Current cyclodextrine

Native cyclodextrins are oligosaccharides composed of six or more D-glucopyranose residues attached by a-1,4-linkages in a cyclic array. The most current cyclodextrins contain six, seven, or eight glucose residues and are named a-cyclodextrin (a-CD), /3-cyclodextrin (/3-CD) and y-cyclodextrin (7-CD), respectively (Figure 1). ... 

It has been demonstrated that the presence of CNTs greatly increases the oxidation peak current of 6-benzylaminopurine. The CNT-modified electrode is suitable for the determination of trace amounts of benzylaminopurine and has the advantages of high sensitivity, quick response, and good stability [86], Wang et al. have studied the electro-catalytic oxidation of thymine at a a-cyclodextrin incorporated CNT coated electrode in an alkaline media. A sensitive detection scheme for thymine has been further developed by using differential pulse voltammetry [87], The electrochemical determination... 

As yet, the number of applications is limited but is likely to grow as instrumentation, mostly based on existing CE systems, and columns are improved and the theory of CEC develops. Current examples include mixtures of polyaromatic hydrocarbons, peptides, proteins, DNA fragments, pharmaceuticals and dyes. Chiral separations are possible using chiral stationary phases or by the addition of cyclodextrins to the buffer (p. 179). In theory, the very high efficiencies attainable in CEC mean high peak capacities and therefore the possibility of separating complex mixtures of hundreds of... 

Fig. 17.15. Determination of the organic impurities (compounds 1-11) in le-vocabastine drug substance. Conditions 225 mM borate buffer, 2.16% w/v SDS + 1.3% w/v hydroxypropyl-/i-cyclodextrin + 10% v/v 2-propanol, pH = 9, 57 cm fused silica capillary (effective length 50 cm) x 75 pm I.D., injection 5 s at 35mbar, 50°C, detection UV 214 nm, current program 0-15min 75-130 pA, 15-40 min 130 pA, 40-60 min 130-200 pA. (a = auto zero).

Fig. 17.16. Determination of the enantiomeric purity of an active pharmaceutical ingredient (main compound = MC). Conditions 30 mM sodium phosphate buffer, pH = 2.3, 10 mM trimethyl /i-cyclodextrin, 35 cm fused silica capillary (effective length 28.5cm) x 75 pm I.D., injection 10 s at 35mbar, 20°C, 20 kV (positive polarity) resulting in a current of approximately 65 pA, detection UV 215 nm.

A first example is represented by the Mn(III)/Mn(II) redox switch. The complexes of Mn(II) and Mn(III) with the water-soluble tetraphenylsulpho-nate porphyrin (TPPS, Chart 13) display significantly different ri values at low magnetic field strength (lower than 1 MHz), but very similar values at the fields currently used in the clinical practice (> 10 MHz) (141). However, the longer electronic relaxation rates of the Mn(II) complex makes its relaxivity dependent on the rotational mobility of the chelate. In fact, upon interacting with a poly-p-cyclodextrin, a 4-fold enhancement of the relaxivity of [Mn(H)-TPPS(H20)2] at 20 MHz has been detected, whereas little effect has been observed for the Mn(III)-complex. The ability of the Mn(II)/Mn(III)... 

Figure 1.8 Use of capillary electrophoresis for separating the diastereomers quinine (QN) and quinidine (QD) (H-QN is hydroquinine, QD-N-OX is quinidine iV-oxide, H-QD is hydroquinidine, 3-OH-QD is 3-hydroxyquinidine, and asterisk is an unidentified impurity). Reprinted from [17], copyright 2001, with permission from Elsevier. (Capillary 47 cm X 75 pm i.d. (40 cm to detector) (Polymicro Technologies) running buffer 50 mM phosphoric acid containing 15 mM /3-cyclodextrin adjusted to pH 2.5 with NaOH voltage 7 kV current 21 pA injection at 0.5 psi for 4 s detector fluorescence (HeCd laser) excitation 325 nm, emission 450 nm.)...

As a third example, consider a passage from the cyclodextrin article (P16). The authors provide useful background information on two types of cyclodextrins used in bioremediation HPBCD and RAMEB. The two cyclodextrins are compared, and the authors explain why RAMEB was chosen over HPBCD, thereby leading up to the current work. 

Therefore, the authors have synthesized heptakis(carboxymethyl)-substituted a-cyclodextrin which was combined with hydrophobic ammonium to afford 9 (Figure 13), whereby the number of carboxylate-ammonium ion pairs was regulated to six. This compound was incorporated into BUM and subjected to singlechannel current measurements. The current-voltage plot gave a single straight line to afford a conductance level of 7.7 pS under several different experimental conditions. Then the modified cyclodextrin successfully controlled the ion channel structure and therefore the conductance. 

A selected terpolymer (20 mg) of the current application was soaked with 0.06 ml of H2O overnight at ambient temperature and then treated with 3.0 ml of a saturated aqueous solution of either a- or 7-cyclodextrin. It was then sonified for 10 minutes and remained undisturbed for 2 days at ambient temperature. The precipitated product was collected by centrifugation and washed alternately with water and acetone and the product dried in a vacuum at 70°C for 2 weeks. Physical property testing results are provided in Table 3. 

A similar chiral environment is given by inclusion to cyclodextrins (CDs), cyclic oligosaccharides (3). The outside of the host molecule is hydrophilic and the inside hydrophobic. The diameters of the cavities are approximately 6 (a), 7-8 (j3), and 9-10 A (7), respectively. Reduction of some prochiral ketone-j3-CD complexes with sodium boro-hydride in water gives the alcoholic products in modest ee (Scheme 2) (4). On the other hand, uncomplexed ketones are reduced with a crystalline CD complex of borane-pyridine complex dispersed in water to form the secondary alcohols in up to 90% ee, but in moderate chemical yields. Fair to excellent enantioselection has been achieved in gaseous hydrohalogenation or halogenation of a- or /3-CD complexes of crotonic or methacrylic acid. These reactions may seem attractive but currently require the use of stoichiometric amounts of the host CD molecules. 

This principle is applied for the potential development in the EPMEs and for obtaining the intensity of the current in amperometric immuno-sensors. For the enantioselective, potentiometric electrodes, it is necessary to find a molecule with a special architecture that can accommodate the enantiomer. In this regard, cyclodextrins and their derivatives, maltodextrins, antibiotics and fullerenes and their derivatives were proposed [17-52]. 

---