Synthesis and Spectroscopic Investigations of Schiff Base Ligand and Its Bimetallic Ag(I) Complex as DNA and BSA Binders

Synthesis, characterization, and biological activities of novel organometallic compounds of rhenium(I) with 2-(2-benzylidenehydrazinyl) benzothiazole Schiff-base derivatives: Molecular docking, ADME, and DFT studies

A series of substituted 2-(2-benzylidenehydrazinyl)benzothiazole Schiff-base derivatives and complexes containing Re(I) were synthesized and analyzed using various characterization techniques, including elemental analysis, conductance measurement, 1H-NMR, FT-IR, and LC-MS. The biological activities of the compounds were evaluated. Binding affinity between the complexes and calf thymus DNA (CT-DNA) was conducted using UV-visible spectroscopy, viscosity measurement, fluorescence spectroscopy, and molecular docking studies, indicating intercalation binding mode. The broth dilution method evaluated antibacterial activity against two Gram-positive and three Gram-negative bacteria. The results demonstrated the effectiveness of each complex against the tested pathogens. The MTT assay examined cytotoxic qualities on MCF-7 cell lines, demonstrating strong cytotoxic effects. The lethality of brine prawn assay was employed to assess the toxicity of the compounds. The Schiff base was optimized using the 6-31 G (d, p) basis set and B3LYP techniques. Density functional theory calculations were performed to compare the bond angles and lengths of the synthesized compounds with experimental values, showing good agreement, and to calculate the related orbital energies. The therapeutic qualities were evaluated using an in silico ADMET model, which verified that the synthesized compounds have qualities similar to those of drugs.

Experimental and computational studies of silver(I) dibenzoylmethane-based complexes, interaction with DNA/RNA/BSA biomolecules, and in vitro cytotoxic activity

Two silver(I) complexes of composition [Ag₂(L)₂] (1) and [Ag(L)(PPh₃)₂](2) (HL = dibenzoyl- methane, PPh₃ = triphenylphosphine) were synthesized and characterized by elemental analysis, FTIR, NMR, XRPD, and UV-visible spectra. The molecular structures of the studied ligands and Ag(I) complexes have been characterized using Density Function Theory (DFT) calculations. This analysis has enabled us to determine the reactivity and the coordination site(s) for each ligand. Ag(I) ion is found to be coordinated with the ligand's oxygens in almost a linear fashion in complex (1), while in complex (2) it adopts a tetrahedral geometry. The interaction compounds with biomolecules; calf thymus (ct DNA), yeast-tRNA, and bovine serum albumin (BSA) were investigated using both absorption and fluorescence spectroscopy. The in vitro cytotoxic studies of the complexes against normal human lung fibroblast (WI38), cancerous breast (MDA-MB-231), mammary gland breast (MCF7), hepatocellular (HePG2), and prostate (PC3) cell lines indicated that the complexes are highly toxic to the cancer cells but less toxic towards the normal one when compared with the ligand. Flow cytometric results showed that complex (1) induced cell cycle arrest at the G2/M phase, and complex (2) at G2/M and S phases. Moreover, the results of apoptotic genes (caspase3 and p53) and anti-apoptotic (Bcl2) led us to suggest an apoptotic killing mechanism of cells rather than a necrotic one.

New N4-Donor Ligands as Supramolecular Guests for DNA and RNA: Synthesis, Structural Characterization, In Silico, Spectrophotometric and Antimicrobial Studies

The present work reports the synthesis of new N4-donor compounds carrying p-xylyl spacers in their structure. Different Schiff base aliphatic N-donors were obtained synthetically and subsequently evaluated for their ability to interact with two models of nucleic acids: calf-thymus DNA (CT-DNA) and the RNA from yeast Saccharomyces cerevisiae (herein simply indicated as RNA). In more detail, by condensing p-xylylenediamine and a series of aldehydes, we obtained the following Schiff base ligands: 2-thiazolecarboxaldehyde (L1), pyridine-2-carboxaldehyde (L2), 5-methylisoxazole-3-carboxaldehyde (L3), 1-methyl-2-imidazolecarboxaldehyde (L4), and quinoline-2-carboxaldehyde (L5). The structural characterisation of the ligands L1-L5 (X-ray, ¹H NMR, ¹³C NMR, elemental analysis) and of the coordination polymers {[CuL1]PF₆}_n (herein referred to as Polymer1) and {[AgL1]BF₄}_n, (herein referred to as Polymer2, X-ray, ¹H NMR, ESI-MS) is herein described in detail. The single crystal X-ray structures of complexes Polymer1 and Polymer2 were also investigated, leading to the description of one-dimensional coordination polymers. The spectroscopic and in silico evaluation of the most promising compounds as DNA and RNA binders, as well as the study of the influence of the 1D supramolecular polymers Polymer1 and Polymer2 on the proliferation of Escherichia coli bacteria, were performed in view of their nucleic acid-modulating and antimicrobial applications. Spectroscopic measurements (UV-Vis) combined with molecular docking calculations suggest that the thiazolecarboxaldehyde derivative L1 is able to bind CT-DNA with a mechanism different from intercalation involving the thiazole ring in the molecular recognition and shows a binding affinity with DNA higher than RNA. Finally, Polymer2 was shown to slow down the proliferation of bacteria much more effectively than the free Ag(I) salt.

An Integrated Analysis of Mechanistic Insights into Biomolecular Interactions and Molecular Dynamics of Bio-Inspired Cu(II) and Zn(II) Complexes towards DNA/BSA/SARS-CoV-2 3CLpro by Molecular Docking-Based Virtual Screening and FRET Detection

Novel constructed bioactive mixed-ligand complexes (1b) [Cu^II(L)₂(phen)] and (2b) [Zn^II(L)₂(phen)] {where, L = 2-(4-morpholinobenzylideneamino)phenol), phen = 1,10-phenanthroline} have been structurally analysed by various analytical and spectroscopic techniques, including, magnetic moments, thermogravimetric analysis, and X-ray crystallography. Various analytical and spectral measurements assigned showed that all complexes appear to have an octahedral geometry. Agar gel electrophoresis's output demonstrated that the Cu(II) complex (1b) had efficient deoxyribonucleic cleavage and complex (2b) demonstrated the partial cleavage accomplished with an oxidation agent, which generates spreadable OH^● through the Fenton type mechanism. The DNA binding constants observed from viscosity, UV-Vis spectral, fluorometric, and electrochemical titrations were in the following sequence: (1b) > (2b) > (HL), which suggests that the complexes (1b-2b) might intercalate DNA, a possibility that is supported by the biothermodynamic measurements. In addition, the observed binding constant results of BSA by electronic absorption and fluorometric titrations indicate that complex (1b) revealed the best binding efficacy as compared to complex (2b) and free ligand. Interestingly, all compounds are found to interact with BSA through a static approach, as further attested by FRET detection. The DFT and molecular docking calculations were also performed to realize the electronic structure, reactivity, and binding capability of all test samples with CT-DNA, BSA, and the SARS-CoV-2 3CL^Pro, which revealed the binding energies were in a range of -8.1 to -8.9, -7.5 to -10.5 and -6.7--8.8 kcal/mol, respectively. The higher reactivity of the complexes than the free ligand is supported by the FMO theory. Among all the observed data for antioxidant properties against DPPH^᛫, ^᛫OH, O₂^-• and NO^᛫ free radicals, complex (1a) had the best biological efficacy. The antimicrobial and cytotoxic characteristics of all test compounds have been studied by screening against certain selected microorganisms as well as against A549, HepG2, MCF-7, and NHDF cell lines, respectively. The observed findings revealed that the activity enhances coordination as compared to free ligand via Overtone's and Tweedy's chelation mechanisms. This is especially encouraging given that in every case, the experimental findings and theoretical detections were in perfect accord.

CD, UV, and In Silico Insights on the Effect of 1,3-Bis(1'-uracilyl)-2-propanone on Serum Albumin Structure

1,3-diaryl-2-propanone derivatives are synthetic compounds used as building blocks for the realization not only of antimicrobial drugs but also of new nanomaterials thanks to their ability to self-assemble in solution and interact with nucleopeptides. However, their ability to interact with proteins is a scarcely investigated theme considering the therapeutic importance that 1,3-diaryl-2-propanones could have in the modulation of protein-driven processes. Within this scope, we investigated the protein binding ability of 1,3-bis(1'-uracilyl)-2-propanone, which was previously synthesized in our laboratory utilizing a Dakin-West reaction and herein indicated as U2O, using bovine serum albumin (BSA) as the model protein. Through circular dichroism (CD) and UV spectroscopy, we demonstrated that the compound, but not the similar thymine derivative T2O, was able to alter the secondary structure of the serum albumin leading to significant consequences in terms of BSA structure with respect to the unbound protein (Δβ-turn + Δβ-sheet = +23.6%, Δα = -16.7%) as revealed in our CD binding studies. Moreover, molecular docking studies suggested that U2O is preferentially housed in the domain IIIB of the protein, and its affinity for the albumin is higher than that of the reference ligand HA 14-1 (HDOCK score (top 1-3 poses): -157.11 ± 1.38 (U2O); -129.80 ± 6.92 (HA 14-1); binding energy: -7.6 kcal/mol (U2O); -5.9 kcal/mol (HA 14-1)) and T2O (HDOCK score (top 1-3 poses): -149.93 ± 2.35; binding energy: -7.0 kcal/mol). Overall, the above findings suggest the ability of 1,3-bis(1'-uracilyl)-2-propanone to bind serum albumins and the observed reduction of the α-helix structure with the concomitant increase in the β-structure are consistent with a partial protein destabilization due to the interaction with U2O.

Bioengineered lipophilic Ru(III) complexes as potential anticancer agents

Lipid-conjugated Ru(III) complexes - designed to obtain lipophilic analogues of the low molecular weight derivative AziRu, which is a NAMI-A-like anticancer agent - have been synthesized and fully characterized. A detailed biophysical investigation, including multiple, integrated techniques, allowed determining their molecular and self-assembling properties in aqueous solutions mimicking the extracellular environment, showing that our design produced a protective effect from hydrolysis of the Ru(III) complexes. In vitro biological experiments, carried out in comparison with AziRu, demonstrated that, among the novel lipophilic Ru(III) complexes synthesized, the compounds derivatized with palmitic and stearic acid, that we named PalmiPyRu and StePyRu respectively, showed attractive features and a promising antiproliferative activity, selective on specific breast cancer phenotypes. To get a deeper insight into their interactions with potential biomacromolecular targets, their ability to bind both bovine serum albumin (BSA), an abundant serum carrier protein, and some DNA model systems, including duplex and G-quadruplex structures, has been investigated by spectroscopic techniques. Inductively coupled plasma-mass spectrometry (ICP-MS) analysis of the ruthenium amount incorporated in human MCF-7 and MDA-MB-231 breast cancer cells, after incubation in parallel experiments with PalmiPyRu and AziRu, showed a markedly higher cell uptake of the lipophilic Ru(III) complex with respect to AziRu. These data confirmed that the proper lipidic tail decorating the metal complex not only favoured the formation of aggregates in the extracellular media but also improved their cell membrane penetration, thus leading to higher antiproliferative activity selective on breast cancer cells.

Oxygen Binding by Co(II) Complexes with Oxime-Containing Schiff Bases in Solution

The present work describes the complexation properties of two oxime-containing Schiff bases (used as ligands), viz. 2-hydroxyimino-N′-[1-(2-pyridyl)ethylidene]propanohydrazone (Hpop) and 2-hydroxyimino-N′-[(pyridine-2-yl)methylidene]propanohydrazone (Hpoa), with Co(II) ions in DMSO/water solution. Volumetric (oxygenation) studies were carried out to determine the uptake of molecular oxygen O₂ in the formation of the complexes Co(II)-Hpop and Co(II)-Hpoa. The acquired data can be useful in the development of oxygen bioinorganic complexes of metal ions with Schiff base ligands in solution. Their properties allow them to be used as synthetic oxygen transporters. Moreover, the binding of dioxygen could play an important role in the research of catalytic activity by such systems.

A study of structure-activity relationship and anion-controlled quinolinyl Ag(I) complexes as antimicrobial and antioxidant agents as well as their interaction with macromolecules

In this communication, we feature the synthesis and in-depth characterization of a series of silver(I) complexes obtained from the complexation of quinolin-4-yl Schiff base ligands ((E)-2-((quinolin-4-ylmethylene)amino)phenol L_a, 2-(quinolin-4-yl)benzo[d]thiazole L_b, (E)-N-(2-fluorophenyl)-1-(quinolin-4-yl)methanimine L_c, (E)-N-(4-chlorophenyl)-1-(quinolin-4-yl)methanimine L_d, (E)-1-(quinolin-4-yl)-N-(p-tolyl)methanimine L_e, (E)-1-(quinolin-4-yl)-N-(thiophen-2-ylmethyl)methanimine L_f) and three different silver(I) anions (nitrate, perchlorate and triflate). Structurally, the complexes adopted different coordination geometries, which included distorted linear or distorted tetrahedral geometry. The complexes were evaluated in vitro for their potential antibacterial and antioxidant activities. In addition, their interactions with calf thymus-DNA (CT-DNA) and bovine serum albumin (BSA) were evaluated. All the complexes had a wide spectrum of effective antibacterial activity against gram-positive and gram-negative bacterial and good antioxidant properties. The interactions of the complexes with CT-DNA and BSA were observed to occur either through intercalation or through a minor groove binder, while the interaction of the complexes with BSA reveals that some of the complexes can strongly quench the fluorescence of BSA through the static mechanism. The molecular docking studies of the complexes were also done to further elucidate the modes of interaction with CT-DNA and BSA.

Protein Binding of Benzofuran Derivatives: A CD Spectroscopic and In Silico Comparative Study of the Effects of 4-Nitrophenyl Functionalized Benzofurans and Benzodifurans on BSA Protein Structure

Benzofuran derivatives are synthetic compounds that are finding an increasing interest in the scientific community not only as building blocks for the realization of new materials, but also as potential drugs thanks to their ability to interact with nucleic acids, interfere with the amyloid peptide aggregation and cancer cell cycle. However, their ability to interact with proteins is a theme still in need of investigation for the therapeutic importance that benzofurans could have in the modulation of protein-driven processes and for the possibility of making use of serum albumins as benzofurans delivery systems. To this scope, we investigated the protein binding ability of two 4-nitrophenyl-functionalized benzofurans previously synthesized in our laboratory and herein indicated as BF1 and BDF1, which differed for the number of furan rings (a single moiety in BF1, two in BDF1), using bovine serum albumin (BSA) as a model protein. By circular dichroism (CD) spectroscopy we demonstrated the ability of the two heteroaromatic compounds to alter the secondary structure of the serum albumin leading to different consequences in terms of BSA thermal stability with respect to the unbound protein (ΔT_m > 3 °C for BF1, −0.8 °C for BDF1 with respect to unbound BSA, in PBS buffer, pH 7.5) as revealed in our CD melting studies. Moreover, a molecular docking study allowed us to compare the possible ligand binding modes of the mono and difuranic derivatives showing that while BF1 is preferentially housed in the interior of protein structure, BDF1 is predicted to bind the albumin surface with a lower affinity than BF1. Interestingly, the different affinity for the protein target predicted computationally was confirmed also experimentally by fluorescence spectroscopy (k_D = 142.4 ± 64.6 nM for BDF1 vs. 28.4 ± 10.1 nM for BF1). Overall, the above findings suggest the ability of benzofurans to bind serum albumins that could act as their carriers in drug delivery applications.

Selective Anticancer and Antimicrobial Metallodrugs Based on Gold(III) Dithiocarbamate Complexes

New dithiocarbamate cycloaurated complexes have been synthesized and their physicochemical and in vitro antitumor properties have been evaluated. All the performed studies highlighted good transport through the blood and biodistribution, according to the balance between the properties of hydrophilicity/lipophilicity and the binding of moderate strength to the BSA protein. Furthermore, none of the complexes exhibited reduction or decomposition reactions, presenting excellent physiological stability. The in vitro cytotoxic effect was evaluated on human colon cancer cell line Caco-2/TC7, and the complexes showed great antiproliferative activity and excellent selectivity, as much less effect was detected on normal Caco-2/TC7 cells. Most of the complexes exhibit antiproliferative activity that was better than or similar to auranofin, and at least nine times better than that of cisplatin. Its action mechanism is still under discussion since no evidence of cell cycle arrest was found, but an antioxidant role was shown for some of the selective complexes. All complexes were also tested as antimicrobial drugs, exhibiting good activity towards S. aureus and E. coli. bacteria and C. albicans and C. neoformans fungi.