Scattering off an oscillating target: Basic mechanisms and their impact on cross sections

We investigate classical scattering off a harmonically oscillating target in two spatial dimensions. The shape of the scatterer is assumed to have a boundary which is locally convex at any point and does not support the presence of any periodic orbits in the corresponding dynamics. As a simple example we consider the scattering of a beam of non-interacting particles off a circular hard scatterer. The performed analysis is focused on experimentally accessible quantities, characterizing the system, like the differential cross sections in the outgoing angle and velocity. Despite the absence of periodic orbits and their manifolds in the dynamics, we show that the cross sections acquire rich and multiple structure when the velocity of the particles in the beam becomes of the same order of magnitude as the maximum velocity of the oscillating target. The underlying dynamical pattern is uniquely determined by the phase of the first collision between the beam particles and the scatterer and possesses a universal profile, dictated by the manifolds of the parabolic orbits, which can be understood both qualitatively as well as quantitatively in terms of scattering off a hard wall. We discuss also the inverse problem concerning the possibility to extract properties of the oscillating target from the differential cross sections.Comment: 18 page

Retention of structurally diverse drugs in human serum albumin chromatography and its potential to simulate plasma protein binding

The retention behavior of 39 structurally diverse neutral, basic and acidic drugs was investigated on an HSA stationary phase using PBS buffer (pH 7.0) and acetonitrile or 2-propanol as organic modifiers. Extrapolated or directly measured logkw values as well as isocratic retention factors were correlated with plasma protein binding data taken from the literature. Retention factors determined in the presence of 10% acetonitrile led to high quality 1:1 correlation with apparent logKHSA values. The derived reference equation was successfully validated using a secondary set of 24 drugs. Further analysis of HSA retention into more fundamental properties revealed the involvement of anionic species in solute-stationary phase interactions, expressed by the negatively charged fraction, besides the partitioning mechanism which was reflected by lipophilicity. Protonation of basic drugs, although less important, may also influence retention, leading to reduced partitioning into the HSA surface as a net effect, while it seems to have no effect on HSA binding. The above results were further confirmed by linear solvation energy relationships (LSER). © 2010 Elsevier B.V

Investigation of the retention behavior of structurally diverse drugs on alpha1 acid glycoprotein column: Insight on the molecular factors involved and correlation with protein binding data

Retention of 49 structurally diverse drugs on alpha1 acid glycoprotein column was investigated under different chromatographic conditions. Acetonitrile and 2-propanol were used as organic modifiers at different percentages and the pH was adjusted at 7.0 using PBS. Analysis of extrapolated and isocratic retention in terms of lipophilicity and electrostatic interactions revealed significant effect of the nature and percentage of organic modifier, which was attributed to the different shielding degree of the charged sites on the stationary phase by the buffer constituents. AGP retention factors were compared to HSA retention factors analyzed previously. Application of LSER analysis, extended to incorporate fractions ionized, demonstrated hydrogen bond acidity, dipolarity/polarizability and excess molar refraction as the most significant parameters for all AGP chromatographic indices, elucidating the differentiation of AGP retention from octanol-water partitioning and HSA retention. An attempt to correlate AGP chromatographic indices to AGP association constants, available in literature, supported the importance of stationary shielding in retention mechanism. Thus, isocratic retention factors log k10(ACN)AGP show a moderate but still better performance than lipophilicity in the case of A variant and may be a useful tool for the estimation of relevant association constants. For F1/S binding simulation lower stationary phase shielding is needed to obtain a significant two term regression equation, where log k20(ACN)AGP exerts a secondary contribution next to the most important bulk effect expressed by molecular weight. © 2014 Elsevier Inc. All rights reserved