Download Simulating the aggregation and surface reactivity of

British Association For Crystal Growth Annual Conference 2017
Simulating the aggregation and surface reactivity of meta-aminobenzoic
acid: implications for crystal growth and polymorphism
1
E. Gaines, * D. Di Tommaso,
1
1
Queen Mary, University of London, United Kingdom
[email protected]
Solvent can have significant effects on the solution thermodynamics and crystallization kinetics of organic
compounds from solution [1]. I will present a computational investigation of the early stages of aggregation of
the organic molecule m-aminobenzoic acid (mABA) in two different solvents, dimethyl sulfoxide (DMSO) and
water, studied using a combination of quantum chemistry, molecular dynamics and free energy methods [2].
In DMSO, the formation of the classic carboxylic (mABA)2 dimer is exergonic and thermodynamically more
favourable than in water. On the other hand, the self-association of dimers to form tetramers (mABA)4 is
thermodynamically possible in water but not in DMSO. Molecular dynamics simulations of mABA solutions at
different concentrations show a significant solvent-dependent aggregation behaviour of mABA. Metadynamics
simulations and microsolvation density functional theory calculations revealed that in DMSO, the energetic
barrier associated to the desolvation of mABA molecules to form dimers and the strength of the mABA-solvent
interactions are significantly larger than in water.
As polymorph selection could occur during growth at the crystal–solution interface, I will also report
simulations of mABA crystals in contact with aqueous and organosulfur solutions, also containing molecular
aggregates of mABA. The stable surfaces of the form-II polymorph of mABA were identified by means of DFT
simulations, which were then used to compute the energetics of adsorption of monomer and oligomers of
mABA, and to quantify the crystal-solvent interactions in terms of radial distribution function, mean residence
time and mean square displacement analyses.
This work shows how the solvent and its specific interaction with the organic solute molecules influences
both the thermodynamics and kinetics of molecular self-assembly. It also highlights the impact of the choice
of solvent and concentration on the growth of surfaces from saturated solutions.
Fig. 1: Aggregationpathwaysofmeta-aminobenzoicacid
References:
[1] R. J. Davey, S. L. M. Schroeder and J. H. ter Horst, Angew. Chem. Int. Ed., 2013, 52, 2-16
[2] E. Gaines and D. Di Tommaso, CrystEngComm., 2016, 18, 2937