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排序方式: 共有107条查询结果,搜索用时 109 毫秒
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Nikolaos Mourtzis Kyriaki Eliadou Konstantina Yannakopoulou 《Supramolecular chemistry》2013,25(8):587-593
Methyl Orange (MO), an azo-dye molecule with an inherent dipole moment, has been used as a probe to explore the influence of anionic or cationic substituents of cyclodextrins (CDs) on the mode of insertion to form pseudorotaxanes, using NMR spectroscopy. MO is oriented in a single mode inside the βCD cavity, with the dimethylamino group localized at the secondary side. This orientation is completely reversed when MO enters the anionic sodium heptakis[6-deoxy-6-(3-thiopropionate)]-βCD (βpsp) cavity, whereas inside the cationic heptakis(6-deoxy-6-amino)-βCD hydrochloride, MO flips once more, to adopt the same orientation as in βCD. In the latter case the water solubility of MO is significantly lowered. The disposition of the guest in βCD and in each βCD derivative in a single mode was attributed principally to anti-parallel dipole-dipole stabilization. In the wider γCD, the availability of more cavity space leads to 1:2 and 2:2 host/guest stoichiometries and the effect of dipoles is of secondary significance. In the anionic sodium octakis[6-deoxy-6-(3-thiopropionate)]-γCD, MO is positioned as in βpsp, but a 1:2 adduct is also detected. Finally, MO does not dissolve in octakis(6-deoxy-6-amino)-γCD hydrochloride solution. 相似文献
3.
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Konstantina E. Chrysomallidou Spyros P. Perlepes Aris Terzis Catherine P. Raptopoulou 《Polyhedron》2010
Reactions of malonic acid (H2mal) with PrCl3·6H2O afforded the known complex [Pr2(mal)3(H2O)6]n (1), and compounds [Pr2(mal)3(H2O)6]n·2nH2O (2·2nH2O), [PrCl(mal)(H2O)3]n·0.5nH2O (3·0.5nH2O) and [Pr(mal)(Hmal)(H2O)3]n·nH2O (4·nH2O) using various reaction ratios, reaction media (H2O, MeOH) and pH values. Analogous reactions with CeCl3·7H2O afforded compounds [Ce2(mal)3(H2O)6]n (5), [CeCl(mal)(H2O)3]n·nH2O (6·nH2O) and [Ce(mal)(Hmal)(H2O)3]n·nH2O (7·nH2O). Compounds 2·2nH2O and 3·0.5nH2O were characterized by X-ray crystallography, and 4–7 by microanalytical and spectroscopic data. The malonate(-2) ligand adopts three different coordination modes in the structures of 1–3, i.e., the μ2-κO:κO′:κO″ and the μ4-κ2O:κO′:κ2O″:κO? in 1 and 2 leading to a 3D network structure, and the μ3-κ2O:κO′:κ2O″:κO? in 3 promoting an 1D structure. The thermal decomposition of 1 and 3·0.5nH2O was monitored by TG/DTA and TG/DTG measurements. The structural features of 1–3 are discussed in terms of known malonato(-2) LnIII and CaII complexes. The bioinorganic chemistry relevance of our results is discussed. 相似文献
5.
Stefanopoulos KL Romanos GE Vangeli OC Mergia K Kanellopoulos NK Koutsioubas A Lairez D 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):7980-7985
Small-angle neutron scattering (SANS), contrast-matching SANS, and nitrogen adsorption have been utilized to investigate the confined ionic liquid (IL) [bmim][PF(6)] phase in ordered mesoporous silica MCM-41 and SBA-15. The results suggest that the pores of SBA-15 are completely filled with IL whereas a small fraction of the pore volume, the pore "core", of MCM-41 is empty. The contrast-matching SANS measurements confirm the enhanced solubility of water in IL. In addition, they provide strong evidence that water does not enter the empty pore core of MCM-41, possibly because of the preferred orientation of the IL molecules in the adsorbed layer. 相似文献
6.
Maffeo D Velkov Z Misiakos K Mergia K Paulidou A Zavali M Mavridis IM Yannakopoulou K 《Journal of colloid and interface science》2011,358(2):369-375
The monitoring of the antibacterial agent triclosan binding at nanomolar concentration from an aqueous solution by employing a well-packed monolayer with a predetermined single orientation made of specifically synthesized 2,3-dimethyl-6-(undec-10-enamide)-6-deoxy-β-cyclodextrin (DMBUA) on a silicon wafer (Si/SiO(2)) coated with a novolac resin is reported. A white light reflectance spectroscopy (WLRS) setup was used for the real-time monitoring of the DMBUA deposition and triclosan binding processes. Film thicknesses obtained by WLRS were in very good agreement with the ones measured by X-ray reflectivity (XRR) experiments. Triclosan binds strongly to the DMBUA monolayer (logK(assoc)=6.68). NMR studies in aqueous solution indicated that the chlorophenolyl ring rather than the dichlorophenyl ring is preferentially inserted into DMBUA cups. The current detecting system that requires no tedious surface chemistry, no thiolated cyclodextrins, no gold surfaces, and no expensive equipment may be useful in capturing small molecules and may permit various applications, e.g., preparation of antimicrobial surfaces. 相似文献
7.
Abstract We analyze mathematical models governing planar flow of chemical reaction from unburnt gasesto burnt gases in certain physical regimes in which diffusive effects such as viscosity and heat conduction aresignificant. These models can be then formulated as the Navier-Stokes equations for exothermically reactingcompressible fluids. We first establish the existence and dynamic behavior, including stability, regularity, andlarge-time behavior, of global discontinuous solutions of large oscillation to the Navier-Stokes equations withconstant adiabatic exponent γ and specific heat C_v. Our approach for the existence and regularity is to combinethe difference approximation techniques with the energy methods, total variation estimates, and weak conver-gence argumeots to deal with large jump discontinuities; and for large-time behavior is an a posteriori argumentdirectly from the weak form of the equations. The approach and ideas we develop here can be applied to solvinga more complicated model where γ 相似文献
8.
Donatella Donatelli Konstantina Trivisa 《Archive for Rational Mechanics and Analysis》2007,185(3):379-408
We consider a multidimensional model for the combustion of compressible reacting fluids. The flow is governed by the Navier–Stokes
in Eulerian coordinates and the chemical reaction is irreversible and is governed by the Arrhenius kinetics. The existence
of globally defined weak solutions is established by using weak convergence methods, compactness and interpolation arguments
in the spirit of Feireisl [16] and P.L. Lions [24]. 相似文献
9.
Gerasimos Daras Dimitris Templalexis Fengoula Avgeri Dikran Tsitsekian Konstantina Karamanou Stamatis Rigas 《Molecules (Basel, Switzerland)》2021,26(14)
The wall is the last frontier of a plant cell involved in modulating growth, development and defense against biotic stresses. Cellulose and additional polysaccharides of plant cell walls are the most abundant biopolymers on earth, having increased in economic value and thereby attracted significant interest in biotechnology. Cellulose biosynthesis constitutes a highly complicated process relying on the formation of cellulose synthase complexes. Cellulose synthase (CesA) and Cellulose synthase-like (Csl) genes encode enzymes that synthesize cellulose and most hemicellulosic polysaccharides. Arabidopsis and rice are invaluable genetic models and reliable representatives of land plants to comprehend cell wall synthesis. During the past two decades, enormous research progress has been made to understand the mechanisms of cellulose synthesis and construction of the plant cell wall. A plethora of cesa and csl mutants have been characterized, providing functional insights into individual protein isoforms. Recent structural studies have uncovered the mode of CesA assembly and the dynamics of cellulose production. Genetics and structural biology have generated new knowledge and have accelerated the pace of discovery in this field, ultimately opening perspectives towards cellulose synthesis manipulation. This review provides an overview of the major breakthroughs gathering previous and recent genetic and structural advancements, focusing on the function of CesA and Csl catalytic domain in plants. 相似文献
10.
We prove the global existence of weak solutions to the Navier-Stokes equations for compressible, heat-conducting flow in one space dimension with large, discontinuous initial data, and we obtain apriori estimates for these solutions which are independent of time, sufficient to determine their asymptotic behavior. In particular, we show that, as time goes to infinity, the solution tends to a constant state determined by the initial mass and the initial energy. and that the magnitudes of singularities in the solution decay to zero. 相似文献