Self-catalyzed Mechanism Research Articles

The impact of the reaction atmosphere on the additive-free growth of Mg2B2O5 nanorods

Although many routes for the production of magnesium borates (Mg2B2O5, Mg3B2O6 and MgB4O7) are well known, the synthesis of single phases is still a challenge. Secondary phases such as other magnesium borates and MgO are commonly observed in the final product. In order to produce high quality Mg2B2O5 nanorods, we developed a study analyzing the influence of different reaction atmospheres on the synthesis of magnesium borate in a tubular furnace. Through this investigation, a strong correlation between the produced borate phases and the composition of the atmospheres was verified. The sample produced under Ar presented Mg2B2O5, Mg3B2O6 and MgO in molar percentages of 36.82%, 35.34% and 27.84% respectively, while the sample synthesized under H2 is composed of 18.9 mol% of Mg3B2O6 and 81.1 mol% of MgO. Mg2B2O5 nanorods with elevated structural homogeneity were successfully produced under hydrogen and acetonitrile. Under this atmosphere only Mg2B2O5 and Mg3B2O6 were produced, with the formation of Mg2B2O5 nanorods representing 87.5 mol% of the sample. The nanorods growth followed a solution-solid-solid (SSS) self-catalyzed mechanism. This synthesis was performed without the assistance of external agents such as catalysts or surfactants, guaranteeing elevated chemical purity for applications in the optical and electronic field. Reflectance and impedance analyses presented a wide range of light absorption and a dielectric character for the nanorods. The produced structure would be very interesting for theranostic applications.

Lewis Acid–Base Bifunctional Crystals with a Three-Dimensional Framework for Selective Coupling of CO2 and Epoxides under Mild and Solvent-Free Conditions

Two Lewis acid–base bifunctional, isostructural metal–organic frameworks (MOFs), [Zn3(Hbtc)2(atz)2]·CH3CN·2CH3OH (MOF-1) and [Co3(Hbtc)2(atz)2]·H2O·2DMF (MOF-2), containing NH2 groups and four-coordinated metal sites were fabricated successfully, and the structures were thoroughly characterized by X-ray crystallography, powder X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and N2 adsorption/desorption techniques. Satisfactorily, the novel MOFs with a three-dimensional framework were highly efficient and stable heterogeneous catalysts for selective fixation of CO2 to cyclic carbonates under mild conditions in the absence of solvent. The influences of various reaction parameters on catalytic performance were systematically investigated. Also the catalysts showed excellent versatility to epoxides with different substituents and could be easily recyclable with high activity. Additionally, the self-catalyzed mechanism as well as synergistic mechanism with tetrabutylammo...

Preparation and growth mechanism of one-dimensional NdB6 nanostructures: nanobelts, nanoawls, and nanotubes

1D NdB6 nanostructures (nanobelts, nanoawls, and nanotubes) have been synthesized through a chemical vapor deposition (CVD) process with a self-catalyzed mechanism.

From Formamide to Adenine: A Self-Catalytic Mechanism for an Abiotic Approach

Mechanisms for abiotic reaction pathways from formamide (H2NCHO) to adenine are presented herein. Formamide is a simple C1 building block hypothesized to be a precursor to many protometabolic compounds. On the basis of a step-by-step mechanism of the reaction pathways, formamide is suggested to be more reactive in addition reactions than HCN. In addition to its simplicity, the formamide self-catalyzed mechanism is energetically (kinetically) more viable than either a water-catalyzed mechanism or noncatalyzed processes. Moreover, this self-catalyzed mechanism accounts for the yields of purine and adenine previously observed in experiments. This mechanism may elucidate processes that were vital for the emergence of life on the early earth.

Facile preparation of hollow amino-functionalized organosilica microspheres by a template-free method

A facile method was developed to fabricate hollow amino-functionalized organosilica microspheres based on the hydrolysis and condensation of 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) in an aqueous system without an additional template and catalyst. The hollow hybrid organosilica microspheres obtained have been characterized by scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption measurements. The results of Fourier transform infrared spectroscopy, solid-state NMR spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis displayed the composition of the synthesized hollow microspheres and the presence of amino groups on the surface. A self-templated and self-catalyzed mechanism for the formation of the hollow microspheres is proposed: the protonated APTES acts as both a catalyst for the reaction and a stabilizer for the hydrophobic precursor droplets, while the droplets themselves act as soft templates, and the consumption of the precursors leads to the formation of a hollow structure. The morphology and the size distribution of the organosilica microspheres can be controlled by tuning the composition of the precursors, and the stirring speed, as well as the reaction temperature. The large cavity with an open hole on the shell and the reactive amino groups on the surface of the hybrid organosilica microspheres promise many potential applications. Examples of employing the microspheres as adsorbents and phase change microcapsules have been presented.

Preformulation stability study of the EGFR inhibitor HKI-272 (Neratinib) and mechanism of degradation

The stability in solution of HKI-272 (Neratinib) was studied as a function of pH. The drug is most stable from pH 3 to 4, and degradation rate increases rapidly around pH 6 and appears to approach a maximum asymptotic limit in the range of pH 812. Pseudo first-order reaction kinetics was observed at all pH values. The structure of the major degradation product indicates that it is formed by a cascade of reactions within the dimethylamino crotonamide group of HKI-272. It is assumed that the rate-determining step is the initial isomerization from allyl amine to enamine functionality, followed by hydrolysis and subsequent cyclization to a stable lactam. The maximum change in degradation rate as a function of pH occurs at about pH 6, which corresponds closely to the theoretical pKa value of the dimethylamino group of HKI-272 when accounting for solvent/temperature effects. The observed relationship between pH and degradation rate is discussed, and a self-catalyzed mechanism for the allylamine-enamine isomerization reaction is proposed. The relevance of these findings to other allylamine drugs is discussed in terms of the relative stability of the allylic anion intermediate through which, the isomerization occurs.

Reevaluating gel-forming mucins' roles in cystic fibrosis lung disease

The existence of mucus plugs, containing mucins, bacteria, and neutrophils, blocking the lower airways in the lung of cystic fibrosis (CF) patients has raised the possibility that production of “abnormal” mucins is a critical characteristic of this disease. The molecular nature, if any, of this abnormality is unknown. Recent studies suggest that CF lung disease progression is characterized by an early phase in which airway surface liquid (ASL) increased dehydration is accompanied by altered pH and levels of reduced glutathione (GSH). In a later phase, bacterial infection and neutrophil invasion lead to increased ASL of concentrations myeloperoxidase and hypochlorous acid (HOCl). Independent studies indicate that gel-forming mucins, the key components of airway mucus, form disulfide-linked polymers through a pH-dependent, likely self-catalyzed mechanism. In this article, we present the hypothesis that increased mucus concentration (dehydration) and altered pH, and levels of GSH, myeloperoxidase, and/or HOCl result in the extracellular formation of additional interchain bonds among airway mucins. These novel interactions would create an atypical mucin network with abnormal viscoelastic and adhesive properties.

The mechanism of protein splicing and its modulation by mutation.

Protein splicing results in the expression of two mature proteins from a single gene. After synthesis of a precursor protein, an internal segment (the intein) is excised and the external domains are joined together. A self-catalyzed mechanism for this cleavage-ligation reaction is presented, based on mutagenesis data and analysis of splicing intermediates. Mutations were used to block various steps in the protein splicing pathway, allowing each isolated step to be studied independently. A linear ester intermediate was identified and functional roles for the four conserved splice junction residues were determined. Understanding the mechanism of protein splicing provides a basis for protein engineering studies. For example, inteins can be constructed which fail to splice, but instead cleave the peptide bond at a chosen splice junction.