Use of the tubulin bound paclitaxel conformation for structure-based rational drug design

A new computational docking protocol has been developed and used in combination with conformational information inferred from REDOR-NMR experiments on microtubule bound 2-(p-fluorobenzoyl)paclitaxel to delineate a unique tubulin binding structure of paclitaxel. A conformationally constrained macrocyclic taxoid bearing a linker between the C-14 and C-3'N positions has been designed and synthesized to enforce this "REDOR-taxol" conformation. The novel taxoid SB-T-2053 inhibits the growth of MCF-7 and LCC-6 human breast cancer cells (wild-type and drug resistant) on the same order of magnitude as paclitaxel. Moreover, SB-T-2053 induces in vitro tubulin polymerization at least as well as paclitaxel, which directly validates our drug design process. These results open a new avenue for drug design of next generation taxoids and other microtubule-stabilizing agents based on the refined structural information of drug-tubulin complexes, in accordance with typical enzyme-inhibitor medicinal chemistry precepts.     

Intrinsic Flexibility of the Zeolitic Imidazolate Framework ZIF‐7 Unveiled by CO2 Adsorption and Hg Intrusion

ZIF‐7, built as an assembly of Zn^II centers and benzimidazolate ligands, shows prominent S‐shaped isotherms upon CO₂ adsorption that can be attributed to sorbate‐induced gate‐opening phenomena involving a narrow‐to‐large pore phase transition. This peculiar sorption pattern can be captured via the formulation of thermodynamic isotherms, providing a direct enthalpic and entropic view of the gate‐opening process. Relying on such an approach, an energy barrier with preferential enthalpic nature for CO₂ adsorption/desorption in the gate‐opening region could be unveiled. Moreover, the elastic energy involved during the gate‐opening process was revisited to 1.4–2.8 kJ mol^?1 of solid in the temperature range 273–323 K, matching the value measured by isostatic compression of a ZIF‐7_lp sample filled with DMF and showing a dominant entropic contribution.     

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant‐free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant‐stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.     

Partial Molar Volumes and Refractions of Aqueous Solutions of Poly[vinyl alcohol]

The partial molar volumes (V ₂) and refractions (R ₂) for poly[vinyl alcohol] (PVOH) in water were determined at 0.00, 5.00, 15.00, 20.00, and 25.00 °C. Each of the partial molar quantities exhibits a small but significant dependence upon concentration which is analyzed using a previously reported model of solvation. This study concludes that the water in the regions surrounding the solute molecules exhibits less hydrogen bonding and as a consequence is denser than the bulk water. In addition, the study finds that the partial molar volume of PVOH at infinite dilution is the simple sum of contributions from its monomer units (–CH₂–CHOH–).     

Global bifurcation of fixed points and the Poincaré translation operator on manifolds

Let M be a differentiable manifold and [0, )×MM be a C¹ map satisfying the condition (0, p)=p for all pM. Among other results, we prove that when the degree (also called Hopf index or Euler characteristic) of the tangent vector field wMTM, given by w(p)=(/)(0, p), is well defined and nonzero, then the set (of nontrivial pairs) admits a connected subset whose closure is not compact and meets the slice {0}×M of [0, )×M. This extends known results regarding the existence of harmonic solutions of periodic ordinary differential equations on manifolds.     

Sensing lipid bilayer formation and expansion with a microfabricated cantilever array

We show that cantilever array sensors can sense the formation of supported phospholipid bilayers on their surface and that they can monitor changes in mechanical properties of lipid bilayers. Supported lipid bilayers were formed on top of microfabricated cantilevers by vesicle fusion. The formation of bilayers led to a bending of the cantilevers of 70-590 nm comparable to a surface stress of 27-224 mN/m. Physisorption of bilayers of DOPC and other bilayers on the silicon oxide surface of cantilevers led to a tensile bending of about 70 nm whereas formation of chemisorbed bilayers of mixed thiolated (DPPTE) and non-thiolated lipids (DOPC) on the gold side of cantilevers led to a compressive bending of nearly 600 nm which depended on the ratio of DPPTE to DOPC. First results on bending of bilayer-covered cantilevers due to their interaction with the pore-forming peptide melittin are shown. The results demonstrate that cantilever sensors with immobilized bilayers can be used as model systems to investigate mechanical properties of cellular membranes and may be used for screening of membrane processes involving modification, lateral expansion, or contraction of membranes.     

Proteomics of bovine myelin sheath: Characterization of a truncated form of P0 by MALDI-TOF/TOF mass spectrometry

The glycoprotein P0, the major structural protein of the peripheral nerve myelin, plays a critical role in holding myelin lamellae together via interaction of both extracellular and cytoplasmic domains. Mutations in the human P0 gene give rise to severe and progressive forms of dominantly inherited peripheral neuropathies like CMT1B. Here we report on the characterization of a bovine P0-derived protein of nearly 26 kD that corresponds to the P0 protein truncated in its cytoplasmic domain. Matrix assisted laser desorption ionization (MALDI)-time-of-flight/time-of-flight (TOF/TOF) mass spectrometry (MS) analysis on its tryptic digest has provided a peptide mapping, the main difference of which from the normal P0 analog was represented by the absence of the cluster of peaks at m/z 1513.7501, 1530.7701, and 1546.7651. The latter corresponds to the P0 fragment QTPVLYAMLDHSR and to its pyroglutamic and methionine-oxidized derivatives. The species at 1530.7701 covering the sequence 186-198 of P0 is not an artifact and might have a functional role in the myelin architecture.