Sorption, enantioselective

Davankov, V.A., Zolotarev, Y.A., and Kurganov, A.A., Ligand-exchange chromatography of racemates. XL Complete resolution of some chelating compounds and nature of sorption enantioselectivity, J. Liquid Chromatogr., 2, 1191, 1979. 

Fig.4 The principle of chiral recognition by gas sensors chiral discrimination by preferential sorption of the enantiomers of N-TFA-alanine methyl ester (N-TFA-Ala-OMe) into enantioselective (R)- and (S)-octyl-Chirasil-Val polymers. The chemical information is transformed into optical signals by the respective transducers...

As mentioned in Section 2, isopropyl phenyl sulfoxide was included in the crystals of 1 with a high enantioselectivity of its (.S )-form. Generally, the inclusion compound of a sulfoxide was prepared by two methods (1) insoluble 1 was simply stirred in the presence of an alkyl phenyl sulfoxide and water (Method A sorption ) and (2) 1 was recrystallized in the presence of the sulfoxide (Method B ... 

Complexes of 2-[2-(4-hydroxy-6-methylpyrimidylazo)-4-sulfochlorido]-a-naphthol with starch are patented for the determination of amylose concentrations.815 Konrad and Musso816 suggested the possibility of separating enantiomers of chiral azo dyes on starch, as the sorption is enantioselective. 

The thermal annealing of the MIP was accompanied by a significant reduction in the swelling and an increase in the apparent dry density of the material. This results in a higher density of the enantioselective binding sites, although they may be less accessible than prior to the thermal treatment. The nitrogen sorption data showed... 

Very recently, Fedin, Kim and colleagues synthesized a homochiral metalorganic polymeric material, [Zn2(bdc)(L-lac)(dmf)] (DMF) (36), by using a one-pot solvothermal reaction of Zn(NO3)2, L-lactic acid (L-H2lac) and 1,4-benzenedicarbox-ylic acid (H2bdc) in DMF [53]. This 3-D homochiral microporous framework exhibited permanent porosity and enantioselective host-guest sorption properties towards several substituted thioether oxides. Although 36 could catalyze the oxidation of thioethers to sulfoxides with size and chemoselectivity, no asymmetric induction was observed. 

Starodubtseva, E.V. (1990) Sorption and catalytic properties of intermetallic compounds in reaction hydrogenation of propylene and enantioselective hydrogenation of ethyl acetoacetate, Cand. Diss. Thesis, N.D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of ihe USSR, Moscow (supervisors Klabimovskii, E.l. and Konenko, I.R.). 

Subsequently, several research groups including Lin, Rosseinsky, Xiong, Fedin and others have designed and synthesized several homochiral porous metal-organic materials capable of enantioselective sorption of chiral organic molecules, which are listed in Table 1. 

The material 6 showed a remarkable catalytic activity in the oxidation of thioethers 13 to sulfoxides 14 by urea hydroperoxide (UHP) or H O (Scheme 2). Although the conversion and selectivity (for 14 over 15, >90%) was reasonable with UHP for the substrates with smaller substituents, 13a and 13b, the ones with bulkier substrates 13c and 13d failed to produce any measurable conversion. The conversion increases to 100% by changing UHP with H O. The catalytic activity of 6 for selective sulfoxidation remains similar even after 30 cycles. Despite the fact that no asymmetric induction was found in the catalytic sulfoxidations, enantioen-riched sulfoxides were obtained by enantioselective sorption of the resulting racemic mixture by the chiral pores of 6, which occured simultaneously with the catalytic process. Thus, after catalytic oxidation of 13a, (5)-14a was preferentially absorbed by the pore of 6 leaving exactly equal amount of the excess ) -enantiomer in the solution phase (-20% ee). The combination of high catalytic activity and enantioselective sorption property of 6 provides a unique opportunity to device a one-step process to produce enantioenriched products. 

By taking advantage of both catalytic activity and enantioselective sorption ability of 6 discussed above, a one-step reaction-purification system was developed to synthesize optically pure sulfoxides. In an illustrative example, PhSMe was chosen as a substrate. A mixture of the sulfide and in 0.01 M of DMF in CHjClj/CHjCN was loaded on top of the column packed with 6 and eluted with the same solvent mixture. The / -isomer of the corresponding sulfoxide was eluted first as it has low affinity with 6, followed by 5 -isomer (Fig. 15). Excess amount of (5-fold) forms about 5% of sulfone (the over-oxidation product), but a little excess (1.5-fold) of the oxidant, even though left out some disulfide in the mixture (con-version=91%), affords pure enantiomers ca. 35% each based on the starting PhSMe to offer a overall isolated yield of 70% (Fig. 15b). This was the first demonstration of an application of CMOPMs in chiral chromatography. Furthermore, the tandem... 

Introduction of relatively weak functional groups, such as carbonyl, hydroxyl, nitro, amide, etc., in the nanochannels of PCPs would affect the monomer alignment, which may lead to precision control of stereoselectivity and regioselectivity of the resulting polymers. In particular, PCPs with either helical or chiral structures on the pore surface are of intense interest in chemistry and such porous solids are potentially useful to find applications in enantioselective sorption/separation and catalysis [34, 38 0, 42, 45]. Of considerable interest is the use of the chiral channels to affect asymmetric polymerizations such as asymmetric selective polymerization of racemic monomers as well as asymmetric polymerization of prochiral monomers, which may give helical polymer conformations. 

Similar slow sorption-desorption kinetics were observed with some other enantioselective phases in liquid chromatography (103-105). Also with highly selective crown ethers or cryptates the release of substrates from their complexes can be extremely slow (A-6). 

In certain cases, a values of 30 or more have been found, which then correspond to A(AG) values in the range of 2 kcal/mol (8.4 kJ/mol). Generally, such values are obtained owing to very low retention of the first enantiomer eluted. This means that a very enantioselective sorption process is operating in the column, i.e., one of the enantiomers is virtually unbound by the CSP for steric reasons. Such phenomena are not easily explained by the three-point interaction model, but rather indicate the operation of a sort of chiral steric exclusion mechanism, more in line with a steric fit concept involving only one binding interaction. ... 

It should be noted that control of water content is key in retaining the enantiopurity of the material, as racem-ization of the L-Asp ligand occurs at high water methanol ratios. The chirality of the framework endows it with enantioselective sorption properties in the vapor uptake of chiral diols, with an observed enantiomeric excess (ee) of 54% for the uptake of 2-methyl-2,4-pentanediol, which fits snugly within the chiral channels of the material... 

Dybtsev DN, Nuzhdin AL, Chun H, Bryliakov KP, Talsi EP, Fedin VP, et al. Permanent microporosity and enantioselective sorption in a chiral open framework. Angew Chem Int Ed 2006 45 916-20. 

Seo JS, Whang D, Lee H, Jun SI, Oh J, Jeon YJ, et al. A homochiral metal-organic material with permanent porosity, enantioselective sorption properties, and catalytic activity. Angew Chem Int Ed... 

Porosity is another important and desired property in crystal engineering it confers potential catalytic and sorption properties.There are several examples that encourage the pursuit of research in this direction. Chiral networks, with enantioselective host-guest functions, are expected to perform chiral separations and catalysis, as shown by recent works. Another area of intense research is the development of coordination networks as materials for gas uptake (Ar, N2, CO2, CH4), particularly H2. Last, but not least, coordination polymers attract chemists through their intrinsic beauty and intriguing structural diversity. 

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