Preparation, spectroscopic and thermal characterization of new charge-transfer complexes of ethidium bromide with π-acceptors. In vitro biological activity studies

Charge-transfer chemistry of two corticosteroids used adjunctively to treat COVID-19. Part II: The CT reaction of hydrocortisone and dexamethasone donors with TCNQ and fluoranil acceptors in five organic solvents

Hydrocortisone (termed as D1) and dexamethasone (termed as D2) are corticosteroids currently used to treat COVID-19. COVID-19 is a disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exploring additional chemical properties of drugs used in the treatment protocols for COVID-19 could help scientists alike improve these treatment protocols and potentially even the vaccines (i.e., Janssen, Moderna, AstraZeneca, Pfizer-BioNTech). In this work, the charge-transfer (CT) properties of these two corticosteroids (D1 and D2) with two universal acceptors: 7,8,8-tetracyanoquinodimethane (termed as TCNQ) and fluoranil (termed as TFQ) in five different solvents were investigated. The examined solvents were MeOH, EtOH, MeCN, CH2Cl2, and CHCl3. The CT interactions formed stable corticosteroid CT complexes in all examined solvents. Several spectroscopic parameters were derived, and the oscillator strength (f) and transition dipole moment (μe.g. ) values revealed that the interaction between the investigated corticosteroids with TCNQ acceptor is much stronger than their interaction with TFQ acceptor. The CT interactions were proposed to process via n → π* transition.

Charge-transfer chemistry of two corticosteroids used adjunctively to treat COVID-19. Part I: Complexation of hydrocortisone and dexamethasone donors with DDQ acceptor in five organic solvents

COVID-19 is the disease caused by a novel coronavirus (CoV) named the severe acute respiratory syndrome coronavirus 2 (termed SARS coronavirus 2 or SARS-CoV-2). Since the first case reported in December 2019, infections caused by this novel virus have led to a continuous global pandemic that has placed an unprecedented burden on health, economic, and social systems worldwide. In response, multiple therapeutic options have been developed to stop this pandemic. One of these options is based on traditional corticosteroids, however, chemical modifications to enhance their efficacy remain largely unexplored. Obtaining additional insight into the chemical and physical properties of pharmacologically effective drugs used to combat COVID-19 will help physicians and researchers alike to improve current treatments and vaccines (i.e., Pfizer-BioNTech, AstraZeneca, Moderna, Janssen). Herein, we examined the charge-transfer properties of two corticosteroids used as adjunctive therapies in the treatment of COVID-19, hydrocortisone and dexamethasone, as donors with 2,3-dichloro-5,6-dicyano-p-benzoquinone as an acceptor in various solvents. We found that the examined donors reacted strongly with the acceptor in CH2Cl2 and CHCl3 solvents to create stable compounds with novel clinical potential.

Charge-transfer chemistry of azithromycin, the antibiotic used worldwide to treat the coronavirus disease (COVID-19). Part III: A green protocol for facile synthesis of complexes with TCNQ, DDQ, and TFQ acceptors

Investigating the chemical properties of molecules used to combat the COVID-19 pandemic is of vital and pressing importance. In continuation of works aimed to explore the charge-transfer chemistry of azithromycin, the antibiotic used worldwide to treat COVID-19, the disease resulting from infection with the novel SARS-CoV-2 virus, in this work, a highly efficient, simple, clean, and eco-friendly protocol was used for the facile synthesis of charge-transfer complexes (CTCs) containing azithromycin and three π-acceptors: 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and tetrafluoro-1,4-benzoquinone (TFQ). This protocol involves grinding bulk azithromycin as the donor (D) with the investigated acceptors at a 1:1 M ratio at room temperature without any solvent. We found that this protocol is environmentally benign, avoids hazardous organic solvents, and generates the desired CTCs with excellent yield (92-95%) in a straightforward means.

Charge-transfer chemistry of azithromycin, the antibiotic used worldwide to treat the coronavirus disease (COVID-19). Part II: Complexation with several π-acceptors (PA, CLA, CHL)

Finding a vaccine or cure for the coronavirus disease (COVID-19) responsible for the worldwide pandemic and its economic, medical, and psychological burdens is one of the most pressing issues presently facing the global community. One of the current treatment protocols involves the antibiotic azithromycin (AZM) alone or in combination with other compounds. Obtaining additional insight into the charge-transfer (CT) chemistry of this antibiotic could help researchers and clinicians to improve such treatment protocols. Toward this aim, we investigated the CT interactions between AZM and three π-acceptors: picric acid (PA), chloranilic acid (CLA), and chloranil (CHL) in MeOH solvent. AZM formed colored products at a 1:1 stoichiometry with the acceptors through intermolecular hydrogen bonding. An n → π* interaction was also proposed for the AZM-CHL CT product. The synthesized CT products had markedly different morphologies from the free reactants, exhibiting a semi-crystalline structure composed of spherical particles with diameters ranging from 50 to 90 nm.

Mechanistic insights into ethidium bromide removal by palygorskite from contaminated water

Ethidium bromide (EtBr)-containing wastewater can be hazardous to biodiversity when released into the soil and water bodies without treatment. EtBr can mutate living microbial cells and pose toxicity to even higher organisms. This work investigated the removal of EtBr from aqueous solutions by a naturally occurring palygorskite (PFl-1) clay mineral via systematic batch adsorption experiments under different physicochemical conditions. EtBr existed in an undissociated form at pH ~7, and was adsorbed on PFl-1 obeying the Freundlich isotherm model. The maximum EtBr adsorption capacity was 285 mmol/kg. The best fitted kinetic model for EtBr adsorption was the pseudo-second order model. The amounts of exchangeable cations desorbed from PFl-1 during EtBr adsorption was linearly correlated to the amounts of EtBr adsorbed, with a slope of 0.97, implying that a cation exchange-based adsorption mechanism was dominating. Additionally, dimerization of EtBr molecules via bromide release assisted an increased EtBr removal by PFl-1 at high adsorbate concentrations. Detailed x-ray diffraction, Fourier transform infrared, scanning electron imaging and energy dispersive x-ray analyses confirmed that EtBr adsorption occurred dominantly on the surface of palygorskite which mineralogically constituted 80% of the bulk PFl-1 adsorbent. A small portion of EtBr was also adsorbed by PFl-1 through intercalation onto the smectite impurity (10%) in PFl-1. This study suggested that PFl-1 could be an excellent natural material for removing EtBr from pharmaceutical and laboratory wastewater.

Enhanced removal of ethidium bromide (EtBr) from aqueous solution using rectorite

Ethidium bromide (EtBr) is an intercalating agent commonly used as nucleic acid fluorescent tag in various techniques of life science field. It is considered as a serious biohazard due to its mutagenicity and carcinogenicity. As such, developing high efficiency and low cost materials as cleanup kits is in urgent need although many methods have already been developed. In this study we take use of the affinity of organic cations for clay minerals of high cation exchange capacity (CEC) and large specific surface area (SSA) and tested the removal of EtBr using rectorite, a type of clay mineral made of 1:1 regularly mixed layers of illite and montmorillonite. Our results showed that the uptake of Et⁺ on rectorite could be as high as 400 mmol/kg and the removal of Et⁺ was extremely fast. Desorption of inorganic cation Ca²⁺ and sorption of counterion Br^- revealed that cation exchange was the dominating mechanism of Et⁺ removal using rectorite. Thermal analyses revealed that the EtBr could be thermally destructed inside the interlayer of rectorite and the material could be thermally regenerated. Thus, clay minerals could have a great potential to be fabricated into cleanup kits for the removal of EtBr in case of spill.

Investigation of charge transfer complexes formed between (S, S)-bis-N,N-sulfonyl bis-L-phenylalanine dimethylester donor with tetracyanoethylene and chloranil as π-acceptors: Experimental and DFT studies

Two novel charge transfer complexes CTC ([D[Formula: see text]TCNE] and [D[Formula: see text]CHL] : D [Formula: see text] (S, S)-bis-N,N-sulfonyl bis-L-phenylalanine dimethylester; TCNE [Formula: see text] Tetracyanoethylene; CHL [Formula: see text] Chloranil) were synthesized and characterized by elemental analysis: Electronic absorption, spectrophotometric titration, IR. The obtained results indicate the formation of 1:1 for both complexes. The experimental studies were complemented by quantum chemical calculations at DFT/CAM-B3LYP level of theory. Optimized geometrical structures, the electronic spectroscopy, excited-state properties and the descriptions of frontier molecular orbitals were computed and discussed by time-dependent density functional theory (TD-DFT). In addition, vibrational frequency calculations, the natural population analysis (NPA) confirms the presence of intermolecular interactions and natural bonding orbitals (NBO) calculation was carried out in order to elucidate the interactions between TCNE [Formula: see text]-acceptor and donor molecule.

Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors

Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, (1)H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

Shedding light on the photostability of two intermolecular charge-transfer complexes between highly fluorescent bis-1,8-naphthalimide dyes and some π-acceptors: a spectroscopic study in solution and solid states

Given the great importance of the various uses of 1,8-naphthalimides in the trends of biology, medicine and industry, the current study focused on extending the scope of these dyes by introducing some of their charge-transfer (CT) complexes. For this purpose, two highly fluorescent bis-1,8-naphthalimide dyes and their complexes with some π-acceptors have been synthesized and characterized spectroscopically. The π-acceptors include picric acid (PA), chloranilic acid (CLA), tetracyanoquinodimethane (TCNQ) and dichlorodicyanobenzoquinone (DDQ). The molecular structure, spectroscopic and fluorescence properties as well as the binding modes were deduced from IR, UV-vis and (1)H NMR spectral studies. The binding ratio of complexation was determined to be 1:1 according to the elemental analyses and photometric titrations. It has been found that the order of acceptance ability for the different acceptors is TCNQ>DDQ>CLA>PA. The photostability of 1,8-naphthalimide dye as a donor and its charge-transfer complex doped in polymethyl methacrylate/PMMA were exposed to UV-Vis radiation and the change in the absorption spectra was achieved at different times during irradiation period.

Nano-structured complexes of reserpine and quinidine drugs with chloranilic acid based on intermolecular H-bond: spectral and surface morphology studies

The study of the drug-acceptor interaction may be useful in understanding the drug-receptor interactions and the mechanism of drug action. Here, complexes of reserpine (Res) and quinidine (Qui) drugs with chloranilic acid (CLA) have been synthesized. Then, these complexes were characterized chemically and structurally using CHN elemental analysis, infrared (IR) and electronic absorption spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The stoichiometry of the H-bonded complex was found to have a 1:1 ratio, so these complexes can be formulated as [(Drug)(CLA)]. IR measurements confirmed the presence of intermolecular H-bond. Application of Debye-Scherrer equation indicates that the formed complexes are in the range of nano-size. The Res complex exhibits a remarkable crystalline morphology. It was also found that the particle size of Res complex is 1.533 time higher than that of Qui complex. Interestingly, free Res molecular weight is higher than that of free Qui by the same ratio (precisely; 1.525).

Spectroscopic investigations of the charge-transfer interaction between the drug reserpine and different acceptors: towards understanding of drug-receptor mechanism

The study of the charge-transfer interaction of the drugs may be useful in understanding the drug-receptor interactions and the mechanism of drug action. Structural and thermal stability of charge-transfer (CT) complexes formed between the drug reserpine (Res) as a donor and quinol (QL), picric acid (PA), tetracyanoquinodimethane (TCNQ) or dichlorodicyanobenzoquinone (DDQ) as acceptors were reported. Elemental analysis, electronic absorption, spectrophotometric titration, IR, Raman, (1)H NMR and X-ray powder diffraction (XRD) were used to characterize the new products. The thermal stability of the synthesized CT complexes was investigated using thermogravimetric (TG) analyses, and the morphology and particle size of these complexes were obtained from scanning electron microscopy (SEM). The stoichiometry of the complexes (donor:acceptor molar ratio) was determined to be 1:1 for all complexes. Accordingly the formed CT complexes could be formulated as [(Res)(QL)], [(Res)(PA)], [(Res)(TCNQ)] and [(Res)(DDQ)]. It was found that the obtained CT complexes are nanoscale, semi-crystalline particles, thermally stable and formed through spontaneous reaction. The results obtained herein are satisfactory for estimation of drug Res in the pharmaceutical form.

Charge-transfer interaction of drug quinidine with quinol, picric acid and DDQ: Spectroscopic characterization and biological activity studies towards understanding the drug-receptor mechanism

Investigation of charge-transfer (CT) complexes of drugs has been recognized as an important phenomenon in understanding of the drug–receptor binding mechanism. Structural, thermal, morphological and biological behavior of CT complexes formed between drug quinidine (Qui) as a donor and quinol (QL), picric acid (PA) or dichlorodicyanobenzoquinone (DDQ) as acceptors were reported. The newly synthesized CT complexes have been spectroscopically characterized via elemental analysis; infrared (IR), Raman, ¹H NMR and electronic absorption spectroscopy; powder X-ray diffraction (PXRD); thermogravimetric (TG) analysis and scanning electron microscopy (SEM). It was found that the obtained complexes are nanoscale, semi-crystalline particles, thermally stable and spontaneous. The molecular composition of the obtained complexes was determined using spectrophotometric titration method and was found to be 1:1 ratios (donor:acceptor). Finally, the biological activities of the obtained CT complexes were tested for their antibacterial activities. The results obtained herein are satisfactory for estimation of drug Qui in the pharmaceutical form.