Search results for "SUBSTITUTION"

Synthesis of a fluorinated graphene oxide-silica nanohybrid: Improving oxygen affinity

2016

An easy method to achieve a fluorinated graphene oxide–silica nanohybrid (GOSF) is presented. Graphene oxide (GO) was synthesized by Hummer's modified method, the GO–silica nanohybrid (GOS) was obtained via Fischer esterification, the fluorinated moiety (3-pentadecafluoroheptyl-5-perfluorophenyl-1,2,4-oxadiazole) was introduced by nucleophilic substitution operated by the hydroxyl functionalities onto the GOS surface. Full characterization of the new materials confirmed the formation of covalent bonds between the graphene oxide/silica hybrid matrix and the fluorinated moieties. The proposed methodology offers an easy way to get fluorinated carbon/silica hybrid nanomaterials avoiding the har…

Investigation of lanthanum substitution effects in yttrium aluminium garnet: importance of solid state NMR and EPR methods

2020

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Phonons in YBa2Cu3O7?x crystals with site-selective oxygen isotope substitution: Frequencies, normal vectors, non-linear properties

1995

Lattice vibrations of YBa2Cu3O7−x crystals with a site-selective isotope substitution18O→16O are investigated theoretically. It is shown that shifts of the frequencies of A1g oxygen vibrations due to this substitution are smaller than under complete one. However, phonon bands and normal vectors are changed much stronger, especially in the case when apical oxygens are substituted. On the basis of the presented analysis anharmonic properties and transition temperatures of the selectively substituted crystals are also briefly discussed.

Study of the Partial Substitution of Pb by Sn in Cs-Pb-Sn-Br Nanocrystals Owing to Obtaining Stable Nanoparticles with Excellent Optical Properties.

2018

Halide perovskites are revolutionizing the photovoltaic and optoelectronic fields with outstanding performances obtained in a remarkably short time. However, two major challenges remain: the long-term stability and the Pb content, due to its toxicity. Despite the great effort carried out to substitute the Pb by a less hazardous element, lead-free perovskite still remains more unstable than lead-containing perovskites and presents lower performance as well. In this work, we demonstrate the colloidal preparation of Cs–Pb–Sn–Br nanoparticles (NPs) where Sn is incorporated up to 18.8%. Significantly, we have demonstrated that the partial substitution of Pb by Sn does not produce a deleterious e…

Increasing the stability of the Ge-containing extra-large pore ITQ-33 zeolite by post-synthetic acid treatments

2018

[EN] Extra-large pore ITQ-33 zeolite (ITT, 18 x 10 x 10-rings) is a very promising catalyst for the catalytic cracking of gasoil but, unfortunately, this material shows a limited hydrothermal stability due to the large germanium content present in the ITQ-33 structure. Taking this into account, the Ge-containing ITQ-33 has been post synthetically modified using different acid procedures with the aim of studying the effect of these treatments on the overall hydrothermal stability of this extra-large pore zeolite. In this sense, the as-prepared ITQ-33 has been treated with different HCl solutions in ethanol (from 0.1 to 1 M), containing also tetraethylorthosilicate (TEOS) as silicon precursor…

Oligo(phenylenevinylene)s with Terminal Donor–Acceptor Substitution This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der …

2002

Amphiphilic dyes for nonlinear optics: Dependence of second harmonic generation on functional group substitution

2008

The use of genetic algorithms to solve the allocation problems in the life cycle inventory

2013

One of the most controversial issues in the development of Life Cycle Inventory (LCI) is the allocation procedure, which consists in the partition and distribution of economic flows and environmental burdens among to each of the products of a multi-output system. Because of the use of the allocation represents a source of uncertainty in the LCI results, the authors present a new approach based on genetic algorithms (GAs) to solve the multi-output systems characterized by a rectangular matrix of technological coefficients, without using computational methods such as the allocation procedure. In this Chapter, the GAs' approach is applied to an ancillary case study related to a cogeneration pr…

Electrochemical reactivity of magnesium porphine : functionalization, oligo-polymerization and application to the synthesis of porphyrins and multi-p…

2012

This work deals with the redox reactivity of magnesium porphine, the study of its electropolymerization and resulting materials, of its functionalization by nucleophiles as well as the mechanistic investigation of the C-C oxidative coupling on a tris-meso-substituted porphyrin model.The electrochemical oxidation of magnesium porphine to its cation radical leads to oligomers in solution and polymers on the electrode, which molecular structure depends on the imposed potential. The reactivity of the cation radical has also been exploited by adding sufficient amount of nucleophiles (pyridine and triphenylphosphine) in the reactional in order to inhibit the oligomerization/polymerization process…

Subtype selective binding properties of substituted linear melanocyte stimulating hormone analogues

2002

The melanocortin receptors are peptide binding G-protein coupled receptors that play a role in important physiological functions such as energy balance, inflammatory processes and several aspects of reproduction. In this study, we synthesised 11 new linear MSH analogues and tested their binding to the human MC receptors (MC1, MC3, MC4 and MC5) expressed in COS cells. Our results show that introduction of Asp in position 4 similarly affects the binding to the MC1, MC4 and MC5 receptors, but drastically lowers the binding to the MC3 receptor. Arg(5) substitution shows relatively high affinity for the MC4 receptor, while the results also give further support for specific importance of His(6) f…