Synthesis, Crystal Structure, Electronic Spectroscopy, Electrochemistry and Biological Studies of Ferrocene-Carbohydrate Conjugates

Probing photoinduced electron transfer events in phenylferrocene-corrole dyad

Herein, we investigated PhFC (10-phenylferrocenyl-5,15-diphenyl corrole), a corrole-based donor-acceptor (D-A) dyad, to understand the energy/electron transfer reaction dynamics. Phenylferrocene acts as the donor moiety when attached to the meso position of the corrole ring in the PhFC D-A system. The photophysical properties of the PhFC dyad and its parent molecule, TPC (5,10,15-triphenyl corrole), were studied by UV-vis spectroscopy, steady state fluorescence spectroscopy, TCSPC and optical microscopy techniques. A slight red shift and broadening of both the Q-band and Soret bands are observed in the absorption spectra of the PhFC dyad in comparison to TPC, representing the weak electronic interaction between the phenylferrocene moiety and corrole ring. The fluorescence emission spectrum of the PhFC dyad is significantly quenched (>80%) in comparison to TPC, attributed to the photoinduced electron transfer (PET) from phenylferrocene to the corrole ring. We observed that the electron transfer rate in the PhFC system is solvent dependent. Our theoretical investigation supported the experimental findings on the electron transfer mechanism. The HOMO and LUMO arrangements of these PhFC dyads demonstrate the electron density distribution and the ability of the donor moieties to transfer electrons to the corrole moiety. Fluorescence lifetime imaging microscopy (FLIM) was used to image the homogeneous lifetime distribution of the PhFC dyad and TPC.

Ferrocenyl Azoles: Versatile N-Containing Heterocycles and their Anticancer Activities

The medicinal chemistry of ferrocene has gained its momentum after the discovery of biological activities of ferrocifen and ferroquine. These ferrocenyl drugs have been designed by replacing the aromatic moiety of the organic drugs, tamoxifen and chloroquine respectively, with a ferrocenyl unit. The promising biological activities of these ferrocenyl drugs have paved a path to explore the medicinal applications of several ferrocenyl conjugates. In these conjugates, the ferrocenyl moiety has played a vital role in enhancing or imparting the anticancer activity to the molecule. The ferrocenyl conjugates induce the cytotoxicity by generating reactive oxygen species and thereby damaging the DNA. In medicinal chemistry, the five membered nitrogen heterocycles (azoles) play a significant role due to their rigid ring structure and hydrogen bonding ability with the biomolecules. Several potent drug candidates with azole groups have been in use as chemotherapeutics. Considering the importance of ferrocenyl moiety and azole groups, several ferrocenyl azole conjugates have been synthesized and screened for their biological activities. Hence, in the view of a wide scope in the development of potent drugs based on ferrocenyl azole conjugates, herein we present the details of synthesis and the anticancer activities of ferrocenyl compounds bearing azole groups such as imidazole, triazoles, thiazole and isoxazoles.

Improving the anticancer activity of fluorinated glucosamine and galactosamine analogs by attachment of a ferrocene or ruthenium tetrazene motif

Acylated N‐acetyl hexosamine hemiacetals are known for their cytotoxicity. We have previously reported that cytotoxicity can be increased by replacing one or more acyloxy groups with fluorine. Herein, we present the synthesis of 4,6‐difluorinated d‐gluco‐ and 4‐fluorinated d‐galacto‐configured hexosamine‐derived glycoconjugates with organoruthenium or ferrocene complexes and their in vitro cytotoxicity against three cancer cell lines (A2780, SK‐OV‐3, and MDA‐MB‐231) and one noncancerous cell line (HEK‐293). The attachment of the organometallic moiety at the 2‐position significantly enhanced the cytotoxicity, especially against triple‐negative MDA‐MB‐231 and the cisplatin resistant SK‐OV‐3 cancer cells. We observed a clear significance of an unprotected and acetyl protected anomeric hydroxyl for the cytotoxicity. Glycoconjugates with a non‐hydrolysable organic or organometallic group at the anomeric position were generally nontoxic. A more detailed analysis revealed that, in particular, complexes with the ruthenium tetrazene complex induced apoptosis in both SK‐OV‐3 and MDA‐MB‐231 cells, as demonstrated by western blot analysis and Annexin V‐FITC/PI staining. The structures of the two most cytotoxic organoruthenium and ferrocene glycoconjugates were confirmed by X‐ray diffraction analysis.

Ferrocene-triazole conjugates: do we know why they are biologically active?

The bioorganometallic chemistry of ferrocene has been gaining significance in recent years. This review presents ferrocene-triazole conjugates displaying significant biological properties. The conjugates have been synthesized via azide-alkyne cycloaddition reactions. The data are summarized according to the type of activity (anticancer, antibacterial and/or antifungal, antiprotozoal, and other effects). The results of studies concerning the understanding of the role of the ferrocene core in their biological activity are highlighted. While generally the mode of action of these organometallic species remains unclear, the importance of redox properties of ferrocene has been postulated in several cases.

Synthesis and Antiparasitic Activity of New Trithiolato-Bridged Dinuclear Ruthenium(II)-arene-carbohydrate Conjugates

Eight novel carbohydrate-tethered trithiolato dinuclear ruthenium(II)-arene complexes were synthesized using CuAAC ‘click’ (Cu(I)-catalyzed azide-alkyne cycloaddition) reactions, and there in vitro activity against transgenic T. gondii tachyzoites constitutively expressing β-galactosidase (T. gondii β-gal) and in non-infected human foreskin fibroblasts, HFF, was determined at 0.1 and 1 µM. When evaluated at 1 µM, seven diruthenium-carbohydrate conjugates strongly impaired parasite proliferation by >90%, while HFF viability was retained at 50% or more, and they were further subjected to the half-maximal inhibitory concentration (IC50) measurement on T. gondii β-gal. Results revealed that the biological activity of the hybrids was influenced both by the nature of the carbohydrate (glucose vs. galactose) appended on ruthenium complex and the type/length of the linker between the two units. 23 and 26, two galactose-based diruthenium conjugates, exhibited low IC50 values and reduced effect on HFF viability when applied at 2.5 µM (23: IC50 = 0.032 µM/HFF viability 92% and 26: IC50 = 0.153 µM/HFF viability 97%). Remarkably, compounds 23 and 26 performed significantly better than the corresponding carbohydrate non-modified diruthenium complexes, showing that this type of conjugates are a promising approach for obtaining new antiparasitic compounds with reduced toxicity.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Has Ferrocene Really Delivered Its Role in Accentuating the Bioactivity of Organic Scaffolds?

Ferrocene is an important structural core in bioorganometallic chemistry because of its inherent stability, excellent redox properties, and low toxicity. Ferroquine and ferrocifen are two of the most notable contributions of ferrocene to medicinal chemistry with remarkable antimalarial and anticancer properties. The improved medicinal properties of these drug candidates highlight the impact that ferrocene can have on the molecular and biological properties of the bioactive compounds. In this Perspective, we investigate the scope and limitations of ferrocene incorporation into organic compounds/natural products on their mode of action and biological activities. We have also discussed the detailed role of ferrocene modifications in influencing the anticancer, antimalarial, and antimicrobial properties of various bioactive moieties to design safer and promising ferrocene-based drugs.

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

Ferrocene-Encapsulated Zn Zeolitic Imidazole Framework (ZIF-8) for Optical and Electrochemical Sensing of Amyloid-β Oligomers and for the Early Diagnosis of Alzheimer's Disease

In this work, the ferrocene-encapsulated Zn zeolitic imidazole framework (ZIF-8) was prepared by the self-assembly of Zn ions and 2-methylimidazole and used for the dual detection of amyloid-beta oligomers (AβO), which is the main neuropathological hallmark of Alzheimer's disease. Ferrocene is an optically and electrochemically active signal which was successfully encapsulated inside of the ZIF-8 and released by the competitive coordination between Zn ions and AβO after being treated with AβO. The released ferrocene content was monitored by ultraviolet/visible spectrophotometry and cyclic voltammetry. The dual determination of AβO played a synergetic role in the quick qualitative and precise quantitative analyses in a wide detection range of 10^-5 to 10² μM and good feasibility in artificial cerebrospinal fluid.

Synthesis, characterization and antimicrobial evaluation of ferrocene–oxime ether benzyl 1H-1,2,3-triazole hybrids

A series of ferrocene–oxime ether benzyl 1H-1,2,3 triazole hybrids has been synthesized by employing Cu(i) catalyzed azide–alkyne [3+2] cycloaddition reaction and their antibacterial and antifungal activities are reported.

A Charge-Transfer Salt Based on Ferrocene/Ferrocenium Pairs and Keggin-Type Polyoxometalates

A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (Fe^III) cations and one ferrocene (Fe^II) molecule per plenary Keggin anion in the crystal structure of [Fe^III (Cp)₂]₄[SiW₁₂O₄₀]·[Fe^II(Cp)₂]·2CH₃OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D_5h symmetry, whereas the conformation in the other one is staggered D_5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak O_POM···C_MeOH-O_MeOH···O_POM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated Fe^III/Fe^II centres has been confirmed by Mössbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.

N-Arylation of ferrocenyl 2,4-thiazolidinedione conjugatesviaa copper-catalysed Chan–Lam cross coupling reaction with aryl boronic acids and their optoelectronic properties

Copper catalysed Chan–LamN-arylation of ferrocenyl 2,4-thiazolidinedione conjugates is described.

From Synthesis to Biological Impact of Pd (II) Complexes: Synthesis, Characterization, and Antimicrobial and Scavenging Activity

The Pd (II) complexes with a series of halosubstituted benzylamine ligands (BLs) have been synthesized and characterized with different spectroscopic technique such as FTIR, UV/Vis, LCMS, ¹H, and ¹³C NMR. Their molecular sustainability in different solvents such as DMSO, DMSO : H₂O, and DMSO : PBS at physiological condition (pH 7.2) was determined by UV/Vis spectrophotometer. The in vitro antibacterial and antifungal activities of the complexes were investigated against Gram-positive and Gram-negative microbes and two different fungi indicated their significant biological potential. Additionally, their antioxidant activity has been analyzed with DPPH^• free radical through spectrophotometric method and the result inferred them as an antioxidant. The stronger antibacterial and antioxidant activities of the synthesized complexes suggested them as a stronger antimicrobial agent. Our study advances the biological importance of palladium (II) amine complexes in the field of antimicrobial and antioxidant activities.

Biological Impact of Pd (II) Complexes: Synthesis, Spectral Characterization, In Vitro Anticancer, CT-DNA Binding, and Antioxidant Activities

A new series of Pd (II) complexes of methyl substituted benzylamine ligands (BLs) has been synthesized and characterized via spectroscopic techniques such as UV/Vis. FTIR, LCMS, ¹H, and ¹³C NMR. The UV/Vis study in DMSO, DMSO + water, and DMSO + PBS buffer (pH = 7.2) confirmed their molecular sustainability in liquids. Their in vitro anticancer activity against breast cancer cell lines such as MCF-7 and MDA-MB-231 makes them interesting for in vivo analysis. Their stronger DNA binding activity (DBA) compared with free ligand suggested them as a good DNA binder. DBA was further confirmed by physicochemical studies such as surface tension and viscosity of complex + DNA which inferred the disruption of DNA and intercalation of complexes, respectively. Their % binding activity, % disruption of DNA base pairs (DNABP), and % intercalating strength are reported in this paper for the first time for better understanding of DNA binding mechanism. Along with this, their scavenging activity (SA) determined through DPPH free radical and the results indicate good antioxidant behaviour of complexes.

Electrochemical analysis of a novel ferrocene derivative as a potential antitumor drug

Ferrocenes represent an interesting group of drugs with potential antitumor properties.

Electrospinning preparation and electrical and biological properties of ferrocene/poly(vinylpyrrolidone) composite nanofibers

Nanofibers containing ferrocene (Fc) have been prepared for the first time by electrospinning. In this paper, Fc was dispersed uniformly throughout the poly(vinypyrrolidone) (PVP) matrix for the purpose of combining the properties of PVP and Fc. The effects of solvents and Fc concentration on the morphologies and diameters of nanofibers were investigated. In the DMF/ethanol solvent, the morphologies of the obtained nanofibers significantly changed with the increase of Fc concentration. The results demonstrated that the morphologies of the nanofibers could be controlled through adjusting solvents and Fc concentration. Scanning electron microscopy (SEM) showed that the diameters of the obtained composite fibers were about 30-200 nm at different Fc concentrations. Thermogravimetric analysis (TGA) results confirmed the presence of ferrocene within the PVP nanofibers. X-ray diffraction (XRD) results showed that the crystalline structure of Fc in the fibers was amorphous after the electrospinning process. A biological evaluation of the antimicrobial activity of Fc/PVP nanofibers was carried out by using Gram-negative Escherichia coli (E. coli) as model organisms. The nanofibers fabricated by this method showed obvious antibacterial activity. Electrochemical properties were characterized based on cyclic voltammetry measurements. The CV results showed redox peaks corresponding to the Fc(+)/Fc couple, which suggested that Fc molecules encapsulated inside PVP nanofibers retian their electrochemical activity. The properties and facile preparation method make the Fc/PVP nanofibers promising for antibacterial and sensing applications.