Petia Bobadova-Parvanova

Parameter calibration of transition-metal elements for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method : Sc, Ti, Fe, Co, and Ni

Recently developed parameters for five first-row transition-metal elements (M = Sc, Ti, Fe, Co, and Ni) in combination with H, C, N, and O as well as the same metal (M-M) for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method have been calibrated. To test their performance a couple sets of compounds have been selected to represent a variety of interactions and bonding schemes that occur frequently in transition-metal containing systems. The results show that the DFTB method with the present parameters in most cases reproduces structural properties very well, but the bond energies and the relative energies of different spin states only qualitatively compared to the B3LYP/SDD+6-31G(d) density functional (DFT) results. An application to the ONIOM(DFT:DFTB) indicates that DFTB works well as the low level method for the ONIOM calculation.

Synthesis and reactivity of 4,4-Dialkoxy-BODIPYs: an experimental and computational study.

A series of boron-disubstituted O-BODIPYs were synthesized, and their structures and spectroscopic properties were investigated using both computational and experimental methods. Three methods were investigated for the preparation of 4,4-dimethoxy-BODIPYs bearing electron-donating or electron-withdrawing 8-aryl groups: method A employs refluxing in the presence of NaOMe/MeOH, method B uses AlCl3 in refluxing dichloromethane followed by addition of methanol as nucleophile, and method C involves activation of the BODIPYs using TMSOTf in refluxing toluene followed by addition of methanol. The yields obtained depend on the method used and the structure of the starting BODIPYs; for example, 1a and 3a were most efficiently prepared using method C (98 and 70%, respectively), while 2a was best prepared by method A (50%). Methods B and C were employed for the synthesis of seven new 4,4-dialkoxy-BODIPYs. 4,4-Dipropargyloxy-BODIPY 1e reacted under Cu(I)-catalyzed alkyne-azide Huisgen cycloaddition conditions to produce 4,4-bis(1,2,3-triazole)-BODIPY 4 in 78% yield. The substitution of the fluorides for alkoxy groups on the BODIPYs had no significant effect on the absorption and emission wavelengths but altered their fluorescence quantum yields. Among this series of dialkoxy-BODIPYs, the 4,4-dipropargyloxy 1e and its corresponding bis(1,2,3-triazole) 4 show the largest quantum yields in toluene and THF, respectively.

The heat of formation of chlorine-isocyanate and the relative stability of isoelectronic molecules : An experimental and theoretical study

Accurate thermochemical data of small molecules are invaluable to the progress of every aspect of chemistry, especially in the atmosphere, combustion and industry. In this work, photofragmentation translational spectroscopy and 1st principles electronic structure theory reveal the literature value of the heat of formation of chlorine-isocyanate to be in error by more than 40 kcalmol. We report a revised experimental value for D0(Cl-NCO) = 51+/-3 kcal/mol which leads to a Delta Hf (ClNCO) = 8.5+/-3 kcal/mol. High level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit give D0(Cl-NCO) = 6.3 kcal/mol, in good agreement with experiment. In light of the present results, the destabilization of azides relative to isoelectronic isocyanates has been evaluated empirically for three pairs of related molecules. It is found to be 90-110 kcal/mol, and has been attributed mainly to the weakening of the N-NN bond relative to the N-CO bond. Electronic structure calculations employing decomposition analysis suggest that, compared to homopolar N2, the (+delta)CO(-delta) pi polarity provides better orbital interaction (charge transfer) and electrostatic attraction and results in a closer encounter and larger stabilization between the fragments and that this is the origin of isoelectronic destabilization of azides relative to the isocyanates.

Synthesis and properties of B-cyano-BODIPYs

A series of boron-functionalized BODIPY dyes with cyano groups were prepared from their corresponding BF2 derivatives using SnCl4/TMSCN at room temperature for 10 min. Replacement of the fluorines by cyano groups reduces the B–N bond lengths, decreases the charge on boron, and causes characteristic 11B NMR chemical shifts. The 4,4′-dicyano-BODIPYs show significantly enhanced stability to acidic conditions (excess TFA) and, with one exception, enhanced fluorescence quantum yields. Furthermore, the B(CN)2-BODIPYs were non-cytotoxic to HEp2 cells, both in the dark and upon exposure to light (1.5 J/cm2), and rapidly accumulated within cells, localizing mainly in the lysosomes, ER and Golgi.