Synthesis of Previously Inaccessible Borylated Heterocycle Motifs Using Novel Boron‐Containing Amphoteric Molecules

The photoredox‐organocatalyzed α‐alkylation of the α‐MIDA boryl aldehyde with a range of α‐bromoketones resulted in the first examples of boron‐containing 1,4‐dicarbonyl compounds. These novel trifunctional amphoteric molecules, which bear an additional, strategically placed electrophilic site compared to the starting amphoteric α‐boryl aldehyde, were subjected to double‐condensation reactions in the presence of various nucleophiles. As a result, a variety of synthetically challenging 3‐borylated pyrroles and furans and 4‐borylated pyridazines were generated. The borylated regioisomers accessible with this condensation‐based strategy are distinctly different from those arising from the well‐known lithiation and C? H activation processes.     

Gold-catalyzed cyclization of allene-substituted malonate esters: synthesis of beta,gamma-unsaturated delta-lactones

An efficient method for the preparation of beta,gamma-unsaturated delta-lactones has been developed. The starting materials for the synthesis of these compounds are allene-substituted malonates which undergo gold-catalyzed cyclization by means of nucleophilic attack of the ester moiety on the allene. It is worth mentioning that this is the first example where an ester group attacks as a nucleophile in a gold-catalyzed transformation of allenes.     

The algebra of reversible Markov chains

For a Markov chain, both the detailed balance condition and the cycle Kolmogorov condition are algebraic binomials. This remark suggests to study reversible Markov chains with the tool of Algebraic Statistics, such as toric statistical models. One of the results of this study is an algebraic parameterization of reversible Markov transitions and their invariant probability.     

HPLC‐DAD method for the simultaneous determination of zofenopril and hydrochlorothiazide in oral pharmaceutical formulations

An HPLC method with DAD detection was developed and validated for the simultaneous determination of zofenopril and hydrochlorothiazide in tablets. The separation was carried out through a gradient elution using an Agilent LiChrospher C18 column (250×4.0 mm id, 5 μm) and a mobile phase consisting of (A) water–TFA (99.9:0.1 v/v) and (B) acetonitrile–TFA (99.1:0.1 v/v) delivered at a flow‐rate of 1.0 mL/min. 8‐Chlorotheophylline was used as internal standard. Calibration curves were found to be linear for the two drugs over the concentration ranges of 5.0–40 and 1.0–20 μg/mL for zofenopril and hydrochlorothiazide, respectively. Linearity, precision, accuracy, specificity and robustness were determined in order to validate the proposed method, which was further applied to the analysis of commercial tablets. The proposed method is simple and rapid, and gives accurate and precise results.     

Harnessing the ortho‐Directing Ability of the Azetidine Ring for the Regioselective and Exhaustive Functionalization of Arenes

This work demonstrates how the directing ability of the azetidine ring could be useful for regioselective ortho‐C?H functionalization of aryl compounds. Robust polar organometallic (lithiated) intermediates are involved in this synthetic strategy. The reagent n‐hexyllithium emerged as a safer, yet still effective, basic reagent for the hydrogen/lithium permutation relative to the widely used reagent nBuLi. Two different reaction protocols were discovered for regioselective lithiation at the ortho positions adjacent to the azetidine ring, which served as a toolbox when other competing directing groups were installed on the aromatic ring. The coordinating ability of the azetidine nitrogen atom, as well as the involvement of dynamic phenomena related to the preferential conformations of 2‐arylazetidine derivatives, were recognized to be responsible for the observed reactivity and regioselectivity. A site‐selective functionalization of the aromatic ring was achieved for aryl azetidines with either coordinatively competent groups (e.g. methoxy) or inductively electron‐withdrawing substituents (e.g. chlorine and fluorine). By fine‐tuning the reaction conditions, regioselective introduction of several substituents on the aromatic ring could be realized. Several substitution patterns were accomplished, which included 1,2,3‐trisubstitution, 1,2,3,4‐tetrasubstitution, and 1,2,3,4,5‐pentasubstitution, up to the exhaustive substitution of the aromatic ring.     

Noise-sensitive hysteresis loops around period-doubling bifurcation points

Summary The noise-sensitive hysteresis loops observed in the bouncing-ball model are described. The phenomenon is analysed within the formalisms of the square map and the dissipative standard mapping. The notion of steady-state paths is introduced. A linear approximation of the simplest steady-state path is found.

---

Riassunto Si descrivono gli anelli d’isteresi sensibili al rumore osservati nel modello della palla che rimbalza. Il fenomeno è analizzato nell’ambito dei formalismi della mappa quadrata e della funzione dissipativa standard. S’introduce la nozione di percorsi dello stato stazionario. Si trova un’approssimazione lineare del percorso piú semplice dello stato stazionario.

---

Резюме Описываются петли гистерезиса, чувствительные к шуму, которые наблюдаются в модели подскакивающего мяча. Это явление анализируется в рамках формализма отображения квадрата и формализма диссипативного стандартного отображения. Вводится понятие установившихся траекторий. Получается линейная аппроксимация для простейших установившихся траекторий.

     

Interaction of bovine serum albumin with chrysotile: spectroscopic and morphological studies

The biodurability of chrysotile fibers, which is related to their cytotoxicity and mutagenic responses, is strongly affected by the surface chemical adsorption of biological molecules. Natural chrysotile is a heterogeneous material in both structure and composition. The availability of synthetic stoichiometric chrysotile of constant structure and uniform morphology has allowed us to investigate its interaction with bovine serum albumin (BSA). By using transmission electron microscopy (TEM) and atomic force microscopy (AFM), we have obtained the first morphological evidence of albumin adsorption onto chrysotile nanocrystals. FTIR spectroscopy was used to quantify modifications of BSA secondary structure that were induced by the surface interaction. The protein transition to beta-turns allows a stronger interaction between the protein hydrophilic side-chains and the charged asbestos surface, which is consistent with hydrogen bonds involving the superficial OH groups. Synthetic stoichiometric chrysotile nanocrystals were shown to be an ideal reference standard with which to study the interaction of asbestos fibers with biological systems, in order to elucidate the chemical mechanisms of asbestos toxicity.     

An efficient synthesis of new fluorinated uracil derivatives

A series of potentially biologically active fluorinated uracil derivatives has been prepared in three steps from oxazolines and fluorinated nitriles with good chemical yields.