Topography of cyclodextrin inclusion complexes. 12. Structural chemistry of linear .alpha.-cyclodextrin-polyiodide complexes. X-ray crystal structures of (.alpha.-cyclodextrin)2.LiI3.I2.8H2O and (.alpha.-cyclodextrin)2.Cd0.5).I5.27H2O. Models for the blue amylose-iodine complex

Abstract

a-Cyclodextrin ( -CD, C36H60O30) is an enzymatic degradation product of amylose (starch). It consists of six (1-*-4) linked glucoses and represents in its annular structure and overall dimensions one turn of the V6 amylose helix. a-CD and starch are able to form inclusion complexes with a variety of guests. With metal iodides in aqueous solution, essentially black, channel-type complexes crystallize in which -CD molecules stack like coins in a roll and in the tubular cavity polyiodide chains are embedded. Depending on the counterion, four different crystal types have been observed: the (pseudo)hexagonal (a-CDL-Kb-b-nFbO (form I), the triclinic (a-CD)2-Lil3'l2-8FI20 (form II), the hexagonal (a-CD)2-BaI2-l2-12H20 (form III), and the tetragonal (a-CD)2-Cdo.5'l5'27H20 (form IV). While for forms I and III only packing of the molecules can be given, the structures of forms II and IV have been studied in detail. In these, countercations are located in interstices between -CD stacks and coordinated with -CD hydroxyls in the case of Li+ (form II) but Cd2+ (form IV) is surrounded by water. This finding suggests that the observed polymorphism is due to different coordination schemes of cations. In complexes II and IV, -CD molecules adopt a "relaxed" form with all 0(5)-C(5)-C(6)-0(6) torsion angles (-)-gauche. They are linked head-to-head via H bonds to form dimers and each dimer accommodates five I atoms. Four of these are in fully occupied positions near planes defined by 0(4) and C( 6) atoms (diameter of cavity ~5.2 Á). The fifth I is where the 0(2), 0(3) rims of adjacent -CD meet and, since the cavity there bulges to ~7 Á, this I is twofold disordered (in ratio 39/61 in II and 50/50 in IV).The polyiodide chain in II is interpreted as (h-b-),, while it is (Is-),, in IV. Distances between I2, I3-, or I5-units are 3.14-4.01 Á, which are in all cases smaller than the van der Waals distance 4.3 Á. The black or blue color effects are due mainly to I-I charge transfer and possibly to I-H but not to I-O interactions. Electrical conductivity is -6 cm-1 along and 10-10 cm-1 perpendicular to the polyiodide chains in these crystals. It is proposed that in the "blue starch-iodine complex" the polyiodide chain is as found in complex II or IV.* Part I 2 of the series "Topography of Cyclodextrin Inclusion Complexes". For part 1 1. see B. Klar. B. Hingerty, and \V. Saenger, Acta Crystallogr., in press.0002-7863/80/1 502-271 OSO 1.00/0 to an aqueous solution of -CD, a cage-type complex of composition -00• 2•4 20 crystallizes as reddish needles.18 Flowever, if iodide anions are present, nearly black crystals showing metallic luster are formed. They belong to the channel-type inclusion compounds and their habitus, colors, and space groups depend strongly on the counterion, Table I. These complexes are of particular interest in relation to the polymeric amylose-iodine complex, because the "infinite columns" of the stacked -CD molecules mimic the amylose helix. The correspondence of matrix dimensions is obvious from the crystal data entere...

Determination of structure and morphology of the cyclodextrins-iodine complexes

“…These units are shaped into Z-like structures. Furthermore, in the α-CD-I 5ˉ complex, α-CD molecules are stacked together to form columns similar to nanotubes, and I 5ˉ ions are located in the columns and nearly linerly arranged in the direction of columns [10]. As it can be seen from the table 1, the results of iodine content in inclusion compounds with α-and β-cyclodextrins obtained from SEM and iodimetrical titration methods are almost similar.…”

Insights on novel particulate self-assembled drug delivery beads based on partial inclusion complexes between triglycerides and cyclodextrins

“…The relative peak intensities obtained from the XRD diffractogram of TG:a-CD complex showed that a-CD molecules were ordered in form of dimers in TG:a-CD inclusion complex ( Figure 5) (Noltemeyer & Saenger, 1980). Likewise, the first inter-planar distance calculated from the diffractograms of beads prepared from Marcol 82/a-CD and Silicon 50cSt oil/g-CD corresponded to the height of channel type a-CD and g-CD dimers, respectively, confirming that CDs in these cases as well were arranged in dimers ( Figure 5).…”

“…Likewise, the first inter-planar distance calculated from the diffractograms of beads prepared from Marcol 82/a-CD and Silicon 50cSt oil/g-CD corresponded to the height of channel type a-CD and g-CD dimers, respectively, confirming that CDs in these cases as well were arranged in dimers ( Figure 5). (Noltemeyer & Saenger, 1980;Porbeni et al, 2001;Kawasaki et al, 2007).…”

Pyridiniumpentaiodid

“…Im allgemeinen sind die Polyiodidketten weitgehend gestreekt, mit Bindungswinkein zwischen 140 und 180 °. Dies gilt auch t'fir die fehlgeordneten, kettenf'trmigen Pentaiodide (a-Cyelodextrin)2Lil3.I2.8H20 (Noltemeyer & Saenger, 1980) und (Benzophenon)gK2I 2 (Coppens, Leung, Ortega, Young & Laporta, 1983). Zickzackf'trmige Ketten yon 15-Ionen wurden dagegen brim (Benzophenon)4LiI 5 gefunden (Leung, Boehme & Coppens, 1981); brim N(CH3)aI 5 sind die l~--Ionen zu Schichten assoziiert (Broeke.ma, Havinga & Wiebenga, 1957;Hath & Rundle, 1951).…”