Formation Constants Research Articles

H+-Selective Electrodes Based on Amine-Type Ionophores: Generalized Theory and A Priori Quantification of Lower and Upper Detection Limits.

A critical analysis of the known theories of functioning of H+-selective electrodes (H+-SEs) based on neutral amine-type carriers is given. A model of specific ion association is proposed, according to which, in membranes plasticized with 2-nitrophenyloctyl ether, the protonated ionophore and cation-exchanger form much stronger ion pairs with inorganic ions extracted from the sample solution than with each other, and simple equations that describe the lower and upper limit detection (pHUDL and pHLDL) are obtained. A feasible and reliable method for quantifying the pKa values of ionophores in the membrane phase from potentiometric data is substantiated. The efficiency of using single-ion partition coefficients and ion pair formation constants for a priori quantitative description of the H+-SE response in solutions of various compositions has been demonstrated for the first time. It is shown that the width of the dynamic response range of such electrodes depends on the nature of the tertiary amino group, and the reasons for the observed effect are discussed.

Microbiological and spectrophotometric methods for the determination of tioconazole: A comparative thermodynamic study

Two sensitive microbiological and charge transfer spectrophotometric methods have been developed for the quantitative determination of the antifungal drug, tioconazole, in its pure form and pharmaceutical preparations. The microbiological assay was based on the agar disk diffusion method by measuring the diameter of the inhibition zones related to different concentrations of tioconazole. The spectrophotometric method relied on charge transfer complex formation between tioconazole as an n-donor and chloranilic acid as a π-acceptor at room temperature. The formed complex was measured at λmax = 530 nm. The molar absorptivity and the formation constant of the formed complex were determined using different models, including the Benesi-Hildebrand, Foster-Hammick-Wardley, Scott, Pushkin-Varshney-Kamoonpuri, and Scatchard equations. Different thermodynamic parameters associated with the complex formation, including the free energy change (ΔG°), the standard enthalpy (ΔH°), and the standard entropy change (ΔS°), were evaluated. The two methods were validated in conformity with ICH-recommended guidelines and employed successfully for the quantification of tioconazole in both pure form and pharmaceutical formulations.

Kinetics and structure reactivity correlation in the oxidation of some para- substituted benzhydrols by benzimidazolium dichromate

The oxidation of some para-substituted benzhydrols by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide (DMSO) medium, results in the formation of corresponding diphenyl ketone. The reaction has been investigated on the condition of pseudo-first order. In terms of both BIDC and hydrogen-ion, the reaction is first order. In the case of benzhydrols, however, Michaelis-Menten type kinetics is observed. At different temperatures, the formation constants and rates of breakdown of benzhydrol-BIDC complexes have been determined. Complex formation thermodynamic parameters and activation parameters for complex decomposition have been computed. The kinetic isotope effect found in the oxidation of benzhydrol ((kH/kD = 5.93 at 293 K) shows that the rate-determining step involved α-C-H bond fission. For the kinetic analysis of the reaction, nineteen organic solvents have been utilized. The solvent impact have been investigated, and found that cation-solvation plays a significant role. A suitable mechanism is proposed based on the kinetic data, solvent effect analysis, and results of various non-kinetic parameters.

Development of a chemometric approach to improve the accuracy of copolymer sequence information obtained from pyrolysis gas-chromatography mass-spectrometry data

Number-average copolymer sequence length information can be obtained by pyrolysis-gas chromatography (Py-GC) by comparing the ratios of formed oligomers (i.e. dimers and trimers). The formation constants of the oligomers and their detection efficiency are not constant for all fragments, however. This can lead to unrepresentative peak ratios in the chromatogram. In these cases, calibration with an external method (e.g. NMR) is required. In this work, we introduce an algorithm that improves the copolymer sequence accuracy yielded from chromatograms with unrepresentative peak areas. The algorithm even functions in cases where oligomer data is missing as the rate of formation of certain oligomers is too low to detect them. One Py-GC measurement and one NMR measurement are required to train the developed algorithm for the determination of average monomer reactivity ratios and relative pyrolysis constants. Afterwards, Py-GC measurements of copolymers containing the same monomers, albeit with different compositions, can be corrected using the previously estimated constants. The algorithm was tested on various styrene-acrylate copolymers, yielding more accurate sequence information, even when limited oligomer information was available.

Optical and Electrochemical Sensing of Co(II), Ni(II) and Cu(II) in DMSO. Pyridyl Thiazole and (Thio)Amide Pincer Ligands versus Di‐2‐pyridyl Ketone Hydrazones

AbstractThe ability of six pincer type molecules (di‐2‐pyridyl ketone acetic acid hydrazone (1), N‐(2,5‐dimethoxyphenyl)‐6‐[(2,5‐dimethoxyphenyl)carbamothioyl]pyridine‐2‐carboxamide (2), 6‐(4,7‐dimethoxy‐2‐benzothiazolyl)‐N‐(2,5‐dimethoxyphenyl)‐2‐pyridinecarboxamide (3), di‐2‐pyridyl ketone thiosemicarbazone (4), bis‐N‐(2,5‐dimethoxyphenyl)pyridine‐2,6‐dicarbothioamide (5), and 6‐(4,7‐dimethoxy‐2‐benzothiazolyl)‐N‐(2,5‐dimethoxyphenyl)‐2‐pyridinecarbothioamide (6)), to detect MBr2 (where M=Co, Ni, and Cu) in DMSO was quantified via formation constants determined from spectrophotometric and voltammetric titrations. The limit of detection (from electronic spectroscopy) of 1–6 ranged from 0.9‐9.5 ppm. The values of β (=log K) for the six species were found to be in the ranges of 4.3–4.9 and 4.0–6.3 for Co(II), 3.9–5.5 and 3.5–4.3 for Ni(II), and 4.0–4.3 and 3.7–5.0 for Cu(II) by UV‐visible and voltammetric methods, respectively. The results suggested that κ3‐NNS (6) and the κ3‐NNO (3) had good affinity for Ni(II) and Cu(II), whereas the κ3‐SNS (5) had greater affinities for Co(II) and Ni(II). The hydrazones (κ3‐NNO, 1 and κ3‐NNS, 4) were generally in the middle of the pack, displaying good affinity for the three metal ions. In a contrasting vein, the κ3‐ONS species (2) was generally the lowest across the pincers. DFT calculations (PBE0/6‐31G(d,p)/SMD) suggested that stable complexes of coordination numbers=4 to 6 were plausible in solution.

Stability of the Inclusion Complexes of Dodecanoic Acid with α-Cyclodextrin, β-Cyclodextrin and 2-HP-β-Cyclodextrin

In the presented work, the stability of the formation of inclusion complexes of dodecanoic acid (lauric acid) with three cyclodextrins, α-cyclodextrin, β-cyclodextrin and 2-HP-β-cyclodextrin, was analyzed from the point of view of the size of the cavity in cyclodextrins, their molar mass and the structure of the studied fatty acid. The measurements were made in a wide temperature range of 283.15-318.15K. The conductometric method was used for these studies. The results obtained allowed us to determine the value of the theoretical limiting molar conductivity (Λm0) of the studied complexes, the values of the inclusion complex formation constants (Kf) and the values of thermodynamic functions (ΔG0, ΔH0 and ΔS0) describing the complexation process in the studied temperature range.

Mechanism of imidazole inhibition of a GH1 β-glucosidase.

Imidazole is largely employed in recombinant protein purification, including GH1 β-glucosidases, but its effect on the enzyme activity is rarely taken into consideration. Computational docking suggested that imidazole interacts with residues forming the active site of the GH1 β-glucosidase from Spodoptera frugiperda (Sfβgly). We confirmed this interaction by showing that imidazole reduces the activity of Sfβgly, which does not result from enzyme covalent modification or promotion of transglycosylation reactions. Instead, this inhibition occurs through a partial competitive mechanism. Imidazole binds to the Sfβgly active site, reducing the substrate affinity by about threefold, whereas the rate constant of product formation remains unchanged. The binding of imidazole within the active site was further confirmed by enzyme kinetic experiments in which imidazole and cellobiose competed to inhibit the hydrolysis of p-nitrophenyl β-glucoside. Finally, imidazole interaction in the active site was also demonstrated by showing that it hinders access of carbodiimide to the Sfβgly catalytic residues, protecting them from chemical inactivation. In conclusion, imidazole binds in the Sfβgly active site, generating a partial competitive inhibition. Considering that GH1 β-glucosidases share conserved active sites, this inhibition phenomenon is probably widespread among these enzymes, and this should be taken into account when considering the characterization of their recombinant forms.

Base-free selective oxidation of monosaccharide into sugar acid by surface-functionalized carbon nanotube composites

Selective oxidation of biomass-derived monosaccharide into high value-added chemicals is highly desirable from sustainability perspectives. Herein, we demonstrate a surface-functionalized carbon nanotube-supported gold (Au/CNT-O and Au/CNT-N) catalyst for base-free oxidation of monosaccharide into sugar acid. Au/CNT-O and Au/CNT-N surfaces successfully introduced oxygen- and nitrogen-containing functional groups, respectively. The highest yields of gluconic acid and xylonic acid were 93.3% and 94.3%, respectively, using Au/CNT-N at 90 °C for 240 min, which is higher than that of using Au/CNT-O. The rate constants for monosaccharide decomposition and sugar acid formation in Au/CNT-N system were higher, while the corresponding activation energy was lower than in Au/CNT-O system. DFT calculation revealed that the mechanism of glucose oxidation to gluconic acid involves the adsorption and activation of O2, adsorption of glucose, dissociation of the formyl C-H bond and formation of O-H bond, and formation and desorption of gluconic acid. The activation energy barrier for the glucose oxidation over Au/CNT-N is lower than that of Au/CNT-O. The nitrogen-containing functional groups are more beneficial for accelerating monosaccharide oxidation and enhancing sugar acid selectivity than oxygen-containing functional groups. This work presents a useful guidance for designing and developing highly active catalysts for producing high-value-added chemicals from biomass.

Promising anticancer agents based on 8-hydroxyquinoline hydrazone copper(II) complexes.

We report the synthesis and characterization of a group of benzoylhydrazones (Ln) derived from 2-carbaldehyde-8-hydroxyquinoline and benzylhydrazides containing distinct para substituents (R = H, Cl, F, CH3, OCH3, OH and NH2, for L1-7, respectively; in L8 isonicotinohydrazide was used instead of benzylhydrazide). Cu(II) complexes were prepared by reaction of each benzoylhydrazone with Cu(II) acetate. All compounds were characterized by elemental analysis and mass spectrometry as well as by FTIR, UV-visible absorption, NMR or electron paramagnetic resonance spectroscopies. Complexes isolated in the solid state (1-8) are either formulated as [Cu(HL)acetate] (with L1 and L4) or as [Cu(Ln)]3 (n = 2, 3, 5, 6, 7 and 8). Single crystal X-ray diffraction studies were done for L5 and [Cu(L5)]3, confirming the trinuclear formulation of several complexes. Proton dissociation constants, lipophilicity and solubility were determined for all free ligands by UV-Vis spectrophotometry in 30% (v/v) DMSO/H2O. Formation constants were determined for [Cu(LH)], [Cu(L)] and [Cu(LH-1)] for L = L1, L5 and L6, and also [Cu(LH-2)] for L = L6, and binding modes are proposed, [Cu(L)] predominating at physiological pH. The redox properties of complexes formed with L1, L5 and L6 are investigated by cyclic voltammetry; the formal redox potentials fall in the range of +377 to +395mV vs. NHE. The binding of the Cu(II)-complexes to bovine serum albumin was evaluated by fluorescence spectroscopy, showing moderate-to-strong interaction and suggesting formation of a ground state complex. The interaction of L1, L3, L5 and L7, and of the corresponding complexes with calf thymus DNA was evaluated by thermal denaturation. The antiproliferative activity of all compounds was evaluated in malignant melanoma (A-375) and lung (A-549) cancer cells. The complexes show higher activity than the corresponding free ligand, and most complexes are more active than cisplatin. Compounds 1, 3, 5, and 8 were selected for additional studies: while these complexes induce reactive oxygen species and double-strand breaks in both cancer cells, their ability to induce cell-death by apoptosis varies. Within the set of compounds tested, 8 emerges as the most promising one, presenting low IC50 values, and high induction of oxidative stress and DNA damage, which eventually lead to high rates of apoptosis.

Permittivity Threshold and Thermodynamics of Integer Charge-Transfer Complexation for an Organic Donor–Acceptor Pair

Molecular charge doping involves the formation of donor-acceptor charge-transfer complexes (CTCs) through integer or partial electron transfer; understanding how local chemical environment impacts complexation is important for controlling the properties of organic materials. We present steady-state and temperature-dependent spectroscopic investigations of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) complexed with the electron donor and hole transport material N,N'-diphenyl-N,N'-di-p-tolylbenzene-1,4-diamine (MPDA). Equilibrium formation constants (KCT) were determined for donor-acceptor pairs dissolved in a series of solvents covering a range of values of permittivity. A threshold for highly favorable complex formation was observed to occur at ϵ ∼ 8-9, with large (>104) and small (<103) values of KCT obtained in solvents of higher and lower permittivity, respectively, but with chloroform (ϵ = 4.81) exhibiting an anomalously high formation constant. Temperature-dependent formation constants were determined in order to evaluate the thermodynamics of complex formation. In 1,2-dichloroethane (ϵ = 10.36) and chlorobenzene (ϵ = 5.62), complex formation is both enthalpically and entropically favorable, with higher enthalpic and entropic stabilization in the solvent with higher permittivity. Complexation in chloroform is exothermic and entropically disfavored, indicating that specific, inner-shell solvent-solute interactions stabilize the charge-separated complex and result in a net increase in local solution structure. Our results provide insight into how modification to the chemical environment may be utilized to support stable integer charge transfer for molecular doping applications and requiring only modest changes in local permittivity.

Metal complexes of 1,4-bis(2-hydroxyethyl) piperazine: Thermodynamic and theoretical approach.

In the present study, the acid-base equilibria of 1,4-bis(2-hydroxyethyl)piperazine (BHEB) and the formation equilibria of complexes with the metal ions Cu(II), Ni(II), Co(II) and Zn(II) are investigated using the potentiometric technique. The acid-dissociation constants of BHEP in the protonated form and the formation constants of the complexes are determined using the Miniquad-75 program in the temperature range (15oC - 35oC). The thermodynamic parameters were determined and discussed. The concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties such as atomic number, ionic radius, electronegativity, and ionization potential are investigated. The complexes were synthesized and characterized by elemental analysis and mass spectra. Density Functional Theory (DFT) calculations have been performed to study the equilibrium geometry of 1,4-bis(2-hydroxyethyl)piperazine and its complexes. The optimization of the structure of the complexes reveals that CuII and CoII complexes have distorted octahedral geometry. NiII complex has a distorted square planar geometry. ZnII complex has a distorted tetrahedral geometry. The calculated total energies, energies of highest occupied molecular orbital (HOMO), energies of lowest unoccupied molecular orbital (LUMO) and dipole moments are reported. The N---N distance for uncoordinated 1,4-bis(2-hydroxyethyl)piperazine is calculated to be 2.870 Å and decreased to 2.588 Å, 2.491 Å, 2.502 Å, 2.479 Å, and 2.552 Å for Cu(II), Co(II), Ni(II) and Zn(II) complexes respectively. Also, bonds connected to N atoms are elongated upon complex formation. The interactions with the receptors as breast cancer oxidoreductase were feasible as evidenced by Docking analysis.

Parameters for the conductometric association for lump and nano CoSO4.7H2O in the presence and absence of fuchsin acid in water at different temperature

ABSTRACT. For lump and nanocobalt sulfate (CoSO4) in pure water, the affiliation and thermodynamic association characteristics were measured at 298.15, 303.15, 308.15, and 313.15 K. Based on the bulk and nano CoSO4 molar conductance, estimates were made for the parameters of the solvation, such as the activity coefficient, free energy of association, enthalpy of association, association constant, and entropy of association. We discussed about each of these solvation parameters. Two stoichiometric complexes were formed by the interaction of bulk and nano CoSO4.7H2O with fuchsin acid: 1:1 and 1:2 In the case of 1:1 (CoSO4.7H2O/fuchsin acid) compared to 1:2 (fuchsin acid in pure water as solvent), the complex Kf and ∆Gf are higher, indicating simpler complex formation. The temperature increase resulted in a drop in the formation constants. The complexation's negative ∆Gf values demonstrate that the process of complex synthesis was spontaneous and that the temperature improved the spontaneity.&#x0D; &#x0D; KEY WORDS: Molar conductance, Association constants, Fuchsin acid, Nano cobalt sulfate salt, Formation constant&#x0D; &#x0D; Bull. Chem. Soc. Ethiop. 2023, 37(3), 789-804. &#x0D; DOI: https://dx.doi.org/10.4314/bcse.v37i3.20

Novel chemically modified carbon paste electrode for the reliable nanomolar detection of propranolol and cyclodextrin inclusion complex investigation

The efficiency of a new potentiometric carbon paste sensor for the fast, easy and selective measurement of propranolol was described. The potentiometric sensor was constructed using propranolol-tungstosilicate ion association as an excellent ionophore in the carbon paste matrix. The developed sensor exhibited a Nernstian slope of 59.2 mV/decade for propranolol over the concentration limit of 1.7 × 10−9 – 2.2 × 10−4 M and a limit of detection 9.3 × 10−10 M. The electrode has a fast response time, satisfactory reproducibility, long lifetime and excellent selectivities for propranolol relative to a diversity of exterior organic and inorganic species. The efficacy of temperature on the potential response of the sensor was investigated, and it was found that the sensor possessed a low temperature coefficient. Potentiometric measurements of propranolol in biological and pharmaceutical samples such as blood serum, urine, milk and tablet were investigated by the proposed sensor, and appropriate recoveries and accuracies were obtained. Moreover, the sensor was applied to examine the inclusion complex formation between propranolol and β-cyclodextrin, and the corresponding formation constant was calculated.

Processes of Complex Formation in an Fe(II)–Fe(III)–H2Sal–C2H5OH–H2O System

Processes of the formation of coordination compounds in the Fe(II)–Fe(III)–H2Sal–C2H5OH–H2O system are studied using the Clark–Nikolsky oxidation potential at a temperature of 298.16 K and an ionic strength of the solution of 1.0 mol/L against a sulfate background. The formation of complexes of the following compositions is established: [FeHSal(H2O)5]2+, [Fe(HSal)2(H2O)4]+, [Fe(HSal)2OH(H2O)3]−, [Fe(HSal)2(OH)2(H2O)3]3−, [FeIIIFeII(HSal)2(OH)2(H2O)8]+, [FeHSal(H2O)5]+, [Fe(HSal)(OH)(H2O)4]0, [FeIIFeIII(HSal)2(OH)2(H2O)8]+. The constants of formation of all complexes are calculated via iteration of the oxidizing function, and the areas of their dominance and maximum degrees of accumulation are determined.

Spectrophotometric Study of Palladium(II) Complexation with Elementary Amino Acids in Aqueous Solution

Complex formation of aqua palladium(II) ions with glycine (Gly), β‑alanine (β-Ala), and taurine (Tau) in aqueous solution was studied by spectrophotometric titration at I = 1.0 mol/L (HClO4 + NaClO4) and T = 25 ± 1°C. A monoligand complex appeared at pH 0 in the H‒Pd–Gly system under the conditions of our experiment; mono- and biscomplexes were formed at pH 1. In the H‒Pd‒β-Ala system, a monoligand complex was formed at pH 1 and mono- and biscomplexes were formed at pH 2. In the H‒Pd‒Tau system, a monoligand complex was formed at pH 1 and 2. Molar absorption coefficients were calculated: the peak absorption occurs at λ = 370 nm and ε = 203 L/(mol cm) for the monoligand glycinate complex [PdGly(H2O)2]+; at λ = 325 nm and ε = 274 L/(mol cm) for the biscomplex [PdGly2]0; at λ = 365 nm and ε = 342 and 297 L/(mol cm) for the β‑alaninate [Pdβ‑Ala(H2O)2]+ and taurinate [PdTau(H2O)2]+ monoligand complexes, respectively; and at λ = 330 nm and ε = 549 L/(mol cm) for the β‑alaninate biscomplex [Pdβ‑Ala2]0. Logarithmic concentration formation constants were calculated for glycinate (log β1 = 15.03 ± 0.07, and log β2 = 28.97 ± 0.28), β-alaninate (log β1 = 13.94 ± 0.05, and log β2 = 25.24 ± 0.06), and taurinate (log β1 = 9.74 ± 0.08) palladium(II) complexes.

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.

Asymmetrical Platinum and Rhodium Dinuclear Complex Strongly Bound to Filled d Complexes by Unbridged Pt-Metal Bonds: Toward Heterometallic-Extended Metal Atom Chains.

Heterometallic extended metal atom chains (EMACs) aligned with three types of metal were rationally synthesized by forming unbridged metal-metal bonds based on the interactions between highest occupied and lowest unoccupied molecular orbitals at the d orbital. These chains form pentanuclear structures aligned as Rh-Pt-M-Pt-Rh with relatively large formation constants of 5.0×1013 M-2 for M=Pt and 6.3×1011 M-2 for M=Pd, while retaining their backbones in solution. In the case of M=Cu, the original Cu(+2) atoms were reduced to Cu(+1) during the synthetic process. Cu(+1) has an unprecedented trigonal bipyramidal coordination geometry. The reported synthesis based on asymmetrical dinuclear complexes provides a guideline for the synthesis of hetero-EMACs to allow several analogs through judicious combinations realized by tuning the number of metal nuclei and metal species.

Structural, mechanical and dynamical stabilities of K2NaMCl6 (M: Cr, Fe) halide perovskites along with electronic and thermal properties

The properties of K2NaMCl6 (M: Cr, Fe) are simulated using density functional theory. The exchange-correlation potential of halide perovskites is projected by generalized gradient approximation and integration of modified Becke–Johnson potential. The structure's stability is defined by optimizing total energy and using the tolerance factor. In contrast, the enthalpy of formation and elastic constants are used to predict the thermodynamical and mechanical stabilities, while phonon calculations for dynamical stability, respectively. The conventional lattice constant obtained is consistent with those reported for similar halide perovskites. Spin-polarized band structure and energy state distribution plots portray these materials' semiconducting behavior in both spin states. The magnetic moment of 3µB and 5µB is obtained for Cr and Fe-based materials, respectively. The magnetic moment is mainly from transition-metal-based constituents. The thermoelectric figure of merit suggests that these materials could be potential candidates for waste heat recovery.

Experimental-theoretical study to determine the pKa values of the ocular hypotensive Dorzolamide from UV–Vis spectroscopy

The pKa values of the ocular hypotensive dorzolamide (Dor) were calculated by experimental UV–Vis spectrophotometric data and with the aid of the Stability Quotients from Absorbance Data (SQUAD) software, resulting in an additional pKa value for this drug. From the global formation constants (log β) calculated with SQUAD, three pKa values were determined: 4.14 ± 0.06, 6.13 ± 0.04, and 8.36 ± 0.01 associating only pKa1 to the secondary amino group. With theoretical calculations, the geometries of all the Dor chemical species involved in acid-base equilibria were optimized using an experimental reproduction criterion (UV–Vis spectra) resulting in four of five possible Dor species: DorH4+, DorH3, DorH2− and DorH2−. The Dor3− species was theoretically shown not to exist or if it is formed, to tend towards the formation of the DorH2−. Finally, a deprotonation pathway is proposed for this drug.

Synthesis and computational studies of novel cobalt(II) and oxovanadium(IV) complexes of quinoline carbaldehyde derivative ligand for antibacterial and antioxidant applications

Novel metal complexes [Co(HL)2(H2O)2)] (1) and [VO(HL)2] (2) were synthesized using 2-((2-hydroxyethyl)amino)quinoline-3-carbaldehyde, ligand in 1:2 metal–ligand ratio in methanolic solution. The compounds were characterized with 1HNMR, 13CNMR, UV–Visible spectroscopy, fluorescence spectroscopy, FTIR Spectroscopy; powder X-Ray Diffraction, Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy, Mass Spectroscopy and thermogravimetric analysis. The FTIR spectral data showed that the ligand is bidentate that bound to metal ions through the nitrogen of amine (NH) and the deprotonated hydroxyl group (OH). The powder XRD and SEM results indicate that both the complexes showed polycrystalline nature. The formation constants of the complexes were determined spectroscopically and the values are 2.05 × 106 and 6.29 × 105 for Co(II) and V(IV) complexes respectively). Both metal complexes are stable at the specified temperatures, and the thermodynamic parameters indicated that the reactions are spontaneous with exothermic nature of metal-ligand interactions. Antibacterial activities of the complexes were evaluated with disk diffusion and agar dilution method. The Co(II) complex showed recognizable bacterial activity, against Pseudomonas aeruginosa with mean inhibition zone of 20.65 ± 0.18, with minimum inhibitory concentration (MIC) values of 3.25 µg/mL. Additionally, the antioxidant activity of the complexes were also determined in vitro using 1,1-diphenyl-2-picryl hydrazyl, in which Co(II) complex showed higher antioxidant activities with half maximal inhibitory concentrations IC50 of 9.15 µg/ml. The results of binding mode of these compounds against receptors Escherichia coli, Pseudomonas aeruginosa and Streptococcus pyogenes were in good agreement with the in vitro biological activity results.