Freeze-drying preparation scheme

The long-chain a-amino acid esters (40), (41), and (42) form bilayers on sonication in water under acidic conditions. Liposomes prepared from (40) and (42) precipitate if the aqueous medium is neutralized by titration with NaOH. Only liposomes made from (41) are stable even in basic solutions, as shown by electron microscopy52). Polypeptide formation in oriented spherical vesicles was confirmed by FT-IR spectroscopy. The liposomal solution of (41) was freeze-dried and the spectrum obtained from the residue was comparable with one of the polycondensed monolayers. The formation of polypeptide vesicles is illustrated in Scheme 4. 

Fig. 38 Preparation scheme of medicaments containing-freeze dried platelets.

Photocoupling of 5-bromouracil to L-tryptophan in frozen aqueous solution or in the solid stale was reported (Scheme 62) [99]. The solid mixture was prepared by evaporation of an aqueous solution or by freeze-drying. 

Preparation of samples for use in RRAs varies. If the substance of interest is in biological fluids (e.g., urine, spinal fluid, plasma) it may be possible to add fluid directly to the RRA. In many instances, however, components (salts, proteins) interfere with assay integrity. In this case, it is necessary to devise a preparation scheme suitable for use with the RRA and which does not alter the quantities of the substance of interest, or to incorporate an appropriate internal standard in the method (e.g., radioactive tracer amounts of the compound of interest preferably labeled with an isotope different from that incorporated in the ligand). In the case of natural product analysis, standard aqueous or organic extraction procedures are followed and the sample is freeze-dried or dried to provide the final preparation. Aqueous fractions can be redissolved in assay buffers whereas dimethylsulfoxide (DMSO) is a useful solvent for organic extracts since many RRAs tolerate < 1 % DMSO in the final assay. 

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