A number of analytical methods and techniques (X‐ray diffraction, FT‐IR and electron paramagnetic resonance spectroscopy, ionic chromatography, scanning electron microscopy, etc.) have been used to study the mode and sites of incorporation of some common inorganic anions (SO42−, NO3− and Cl−) in the calcite crystal lattice. Calcite, the thermodynamically stable calcium carbonate polymorph under standard conditions, was prepared by spontaneous precipitation from calcium hydroxide and carbonic acid solutions. The particular co‐anion was added into the carbonic acid solution in the form of a calcium salt before mixing the reactants. The system prepared in such a way is particularly suitable for investigating the mode of foreign anion incorporation into the crystal lattice of calcite. Apart from the constituent ions and the products of water protolysis, this system contains only the co‐anion examined. In order to study the local environment in the calcite crystal lattice by EPR spectroscopy, Mn2+ was used as a paramagnetic substitute for Ca2+. The experiments were performed at 25 °C and the samples for analyses were taken after a predetermined ageing time of 20 min. It was found that the co‐anions, when added in the concentrations examined, did not affect the morphology of the calcite crystals but were incorporated into the calcite structure. The largest distortion of the calcite structure was obtained when sulfate ions were added. The measured parameters of the calcite unit cell are given, the results obtained are discussed and a model that explains the possible mode and sites of sulfate incorporation is presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The interaction of immunostimulating compounds, the peptidoglycan monomer (PGM) and structurally related adamantyltripeptides (AdTP1 and AdTP2), respectively, with phospholipids in liposomal bilayers were investigated by electron paramagnetic resonance spectroscopy. (1). The fatty acids bearing the nitroxide spin label at different positions along the acyl chain were used to investigate the interaction of tested compounds with negatively charged multilamellar liposomes. Electron spin resonance (ESR) spectra were studied at 290 and 310 K. The entrapment of the adamantyltripeptides affected the motional properties of all spin labelled lipids, while the entrapment of PGM had no effect. (2). Spin labelled PGM was prepared and the novel compound bearing the spin label attached via the amino group of diaminopimelic acid was chromatographically purified and chemically characterized. The rotational correlation time of the spin labelled molecule dissolved in buffer at pH 7.4 was studied as a function of temperature. The conformational change was observed above 300 K. The same effect was observed with the spin labelled PGM incorporated into liposomes. Such effect was not observed when the spin labelled PGM was studied at alkaline pH, probably due to the hydrolysis of PGM molecule. The study of possible interaction with liposomal membrane is relevant to the use of tested compounds incorporated into liposomes, as adjuvants in vivo.

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