Sonochemical degradation of cyclic nitroxides in aqueous solution

A case study on the influence of hydrophilicity on the signal enhancement by dynamic nuclear polarization

In this work, the behavior of four different commercially available polarizing agents is investigated employing the non-ionic model surfactant 1-octanol as analyte. A relative method for the comparison of the proportion of the direct and indirect polarization transfer pathways is established, allowing a direct comparison of the polarization efficacy for different radicals and different parts of the 1-octanol molecule despite differences in radical concentration or sample amount. With this approach, it could be demonstrated that the hydrophilicity is a key factor in the way polarization is transferred from the polarizing agent to the analyte. These findings are confirmed by the determination of buildup times T_b, illustrating that the choice of polarizing agent plays an essential role in ensuring an optimal polarization transfer and therefore the maximum amount of enhancement possible for DNP enhanced NMR measurements.

Nanoscale structure and dynamics of thermoresponsive single-chain nanoparticles investigated by EPR spectroscopy

We characterize temperature-dependent macroscopic and nanoscopic phase transitions and nanoscopic pre-transitions of water-soluble single chain nanoparticles (SCNPs). The studied SCNPs are based on polymers displaying lower-critical solution temperature (LCST) behavior and show nanoscale compartmentation. SCNPs are amenable to continuous wave electron paramagnetic resonance (CW EPR) spectroscopy to study how amphiphilic, non-covalently added nitroxide spin probes or covalently attached spin labels sample their environment concerning nanoscale structures (polarity, hydrophilicity/-phobicity) and dynamics. These SCNPs are formed through single-chain collapse and have been shown to have nanosized compartments that are rigidified during the crosslinking process. We analyze the temperature-dependent phase transitions of spin-labeled SCNPs by rigorous spectral simulations of a series of multicomponent EPR-spectra that derive from the nanoinhomogeneities (1) that are due to the single-chain compartmentation in SCNPs and (2) the transformation upon temperature change due to the LCST behavior. These transitions of the SCNPs and their respective polymer precursors can be monitored and understood on the nanoscale by following EPR-spectroscopic parameters like hyperfine couplings that depend on the surrounding solvent molecules or Heisenberg spin exchange between small molecule spin probes or covalently attached spin labels in the nanocompartments. In particular, for one SCNP, we find an interesting behavior that we ascribe to the properties of the nanosized inner core with continuous effects before and jump-like changes after the macroscopic thermal collapse, indicating highly efficient desolvation and compaction upon an increase in temperature and aggregation of individual nanoparticles above the collapse temperature.

Physical and chemical effects of acoustic cavitation in selected ultrasonic cleaning applications

Acoustic cavitation in a liquid medium generates several physical and chemical effects. The oscillation and collapse of cavitation bubbles, driven at low ultrasonic frequencies (e.g., 20 kHz), can generate strong shear forces, microjets, microstreaming and shockwaves. Such strong physical forces have been used in cleaning and flux improvement of ultrafiltration processes. These physical effects have also been shown to deactivate pathogens. The efficiency of deactivation of pathogens is not only dependent on ultrasonic experimental parameters, but also on the properties of the pathogens themselves. Bacteria with thick shell wall are found to be resistant to ultrasonic deactivation process. Some evidence does suggest that the chemical effects (radicals) of acoustic cavitation are also effective in deactivating pathogens. Another aspect of cleaning, namely, purification of water contaminated with organic and inorganic pollutants, has also been discussed in detail. Strong oxidising agents produced within acoustic cavitation bubbles could be used to degrade organic pollutants and convert toxic inorganic pollutants to less harmful substances. The effect of ultrasonic frequency and surface activity of solutes on the sonochemical degradation efficiency has also been discussed in this overview.

Enhanced ozonation of selected pharmaceutical compounds by sonolysis

In search of new options to achieve removal of pharmaceuticals in the environment, combined ultrasound and ozonation has become a focus of intense investigation for wastewater treatment. In this study, three pharmaceuticals were selected as model compounds for degradation experiments: diclofenac (DCF), sulfamethoxazole (SMX) and carbamazepine (CBZ). Comparison of the degradation rates for both ozonation and combined ultrasound/ozonation treatments was performed on single synthetic solutions as well as on a mixture of the selected pharmaceuticals, under different experimental conditions. For single synthetic solutions, the efficiency removal for ozonation reached 73%, 51% and 59% after 40 min for DCF, SMX and CBZ, respectively. Comparable results were obtained for pharmaceuticals in mixture. However, the combined ultrasound/ozone treatment was found to increase degradation efficiencies for both DCF and SMX single solutions up to 94% and 61%, respectively, whereas lower removal yields, up to 56%, was noted for CBZ. Likewise, when the combined treatment was applied to the mixture, relatively low removal efficiencies was found for CBZ (44%) and 90% degradation yield was achieved for DCF.

Kinetics and mechanism of sonochemical degradation of pharmaceuticals in municipal wastewater

A series of six pharmaceuticals were degraded by continuous wave (CW) and pulsed wave (PW) ultrasound at 205 kHz using deionized water, wastewater effluent, and its isolated organic matter matrices. In deionized water, we observed that hydrophobicity is superior to diffusivity (D(W)) for predicting degradation kinetics. Enhancements in degradation kinetics by the PW mode were greatest for the highest DW (i.e., fluorouracil (5-FU)) and K(OW) (i.e., lovastatin (LOVS)) compounds, indicating that a pharmaceutical with either high diffusivity and low hydrophobicity or low diffusivity and high hydrophobicity benefits from additional time to populate the bubble-water interface during the silent cycle of PW ultrasound. Degradation of 5-FU and LOVS were inhibited by wastewater effluent to a greater extent than the other pharmaceuticals. In addition, a pulse enhancement (PE) for 5-FU and LOVS was not present in wastewater effluent. Irradiating 5-FU and LOVS in hydrophobic (HPO), transphilic (TPI), and hydrophilic (HPI) fractions of effluent organic matter (EfOM) showed that the TPI fraction reduced the PE the most, followed by the HPI and HPO fractions. The smaller size of the TPI over the HPO fraction and higher hydrophobicity of TPI over HPI implicate both size and hydrophobicity of EfOM in hindering degradation of pharmaceuticals.

High field dynamic nuclear polarization NMR with surfactant sheltered biradicals

We illustrate the ability to place a water-insoluble biradical, bTbk, into a glycerol/water matrix with the assistance of a surfactant, sodium octyl sulfate (SOS). This surfactant approach enables a previously water insoluble biradical, bTbk, with favorable electron-electron dipolar coupling to be used for dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments in frozen, glassy, aqueous media. Nuclear Overhauser enhancement (NOE) and paramagnetic relaxation enhancement (PRE) experiments are conducted to determine the distribution of urea and several biradicals within the SOS macromolecular assembly. We also demonstrate that SOS assemblies are an effective approach by which mixed biradicals are created through an assembly process.