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The pyridoxal-semicarbazone (PLSC) ligand and its transition metal complexes have shown significant biological activity. In this contribution, a novel nickel(II)-PLSC complex, [Ni(PLSC)(SO4)(H2O)2], was obtained, and its structure was determined by X-ray crystallographic analysis, FTIR, and UV-VIS spectroscopy. The sulfate ion is directly coordinated to the central metal ion. The intermolecular stabilization interactions were examined using Hirshfeld surface analysis. The crystal structure was optimized by a B3LYP functional using two pseudopotentials for nickel(II) (LanL2DZ and def2-TZVP) together with a 6-311++G(d,p) basis set for non-metallic atoms. The experimental and theoretical bond lengths and angles were compared, and the appropriate level of theory was determined. The stabilization interactions within the coordination sphere were investigated by the Quantum Theory of Atoms in Molecules (QTAIM). The antioxidant activity towards hydroxyl and ascorbyl radicals was measured by EPR spectroscopy. The interactions between Human Serum Albumin (HSA) and the complex were examined by spectrofluorimetric titration and a molecular docking study. The mechanism of binding to DNA was analyzed by complex fluorescence quenching, potassium iodide quenching, and ethidium bromide displacement studies in conjunction with molecular docking simulations. [ABSTRACT FROM AUTHOR]

New Cu(II) complexes with pyridoxal-aminoguanidine (PLAG) ligands and different counterions (SO42− and NO3−) were prepared and their crystal structures were solved by the X-ray crystallography. The geometries of the obtained complexes significantly depended on the counterions, leading to the square-pyramidal structure of [Cu(PLAG)NO3H2O]NO3 (complex 1) and square-planar structure of [Cu(PLAG)H2O]SO4 (complex 2). The intermolecular interactions were examined using the Hirshfeld surface analysis. The theoretical structures of these complexes were obtained by optimization at the B3LYP/6-311++G(d,p)(H,C,N,O,S)/LanL2DZ(Cu) level of theory. The Quantum Theory of Atoms in Molecules (QTAIM) was applied to assess the strength and type of the intramolecular interactions and the overall stability of the structures. The interactions between the complexes and transport proteins (human serum albumin (HSA)) and calf thymus DNA (CT-DNA) were examined by spectrofluorometric/spectrophotometric titration and molecular docking. The binding mechanism to DNA was assessed by potassium iodide quenching experiments. The importance of counterions for binding was shown by comparing the experimental and theoretical results and the examination of binding at the molecular level. [ABSTRACT FROM AUTHOR]

Ru(II)‐arene compounds are being investigated as anticancer agents due to the biocompatibility of ruthenium and their structural diversity. Two newly synthesized Ru(II) complexes, [RuCl(η6‐p‐cymene)(3‐DNPH)] (chlorido(η6‐p‐cymene)(3‐nitrophenylhydrazine‐k2N,N′)ruthenium(II)) (1) and [RuCl(η6‐p‐cymene)(3‐CNPH)] (chlorido(3‐chlorophenylhydrazine‐k2N,N′)(η6‐p‐cymene)ruthenium(II)) (2), are experimentally (IR, NMR) and theoretically (B3LYP/6‐31+G(d,p)(H,C,N,Cl)/LanL2DZ(Ru)) characterized. Experimental and theoretical values of 1H and 13C chemical shifts and position of the most intense vibrational bands showed high correlation coefficients and low mean absolute errors, proving the predicted structure and applicability of the selected level of theory. Cell viability studies performed on MDA‐MB‐468, BT‐474, and PC3 cells using MTT and CV assay indicated the activity of the second complex similar to the activity of cisplatin towards BT‐474 breast cancer cells. The spectrofluorimetric measurements of Bovine Serum Albumin showed the binding process's spontaneity of complexes and protein, with a binding energy of around −30 kJ mol−1. Detailed molecular docking analysis allowed the elucidation of the binding mechanism through specific intermolecular interactions. Both compounds showed a higher affinity towards BSA than naproxen and cisplatin. Molecular docking simulations proved the spontaneity of the complexes binding to DNA. Based on these promising results, further biological examinations of these compounds are advised. [ABSTRACT FROM AUTHOR]

The antiradical activity of L-3,4-dihydroxyphenylalanine (L-DOPA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid and tyrosine towards 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt radical (ABTS-) was investigated experimentally and theoretically by UV–Vis spectroscopy and the DFT theory. The importance of the catechol moiety for this reaction was proven due to the formation of intramolecular hydrogen bond in the formed anions and radicals. The results indicated L-DOPA and DOPAC were more potent radical scavengers than homovanillic acid and tyrosine just because of intramolecular hydrogen bond formation. Based on experimental spectra, it was proved that electron transfer led to the reduction of ABTS•-. The values of thermodynamic parameters were used to predict the preferred mechanism. The reaction rates were calculated for the electron transfer processes and it was shown that these were both kinetically and thermodynamically driven processes. Based on the reaction rate values, thermodynamic parameters, and present species, as determined by electronic spectra, it was concluded that single proton loss electron transfer (SPLET) is the dominant reaction mechanism in the investigated system. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172040 and Grant no. 172015]

The spectrofluorometric method, based on fluorescence properties of aluminium (III)–hesperidin complex, for the determination of hesperidin in human plasma and pharmaceutical forms has been developed and validated. The complex shows strong emission in the presence of surfactant betain sulfonate SB 12 at 476 nm with excitation at 390 nm. Linearity range in pharmaceutical forms of hesperidin was 0.06 – 24.4 μg mL-1 with LOD 0.016 μg mL-1 and LOQ 0.049 μg mL-1. Recovery values in the range 99.3 – 99.7% indicate good accuracy of the method. A linear dependence of the intensity of fluorescence of the complex on the concentration of hesperidin in plasma was obtained in concentration range from 0.1 – 12.2 μg mL-1. The LOD was 0.032 μg mL-1 while LOQ was 0.096 μg mL-1. Recovery values were in the range 98.4 – 99.8%. The reliability of the method was checked by LC-MS/MS method for plasma samples and HPLC/UV method for tablets with direct determination of hesperidin after separation. Linearity range in determination of hesperidin in pharmaceutical forms was obtained in the range from 0.05 to 10.00 μg mL-1. The LOD was 0.01 μg mL-1 and LOQ was 0.03 μg mL-1. Linearity range in plasma determination of hesperidin was 0.02 – 10.00 μg mL-1 with LOD 0.005 μg mL-1 and LOQ 0.015 μg mL-1. Good agreement between two methods indicate the usability of the proposed spectroflurometric method for the simple, precise and accurate determination of hesperidin in clinical and quality control laboratories.

In this work, the matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectra of two cationic complexes, i.e., [PdCl(dien)]Cl and [Ru(en)2Cl2]Cl, acquired under different conditions were analyzed. The spectra were recorded with three matrices with or without trifluoroacetic acid (TFA), i.e., two traditional matrices, i.e., 2,5-dihydroxybenzoic acid and α-cyano-hydroxycinnamic acid, and one flavonoid, quercetin. The spectra acquired with quercetin appeared to be the simplest, whereas in the spectra obtained with other matrices, peaks arising either from the addition of matrix molecules or from the fragmentation products were detectable. Addition of TFA did not complicate the spectra of the Pd(II) and Ru(III) complexes when the traditional matrices were used. On the other hand, the spectra of Pd complex were simpler, whereas the addition of TFA in the case of the Ru complex resulted in a higher number of peaks, some of which could not be identified. Taken together, the results of this study once more emphasize the differences arising in the MALDI-TOF mass spectra of transition metal complexes in dependence on the applied matrix.

In the present work the structural transformations of malvin in aqueous acetate buffer solutions were investigated over a wide pH range under in vitro conditions using electronic absorption spectroscopy. In addition to the spectroabsorptiometric investigation, the voltammetric behavior and the mechanism of the redox process of this molecule were studied, in order to define its antioxidant properties. The electronic absorption spectra reveal that the structural changes of malvin, caused by changes in the pH of the medium, lead to changes in the voltammetric behaviour of this molecule. The dependence of the oxidation potential of malvin on pH, which can be explained by the presence of different electroactive molecular structures of malvin at different pH values, indicates different mechanisms of the electrode process. The voltammetric activity of malvin is compared semiquantitatively with the voltammetric activity of a standard synthetic antioxidant, BHA, and a natural antioxidant, quercetin.

The infrared spectra of the copigments of malvin with several organic acids: caffeic, ferulic, sinapic, chlorogenic, and tannic, were analyzed in order to elucidate the bonding of the molecules in the copigments. It was established that copigmentation is realized through hydrogen bonding between malvin molecules and the acids under study. The infrared spectra reveal that two groups of hydrogen bonds are formed, which include interactions of different molecular structures: hydroxy groups (bands around 3500 cm-1) and oxonium ions of the molecules (bands below 3000 cm-1). The formed hydrogen bonds were found to be of different strengths. The strengths of the hydrogen bonds were tentatively correlated with thermodynamic properties of the corresponding copigmentation reactions.

Ruthenium(II)–arene complexes have gained significant research interest due to their possible application in cancer therapy. In this contribution two new complexes are described, namely [{RuCl(η6-p-cymene)}2(μ-Cl)(μ-1-N,N′-naphthyl)]X (X = Cl, 1; PF6, 2), which were fully characterized by IR, NMR, and elemental microanalysis. Furthermore, the structure of 2 in the solid state was determined by a single crystal X-ray crystallographic study, confirming the composition of the crystals as 2·2MeOH. The Hirshfeld surface analysis was employed for the investigation of interactions that govern the crystal structure of 2·2MeOH. The structural data for 2 out of 2·2MeOH was used for the theoretical analysis of the cationic part [{RuCl(η6-p-cymene)}2(μ-Cl)(μ-1-N,N′-naphthyl)]+ (2a) which is common to both 1 and 2. The density functional theory, at B3LYP/6-31+G(d,p) basis set for H, C, N, and Cl atoms and LanL2DZ for Ru ions, was used for the optimization of the 2a structure. The natural bond orbital and quantum theory of atoms in molecules analyses were employed to quantify the intramolecular interactions. The reproduction of experimental IR and NMR spectra proved the applicability of the chosen level of theory. The binding of 1 to bovine serum albumin was examined by spectrofluorimetry and molecular docking, with complementary results obtained. Compound 1 acted as a radical scavenger towards DPPH• and HO• radicals, along with high activity towards cancer prostate and colon cell lines. [ABSTRACT FROM AUTHOR]

Research into the essence of the process of copigmentation of anthocyan molecules was continued by applying IR spectroscopy, in an attempt to elucidate the formation mechanism of copigment molecules between malvin chloride and several variously substituted flavones. Analysis of the IR spectra of the formed copigments revealed that the process of copigmentation is achieved via the formation of hydrogen bonds. The strength of the formed hydrogen bonds was correlated with the equilibrium constants of the processes of copigmentation of these molecules. The found correlation was in accordance with the supposed mechanism of the copigmentation reaction.

The reaction of copigmentation of malvidin 3,5-diglucoside and tannic acid of the ester type was studied. The interactions of these molecules were observed via UV-VIS absorption spectroscopy. It was established that the pH of the medium, the concentration of the copigmentating molecules, and the temperature affect the copigmentation process. The calculated equilibrium constant of the reaction of pH 3.00 is K = 226.9, and at pH 3.65 it is K = 277.0. The change of the Gibbs free energy in pH 3.00 buffer is ΔG =-13.4 kJ/mol, and in pH 3.65 buffer it is DG =-13.9 kJ/mol. The stoichiometric ratio of the components in the copigment is 1:1, at both pH values. It is evident from the calculated values of the thermodynamic functions that the process is thermodynamically favorable in the lower temperature range. Temperature appears as the basic parameter of the thermodynamic feasability of the process, since the copigmentation process is exothermic (ΔHpH=3.00 = -41.6 kJ/mol and ΔHpH=3.65 = -41.6 kJ/mol) and proceeds with a decrease in entropy (ΔSpH=3.00 = -94.4 J/mol K and ΔSpH=3.65 = -92.7 J/mol K).