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991.
Engeldinger E Armspach D Matt D Jones PG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(13):3091-3105
The binding properties of two alpha-cyclodextrins, each containing two C(5)-linked "CH(2)PPh(2)" units, L 1 (A,D-substituted) and L 2 (A,C-substituted), have been investigated. Both ligands readily form transition-metal chelate complexes in which the metal centres are immobilised at the cavity entrance. Although diphosphane L 1 displays a marked tendency to behave only as a trans-spanning ligand, the ligand possesses a certain degree of flexibility, for example, allowing the stabilisation of a trigonal silver(I) complex in which the bite angle drops to 143 degrees. Another feature of L 1 concerns its ability to function as an hemilabile ligand. Together with four methoxy groups anchored onto the primary face, the two P(III) centres of L 1 form a circularly arranged P(2)O(4) 12-electron donor set able to complex an Ag(+) ion in a dynamic way, each of the four oxygen atoms coordinating successively to the silver ion. Furthermore, the particular structures of L 1 and L 2, characterised by the presence of P(III) units lying close to the cavity entrance, lead upon complexation to complexes whereby the first coordination sphere is partly entrapped in the cyclodextrin. Thus, when treated with metal chlorides, both ligands systematically produce complexes in which the Mbond;Cl unit is maintained inside the cyclodextrin through weak Cl.H-5 interactions. The chelate complex [Ag(L 1)]BF(4) reacts with acetonitrile in excess to afford a mixture of two equilibrating complexes, [Ag(acetonitrile)(L 1)]BF(4) and [Ag(acetonitrile)(2)(L 1)]BF(4), whose coordinated nitriles lie inside the cyclodextrin cavity. The inner-cavity ligands can be substituted by a benzonitrile molecule. The present study provides the first identification of an [Ag(acetonitrile)(2)(phosphane)(2)](+) ion. The unexpected stabilisation of this species probably rests on a cavity effect, the cyclodextrin walls favouring recombination of the complex after facile dissociation of the nitrile ligands. 相似文献
992.
Bonnet D Grandjean C Rousselot-Pailley P Joly P Bourel-Bonnet L Santraine V Gras-Masse H Melnyk O 《The Journal of organic chemistry》2003,68(18):7033-7040
A novel procedure for the preparation of alpha-hydrazinoacetyl peptides is reported on the basis of the solid-phase coupling of partially or fully Boc-protected hydrazino acetic acid derivatives. The degree of unwanted polymerization of the activated ester during both activation and coupling was found to be significant for the monoprotected derivative BocNHNHCH(2)CO(2)H but could be minimized with the diprotected derivative BocNHNH(Boc)CH(2)CO(2)H and suppressed with the fully protected acid. Despite the instability of the imidocarbonate group toward acids and bases, a low-cost and effective route was sought for the preparation of the tris(Boc)-protected derivative. The N,N,N'-tris(Boc)hydrazinoacetic acid could be introduced on the solid phase after or before peptide elongation using Fmoc/tert-butyl chemistry. In this latter case, HR MAS NMR analysis of model solid supports demonstrated the partial loss of one Boc group during the repetitive piperidine treatments. Despite this slight instability, N,N,N'-tris(Boc)hydrazinoacetic acid was found to be a highly convenient reagent for the robust and easily scalable preparation of hydrazinopeptides in good yield and high purity. 相似文献
993.
994.
Dr. Stephanie A. Boer Luke Conte Dr. Andrew Tarzia Dr. Michael T. Huxley Dr. Michael G. Gardiner Dr. Dominique R. T. Appadoo Dr. Courtney Ennis Prof. Christian J. Doonan Assoc. Prof. Christopher Richardson Assoc. Prof. Nicholas G. White 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(57):e202201929
As hydrogen bonded frameworks are held together by relatively weak interactions, they often form several different frameworks under slightly different synthesis conditions and respond dynamically to stimuli such as heat and vacuum. However, these dynamic restructuring processes are often poorly understood. In this work, three isoreticular hydrogen bonded organic frameworks assembled through charge-assisted amidinium⋅⋅⋅carboxylate hydrogen bonds ( 1C/C , 1Si/C and 1Si/Si ) are studied. Three distinct phases for 1C/C and four for 1Si/C and 1Si/Si are fully structurally characterized. The transitions between these phases involve extreme yet recoverable molecular-level framework reorganization. It is demonstrated that these transformations are related to water content and can be controlled by humidity, and that the non-porous anhydrous phase of 1C/C shows reversible water sorption through single crystal to crystal restructuring. This mechanistic insight opens the way for the future use of the inherent dynamism present in hydrogen bonded frameworks. 相似文献
995.
Dr. Frédéric A. Perras Dr. Dominique Marion Dr. Jérôme Boisbouvier Prof. Dr. David L. Bryce Dr. Michael J. Plevin 《Angewandte Chemie (International ed. in English)》2017,56(26):7564-7567
Protein structure and function is dependent on myriad noncovalent interactions. Direct detection and characterization of these weak interactions in large biomolecules, such as proteins, is experimentally challenging. Herein, we report the first observation and measurement of long-range “through-space” scalar couplings between methyl and backbone carbonyl groups in proteins. These J couplings are indicative of the presence of noncovalent C−H⋅⋅⋅π hydrogen-bond-like interactions involving the amide π network. Experimentally detected scalar couplings were corroborated by a natural bond orbital analysis, which revealed the orbital nature of the interaction and the origins of the through-space J couplings. The experimental observation of this type of CH⋅⋅⋅π interaction adds a new dimension to the study of protein structure, function, and dynamics by NMR spectroscopy. 相似文献
996.
This paper presents results on the rheological behaviour of suspensions of two kinds of TiO2 particles in two different polymer solutions. The particles differ in their hydrophilic or hydrophobic properties. The dispersing
media are a solution of high molecular weight polyisobutylene in decalin and a solution of a low molecular weight polybutene
in decalin. The concentrations of polymer are adjusted in order to get the same zero shear viscosity. The shear viscosity
measurements display an apparent yield stress in some cases. The existence and the values of the yield stress depend on the
volume fraction of solid particles and on the type of particles. The evolution of the intrinsic viscosity and of the maximum
packing fraction vs the shear rate is interpreted in terms of evolution of the size and of the shape of aggregates of particles
under shear. The effect of temperature on the development of the yield stress is also discussed. The results are completed
by microscopic observations. 相似文献
997.
The dynamics of a structurally non-linear two-dimensional airfoil in turbulent flow is investigated numerically using a Monte
Carlo approach. Both the longitudinal and vertical components of turbulence, corresponding to parametric (multiplicative)
and external (additive) excitation, respectively, are modelled. The properties of the airfoil are chosen such that the underlying
non-excited, deterministic system exhibits binary flutter; the loss of stability of the equilibrium point due to flutter then
leads to a limit cycle oscillation (LCO) via a supercritical Hopf bifurcation. For the random system, the results are examined
in terms of the probability structure of the response and the largest Lyapunov exponent. The airfoil response is interpreted
from the point of view of the concepts of D- and P-bifurcations, as defined in random bifurcation theory. It is found that
the bifurcation is characterized by a change in shape of the response probability structure, while no discontinuity in the
variation of the largest Lyapunov exponent with airspeed is observed. In this sense, the trivial bifurcation obtained for
the deterministic airfoil, where the D- and P-bifurcations coincide, appears only as a P-bifurcation for the random case.
At low levels of turbulence intensity, the Gaussian-like bell-shaped bi-dimensional PDF bifurcates into a crater shape; this
is interpreted as a random fixed point bifurcating into a random LCO. At higher levels of turbulence intensity, the post-bifurcation
PDF loses its underlying deterministic LCO structure. The crater is transformed into a two-peaked shape, with a saddle at
the origin. From a more universal point of view, the robustness of the random bifurcation scenario is critiqued in light of
the relative importance of the two components of turbulent excitation. 相似文献
998.
999.
Fatima Bouhtit Mehdi Najar Doua Moussa Agha Rahma Melki Mustapha Najimi Khalid Sadki Noureddine Boukhatem Dominique Bron Nathalie Meuleman Abdellah Hamal Laurence Lagneaux Philippe Lewalle Makram Merimi 《Molecules (Basel, Switzerland)》2021,26(2)
Acute myeloid leukemia (AML) is a cancer of the myeloid lineage of blood cells, and treatment for AML is lengthy and can be very expensive. Medicinal plants and their bioactive molecules are potential candidates for improving human health. In this work, we studied the effect of Ptychotis verticillata (PV) essential oil and its derivatives, carvacrol and thymol, in AML cell lines. We demonstrated that a combination of carvacrol and thymol induced tumor cell death with low toxicity on normal cells. Mechanistically, we highlighted that different molecular pathways, including apoptosis, oxidative, reticular stress, autophagy, and necrosis, are implicated in this potential synergistic effect. Using quantitative RT-PCR, Western blotting, and apoptosis inhibitors, we showed that cell death induced by the carvacrol and thymol combination is caspase-dependent in the HL60 cell line and caspase-independent in the other cell lines tested. Further investigations should focus on improving the manufacturing of these compounds and understanding their anti-tumoral mechanisms of action. These efforts will lead to an increase in the efficiency of the oncotherapy strategy regarding AML. 相似文献
1000.
“Hummingbird” Behaviour of N‐Heterocyclic Carbenes Stabilises Out‐of‐Plane Bonding of AuCl and CuCl Units
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Matthieu Teci Dr. Eric Brenner Dr. Dominique Matt Christophe Gourlaouen Loic Toupet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):10997-11000
An N‐heterocyclic carbene substituted by two expanded 9‐ethyl‐9‐fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the Au?X rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X‐ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone‐pair axis, combined with the stabilisation provided by weak CH???Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl???H bonds are likely to cooperate with the H???Au interactions to stabilise the out‐of‐plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere. 相似文献