Pulse radiolysis of aqueous solutions of carboxy, carbamido and pyridyl derivatives of pyridine

Radiolytic Evaluation of 3,4,3-LI(1,2-HOPO) in Aqueous Solutions

The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and f-element separation technologies, two applications that require optimal performance in radiation environments. However, the radiation robustness of HOPO is currently unknown. Here, we employ a combination of time-resolved (electron pulse) and steady-state (alpha self-radiolysis) irradiation techniques to elucidate the basic chemistry of HOPO and its f-element complexes in aqueous radiation environments. Chemical kinetics were measured for the reaction of HOPO and its Nd(III) ion complex ([Nd^III(HOPO)]^-) with key aqueous radiation-induced radical transients (e_aq^-, H^• atom, and ^•OH and NO₃^• radicals). The reaction of HOPO with the e_aq^- is believed to proceed via reduction of the hydroxypyridinone moiety, while transient adduct spectra indicate that reactions with the H^• atom and ^•OH and NO₃^• radicals proceeded by addition to HOPO's hydroxypyridinone rings, potentially allowing for the generation of an extensive suite of addition products. Complementary steady-state ²⁴¹Am(III)-HOPO complex ([²⁴¹Am^III(HOPO)]^-) irradiations showed the gradual release of ²⁴¹Am(III) ions with increasing alpha dose up to 100 kGy, although complete ligand destruction was not observed.

A novel method for textile odor removal using engineered water nanostructures

The malodor attached to textiles not only causes indoor environmental pollution but also endangers people's health even at low concentrations. Existing technologies cannot effectively eliminate the odor. Herein, an effective and environmentally friendly technology was proposed to address this challenging issue. This technology utilizes electrospraying process to produce Engineered Water Nanostructures (EWNS) in a controllable manner. Upon application of a high voltage to the Taylor cone, EWNS can be generated from the condensed vapor water through a Peltier element. Smoking, cooking and perspiration, considered the typical indoor malodorous gases emitted from human activities, were studied in this paper. A headspace SPME method in conjunction with GC-MS was employed for the extraction, detection and quantification of any odor residues. Results indicated that EWNS played a significant role in the deodorization process with removal efficiencies for the three odors were 95.3 ± 0.1%, 100.0 ± 0.0% and 43.7 ± 2.3%, respectively. The Reactive Oxygen Species (ROS) contained in the EWNS, mainly hydroxyl (OH˙) and superoxide radicals are the possible mechanisms for the odor removal. These ROS are strong oxidative and highly reactive and have the ability to convert odorous compounds to non-odorous compounds through various chemical reaction mechanisms. This study showed clearly the potential of the proposed method in the field of odor removal and can be applied in the battle against indoor air pollution.

Computational, electrochemical, and spectroscopic studies of two mononuclear cobaloximes: the influence of an axial pyridine and solvent on the redox behaviour and evidence for pyridine coordination to cobalt(i) and cobalt(ii) metal centres

[Co(dmgBF2)2(H2O)2] (where dmgBF2 = difluoroboryldimethylglyoximato) was used to synthesize [Co(dmgBF2)2(H2O)(py)]·0.5(CH3)2CO (where py = pyridine) in acetone. The formulation of complex was confirmed by elemental analysis, high resolution MS, and various spectroscopic techniques. The complex [Co(dmgBF2)2(solv)(py)] (where solv = solvent) was readily formed in situ upon the addition of pyridine to complex . A spectrophotometric titration involving complex and pyridine proved the formation of such a species, with formation constants, log K = 5.5, 5.1, 5.0, 4.4, and 3.1 in 2-butanone, dichloromethane, acetone, 1,2-difluorobenzene/acetone (4 : 1, v/v), and acetonitrile, respectively, at 20 °C. In strongly coordinating solvents, such as acetonitrile, the lower magnitude of K along with cyclic voltammetry, NMR, and UV-visible spectroscopic measurements indicated extensive dissociation of the axial pyridine. In strongly coordinating solvents, [Co(dmgBF2)2(solv)(py)] can only be distinguished from [Co(dmgBF2)2(solv)2] upon addition of an excess of pyridine, however, in weakly coordinating solvents the distinctions were apparent without the need for excess pyridine. The coordination of pyridine to the cobalt(ii) centre diminished the peak current at the Epc value of the Co(I/0) redox couple, which was indicative of the relative position of the reaction equilibrium. Herein we report the first experimental and theoretical (59)Co NMR spectroscopic data for the formation of Co(i) species of reduced cobaloximes in the presence and absence of py (and its derivatives) in CD3CN. From spectroelectrochemical studies, it was found that pyridine coordination to a cobalt(i) metal centre is more favourable than coordination to a cobalt(ii) metal centre as evident by the larger formation constant, log K = 4.6 versus 3.1, respectively, in acetonitrile at 20 °C. The electrosynthesis of hydrogen by complexes and in various solvents demonstrated the dramatic effects of the axial ligand and the solvent on the turnover number of the respective catalyst.

Addition-elimination in the reaction of alpha-hydroxyalkyl radicals with 3,5-pyridinedicarboxylic acid and nicotinic acid: example of inner sphere organic electron transfer

Reactions of alpha-hydroxyalkyl radicals with 3,5-pyridinedicarboxylic acid (3,5-PDCA) and nicotinic acid (NA) were studied at appropriate pHs in aqueous solutions by pulse radiolysis technique. At pH 1, CH(3)C*HOH and *CH(2)OH radicals were found to react with 3,5-PDCA by rate constants of 2.2 x 10(9) and 5.1 x 10(8) dm(3) mol(-1) s(-1), respectively, giving radical adduct species. The adduct species formed in the reaction of CH(3)C*HOH radicals with 3,5-PDCA underwent unimolecular decay (k = 9.8 x 10(4) s(-1)) giving pyridinyl radicals. Reaction of (CH(3))(2)C*OH, CH(3)C*HOH, and *CH(2)OH radicals with NA at pH 3.3 gave the adduct species which subsequently decayed to the pyridinyl radicals. At pH 1, wherein NA is present in the protonated form, (CH(3))(2)C*OH radicals directly transfer electrons to NA, whereas CH(3)C*HOH and *CH(2)OH radicals react with higher rate constants compared with those at pH 3.3, initially giving the adduct species which subsequently undergo elimination reaction giving pyridinyl radicals. Reactions of alpha-hydroxyalkyl radicals with 3,5-pyridinedicarboxylic acid and nicotinic acid are found to proceed by an addition-elimination pathway that provides one of the few examples of organic inner sphere electron-transfer reactions. Rate constant for the addition reaction as well as rate of elimination varies with the reduction potential of alpha-hydroxyalkyl radicals.

Time-Dependent Radiolytic Yields of the Solvated Electrons in 1,2-Ethanediol, 1,2-Propanediol, and 1,3-Propanediol from Picosecond to Microsecond

The absorption spectra of the solvated electron in 1,2-ethanediol (12ED), 1,2-propanediol (12PD), and 1,3-propanediol (13PD) have been determined by nanosecond pulse radiolysis techniques. The maximum of the absorption band located at 570, 565, and 575 nm for these three solvents, respectively. With 4,4'-bipyridine (44Bpy) as a scavenger, the molar extinction coefficients at the absorption maximum of the solvated electron spectrum have been evaluated to be 900, 970, and 1000 mol-1 m2 for 12ED, 12PD, and 13PD, respectively. These values are two-thirds or three-fourths of the value usually reported in the literature. With these extinction coefficients, picosecond pulse radiolysis studies have allowed us to depict the radiolytic yield of the solvated electron in these solvents as a function of time from picosecond to microsecond. The radiolytic yield in these viscous solvents is found to be strongly different from that of water solution.

Pulse Radiolysis of 4,4‘-Bipyridyl Aqueous Solutions at Elevated Temperatures: Spectral Changes and Reaction Kinetics up to 400 °C

The spectral changes as well as the reaction kinetics of the transient species of 4,4'-bipyridyl (4,4'-bpy) have been experimentally investigated by pulse radiolysis techniques up to 400 degrees C. The results show that the transient species such as OH adduct 4,4'-bpyOH*, monoprotonated electron adduct 4,4'-bpyH*, and doubly protonated electron adduct 4,4'-bpyH2+* have 15-20 nm blue shifts from room temperature to 400 degrees C. For a deaerated neutral solution of 4,4'-bpy in the presence of tert-butyl alcohol, ethanol, or NaCOOH, the doubly protonated electron adduct is the main transient species at room temperature. But at temperatures > 350 degrees C, a monoprotonated form, the N-hydro radical 4,4'-bpyH*, becomes predominant. Interestingly, at room temperature, CO2-* could not efficiently react with 4,4'-bpy, but the reaction was accelerated with increasing temperature; at 350 degrees C, this reaction completed within 2 mus. Using an alkaline solution (pH = 11.5) of 4,4'-bpy in the presence of tert-butyl alcohol, we studied the N-hydro radical 4,4'-bpyH* from room temperature to 400 degrees C at 25 MPa. An estimation of the temperature-dependent G(e(aq)-) at 25 MPa agrees with our previous result with methyl viologen as a scavenger.