Polymorphism of pure p-tert-butylcalix[4]arene: conclusive identification of the phase obtained by desolvation

In its pure form, the well-known host compound p-tert-butylcalix[4]arene forms at least two polymorphs; one of these phases is now identified as that formed upon guest removal.     

Covalently Immobilizable Tris(Pyridino)-Crown Ether for Separation of Amines Based on Their Degree of Substitution

A great number of biologically active compounds contain at least one amine function. Appropriate selectivity can only be accomplished in a few cases upon the substitution of these groups, thus functionalization of amines generally results in a mixture of them. The separation of these derivatives with very similar characteristics can only be performed on a preparative scale or by applying pre-optimized HPLC methods. A tris(pyridino)-crown ether was designed and synthetized for overcoming these limitations at a molecular level. It is demonstrated, that this selector molecule is able to distinguish protonated primary, secondary and tertiary amines by the formation of reversible complexes with different stabilities. This degree of substitution-specific molecular recognition of amines opens the door to develop separation processes primarily focusing on the purification of biologically active compounds in a nanomolar scale.     

A convenient separation of ursolic and oleanolic acid

A convenient route has been developed to separate regioisomeric ursolic and oleanolic acid by treating the mixture with mCPBA or formic acid/hydrogen peroxide.