Spectrophotometric Titration Method Research Articles

Charge-Transfer Interactions Between Antibiotics and Small Organic Acids: Spectroscopic Characterization and Computational Investigation

Six new charge-transfer complexes using ofloxacin (OFL) and sulfamethazine (SMR) as electron donors and coumaric acid (COA), cinnamic acid (CNA), and salicylic acid (SAA) as acceptors via equimolar mixture have been synthesized. The experiment used UV-vis spectroscopy to determine the formation of the complex in methanol through the presence of a new broad absorption band with a maximum wavelength in the 200-400 nm range. The molecular composition of the charge-transfer complexes was determined by the spectrophotometric titration method and found to be 1:1 (donor: acceptor). These complexes have been characterized by infrared (FTIR) and scanning electron microscopy (SEM). In the FTIR spectra, the CT complexes showed a wavelength shift compared to the reactants. The complexes exhibited various morphologies by SEM, including spherical particles, short rods, and flattened shapes. Additionally, quantum chemical calculations at the DFT/B3LYP level of theory investigated the complexes' steady-state structures, energies, and charge densities. The intermolecular binding energies was negative, indicating that the reactions of the six complexes proceeded spontaneously. There was strong van der Waals forces and hydrogen bonds between the donor and acceptor, which contributed to the complexes' strong molecular stability. The C-N and N-H groups in the donor molecule, and the -COOH group in the acceptor molecule, played key roles in the complexation process. DFT calculation results were appropriate to support our experimental results. This study highlights the molecular mechanisms of donor and acceptor action in charge-transfer interactions, providing a theoretical basis for the synthesis of antibiotic complexes and the removal of antibiotics.

Temperature Changes in Luminescence of Mixed Complexes of Terbium and Samarium with Organic Ligands Based on 2,2-bipyridyldicarboxamides

Solutions in acetonitrile of three mixed complexes of rare earth elements (terbium and samarium) with organic ligands with various pyridine substituents were studied in this work. The ratios of ligands and metals in the resulting complexes were determined, and the stability constants of samarium complexes were calculated using the spectrophotometric titration method. Measurements of absorption, emission and excitation spectra of luminescence, luminescence kinetics of solutions of mixed complexes of rare earth elements with an excess of metal relative to the ligand were carried out at various temperatures in the range 298–328 K. An increase of luminescence intensity of a samarium ion in complex upon heating has been discovered for the first time. The dependences of the luminescence quantum yield and lifetime of mixed complexes on temperature were obtained. A thermometric parameter — the ratio of the integral luminescence intensities of samarium and terbium ions — was proposed, and the temperature sensitivity coefficient of this parameter was determined for different complexes.

Ligand-binding characteristics of CYP51 Mycobacterium tuberculosis in relation to marine steroid compounds

CYP51 steroid-14α-demethylases are members of a large superfamily of cytochrome P450 enzymes found in all kingdoms of living organisms, and catalyze the 14α-demethylation reaction of a number of natural steroids, including lanosterol, obtusifoliol, and 24,25-dihydrolanosterol. CYP51 are important components of the eukaryotic steroid biosynthetic chain, and thus represent one of the main targets for antifungal therapy. A 14α-demethylase CYP51 homologous gene has also been found in the genome of Mycobacterium tuberculosis. At the same time, M. tuberculosis lacks the de novo pathway for steroid biosynthesis. Conservation of CYP51 among the Mycobacterium genus and colocalization in the genome with 3Fe-4S ferredoxin Rv0763c, which maintains its catalytic activity in vitro, may indirectly indicate the involvement of MTCYP51 in a biochemical process important for mycobacteria. In order to characterize the specificity of the MTCYP51 active site to various compounds of isoprenoid nature, we obtained a highly purified MTCYP51 and, using spectrophotometric titration and surface plasmon resonance methods, studied the interaction of MTCYP51 with steroids from marine organisms obtained in the Pacific Institute of Bioorganic Chemistry of the Far Eastern Branch of the Russian Academy of Sciences. The investigated compounds represent a wide range of evolutionarily ancient isoprenoids. The results showed that MTCYP51 is able to bind structurally diverse steroid derivatives in the active site. The conducted studies suggest the biological role of MTCYP51 for pathogenic mycobacteria, which consists in the binding and possible metabolism of exogenous bioregulatory isoprenoids in vivo.

Effect of the stability of 1,3-bis(diphenylphosphoryl)-2-oxapropane complexes on the separation of lanthanide ions and their detection.

Phosphoryl podands of neutral type with a flexible ethylene glycol chain and diphenylphosphorylmethyl end groups are known for their complexation properties towards various cations. In this work, the complexation process between 1,3-bis(diphenylphosphoryl)-2-oxapropane (L) and lanthanide ions was studied. Namely, the stability constants of lanthanide complexes with L in acetonitrile were estimated by the method of spectrophotometric titration. It was found that the stability constants of Ln3+ complexes with L increase in the lanthanide series, which is consistent with the extraction and ion-selective properties of L. The extraction ability of L and this ligand in the presence of ionic liquids (ILs) such as methyltrioctylammonium nitrate (MTOAN) and bis[(trifluoromethyl)sulfonyl]imide 1-butyl-3-methylimidazolium (C4mimTf2N) was studied. It was found that in the presence of ILs, L extracts the elements of the yttrium subgroup of lanthanides much better than those of the cerium subgroup: SFLu/Ce(L-MTOAN) = 2.29; SFLu/Ce(L-C4mimTf2N) = 110.38. The use of the L-C4mimTf2N mixture in the processes of lanthanide separation into subgroups is much more efficient than the use of L without the addition of ILs or the use of the L-MTOAN mixture. The ion-selective properties of L towards Ln3+ ions were studied. Podand L exhibits potentiometric selectivity to Lu3+ ions.

Molecular Cloning, Heterologous Expression, Purification, and Evaluation of Protein-Ligand Interactions of CYP51 of Candida krusei Azole-Resistant Fungal Strain.

Due to the increasing prevalence of fungal diseases caused by fungi of the genus Candida and the development of pathogen resistance to available drugs, the need to find new effective antifungal agents has increased. Azole antifungals, which are inhibitors of sterol-14α-demethylase or CYP51, have been widely used in the treatment of fungal infections over the past two decades. Of special interest is the study of C. krusei CYP51, since this fungus exhibit resistance not only to azoles, but also to other antifungal drugs and there is no available information about the ligand-binding properties of CYP51 of this pathogen. We expressed recombinant C. krusei CYP51 in E. coli cells and obtained a highly purified protein. Application of the method of spectrophotometric titration allowed us to study the interaction of C. krusei CYP51 with various ligands. In the present work, the interaction of C. krusei CYP51 with azole inhibitors, and natural and synthesized steroid derivatives was evaluated. The obtained data indicate that the resistance of C. krusei to azoles is not due to the structural features of CYP51 of this microorganism, but rather to another mechanism. Promising ligands that demonstrated sufficiently strong binding in the micromolar range to C. krusei CYP51 were identified, including compounds 99 (Kd = 1.02 ± 0.14 µM) and Ch-4 (Kd = 6.95 ± 0.80 µM). The revealed structural features of the interaction of ligands with the active site of C. krusei CYP51 can be taken into account in the further development of new selective modulators of the activity of this enzyme.

Supramolecular Hybrid Complexes Based on Octahedral Molybdenum(II) Iodide Cluster and Zinc(II) Porphyrin

The possibility of the formation of supramolecular hybrids based on two photosensitizers, an octahedral molybdenum(II) iodide cluster with six terminal isonicotinate ligands (Bu4N)2[{Mo6I8}(OOC–C5H4N)6] (PyMoC, C) and A4-type zinc(II) porphyrin (ZnTPP, P), has been demonstrated. Spectrophotometric and NMR titration methods have shown that the formation of CPn complexes (n = 1–6) occurs in solutions of noncoordinating chlorinated solvents due to the formation of metal–N-ligand coordination bonds between the components. The use of an octahedral cluster as a hexatopic N-ligand and the lability of the Zn···NPy bonds together lead to the formation of a series of CPn complexes (n = 1–6), which are in dynamic equilibrium in solution. Nevertheless, conditions have been selected to isolate single crystals of individual forms CP4 + 2 and CP6 + 2, and their structures have been determined by X-ray diffraction analysis. The PyMoC cluster turns out to coordinate four or six ZnTPP molecules, respectively, while both structures contain two “extramolecules” of zinc(II) porphyrin bound to the cluster via hydrogen bonds involving the oxygen atoms of the isonicotinate groups and protons of water axially coordinated to the porphyrin metal center.

Uv-spectroscopic and iodometric back titration analysis of total caffeine content of energy drinks available in markets in cross river state, south-south, nigeria

Caffeine is an active ingredient of energy drinks that is often consumed to improve cognizance and physical cum mental alertness. This research aims to quantitatively analyze the caffeine content in serving volumes of energy drinks by spectrophotometric and iodometric back titration methods. In the spectrophotometric method, the determination of caffeine content was carried out using a maximum wavelength of 270 nm. The results show that the caffeine contents of the energy drinks were 37.40 mg/200 mL (Passion) < 64.73 mg/250 mL (Bullet) < 82.70 mg/355 mL (Power Horse) < 86.30 mg/400 mL (Predator) < 114.68 mg/500 mL (Fearless) while the iodometric back titration method showed 57.50 mg/250 mL, 165.00 mg/500 mL, 160.00 mg/400 mL, 117.15 mg/355 mL and 40 mg/200 mL respectively for Bullet, fearless, Predator, Power Horse and Passion. The labeled claims on the energy drinks were 78.75 mg/250 mL, 157.50 mg/500 mL, 120.00 mg/400 mL, 133.60 mg/355 mL and 50 mg/200 mL respectively for Bullet, fearless, Predator, Power Horse and Passion which indicates that manufacturers reported higher values of caffeine content in their product possibly to make it attractive to consumers.

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.

A detailed experimental and computational study of Cd complexes with pyridyl‐based thiazolyl hydrazones

Interest in Cd complexes has been growing in recent years. Cd complexes are considered a potential solution in the search for novel antibiotics that can fight antimicrobial resistance. In addition, Cd complexes draw attention to material chemistry. The main objective of this work was to prepare the first Cd(II) complexes with anionic forms of pyridine‐based thiazolyl hydrazone (THs) ligands HLS2[(E)‐4‐(4‐methoxyphenyl)‐2‐(2‐[pyridine‐2‐ylmethylene]hydrazinyl)thiazole] and HLS3[(E)‐2‐(2‐[pyridine‐2‐ylmethylene]hydrazinyl)‐4‐(p‐tolyl)thiazole] and perform their structural and spectroscopic characterization, as well as stability in solution and upon heating. Studies related to their biological activities and possible electrochromic applications are also being conducted. Complexes [Cd(HLS2)2] (1) and [Cd(HLS3)2] (2) have been characterized by a single‐crystal X‐ray diffraction and computational analysis of intermolecular interactions responsible for their solid‐state structures was performed. Thermal stability of1and2in the solid‐state was analyzed by TGA/MS, where as their solution stability was determined by the spectrophotometric titration method. Electrochemical andin situUV–Vis spectroelectrochemical analyses of1and2were carried out to determine redox mechanisms and the influence of the substituents and electrolytes on their redox responses. The antioxidant capacity of both complexes was tested in antioxidant assays, while their antimicrobial activity was tested against five Gram‐positive and four Gram‐negative bacteria, as well as against three fungi. The obtained results indicate their potent antioxidant capacity. The antimicrobial activity of investigated compounds on almost all tested bacterial strains was stronger than that of the standard antibiotic erythromycin. The results of docking studies indicate that the minor groove DNA is the possible biological target of1and2.

Investigation of The Chemical Reactions of 2, 4, 6-Trinitrophenol with Thiocyanate Ion in Acidic Condition: Kinetic Approach

The rate and overall observed chemical change of the redox reaction between 2, 4, 6-trinitrophenol (TNP) and thiocyanate ion (SCN–) was investigated under a constant concentration of ionic strength, [????!] and λmax = 360 nm using a spectrophotometric titration method. The research aim is to study stoichiometry, order of reaction, the influence of acid, and the effect of change in ionic concentration on the reaction speed. The stoichiometry discovered gave a 1:2 molar proportion of TNP against SCN–. The reaction is 1st - order in relation to TNP and 1st – order in relation to SCN– hence, a 2nd -order overall for the system. An acid-dependence rate constant on TNP was positive for the TNP – SCN– system. A positive salt effect was observed in the system. An increase in the concentration of added cations and anions (Mn2+, NO3− and PO43−) had no influence on the speed of the reaction. The spectroscopic and kinetic results did not show any intermediate complex emergence all through the reaction. On grounds of the experimental results attained, a presumptive mechanism in favor of an outer-sphere mechanism has been recommended.

Supramolecular charge-transfer complex generated by the interaction between tin(II) 2,3-naphtalocyanine as a donor with DDQ as an acceptor: Spectroscopic studies in solution state and theoretical calculations

The charge-transfer (CT) phenomenon has attracted the attention of many researchers since it was discovered by Robert Mulliken in 1969. Complexes generated through CT interactions have contributed to industrial processing, technological development, and clinical pharmacology. Here, tin(II) 2,3-naphtalocyanine molecule (termed as SnNc) as a donor was reacted with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as an acceptor in acetonitrile solvent. This yielded a dark brown CT complex formulated as [(SnNc)(DDQ)2]. The resulting CT complex was compositionally (elemental analysis, spectrophotometric titration method, and Job’s continuous variation method), structurally (UV–visible, IR and 1H NMR spectroscopies, and thermal measurements), and theoretically (DFT/TD-DFT calculations) characterized. Electronic charges were transferred from SnNc to DDQ via n → π* transitions in the [(SnNc)(DDQ)2] complex. The experimental data were corroborated with DFT/TD-DFT calculations using B3LYP/LanL2DZ theory level. The energy of the CT reaction and other important parameters were also calculated.

Prototropic tautomerism of (E)-N-((4-((2-hydroxy-5-methoxybenzylidene) amino)phenyl)sulfonyl)acetamide and its coordination abilities towards Ru, Rh, and Ir trivalent metal ions

The Schiff base (E)-N-((4-((2-hydroxy-5-methoxybenzylidene)amino)phenyl)sulfonyl) acetamide (ScB-SAM) has been synthesized bytheir condensation at room temperature in ethanol. X-ray crystallographic analysis revealed that the keto-enol tautomerism of its solid state exists as a complex equilibria system that is stabilized intramolecular hydrogen bond. The enol, keto and mixed enol-zwitterionic forms were observed in the crystal structure. The crystallographic results were supported by ATR, and UV–Vis. Physical properties were determined in different polar and nonpolar solvents and solid state. All above experimental results were then compared with DFT calculations. Additionally, the stabilities of the trivalent: iridium, rhodium and ruthenium ions complexes with ScB-SAM have also been investigated by spectrophotometric titration methods in water. The data showed that the examined coordination compounds were stable in solution based on the values of their stability constants found.

Synthesis, characterization, potential antimicrobial, antioxidant, anticancer, DNA binding, and molecular docking activities and DFT on novel Co(II), Ni(II), VO(II), Cr(III), and La(III) Schiff base complexes

In this study, five novel complexes for Co(II), Ni(II), VO(II), Cr(III), and La(III) ions were synthesized from a tridentate NNO monobasic chelating Schiff base ligand, (Z)‐2‐((pyridin‐2‐ylimino)methyl)phenol (HL). Spectral and analytical tools were applied to elucidate the structural compositions of the new compounds. Then, geometry optimization was conducted for all the syntheses by the Gaussian 09 program via the density functional theory method to obtain optimal structures and the most essential parameters. Moreover, the biochemical behaviors of all the syntheses were explored based on the reactivity, which was tested against various cancer cell lines (HepG‐2, MCF‐7, and HCT‐116). The complexes exhibited an interestingly antiproliferative potential against human cancer cell lines, and the cytotoxicities of the new complexes were arranged to follow the order: VOL > CrL > NiL > LaL > CoL > HL. The antioxidant behaviors of the complexes were studied using the DPPH assay, and VOL showed the maximum antioxidant activity, followed by LaL. The antibacterial activities of the HL ligand and its complexes were studied. Moreover, the binding nature of the complexes with calf thymus DNA (CT‐DNA) was investigated based on the spectrophotometric absorption titration, viscosity, and gel electrophoresis methods. The binding ability of the complexes with CT‐DNA was proposed to be just intercalation or replacement mode. The intrinsic binding constant Kb was calculated and arranged based on the following order: VOL (5.2 × 105) > CrL (3.6 × 105) > NiL (3.3 × 105) > LaL (3.0 × 105) > CoL (1.12 × 105) mol−1 dm−3. Docking investigations were performed using the receptors of COVID‐19's main protease viral protein (PDB ID: 6LU7) and Escherichia coli (gram [–ve] bacteria [PDB ID: 1fj4]).

Spectrophotometric Study of Bridging N-Donor Ligand-Induced Supramolecular Assembly of Conjugated Zn-Trisporphyrin with a Triphenylamine Core.

This article studies the supramolecular assembly behavior of a Zn-trisporphyrin conjugate containing a triphenylamine core (1) with bridging N-donor ligands using the UV-vis spectrophotometric titration method at micromolar concentrations. Our results show that pyridine, a non-bridging ligand, formed a 3:1 open complex with 1. The corresponding binding constant was estimated to be (2.7 ± 0.15) × 1014 M−3. In contrast, bridging ligands, 4,4-bipyridine (BIPY) and 1,3-di(4-pyridyl)propane (DPYP), formed stable 3:2 double-decker complexes with 1 in solution, which collapsed to yield a 3:1 open complex when excess BIPY or DPYP was added. The binding constants for forming BIPY and DPYP double-decker complexes were estimated to be (9.26 ± 0.07) × 1027 M−4 and (3.62 ± 0.16) × 1027 M−4, respectively. The UV-vis titration profiles supported the conclusion that the degradation of the 3:2 double-decker 1∙BIPY complex is less favorable compared to that of 1∙DPYP. Consequently, the formation of the 3:1 1∙DPYP open complex proceeded more readily than that of 1∙BIPY.

Self-Assembled Manganese(I)-Based Selenolato-Bridged Tetranuclear Metallorectangles: Host-Guest Interaction, Anticancer, and CO-Releasing Studies.

Supramolecular one-step self-assembly of dimanganese decacarbonyl, diaryl diselenide, and linear dipyridyl ligands (L = pyrazine (pz), 4,4'-bipyridine (bpy), and trans-1,2-bis(4-pyridyl)ethylene (bpe)) has resulted in the formation of selenolato-bridged manganese(I)-based metallorectangles. The synthesis of tetranuclear Mn(I)-based metallorectangles [{(CO)3Mn(μ-SeR)2Mn(CO)3}2(μ-L)2] (1-6) was facilitated by the oxidative addition of diaryl diselenide to dimanganese decacarbonyl with the simultaneous coordination of linear bidentate pyridyl linker in an orthogonal fashion. Formation of metallorectangles 1-6 was ascertained using IR, UV-vis, NMR spectroscopic techniques, and elemental analyses. The molecular mass of compounds 2, 4, and 6 were determined by ESI-mass spectrometry. Solid-state structural elucidation of 2, 3, and 6 by single-crystal X-ray diffraction methods revealed a rectangular framework wherein selenolato-bridges and pyridyl ligands define the shorter and longer edges, respectively. Also, the guest binding capability of metallorectangles 3 and 5 with different aromatic guests was studied using UV-vis absorption and emission spectrophotometric titration methods that affirmed strong host-guest binding interactions. The formation of the host-guest complex between metallorectangle 3 and pyrene has been explicitly corroborated by the single-crystal X-ray structure of 3•pyrene. Moreover, select metallorectangles 1-4 and 6 were studied to explore their anticancer activity, while CO-releasing ability of metallorectangle 2 was further appraised using equine heart myoglobin assay.

Antibacterial Activity of Co(III) Complexes with Diamine Chelate Ligands against a Broad Spectrum of Bacteria with a DNA Interaction Mechanism.

Cobalt coordination complexes are very attractive compounds for their therapeutic uses as antiviral, antibacterial, antifungal, antiparasitic, or antitumor agents. Two Co(III) complexes with diamine chelate ligands ([CoCl2(dap)2]Cl (1) and [CoCl2(en)2]Cl (2)) (where dap = 1,3-diaminopropane, en = ethylenediamine) were synthesized and characterized by elemental analysis, an ATR technique, and a scan method and sequentially tested against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration results revealed that anaerobic and microaerophilic bacteria were found to be the most sensitive; the serial passages assay presented insignificant increases in bacterial resistance to both compounds after 20 passages. The synergy assay showed a significant reduction in the MIC values of nalidixic acid when combined with Compounds (1) or (2). The assessment of cell damage by the complexes was performed using scanning electron microscopy, transmission electron microscopy, and confocal microscopy, which indicated cell membrane permeability, deformation, and altered cell morphology. DNA interaction studies of the Co(III) complexes with plasmid pBR322 using spectrophotometric titration methods revealed that the interaction between Complex (1) or (2) and DNA suggested an electrostatic and intercalative mode of binding, respectively. Furthermore, the DNA cleavage ability of compounds by agarose gel electrophoresis showed nuclease activity for both complexes. The results suggest that the effect of the tested compounds against bacteria can be complex.

Synthesis, structure and basic properties of 5,10,15,20-tetrakis[4′-(benzoxazole-2-yl)phenyl]-21,23-dithiaporphyrin

The synthesis of 5,10,15,20-tetrakis [4 '- (benzoxazol-2-yl) phenyl] -21,23-dithiaporphyrin was carried out by the reaction of metal complex catalysis. In this work, quantum chemical calculations were performed in the DFT approximation (hybrid functional B3LYP) with a set of 6–21 G basis functions. The resulting compound was identified by electron absorption, 1H NMR spectroscopy and mass spectrometry. The basic properties of heterosubstituted ligand in comparison with the classical porphyrin analogue and unsubstituted TPP were studied by the spectrophotometric titration method in an acetonitrile - perchloric acid system. The basicity constants for the first and second steps and the ranges of existence of the protonated forms of 5,10,15,20-tetrakis [4 '- (benzoxazol-2-yl) phenyl] -21,23-dithiaporphyrin and its classical analog were determined.

Solution, and solid investigations on the charge–transfer complexation between seproxetine as a selective serotonin reuptake inhibitor drug with six kinds of π–electron acceptors

The study in this article deals with the donor–acceptor interaction between seproxetine (SRX) donor and π–electron acceptors such as picric acid, dinitrobenzene, p-nitro benzoic acid, 2,6-dichloroquinone-4-chloroimide, 2,6-dibromoquinone-4-chloroimide, and 7,7′,8,8′-tetracyanoquinodi methane which can be referred to by the following chemical abbreviations “PA, DNB, p-NBA, DCQ, DBQ, and TCNQ” respectively, in a liquid medium, and the associated complexes in the solid form were also isolated and characterized. A spectrophotometric titration method was employed to the quantitative analyses of seproxetine HCl in pure form. The stoichiometric analysis based on the molar ratio technique was found to be 1:1 (SRX: π–acceptor) regarding the charge–transfer interactions between the electrons of donor and acceptors. The different physical spectroscopic parameters “formation constant (KCT), molar extinction coefficient (εCT), standard free energy (∆Go), oscillator strength (ƒ), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID)” were calculated according to the spectroscopic data. The charge–transfer complexes which isolated in solid form were well characterized using some of analytical tools “microanalytical, molar conductance, FTIR, 1H-NMR and X-ray powder diffraction”. Thermal stability of solid charge transfer complexes was investigated using TG/DTG thermogravimetric technique. The kinetic thermodynamic values were calculated upon the thermal decomposition diagrams. The surface morphology, particle size and the elementary percentages of the solid SRX charge–transfer complexes were investigated with the help of scanning (SEM) and transmission (TEM) electron microscopies as well as energy-dispersive X-ray spectroscopy (EDX)

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.

Complexation Reactions between N,N '-Diethyl-N,N '-Difluorophenyl-2,2'-Bipyridyl-6,6-Dicarboxamides with Europium in Ethanol: Spectrophotometric and Isothermal Titration Calorimetry Studies

In this work, we studied the thermodynamic parameters of the complexation reaction between europium and N,N '-diethyl-N,N '-difluorophenyl-2,2'-bipyridyl-6,6'-dicarboxamides in ethanol. The complexation reaction lead to one complex particle with 1 : 1 metal : ligand composition. Spectrophotometric and calorimetric titration methods were used for determination of the stability of complexes. According to our data, the fluorine atom in the meta-position in the ligand (log K = 3.59) increases the stability of complexes, enthalpy and entropy compared with the para-position (log K = 3.26). Comparison of two parameters ΔrH and TΔrS for the 3-F ligand (–8.6 and 14.15 kJ/mol, respectively) shows that they are lower than that of for the 4-F ligand (–15.5 and 10.19 kJ/mol, respectively).