Dr Alpesh Malde (Research Fellow, MD Group, SCMB)

TitleUsing theory to reconcile experiment: Thermodynamics of guest:host binding

Abstract: Chemically synthesized in 1904 and successfully crystallized and identified in 1981, Cucurbiturils have ability to form guest:host complexes with a range of chemically diverse molecules. Cucurbiturils are rigid cavity molecules made up of glycoluril building blocks. There is a wealth of structural (X-ray, NMR) and binding (ITC) data is available, making it an attractive dataset for development and testing of computational methods. In the present study, binding of small guest molecules (acetone, cyclopentanone, dimethyl formamide and dimethylsulfoxide) to CB[7] (Cucurbituril with 7 glycoluril monomers) have been investigated. The computational investigation reveal that the proposed mechanisms of high-affinity binding in literature, namely release of high-energy water molecules and desolvation penalty of guest molecules, fail to explain the observed relatively high binding free energy of cyclopentanone to CB[7]. Instead, guest:host binding stoichiometry, as identified by molecular dynamics simulations and validated by the free energy calculations, explains the high binding affinity of cyclopentanone towards CB[7].


Yuan Su (PhD, Bernhardt/Wang Group, AIBN)


TitleEffect of carbon chain length of organic salts on the thermodynamic stability of methane hydrate

Abstract: This study presents the phase equilibrium conditions for methane hydrate with one of the following organic ammonium salts differing in carbon chain length: tetramethylammonium bromide (TMAB), tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPrAB), tetrabutylammonium bromide (TBAB), and tetrapentylammonium bromide (TPeAB). The hydrate phase equilibrium measurements were conducted for a temperature range of 279.41 to 291.85 K and pressure range of 4.79 to 14.32 MPa using the step-heating pressure search method. The addition of TBAB or TPeAB shifts the phase equilibria of the semiclathrate hydrates (SCHs) of CH₄ to a lower pressure/higher temperature zone. At a given temperature, increasing the mole fraction of TBAB and TPeAB from 0.294 mol % to 0.620 mol % made the shift in phase equilibrium conditions greater. At a given dosage, TBAB consistently outperformed TPeAB in thermodynamically promoting methane hydrate formation. TMAB, TEAB or TPrAB slightly shifts the phase equilibrium conditions to a higher pressure/lower temperature region. We analysed the hydrate phase equilibrium data for TMAB, TEAB, and TPrAB using the colligative property equation and compared them with the phase equilibrium data of a CH₄ and salt water system. The results suggest that these three salts have a small hydrate inhibiting effect that is comparable to NaCl.