ABSTRACT
We present here the most active synthetic Ni superoxide dismutase (NiSOD) mimic reported to date. Reactive oxygen species are aggressive compounds, which concentrations are tightly regulated in vivo. Among them, the superoxide anion, O2⸱-, is controlled by superoxide dismutases. Capitalizing on the versatility of the Amino-Terminal CuII- and NiII-binding (ATCUN) peptide motif, we introduced positive charges around the NiII center to favor the interaction with the superoxide radical anion. At physiological pH, the pentapeptide H-Cys-His-Cys-Arg-Arg-NH2 coordinates NiII after the deprotonation of one thiol, two amides, and either the second thiol or the N-terminal ammonium, leading to an equilibrium between the two N3S1 and N2S2 coordination modes. Under catalytic conditions, a kcat value of 8.6(4) x 106 L.mol-1.s-1 was measured. Within the first second, the catalyst remained undegraded with quantitative consumption of O2⸱- (completed up to 37 catalytic cycles). An extra arginine (Arg) was introduced at the peptide C-terminus to increase the global charge of the NiII complex from +1 to + 2. This had no effect on the catalytic performance, highlighting the critical role of charge distribution in space as a determining factor influencing the reactivity.
ABSTRACT
We report the isolation and study of dimers stemming from popular thiazol-2-ylidene organocatalysts. The model featuring 2,6-di(isopropyl)phenyl (Dipp) N-substituents was found to be a stronger reducing agent (Eox = -0.8 V vs SCE) than bis(thiazol-2-ylidenes) previously studied in the literature. In addition, a remarkable potential gap between the first and second oxidation of the dimer also allows for the isolation of the corresponding air-persistent radical cation. The latter is an unexpected efficient promoter of the radical transformation of α-bromoamides into oxindoles.
ABSTRACT
We present the simple synthesis of a star-shape non-fullerene acceptor (NFA) for application in organic solar cells. This NFA possesses a D(A)3 structure in which the electron-donating core is an aza-triangulene unit and we report the first crystal structure for a star shape NFA based on this motive. We fully characterized this molecule's optoelectronic properties in solution and thin films, investigating its photovoltaic properties when blended with PTB7-Th as the electron donor component. We demonstrate that the aza-triangulene core leads to a strong absorption in the visible range with an absorption edge going from 700 nm in solution to above 850 nm in the solid state. The transport properties of the pristine molecule were investigated in field effect transistors (OFETs) and in blends with PTB7-Th following a Space-Charge-Limited Current (SCLC) protocol. We found that the mobility of electrons measured in films deposited from o-xylene and chlorobenzene are quite similar (up to 2.70 × 10-4 cm2 V-1 s-1) and that the values are not significantly modified by thermal annealing. The new NFA combined with PTB7-Th in the active layer of inverted solar cells leads to a power conversion efficiency of around 6.3% (active area 0.16 cm2) when processed from non-chlorinated solvents without thermal annealing. Thanks to impedance spectroscopy measurements performed on the solar cells, we show that the charge collection efficiency of the devices is limited by the transport properties rather than by recombination kinetics. Finally, we investigated the stability of this new NFA in various conditions and show that the star-shape molecule is more resistant against photolysis in the presence and absence of oxygen than ITIC.
ABSTRACT
The cellular level of reactive oxygen species (ROS) has to be controlled to avoid some pathologies, especially those linked to oxidative stress. One strategy for designing antioxidants consists of modeling natural enzymes involved in ROS degradation. Among them, nickel superoxide dismutase (NiSOD) catalyzes the dismutation of the superoxide radical anion, O2â¢-, into O2 and H2O2. We report here Ni complexes with tripeptides derived from the amino-terminal CuII- and NiII-binding (ATCUN) motif that mimics some structural features found in the active site of the NiSOD. A series of six mononuclear NiII complexes were investigated in water at physiological pH with different first coordination spheres, from compounds with a N3S to N2S2 set, and also complexes that are in equilibrium between the N-coordination (N3S) and S-coordination (N2S2). They were fully characterized by a combination of spectroscopic techniques, including 1H NMR, UV-vis, circular dichroism, and X-ray absorption spectroscopy, together with theoretical calculations and their redox properties studied by cyclic voltammetry. They all display SOD-like activity, with a kcat ranging between 0.5 and 2.0 × 106 M-1 s-1. The complexes in which the two coordination modes are in equilibrium are the most efficient, suggesting a beneficial effect of a nearby proton relay.
Subject(s)
Hydrogen Peroxide , Superoxide Dismutase , Reactive Oxygen Species , Hydrogen Peroxide/chemistry , Superoxide Dismutase/chemistry , Oxidation-Reduction , Superoxides/chemistry , Nickel/chemistryABSTRACT
We report the synthesis and structural study of 2-substituted 1,3-bis(dimethylamino)pentalenes. The two electrons donating substituents shift the formally anti-aromatic pattern toward more suitable polarized structures. A subtle steric trade-off can result either in planar cyclopentadienyl vinamidiniums or in distorted structures featuring a pyramidalized ylidic carbon adjacent to a stabilized π-conjugated iminium (polymethine). This latter pattern mimics a postulated activated distorted geometry for key Breslow intermediates in the active site of thiamine-dependent enzymes. It highlights how the energetic drive to avoid anti-aromaticity can be used to access models for unconventional distorted conformations of organic molecules.
ABSTRACT
An air-stable (amino)(amido)radical was synthesized by reacting a cyclic (alkyl)(amino)carbene with carbazoyl chloride, followed by one-electron reduction. We show that an adjacent radical center weakens the amide bond. It enables the amino group to act as a strong acceptor under steric contraint, thus enhancing the stabilizing capto-dative effect.
Subject(s)
Amides , Lizards , Animals , Oxidation-Reduction , Chlorides , ElectronsABSTRACT
Lanthanide(III) (Ln3+) complexes feature desirable luminescence properties for cell microscopy imaging, but cytosolic delivery of Ln3+ complexes and their use for 2P imaging of live cells are challenging. In this article, we describe the synthesis and spectroscopic characterizations of a series of Ln3+ complexes based on two ligands, L1 and L2, featuring extended picolinate push-pull antennas for longer wavelength absorption and 2P absorption properties as well as a free carboxylate function for conjugation to peptides. Several cell penetrating peptide/Ln3+ complex conjugates were then prepared with the most interesting luminescent complexes, Tb(L1) and Eu(L2), and with two cell penetrating peptides (CPPs), ZF5.3 and TP2. A spectroscopic analysis demonstrates that the luminescence properties of the complexes are not affected by conjugation to the peptide. The conjugates were evaluated for one-photon (1P) time-gated microscopy imaging, which suppresses biological background fluorescence, and 2P confocal microscopy. Whereas TP2-based conjugates were unable to enter cells, successful 1P and 2P imaging was performed with ZF5.3[Tb(L1)]. 2P confocal imaging suggests proper internalization and cytosolic delivery as expected for this CPP. Noteworthy, 2P confocal microscopy also allowed characterization of the luminescence properties of the complex (spectrum, lifetime) within the cell, opening the way to functional luminescent probes for 2P confocal imaging of live cells.
Subject(s)
Lanthanoid Series Elements , Lanthanoid Series Elements/chemistry , Luminescence , Microscopy/methods , Photons , Ligands , PeptidesABSTRACT
Molecular hydrogen (H2) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H2 production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [RhIII(tpy)(CH3CN)Cl2](CF3SO3) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H2 in water in the presence of the [Ru(bpy)3]Cl2 (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 µM of Ru, the Rh-tpy catalyst produces H2 with turnover number versus catalyst (TONCat*) of 300 at a Rh concentration of 10 µM, and up to 1000 at a concentration of 1 µM. The photocatalytic performance of Ru/Rh-tpy/HA-/H2A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [RhIII(dmbpy)2Cl2]+ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [RhI(tpy)Cl] (RhI-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Epc(RhIII/RhI) = -0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [RuII(bpy)(bpyâ¢-)]+ (Ru-) (E1/2(RuII/Ru-) = -1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern-Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru-) were then able to activate the RhIII-tpy H2-evolving catalyst by reduction generating RhI-tpy, which can react with a proton on a sub-nanosecond time scale to form a RhIII(H)-tpy hydride, the key intermediate for H2 evolution.
ABSTRACT
We report a peculiar Stenhouse salt. It does not evolve into cyclopentenones upon basification, due to the steric hindrance of its bulky stable carbene patterns. This allowed for the observation and characterization of the transient open-chain neutral derivative, which was isolated as its cyclized form. The latter features an unusually long reactive C-O bond (150 pm) and a rich electrochemistry, including oxidation into an air-persistent radical cation.
ABSTRACT
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor.
Subject(s)
Ferric Compounds , Iron , Ferric Compounds/chemistry , Models, Molecular , Catalysis , Iron/chemistry , Ferrous Compounds/chemistryABSTRACT
Surface integration of molecular catalysts inspired from the active sites of hydrogenase enzymes represents a promising route towards developing noble metal-free and sustainable technologies for H2 production. Efficient and stable catalyst anchoring is a key aspect to enable this approach. Herein, we report the preparation and electrochemical characterization of an original diironhexacarbonyl complex including two pyrene groups per catalytic unit in order to allow for its smooth integration, through π-interactions, onto multiwalled carbon nanotube-based electrodes. In this configuration, the grafted catalyst could reach turnover numbers for H2 production (TONH2 ) of up to 4±2×103 within 20â h of bulk electrolysis, operating at neutral pH. Post operando analysis of catalyst functionalized electrodes revealed the degradation of the catalytic unit occurred via loss of the iron carbonyl units, while the anchoring groups and most part of the ligand remained attached onto multiwalled carbon nanotubes.
Subject(s)
Hydrogenase , Nanotubes, Carbon , Hydrogenase/chemistry , Nanotubes, Carbon/chemistry , Hydrogen/chemistry , Catalysis , ElectrodesABSTRACT
Nickel superoxide dismutase (NiSOD) is an enzyme that protects cells against O2·-. While the structure of its active site is known, the mechanism of the catalytic cycle is still not elucidated. Its active site displays a square planar NiII center with two thiolates, the terminal amine and an amidate. We report here a bioinspired NiII complex built on an ATCUN-like binding motif modulated with one cysteine, which demonstrates catalytic SOD activity in water (kcat = 8.4(2) × 105 M-1 s-1 at pH = 8.1). Its reactivity with O2·- was also studied in acetonitrile allowing trapping two different short-lived species that were characterized by electron paramagnetic resonance or spectroelectrochemistry and a combination of density functional theory (DFT) and time-dependent DFT calculations. Based on these observations, we propose that O2·- interacts first with the complex outer sphere through a H-bond with the peptide scaffold in a [NiIIO2·-] species. This first species could then evolve into a NiIII hydroperoxo inner sphere species through a reaction driven by protonation that is thermodynamically highly favored according to DFT calculations.
Subject(s)
Biomimetic Materials/chemistry , Coordination Complexes/chemistry , Superoxides/chemistry , Catalysis , Density Functional Theory , Models, Chemical , Molecular Structure , Nickel/chemistry , Superoxide Dismutase/chemistryABSTRACT
Imidazole thiones appear as interesting building blocks for Cu(I) chelation and protection against Cu-mediated oxidative stress. Therefore, a series of tripodal molecules derived from nitrilotriacetic acid appended with three imidazole thiones belonging either to histamine-like or histidine-like moieties were synthesized. These tripods demonstrate intermediate affinity between that previously measured for tripodal analogues bearing three thiol moieties such as cysteine and those grafted with three thioethers, like methionines, consistently with the thione group in the imidazole thione moiety existing as a tautomer between a thiol and a thione. The two non-alkylated tripods derived from thioimidazole, TH and TH* demonstrated three orders of magnitude larger affinity for Cu(I) (logKpH 7.4 = 14.3) than their analogues derived from N,N'-dialkylated thioimidazole TMe and TEt (logKpH 7.4 = 11-11.6). Their efficiency to inhibit Cu-mediated oxidative stress is demonstrated by several assays involving ascorbate consumption or biomolecule damages and correlates with their ability to chelate Cu(I), related to their conditional complexation constants at pH 7.4. The two non-alkylated tripods derived from thioimidazole, TH and TH* are significantly more powerful in reducing Cu-mediated oxidative stress than their analogues derived from N,N'-dialkylated thioimidazole TMe and TEt.
Subject(s)
Antioxidants/chemistry , Chelating Agents/chemistry , Coordination Complexes/chemistry , Imidazoles/chemistry , Oxidative Stress/drug effects , Thiones/chemistry , Antioxidants/chemical synthesis , Ascorbic Acid/chemistry , Chelating Agents/chemical synthesis , Coordination Complexes/chemical synthesis , Copper/chemistry , DNA/drug effects , DNA Cleavage/drug effects , Imidazoles/chemical synthesis , Ligands , Oxidation-Reduction , Plasmids/drug effects , Protein Carbonylation/drug effects , Thiones/chemical synthesisABSTRACT
We report on the isolation of a new family of µ-carboxylato-bridged metallocrown (MC) compounds by self-assembly of the recently isolated hexadentate tris(2-pyridylmethyl)amine ligand tpada2- incorporating two carboxylate units with metal cations. Twelve-membered MCs of manganese of the type 12-MC-3, namely, [{MnII(tpada)}3(M)(H2O)n]2+ (Mn3M) (M = Mn2+ (n = 0), Ca2+ (n = 1), or Sr2+ (n = 2)), were structurally characterized. The metallamacrocycles connectivity consisting in three -[Mn-O-C-O]- repeating units is provided by one carboxylate unit of the three tpada2- ligands, while the second carboxylate coordinated a fourth cation in the central cavity of the MC, Mn2+ or an alkaline earth metal, Ca2+ or Sr2+. Mn3Ca and {Mn3Sr}2 join the small family of heterometallic manganese-calcium complexes and even rarer manganese-strontium complexes as models of the OEC of photosystem II (PSII). A 8-MC-4 of strontium of the molecular wheel type with four -[Sr-O]- repeating unit was also isolated by self-assembly of the tpada2- ligand with Sr2+. This complex, namely, [Sr(tpada)(OH2)]4 (Sr4), does not incorporate any cation in the central cavity but instead four water molecules coordinated to each Sr2+. Electrochemical investigations coupled to UV-visible absorption and EPR spectroscopies as well as electrospray mass spectrometry reveal the stability of the 12-MC-3 tetranuclear structures in solution, both in the initial oxidation state, MnII3M, as well as in the three-electrons oxidized state, MnIII3M. Indeed, the cyclic voltammogram of all these complexes exhibits three-successive reversible oxidation waves between +0.5 and +0.9 V corresponding to the successive one-electron oxidation of the Mn(II) ion into Mn(III) of the three {Mn(tpada)} units constituting the ring, which are fully maintained after bulk electrolysis.
ABSTRACT
The interest in ratiometric luminescent probes that detect and quantify a specific analyte is growing. Owing to their special luminescence properties, lanthanide(III) cations offer attractive opportunities for the design of dual-color ratiometric probes. Here, the design principle of hetero-bis-lanthanide peptide conjugates by using native chemical ligation is described for perfect control of the localization of each lanthanide cation within the molecule. Two zinc-responsive probes, r-LZF1Tb|Cs124|Eu and r-LZF1Eu|Cs124|Tb are described on the basis of a zinc finger peptide and two DOTA (DOTA=1,4,7,10-tetraaza-cyclododecane-1,4,7,10-tetraacetic acid) complexes of terbium and europium. Both display dual-color ratiometric emission in response to the presence of Zn2+ . By using a screening approach, anthracene was identified for the sensitization of the luminescence of two near-infrared-emitting lanthanides, Yb3+ and Nd3+ . Thus, two novel zinc-responsive hetero-bis-lanthanide probes, r-LZF3Yb|Anthra|Nd and r-LZF3Nd|Anthra|Yb were assembled, the former offering a neat ratiometric response to Zn2+ with emission in the near-infrared around 1000â nm, which is unprecedented.
Subject(s)
Lanthanoid Series Elements , Peptides/chemistry , Europium/chemistry , Luminescence , Terbium/chemistry , Zinc/chemistryABSTRACT
Inspection of Oxygen Reduction Reactions (ORRs) using a mixed-valent Cu2S complex as a pre-catalyst revealed a tuneable H2O2vs. H2O production under mild conditions by controlling the amount of sacrificial reducer. The fully reduced bisCuI state is the main active species in solution, with fast kinetics. This new catalytic system is robust for H2O2 production with several cycles achieved and opens up perspectives for integration into devices.
ABSTRACT
We report on the synthesis and structural characterization of the cobalt pentanuclear helicate complex from the rigid tetradentate bis(2-pyridyl)-3,5-pyrazolate ligand bpp-, namely, [{CoII(µ-bpp)3}2CoII3(µ3-OH)]3+ (13+), in which a trinuclear {CoII3(µ3-OH)} core is wrapped by two {CoII(µ-bpp)3} units. The cyclic voltammogram of 13+ in CH3CN revealed seven successive reversible one-electron waves, in the 0 and -3.0 V potential range, highlighting the remarkable stability of such architecture in several redox states. Two mixed-valent states of this complex, the two-electron-oxidized CoII3CoIII2 (15+) and the one-electron-reduced species CoICoII4 (12+), were generated by bulk electrolyses and successfully characterized by single-crystal X-ray diffraction among the eight redox levels between CoI5 and CoII3CoIII2 that can be accessed under electrochemical conditions. Because of the crystallographic characterization of 15+ and 12+, the five reduction processes located at E1/2 values of -1.63 (13+/2+), -1.88 (12+/+), -2.14 (1+/0), -2.40 (10/-), and -2.60 V (1-/2-) versus Ag/AgNO3 were unambiguously assigned to the successive reduction of each of the five Co(II) ions to Co(I), starting with the three ions located in the central core followed by the two apical ions. The two other redox events at E1/2 values of -0.21 (14+/3+) and -0.11 V (15+/4+) are assigned to the successive oxidation of the apical Co(II) ions to Co(III). The Co(I) complexes are rare, and the stabilization of a Co(I) within a trinuclear µ-hydroxo core in the reduced species, 12+, 1+, 10, 1-, and 12-, is probably the result of the particular structure of this complex in the presence of the two apical sites that maintain the trinuclear core through the six bridging bpp- ligands. The spectroscopic characteristics of 12+, 13+, and 15+ (ultraviolet-visible and X-band electron paramagnetic resonance) are also described as well as their magnetic properties in the solid state.
ABSTRACT
Oxyallyl derivatives are typically elusive compounds. Even recently reported "stabilized" 1,3-diaminooxyallyl species are still highly reactive and have short lifetimes at room temperature. Herein, we report the synthesis and preliminary study of mesoionic pyrimidine derivatives that feature 1,3-bis(dimethylamino)oxyallyl patterns with an unprecedented level of stabilization. The latter are not only insensitive towards air and moisture, but they are also compatible with the formation of an ancillary stable N-heterocyclic carbene moiety. As the oxyallyl pattern is proton-responsive, it allows the reversible switching of the electronic properties of the carbene, as a ligand.
ABSTRACT
[Co(bapbpy)Cl]+ (bapbpy: 6,6'-bis(2-aminopyridyl)-2,2'-bipyridine) is a polypyridyl cobalt(II) complex bearing both a redox-active bipyridine ligand and pendant proton relays. This compound catalyzes electro-assisted H2 evolution in DMF with distinct mechanisms depending on the strength of the acid used as the proton source (pKa values ranging from 3.4 to 13.5 in DMF) and the applied potential. Electrochemical studies combining cyclic voltammetry and bulk electrolysis measurements enabled one to bring out four distinct catalytic processes. Where applicable, relevant kinetic information were obtained using either foot-of-the-wave analysis (FOWA) or analytical treatment of bulk electrolysis experiments. Among the different catalytic pathways identified in this study, a clear relationship between the catalyst performances and stability was evidenced. These results draw attention to a number of interesting considerations and may help in the development of future adequately designed catalysts.
ABSTRACT
The superoxide dismutase (SOD) activity of mononuclear NiII complexes, whose structures are inspired by the NiSOD, has been investigated. They have been designed with a sulfur-rich pseudopeptide ligand, derived from nitrilotriacetic acid (NTA), where the three acid functions are grafted with cysteines (L3S). Two mononuclear complexes, which exist in pH-dependent proportions, have been fully characterized by a combination of spectroscopic techniques including 1H NMR, UV-vis, circular dichroism, and X-ray absorption spectroscopy, together with theoretical calculations. They display similar square-planar S3O coordination, with the three thiolates of the three cysteine moieties from L3S coordinated to the NiII ion, together with either a water molecule at physiological pH, as [NiL3S(OH2)]-, or a hydroxo ion in more basic conditions, as [NiL3S(OH)]2-. The 1H NMR study has revealed that contrary to the hydroxo ligand, the bound water molecule is labile. The cyclic voltammogram of both complexes displays an irreversible one-electron oxidation process assigned to the NiII/NiIII redox system with Epa = 0.48 and 0.31 V versus SCE for NiL3S(OH2) and NiL3S(OH), respectively. The SOD activity of both complexes has been tested. On the basis of the xanthine oxidase assay, an IC50 of about 1 µM has been measured at pH 7.4, where NiL3S(OH2) is mainly present (93% of the NiII species), while the IC50 is larger than 100 µM at pH 9.6, where NiL3S(OH) is the major species (92% of the NiII species). Interestingly, only NiL3S(OH2) displays SOD activity, suggesting that the presence of a labile ligand is required. The SOD activity has been also evaluated under catalytic conditions at pH 7.75, where the ratio between NiL3S(OH2)/ NiL3S(OH) is about (86:14), and a rate constant, kcat = 1.8 × 105 M-1 s-1, has been measured. NiL3S(OH2) is thus the first low-molecular weight, synthetic, bioinspired Ni complex that displays catalytic SOD activity in water at physiological pH, although it does not contain any N-donor ligand in its first coordination sphere, as in the NiSOD. Overall, the data show that a key structural feature is the presence of a labile ligand in the coordination sphere of the NiII ion.