Single-Crystal Plasticity Defies Bulk-Phase Mechanics in Isoniazid Cocrystals with Analogous Coformers
作者:Jay Prakash Yadav、Ram Naresh Yadav、Praveer Sihota、Hongbo Chen、Chenguang Wang、Changquan Calvin Sun、Navin Kumar、Arvind Bansal、Sanyog Jain
DOI:10.1021/acs.cgd.9b00247
日期:2019.8.7
The crystal structures of four INZ cocrystals with analogous crystal coformers were probed to understand the relationships among molecular packing, H-bonding dimensionality, single-crystal plasticity, and bulk mechanical behavior. These structurally analogous coformers coherently directed H-bonds by “philic” functionalities (−OH and −COOH) and vdW interactions by a “phobic” scaffold (—C6H5–n, where n = 0, 1, 3). In comparison to INZ:2HBA and INZ:4HBA, INZ:BA and INZ:GA exhibited higher plasticity and, hence, better tableting performance due to larger bonding area and higher tensile strength. The rank order of apparent yield pressure and incipient plasticity quantified from “in-die” Heckel analysis of the bulk phase, INZ:2HBA > INZ:4HBA > INZ:GA > INZ:BA, however, does not match that of nanomechanical hardness and elastic modulus, INZ:BA > INZ:2HBA > INZ:4HBA > INZ:GA. The discrepancy may be attributed to the anisotropy in crystal mechanical properties, where the stiffness of the dominant crystal faces probed with nanoindentation may grossly deviate from the bulk mechanical behavior. Therefore, nanomechanical attributes are more predictive of more isotropic molecular crystals, such as 3D H-bonded or interlocked structures, in comparison to those exhibiting gross structural anisotropy, such as crystals with distinct molecular layers that favor facile slip. Hence, the accurate prediction of bulk behavior on the basis of nanomechanical characterization requires the incorporation of crystal shape and packing as well as knowledge of facet-specific mechanical properties. Moreover, the prediction of bonding strength on the basis of molecular packing is still warranted when the crystallographic molecular slip may cause a deviation in the proposed relationship.
我们研究了四种具有类似晶体共形体的 INZ 共晶体的晶体结构,以了解分子堆积、H 键维度、单晶可塑性和块体机械行为之间的关系。这些结构类似的共晶体通过 "philic "官能团(-OH 和 -COOH)和 "phobic "支架(-
C6H5-n,其中 n = 0、1、3)的 vdW 相互作用相干地引导 H 键。与 INZ:2HBA 和 INZ:4HBA 相比,INZ:BA 和 INZ:GA 具有更大的键合面积和更高的拉伸强度,因而具有更高的可塑性和更好的压片性能。然而,从 "模内 "海克尔分析中量化的体相表观屈服压力和瞬时塑性的排名顺序(INZ:2HBA > INZ:4HBA > INZ:GA > INZ:BA)与纳米机械硬度和弹性模量的排名顺序(INZ:BA > INZ:2HBA > INZ:4HBA > INZ:GA)并不一致。造成这种差异的原因可能是晶体机械特性的各向异性,其中用纳米压痕法探测的主要晶面的刚度可能与块体机械行为严重偏离。因此,纳米机械属性更能预测各向同性更强的分子晶体,如三维 H 键或互锁结构,而不是那些表现出严重结构各向异性的晶体,如具有明显分子层的晶体,它们更容易滑动。因此,要在纳米力学特性分析的基础上准确预测块体行为,就必须结合晶体形状和堆积以及切面特定力学性能的知识。此外,当晶体学分子滑移可能导致所提出的关系出现偏差时,仍然需要根据分子堆积预测结合强度。