Atomistic modeling of zeolitic materials

A review with 166 refs. on modeling the structure and properties of the bare zeolitic framework. The topics include modeling methods and interat. potential developmen

Lattice mechanical study of the structure of dodecasil-3C

A recently developed partial charge potential model for SiO2 polymorphs, derived from quantum chem. calcns., was applied to the calcn. of the lattice energy-minimized structure and phys. properties of the low-d. SiO2 crystal Dodecasil-3C. Calcns. were performed using Ewald summations and without symmetry constraints. Results are compared with calcns. using the shell model of Sanders et al. (1983). Best agreement between exptl. and theor. predicted elastic consts. is achieved assuming a triclinic structure. To establish lattice stability, the vibrational frequency spectrum was calcd. For structures with imaginary frequencies, the corresponding at. displacements are used to deform the quasi-stationary geometry. On lattice energy minimization, the deformed structure transforms to a stable energy min. The large anisotropic temp. factors obsd. exptl. are mainly due to static disorder in at. position

Modeling of structure and vibrational spectra of aluminophosphate AlPO4 5 and its silica analog SSZ 24

In this study, the structural and vibrational properties of the AlPO4 structure AlPO4-5 and the silica structure SSZ-24 are compared. Lattice energy calcns. are done using existing potential parameter sets suitable for silicas and AlPO4's. For the computation of vibrational spectra of silica systems, force consts. derived by Etchepare et al. are used. For AlPO4 spectra simulations, a new force field is presented that is based on a fit on vibrational frequencies of a-berlinite, the AlPO4 analog of a-quartz. Lattice energy calcns. result in a symmetry of AlPO4-5 and SSZ-24 that is lower than derived exptl. A shift of layers is obsd. for both structures when a potential with partial charges is used. These results are indicative for an underestn. of the charges used in the partial charge model. The influence of structure on spectra is shown to be rather weak. The main differences between the spectra of AlPO4-5 and SSZ-24 are due to the interat. force const

Lattice-relaxation of zeolites

Quantum-chemical cluster calculations as well as solid-state chemical lattice-calculations indicate that zeolitic SiO2- and AlPO4-structures are flexible structures. The structures reflect the subtle balance of electrostatic and covalent interactions. The different electrostatic interactions lower the symmetry of layered AlPO4-structures compared to that of the corresponding SiO2-compounds. The result is a smaller zeolite-channel dimension for the AlPO4-structure compared to that of the corresponding SiO2-network. Deprotonation of the zeolite-lattice leads to large local changes in geometry that changes acidity compared to that predicted for a non-flexible lattice. Changes in lattice vibrational frequencies are consistent with the theoretically predicted relaxation of the zeolite-lattic

Association between paclitaxel clearance and tumor response in patients with esophageal cancer

Inter-individual variability in paclitaxel pharmacokinetics may play a role in the response to chemotherapy. Therefore, we studied the association between paclitaxel clearance and treatment response in patients with esophageal cancer. All patients who received paclitaxel (plus carboplatin) treatment for esophageal cancer between 2007 and 2013 were included. The treatment was given as neoadjuvant chemoradiotherapy (nCRT), induction chemotherapy (iCT), or palliative chemotherapy (pCT). The treatment response was assessed by the tumor regression grade (TRG) or by the RECIST1.1 criteria, respectively. The unbound paclitaxel clearance (CL) was estimated with NONMEM. The log-transformed clearance was related to response with ANOVA and independent sample t-tests. A total of 166 patients were included, of whom 113 received nCRT, 23 iCT and 30 pCT. In patients receiving nCRT, paclitaxel clearance was not associated with tumor regression grade (p-value = 0.25), nor with pathologically complete response (geometric mean 561.6 L/h) and residual disease (geometric mean 566.1 L/h, p-value = 0.90). In patients who underwent iCT or pCT, also no association between paclitaxel clearance and RECIST outcome was identified (iCT: p-value = 0.08 and pCT: p-value = 0.81, respectively). In conclusion, systemic paclitaxel exposure was not associated with response to common paclitaxel-based treatment regimens for esophageal cancer. Future studies should focus on tumor exposure in relation to systemic exposure and treatment outcome