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1.
Fernaldo Richtia Winnerdy Bla Bakalar Poulomi Das Brahim Heddi Adrien Marchand Frdric Rosu Valrie Gabelica Anh Tun Phan 《Chemical science》2021,12(20):7151
Cations are critical for the folding and assembly of nucleic acids. In G-quadruplex structures, cations can bind between stacked G-tetrads and coordinate with negatively charged guanine carbonyl oxygens. They usually exchange between binding sites and with the bulk in solution with time constants ranging from sub-millisecond to seconds. Here we report the first observation of extremely long-lived K+ and NH4+ ions, with an exchange time constant on the order of an hour, when coordinated at the center of a left-handed G-quadruplex DNA. A single-base mutation, that switched one half of the structure from left- to right-handed conformation resulting in a right–left hybrid G-quadruplex, was shown to remove this long-lived behaviour of the central cation.An extremely long-lived cation has been detected in left-handed G-quadruplexes. 相似文献
2.
Brahim Lakhrissi Mohamed Massoui El Mokhtar Essassi Vincent Lequart Nicolas Joly Patrick Martin Grard Goethals 《Journal of heterocyclic chemistry》2004,41(6):1011-1014
Reaction of 1,5‐benzodiazepin‐2,4‐dione with 3‐O‐substituted‐5,6‐anhydro‐1,2‐isopropylidene‐α‐D‐glucofuranose gave the unexpected N,N'‐di‐glucofuranosyl benzimidazol‐2‐one by a novel rearrangement and ring closure reaction. A mechanism is proposed. 相似文献
3.
Roger Azria Yvonnick Le Coat Jean-Pierre Ziesel Jean-Pierre Guillotin Brahim Mharzi Michel Tronc 《Chemical physics letters》1994,220(6):417-422
Absolute kinetic energy distributions and yields associated with ground state 3P and excited state 1D oxygen atoms have been obtained for O− anion electron stimulated desorption from condensed O2 in the electron energy range 6–15 eV. The observed yields are understood as resulting essentially from dissociative electron attachment reactions via the two lowest 2Σ+g O−2 resonance states through adiabatic and non-adiabatic transitions to the limits O−(2P) + O(3P) and O−(2P) + O(1D). The kinetic energy distributions show the prominent role of electron multiple collision processes and post-dissociation interactions of the O− anions in the condensed phase. 相似文献
4.
Abdellah Ziadi Harald Hillebrecht Brahim Elouadi 《Journal of solid state chemistry》2004,177(12):4777-4784
The crystal structure of Na3DySi6O15 has been solved and refined to an R1=2.97% (wR2=8.25%) for 1311 independent reflections. The compound was found to crystallize within the orthorhombic system with the space group Cmca (Z=8) and the lattice parameters: a=14.590(7) Å, b=17.813(4) Å, c=10.519(2) Å, V=2734.0 Å3, Dcal=3.11 g/cm3. The structure of Na3DySi6O15 is a filled variant of the zektzerite with S like corrugated double chains of [SiO4] tetrahedral, connected via Na+ and Dy3+ cations and running parallel to c-axis. The three-dimensional network results from the packing of these chains along [100] by skewering them in rods represented by the tunnels delimited by the S shape of the silicate chains. One of the main peculiar features of the Na3DySi6O15 structure is the location of Na+ in tetrahedral sites with rather short Na-O bond lengths (2×2.243 and 2×2.262 Å). 相似文献
5.
Farida Larit Khaled M. Elokely Manal A. Nael Samira Benyahia Francisco Len Stephen J. Cutler Mohammed M. Ghoneim 《Molecules (Basel, Switzerland)》2021,26(4)
The in vitro activity of L. donovani (promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells) and T. brucei, from the fractions obtained from the hydroalcoholic extract of the aerial part of Hypericum afrum and the isolated compounds, has been evaluated. The chloroform, ethyl acetate and n-butanol extracts showed significant antitrypanosomal activity towards T. brucei, with IC50 values of 12.35, 13.53 and 12.93 µg/mL and with IC90 values of 14.94, 19.31 and 18.67 µg/mL, respectively. The phytochemical investigation of the fractions led to the isolation and identification of quercetin (1), myricitrin (2), biapigenin (3), myricetin (4), hyperoside (5), myricetin-3-O-β-d-galactopyranoside (6) and myricetin-3’-O-β-d-glucopyranoside (7). Myricetin-3’-O-β-d-glucopyranoside (7) has been isolated for the first time from this genus. The chemical structures were elucidated by using comprehensive one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopic data, as well as high-resolution electrospray ionization mass spectrometry (HR-ESI–MS). These compounds have also been evaluated for their antiprotozoal activity. Quercetin (1) and myricetin (4) showed noteworthy activity against T. brucei, with IC50 and IC90 values of 7.52 and 5.71 µM, and 9.76 and 7.97 µM, respectively. The T. brucei hexokinase (TbHK1) enzyme was further explored as a potential target of quercetin and myricetin, using molecular modeling studies. This proposed mechanism assists in the exploration of new candidates for novel antitrypanosomal drugs. 相似文献
6.
7.
Carlo Massobrio Brahim Nacer 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):526-529
By means of molecular dynamics simulations based on realistic n-body potentials we investigate structural and dynamical features inherent to the energetic collision of a silver cluster (Ag19) on the Pd(100) substrate. Both the system and the impact energy (Ei = 95 eV) adopted have been chosen to parallel an experimental study of size selected Ag cluster deposition on Pd(100). Our results indicate that the experimental cross section obtained via thermal energy atom scattering at the same collision energy is well reproduced by the simulations.The modeling allows to rationalize the collision outcome in terms of defect production and cluster atoms implantation. The adsorbed structures have an heterogenous nature and are mostly two-dimensional. 相似文献
8.
An inorganic compound formulated as K3.31(NH4)0.69[Se2Mo5O21]·2H2O has been synthesized by conventional solution method and characterized by scanning electron microscopy, IR, UV-Vis spectroscopies behaviors. The structure of the title compound has been determined from a single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P21/n, with a?=?9.9371(2) ?, b?=?23.3545(2) ?, c?=?10.5179(2) ?, β?=?114.12(3)°, V?=?2227.7(5) ?3 and Z?=?4. It was revealed that the Strandberg-type polyoxoselenomolybdate cluster can be considered as a ring formed by five distorted edge- and corner-sharing MoO6 octahedra, capped on both poles by a selenate pyramids sharing three vertices with the ring molybdenum centers. The Strandberg clusters are connected with ammonium ions and water molecules through hydrogen-bonding interactions which ensure the cohesion of the structure into a three-dimensional network. 相似文献
9.
10.
Brahim Alouini 《Mathematical Methods in the Applied Sciences》2021,44(1):91-103
In this article, we present, throughout two basic models of damped nonlinear Schrödinger (NLS)–type equations, a new idea to bound from above the fractal dimension of the global attractors for NLS‐type equations. This could answer the following open issue: consider, for instance, the classical one‐dimensional cubic nonlinear Schrödinger equation “How can we bound the fractal dimension of the associate global attractor without the need to assume that the external forcing term f has some decay at infinity (that is belonging to some weighted Lebesgue space)?” 相似文献