@article { ISI:000264717200003, title = {Structural phase transitions of syndiotactic polystyrene}, journal = {Progress in Polymer Science}, volume = {34}, number = {3}, year = {2009}, month = {MAR}, pages = {280-315}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Syndiotactic polystyrene (sPS) exhibits four crystal modifications (alpha, beta, gamma, and delta), along with intermediate forms with different molecular conformations, as well as different chain-packing structures. The extensive literature on the crystal structures exhibited by sPS is reviewed herein, including, the mechanisms of phenomena such as solvent-induced crystallization, thermally induced crystallization and gelation, and the phase transitions among the various crystalline forms. The latter have been studied by static and dynamic wide-angle and small-angle X-ray scattering, infrared and Raman spectra, and neutron scattering, etc., in addition to computer simulations. (C) 2009 Elsevier Ltd. All rights reserved.

}, keywords = {crystal structure, Gelation, phase transition, polymorphism, Solvent-induced crystallization, Syndiotactic polystyrene}, issn = {0079-6700}, doi = {10.1016/j.progpolymsci.2008.11.002}, author = {Gowd, E. Bhoje and Tashiro, Kohji and Ramesh, C.} } @article { ISI:000281980600018, title = {Conformational polymorphism in racemic 2,4-Di-o-Benzoyl-6-o-Tosyl myo-Inositol 1,3,5-Orthoacetate}, journal = {Journal of Structural Chemistry}, volume = {51}, number = {4}, year = {2010}, month = {AUG}, pages = {725-730}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The title compound, C(29)H(26)O(10)S, yields two conformational polymorphs concomitantly from dichloromethane-methanol mixture; the major polymorph grows as plates (Form I, monoclinic, P2(1)/n) and the minor polymorph grows as needles (Form II, triclinic, P-1). The two forms differ mainly in orientation of the tosyl group. In Form I, sulfonyl oxygen of the tosyl group makes intermolecular C -HaEuro broken vertical bar O interactions, whereas the same group in Form II is involved in an intramolecular short dipolar S=OaEuro broken vertical bar C=O (sulfonyl-carbonyl) contact. The molecular organization and the influence of various weak non-covalent interactions that stabilize these conformers in the crystal lattices are discussed.

}, keywords = {Conformation, crystal structure, dipolar interactions, Inositol, non-covalent interactions, polymorphism, sulfonyl-carbonyl contact}, issn = {0022-4766}, doi = {10.1007/s10947-010-0107-y}, author = {Manoj, Kochunnoonny and Gonnade, Rajesh G. and Bhadbhade, Mohan M. and Shashidhar, M. S.} } @article { ISI:000330613400010, title = {Crystallization: key thermodynamic, kinetic and hydrodynamic aspects}, journal = {Sadhana-Academy Proceedings in Engineering Sciences}, volume = {38}, number = {6}, year = {2013}, month = {DEC}, pages = {1287-1337}, publisher = {INDIAN ACAD SCIENCES}, address = {C V RAMAN AVENUE, SADASHIVANAGAR, P B \#8005, BANGALORE 560 080, INDIA}, abstract = {

Crystallization is extensively used in different industrial applications, including the production of a wide range of materials such as fertilizers, detergents, food and pharmaceutical products, as well as in the mineral processing industries and treatment of waste effluents. In spite of the wide-spread use of crystallization, a clear understanding of the thermodynamic, kinetic and hydrodynamic aspects of the design methodologies are not yet well established. More often than not crystallization is still considered an art especially in fine-chemicals, pharmaceuticals and life-sciences sector. It is essential to understand and relate key thermodynamic, kinetic and hydrodynamic aspects to crystallizer performance, not just in terms of yield but also in terms of product quality (characterized by particle size distribution, morphology, polymorphism and the amount of strain as well as the uptake of solvent or impurities in the crystal lattice). This paper attempts to do that by critically reviewing published experimental and modelling studies on establishing and enhancing state-of-the-art thermodynamic, kinetic and hydrodynamic aspects of crystallization. Efforts are made to discuss and raise points for emerging modelling tools needed for a flexible design and operation of crystallizers and crystallization processes that are needed to meet the ever increasing demand on precise product specifications. Focus is on bringing out the trends which can be used as perspectives for future studies in this field.

}, keywords = {CFD, Crystallization, growth, Nucleation, polymorphism, supersaturation}, issn = {0256-2499}, author = {Vedantam, Sreepriya and Ranade, Vivek V.} } @article { ISI:000315306200009, title = {Effect of clay and of electrospinning on the polymorphism, structure and morphology of poly(vinylidene fluoride)}, journal = {European Polymer Journal}, volume = {49}, number = {1}, year = {2013}, month = {JAN}, pages = {90-99}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Electrospun poly(vinylidene fluoride) (PVDF) fibers, containing different amounts of montmorillonite clay were produced, in order to study the effect of clay and of the electrospinning process on the polymorphism, structure and morphology of the PVDF matrix, Clay acted as a processing aid agent, avoiding the formation of beads and improving the quality of the fibers. Clay and the electrospinning process acted synergically on the chain mobility, favoring the formation of beta phase of PVDF, the most valuable for its piezoelectric properties, and shaping its semicrystalline morphology. Electrospinning did not significantly aid the dispersion of clay within the matrix. The interplay of formulation and processing in these composites allowed to obtain PVDF-based materials with varying polymorphism, structure and morphology, offering the possibility to ultimately control their functional properties. (C) 2012 Elsevier Ltd. All rights reserved.

}, keywords = {Composite, electrospinning, Poly(vinylidene fluoride), Polymer, polymorphism, SAXS}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2012.09.023}, author = {Neppalli, Ramesh and Wanjale, Santosh and Birajdar, Mallinath S. and Causin, Valerio} } @article {45740, title = {Mechanochemical synthesis of N-salicylideneaniline: thermosalient effect of polymorphic crystals}, journal = {IUCRJ}, volume = {4}, year = {2017}, month = {MAY}, pages = {243-250}, type = {Article}, abstract = {

Polymorphs of the dichloro derivative of N-salicylideneaniline exhibit mechanical responses such as jumping (Forms I and III) and exploding (Form II) in its three polymorphs. The molecules are connected via the amide N-H center dot center dot center dot O dimer synthon and C-Cl center dot center dot center dot O halogen bond in the three crystal structures. A fourth high-temperature Form IV was confirmed by variable-temperature single-crystal X-ray diffraction at 180 degrees C. The behaviour of jumping exhibited by the polymorphic crystals of Forms I and III is due to the layered sheet morphology and the transmission of thermal stress in a single direction, compared with the corrugated sheet structure of Form II such that heat dissipation is more isotropic causing blasting. The role of weak C-Cl center dot center dot center dot O interactions in the thermal response of molecular crystals is discussed.

}, keywords = {crystal design, crystal engineering, Halogen bonding, hydrogen bonding, intermolecular interactions, materials science, mechanochemistry, polymorphism}, issn = {2052-2525}, doi = {10.1107/S2052252517004043}, author = {Mittapalli, Sudhir and Perumalla, D. Sravanakumar and Nangia, Ashwini} } @article {46162, title = {Porosity switching in polymorphic porous organic cages with exceptional chemical stability}, journal = {Angewandte Chemie-International Edition}, volume = {58}, year = {2019}, month = {MAR}, pages = {4243-4247}, type = {Article}, abstract = {

Porous solids that can be switched between different forms with distinct physical properties are appealing candidates for separation, catalysis, and host-guest chemistry. In this regard, porous organic cages (POCs) are of profound interest because of their solution-state accessibility. However, the application of POCs is limited by poor chemical stability. Synthesis of an exceptionally stable imine-linked (4+6) porous organic cage (TpOMe-CDA) is reported using 2,4,6-trimethoxy-1,3,5-triformyl benzene (TpOMe) as a precursor aldehyde. Introduction of the -OMe functional group to the aldehyde creates significant steric and hydrophobic characteristics in the environment around the imine bonds that protects the cage molecules from hydrolysis in the presence of acids or bases. The electronic effect of the -OMe group also plays an important role in enhancing the stability of the reported POCs. As a consequence, TpOMe-CDA reveals exceptional chemical stability in neutral, acidic and basic conditions, even in 12m NaOH. Interestingly, TpOMe-CDA exists in three different porous and non-porous polymorphic forms (, , and ) with respect to differences in crystallographic packing and the orientation of the flexible methoxy groups. All of the polymorphs retain their crystallinity even after treatment with acids and bases. All the polymorphs of TpOMe-CDA differ significantly in their properties as well as morphology and could be reversibly switched in the presence of an external stimulus.

}, keywords = {chemical stability, Morphology, organic cages, polymorphism, porosity switching}, issn = {1433-7851}, doi = {10.1002/anie.201813773}, author = {Bera, Saibal and Dey, Kaushik and Pal, Tapan K. and Halder, Arjun and Tothadi, Srinu and Karak, Suvendu and Addicoat, Matthew and Banerjee, Rahul} } @article {49106, title = {In situ monitoring of competitive coformer exchange reaction by 1H MAS solid-state NMR}, journal = {Molecualr Pharmaceutics}, volume = {21}, year = {2024}, month = {FEB }, pages = {1479-1489}, type = {Article}, abstract = {

In a competitive coformer exchange reaction, a recent topic of interest in pharmaceutical research, the coformer in a pharmaceutical cocrystal is exchanged with another coformer that is expected to form a cocrystal that is more stable. There will be a competition between coformers to form the most stable product through the formation of hydrogen bonds. This will cause destabilization of the pharmaceutical products during processing or storage. Therefore, it is important to develop a mechanistic understanding of this transformation by monitoring each and every step of the reaction, employing a technique such as H-1 nuclear magnetic resonance (NMR). In this study, an in situ monitoring of a coformer exchange reaction is carried out by H-1 magic angle spinning (MAS) solid-state NMR (SSNMR) at a spinning frequency of 60 kHz. The changes in caffeine maleic acid cocrystals on addition of glutaric acid and caffeine glutaric cocrystals on addition of maleic acid were monitored. In all of the reactions, it has been observed that caffeine glutaric acid Form I is formed. When glutaric acid was added to 2:1 caffeine maleic acid, the formation of metastable 1:1 caffeine glutaric acid Form I was observed at the start of the experiment, indicating that the centrifugal pressure is enough for the formation. The difference in the end product of the reactions with a similar reaction pathway of 1:1 and 2:1 reactant stoichiometry indicates that a complete replacement of maleic acid has occurred only in the 1:1 stoichiometry of the reactants. The polymorphic transition of caffeine glutaric acid Form II to Form I at higher temperatures was a crucial reason that triggered the exchange of glutaric acid with maleic acid in the reaction of caffeine glutaric acid and maleic acid. Our results are novel since the new reaction pathways in competitive coformer exchange reactions enabled understanding the remarkable role of stoichiometry, polymorphism, temperature, and centrifugal pressure.

}, keywords = {caffeine cocrystal, coformer exchange reaction, in situ monitoring, polymorphism, Solid-state NMR}, issn = {1543-8384}, doi = {10.1021/acs.molpharmaceut.3c01118}, author = {Hareendran, Chaithanya and Alsirawan, Bashir and Paradkar, Anant and Ajithkumar, T. G.} }