Vesna D. Vitnik

Antioxidant properties of selected 4-phenyl hydroxycoumarins: Integrated in vitro and computational studies.

A study on the structure-activity relationship of three hydroxy 4-phenyl coumarins, carried out by employing a series of different chemical cell-free tests is presented. Different assays involving one redox reaction with the oxidant (DPPH, ABTS, FRAP and CUPRAC) were employed. Further, the measurement of inhibition of oxidative degradation, such as lipid peroxidation, was used to define compound antioxidant activity. Our results confirm the good antioxidant activity of the 7,8-dihydroxy-4-phenyl coumarin and moderate antioxidant activity of 5,7-dihydroxy-4-phenyl coumarin. In this work, quantum chemical calculations based on density functional theory have been employed at B3LYP/6-311++G(d,p) level of theory to study the influence of number and position of hydroxyl groups in coumarin molecules on antioxidant activity. Calculated values for HOMO and LUMO energies, energy gap, stabilization energies and spin density distribution confirmed experimental results and were used for SAR definition. For determination of reaction mechanism in gas phase and selected solvents bond dissociation enthalpy, adiabatic ionization potential, proton dissociation enthalpy, proton affinity, electron transfer enthalpy and gas phase acidity have been calculated. Hydrogen Atom Transfer mechanism in vacuum and Single-Electron Transfer followed by the Proton Transfer mechanism in other studied systems are most probable free radical scavenging pathways. On the basis of these findings, these hydroxy 4-phenyl coumarins may be considered as potential therapeutic candidates for pathological conditions characterized by free radical overproduction.

Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of potent antiepileptic drug 1-(4-chloro-phenyl)-3-phenyl-succinimide.

This study represents an integrated approach towards understanding the vibrational, electronic, NMR, and structural aspects, and reactivity of 1-(4-chloro-phenyl)-3-phenyl-succinimide (CPPS). A detailed interpretation of the FT-IR, UV and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) B3LYP method using 6-31G(d,p) and 6-311++G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the σ(*) and π(*) antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV-Vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.

Synthesis, structure and solvatochromic properties of some novel 5-arylazo-6-hydroxy-4-phenyl-3-cyano-2-pyridone dyes

BackgroundA series of some novel arylazo pyridone dyes was synthesized from the corresponding diazonium salt and 6-hydroxy-4-phenyl-3-cyano-2-pyridone using a classical reaction for the synthesis of the azo compounds.ResultsThe structure of the dyes was confirmed by UV-vis, FT-IR, 1H NMR and 13C NMR spectroscopic techniques and elemental analysis. The solvatochromic behavior of the dyes was evaluated with respect to their visible absorption properties in various solvents.ConclusionsThe azo-hydrazone tautomeric equilibration was found to depend on the substituents as well as on the solvent. The geometry data of the investigated dyes were obtained using DFT quantum-chemical calculations. The obtained calculational results are in very good agreement with the experimental data.

The spectroscopic (FT-IR, FT-Raman, l3C, 1H NMR and UV) and NBO analyses of 4-bromo-1-(ethoxycarbonyl)piperidine-4-carboxylic acid

In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of 4-bromo-1-(ethoxycarbonyl)piperidine-4-carboxylic acid (BEPA). BEPA has been characterized by FT-IR, FT-Raman, (1)H NMR, (13)C NMR and UV spectroscopy. The FT-IR and FT-Raman spectra of BEPA were recorded in the solid phase. The optimized geometry was calculated by B3LYP and M06-2X methods using 6-311G(d,p) basis set. The FT-IR and FT-Raman spectra of BEPA were calculated at the same level and were interpreted in terms of Potential Energy Distribution (PED) analysis. The scaled theoretical wavenumber showed very good agreement with the experimental values. The (1)H and (l3)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Independent Atomic Orbital (GIAO) method. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using Natural Bond Orbital (NBO) analysis. Density plots over the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) energy surface directly identifies the donor and acceptor atoms in the molecule. It also provides information about the charge transfer within the molecule. To obtain chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is plotted over the optimized geometry of the molecule.

New derivatives of hydantoin as potential antiproliferative agents: biological and structural characterization in combination with quantum chemical calculations

Two new series of hydantoin derivatives, 3-(4-substituted benzyl)-5,5-diphenyl- and 3-(4-substituted benzyl)-5-ethyl-5-phenylhydantoins, were synthesized and their antiproliferative activity was tested against human colon cancer HCT-116 and breast cancer MDA-MB-231 cell lines. The presence of different substituents on both hydantoin and benzyl moieties changed the antiproliferative activity of the investigated hydantoins, whereby most of the compounds showed superior antiproliferative activity against MDA-MB-231 than against the HCT-116 cell line. The structure of three compounds was studied by single-crystal X-ray diffraction. The general structural characteristic is the presence of N–H···O hydrogen bonds in crystal packings. The molecular geometry and bonding features of the investigated hydantoins in the ground states were calculated using the density functional method. The relationship between structure and antiproliferative activity was discussed. The data presented in this investigation afford guidelines for the preparation of new hydantoin derivatives with greater antiproliferative activity.Graphical Abstract

Towards understanding intermolecular interactions in hydantoin derivatives: the case of cycloalkane-5-spirohydantoins tethered with a halogenated benzyl moiety

A series of cycloalkane-5-spirohydantoins bearing a halogeno substituted benzyl group (X = Cl and Br) in position 3 has been synthesized and their structures (1–6) have been determined by a single crystal X-ray diffraction method. These compounds have multiple functional groups, which allow greater competition and/or cooperation among the different intermolecular interactions in the formation of their crystal structures. The molecules are linked together by paired N–H⋯O hydrogen bonds in R22(8) rings, while the C–H⋯O interactions lead to their further association into double chains. The contribution of the cycloalkyl ring depends on its conformational flexibility and the multiple C–H donor implications. In the case of compounds 1–4 bearing the cyclopentyl or the cyclohexyl ring, halogen bonding (X⋯O) interactions give rise to a supramolecular pseudo-hexagonal network. In addition, the C–H⋯X interactions with a higher degree of multifurcation at the halogen acceptor have an important role in the formation of the crystal structure. Regarding compounds 5 and 6 with the cycloheptane ring, the X⋯O interaction is absent, and along with the C–H⋯X interactions, these compounds realize an alternative crystal structure with an emphasis on the X⋯π interactions. The lattice energies of all these crystal structures, as well as the intermolecular pair energies, have been calculated using PIXEL and further partitioned into coulombic, dispersive, polarization and repulsive factors. The crystal structures have also been subjected to Hirshfeld surface analysis which reveals that approximately 75% of the close contacts correspond to relatively weak interactions. The application of both concepts has provided a new insight into the relationship between the molecular interactions and crystal structures of the hydantoin derivatives.

Solvatochromic and quantum chemical investigations of newly synthesized succinimides: substituent effect on intramolecular charge transfer

Two series of 1-aryl-3-phenyl- and 1-aryl-3,3-diphenylpyrrolidine-2,5-diones were synthesized and their solvatochromic properties were studied in a set of 15 solvents of different polarity. The effect of specific and non-specific solvent–solute interactions on the position of their absorption bands was evaluated by using the solvent parameter sets of Kamlet and Taft. The interpretation of the effect of different substituent patterns on the solvatochromic properties of the investigated compounds was based on quantum chemical calculations performed by the density functional theory (DFT)/CAM-B3LYP method using the 6-311G(d,p) basis set. The theoretical absorption frequencies show very good agreement with the experimental values. The energy gaps between the HOMO and LUMO orbitals were also analyzed. It is demonstrated that different substituents change the conjugation effect and further determine the pathways of intramolecular charge transfer.Graphical abstract

CCDC 1509613: Experimental Crystal Structure Determination

Related Article: Anita Lazic, Nemanja Trisovic, Lidija Radovanovic, Jelena Rogan, Dejan Poleti, Željko Vitnik, Vesna Vitnik, Gordana Uscumlic|2017|CrystEngComm|19|469|doi:10.1039/C6CE02210C

CCDC 1509614: Experimental Crystal Structure Determination

Related Article: Anita Lazic, Nemanja Trisovic, Lidija Radovanovic, Jelena Rogan, Dejan Poleti, Željko Vitnik, Vesna Vitnik, Gordana Uscumlic|2017|CrystEngComm|19|469|doi:10.1039/C6CE02210C

Carbenic vs. ionic mechanistic pathway in reaction of cyclohexanone with bromoform.

AbstractThe extensive computation study was done to elucidate the mechanism of formation dibromoepoxide from cyclohexanone and bromoform. In this reaction, the formation of dihaloepoxide 2 is postulated as a key step that determines the distribution and stereochemistry of products. Two mechanistic paths of reaction were investigated: the addition of dibromocarbene to carbonyl group of ketone, and the addition of tribromomethyl carbanion to the same (C=O) group. The mechanisms for the addition reactions of dibromocarbenes and tribromomethyl carbanions with cyclohexanone have been investigated using ab initio HF/6-311++G** and MP2/6-311+G* level of theory. Solvent effects on these reactions have been explored by calculations which included a continuum polarizable conductor model (CPCM) for the solvent (H2O). The calculations showed that both mechanisms are possible and are exothermic, but have markedly different activation energies. FigureMechanistic pathways for the reaction of cyclohexanone with bromoform and PE map for ionic mechanism (path 2).