@article { ISI:000303366000001, title = {Polymorphs, salts, and cocrystals: what{\textquoteright}s in a name?}, journal = {Crystal Growth \& Design}, volume = {12}, number = {5}, year = {2012}, month = {MAY}, pages = {2147-2152}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The December 2011 release of a draft United States Food and Drug Administration (FDA) guidance concerning regulatory classification of pharmaceutical cocrystals of active pharmaceutical ingredients (APIs) addressed two matters of topical interest to the crystal engineering and pharmaceutical science communities: (1) a proposed definition of cocrystals; (2) a proposed classification of pharmaceutical cocrystals as dissociable {\textquoteleft}{\textquoteleft}API-excipient{\textquoteright}{\textquoteright} molecular complexes. The Indo U.S. Bilateral Meeting sponsored by the Indo-U.S. Science and Technology Forum titled The Evolving Role of Solid State Chemistry in Pharmaceutical Science was held in Manesar near Delhi, India, from February 2-4, 2012. A session of the meeting was devoted to discussion of the FDA guidance draft. The debate generated strong consensus on the need to define cocrystals more broadly and to classify them like salts. It was also concluded that the diversity of API crystal forms makes it difficult to classify solid forms into three categories that are mutually exclusive. This perspective summarizes the discussion in the Indo-U.S. Bilateral Meeting and includes contributions from researchers who were not participants in the meeting.

}, issn = {1528-7483}, doi = {10.1021/cg3002948}, author = {Aitipamula, Srinivasulu and Banerjee, Rahul and Bansal, Arvind K. and Biradha, Kumar and Cheney, Miranda L. and Choudhury, Angshuman Roy and Desiraju, Gautam R. and Dikundwar, Amol G. and Dubey, Ritesh and Duggirala, Nagakiran and Ghogale, Preetam P. and Ghosh, Soumyajit and Goswami, Pramod Kumar and Goud, N. Rajesh and Jetti, Ram R. K. R. and Karpinski, Piotr and Kaushik, Poonam and Kumar, Dinesh and Kumar, Vineet and Moulton, Brian and Mukherjee, Arijit and Mukherjee, Gargi and Myerson, Allan S. and Puri, Vibha and Ramanan, Arunachalam and Rajamannar, T. and Reddy, C. Malla and Rodriguez-Hornedo, Nair and Rogers, Robin D. and Row, T. N. Guru and Sanphui, Palash and Shan, Ning and Shete, Ganesh and Singh, Amit and Sun, Changquan C. and Swift, Jennifer A. and Thaimattam, Ram and Thakur, Tejender S. and Thaper, Rajesh Kumar and Thomas, Sajesh P. and Tothadi, Srinu and Vangala, Venu R. and Variankaval, Narayan and Vishweshwar, Peddy and Weyna, David R. and Zaworotko, Michael J.} } @article { ISI:000306942300059, title = {Polymorphs, salts and cocrystals: what{\textquoteright}s in a name? (vol 12, pg 2147, 2012)}, journal = {Crystal Growth \& Design}, volume = {12}, number = {8}, year = {2012}, month = {AUG}, pages = {4290-4291}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, issn = {1528-7483}, doi = {10.1021/cg300704b}, author = {Aitipamula, Srinivasulu and Banerjee, Rahul and Bansal, Arvind K. and Biradha, Kumar and Cheney, Miranda L. and Choudhury, Angshuman Roy and Desiraju, Gautam R. and Dikundwar, Amol G. and Dubey, Ritesh and Duggirala, Nagakiran and Ghogale, Preetam P. and Ghosh, Soumyajit and Goswami, Pramod Kumar and Goud, N. Rajesh and Jetti, Ram R. K. R. and Karpinski, Piotr and Kaushik, Poonam and Kumar, Dinesh and Kumar, Vineet and Moulton, Brian and Mukherjee, Arijit and Mukherjee, Gargi and Myerson, Allan S. and Puri, Vibha and Ramanan, Arunachalam and Rajamannar, T. and Reddy, C. Malla and Rodriguez-Hornedo, Nair and Rogers, Robin D. and Row, T. N. Guru and Sanphui, Palash and Shan, Ning and Shete, Ganesh and Singh, Amit and Sun, Changquan C. and Swift, Jennifer A. and Thaimattam, Ram and Thakur, Tejender S. and Thaper, Rajesh Kumar and Thomas, Sajesh P. and Tothadi, Srinu and Vangala, Venu R. and Vishweshwar, Peddy and Weyna, David R. and Zaworotko, Michael J.} } @article {46187, title = {Remarkably distinct mechanical flexibility in three structurally similar semiconducting organic crystals studied by nanoindentation and molecular dynamics}, journal = {Chemistry of Materials}, volume = {31}, year = {2019}, month = {FEB}, pages = {1391-1402}, type = {Article}, abstract = {

Distinct macroscopic mechanical responses of the three crystals of naphthalene diimide derivatives, 1Me, 1Et, and 1nPr, studied here are very intriguing because their molecular structures are very similar, with the difference only in the alkyl chain length. Among the three crystals examined, 1Me shows highly plastic bending nature, 1Et shows elastic flexibility, and 1nPr is brittle. A detailed investigation by nanoindentation and molecular dynamics (MD) simulations allowed us to correlate their distinct mechanical responses with the way the weak interactions pack in crystal structures. The elastic modulus (E) of 1Me is nearly an order of magnitude lower than that of 1Et, whereas hardness (H) is less than half. The low values of E and H of 1Me indicate that these crystals are highly compliant and offer a low resistance to plastic flow. As the knowledge of hardness and elastic modulus of molecular crystals alone is insufficient to capture their macroscopic mechanical deformation nature, that is, elastic, brittle, or plastic, we have employed three-point bending tests using the nanoindentation technique. This allowed a quantitative evaluation of flexibility of the three mechanically distinct semiconducting molecular crystals, which is important for designing larger-scale applications; these were complemented with detailed MD simulations. The elastic 1Et crystals showed remarkable flexibility even after 1000 cycles. The results emphasize that the alkyl side chains in functional organic crystals may be exploited for tuning their self-assembly as well as their mechanical properties. Hence, the study has broad implications, for example, in crystal engineering of various flexible, ordered molecular materials.

}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.8b04800}, author = {Devarapalli, Ramesh and Kadambi, Sourabh Bhagwan and Chen, Chun-Teh and Krishna, Gamidi Rama and Kammari, Bal Raju and Buehler, Markus J. and Ramamurty, Upadrasta and Reddy, C. Malla} } @article {48417, title = {Dual nanomechanics in anisotropic porous covalent organic framework janus-type thin films}, journal = {Journal of the American Chemical Society}, volume = {144}, year = {2022}, month = {JAN}, pages = {400-409}, type = {Article}, abstract = {

Empowered by crystalline ordered structures and homogeneous fabrication techniques, covalent organic frameworks (COFs) have been realized with uniform morphologies and isotropic properties. However, such homogeneity often hinders various surface-dependent properties observed in asymmetric nanostructures. The challenge remains to induce heterogeneity in COFs by creating an asymmetric superstructure such as a Janus thin film. In this regard, we propose a versatile yet straightforward interfacial layer-grafting strategy to fabricate free-standing Janus-type COF-graphene thin films. Herein, two-dimensional graphene sheets were utilized as the suitable grafter due to the possibility of noncovalent interactions between the layers. The versatility of the approach was demonstrated by fabricating two distinct Janus-type films, with the COF surface interwoven with nanofibers and nanospheres. The Janus-type films showcase opposing surface morphologies originating from graphene sheets and COF nanofibers or nanospheres, preserving the porosity (552-600 m(2) g(-1)). The unique surface chemistries of the constituent layers further endow the films with orthogonal mechanical properties, as confirmed by the nanoindentation technique. Interestingly, the graphene sheets favor the Janus-type assembly of COF nanofibers over the nanospheres. This is reflected in the better nanomechanical properties of COFfiber-graphene films (E-gra(phene) = 300-1200 MPa; E-COF( )= 15-60 MPa) compared to the COFsphere-graphene films (E-gra(phe)ne = 11-14 MPa; E-CO(F )= 2-5 MPa). These results indicate a direct relationship between the mechanical properties and homo/heterogeneity of Janus-type COF films.

}, issn = {0002-7863}, doi = {10.1021/jacs.1c10263}, author = {Mohata, Shibani and Dey, Kaushik and Bhunia, Surojit and Thomas, Neethu and Gowd, E. Bhoje and Ajithkumar, Thalasseril G. and Reddy, C. Malla and Banerjee, Rahul} } @article {48416, title = {Viscoelastic covalent organic nanotube fabric via macroscopic entanglement}, journal = {Journal of the American Chemical Society}, volume = {144}, year = {2022}, month = {SEP }, pages = {16052-16059}, type = {Article}, abstract = {

Covalent organic nanotubes (CONTs) are one-dimensional porous frameworks constructed from organic building blocks via dynamic covalent chemistry. CONTs are synthesized as insoluble powder that restricts their potential applications. The judicious selection of 2,2{\textquoteright}-bipyridine-5,5{\textquoteright}-dicarbaldehyde and tetraaminotriptycene as building blocks for TAT-BPy CONTs has led to constructing flexible yet robust and self-standing fabric up to 3 mu m thickness. The TAT-BPy CONTs and TAT-BPy CONT fabric have been characterized by solid-state one-dimensional (1D) C-13 CP-MAS, two-dimensional (2D) C-13-H-1 correlation NMR, 2D H-1-H-1 DQ-SQ NMR, and 2D N-14-H-1 correlation NMR spectroscopy. The mechanism of fabric formation has been established by using high-resolution transmission electron microscopy and scanning electron microscopy techniques. The as-synthesized viscoelastic TAT-BPy CONT fabric exhibits high mechanical strength with a reduced modulus (E-r) of 8 (+/- 3) GPa and hardness (H) of 0.6 (+/- 0.3) GPa. Interestingly, the viscoelastic fabric shows time-dependent elastic depth recovery up to 50-70\%.

}, issn = {0002-7863}, doi = {10.1021/jacs.2c06133}, author = {Koner, Kalipada and Das, Susobhan and Mohata, Shibani and Duong, Nghia Tuan and Nishiyama, Yusuke and Kandambeth, Sharath and Karak, Suvendu and Reddy, C. Malla and Banerjee, Rahul} } @article {49056, title = {Water-chain mediated proton conductivity in mechanically flexible redox-active organic single crystals}, journal = {Journal of Materials Chemistry A}, volume = {12}, year = {2024}, month = {MAR }, pages = {5866-5874}, type = {Article}, abstract = {

Investigating electrochemical features of proton-conducting organic crystalline materials is relevant in developing efficient energy storage and conversion devices. However, the poor structural flexibility of the crystalline materials at the molecular level often impedes hydrogen bond reorganization of the proton carriers during proton migration, ultimately leading to low ionic conductivity. Here, we report crystals of azobenzene, functionalized with dipicolylamine at both ends (Azo-DPA), which contain an extended hydrogen-bonding network with water molecules in its structure. Interestingly, the crystals display remarkable mechanical flexibility explicitly probed by the nanoindentation technique. The mechanically flexible neutral organic crystals devoid of any acidic moieties (-COOH, -PO3H2, etc.) within the system, exhibit promising proton conductivity (1.63 x 10-4 S cm-1 at 30 degrees C under 95\% relative humidity) which is almost 100 times better compared to the neutral organic systems reported to date. Mechanically flexible redox-active crystalline organic material (Azo-DPA) capable of impressive proton conduction was employed as an electrode material for the first time in an aqueous battery containing Zn2+ ions. The experimental and theoretical studies on the charge storage mechanism revealed the redox activity of the azo (-N 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 N-) centers involving reversible insertion/extraction of protons and Zn2+ ions. Ultimately, the electrode displayed a specific capacity similar to 49 mA h g-1 with almost 100\% retention after 1400 cycles, encouraging the scope of redox-active organic crystalline materials for energy storage applications. Investigating the electrochemical features of proton-conducting flexible organic crystalline materials is crucial for the development of efficient energy storage and conversion devices.

}, issn = {2050-7488}, doi = {10.1039/d3ta05797f}, author = {Hossain, Munshi Sahid and Ghosh, Meena and Mondal, Amit and Ajmal, P. and Saha, Monochura and Reddy, C. Malla and Kurungot, Sreekumar and Bandyopadhyay, Subhajit} } @article {50083, title = {Fast self-healing in a layered molecular crystal mediated by stress-induced symmetry breaking}, journal = {Nature Communications}, volume = {17}, year = {2026}, month = {FEB}, pages = {2525}, type = {Article}, abstract = {

In recent years, symmetry-breaking has emerged as a powerful tool for significantly altering various physical properties in 2D layered materials. However, the breaking of symmetry by means of mechanical stress in organic crystals remains elusive. Here, we demonstrate a simple approach to engineer symmetry-breaking through mechanical stress fields in a layered molecular crystal, resulting in autonomous and fast self-healing under ambient temperature and pressure conditions. Fracture mechanics analysis reveals that the crystal adheres to an elasto-plastic model, with formation of a plastic zone at the crack tip, which prevents further crack propagation, facilitating the self-healing process. Spatially resolved Raman mapping reveals that the crack formation is accompanied by a distinct symmetry-breaking mechanism at the microstructural level. A six-fold increase in non-linear second harmonic (SH) activity, triggered by mechanical perturbation, further validates the local symmetry breaking in an otherwise centrosymmetric crystal. Furthermore, symmetry is restored following successful healing, as evidenced by the disappearance of the SH signal in the healed regions. This study not only broadens the scope of self-healing mechanisms viable in molecular materials but also offers key insights into the role of symmetry breaking and its potential for related technological applications.

}, doi = {10.1038/s41467-026-68987-z}, author = {Ghosh, Ishita and Biswas, Rabindra and Tanwar, Manushree and Bhunia, Surojit and Das, Kaustav and Torris, Arun and Mondal, Amit and Raghunathan, Varun and Kumar, Rajesh and Reddy, C. Malla} }