Benzimidazole Ligands Research Articles

Cationic Ru(II), Rh(III) and Ir(III) complexes containing cyclic π-perimeter and 2-aminophenyl benzimidazole ligands: Synthesis, molecular structure, DNA and protein binding, cytotoxicity and anticancer activity

Synthesis, characterization, DNA and protein binding as well as anticancer activity of the organometallic complexes [(η6-C6H6)RuCl(APBI)]Cl (1), [(η6-p-MeC6H4Pri)RuCl(APBI)]Cl (2), [(η6-C6Me6)RuCl(APBI)]Cl (3), [(η5-C5Me5)RhCl(APBI)]Cl·H2O (4) and [(η5-C5Me5)IrCl(APBI)]Cl·H2O (5) containing 2-aminophenyl benzimidazole (APBI) have been described. The complexes 1–5 exhibited strong DNA, protein binding and anticancer activity against cervical cancer (SiHa) cell line. Their binding with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) have been examined by absorption and emission spectral studies. Strong interactions between complexes and CT-DNA have been affirmed by absorption spectral and EthBr displacement studies, while interaction with BSA via static quenching explored by fluorescence titration, synchronous and 3D fluorescence spectroscopy. The interactions between 1–5 and DNA has also been scrutinized by 1H NMR spectral studies using guanosine as a model for DNA. These results have been supported by DFT calculations and molecular docking studies. Cytotoxicity, apoptosis and in vitro anticancer activity of 1–5 toward SiHa cell line have been investigated by MTT assay and acridine (AO)/ethidium bromide (EthBr) fluorescence staining. Overall results revealed that DNA and protein binding, as well as anticancer activity of 1–5 follows the order as 5 > 3 > 2 > 1 > 4.

Syntheses, crystal structures, and luminescent properties of three metal coordination polymers based on adipic acid and 2-(pyridine-3-yl)-(1H)-benzimidazole

Three new metal coordination polymers constructed from adipic acid and 2-(pyridin-3-yl)-(1H)-benzimidazole ligands, [M(ADP)(3PBI)2(H2O)2]·2H2O (M = Ni and Co for 1 and 2, respectively) and [Cd(ADP)(3PBI)(H2O)] (3) [ADP = adipic acid dianion; 3PBI = 2-(pyridin-3-yl)-(1H)-benzimidazole], have been synthesized by hydrothermal reactions and were characterized by X-ray single-crystal diffraction, elemental analyses, IR, powder X-ray diffraction, and thermogravimetry. Complexes 1 and 2 are isostructural. Both form a 1-D linear chain structure, which is further assembled into a 3-D supramolecular framework by π⋯π stacking and hydrogen bonding interactions. Complex 3 possesses a binuclear unit and displays a 2-D layer which is further extended to a 3-D supramolecular architecture via hydrogen bonding and other weak packing interactions. The luminescent properties of 3 were investigated in the solid state at room temperature.

Crystal structures, in situ synthesis in aqua conditions and luminescent properties of benzimidazole ligands and cadmium coordination complexes

Three cadmium complexes, [Cd(L2)2(H2O)4]·H2O (1), [Cd(L2)2(H2O)4]·8H2O (2), [Cd2(L3)2(SO4)(4,4′-bpy)0.5(H2O)3]·2.5H2O (3) have been obtained from L1 ligand and auxiliary ligand in hydrothermal conditions. The crystal structures reveal that L2·H2O can be transformed from L1 directly in hot water conditions, while L3 emerge in coordination complex via in situ reactions of L1 ligand. Complexes 1 and 2 are zero dimensional coordination complexes and there are interesting T12(4) water tapes exist in complex 2. 3 is three dimensional supramolecular structure which is comprised of interpenetrated one dimensional chains. The luminescent properties have been measured and show that the emission peaks are similar between L2·H2O and complex 1, but take place bathochromic shift for complex 2 which should be tentatively relative to conjugation of organic ligands and metal coordination reaction.

Structures and Fluorescent Properties of Cadmium(II) Complexes with 1D and 2D Structures Based on Tridentate Benzimidazole Ligands

AbstractThe cadmium(II) complexes [CdL1(m‐nba)2] (1), [CdL1(p‐nba)2]·C2H5OH (2), [CdL2(p‐nba)2]·CH3OH (3), and [CdL2(p‐nbat)2] (4) containing the ligands L1 and L2 [L1 = 2,6‐bis(benzimidazol‐2‐yl)pyridine, L2 = bis(2‐benzimidazolylmethyl)amine] were synthesized and characterized (m‐nba, p‐nba, and p‐nbat are the anions of p‐nitrobenzoic acid, m‐nitrobenzoic acid, and p‐nitrobenzeneacetic acid, respectively). The complexes were investigated by X‐ray single crystal diffraction, elemental analysis as well as IR and fluorescence spectroscopy. Compounds 1–3 contain a distorted pentagonal bipyramidal coordination sphere with CdII coordinated by two carboxylate ligands in bidentate‐chelating mode, whereas complex 4 exhibits a distorted octahedral arrangement with one carboxylate ligand in bidentate‐chelating and the other in monodentate coordination mode. 1 and 2 form a 1D chain interplayed by hydrogen bonding and strong π–π stacking interactions. 3 and 4 vary from 1D chain into 2D single‐layer and double‐layer networks because of more extensive hydrogen bonding interactions. The complexes show emission maxima in the blue region in the solid state and emission bands are red‐shifted compared to those of the free ligands.

Fluorescence signaling of hydrogen sulfide in broad pH range using a copper complex based on BINOL-benzimidazole ligands.

A weakly fluorescent complex derived from a binaphthol-benzimidazole ligand was designed and synthesized for hydrogen sulfide at different pH conditions. It was demonstrated that the probe showed the same reactivity to various hydrogen sulfide species in a broad range of pH values to generate highly fluorescent product through a displacement reaction mechanism, whereas the product's fluorescence spectrum exhibited a hypsochromic shift of ∼73 nm (2393 cm(-1)) as pH increased from neutral to basic, which can be used for distinguishing the various species of hydrogen sulfide. This turn-on fluorescence probe was highly selective and sensitive to hydrogen sulfide with a detection limit of 0.11 μM. It was then applied for evaluating the total content of sulfide (including hydrogen sulfide, hydrosulfide, and sulfide) as well as for the visual detection of gaseous H2S in air using a simple test paper strip.

Synthesis and Characterization of Ruthenium(II) Complexes Bearing Benzimidazole Ligands: For Transfer Hydrogenation Catalysis

Ru(II) complexes with the general formula [RuCl2(p-cymene)(L1-3)], K1–3, (L1–3: monodentate benzimidazole ligands), [RuCl2(L5–6)(S)], K4–7, (L5–6: tridentate benzimidazole ligands, S: Solvents [methanol or acetonitrile]), and [RuCl2(L5)(L1–2)], K8–9, were synthesized from [RuCl2(p–cymene)]2 dimer and mono- and tridentate benzimidazole ligands. The compounds were characterized by elemental analysis, IR, UV-Vis, and NMR. The synthesized Ru(II) complexes (K1–9) were tested as catalysts for the transfer hydrogenation (TH) of acetophenone to secondary alcohols in the presence of KOH using 2–propanol as a hydrogen source at 82°C. All complexes were active catalysts for TH of acetophenone with good yields under mild conditions (after 60 minutes, yields of up to 97%).

Syntheses and Characterization of Three New Compounds Based on Terephthalate and 2‐(2‐Pyridin‐4‐yl‐vinyl)benzimidazole Ligands

AbstractThree new compounds based on H2BDC and PyBImE [H2BDC = 1,4‐benzenedicarboxylatic acid, PyBImE = 2‐(2‐pyridin‐4‐yl‐vinyl)benzimidazole], namely, [Co(PyBImE)(BDC)(H2O)2] (1), [Co(PyBImE)2(HBDC)(BDC)0.5] (2), and [(HPyBImE)+·(BDC)2–0.5·(H2BDC)0.5] (3), were synthesized by hydrothermal methods and characterized by single‐crystal X‐ray diffraction. Compound 1 is a one‐dimensional chain bridged by terephthalate in a bis(monodentate) fashion. In the complex the nitrogen atom from NBIm and the coordination water molecule complete the coordination sphere. In complex 2, the dinuclear cobalt units are bridged by terephthalate in a bis(bidentate) fashion into a one‐dimensional chain, but different from complex 1, the nitrogen atom from NPy and the oxygen atom from hydrogenterephthalate complete the coordination sphere. Complex 3 is a co‐crystal with PyBImE and H2BDC in a 1:1 ratio and the transfer of hydrogen atoms leads the complex into a salt. Interesting supramolecular structures are shown due to the hydrogen bonding as well as π···π interactions in the three complexes. Thermal and magnetic properties of 1 and 2 were also studied.

2-(2-Hydroxyphenyl)benzimidazole-based four-coordinate boron-containing materials with highly efficient deep-blue photoluminescence and electroluminescence.

Two novel four-coordinate boron-containing emitters 1 and 2 with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of 1 or 2 exhibited high electron and hole mobility in the same order of magnitude 10(-4), as determined by time-of-flight. The fabricated electroluminescent devices that employed 1 or 2 as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.15, Y = 0.09) and (X = 0.16, Y = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes.

Synthesis and characterization of two cobalt(II) coordination polymers based on 5-tert-butyl isophthalic acid and bis(benzimidazole) ligands

Two cobalt(II) coordination polymers, namely [Co(bbdmbm)(tbi)·H2O]n (1) and [Co(bmb)1.5(tbi)]n (2), (bbdmbm = 1,1′-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole), bmb = 1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene, H2tbi = 5-tert-butyl isophthalic acid), have been synthesized and characterized by physico-chemical and spectroscopic methods and also by single-crystal X-ray diffraction. Complex 1 features a 1D ladder-like chain and is further extended into a 3D supramolecular architecture via strong O–H···O hydrogen bonds. Complex 2 exhibits a 2D corrugated (4,4) network constructed with bmb and tbi ligands, which is further assembled into a 3D 3,4,4-connected supramolecular framework with 3,4,4T25 topology through weak C–H···O hydrogen-bonding interactions. The fluorescence properties and catalytic activities of both complexes for the degradation of Congo red in a Fenton-like process have been investigated.

Synthesis, characterization, and microwave-assisted catalytic activity in Heck, Suzuki, Sonogashira, and Buchwald--Hartwig cross-coupling reactions of novel benzimidazole salts bearing N-phthalimidoethyl and benzyl moieties

Five novel benzimidazole salts (1-5) having N-phthalimidoethyl and 4-substituted benzyl were synthesized and identified by $^{1}$H NMR, $^{13}$C NMR, and IR spectroscopic methods and microanalysis. A mixture of the benzimidazole salts (1-5), Pd(OAc)$_{2}$, and K$_{2}$CO$_{3}$ in DMF-H$_{2}$O catalyzed, in high yield, the Suzuki-Miyaura and the Heck-Mizoroki cross-coupling reactions assisted by microwave irradiation in 5 min. The novel benzimidazole salts (1-5), Pd(OAc)$_{2}$, Cs$_{2}$CO$_{3}$, PEG, and Cu nanoparticles catalyzed, in high yield, the Sonogashira coupling reaction promoted by microwave irradiation in 10 min. The same benzimidazole salts (1-5), Pd(OAc)$_{2}$, Cs$_{2}$CO$_{3}$, and TBAB catalyzed, in moderate or low yield, the Buchwald-Hartwig reaction assisted by microwave irradiation in 60 min. The efficiency of the catalyst system in these four reactions was discussed as well as the electron-releasing and withdrawing substituent effects on the benzimidazole ligands.

Visible light assisted photocatalytic reduction of CO2 using a graphene oxide supported heteroleptic ruthenium complex

A new heteroleptic ruthenium complex containing 2-thiophenyl benzimidazole ligands was synthesized using a microwave technique and was immobilized to graphene oxide via covalent attachment.

Monomer–Dimer Divergent Behavior toward DNA in a Half-Sandwich Ruthenium(II) Aqua Complex. Antiproliferative Biphasic Activity

The complex [(η6-p-cymene)Ru(OH2)(κ2-N,N-HL1)](OTf)2 (HL1 = 2-pyridin-2-yl-1H-benzimidazole), [2c](OTf)2, undergoes easy deprotonation of the N–H group at physiological pH, producing [(η6-p-cymene)Ru(OH2)(κ2-N,N-L1)]+, [2c′]+, prone to dimerization both in solution and in the solid state. X-ray measurements on [2c′]BF4 have shown that dimer units are formed in the solid state by a combination of π–π stacking contacts between the aromatic rings of [L1]− and hydrogen bonding involving the water molecules coordinated to the metal center and the deprotonated imidazolyl N atom. The T-jump kinetic curves of the 2D ↔ D2 equilibrium recorded in the microsecond time scale have allowed us to determine the parameters of the dimerization process. The dimer content diminishes as the ionic strength drops. The different kinetic and thermodynamic techniques have all shown that the monomer reacts with DNA, producing the bifunctional intercalated (through the benzimidazole ligand)-covalent (Ru/N7G) [(η6-p-cymene)Ru(κ2-N,N-L1)]/DNA complex. The cytotoxic activity of [2c′]+ was evaluated against human lung carcinoma cells (A549) by the MTT cell viability assay. Interestingly, the percentage of surviving cells as a function of the [2c′]+ content displayed biphasic behavior, interpreted as a result of the rise in the dimer content of [2c′]+. As only the monomer can react with DNA, a reasonable correlation between cytotoxic activity and formation of the [(η6-p-cymene)Ru(κ2-N,N-L1)]/DNA complex is established.

Syntheses, structures, and fluorescent properties of four Co(II) coordination polymers based on 5-hydroxyisophthalic acid and structurally related bis(benzimidazole) ligands

Four cobalt(II) coordination polymers, {[Co(HO-BDC)(bbp)]}n (1), {[Co(HO-BDC)(bmbp)2]·(H2O)2}n (2), {[Co(HO-BDC)(bbb)]}n (3), and {[Co2(HO-BDC)2(bmbb)2]·(H2O)3}n (4), where HO-H2BDC = 5-hydroxyisophthalic acid, bbp = 1,3-bis(benzimidazol-1-yl)propane, bmbp = 1,3-bis(2-methyl-benzimidazol-1-yl)propane, bbb = 1,4-bis(benzimidazol-1-yl)butane, and bmbb = 1,4-bis(2-methyl-benzimidazol-1-yl)butane, have been synthesized and characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, thermogravimetric analyses, and fluorescence properties. Compounds 1 and 3 are 4-connected 2-D networks with (44·62) topology. Compound 2 is a 1-D chain, while 4 features a 1-D ladder. These 1-D and 2-D complexes are further connected by hydrogen bonds to form 3-D supramolecular architectures. Complexes 1–4 showed very strong yellow luminescence emission.

Transfer hydrogenation of ketones in the presence of half sandwich ruthenium (II) complexes bearing imidazoline and benzimidazole ligand

Transfer hydrogenation of ketones in the presence of half sandwich ruthenium (II) complexes bearing imidazoline and benzimidazole ligand

Synthesis and characterization of three cobalt(II) coordination polymers with tetrabromoterephthalic acid and flexible bis(benzimidazole) ligands

Three cobalt(II) coordination polymers, namely {[Co(tbta)(pbdmbm)]·0.5H2O} n (1), [Co(tbta)(bbdmbm) (H2O)2] n (2), and [Co(tbta)(bbbm)] n (3), have been hydrothermally synthesized by self-assembly of cobalt(II) nitrate with tetrabromoterephthalic acid (H2tbta) and three flexible bis(benzimidazole) ligands, respectively, 1,1′-(1,4-butanediyl)bis-1H-benzimidazole (bbbm), 1,1′-(1,3-propanediyl)bis(5,6-dimethylbenzimidazole) (pbdmbm), and 1,1′-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole) (bbdmbm). Single-crystal X-ray diffraction analysis reveals that complex 1 has a 1D ladder-like chain structure, while both complexes 2 and 3 feature a uninodal 2D (4, 4) layer structure with a {44.62}-sql topology. Additionally, the fluorescence properties and catalytic activities of the complexes for degradation of congo red by a Fenton-like process were investigated.

Synthesis, crystal structure and DNA interaction studies of a 2D cadmium(II) coordination polymer constructed from 2-(2-pyridyl)benzimidazole

A new complex associated with Cd2+, [Cd(OH-H2Bdc)(2-Pbim)]n (1), (OH-H2Bdc = 5-hydroxyisophthalic acid, 2-Pbim = 2-(2-pyridyl)benzimidazole), has been synthesised under hydrothermal conditions and characterised by elemental analysis, FT-IR spectroscopy, TG/DTG and fluorescence spectrum. Its in vitro cytotoxicity towards four selected tumour cell lines has been evaluated by an microculture tetrozolium assay, the results suggest that complex 1 displays greater inhibition than the free benzimidazole ligand. On the basis of the combination of absorption titration and fluorescence emission titration, the binding mode of complex 1 to calf thymus DNA has been investigated. Complex 1 can interact with the base pairs of double-helical DNA via the combined mode of intercalation and groove binding with larger binding constants.

Synthesis, characterization, and antimicrobial properties of two Cu(II) complexes derived from a benzimidazole ligand

Two copper(II) complexes, [Cu(L)2](ClO4)2] and [Cu(L)(bipy)](ClO4)2, were prepared and characterized by the spectroscopic and analytic methods, where L is N-butylbenzimidazole and bipy is 2,2′-bipyridine. Single crystals of [Cu(L)(bipy)](ClO4)2 suitable for X-ray diffraction study were obtained by slow diffusion of diethyl ether into a DMF solution of the complex and the complex was found to crystallize as [Cu(L)(bipy)](ClO4)2·DMF. The asymmetric unit contains one [Cu(L)(bipy)]2+, two uncoordinated perchlorates, and one DMF solvate. Coordination geometry around Cu(II) is distorted square pyramidal with τ value of 0.31. Thermal properties of the complexes were examined by thermogravimetric analysis, indicating that the complexes are thermally stable to 310 °C. The metal complexes were screened for their in vitro antibacterial and antifungal activities Bacillus subtilis and Bacillus cereus (as Gram(+) bacteria), Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae (as Gram(–) bacteria), and Saccharomyces cerevisiae, Candida utilis, and Candida albicans (as yeasts). The complexes show antibacterial and antifungal activities against bacteria and yeasts.

Zinc complexes of 1-Propyl-2-(2-tosylaminophenyl)-5-aminobenzimidazole: Synthesis, structure, and luminescence properties

1-Alkyl-2-(2-tosylaminophenyl)-5-aminobenzimidazole and related zinc complexes are synthesized. The structure of the complex with zinc pivalate is determined by X-ray diffraction analysis. The fluorescence with the anomalous Stokes shift of the benzimidazole ligand system in solution is transformed into the fluorescence with the normal Stokes shift upon complex formation due to blocking the mechanism of intramolecular proton transfer in the excited state or upon the transition to the crystalline state formed by zwitterionic forms that are generated due to the proton transfer from the sulfonamide group to the amino group.

Synthesis, photophysical and electrochemical properties of iridium(III) complexes with 2-aryl-1-phenylbenzimidazoles

A series of mixed-ligand cyclometalated iridium(III) complexes with 2-aryl-1-phenylbenzimidazoles (where aryl is phenyl, 4-chlorophenyl, 4-(N,N-dimethylamino)phenyl, 3,4-dimethoxyphenyl, and 2-thienyl) and 11-carboxydipyrido[3,2-a:2′,3′-c]phenazine have been synthesized and characterized by 1H NMR and 31P NMR spectroscopy and mass spectrometry. The electron absorption spectra (EASs) of the complexes are observed to contain charge-transfer bands in the low-energy region (below 600 nm, ɛ ≈ (1–3) × 103 mol/(L cm)). The bands experience appreciable bathochromic shifts as the electron-donating properties of a benzimidazole ligand strengthen. The complexes manifest luminescence in the yellow-red spectral region. According to alternating current voltammetry data, reversible and quasi-reversible redox transitions (E ox ≈ 1.2–1.7 V with respect to SHE, CH3CN) are observed in solutions of the studied complexes.

Intrinsic flexibility of the zeolitic imidazolate framework ZIF-7 unveiled by CO₂ adsorption and Hg intrusion.

ZIF-7, built as an assembly of Zn(II) centers and benzimidazolate ligands, shows prominent S-shaped isotherms upon CO2 adsorption that can be attributed to sorbate-induced gate-opening phenomena involving a narrow-to-large pore phase transition. This peculiar sorption pattern can be captured via the formulation of thermodynamic isotherms, providing a direct enthalpic and entropic view of the gate-opening process. Relying on such an approach, an energy barrier with preferential enthalpic nature for CO2 adsorption/desorption in the gate-opening region could be unveiled. Moreover, the elastic energy involved during the gate-opening process was revisited to 1.4-2.8 kJ mol(-1) of solid in the temperature range 273-323 K, matching the value measured by isostatic compression of a ZIF-7_lp sample filled with DMF and showing a dominant entropic contribution.