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Point Properties (point + property)
Selected AbstractsInteractions of the "piano-stool" [ruthenium(II) (,6 -arene)(en)CL]+ complexes with water and nucleobases; ab initio and DFT studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2009k Futera Abstract Piano stool ruthenium complexes of the composition [Ru(II)(,6 -arene)(en)Cl]+/2+ (en = ethylenediamine) represent an emerging class of cisplatin-analogue anticancer drug candidates. In this study, we use computational quantum chemistry to characterize the structure, stability and reactivity of these compounds. All these structures were optimized at DFT(B3LYP)/6-31G(d) level and their single point properties were determined by the MP2/6-31++G(2df,2pd) method. Thermodynamic parameters and rate constants were determined for the aquation process, as a replacement of the initial chloro ligand by water and subsequent exchange reaction of aqua ligand by nucleobases. The computations were carried out at several levels of DFT and ab initio theories (B3LYP, MP2 and CCSD) utilizing a range of bases sets (from 6-31G(d) to aug-cc-pVQZ). Excellent agreement with experimental results for aquation process was obtained at the CCSD level and reasonable match was achieved also with the B3LYP/6-31++G(2df,2pd) method. This level was used also for nucleobase-water exchange reaction where a smaller rate constant for guanine exchange was found in comparison with adenine. Although adenine follows a simple replacement mechanism, guanine complex passes by a two-step mechanism. At first, Ru-O6(G) adduct is formed, which is transformed through a chelate TS2 to the Ru-N7(G) final complex. In case of guanine, the exchange reaction is more favorable thermodynamically (releasing in total by about 8 kcal/mol) but according to our results, the rate constant for guanine substitution is slightly smaller than the analogous constant in adenine case when reaction course from local minimum is considered. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Safe-steering of batch process systemsAICHE JOURNAL, Issue 11 2009Siam Aumi Abstract This work considers the problem of controlling batch processes to achieve a desired final product quality subject to input constraints and faults in the control actuators. Specifically, faults are considered that cannot be handled via robust control approaches, and preclude the ability to reach the desired end-point, necessitating fault-rectification. A safe-steering framework is developed to address the problem of determining how to utilize the functioning inputs during fault rectification to ensure that after fault-rectification, the desired product properties can be reached upon batch termination. To this end, first a novel reverse-time reachability region (we define the reverse time reachability region as the set of states from where the desired end point can be reached by batch termination) based MPC is formulated that reduces online computations, as well as provides a useful tool for handling faults. Next, a safe-steering framework is developed that utilizes the reverse-time reachability region based MPC in steering the state trajectory during fault rectification to enable (upon fault recovery) the achieving of the desired end point properties by batch termination. The proposed controller and safe-steering framework are illustrated using a fed-batch process example. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Experimental charge-density study of paracetamol , multipole refinement in the presence of a disordered methyl groupACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2009Joanna M. B A high-resolution single-crystal X-ray study of paracetamol has been performed at 85,K. Different approaches to modeling the experimental electron density (ED) were tested for the dynamically disordered portions of the molecule in order to check to what extent it is possible to obtain a proper ED distribution in the ordered part. Models were examined in which the methyl-group ED was built from pseudoatoms taken from the University at Buffalo Pseudoatom Databank or the Invariom database, with multipole parameters for the remaining atoms being obtained from free refinement. The ,, restricted multipolar model (KRMM) and free ,, refinements were compared; restriction of the ,, parameters was essential in order to obtain values of the electrostatic interaction energy consistent with the results of theoretical single-point periodic calculations. After simultaneous use of KRMM refinement and the databases to model the methyl group, the bond critical point properties and interaction electrostatic energy values were found to be closer to those obtained from theory. Additionally, some discrepancies in the ED distribution and dipole moment among transferred aspherical atom model refinements utilizing both theoretical databases and parameters from theoretical periodic calculations are shown. Including the influence of the crystal field in the periodic calculations increases the ED in the hydroxyl and amide groups, thus leading to higher values of the electrostatic interaction energy, changes in the electrostatic potential values mapped on the isodensity surface and changes in the shape of the anisotropic displacement parameters with respect to results found for both database models. [source] On the origin of topological differences between experimental and theoretical crystal charge densitiesACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2000Anatoliy Volkov Topological analysis of experimental and theoretical (molecular and crystal) electron densities of p -nitroaniline and p -amino- p,-nitrobiphenyl reveals considerable discrepancies between experiment and theory for the bond critical points properties. Particularly large differences occur for the positive curvature along the bond path (,3). The differences become somewhat smaller when more extended basis sets and correlation effects are introduced in the theoretical calculations. The effect of the crystal matrix on the properties of bond critical points is evaluated for the p -nitroaniline molecule using the 6-21G** and 6-31G** basis sets. The differences between the isolated molecule and the molecule in the crystal are too small to explain the quantitative disagreement between the theoretical and experimental topologies reported in the literature and found in the current study. For most bonds, the observed changes in the properties of the electron density agree well for both basis sets but some discrepancies are found for changes in ,3 for N,H and aromatic C,C bonds. When the theoretical densities are projected into the multipole density functions through refinement of the theoretical structure factors, the topological properties change and differences between theory and experiment are reduced. The main origin of the observed discrepancies is attributed to the nature of the radial functions in the experimental multipole model. [source] | ||||||||||