In the next decades, the influence of wildfires in controlling the cycling and composition of soil organic matter (SOM) globally and in the western U.S. is expected to grow. While the impact of fires on bulk SOM has been extensively studied, the extent at which heating of soil affects the soluble component of SOM remains unclear. Here we investigated the thermal transformations of water‐extractable organic matter (WEOM) by examining the changes in the distribution of carbon (C) functional groups in WEOM from soils heated at low and intermediate temperatures. WEOM (<0.7 µm particle size) was extracted from topsoils (0–5 cm depth) of five soil series formed from a nonglaciated granitic bedrock and sampled along a Sierra Nevada climosequence. Soils were heated in a muffle furnace at 150°C, 250°C, and 350°C for 1 h. The extracted solution was analyzed for WEOM aromaticity, mean molecular weight, organic C (OC) concentration, and major structural components by employing optical spectrophotometry and liquid‐state 1H‐NMR spectroscopy. At 150°C and 250°C, OC concentrations increased relative to the thermally unaltered samples, with losses of oxygenated functional C groups and enrichment of aliphatic C structures observed at 250°C. Conversely, OC concentration and mean molecular weight decreased as heating increased from 250°C to 350°C, whereas WEOC became more enriched in aromatic C structures. Our results suggest that low and intermediate fire intensities significantly alter the nature of dissolved organic matter exported from soils to rivers in the Sierra Nevada and beyond.

With the rise in fluorinated pharmaceuticals, it is becoming increasingly important to develop new 19 F NMR-based methods to assist in their analysis. Crucially, obtaining information regarding the conformational dynamics of a molecule in solution can aid the design of strongly binding therapeutics. Herein, we report the development of a 2D 1 H-19 F Heteronuclear Overhauser Spectroscopy (HOESY) experiment to measure 1 H-19 F internuclear distances, with accuracies of~5% when compared with 1 H-19 F internuclear distances calculated by quantum chemical methods. We demonstrate that correcting for cross-relaxation of 1 H, using the diagonal peaks from the 2D 1 H-1 H Nuclear Overhauser Enhancement Spectroscopy (NOESY), is critical in obtaining accurate values for 1 H-19 F internuclear distances. Finally, we show that by using the proposed method to measure 1 H-19 F internuclear distances, we are able to determine the relative stereochemistry of two fluorinated pharmaceuticals.

Many central African soils are sandy single‐grain‐structure materials developing under semiarid conditions, and derived from the underlying granite. To obtain a useful size distribution function for the nonclay fraction required a quantitative model for granite disintegration.Methods of characterizing particulate distributions are briefly reviewed with reference to the mechanisms giving rise to them. J. G. Bennett's (1936) description of brittle solid disintegration has been extended to yield the incomplete gamma function as a descriptor of the product of granite disintegration. This is discussed and compared with the log‐normal and Weibull functions in terms of postulated mechanisms.It is concluded that the mechanism presented here more closely approximates the disintegration process than those yielding the above two functions, and that the resulting incomplete gamma function should be a reasonable basic descriptor of the particle‐size distribution of disintegrating granite.

The object of this study was to test the previously developed two‐parameter incomplete gamma function as a descriptor for the > 0.002‐mm fraction of some semiarid, sandy, granite‐derived soils from south‐central Africa (southern Rhodesia). Samples were taken from profiles at five locations. Three of these locations had been previously selected for sampling disintegrating granite, and one was a medium rainfall site. Particle‐size distributions were obtained using the standard sieving and pipette method. For materials > 10 mm Martin's diameter was measured directly. The incomplete gamma described the data reasonably well. The two distribution parameters, α, the weathering index, and ρ, the scale factor, varied as expected. The mean and standard deviation increased with depth as expected. On the basis of the behavior of ρ the profiles tested were separated into two groups. Grouping according to the variation of α yielded the same two groups. The difference between the two groups could perhaps be the degree of development. However, more comparisons are necessary to check this.

The object of this study was to test the incomplete gamma function previously developed as a descriptor for grapite disintegration. Samples of disintegrating granite were taken from several sites at three locations in a hot semiarid environment in south‐central Africa (southern Rhodesia). These samples were from surface rock, profile corestones, and disintegrating rock at the base of the soil profile. Particlesize distributions were obtained using the standard sieving and pipette method. For materials > 10 mm, Martin's diameter was measured directly.The incomplete gamma function was fitted to these data, and also to U.S. and French data from the literature, for granite in an apparently similar state of disintegration. The values for the degree‐of‐disintegration parameter were fairly uniform. The mode of disintegration appeared the same regardless of site. The two‐parameter incomplete gamma distribution was found to be a reasonably good descriptor of the particle‐size distribution of disintegrating granite. The mean size appeared to be a sensitive and useful single‐valued descriptor for these distributions.