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Molecular Basis for the Mechanical Response of Sulfa Drug Crystals

S. SeethaLekshmi, M. S. R. N Kiran, U. Ramamurty and S. Varughese*

Appreciating the nanomechanical response in crystalline materials demands one to comprehend on the elastic and plastic deformation mechanisms occurring in the vicinity of the nanoindenter tip, in terms of the underlying crystal structures. We combined the nanoindentation data with structural and computational inputs to derive a molecular-level understanding of the nanomechanical response in eight prototypical sulfa drug molecular crystals. The magnitude of the modulus, E, is strongly connected to the non-covalent bond features?the bond strength, the relative orientation with the measured crystal facet as well as their disposition in the crystal lattice. Additional features deciphered from the current studies are: i) robust synthons well-isolated by weak and dispersive interactions reduce the material stiffness; in contrast, interweaving of interactions with diverse energetics fortifies the crystal packing; ii) mere observation of layered structures with orthogonal distribution of strong and weak interactions is a prerequisite but inadequate to attain higher plasticity, and iii) interlocked molecular arrangements prevent long-range sliding of molecular planes and hence lead to enhanced E. Within a broader perspective, the observations are remarkable in deriving a molecular basis of the mechanical properties of crystalline solids, which can be exploited through crystal engineering for the purposeful design of materials with specific properties.

Chemistry A European Journal, 2018, 24, 10.1002/chem.201803987

Pictorial Abstract