Biomedical subjects
Publications and source records attributed to Branka Kovac.
The electronic structures of several N-substituted phthalimides have been investigated by UV photoelectron spectroscopy and outer valence Greens function calculations. Some spectra reveal the presence of photofragmentation and photoelimination processes related to the decay of the aminium radical cation. We compared the fragmentation mechanisms in the gas phase and in the solution.
HeI and HeII photoelectron spectra of persistent free radical: 2,2,6,6-tetramethyl-4-(methylsulfonyloxy)piperidinyl-1-oxide (CH3SO3-TEMPO) have been measured. The analysis of the electronic structure is based on comparison with the spectra of related radicals and with DFT calculations. The electronic structure of the nitroxide group in the title radical seems unaffected by the presence of substituent group. This is consistent with results observed for other nitroxide radicals and with the electrochemical oxidation potentials.
The electronic structure of all isomeric dihalobenzenes C6H4XY (X, Y = Cl, Br, I) has been investigated by HeI/HeII photoelectron spectroscopy, Green's functions calculations, and comparison with the spectra of related dihalobenzenes C6H4X2 (X = Cl, Br, I). The careful analysis of measured pi orbital and halogen lone pair ionization energies enabled us to describe substituent effects in terms of resonance, inductive, steric, and spin-orbit coupling interactions.
HeI photoelectron spectra of three terpenes: alpha-pinene, pulegone and cembrene have been measured. The analysis of their electronic structure is based on the comparison of measured spectra with those of related compounds and on the comparison with molecular structures of studied compounds. We discuss changes in ionization energies of C-C double bonds which are situated at different positions along the rings.
HeI photoelectron spectrum of 2-azabicyclo[2.2.1]hept-5-en-3-one (Vince lactam) has been measured. The assignment of the spectrum was made by comparison with photoelectron spectra of related compounds and by taking into account the lactam's molecular structure. The analysis of the electronic structure of amide group, in terms of inductive and conjugative effects, is presented on the basis of photoelectron spectroscopic data.
HeI and HeII photoelectron spectra of 6-chloro-1,3-dimethyluracil have been measured. The assignment of the spectrum was made by comparison with photoelectron spectra of related compounds and by high-level OVGF calculations. The electronic structure changes in substituted nucleobases are discussed on the basis of photoelectron spectroscopic data. The electronic structure data are compared with structure-activity relationships regarding enzyme inhibition and complex formation. The electronic structure data give some insight into the nature of binding between nucleobases' derivatives and different enzymes whose activity they inhibit.
The molecular and electronic structures of 10 free nitroxide radicals have been investigated by HeI/HeII photoelectron spectroscopy (UPS), DFT calculations, and comparison with the spectra of related compounds. We observe that the electronic structure of the nitroxide group is unaffected by substitution except in a carbonyl derivative where nitroxide group orbitals are noticeably stabilized. Also, we have detected small variations in the photoionization cross-sections for singlet and triplet states of cation, the states belonging to the same electron configuration. The relationship between electronic structure and radical reactivity is discussed, and an experimentally based estimate of delocalization energy of the unpaired electron is given. Some conflicting kinetic data on radical reactivity have been analyzed in view of the UPS results.
The molecular and electronic structure of eight substituted quinolines has been investigated by HeI/HeII photoelectron spectroscopy, Green's function calculations, and comparison with the spectra of related compounds. The correlation between nitrogen lone pair ionization energies and basicity in 18 substituted quinolines is discussed. The influence of different substituents has been quantified via the scheme that is based on experimental energy shifts. The relationships between nitrogen ionization energies, pK(a) values, and medicinal activity are also discussed.
The electronic structures of the anti-HIV drug zidovudine (AZT) and antimalarial drug artemisinine have been investigated by UV photoelectron spectroscopy (UPS), MO calculations, and comparison with the spectra of related molecules. The analysis of their electronic structure is correlated with known biological activities.
The ligation of Cr+ and Fe+ with 4,9-diazapyrene (DAP) within a Fourier transform mass spectrometer was studied and compared with previous results for the ligands pyrene (Py) and 9-azaphenanthrene (Ap). The results confirm that Fe+, which reacts more slowly but in the same way as Cr+ to bind two Py ligands, behaves quite differently with the nitrogen heterocycles DAP and Ap: it reacts rapidly and it binds three and four of them, respectively.
The electronic structure of several cyclic, saturated and unsaturated amines and imines has been investigated by UV photoelectron spectroscopy (UPS). The analysis of spectra has been performed with DFT and OVGF calculations and comparison with the UPS spectra of related compounds. The extent and type of nitrogen lone pair interactions is discussed because nitrogen lone pairs are the most important functional groups present in these molecules. The magnitude of interactions was found to depend on the spatial orientation and rigidity of mutual positions of the lone pairs, rather than on their spatial distance.
We report the study of the electronic structure of CHFI(2), CHBrI(2), CHBr(2)I, CHClI(2), and CHCl(2)I using VUV photoelectron spectroscopy (UPS). The lone pair orbital interactions are discussed on the basis of experimental results and comparisons with other halomethanes.
The electronic structure of coumarin derivatives has been investigated by a combination of UV photoelectron spectra (UPS), semi-empirical MO calculations and comparison with the spectra of related coumarins. The influence of substituents on the S0 and S1 electronic states energies is discussed.
We present data on the electronic structure, polarity and relative stability of 14 common sesquiterpenes. The data were obtained by a combination of spectroscopic and high-level theoretical analysis. The discussion also includes comments on possible implication of molecular properties for physiological behaviour.