RESUMO
The development of polymers with built-in sensors that provide readily perceptible optical warning signs of mechanical events has received considerable interest. A simple and versatile concept to bestow polymers with mechanochromic behavior is the incorporation of dye-filled microcapsules. Such capsules release their cargo when their shell is damaged, and the dye is subsequently activated through a chemical or physical change that causes a chromogenic response. Here, we report the preparation of fluorescent poly(urea-formaldehyde) microcapsules containing solutions of a solvatochromic cyanostilbene dye and their integration in different polymers. When objects made from such composites are damaged, the dye solution is released from the containers, diffuses into the matrix, and the solvent evaporates. As a result, the polarity around the dye molecules changes, and this leads to a change of the fluorescence color. Alternatively, the dye is blended into the polymer matrix, microcapsules are loaded with a solvent, and the release of the latter triggers the color change. Both mechanisms afford ratiometric signals because the capsules that remain intact or dye molecules that are not exposed to the solvent can be used as a built-in reference; therefore, a quantitative assessment of the damage inflicted on the material is a priori possible.
Assuntos
Corantes Fluorescentes/química , Formaldeído/química , Polímeros/química , Ureia/química , Cápsulas/síntese química , Cápsulas/química , Corantes Fluorescentes/síntese química , Formaldeído/síntese química , Fenômenos Mecânicos , Estrutura Molecular , Tamanho da Partícula , Polímeros/síntese química , Ureia/síntese químicaRESUMO
In this study, an innovative, facile, and low-cost method is developed to prepare phenolic resin (PR) containing boron and silicon (BSiPR). BSiPR is synthesized by a solvent-free, one-pot method using boric acid as the coupling agent instead of silane, and methyltriethoxysilane as the silicon source. The results show that boron and silicon elements are introduced into PR via BOC and BOSi structures. The char yield of the resulting resin at 800 °C is improved to 76%. The reasons for higher char yield are investigated. The formation of BOC can reduce the content of phenolic hydroxyl, which helps to decrease the weight loss. B2 O3 is also formed at 400 °C, and it can prevent the release of carbon oxides. Moreover, thermally stable BOSi and SiO structures remain stable during the pyrolysis. In addition, the mechanical and ablative properties of fiber-reinforced composites are also enhanced.
Assuntos
Ácidos Bóricos/química , Boro/química , Carvão Vegetal/química , Formaldeído/síntese química , Fenóis/síntese química , Polímeros/síntese química , Silício/química , Formaldeído/química , Teste de Materiais , Fenóis/química , Polímeros/química , Propriedades de SuperfícieRESUMO
Poly(urea-formaldehyde) (PUF) microcapsules filled with dicyclopentadiene (DCPD) were prepared by in situ polymerisation and the effect of synthesis parameters, such as pH of the solution and agitation rate, on microcapsules size and shell thickness was evaluated. Scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR) were performed. Adjusted pH conditions (pH = 3.5) and agitation rate (1350 RPM) were found using a design of experiments (DOE). SEM results indicated that microcapsule size was directly affected by agitation rate, whereas shell thickness was mostly affected by pH. After obtaining adjusted synthesis conditions, microcapsules presenting mean size of 60 µm and mean shell thickness of 4 µm were embedded in an epoxy matrix for evaluating the self-healing effect. FTIR and SEM analyses in damaged samples suggested that a healing agent was delivered to the crack location.
Assuntos
Cápsulas/síntese química , Formaldeído/síntese química , Polímeros/síntese química , Cápsulas/química , Técnicas de Química Sintética , Composição de Medicamentos , Formaldeído/química , Concentração de Íons de Hidrogênio , Indenos/administração & dosagem , Tamanho da Partícula , Polimerização , Polímeros/químicaRESUMO
Highly ordered mesoporous resol-type phenolic resin and the corresponding mesoporous carbon materials were synthesized by using poly(ethylene oxide-b-caprolactone) (PEO-b-PCL) diblock copolymer as a soft template. The self-assembled mesoporous phenolic resin was found to form only in a specific resol concentration range of 40-70â wt % due to an intriguing balance of hydrogen-bonding interactions in the resol/PEO-b-PCL mixtures. Furthermore, morphological transitions of the mesostructures from disordered to gyroid to cylindrical and finally to disordered micelle structure were observed with increasing resol concentration. By calcination under nitrogen atmosphere at 800 °C, the bicontinuous mesostructured gyroid phenolic resin could be converted to mesoporous carbon with large pore size without collapse of the original mesostructure. Furthermore, post-treatment of the mesoporous gyroid phenolic resin with melamine gave rise to N-doped mesoporous carbon with unique electronic properties for realizing high CO2 adsorption capacity (6.72â mmol g-1 at 0 °C).
Assuntos
Carbono/química , Formaldeído/química , Nitrogênio/química , Fenóis/química , Poliésteres/química , Polímeros/química , Adsorção , Varredura Diferencial de Calorimetria , Dióxido de Carbono/química , Formaldeído/síntese química , Microscopia Eletrônica de Transmissão , Fenóis/síntese química , Poliésteres/síntese química , Polímeros/síntese química , Porosidade , Espalhamento a Baixo Ângulo , Triazinas/química , Difração de Raios XRESUMO
A solution phase synthesis of peptide nucleic acid monomers and dimers was developed by using microwave-promoted Ugi multicomponent reactions. A mixture of a functionalized amine, a carboxymethyl nucleobase, paraformaldehyde and an isocyanide as building blocks generates PNA monomers which are then partially deprotected and used in a second Ugi 4CC reaction, leading to PNA dimers. Conformational rotamers were identified by using NMR and MD simulations.
Assuntos
Ácidos Nucleicos Peptídicos/síntese química , Cianetos/síntese química , Cianetos/química , Dimerização , Formaldeído/síntese química , Formaldeído/química , Espectroscopia de Ressonância Magnética , Micro-Ondas , Simulação de Dinâmica Molecular , Ácidos Nucleicos Peptídicos/química , Polímeros/síntese química , Polímeros/químicaRESUMO
Ag nanoparticles (NPs) were loaded onto the surface of phenol formaldehyde resin (PFR) NPs without any reducing agent. The as-synthesized PFR@Ag composites have low cytotoxicity, which makes them promising antibacterial agents. Furthermore, the good fluorescence of PFR could be used for cell imaging.
Assuntos
Antibacterianos/síntese química , Antibacterianos/farmacologia , Formaldeído/síntese química , Formaldeído/farmacologia , Fenóis/síntese química , Fenóis/farmacologia , Polímeros/síntese química , Polímeros/farmacologia , Prata/farmacologia , Antibacterianos/química , Sobrevivência Celular/efeitos dos fármacos , Escherichia coli/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Corantes Fluorescentes/síntese química , Corantes Fluorescentes/química , Corantes Fluorescentes/farmacologia , Formaldeído/química , Células HeLa , Humanos , Fenóis/química , Polímeros/química , Prata/químicaRESUMO
It is well established that adding methanol to water could significantly enhance H2 production by TiO2. Recently, we have found that methanol can be photocatalytically dissociated on TiO2(110) at 400 nm via a stepwise mechanism. However, how molecular hydrogen can be formed from the photocatalyzed methanol/TiO2(110) surface is still not clear. In this work, we have investigated deuterium formation from photocatalysis of the fully deuterated methanol (CD3OD) on TiO2(110) at 400 nm using a temperature programmed desorption (TPD) technique. Photocatalytic dissociation products formaldehyde (CD2O) and D-atoms on BBO sites (via D2O TPD product) have been detected. In addition to D2O formation by heating the photocatalyzed methanol/TiO2(110) surface, we have also observed D2 product formation. D2 is clearly formed via thermal recombination of the D-atoms on the BBO sites from photocatalysis of methanol. Experimental results indicate that D2O formation is more important than D2 formation and that D2 formation is clearly affected by the D2O formation process.
Assuntos
Formaldeído/síntese química , Hidrogênio/química , Metanol/química , Processos Fotoquímicos , Titânio/química , Catálise , Formaldeído/química , Propriedades de SuperfícieRESUMO
We disclose the first catalytic activation of carbohydrates as formaldehyde equivalents to generate acyl anions as one-carbon nucleophilic units for a Stetter reaction. The activation involves N-heterocyclic carbene (NHC)-catalyzed C-C bond cleavage of carbohydrates via a retro-benzoin-type process to generate the acyl anion intermediates. This Stetter reaction constitutes the first success in generating formal formaldehyde-derived acyl anions as one-carbon nucleophiles for non-self-benzoin processes. The renewable nature of carbohydrates, accessible from biomass, further highlights the practical potential of this fundamentally interesting catalytic activation.
Assuntos
Carboidratos/química , Formaldeído/síntese química , Compostos Heterocíclicos/química , Cetonas/química , Metano/análogos & derivados , Catálise , Formaldeído/química , Metano/química , Estrutura MolecularRESUMO
Reaction of CO with H2 on neutral FemSn clusters in a fast flow reactor is investigated both experimentally and theoretically. Single photon ionization at 118 nm is used to detect neutral cluster distributions through time of flight mass spectrometry. FemSn clusters are generated through laser ablation of a mixed iron-sulfur target in the presence of a pure helium carrier gas. A strong size dependent reactivity of (FeS)m clusters toward CO is characterized. The reaction FeS + CO â Fe + OCS is found for the FeS cluster, and the association product Fe2S2CO is observed for the Fe2S2 cluster. Products Fe2S2(13)COH2 and Fe2S2(13)COH4 are identified for reactions of (13)CO and H2 on Fe2S2 clusters: this suggests that the Fe2S2 cluster has a high catalytic activity for hydrogenation reactions of CO to form formaldehyde and methanol. Density functional theory (DFT) calculations are performed to explore the potential energy surfaces for the two reactions: Fe2S2 + CO + 2H2 â Fe2S2 + CH3OH; and Fe2S2 + CO + H2 â Fe2S2 + CH2O. A barrierless, thermodynamically favorable pathway is obtained for both catalytic processes. Catalytic cycles for formaldehyde and methanol formation from CO and H2 on a Fe2S2 cluster are proposed based on our experimental and theoretical investigations. The various reaction mechanisms explored by DFT are in good agreement with the experimental results. Condensed phase iron sulfide, which contains exposed Fe2S2 units on its surface, is suggested to be a good catalyst for low temperature formaldehyde/methanol synthesis.
Assuntos
Monóxido de Carbono/química , Formaldeído/síntese química , Hidrogênio/química , Proteínas Ferro-Enxofre/química , Metanol/síntese química , Catálise , Formaldeído/química , Gases/química , Metanol/química , Teoria Quântica , TermodinâmicaRESUMO
Methanol is the future and clean fuel, and its chemistry on metal surfaces has received much attention. In this paper we explore methanol dissociation on the clean and O or OH covered PdZn(111) that mimics Pd∕ZnO catalyst studied as a promising catalyst for methanol steam reforming, using density functional theory at PW91 level and slab model. Our study demonstrates that unlike the situation on Pd (111), methanol preferentially undergoes the O-H bond scission on the PdZn (111). The presence of O and OH species hinders the C-H bond dissociation, but significantly reduces the O-H bond-breaking barrier. The present results indicate that in the course of methanol steam reforming, methanol first loses the hydrogen atom of the hydroxyl group, forming methoxy. This step is greatly enhanced when there are O and∕or OH species (i.e., after water dissociation happens). Analyses reveal that CH2O is formed mainly from CH3O, not from CH2OH.
Assuntos
Hidróxidos/química , Metanol/química , Oxigênio/química , Paládio/química , Teoria Quântica , Zinco/química , Adsorção , Formaldeído/síntese química , Formaldeído/química , Propriedades de SuperfícieRESUMO
Mannich bases 2a-f derived from 3,4-dimethylphenol (1), formaldehyde and different amines are prepared and subjected to spectral (IR, (1)H and (13)C NMR) and elemental analyses. The inhibition of two human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II, with 1 and synthesized Mannich bases 2a-f and acetazolamide (AAZ) as a control compound was investigated in vitro by using the hydratase and esterase assays. In relation to hydratase and esterase activities of the half maximal inhibitory concentration (IC(50)) and the inhibition equilibrium constants (K(i))values were determined. Only two compounds (2a and 2e)exhibit weak hCA II inhibitory effects on esterase activity. IC(50) and Ki values for 2a and 2e with respect to esterase activity of hCA II are0.88 × 10(3) and 6.3-7.6 µM and 0.44 × 10(3) and 19.0-96.4 µM,respectively. On the contrary, compounds 2b and 2d might be used as CA activators due to increasing esterase activity of hCA I and hCA II isozymes.
Assuntos
Aminas/farmacologia , Inibidores da Anidrase Carbônica/farmacologia , Anidrases Carbônicas/metabolismo , Formaldeído/farmacologia , Xilenos/farmacologia , Aminas/síntese química , Aminas/química , Inibidores da Anidrase Carbônica/síntese química , Inibidores da Anidrase Carbônica/química , Anidrases Carbônicas/isolamento & purificação , Relação Dose-Resposta a Droga , Eritrócitos/enzimologia , Formaldeído/síntese química , Formaldeído/química , Humanos , Estrutura Molecular , Isoformas de Proteínas/antagonistas & inibidores , Isoformas de Proteínas/isolamento & purificação , Isoformas de Proteínas/metabolismo , Relação Estrutura-Atividade , Xilenos/síntese química , Xilenos/químicaRESUMO
Multifunctional Ag@Au@ phenol formaldehyde resin (PFR) particles loaded with folic acids (FA) have been designed for killing tumor cells through photothermy conversion under the irradiation of near-infrared (NIR) light. Possessing the virtue of good fluorescence, low toxicity, and good targeting, the nanocomposite consists of an Ag core, an Au layer, a PFR shell, and folic acids on the PFR shell. The Ag@PFR core-shell structure can be prepared with a simple hydrothermal method after preheating. We then filled the PFR shell with a layer of Au by heating and modified the shell with polyelectrolyte to change its surface charge state. To capture tumor cells actively, FA molecules were attached onto the surface of the Ag@Au@PFR particles in the presence of 1-ethyl-3-(3-dimethly aminopropyl) carbodiimide (EDAC) and N-hydroxysuccinimide (NHS). Owing to the excellent property of Au NPs and Ag NPs as photothermal conversion agents, the Ag@Au@ PFR@FA particles can be utilized to kill tumor cells when exposed to NIR light.
Assuntos
Ácido Fólico/química , Formaldeído/química , Formaldeído/síntese química , Nanopartículas Metálicas/química , Nanopartículas Metálicas/uso terapêutico , Fenol/química , Fenol/síntese química , Fenóis/química , Fenóis/síntese química , Polímeros/química , Polímeros/síntese química , Prata/química , Prata/uso terapêutico , Fotometria , Fototerapia , Espectroscopia de Luz Próxima ao Infravermelho , Succinimidas/químicaRESUMO
A magnetic, sensitive, and selective fluorescence resonance energy transfer (FRET) probe for detection of thiols in living cells was designed and prepared. The FRET probe consists of an Fe(3)O(4) core, a green-luminescent phenol formaldehyde resin (PFR) shell, and Au nanoparticles (NPs) as FRET quenching agent on the surface of the PFR shell. The Fe(3)O(4) NPs were used as the core and coated with green-luminescent PFR nanoshells by a simple hydrothermal approach. Au NPs were then loaded onto the surface of the PFR shell by electric charge absorption between Fe(3)O(4)@PFR and Au NPs after modifying the Fe(3)O(4)@PFR nanocomposites with polymers to alter the charge of the PFR shell. Thus, a FRET probe can be designed on the basis of the quenching effect of Au NPs on the fluorescence of Fe(3)O(4)@PFR nanocomposites. This magnetic and sensitive FRET probe was used to detect three kinds of primary biological thiols (glutathione, homocysteine, and cysteine) in cells. Such a multifunctional fluorescent probe shows advantages of strong magnetism for sample separation, sensitive response for sample detection, and low toxicity without injury to cellular components.
Assuntos
Técnicas de Química Analítica/métodos , Compostos Férricos/química , Formaldeído/química , Ouro/química , Magnetismo , Nanopartículas Metálicas/química , Fenóis/química , Polímeros/química , Compostos de Sulfidrila/análise , Células/química , Compostos Férricos/síntese química , Transferência Ressonante de Energia de Fluorescência , Corantes Fluorescentes/química , Formaldeído/síntese química , Células HeLa , Humanos , Limite de Detecção , Microscopia Eletrônica de Varredura , Fenóis/síntese química , Polímeros/síntese químicaRESUMO
A mild and efficient synthesis of 1-aryl-1-fluoroethenes from benzothiazolyl (aryl)fluoromethyl sulfones and paraformaldehyde, under DBU- or Cs(2)CO(3)-mediated conditions at room temperature, is described. A comparable diethyl fluoro(naphthalen-2-yl)methylphosphonate reagent does not react with paraformaldehyde under these mild conditions. The utility of the methodology for synthesis of terminal α-fluoroalkenes bearing electron-withdrawing functionalities is also shown.
Assuntos
Técnicas de Química Sintética/métodos , Etilenos/síntese química , Flúor/química , Técnicas de Química Sintética/economia , Etilenos/química , Formaldeído/síntese química , Formaldeído/química , Halogenação , Polímeros/síntese química , Polímeros/química , Sulfonas/síntese química , Sulfonas/químicaRESUMO
Density functional theory was used to study the mechanism for the oxidation of methanol to formaldehyde. A vanadium oxide cluster O=V(OH)(3) has been utilized to represent the catalytic system under hydrated conditions, i.e., in the presence of V-OH hydroxyl groups. Two types of methoxy-intermediates have been considered: a penta-coordinate methoxy-intermediate (OH)(4)V(OCH(3)) and a tetrahedral methoxy-intermediate (OH)(2)VO(OCH(3))(H(2)O). The most plausible reaction pathway corresponds to the process involving first the formation of the tetrahedral methoxide, and a subsequent rate-limiting step where hydrogen is transferred from the methoxy groups toward the oxygen atom of the vanadyl V=O site. The reaction mechanism is a typical two-state reactivity process due to a change of the multiplicity (reactive singlet --> product triplet) along the reaction coordinate accompanied by a reduction of the vanadium center from V(V) (d(0)) to V(III) (d(2)). Minimum energy crossing points were localized and possible spin inversion processes are discussed by means of the intrinsic reaction coordinate approach to find the most favorable reaction pathways. The hydration effect is found to be mainly the destabilization of the methoxy intermediates. An alternative reaction pathway with a lower apparent barrier is presented.
Assuntos
Simulação por Computador , Formaldeído/síntese química , Metanol/química , Compostos de Vanádio/química , Catálise , Formaldeído/química , OxirreduçãoRESUMO
One-pot hydrothermal process has been developed to synthesize uniform Te@phenol formaldehyde resin core-shell nanowires with unique fluorescent properties. A synergistic soft-hard template mechanism has been proposed to explain the formation of the core-shell nanowires. The Te@phenol formaldehyde resin core-shell nanowires display unique fluorescent properties, which give strong luminescent emission in the blue-violet and green regions with excitation wavelengths of 270 nm and 402 nm, respectively.
Assuntos
Materiais Biocompatíveis/síntese química , Formaldeído/síntese química , Nanotecnologia/métodos , Nanofios/química , Tamanho da Partícula , Fenóis/síntese química , Polímeros/síntese química , Materiais Biocompatíveis/química , Sobrevivência Celular , Células HeLa , Humanos , Microscopia de Fluorescência , Nanopartículas/química , Nanofios/ultraestrutura , Espectroscopia Fotoeletrônica , Telúrio , Temperatura , Difração de Raios XRESUMO
The successive hydrogenation of CO has been investigated by two methods. The first is hydrogenation of a CO surface. The second is co-injection of CO molecules and H atoms. Both methods have been performed at 3 and 10 K. In the first method, the interaction of H atoms with solid CO at 10 K shows that CO is consumed to form H(2)CO and CH(3)OH. No trace of species such as HCO and CH(3)O is detected. No product was observed when the same experiment was performed at 3 K. In the second method, when H and CO are codeposited at 10 K, HCO and CH(3)O are observed. In fact, the yield of these intermediate species depends on the amount of the H radicals interacting with CO molecules. At 3 K, the presence of H(2) in the solid screens the hydrogenation reaction. This causes a termination for the reaction in the stage of the formation of HCO and H(2)CO. At 10 K, H(2) cannot condense, and the reaction between CO and H is total. In this case, species such as HCO, H(2)CO, CH(3)O, and CH(3)OH are observed.
Assuntos
Monóxido de Carbono/química , Formaldeído/síntese química , Metanol/síntese química , Simulação por Computador , Formaldeído/química , Hidrogenação , Metanol/química , Propriedades de SuperfícieRESUMO
Formaldehyde was detected in dialdehyde carboxymethyl cellulose (DCMC) tanning agent prepared through periodate oxidation of sodium carboxymethyl cellulose (CMC). Formaldehyde was then introduced into leather through DCMC tanning, which poses a potential risk to human health. The formation mechanism of formaldehyde in DCMC was investigated by composition analysis and intermediate identification of DCMC with different polymerization degrees and sugar unit structures. Formaldehyde was derived from the overoxidation of C-6 on the reducing glucose residue of CMC. Moreover, glucose was produced from the concomitant degradation of CMC during oxidation, and then oxidized to liberate formaldehyde. The low degradation degree and high degree of substitution of CMC reduced the possibility of the formation of reducing glucose residue and glucose during oxidation, thereby resulting in low formaldehyde content in DCMC and DCMC-tanned leather. These findings serve as a foundation for the minimization of formaldehyde in DCMC and the development of ecological tanning approach.
Assuntos
Carboximetilcelulose Sódica/química , Celulose/análogos & derivados , Formaldeído/síntese química , Curtume , Configuração de Carboidratos , Celulose/química , Formaldeído/química , OxirreduçãoRESUMO
An imidazolium ionic-liquid-modified phenolic resin (ILPR) was synthesized using 3-aminophenol as a functional monomer, glyoxylic acid as a green cross-linker, and polyethylene glycol 6000 as a porogen. The obtained ILPR showed better extraction of benzoylurea plant hormones thidiazuron and forchlorfenuron than the unmodified phenolic resin because the imidazolium IL provides more interaction modes with the analytes. ILPR, as a tailored adsorbent for solid-phase extraction, was coupled with high-performance liquid chromatography (ILPRâSPEâHPLC) for the simultaneous determination of thidiazuron and forchlorfenuron in cucumbers. Good linearity of the ILPRâSPEâHPLC method was obtained, ranging from 0.0100 to 5.00 µg g-1 with a correlation coefficient (r) ≥ 0.9999. The recoveries of spiked samples ranged from 91.4% to 100.7% with a relative standard deviation of ≤ 6.0%.
Assuntos
Cucumis sativus/química , Formaldeído/química , Imidazóis/química , Líquidos Iônicos/química , Fenóis/química , Compostos de Fenilureia/isolamento & purificação , Polímeros/química , Piridinas/isolamento & purificação , Extração em Fase Sólida/métodos , Tiadiazóis/isolamento & purificação , Cromatografia Líquida de Alta Pressão , Formaldeído/síntese química , Líquidos Iônicos/síntese química , Cinética , Fenóis/síntese química , Polímeros/síntese química , Reprodutibilidade dos TestesRESUMO
In this study, porous magnetic resin grafted chitosan (R-g-Ch) beads were prepared for removal of 4-chlorophenol and phenol from aqueous solutions. The R-g-Ch beads were characterized by vibrating sample magnetometer, Fourier-transform infrared spectroscopy, scanning electron microscopy and thermogravimetry methods. The removal of the phenolic compounds was optimized by varying the experimental conditions. Results herein are well fitted to the pseudo-second order kinetic and Langmuir isotherm. The maximum adsorption capacity of phenol and 4-chlorophenol were found to be 188.6 and 99â¯mg/g, respectively. The thermodynamic studies suggested that the adsorption process was exothermic, irreversible and feasible within the range of 298-318â¯K.