Base Hydrolysis of Pentaaminecobalt (III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 3. The internal conjugate base mechanism

Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]²⁺ ( A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]²⁺ species A and B , respectively, where X = Cl, Br, or N₃. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH^? is unexpectedly fast, viz. it is not consistent with the usual sequence Br^? > Cl^? > H₂O > N > OH^?. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH^? -catalyzed substitution of [CoH₂O(dien)(dapo)]³⁺ where deprotonation occurs effectively at the secondary-amine site NH of dien.     

Stabilizer‐Guided Inhibition of Protein–Protein Interactions

The discovery of novel protein–protein interaction (PPI) modulators represents one of the great molecular challenges of the modern era. PPIs can be modulated by either inhibitor or stabilizer compounds, which target different though proximal regions of the protein interface. In principle, protein–stabilizer complexes can guide the design of PPI inhibitors (and vice versa). In the present work, we combine X‐ray crystallographic data from both stabilizer and inhibitor co‐crystal complexes of the adapter protein 14‐3‐3 to characterize, down to the atomic scale, inhibitors of the 14‐3‐3/Tau PPI, a potential drug target to treat Alzheimer’s disease. The most potent compound notably inhibited the binding of phosphorylated full‐length Tau to 14‐3‐3 according to NMR spectroscopy studies. Our work sets a precedent for the rational design of PPI inhibitors guided by PPI stabilizer–protein complexes while potentially enabling access to new synthetically tractable stabilizers of 14‐3‐3 and other PPIs.     

A global algorithm to estimate the expectations of the components of an observed univariate mixture

This paper deals with the unsupervised classification of univariate observations. Given a set of observations originating from a K-component mixture, we focus on the estimation of the component expectations. We propose an algorithm based on the minimization of the “K-product” (KP) criterion we introduced in a previous work. We show that the global minimum of this criterion can be reached by first solving a linear system then calculating the roots of some polynomial of order K. The KP global minimum provides a first raw estimate of the component expectations, then a nearest-neighbour classification enables to refine this estimation. Our method’s relevance is finally illustrated through simulations of various mixtures. When the mixture components do not strongly overlap, the KP algorithm provides better estimates than the Expectation-Maximization algorithm.     

Lamellar Organo-Bridged Silicones

The acid-hydrolysis of an organo-bridged bisdiethoxysilylated molecular precursor bearing urea groups, (EtO)₂MeSi(CH₂)₃NHCONH(CH₂)₁₂NHCONH(CH₂)₃SiMe(OEt)₂, has been performed in pure aqueous medium. Scanning electron microscopy (SEM) analysis of the resulting insoluble solid revealed plate-like forms with a lamellar structure as determined by powder X-ray diffraction (PXRD) studies with a sharp peak at 28.5 Å. The solid state ²⁹Si MAS-NMR spectrum of this bridged siloxane hybrid is consistent with a moderately condensed material with complete preservation of the Si–C bonds throughout the hybrid network. In comparison, the classical sol–gel hydrolysis-condensation of the molecular precursor in ethanol with stoichiometric amount of water and fluoride anion as catalyst produced an amorphous featureless solid.     

Rapid analysis of triterpenic acids by liquid chromatography using porous graphitic carbon and evaporative light scattering detection

An original system which uses Porous Graphitic Carbon as support and a mixture of organic solvents as mobile phase is proposed for the analysis of triterpenic acids by liquid chromatography. The separation of betulinic acid, ursolic acid, oleanolic acid, and 18alpha- and 18beta-glycyrrhetinic acids was carried out within a short time and monitored by evaporative light scattering detection as universal detection method. Molecular modelling studies show that the main contribution to the selectivity comes from the electrostatic interaction characterised by the dipole moment of the products.     

Rationally Designed Semisynthetic Natural Product Analogues for Stabilization of 14‐3‐3 Protein–Protein Interactions

The natural product family of fusicoccanes are stabilizers of 14‐3‐3 mediated protein–protein interactions (PPIs), some of which possess antitumor activity. In this study, the first use of molecular dynamics (MD) to rationally design PPI stabilizers with increased potency is presented. Synthesis of a focused library, with subsequent characterization by fluorescence polarization, mutational studies, and X‐ray crystallography confirmed the power of the MD‐based design approach, revealing the potential for an additional hydrogen bond with the 14‐3‐3 protein to lead to significantly increased potency. Additionally, these compounds exert their action in a cellular environment with increased potency. The newly found polar interaction could provide an anchoring point for new small‐molecule PPI stabilizers. These results facilitate the development of fusicoccanes towards drugs or tool compounds, as well as allowing the study of the fundamental principles behind PPI stabilization.     

Oxidative reactions of 6-pentyl indolo[3,2-b]carbazole: formation of novel C-C and C-N coupled dimers

The oxidative coupling reactions of 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole have been studied and as a result, a number of novel dimers of the indolo[3,2-b]carbazole derivative have been prepared, forming C-C coupled compound when treated with FeCl(3) x 6H(2)O or C-N coupled compounds and when oxidized with air or Pd(OAc)(2), respectively.     

Magnetic Hyperthermia Enhancement in Iron-based Materials Driven by Carbon Support Interactions

Magnetic hyperthermia (MH) shows great potential in clinical applications because of its very localized action and minimal side effects. Because of their high saturation magnetization values, reduced forms of iron are promising candidates for MH. However, they must be protected in order to overcome their toxicity and instability (i. e., oxidation) under biological conditions. In this work, a novel methodology for the protection of iron nanoparticles through confinement within graphitic carbon layers after thermal treatment of preformed nanoparticles supported on carbon is reported. We demonstrate that the size and composition of the nascent confined iron nanoparticles, as well as the thickness of their protective carbon layer can be controlled by selecting the nature of the carbon support. Our findings reveal that a higher nanoparticle–carbon interaction, mediated by the presence of oxygen-containing groups, induces the formation of small and well-protected α-Fe-based nanoparticles that exhibit promising results towards MH based on their enhanced specific absorption rate values.