The Experts below are selected from a list of 990 Experts worldwide ranked by ideXlab platform
Fernando Aparecido Sigoli - One of the best experts on this subject based on the ideXlab platform.
-
Particle size tailoring and luminescence of europium(III)-doped gadolinium oxide obtained by the modified homogeneous precipitation method: Dielectric constant and counter anion effects
Holanda, 2015Co-Authors: Gaspar Rdl, Italo Odone Mazali, Fernando Aparecido SigoliAbstract:Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This work reports on controlling the particle size distribution of europium(III)-doped gadolinium oxide samples prepared through a Topochemical Reaction carried out by thermal treatment of europium(III)-doped gadolinium hydroxycarbonate. Hydroxycarbonate samples were obtained by a modified homogeneous precipitation method using different solvent mixtures, such as water:ethanol, water:ethylene glycol, water:tert-butanol, and different counter ions such as nitrate and chloride. The luminescent properties of the oxide samples, are characteristics of europium(III) ions, with the hypersensitive transition ((5)D(0) --> (7)F(2)) being the most intense emission peak and the emission lifetime values are typical for this system. The spherical particle size distribution of europium(III)-doped gadolinium oxide can be tailored by selecting the counter anion types, the chemical nature of the alcohol and the dielectric constant of the Reaction media. The appropriate control of these parameters allows the preparation of rare-earth doped gadolinium samples having monomodal particle size distributions with mean sizes between 30 and 90 nanometers. (C) 2010 Elsevier B.V. All rights reserved.36741699155160Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq
-
particle size tailoring and luminescence of europium iii doped gadolinium oxide obtained by the modified homogeneous precipitation method dielectric constant and counter anion effects
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010Co-Authors: Rafael D L Gaspar, Italo Odone Mazali, Fernando Aparecido SigoliAbstract:Abstract This work reports on controlling the particle size distribution of europium(III)-doped gadolinium oxide samples prepared through a Topochemical Reaction carried out by thermal treatment of europium(III)-doped gadolinium hydroxycarbonate. Hydroxycarbonate samples were obtained by a modified homogeneous precipitation method using different solvent mixtures, such as water:ethanol, water:ethylene glycol, water:tert-butanol, and different counter ions such as nitrate and chloride. The luminescent properties of the oxide samples, are characteristics of europium(III) ions, with the hypersensitive transition (5D0 → 7F2) being the most intense emission peak and the emission lifetime values are typical for this system. The spherical particle size distribution of europium(III)-doped gadolinium oxide can be tailored by selecting the counter anion types, the chemical nature of the alcohol and the dielectric constant of the Reaction media. The appropriate control of these parameters allows the preparation of rare-earth doped gadolinium samples having monomodal particle size distributions with mean sizes between 30 and 90 nanometers.
Marcel Mayor - One of the best experts on this subject based on the ideXlab platform.
-
molecular weaving via surface templated epitaxy of crystalline coordination networks
Nature Communications, 2017Co-Authors: Zhengbang Wang, Alfred Blaszczyk, Olaf Fuhr, Stefan Heissler, Christoph Woll, Marcel MayorAbstract:One of the dream Reactions in polymer chemistry is the bottom-up, self-assembled synthesis of polymer fabrics, with interwoven, one-dimensional fibres of monomolecular thickness forming planar pieces of textiles. We have made a major step towards realizing this goal by assembling sophisticated, quadritopic linkers into surface-mounted metal-organic frameworks. By sandwiching these quadritopic linkers between sacrificial metal-organic framework thin films, we obtained multi-heteroepitaxial, crystalline systems. In a next step, Glaser–Hay coupling of triple bonds in the quadritopic linkers yields linear, interwoven polymer chains. X-ray diffraction studies revealed that this Topochemical Reaction leaves the MOF backbone completely intact. After removing the metal ions, the textile sheets can be transferred onto different supports and imaged using scanning electron microscopy and atomic-force microscopy. The individual polymer strands forming the two-dimensional textiles have lengths on the order of 200 nm, as evidenced by atomic-force microscopy images recorded from the disassembled textiles. The self-assembly of polymer threads into interwoven textiles is an important goal in polymer chemistry. Here the authors assemble interwoven polymer chains by cross-linking acetylene functionalized ligands in surface-mounted MOFs and subsequent removal of the metal ions affords 2D textile sheets.
Kana M Sureshan - One of the best experts on this subject based on the ideXlab platform.
-
solid state synthesis of two different polymers in a single crystal a miscible polymer blend from a Topochemical Reaction
Angewandte Chemie, 2019Co-Authors: Kuntrapakam Hema, Kana M SureshanAbstract:The Topochemical synthesis of a miscible polymer blend is described. The azide- and alkyne-decorated tetrol 1 crystallizes as two different conformers. Both conformers exhibit self-sorted head-to-tail alignment with proximally placed reacting groups such that Topochemical polymerization yields two types of polymer chains, each containing only one type of conformer. The orientation of complementary reactive groups in one of the head-to-tail-arranged conformers favors the formation of cis-triazole linkages, and the other favors the trans-triazole linkages. Crystals of 1 on heating gave a perfect polymer blend containing equal amounts of cis-triazole-linked and trans-triazole-linked polymers. As each conformer is H-bonded to four conformers of the other kind, the polymerization yields a perfect polymer blend wherein each polymer chain is surrounded by chains of the other type. Thus, the molecular ordering in the prepolymerized state in a crystal is utilized to create a polymer blend.
-
chirality controlled spontaneous twisting of crystals due to thermal Topochemical Reaction
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Rishika Rai, Baiju P Krishnan, Kana M SureshanAbstract:Crystals that show mechanical response against various stimuli are of great interest. These stimuli induce polymorphic transitions, isomerizations, or chemical Reactions in the crystal and the strain generated between the daughter and parent domains is transcribed into mechanical response. We observed that the crystals of modified dipeptide LL (N 3 -l-Ala-l-Val-NHCH 2 C≡CH) undergo spontaneous twisting to form right-handed twisted crystals not only at room temperature but also at 0 °C over time. Using various spectroscopic techniques, we have established that the twisting is due to the spontaneous Topochemical azide–alkyne cycloaddition (TAAC) Reaction at room temperature or lower temperatures. The rate of twisting can be increased by heating, exploiting the faster kinetics of the TAAC Reaction at higher temperatures. To address the role of molecular chirality in the direction of twisting the enantiomer of dipeptide LL, N 3 -d-Ala-d-Val-NHCH 2 C≡CH (DD), was synthesized and Topochemical reactivity and mechanoresponse of its crystals were studied. We have found that dipeptide DD not only underwent TAAC Reaction, giving 1,4-triazole–linked pseudopolypeptides of d-amino acids, but also underwent twisting with opposite handedness (left-handed twisting), establishing the role of molecular chirality in controlling the direction of mechanoresponse. This paper reports ( i ) a mechanical response due to a thermal Reaction and ( ii ) a spontaneous mechanical response in crystals and ( iii ) explains the role of molecular chirality in the handedness of the macroscopic mechanical response.
-
three way competition in a Topochemical Reaction permutative azide alkyne cycloaddition Reactions leading to a vast library of products in the crystal
CrystEngComm, 2018Co-Authors: Kuntrapakam Hema, Kana M SureshanAbstract:5-Azido-3-O-propargyl-1,2-O-isopropylidene-α-D-ribofuranose (1) showed the possibility of undergoing Topochemical azide–alkyne cycloaddition (TAAC) Reaction to form 1,5-triazolyl linked polymers in the crystal. Surprisingly, when thermally activated, the molecules reach a conformational equilibrium wherein the native conformer reacts intermolecularly to form a 1,5-triazolyl linkage but the other conformer reacts either intermolecularly to form a 1,4-triazolyl linkage or intramolecularly to form 2. Thus, the TAAC Reaction adopts three competing pathways, of which two generate two different types of linkages for chain-growth and the third one generates a chain breaker. While the random occurrence of the chain-breaker Reaction ensures the formation of oligomers of different sizes, the permutative occurrence of two types of linkages in any n-mer produces 2n different oligomers of the same size.
-
Topochemical Azide–Alkyne Cycloaddition Reaction in Gels: Size-Tunable Synthesis of Triazole-Linked Polypeptides
2017Co-Authors: Baiju P. Krishnan, Kana M SureshanAbstract:Though Topochemical Reactions are attractive, the difficulty associated with crystallization such as low yield, unsuitability for large-scale synthesis, etc. warranted the exploitation of other self-assembled media for Topochemical Reactions. We synthesized a dipeptide gelator decorated with azide and alkyne at its termini, N3-Ala-Val-NHCH2-CCH, which is designed to self-assemble through intermolecular hydrogen bonds to β-sheets thereby placing the azide and alkyne motifs in proximity. As anticipated, this peptide forms gels in organic solvents and water via hydrogen-bonded β-sheet assembly as evidenced from IR spectroscopy and PXRD profiling. The microscopic fibers present in organogel and hydrogel have different morphology as was evident from scanning electron microscopy (SEM) imaging of their xerogels, XGh (xerogel made from hydrogel) and XGo (xerogel made from organogel). Heating of xerogels at 80 °C resulted in the Topochemical azide–alkyne cycloaddition (TAAC) polymerization to 1,4-triazole-linked oligopeptides. Under identical conditions, XGo produced larger oligopeptides, and XGh produced smaller peptides, as evidenced from MALDI-TOF spectrometry. We have also shown that degree of TAAC polymerization can be controlled by changing gel fiber thickness, which in turn can be controlled by concentration. SEM studies suggested the morphological intactness of the fibers even after the Reaction, and their PXRD profiles revealed that both XGh and XGo undergo fiber-to-fiber oligomerization without losing their crystallinity. In contrast to crystals, the xerogels undergo TAAC polymerization in two distinct stages as shown by DSC analyses. Interestingly, XGh and XGo undergo spontaneous TAAC polymerization at room temperature; the latter shows faster kinetics. This is not only the first demonstration of the use of xerogels for thermally induced Topochemical polymerization but also the first report on a spontaneous Topochemical Reaction in xerogels
-
supramolecular design of a bicomponent Topochemical Reaction between two non identical molecules
Chemical Communications, 2013Co-Authors: Baiju P Krishnan, Shyama Ramakrishnan, Kana M SureshanAbstract:We report the first design of a Topochemical Reaction between two non-identical reactants using a supramolecular chemistry approach. A coassembly of two sugar-based organogelators with complementary reacting motifs, viz. azides and alkynes, undergoes Topochemical Huisgen Reaction between them.
J Podworny - One of the best experts on this subject based on the ideXlab platform.
-
kinetics of the Topochemical Reaction of the solid solutions of magnesia spinels mg cr0 5fe0 5 2o4 mg al0 5cr0 5 2o4 mg al0 5fe0 5 2o4 with sulphur oxides
Thermochimica Acta, 2019Co-Authors: Anna Gerle, J Piotrowski, J PodwornyAbstract:Abstract Spinel-containing materials belong to an important group of refractories used as high-temperature unit linings. A crucial element of the conditions in which they are used is gaseous corrosion caused by sulphur oxides: SO2 and SO3. In previous investigations into Reactions of magnesia spinels with sulphur oxides it was found that spinels’ reactivity could be considerably influenced by a phase transition (order – disorder) in the cation sublattice, resulting in a change of their reactivity in relation to SO2/SO3. The aim of the study was to investigate the kinetics of Topochemical Reactions between equimolar solid solutions of magnesia spinels and sulphur oxides before and after the order – disorder phase transformation in the structure begins. Research into the Reaction of equimolar solid solutions Mg(Cr0.5Fe0.5)2O4, Mg(Al0.5Cr0.5)2O4, Mg(Al0.5Fe0.5)2O4 with SO3 was undertaken due to the fact that spinels form solid solutions in basic refractories. To conduct kinetic measurements, a semi-flow reactor was designed and constructed, in which investigations were carried out at the temperatures of 773 and 973 K and time range: 0–7 h. A mixture of air and SO2 (13%) was used. The obtained results have been compared with the kinetic results from the previous work obtained on two-cation spinels: MgAl2O4, MgFe2O4, MgCr2O4. The influence of the degree of inversion in spinel structure on the kinetics of the process was discussed.
Rafael D L Gaspar - One of the best experts on this subject based on the ideXlab platform.
-
particle size tailoring and luminescence of europium iii doped gadolinium oxide obtained by the modified homogeneous precipitation method dielectric constant and counter anion effects
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010Co-Authors: Rafael D L Gaspar, Italo Odone Mazali, Fernando Aparecido SigoliAbstract:Abstract This work reports on controlling the particle size distribution of europium(III)-doped gadolinium oxide samples prepared through a Topochemical Reaction carried out by thermal treatment of europium(III)-doped gadolinium hydroxycarbonate. Hydroxycarbonate samples were obtained by a modified homogeneous precipitation method using different solvent mixtures, such as water:ethanol, water:ethylene glycol, water:tert-butanol, and different counter ions such as nitrate and chloride. The luminescent properties of the oxide samples, are characteristics of europium(III) ions, with the hypersensitive transition (5D0 → 7F2) being the most intense emission peak and the emission lifetime values are typical for this system. The spherical particle size distribution of europium(III)-doped gadolinium oxide can be tailored by selecting the counter anion types, the chemical nature of the alcohol and the dielectric constant of the Reaction media. The appropriate control of these parameters allows the preparation of rare-earth doped gadolinium samples having monomodal particle size distributions with mean sizes between 30 and 90 nanometers.
