Reversible Exchange Research Articles

Screening of Protein-Ligand Binding Using a SABRE Hyperpolarized Reporter.

Hyperpolarization through signal amplification by reversible exchange (SABRE) provides a facile means to enhance nuclear magnetic resonance (NMR) signals of small molecules containing an N-heterocycle or other binding site for a polarization transfer catalyst. A purpose-designed reporter ligand, which is capable of binding both to a target protein and to the catalyst, makes the sensitivity enhancement by this technique compatible with the measurement of a range of biomolecular interactions. The 1H polarization of the reporter ligand 4-amidinopyridine, which is targeting trypsin, is used to screen ligands that are not themselves hyperpolarizable by SABRE. The respective protein-ligand dissociation constants (KD) are determined by an observed change in the R2 relaxation rate of the reporter. A calculation of expected signal changes indicates that the accessible ligand KD values extend over several orders of magnitude, while the concentrations of target proteins and ligands can be reduced considering the sensitivity gains from hyperpolarization. In general, the design of a single, weakly binding ligand for a target protein enables the use of SABRE hyperpolarization for ligand screening or other biophysical studies involving macromolecular interactions.

Geochemical behavior and fate of arsenic in middle Gangetic plain, Terai region of India, and its health risk quantification using Monte Carlo simulation and sensitivity analysis

The present study investigates the groundwater solute chemistry, hydrogeochemical behavior of arsenic (As) and the assessment of health risks through ingestion and dermal contact pathways to the adults and children of the Bahraich district, falling under the middle Gangetic plain, Ghaghara river sub-basin, Terai region of India. A Monte Carlo simulation and a sensitivity analysis were also performed to quantify the uncertainties and impact of various input variables in risk calculations, respectively. Concentrations major ions (Ca2+, Mg2+, Na+, K+, SO42−, PO43− NO3−, HCO3−, F− and Cl−), dissolved organic carbon (DOC), and trace metals (As, Fe, and Mn) as well as physical parameters (EC, pH, and Eh) were measured on the collected groundwater and river water samples. The concentration of As in the groundwater samples was found in range between 0.64 μg/L to 104 μg/L and ∼37% of the samples had As>10 μg/L (WHO and BIS acceptable limit of 10 μg/L for drinking water). River water samples also displayed high As concentrations (mean of 14 μg/L) with ∼73% of samples having As>10 μg/L, which could be attributed to infiltration from As-enriched sallow groundwater of the nearby regions. The groundwater of the study area was predominantly of Ca2+-Mg2+-HCO3- type. Bivariate weathering plots showed groundwater was influenced by silicate weathering and carbonate dissolution, along with the ion exchange and reverse ion exchange processes, with a minor contribution from evaporate dissolution. Most of the groundwater samples (n = 57) were anoxic and had low SO42− and NO3−, and high Mn, Fe and DOC concentrations. The observed values and correlations between various measured parameters, including groundwater As concentrations and saturation indices calculations, indicated the reductive dissolution of iron oxyhydroxide as the major process for As mobilization in the study area. The results of total non-carcinogenic risk (HI) estimated by the deterministic and probabilistic techniques were nearly identical for both adults and children, but an overestimation was observed in the case of carcinogenic risk calculated by the deterministic approach. Health risk results also showed that children were more susceptible to non-carcinogenic risk, whereas adults were at a higher risk of cancer in the study area. Sensitivity analysis indicated that the concentration of As in groundwater and exposure duration (ED) were the most effective variables for non-carcinogenic (HI) and carcinogenic (TILCR) risk estimation in both adults and children.

Experimental Study of the Characteristic of a PEM Reversible Fuel Cell

Renewable energy sources are the proper way to protect and preserve the natural resources of the only planet we inhabit. The fuel cell is an interesting solution in the field of renewable energy sources. These devices convert the chemical energy from hydrogen and oxygen into electrical and thermal energy. The present paper, therefore, focuses exclusively on their ability to generate electricity, their energy efficiency, quiet mode of operation, and environmental compatibility. The polymer electrolyte membrane fuel cell coverts the energy at high density of power. The weight and cost of this cells are lower than the other kind of fuel cell. A reversible proton exchange membrane fuel cell is a kind of PEM fuel cell. It can operate in two modes - fuel cell mode and electrolyzer mode. Presented in the current paper are the experimental studies conducted into the operation of the fuel cell in electrolyzer and fuel cell mode. The relevant parameters and characteristics obtained from experiments are analyzed in relation to the mode of operation.

Uptake Mechanisms of a Novel, Activated Carbon-Based Equilibrium Passive Sampler for Estimating Porewater Methylmercury.

We describe the validation of a novel polymeric equilibrium passive sampler comprised of agarose gel with embedded activated carbon particles (ag+AC), to estimate aqueous monomethylmercury (MeHg) concentrations. Sampler behavior was tested using a combination of idealized media and realistic sediment microcosms. Isotherm bottle experiments with ag+AC polymers were conducted to constrain partitioning to these materials by various environmentally relevant species of MeHg bound to dissolved organic matter (MeHgDOM) across a range of sizes and character. Log of partitioning coefficients for passive samplers (Kps ) ranged from 1.98 ± 0.09 for MeHg bound to Suwannee River humic acid to 3.15 ± 0.05 for MeHg complexed with Upper Mississippi River natural organic matter. Reversible equilibrium exchange of environmentally relevant MeHg species was demonstrated through a series of dual isotope-labeled exchange experiments. Isotopically labeled MeHgDOM species approached equilibrium in the samplers over 14 days, while mass balance was maintained, providing strong evidence that the ag+AC polymer material is capable of equilibrium measurements of environmentally relevant MeHg species within a reasonable deployment time frame. Samplers deployed across the sediment-water interface of sediment microcosms estimated both overlying water and porewater MeHg concentrations within a factor of 2 to 4 of measured values, based on the average measured Kps values for species of MeHg bound to natural organic matter in the isotherm experiments. Taken together, our results indicate that ag+AC polymers, used as equilibrium samplers, can provide accurate MeHg estimations across many site chemistries, with a simple back-calculation based on a standardized Kps. Environ Toxicol Chem 2022;41:2052-2064. © 2022 SETAC.

Relayed hyperpolarization for zero-field nuclear magnetic resonance.

Zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) is a rapidly developing form of spectroscopy that provides rich spectroscopic information in the absence of large magnetic fields. However, signal acquisition still requires a mechanism for generating a bulk magnetic moment for detection, and the currently used methods only apply to a limited pool of chemicals or come at prohibitively high cost. We demonstrate that the parahydrogen-based SABRE (signal amplification by reversible exchange)–Relay method can be used as a more general means of generating hyperpolarized analytes for ZULF NMR by observing zero-field J-spectra of [13C]-methanol, [1-13C]-ethanol, and [2-13C]-ethanol in both 13C-isotopically enriched and natural abundance samples. We explore the magnetic field dependence of the SABRE-Relay efficiency and show the existence of a second maximum at 19.0 ± 0.3 mT. Despite presence of water, SABRE-Relay is used to hyperpolarize ethanol extracted from a store-bought sample of vodka (%PH ~ 0.1%).

The application of hydrogeochemical and stable isotope data to decipher the origin and evolution of hot springs in the Rawadanau Basin, Indonesia

The emergence of hot springs is usually associated with hydrothermal prospects. This paper discusses the certainty of the nature, type, and origin of the hot springs found in the Rawadanau Basin, Indonesia. The approach in this study is to use hydro-chemical characteristics and stable isotopes. Besides measuring field data, laboratory analyzes were also carried out - hydrogeochemical analysis including cations and anions and stable isotopes analyses. Twenty-one hot springs have been reported. The temperature varied from 31.2 to 54.6 °C; the pH was 6.8 and 7.7, and EC was between 1099 and 4460 μS/cm. There are three water types of Mg-Ca-HCO3-Cl, Mg-Ca-HCO3 in the northern, and Na-Cl in the southern. Chloro-alkaline indices implied that ion exchange and reverse ion exchange influenced the hydrogeochemistry of hot springs. The δ18O and δ2H values varied between -8.6 to -4.6‰ (δ18O) and from -57.0 to -32.4 ‰ (δ2H), lay to the local meteoric water line, indicating that the thermal waters are meteoric local in origin and originated from precipitation. The hot springs in the study area originate from meteoric water and interact with geothermal fluids from confined aquifers that flow to the surface through fractures and faults. The reservoir temperature approach 150 °C is based on chalcedony; and the reservoir depth is about 1.1 km.

Selection of assembly complexity in a space of tetrapeptides

In this issue of <i>Chem</i>, Ulijn and co-workers show how peptide designs can be selected in a vast sequence space by reversible enzymic exchange, which produces arrays of tetrapeptides, and this is modulated by the nature of the environment.

Atomic memory based on recoil-induced resonances

In this work, we perform a detailed theoretical and experimental investigation of an atomic memory based on recoil-induced resonance in cold cesium atoms. We consider the interaction of nearly degenerate pump and probe beams with an ensemble of two-level atoms. A full theoretical density matrix calculation in the extended Hilbert space of the internal and external atomic degrees of freedom allows us to obtain, from first principles, the transient and stationary responses determining the probe transmission and the forward four-wave-mixing spectra. These two signals are generated together at the same order of perturbation with respect to the intensities of pump and probe beams. Moreover, we have investigated the storage of optical information on the spatial modes of light beams in the atomic external degrees of freedom, which provided a simple interpretation for the previously reported nonvolatile character of this memory. The retrieved signals after storage reveal the equivalent role of probe transmission and four-wave mixing, as the two signals have similar amplitudes. Probe transmission and forward four-wave-mixing spectra were then experimentally measured for both continuous excitation and after storage. The experimental observations are in good agreement with the developed theory, and they open another pathway for the reversible exchange of optical information with atomic systems.

Total Dissolved Solids and Their Removal Techniques

Total dissolved solids (TDS) due to both geogenic and anthropogenic contaminations, is one of the preliminary as well as essential parameters among others to describe water quality. It includes organic and inorganic components, heavy metals, salts, other dissolved substances, and others due to indiscriminate disposal of untreated domestic and industrial effluents, urban and/or agricultural runoff which exists in the form of micro or nano level in nature. Higher TDS levels in water severely impact health and the environment. For instance, it causes gastrointestinal, cardiovascular, genotoxic, respiratory, skin, and hepatic effects in humans. High TDS level (&gt; 500 ppm) results in excessive scaling in household appliances (e.g., pipes, heaters, and boilers) thereby reducing their efficiency. Therefore, the removal of TDS from various water matrices is taking paramount importance to minimize its impact on health and the environment. Various TDS removal technologies based on the membrane, ion, and temperature gradient are employed to treat water. In this review paper, several TDS removal technologies for instance reverse osmosis, nanofiltration, distillation, ultrafiltration, forward osmosis, precipitation, desalination, ion exchange, electrochemical techniques, electrodialysis, electrolysis, electrocoagulation, and adsorption are discussed in detail.

Hydro-Geochemical Applications and Multivariate Analysis to Assess the Water–Rock Interaction in Arid Environments

Thirty groundwater samples were taken from Assiut’s northern outskirts. The physicochemical properties of these samples were investigated. For the evaluation of water–rock interaction, the saturation index (SI), chloro-alkaline indices (CAI1 and CAI2), Gibbs ratios for cations and anions (GC and GA), principal component analysis (PCA), and hierarchical cluster analysis (HCA) were used. (1) With the exception of five samples that were supersaturated, the rest of the groundwater samples were under-saturated with carbonate mineral dissolution (calcite, dolomite, and aragonite) and evaporite mineral dissolution (anhydrite, gypsum, halite, and sylvite). (2) The presence of ion exchange between alkali elements (Na+ + K+) and earth alkaline elements (Ca2+ + Mg2+) is explained by the positive values of the chloro-alkaline indices. (3) In four groundwater samples, negative chloro-alkaline indices suggest reverse ion exchange and an increasing alkali element content. (4) The Gibbs diagram demonstrates that, with the exception of four samples that reflect saline groundwater, the majority of the groundwater samples are freshwater recharging from the fresh surface water in the research area. (5) Groundwater types include Ca-HCO3 (11%), Mg-HCO3 (48%), Na-HCO3 (23%), Mg-Cl (13%), and Na-Cl (3%). (6) The alkali, earth alkaline elements, and sulphate are the key controls on groundwater salinity, according to PCA and HCA. (7) The somewhat saline groundwater in the research area’s western desert margins should not be used since it poses a health danger to people.

A transthyretin monomer intermediate undergoes local unfolding and transient interaction with oligomers in a kinetically concerted aggregation pathway

Transthyretin (TTR) amyloidosis is associated with tissue deposition of TTR aggregates. TTR aggregation is initiated by dissociation of the native tetramer to form a monomeric intermediate, which locally unfolds and assembles into soluble oligomers and higher-order aggregates. However, a detailed mechanistic understanding requires kinetic and structural characterization of the low population intermediates formed. Here, we show that the monomeric intermediate exchanges with an ensemble of oligomers on the millisecond timescale. This transient and reversible exchange causes broadening of the 19F resonance of a trifluoromethyl probe coupled to the monomeric intermediate at S85C. We show the 19F linewidth and R2 relaxation rate increase with increasing concentration of the oligomer. Furthermore, introduction of 19F probes at additional TTR sites yielded distinct 19F chemical shifts for the TTR tetramer and monomer when the trifluoromethyl probe was attached at S100C, located near the same subunit interface as S85C, but not with probes attached at S46C or E63C, which are distant from any interfaces. The 19F probe at E63C shows that part of the DE loop, which is solvent accessible in the tetramer, becomes more buried in the NMR-visible oligomers. Finally, using backbone amides as probes, we show that parts of the EF helix and H-strand become highly flexible in the otherwise structured monomeric intermediate at acidic pH. We further find that TTR aggregation can be reversed by increasing pH. Taken together, this work provides insights into location-dependent conformational changes in the reversible early steps of a kinetically concerted TTR aggregation pathway.

Analysis of Complex Mixtures by Chemosensing NMR Using para-Hydrogen-Induced Hyperpolarization.

ConspectusNuclear magnetic resonance (NMR) is a powerful technique for chemical analysis. The use of NMR to investigate dilute analytes in complex systems is, however, hampered by its relatively low sensitivity. An additional obstacle is represented by the NMR signal overlap. Because solutes in a complex mixture are usually not isotopically labeled, NMR studies are often limited to 1H measurements, which, because of the modest dispersion of the 1H resonances (typically ∼10 ppm), can result in challenging signal crowding. The low NMR sensitivity issue can be alleviated by nuclear spin hyperpolarization (i.e., transiently increasing the differences in nuclear spin populations), which determines large NMR signal enhancements. This has been demonstrated for hyperpolarization methods such as dynamic nuclear polarization, spin-exchange optical pumping and para-hydrogen-induced polarization (PHIP). In particular, PHIP has grown into a fast, efficient, and versatile technique since the recent discovery of non-hydrogenative routes to achieve nuclear spin hyperpolarization.For instance, signal amplification by reversible exchange (SABRE) can generate proton as well as heteronuclear spin hyperpolarization in a few seconds in compounds that are able to transiently bind to an iridium catalyst in the presence of para-hydrogen in solution. The hyperpolarization transfer catalyst acts as a chemosensor in the sense that it is selective for analytes that can coordinate to the metal center, such as nitrogen-containing aromatic heterocycles, sulfur heteroaromatic compounds, nitriles, Schiff bases, diaziridines, carboxylic acids, and amines. We have demonstrated that the signal enhancement achieved by SABRE allows rapid NMR detection and quantification of a mixture of substrates down to low-micromolar concentration. Furthermore, in the transient complex, the spin configuration of p-H2 can be easily converted to spin hyperpolarization to produce up to 1000-fold enhanced NMR hydride signals. Because the hydrides’ chemical shifts are highly sensitive to the structure of the analyte associating with the iridium complex, they can be employed as hyperpolarized “probes” to signal the presence of specific compounds in the mixture. This indirect detection of the analytes in solution provides important benefits in the case of complex systems, as hydrides resonate in a region of the 1H spectrum (at ca. −20 ppm) that is generally signal-free. The enhanced sensitivity provided by non-hydrogenative PHIP (nhPHIP), together with the absence of interference from the complex matrix (usually resonating between 0 and 10 ppm), set the detection limit for this NMR chemosensor down to sub-μM concentrations, approximately 3 orders of magnitude lower than for conventional NMR. This nhPHIP approach represents, therefore, a powerful tool for NMR analysis of dilute substrates in complex mixtures as it addresses at once the issues of signal crowding and NMR sensitivity. Importantly, being performed at high field inside the NMR spectrometer, the method allows for rapid acquisition of multiple scans, multidimensional hyperpolarized NMR spectra, in a fashion comparable to that of standard NMR measurements.In this Account, we focus on our chemosensing NMR technology, detailing its principles, advantages, and limitations and presenting a number of applications to real systems such as biofluids, beverages, and natural extracts.

Conceptual Evaluation of Factors Controlling Groundwater Chemistry in Ad-Dawadmi, Saudi Arabia, Using Visualization and Multiple Lines of Evidence

Understanding the hydrogeochemical and physicochemical processes and factors controlling the chemical characteristics of groundwater (GW) is essential in water resources studies. In this work, the authors explored, applied, and evaluated the practicality of a series of analysis methods, exploring their ability to improve the representation of the generic GW chemical datasets. The demonstration resulted in a detailed explanation of findings and interpretations, which benefits newcomers who may not be experts in managing such data. Visualization-based, facile, readily readable, and interpretable graphs were tuned and applied to identify the interconnected controlling factors. The examined varieties were bubble diagrams, 3D surface plots, and scatter box plot matrices. Box plot matrices yielded intensive information about the significant interacting parameters in one graph. Employing bubble diagrams produced vast detail, allowing the identification of the significant processes and enabling the recognition of internally acting mechanisms that were otherwise hidden. The identified GW evolution processes include aerosol dissolution, evaporation, direct and reverse ion exchange, precipitation of calcium salts, flushing out of soil-bounded salts, and rock weathering. pH and HCO3− fluctuations coupled with evaporation were recognized as prominent factors giving rise to the vicious salinization cycle, which is thought to be the process causing the worst deterioration in the GW quality and the salinity within the study area.

Characterization of interfacial bonding properties of Vitrimer resin/ T700 fibre

ABSTRACT Reversible bond exchange reaction gives Vitrimer resin the advantages of being recyclable and reprocessing. So the characterization of the interfacial bonding properties between Vitrimer and carbon fibre is of great interest for aerospace applications. In this study, a kind of thermosetting resin containing bond exchange reaction was configured by adding zinc acetylacetonate catalyst to the conventional thermosetting resin. The force–displacement curve was obtained by microbond tests, and the experimental results showed that the newly configured resin has higher interfacial shear strength. A finite element simulation was established based on cohesive contact model (CZM), and the interface parameters of the CZM were inverted by using finite element update method (FEUM) in combination with the experimental data. And the pull-out force–displacement curves obtained from the numerical simulation are in good agreement with the experimental data. The interfacial stress transfer and debonding failure behavior is further discussed.

Healable, recyclable and mechanically robust elastomers with multiple dynamic cross-linking bonds

The cross-linked network structure bestows rubber with excellent mechanical properties, but it greatly limits the self-healing and reprocessing ability of rubber. Herein, to address the above problem, we propose a simple cross-linking strategy with the cross-linker consisting of triple dynamic covalent bonds to vulcanize epoxidized natural rubber (ENR). A dynamic covalent network remarkably enhanced the mechanical properties of ENR through the combination of dynamic covalent bonds in the cross-linked network. At the same time, abundant dynamic covalent bonds rearranged the network topology through reversible exchange. As a result, a novel self-healing ENR with high tensile strength (2.06 ± 0.12 MPa) has been successfully developed. The ENR exhibits a high (97 ± 3%) self-healing efficiency (after 30 h at 70 °C) without applying any external force. Furthermore, it can be recycled more than three times. This work could enlighten researchers in academia and industry to develop self-healing elastomers with mechanical strength and reprocessing ability. • A novel cross-linker containing triple dynamic covalent bonds was synthesized. • Triple dynamic covalent bonds is simultaneously introduced into the cross-linked network. • The covalent cross-linking driven by dynamic covalent bonds reinforce the mechanical properties of rubber. • Reversible interactions enable the self-healing ability and recyclability of rubber.

Hydrogeochemical Characteristics of the Haiyuan-Liupanshan Seismic Belt at the Northeastern Edge of the Tibet Plateau

The hydrogeochemical characteristics and groundwater recharge environments along the deep-cut Haiyuan-Liupanshan fault zone (HLFZ) were investigated by major ion and isotopic compositions (δ18O and δD) of the water samples collected at 14 sites from 2016 to 2017. The Schukalev classification method, fuzzy membership function, the proportion coefficients of major ions and principal component analysis (PCA) were adopted to analysis the hydrogeochemistry, water quality, origins and controlling factors of groundwater. In terms of chemical types, the sites along HLFZ can be divided into two groups. Specifically, the Group 1 is in the north and west part of the HLFZ and the water samples are characterized by higher salinity and enriched in Na+ and SO42-, reflecting the control of evaporate dissolution in cretaceous and tertiary aquifers, reverse ionic exchange, stronger water-rock reaction and deep fluids. The higher concentrations of Ca2+ + Mg2+ and HCO3- were found in Group 2, which is located in the southeast of the HLFZ and may be attributed to carbonate weathering and the recharge of karst fissure water from ordovician dolomite and limestone. Contamination of groundwater in HLFZ is severe, with 78.6% of the sites classified as grade V, which means they cannot be used for drinking water or agriculture. The primary contaminants found in Group 1 are TDS, Na+, Cl- and SO42- and the exceedance in NO3-and pH value affect water quality in the Group 2. The 18O and δD values of groundwater in HLFZ indicated that meteoric water contributed dominantly to the groundwater and it was influenced by the water cycle and water-rock reaction. Furthermore, tectonic movement, seismicity, and the level of deformation along different segments of HLFZ are important factors in the migration of deep to shallow groundwater, and water-rock reactions during groundwater migration, which results in differences in chemical composition of the groundwater between Group 1 and Group 2. Most of the sites with higher TDS in HLFZ fall on the a higher stress state region (represented by a low b value&lt;0.75), which reflected a possible evidence of seismic activity affected the hydrogeochemistry of groundwater.

Genesis of uranium containing groundwater in the Brahmaputra floodplain of Assam: Hydrogeochemistry and its associated health risk

Groundwater uranium (U) content and the major hydrogeochemical processes were evaluated for six districts of Assam, lying mostly on the central and northern region of the Brahmaputra floodplain. A total of 504 groundwater samples were collected using the grid sampling technique. Uranium concentrations analysed using LED fluorimeter model LF-2a, ranged from below detection limit (BDL) to 13.5 μgL−1. All the U concentrations were found to be well below the prescribed limits of AERB, WHO and USEPA. The highest groundwater U was recorded in a sample from Nagaon, a central Brahmaputra floodplain district. The SEM-EDX spectra of the sediment samples revealed geogenic presence of U in the floodplain. A comparative assessment between the relationships of U with other groundwater parameters revealed that shallow aquifers provided more feasibility for elemental interactions and hence more mobility of U species. The correlation statistics in shallow aquifers depicted the importance of alkalinity on U release and mobilization. Uranium release during weathering of the geological strata was signified by the relationship of U with EC, TDS and salinity. The role played by pH and ORP in dissolution of U in the floodplain was not strong. The dominant water type in the study was Mg–HCO3, which was associated with higher U concentration. This revealed the positive role of carbonate dissolution towards U release in the floodplain. Hydrogeochemical investigation further implied for greater silicate weathering and ion exchange compared to that of carbonate weathering and reverse ion exchange processes. The calculated undersaturation of calcite, dolomite and gypsum explained their role as source minerals in the floodplain. Uranium dissolution and mobilization was found to have positive association with carbonate weathering, as depicted by its significant relationship with calcite, dolomite and gypsum. Health risk, both radiological and chemical, relating to U ingestion through drinking water was absent within the floodplain.

Synthesis, characterization, ion-exchange, and catalytic properties of three isostructural copper(II) coordination polymers with a flexible bis(triazole) ligand

Ion-exchange processes are shown to occur in several coordination polymers (CPs) and their unique subclass of metal-organic frameworks (MOFs). The development of fast and economical routes to stable ion-exchange CP materials is important to broaden the range of applications for these materials. Herein, we report a greatly improved synthesis and coordinated anion exchange of three new copper(II) coordination polymers [Cu(Fbtx)2(NO3)2]n (1), [Cu(Fbtx)2(BF4)2]n (2) and [Cu(Fbtx)2(SO4)]n (3) (Fbtx ​= ​1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene) under the microwave-assisted hydrothermal conditions. The three Cu-CPs are crystallographically isostructural, exhibiting two-dimensional layered structures with the 44-sql topology. Complexes 1–3 display good thermal stability and excellent chemical stability in organic solvents and aqueous solutions with wide pH range of 1–13. The anion-exchange functions of the series of sql-type coordination networks were monitored by using powder X-ray diffraction, infrared spectroscopy and ion chromatography. The results revealed that these complexes can undergo anion-exchange under microwave irradiation, and the reversible exchange process depends on the size of the anions. These materials were demonstrated to be efficient heterogeneous catalysts for the direct carboxylation of 1-ethynylbenzene with CO2 under mild conditions, and various propiolic acids were synthesized in moderate to good yields under optimized reaction conditions. Moreover, the catalyst could be recycled up to five times with the retention of both catalytic activity and crystal structure.

Real-Time High-Sensitivity Reaction Monitoring of Important Nitrogen-Cycle Synthons by 15N Hyperpolarized Nuclear Magnetic Resonance.

Here, we show how signal amplification by reversible exchange hyperpolarization of a range of 15N-containing synthons can be used to enable studies of their reactivity by 15N nuclear magnetic resonance (NO2– (28% polarization), ND3 (3%), PhCH2NH2 (5%), NaN3 (3%), and NO3– (0.1%)). A range of iridium-based spin-polarization transfer catalysts are used, which for NO2– work optimally as an amino-derived carbene-containing complex with a DMAP-d2 coligand. We harness long 15N spin-order lifetimes to probe in situ reactivity out to 3 × T1. In the case of NO2– (T1 17.7 s at 9.4 T), we monitor PhNH2 diazotization in acidic solution. The resulting diazonium salt (15N-T1 38 s) forms within 30 s, and its subsequent reaction with NaN3 leads to the detection of hyperpolarized PhN3 (T1 192 s) in a second step via the formation of an identified cyclic pentazole intermediate. The role of PhN3 and NaN3 in copper-free click chemistry is exemplified for hyperpolarized triazole (T1 < 10 s) formation when they react with a strained alkyne. We also demonstrate simple routes to hyperpolarized N2 in addition to showing how utilization of 15N-polarized PhCH2NH2 enables the probing of amidation, sulfonamidation, and imine formation. Hyperpolarized ND3 is used to probe imine and ND4+ (T1 33.6 s) formation. Furthermore, for NO2–, we also demonstrate how the 15N-magnetic resonance imaging monitoring of biphasic catalysis confirms the successful preparation of an aqueous bolus of hyperpolarized 15NO2– in seconds with 8% polarization. Hence, we create a versatile tool to probe organic transformations that has significant relevance for the synthesis of future hyperpolarized pharmaceuticals.

Understanding the determinants of consumers' reverse exchange intention as an approach to e-waste recycling: a developing country perspective

PurposeEnd-of-life electronic products exchange (EEPE) program could be an effective approach to e-waste recycling that requires consumers' participation. Thus, it is highly recommended to study factors stirring consumer behavior with regard to EEPE programs, which is largely under-explored in the existing literature. Hence, grounding on the Theory of Planned Behavior (TPB) and Attitude-Behavior-Context (A-B-C) model, this study attempts to understand the determinants of consumers' EEPE intention by adding contextual and non-cognitive factors to the proposed research model.Design/methodology/approachEmploying a purposive sampling technique, respondents were drawn from university students and general consumers of electronic products in a developing country. Factor analysis, structural equation modeling (SEM) and SPSS PROCESS were used to analyze the collected data.FindingsEmpirical results confirm that subjective norm has the strongest positive impact on EEPE intention. Following this, attitude toward EEPE and perceived behavioral control play positive mediating roles in determining EEPE intention. Moreover, government initiatives moderate the unsolicited “attitude–intention gap”.Practical implicationsDrawing on this study's outcomes, the study urges to form comprehensive awareness-building campaigns, rules and regulations regarding proper e-waste management, promote “exchange offer” programs and educational programs to encourage EEPE.Originality/valueThis study makes two fresh contributions to the extant literature. First, by coupling the TPB and A-B-C theory, this study showed that both attitude (i.e. attitude toward EEPE) and context (i.e. government initiatives) are essential in eliciting individual-level post-consumption pro-environmental behavior (PEB) (i.e. EEPE). Second, government initiatives elucidate the attitude–intention gap in the reverse logistics context, especially in developing countries.