The result is presented as the top trace of Figure 2(a). As shown in the graph, the presence of cyclosporin results in chemical shift variations in POLYA resonances, indicating rapid exchange kinetics. These downfield 1H chemical shift variations were observed with increasing R. Since no clear conclusion could be drawn from Higuchi solubility diagrams, we attempted to plot in a Job-plot manner the weighted chemical shift variations in these resonances as a function Inhibitors,research,lifescience,medical of the molar fraction of POLYA. In the case of inclusion complex formation, such plots allow a maximum to be
observed for the fraction corresponding to the stoichiometry (Job-plot method) [17, 24] (Figure 2(b)). Such a maximum was observed on all traces for F = 0.5, suggesting an apparent 1:1
stoichiometry of this association (even if the asymmetrical shape of the curves and the variations observed in all resonances run counter to a simple inclusion). Inhibitors,research,lifescience,medical Despite its probable meaninglessness, an apparent constant Ka was calculated mathematically , giving a coarse estimation of logKa≈4.2–4.8M−1. This led us to select a 1/1 preparation for the following experiments using the spray-dried dispersion method. As, on the one hand, POLYA was supposed to enhance the biodisponibility of CYSP and, on the Inhibitors,research,lifescience,medical other, the interactions of water insoluble CYSP with membranes had been investigated in previous studies, it was of interest to explore such interactions of POLYA and especially of the POLYA/CYSP complex itself with membranes. This study is proposed in the next section. 3.2. Interactions with Membranes Homogeneously prepared systems consisting of synthetic phospholipid dispersions (MLV) offer a suitable tool
with which Inhibitors,research,lifescience,medical both structural and dynamic consequences of drug-membrane interactions are observed. The results are presented in this section, using 31P- Inhibitors,research,lifescience,medical and 2H-NMR spectroscopy and ESR spectroscopy on CYSP, POLYA, and a 1/1 complex (ASD) containing MLV of DMPC. 3.3. Membrane Dynamics Study by 31P-2H-NMR and ESR 3.3.1. The Polar Head Group Level: Protein Tyrosine Kinase inhibitor 31P-NMR Experiments As shown in the insert in Figure 3, the 31P-NMR spectrum of the pure DMPC dispersion (MLV) was typical of an axially symmetric powder pattern, with a chemical shift anisotropy of 58ppm Dipeptidyl peptidase typical of DMPC bilayers in their liquid crystalline phase (298K) . The chemical shift difference between the lowfield and highfield edges of the 31P-NMR spectrum is called the chemical shift anisotropy (CSA, ppm) and is directly related to fluidity reorientation at the polar head level where the phosphorus nuclei are located. Hence, a mobile phosphorus group gives a single narrow resonance (several Hz) as detected in a true solution or with small structures (micelles), while solid state phosphorus gives extremely broad contributions (greater than 100ppm).