@article { ISI:000320036300013,
	title = {Ant-pro reverse-turn motif. structural features and conformational characteristics},
	journal = {European Journal of Organic Chemistry},
	number = {17, SI},
	year = {2013},
	month = {JUN},
	pages = {3529-3542},
	publisher = {WILEY-V C H VERLAG GMBH},
	address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY},
	abstract = {<p>This article details the characteristic conformational features of the Ant-Pro reverse turn ? a folded pseudo -turn motif that displays a closed nine-membered-ring hydrogen-bonded network involving just two amino acid residues, namely anthranilic acid (Ant; a constrained -amino acid), and proline (Pro; a constrained -amino acid). The results from the extensive investigation of ten crystal structures and their NMR conformations in the solution state provide a clear idea about the conformational characteristics of the Ant-Pro reverse turn. The Ant and Pro residues, which form the turn segment, maintain a perfect antiperiplanar orientation throughout, leaving little possibility for the formation of the otherwise possible six-membered hydrogen-bonding that requires a coplanar disposition of the two amino acid residues, as clearly evident from investigation of several crystal structures. The closed hydrogen-bonded network observed in the Ant-Pro reverse turn motif, formed in the forward direction of the sequence (12 amino acid interactions) involving only two amino acid residues, is in stark contrast to the native -turns that involve four residues to form hydrogen-bonded network featuring backward 14 amino acid interactions. The readily available two-residue Ant-Pro motif raises the possibility of a practical utility, particularly in the application of rigidifying flexible peptide backbones by inserting the robust Ant-Pro reverse turn motifs into their backbone.</p>},
	keywords = {Peptides, Peptidomimetics, Protein folding, Protein structures},
	issn = {1434-193X},
	doi = {10.1002/ejoc.201201739},
	author = {Thorat, Vijaykumar H. and Ingole, Tukaram S. and Vijayadas, Kuruppanthara N. and Nair, Roshna V. and Kale, Sangram S. and Ramesh, Veera V. E. and Davis, Hilda C. and Prabhakaran, Panchami and Gonnade, Rajesh G. and Gawade, Rupesh L. and Puranik, Vedavati G. and Rajamohanan, Pattuparambil R. and Sanjayan, Gangadhar J.}
}
@article {46399,
	title = {Additive induced capture of elusive polymorphs of conformationally flexible Sulfonamides/Sulfoesters},
	journal = {Acta Crystallographica A-Foundation and Advances},
	volume = {70},
	year = {2014},
	month = {MAY},
	pages = {C776},
	type = {Meeting Abstract},
	keywords = {additive induced polymorphism, intermolecular interactions, phase transition},
	issn = {2053-2733},
	author = {Shaikh, Samir Rashid and Gawade, Rupesh L. and Chakravarty, Debamitra K. and Puranik, Vedavati G. and Gonnade, Rajesh}
}
@article { ISI:000373747700077,
	title = {Additive mediated syn-anti conformational tuning at nucleation to capture elusive polymorphs: remarkable role of extended pi-stacking interactions in driving the self-assembly},
	journal = {Crystal Growth \& Design},
	volume = {16},
	number = {4},
	year = {2016},
	month = {APR},
	pages = {2416-2428},
	publisher = {AMER CHEMICAL SOC},
	address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA},
	abstract = {<p>Understanding the process of prenucleation clustering at supersaturating stage is of significant importance to envisage the polymorphism in crystalline materials. Preferential formation of a thermodynamically stable crystal form suggests energetically favored patterns of interactions which control molecular aggregation during nucleation. Introduction of additives during crystallization is sometimes used as a suitable strategy to obtain metastable polymorphs in cases where it is not easy to capture the same by conventional crystallization methods. Comparative analysis of energy relationships and intermolecular interactions between thermodynamically stable and metastable crystal forms provides valuable clues about the nature of growth synthons at prenucleation clustering and preferential crystallization of the thermodynamic form. Conformationally flexible sulfonamide/sulfoester derivatives constituting electron rich and electron deficient aromatic rings were synthesized to study the interplay between pi-stacking and hydrogen bonding synthons. We have identified and characterized the thermodynamically stable and metastable elusive polymorphs of aromatic sulfonamides 1 and 2 and sulfoesters 3 and 4. However, these compounds eluded polymorphism during crystallisation from various common solvents/conditions and only produced thermodynamically stable crystals forms (form I crystals). Surprisingly, exploitation of pyrazinamide as an additive in different stoichiometric ratios during crystallization gave elusive polymorphs [three for 1 (form 1II, form 1III, and form 1IV) and one each for 2 (form 2II), 3 (form 3II), and 4 (form 4II)]. Molecules in stable crystal forms of these compounds are linked via extended chains of parallel displaced pi...pi stacking interactions that seem to play a vital role in driving the self-assembly of molecules and subsequently governing the nucleation process. In contrast, molecules in metastable polymorphs are devoid of such extended pi-stacking assemblies. Interestingly, differential scanning calorimetry, hot stage microscopy, and X-ray crystallographic studies confirmed the thermal crystal-to-crystal transition of all three metastable polymorphs of 1 (form 1II, form 1III, and form 1IV) to its thermodynamically stable crystal form (form 1I). Conformational analysis of molecule 1 using density functional theory calculations also validated higher stability for syn conformation (observed in Form 1I crystals) over anti and midway conformations (seen in metastable polymorphs). Melt crystallization of form 1I crystals of 1 on the larger face (001) of delta-pyrazinamide and lattice matching analysis (GRACE) revealed that the layered arrangement of molecules of delta-pyrazinamide (on 001 face) during heterogeneous nucleation acts as a template (heteroepitaxy) to provide a preferential site for the nucleation of new metastable polymorphs by selectively inhibiting the most preferred crystal form from growing into the nucleus. Solution state one- and two-dimensional (NOESY) H-1 NMR, scanning electron microscopy, and a Cambridge Structural Database survey were conducted to substantiate the role of additives during crystallization.</p>},
	issn = {1528-7483},
	doi = {10.1021/acs.cgd.6b00204},
	author = {Gawade, Rupesh L. and Chakravarty, Debamitra K. and Kotmale, Amol and Sangtani, Ekta and Joshi, Pranaya V. and Ahmed, Awais and Mane, Manoj V. and Das, Susanta and Vanka, Kumar and Rajamohanan, Pattuparambil R. and Puranik, Vedavati G. and Gonnade, Rajesh G.}
}
