caa a22 4500 463184009 CHVBK 20180406164847.0 cr unu---uuuuu 170326e20070101xx s 000 0 eng 10.1007/s10870-006-9140-2 doi (NATIONALLICENCE)springer-10.1007/s10870-006-9140-2 X-ray structures of fifty year old crystals of cholesterol iodide forms I and II [Elektronische Daten] [Rex Palmer, Hilda Palmer, Christopher Frampton, Brian Potter] The molecular framework of steroids was firmly established from the successful X-ray analysis of cholesteryl iodide crystals over fifty years ago. At the time, this was a triumph for the rapidly developing technique of X-ray crystallography. We describe here new analyses of cholesteryl iodide using crystals of forms I and II(A) which are at least 50 years old. Comparison of these two structures reveals subtle differences in the geometry of the steroid skeleton, the attached side chain and the covalently bound iodine. The crystals of both forms occur in the same monoclinic space group, P21, with similar but nevertheless different unit cells, particularly in the b-axis length. As a consequence, there are subtle differences in the packing mechanisms of the two polymorphs. The two forms were originally classified by Bernal and Crowfoot, on the basis of their studies of more than 60 crystals of sterols and sterol derivatives, as "normal, type A - the common form” (corresponding to form II) and "reverse or type B” (corresponding to form I), respectively. Those crystals of form I which have survived for almost 55 years are poor X-ray diffractors at room temperature and have been analysed at liquid N temperature, diffracting well under these conditions. Form II crystals diffract well at room temperature and for this reason the crystals were not cooled. The main differences in geometry occur in the side-chain which is disordered in the room temperature form II crystals, whilst the individual ring conformations in the steroid skeleton are similar, ring A being a strained chair, ring B a 7α/8β half-chair, ring C a symmetrical chair and D a 13β/14α half-chair. (A) Originally denoted Forms B and A respectively. See Additional Note (A) for explanation. Springer Science+Business Media, Inc., 2006 Sterols nationallicence cholesterol nationallicence polymorphic crystal structures nationallicence solid state transformation nationallicence room temperature nationallicence liquid nitrogen temperature nationallicence Palmer Rex School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut Palmer Hilda School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut Frampton Christopher Department of Chemistry, University of Southampton, Highfield, SO171BJ,, Southampton, UK aut Potter Brian School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut Journal of Chemical Crystallography Kluwer Academic Publishers-Plenum Publishers; http://www.springer-ny.com 37/1(2007-01-01), 1-14 1074-1542 37:1<1 2007 37 10870 https://doi.org/10.1007/s10870-006-9140-2 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10870-006-9140-2 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Palmer Rex School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut NATIONALLICENCE 700 1- Palmer Hilda School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut NATIONALLICENCE 700 1- Frampton Christopher Department of Chemistry, University of Southampton, Highfield, SO171BJ,, Southampton, UK aut NATIONALLICENCE 700 1- Potter Brian School of Crystallography, Birkbeck College, University of London, Malet Street, WC1E 7HX,, London, UK aut NATIONALLICENCE 773 0- Journal of Chemical Crystallography Kluwer Academic Publishers-Plenum Publishers; http://www.springer-ny.com 37/1(2007-01-01), 1-14 1074-1542 37:1<1 2007 37 10870 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer