Biomedical subjects

Isabella Hyla-Kryspin

Publications and source records attributed to Isabella Hyla-Kryspin.

4 recordsLinked to original sources

PubMed2005

Redox site confinement in highly unsymmetric dimanganese complexes.

A set of highly preorganized pyrazolate-bridged dimanganese complexes L(Mn)MnX have been prepared and structurally characterized. They can be described as hybrid organometallic/Werner-type systems that consist of a low-spin CpMn(I)(CO)2 subunit (Mn1) and a proximate tripodal tetradentate {N4} binding pocket accommodating a high-spin Mn(II) ion (Mn2), with Mn...Mn distances of approximately 4.3 A and different coligands bound to Mn2. Density functional theory (DFT) calculations (both the hybrid B3LYP and the pure BP86 functionals and the all-electron basis sets 6-311G and 6-311G*) confirm that the valence alpha and beta Kohn-Sham molecular orbitals (MOs) of these mixed-valent Mn(I)Mn(II) compounds have predominant Mn(3d) character and an almost perfectly localized nature: all five unpaired electrons are essentially localized at the Werner-type Mn2, whereas Mn1 possesses an effective closed-shell structure with the MOs of highest energy centered there. One-electron oxidation occurs in a clean process at approximately E(1/2) = -0.6 V (versus ferrocene/ferrocinium), giving the low-spin/high-spin Mn(II)Mn(II) species. UV/vis and IR spectroelectrochemistry as well as a detailed theoretical analysis reveal that the redox process takes place with strict site control at the organometallic subunit, while it does not significantly influence the spin and charge distribution on the Werner-type site. Positions and shifts of the nu(C[triple bond]O) absorptions are largely reproduced by the DFT calculations. These systems thus represent an exceptional example of the effect the unsymmetry of a dinucleating ligand scaffold has on the spin and charge distribution in homobimetallic complexes and might offer interesting prospects for the study of the cooperative effects of bimetallic arrays.

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PubMed2005

The gas phase acidity of oligofluorobenzenes and oligochlorobenzenes: about the additivity or non-additivity of substituent effects.

The deprotonation energies of benzene, fluorobenzene, all di-, tri-, and tetrafluorobenzenes, pentafluorobenzene, chlorobenzene, all di-, tri-, and tetrachlorobenzenes, and pentachlorobenzene have been calculated at various levels of second-order Moller-Plesset and density functional theory. Taking the previously determined experimental data as a benchmark, good agreement was achieved in the chloro series even with moderate computational effort, whereas more extended basis sets have to be used to obtain meaningful numbers in the fluoro series. Apparently, most extensive electron correlation is required to avoid artifacts caused by the proximity of nonbonding lone pairs at the carbanionic center and at the fluorine atoms. When two or more fluorine substituents were introduced in the same aromatic ring, their individual effects (as defined by position-dependent acidity increments) proved to be perfectly additive in the entire series. In contrast, the acidifying effect of chloro substituents was found to level off when the number of such halogens increases. Additivity or non-additivity of element effects cannot be ascertained after having merely compared the acidity of mono- and disubstituted substrates, but only after having moved to higher degrees of substitution.

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PubMed2004

Weak hydrogen bridges: a systematic theoretical study on the nature and strength of C--H...F--C interactions.

We present a comparative study on the nature and strength of weak hydrogen bonding between the C(sp3)-H, C(sp2)-H, and C(sp)-H donor bonds and F-C(sp3) acceptors. The series of molecules CH3F.CH4 (2 a, 2 b), CH3F.C2H4 (3), CH3F.C2H2 (4), as well as model complexes of experimentally characterized 2-fluoro-2-phenylcyclopropane derivatives, C3H6.C3H5F (5 a, 5 b) and C3H5F.C3H5F (6) were investigated. Comparative studies were also performed for two conformers of the methane dimer (1 a, 1 b). The calculations were carried out in hierarchies of basis sets [SV(d,p), TZV(d,p), aug-TZV(d,p), TZV(2df,2pd), aug-TZV(2df,2pd), QZV(3d2fg,2pd), aug-QZV(3d2fg,2pdf)] by means of ab initio [HF, MP2, QCISD, QCISD(T)] methods and density functional theory (DFT/B3LYP, DFT/PBE). It is shown that well-balanced basis sets of at least TZV(2df,2pd) quality are needed for a proper description of the weakly bonded systems. In the case of 2, 3, 5, and 6, the dispersion interaction is the dominant term of the entire attraction, which is not accounted for at the B3LYP level. Significant electrostatic contributions are observed for 6 and 3. For 4, these forces have a dominating contribution to the hydrogen bonding. The C(sp)--H...F--C(sp(3)) interaction in 4, though weak, exhibits the same characteristics as conventional hydrogen bridges. Despite showing longer H.F/H contacts compared to 1 a, 2 a, and 5 a the bifurcated structures, 1 b, 2 b, 5 b, are characterized by larger dispersion interactions leading to stronger bonding. For the systems with only one H.F contact, the MP2/QZV(3d2fg,2pd) interaction energy increases in the order 2 a (-1.62 kJ mol(-1)), 3 (-2.79 kJ mol(-1)), 5 a (-5.97 kJ mol(-1)), 4 (-7.25 kJ mol(-1)), and 6 (-10.02 kJ mol(-1)). This contradicts the estimated proton donor ability of the C--H bonds (2 a<5 a<3<6<4).

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PubMed2003

Electronic coupling in a highly preorganized bimetallic complex comprising pyrazolate-bridged CpMn(CO)2 moieties.

By means of a multistep synthetic procedure a dimanganese complex has been prepared, in which a N,N'-bridging pyrazolate ligand spans two CpMn(CO)(2) subunits in a highly preorganized chelate arrangement. The Xray crystallographic analyses of the Mn(I)Mn(I) complex K(+)1(-) and of its non-chelate precursor complex elucidate details of the molecular structure, in particular an unusual pyrazolate binding mode in the solid state and intertwining of the CO ligands in the crowded bimetallic array 1(-). The Mn(I)Mn(I) compound (1(-)), the mixed-valent Mn(I)Mn(II) (1), and the oxidized Mn(II)Mn(II) form (1(+)) have been characterized by various analytical and spectrosopic methods, such as electrochemistry, variable-temperature EPR spectroscopy, IR spectroelectrochemistry, and UV/Vis/NIR spectroelectrochemistry as well as by DFT and TD-DFT calculations. Strong electronic coupling in the mixed-valent complex is observed, but time- (and temperature-) dependent valence detrapping occurs, thus placing 1 in class II according to the Robin and Day assignment, close to the class II/III transition. From variable-temperature EPR spectroscopy a rough estimate of the activation energy and rate for thermal electron transfer can be deduced, with E(th) ( not equal )=13.6 kJ mol(-1) and k(th)=2.6 x 10(10) s(-1) at 298 K. Unexpectedly, no intervalence CT transition for 1 is detected in solution, but one appears in the optical spectrum of solid 1. The conclusions drawn from experiments are fully supported by DFT calculations that were carried out for all three forms of the dimanganese complex. A broken symmetry treatment for mixed-valent 1 reveals almost perfect localization of both spin and charge on one Mn center. According to TD-DFT the first excited states of 1 give rise to the IT processes in the NIR-energy region, as observed in the solid-state spectrum. The HOMOs are located at the Mn ions and are favorably arranged for pi interactions with the bridging pyrazolate.

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