Spectrophotometric and thermodynamic studies on the 1:1 charge transfer interaction of several clinically important drugs with tetracyanoethylene in solution-state: Part one

Universal Measure for the Impact of Adiabaticity on Quantum Transitions

Adiabaticity is crucial for our understanding of complex quantum dynamics and thus for advancing fundamental physics and technology, but its impact cannot yet be quantified in complex but common cases where dynamics is only partially adiabatic, several eigenstates are simultaneously populated and transitions between noneigenstates are of key interest. We construct a universally applicable measure that can quantify the adiabaticity of quantum transitions in an arbitrary basis. Our measure distinguishes transitions that occur due to the adiabatic change of populated system eigenstates from transitions that occur due to beating between several eigenstates and can handle nonadiabatic events. While all quantum dynamics fall within the scope of the measure, we demonstrate its usage and utility through two important material science problems-energy and charge transfer-where adiabaticity could be effected by nuclear motion and its quantification will aid not only in unraveling mechanisms but also in system design, for example, of light harvesting systems.

Procainamide Charge Transfer Complexes with Chloranilic Acid and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone: Experimental and Theoretical Study

The formation of charge transfer (CT) complexes between bioactive molecules and/or organic molecules is an important aspect in order to understand ‘molecule-receptor’ interactions. Here, we have synthesized two new CT complexes, procainamide-chloranilic acid (PA-ChA) and procainamide-2,3-dichloro-5,6-dicyano-1,4-benzoquinone (PA-DDQ), from electron donor procainamide (PA), electron acceptor chloranilic acid (ChA), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The structures of these two CT complexes were elucidated/characterized using FTIR, NMR, and many other spectroscopic methods. A stability study of each complex was conducted for the first time using various spectroscopic parameters (e.g., formation constant, molar extinction coefficient, ionization potential oscillator strength, dipole moment, and standard free energy). The formation of CT complexes in solution was confirmed by spectrophotometric determination. The molecular composition of each complex was determined using the spectrophotometric titration method and gave a 1:1 (donor:acceptor) ratio. In addition, the formation constant was determined using the Benesi–Hildebrand equation. To understand the noncovalent interactions of the complexes, density functional theory (DFT) calculations were performed using the ωB97XD/6-311++G(2d,p) level of theory. The DFT-computed interaction energies (ΔIEs) and the Gibbs free energies (ΔGs) were in the same order as observed experimentally. The DFT-calculated results strongly support our experimental results.

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 (μ_e.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.

Enhancement of Haloperidol Binding Affinity to Dopamine Receptor Via Forming a Charge-Transfer Complex with Picric Acid and 7,7,8,8-Tetracyanoquinodimethane for Improvement of the Antipsychotic Efficacy

Haloperidol (HPL) is a typical antipsychotic drug used to treat acute psychotic conditions, delirium, and schizophrenia. Solid charge transfer (CT) products of HPL with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and picric acid (PA) have not been reported till date. Therefore, we conducted this study to investigate the donor–acceptor CT interactions between HPL (donor) and TCNQ and PA (π-acceptors) in liquid and solid states. The complete spectroscopic and analytical analyses deduced that the stoichiometry of these synthesized complexes was 1:1 molar ratio. Molecular docking calculations were performed for HPL as a donor and the resulting CT complexes with TCNQ and PA as acceptors with two protein receptors, serotonin and dopamine, to study the comparative interactions among them, as they are important neurotransmitters that play a large role in mental health. A molecular dynamics simulation was ran for 100 ns with the output from AutoDock Vina to refine docking results and better examine the molecular processes of receptor–ligand interactions. When compared to the reactant donor, the CT complex [(HPL)(TCNQ)] interacted with serotonin and dopamine more efficiently than HPL only. CT complex [(HPL)(TCNQ)] with dopamine (CTtD) showed the greatest binding energy value among all. Additionally, CTtD complex established more a stable interaction with dopamine than HPL–dopamine.

Intermolecular interactions of tetracyanoethylene (TCNE) and fumaronitrile (FN) with minor amines: A combined UV–Vis and EPR study

In this paper, the nature of interactions between two cyanocarbons—tetracyanoethylene (TCNE) and fumaronitrile (FN)—and a series of four secondary amines possessing a general formula C4HxN (x = 5–11) is thoroughly scrutinized. For all of the TCNE–amine pairs, tricyanovinylation (TCV) reaction is observed; however, only for pyrrole, it is accompanied with a visible charge-transfer (CT) complex formation—no such chemical individuals, characteristic for TCNE, have been noticed for aliphatic and alicyclic amines. On the contrary, FN forms such complexes with all the amines studied. Interestingly, a rather unexpected reaction of FN with alicyclic amines has been observed. The recorded electron paramagnetic resonance (EPR) spectra indicate the presence of both TCNE●− and FN●− radicals in the analyzed samples, assigned to a complete charge (electron) transfer process within the CT complexes, whose efficiency can be additionally enhanced by photoirradiation. The origination of the former radical, whose presence is observed also in the TCNE–diethylamine mixture, is as well proposed to result indirectly from the TCV reaction, occurring for this system. Finally, the superhyperfine structure of EPR spectra, indicating the existence of some secondary interactions of the radicals with surrounding compounds, is discussed. Formation of CT complexes and tricyanovinylates has been investigated and characterized with UV–Vis spectroscopy, while the presence of (cyano)radicals in the analyzed mixtures has been evidenced by (photoinduced) EPR measurements. Interpretation of the experimental results is also supplemented with computer simulations including density functional theory calculations.

New Charge Transfer Complexes of K+-Channel-Blocker Drug (Amifampridine; AMFP) for Sensitive Detection; Solution Investigations and DFT Studies

UV-Vis spectroscopy was used to investigate two new charge transfer (CT) complexes formed between the K⁺-channel-blocker amifampridine (AMFP) drug and the two π-acceptors 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in different solvents. The molecular composition of the new CT complexes was estimated using the continuous variations method and found to be 1:1 for both complexes. The formed CT complexes' electronic spectra data were further employed for calculating the formation constants (K_CT), molar extinction coefficients (ε_CT), and physical parameters at various temperatures, and the results demonstrated the high stability of both complexes. In addition, sensitive spectrophotometric methods for quantifying AMFP in its pure form were proposed and statistically validated. Furthermore, DFT calculations were used to predict the molecular structures of AMFP-DDQ and AMFP-TCNE complexes in CHCl₃. TD-DFT calculations were also used to predict the electronic spectra of both complexes. A CT-based transition band (exp. 399 and 417 nm) for the AMFP-TCNE complex was calculated at 411.5 nm (f = 0.105, HOMO-1 → LUMO). The two absorption bands at 459 nm (calc. 426.9 nm, f = 0.054) and 584 nm (calc. 628.1 nm, f = 0.111) of the AMFP-DDQ complex were theoretically assigned to HOMO-1 → LUMO and HOMO → LUMO excitations, respectively.

Charge-transfer complexation of TCNE with azithromycin, the antibiotic used worldwide to treat the coronavirus disease (COVID-19). Part IV: A comparison between solid and liquid interactions

Finding a cure or vaccine for the coronavirus disease (COVID-19) is the most pressing issue facing the world in 2020 and 2021. One of the more promising current treatment protocols is based on the antibiotic azithromycin (AZM) alone or in combination with other drugs (e.g., chloroquine, hydroxychloroquine). We believe gaining new insight into the charge-transfer (CT) chemistry of this antibiotic will help researchers and physicians alike to improve these treatment protocols. Therefore, in this work, we examine the CT interaction between AZM (donor) and tetracyanoethylene (TCNE, acceptor) in either solid or liquid forms. We found that, for both phases of starting materials, AZM reacted strongly with TCNE to produce a colored, stable complex with 1:2 AZM to TCNE stoichiometry via a n → π* transition (AZM → TCNE). Even though both methodologies yielded the same product, we recommend the solid-solid interaction since it is more straightforward, environmentally friendly, and cost- and time-effective.

Preparation, spectroscopic, characterizations and biological studies of new charge transfer complexes formed between fluconazole drug with various acceptors

Charge transfer complexes developed during the interaction of Fluconazole drug (FLU) as an electron donor with different types of electron acceptors, including σ-type as iodine (I₂), and π-types as 2,3-dinitrosalsylic acid (HDNS), Tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The formed complexes were characterized using various techniques as UV-Vis spectra, Thermal analyses, spectrophotometric measurements, ¹H NMR and FTIR Spectroscopy. It was found that the stoichiometry of all developed complexes was a 1:1 M ratio between fluconazole and acceptors (I₂, HDNS, TCNE and DDQ). The characteristic physical parameters data such as ionization potential (I_D), The oscillator strength (ƒ), formation constant (K_CT), transition dipole moment (μ), free energy (ΔG), and energy of interaction (E_CT) of the formed CT-complexes have also been reported. Eventually, the synthesized complexes were screened for their microbial and antioxidant activities.

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.

Charge-transfer chemistry of azithromycin, the antibiotic used worldwide to treat the coronavirus disease (COVID-19). Part I: Complexation with iodine in different solvents

Around the world, the antibiotic azithromycin (AZM) is currently being used to treat the coronavirus disease (COVID-19) in conjunction with hydroxychloroquine or chloroquine. Investigating the chemical and physical properties of compounds used alone or in combination to combat the COVID-19 pandemic is of vital and pressing importance. The purpose of this study was to characterize the charge transfer (CT) complexation of AZM with iodine in four different solvents: CH2Cl2, CHCl3, CCl4, and C6H5Cl. AZM reacted with iodine at a 1:1 M ratio (AZM to I2) in the CHCl3 solvent and a 1:2 M ratio in the other three solvents, as evidenced by data obtained from an elemental analysis of the solid CT products and spectrophotometric titration and Job's continuous variation method for the soluble CT products. Data obtained from UV-visible and Raman spectroscopies indicated that AZM strongly interacted with iodine in the CH2Cl2, CCl4, and C6H5Cl solvents by a physically potent n→σ* interaction to produce a tri-iodide complex formulated as [AZM·I+]I3 -. XRD and TEM analyses revealed that, in all solvents, the AZM-I2 complex possessed an amorphous structure composed of spherical particles ranging from 80 to 110 nm that tended to aggregate into clusters. The findings described in the present study will hopefully contribute to optimizing the treatment protocols for COVID-19.

Measurements and correlations in solution-state for charge transfer products caused from the 1:2 complexation of TCNE acceptor with several important drugs

In our previous work, we highlighted the thermodynamic and spectroscopic characteristics of the 1:1 charge transfer (CT) complexation of TCNE acceptor with various medically important drugs. Continuing that work, we further examine drugs that react with the TCNE acceptor via a 1:2 interaction. The examined drugs are atenolol, quinidine, cimetidine, reserpine, and levofloxacin. We aimed through this study to: i) make the spectrophotometric and thermodynamic data of the examined drugs, both initially and when reacted via a 1:2 M ratio with the TCNE acceptor, available to use in the determination or detection of these drugs in pharmaceuticals and other environments; and ii) compare the mode of interactions and the spectrophotometric and thermodynamic properties between drugs that react via a 1:1 or 1:2 ratio with the TCNE acceptor. To achieve these aims, the five examined drugs were reacted with TCNE in acetonitrile (MeCN) solvent at room temperature. Several thermodynamic and spectroscopic data were experimentally estimated using the van't Hoff and the Benesi-Hildebrand equations and discussed.

Application of a definitive screening design for the synthesis of a charge-transfer complex of sparfloxacin with tetracyanoethylene: spectroscopic, thermodynamic, kinetics, and DFT computational studies

Herein, a spectrochemical approach was adopted to study the charge-transfer (CT) complexation of sparfloxacin (SFX) with tetracyanoethylene (TCNE). In this study, a three-level design of experiments (DOE) involving a definitive screening design (DSD) was implemented. This is the first effort to operate this new category of design to determine a pharmaceutical compound in its pure form and in formulations. The proposed design allowed the establishment of a regression model that described the relation between the factorial input and the response surface. Moreover, two charge-transfer states (CTSs) were observed at 390 and 464 nm. The DFT calculations conducted using B3LYP/6-31+G showed that SFX had several donation sites (donor, D), whereas TCNE had two acceptor (A) sites. The two states were influenced differently by the experimental conditions as per the findings of the DSD analysis. In general, the diluting solvent had the largest impact. Probability plots, histograms, individual value plots, residual plots as well as analysis of variance (ANOVA) were delineated at the 95.0% confidence interval (CI). A Job's plot showed that a 1 : 1 complex was formed. The results were further confirmed using Benesi–Hildebrand plots. The proposed approach was proved to be linear in the range of 10–90 μg mL⁻¹ SFX when the absorbance was measured at 464 nm. Different set-ups were adopted for studying the reaction kinetics. Analytical method performance was assessed following the ICH guiding principles, and the results obtained were found to be satisfactory. Complex formation was found to be an exothermic reaction.

A spectrochemical approach was adopted to study the charge-transfer (CT) complexation of sparfloxacin (SFX) with tetracyanoethylene (TCNE). Definitive screening design (DSD) was used to investigate the reaction variables.

Cation Dependence of the Dimerization Enthalpy for A2 [tetracyanoethylene]2 (A=NMe4 , Mepy, NEt4 ) Possessing a Long, Multicenter Bond

[TCNE]^.- (TCNE=tetracyanoethylene) has been isolated as D_2h π-[TCNE]₂^2- possessing a long, 2.9 Å multicenter 2-electron-4-center (2e^- /4c) C-C bond, and as C₂ π-[TCNE]₂^2- possessing a longer, 3.04 Å multicenter 2e^- /6c (4 C+2 N atoms) bond. Temperature-dependent UV/Vis spectroscopic measurements in 2-methyltetrahydrofuran (MeTHF) has led to the determination of the dimerization, 2[TCNE]^.- ⇌π-[TCNE]₂^2- , equilibrium constants, K_eq (T), [[TCNE]₂^2- ]/[[TCNE]^.- ]² , enthalpy, ΔH, and entropy, ΔS, of dimerization for [Mepy]₂ [TCNE]₂ (Mepy=N-methylpyridinium, H₃ CNC₅ H₅⁺ ) possessing D_2h π-[TCNE]₂^2- and [NMe₄ ]₂ [TCNE]₂ possessing C₂ π-[TCNE]₂^2- conformations in the solid state; however, both form D_2h π-[TCNE]₂^2- in MeTHF solution. Based on ΔH=-3.6±0.1 kcal mol^-1 (-15.2 kJ mol^-1 ), and ΔS=-11±1 eu (-47 J mol^-1  K^-1 ) and ΔH=-2.4±0.2 kcal mol^-1 (-10.2 kJ mol^-1 ), and ΔS=-8±1 eu (-32 J mol^-1  K^-1 ) in MeTHF for [NMe₄ ]₂ [TCNE]₂ and [Mepy]₂ [TCNE]₂ , respectively, the calculated K_eq (298 K) are 1.6 and 1.3 m^-1 , respectively. The observed K_eq (145 K) are 3 and 2 orders of magnitude greater for [NMe₄ ]₂ [TCNE]₂ and [Mepy]₂ [TCNE]₂ , respectively. The K_eq (130 K) is 4470, 257, ≈0.8, and ≪0.1 m^-1 for [NMe₄ ]₂ [TCNE]₂ , [Mepy]₂ [TCNE]₂ , [NEt₄ ]₂ [TCNE]₂ , and [N(nBu)₄ ]₂ [TCNE]₂ , respectively, decreasing with increasing cation size. At standard conditions and below ambient temperature the equilibrium favors the dimer for the NMe₄⁺ and Mepy⁺ cations. From the decreasing enthalpy, NMe₄⁺ >Mepy⁺ , along with the decrease in dimer formation K_eq (T) as NMe₄⁺ >Mepy⁺ >NEt₄⁺ >N(nBu)₄⁺ , the dimer bond energy decreases with increasing cation size in MeTHF. This is attributed to a decrease in the [A]⁺ ⋅⋅⋅[TCNE]^- attractive interactions with increasing cation size. Solid state UV/Vis spectroscopic determinations of [NMe₄ ]₂ [TCNE]₂ are reported and compared to D_2h π-[TCNE]₂^2- conformers. The feasibility and limitations of temperature-dependent electron paramagnetic resonance (EPR) measurements for the determination of K_eq (T) are also discussed.