Cyclodextrins alcohol addition

The distribution of a-, P- and y-CDs is highly dependent on the origin of biocatalyst used (See section on Cyclodextrin Glucanotransferases). Product distributions maybe altered by the addition of specific precipitants, such as aromatics and long chain alcohols 9, 20), Depending on molecular size, these precipitants preferentially complex with specific CD species and are removed from solution. 

Because of their low solubilities in the aqueous phase, the hydroformylation of higher alkenes (>C2) is still a challenging problem. In addition to fluorous biphasic catalysis, possible solutions, which have been addressed, include the addition of surfactants240,241 or the use of amphiphilic ligands242-244 to enhance mutual solubility or mobility of the components across the phase boundary and thereby increase the rate of reaction. The use of polar solvents such as alcohols,245 p-cyclodextrin,246 cyclodextrin ligands,247 248 thermoregulated phase-transfer... 

A remarkably high diastereoselective excess was obtained in the addition of the anion of (S)-(-)-methyl 1-naphthyl sulfoxide to n-alkyl phenyl ketones. The sulfoxide was prepared in optically pure form by oxidation of the complex of methyl 1-naphthyl sulfide and 13-cyclodextrin with peracetic acid followed by crystallization. Desulfurization of the adducts provided enantiomerically pure tertiary alcohols (393]. 

Because the steric effect contributes to the complex formation between guest and host, the chiral resolution on these CSPs is affected by the structures of the analytes. Amino acids, amino alcohols, and derivatives of amines are the best classes for studying the effect of analyte structures on the chiral resolution. The effect of analyte structures on the chiral resolution may be obtained from the work of Hyun et al. [47,48]. The authors studied the chiral resolution of amino alcohols, amides, amino esters, and amino carbonyls. The effects of the substituents on the chiral resolution of some racemic compounds are shown in Table 6. A perusal of this table indicates the dominant effect of steric interactions on chiral resolution. Furthermore, an improved resolution of the racemic compounds, having phenyl moieties as the substituents, may be observed from this Table 6. ft may be the result of the presence of n—n interactions between the CCE and racemates. Generally, the resolution decreases with the addition of bulky groups, which may be caused by the steric effects. In addition, some anions have been used as the mobile phase additives for the improvement of the chiral resolution of amino acids [76]. Recently, Machida et al. [69] reported the use of some mobile phase additives for the improvement of chiral resolution. They observed an improvement in the chiral resolution of some hydrophobic amino compound using cyclodextrins and cations as mobile phase additives. 

The enzymatic polymerization of phenols in aqueous solutions often resulted in low yield of the insoluble polymer. The peroxidase-catalyzed polymerization of phenol took place in presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in buffer [32], Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Even for water-insoluble m-substituted phenols, the addition of 2,6-di-0-methyl-(3-cyclodextrin (DM-P-CD) enabled the enzymatic polymerization in a buffer [33]. The water-soluble complex of the monomer and DM-P-CD was formed, which was polymerized by HRP to give a soluble polymer. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution [34],... 

Frequently, co-solvents are added to aqueous cyclodextrin solutions in most cases, these co-solvents are employed to solubilize the probes. In Section IV.C, the decrease of the exit rate constant of triplet xanthone from CDs with the addition of alcohols was described. This effect was also apparent when studying the dynamics of 1-halonaphthalenes with P-CD in the presence of acetonitrile [141]. When the nitrite ion was used as quencher, the association rate constants decreased in the presence of the organic solvent while the dissociation rate constant increased (Table 21). The main rationalization to explain the change in mobility properties was that acetonitrile was small enough to coinclude inside the cavity a small amount of acetonitrile could preferentially solvate the entrances of the CD thereby leading to a different environment for the probe. 

Chiral mobile phase additives provide a more versatile and cost-effective approach for enantiomer separations in thin-layer chromatography. Typically, chemically bonded layers with cyclodextrin and its derivatives, bovine serum albumin, or macrocyclic glycopeptides are used as chiral additives in the reversed-phase mode [59,60,172-178]. For [5- and y-cyclodextrins and their derivatives, a 0.1 to 0.5 M aqueous methanol or acetonitrile solution of the chiral selector is used as the mobile phase. Bovine serum albumin is generally used at concentrations of 1-8 % (w/v) in an aqueous acetate buffer of pH 5 to 7 or in a 0.5 M acetic acid solution, in either case with from 3-40 % (v/v) propan-2-ol (or another aliphatic alcohol), added to control retention. Enantioselectivity usually increases with an increase in concentration of the chiral selector, and may be non existent at low concentrations of the chiral selector. 

Huang, MB, HK Li, GL Li, CT Yan and LP Wang (1996). Planar chromatographic direct separation of some aromatic amino acids and aromatic amino alcohols into enantiomers using cyclodextrin mobile phase additives. Journal of Chromatography A, 742, 289-294. 

Acenaphthene n-Amyl alcohol Arachidic acid Arachidyl alcohol Benzidine dihydrochloride 2-Butyl octanoic acid Butyloctanol Calcium sulfate Cetylarachidol Cocamine Cocopropylenediamine Cyclodextrin p-Cyclodextrin 1,10-Decanediol 2-Decyl tetradecanoic acid Dihydroxyethyl cocamine oxide Dodecylhexadecanol 2-Hexyl decanoic acid Hydroxypropyl-o-cyclodextrin Hydroxypropyl-P-cyclodextrin Hydroxypropyl-y-cyclodextrin 12-Hydroxystearyl alcohol Isobutyl oleate Kelp Lead phthalate, basic Methoxyethanol 2-Methoxy-5-nitroaniline Methoxy tripropylene glycol acrylate Methylene chloride 2-Octyl dodecanoic acid Oleamine PEG-25 castor oil PEG-30 castor oil PEG-36 castor oil PEG-40 castor oil PEG-200 castor oil PEG-5 hydrogenated castor oil PEG-25 hydrogenated castor oil Polyamide Polysorbate 85 Pyridine Quartz Sodium isopropyl naphthalene sulfonate Soybean (Glycine soja) meal Sucrose Sulfur Tallow amine N-Tallow-1,3-diaminopropane dioleate p-Toluene sulfonic acid Tri methyl amine Tungstic acid Undecylenic acid Vinyl compounds and polymers plastics additive... 

Another important reaction involving a,p-unsaturated ketones is their reduction by hydrides, notably with respect to their ability to provide allylic alcohols which are important synthetic intermediates. In 1985, Chenevert and colleagues reported their study of the reduction of cyclohexen-2-one by sodium borohydride in the presence of additives such as of cyclodextrins or amylase. ° They found that p-cyclodextrin favored the double reduction of the a,p-unsaturated ketones system. This meant that the Michael type reduction occurring at the l,4 -extremity of the enone was significantly accelerated vs. the 1,2 . Oppositely, the reaction in the presence of a-cyclodextrin or amylose was limited to the 1,2-reduction leading to the allylic alcohol. 

Lignin-related polymers were synthesised. Coniferyl alcohol (4-hydroxy-3-methoxycinnamyl alcohol, CoA), a phenolic lignin monomer (monolignol) contained in plant cell walls, was polymerised in the presence of a-cyclodextrin (a-CD) in a HRP/H2O2 system. The presence of a-CD led to the product polymer containing 8-0-4 -richer linkages, compared with the no-additive case. This is probably due to the inclusion complex formation between CoA and a-CD, which suppresses other linkages such as 8-5 and 8-8, due to the steric hindrance of the complex [179]. 

Of course, the above considerations are valid only if the presence of fert-butyl alcohol does not lower the collapse temperature of the formulation. For sucrose-based formulations, Kasraian and DeLuca (1995a) showed that the addition of tert-butyl alcohol does not alter the collapse temperature however, there are cases where the presence of an organic solvent together with water can reduce the collapse temperature of the formulation. As an example, Liu et al. (2005) showed that the collapse temperature of sulfobutylether-7-P-cyclodextrin formulation was reduced by 2 °C when a 5% (w/w) fert-butyl alcohol aqueous solution was used. 

The low vapor pressure and high thermal stability of CILs render them suitable for enantioseparations in gas chromatography (GC). Recently, CILs have been used as chiral stationary phases (CSPs) in GC [40]. Armstrong and coworkers carried out enantiomeric separation of chiral alcohols and diols, chiral sulfoxides, some chiral epoxides and acetamides using a CIL based on ephedrinium salt. Using an ephedrinium CIL (4) as the CSP, enantiomeric separation of alcohols and diols was achieved (Fig. 1). The presence of both enantiomeric forms of ephedrine makes it possible to produce CSPs of opposite stereochemistry, which could reverse the enantiomeric elution order of the analytes. This offers an additional advantage that may not be easily achieved with common and widely used chiral selectors in GC such as the cyclodextrins. However, there was a decrease in enantiomeric recognition ability of the CSP after a week which the authors attributed to dehydration-induced... 

TbADH Thermaonaerobium brockii alcohol dehydrogenase) and 12 other commercial CREDs were used to reduce phenylethyl ketone 46 as shown in Scheme 6.18. a-, 3- and y-Cydodextrins were used as additives to alter the enan-tiosdectivity and decrease the reaction rate. The studies showed that CRED 122, in the presence of increasing concentration of y-cyclodextrin, led to a decrease in enantiopurity of the desired (R) product however, when the molar ratio of cydodexuin reached 3.8, the configuration of the alcohol was swapped to (S). The decreased activity of the enzyme was attributed to transformation of the enzymes a-helix to the p-sheet or to a random coil. Maximum activity was as-sodated vdth maximum amount of a-helix content [28]. 

Efficient biphasic catalysis relies on the rapid mass transfer across the aqueous and organic phases. As indicated, this poses a problem for higher olefins because of their insolubility in water. To tackle the issue and thus to increase the hydroformylation rates, additives, such as co-solvents, surfactants, or modified cyclodextrins, have been explored. A water-miscible organic cosolvent such as an alcohol could increase the solubility of alkenes in the aqueous phase or the catalyst in the organic phase. For example, using [Rh(p-S Bu)(CO)(m-TPPTS)]2 as a catalyst, hydroformylation of 1-octene gave less than 24% conversion after 15 h in water at 80 °C but it reached 90% conversion in 10 h in water/methanol (3 1) [28]. Using Rh-1, 1-dodecene was hydroformylated with 42% conversion to aldehydes in a mixture solvent of water/propanol, while no hydroformylation was observed at all in water alone under identical conditions [29]. The same trend was observed in the reaction of 1-octene catalyzed by Co/BiphTS (BiphTS, trisulfonated tris(biphenyl)phosphine) [30]. 

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