Engineering of chitosan-hydroxyapatite-magnetite hierarchical scaffolds for guided bone growth

Bioabsorbable materials have received increasing attention as innovative systems for the development of osteoconductive biomaterials for bone tissue engineering. In this paper, chitosan-based composites were synthesized adding hydroxyapatite and/or magnetite in a chitosan matrix by in situ precipitation technique. Composites were characterized by optical and electron microscopy, thermogravimetric analyses (TGA), x-ray diffraction (XRD), and in vitro cell culture studies. Hydroxyapatite and magnetite were found to be homogeneously dispersed in the chitosan matrix and the composites showed superior biocompatibility and the ability to support cell attachment and proliferation; in particular, the chitosan/hydroxyapatite/magnetite composite (CS/HA/MGN) demonstrated superior bioactivity with respect to pure chitosan (CS) and to the chitosan/hydroxyapatite (CS/HA) scaffolds

in 1-(trifluoroacetylamino)naphthaquinone:

a CASPT2//CASSCF computational study

A theoretical study of the lowest electronic states of azobenzene: the role of torsion coordinate in the cis-trans photoisomerization

In the present paper we report the results of a multiconfigurational computational study on potentialenergy curves of azobenzene along the NN twisting to clarify the role of this coordinate in the decay of the S2(ππ*) and S1(nπ*) states. We have found that there is a singlet state, S3 at the trans geometry, on the basis of the doubly excited configuration n2π*2, that has a deep minimum at about 90°of twisting, where it is the lowest excited singlet state. The existence of this state provides an explanation for the short lifetime of S2(ππ*) and for the wavelength-dependence of azobenzene photochemistry. We have characterized the S1(nπ*) state by calculating its vibrational frequencies, which are found to correspond to the recently observed transient Raman spectrum. We have also computed the potential-energy curve for the triplet T1(nπ*) at the density functional theory B3LYP level, which indicates that in this state the isomerization occurs along the twisting coordinate

On the Mechanism of the cis-trans Isomerization in the Lowest Electronic States of Azobenzene: S0, S1, and T1

In this paper, we identify the most efficient decay and isomerization route of the S1, T1, and S0 states of azobenzene. By use of quantum chemical methods, we have searched for the transition states (TS) on the S1 potential energy surface and for the S0/S1 conical intersections (CIs) that are closer to the minimum energy path on the S1. We found only one TS, at 60° of CNNC torsion from the E isomer, which requires an activation energy of only 2 kcal/mol. The lowest energy CIs, lying also 2 kcal/mol above the S1 minimum, were found on the torsion pathway for CNNC angles in the range 95−90°. The lowest CI along the inversion path was found ca. 25 kcal/mol higher than the S1 minimum and was characterized by a highly asymmetric molecular structure with one NNC angle of 174°. These results indicate that the S1 state decay involves mainly the torsion route and that the inversion mechanism may play a role only if the molecule is excited with an excess energy of at least 25 kcal/mol with respect to the S1 minimum of the E isomer. We have calculated the spin−orbit couplings between S0 and T1 at several geometries along the CNNC torsion coordinate. These spin−orbit couplings were about 20−30 cm-1 for all the geometries considered. Since the potential energy curves of S0 and T1 cross in the region of twisted CNNC angle, these couplings are large enough to ensure that the T1 lifetime is very short (10 ps) and that thermal isomerization can proceed via the nonadiabatic torsion route involving the S0−T1−S0 crossing with preexponential factor and activation energy in agreement with the values obtained from kinetic measures

On the Mechanism of the cis-trans Isomerization in the Lowest Electronic States of Azobenzene: S0, S1, and T1

In this paper, we identify the most efficient decay and isomerization route of the S1, T1, and S0 states of azobenzene. By use of quantum chemical methods, we have searched for the transition states (TS) on the S1 potential energy surface and for the S0/S1 conical intersections (CIs) that are closer to the minimum energy path on the S1. We found only one TS, at 60° of CNNC torsion from the E isomer, which requires an activation energy of only 2 kcal/mol. The lowest energy CIs, lying also 2 kcal/mol above the S1 minimum, were found on the torsion pathway for CNNC angles in the range 95−90°. The lowest CI along the inversion path was found ca. 25 kcal/mol higher than the S1 minimum and was characterized by a highly asymmetric molecular structure with one NNC angle of 174°. These results indicate that the S1 state decay involves mainly the torsion route and that the inversion mechanism may play a role only if the molecule is excited with an excess energy of at least 25 kcal/mol with respect to the S1 minimum of the E isomer. We have calculated the spin−orbit couplings between S0 and T1 at several geometries along the CNNC torsion coordinate. These spin−orbit couplings were about 20−30 cm-1 for all the geometries considered. Since the potential energy curves of S0 and T1 cross in the region of twisted CNNC angle, these couplings are large enough to ensure that the T1 lifetime is very short (10 ps) and that thermal isomerization can proceed via the nonadiabatic torsion route involving the S0−T1−S0 crossing with preexponential factor and activation energy in agreement with the values obtained from kinetic measures

CHARGE REDISTRIBUTION IN THE β\beta-NAPHTHOL-WATER COMPLEX AS MEASURED BY HIGH RESOLUTION STARK SPECTROSCOPY IN THE GAS PHASE

Work supported by NSF (CHE-0911117).Author Institution: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260; Department of Chemistry, University of Minnesota, Minneapolis, MN 55455The extensively studied photoacid $\beta$-naphthol exhibits a large decrease in p$K_{a}$ upon irradiation with ultraviolet light, in the condensed phase. $\beta$-naphthol is almost 10 million times more acidic in the excited electronic state, compared to the ground state. Motivated by this fact, we report here the measurement of the electronic dipole moments of the $\beta$-naphthol-water complex in both electronic states, from which estimates of the charge transfer from solute to solvent in both states will be made. Comparisons to $ab$ $initio$ and density functional theory calculations will also be reported., 5530 (2000).