02289nas a2200265   4500008004100000022001400041245013500055210006900190260007300259300001200332490000800344520125900352653001801611653003201629653004501661653003001706653001501736653002201751100002401773700002801797700002401825700002101849700002201870856013101892       2009                        eng d  a0022-286000aMagnetic phase transition in valence tautomers as polymorphs of 3-iodolawsone: Single crystal X-ray structure, DSC and EPR studies0 aMagnetic phase transition in valence tautomers as polymorphs of   aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcDEC  a328-3350 v9383 a<p>Three polymorphs of 3-iodolawsone (I-III) have been isolated and characterized by single crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and differential scanning calorimetry (DSC) techniques. Polymorphs I and II were crystallized from methanol in two different valence tautomeric forms: hydroxynaphthoquinone (HNQ) and hydroxynaphthoseimquinone (HNSQ) as needles and thick plates, respectively. Polymorph III was crystallized from ethanol in HNQ form, as thin plates Chiral crystals of I belongs to the orthorhombic P2(1)2(1)2(1) space group: II and III belong to the monochnic non-centrosymmetric space group Cc. The molecules are packed via O-H O bonding and pi . pi stacking interactions. The study reveals that relatively stronger intermolecular H-bonding (2.02 angstrom) and most favoured pi . pi stacking (similar to 3 49 angstrom) interactions lead II to HNSQ radicals, presence of which was confirmed by EPR (g = 2.0052) spectroscopy. Interestingly, these materials exhibit crystal-to-crystal magnetic phase transition from polymorph I (diamagnetic) to polymorph II (paramagnetic structure) at 171.1 degrees C as identified by DSC and X-ray crystallographic studies (C) 2009 Elsevier B.V. All rights reserved</p>10a3-Iodolawsone10aHydroxynaphthoquinone (HNQ)10aHydroxynaphthosemiquinone radical (HNSQ)10aMagnetic phase transition10aPolymorphs10aValence tautomers1 aZaware, Santosh, B.1 aDagade-Waghmode, Shobha1 aGonnade, Rajesh, G.1 aSrinivas, Darbha1 aRane, Sandhya, Y.  uhttps://library.ncl.res.in/content/magnetic-phase-transition-valence-tautomers-polymorphs-3-iodolawsone-single-crystal-x-ray-002533nas a2200277   4500008004100000245016800041210006900209260000800278300001200286490000700298520154600305653003001851653001901881653002101900653002201921653001601943653001501959100002401974700002501998700002402023700002402047700001702071700002402088700002402112856011902136       2020                        eng d00aFive concomitant polymorphs of a green fluorescent protein chromophore (GFPc) analogue: understanding variations in photoluminescence with pi-stacking interactions0 aFive concomitant polymorphs of a green fluorescent protein chrom  cOCT  a850-8640 v763 a<p>The synthetically modified green fluorescent protein chromophore analogue 3,4,5-trimethoxybenzylidene imidazolinone (1) yielded five polymorphs (I, II, III, IV, V) concomitantly irrespective of the solvent used for crystallization. The pentamorphic modification of 1 is solely due to the interplay of iso-energetic weak intermolecular interactions in molecular associations as well as the conformational flexibility offered by a C-C single bond, which connects the electron-deficient moiety imidazolinone with the electron-rich trimethoxybenzylidene group. A common structural feature observed in all the polymorphs is the formation of a `zero-dimensional' centrosymmetric dimeric unit through a short and linear C-H center dot center dot center dot O hydrogen bond engaging phenyl C-H and imidazolinone carbonyl oxygen. However, the networking of these dimeric units showed a subtle difference in all the polymorphs. The 2D isostructurality was observed between polymorphs I, II and III, while the other two polymorphs IV and V revealed only `zero-dimensional' isostructurality. The different fluorescence emissions of Form I (blue) and Forms II to V (yellow) were attributed to the differences in pi-stacking interactions. It shows that one can modulate the photophysical properties of these smart materials by slightly altering their crystal structure. Such an approach will aid in developing new multi-colour organic fluorescent materials of varying crystal structures for live-cell imaging and fluorescent sensing applications.</p>
10agreen fluorescent protein10ahydrogen bonds10aisostructurality10aphotoluminescence10api-stacking10aPolymorphs1 aMali, Bhupendra, P.1 aDash, Soumya, Ranjan1 aNikam, Shrikant, B.1 aPuthuvakkal, Anisha1 aVanka, Kumar1 aManoj, Kochunnoonny1 aGonnade, Rajesh, G.  uhttps://library.ncl.res.in/content/five-concomitant-polymorphs-green-fluorescent-protein-chromophore-gfpc-analogue