Biological labelling reagents and probes derived from luminescent transition metal polypyridine complexes

A Dinuclear Osmium(II) Complex Near-Infrared Nanoscopy Probe for Nuclear DNA

With the aim of developing photostable near-infrared cell imaging probes, a convenient route to the synthesis of heteroleptic Os^II complexes containing the Os(TAP)₂ fragment is reported. This method was used to synthesize the dinuclear Os^II complex, [{Os(TAP)₂}₂tpphz]⁴⁺ (where tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2''-h:2‴,3'''-j]phenazine and TAP = 1,4,5,8- tetraazaphenanthrene). Using a combination of resonance Raman and time-resolved absorption spectroscopy, as well as computational studies, the excited state dynamics of the new complex were dissected. These studies revealed that, although the complex has several close lying excited states, its near-infrared, NIR, emission (λ_max = 780 nm) is due to a low-lying Os → TAP based ³MCLT state. Cell-based studies revealed that unlike its Ru^II analogue, the new complex is neither cytotoxic nor photocytotoxic. However, as it is highly photostable as well as live-cell permeant and displays NIR luminescence within the biological optical window, its properties make it an ideal probe for optical microscopy, demonstrated by its use as a super-resolution NIR STED probe for nuclear DNA.

Nanoparticles Functionalised with Re(I) Tricarbonyl Complexes for Cancer Theranostics

Globally, cancer is the second (to cardiovascular diseases) leading cause of death. Regardless of various efforts (i.e., finance, research, and workforce) to advance novel cancer theranostics (diagnosis and therapy), there have been few successful attempts towards ongoing clinical treatment options as a result of the complications posed by cancerous tumors. In recent years, the application of magnetic nanomedicine as theranostic devices has garnered enormous attention in cancer treatment research. Magnetic nanoparticles (MNPs) are capable of tuning the magnetic field in their environment, which positively impacts theranostic applications in nanomedicine significantly. MNPs are utilized as contrasting agents for cancer diagnosis, molecular imaging, hyperfusion region visualization, and T cell-based radiotherapy because of their interesting features of small size, high reactive surface area, target ability to cells, and functionalization capability. Radiolabelling of NPs is a powerful diagnostic approach in nuclear medicine imaging and therapy. The use of luminescent radioactive rhenium(I), 188/186Re, tricarbonyl complexes functionalised with magnetite Fe3O4 NPs in nanomedicine has improved the diagnosis and therapy of cancer tumors. This is because the combination of Re(I) with MNPs can improve low distribution and cell penetration into deeper tissues.

Role of the ancillary ligand in controlling the lysozyme affinity and electronic properties of terpyridine fac-Re(CO)3 complexes

The lysozyme binding affinity and the electronic properties of [ReX(CO)3(terpy-κ2N1,N2)] (X = Br- and triazolateCOOCH2CH3,CF3) were reported. The triazolate complex was prepared in a [3 + 2] cycloaddition click reaction. The bromo compound reacted with lysozyme affording adducts with Re(CO)3+ fragments, while the triazolate compound persisted. A red shift of the MLCT band of the triazolate compound in progressively less polar solvents may be due to the negative solvatochromism.

Tricarbonyl triazolato Re(i) compounds of pyridylbenzimidazole ligands: spectroscopic and antimicrobial activity evaluation

Catalyst-free [3+2] cycloaddition coupling between [Re_n(N₃)_n(CO)_3nL] (n = 1, L = 1-ethyl-2-(pyridin-2-yl)benzimidazole (L¹) and n = 2, L = 1,1′-(hexane-1,6-diyl)bis[2-(pyridin-2-yl)-1H-benzimidazole] (L²)) and dimethyl acetylene dicarboxylate (DMAD) afforded mono- and binuclear triazolate complexes. Spectroscopic data presented unambiguous evidence for isomerization of the kinetically formed N(1) bound triazolate isomer into the N(2) analogue. The solvatochromism properties were assessed by UV/Vis spectroscopy with the aid of time dependent density functional theory calculations. The free ligands and their tricarbonyl triazolato Re(i) complexes were screened for their potential antimicrobial activity against different bacterial and fungal pathogens.

The antimicrobial activity and solvatochromism properties of mono- and binuclear tricarbonyl triazolato Re(i) complexes of pyridylbenzimidazole, formed by catalyst-free [3+2] cycloaddition reaction, were examined.

Dinuclear Rhenium Complexes with a Bridging Helicene-bis-bipyridine Ligand: Synthesis, Structure, and Photophysical and Chiroptical Properties

By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO)3 Cl}2 (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10-3 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

Triazole-based osmium(ii) complexes displaying red/near-IR luminescence: antimicrobial activity and super-resolution imaging

Cellular uptake, luminescence imaging and antimicrobial activity against clinically relevant methicillin-resistant S. aureus (MRSA) bacteria are reported. The osmium(ii) complexes [Os(N^N)3]2+ (N^N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (1 2+); 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2 2+); 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3 2+)) were prepared and isolated as the chloride salts of their meridional and facial isomers. The complexes display prominent spin-forbidden ground state to triplet metal-to-ligand charge transfer (3MLCT) state absorption bands enabling excitation as low as 600 nm for fac/mer-3 2+ and observation of emission in aqueous solution in the deep-red/near-IR regions of the spectrum. Cellular uptake studies within MRSA cells show antimicrobial activity for 1 2+ and 2 2+ with greater toxicity for the meridional isomers in each case and mer-1 2+ showing the greatest potency (32 μg mL-1 in defined minimal media). Super-resolution imaging experiments demonstrate binding of mer- and fac-1 2+ to bacterial DNA with high Pearson's colocalisation coefficients (up to 0.95 using DAPI). Phototoxicity studies showed the complexes exhibited a higher antimicrobial activity upon irradiation with light.

Mononuclear ruthenium(ii) theranostic complexes that function as broad-spectrum antimicrobials in therapeutically resistant pathogens through interaction with DNA

Six luminescent, mononuclear ruthenium(ii) complexes based on the tetrapyridophenazine (tpphz) and dipyridophenazine (dppz) ligands are reported. The therapeutic activities of the complexes against Gram-negative bacteria (E. coli, A. baumannii, P. aeruginosa) and Gram-positive bacteria (E. faecalis and S. aureus) including pathogenic multi- and pan-drug resistant strains were assessed. Estimated minimum inhibitory and bactericidal concentrations show the activity of the lead compound is comparable to ampicillin and oxacillin in therapeutically sensitive strains and this activity was retained in resistant strains. Unlike related dinuclear analogues the lead compound does not damage bacterial membranes but is still rapidly taken up by both Gram-positive and Gram-negative bacteria in a glucose independent manner. Direct imaging of the complexes through super-resolution nanoscopy and transmission electron microscopy reveals that once internalized the complexes' intracellular target for both Gram-negative and Gram-positive strains is bacterial DNA. Model toxicity screens showed the compound is non-toxic to Galleria mellonella even at exposure concentrations that are orders of magnitude higher than the bacterial MIC.

Electron Transfer in Nitrogenase

Nitrogenase is the only enzyme capable of reducing N2 to NH3. This challenging reaction requires the coordinated transfer of multiple electrons from the reductase, Fe-protein, to the catalytic component, MoFe-protein, in an ATP-dependent fashion. In the last two decades, there have been significant advances in our understanding of how nitrogenase orchestrates electron transfer (ET) from the Fe-protein to the catalytic site of MoFe-protein and how energy from ATP hydrolysis transduces the ET processes. In this review, we summarize these advances, with focus on the structural and thermodynamic redox properties of nitrogenase component proteins and their complexes, as well as on new insights regarding the mechanism of ET reactions during catalysis and how they are coupled to ATP hydrolysis. We also discuss recently developed chemical, photochemical, and electrochemical methods for uncoupling substrate reduction from ATP hydrolysis, which may provide new avenues for studying the catalytic mechanism of nitrogenase.

Responsive ruthenium complex probe for phosphorescence and time-gated luminescence detection of bisulfite

Sensitive and selective quantification of specific analytes is of great significance in analytical and environmental sciences, as well as in the food industry. Herein, we report the design, synthesis, characterization, and application of a responsive ruthenium(ii) complex probe, Ru-azo, for phosphorescence and time-gated luminescence (TGL) detection of bisulfite, an important additive in the food industry. Upon a specific nucleophilic addition reaction between bisulfite and the azo group of Ru-azo, a new ruthenium(ii) complex, Ru-SO3, was obtained, which resulted in a remarkable increase in phosphorescence intensity, allowing the bisulfite detection to be achieved. In addition, long-lived emissions of Ru-azo (τ = 258 ns) and Ru-SO3 (τ = 261 ns) also enabled the TGL detection of bisulfite in autofluorescence-rich food samples. Through theoretical computations, the photoinduced electron transfer (PET) process within the ruthenium(ii) complex was validated, which unveiled the rationality of the luminescence "off-on" response of Ru-azo to bisulfite. The probe showed advantages of good water solubility, and high sensitivity, selectivity and accuracy for responding to bisulfite, facilitating its application in phosphorescence and TGL detection of bisulfite in aqueous and food samples.

Light-driven electron injection from a biotinylated triarylamine donor to [Ru(diimine)3](2+)-labeled streptavidin

Electron transfer from a biotinylated electron donor to photochemically generated Ru(iii) complexes covalently anchored to streptavidin is demonstrated by means of time-resolved laser spectroscopy. Through site-selective mutagenesis, a single cysteine residue was engineered at four different positions on streptavidin, and a Ru(ii) tris-diimine complex was then bioconjugated to the exposed cysteines. A biotinylated triarylamine electron donor was added to the Ru(ii)-modified streptavidins to afford dyads localized within a streptavidin host. The resulting systems were subjected to electron transfer studies. In some of the explored mutants, the phototriggered electron transfer between triarylamine and Ru(iii) is complete within 10 ns, thus highlighting the potential of such artificial metalloenzymes to perform photoredox catalysis.

Sensitive determination of lysozyme by using a luminescent and colorimetric probe based on the aggregation of gold nanoparticles induced by an anionic ruthenate(II) complex

The negatively charged ruthenate(II) complex [Ru(bpy)(PPh₃)(CN)₃]^- and gold nanoparticles (AuNPs) were used for detecting lysozyme (LYS). The luminescence of the ruthenate(II) complex is quenched by AuNPs, and this induces the aggregation of AuNPs and a color change from red to blue. After addition of lysozyme, the positively charged lysozyme and the negatively charged ruthenate(II) complex bind each other by electrostatic interaction firstly. This prevents AuNPs from aggregation and quenches the emission of the ruthenate(II) complex. Its luminescence and the degree of aggregation of the AuNPs can be used to quantify LYS. The fluorometric calibration plot is linear in the 0.01 to 0.20 μM LYS concentration range, and the calibration plot is linear between 0.02 and 0.20 μM of LYS. The color of the solution can be easily distinguished by bare eyes at 0.08 μM or higher concentration of LYS. The applicability of the method was verified by the correct analysis of LYS in chicken egg white. Graphical abstract Schematic of a luminometric and colorimetric probe based on the induced aggregation of gold nanoparticles by an anionic luminescent ruthenate(II) complex or sensitive lysozyme detection.

Efficient green phosphorescent Ir(iii) complexes with β-diketonate ancillary ligands

Three new iridium complexes with β-diketonate ancillary ligands were synthesized as emissive materials for organic light-emitting devices.

Streptavidin as a Scaffold for Light-Induced Long-Lived Charge Separation

Long-lived photo-driven charge separation is demonstrated by assembling a triad on a protein scaffold. For this purpose, a biotinylated triarylamine was added to a Ru^II -streptavidin conjugate bearing a methyl viologen electron acceptor covalently linked to the N-terminus of streptavidin. To improve the rate and lifetime of the electron transfer, a negative patch consisting of up to three additional negatively charged amino acids was engineered through mutagenesis close to the biotin-binding pocket of streptavidin. Time-resolved laser spectroscopy revealed that the covalent attachment and the negative patch were beneficial for charge separation within the streptavidin hosted triad; the charge separated state was generated within the duration of the excitation laser pulse, and lifetimes up to 3120 ns could be achieved with the optimized supramolecular triad.

Methylation of Ir(iii)-tetrazolato complexes: an effective route to modulate the emission outputs and to switch to antimicrobial properties

Two neutral cyclometalated Ir(iii)-tetrazolato complexes that differ by variations of the substituents on either the phenylpyridine or the tetrazolate ligand have been converted into the corresponding methylated and cationic analogues. NMR (¹H and ¹³C) characterization of the Ir(iii) complexes provided the results in agreement with the chemo- and regioselective character of methylation at the N-3 position of the Ir(iii)-coordinated tetrazolato ring. This evidence was further corroborated by the analysis of the molecular structures of the cationic complexes obtained by X-ray diffraction. In view of the photophysical properties, the addition of a methyl moiety to neutral Ir(iii) tetrazolates, which behave as sky-blue or orange phosphors, caused a systematic red shift of their phosphorescence output. The transformation of neutral Ir(iii) tetrazolates into cationic Ir(iii)-tetrazole complexes was screened for any eventual antimicrobial activity in vitro against Gram negative (E. coli) and Gram positive (D. radiodurans) microorganisms. While both kinds of complexes were not active against E. coli, the conversion of the neutral Ir(iii) tetrazolates into the corresponding methylated and cationic Ir(iii)tetrazole derivatives determined the turn-on of a good to excellent antimicrobial activity toward Gram positive Deinococcus radiodurans, a non-pathogenic bacterium that is listed as one of the toughest microorganisms in light of its outstanding resistance to radiation and oxidative stress.

Long-Lived Polypyridyl Based Mononuclear Ruthenium Complexes: Synthesis, Structure, and Azo Dye Decomposition

Two mononuclear ruthenium complexes [(bpy)₂Ru^IIL₁/L₂](ClO₄)₂ ([1]²⁺/[2]²⁺) (bpy-2,2' bipyridine, L₁ = 2,3-di(pyridin-2-yl)pyrazino[2,3-f][1,10]phenanthroline) and L₂ = 2,3-di(thiophen-2-yl)pyrazino[2,3-f][1,10]phenanthroline have been synthesized. The complexes have been characterized using various analytical techniques. The complex [1]²⁺ has further been characterized by its single crystal X-ray structure suggesting ruthenium is coordinating through the N donors of phenanthroline end. Theoretical investigation suggests that the HOMOs of both complexes are composed of pyridine and pyrazine unit of ligands L₁ and L₂ whereas the LUMOs are formed by the contribution of bipyridine units. The low energy bands at ∼480 nm of the complexes can be assigned as MLCT with partial contribution from ligand transitions, whereas the rest are ligand centered. The complexes have shown Ru^II/Ru^III oxidation couples at E_1/2 at 1.26 (70 mV) V and 1.28 (62 mV) V for [1]²⁺ and [2]²⁺ vs Ag/AgCl, respectively, suggesting no significant role of distal thiophene or pyridine units of the ligands. The complexes are emissive and display solvent dependent emission properties. Both complexes have shown highest emission quantum yield and lifetime in DMSO (ϕ = 0.05 and τ_avg = 460 ns and λ_max^em at 620 nm for [1]²⁺; ϕ = 0.043 and τ_avg = 425 ns and λ_max^em at 635 nm for [2]²⁺). Further, the long luminescent lifetime of these complexes has been utilized to generate reactive oxygen species for efficient azo dye decomposition.

Luminescent Re(I) Carbonyl Complexes as Trackable PhotoCORMs for CO delivery to Cellular Targets

A family of Re(I) carbonyl complexes of general formula [ReX(CO)3(phen)]0/1+ (where X = Cl-, CF3SO3-, MeCN, PPh3, and methylimidazole) derived from 1,10-phenanthroline (phen) exhibits variable emission characteristics depending on the presence of the sixth ancillary ligand/group (X). All complexes but with X = MeCN exhibit moderate CO release upon irradiation with low-power UV light and are indefinitely stable in anaerobic/aerobic environment in solution as well as in solid state when kept under dark condition. These CO donors liberate three, one, or no CO depending on the nature of sixth ligand upon illumination as studied with the aid of time-dependent IR spectroscopy. Results of excited-state density functional theory (DFT) and time-dependent DFT calculations provided insight into the origin of the emission characteristics of these complexes. The luminescent rheinum(I) photoCORMs uniformly displayed efficient cellular internalization by the human breast adenocarcinoma cells, MDA-MB-231, while the complex with PPh3 as ancillary ligand showed moderate nuclear localization in addition to the cytosolic distribution. These species hold significant promise as theranostic photoCORMs (photoinduced CO releasing molecules), where the entry of the pro-drug can be tracked within the cellular matrices.

Synthesis and characterization of green-emitting Ir(iii) complexes based on a functionalized benzimidazole ligand

Two new Ir(iii) complexes containing a functionalized benzimidazole ligand (L) were successfully synthesized for use in green phosphorescent organic light-emitting diodes.

Pyridylpyrazole N^N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(iii) complexes and solution-processable PhOLEDs

A blue phosphorescent emitter for PhOLEDs with brightness of 5400 cd m⁻² at 10 V and λELmax 460 nm, CIE_x,y (0.15, 0.21).

A luminescent and colorimetric probe based on the functionalization of gold nanoparticles by ruthenium(ii) complexes for heparin detection

A colorimetric and luminescent bifunctional Ru(ii) complex-modified gold nanoprobe for the sensing of heparin in Tris-HCl buffer (pH 7.4) and 1% fetal bovine serum (FBS) was developed.

A novel route towards water-soluble luminescent iridium(iii) complexes via a hydroxy-bridged dinuclear precursor

The synthesis and photophysical characterization of a new family of luminescent water-soluble ionic iridium(iii) complexes of the general formula [(ppy)₂Ir(bpy)]X are reported. The Ir(iii) complexes incorporate a cyclometalated 2-phenylpyridine (ppy), the ancillary ligand 2,2'-bipyridyl (bpy) and different counterions (X^- = EtO^-, OH^-, EtOCH₂CO₂^-, MeOCH₂CO₂^-). These complexes were obtained starting from the cyclometalated Ir(iii) chloro-bridged dimer [(ppy)₂Ir(μ-Cl)]₂, for the first time synthesized through a new microwave assisted synthetic procedure, and subsequently converted into the corresponding hydroxy-bridged dimer [(ppy)₂Ir(μ-OH)]₂. The latter was eventually used as a sole reagent for the synthesis of all the reported complexes by simply varying the nature of the reaction solvent from water to alcohols and glycol ethers. This study demonstrates the versatility of the [(ppy)₂Ir(μ-OH)]₂ complex as a precursor to water soluble ionic Ir(iii) complexes. Indeed, [(ppy)₂Ir(μ-OH)]₂ has shown its peculiar chemical reactivity due to both a strong base character and an unexpected oxidative ability towards the alcoholic function of glycol ethers. All the synthesized complexes exhibit, in water solution, an orange emission centred at 606 nm. Moreover, all complexes display the ability to give rise to gel phases in water upon increasing their concentration, and the photophysical study evidenced the various interactions governing the gelification process. The water-solubility of these new luminescent Ir(iii) complexes makes them potentially useful in bio-related systems.

A photoactivatable Znsalen complex for super-resolution imaging of mitochondria in living cells

We report the first transition metal complex, Znsalen J-S-Alk, as a photoactivatable probe for super-resolution imaging of mitochondria.

Highly efficient phosphorescent materials based on Ir(iii) complexes-grafted on a polyhedral oligomeric silsesquioxane core

Three hybrid materials containing a POSS core were synthesized and characterized, in which two materials were used for light-emitting devices.

Photophysical and photochemical studies of tricarbonyl rhenium(i) N-heterocyclic carbene complexes containing azide and triazolate ligands

Rhenium NHC complexes bound to azide anions readily react with alkynes to form the corresponding triazolate complexes, a new class of photochemically active species.

Theoretical study on a series of iridium complexes with low efficiency roll-off property

A series of heteroleptic cyclometalated Ir (III) complexes for OLEDs application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of (piq)₂Ir(acac) (labeled 1) and theoretically designed models (piq)₂Ir(dpis) (labeled 2), (4Fpiq)₂Ir(dpis) (labeled 3), (4F5M-piq)₂Ir(dpis) (labeled 4), (4,5-2F-piq)₂Ir(dpis) (labeled 5) and (5-F-piq)₂Ir(dpis) (labeled 6) were investigated with density functional theory (DFT)-based approaches, where, piq=1-phenylisoquinolato, acac=acetylacetonate and dpis=diphenylimidodisilicate. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy-transfer mechanism of these complexes also be analyzed here, and the result shown that the complexes 1-6 are having the low efficiency roll-off property. Except that, the oscillator strength analyze shown that the complexes 2-6, which were designed by theory, are suitable for OLED since their high oscillator strength property.

Synthesis and photo- and electro-luminescent properties of Ir(iii) complexes attached to polyhedral oligomeric silsesquioxane materials

Two new POSS materials with an emissive Ir(iii) complex and carbazole units were successfully synthesized. Their photophysical and electrochemical properties, thermal stabilities and solution processed light-emitting devices were investigated.

Phosphorescent proteins for bio-imaging and site selective bio-conjugation of peptides and proteins with luminescent cyclometalated iridium(III) complexes

A new bio-conjugation reaction for site selective modification of proteins and peptides with phosphorescent iridium(III) complexes has been developed; the Ir(III)-modified proteins and peptides display long emission lifetimes and large Stoke shifts that can be used for bio-imaging studies.