 3 donor metalloligand for the synthesis of four new Cu(ii)-Mn(ii) complexes, [(CuL)MnCl 2 ] (2), [(CuL)Mn(NO 3 ) 2 (CH 3 OH)] n (3), {[(CuL)Mn(benz)(H 2 O)] 2 ·(CuL) 2 (ClO 4 ) 2 } (4) and [(CuL)Mn(benz)Cl] 2 (5) (where benz = benzoate). Single-crystal structural analyses reveal that 2 is a dinuclear complex while complex 3 is polymeric with a repeating dinuclear [(CuL)Mn(NO 3 ) 2 (CH 3 OH)] unit, linked via the nitrate ion. Both 4 and 5 are discrete tetranuclear complexes, where the dinuclear units [(CuL)Mn(benz)(H 2 O)] and [(CuL)Mn(benz)Cl] are connected by double benzoate and double chloride bridges, respectively. In complex 4, two monomeric [CuL] units are cocrystallized with the tetranuclear complex. An important difference in the structure of 4 from the other three complexes is that one solvent water molecule is coordinated to each Mn(ii) ion, which makes complex 4 catalytically very active towards mimicking catecholase and phenoxazinone synthase-like oxidation reactions. The turnover numbers (k cat ) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 399 h -1 and 230 h -1 , respectively. The evidence of the intermediate species in the mass spectra indicates possible heterometallic cooperation where the Mn(ii) center helps in substrate binding and Cu(ii) participates in the oxidation reactions with molecular oxygen. Cyclic voltammetry measurements suggest the reduction of Cu(ii) to Cu(i) during the catalytic process. Temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 2-5 are antiferromagnetically coupled with the exchange coupling constants (J) of J = -13.5 cm -1 and J = -13.5 cm -1 for 2 and 3, respectively, J 1 = -12.6 cm -1 and J 2 = -1.20 cm -1 for complex 4 and J 1 = -13.24 cm -1 and J 2 = 0.36 cm -1 for complex 5 as is expected from the Cu-O-Mn bridging angles.

Three peroxidovanadium(v) compounds with different ligands (L1-L3) {L1 = N-tris(hydroxymethyl)methylglycine; L2 = ethylenediamine-N,N'-diacetic acid; L3 = 2,2-[(2-amino-2-oxoethyl)imino]diacetic acid} were first synthesized, characterized and further investigated for their anticancer activities under the mediation of transition metal cations. Encouragingly, all compounds showed preferentially enhanced cytotoxicity toward cancer cells (MCF-7 and A549) compared to normal cells (BEAS-2B) under the mediation of transition metal cations (Mn2+ or Fe2+), especially for Mn2+. It was noted that cell death was triggered by the transition metal cation-mediated peroxidovanadium(v) compounds through the induction of early apoptosis, inhibition of cell cycles, and boosting the generation of intracellular reactive oxygen species (ROS). Mechanistic studies further elucidated the vital roles of an acidic environment and transition metal cations for the anticancer activity of peroxidovanadium(v) compounds. Therefore, this study will offer precious insight into the development of the transition metal cation-mediated peroxidovanadium(v) compounds for further clinical translation.

Recent developments in Mn biology have added new physiological and pathophysiological roles of this essential metal ion to the already existing repertoire of indispensable biological roles of Mn ions. Notably, the discovery of Mn 2+ specific transporters, maladies related to mutations in these transporters, and evidence of the role of labile Mn 2+ species as anti-oxidants have initiated studies targeted at elucidating Mn ion regulation and pathways implicated in pathological conditions. Closely inter-linked with the quest for understanding metal ion homeostasis are basic questions like "How are metal ions installed in their correct biological addresses where they need to function?" and "Are dynamic changes in metal ion distribution functionally relevant?" These questions become more critical in the context of Mn 2+ ions, which have inherently low binding affinities toward most ligands and hence would always face competing metal ions in the biological milieu. In the emerging context of functional roles of the labile Mn 2+ ion pool, the development of chemical tools and techniques that can provide information on the location, distribution and dynamic changes in these parameters under physiological and pathophysiological conditions becomes imperative. In this frontier article, we discuss the challenges that had left Mn 2+ ions lagging behind in the race for the development of chemical tools and recent approaches that addressed these challenges to develop tools and techniques that can illuminate Mn ions in living systems.

Synthetic Cu complexes have been widely investigated as model systems for catechol oxidase enzymes. The catechol oxidase reactivity of Mn complexes has been less explored, and the effect of metal substitution in catecholase mimics has not been explored. A series of Mn and Cu complexes supported by the same poly-benzimidazole ligand framework have been synthesised and investigated in catecholase activity in acetonitrile medium using 3,5-di-tert-butylcatechol (3,5-DTBC) as a substrate. The Cu complexes proved to be good catechol oxidase mimics with moderate k cat values (∼45 h -1 ). The kinetic parameters for Mn complexes exhibited lower k cat values (∼8-40 h -1 ) when compared to the Cu complexes. Our findings demonstrate that later transition metals supported by relatively electron rich ligands yield the highest k cat values for catechol oxidation.

A new mononuclear Ni(ii) complex, [NiL] (1) of an unsymmetrically dicondensed N2O2 donor ligand, H2L (where H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), has been synthesized. Complex 1, on reaction with Mn(ii) in the presence of different co-anions, yielded three heterometallic NiII-MnII complexes, [(NiL)2Mn(NCS)2]·CH3CN (2), [(NiL)2Mn(N3)(H2O)](ClO4)·H2O (3) and [{(NiL)2Mn(H2O)}2(μ1,3-N3)](ClO4)3 (4). Single crystal structural analyses show that complexes 2 and 3 contain similar bent trinuclear NiII2MnII structures, with the difference that in complex 2 two SCN- ions and in 3, one N3- and one H2O molecule are coordinated to the Mn(ii) centre. Complex 4 possesses a hexanuclear structure, in which two trinuclear NiII2MnII units are connected via a single μ1,3-azido bridge. Variable temperature dc molar magnetic susceptibility measurements reveal that the two Mn(ii) centres in complex 4 are antiferromagnetically coupled with an exchange coupling constant (J) of -3.73 cm-1. Among the three heterometallic complexes, only 3 and 4 show bio-mimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers (Kcat) of complexes 3 and 4 are 984 and 2081 h-1, respectively, whereas for phenoxazinone synthase-like activity, the turnover numbers of complexes 3 and 4 are 6351 and 10 545 h-1, respectively. The high catalytic oxidase activities of complexes 3 and 4 in contrast to the inactivity of complex 2 are attributed to the coordination of a water molecule to the Mn(ii) centre in the former structures, which facilitates the binding of the substrate with the catalyst. Mass spectral analyses suggest the probable formation of a complex-substrate intermediate in these catalytic reactions and cyclic voltammetry measurements show that Ni(ii) is reducible to Ni(i).

[Mn(CO) 3 (2,2'-bipyridine)(PPh 3 )](ClO 4 ) (1), a novel photoactive CO-releasing molecule, has been prepared and fully characterized. Besides, silk fibroin nanoparticles (SFNs) have been used, for the first time, as vehicles of 1 leading to the hybrid material 1@SFNs that shows an enhanced CO-delivery.

In the research field of MRI contrast agents (CAs), amphiphilic paramagnetic complexes are typically sought for the increased plasmatic half-life and high relaxivity values, but limited examples of amphiphilic Mn 2+ -based CAs have been reported to date. In this work the Mn 2+ -complexes of six original amphiphilic ligands (three EDTA-like ligands and three 1,4-DO2A derivatives) embodying one or two aliphatic chains were evaluated as potential MRI contrast agents and compared. Strong self-association into micelles resulted in a relaxivity (r 1 ) enhancement (ca. 80% with respect to MnEDTA) as a consequence of the increased molecular tumbling rate of the supramolecular aggregate. In the case of bis-substituted systems the r 1 gain is much higher due to the restricted local rotation of the chelates about the pendant aliphatic chains (r 1 in the range 12.6-18.4 mM -1 s -1 , 2-3 times higher than for the micelles obtained with single-chain EDTA systems). Furthermore, these amphiphilic chelates tightly bind to human serum albumin (HSA) with association constants K A in the range 10 4 -10 5 M -1 . The resulting supramolecular adducts achieve remarkable relaxivity values, in the range 50-60 mM -1 s -1 for the MnEDTA-like chelates and 27-30 mM -1 s -1 for the 1,4-DO2A-like systems (at 298 K and 20 MHz), thanks to their fast water exchange rate.

The present study aims to formulate a common synthetic strategy for preparing quantum dots (QDs) in a greener way by using combination of popular methods, viz. a colloidal method with suitable capping agent and low molecular weight gel based synthesis. Pyridine dicarboxylic acid (PDC) in presence of AlCl3 forms a stable metallogel, which serves as an excellent medium for selective ZnS QD synthesis. The aromatic pyridine moiety, well known for being a capping agent, indeed plays its part in the run up to QD synthesis. To the best of our knowledge, this is the first example of a metallogel based doped ZnS QD synthesis. Altering the doping material and its composition changes the properties of the QDs, but herein we also tried to establish how these changes affect the gel morphology and stability of both gel and QDs. We further demonstrate, by using live cell confocal microscopy, the delivery of QDs Cu ZnS and MnZnS nanomaterials in the nucleus and the cytoplasm of human breast cancer cells (MCF7), implicating the use of metallogel based QDs for bio-imaging and bio-labeling.

Bio-inspired manganese [Mn(N 5 Py)(H 2 O)(CH 3 OH)](ClO 4 ) 2 (1) and iron [Fe(N 5 Py)(H 2 O)(ClO 4 )]ClO 4 (2) complexes derived from a pentadentate ligand (N 5 Py = 2,6-bis((E)-1-phenyl-2-(pyridin-2-ylmethylene)hydrazinyl)pyridine) framework containing a N 5 binding motif were synthesized and characterized using different spectroscopic methods. The molecular structures of complexes 1 and 2 were determined by X-ray crystallography. These complexes were found to be stable under physiological conditions and exhibited an excellent superoxide dismutase (SOD) activity. The SOD activity was determined by a xanthine-xanthine oxidase-nitro blue tetrazolium assay and the IC 50 values were determined to be 1.53 and 2.09 μM, respectively.

CpsB is a metal ion-dependent hydrolase involved in the biosynthesis of capsular polysaccharides in bacterial organisms. The enzyme has been proposed as a promising target for novel chemotherapeutics to combat antibiotic resistance. The crystal structure of CpsB indicated the presence of as many as three closely spaced metal ions, modelled as Mn 2+ , in the active site. While the preferred metal ion composition in vivo is obscure Mn 2+ and Co 2+ have been demonstrated to be most effective in reconstituting activity. Using isothermal titration calorimetry (ITC) we have demonstrated that, in contrast to the crystal structure, only two Mn 2+ or Co 2+ ions bind to a monomer of CpsB. This observation is in agreement with magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) data that indicate the presence of two weakly ferromagnetically coupled Co 2+ ions in the active site of catalytically active CpsB. While CpsB is known to be a phosphoesterase we have also been able to demonstrate that this enzyme is efficient in hydrolyzing the β-lactam substrate nitrocefin. Steady-state and stopped-flow kinetics measurements further indicated that phosphoesters and nitrocefin undergo catalysis in a conserved manner with a metal ion-bridging hydroxide acting as a nucleophile. Thus, the combined physicochemical studies demonstrate that CpsB is a novel member of the dinuclear metallohydrolase family.

The synthesized lithium (S)-6,6'-(1-carboxyethylazanediyl)bis(methylene)dipicolinate (Li 3 cbda) is a new chiral, alanine-based ligand bearing two picolinate functionalities. The trianionic form of the ligand [(cbda) 3- ] constitutes a seven-coordinate, water-soluble, pentagonal bipyramidal Mn(ii) complex (1). The structural analysis reveals the presence of a water coordinating site in the complex. The complex is thermodynamically very stable, and the stability is not affected by the presence of physiological anions (HCO 3 - , PO 4 3- , and F - ). The pH of the medium exerts a small effect on the stability of the complex. The r 1 relaxivity of 3.02 mM -1 s -1 is exhibited by the complex at 1.41 T, pH ∼7.4, and 25 °C. Phantom images obtained via a clinical MRI BRIVO MR355 system established concentration-dependent signal enhancement by the complex. The cytotoxicity test confirmed complex 1 as a biocompatible potential T 1 -weighted MRI contrast agent.

We report the synthesis, crystal structure, thermal, dielectric, phonon and magnetic properties of the [CH 3 C(NH 2 ) 2 ][Mn(HCOO) 3 ] (AceMn) compound. Our results show that this compound crystallizes in the perovskite-like orthorhombic structure, space group Imma. It undergoes a structural phase transition at 304 K into a monoclinic structure, space group P2 1 /n. X-ray diffraction, dielectric, IR and Raman studies show that the ordering of the acetamidinium cations triggers the phase transition. Low-temperature magnetic studies show that this compound exhibits weak ferromagnetic properties below 9.0 K.

We report two novel macrocyclic ligands based on the 1,4-DO2AM platform (1,4-DO2AM = 2,2'-(1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetamide) and containing two benzyl groups attached either to the nitrogen atoms of the macrocyclic unit (1,4-BzDO2AM) or to the amide pendant arms (1,4-DO2AMBz). The protonation constants of the ligands and the stability constants of their Mn 2+ complexes were determined using pH potentiometry. The introduction of benzyl groups results in a slight decrease of the stability constants of the Mn 2+ complexes and a slight increase of their acid-catalysed dissociation reactions. A detailed relaxometric characterisation of the complexes using nuclear magnetic dispersion relaxation (NMRD) and 17 O NMR studies indicated that the increase in molecular weight associated with the presence of benzyl groups results in a remarkable increase of proton relaxivities r 1p , which take values of 3.8, 3.5 and 2.5 mM -1 s -1 for [Mn(1,4-BzDO2AM)] 2+ , [Mn(1,4-DO2AMBz)] 2+ and [Mn(1,4-DO2AM)] 2+ (at 25 °C and 20 MHz). The [Mn(1,4-BzDO2AM)] 2+ and [Mn(1,4-DO2AMBz)] 2+ complexes form relatively strong adducts with Human Serum Albumin (HSA) with association constants of (3.9 ± 0.6) × 10 3 and (2.0 ± 0.3) × 10 3 M -1 , respectively. The interaction with the protein slows down the rotational tumbling of the complex in solution, which results in adducts endowed with remarkably high proton relaxivities (r 1p b = 18.5 ± 0.7 and 27.4 ± 1.4 mM -1 s -1 for [Mn(1,4-BzDO2AM)] 2+ and [Mn(1,4-DO2AMBz)] 2+ , respectively).

In this study, [2-(2-morpholin-4-ylethoxy)ethoxy] group substituted zinc(ii), manganese(iii) and copper(ii) phthalocyanines 2-4 and their water soluble derivatives 2a, 3a and 4a were synthesized and the interactions of compounds 2a, 3a and 4a with CT-DNA and supercoiled pBR322 plasmid DNA were investigated. The results of binding experiments showed that these compounds were able to interact with CT-DNA via intercalative mode with a strong binding affinity in the order 3a > 2a > 4a. DNA-photocleavage activities of compounds 2a, 3a and 4a were determined. These compounds cleaved supercoiled pBR322 plasmid DNA efficiently under irradiation at 650 nm for 2a and 4a, and at 750 nm for 3a. These compounds displayed remarkable inhibitory activities against topoisomerase I enzyme in a dose-dependent manner. All of these results suggest that these phthalocyanines might be suitable anticancer agents due to their strong binding affinities, significant cleavage activities and effective topoisomerase I inhibition.

The discovery of salutary effects of low doses of carbon monoxide (CO) has spurred interest in designing exogenous molecules that can deliver CO to biological targets under controlled conditions. Herein we report a water-soluble photosensitive manganese carbonyl complex [MnBr(CO)3(pyTAm)] (2) (pyTAm = 2-(pyridyl)imino-triazaadamantane) that can be triggered to release CO upon exposure to visible light. Inclusion of a triazaadamantyl pharmacophore into the coligand of 2 improves its stability and solubility in water. Change in the coligand from 2-(pyridyl)imino-triazaadamantane to 2-(pyridyl)iminoadamantane (pyAm) or 2-(quinonyl)imino-triazaadamantane (qyTAm) dramatically alters these desired properties of the photoCORM. In addition to structures and CO-releasing properties of the three analogous complexes 1-3 from these three α-diimine ligands, theoretical calculations have been performed to determine the origin of Mn-CO bond labilization upon illumination. Rapid delivery of CO to myoglobin under physiological conditions attests the potential of 2 as a biocompatible photoCORM.

A protected 30-amino acid fragment, Acetyl-SPDEKHELMIQLQKLDYTVGFCGDGANDCG-Amide, Acetyl-Ser-Pro-Asp-Glu-Lys-His-Glu-Leu-Met-Ile-Gln-Leu-Gln-Lys-Leu-Asp-Tyr-Thr-Val-Gly-Phe-Cys-Gly-Asp-Gly-Ala-Asn-Asp-Cys-Gly-Amide, encompassing the sequence from residues 1164 to 1193 in the encoded protein from Parkinson's disease gene Park9 (YPk9), was studied for manganese and zinc binding. Manganese exposure is considered to be an environmental risk factor connected to PD and PD-like syndrome. Research into the genetic and environmental risk factors involved in disease susceptibility has recently uncovered a link existing between Park9 and manganese. It seems that manganese binding to Park9 (YPk9) protein is involved in the detoxification mechanism exerted by this protein against manganese toxicity. In this study, we used potentiometric, mono- and bi-dimensional (TOCSY, HSQC) NMR, EPR and ESI-MS measurements to analyze complex formation and metal binding sites in the peptide fragment. Presumably octahedral species, in which the Mn(II) ion was bound to oxygens of the carboxyl groups of Glu and Asp, and species where the involvement of sulfur from Cys and nitrogen from His residues, depending on the metal to ligand molar ratio, were detected for manganese coordination. Structural changes in the 30-amino acid fragment were triggered by Zn(II) interaction. A general decrease in the intensity of NMR signals was detected, suggesting the occurrence of chemical exchange among some coordinated species in an intermediate NMR timescale. The coordination may involve both S and N donor atoms from cysteine as well as histidine residues, together with O donor atoms from glutamic and aspartic residues.

Radiolabelling using isotopic mixtures of (52g/55)Mn(ii) offers fast and easy access to new small molecule PET/MR tracers, composed of chemically identical reporting units. trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) was radiolabelled with carrier-added (52g)Mn(ii) in >99% radiochemical yield, producing the first manganese-based bimodal PET/MR probe. The Mn-CDTA chelate was shown to be very stable to air oxidation and sufficiently inert to decomplexation in blood serum. These data sparked our interest in functionalized CDTA ligands for the design of optimized PET/MR tracers.

Two "end-off" compartmental ligands, 2-formyl-4-chloro-6-N-ethylmorpholine-iminomethyl-phenol (HL1) and 2-formyl-4-methyl-6-N-ethylpyrrolidine-iminomethyl-phenol (HL2) have been designed and three complexes of Mn(ii), one mono-, one di- and a polynuclear, namely Mn(L1)(SCN)2(H2O)] (), [Mn2(L1)(OAc)2](BPh4)] (), and [Mn2(L2)(OAc)2(dca)]n () have been synthesized and structurally characterized. Variable temperature magnetic studies of and have been performed and data analyses reveal that Mn centers are antiferromagnetic coupled with J = -9.15 cm(-1) and J = -46.89, respectively. Catecholase activity of all the complexes has been investigated using 3,5-di-tert-butyl catechol (3,5-DTBC). All are highly active and the activity order on the basis of the kcat value is > > . In order to unveil whether the metal centered redox participation or the radical pathway is responsible for the catecholase-like activity of the complexes, detailed EPR and cyclic voltammetric (CV) studies have been performed. In addition to the six-line EPR spectrum characteristic to Mn(ii), an additional peak at g ∼ 2 is observed when the EPR study is done with the mixture of 3,5-DTBC and the catalyst, suggesting the formation of an organic radical, most likely ligand centered. The CV experiment with the mixture of 3,5-DTBC and the catalyst reveals ligand centered reduction rather than reduction of Mn(ii) to Mn(i). It is thus inferred that complexes show catecholase-like activity due to radical generation.

Mn(2+) chelating tags for Mn(2+)-Mn(2+) distance measurements by pulse EPR spectroscopy were developed. They feature a stable C-S conjugation to the protein, high reactivity towards cysteine thiols and short and rigid linkers that can be used in distance measurements with high resolution under reductive conditions. Double electron-electron resonance measurements at 95 GHz on ubiquitin labeled with these tags showed the expected narrow distance distribution.

Nanocrystalline biocompatible single-phase Mn-doped A-type carbonated hydroxyapatite (A-cHAp) powder has been synthesized by mechanical alloying of a stoichiometric mixture of CaCO3, CaHPO4·2H2O and MnO powder for 10 h at room temperature under open air. The A-type carbonation in HAp (substitution of CO3(2-) for OH(-)) is confirmed by FTIR analysis. Microstructure characterization in terms of lattice imperfections and phase quantification of ball milled samples are made by analyzing XRD patterns employing the Rietveld structure refinement method. Rietveld analysis of XRD patterns recorded from Mn-doped HAp samples has been used to locate Mn(2+) cations in HAp. The Ca2 vacancy site is found to be more favorable for Mn substitution. Microstructure characterization by HRTEM corroborates the findings of the X-ray analysis where the presence of a significant amount of amorphous phase of HAp analogous to indigenous bone mineral is clearly found. MTT assay shows sufficiently high percentage cell viability confirming the cytocompatibility of the sample.

We describe the synthesis of new manganese(ii) and manganese(iii) complexes containing the bidentate ligands 2-(3-pyrazolyl)pyridine, pypz-H, and 3(5)-(2-hydroxyphenyl)pyrazole, HOphpz-H, with formula [MnX2(pypz-H)2] (X = Cl(-), 1, CF3SO3(-), 2, OAc(-), 3 or NO3(-) (4)), [MnCl2(pypz-H)(H2O)2], 5, or [MnCl(Ophpz-H)2], 6. All the complexes have been characterized through analytical, spectroscopic and electrochemical techniques. Single X-ray structure analysis revealed a six-coordinated Mn(ii) ion in complexes 1-5, and a five-coordinated Mn(iii) ion in complex 6. Compound 5 is the first co-crystal of Mn(ii) containing Cl and H2O ligands together with bidentate nitrogen ligands. The catalytic activity of complexes 1-6 has been tested with regard to the epoxidation of styrene and, in the case of 1, 5 and 6, other alkenes have been epoxidized using peracetic acid as oxidant in different media, among which glycerol, a green solvent never used in epoxidation reactions using peracetic acid as oxidant. The catalysts show moderate to high conversions and selectivities towards the corresponding epoxides. For complexes 1, 5 and 6, a certain degree of cis→trans isomerization is observed in the case of cis-β-methylstyrene. These observations have been explained through computational calculations. The reutilization of catalysts 1 and 6 for the epoxidation of alkenes has been evaluated in [bmim] : acetonitrile mixture (bmim = 1-butyl-3-methylimidazolium), allowing the effective recyclability of the catalytic system and keeping high conversion and selectivity values up to 12 successive runs, in all cases.

Synthesis of new efficient catalysts inspired by Nature is a key goal in the production of clean fuel. Different compounds based on manganese oxide have been investigated in order to find their water-oxidation activity. Herein, we introduce a novel engineered polypeptide containing tyrosine around nano-sized manganese-calcium oxide, which was shown to be a highly active catalyst toward water oxidation at low overpotential (240 mV), with high turnover frequency of 1.5 × 10(-2) s(-1) at pH = 6.3 in the Mn(III)/Mn(IV) oxidation range. The compound is a novel structural and efficient functional model for the water-oxidizing complex in Photosystem II. A new proposed clever strategy used by Nature in water oxidation is also discussed. The new model of the water-oxidizing complex opens a new perspective for synthesis of efficient water-oxidation catalysts.

In the present work, the usefulness of ultrasonic power as a dispersion and mixing tool to accelerate the adsorption of Safranin O (SO), methylene blue (MB), Pb(2+) ions and Cr(3+) ions onto the novel composite Fe3O4-NPs-AC adsorbent was investigated. This new material was extensively characterized and analyzed by different techniques such as XRD, FESEM, Raman spectroscopy and FT-IR. Central composite design (CCD) based on designed runs revealed that adsorbent mass, sonication time, MB concentration, SO concentration, Pb(2+) ion and Cr(3+) ion concentration and some of their interactions have significant contributions to the target compounds removal percentages. A combination of response surface methodology and Design-Expert software was used to qualify and estimate the influence and magnitude of each terms contribution to the response. An optimization study using the following investigated increments of the effective variables, adsorbent mass (0.01-0.03 g), sonication time (2-6 min), initial dye concentration (5-25 mg L(-1)), and initial metal ion concentration (20-60 mg L(-1)), revealed that fixing the experimental variables at 0.025 g of Mn-Fe3O4-NPs-AC, with a 3 min sonication time, and 20 mg L(-1) of MB, 10 mg L(-1) of SO, 38 mg L(-1) of Pb(2+) ions and 42 mg L(-1) of Cr(3+) ions at room temperature lead to the achievement of the best characteristics and performance. Conduction of 32 experiments according to the limitations of CCD and a subsequent analysis of variance (ANOVA) gave useful information about the significant and also approximate contributions of each term (main and interaction of variables) in an empirical equation for the expected response. The results indicate that the R(2) values are more than 0.988 and the adjusted R(2) values are in reasonable agreement with R(2). Under the optimal conditions, the MB, SO, Pb(2+) ion and Cr(3+) ion removal efficiencies reached 99.54%, 98.87%, 80.25% and 99.54% after 3 min, while their equilibrium data with high performance can be represented by Langmuir isotherms and a pseudo second-order kinetic model. The maximum adsorption capacities for the single component system, 229.4 mg g(-1) for MB, 159.7 mg g(-1) for SO, 139.5 mg g(-1) for Pb(2+) ions and 267.4 mg g(-1) for Cr(3+) ions, support the high efficiency of Mn-Fe3O4-NPs-AC as a new adsorbent.

Two manganese(i) carbonyl complexes derived from α,α'-diimine ligands with extended conjugated framework namely [MnBr(CO)3(BIAN)] () and [MnBr(CO)3(MIAN)] (), have been synthesized and structurally characterized. Unlike the previously reported photoactive CO-releasing molecules (photoCORMs), these two complexes exhibit unusually high sensitivity toward low power (0.3-10 mW) visible light (λ ≥ 520 nm) even in the solid state and rapidly release carbon monoxide (CO) upon illumination. The role of the ligand frames in such activity has been examined with the help of theoretical calculations. Application of these photoCORMs in delivering high fluxes of CO to biological targets is anticipated.

In order to get insights into the metal ion effects and the carboxylate effects on enzymatic activity, a series of the carboxylate ligand supported transition metal complexes [M(II)L(OAc)] (M = Mn (), Fe (), Co (), Ni (), Cu () and Zn (); LH = 2-{[bis-(pyridin-2-ylmethyl)amino]methyl}-4-methoxy benzoic acid) were synthesized and characterized as structural and functional models for the active sites of various M(II)-substituted resting quercetin 2,3-dioxygenases (2,3-QD). Their structures, spectroscopic features, redox properties, as well as the catalytic reactivity toward the substrate flavonol and O2 have been investigated in detail. The model complexes show higher enzymatic reactivities in the catalytic dioxygenation (oxidative ring opening) of the substrate flavonol at lower temperatures (55-100 °C), presumably caused by the carboxylate group in the supporting model ligand, which could lower the redox potential of the bound substrate flavonolate by electron donation. The catalytic reactivity of [M(II)L(OAc)] exhibits notable differences and it is in a metal ion dependent order of Co () > Ni () > Zn () > Fe () > Mn () > Cu (). The differences in the reactivities among them could be ascribed to the redox potential of the bound substrate flavonolate, which was drastically influenced by the metal ions via tuning the electron density of flavonolate, providing important insights into the metal ion effects and the carboxylate effects on the enzymatic activity of various M(II)-substituted 2,3-QD. Our model complexes [M(II)L(OAc)] are the first examples of a series of structural and functional models of various M(II)-substituted resting 2,3-QD.

Ligand H4bedik was reacted with MnCl2·4H2O at pH ∼ 6.5 to give a highly water-soluble and water-coordinated Mn(ii) complex (). The complex was found to show r1 = 3.11 mM(-1) s(-1) per Mn(ii) at 1.4 T and 6.26 mM(-1) s(-1) per Mn(ii) at 14.1 T at 25 °C, pH = 7.4. In addition to r1, the r2 at 14.1 T was found to be 132.78 mM(-1) s(-1) per Mn(ii) at 25 °C, pH = 7.4.

The synthesis and photodecomposition behaviour of a family of CO releasing molecules (CORMs) based on [Mn(CO)3bpy] derivatives connected to a semiconductor Quantum Dot (QD) sensitizer is described here. Compared to the non-sensitized complexes, such systems show a 2 to 6-fold increase of the photodecomposition rate upon irradiation with visible light.

The ability to encapsulate hydrophobic ferrites in colloidal superparticle structures of an a-telechelic hexadecyl-functionalized poly(methacrylic acid) (C16H33-PMAA) polymer with a linear architecture was investigated and compared with that of two amphiphilic comb-type water-soluble copolymers, namely, P(ANa-co-DAAm) and P(MANa-co-DMA), which are comprised of a poly(sodium acrylate) or poly(sodium methacrylate) backbone and pendent dodecyl acrylamide or dodecyl methacrylate chains, respectively. In the case of C16H33-PMAA, the pH-sensitive self-assembly behavior, which was studied through Nile Red probing and TEM, was related to its encapsulation properties. Hydrophobic MFe2O4 nanoparticles coated with oleylamine (MFe2O4@OAm MNPs, where M = Co, Mn, Ni) with a similar shape and size (∼9 nm) and magnetization values of 87.4, 63.1 and 55.0 emu g(-1) for CoFe2O4@OAm, MnFe2O4@OAm and NiFe2O4@OAm, respectively, were successfully encapsulated into the hydrophobic cores of spherical micellar structures formed by the copolymers in an aqueous solution through a solvent mixing procedure. The synthesized magnetic colloidal superparticles fell in the static dephasing regime (SDR). NMR relaxivity measurements of MFe2O4@P(ANa-co-DAAm), MFe2O4@P(MANa-co-DMA) and MFe2O4@C16H33-PMAA at pH = 4.5 and pH = 7 (where M = Co, Mn, Ni) at 11.7 T were recorded and the transverse relaxivity (r2) (mM(-1) s(-1)) was determined. Among all, the CoFe2O4@polymers demonstrated the highest r2 relaxivity values, ranging from 61.6 for CoFe2O4@C16H33-PMAA (pH = 7) to 316.0 mM(-1) s(-1) for CoFe2O4@P(ANa-co-DAAm). The relaxation efficiency (r1 and r2) of CoFe2O4@P(ANa-co-DAAm) was investigated further by magnetic resonance imaging (MRI) at 1.5 T and 3 T and the r2/r1 ratios were found to be 16.5 and 18.2, respectively, indicating its potential use as a T2 contrast agent.

The syntheses of M(ii) (M = Mn, Fe, Co) complexes bearing the tris(5-cycloaminoazafulvene-2-methyl)amine (H3N(afa(Cy))3) ligand in its datively coordinated, tautomeric form is reported. The metal-azafulvene complexes [N(afa(Cy))3M](OTf)2 are generated in high yields, featuring a secondary coordination sphere composed of amino moieties from the ligand platform. To investigate the ability of the hydrogen bonding network to support hydrogen-bond accepting, coordinating anions, pseudohalide derivatives, [N(afa(Cy))3MX](OTf) (X = NCS(-), NCO(-), N3(-)) were synthesized by exposure of [N(afa(Cy))3M](OTf)2 to an equivalent of the corresponding salt, [((n)Bu)4N](X). Structural characterization of the products reveals two isomorphs of the desired species. One complex features a single hydrogen bonding interaction with the pseudohalide, while the second compound has two H-bonds from the secondary coordination sphere to the coordinated anion. These complexes showcase the structural and electron flexibility of the ligand platform, presenting a scaffold capable of accessing a different number of hydrogen bonds for stabilizing a given moiety.

One Mn(II) coordination polymer, [Mn(o-(NO2)C6H4COO)2(pyz)(H2O)]n (1), has been synthesized and oxidized with n-Bu4NMnO4 in non-aqueous media to two mixed-valence hexanuclear Mn(II/III) complexes [MnIII2MnII4O2(pyz)0.61/(MeOH)0.39(o-(NO2)C6H4COO)10·(H2O)·{(CH3)2CO}2]·(CH3)2CO (2) and [MnIII2MnII4O2(pyz)0.28/(MeCN)3.72(o-(NO2)C6H4COO)10·(H2O)] (3) (where pyz = pyrazine). All three complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, and variable-temperature magnetic measurements. The structural analyses reveal that complex 1 is comprised of linear chains of pyz bridged Mn(II), which are further linked to one another by syn–anti carboxylate bridges, giving rise to a two-dimensional (2D) net. Complexes 2 and 3 feature mixed valence [MnIII2MnII4] units in which each of the six manganese centres reside in an octahedral environment. Apart from the variations in terminal ligands (acetone for 2 and acetonitrile for 3), the complexes are very similar. Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, the catecholase-like activity of the complexes has been studied and it is found that the mixed valent Mn6 complexes (2 and 3) are much more active towards aerial oxidation of catechol compared to the Mn(II) complex (1). Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed the presence of antiferromagnetic coupling in all three complexes. The magnetic data have been fitted with a 2D quadratic model derived by Lines, giving the exchange constant J/kB = −0.0788(5) K for 1. For 2 and 3, antiferromagnetic interactions within the Mn6 cluster have been fitted with models containing three exchange constants: JA/kB = −70 K, JB/kB = −0.5 K, JC/kB = −2.9 K for 2 and JA/kB = −60 K, JB/kB = −0.3 K, JC/kB = −2.8 K for 3.

Three five-coordinate, high spin manganese(ii) "picket fence" porphyrin complexes, [Mn(TpivPP)(L)] (TpivPP = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrinato; L = 1-MeIm (1-methylimidazole), 1-EtIm (1-ethylimidazole) and 2-MeHIm (2-methylimidazole)), are synthesized and studied by single-crystal X-ray, UV-vis and electronic paramagnetic resonance (EPR) spectroscopy. Structural parameters are investigated and compared with analogues. Low temperature (90 K), high field EPR studies of [Mn(TpivPP)(1-MeIm)] and [Mn(TpivPP)(2-MeHIm)] showed five resonances including characteristic signals at ∼5.9 and ∼2.0. The simulations of the EPR spectra give the zero field splitting (zfs) parameters (D, E and λ) and the hyperfine coupling constant (A).

Redox-inactive metal ions can modulate the reactivity of redox-active metal ions in a variety of biological and chemical oxidations. Many synthetic models have been developed to help address the elusive roles of these redox-inactive metal ions. Using a non-heme manganese(II) complex as the model, the influence of redox-inactive metal ions as a Lewis acid on its catalytic efficiency in oxygen atom transfer was investigated. In the absence of redox-inactive metal ions, the manganese(II) catalyst is very sluggish, for example, in cyclooctene epoxidation, providing only 9.9% conversion with 4.1% yield of epoxide. However, addition of 2 equiv. of Al(3+) to the manganese(II) catalyst sharply improves the epoxidation, providing up to 97.8% conversion with 91.4% yield of epoxide. EPR studies of the manganese(II) catalyst in the presence of an oxidant reveal a 16-line hyperfine structure centered at g = 2.0, clearly indicating the formation of a mixed valent di-μ-oxo-bridged diamond core, Mn(III)-(μ-O)2-Mn(IV). The presence of a Lewis acid like Al(3+) causes the dissociation of this diamond Mn(III)-(μ-O)2-Mn(IV) core to form monomeric manganese(iv) species which is responsible for improved epoxidation efficiency. This promotional effect has also been observed in other manganese complexes bearing various non-heme ligands. The findings presented here have provided a promising strategy to explore the catalytic reactivity of some di-μ-oxo-bridged complexes by adding non-redox metal ions to in situ dissociate those dimeric cores and may also provide clues to understand the mechanism of methane monooxygenase which has a similar diiron diamond core as the intermediate.

In vitro selection was performed to search for RNA-cleaving DNAzymes catalytically active with Cd(2+) ions from the oligonucleotide combinatorial library with a 23-nucleotide random region. All the selected, catalytically active variants turned out to belong to the 8-17 type DNAzyme. Three DNAzymes were prepared in shortened, cis-acting versions which were subjected to a detailed study of the kinetic properties and metal ion preferences. Although the selection protocol was designed for Cd(2+)-dependent DNAzymes, the variants showed broader metal ion specificity. They preferred Cd(2+) but were also active with Mn(2+) and Zn(2+), suggesting that binding of the catalytic ion does not require an extremely specific coordination pattern. The unexpected decrease of the catalytic activity of the variants along with the temperature increase suggested that some changes occurred in their structures or the rate-limiting step of the reaction was changed. Two elements of the catalytic core of DNAzyme 1/VIIWS, the nucleotide at position 12 and the three-base-pair hairpin motif, were mutated. The presence of a purine residue at position 12 was crucial for the catalytic activity but the changes at that position had a relatively small influence on the metal ion preferences of this variant. The middle base pair of the three-base-pair hairpin was changed from A-T to C-G interaction. The catalytic activity of the mutated variant was increased with Zn(2+), decreased with Mn(2+), and was not changed in the presence of Cd(2+) ions. Clearly, this base pair was important for defining the metal ion preferences of the DNAzyme 1/VIIWS.