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Wiktor Kemula wśród pionierów chemii supramolekularnej

Lipkowski J., Sybilska D.

Kwartalnik Historii Nauki i Techniki

2002

R. 47, nr 1

47--54

Professor Wiktor Kemula, recognizing the importance of chemical analysis for the economic progress of the society, systematically applied new achievements of physical chemistry to the analytical procedures. After having successfully developed the chromatopolarography, he tried to apply varous types of sorbents for chromatographic separations. Application of clathrates, or inclusion compunds, as the sorbents led to the clathrate chromatography', where the separation of the guests depended mostly on their geometric fitting to the host cavities. Recognition of the structures of the clathrates, of the mechanisms of sorption, the separations of isomers, specially of the aliphatic and aromatic nitrocompounds, were at the time notable achievements. Other principles of detection - adsorption-sensitive AC polarography - allowed to W. Kemula and his coworkers to widen the scope of the method to many electro-inactive compounds. Being formally long retired, he worked out new ideas of elektrokinetic detection, and left it to his students. In the early 80th he was active in starting the series of symposia on supramolecular chemistry, and was one of the founders of the Journal o f Inclusion Phenomena. Every few years he introduced in his laboratory new methods - thermogravimetry, X-ray structural investigations. His ideas are continued and modernized by his onetime students, in the Institute of Physical Chemistry of the Polish Academy of Sciences. The clathrates were slowly replaced by the cyclodextrines, which permitted to develop a new field - chiral separation, very important and prospective in the analysis of drugs or food additives.

Cyclodextrins as chiral additives for chromatographic separation of some mandelic acid esters into enantiomers

Bielejewska A., Łukasik B., Duszczyk K., Sybilska D.

Chemia Analityczna

2002

Vol. 47, No. 3

419-427

Chromatographic behaviour of mandelic acid and its (methyl, ethyl,n-propyl and n-butyl) esters have been studied in RP-HPLC system modified with alfa, beta, gama-cyclodextrins and permethylated alfa-cyclodextrin. It has been found that although native cyclodextrins form with esters a relatively stable complexes of 1:1 stoichiometry, which do not recognize enantio-mers. On the contrary, permethylated alfa-cyclodextrin permits efficient separation of optical isomers. Improved separations have been observed with the lengthening of aliphatic chain in an ester molecule. The enantiomers of esters have been always eluted with the same sequence: first R(-) enantiomer, second the S(+) one, while the order was inverse for free mandelic acid optical isomers. This difference may suggest dissimilar manner of attachment. The attempts to discuss the results in the light of Dalgliesh three point attachment concept have been undertaken. It was assumed that hydrophobic interactions between methyl groups of permethylated Beta-cyclodextrin and alkyl group of ester produce diversity in attachment of enantiomers. In optimization procedure/.e. to obtain base line separation at the shortest time of analysis three parameters have been taken into account; temperature, methanol concentration and native/Beta-cyclodextrin addition. In effect the use of addition of Beta-cyclodextrin is worth to recommendation.

Zbadano chromatograficzne zachowanie się kwasu migdałowego i jego estrów (metylowego-, etylowego-, /n-propylowego i n-bultylowego) w układach RP-HPLC zmodyfikowanych alfa, beta, Gamma- cyklodekstrynami i permetylowaną Beta-cyklodekstryną. Stwierdzono, że naturalne cyklodekstryny tworzą z estrami stosunkowo trwałe kompleksy o stechiometrii 1:1. Nie następuje jednak rozróżnianie enancjomerów estrów. Skuteczne rozdzielanie izomerów optycznych badanych estrów umożliwia natomiast permetylowana Beta-cyklodekstryna Wzmocnienie enancjoselektywności obserwowano wraz z wydłużeniem łańcucha bocznego estrów. Enancjomery estrów były wymywane zawsze w tej samej kolejności; R(+) pierwszy, a drugi S (-), podczas gdy porządek wymywania enancjomerów kwasu migdałowego był odwrotny, co może sugerować różny sposób zaczepienia. Podjęto próby rozpatrzenia wyników w świetle idei trójpunktowego zaczepienia Dalgliesha. Przyjęto, że hydrofobowe oddziaływania między metylowymi grupami pennetylowanej Beta-cyklodekstryny i alkilami estrów sąpodstawązróżnicowania zaczepienia enancjomerów. W toku optymalizacji, aby otrzymać rozdzielenie do linii podstawowej w najkrótszym czasie analizy, wzięto pod uwagę trzy parametry: temperaturę, stężenie metanolu i dodatek Beta-cyklodekstryny. W rezultacie dodatek Beta-cyklodekstryny okazał się godny polecenia.