Low Dipole Moment Research Articles

Dissolved ammonia catalyzes proto-dolomite precipitation at Earth surface temperature

Marine carbonate rocks are the major reservoir of carbon through CaCO3 and CaMg(CO3)2 precipitation extracting CO2/HCO3- from the atmosphere/oceans; hence dolomite is one of the major sinks in the global carbon cycle. Most ancient dolomite has been considered as mainly precipitated under Earth surface conditions. Previous studies have demonstrated that microbes can mediate dolomite formation. However, the “microbial dolomite” model is not sufficient to explain the dolomite that shows no or little evidence of a microbial origin. Although attempted for decades, the synthesis of inorganically-produced dolomite at normal temperatures (<50 °C) has been relatively unsuccessful. Hence, this "dolomite enigma" has been one principal research focus this century. Here we demonstrate that NH3 catalyzes proto-dolomite precipitation inorganically with higher Mg/Ca molar ratios and CO32- activity at normal temperatures of 30 °C and 40 °C. NH3 dissolution increases the alkalinity of the solution and transformes into NH4+ ions, which prefer to bond with H2O on Mg[(H2O)6]2+ rather than free H2O, thus releasing Mg2+ to facilitate proto-dolomite nucleation. Furthermore, the low dielectric constant and low dipole moment allow NH4+ absorbed on crystal surfaces to lower the energy barrier of Mg[(H2O)6]2+ dehydration, promoting proto-dolomite nucleis growth. The system for proto-dolomite precipitation in our experiments closely simulates the natural aqueous environment. This study brings new insights to understanding the mechanisms of dolomite precipitation in natural waters.

Molecular guidelines for promising antimicrobial agents

Antimicrobial resistance presents a pressing challenge to public health, which requires the search for novel antimicrobial agents. Various experimental and theoretical methods are employed to understand drug-target interactions and propose multistep solutions. Nonetheless, efficient screening of drug databases requires rapid and precise numerical analysis to validate antimicrobial efficacy. Diptool addresses this need by predicting free energy barriers and local minima for drug translocation across lipid membranes. In the current study employing Diptool free energy predictions, the thermodynamic commonalities between selected antimicrobial molecules were characterized and investigated. To this end, various clustering methods were used to identify promising groups with antimicrobial activity. Furthermore, the molecular fingerprinting and machine learning approach (ML) revealed common structural elements and physicochemical parameters in these clusters, such as long carbon chains, charged ammonium groups, and low dipole moments. This led to the establishment of guidelines for the selection of effective antimicrobial candidates based on partition coefficients (logP) and molecular mass ranges. These guidelines were implemented within the Reinforcement Learning for Structural Evolution (ReLeaSE) framework, generating new chemicals with desired properties. Interestingly, ReLeaSE produced molecules with structural profiles similar to the antimicrobial agents tested, confirming the importance of the identified features. In conclusion, this study demonstrates the ability of molecular fingerprinting and AI-driven methods to identify promising antimicrobial agents with a broad range of properties. These findings deliver substantial implications for the development of antimicrobial drugs and the ongoing battle against antibiotic-resistant bacteria.

Controlling collisional loss and scattering lengths of ultracold dipolar molecules with static electric fields

Trapped samples of ultracold molecules are often short-lived because close collisions between them result in trap loss. We investigate the use of shielding with static electric fields to create repulsive barriers between polar molecules to prevent such loss. Shielding is very effective even for RbCs, with a relatively low dipole moment, and even more effective for molecules such as NaK, NaRb, and NaCs, with progressively larger dipoles. Varying the electric field allows substantial control over the scattering length, which will be crucial for the stability or collapse of molecular Bose-Einstein condensates. This arises because the dipole-dipole interaction creates a long-range attraction that is tunable with electric field. For RbCs, the scattering length is positive across the range where shielding is effective because the repulsion responsible for shielding dominates. For NaK, the scattering length can be tuned across zero to negative values. For NaRb and NaCs, the attraction is strong enough to support tetra-atomic bound states, and the scattering length passes through resonant poles where these states cross threshold. For KAg and CsAg, there are multiple bound states and multiple poles. For each molecule, we calculate the variation of the scattering length with field and comment on the possibilities for exploring new physics. Published by the American Physical Society 2024

Fine-tuning of organic optical double-donor NLO chromophores with DA-supported functional groups.

New strategic chromophores with updated fine-tuning of previously reported BLD1 and BLD3 chromophores were designed. BLD1 and BLD3 have silicon functional groups on the donor unit, and the bridge has a good chance of self-assembling, so in the present study we fine-tuned the isolating groups to the bulky cyclic alkene to improve their dipole moment and organic electro-optic (OEO) properties as well. To demonstrate the impact of cyclic alkenes on the electron-donating groups in sensible NLO chromophore designs, a thorough analysis and comparison of the chromophore synthesis, UV-Vis calculations, solvatochromic behavior of the chromophore, DFT quantum mechanical calculations, thermal stabilities, and much lower dipole moments was conducted.

Unveiling the Antifouling Potential of Stabilized Poly(phosphorus ylides).

Zwitterionic polymers have emerged as highly attractive building blocks for antifouling coatings in biomedical applications. Notably, these polymers offer effective alternatives to the widely used poly(ethylene glycol) (PEG), which has raised concerns regarding its immunotoxicity and the development of PEG-specific antibodies. Polymeric ylides, a largely overlooked class of zwitterionic polymers, have been reported as effective antifouling scaffolds. However, the reported subclasses, poly(sulfur ylides) and N-oxides, lack structural diversity and chemical variability. In this study, we present the synthesis and characterization of polymeric phosphorus ylides as an unexplored class of poly(ylides) with significantly increased structural diversity, which is of high value when designing future ylide-based antifouling materials. Our findings demonstrate that, owing to their low dipole moments and hydration layers, these polymeric phosphorus ylides significantly reduce bacterial attachment. Furthermore, we observe selective toxicity toward bacteria rather than mammalian cells. The bactericidal nature of poly(phosphorus ylides), coupled with their expanded chemical space, provides a distinct advantage over existing materials, including zwitterionic polymers from betaine scaffolds. We anticipate that these unexplored structures will broaden the scope of antifouling applications for poly(ylides).

Sustainable utilization of anthraquinone-rich Rheum officinale as electron shuttle in microbial fuel cell: Strategy for stimulating monohydric phenols degradation and bioelectricity generation

In an aim to completely degrade refractory phenolic compounds for effective wastewater treatment, a sustainable strategy using anthraquinone-rich herbal plant contents as electron shuttles is presented. This study is the first attempt of treating four different chemical structures of monohydric phenols, while simultaneously generate low-carbon electricity in a microbial fuel cell. An electron shuttle-mediated strategy was introduced to investigate the effect of electron shuttle against the degradation of phenolic pollutants and bioelectricity generation, by employing Rheum officinale extract as electron shuttle. Results revealed that there was a two-fold increase in chemical oxygen demand (COD) removal, degradation extent of phenol and cresol isomers, output voltage and power density of MFC, compared to the mediator-free MFC system. The degradation of phenol yielded higher COD removal, degradation efficiency, output voltage and power generation over cresol isomers, with and without the application of electron shuttle. A complete removal of COD and phenol, with output voltage of 620.06 mV and power density of 252.49 mW/m2 were obtained. Phenol outperformed cresol isomers with regard to its sole activating hydroxy (−OH) group, lower dipole moment and higher electronic conductivity (8.53 mS/cm). Conversely, meta-cresol exhibited the lowest removal efficiency and power generation, ascribed to greater inductive influence of methyl group in meta position on the dissociation energy of the − OH group. Moreover, detection of the phenolic intermediates by gas chromatograph-mass spectrometer analysis was conducted, and detailed degradation pathways were presented.

Exploring phosphoryl oxygen basicity in U(VI) complexation: A comparative study from trialkyl phosphate to phosphine oxide.

The conventional argument that extraction efficiency depends on the "basicity of the phosphoryl oxygen" is thoroughly examined in this study. The analysis involves studying the electronic structures of various ligands, such as phosphate, phosphonate, phosphinate, and phosphine oxide, as well as variations in their alkyl chain length, and their corresponding uranium complexes. The studies revealed a significant amount of destabilizing strain and steric repulsion for ligands having longer alkyl chains upon complexation. A considerable amount of stabilizing orbital and dispersion interactions compensate for these repulsions, forming stable complexes. Dispersion interactions become more significant upon chain elongation and are mainly responsible for the preference for U(VI) metal ions by ligands with lengthy alkyl chain units. The preference of phosphine oxide ligands for U(VI) is analyzed within the context of enhanced orbital interactions resulting from the energetically close donor (ligand) and acceptor (metal nitrate) orbitals. Additionally, dispersion-based interactions also become significant, especially with larger chain lengths. The electronegative environment around the phosphorus atom, along with the existence of low-dipole moment structures, is also examined in relation to their possible role in solvent extraction and their influence on the selectivity of ligands for uranyl species.

Discovery of the Elusive Carbonic Acid (HOCOOH) in Space

A quarter century after the detection of the last interstellar carboxylic acid, acetic acid (CH3COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic center molecular cloud G+0.693–0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also directly identified several pairs of unblended lines in the astronomical data (between 75 and 120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of N = (6.4 ± 0.4) × 1012 cm−2, which yields an abundance with respect to molecular H2 of 4.7 × 10−11. Meanwhile, the extremely low dipole moment (about 15 times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H2 of ≤1.2 × 10−9, which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis/cis-trans ratio of ≤25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis-formic acid. Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the solar system, which could be inherited during the star formation process.

Determination of the solubility profile of isophthalic acid in some aqueous solutions of betaine-based deep eutectic solvents: Study the extent of H-bonding interactions between starting materials of deep eutectic solvents in aqueous medium

The equilibrium solubility of isophthalic acid (IPA) in three aqueous solutions of betaine/propylene glycol (Bet/PG, 1:5 M ratio), betaine/ethylene glycol (Bet/EG, 1:3 M ratio) and betaine/glycerol (Bet/Gly, 1:3 M ratio) deep eutectic solvents (DESs) (1) was determined experimentally by utilizing a shake-flask method at 293.15–313.15 K covering the whole composition range at atmospheric pressure (≈85 kPa). For three investigated systems, an increase in solubility was observed by decreasing water mass fraction; so that, the lowest and highest solubilities were in water at 293.15 K and pure DESs at 323.15 K, respectively. Also, the mixtures containing PG presented the higher values of the solubility than that of EG or Gly which may be attributed to its lower dipole moment and dielectric constant (2.27 D, 32.0) than the others. By representation the derived equilibrium solubilities with models of Jouyban-Acree, Jouyban-Acree-van't Hoff, NRTL and Wilson a maximum overall mean relative deviation of 15.9% was achieved. Moreover, the solubilities of IPA in ternary (Bet + PG, EG or Gly + water) mixtures at 298.15 were measured to investigate the extent of H-bonding interactions of Bet with PG, EG or Gly into DESs in the presence of water by comparing IPA solubility data for each binary (DES + water) system and the corresponding ternary mixtures. The results suggested that the H-bonding interactions between two components of DESs were disappeared when the water content was exceeded 60% (g/g). This result more explored by recording 1H NMR spectra of diluted DESs with deuterium dioxide. Eventually, an endothermic and enthalpy-driven process in most mixtures was determined by thermodynamic analysis of IPA dissolution and mixing processes based on the modified van't Hoff equation.

Impact of symmetry breaking on the performance of non-fullerene acceptors (NFAs) for photo and thermally stable organic solar cells (OSCs): A DFT-based interrogation and investigation

Simultaneous enhancement in the fill factor (FF) and power conversion efficiency (PCE) is a crucial task for the development of photovoltaic (PV) devices. In addition, symmetrical acceptor molecules lack photo and thermal stability due to low extinction coefficient and dipole moment. Breaking of symmetry in typical fullerene-free acceptors brings high values of dipole moments along with crystalline features. In this regard, a series of new acceptor molecules have been designed by deep end-capped remodeling of the IPC-BEH-IC2F. Newly remodeled systems disclosed high values of electronic charge shifting and perfect molecular packing. The impact of symmetry breaking is examined through density functional theory (DFT) and time-dependent density functional theory (TDDFT) at CAM-B3LYP/6-311G(d,p) level. Photovoltaic and geometric aspects like frontier molecular orbitals (FMOs), excitation energy, open circuit voltage (Voc), FF%, and PCE have been computed theoretically. Reshaped systems expressed high mobilities of the electrons and holes towards the metal electrodes together with easy excitation of the exciton. High Voc enhances the FF% and PCE in the SGS-1 to SGS-4. Results of all analyses showed that SGS-1 to SGS-4 are well-designed systems for the development of the highly efficient active layer for OSCs.

Global Geomagnetic Field Evolution From 900 to 700 ka Including the Matuyama‐Brunhes Reversal

AbstractPolarity reversals and excursions are the most significant geomagnetic field changes generated in the liquid outer core of the Earth, therefore studying them helps understand geodynamo processes. This study examines the Matuyama‐Brunhes (MB) reversal using a new reconstruction of the global geomagnetic field based on paleomagnetic data, termed Global Geomagnetic Field Model for the MB reversal (GGFMB). GGFMB covers 900–700 ka, including late Matuyama and early Brunhes. This allows us to also investigate the Kamikatsura excursion (ca. 888 ka). The model is based on 38 high‐quality paleomagnetic sediment records with age control mostly independent of the magnetic signal. GGFMB suggests that the MB reversal began about ∼799 ka, when non‐dipole field components increased and the axial dipole component decreased. The transitional fields first appeared on Earth's surface in the high‐latitude southern hemisphere and equatorial regions. The minimum dipole strength was reached around 780 ka and the axial dipole changed sign. After ∼10 Kyr, the field stabilized in the normal polarity of the early Brunhes. The MB reversal lasted ∼29 Kyr (from 799 to 770 ka) and had slower rate of dipole decay than recovery as well as lower dipole moment for several millennia before than after the reversal. According to GGFMB, the dipole moment during the Kamikatsura excursion was approximately half that of the current field and it was a regional excursion observed only over eastern Asia and North America. Our sediment data collection is heavily biased toward the northern hemisphere, thus more southern hemisphere records are needed to demonstrate GGFMB's robustness in this region.

Cysteine as an Alternative Eco-Friendly Corrosion Inhibitor for Absorption-Based Carbon Capture Plants.

Inorganic corrosion inhibitors are commonly applied to mitigate severe corrosion in absorption-based carbon capture plants. They are, however, not environmentally friendly, posing a health risk, harming the environment, and making chemical handling and disposal costly. Therefore, this study evaluated the corrosion inhibition performance of an amino acid, namely cysteine, with the aim of providing an eco-friendly alternative to the commercial inorganic corrosion inhibitors. Electrochemical and weight loss corrosion measurements showed that cysteine was effective in protecting carbon steel at all process operating conditions. At 80 °C, a 500 ppm cysteine could provide up to 83% and 99% inhibition efficiency under static and dynamic flow conditions, respectively. Its inhibition efficiency could be improved when the cysteine concentration, solution temperature, and flow condition were altered. Cysteine was an anodic corrosion inhibitor and underwent spontaneous, endothermic, and combined physical and chemical adsorption that followed the Langmuir adsorption isotherm model. The quantum chemical analysis indicated that cysteine had a high reactivity with metal surfaces due to its low energy gap and high dipole moment. The EDX analysis revealed a significant sulphur content on the metal substrate, indicating that cysteine's mercapto group played an integral role in forming an effective adsorption layer on the metal interface.

Theoretical Analysis of the Role of Water in Ligand Binding to Cucurbit[n]uril of Different Sizes.

The role of water in host-ligand binding was investigated using a combination of molecular dynamics simulation and three-dimensional reference interaction site model theory. Three different hosts were selected (CB6, CB7, and CB8). Six organic molecules were used as representative ligands: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), cyclopentanone (CPN), and pyrrole. From the binding free energy and its components, we divided the ligands into two groups: those with relatively small molecular size (DMSO, DMF, acetone, and pyrrole) and those with relatively large molecular size (DBO and CPN). We established that the solvent water in the CB6 cavity can be completely displaced by small ligands, resulting in a greater binding affinity compared with larger CBs, except in the case of the small pyrrole ligand, due to outstanding intrinsic properties such as the relatively high hydrophobicity and low dipole moment. In the case of the large ligands, the solvent water can be displaced by DBO and CPN in both CB6 and CB7; there were similar tendencies in their binding affinities, with the greatest affinity in the CB7 complexes. However, the tendencies of the binding affinity components are completely different due to the difference between the complex structure and the solvation structure when a ligand binds with a CB structure. The binding affinities suggest that the size fit between the ligand and CB cannot guarantee the greatest binding affinity gain because the binding structure and intrinsic properties of CB and ligand equally play a crucial role.

Tuning Perovskite Surface Polarity via Dipole Moment Engineering for Efficient Hole-Transport-Layer-Free Sn-Pb Mixed-Perovskite Solar Cells.

Post-treatment has been recognized as one of the effective methods for passivating the underlying defects in perovskite solar cells (PSCs), but little attention has been paid to how to pick suitable passivation agents with diverse isomers for efficient PSCs, particularly for the tin-lead (Sn-Pb) mixed PSCs. Here, we introduce the dependence of the power conversion efficiency (PCE) on a dipole moment for surface passivator screening, in which we chose three trifluoromethyl-phenylethylamine hydroiodide (CF3-PEAI) isomers as surface-treatment materials for hole-transport-layer-free (HTL-free) Sn-Pb mixed PSCs. The different positions of the -CF3 group for the CF3-PEAI isomer result in different dipole moments, which influences the interaction between CF3-PEAI and lead iodide. The para position CF3 with the highest dipole moment exhibits a higher PCE than the ortho-position with a lower dipole moment, which is attributed to the large dipole moment on the surface that could tune the surface polarity from p-type to n-type, facilitating electron charge transport in the HTL-free Sn-Pb mixed PSCs. An ultrathin 2D layer is formed on the perovskite surface to passivate the surface defects, which is responsible for the enhancement of the PCE and stability of the PSCs. As a result, the open-circuit voltage (VOC) of the device is improved from 0.775 to 0.824 V, yielding a champion PCE of 20.17%, which is one of the highest PCEs among the reported HTL-free Sn-Pb mixed PSCs. The device also shows improved stability with remaining 75% of its initial PCEs after storage in N2 for 700 h.

Toward the design of inorganic–organic hybrid Ir(III) complexes containing borazine and benzene ligands with excellent second-order NLO responses: An appropriate substitution and π-conjugated extension

The high nonlinear optical (NLO) efficiency and good chemical stability render inorganic–organic hybrid materials widely applied in NLO filed. In this paper, we theoretically design a sequence of new cationic Ir(III) complexes based on parent complex Ir[(C^N)2(N^N)]+ (C^N = 2-phenylpyridine, N^N = 2,2′-bipyridine) through substituting pyridine by borazine ligands or extending borazine/benzene ligands on C^N/N^N position. The geometric and electronic structures, second-order NLO properties and absorption spectrum are evaluated by employing density functional theory (DFT) and time-dependent DFT methods. All designed complexes have smaller HOMO-LUMO energy gaps (0.74–1.82 eV) than parent complex (2.78 eV). N-5 (with borazine-benzene-borazine π-conjugated long chain on N^N ligands) has an unusually small Egap of 0.74 eV which may facilitate an easier electronic transition than other complexes. Interestingly, introducing borazine ligands on parent complex can increase first hyperpolarizability (βtot), but further addition of borazine not lead to positive effect on increasing βtot values. Hybridizing borazine and benzene ligands significantly improve the second-order NLO properties. Thereinto, the maximum βtot of N-5 is found to be 27,648 a.u. which is about 22 times larger than parent complex. The origin of largest βtot values can be reasonably explained by the two-level model due to low transition energy and high transition dipole moment. Further, the UV–Vis spectrum analysis is performed for all complexes, indicating that substituting or hybridizing inorganic and organic ligands are feasible way to make the maximum absorption wavelength red-shifted toward longer wavelength. Our proposed complexes may be used as efficient infrared (IR) NLO materials because of there is no obvious absorption detected in the IR region. This work may offer valuable guidelines for designing high-performance second-order NLO materials.

Mass transfer kinetics and quality evaluation of tomato seed oil extracted using emerging technologies

The Present study was conducted to extract tomato seed oil using emerging technologies which include moderate electric field (MEF), low temperature microwave (MW), radio-frequency (RF), power ultrasound (US) and combined low temperature microwave-power ultrasound (MWUS) at different solid to liquid (S/L) ratio and power level. A green solvent (ethanol: ethyl acetate) was used to extract the oil from tomato seed and a mass transfer kinetic study was studied to find the extraction kinetics and effect of different treatments. MWUS assisted extracted oil was observed to have the highest extraction yield (23.07%) as well as the best quality of oil extracted. The extracted oil using MWUS treatment was mainly composed of PUFA (Linoleic acid), MUFA (Oleic acid) and Stearic acid. Low temperature microwave-ultrasound assisted extraction (MUAE) increased the linoleic, stearic and oleic acid content by 30.91, 5.16 and 7.29% respectively in tomato seed oil composition compared to the conventional Soxhlet extraction (SXE) method. Industrial relevanceThe novel ‘Low temperature microwave-ultrasound assisted extraction (MUAE)’ technology presents a promising result combination of emerging technology for the extraction of oil. The impact of low temperature dipole moment of microwave followed by low intensity ultrasound cavitation leads to the breakdown of the tomato seed matrix. Further, this combination improved the extraction yield although the solvent used very lower solubility compared to conventional solvents. The quality of the extracted oil following MUAE technology was found to be much better than conventional extraction. Hence this combination presents a good scope for application in the food industry, with good commercial value and being environmentally friendly makes it more acceptable.

Comparative study of dihydroxybenzene isomers degradation and bioelectricity generation using CuO as cathodic catalyst in double chambered microbial fuel cell

A double chambered microbial fuel cell (MFC) showed enormous capacity in the simultaneous degradation of synthetic wastewater and dihydroxybenzene isomers (catechol, resorcinol and hydroquinone) and concurrently with bioelectricity generation. Operating parameter such as effect of catalyst on MFC system was evaluated using bare carbon plate and copper (II) oxide (CuO) loaded carbon plate as cathodes, respectively, in terms of chemical oxygen demand (COD) and dihydroxybenzene isomers removal efficiency, maximum voltage output and power density. Results revealed that the application of CuO loaded carbon plate was more effective in the COD removal of synthetic wastewater in the anodic chamber and degradation of dihydroxybenzene isomers in the cathodic chamber. Compared with the bare carbon plate as cathode, the COD removal efficiency of synthetic wastewater, removal rate of dihydroxybenzene isomers and maximum voltage output increased 20, 100 and 31 %, respectively, when CuO was applied as cathodic catalyst. Among the dihydroxybenzene isomers, hydroquinone exhibited the best performance in both absence and presence of catalyst in the MFC. The position of the substituent of hydroxyl groups possessed significant effect on the reaction rate, reactivity and conductivity of dihydroxybenzene isomers. Hydroquinone was more susceptible to be degraded than that of catechol and resorcinol due to its lower dipole moment which eased the bond cleavage. The intermediate products of degradation of catechol, resorcinol and hydroquinone were determined using gas chromatograph-mass spectrometer and the degradation pathways were proposed.

Effect of the TrFE Content on the Crystallization and SSA Thermal Fractionation of P(VDF-co-TrFE) Copolymers.

In this contribution, we study the effect of trifluoro ethylene (TrFE) comonomer content (samples with 80/20, 75/25, and 70/30 VDF/TrFE molar ratios were used) on the crystallization in P(VDF-co-TrFE) in comparison with a PVDF (Poly(vinylidene fluoride)) homopolymer. Employing Polarized Light Optical Microscopy (PLOM), the growth rates of spherulites or axialites were determined. Differential Scanning Calorimetry (DSC) was used to determine overall crystallization rates, self-nucleation, and Successive Self-nucleation and Annealing (SSA) thermal fractionation. The ferroelectric character of the samples was explored by polarization measurements. The results indicate that TrFE inclusion can limit the overall crystallization of the copolymer samples, especially for the ones with 20 and 25% TrFE. Self-nucleation measurements in PVDF indicate that the homopolymer can be self-nucleated, exhibiting the classic three Domains. However, the increased nucleation capacity in the copolymers provokes the absence of the self-nucleation Domain II. The PVDF displays a monomodal distribution of thermal fractions after SSA, but the P(VDF-co-TrFE) copolymers do not experience thermal fractionation, apparently due to TrFE incorporation in the PVDF crystals. Finally, the maximum and remnant polarization increases with increasing TrFE content up to a maximum of 25% TrFE content, after which it starts to decrease due to the lower dipole moment of the TrFE defect inclusion within the PVDF crystals.

Hybrid Electrocatalysts Composed of PtSn, Ru or PtRu Nanoparticles for Low-Temperature Oxidation of Dimethyl Ether Fuel

The science and technology of proton-exchange membrane (PEM) low-temperature fuel cells is a subject of intense during recent years, particularly with use of hydrogen gas due to its molecular simplicity and fast kinetics of its electrooxidation. However, there are still many fundamental problems to be resolved with respect to generation of pure hydrogen and related pollution side effects, the low density and safety of hydrogen storage and distribution. Thus, there are parallel studies involving such simple organic molecules as methanol, formic acid or ethanol as substitute fuels for a wide range of potential applications. Among important obstacles are slow kinetics of electrocatalytic oxidations of fuels and insufficient durability of operation of catalysts that includes poisoning of active sites by strong adsorption of the reaction intermediate products (e.g. CO-type adsorbates), in addition the fuel cross-over through the membrane, which depolarizes the cathode and decreases its activity. While methanol, which has been the most extensively studied, faces the problem of toxicity and challenges mentioned above, the low electrocatalytic efficiency of the formic acid oxidation (only 2-electron-process) is complicated by corrosion phenomena. When it comes to the electrooxidation of ethanol, extra problems concern difficulty of the strong C-C bond breaking and excessive formation of undesirable intermediate products, acetaldehyde and acetic acid. Dimethyl ether (DME), or methoxymethane having formula CH3OCH3, is the simplest ether, and it can be considered as an isomer of another small organic molecule, ethanol, but with a different functional group. DME is a colorless gas that has been demonstrated in a variety of fuel applications, e.g. as an aerosol propellant or substitute for propane in LPG. DME can be viewed as the synthetic second generation biofuel, which can be produced from lignocellulosic biomass biogas or methane from agricultural waste. With respect to potential applications in low-temperature fuel cells, DME could be an attractive simple fuel due to its high energy density, low toxicity, liquefied easy storage, as well as the molecule’s low dipole moment that should diminish crossover through Nafion membrane, when compared to methanol, ethanol and formic acid. The stoichiometric complete electrochemical oxidation of DME requires three H2O-molecules, produces two CO2-molecules, and yields as many as twelve electrons. Obviously the multi-electron and multi-proton electrode process are complex and composed of distinct and competing reaction pathways and, thus, they are subject to kinetic limitations. The main constraints related to application of common Pt-based catalysts (e.g. Pt and bimetallic PtRu) in direct DME fuel cells concern the system’s low practical electrooxidation efficiency.In the present study, electrocatalytic activity of Vulcan-supported PtSn (PtSn/V) nanostructured alloys toward electrooxidation of dimethyl ether (DME) has been significantly enhanced in acid medium (0.5 mol dm-3 H2SO4) by intentional and controlled decoration of PtSn/V with ruthenium black or bimetallic PtRu nanoparticles. The enhancement effect concerns both shifting the onset potential for the DME-oxidation toward less positive values and increase of the DME electrocatalytic current densities recorded under both cyclic voltammetric and chronoamperometric conditions. The activating capabilities of ruthenium nanostructures seem to originate from the existence of reactive ruthenium oxo/hydroxo groups (even below 0.45 V vs. RHE) on their surfaces capable of inducing the oxidative removal of poisoning (CO-type) adsorbates from the neighboring platinum catalytic sites. In that respect, the Ru-oxo species originating from Ru or PtRu additives seem to support activity of Sn co-catalytic sites interacting with Pt within the PtSn heterogenous alloy. The Ru-decorated PtSn/V and, in particular, PtSn/V admixed with PtRu exhibit very high activity toward the oxidation of methanol which is also an important DME-oxidation intermediate. On the whole, the hybrid materials composed of Vulcan-supported PtSn decorated with Ru or PtRu nanoparticles seem to act as multifunctional nanoreactors inducing not only stripping of poisoning adsorbates but also catalyzing oxidation of the DME-reaction intermediates (methanol). Despite possible differences in the DME-electrooxidation mechanisms at the hybrid and single component systems, the dissociation of H3C-O-CH3 molecule, which involves C-O bond breaking, formation of the methanol reaction intermediate and CO-type poisoning adsorbates should be operative.

Microwave-induced Conversion of Electromagnetic Energy into Heat Energy in Different Solvents: Synthesis of β-lactams

In this work, the stereospecific synthesis of optically active cis β-lactams under diverse microwave-induced conditions using diverse solvents was reported. The effects of low tanδ values of the solvents are found to be more crucial than solvents with high dipole moments and dielectric constants. The results indicated that for the synthesis of β-lactams solvents with low tanδ and high dipole moment and high dielectric constant are necessary. Best of the knowledge this is the first report that examined the importance of tanδ values of the solvents in β-lactams synthesis.