Piezoelectric PVDF-TrFE nanocomposite mats filled with BaTiO3 nanofibers: The effect of poling conditions

BaTiO₃ nanofibers (BT NFs), prepared by electrospinning, were used as a filler for electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanocomposite mats. The phase structure and the effect of poling conditions on the piezoelectric properties of PVDF-TrFE/BT nanocomposites were investigated. The results showed an improved degree of crystallinity (78.6%) and a high β-crystal phase (up to 98.3%) in all electrospun samples, independent of the nanofiber content. The two-step poling method, applying electric fields of opposite polarity, led to significantly improved piezoelectric constants d₃₃ (−31.7 pC N⁻¹), strongly dependent on the added BaTiO₃ nanofibers. The inclusion of piezoelectric ceramic nanofibers into a polymer matrix, easily carried out by means of electrospinning, followed by an ad hoc optimized poling treatment, allowed to develop flexible materials with enhanced piezoelectric properties, potentially exploitable in innovative conversion systems used in wearable and sensing devices.     

Temperature-Dependent NMR and CD Spectra of β-Peptides: On the Thermal Stability of β-Peptide Helices – Is the Folding Process of β-Peptides Non-cooperative?

Temperature-dependent NMR and CD spectra of methanol solutions of a β-hexapeptide and of a β-heptapeptide at temperatures between 298 and 393 K are reported. They establish the fact that the 3₁₄-helical secondary structures of the two β-peptides, 1 and 2 , do not `melt' in the temperature range investigated. This is in sharp contrast to the behavior of the helices of α-peptides and proteins which undergo cooperative unfolding (`denaturing') upon heating. A non-cooperative mechanism is proposed, with a stepwise, rather than an `un-zipping' opening of H-bonded rings (cf. Fig. 6). The experimental results are regarded as evidence that, of the three effects which have been identified as contributing to the stability of β-peptide helices, i.e., H-bonding, hydrophobic interactions, and ethane staggering, the latter one is predominant.     

Proton to hydride umpolung at a phosphonium center via electron relay: a new strategy for main-group based water reduction

Generation of dihydrogen from water splitting, also known as water reduction, is a key process to access a sustainable hydrogen economy for energy production and usage. The key step is the selective reduction of a protic hydrogen to an accessible and reactive hydride, which has proven difficult at a p-block element. Although frustrated Lewis pair (FLP) chemistry is well known for water activation by heterolytic H–OH bond cleavage, to the best of our knowledge, there has been only one case showing water reduction by metal-free FLP systems to date, in which silylene (Si^II) was used as the Lewis base. This work reports the molecular design and synthesis of an ortho-phenylene linked bisborane-functionalized phosphine, which reacts with water stoichiometrically to generate H₂ and phosphine oxide quantitatively under ambient conditions. Computational investigations revealed an unprecedented multi-centered electron relay mechanism offered by the molecular framework, shuttling a pair of electrons from hydroxide (OH⁻) in water to the separated proton through a borane-phosphonium-borane path. This simple molecular design and its water reduction mechanism opens new avenues for this main-group chemistry in their growing roles in chemical transformations.

A (bisborane)triarylphosphine was developed to spontaneously generate H₂ from water under ambient conditions, revealing an unprecedented multi-centered electron relay mechanism for a metal-free umpolung of proton to hydride.     

Transition structure for the retroene-type elimination reaction of propene from allylamines

The transition-state geometries of retroene elimination reactions of propene from allylamines have been calculated by using the semiempirical AM1 method. The most favored geometry resembles a half chair or a flattened boat. It is also found that the transition states are of polar character and that the negative charge on the N atom decreases in the transition state; thus, the reaction is favored by electron donor substituents on the nitrogen atom, as observed experimentally. © 1997 John Wiley & Sons, Inc.     

Numerical Investigation of a MILD Combustion Burner: Analysis of Mixing Field, Chemical Kinetics and Turbulence-Chemistry Interaction

A numerical study of a jet-in-hot coflow (JHC) burner emulating Moderate or Intense Low-oxygen Dilution (MILD) combustion conditions was carried out by solving the Reynolds Averaged Navier-Stokes equations in a two-dimensional axisymmetric domain and using the Eddy Dissipation Concept (EDC) for the turbulence-chemistry interaction treatment. A systematic methodology was used to analyze all possible sources of discrepancies observed between experimental and numerical data, trying to shedding light on the suitability of specific models for MILD combustion. In this regard, the deficiencies that may come from turbulence model or kinetic scheme have been shown by comparative study on four variants of the k-ε model (i.e. the standard, modified, realizable and RNG) together with the Reynolds stress model and three kinetic schemes namely KEE-58, DRM-19 and DRM-22. A variation of an EDC parameter (i.e. increasing the constant of the fine structure residence time) was proposed for better consideration of MILD combustion features and to overcome the over-prediction of peak temperature observed at downstream. In such a manner encouraging results were also obtained for the prediction of major combustion products as well as for CO and OH.     

Reaction Environment Modification in Covalent Organic Frameworks for Catalytic Performance Enhancement

Herein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer‐sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5‐hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1‐methyl‐2‐pyrrolidinone and ionic liquid.     

Iron-Electrocatalyzed C−H Arylations: Mechanistic Insights into Oxidation-Induced Reductive Elimination for Ferraelectrocatalysis

Despite major advances, organometallic C−H transformations are dominated by precious 5d and 4d transition metals, such as iridium, palladium and rhodium. In contrast, the unique potential of less toxic Earth-abundant 3d metals has been underexplored. While iron is the most naturally abundant transition metal, its use in oxidative, organometallic C−H activation has faced major limitations due to the need for superstoichiometric amounts of corrosive, cost-intensive DCIB as the sacrificial oxidant. To fully address these restrictions, we describe herein the unprecedented merger of electrosynthesis with iron-catalyzed C−H activation through oxidation-induced reductive elimination. Thus, ferra- and manganaelectro-catalyzed C−H arylations were accomplished at mild reaction temperatures with ample scope by the action of sustainable iron catalysts, employing electricity as a benign oxidant.     

Electrochemical Monitoring of Saos‐2 Cell Differentiation on Pyrolytic Carbon Electrodes

In this study we establish an electrochemical platform based on two dimensional (2D) pyrolytic carbon electrodes for in vitro analysis of osteoblast differentiation. Electrochemical impedance spectroscopy (EIS) was used to monitor cell adhesion and proliferation, while an electrochemical assay based on square wave voltammetry (SWV) was applied to measure the activity of the differentiation marker alkaline phosphatase (ALP). 2D pyrolytic carbon electrodes were fabricated and used to monitor Saos‐2 cell differentiation for a period of up to 21 days. With this method it was possible to detect a faster increase of ALP activity for cells cultured in medium supplemented with differentiation factors compared to cells cultured in growth medium. This was confirmed by the results obtained with Alizarin Red staining, showing that cells subjected to osteogenic medium went through the entire differentiation process, from proliferation to mineralization. Finally, for the first time, real‐time monitoring of ALP activity combined with continuous EIS monitoring of the same cell culture was achieved using the pyrolytic carbon electrodes.     

Pradimicin-IRD from Amycolatopsis sp. IRD-009 and its antimicrobial and cytotoxic activities

A new polycyclic antibiotic, pradimicin-IRD, was isolated from actinobacteria Amycolatopsis sp. IRD-009 recovered from soil of Brazilian rainforest undergoing restoration area. This molecule is the major compound produced in solid culture media. The new compound was detected by a focused method of precursor ion (high-performance liquid chromatography coupled to tandem mass spectrometer) developed previously to identify unusual aminoglycosyl sugar moieties. The compound was isolated and its structure was, therefore, elucidated by high-resolution mass spectrometry, and 1D and 2D nuclear magnetic resonance experiments. Pradimicin-IRD displayed potential antimicrobial activity against Streptococcus agalactiae (MIC 3.1 μg/mL), Pseudomonas aeruginosa (MIC 3.1 μg/mL) and Staphylococcus aureus (MIC 3.1 μg/mL), and also cytotoxicity against tumour and non-tumour cell lines with IC₅₀ values ranging from 0.8 μM in HCT-116 colon carcinoma cells to 2.7 μM in MM 200 melanoma cells. Particularly, these biological properties are described for the first time for this chemical class.     

A Study of Graphene‐Based Copper Catalysts: Copper(I) Nanoplatelets for Batch and Continuous‐Flow Applications

The use of graphene derivatives as supports improves the properties of heterogeneous catalysts, with graphene oxide (GO) being the most frequently employed. To explore greener possibilities as well as to get some insights into the role of the different graphenic supports (GO, rGO, carbon black, and graphite nanoplatelets), we prepared, under the same standard conditions, a variety of heterogeneous Cu catalysts and systematically evaluated their composition and catalytic activity in azide–alkyne cycloadditions as a model reaction. The use of sustainable graphite nanoplatelets (GNPs) afforded a stable Cu^I catalyst with good recyclability properties, which are compatible with flow conditions, and able to catalyze other reactions such as the regio‐ and stereoselective sulfonylation of alkynes (addition reaction) and the Meerwein arylation (single electron transfer process).