Imidazolyl Ring Research Articles

Corrosion inhibition effect of several amino acids on an Al-Zn-Mg-Cu alloy: Electrochemical study, DFT and MD simulation

The corrosion inhibition performance of three amino acids, namely L-Phenylalanine (Phe), L-Methionine (Met) and L-Histidine (His) on 7150 Al alloy in 0.1 M HCl + 1 M NaCl solution was investigated by using electrochemical impedance spectroscopy (EIS), cyclic polarization, DFT and MD simulations. Electrochemical results indicate that all the studied amino acid inhibitors are cathodic type, and the inhibition efficiency follows the following order under all studied temperatures (25, 35 and 45 ℃): His > Met > Phe. A strong correlation between corrosion inhibition efficiency and DFT parameters is not evident, but the adsorption sites (N and O of NH2-COOH-, S atom of Met and two N atoms in the imidazolyl ring of His) can be determined by Fukui indices and Mulliken charges of the local atoms. In addition, MD simulations indicate that corrosion inhibition efficiency increases with the decreasing of adsorption energy.

Spin and dielectric transitions promoted by dimerization of anionic radical stacks and volume-conserving motion of cations in an ion-pair compound.

Demonstrating the mechanism of a structural phase transition (SPT) is significantly important for guiding the precise design of new phase transition materials. Herein, an ion-pair compound [DPIm][Ni(mnt)2] (1, DPIm+ = 1,3-dipropylimidazolium and mnt2- = maleonitriledithiolate) has been obtained and thoroughly characterized through microanalysis, spectral, and thermal analysis techniques. The [Ni(mnt)2]- anions form columnar stacks, featuring one-dimensional (1D) S = ½ spin chains. 1 undergoes an SPT, associated with thermal, magnetic, and dielectric anomalies. The SPT results from the competition between antiferromagnetic (AFM) coupling interactions within anion stacks and elastic deformation of the lattice. The magnetic anomaly arises from changes in the magnetic coupling constant within an anion stack between two phases, while the dielectric anomaly is due to the volume-conserving motion of the imidazolyl ring in the cation. 1 exhibits high-κ characteristics, attributed to the electron polarization of both anions and cations, ion displacement, and dipole orientation polarization of cations. It is also demonstrated that a longer dialkyl chain inhibits the rotational freedom of the imidazolyl ring, resulting in the absence of a plastic crystal state in 1 compared to others containing [Ni(mnt)2]- and dialkylimidazolium.

New vanadium mediated one-pot in situ (L)-histidine based ligand cyclization and aerobic dehydrogenative aromatization

New vanadium mediated in situ cyclization and subsequent aerobic dehydrogenative aromatization of two (L)-histidine based ligands viz. salicylidene-L-histidine and 5-bromosalicylidene-L-histidine have been reported here. Oxidative cyclization resulted from the intra ligand CC bond formation between C(sp2) of (L)-histidine imidazolyl ring and the imine CH. The newly synthesized dioxovanadium(V) complexes of cyclized ligands namely [n-Bu4N][VO2(L1)], 1 (H2L1 = 4-(2-Hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) and [n-Bu4N][VO2(L2)], 2 (H2L2 = 4-(5-Bromo-2-hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) have been characterized by 1H NMR, ESI-HRMS and IR techniques. Further, the structure of complex [n-Bu4N][VO2(L1)], 1 has been determined unambiguously by single crystal X-ray crystallography.

Fabrication of a one‐dimensional copper(I) cyanide bearing 4,4′‐bis(imidazoly)biphenyl) polymer as a recyclable luminescent sensing material for sensitive detection of nitrofurazone

• A new 1D Cu(I)-cyanide coordination polymer (CP) bearing 4,4′-bis(imidazoly)biphenyl synthesized. • The CP forms 2D supramolecular architecture through π•••π interactions exhibited luminescent properties. • The CP used as luminescent sensor to detect antibiotics especially nitrofurazone. A new cyanide-bridged coordination polymer with formula {[C u 1 2 (CN)( bb ) 2 ]·NO 3 ·H 2 O} n ( 1 ) (bb = 4,4′-bis(imidazoly)biphenyl), has been synthesized and characterized by microanalyses, FTIR and single crystal X-ray diffraction. The single crystal X-ray studied indicated that 1 possesses a parallel one-dimensional (1D) chain, which is woven to produce a 2D supramolecular architecture held by π···π interactions between imidazolyl rings and phenyl rings with separation of 3.873 Å and 3.789 Å, respectively. The photoluminescence sensing investigation on 1 revealed that it could be used as a recyclable fluorescent sensor for antibiotics and the polymer offers sensitive and selective detection of nitrofurazone (NFZ), with high K SV value (1.01 × 10 3 M − 1 ) and low detection limit (1.53 ppm). The plausible mechanism using which the CP exhibited sensing of antibiotics has been proposed using theoretical calculations. A new Cu(I)-cyanide coordination polymer synthesized and used as sensor for antibiotics

Rational Design, Chemical Syntheses, and Biological Evaluations of Peripherally Selective Mu Opioid Receptor Ligands as Potential Opioid Induced Constipation Treatment.

Opioid-induced constipation (OIC) is a common adverse effect of opioid analgesics. Peripherally acting μ opioid receptor antagonists (PAMORAs) can be applied in the treatment of OIC without compromising the analgesic effects. NAP, a 6β-N-4-pyridyl-substituted naltrexamine derivative, was previously identified as a potent and selective MOR antagonist mainly acting peripherally but with some CNS effects. Herein, we introduced a highly polar aromatic moiety, for example, a pyrazolyl or imidazolyl ring to decrease CNS MPO scores in order to reduce passive BBB permeability. Four compounds 2, 5, 17, and 19, when administered orally, were able to increase intestinal motility during morphine-induced constipation in the carmine red dye assays. Among them, compound 19 (p.o.) improved GI tract motility by 75% while orally administered NAP and methylnaltrexone showed no significant effects at the same dose. Thus, this compound seemed a promising agent to be further developed as an oral treatment for OIC.

New fac-[ReI(CO)3(Ltri)]Y complexes of linear N,N′,N′′-tridentate ligands (Ltri) with terminal imidazolyl or pyridyl ring (N and N′′) and central tertiary sulfonamide (N′) N-donors. Effects of size and substituents of the terminal N-donor rings and the rarely found direct sulfonamide N to metal bond

fac-[Re(CO)3Ltri]Y (Y = ClO4- or PF6-) complexes were prepared with N,N',N''-donor tridentate ligands (Ltri), N(SO2R)1,1′-Me2dma and N(SO2R)Mendpa (R = Me or Tol). The two new N(SO2R)1,1′-Me2dma ligands are derivatives of the parent ligand, N(H)1,1′-Me2dma (bis(1-methyl-2-methylimidazolyl)amine), by having the central N within a tertiary sulfonamide group instead of a secondary amine group. In addition to having a tertiary sulfonamide group, the N(SO2R)Mendpa ligands differ from the parent ligand, N(H)dpa (2-picolylamine), by having Me groups at the 6,6′- (n = 2) or 3,3′,5,5′- (n = 4) positions of the pyridyl rings. Ltri is facially coordinated with a Re—N' (sulfonamide N) bond of normal length. Only the Ltri = N(SO2R)6,6′-Me2dpa complexes exhibit ligand dissociation over time in DMSO‑d6, a finding attributable to Re—N and Re—N'' bond weakening caused by the steric effect of the pyridyl 6,6′-Me groups projecting toward the coordination sphere, while the Ltri = N(SO2R)1,1′-Me2dma and N(SO2R)3,3′,5,5′-Me4dpa complexes are indefinitely robust in solution. In contrast to the similar behavior of fac-[Re(CO)3Ltri]Y complexes for Ltri = N(SO2R)1,1′-Me2dma and N(SO2R)3,3′,5,5′-Me4dpa, only the latter dissociates over time in DMSO‑d6 for [Pt(“Ltri”)Cl2] complexes (unpublished), where the sulfonamide N in “Ltri” is not bound, forming a rare 8-membered chelate ring. On the basis of NMR and X-ray crystallographic data, we attribute the high robustness of [Pt(N(SO2R)1,1'-Me2dma)Cl2] mainly to the presence of the terminal N imidazolyl donors. The smaller imidazolyl moieties for Ltri = N(SO2R)1,1'-Me2dma (relative to the pyridyl rings in the dpa ligands) make dma ligands a better platform for developing fac-[99mTc(CO)3Ltri]Y diagnostic agents and also most probably for developing Pt(II) anticancer drugs.

To Be, or Not to Be, an Inhibitor: A Comparison of Azole Interactions with and Oxidation by a Cytochrome P450 Enzyme.

The cytochrome P450 (CYP) superfamily of heme monooxygenases is involved in a range of important chemical biotransformations across nature. Azole-containing molecules have been developed as drugs that bind to the heme center of these enzymes, inhibiting their function. The optical spectrum of CYP enzymes after the addition of these inhibitors is used to assess how the molecules bind. Here we use the bacterial CYP199A4 enzyme, from Rhodopseudomonas palustris HaA2, to compare how imidazolyl and triazolyl inhibitors bind to ferric and ferrous heme. 4-(Imidazol-1-yl)benzoic acid induced a red shift in the Soret wavelength (424 nm) in the ferric enzyme along with an increase and a decrease in the intensities of the δ and α bands, respectively. 4-(1H-1,2,4-Triazol-1-yl)benzoic acid binds to CYP199A4 with a 10-fold lower affinity and induces a smaller red shift in the Soret band. The crystal structures of CYP199A4 with these two inhibitors confirmed that these differences in the optical spectra were due to coordination of the imidazolyl ligand to the ferric Fe, but the triazolyl inhibitor interacts with, rather than displaces, the ferric aqua ligand. Additional water molecules were present in the active site of 4-(1H-1,2,4-triazol-1-yl)benzoic acid-bound CYP199A4. The space required to accommodate these additional water molecules in the active site necessitates changes in the position of the hydrophobic phenylalanine 298 residue. Upon reduction of the heme, the imidazole-based inhibitor Fe-N ligation was not retained. A 5-coordinate heme was also the predominant species in 4-(1H-1,2,4-triazol-1-yl)benzoic acid-bound ferrous CYP199A4, but there was an obvious shoulder at 447 nm indicative of some degree of Fe-N coordination. Rather than inhibit CYP199A4, 4-(imidazol-1-yl)benzoic acid was a substrate and was oxidized to generate a metabolite derived from ring opening of the imidazolyl ring: 4-[[2-(formylamino)acetyl]amino]benzoic acid.

Homoleptic Mononuclear Tris‐Chelate Complexes of FeII, CoII, NiII, and ZnII Based on a Redox‐Active Imidazolyl‐2‐thione Ligand: Structural and Electrochemical Correlation

Five mononuclear tris‐chelate complexes of FeII, CoII, NiII and ZnII, containing the bidentate ligand 3‐methyl‐1‐(2‐pyridyl)imidazolyl‐2‐thione (L), have been synthesised and characterised, namely [MII(L)3](BF4)2, where M = Fe (1), Co (2), Ni (3) and Zn (4), and [FeII(L)3](PF6)2 {1‐(PF6)2}. The complexes have been characterised by standard methods and single‐crystal X‐ray diffraction, showing that all the complexes are isostructural and isomorphs, crystallising in the P1 space group, except for 1‐(PF6)2, which crystallises in the P21/c, as expected due to the different size and symmetry of the anion. The metal centre is found in a distorted meridional‐N3S3 octahedral geometry. In all the complexes, two ligand strands within the same complex cation unit interact via an almost perfect face‐to‐face π–π stacking. The double intramolecular interaction occurs between a pyridyl ring of one ligand strand and an imidazolyl ring of a second ligand strand and vice versa. The FeII and CoII complexes, 1 and 2, are stabilised in the high spin state, based on the bond lengths and angles obtained by SC‐XRD and by VT‐magnetic studies in the solid state and NMR Evans method in CD3CN solution. The cyclic voltammetry behaviour for compounds 1–4 showed an EC mechanism for the oxidation process, in which two ligand strands are electrochemically oxidised, instead of the metal centre, followed by a chemical process (de‐coordination and dimerisation). Whereas, the reduction process involved metal electrodeposition for the FeII, NiII and ZnII complexes. In the case of the CoII complex, the voltammetric response suggested a multistep decomposition process during the electrochemical reduction. Finally, a linear correlation between the oxidation potential of the ligand and the average M–N bond length has been found, permitting the modification of the oxidation potential by selection of the metal centre.

Anion-directed assembly of three cationic silver(I) coordination polymers with bis(imidazolyl)-based linker: Structural characterization and anion exchange study

Three cationic silver(I) coordination polymers, namely {[Ag2(μ-bib)3](SO3CF3)2·(CH3CN)}n (1), {[Ag(μ-bib)](NO3)·(H2O)}n (2), and {[Ag(μ-bib)]BF4}n (3), have been prepared using flexible bis(imidazolyl)butane (bib) ligand and silver salts of different anions. All compounds are characterized by FT-IR, PXRD, elemental analysis, and single-crystal X-ray diffraction. Compound 1, containing triflate (SO3CF3−) anions, exhibits a two dimensional 63-hcb network with an amazing ABCDEF packing mode of the single hexagonal layers. Compound 2, containing nitrate ions, forms a simple one dimensional wavy chain, while compound 3 with BF4− anions, shows a double helix DNA-shaped structure stabilized by Ag⋯Ag interactions between the two strands. The anions in the structures 1–3 are non-coordinating and participate in weak H-bonding, while imidazolyl rings are involved in π⋯π stacking interactions. Anion exchange experiments in aqueous solution, monitored by FT-IR and PXRD analyses, reveal interesting structural transformations.

Homo- and Heteropolymetallic Complexes of the Hybrid, Ambidentate N-Heterocyclic Carbene Ligand IMes-acac.

The anionic 5-acetylimidazol-2-ylidene-4-olate 1–, named as “IMes-acac”, is composed of fused diaminocarbene and acetylacetonato units in the same IMes-based imidazolyl ring. The bifunctional compound 1– is shown to act as an effective, ditopic bridging ligand for transition metal centers. Several new complexes supported by this ligand were prepared, including the complex [RuCl(p-Cym)(κ2O,O–1·H)](BF4) (2), which can be regarded as a metallated imidazolium salt, the homobimetallic complex [((COD)Rh)(RhCl(COD))(μ-1κ2O,O:2κ1C–1)] (4), the heterobimetallic complexes [((p-Cym)ClRu)(RhCl(COD))(μ-1κ2O,O:2κ1C–1)] (3), [((p-Cym)ClRu)(RhCl(CO)2)(μ-1κ2O,O:2κ1C–1)] (5), [((p-Cym)ClRu)(Cu(IPr))(μ-1κ2O,O:2κ1C–1)] (9), the anionic homoleptic Cu(I) complexes [Cu(κ1C–1)2]K ([10]K) and [Cu(κ1C–1)2](NEt4) ([10](NEt4)), and the heterotrimetallic complex [((p-Cym)RuCl)2(Cu)(μ-1κ2O,O:3κ1C–1)(μ-2κ2O,O:3κ1C–1)](PF6) (11). Preliminary studies on the possible preparation of supramolecular metallopolymers and electrochemical studies on the series of complexes are also reported.

Selective Synthesis of Site-Differentiated Fe4S4 and Fe6S6 Clusters.

Obtaining rational control over the structure and nuclearity of metalloclusters is an ongoing challenge in synthetic Fe-S cluster chemistry. We report a new family of tridentate imidazolin-2-imine ligands L(NImR)3 that can bind [Fe4S4]2+ or [Fe6S6]3+ clusters, depending on the steric profile of the ligand and the reaction stoichiometry. A high-yielding synthetic route to L(NImR)3 ligands (where R is the imidazolyl N substituents) from trianiline and 2-chloroimidazolium precursors is described. For L(NImMe)3 (tris(1,3,5-(3-( N, N-dimethyl-4,5-diphenylimidazolin-2-imino)phenylmethyl))benzene), metalation with 1 equiv of [Ph4P]2[Fe4S4Cl4] and 3 equiv of NaBPh4 furnishes a mixture of products, but adjusting the stoichiometry to 1.5 equiv of [Ph4P]2[Fe4S4Cl4] provides (L(NImMe)3)Fe6S6Cl6 in high yield. Formation of an [Fe6S6]3+ cluster using L(NImTol)3 (tris(1,3,5-(3-( N, N-bis(4-methylphenyl)-4,5-diphenylimidazolin-2-imino)phenylmethyl))benzene) is not observed; instead, the [Fe4S4]2+ cluster [(L(NImTol)3)(Fe4S4Cl)][BPh4] is cleanly generated when 1 equiv of [Ph4P]2[Fe4S4Cl4] is employed. The selectivity for cluster nuclearity is rationalized by the orientation of the imidazolyl rings whereby long N-imidazolyl substituents preclude formation of [Fe6S6]3+ clusters but not [Fe4S4]2+ clusters. Thus, the structure and nuclearity of L(NImR)3-bound Fe-S clusters may be selectively controlled through rational modification the ligand's substituents.

Unveiling the redox-active character of imidazolin-2-thiones derived from amino-substituted N-heterocyclic carbenes.

IMes-derived thioureas in which the imidazolyl ring is directly substituted by one or two dimethylamino groups are redox-active, exhibiting one and two oxidized states, respectively. The structure, stability, and electronics of the oxidized species are investigated, emphasizing the decisive role of the amino substituents.

(Aminomethylene)phosphonate Analogues as ZnII Chelators: Synthesis and Characterization

A series of (aminomethylene)phosphonate (AMP) analogues, 8–14, bearing one or two heterocyclic moieties (imidazolyl, pyridyl, and thiazolyl) on the aminomethylene group, were synthesized as potential ZnII chelators. The complexes of analogues 8–14 with ZnII ions were characterized by their stoichiometry, geometry, coordination sites, acid/base equilibria, and stability constants. Analogues 8–14 form stable water‐soluble 2:1 L/ZnII complexes, as established by ZnII titration, monitored by UV/Vis spectrophotometry and by 1H and 31P NMR spectroscopy. Acidity and stability constants were established for each derivative by potentiometric pH titrations. ML2 type ZnII complexes of AMP, bearing either an imidazolyl or pyridyl moiety, 8, 10, and 12, exhibit high log β values (17.68, 16.92, and 16.65, respectively), while for the AMP‐thiazolyl (14) complex with ZnII, log β is 12.53. Generally, ligands 9, 11, and 13, bearing two heterocyclic moieties, present higher log β values (22.25, 21.00, and 18.28, respectively) vs. analogues bearing one heterocyclic moiety. Additionally, based on 1H, 13C, and 31P NMR spectroscopic data, we propose a structure of the AMP‐(Im)2‐ZnII complex in solution, where the ZnII coordination sites involve the phosphonate moiety and both imidazolyl rings of the two binding molecules, forming an octahedral geometry around the ZnII ion. In summary, we propose a new family of water‐soluble high‐affinity ZnII chelators, in particular AMP‐(Im)2, which forms the most stable complex (log β 22).

Threading the needle: guest transport in a versatile 0D porous molecular crystal.

Porous host crystals of the metallocycle [Cu2(1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene)2Cl4]·2CH3OH are permeable to a series of small organic guests despite their lack of permanent channels. It is inferred from single crystal X-ray diffraction that transport of the guest molecules is facilitated by "flapping" of the imidazolyl rings.

Au-complex containing phosphino and imidazolyl moieties as a bi-functional catalyst for one-pot synthesis of pyridine derivatives

The complex of Au-L1 containing imidazolyl ring and the phosphine-ligated-Au moiety was synthesized and applied as the efficient bi-functional catalyst for the one-pot sequential condensation/annulation reaction for the synthesis of pyridine derivatives. It was found that, as for Au-L1, the involved imidazolyl group acted as a Lewis base to catalyze the condensation of carbonyl compounds with propargylamine to form the imino intermediate, and the involved Au+-complex species with alkynophilicity corresponded to the subsequent activation of imino-tailed alkynyl to afford dehydropyridine intermediate. The latter proceeded auto-oxidation reaction to afford the pyridine derivatives. The observed sequential catalysis over Au-L1 proved more efficient than that over the mechanical mixtures of the Au-complex (Au-L2) and N-methylimidazole, because the free N-methylimidazole as an N-containing donor competed with the alkyne substrate to coordinate to Au-center. Moreover, Au-L1 exhibited good generality to a wide range of the substrates for the synthesis of 2,3-fused pyridine derivatives and 2-aryl(heteroaryl)-substituted pyridines.

Crystal structure of a one-dimensional looped-chain silver(I) coordination polymer: catena-poly[[silver(I)-bis-{μ-4-[1-(5'-isopropyl-[1,1':3',1''-terphen-yl]-2'-yl)-1H-imidazol-2-yl]pyridine-κ(2) N:N'}] nitrate methanol monosolvate monohydrate

In the title compound, {[Ag(C29H25N3)2]NO3·CH3OH·H2O} n , the Ag(I) cation is four-coordinated by two pyridine N atoms and two imidazole N atoms from four individual 4-(1-(5'-isopropyl-[1,1':3',1''-terphen-yl]-2'-yl)-1H-imidazol-2-yl)pyridine (i-pro-pyim) ligands. This gives rise to a highly distorted tetra-hedral geometry with bond angles falling in the range 100.33 (19)-122.76 (19)°. Two crystallographically independent i-pro-pyim ligands (A and B) adopt very similar conformations to one another, such that the dihedral angles between the pyridyl and imidazolyl rings in the two ligands are 40.7 (3) and 42.2 (3)°, respectively. Each i-pro-pyim ligand binds two symmetry-related Ag(+) cations, leading to the formation of 14-membered cyclic dimers, in which the Ag(I) atoms are separated by 6.963 (2) Å for the Ag-A 2-Ag dimer and 7.020 (2) Å for Ag-B 2-Ag. These cyclic dimers are alternately connected to each other by sharing Ag(I) atoms, resulting in the formation of a looped-chain structure extending along the [100] direction. Moreover, adjacent looped chains are connected by inter-molecular π-π inter-actions [centroid-to-centroid distance = 3.689 (4) Å], giving rise to the formation of a two-dimensional supra-molecular network propagating parallel to (110). Several inter-molecular C-H⋯O and O-H⋯O hydrogen bonds further contribute to the stabilization of the crystal structure.

Observation of novel dielectric bistability in a nickel-dithiolene ion-pair compound

An ion-pair compound, 1,10-bis(1-methylimidazolium)decane bis(maleonitriodithiolato)nickelate (1), was synthesized and single crystal structurally characterized. The bis(maleonitriodithiolato)nickelate anions and dication formed the layered stacks in the crystal. A dielectric relaxation was observed in low-frequency region and could be attributed to local dipole or molecular motion in 1. The relaxation process for 1 was fitted using Cole–Cole model function. Furthermore, this ion-pair compound shows novel dielectric bistability and dielectric phase transition around 90°C, which is probably arise from the disorder-to-order transformation of alkyl chains and the conformation rotation of imidazolyl rings. This study provided a new strategy for the design of dielectric bistable system.

CNC-Pincer Rare-Earth Metal Amido Complexes with a Diarylamido Linked Biscarbene Ligand: Synthesis, Characterization, and Catalytic Activity

In preparation of CNC-pincer rare-earth metal amido complexes with a diarylamido linked biscarbene ligand, it is found that conditions have a key influence on final products. Reaction of a THF suspension of bis[2-(3-benzylimidazolium)-4-methylphenyl]amine dichlorides (H3LCl2) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Yb, Eu, Sm) in THF at room temperature afforded the only unexpected fused-heterocyclic compound 8,9-dibenzyl-3,14-dimethyl-8a,9-dihydro-8H-benzo[4,5]imidazo[2′,1′:2,3]imidazo[1,2-a]imidazo[2,1-c]quinoxaline (1) containing an imidazolyl ring and a piperidyl ring, which formed through carbene C–C and C–N coupling. However, the reaction of H3LCl2 with [(Me3Si)2N]3Er(μ-Cl)Li(THF)3 in toluene afforded the CNC-pincer erbium amido complex incorporating a diarylamido linked biscarbene ligand LEr[N(SiMe3)2]2 (2) in low yield and the above fused-heterocyclic compound 1. The stepwise reaction of H3LCl2 with strong bases (n-BuLi or LiCH2SiMe3) in THF for 4 h, followed by treatment with [(Me3Si)2N]3RE(μ-Cl)...

The formation of peroxide degradation products of photochromic triphenylimidazolyl radical-dimers

Following the recent report of Abe and co-workers (Phys. Chem. Chem. Phys., 2012, 14, 5855) of the isolation of a bridging peroxide of a naphthalene-tethered bisimidazolyl diradical, it is reported herein that this degradation pathway is a more general phenomenon for the chromic dimers of 2,4,5-triphenylimidazolyl radical (TPIR) materials, with non-tethered TPIRs forming similar oxygen adducts. The peroxides of two derivatives have been characterised by single crystal X-ray diffraction (SC-XRD) and it is identified that the 4-position of the imidazolyl ring is the site susceptible to reaction with oxygen. Furthermore, mass spectrometry has been used to show that for a range of five known, non-tethered derivatives, peroxide formation can be detected within 30 minutes when samples are irradiated under an oxygen atmosphere, thus presenting a significant challenge to the long term use of this class of material in colour-switching device applications.

A switching cascade of hydrazone-based rotary switches through coordination-coupled proton relays

Imidazole, a subunit of histidine, plays a crucial role in proton-relay processes that are important for various biological activities, such as metal efflux, viral replication and photosynthesis. We show here how an imidazolyl ring incorporated into a rotary switch based on a hydrazone enables a switching cascade that involves proton relay between two different switches. The switching process starts with a single input, zinc(II), that initiates an E/Z isomerization in the hydrazone system through a coordination-coupled proton transfer. The resulting imidazolium ring is unusually acidic and, through proton relay, activates the E/Z isomerization of a non-coordinating pyridine-containing hydrazone switch. We hypothesize that the reduction in the acid dissociation constant of the imidazolium ring results from a combination of electrostatic and conformational effects, the study of which might help elucidate the proton-coupled electron-transfer mechanism in photosynthetic bacteria.