The photodissociation dynamics of the thiophenoxy radical (C6H5S) have been investigated using fast beam coincidence translational spectroscopy. Thiophenoxy radicals were produced by photodetachment ...of the thiophenoxide anion followed by photodissociation at 248 nm (5.0 eV), 193 nm (6.4 eV), and 157 nm (7.9 eV). Experimental results indicate two major competing dissociation channels leading to SH + C6H4 (o-benzyne) and CS + C5H5 (cyclopentadienyl) with a minor contribution of S + C6H5 (phenyl). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Transition states and minima for each reaction pathway were calculated using density functional theory to facilitate experimental interpretation. The proposed dissociation mechanism involves internal conversion from the initially prepared electronic excited state to the ground electronic state followed by statistical dissociation. Calculations show that SH loss involves a single isomerization step followed by simple bond fission. For both SH and S loss, C–S bond cleavage proceeds without an exit barrier. By contrast, the CS loss pathway entails multiple transition states and minima as it undergoes five membered ring formation and presents a small barrier with respect to products. The calculated reaction pathway is consistent with the experimental translational energy distributions in which the CS loss channel has a broader distribution peaking farther away from zero than the corresponding distributions for SH loss.
Discussion can be an important and powerful tool in efforts to build a more diverse, equitable, and inclusive future for STEM (i.e., science, technology, engineering, and mathematics). However, ...facilitating discussions on difficult, complex, and often uncomfortable issues, like racism and sexism, can feel daunting. We outline a series of steps that can be used by educators to facilitate productive discussions that empower everyone to listen, contribute, learn, and ultimately act to transform STEM.
Inverse gas chromatography (IGC) was used to characterize dispersive surface energies γSD and cohesive Hamaker constants Aii for RDX, PETN, TNT, ammonium nitrate (AN), and AN‐based explosives at 303 ...K. The γSD for RDX at 303 K is compared to previous studies and generally found to be in good agreement, substantiating the use of NESTT training materials to characterize explosives via IGC. Additionally, the effect of the amount of fuel in the AN mixtures on γSD is examined using simple linear regression. Finally, the IGC‐predicted Aii values are compared to Lifshitz estimations for Aii of RDX, PETN, TNT, and AN.
Dissolved organic matter (DOM) in lakes across elevation gradients is a complex function of topography, climate, vegetation coverage, land use, and lake properties. To examine sources and processing ...of DOM from sea level to mountain lakes (3–1,574 m), we measured dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) optical properties, lake characteristics, and water quality parameters in 62 freshwater lakes in the Pacific Northwest, USA. Higher elevation lakes had lower DOC concentrations and absorbance. These lakes had higher forest cover and minimal wetlands in their watershed, in addition to low nutrients, water temperatures, and chlorophyll a in the lake itself. Two humic‐like and one protein‐like fluorescent component were identified from excitation‐emission matrix spectroscopy. The index of recent autochthonous contribution (BIX), fluorescence index (FIX), and SR optical indices showed that most lakes were dominated by terrestrially derived material. The humification index (HIX) and specific ultra‐violet absorbance (SUVA254) were consistent with more aromatic humic CDOM at lower elevations. The lower fluorescence of humic‐like components at higher elevation was attributed to lower inputs from vegetation. The relative contribution of the protein‐like component increased at higher elevation. This may be due to reduced allochthonous terrestrial inputs relative to in situ production of autochthonous material or increased photochemical/biological degradation of allochthonous material. Differences in optical characteristics associated with the amount and source of CDOM were observed across the elevational gradient. These differences were driven by characteristics at both within‐lake and watershed scales.
Plain Language Summary
Dissolved organic matter (DOM) in lakes is an important part of the global carbon cycle. The amounts, sources, and properties of DOM can vary as a function of lake elevation due to changes in vegetation, lake properties, climate, and topography. To assess these patterns, we studied DOM in 62 lakes ranging from sea level to mountain lakes in the Pacific Northwest region of the USA. Lower elevation lakes had higher levels of DOM, attributed to higher inputs from the terrestrial environment. Higher elevation lakes had lower wetland coverage within their watershed. Results also indicated that some lakes had DOM that came from microbial production in the lake waters. This was more important in higher elevation lakes that had lower amounts of DOM from vegetation in the watershed. Differences in DOM amount and source were observed across the elevational gradient, driven by an interplay of characteristics at both within‐lake and watershed scales.
Key Points
Dissolved organic carbon and chromophoric dissolved organic matter amounts decrease in lakes at higher elevations with lower wetland and agricultural land cover
Most lakes are dominated by allochthonous terrestrial material, with more aromatic humified material at lower elevations
Relative contribution of autochthonous material is more important at higher elevations, possibly due to shifts in vegetation types
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•Opioids are important pain-relieving drugs but also carry a risk of harmful side effects.•Decreasing the pKa of the opioid amine group promotes selective binding in inflamed ...tissue.•Fluorinated morphine derivatives are calculated to have lower pKa’s for pH -specific binding.
Opioids such as morphine are important pain-relieving drugs but also carry a risk of harmful side effects including addiction. Morphine is active in both healthy and inflamed tissue, however, decreasing the pKa of the biochemically-active amine group can promote selective binding in the more acidic conditions of inflamed tissue and reduce harmful side effects associated with opioids. Herein, we explore the impact of fluorination on the pKa of fluoromorphine derivatives to identify which will bind selectively in inflamed tissue. Theoretical pKa values are determined at the M06-2X(SMD)/aug-cc-pVDZ level of theory by calculating the ΔGaq values for the amine deprotonation reactions.
Abstract
Temperature‐dependent rate constants for the reactions of CH
2
OO with acetone (Ac), biacetyl (BiAc), and acetylacetone (AcAc) have been measured over the range 275–335 K using a flash ...photolysis, transient absorption spectroscopy technique. The measurements were performed at a total pressure of ∼80 Torr in N
2
bath gas, which corresponds to the high‐pressure limit for these reactions. All three reactions show linear Arrhenius plots with negative temperature dependences. Rate constants increase in the order Ac < AcAc « BiAc across the temperature range; at 295 K the rate constants are
k
Ac
= (4.8 ± 0.4) × 10
–13
cm
3
s
–1
,
k
AcAc
= (8.0 ± 0.7) × 10
–13
cm
3
s
–1
, and
k
BiAc
= (1.10 ± 0.09) × 10
–11
cm
3
s
–1
. Sensitivity to temperature, characterized by the magnitude of the negative activation energy, increases in the order AcAc < BiAc < Ac (
E
a
/
R
values of –1830 ± 170 K, –1260 ± 170 K, and –460 ± 180 K, respectively). CBS‐QB3 calculations show that the Ac and BiAc reactions proceed via formation of an entrance channel complex followed by 1,3‐dipolar cycloaddition to form secondary ozonide products via a submerged transition state. For the BiAc reaction, the rate limiting step appears to be rearrangement of a long‐range van der Waals complex into the short‐range complex that subsequently leads directly to the cycloaddition transition state with a very low energy barrier. The calculations show that two reaction pathways are competitive for AcAc with nearly identical transition state free energies (Δ
G
° = +10.1 kcal mol
–1
at 298 K) found for cycloaddition at the C=O and at the C=C site of the dominant enolone tautomer. The weak temperature dependence observed is likely due to competition between these pathways.
The increased use of ethanol as an additive in gasoline is expected to increase atmospheric ethanol levels. Understanding future impacts requires an understanding of the current atmospheric ethanol ...budget. Air-sea exchange is one of the largest sources of uncertainty in budget estimates. Understanding processes that produce or destroy ethanol in seawater will help constrain air-sea exchange estimates. The rate of biological consumption of ethanol in seawater was measured in Southern California surface coastal water sampled from a tidally flushed river mouth over a six-month period. First-order rate constants (k) for biological degradation of approximately ambient ethanol levels of 89 nM ranged from zero to 1.9 ± 0.1 × 10−2 min−1 with an average of 3.8 ± 5.9 × 10−3 min−1 (n = 20). This corresponds to an average biological turnover time (1/k) of approximately 4.4 h or an average biological half-life (0.693/k) of approximately 3 h. There were several rain events over this time period resulting in flow from upstream in the river; these were associated with increased bacterial levels, higher absorption coefficients and reduced salinity. Rate constants, in general, increased with the number of bacterial colony forming units in the water sample. Excluding the two rate constant maxima events the background biological degradation rate constant in the absence of rain/bacteria input from upstream, is 1.3 ± 1.0 × 10−3 min−1. This corresponds to an average biological turnover time of approximately 13 h and an average biological half-life of approximately 9 h. Autoclaved samples (to remove bacteria) showed no measurable ethanol degradation, suggesting that chemical loss processes are not significant.
•The average rate constant for degradation by bacteria is 1.3 ± 1.0 × 10−3 min−1.•This gives an average biological turnover time of 13 h and half-life of 9 h.•Chemical loss is not significant in autoclaved samples (to remove bacteria).•Photochemical degradation is very small relative to biological degradation.
Patients who receive chimeric antigen receptor (CAR)-T cells that are enriched in memory T cells exhibit better disease control as a result of increased expansion and persistence of the CAR-T cells. ...Human memory T cells include stem-like CD8
memory T cell progenitors that can become either functional stem-like T (T
) cells or dysfunctional T progenitor exhausted (T
) cells. To that end, we demonstrated that T
cells were less abundant in infused CAR-T cell products in a phase 1 clinical trial testing Lewis Y-CAR-T cells (NCT03851146), and the infused CAR-T cells displayed poor persistence in patients. To address this issue, we developed a production protocol to generate T
-like CAR-T cells enriched for expression of genes in cell replication pathways. Compared with conventional CAR-T cells, T
-like CAR-T cells had enhanced proliferative capacity and increased cytokine secretion after CAR stimulation, including after chronic CAR stimulation in vitro. These responses were dependent on the presence of CD4
T cells during T
-like CAR-T cell production. Adoptive transfer of T
-like CAR-T cells induced better control of established tumors and resistance to tumor rechallenge in preclinical models. These more favorable outcomes were associated with increased persistence of T
-like CAR-T cells and an increased memory T cell pool. Last, T
-like CAR-T cells and anti-programmed cell death protein 1 (PD-1) treatment eradicated established tumors, and this was associated with increased tumor-infiltrating CD8
CAR
T cells producing interferon-γ. In conclusion, our CAR-T cell protocol generated T
-like CAR-T cells with enhanced therapeutic efficacy, resulting in increased proliferative capacity and persistence in vivo.
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