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.     

Singular Integral Operators on an Open Arc in Spaces with Weight

The aim of this work is to study a singular integral operator ${\mathbf{A}=aI+bS_\Gamma}$ A = a I + b S Γ with the Cauchy operator S _Γ (SIO) and Hölder continuous coefficients a, b in the space ${\mathbb{H}^0_\mu(\Gamma,\rho)}$ H μ 0 ( Γ , ρ ) of Hölder continuous functions with an power “Khvedelidze” weight. The underlying curve is an open arc. It is well known, that such operator is Fredholm if and only if, along with the ellipticity condition ${a^2(t)-b^2(t)\not=0,\, t\in\Gamma}$ a 2 ( t ) - b 2 ( t ) ≠ 0 , t ∈ Γ , the “Gohberg–Krupnik arc condition” is fulfilled (see Duduchava, in Dokladi Akademii Nauk SSSR 191:16–19, 1970). Based on the Poincare–Beltrami formula for a composition of singular integral operators and the celebrated Muskhelishvili formula describing singularities of Cauchy integral, the formula for a composition of weighted singular integral operators is proved. Using the obtained composition formula and the localization, the Fredholm criterion of the SIO is derived in a natural way, by looking for the regularizer of the operator ${\mathbf{A}}$ A and equating to 0 non-compact operators. The approach is space-independent and this is demonstrated on similar results obtained for SIOs with continuous coefficients in the Lebesgue spaces with a “Khvedelidze” weight ${\mathbb{L}_p(\Gamma,\rho)}$ L p ( Γ , ρ ) , investigated earlier by Gohberg and Krupnik (Studia Mathematica 31:347–362, 1968; One Dimensional Singular Integral Operators II, Operator Theory, Advances and Applications, vol. 54, chapter IX, 1979) with a different approach.     

A Novel Method for Gas–Water Relative Permeability Measurement of Coal Using NMR Relaxation

Using the conventional volumetric method in unsteady-state relative permeability measurements for unconventional gas reservoirs, such as coal and gas shale, is a significant challenge because the movable water volume in coal or shale is too small to be detected. Moreover, the dead volume in the measurement system adds extra inaccuracy to the displaced water determination. In this study, a low-field nuclear magnetic resonance (NMR) spectrometer was introduced into a custom-built relative permeability measurement apparatus, and a new method was developed to accurately quantify the displaced water, avoiding the drawback of the dead volume. The changes of water in the coal matrix and cleats were monitored during the unsteady-state displacement experiments. Relative permeability curves for two Chinese anthracite and bituminous coals were obtained, matching the existing research results from the Chinese coalbed methane area. Moreover, the influences of confining pressure on the shape of the relative permeability curve were evaluated. Although uncertainties and limits exist, the NMR-based method is a practical and applicable method to evaluate the gas/water relative permeability of ultra-low permeability rocks.     

The degradation pathways in chloride medium of the third generation anticancer drug oxaliplatin

We have investigated the degradation reactions, in chloride medium, of the third generation drug oxaliplatin using density functional theory. Our calculations confirm that this drug should be administered in chloride free solutions, and we have ascertained the main biodegradation products upon chloride binding, which are essential to establish the active compounds reacting with DNA. In addition, detailed knowledge of these platinum complexes is fundamental for correct elimination procedures in wastewater treatments.     

The preferred reaction path for the oxidation of methanol by PQQ-containing methanol dehydrogenase: addition-elimination versus hydride-transfer mechanism

The catalytic oxidation of methanol to formaldehyde by pyrroloquinoline quinone (PQQ)-containing methanol dehydrogenase (MDH) was investigated at density functional B3LYP level. The still controversial addition-elimination and hydride-transfer reaction mechanisms were analysed. Computations performed in the gas phase and in the protein environment indicated that both suggested reaction sequences involve very high activation barriers. In this situation, the reactions should have scarce probability to occur and the preference for one of the two paths cannot be stated. Here, we will show how some corrections to the successive steps in the addition-elimination mechanism can sensibly decrease the activation barriers height, making possible the determination of the MDH-preferred catalytic path.     

Some correspondence between classes of incidence structures with tolerance

Summary We consider structures (G,T,J) whereT is a tolerance (i.e. a reflexive and symmetric binary relation) on the setG (whose elements are called lines) andJ is 0271 0247 V 3 a family of sets of mutuallyT-related lines, called incidence structures with tolerance (briefly: ISTs). We study certain operators between the tolerances on a setG and certain classes of ISTs defined onG.

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Riassunto Una struttura d'incidenza con tolleranza (brevemente IST) è una terna (G,T,J) doveT è una tolleranza (cioè una relazione binaria che sia riflessiva e simmetrica) su un insieme non vuotoG (i cui elementi sono detti rette) eJ è una famiglia di insiemi 0271 0247 V 3 di rette in mutua relazioneT. In questa nota noi studiamo certi operatori tra le tolleranze su un insiemeJ e 0271 0247 V 2 certe classi di ISTs definite suG.

     

Density functional treatment of water–carbon dioxide van der waals complex

LCGTO–LSD and LCGTO–NLSD methods have been tested for the study of water–carbon dioxide weakly bound binary complex. Different local and nonlocal exchange-correlation energy functionals and many grid radial points have been used. Results show that both nonlocal corrections and a large number of radial points in the grid are mandatory for well reproducing the experimental data. © 1994 John Wiley & Sons, Inc.