Alexandra Simperler

Modeling the framework stability and catalytic activity of pure and transition metal-doped zeotypes

We present a thorough computational study of transition metal-doped zeolite and aluminophosphate (AIPO) frameworks. The structural and electronic chemistry of the dopants is examined with ab initio quantum mechanical calculations, and the results correlated with the Bronsted and Lewis acid strength, and with the redox potential of the dopant ions in the framework. The energetics of doping is provided, and is employed to analyze the mode of dopant incorporation, and its site ordering in the microporous framework. In total, 23 dopant ions are examined in the isostructural framework of chabasite and AlPO-34. These cover most of the isomorphous framework replacements known to occur experimentally, but also framework replacements that have not yet been achieved. In this case, ab initio modeling techniques are employed in a predictive way. Finally, we present a computational study of the alkene epoxidation on titanosilicates, that covers the whole catalytic cycle

The Extremely High Specificity of N-Methyldicyclohexylamine for the Production of the Large-Pore Microporous AFI Material

We describe a highly efficient synthesis of microporous aluminophosphate AlPO4-5 and its heteroatom-substituted variants, using N-methyldicyclohexylamine as a structure-directing agent that, in addition, does not result in the formation of any other microporous phase over the widest range of composition, temperature and pH conditions ever reported.

Correlation of melting points of inositols with hydrogen bonding patterns

The melting points of seven inositol isomers cover a range of 180–350 °C although the only difference between them is the ratio of axially/equatorially orientated hydroxyl groups. All seven isomers feature infinite and finite hydrogen bond patterns and the type and occurrence of these patterns are explored as useful criteria for the prediction of melting points. All the patterns are classified into chain and ring motifs and atomistic and quantum chemical calculations are employed to evaluate the strength of interaction between pairs of molecules contributing to a pattern. There are four types of hydrogen bonded chains with three different types of molecular interactions—one strong and two weak ones. All high melting inositols (scyllo-, neo- and epi-inositol) possess infinite hydrogen bonded double chains with strong links and the number of chains per molecule correlates with their melting points. The lowest melting isomer (allo-inositol) shows no such double chains and only two single hydrogen bonded chains.

Lactonisation--a degradation pathway for active pharmaceutical compounds: an in silico study in amorphous trehalose.

The lactonisation of a CCR1 inhibitor (CC chemokine receptor 1, involved in autoimmune diseases) featuring a hydroxyl group in a gamma-position (gamma-OH) with respect to an amide group has been investigated in silico. The two key steps of the lactonisation reaction are (i) rearrangement to an optimal conformation and (ii) the formation of the lactone (ring closure) and expulsion of NH3. Quantum chemical calculations in the gas phase were employed to identify conformers of the molecule with favorable starting geometries for a lactonisation reaction. In total, calculations of 1296 conformers revealed that it is energetically feasible for an inhibitor molecule to adopt a conformation where the carbon atom of the amide group (C(amide)) is suitably close to the oxygen atom of the gamma-OH (O(gamma)) to facilitate a successful lactonisation reaction. Additionally, molecular dynamics methods were used to show that rearrangement to a suitable conformer for lactonisation to occur happens to a lesser extent when the CCR1 inhibitor was embedded in an amorphous trehalose matrix (a model carbohydrate excipient). The mechanism of the actual lactonisation was investigated using the complete Linear Synchronous Transit/Quadratic Synchronous Transit (LST/QST) method. This was performed in both the gas phase and in water and was found to be a concerted reaction.

Characterisation and evaluation of hypothetical zeolite frameworks

Abstract A series of hypothetical zeolites, derived from the results of tiling theory, has been evaluated using computational chemistry techniques. Simulated heats of formation (i.e. the lattice energy with respect to α-quartz or α-berlinite for silica polymorphs and AlPO 4 polymorphs, respectively) are used as an initial criterion for the chemical “feasibility” of these structures. This data is further correlated with various structural and topological properties, such as framework density, coordination sequences, accessible volume and internal surface. Uninodal frameworks have been treated both as silica and AlPO 4 polymorphs, and comparisons made between the two compositions. Finally, we discuss three hypothetical structures with respect to their feasibility, structural properties and secondary/periodic building units.

13-P-16-Theoretical investigation of the chemical shift anisotropy of toluene adsorbed on zeolite X

Publisher Summary This chapter presents a theoretical investigation of the chemical shift anisotropy of toluene adsorbed on zeolite X. Adsorption of toluene on zeolites lithium (Li)-X, sodium (Na)-X, potassium (K)-X, rubidium (Rb)-X, and cesium (Cs)-X has been investigated with quantum chemical methods. Calculations of geometries, Mulliken partial charges, and 13 C chemical shift parameters of clusters representing the catalytically active site are presented. The polarization of the toluene carbons is the first step in alkylation reactions catalyzed by zeolites and, at an early stage, will influence the outcome of the reaction. The simultaneous influence of the Lewis acidic cation and the basicity of the zeolite are responsible for altering the electron distribution within the toluene and thus, affecting the outcome of an alkylation reaction.