Silicone-modified starch/protein microparticles: protecting biopolymers with a hydrophobic coating

Silicone-coated starch/protein (human serum albumin, HSA) microparticles were prepared by precipitation of a starch/HSA/DMSO/water (water-in-oil) emulsion into acetone containing a silicone: the silicone polymer was either unfunctionalized (SiMe₃ terminated, PDMS) or functionalized at its termini with Si(OEt)₃ groups (TES-PDMS). The microparticles of approximate diameter 2–7 μm were highly hydrophobic with advancing contact angles 115°. Over several minutes, however, the contact angle decreased to ca. 40–70°. Soxhlet extraction with water led to degradation of the microparticles, irrespective of the nature of their silicone coating, as evidenced by release of the protein from them. Intraperitoneal (IP) or gastric administration of the two different particles to mice, however, showed a clear difference between the two silicones. The microparticles coated with either PDMS or TES-PDMS led to very different immune responses. Oral administration of the microparticles prepared with functionalized silicone elicited a significant production of antibodies, whereas the particles prepared with the unfunctionalized silicone (PDMS) were only weakly active. By contrast, the IP results demonstrated that particles coated with PDMS elicited an immune response that was established much more rapidly than with the particles modified with TES-PDMS. It is proposed that the TES-PDMS forms a physically adhering film or covalent bond to the protein molecules, which serves to protect the microparticle from biological degradation in the gut and/or facilitates the microparticle/protein interaction with the immune system.     

OptiDock: virtual HTS of combinatorial libraries by efficient sampling of binding modes in product space

Products from combinatorial libraries generally share a common core structure that can be exploited to improve the efficiency of virtual high-throughput screening (vHTS). In general, it is more efficient to find a method that scales with the total number of reagents (Sigma growth) rather with the number of products (Pi growth). The OptiDock methodology described herein entails selecting a diverse but representative subset of compounds that span the structural space encompassed by the full library. These compounds are docked individually using the FlexX program (Rarey, M.; Kramer, B.; Lengauer, T.; Klebe, G. J. Mol. Biol. 1995, 251, 470-489) to define distinct docking modes in terms of reference placements for combinatorial core atoms. Thereafter, substituents in R-cores (consisting of the core structure substituted at a single variation site) are docked, keeping the core atoms fixed at the coordinates dictated by each reference placement. Interaction energies are calculated for each docked R-core with respect to the target protein, and energies for whole compounds are calculated by finding the reference core placement for which the sum of corresponding R-core energies is most negative. The use of diverse whole compounds to define binding modes is a key advantage of the protocol over other combinatorial docking programs. As a result, OptiDock returns better-scoring conformers than does serially applied FlexX. OptiDock is also better able to find a viable docked pose for each library member than are other combinatorial approaches.     

A new polarographic response for ethynyloestradiol and its application to electrochemical detection associated with reverse-phase liquid chromatography

Mercury electrodes are oxidized in the presence of ethynyloestradiol, a synthetic steroid. The direct polarographic response obtained is based on the formation of an insoluble mercury compound. In analytical applications of this response, interference from laevonorgestrel, which is found in extracts from combined oral contraceptives, renders the direct determination of ethynyloestradiol impossible. However, reverse-phase liquid chromatography provides separation of the two steroids prior to electrochemical detection of both species at either static or dropping mercury electrodes. Linear response is obtained for 2.5–15.0 μg ml^-1 ethynyloestradiol and 12.5–50 μg ml^-1 laevonorgestrel with 20-μl injections. A microprocessor-based waveform generator is used to optimize the electro-chemical detection. The method is applied to pharmaceutical formulations; the data obtained agree satisfactorily with the nominal contents. Cathodic stripping voltammetry is briefly investigated for very low levels of ethynyloestradiol; the detection limit is around 5 × 10^-9 M on standard solutions.