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Lanthanide Ion Interaction with a Crown Ether Methacrylic Polymer, Poly(1,4,7,10-tetraoxacyclododecan-2-ylmethyl methacrylate), as Seen by Spectroscopic, Calorimetric, and Theoretical Studies

Tapia, M. J.; Burrows, H. D.; García, J. M.; García, F.; Pais, A. A. C. C.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.74%
The interaction between trivalent lanthanide ions and the polymer poly(1,4,7,10-tetraoxacyclododecan-2-ylmethyl methacrylate) (PCR4) containing pendant 1,4,7,10-tetraoxacyclododecane (12-crown-4) groups has been studied by various spectroscopic techniques, calorimetry and theoretical calculations. Evidence for the binding of Eu(III), Tb(III), and Ce(III) ions and PCR4 in solution was obtained by the lanthanide-induced 1H and 13C NMR shifts and the decay of Tb(III) luminescence. From the isotope effect observed on the decay of luminescence of Tb(III) bound to PCR4 in H2O and D2O solutions, it is suggested that complexation leads to a decrease in the number of water molecules from 8 or 9 to 7. In the solid state, studies by differential scanning calorimetry (DSC) show that the interaction between Ce(III), Tb(III), and Li(I) ions and PCR4 leads to an increase in the glass transition temperature (Tg) of the polymer. Electron paramagnetic resonance (EPR) spectra of Gd(III) in the presence of the polymer are quite similar to those in aqueous solution, while Tb(III) emission is quenched by Ce(III) with nearly the same rate constants in water and aqueous PCR4 solutions, and the Ce(III) emission maxima are only very slightly shifted in the presence of the polymer...

Tetra-crowned porphyrin as P450 biomimetic model for carbamazepine oxidation

Silva Filho, Juvenal Carolino da; LEOD, Tatiana C. O. Mac; GOTARDO, Maria Carolina A. F.; ASSIS, Marilda das Dores
Fonte: ARKAT USA INC Publicador: ARKAT USA INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.63%
A substituted porphyrin bearing four crown ether units, H(2)(TCP), was synthesized from the reaction between (5,10,15,20-tetra(o-aminophenyl) porphyrin) and the acyl derivative of the ether (4-carboxy-18-crown-6). The free-base porphyrin was characterized by C, N, and H elemental analysis; UV-vis and IR spectroscopies; and (1)H NMR. The corresponding ironporphyrin, Fe(TCP)Cl, was obtained via iron insertion into H(2)(TCP). Fe(TCP)Cl was employed as catalyst for carbamazepine (CBZ) oxidation by iodosylbenzene (PhIO), 3-chloroperoxybenzoic acid (m-CPBA) or sodium hypochlorite (NaOCl), in methanol or in a biphasic water/dichloroethane system. The crowned ironporphyrin proved to be a highly efficient and selective catalyst for CBZ epoxidation even in the biphasic dichloroethane /H(2)O system, with no need for an additional phase transfer agent.; FAPESP; CNPq; CAPES

New insights on reaction pathway selectivity promoted by crown ether phase-transfer catalysis: Model ab initio calculations of nucleophilic fluorination

Pliego, Josefredo R., Jr.; Riveros, Jose M.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.89%
Crown ethers have the ability of solubilizing inorganic salts in apolar solvents and to promote chemical reactions by phase-transfer catalysis. However, details on how crown ethers catalyze ionic S(N)2 reactions and control selectivity are not well understood. In this work, we have used high level theoretical calculations to shed light on the details of phase-transfer catalysis mechanism of KF reaction with alkyl halides promoted by 18-crown-6. A complete analysis of the of the model reaction between KF(18-crown-6) and ethyl bromide reveals that the calculations can accurately predict the product ratio and the overall kinetics. Our results point out the importance of the K* ion and of the crown ether ring in determining product selectivity. While the K* ion favors the S(N)2 over the E2 anti pathway, the crown ether ring favors the S(N)2 over E2 syn route. The combination effects lead to a predicted 94% for the S(N)2 pathway in excellent agreement with the experimental value of 92%. A detailed analysis of the overall mechanism of the reaction under phase-transfer conditions also reveals that the KBr product generated in the nucleophilic fluorination acts as an inhibitor of the 18-crown-6 catalyst and it is responsible for the observed slow reaction rate. (C) 2012 Elsevier B.V. All rights reserved.; Brazilian Research Council (CNPq); Brazilian Research Council (CNPq); Brazilian Office of Higher Education (CAPES); Brazilian Office of Higher Education (CAPES); Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG); Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG); Institute for Science and Technology of Materials (INOMAT); Institute for Science and Technology of Materials (INOMAT)

Nova classe de porfirinas substituídas com éter coroa: Aplicação analítica e atividade catalítica na oxidação de hidrocarbonetos e do fármaco carbamazepina; New class of crowned porphyrins: analytical application and catalytic activity in the oxidation of hydrocarbons and carbamazepine drug.

Silva Filho, Juvenal Carolino da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/11/2006 PT
Relevância na Pesquisa
46.9%
Neste trabalho foi realizada a síntese, purificação e caracterização de uma tetra crowned porfirina, a 5,10,15,20-tetraquis[2-(hexaoxacicloexadecano-3-amidafenil)]-porfirina, H2TCP, bem como a correspondente ferroporfirina, (FeTCP)Cl. Foi investigado a atividade catalítica desta ferroporfirina e da ferroporfirina mono-crowned substituída, (FeMCP)Cl, sintetizada anteriormente, na oxidação dos substratos (z)-ciclooocteno, estireno, cicloexano e do fármaco carbamazepina, por vários oxidantes: iodosilbenzeno, ácido meta-cloroperbenzóico e hipoclorito de sódio, em meio homogêneo (MeOH ou ACN) e bifásico (C2H4Cl2/H2O). Os resultados revelaram que estes sistemas metaloporfirinicos podem ser considerados bons modelos biomiméticos das enzimas citocromo P450, para oxidação dos substrados estudados, levando ao mesmo produto obtido in vivo na oxidação do fármaco carbamazepina, o cabamazepina-epóxido. Os rendimentos dos produtos de oxidação catalisada pelas ferro crowned porfirinas são, na maioria dos casos, mais expressivos do que aqueles observados com as metaloporfirinas amino-substituídas precursoras. Estes resultados indicam que o substituinte éter coroa confere maior estabilidade e reatividade ao catalisador...

Alkali-Ion-Crown Ether in Art and Conservation: The Applied Bioinorganic Chemistry Approach

Hilfrich, Uwe; Taylor, Harold; Weser, Ulrich
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em //2004 EN
Relevância na Pesquisa
46.63%
Dried varnish is rich in many ester moieties, which may be broken down into small, soluble compounds by esterase activity or alkaline hydrolysis. Two methods for varnish removal have been developed, including the treatment of either lipase or RbOH / PEG-400 crown ether which allow aged oil varnishes or paint coverings to be removed or thinned. These techniques are designed to proceed in a controlled manner without damaging lower paint or base layers. Unfortunately, lipase did not react with the aged ester groups of dried linseed oil varnish. Surprisingly, the varnish came off in the presence of Tris buffer alone which, in addition, formed reactive metal complexes. A better choice was the use of high Mr alkali ion polyethylene glycol–400 (PEG-400) crown ether type chelates. PEG-400 complexes alkali ions including rubidium and other alkaliions impeding the diffusion of their basic counter ions into lower varnish or paint layers. Possible migration of alkali metal ions into the paint layer during alkaline varnish removal was determined by labelling the cleansing solutions with 86Rb. Fortunately, varnish is degraded on the surface only. Lower paint or varnish layers are not attacked even if chemically similar to the varnish or over painting to be removed as virtually no 86Rb was detected on the paint surface.

Photodissociation of Non-Covalent Peptide-Crown Ether Complexes

Wilson, Jeffrey J.; Kirkovits, Gregory J.; Sessler, Jonathan L.; Brodbelt, Jennifer S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.8%
Highly chromogenic 18-crown-6-dipyrrolylquinoxaline coordinates primary amines of peptides, forming non-covalent complexes that can be transferred to the gas phase by electrospray ionization. The appended chromogenic crown ether facilitates efficient energy transfer to the peptide upon ultraviolet irradiation in the gas phase, resulting in diagnostic peptide fragmentation. Collisional activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) of these non-covalent complexes results only in their disassembly with the charge retained on either the peptide or crown ether, yielding no sequence ions. Upon UV photon absorption the intermolecular energy transfer is facilitated by the fast activation time scale of UVPD (< 10 ns) and by the collectively strong hydrogen bonding between the crown ether and peptide, thus allowing effective transfer of energy to the peptide moiety prior to disruption of the intermolecular hydrogen bonds.

Effect of Crown Ether Ring Size on Binding and Fluorescence Response to Saxitoxin in Anthracylmethyl Monoaza Crown Ether Chemosensors‡

Mao, Hua; Thorne, John B.; Pharr, Jennifer S.; Gawley, Robert E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2006 EN
Relevância na Pesquisa
46.83%
Convenient macrocyclization synthetic routes for the preparation of different-sized monoaza anthracylmethyl crown ether chemsensors (15-crown-5, 18-crown-6, 21-crown-7, 24-crown-8 and 27-crown-9) are described. Evaluation of these crowns as chemosensors for saxitoxin revealed that the larger crowns have moderately higher binding constants, with the 27-crown-9 chemosensor having the largest binding constant: 2.29×105 M−1. Fluorescence enhancements of 100% were observed at saxitoxin concentrations of 5 μM, which is close to the detection limit in mouse bioassay.

Molecular Recognition of Arginine by Supramolecular Complexation with Calixarene Crown Ether Based on Surface Plasmon Resonance

Chen, Hongxia; Gu, Limin; Yin, Yongmei; Koh, Kwangnak; Lee, Jaebeom
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 04/04/2011 EN
Relevância na Pesquisa
46.74%
Arginine plays an important role in cell division and the functioning of the immune system. We describe a novel method by which arginine can be identified using an artificial monolayer based on surface plasmon resonance (SPR). The affinity of arginine binding its recognition molecular was compared to that of lysine. In fabrication of an arginine sensing interface, a calix[4]crown ether monolayer was anchored onto a gold surface and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The interaction between arginine and its host compound was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Recognition of calix[4]crown monolayer was assessed by the selective binding of arginine. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of arginine under aqueous conditions.

UV resonance Raman study of cation–π interactions in an indole crown ether

Schlamadinger, Diana E.; Daschbach, Megan M.; Gokel, George W.; Kim, Judy E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.76%
UV resonance Raman (UVRR) spectroscopy is used to probe changes in vibrational structure associated with cation–π interactions for the most prevalent amino acid π –donor, tryptophan. The model compound studied here is a diaza crown ether with two indole substituents. In the presence of sodium or potassium sequestered in the crown ether, or a protonated diaza group on the compound, the indole moieties participate in a cation–π interaction in which the pyrrolo group acts as the primary π-donor. Systematic shifts in relative intensity in the 760–780 cm−1 region are observed upon formation of this cation–π interaction; we propose that these modifications reflect shifts of the delocalized, ring-breathing W18 and hydrogen-out-of-plane (HOOP) vibrational modes in this spectral region. The observed changes are attributed to perturbations of the π-electron density as well as of normal modes that involve large displacement of the hydrogen atom on the C2 position of the pyrrole ring. Modest variations in the UVRR spectra for the three complexes studied here are correlated to differences in cation–π strength. Specifically, the UVRR spectrum of the sodium-bound complex differs from those of the potassium-bound or protonated-diaza complexes...

The synthesis and investigation of the electronic properties of crown ether, [2]-catenane, and [2]-rotaxane architectures

Simone, Davide Louis, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 244 leaves; 11490047 bytes; 11489801 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
46.93%
Scope. The body of work described in this thesis focuses on the synthesis of donor-acceptor architectures of the pseudorotaxane, rotaxane, and catenane genres. The binding constants of thiophene and phenylene-ethynylene based crown ethers are determined via fluorescence quenching titrations, in an attempt to correlate structure with binding affinities. The insight obtained from the binding constant determinations allows for the proper choice of crown ether for the formation of [2]-catenanes and [2]-rotaxanes. The electronic properties of these complexes are then probed by electrochemical, spectroelectrochemical, and conductivity measurements. The potential of a poly([2]-catenane) as a photoconductive polymer is also investigated. The obstacles encountered in synthesizing poly([2]-rotaxanes) is also discussed, with emphasis on end-group strategies that aid in thwarting electrochemically induced dethreading. Chapter 1. This chapter provides a broad overview of the physical methods utilized in this thesis. Electrochemical methods are covered, with particular emphasis on oxidative polymerization of heteroaromatic monomers. Correlation between electrode phenomena and cyclic voltammogram waveshapes is included, in order to reinforce an understanding of the various electrochemical processes. Electroactive catenane and rotaxane supramolecules feature prominent in the literature...

Novel crown ether assemblies: the role of isobenzofurans for attaching crown ethers to rigid molecular racks in a geometrically precise fashion

Warrener, R.N.; Wang, S.D.; Russell, R.A.; Gunter, M.J.
Fonte: Thieme Medical Publicador: Thieme Medical
Tipo: Artigo de Revista Científica
Publicado em //1997 EN
Relevância na Pesquisa
56.64%
Rigid polyalicyclic nanostructures with extended and U-shaped geometry and functionalised with 15-crown-5 rings have been prepared from molrac mono or bisalkenes and new crown ether isobenzofurans; substituents in the 1,3-position of the isobenzofuran are used to modify stereospecifities in the cycloaddition process thereby acting as geometrical control agents in the construction process.; Ronald N. Warrener, Shudong Wang, Richard A. Russell, Maxwell J. Gunter

Field-Dependent Effect of Crown Ether (18-Crown-6) on Ionic Conductance of α-Hemolysin Channels

Bezrukov, Sergey M.; Krasilnikov, Oleg V.; Yuldasheva, Liliya N.; Berezhkovskii, Alexander M.; Rodrigues, Claudio G.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /11/2004 EN
Relevância na Pesquisa
46.75%
Closing linear poly(ethylene glycol) (PEG) into a circular “crown” dramatically changes its dynamics in the α-hemolysin channel. In the electrically neutral crown ether (C2H4O)6, six ethylene oxide monomers are linked into a circle that gives the molecule ion-complexing capacity and increases its rigidity. As with linear PEG, addition of the crown to the membrane-bathing solution decreases the ionic conductance of the channel and generates additional conductance noise. However, in contrast to linear PEG, both the conductance reduction (reporting on crown partitioning into the channel pore) and the noise (reporting on crown dynamics in the pore) now depend on voltage strongly and nonmonotonically. Within the whole frequency range accessible in channel reconstitution experiments, the noise power spectrum is “white”, showing that crown exchange between the channel and the bulk solution is fast. Analyzing these data in the framework of a Markovian two-state model, we are able to characterize the process quantitatively. We show that the lifetime of the crown in the channel reaches its maximum (a few microseconds) at about the same voltage (∼100 mV, negative from the side of protein addition) where the crown's reduction of the channel conductance is most pronounced. Our interpretation is that...

Electrochemical behavior of lithium intercalated in a molybdenum disulfide-crown ether nanocomposite

Benavente Espinosa, Eglantina; González, G.; Mirabal, N.; Gómez-Romero, P.; Santa Ana, M. A.
Fonte: 2007 Elsevier Ltd. Publicador: 2007 Elsevier Ltd.
Tipo: Artículo de revista
EN
Relevância na Pesquisa
46.83%
A new nanocomposite, obtained from the intercalation of the cyclic ether 12-Crown-4 into MoS2, Li0.32MoS2(12-Crown-4)0.19, is described. The laminar product has an interlaminar distance of 14.4A° . The electrical conductivity of the nanocomposite varies from2.5×10−2 to 4.3×10−2 S cm−1 in the range 25–77 ◦C, being about four times higher than the analogous poly(ethylene oxide) (PEO) derivative at room temperature. The electrochemical step-wise galvanostatic intercalation or de-intercalation of lithium, leading to LixMoS2(12-Crown-4)0.19 with x in the range 0.07–1.0, indicates a Li/Li+ pair average potential of 2.8V. The electrochemical lithium diffusion coefficients in the crown ether intercalates, determined by galvanostatic pulse relaxation between 15 and 37 ◦C at different lithium intercalation degrees, are higher than those of the PEO derivatives under similar conditions, being however the diffusion mechanism rather more complex. The variation of both, the lithium diffusion activation enthalpy and the quasi-equilibrium potentials, with the lithium content shows there are two different limit behaviors, at low and high lithium intercalation degree, respectively. These features are discussed by considering the high stability of the Li-crown ether complex and the different chemical environments found by lithium along the intercalation process.; Partial support of FONDECYT (Grant 105 0344)...

An efficient synthesis of bis(calix[4]arenes) bis(crown ether)-substituted calix[4]arenes, aza-crown calix[4]arenes, and thiaza-crown calix[4]arenes

Torres Pinedo, Antonio; Saitz B., C.; Santoyo González, Francisco
Fonte: WILEY-V C H VERLAG GMBH Publicador: WILEY-V C H VERLAG GMBH
Tipo: Artículo de revista
EN
Relevância na Pesquisa
46.81%
Artículo de publicación ISI; The easy transformation of 5,11,17,23-tetra-tert-butyl-25,27-bis(aminoethoxy)-26,28-dihydroxycalix[4]arene (2) into 5,11,17,23-tetra-tert-butyl-26,28-dihydroxy-25,27-bis(2-iso-thiocyanoethoxy)calix[4]arene (3) and 5,11,17,23-tetra-tert-butyl-25,27-bis(chloroacetamidoethoxy)-26 calix[4]arene (4) has been exploited for the development of an efficient and expeditious synthesis of a variety of calix[4]arene derivatives [bis(calix[4]arenes), bis(crown ether) calix[4]arenes, aza-crown calix[4]arenes, and thiaza-crown calix[4]arenes]. The functionality of compounds 2 and 3 allowed the formation of intramolecular bridges, leading to capped calix[4]arenes (compounds 5, 10, and 14) as well as to the construction of double calix[4]arene units by means of spacers containing thiourea or amide-sulfur groups (compounds 6 and 15, respectively). In addition, the bis(isothiocyanate) derivative 3 gave access to a high-yield preparation of heteroditopic bis(crown ether) calix[4]arenes (7-9) from commercial amino crown ethers.

Thermopower of crown-ether-bridged anthraquinones

Ismael, A. K.; Grace, I.; Lambert, C. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/10/2015
Relevância na Pesquisa
46.84%
We investigate strategies for increasing the thermopower of crown-ether-bridged anthraquinones. The novel design feature of these molecules is the presence of either (1) crown-ether or (2) diaza-crown-ether bridges attached to the side of the current-carrying anthraquinone wire. The crown-ether side groups selectively bind alkali- metal cations and when combined with TCNE or TTF dopants, provide a large phase-space for optimising thermoelectric properties. We find that the optimum combination of cations and dopants depends on the temperature range of interest. The thermopowers of both 1 and 2 are negative and at room temperature are optimised by binding with TTF alone, achieving thermpowers of -600 microvolts/K and -285 microvolts/K respectively. At much lower temperatures, which are relevant to cascade coolers, we find that for 1, a combination of TTF and Na+ yields a maximum thermopower of -710 microvolts/K at 70K, whereas a combination of TTF and Li+ yields a maximum thermopower of -600 microvolts/K at 90K. For 2, we find that TTF doping yields a maximum thermopower of -800 microvolts/K at 90K, whereas at 50K, the largest thermopower (of -600 microvolts/K) is obtain by a combination TTF and K+ doping. At room temperature, we obtain power factors of 73 microwatts/m.K2 for 1 (in combination with TTF and Na+ ) and 90 microwatts/m.K2 for 2 (with TTF). These are higher or comparable with reported power factors of other organic materials.

Electrochemical behavior of lithium intercalated in a molybdenum disulfide-crown ether nanocomposite

Santa Ana, María Angélica; Mirabal, N.; Benavente, Eglantina; Gómez-Romero, P.; González, Guillermo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
Relevância na Pesquisa
66.9%
A new nanocomposite, obtained from the intercalation of the cyclic ether 12-Crown-4 into MoS2, Li0.32MoS2(12-Crown-4)0.19, is described. The laminar product has an interlaminar distance of 14.4 Å. The electrical conductivity of the nanocomposite varies from 2.5 × 10−2 to 4.3 × 10−2 S cm−1 in the range 25–77 °C, being about four times higher than the analogous poly(ethylene oxide) (PEO) derivative at room temperature. The electrochemical step-wise galvanostatic intercalation or de-intercalation of lithium, leading to LixMoS2(12-Crown-4)0.19 with x in the range 0.07–1.0, indicates a Li/Li+ pair average potential of 2.8 V. The electrochemical lithium diffusion coefficients in the crown ether intercalates, determined by galvanostatic pulse relaxation between 15 and 37 °C at different lithium intercalation degrees, are higher than those of the PEO derivatives under similar conditions, being however the diffusion mechanism rather more complex. The variation of both, the lithium diffusion activation enthalpy and the quasi-equilibrium potentials, with the lithium content shows there are two different limit behaviors, at low and high lithium intercalation degree, respectively. These features are discussed by considering the high stability of the Li-crown ether complex and the different chemical environments found by lithium along the intercalation process.; Partial support of FONDECYT (Grant 105 0344)...

(Beta)-Barium borate thin film formation on silicon through metal organic decompostion of two novel precursors, barium dimesitylborinate and barium (18-crown-6) Cyclotriboroxane

Gross, Timothy M.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
46.91%
Two novel precursors, barium dimesitylborinate and barium (18-crown-6) cyclotriboroxane, were synthesized to produce thin films of p-barium borate (P-Ba3B60i2) via the metal organic decomposition (MOD) process. The two precursor reagents were characterized by nuclear magnetic resonance, infrared spectroscopy, differential thermal analysis (DSC), thermal gravimetric analysis (TGA), and elemental analysis. The MOD process was initially used to produce P-barium borate powders. The powders were heated for 1 hour under oxygen flow at various temperatures. The formation of p-barium borate was confirmed by powder X-ray diffraction of the products of thermolysis of both precursors, p-barium borate formation occurred at 800 C and 550 C for barium dimesitylborinate and barium (crown ether) cyclotriboroxane, respectively. Thin films of both precursor compounds were produced by a spin coating process. The substrates used were silicon wafers with a (100) orientation. Tetrahydrofuran was found to be a good solvent for the barium dimesitylborinate precursor. Ethanol was used for barium (crown ether) cyclotriboroxane. Again, the MOD process was used. The films were heated to various temperatures for various times under flowing oxygen. The films were then analyzed by thin film X-ray diffraction to determine if p-barium borate was formed. Due to substrate interaction thin films produced from the barium dimesitylborinate precursor did not contain P-barium borate. However...

Crown Ether Ditopic Receptors for Ammonium Salts with High Affinity for Amino Acid Ester Salts

Rosete-Luna,Sharon; Medrano,Felipe; Bernal-Uruchurtu,Margarita I.; Godoy-Alcántar,Carolina
Fonte: Sociedad Química de México A.C. Publicador: Sociedad Química de México A.C.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2009 EN
Relevância na Pesquisa
56.53%
Two bis crown ether receptors were synthesized and tested as host molecules for protonated forms of alkyl amines and amino acid esters. Molecular recognition studies were conducted in CH2Cl2:MeOH (92:8) by spectrophotometric UV/Vis titrations and by spectrometric ¹H NMR titrations in CDCl3. The calculated binding constants are in the range 10²-10(5) M-1. A high affinity for L-amino acid methyl ester derivatives was found. A theoretical study at the DFT level of the synthesized receptor and some analog ligands with three different ammonium ions helps to rationalize the experimentally found trends.

Complex Formation Between Alkaline-Earth Cations and Anthraquinone Crown Ethers in Methanol and Acetonitrile

Costa,J.M. Caridade; Rodrigues,P.M.S.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 EN
Relevância na Pesquisa
56.59%
Formation of complexes of alkaline-earth cations with crown ethers containing an anthraquinone unit (AQ18C6 and AQ21C7) was investigated in methanol and acetonitrile solutions. Stability constants of the resulting complexes were estimated by means of potentiometric methods. The results obtained show the formation of complexes of the LM2+ type for all alkaline-earth ions; for the larger cations, (Sr2+ and Ba2+) and in excess of ligand, L2M2+ complexes were also detected. The most stable complexes were obtained with Ba2+ cation and for both ligands. The binding strength for the cations towards AQ18C6 and AQ21C7 ligands and in both solvents, increased in the order, Mg2+ < Ca2+ < Sr2+ < Ba2+. The results of this study suggest that on the 1:1 complexes, the size of the cation and its fit into the macrocyclic internal cavity of the ligand was a dominant factor on the coordination binding. The number of donor atoms in the ring of the macrocycle does not affect the binding strength and the AQ18C6 complexes have larger stability than the corresponding AQ21C7 complexes. The presence of an anthraquinone unit on the structure of the crown ether induced a decrease of the cation binding strength. The external carbonyl group of the ligand molecules was not involved on the coordination to the cation. Considering the two solvents...

Fluorescent sensing and determination of mercury (II) ions in water

Ncube,Phendukani; Krause,Rui WM; Ndinteh,Derek T; Mamba,Bhekie B
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
Relevância na Pesquisa
46.63%
The presence of heavy metals released from industrial activities into water streams is an ever-growing challenge to ensuring a safe and clean aquatic environment. Detection and determination of the levels of these heavy metals in wastewater is an important step before any measures can be taken. In this study we report on a fluorescent sensing probe based on a naphthyl azo dye modified dibenzo-18-crown-6-ether (DB18C6) for the detection and determination of mercury (II) ions in water. The probe showed high sensitivity and selectivity towards the mercury (II) ion among various alkali, alkaline earth, and transition metal ions. The mercury (II) ion quenched the fluorescence of the probe. Stern-Volmer quenching constants (Ksv) were found to be highest for Hg2+ ion at 1.18 x 10(5) M-1 compared to 3.85 x 10(4) M-1 for copper (II) ion. The stoichiometry of the sensor-metal ion interaction was found to be 1:1 for both metal ions using Job plots. The detection limit for Hg2+ was 1.25 x 10-8 M. The dye modified crown ether was then used to detect mercury in a water sample from a coalfired power plant and to determine the amount of mercury in the water sample.