Roles of HNO x and Carboxylic Acids in the Thermal Stability of Nitroplasticizer.

In the thermal aging of nitroplasticizer (NP), the produced nitrous acid (HONO) can decompose into reactive nitro-oxide species and nitric acid (HNO3). These volatile species are prone to cause cascaded deterioration of NP and give rise to various acidic constituents. To gain insight on the early stage of NP degradation, an adequate method for measuring changes in the concentrations of HONO, HNO3, and related acidic species is imperative. The typical assessment of acidity in nonaqueous solutions (i.e., acid number) cannot differentiate acidic species and thus presents difficulty in the measurement of HONO and HNO3 at a micromolar concentration level. Using liquid-liquid extraction and ion chromatography (IC), we developed a fast and unambiguous analytical method to accurately determine the concentration of HONO, HNO3, acetic/formic acids, and oxalic acid in aged NP samples. Given by the overlay analysis results of liquid chromatography coupled with quadrupole time-of-flight mass spectrometry and IC, the prominent increase of produced HONO after the depletion of antioxidants is the primary cause of HNO3 formation in the late stage of NP degradation, which results in the acid-catalyzed hydrolysis of NP into 2,2-dinitropropanol and acetic/formic acids. Our study has demonstrated that the aging temperature plays a crucial role in accelerating the formation and decomposition of HONO, which consequently increases the acidity of aged NP samples and hence accelerates the hydrolyzation of NP. Therefore, to prevent NP from undergoing rapid degradation, we suggest that the concentration of HNO3 should be maintained below 1.35 mM and the temperature under 38 °C.

Field experiments of surface water to groundwater recharge to characterize the mobility of uranium and vanadium at a former mill tailing site.

Characterizing the mobility of uranium and vanadium in groundwater with a hydraulic connection to surface water is important to inform the best management practices of former mill tailing sites. In this study, the recharge of river water to the unsaturated and saturated zones of a uranium-contaminated alluvial aquifer was simulated in a series of forced-gradient single- and multi-well injection-extraction tests. The injection fluid (river water) was traced with natural and artificial tracers that included halides, fluorobenzoates, lithium, and naphthalene sulfonate to characterize the potential mass transport mechanisms of uranium and vanadium. The extraction fluid (river water/groundwater mixture) was analyzed for the tracers, uranium, and vanadium. The results from the tracers indicated that matrix diffusion was likely negligible over the spatiotemporal scales of the tests as evident by nearly identical breakthrough curves of the halides and fluorobenzoates. In contrast, the breakthrough curves of lithium and naphthalene sulfonate indicated that sorption by cation exchange and sorption to organic matter, respectively, were potential mass transport mechanisms of uranium and vanadium. Uranium was mobilized in the saturated zone containing gypsum (gypsum-rich zone), the vadose zone (vadose-rich zone), and the saturated zone containing organic carbon (organic-rich zone) whereas vanadium was mobilized only in the saturated gypsum-rich zone. The mechanisms responsible for the mobilization of uranium and vanadium were likely dissolution of uranium- and vanadium-bearing minerals and/or desorption from the gypsum-rich zone, flushing of uranium from the vadose-rich zone, and desorption of uranium from the organic-rich zone due to the natural contrast in the geochemistry between the river water and groundwater. The experimental design of this study was unique in that it employed the use of multiple natural and artificial tracers coupled with a direct injection of native river water to groundwater. These results demonstrated that natural recharge and flooding events at former mill tailing sites can mobilize uranium, and possibly vanadium, and contribute to persistent levels of groundwater contamination.

Hemoglobin parameters from diffuse reflectance data.

Tissue vasculature is altered when cancer develops. Consequently, noninvasive methods of monitoring blood vessel size, density, and oxygenation would be valuable. Simple spectroscopy employing fiber optic probes to measure backscattering can potentially determine hemoglobin parameters. However, heterogeneity of blood distribution, the dependence of the tissue-volume-sampled on scattering and absorption, and the potential compression of tissue all hinder the accurate determination of hemoglobin parameters. We address each of these issues. A simple derivation of a correction factor for the absorption coefficient, µa, is presented. This correction factor depends not only on the vessel size, as others have shown, but also on the density of blood vessels. Monte Carlo simulations were used to determine the dependence of an effective pathlength of light through tissue which is parameterized as a ninth-order polynomial function of µa. The hemoglobin bands of backscattering spectra of cervical tissue are fit using these expressions to obtain effective blood vessel size and density, tissue hemoglobin concentration, and oxygenation. Hemoglobin concentration and vessel density were found to depend on the pressure applied during in vivo acquisition of the spectra. It is also shown that determined vessel size depends on the blood hemoglobin concentration used.

Effects of acetic acid on light scattering from cells.

Acetic acid has been used for decades as an aid for the detection of precancerous cervical lesions, and the use of acetic acid is being investigated in several other tissues. Nonetheless, the mechanism of acetowhitening is unclear. This work tests some of the hypotheses in the literature and measures changes in light scattering specific to the nucleus and the cytoplasm. Wide angle side scattering from both the nucleus and the cytoplasm increases with acetic application to tumorigenic cells, with the increase in nuclear scattering being greater. In one cell line, the changes in nuclear scattering are likely due to an increase in number or scattering efficiency of scattering centers smaller than the wavelength of excitation light. There are likely several cellular changes that cause acetowhitening and the cellular changes may differ with cell type. These results should lead to a better understanding of acetowhitening and potentially the development of adjunct techniques to improve the utility of acetic acid application. For the well-studied case of cervical tissue, acetowhitening has been shown to be sensitive, but not specific for oncogenic changes needing treatment.

Correlating light scattering with internal cellular structures.

The origins of side scattering from a fibroblast and cervical cell line were determined by comparing side-scatter images with images stained for lysosomes, nuclei, and mitochondria on a cell by cell basis. Lysosomes or nuclei are the most efficient type of scatterer depending on the cell type and incident light polarization. The relative scattering efficiencies of lysosomes and mitochondria were the same for both cell lines, while the scattering efficiencies of the nuclei differed. The percent of 90° scattering from the nucleus, mitochondria, and lysosomes as well as the group of other internal cellular objects was estimated. The nucleus was the largest contributor to side scatter in the cervical carcinoma cells. The contributions of lysosomes, mitochondria, the nucleus, and particles unstained by either Hoechst, LysoSensor or MitoTracker ranges from ∼20% to ∼30% in fibroblast cells. The contribution of lysosomes to side scatter was much stronger when the incident light was polarized perpendicular to the scattering plane than when the polarization of the side scatter laser was parallel to the scattering plane. This dependence on side scatter polarization indicates that lysosomes contain scattering structures that are much smaller than the wavelength of light used in the measurements (785 nm). In conclusion, mitochondria were not found to be either the most efficient scatterer or to have the largest contribution to scattering in either cell line, in contrast to previous reports. Rather lysosomes, nuclei and unknown particles all have significant contributions to 90° scattering and the contributions of some of these particles can be modulated by changing the polarization of the incident light.