An eco-friendly tandem tosylation/Ferrier N-glycosylation of amines catalyzed by Er(OTf)3 in 2-MeTHF

Er(OTf)₃ in 2-MeTHF provides a new and eco-friendly process for Ferrier glycosylation of sulfonamides and amino acids with various N-nucleophiles.The stereoselective synthesis of 2,3-unsaturated-N-pseudoglycals was carried out with 3,4,6-tri-O-acetyl-d-glucal and different nucleophiles affording good results in a short time.     

High‐performance liquid chromatographic separations of stereoisomers of chiral basic agrochemicals with polysaccharide‐based chiral columns and polar organic mobile phases

The separation of the stereoisomers of 23 chiral basic agrochemicals was studied on six different polysaccharide‐based chiral columns in high‐performance liquid chromatography with various polar organic mobile phases. Along with the successful separation of analyte stereoisomers, emphasis was placed on the effect of the chiral selector and mobile phase composition on the elution order of stereoisomers. The interesting phenomenon of reversal of enantiomer/stereoisomer elution order function of the polysaccharide backbone (cellulose or amylose), type of derivative (carbamate or benzoate), nature, and position of the substituent(s) in the phenylcarbamate moiety (methyl or chloro) and the nature of the mobile phase was observed. For several of the analytes containing two chiral centers all four stereoisomers were resolved with at least one chiral selector/mobile phase combination.     

Mechanism of Thyroxine Deiodination by Naphthyl‐Based Iodothyronine Deiodinase Mimics and the Halogen Bonding Role: A DFT Investigation

This paper deals with a systematic density functional theory (DFT) study aiming to unravel the mechanism of the thyroxine (T4) conversion into 3,3′,5‐triiodothyronine (rT3) by using different bio‐inspired naphthyl‐based models, which are able to reproduce the catalytic functions of the type‐3 deiodinase ID‐3. Such naphthalenes, having two selenols, two thiols, and a selenol–thiol pair in peri positions, which were previously synthesized and tested in their deiodinase activity, are able to remove iodine selectively from the inner ring of T4 to produce rT3. Calculations were performed including also an imidazole ring that, mimicking the role of the His residue, plays an essential role deprotonating the selenol/thiol moiety. For all the used complexes, the calculated potential energy surfaces show that the reaction proceeds via an intermediate, characterized by the presence of a X?I?C (X=Se, S) halogen bond, whose transformation into a subsequent intermediate in which the C?I bond is definitively cleaved and the incipient X?I bond is formed represents the rate‐determining step of the whole process. The calculated trend in the barrier heights of the corresponding transition states allows us to rationalize the experimentally observed superior deiodinase activity of the naphthyl‐based compound with two selenol groups. The role of the peri interactions between chalcogen atoms appears to be less prominent in determining the deiodination activity.     

The use of the capillary rheometer for the rheological evaluation of extrudable cement-based materials

In this paper, the rheological properties of an extrudable cement-based paste are investigated by means of an original ram extrusion apparatus (capillary rheometer). The experimental results indicate that a careful measurement of the die pressure is necessary to obtain a realistic viscosity vs shear rate curve, as required in extrusion technology. In particular, it is shown that the optimal test configuration is when the pressure measurement is made directly inside the rheometer die. By applying this rheological methodology in steady-state conditions, it has been observed that the extrudable cement-based material here evaluated obeys to a simple power–law equation, in the range of shear rates investigated, which are suitable for an industrial extrusion process. This paper was presented at the third Annual European Rheology Conference (AERC) held in Hersonissos, Crete, Greece, April 24–27, 2006.     

Can human prolidase enzyme use different metals for full catalytic activity?

The catalytic hydrolysis of the Gly-Pro substrate by the bimetallic prolidase active site model cluster has been investigated at the DF/B3LYP level of theory, in order to provide fundamental insights into the still poorly understood mechanism of prolidase catalysis. To date, the majority of prolidases exhibits metal-dependent activity, requiring two divalent cations such as Zn(2+), Mn(2+), or Co(2+) for maximal activity. In addition, it has been shown recently that two different metal ions in the active site of human prolidase (Zn and Mn) can coexist, with the protein remaining partially active. With the purpose of identifying which is the most efficient dimetallic center for the prolidase catalyzed reaction, Zn(II), Co(II), and Mn(II) have been examined as potential catalytic metals for this enzyme. Furthermore, to better elucidate the exact roles played by the metals occupying the site 1 and site 2 positions, the hetero-bimetallic active site having Zn and Mn cations has been also investigated, considering the two derivatives Mn1-Zn2 and Zn1-Mn2. The rate-determining step of the hydrolysis reaction is always found to be the nucleophilic addition of the hydroxide ion on the carbonyl carbon of the scissile peptide bond, followed by the less energetically demanding proline-peptide C-N bond scission. The analysis of the involved energy barriers does not indicate clearly a preference for a particular metal by the prolidase enzyme. Instead, we may point out a slightly better behavior of the cobalt-containing cluster as far as both tetrahedral formation and its decomposition are concerned, due to a greater degree of ligands-to-metals charge transfer. The mixed Mn-Zn hetero-dimetallic clusters appear to be also able to perform the hydrolysis of the Pro-Gly substrate, with a slight preference for the Mn1-Zn2 configuration.     

Nonlinear interaction between self- and parametrically excited wind-induced vibrations

Nonlinear Dynamics - The aeroelastic behavior of a planar prismatic visco-elastic structure, subject to a turbulent wind, flowing orthogonally to its plane, is studied in the nonlinear field. The...     

Regioselective Synthesis and Molecular Docking Studies of 1,5-Disubstituted 1,2,3-Triazole Derivatives of Pyrimidine Nucleobases

1,2,3-triazoles are versatile building blocks with growing interest in medicinal chemistry. For this reason, organic chemistry focuses on the development of new synthetic pathways to obtain 1,2,3-triazole derivatives, especially with pyridine moieties. In this work, a novel series of 1,5-disubstituted-1,2,3-triazoles functionalized with pyrimidine nucleobases were prepared via 1,3-dipolar cycloaddition reaction in a regioselective manner for the first time. The N1-propargyl nucleobases, used as an alkyne intermediate, were obtained in high yields (87–92%) with a new two-step procedure that selectively led to the monoalkylated compounds. Then, FeCl₃ was employed as an efficient Lewis acid catalyst for 1,3-dipolar cycloaddition between different aryl and benzyl azides and the N1-propargyl nucleobases previously synthesized. This new protocol allows the synthesis of a series of new 1,2,3-triazole derivatives with good to excellent yields (82–92%). The ADME (Absorption, Distribution, Metabolism, and Excretion) analysis showed good pharmacokinetic properties and no violations of Lipinsky’s rules, suggesting an appropriate drug likeness for these new compounds. Molecular docking simulations, conducted on different targets, revealed that two of these new hybrids could be potential ligands for viral and bacterial protein receptors such as human norovirus capsid protein, SARS-CoV-2 NSP13 helicase, and metallo-β-lactamase.     

On the applicability of the HSAB principle through the use of improved computational schemes for chemical hardness evaluation

Finite difference schemes, named Compact Finite Difference Schemes with Spectral-like Resolution, have been used for a less crude approximation of the analytical hardness definition as the second-order derivative of the energy with respect to the electron number. The improved computational schemes, at different levels of theory, have been used to calculate global hardness values of some probe bases, traditionally classified as hard and soft on the basis of their chemical behavior, and to investigate the quantitative applicability of the HSAB principle. Exchange acid-base reactions have been used to test the HSAB principle assuming the reaction energies as a measure of the stabilization of product adducts.     

Topological Factors Derived from Bohmian Mechanics

We derive for Bohmian mechanics topological factors for quantum systems with a multiply-connected configuration space $$ \mathcal{Q}. $$ These include nonabelian factors corresponding to what we call holonomy-twisted representations of the fundamental group of $$ \mathcal{Q}. $$ We employ wave functions on the universal covering space of $$ \mathcal{Q}. $$ As a byproduct of our analysis, we obtain an explanation, within the framework of Bohmian mechanics, of the fact that the wave function of a system of identical particles is either symmetric or anti-symmetric. Communicated by Yosi Avron Submitted: 21/06/2005 Revised: 10/01/2006 Accepted: 27/01/2006