Development and Application of Ruthenium(II) and Iridium(III) Based Complexes for Anion Sensing

Dual-color and specific luminescence detection of Pd2+ ions using iridium(III) complex-based probes in food samples

The toxicity of palladium (Pd) is highly associated with its oxidative states, thus it is important to develop specific detection methods for Pd2+ ions in food and environmental systems. However, the reliable and selective detection of Pd2+ ions remains challenging. Here, we report two iridium(III) complexes with dual colors (717 nm and 637 nm) for the specific detection of Pd2+ ions, with the 3,3'-diamino group being used as a specific recognition unit for Pd2+ ions for the first time. The dual-color probes showed a luminescence quenching response to Pd2+ ions in aqueous solution within 1 min, along with an obvious color change under UV irradiation. Moreover, complexes 1-2 allow sensitive and selective detection of Pd2+ ions with a limit of detection (LOD) of 0.69 μM and 0.26 μM, respectively, showing a good linear response for Pd2+ ions in the range of 1-13 μM (R2 = 0.985) and 1-9 μM (R2 = 0.996). Finally, the probes were successfully applied for the detection of Pd2+ ions in food and environmental samples with good recoveries ranging from 85.4 to 118.7 %, providing a robust analytical tool for Pd2+ ions quantification for onsite setting.

Current Context of Designing Phototheranostic Cyclometalated Iridium (III) Complexes to Open a New Avenue in Cancer Therapy

Photo-induced chemotherapy offers the best option for the selective treatment of cancer among all the prevailing modalities. Iridium (III) complexes, flourished with excellent photophysical and photochemical properties, have been considered to be superior for undergoing photo-responsive cancer therapy. Large Stokes shift, long-lived triplet excited state, photostability, and tuneable emission have rendered its excellence as a phototheranostic agent. In particular, the cyclometalated Ir (III) complexes and their respective nanoparticles have made a strong niche in the arena of cancer therapy. In recent years, Ir (III) based complexes have shown promising utilities as both imaging and therapeutic agents as well. Therefore, this review summarises the recent advances in the strategic designing of cyclometalated Ir(III) complexes to augment their phototheranostic applications in precision medicine.

Quinoline conjugates for enhanced antimalarial activity: a review on synthesis by molecular hybridization and structure-activity relationship (SAR) investigation

Malaria, caused by the various Plasmodium falciparum strains, has been one of the deadliest diseases spread across the world. Over the years, several researchers have been employed to analyse molecular hybridization techniques for the synthesis of combination drugs to overcome the resistance gained by the parasite against the existing drugs. Hence, some of the significant contributions since 2019 till date have been summarised in the present review. Based on structure, the hybrids have been classified into bi-pharmacophores - having two pharmacologically active groups, tri-pharmacophores - having three pharmacologically active groups, metal-based and other miscellaneous hybrids. A thorough study of existing molecules could also reveal new leads for the development of anti-malarial agents with efficacy better than the preceding ones.

A Potent Bis-Heteroleptic Ruthenium(II) Complex-Based Chalcogen Bonding Receptor for Selective Sensing of Phosphates

The incorporation of a selenoimidazolium-based chalcogen bond (ChB) donor into a bis-heteroleptic Ru(II) complex (Ru-Se) has been designed for the first time to explore its anion-sensing properties and understand its selectivity to specific classes of anions. Photophysical studies demonstrate the receptor's selectivity toward phosphates, while 1H NMR displays its ability to recognize both I- and H2PO4- among the different halides and oxoanions through ChB interaction in CH3CN and dimethyl sulfoxide-d6 solvents, respectively. Additionally, microscopic studies such as DLS and TEM reveal that the selective turn-on sensing of H2PO4- and HP2O73- compared to I- is driven by supramolecular aggregation behavior. Hence, the successful fabrication of a selenium ChB-based Ru(II) complex makes it a promising candidate for anion monitoring in supramolecular chemistry.

Exploring pectinolytic yeast diversity: toward effective polygalacturonase producers for applications in wine-making

Pectinolytic enzymes secreted by yeasts have an untapped potential in industry, particularly in wine-making. This study addresses the limitations of the current screening methods in reliably predicting the capacity of pectinolytic yeast strains to secrete polygalacturonase (PGase) under industrial conditions, suggesting a novel screening approach. Using the context of wine-making as an example, a diverse collection of 512 yeast strains from 17 species was analysed for PGase secretion, a key enzyme in pectinolysis. The traditional halo assay on solid yeast-pepton-dextrose (YPD) medium revealed 118 strains from nine genera being PGase positive. Screening these strains by incubating them at 20°C on a solid synthetic grape juice medium containing polygalacturonic acid (PG) significantly reduced the number of promising strains to 35. They belong to five genera: Kluyveromyces sp., Cryptococcus, Pichia, Torulaspora, and Rhodotorula. Afterward, a newly developed pectin-iodine assay was used to precisely quantify the PGase activity of the best-performing strains in a liquid medium. Strains from Kluyveromyces and Cryptococcus sp. stood out regarding high pectinolytic activity. Our methodological advancements tailored to identify highly promising pectinolytic yeasts for industrial use open new avenues for wine-making and other industrial processes encompassing media rich in pectin and sugars.

Iridium(III) coordination compounds based on organophosphorus ancillary ligands showing cytotoxicity against breast cancer cells and Fe(III) luminescent sensing

Three phosphorescent iridium(III) complexes consisting bis-diphosphine ligands were prepared and characterized by single-crystal XRD, CHN analysis, spectroscopic techniques, cyclic voltammetry, and DFT. The synthesized complexes were the three monomeric [Ir(ppy)2(L1)Cl] (1), [Ir(ppy)2(L2)]Cl (2) and [Ir(ppy)2(L3)]Cl (3) where L1 = bis-(diphenylphosphino)methane (dppm), L2 = bis-(diphenylphosphino)propane (dppp) and L3 = bis-(diphenylphosphino)benzene (dppbe). Complexes 1-3 gave an absorption band between 240 to 380 nm in both CH2Cl2 and DMSO, which is assigned as a charge transfer transition based on theoretical calculation. They showed a blue-green emission at 460-520 nm in DMSO with an absolute quantum efficiency of 0.013-0.046 at room temperature. The selective photo-induced electron transfer (PET) by Fe3+ in DMSO, was studied to obey the Rehm-Weller principle. The 1:1 binding soichiometry between 1-3 and Fe3+ was established by Job's plot. The binding constants (Ka) were determined using the Benesi-Hildebrand plot. All the complexes are extremely more potent than cisplatin for in vitro antiproliferative activity towards the human breast cancer cells, HCC1937, MCF-7, and MDA-MB-231. The values of IC50 were in the range of 0.077-0.485 μM, and 1 exhibited the most effective IC50 against MDA-MB-231 cell line, the triple-negative breast cancer cell. Their lipophilicities (log P) were also examined to explain the penetration ability of the studied complexes towards cell barriers, and transport to the molecular target.

Recent Advances in Fluorescent Based Chemical Probes for the Detection of Perchlorate Ions

This review highlights recent advancements and challenges in fluorescence-based chemical sensors for selective and sensitive detection of perchlorate, a persistent environmental pollutant and global concern due to its health and safety implications. Perchlorate is a highly persistent inorganic pollutant found in drinking water, soil, and air, with known endocrine-disruptive properties due to its interference with iodide uptake by the thyroid gland. Human exposure mainly occurs through contaminated water and food. Additionally, perchlorates are prevalent in improvised explosives, causing numerous civilian casualties, making their detection important in a worldwide aspect. Fluorescence-based chemical sensors provide a valuable tool for the selective detection of perchlorate ions due to their simplicity and applicability across various fields, including biology, pharmacology, military, and environmental science. This review article overviews perchlorate chemistry, occurrence, and remediation strategies, compares regulatory limits, and examines fluorescence-based detection mechanisms. It systematically summarizes recent advancements in designing at least a dozen fluorescence-based chemical materials for detecting perchlorate in the environment over the past decade. Key focus areas include the design and molecular architecture of synthetic chemical chromophores for perchlorate sensing and the photochemistry mechanisms driving their effectiveness. The main findings indicate that there has been significant progress in the development of reliable and robust fluorescence-based sensors with higher selectivity and sensitivity for perchlorate detection. However, several challenges remain, such as improving detection limits and sensor stability. The review outlines potential future research directions, emphasizing the need for further innovation in sensor design and development. It aims to enhance understanding and spur advances that could create more efficient and robust chemical scaffolds for perchlorate sensing. By addressing current limitations and identifying opportunities for improvement, the review provides a comprehensive resource for researchers working to develop better detection methods for this significant environmental pollutant.

Cellular Phosphate Sensing and Anion Binding by an Azacrown-Calixpyrrole Hybrid

A hybrid receptor-sensor for anions originating from the merging of positively charged ammonium moieties for electrostatic attraction/stronger binding of azacrowns with directionality of calixpyrrole hydrogen bond donors for selectivity is investigated. As demonstrated this hybrid receptor-sensor shows a remarkable selectivity for orthophosphate even in the presence of other phosphates and anions found in cellular materials (Kassoc H2PO4 ->H2P2O7 2->AMP-≫ADP2- or ATP3- over halides, nitrate, or hydrogen sulfate; all Na+ salts in water) but also cellular polyphosphate or phospholipids. This selectivity is harnessed in a real-time monitoring of cell lysis by lysozyme, which releases orthophosphate and other phosphates and anions from the cells. This sensitive (LOD 0.4 μM) fluorescence-based microscale method compares favorably with the state-of-the-art techniques but can easily be practiced in a high-throughput screening (HTS) manner. The anion binding and selectivity in aqueous solutions were investigated by NMR and put in context with phosphate binding of the parent calix[4]pyrrole. The microscopic understanding of anion binding by the hybrid receptor was then obtained from a combination of density functional theory (DFT), classical molecular dynamics (MD) with explicit water solvation, and ab initio MD (AIMD) simulations. Correlating the NMR and fluorescence binding data with studies of solvation of the receptor, phosphate anion, and the resulting complex confirms the binding is largely driven by entropic component (TΔS) associated with receptor and anion desolvation.

Transition Metal Complexes with Appended Benzimidazole Groups for Sensing Dihydrogenphosphate

Four new complexes [Ru(bpy)2(bbib)](PF6)2, [Ru(phen)2(bbib)](PF6)2, [Re(CO)3(bbib)(py)](PF6) and [Ir(ppy)2(bbib)](PF6) [where bbib=4,4'-bis(benzimidazol-2-yl)-2,2'-bipyridine] have been prepared and their photophysical properties determined. Their behaviour has been studied with a variety of anions in acetonitrile, DMSO and 10 % aquated DMSO. Acetate and dihydrogenphosphate demonstrate a redshift in the bbib ligand associated absorptions suggesting that the ligand is strongly interacting with these anions. The 3MLCT emissive state is sensitive to the introduction of small quantities of anion (sub-stoichiometric quantities) and significant quenching is typically observed with acetate, although this is less pronounced in the presence of water. The emissive behaviour with dihydrogenphosphate is variable, showing systematic changes as anion concentration increases with several distinct interactions evident. 1H- and 31P-NMR titrations in a 10 % D2O-DMSO-D6 mixture suggest that with dihydrogenphosphate, the imidazole group is able to act as both a proton acceptor and donor. It appears that all four complexes can form a {[complex]2-H2PO4} "dimer", a one-to-one species (which the X-ray crystallography study suggests is dimeric in the solid-state), and a complex with a combined bis(dihydrogenphosphate) complex anion. The speciation relies on complex equilibria dependent on several factors including the complex charge, the hydrophobicity of the associated ligands, and the solvent.

Hydrothermal synthesis, structures, and catalytic performance of five coordination compounds driven by 5-aminoisophthalic acid

An amino-functionalized-dicarboxylic acid, 5-aminoisophthalic acid (H2aipa), was used as a versatile building block to synthesize a series of five novel coordination compounds under hydrothermal conditions and formulated as [Co(μ3-aipa)(2,2'-H2biim)] n (1), [Ni2(μ-aipa)2(2,2'-H2biim)2(H2O)4]·4H2O (2), {[Cd(μ3-aipa)(2,2'-H2biim)]·H2O} n (3), {[Ni(μ-aipa)(μ-bpb)]·0.5bpb·H2O} n (4), and {[Ni2(μ-aipa)(μ3-aipa)(μ-dpea)2(H2O)][Ni(μ-aipa)(μ-dpea)(H2O)]·8H2O} n (5). Three supporting ligands (2,2'-biimidazole (H2biim),1,4-bis(pyrid-4-yl)benzene (bpb), and 1,2-di(4-pyridyl)ethane (dpea)) were used in the synthesis. The structures of the studied products 1-5 vary significantly, ranging from a 0D dimer (2), 2D sheets (1, 3 and 4) to 3D + 2D interpenetrated frameworks (5). Furthermore, these compounds were evaluated as heterogeneous catalysts for the Knoevenagel reaction, achieving high product yields under optimized conditions. In addition, we also investigated various reaction parameters, substrate scope, and assessed the feasibility of catalyst recycling. This thorough investigation highlights the versatility of H2aipa as a dicarboxylate building block in the formation of functional coordination polymers.

Naphthalene Diimide and Bis-Heteroleptic Ru(II) Complex-Based Hybrid Molecule with 3-in-1 Functionalities

Multipurpose applications of a newly developed homobimetallic Ru(II) complex, Ru-NDI[PF6]4, which incorporates 1,10-phenanthroline and triazole-pyridine ligands and linked via a (-CH2-)3 spacer to the reputed anion-π interacting NDI system, are described. Solution-state studies of the bimetallic complex, including EPR, PL, UV-vis, and NMR experiments, reveal two sequential one-electron transfers to the NDI unit, generating NDI⋅- and NDI2- in the presence of F- selectively. This process inhibits the primary electron transfer from Ru(II) to the NDI unit, thereby allowing the 3MLCT-based emission of the complex to be recovered, resulting in a corresponding ten-fold increase in luminescence intensity. DFT and TD-DFT computational studies further elucidate the experimentally observed absorption spectra of the complex. Secondly, CT-DNA binding studies with the complex are performed using various spectroscopic analyses such as UV-vis, PL, and CD. Comparative DNA binding studies employing EB and molecular docking reveal that the binding with CT-DNA occurs through both intercalative and groove binding modalities. Thirdly, the photocatalytic activities of the complex towards C-C, C-N, and C-O bond formation in organic cross-coupling reactions, including the amidation of α-keto acids to amines and the oxidation of alcohol to aldehydes, are also demonstrated.

Development of Ru-polypyridyl complexes for real-time monitoring of Aβ oligomers and inhibition of Aβ fibril formation

The aggregation of amyloid-β (Aβ) is one of the important pathological markers of Alzheimer's disease. Ruthenium(II) complexes have good stability, low cytotoxicity, a high fluorescence quantum yield, and a good Stokes shift as fluorescent probes. Based on this, we constructed a fluorescent probe for in vivo real-time imaging and inhibition of Aβ-fibril formation using a complex of Ru polypyridine with organic fluorophores (N,N-dimethylaniline) and hydrophobic peptides (KLVFF). DLS and TEM studies have shown that Ru-YH has an inhibitory effect on the fibrotic aggregation of Aβ. Both in vivo and in vitro studies have shown that Ru-WJ and Ru-YH can quickly cross the blood-brain barrier and successfully detect Aβ in early (2.5-month old) transgenic mouse models. In summary, we have explored the potential of Ru complex based biological probes for early diagnosis and inhibition of AD.

Hydrothermal Assembly, Structural Multiplicity, and Catalytic Knoevenagel Condensation Reaction of a Series of Coordination Polymers Based on a Pyridine-Tricarboxylic Acid

A pyridine-tricarboxylic acid, 5-(3',5'-dicarboxylphenyl)nicotinic acid (H3dpna), was employed as a adjustable block to assemble a series of coordination polymers under hydrothermal conditions. The seven new coordination polymers were formulated as [Co(μ3-Hdpna)(μ-dpey)]n·nH2O (1), [Zn4.5(μ6-dpna)3(phen)3]n (2), [Co1.5(μ6-dpna)(2,2'-bipy)]n (3), [Zn1.5(μ6-dpna)(2,2'-bipy)]n (4), [Co3(μ3-dpna)2(4,4'-bipy)2(H2O)8]n·2nH2O (5),[Co(bpb)2(H2O)4]n[Co2(μ3-dpna)2(H2O)4]n·3nH2O (6), and [Mn1.5(μ6-dpna)(μ-dpea)]n (7), wherein 1,2-di(4-pyridyl)ethylene (dpey), 1,10-phenanthroline (phen), 2,2'-bipyridine(2,2'-bipy),4,4'-bipyridine(4,4'-bipy),1,4-bis(pyrid-4-yl)benzene (bpb), and 1,2-di(4-pyridyl)ethane (dpea) were employed as auxiliary ligands. The structural variation of polymers 1-7 spans the range from a 2D sheet (1-4, 6, and 7) to a 3D metal-organic framework (MOF, 5). Polymers 1-7 were investigated as heterogeneous catalysts in the Knoevenagel condensation reaction, leading to high condensation product yields (up to 100%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were also researched. This work broadens the application of H3dpna as a versatile tricarboxylate block for the fabrication of functional coordination polymers.

Fine-Tuning of the Optical and Electrochemical Properties of Ruthenium(II) Complexes with 2-Arylbenzimidazoles and 4,4'-Dimethoxycarbonyl-2,2'-bipyridine

A series of cyclometalated complexes of ruthenium (II) with four different substituents in the aryl fragment of benzimidazole was synthesized in order to study the effect of substituent donation on the electronic structure of the substances. The resulting complexes were studied using X-ray diffraction, NMR spectroscopy, MALDI mass spectrometry, electron absorption spectroscopy, luminescence spectroscopy, and cyclic voltammetry as well as DFT/TDDFT was also used to interpret the results. All the complexes have intense absorption in the range of up to 700 nm, the triplet nature of the excited state was confirmed by measurement of luminescence decay. With an increase in substituent donation, a red shift of the absorption and emission bands occurs, and the lifetime of the excited state and the redox potential of the complex decrease. The combination of these properties shows that the complexes are excellent dyes and can be used as photosensitizers.