Heterocyclic (pyrazine)carboxamide Ru(ii) complexes: structural, experimental and theoretical studies of interactions with biomolecules and cytotoxicity

Treatments of N-(1H-benzo[d]imidazol-2-yl)pyrazine-2-carboxamide (HL1) and N-(benzo[d]thiazol-2-yl)pyrazine-2-carboxamide carboxamide ligands (HL2) with [Ru(p-cymene)Cl2]2 and [Ru(PPh3)3Cl2] precursors afforded the respective Ru(ii) complexes [Ru(L1)(p-cymene)Cl] (Ru1), [Ru(L2)(p-cymene)Cl] (Ru2), [Ru(L1)(PPh3)2Cl] (Ru3), and [Ru(L2)(PPh3)2Cl] (Ru4). These complexes were characterized by NMR, FT-IR spectroscopies, mass spectrometry, elemental analyses, and crystal X-ray crystallography for Ru2. The molecular structure of complex Ru2 contains one mono-anionic bidentate bound ligand and display pseudo-octahedral piano stool geometry around the Ru(ii) atom. The interactions with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were investigated by spectroscopic techniques. The experimental binding studies suggest that complexes Ru1-Ru4 interact with DNA, primarily through minor groove binding, as supported by molecular docking results. Additionally, these complexes exhibit strong quenching of the fluorescence of tryptophan residues in BSA, displaying static quenching. The in vitro cytotoxicity studies of compounds Ru1-Ru4 were assessed in cancer cell lines (A549, PC-3, HT-29, Caco-2, and HeLa), as well as a non-cancer line (KMST-6). Compounds Ru1 and Ru2 exhibited superior cytotoxicity compared to Ru3 and Ru4. The in vitro cytotoxicity and selectivity of compounds Ru1 and Ru2 against A549, PC-3, and Caco-2 cell lines surpassed that of cisplatin.

Comparative Analysis of Mononuclear 1:1 and 2:1 Tetravalent Actinide (U, Th, Np) Complexes: Crystal Structure, Spectroscopy, and Electrochemistry

Six mononuclear tetravalent actinide complexes (1-6) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (HL^pr). The HL^pr is treated with tetravalent actinide elements in varied stoichiometries to afford mononuclear 1:1 complexes [MCl₃-L^pr·nTHF] (1-3) and 2:1 complexes [MCl₂-L₂^pr] (4-6) (M = Th⁴⁺ (1 and 4), U⁴⁺ (2 and 5), and Np⁴⁺ (3 and 6)). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography. UV-vis spectroscopy revealed more red-shifted absorption spectra for 2:1 complexes as compared to 1:1 complexes. ¹H NMR of Th(IV) complexes exhibit diamagnetic spectra, whereas U(IV) and Np(IV) complexes revealed paramagnetically shifted ¹H NMR. Interestingly, NMR signals are paramagnetically shifted between -70 and 40 ppm in 2 and 3 but are confined within -35 to 25 ppm in 2:1 complexes 5 and 6. Single-crystal structures for 1:1 complexes revealed an eight-coordinated Th(IV) complex (1) and seven-coordinated U(IV) (2) and Np(IV) (3) complexes. However, all 2:1 complexes 4-6 were isolated as eight-coordinated isostructural molecules. The geometry around the Th⁴⁺ center in 1 is found to be trigonal dodecahedral and capped trigonal prismatic around U(IV) and Np(IV) centers in 2 and 3, respectively. However, An⁴⁺ centers in 2:1 complexes are present in dodecahedral geometry. Importantly, 2:1 complexes exhibit increased bond distances in comparison to their 1:1 counterparts as well as interesting bond modulation with respect to ionic radii of An(IV) centers. Cyclic voltammetry displays an increased oxidation potential of the ligand by 300-500 mV, after coordination with An⁴⁺. CV studies indicate Th(IV)/Th(II) reduction beyond -2.3 V, whereas attempts were made to identify redox potentials for U(IV) and Np(IV) centers. Spectroscopic binding studies reveal that complex stability in 1:1 stoichiometry follows the order Th⁴⁺ ≈ U⁴⁺ > Np⁴⁺.

Carboxamide carbonyl-ruthenium(ii) complexes: detailed structural and mechanistic studies in the transfer hydrogenation of ketones

The organo-carboxamide carbonyl-ruthenium(ii) complexes displayed moderate catalytic activities in the transfer hydrogenation of a broad spectrum of ketones.

Selective Detection of Picric Acid and Pyrosulfate Ion by Nickel Complexes Offering a Hydrogen-Bonding-Based Cavity

This work describes the synthesis and characterization of three mononuclear nickel complexes supported with amide-based pincer ligands. All three complexes presented an H-bonding-based cavity due to the migration of amidic protons to the appended heterocyclic rings that formed H-bonds with the metal-ligated solvent molecule(s). These complexes functioned as the nanomolar chemosensors for the detection of picric acid and pyrosulfate ion as inferred by the detailed absorption and emission spectral studies while further supported with FTIR, NMR, and mass spectra of the isolated products. We also illustrate a few practical detection methods for the sensing of picric acid in the solution state as the naked-eye colorimetric methods and in the solid state by employing polystyrene films.

Dipicolinamide and isophthalamide based fluorescent chemosensors: recognition and detection of assorted analytes

This perspective focuses on a variety of fluorescent receptors based on dipicolinamide and isophthalamide groups and their significant roles in the molecular recognition, sensing and detection of assorted analytes ranging from metal ions, anions, neutral molecules, drugs and explosives. Both the "turn-on" and "turn-off" nature of sensing highlights noteworthy applications in many fields encompassing biological, medicinal, environmental and analytical disciplines.

Ruthenium complexes of phosphine-amide based ligands as efficient catalysts for transfer hydrogenation reactions

This work presents three mononuclear Ru(ii) complexes of tridentate phosphine-carboxamide based ligands providing a NNP coordination environment. The octahedral Ru(ii) ion shows additional coordination with co-ligands; CO, Cl and CH3OH. All three Ru(ii) complexes were thoroughly characterized including their crystal structures. These Ru(ii) complexes were utilized as catalysts for the transfer hydrogenation of assorted carbonyl compounds, including some challenging biologically relevant substrates, using isopropanol as the hydrogen source. The binding studies illustrated the coordination of the isopropoxide ion by replacing a Ru-ligated chloride ion followed by the generation of the Ru-H intermediate that was isolated and characterized and was found to be involved in the catalysis.

Half-Sandwich Ruthenium Complexes of Amide-Phosphine Based Ligands: H-Bonding Cavity Assisted Binding and Reduction of Nitro-substrates

We present synthesis and characterization of two half-sandwich Ru(II) complexes supported with amide-phosphine based ligands. These complexes presented a pyridine-2,6-dicarboxamide based pincer cavity, decorated with hydrogen bonds, that participated in the binding of nitro-substrates closer to the Ru(II) centers, which is further supported with binding and docking studies. These ruthenium complexes functioned as the noteworthy catalysts for the borohydride mediated reduction of assorted nitro-substrates. Mechanistic studies not only confirmed the intermediacy of [Ru-H] in the reduction but also asserted the involvement of several organic intermediates during the course of the catalysis. A similar Ru(II) complex that lacked pyridine-2,6-dicarboxamide based pincer cavity substantiated its unique role both in the substrate binding and the subsequent catalysis.

Cobalt mediated N-alkylation of amines by alcohols: role of hydrogen bonding pocket

Cobalt complexes of amide-based pincers provide a H-bonding pocket that binds a reagent in the vicinity of the metal center. These complexes function as catalysts for the N-alkylation of amines using alcohols via a borrowing hydrogen strategy.

The impact of metal coordination on the assembly of bis(indolyl)methane-naphthalene-diimide amphiphiles

The self-assembly and coordination of amphiphiles comprised of naphthalenediimide (NDI) and bis(indolyl)methane (BIM) chromophores were investigated as a function of pH and metal. As observed by TEM, SEM and AFM imaging, the self-assembly of NDI-BIM 1 produced irregular nanostructures at neutral pH in CH3CN-H2O (1 : 1); whereas, well-defined nanotubes were observed at pH 2. Conversely, Fmoc-protected, NDI-BIM 2 formed nanotubes at neutral pH and nonspecific aggregates at pH 2. Upon coordination of Cu2+ ions to the bis(indoyl)methane moiety, a reorganization from nanotubes to vesicular structures was observed.

Selective sensing of ATP by hydroxide-bridged dizinc(ii) complexes offering a hydrogen bonding cavity

This work illustrates the highly selective fluorescence detection of ATP in the presence of other competing anions, such as AMP, ADP, PPi and other phosphates by using a set of hydroxide-bridged dizinc(ii) complexes offering a cavity lined with hydrogen bonds and other interactive forces. ATP, as a whole, was recognized by the synergic combination of Zn-phosphate bonding, ππ stacking between the adenine ring of ATP and the pyridine ring of the dizinc complex and hydrogen bonding interactions that modulate the cavity structure of the dizinc complexes.

Indole-based colori/fluorimetric probe for selective detection of Cu2+ and application in living cell imaging

A highly sensitive and selective indole-based probe IHT exhibited obvious color change from colorless to violet easily detected by naked eye as well as 'turn on' fluorescence response to Cu²⁺ ion at physiological pH condition. The detection limit was determined to be as low as 8.93 × 10^-8 M, which was much lower than drinking water permission concentrations by the United States Environmental Protection Agency. The 1:2 binding mechanism was well confirmed by fluorescence titration, Job's plot, HRMS, IR analysis and DFT calculations. Furthermore, the probe IHT was successfully used for fluorescence imaging of Cu²⁺ ion in living cells.

Detection of Al3+ and Fe3+ ions by nitrobenzoxadiazole bearing pyridine-2,6-dicarboxamide based chemosensors: effect of solvents on detection

Hybrid chemosensors, based on a pyridine-2,6-dicarboxamide fragment while containing a 4-nitrobenzoxadiazole group, are used for the sensing of Al³⁺ and Fe³⁺ ions where detection was significantly controlled by the selection of a solvent.

Design and synthesis of new functionalized 8-(thiophen-2-yl)-1,2,3,4-tetrahydroquinolines as turn-off chemosensors for selective recognition of Pd2+ ions

Functionalized 8-thienyl-1,2,3,4-tetrahydroquinoline was synthesized as a fluorescent turn-off chemosensor for selective recognition of Pd²⁺ ions with a low detection limit.

Pyrene-appended bipyridine hydrazone ligand as a turn-on sensor for Cu2+ and its bioimaging application

A pyrene-appended bipyridine hydrazone-based ligand, HL, was synthesized and characterized by spectroscopic methods. Upon complexation with Cu(ii), HL formed a hexanuclear paddlewheel metal–organic macrocycle (MOM) via self-assembly with a high association constant with the molecular formula of [Cu₆L₆(NO₃)₆]. Intermolecular and intramolecular π–π interactions were demonstrated in this hexanuclear Cu(ii) complex. Further, it was observed that HL had the potential to detect a trace level of Cu(ii) ion selectively among a wide range of biologically relevant metal ions in aqueous medium at physiological pH. Using HL, it was feasible to sense copper(ii) ions in living cells due to its good cell permeability and high solubility under physiological conditions along with its high IC₅₀ value. The low detection limit, high sensitivity and good reproducibility make this Cu–sensor very promising. The complex (MOM) formed between the ligand and Cu(ii) was found to be 1 : 1 on the basis of fluorescence titrations and was confirmed by ESI-MS. Moreover, single-crystal study of the hexanuclear self-assembled fluorescent species provided better insight into its chemistry, e.g. coordination environment and binding mode, unlike most of the metal sensors due to the lack of a single-crystal structure of the metal sensor complex. Cytotoxicity assay and bioimaging were performed in living cells (Vero cells), giving green fluorescent images. Fluorescence lifetime measurements and theoretical calculations were carried out. The morphology and topographic details on the surface of the metal–organic macrocycle (MOM) were studied by field-emission scanning electron microscopy (FESEM).

A pyrene-based “turn-on” Cu(ii) sensor provides a chemiluminescent Cu₆ metal organic macrocycle (MOM) applicable for live cell imaging.

Turn-On Fluorescent Sensors for the Selective Detection of Al3+ (and Ga3+) and PPi Ions

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of L1-L4 in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between L4 and Al³⁺/Ga³⁺ ions. The solution-generated [L-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.

Oxo-bridged trinuclear and tetranuclear manganese complexes supported with nitrogen donor ligands: syntheses, structures and properties

This work illustrates syntheses, structures, redox and magnetic properties as well as catalase activities of rare μ₃-oxo bridged mixed-valent trinuclear Mn^IIMn^III complexes (1 and 2) and a μ₄-oxo bridged tetranuclear MnII4 complex (3) supported with nitrogen donor ligands.

Applications of Nanomaterials Based on Magnetite and Mesoporous Silica on the Selective Detection of Zinc Ion in Live Cell Imaging

Functionalized magnetite nanoparticles (FMNPs) and functionalized mesoporous silica nanoparticles (FMSNs) were synthesized by the conjugation of magnetite and mesoporous silica with the small and fluorogenic benzothiazole ligand, that is, 2(2-hydroxyphenyl)benzothiazole (hpbtz). The synthesized fluorescent nanoparticles were characterized by FTIR, XRD, XRF, ¹³C CP MAS NMR, BET, and TEM. The photophysical behavior of FMNPs and FMSNs in ethanol was studied using fluorescence spectroscopy. The modification of magnetite and silica scaffolds with the highly fluorescent benzothiazole ligand enabled the nanoparticles to be used as selective and sensitive optical probes for zinc ion detection. Moreover, the presence of hpbtz in FMNPs and FMSNs induced efficient cell viability and zinc ion uptake, with desirable signaling in the normal human kidney epithelial (Hek293) cell line. The significant viability of FMNPs and FMSNs (80% and 92%, respectively) indicates a potential applicability of these nanoparticles as in vitro imaging agents. The calculated limit of detections (LODs) were found to be 2.53 × 10⁻⁶ and 2.55 × 10⁻⁶ M for Fe₃O₄-H@hpbtz and MSN-Et₃N-IPTMS-hpbtz-f1, respectively. FMSNs showed more pronounced zinc signaling relative to FMNPs, as a result of the more efficient penetration into the cells.

BINOL-based differential chromo-fluorescent sensor and its application in miniaturized 1-2/4-2 bit encoders and decoders

A BINOL (1,1′-bi-2-naphthol)-based probe 1 with a diamide group has been synthesized and investigated for its photophysical behavior towards various cations and anions.

Modulating the DNA cleavage ability of copper(ii) Schiff bases through ternary complex formation

Copper(ii) Schiff-bases were electrochemically synthesized and characterized. The presence of co-ligands such as 2,2′-bpy or phen in the metal coordination environment increases the DNA cleavage efficiency.

Detection of sulfide ion and gaseous H2S using a series of pyridine-2,6-dicarboxamide based scaffolds

This work presents a series of pyridine-2,6-dicarboxamide based scaffolds with different appendages and their roles as chemosensors for the selective detection of S²⁻ ion, as well as gaseous H₂S, in primarily aqueous media.

A metalloligand appended with benzimidazole rings: tetranuclear [CoZn3] and [CoCd3] complexes and their catalytic applications

A novel Co³⁺-based metalloligand, offering appended benzimidazole rings, has been utilized for the synthesis of catalytically active tetranuclear [CoZn₃] and [CoCd₃] heterometallic coordination complexes.

Polymerization led selective detection and removal of Zn2+and Cd2+ions: isolation of Zn- and Cd-MOFs and reversibility studies

Two post-functionalized chemosensors display remarkable sensing of Zn²⁺and Cd²⁺ionsviagenerating corresponding metal–organic frameworks (MOFs), whereas nitrate and nitrite ions reverse the MOF-polymerization process.

Selective fluorescent turn-off sensing of Pd2+ ion: applications as paper strips, polystyrene films, and in cell imaging

Pyridine-2,6-dicarboxamide based scaffolds with appended naphthyl groups act as fluorescent probes for the selective detection of Pd²⁺ ions in aqueous medium and have applications as paper-strip sensors, as polystyrene films, and in cell imaging.

Fluorescent detection of multiple ions by two related chemosensors: structural elucidations and logic gate applications

Two related chemosensors L1 and L2 display selective detection of multiple ions (Cu²⁺, Al³⁺, Cd²⁺ and S²⁻) as a result of minor variation of functional groups at a remote arene ring.

Hydroxide-bridged dicopper complexes: the influence of secondary coordination sphere on structure and catecholase activity

This work illustrates the syntheses, structures and catecholase activities of dicopper(ii) complexes having a Cu(μ-OH)Cu core encased within a secondary coordination sphere intricately created by appended heterocyclic rings.

Detection of the anticoagulant drug warfarin by palladium complexes

This work illustrates the application of palladium complexes in the significant sensing of warfarin, a commercial anticoagulant drug, not only in organic solvents but also in aqueous medium.

A Schiff's base receptor for red fluorescence live cell imaging of Zn2+ ions in zebrafish embryos and naked eye detection of Ni2+ ions for bio-analytical applications

A quinoline based chemosensor for dual detection of Ni²⁺/Zn²⁺ ions and its bio-analytical applications.

Biosorption of Zn2+, Ni2+ and Co2+ from water samples onto Yarrowia lipolytica ISF7 using a response surface methodology, and analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES)

A response surface methodology (RSM) was employed to interpret biosorption efficiency.

The wonderful world of pyridine-2,6-dicarboxamide based scaffolds

This perspective focusses on a variety of scaffolds based on a pyridine-2,6-dicarboxamide fragment and their noteworthy roles in coordination chemistry, biomimetic studies, catalysis, and sensing.

A highly selective, sensitive and reversible fluorescence chemosensor for Zn2+ and its cell viability

A new ligand (H2L) was synthesized and designed for sensing properties. H2L shows fluorescence ‘switch ON’ with Zn²⁺ ions with a detection limit of 1.47 μM. The H2L and 1 showed marginal toxicity against MCF-7 and A375 cell lines.