Quantum scattering calculations are reported for the reactions OR + RCl-t H 2 0 + CI and OR + HBr-tH 2 0+ Br. The rotating bond approximation is used. This involves the explicit treatment of the bending vibration and local OR stretching vibration in H 2 0 together with the vibration of HX (X=CI,Br) and rotation of OH. Simple potential energy surfaces for the reactions are used which contain an accurate potential for H 2 0. The transition state of the potential for the OH + HCI reaction agrees quite well with ab initio data. The most likely product vibrational state of H 2 0 is the ground state for the OR(j =0) + HCI reaction, and the combination band that has one quantum of energy in the H 2 0 bending mode and one quantum in the local OH stretching mode of H 2 0 for the OH(j =0) + HBr reaction. The reaction cross sections are found to depend on e2j + 1) -I, where j is the initial rotational quantum number of OH. This results in a T-I12 dependence in the rate constant fur the OH + HBr reaction at low temperatures, in agreement with experiment.3704
The state-selected vibrational relaxation rates in O2+O2 collisions, with one O2 molecule in a highly vibrationally excited state, have been calculated from first principles. The vibrationally close-coupled, rotationally infinite order sudden approximation has been used to treat the collision dynamics and a potential energy surface based on high quality ab initio calculations, which include the variation of the O2 vibrational coordinates, has been developed. The calculated relaxation rates are in good agreement with those obtained from experiment for 8≤v<26 but fail to reproduce the sharp increase observed experimentally for v≥26 indicating the onset of a new vibrational relaxation mechanism.
Ab initio electronic structure calculations on several low-lying valence states of B, have been carried out using correlation-consistent polarized valence double-zeta basis sets and completeactive-space self-consistent field treatments of electron correlation. Stable triangular structures, linear structures, and Jahn-Teller unstable structures are all observed. Equilibrium geometries, energies, and local harmonic vibrational frequencies are determined for various locally stable structures of several states. Several of the local minima are found to be unstable or metastable when zero-point vibrational energy is included; as a result, fluxional species are predicted to occur for certain B, states. Transition states connecting local minima are found and characterized in terrns of energies, geometries, and local harmonic vibrational frequencies. The ground state of B, is predicted to have an equilateral triangular structure and to be of 2A { symmetry in the Dxh point group. Dipole and vibronically allowed vertical transition energies to other states are also considered.
As part of our research efforts in the area of titanium-based antitumor agents, we have investigated the cytotoxic activity of [Ti(4)(maltolato)(8)(mu-O)(4)], (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(3) and CO(2)CH(2)CH(3)), and three water-soluble titanocene-amino acid complexes-[Cp(2)Ti(aa)(2)]Cl(2) (aa = L: -cysteine, L: -methionine, and D: -penicillamine)-on the human colon adenocarcinoma cell line, HT-29. The capacity of [Ti(4)(maltolato)(8)(mu-O)(4)] to donate Ti(IV) to human apo-transferrin and its hydrolytic stability have been investigated and compared to the previously reported data on modified titanocenes with either hydrophilic ancillary ligands or the functionalized cyclopentadienyl ligands. Notably, the titanium-maltolato complex does not transfer Ti(VI) to human apo-transferrin at any time within the first seven days of its interaction, demonstrating the inert character of this species. Stability studies on these complexes have shown that titanocene complexes decompose at physiological pH while the [Ti(4)(maltolato)(8)(mu-O)(4)] complex is stable at this pH without any notable decomposition for a period of ten days. The antitumor activity of these complexes against colon cancer HT-29 cells was determined using an MTT cell viability assay at 72 and 96 h. The titanocene-amino acid and the (Cp-R)(2)TiCl(2)/(Cp-R)CpTiCl(2) (R = CO(2)CH(3)) complexes were not biologically active when human transferrin was absent; they also were inactive when human transferrin was present at dose-equivalent concentrations. (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(2)CH(3)) showed cytotoxic activity in HT-29 cells comparable to that which is displayed by titanocene dichloride. The titanium-maltolato complex had higher levels of cytotoxic activity than any other titanocene complex investigated. Transferrin may be important in protecting the titanium center from hydrolysis, but this may be achieved by selecting ligands that could result in hydrolytically stable, yet active, complexes.
Functionalization of cyclopentadienyl (Cp) ligands and incorporation of these into a Ti(IV) center require careful design and selection of the appropriate synthetic routes to obtain the desired product in reasonably good yields. As part of our research efforts in the area of titanocene antitumor agents, we have revisited the synthesis of Cp rings with electron-withdrawing groups and their corresponding titanocene dichlorides, (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2), where R is CO(2)CH(3) and CO(2)CH(2)CH(3). These complexes were characterized by elemental analysis and (1)H and (13)C NMR and IR spectroscopies. This report presents the first detailed synthetic route for (Cp-CO(2)CH(2)CH(3))CpTiCl(2) and provides an alternate route for synthesis of (Cp-R)(2)TiCl(2) complexes. The ability of these complexes to deliver Ti(IV) to apotransferrin was investigated to elucidate how the functionalized Cp ligands affect the titanium intake by apotransferrin. The subject complexes transfer Ti(IV) to human apotransferrin, loading both N- and C-lobes. The antitumor activity of these complexes against HT-29 cancer colon cells was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Carboethoxy Cp functionalization results in complexes with a toxicity comparable to that of titanocene dichloride. The carbomethoxy-functionalized complexes proved to be nonactive at the time intervals studied here, regardless of their ability to donate the titanium atom to human apotransferrin.
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