Analysis of the CO2 and NH3 Reaction in an Aqueous Solution by 2D IR COS: Formation of Bicarbonate and Carbamate

Urease-Powered Micromotors with Spatially Selective Distribution of Enzymes for Capturing and Sensing Exosomes

Enzyme-catalyzed micro/nanomotors (MNMs) exhibit tremendous potential for biological isolation and sensing, because of their biocompatibility, versatility, and ready access to biofuel. However, flow field generated by enzyme-catalyzed reactions might significantly hinder performance of surface-linked functional moieties, e.g., the binding interaction between MNMs and target cargos. Herein, we develop enzymatic micromotors with spatially selective distribution of urease to enable the independent operation of various modules and facilitate the capture and sensing of exosomes. When urease is modified into the motors' cavity, the flow field from enzyme catalysis has little effect on the exterior surface of the motors. The active motion and encapsulating urease internally result in enhancement of ∼35% and 18% in binding efficiency of target cargos, e.g., exosomes as an example here, compared to their static counterparts and moving micromotors with urease modified externally, respectively. Once exosomes are trapped, they can be transferred to a clean environment by the motors for Raman signal detection and/or identification using the surface Raman enhancement scattering (SERS) effect of coated gold nanoshell. The biocatalytic micromotors, achieving spatial separation between driving module and function module, offer considerable promise for future design of multifunctional MNMs in biomedicine and diagnostics.

Fe-Catalyzed CO2 Adsorption over Hexagonal Boron Nitride with the Presence of H2O

The energy barrier of CO₂ chemically adsorbed on hexagonal boron nitride (h-BN) is relatively big. In order to cut down the energy barriers and facilitate fast adsorption of CO₂, it is necessary to apply catalysts as a promoter. In this study, single-atom iron is introduced as the catalyst to reduce the energy barriers of CO₂ adsorbed on pure/doped h-BN. Through density functional theory calculations, catalytic reaction mechanisms, stability of single-atom iron fixed on adsorbents, CO₂ adsorption characteristics, and features of thermodynamics/reaction dynamics during adsorption processes are fully investigated to explain the catalytic effects of single-atom iron on CO₂ chemisorption. According to calculations, when CO₂ and OH^- get into activated states (i.e., CO₂^•- and ^•OH) with the help of single-atom iron, their chemical activities will be promoted to a large degree, which makes the transition state (TS) energy barrier of HCO₃^- to decrease by 92.54%. In the meantime, it is proved that single-atom iron could be stably fixed on doped h-BN with the binding energy larger than 2 eV to achieve sustainable catalysis. With the presence of single-atom iron, TS energy barriers of CO₂ adsorbed on h-BN with the presence of H₂O decreased by 94.39, 78.87, and 30.63% over pure h-BN, 3C-doped h-BN, and 3N-doped h-BN, respectively. In the meantime, thermodynamic analyses indicate that TS energy barriers are mainly determined by element doping and temperatures are a little beneficial to the reduction of TS energy barriers. With the above aspects combined, the results of this study could supply crucial information for massively and quickly capturing CO₂ in real industries.

Synthetic connectivity, emergence, and self-regeneration in the network of prebiotic chemistry

The challenge of prebiotic chemistry is to trace the syntheses of life’s key building blocks from a handful of primordial substrates. Here we report a forward-synthesis algorithm that generates a full network of prebiotic chemical reactions accessible from these substrates under generally accepted conditions. This network contains both reported and previously unidentified routes to biotic targets, as well as plausible syntheses of abiotic molecules. It also exhibits three forms of nontrivial chemical emergence, as the molecules within the network can act as catalysts of downstream reaction types; form functional chemical systems, including self-regenerating cycles; and produce surfactants relevant to primitive forms of biological compartmentalization. To support these claims, computer-predicted, prebiotic syntheses of several biotic molecules as well as a multistep, self-regenerative cycle of iminodiacetic acid were validated by experiment.

Transport studies of ionic solutes through chitosan/chondroitin sulfate A (CHI/CS) polyelectrolyte multilayer membranes

Nano scale assembling has led to the capability to directly control and enhance the capabilities and properties of a material through change of its structural makeup at the nano scale. A novel class of functional layers in which various properties can be tunable via in situ modifications of nanostructure through stimuli such as pH, capping, and salt addition provides a promising strategy to develop polyion responsive polyelectrolyte multilayer membranes (PEM’s). The concentration (diffusion dialysis) and pressure dependent (ultrafiltration) studies of solution containing polyvalent ions through the chitosan/chondroitin sulfate A (CHI/CS) multilayers fabricated on ultipore membrane have been studied. The characterization of the bilayer pair was done with analytical instruments like ATR-FTIR, spectroscopic ellipsometry, SEM, AFM and finally TGA for water holding capacity. The characterization of bilayer pairs demonstrated the stability and integrity of bilayer pair. An important bilayer property such as water holding capacity and ion permeability across it was examined and a positive correlation was found with increase in number of bilayers. The possibility of capping a fabricated bilayer with another polyelectrolyte, polyethylene glycol (PEG) was used to examine the extend of efficiency. The permeation rate of ions across bilayers increased with makeup salt concentration was observed with capping. An increase in selectivity was observed with increase in the number of bilayers for Na+/Cu2+, Na+/Ag+ and Na+/Mn3+. 12.5 hybrid CHI/CS-PEG membranes shows a selectivity of 38.52 for Cl−/PO4 3− with a permeation rate of 37.54 × 10–5 cms−1 and 4.23 × 10–5 cms−1 respectively for Cl− and PO4 3−. The transport profile of a model vitamin, ascorbic acid (AA) through CHI/CS multilayers showed the capability of bilayer membrane for selective solute transport.

(3-Ammonio-2,2-dimethyl-propyl)carbamate Dihydrate

(3-Ammonio-2,2-dimethylpropyl)carbamate dihydrate was synthesised. The title compound was characterised by single crystal X-ray diffraction and IR-/Raman-spectroscopy. It has been demonstrated that a mixture of dilute acetic acid and 2,2-dimethyl-1,3-diaminopropane is able to capture CO2 spontaneously from the atmosphere. An intramolecular hydrogen bond stabilises the conformation of the ylide-type title molecule. Intermolecular hydrogen bonds between all moieties connect them to a strand-type chain structure.

Vibrational Characterization of Radical Ion Adducts between Imidazole and CO2

We address the molecular level origins of the dramatic difference in the catalytic mechanisms of CO₂ activation by the seemingly similar molecules pyridine (Py) and imidazole (Im). This is accomplished by comparing the fundamental interactions of CO₂ radical anions with Py and Im in the isolated, gas phase PyCO₂^- and ImCO₂^- complexes. These species are prepared by condensation of the neutral compounds onto a (CO₂) _n^- cluster ion beam by entrainment in a supersonic jet ion source. The structures of the anionic complexes are determined by theoretical analysis of their vibrational spectra, obtained by IR photodissociation of weakly bound CO₂ molecules in a photofragmentation mass spectrometer. Although the radical PyCO₂^- system adopts a carbamate-like configuration corresponding to formation of an N-C covalent bond, the ImCO₂^- species is revealed to be best described as an ion-molecule complex in which an oxygen atom in the CO₂^- radical anion is H-bonded to the NH group. Species that feature a covalent N-C interaction in ImCO₂^- are calculated to be locally stable structures, but are much higher in energy than the largely electrostatically bound ion-molecule complex. These results support the suggestion from solution phase electrochemical studies (Bocarsly et al. ACS Catal. 2012, 2, 1684-1692) that the N atoms are not directly involved in the catalytic activation of CO₂ by Im.

Anion-Exchange Membrane Fuel Cells with Improved CO2 Tolerance: Impact of Chemically Induced Bicarbonate Ion Consumption

Over the last few decades, because of the significant development of anion exchange membranes, increasing efforts have been devoted the realization of anion exchange membrane fuel cells (AEMFCs) that operate with the supply of hydrogen generated on-site. In this paper, ammonia was selected as a hydrogen source, following which the effect of conceivable impurities, unreacted NH₃ and atmospheric CO₂, on the performance of AEMFCs was established. As expected, we show that these impurities worsen the performance of AEMFCs significantly. Furthermore, with the help of in situ attenuated total reflection infrared (ATR-IR) spectroscopy, it was revealed that the degradation of the cell performance was primarily due to the inhibition of the hydrogen oxidation reaction (HOR). This is attributed to the active site occupation by CO-related adspecies derived from (bi)carbonate adspecies. Interestingly, this degradation in the HOR activity is suppressed in the presence of both NH₃ and HCO₃^- because of the bicarbonate ion consumption reaction induced by the existence of NH₃. Further analysis using in situ ATR-IR and electrochemical methods revealed that the poisonous CO-related adspecies were completely removed under NH₃-HCO₃^- conditions, accompanied by the improvement in HOR activity. Finally, a fuel cell test was conducted by using the practical AEMFC with the supply of NH₃-contained H₂ gas to the anode and ambient air to the cathode. The result confirmed the validity of this positive effect of NH₃-HCO₃^- coexistence on CO₂-tolerence of AEMFCs. The cell performance achieved nearly 95% of that without any impurity in the fuels. These results clearly show the impact of the chemically induced bicarbonate ion consumption reaction on the realization of highly CO₂-tolerent AEMFCs.

Tandem mass spectrometry measurement of the collision products of carbamate anions derived from CO2 capture sorbents: paving the way for accurate quantitation

The reaction between CO(2) and aqueous amines to produce a charged carbamate product plays a crucial role in post-combustion capture chemistry when primary and secondary amines are used. In this paper, we report the low energy negative-ion CID results for several anionic carbamates derived from primary and secondary amines commonly used as post-combustion capture solvents. The study was performed using the modern equivalent of a triple quadrupole instrument equipped with a T-wave collision cell. Deuterium labeling of 2-aminoethanol (1,1,2,2,-d(4)-2-aminoethanol) and computations at the M06-2X/6-311++G(d,p) level were used to confirm the identity of the fragmentation products for 2-hydroxyethylcarbamate (derived from 2-aminoethanol), in particular the ions CN(-), NCO(-) and facile neutral losses of CO(2) and water; there is precedent for the latter in condensed phase isocyanate chemistry. The fragmentations of 2-hydroxyethylcarbamate were generalized for carbamate anions derived from other capture amines, including ethylenediamine, diethanolamine, and piperazine. We also report unequivocal evidence for the existence of carbamate anions derived from sterically hindered amines (Tris(2-hydroxymethyl)aminomethane and 2-methyl-2-aminopropanol). For the suite of carbamates investigated, diagnostic losses include the decarboxylation product (-CO(2), 44 mass units), loss of 46 mass units and the fragments NCO(-) (m/z 42) and CN(-) (m/z 26). We also report low energy CID results for the dicarbamate dianion ((-)O(2)CNHC(2)H(4)NHCO(2)(-)) commonly encountered in CO(2) capture solution utilizing ethylenediamine. Finally, we demonstrate a promising ion chromatography-MS based procedure for the separation and quantitation of aqueous anionic carbamates, which is based on the reported CID findings. The availability of accurate quantitation methods for ionic CO(2) capture products could lead to dynamic operational tuning of CO(2) capture-plants and, thus, cost-savings via real-time manipulation of solvent regeneration energies.