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1.
Chemosphere ; 239: 124763, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31526989

RESUMO

Nonredox metal ions have been widely recognized to be important in a wide range of biological and chemical oxidations as Lewis acids (LA). However, the role of LA in peroxymonosulfate (PMS) activation for wastewater treatment has not been considered until now. This study shows that oxidizing power of PMS can be promoted after binding nonredox metal ions such as Ca2+ as LA, leading to the easier reduction of the oxidant to radicals and substantial enhancement of dye degradation by employing manganese oxides OMS-2 as model catalysts. Increased with Lewis acidity of the metal ion, the rate of PMS decomposition enhanced linearly, while the dye degradation rate first increased and then declined due to the formation of a larger amount of dioxygen. The interactions between Ca2+ and PMS were further investigated by Raman, cyclic voltammetry and XPS; and the detailed mechanism of PMS activation was proposed. The performance of Ca2++OMS-2/PMS system under different conditions was also studied. The findings indicate the importance of LA in PMS activation reaction and their role must be considered in other transition metal oxides/PMS systems. It will be also helpful to design new and highly active catalysts for the reactions.


Assuntos
Ácidos de Lewis/química , Compostos de Manganês/química , Óxidos/química , Peróxidos/química , Poluentes Químicos da Água/química , Cálcio/química , Catálise , Corantes/química , Oxidantes/química , Oxirredução , Soluções , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química
2.
Molecules ; 25(1)2019 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-31861869

RESUMO

The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by 27Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH3 and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH3 sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na+ to NH4+ and decomposition of NH4+ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character.


Assuntos
Alumínio/química , Ácidos de Lewis/química , Espectroscopia de Ressonância Magnética , Zeolitas/química , Espectrofotometria Infravermelho
3.
Top Curr Chem (Cham) ; 377(6): 35, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31720874

RESUMO

N-Heterocyclic carbene (NHC) catalysis can access umpolung reactivity of carbonyl compounds as acyl anions, enolates and homoenolates. Considerable progress has been made in asymmetric transformation by the introduction of chirality to the NHC scaffold. However, the single catalyst system has limitations in chemo-, regio- and stereoselectivity. A solution to these problems has recently emerged with the synergistic combination of NHC catalysis and metal catalysis. A number of NHC/metal combinations have been found not only to improve reactivity and stereoselectivity, but also to enable access to unprecedented transformations. This paper highlights examples of successful asymmetric NHC/metal cooperative catalysis.


Assuntos
Metais/química , Metano/análogos & derivados , Catálise , Complexos de Coordenação/química , Compostos Heterocíclicos/química , Ácidos de Lewis/química , Metano/química , Estereoisomerismo
4.
Top Curr Chem (Cham) ; 378(1): 1, 2019 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-31761979

RESUMO

Organocatalysis-the branch of catalysis featuring small organic molecules as the catalysts-has, in the last decade, become of central importance in the field of asymmetric catalysis, so much that it is now comparable to metal catalysis and biocatalysis. Organocatalysis is rationalized and classified by a number of so-called activation modes, based on the formation of a covalent or not-covalent intermediate between the organocatalyst and the organic substrate. Among all the organocatalytic activation modes, enamine and iminium catalysis are widely used for the practical preparation of valuable products and intermediates, both in academic and industrial contexts. In both cases, chiral amines are employed as catalysts. Enamine activation mode is generally employed in the reaction with electrophiles, while nucleophiles require the iminium activation mode. Commonly, in both modes, the reaction occurs through well-organized transitions states. A large variety of partners can react with enamines and iminium ions, due to their sufficient nucleophilicity and electrophilicity, respectively. However, despite the success, organocatalysis still suffers from narrow scopes and applications. Multicatalysis is a possible solution for these drawbacks because the two different catalysts can synergistically activate the substrates, with a simultaneous activation of the two different reaction partners. In particular, in this review we will summarize the reported processes featuring Lewis acid catalysis and organocatalytic activation modes synergically acting and not interfering with each other. We will focus our attention on the description of processes in which good results cannot be achieved independently by organocatalysis or Lewis acid catalysis. In these examples of cooperative dual catalysis, a number of new organic transformations have been developed. The review will focus on the possible strategies, the choice of the Lewis acid and the catalytic cycles involved in the effective reported combination. Additionally, some important key points regarding the rationale for the effective combinations will be also included. π-Activation of organic substrates by Lewis acids, via formation of electrophilic intermediates, and their reaction with enamines will be also discussed in this review.


Assuntos
Aminoácidos/química , Ácidos de Lewis/química , Catálise , Estrutura Molecular , Estereoisomerismo
5.
Top Curr Chem (Cham) ; 377(6): 31, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31654245

RESUMO

Cooperative dual catalysis and bifunctional catalysis have emerged as reliable strategies for the development of hitherto difficult asymmetric transformations because they could deliver new reactivity and selectivity, and allow for the employment of substrates not amenable to reaction systems relying on a single, monofunctional catalysts. Furthermore, these modes of catalysis often improve yields and stereoselectivities via the precise recognition and simultaneous activation of nucleophiles and electrophiles. Efforts towards utilizing chiral cationic organic catalysts for asymmetric cooperative catalysis with metal complexes have provided a unique platform to address the challenging issues associated with reaction development. Chiral onium ions, such as tetraalkylammonium, guanidinium, and azolium ions, are employed mainly to control the reactivity and stereochemistry of anionic intermediates through electrostatic and hydrogen-bonding interactions. Metal complexes complement the synergy of the catalysis by activating the substrates via the formation of electrophilic π-allyl complexes, Lewis acid-base adducts, nucleophilic ate complexes, etc. The electrostatic interactions between cations and anions also offer a means to construct complex molecular assemblies, and, thus, onium ions are useful not only for controlling pairing with anionic species, but also for the design of supramolecular catalysts. The combination of onium ions and metal complexes leads to the introduction of novel concepts and powerful strategies for the development of catalysts and chemical transformations.


Assuntos
Ligantes , Metais/química , Carbono/química , Catálise , Cátions/química , Complexos de Coordenação/química , Ácidos de Lewis/química , Bases de Schiff/química , Estereoisomerismo
6.
Molecules ; 24(18)2019 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-31547416

RESUMO

Various types of σ-hole bond complexes were formed with FX, HFY, H2FZ, and H3FT (X = Cl, Br, I; Y = S, Se, Te; Z = P, As, Sb; T = Si, Ge, Sn) as Lewis acid. In order to examine their interactions with a protein, N-methylacetamide (NMA), a model of the peptide linkage was used as the base. These noncovalent bonds were compared by computational means with H-bonds formed by NMA with XH molecules (X = F, Cl, Br, I). In all cases, the A-F bond, which lies opposite the base and is responsible for the σ-hole on the A atom (A refers to the bridging atom), elongates and its stretching frequency undergoes a shift to the red with a band intensification, much as what occurs for the X-H bond in a H-bond (HB). Unlike the NMR shielding decrease seen in the bridging proton of a H-bond, the shielding of the bridging A atom is increased. The spectroscopic changes within NMA are similar for H-bonds and the other noncovalent bonds. The C=O bond of the amide is lengthened and its stretching frequency red-shifted and intensified. The amide II band shifts to higher frequency and undergoes a small band weakening. The NMR shielding of the O atom directly involved in the bond rises, whereas the C and N atoms both undergo a shielding decrease. The frequency shifts of the amide I and II bands of the base as well as the shielding changes of the three pertinent NMA atoms correlate well with the strength of the noncovalent bond.


Assuntos
Calcogênios/química , Halogênios/química , Proteínas/química , Acetamidas/química , Hidrogênio/química , Ligação de Hidrogênio , Ácidos de Lewis/química , Ressonância Magnética Nuclear Biomolecular , Espectrofotometria Infravermelho
7.
Chem Commun (Camb) ; 55(44): 6151-6164, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31093637

RESUMO

Chiral tetrahydrocarbazoles (THCs) are prevalent in numerous natural indole alkaloids as well as synthetic pharmaceuticals, and exhibit a broad spectrum of bioactivities. As such, the development of efficient synthetic methodologies for the synthesis of chiral THCs is of substantial interest. The advent of asymmetric catalysis provides a powerful platform to assemble chiral THC motifs and great efforts have been devoted to this field over the past decades. In this feature article, we summarise recent advances in catalytic asymmetric synthesis of THCs, with particular emphases on reaction types and reaction mechanism.


Assuntos
Carbazóis/síntese química , Alquilação , Carbazóis/química , Catálise , Reação de Cicloadição , Indóis/química , Ácidos de Lewis/química , Estrutura Molecular , Estereoisomerismo
8.
Chem Pharm Bull (Tokyo) ; 67(6): 587-593, 2019 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-30944268

RESUMO

Formylations of fluorine-containing aromatic compounds with dichloromethyl alkyl ethers have been investigated. Dichloromethyl propyl ether and dichloromethyl butyl ether have been applied for the formylation of fluorine-containing anisoles to give the corresponding aldehydes in good yields. Application of these ethers is preferable to that of methyl ether, which is prepared from volatile methyl formate. Reaction of fluorine-containing phenols with these dichloromethyl alkyl ethers did not give salicylaldehyde derivatives, leading instead to corresponding aryl formates in high yields. A plausible mechanism is discussed.


Assuntos
Éter Bisclorometílico/química , Flúor/química , Aldeídos/química , Derivados de Benzeno/química , Éteres/química , Ácidos de Lewis/química
9.
Environ Sci Pollut Res Int ; 26(15): 15373-15380, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30937738

RESUMO

Alumina has been used as a catalyst for ozonation, surface hydroxyl on which is regarded as the active center for ozone attack, but the influences of hydroxyl generation are still vague. Here, we prepared alumina with different hydroxyl concentrations by adjusting calcination temperatures, of which the catalytic activity was evaluated with the mineralization degree of phenol, and then revealed the active sites of hydroxyl generation with characterization of XRD, Py-IR, and NH3-TPD. The results show that the greater the hydroxyl concentration, the higher the catalytic activity, demonstrating that surface hydroxyl contributes to its catalytic activity. The effect of calcination temperatures on hydroxyl concentration and catalytic activity is in accordance with the amount of weak Lewis acid sites on the surface of alumina, illustrating the surface hydroxyl derived from the decomposition of water adsorbed on weak Lewis acid sites. However, the catalytic performance of the alumina decreases slowly in a long-term reaction owing to the active center reduction resulted from the coverage by organic acids from phenol degradation. The present work reveals the influences of hydroxyl generation which are beneficial for adjusting surface hydroxyl regarded as active site for ozone attack and the reason of catalyst deactivation, which provides guideline for the rational design of catalyst.


Assuntos
Óxido de Alumínio/química , Radical Hidroxila/química , Ozônio/química , Fenol/química , Poluentes Químicos da Água/química , Adsorção , Catálise , Ácidos de Lewis/química , Temperatura , Purificação da Água/métodos , Difração de Raios X
10.
Dalton Trans ; 48(20): 6685-6689, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-30997474

RESUMO

Bifunctional Lewis acidic group 15 compounds have emerged as appealing platforms for anion sensing and organocatalysis. As part of our interest in the chemistry of these compounds, we have now compared the catalytic properties of [o-(MePPh2)C6H4SbPh2]+ ([3]+), [o-(PPh2)C6H4SbPh3]+ ([4]+), [o-(MePPh2)C6H4SbPh3]2+ ([5]2+), and [o-C6H4(SbMePh2)2]2+ ([6]2+) using the transfer hydrogenation of 2-phenyl-quinoline and 3-bromoquinoline with a Hantzsch ester benchmark reactions. This study, which also involved an evaluation of the catalytic properties of [Ph4Sb]+ and [Ph3MeP]+, shows that antimony cations are generally more active than their phosphorus counterparts and neutral stiboranes. Our results also demonstrate that dicationic systems such as [6]2+ are superior activators.


Assuntos
Antimônio/química , Derivados de Benzeno/química , Ácidos de Lewis/química , Compostos Organometálicos/química , Compostos Organofosforados/química , Quinolinas/química , Boratos/química , Catálise , Cátions , Hidrogenação , Estrutura Molecular , Fosfinas/química , Estereoisomerismo , Relação Estrutura-Atividade
11.
Inorg Chem ; 58(8): 5154-5162, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30907585

RESUMO

The metal-mediated activation of PhNO represents an important starting point for understanding the reactivity patterns of nitrosoarenes in biological systems and catalysis. Here we report that the pyrazole-based dinickel(II) dihydride complex [KL(NiH)2] (1) reacts with PhNO to eliminate dihydrogen concomitant with binding of the doubly reduced substrate in µ-κ(O):κ(N) mode in the bimetallic pocket of [KLNi2(PhNO)] (2). The addition of [2,2,2]cryptand leads to the ionic complex [K(crypt)][LNi2(PhNO)] (3). Structural and spectroscopic analyses evidence that interaction with the Lewis acidic K+ in 2 causes significant elongation and weakening of the substrate's N-O bond [ dN-O = 1.487(12) Å in 2 vs 1.374(4) Å in 3]. Complex 2 (or 3) reacts with [FeCp*2][PF6] to give LNi2(PhNO) (4), which is shown by electron paramagnetic resonance and IR spectroscopies and density functional theory calculations to feature two low-spin d8 nickel(II) ions and a bridging (PhNO)•- radical anion ligand, with the out-of-plane π*(NO) being the singly occupied molecular orbital. Cyclic voltammetry and UV-vis spectroelectrochemical experiments show that 4 and the anion of 3 can be reversibly interconverted at very low potential ( E1/2 = -1.53 V vs Fc/Fc+). Protonation of 2 leads to the N-phenylhydroxylamine complex [LNi2(ONHPh)] (5) with a long N-O bond of 1.464(2) Å, and titration studies suggest a p Ka of around 23-25 in tetrahydrofuran. This allows one to derive a bond dissociation energy of 62-65 kcal mol-1 for the N-H bond of 5. Accordingly, 5 readily reacts with the phenoxy radical 2,4,6- tBu3C6H2O• to yield 4. This work demonstrates the reductive binding of PhNO without prior formation of unstable nickel(I) species and the redox noninnocence of the PhNO ligand in the less common µ-κ(O):κ(N) bridging mode. Thermodynamic data for H-atom-abstraction chemistry at the activated PhNO may be valuable for understanding the reactivity patterns of the transient but biologically relevant nitroxyl (HNO) ligand.


Assuntos
Níquel/química , Compostos Nitrosos/química , Sítios de Ligação , Teoria da Densidade Funcional , Furanos/química , Ácidos de Lewis/química , Ligantes , Oxirredução , Prótons , Espectrofotometria Ultravioleta , Termodinâmica
12.
Org Lett ; 21(7): 2307-2311, 2019 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-30907595

RESUMO

Formal [5 + 1] cycloadditions between aryl-substituted vinylcyclopropanes and nitrenoid precursors are reported. The method, which employs Rh2(esp)2 as a catalyst, leads to the highly regioselective formation of substituted tetrahydropyridines. Preliminary mechanistic studies support a stepwise, polar mechanism enabled by the previously observed Lewis acidity of Rh-nitrenoids. Overall, this work expands the application of nitrene-transfer cycloaddition, a relatively underexplored approach to heterocycle synthesis, to the formation of six-membered rings.


Assuntos
Iminas/síntese química , Ácidos de Lewis/química , Compostos de Vinila/síntese química , Catálise , Reação de Cicloadição , Iminas/química , Estrutura Molecular , Compostos de Vinila/química
13.
Molecules ; 24(2)2019 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-30669606

RESUMO

In our studies on the catalytic activity of Group IVB transition metal Lewis acids, Hf(OTf)4 was identified as a highly potent catalyst for "one-pot, three-component" Biginelli reaction. More importantly, it was found that solvent-free conditions, in contrast to solvent-based conditions, could dramatically promote the Hf(OTf)4-catalyzed formation of 3,4-dihydro-pyrimidin-2-(1H)-ones. To provide a mechanistic explanation, we closely examined the catalytic effects of Hf(OTf)4 on all three potential reaction pathways in both "sequential bimolecular condensations" and "one-pot, three-component" manners. The experimental results showed that the synergistic effects of solvent-free conditions and Hf(OTf)4 catalysis not only drastically accelerate Biginelli reaction by enhancing the imine route and activating the enamine route but also avoid the formation of Knoevenagel adduct, which may lead to an undesired byproduct. In addition, ¹H-MMR tracing of the H-D exchange reaction of methyl acetoacetate in MeOH-d4 indicated that Hf(IV) cation may significantly accelerate ketone-enol tautomerization and activate the ß-ketone moiety, thereby contributing to the overall reaction rate.


Assuntos
Háfnio/química , Ácidos de Lewis/química , Metais/química , Pirimidinonas/síntese química , Solventes/química , Catálise , Técnicas de Química Sintética , Estrutura Molecular , Pirimidinonas/química
14.
Macromol Rapid Commun ; 40(10): e1800877, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30650236

RESUMO

Good control of tacticity, molecular weight, and architecture is attained via atom transfer radical polymerization (ATRP) of N-hydroxyethyl acrylamide (HEAA), in a one-pot process in the presence of Y(OTf)3 . The effect of temperature, ratio of [Y(OTf)3 ]/[HEAA], and ATRP procedure on the tacticity and degree of control over the polymerization is investigated in detail. Under optimal conditions, using photo ATRP and 15% Y(OTf)3, the content of meso dyads (m) can be increased from 42% to 80% in a homopolymer with a dispersity D = 1.22. Well-defined stereoblock copolymers, atactic- b -isotactic poly(HEAA), with D = 1.27, are obtained by adding Y(OTf)3 at a specific conversion, initially started without Y(OTf)3 .


Assuntos
Acrilamidas/síntese química , Ácidos de Lewis/química , Polimerização , Polímeros/síntese química , Acrilamidas/química , Ácidos de Lewis/síntese química , Peso Molecular , Polímeros/química , Temperatura
15.
Molecules ; 24(3)2019 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-30691072

RESUMO

The utility of an electron-deficient, air stable, and commercially available Lewis acid tris(pentafluorophenyl)borane has recently been comprehensively explored. While being as reactive as its distant cousin boron trichloride, it has been shown to be much more stable and capable of catalyzing a variety of powerful transformations, even in the presence of water. The focus of this review will be to highlight those catalytic reactions that utilize a silane as a stoichiometric reductant in conjunction with tris(pentafluorophenyl) borane in the reduction of alcohols, carbonyls, or carbonyl-like derivatives.


Assuntos
Boranos/química , Hidrocarbonetos Fluorados/química , Silanos/química , Álcoois/química , Catálise , Fenômenos Químicos , Ésteres/química , Ácidos de Lewis/química , Oxirredução
16.
Carbohydr Res ; 472: 65-71, 2019 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-30496874

RESUMO

The Lewis acid-catalyzed nucleophilic opening of a D-gluco-configured bicyclic hemiaminal has been examined. Several Lewis acids and silylated nucleophiles have been screened allowing the introduction of acetophenone, phosphonate or nitrile at the pseudoanomeric position in satisfactory yields and high 1,2 trans stereoselectivities. Their skeletal rearrangement triggered by the N-benzyl anchimeric assistance provided the corresponding L-ido-configured piperidines displaying various functional groups at C-6 position in good yield.


Assuntos
Imino Açúcares/química , Ácidos de Lewis/química , Piperidinas/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Catálise , Estrutura Molecular , Estereoisomerismo
17.
Carbohydr Res ; 471: 85-94, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30508660

RESUMO

Pentopyranoside and 6-deoxyhexopyranosides, such as those from d-xylose, l-arabinose and l-fucose are components of natural products, oligosaccharides or polysaccharides. Lewis acid promoted anomerisation of some of their alkyl O- and S-glycopyranosides is reported here. SnCl4 was more successful than TiCl4, with the latter giving the glycosyl chloride by-product in some cases, and both were superior to BF3OEt2. Kinetics study using 1H NMR spectroscopy showed an order of reactivity: O-xylopyranoside > O-arabinopyranoside > O-fucopyranoside. Benzoylated glycosides were more reactive than acetylated glycosides. The reactivity of S-glycosides was greater than that of O-glycosides for both arabinose and fucose derivatives; the reactivity of O- and S-xylopyranosides was similar. The highest stereoselectivities were observed for fucopyranosides. The ß-d-xylopyranoside and α-l-arabinopyranoside reactants are conformationally more flexible than ß-l-fucopyranosides.


Assuntos
Glicosídeos/síntese química , Ácidos de Lewis/química , Acetilação , Glicosídeos/química , Estrutura Molecular , Espectroscopia de Prótons por Ressonância Magnética
18.
Environ Sci Pollut Res Int ; 26(2): 1706-1715, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30448951

RESUMO

A series of Fe/ZSM-5 catalysts with different Fe contents were prepared by impregnation method. The catalysts were characterized by TEM, XRD, H2 temperature-programed reduction (H2-TPR), temperature-programed desorption of ammonia (NH3-TPD), and in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), and the catalytic activity test was also carried out on selective catalytic reduction (SCR) denitration device. Results showed that the single metal iron-supported ZSM-5 catalyst has high deNOx activity in the medium-high temperature range, and the optimal loading of Fe active component is 10 wt%; the deNOx efficiency over 80% at the range of 350-450 °C and 431 °C reaches the maximum of 96.91%. Iron species can be finely dispersed on the surface of the carrier as amorphous oxides, and the crystalline structure of zeolite is retained. The significant redox performance, highly dispersed nanoparticles, and rich Lewis acid sites on the surface of catalyst are favorable for the SCR denitration reaction. Fe/ZSM-5 10 wt% catalyst has rich Lewis acid sites and less B acid sites and Lewis acidic sites play an important role during the reaction. Only Eley-Rideal (E-R) mechanism existed during the NH3-SCR reaction process, and there is no denitration reaction being accomplished by L-H mechanism at 150 °C.


Assuntos
Amônia/química , Ferro/química , Óxidos de Nitrogênio/química , Poluentes Atmosféricos/química , Poluição do Ar/prevenção & controle , Catálise , Ácidos de Lewis/química , Microscopia Eletrônica de Transmissão , Oxirredução , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Difração de Raios X
19.
Macromol Biosci ; 18(12): e1800336, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30408332

RESUMO

The [2+2] cycloaddition-retroelectrocyclization (CA-RE) between N,N-dialkylaniline-substituted alkynes and 7,7,8,8-tetracyanoquinodimethane (TCNQ) is employed to fabricate functional cross-linked polymer films containing the intramolecular charge-transfer (CT) chromophores at the cross-linking points. Polystyrene bearing N,N-dialkylaniline-substituted alkynes (P1) and TCNQ polyester (P2) are mixed in tetrahydrofuran (THF), then this solution is spray-coated onto an indium tin oxide or glass plate. Heating to 100 °C initiates the [2+2] CA-RE reaction, resulting in the formation of cross-linked polymer films. The reaction progress and completion are evaluated by monitoring the CT absorption band and cyano vibration peaks. The resulting cross-linked polymer films show reversible cathodic electrochromism between the neutral and anion radical states. In addition, they also display the visual detection behavior of protic acids and Lewis acids, such as Ag+ ions. Accordingly, the Ag+ ion-loaded polymer films are prepared, and their antibacterial activities are studied. As more Ag+ ions are loaded, the CT band more bathochromically shifts and more potent antibacterial activities are obtained. Therefore, the antibacterial activity of the polymer films can be visually recognized by the film colors. Furthermore, the loaded Ag+ ions can be released from the polymer films by application of an electrochemical potential.


Assuntos
Compostos de Anilina/química , Antibacterianos/síntese química , Complexos de Coordenação/síntese química , Escherichia coli/efeitos dos fármacos , Nitrilos/química , Prata/química , Alquinos/química , Antibacterianos/farmacologia , Cátions Monovalentes , Cor , Complexos de Coordenação/farmacologia , Reagentes para Ligações Cruzadas/química , Reação de Cicloadição , Escherichia coli/crescimento & desenvolvimento , Furanos/química , Vidro/química , Temperatura Alta , Ácidos de Lewis/química , Testes de Sensibilidade Microbiana , Poliestirenos/química , Prata/farmacologia , Solventes/química , Eletricidade Estática , Compostos de Estanho/química
20.
J Chromatogr A ; 1580: 134-141, 2018 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-30389207

RESUMO

Melamine and thiourea-derived graphitic carbon nitrides (M-GCN/T-GCN) were synthesized and characterized. The surface properties were investigated using inverse gas chromatography (IGC) and compared. Net retention volumes of M-GCN and T-GCN were measured with n-alkanes (C5-C10) and polar probes. The London dispersive surface free energies (γsd), calculated using Schultz and Dorris-Gray methods, decreased linearly with increasing temperature. The specific components of the enthalpy and entropy of adsorption for the polar probes were obtained using the Schultz, Dong, and Sawyer-Brookman methods. The Gutmann's Lewis acid-base parameters, Ka and Kb, were determined using the surface free energy (ΔGaS) via these methods. The surface character 'S' values (Kb/Ka) of M-GCN and T-GCN using the respective methods are 4.04, 3.78, and 5.08 and 4.11, 5.27, and 2.86. Hence, the surfaces contain more basic than acidic sites and could interact strongly with acidic media. Thus, IGC elucidates the surface charges of the GCN matrix resulting from surface chemical modification.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Gasosa , Nitrilos/química , Tioureia/química , Triazinas/química , Adsorção , Grafite/química , Concentração de Íons de Hidrogênio , Ácidos de Lewis/química , Bases de Lewis/química , Polimerização , Propriedades de Superfície , Temperatura , Termodinâmica
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