Remarkably efficient removal of toxic bromate from drinking water with a porphyrin–viologen covalent organic framework

The presence of carcinogenic bromate (BrO₃⁻) in drinking water became a global concern and efforts towards its removal mainly focused on addressing the source. Herein, we rationally designed a porphyrin-based covalent organic framework (PV-COF) with a cationic surface to provide electrostatic interactions and a porphyrin core to induce hydrogen bonding interactions for the efficient removal of BrO₃⁻ from water. Through H-bonding and electrostatic interactions, PV-COF exhibited an exceptional bromate removal efficiency (maximum adsorption capacity, Q_max: 203.8 mg g⁻¹) with the fastest uptake rate (k_ads) of 191.45 g mg⁻¹ min⁻¹. The bromate concentration was reduced to far below the allowed concentration in drinking water (10 ppb) within 20 minutes. We studied the relationship between bromate adsorption and COF surface modification by metalation of the porphyrinic core or neutralization of the viologen linkers by chemical reduction. The bromate adsorption mechanism was studied by EDAX mapping and molecular simulations, and it was found that ion exchange and hydrogen bonding formation drive the adsorption. Importantly, PV-COF could be easily recycled several times without compromising its adsorption efficiency.

A cationic COF removes carcinogenic bromate with a remarkable rate constant of 191.45 g mg⁻¹ min⁻¹.     

Radiochemical separation of Mn/II/ with 1,2,3-benzotriazole into 1-octanol employing solvent extraction technique

1,2,3-Benzotriazole /1,2,3-BT/ has been used for the radiochemical separation of Mn/II/ employing solvent extraction technique. Based on various parameters such as pH effect, time of equilibration and effect of various solvents, etc. the ideal conditions for the extraction of Mn/II/ was evaluated. The stoichiometry of the metal to reagent was determined by the substoichiometric extraction and slope-ratio method and found to be 12. The effect of anions on the extraction value of Mn/II/ revealed that a large number of anions do not interfere. Separation factors for various elements were also studied and the extraction found to be selective.     

Catalytic resonance theory: parallel reaction pathway control

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site can be achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10⁻⁶ < f < 10⁴ Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of simulated chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

Branched catalytic reaction networks with oscillating chemical pathways perfectly select for reaction products at varying frequency.     

Elastic scattering of electrons by benzene

Relative differential cross-sections for the elastic scattering of electrons from benzene have been measured at incident energies 300, 500, 700 and 900eV and for scattering angles between 30° and 120°. The results are discussed and compared with the independent atom model (IAM) calculations. Two different sets of scattering amplitudes for the constituent atoms of benzene were used in these calculations, one obtained from first Born approximation and the other from partial wave analysis of the Dirac equation. Only the static interaction was taken into account in the calculations. The higher the incident energy, the better is the observed agreement between experiment and theory. This indicates that at higher energies, absorption, exchange and polarization effects are not significant as compared to the static interaction and that the IAM satisfactorily predicts the interference of scattering from the individual atoms of C₆H₆.     

Substoichiometric thermal neutron activation analysis determination of ruthenium in complex matrices

Complex matrices, namely ores and catalysts, have been analyzed for trace amount of ruthenium employing thermal neutron-activation analysis, involving substoichiometric solvent extraction of Ru/III/ with 2-mercaptobenzothiazole into chloroform. Three samples and a standard can be processed and counted within three hours.     

Sequential determination of thorium and rare earths with EDTA and kojic acid

Kojic acid can be used instead of acetylacetone to form a ternary complex with Th-EDTA that is more stable than the corresponding Xylenol Orange ternary complex, thus making it possible to titrate lanthanides with EDTA at pH 5.5 after titration of thorium at pH 2.     

Lactone enols are stable in the gas phase but highly unstable in solution

2-Hydroxyoxol-2-ene (C(5)-1), the enol tautomer of gamma-butyrolactone, was generated in the gas phase as the first representative of the hitherto elusive class of lactone enols and shown by neutralization-reionization mass spectrometry to be remarkably stable as an isolated species. Ab initio calculations by QCISD(T)/6-311+G(3df,2p) provided the enthalpies of formation, proton affinities, and gas-phase basicities for gaseous lactone enols with four- (C(4)-1), five- (C(5)-1), and six-membered rings (C(6)-1). The acid-base properties of C(4)-C(6) lactones and enols and reference carboxylic acid enols CH(2)=C(OH)(2) (3) and CH(2)=C(OH)OCH(3) (4) were also calculated in aqueous solution. The C(4)-C(6) lactone enols show gas-phase proton affinities in the range of 933-944 kJ mol(-)(1) and acidities in the range of 1401-1458 kJ mol(-)(1). In aqueous solution, the lactone enols are 15-20 orders of magnitude more acidic than the corresponding lactones, with enol pK(a) values increasing from 5.6 (C(4)-1) to 14.5 (C(6)-1). Lactone enols are moderately weak bases in water with pK(BH) in the range of 3.9-8.1, whereas the lactones are extremely weak bases of pK(BH) in the range of -10.5 to -17.4. The acid-base properties of lactone enols point to their high reactivity in protic solvents and explain why no lactone enols have been detected thus far in solution studies.     

ZrCl4-Catalyzed C-O Bond to C-N Bond Formation: Synthesis of 1,2,3-Triazoles and Their Biological Evaluation

A simple and efficient protocol was developed for the synthesis of aryl azides directly from aryl carbinols using ZrCl₄ as a Lewis acid catalyst. The azides were converted to novel triazoles under click reaction conditions, which were evaluated for their antimicrobial activity against various strains.