MIT Unit Affiliation:
Lab Affiliation(s):
Trout Research Group
Post Doc Sponsor / Advisor:
Prof. Bernhardt L. Trout and Prof. Allan S. Myerson
Areas of Expertise:
  • Crystal engineering
  • Co-crystallization
  • Heterogeneous nucleation and pharmaceutical polymorphism
Date PhD Completed:
December, 2015
Expected End Date of Post Doctoral Position:
January 31, 2018

Tharanga Wijethunga

  • Post Doctoral

MIT Unit Affiliation: 

  • Chemical Engineering

Lab Affiliation(s): 

Trout Research Group

Post Doc Sponsor / Advisor: 

Prof. Bernhardt L. Trout and Prof. Allan S. Myerson

Date PhD Completed: 

Dec, 2015

Top 3 Areas of Expertise: 

Crystal engineering
Co-crystallization
Heterogeneous nucleation and pharmaceutical polymorphism

Expected End Date of Post Doctoral Position: 

January 31, 2018

CV: 

Research Projects: 

  •  Applied biocompatible crystalline heterosurfaces to enhance the nucleation rate of acetaminophen. Xylitol was identified as one of the best substrates reported so far in inducing the nucleation of acetaminophen. The mechanism of epitaxial growth in these systems was proposed employing molecular dynamics simulations in collaboration with theorists.
  •  Implemented a Raman spectroscopy based technique for face indexing of complex crystalline systems.
  •  Utilizing crystalline heterosurfaces and polymeric heterosurfaces to control the nucleation and polymorphic selection of active pharmaceutical ingredients (APIs). 

Thesis Title: 

Hydrogen- and halogen-bond driven co-crystallizations: from fundamental supramolecular chemistry to practical materials science

Thesis Abstract: 

A series of co-crystallizations between four biimidazole based compounds with nine symmetric aliphatic di-acids and fifteen perfluorinated halogen-bond donors were carried out to determine if a MEPS based ranking can be used to effectively assign selectivity in hydrogen- and halogen-bond interactions. The results suggested that a simple electrostatic view provides a reliable tool for successfully implementing the practical co-crystal synthesis with desired connectivity.

MEPS based selectivity guidelines for halogen-bond interactions were explored in co-crystallizations between twelve asymmetric ditopic acceptors and nine halogen-bond donors. If the difference between the two acceptor sites is below 35 kJ/mol, no selectivity was observed; above 65 kJ/mol halogen bond selectivity dominates and mid ΔE range was recognized as the grey area where predictions cannot be made.

To examine competition between hydrogen and halogen bonds, five heteroaryl-2-imidazoles were co-crystallized with fifteen halogen-bond donors. It was found that halogen bonds prefer best the acceptor site, demonstrating that a suitably activated halogen-bond donor can compete with a strong hydrogen-bond donor.

The benefits of ‘double activation’ for promoting halogen bond effectiveness was explored with nine haloethynylnitrobenzenes. The positive potential on halogen atoms was enhanced through a combination of an sp-hybridized carbon and electron-withdrawing nitro group(s). Iodoethynylnitrobenzenes were identified as the most effective halogen-bond donors reported to date and the compounds were exploited for the interaction preferences of nitro group and nitro⋯X-Csp interactions were identified as synthetic tools for energetic co-crystal assembly.

A synthetic strategy for the deliberate assembly of molecular polygons was developed utilizing bifurcated halogen bonds constructed from N-oxides and complementary halogen-bond donors via co-crystallization.

A convenient, effective, and scalable protocol for stabilizing volatile liquid chemicals with co-crystallization was achieved. Through the use of halogen-bonding, liquid iodoperfluoroalkanes were transformed into crystalline materials with low-vapor pressure, considerable thermal stability and moisture resistance.

To stabilize the energetic compound ethylenedinitramine, a co-crystallization approach targeting the acidic protons was employed. Eight co-crystals were obtained and the acceptors were identified as supramolecular protecting groups leading to diminished reactivity and enhanced stability while retaining the desirable energetic properties.

5 Recent Papers: 

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1.    Wijethunga, T.K.; Baftizadeh, F.; Stojaković, J.; Myerson, A.S.; Trout, B.L. “Experimental and mechanistic study of the heterogeneous nucleation and epitaxy of acetaminophen with biocompatible crystalline substrates”, Cryst. Growth Des. 2017, 17, 3783-3795.

2.    Wijethunga, T.K.; Aakeröy, C.B.; Desper, J.; Đakovic, M. “A new tecton with parallel halogen-bond donors: A path to supramolecular rectangles”, Acta Crystallographica Section B, 2017, B73, 163-167.

3.      Aakeröy, C.B.; Wijethunga, T.K.; Desper, J.; Đakovic, M. “Electrostatic Potential Differences and Halogen-Bond Selectivity”, Cryst. Growth Des. 2016, 16, 3662-2670.

4.      Aakeröy, C.B.; Wijethunga, T.K.; Desper, J.; Đakovic, M. “Crystal engineering with iodoethynylnitrobenzenes: A group of highly effective halogen-bond donors”, Cryst. Growth Des. 2015, 15, 3853-3861.

5.      Aakeröy, C.B.; Wijethunga, T.K.; Desper, J. “Crystal engineering of energetic materials: Co-crystals of ethylenedinitramine (EDNA) with modified performance and improved chemical stability”, Chem. Eur. J. 2015, 21, 11029-11037 (Featured on the cover).

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