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A universal and novel strategy for the immobilization of polymers has been developed for studying the interaction between plasmid DNA and synthetic polymers with surface plasmon resonance spectrometry. The introduction of thiol moieties in polymers has been applied for a reliable determination of apparent kinetic rate constants between plasmid DNA and the nonviral carrier polymers. Thiolated poly(L-lysine) and poly[(2-dimethylamino)ethyl methacrylate] yielded reproducible sensor surfaces, contrary to the nonthiolated polymers. The knowledge of the kinetic parameters may play a crucial role in the development of nonviral carrier systems for gene therapy, because the dissociation rate constant is strongly correlated to the effectiveness of cell transfection.

A recently developed liposome sandwich immunoassay for interferon-[Gamma] (IFN-[Gamma]), to be applied in microtiter plates, is tailored for surface plasmon resonance (SPR) spectrometry. The assay is performed on a thin ([approximately]20 nm) polystyrene layer that covers a gold surface. This way, analytical data obtained from microtiter plate technology can directly be extrapolated toward SPR. For assaying the antigen IFN-[Gamma], a 16-kDa cytokine, a capture monoclonal antibody is physically adsorbed onto the polystyrene surface. After addition of the sample containing IFN[Gamma], a biotinylated detecting antibody is added. Avidin is used as a bridging molecule between the biotinylated antibody and the biotinylated liposomes. All solutions are prepared with PBS buffer (10 mM, pH 7.4). This avoids additional changes in index of refraction caused by the use of various buffer solutions in immunoassays on microtiter plates for coating, binding, and washing procedures. It is shown that, when liposomes are used, a substantial enhancement of the detection limit is achieved. The 'liposome' strategy improves the sensitivity for the IFN-[Gamma] assay [approximately] 4 x [10.sup.4] times and the detection limit to low picomolar. The method is generally applicable to other sandwich immunoassays.

Degradation products of the peptides gonadorelin and its analogues buserelin, goserelin, and triptorelin were characterized with LC/MS, chiral amino acid analysis, and FAB-MS(-MS). Differences in chemical structures of gonadorelin, its analogues, and their respective decomposition products were evaluated in relation to the putative degradation mechanisms. In acidic solution, gonadorelin and triptorelin are deamidated, whereas buserelin and goserelin undergo debutylation. In the pH range 5-6, the peptide backbone of all four analogues is hydrolyzed at the N-terminal side of the 4serine residue. The hydroxyl moiety of the 4serine residue catalyzes this hydrolysis. Goserelin possesses an azaglycinamide residue, which is also subject to degradation in the neutral pH region. At pH > 7, 4serine epimerization is the main pathway of degradation of all four peptides. Parallel to the epimersation, hydrolysis of gonadorelin, goserelin, and triptorelin occurs.

The basic hexapeptide antagonist [Arg6,D-Trp7,9,MePhe8]substance P (6-11) was degraded in acid and alkaline media. In acid solution, only one degradation product is found whereas in alkaline solution at least six products are formed. These compounds were analytically characterized and structurally identified by reversed-phase high-performance liquid chromatography, capillary electrophoresis, liquid chromatography/mass spectrometry, fast atom bombardment tandem mass spectrometry, optical rotation analysis, and chiral gas chromatography. The product formed in acidic solution is the terminally deamidated antagonist [[Arg.sup.6],D-[Trp.sup.7,9],Me[Phe.sup.8]]substance P (6-11); this product was also found in alkaline degradation mixtures. Other important degradation products originate from racemization of the amino acid residue L-Met, formation of ornithine from Arg, and the oxidation of Met to its sulfoxide form.