Cyclodextrins improvement

Rode, T., Frauen, M., Muller, B. W., Dusing, FI. J., Schonrock, U., Mundt, C., andV fenck, FI. 2003. Complex formation ofsericoside with hydrophilic cyclodextrins improvement of solubility and skin penetration in topical emulsion based formulatiorfsur. J. Pharm. Biopharm. 55 191-198. 

Another type of absorption enhancer, which has been shown to have a better safety profile, is cyclodextrin (CD) [39]. CDs have been shown to form inclusion complexes with lipophilic drugs, thereby improving their aqueous solubility and stability. A powdered insulin formulation containing dimethyl-(3-cyclodextrin improved the absolute bioavailability of insulin by 13% in rabbits compared to a control liquid formulation (1%) of insulin with dimethyl-(3-cyclodextrin [40]. Recently, hydroxypropyl (3-cyclodextrin has been shown to be more effective for enhancing the nasal absorption of acyclovir than a range of other absorption enhancers in vivo [41]. 

Cyclodextrins improve chemical stability, increase the drug s bioavailability, and decrease local irritation. However, the improvement of ocular bioavailability seems to be limited by the very slow dissociation of the complexes in the precorneal tear fluid. 

Hydrogenation of methyl phenylglyoxylate with Rh-, Ir- and Pd-based catalysts containing chelating diamine ligands was studied in methanol and in MeOH/H20 mixtures. High conversions (95-100%) could be achieved in 15-20 h (r.t., 50 bar H2), however the enantioselectivity was only modest (e.e. 10-50 %). Even that was diminished in MeOH/H20 70/30. However, addition of p-cyclodextrin improved the yield and restored the e.e. up to the value observed in MeOH (Scheme 3.20) [207],... 

The preferential affinity to EtOH depends on the balance between the hydro-philicity and the hydrophobicity of the membrane s material (Huang 1991). Qiu and Peinemann (2006) developed novel organic nanocomposite membrane for PV. The basic polymers were PDMS and poly(l-trimethylsilyl-l-propyne) (PTMSP). By implanting the hydrophobic organic molecules in PTMSP and PDMS, permselectivity to EtOH was enhanced. For example, PDMS with 20 wt% a-cyclodextrins provides a separation factor of 12 for EtOH (5 wt%)-water (95 wt%). Similarly, PTMSP with only 8 wt% a-cyclodextrins improved the enrichment of the low concentration of EtOH from 5 to 48 wt% and maintained the flux at 9 kg pm/m h. They claimed that the increased performance in EtOH-water separation with this organic nanocomposite membrane may lead to the practical industrial application by means of the PV process to produce bioethanol. 

An interesting case of a cathodic substitution is the EuCh-mediated reduction of oxygen that reacts with aliphatic CH bonds. The selectivity of 1-H 2-H 3-H being 1 6 19 was attributed to a radical intermediate, while in the aromatic substitution the preferred ortho- and para-substitution points to an electrophilic oxygen species [96]. In the FeCls-mediated oxygenation of n-hexane in a fuel cell, the addition of a- and /3-cyclodextrins improved the selectivity toward oxygenation of the terminal CHs-groups due to inclusion of the -hexane in the cyclodextrin cavity [97]. 

The effect of the addition of unmodified cyclodextrins to a reaction mixture on the aqueous hydroformylation of 1-decene is rather small. The conversion was enhanced hy a factor 2 upon the addition of P-cyclodextrin. The modified P-cyclodextrins improved the activity to a greater extent in the optimized situation the activity increased with a factor of 14. These modified cyclodextrins are more efficient since they are soluble in both the organic phase and the aqueous phase thereby improving the efficiency of the substrate transfer process. Similar to the systems described above, the isomerization was suppressed under these optimized conditions. However, internal alkenes could not be hydroformylated using this system. Another striking difference is the selectivity of the reaction. The addition of the modified cyclodextrins resulted in a decrease of the l b ratio (2.7 to 1.9), whereas Reetz reported an increase for his supramolecular system So far no sohd explanation has been found for this difference. 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

Addition of a chiral carrier can improve the enantioselective transport through the membrane by preferentially forming a complex with one enantiomer. Typically, chiral selectors such as cyclodextrins (e.g. (4)) and crown ethers (e.g. (5) [21]) are applied. Due to the apolar character of the inner surface and the hydrophilic external surface of cyclodextrins, these molecules are able to transport apolar compounds through an aqueous phase to an organic phase, whereas the opposite mechanism is valid for crown ethers. 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Lockwood SF, O Malley S, and Mosher GL. 2003. Improved aqueous solubility of crystalline astaxanthin (3,3,-dihydroxy-P,P-carotene-4,4,-dione) by Captisol (sulfobutyl ether P-cyclodextrin). Journal of Pharmaceutical Sciences 92(4) 922-926. 

It has been claimed that complexes of P-cyclodextrin with anionic surfactants, notably higher fatty alcohol ethoxylates, improve scouring efficiency on cotton and wool in laboratory-scale processing [34]. Residual surfactants carried over from preparation can have undesirable effects in subsequent processing. When cyclodextrins complex with surfactants, their surface activity is reduced. Hence cyclodextrins are potentially useful for the removal of residual amounts of surfactants from substrates [35]. The use of a- and P-cyclodextrins has been studied in this context with one cationic, one anionic and four... 

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... 

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