Derivatization microcrystallinity

Distinction should be made at this time between diastereoisomers and enantiomers. The former are characterized by the presence of at least two closely associated asymmetric centers in the molecular structure, either of which can epimerize. Altogether then there are two pairs of enantiomers for a total of four stereochemically unique individuals. Diastereoisomers have different physical properties and as a result discriminations, and even separations, can be done relatively easily. Enantiomers on the other hand differ in only one physical property, i.e. the direction of rotation of polarized light. Reaction of an enantiomeric racemic mixture with a third chiral species will produce a mixture of diastereomers therefore facilitating their identification or their separation. Early examples of this were the separations done by fractional crystallization of salts produced by a derivatization reaction with, for example, the alkaloid (-)-brucine. Fractional crystallization would never seem to be an effective analytical method yet it was used with some success in a forensic sciences context to confirm the presence of (L)-cocaine by a carefully contrived microcrystalline test. The physical properties... 

Microcrystalline cellulose II, like the cellulose I form, does not possess enough mechanical strength to be used as an HPLC-CSP Although its triacetate derivative, CTA-II, can be used as an HPLC support, it is not as useful a CSP as CTA-I (47). Ichida et al. (48) were able to improve on the properties of derivatized cellulose II by depolymerization, followed by coating on macroporous silica gel. In this manner, they created a number of new CSPs, the cellulosic CSPs, based on ester and carbamate derivatives of cellulose (see Table 2). 

An obvious extension of the CBM-fusion technology is to enable a single-step purification and immobilization of fusion proteins by generating active CBM-Protein. Moreover, the utilization of the carbohydrate affinity system, such as cellulose, is attractive because it does not require a derivatized matrix, and cellulose is available in a variety of inexpensive forms, such as preformed microporous beads, highly adsorbent sponges or cloth and microcrystalline powders [181]. 

Colloidal zinc phenylphosphonate can be prepared by stirring the microcrystalline solid in a solution containing a substoichiometric amount of Z1OCI2 (15,16). A mole ratio of 1 Zif25 Zn is sufficient to prepare colloidal suspensions of the zinc salts. These zinc phenylphosphonate particles, capped with Zr, adhere readily to gold surfaces primed with a monolayer of 4-mercaptobutylphosphonic acid. Gold QCM electrodes derivatized in... 

Both polymers are very poor chiral selectors in their native state but exhibit enhanced selectivity when derivatized as esters or carbamates derivatives. Microcrystalline cellulose triaeetate (MCTA) was the first derivative used in LC mostly in the reversed-phase mode. Chiral recognition by MCTA is mainly ascribed to its microcrystallinity as confirmed by Okamoto et al. [43,44] and then Francotte et al. [45], who have shown the influence of the crystalline arrangements on the enantioseparation. 

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