Acids, cyclodextrin effect

Long-chain aliphatic olefins give only insufficient conversion to the acids due to low solubility and isomerization side reactions. In order to overcome these problems the effect of co-solvents and chemically modified /i-cyclodextrins as additives was investigated for the hydrocarboxylation of 1-decene [23], Without such a promoter, conversion and acid selectivity are low, 10% and 20% respectively. Addition of co-solvents significantly increases conversion, but does not reduce the isomerization. In contrast, the addition of dimethyl-/i-cyclodextrin increased conversion and induced 90% selectivity toward the acids. This effect is rationalized by a host/ guest complex of the cyclic carbohydrate and the olefin which prevents isomerization of the double bond. This pronounced chemoselectivity effect of cyclodextrins is also observed in the hydroformylation and the Wacker oxidation of water-insoluble olefins [24, 25]. More recent studies of the biphasic hydrocarboxylation include the reaction of vinyl aromatic compounds to the isomeric arylpropanoic acids [29, 30], and of small, sparingly water-soluble alkenes such as propene [31]. 

Scalia S, Mohnari A, Casolari A, Maldotti A. 2004. Complexation of the sunscreen agent, phenyl-benzimidazole sulphonic acid with cyclodextrins Effect on stability and photo-induced free radical formation. European Journal of Pharmaceutical Sciences 22(4) 241-249. 

The tetrahydrophthalic ester of prednisolone, an anti-inflammatory drug, consists of two diastereoisomers. Olszewska et al. [66] describes the effect of addition of an optically active compound (amino acids, cyclodextrins, camphosulfonic acid) on the capacity ratios, k, and separation factors of these diastereoisomers by TLC. They used both mobile phases containing a chiral additive and stationary phases impregnated with an optically active compound, for example, silica gel plates impregnated with amino acids. The best resolution was obtained by impregnation of the stationary phase with o-camphosulfonic acid and copper acetate, and use of dichloromethane-isopropanol (90+10, v/v) as mobile phase. The addition of chiral compound to the mobile phase had less effect on the resolution of diastereoisomers. 

Kim YH, Cho DW, Yoon M, Kim D (1996) Observation of hydrogen-bonding effects on twisted intramolecular charge transfer of p-(N, N-diethylamino) benzoic acid in aqueous cyclodextrin solutions. J Phys Chem 100(39) 15670-15676... 

Piel et al. [109] studied the pharmacokinetics of miconazole after intravenous administration to six sheep (4 mg/kg) of three aqueous solutions - a marketed micellar solution containing polyoxyl-35 castor oil was compared with two solutions both containing 50 pM lactic acid and a cyclodextrin derivative (100 pM hydro-xylpropyl-/l-cyclodextrin or 50 pM sulfobutyl ether (SBE7)-/i-cyclodextrin. This work demonstrated that these cyclodextrin derivatives have no effect on the pharmacokinetics of miconazole by comparison with the micellar solution. The plasma concentration-time curves have shown that there is no significant difference between the three solutions. 

Tetrahedral intermediates, derived from carboxylic acids, spectroscopic detection and the investigation of their properties, 21, 37 Topochemical phenomena in solid-state chemistry, 15, 63 Transition state structure, crystallographic approaches to, 29, 87 Transition state structure, in solution, effective charge and, 27, 1 Transition state structure, secondary deuterium isotope effects and, 31, 143 Transition states, structure in solution, cross-interaction constants and, 27, 57 Transition states, the stabilization of by cyclodextrins and other catalysts, 29, 1 Transition states, theory revisited, 28, 139... 

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

In recent years, supramolecular chemistry has produced a number of systems which have been shown to be able to effectively catalyze a Diels-Alder reaction. Most systems selectively afforded only one diastereomer because of a pre-organized orientation of the reactants. These systems include cyclodextrines, of which applications in Diels-Alder chemistry have recently been reviewed89. Some other kinds of non-Lewis acid catalyzed Diels-Alder reactions, including catalysis by proteins and ultrasound, have been discussed by Pindur and colleagues90. 

Literature data on cytotoxic effects of photoexcited fullerene C60 are controversial. In the studies on transformed B-lymphocytes of Raji fine, phototoxic action of water-soluble carboxy-C60 was not revealed even upon its concentration of 5 x 10 5 M (Irie et al., 1996). In the study (Kamat et al., 2000) damaging effect of fullerenes C60 in dependence on intensity of irradiation toward CHO cells has been demonstrated. Using microsomal fraction of rat liver that was treated with C -cyclodextrin complex, it was shown that already in 5-30 min after UV-irradiation the accumulation of LPO products occurs that is suppressed by antioxidants like ascorbic acid and a-tocopherol. Similar effect of fullerenes C60 has been revealed in microsomal fraction of the cells of ascitic sarcoma 180 (Kamat et al., 2000). 

Hydrogenation of unsaturated carboxylic acids, such as acrylic, methacryUc, maleic, fumaric, cinnamic etc. acids was studied in aqueous solutions with a RhCU/TPPTS catalyst in the presence of p-CD and permethylated P-cyclodextrin [7]. In general, cyclodextrins caused an acceleration of these reactions. It is hard to make firm conclusions with regard the nature of this effect, since the catalyst itself is rather undefined (probably a phosphine-stabilized colloidal rhodium suspension, see 3.1.2) moreover the interaction of the substrates with the cyclodextrins was not studied separately. 

Decene was hydrocarboxylated with a [PdClaj/TPPTS catalyst in acidic aqueous solutions (pH adjusted to 1.8) in the presence of various chemically modified cyclodextrins (Scheme 10.11) [18]. As in most cases, the best results were obtained with DiOMe-P-CD. In an interesting series of reactions 1-decene was hydrocarboxylated in 50 50 mixtures with other compounds. Although all additives decreased somewhat the rate of 1-decene hydroformylation, the order of this inhibitory effect was 1,3,5-trimethylbenzene < cumene < undecanoic acid, which corresponds to the order of the increasing stability of the inclusion complexes of additives with p-CD, at least for 1,3,5-trimethylbenzene (60 M ) and cumene (1200 M ). These results clearly show the possible effect of competition of the various components in the reaction mixture for the cyclodextrin. 

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