Molecular Recognition of Cyanide by a Dicopper(II) Macrocyclic Ionophore: Construction of a Cyanide-Selective Liquid-Membrane Electrode
✍ Scribed by Dipl.-Chem. Benedikt Ahlers; Prof. Dr. Karl Cammann; Dipl.-Chem. Sabine Warzeska; Dr. Roland Krämer
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 393 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
the cyclodextrin channel, which can only be explained by strong intermolecular interactions.
Very surprising was our observation that these polyamide inclusion compounds are water-soluble. The 'H NMR spectrum of [2-(1 a),], in D,O (Fig. 1 b) shows the signals of cyclodextrin and polyamide. Although these are slightly broader than the corresponding signals of the monomers, they indicate the existence of a real solution. The signals of [2.
(1 a)z],, in [D,]DMSO/ CD,COOD are better resolved, and the sharp signal for H-1 of 1 a proves that the C,-symmetry of the x-cyclodextrin has been retained. Thus a reaction between the guest and cyclodextrin can be ruled out. The integration supports a coverage of the polyamide chain with two cyclodextrin units per repeating unit. This very high coverage explains the good solubility.
If the solution of the polyamide inclusion compound
, is allowed to stand for several hours, a precipitate forms in which the cyclodextrin content is reduced by 30% with respect to [2*( 1 a)J,. Apparently, the solubilizing cyclodextrins slowly unthread, with the result that free polymer chain ends can aggregate to allow the inclusion compound to precipitate. Due to the lack of mobility, the rings that are still threaded cannot slip off. The inclusion compound of polymer [4-(1 a)Jn is soluble in water for an unlimited time. Thus the methyl substituents of the piperazine moiety seem to prevent the rings from slipping off the polymer chain.
The pure pol yamides were isolated by cleaving the threaded cyclodextrins with dilute HCI. The yields of the pure polyamides, for example. polyamide-I 1 from [2.(1 a),]-, was greater than 90 ' / o . The molecular masses were determined by gel permeation chromatography after N-trifl u o r ~a c y l a t i o n . ~' ~~ The molecular mass of M , = 4500 gmol-', which was obtained for 2, corresponds to about 16 repeating units.["'
With this solid-state polycondensation it is, in principle, possible to synthesize polyrotaxanes on any scale. Furthermore, this methodology might be applicable for the synthesis of rigidchain, aromatic polyamides. Due to their good water-solubility, polymeric inclusion compounds could, for instance, be used for the coating of metals, polymers or textile surfaces with pol yamides. Composite materials of the polyamide inclusion compounds and hydrophilic polymers, such as starch, might also be obtained.
E-xperimen ful Procedure
General. The ' H NMR spectra were obtained at 400 MHz. and the X-ray powder diffractograms performed on a Siemens-WAXS-S-5000 diffractometer at 22 "C.
[2.(1 a)J: 2 ( 5 g. 24.9 mmol) and 1 a (125 g, 129 mmol) were dissolved in water (250 mL) and heated to 80 C upon stirring. The clear solution was then quickly cooled to 5 C. The resulting white precipitate was filtered, washed with water (400mL). and dried in vacuo. Yield: 39.8g (65%). ' H N M R ([D,jDMSO/