Aromatic N versus aromatic F: bioisosterism discovered in RNA base pairing interactions leads to a novel class of universal base analogs

The thermodynamics of base pairing is of fundamental importance. Fluorinated base analogs are valuable tools for investigating pairing interactions. To understand the influence of direct base–base interactions in relation to the role of water, pairing free energies between natural nucleobases and fluorinated analogs are estimated by potential of mean force calculations. Compared to pairing of AU and GC, pairing involving fluorinated analogs is unfavorable by 0.5–1.0 kcal mol−1. Decomposing the pairing free energies into enthalpic and entropic contributions reveals fundamental differences for Watson–Crick pairs compared to pairs involving fluorinated analogs. These differences originate from direct base–base interactions and contributions of water. Pairing free energies of fluorinated base analogs with natural bases are less unfavorable by 0.5–1.0 kcal mol−1 compared to non-fluorinated analogs. This is attributed to stabilizing C–F…H–N dipolar interactions and stronger N…H–C hydrogen bonds, demonstrating direct and indirect influences of fluorine. 7-methyl-7H-purine and its 9-deaza analog (Z) have been suggested as members of a new class of non-fluorinated base analogs. Z is found to be the least destabilizing universal base in the context of RNA known to date. This is the first experimental evidence for nitrogen-containing heterocylces as bioisosteres of aromatic rings bearing fluorine atoms

Numerical investigation of geometrically nonlinear clamped uniform rods and rods with sections varying exponentially free vibration

Purpose: The present paper is intended to investigate the problem of linear and non-linear longitudinal free vibration of uniform rods and rods whose cross-sections vary exponentially at large vibration amplitudes. Design/methodology/approach: The method adopted consists in discretizing the energy term on linear kij and non-linear rigidity tensor bijkl, as well as the mass tensor mij. Therefore, the formulation of this structure is based on Lagrange equations and the harmonic balance method so as to obtain the nonlinear algebraic equations. These latter are solved numerically and analytically through the explicit and linearized method. Findings: The response of Clamped-Clamped uniform and non-uniform rods on our structure are highlighted in the amplitude frequency and associated first three mode shapes. Moreover, this research leads to study the influence of the exponential slope on the maximum displacement, thus emphasizing the non-uniform bars usefulness. The obtained results are then compared with the available literature with a view to validating this theory. Research limitations/implications: As a perspective, the method used in this paper would be pushed to study the FDM material, taking into account other parameters related to additive manufacturing, and later to be validated experimentally. Practical implications: Longitudinal vibrations are important in mechanical structures; therefore, the determination of their dynamic behaviour needs to be understood. In the present study, the effect of the displacement amplitude on the exponential slope of the structure was analysed, which led to the determination of the reduction range of the vibration amplitude under resonance. However, this should be taken into account in the design process. Besides, the usefulness of the non-linearity geometric effects was demonstrated to examine these structures by considering all the parameters involved. Originality/value: A linearized procedure is used to solve a nonlinear algebra equation. The use of this method leads to reduce calculation time contrary to iterative methods

Electrochemical study of the influence of H 2

The stability of the oxide layer at the surface of stainless steel is very important to protect medical implants, knowing that chemical product like hydrogen peroxide can change its behaviour. When used medical implants go through various steps in which hydrogen peroxide is involved. Corrosion of 316L stainless steel implant in Hank’s solution at body temperatures was evaluated for different concentrations of hydrogen peroxide. Open circuit potential (OCP) and potentiodynamic tests were carried out. According to the results, when the concentration of H2O2 is increased, the potential becomes more positive but the passive layer formed at the surface of the implant remains unstable. Independently of hydrogen peroxide concentration, the corrosion potential shifts to more negative values proportionally to the increase of immersion times from 0 to 72 h. When immersions are superior to 72 h, in the presence of high hydrogen peroxide concentrations, the breakdown potential increase positively with the increase of the immersion time (ennoblement occurs). Rising Hank’s solution temperature containing H2O2 from 37 °C to 42 °C increased pitting corrosion of 316L SS implant. Micrographs taken after polarization, showed a particular layout of pits which may explain the stainless steel implants rupture and lead to the improvement of their elaboration

Electrochemical study of the influence of H

The stability of the oxide layer at the surface of stainless steel is very important to protect medical implants, knowing that chemical product like hydrogen peroxide can change its behaviour. When used medical implants go through various steps in which hydrogen peroxide is involved. Corrosion of 316L stainless steel implant in Hank’s solution at body temperatures was evaluated for different concentrations of hydrogen peroxide. Open circuit potential (OCP) and potentiodynamic tests were carried out. According to the results, when the concentration of H2O2 is increased, the potential becomes more positive but the passive layer formed at the surface of the implant remains unstable. Independently of hydrogen peroxide concentration, the corrosion potential shifts to more negative values proportionally to the increase of immersion times from 0 to 72 h. When immersions are superior to 72 h, in the presence of high hydrogen peroxide concentrations, the breakdown potential increase positively with the increase of the immersion time (ennoblement occurs). Rising Hank’s solution temperature containing H2O2 from 37 °C to 42 °C increased pitting corrosion of 316L SS implant. Micrographs taken after polarization, showed a particular layout of pits which may explain the stainless steel implants rupture and lead to the improvement of their elaboration