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In order to assess the environmental risk of a pharmaceutical, information is needed on the sorption of the compound to solids. Here we use a high-quality database of measured sorption coefficients, all determined following internationally recognised protocols, to evaluate models that have been proposed for estimating sorption of pharmaceuticals from chemical structure, some of which are already being used for environmental risk assessment and prioritization purposes. Our analyses demonstrate that octanol-water partition coefficient (Kow) alone is not an effective predictor of ionisable pharmaceutical sorption in soils. Polyparameter models based on pharmaceutical characteristics in combination with key soil properties, such as cation exchange capacity, increase model complexity but yield an improvement in the predictive capability of soil sorption models. Nevertheless, as the models included in this analysis were only able to predict a maximum of 71% and 67% of the sorption coefficients for the compounds to within one log unit of the corresponding measured value in soils and sludge, respectively, there is a need for new models to be developed to better predict the sorption of ionisable pharmaceuticals in soil and sludge systems. The variation in sorption coefficients, even for a single pharmaceutical across different solid types, makes this an inherently difficult task, and therefore requires a broad understanding of both chemical and sorbent properties driving the sorption process.

Benzidine has been marked as a priority chemical on the National Priorities List by the U.S. Environmental Protection Agency because of its carcinogenic nature. Benzidine sorbs to the sediment matrix after entering water-sediment ecosystems and undergoes at least three different fate processes, including cation exchange, hydrophobic partitioning, and covalent binding. Sediment samples taken from Lake Macatawa (MI, USA) were used after drying and grinding treatments in this study. Sorption experiments were conducted in the buffered deionized water-sediment slurries with a pH range of approximately 3 to 7. Experimental results indicated that low pH conditions (e.g., pH 3.2) favored sorption of benzidine onto sediment, where a large proportion of benzidine species protonated and sorbed predominantly through the fast cation exchange process. Sorption kinetics data suggested that reactions between protons and carbonate components residing in the sediment matrices led to a shift of sorption mechanisms from cation exchange to hydrophobic partitioning, covalent binding, or both when the slurry pH increased from 3 to 7. A sorption mechanism-based model is presented to describe benzidine sorption behavior in the sediment-water systems at different pH values. This model comprises three components mathematically: the linear hydrophobic partitioning, Langmuir-type covalent binding, and quadratic cation exchange. On the basis of nonlinear regression, this model fits the experimental data well. The organic carbon-normalized distribution coefficient value calculated from this model (1,914 L/kg at pH 6.9), and the available covalent binding sites in the sediment matrices were 27 to 52 mmol/kg organic carbon in the pH range of 5.0 to 6.9. The predicted model parameters are in good agreement with the reported literature values. By this model, the individual contribution from each sorption mechanism can be quantified with a wide pH range (e.g., from pH 3 to 7). This model strategy could provide an alternative way to predict the complex sorption processes of aromatic amines containing one or two amino groups in the aqueous-sediment environment.

Biomolecular condensates regulate cellular function by compartmentalizing molecules without a surrounding membrane. Condensate function arises from the specific exclusion or enrichment of molecules. Thus, understanding condensate composition is critical to characterizing condensate function. Whereas principles defining macromolecular composition have been described, understanding of small-molecule composition remains limited. Here we quantified the partitioning of ~1,700 biologically relevant small molecules into condensates composed of different macromolecules. Partitioning varied nearly a million-fold across compounds but was correlated among condensates, indicating that disparate condensates are physically similar. For one system, the enriched compounds did not generally bind macromolecules with high affinity under conditions where condensates do not form, suggesting that partitioning is not governed by site-specific interactions. Correspondingly, a machine learning model accurately predicts partitioning using only computed physicochemical features of the compounds, chiefly those related to solubility and hydrophobicity. These results suggest that a hydrophobic environment emerges upon condensate formation, driving the enrichment and exclusion of small molecules. Biomolecular condensates compartmentalize molecules without membranes. Understanding condensate composition is important given that their function relies on the selective exclusion or enrichment of molecules. Now, investigating small-molecule partitioning reveals variations across compounds, yet correlations indicate physical similarities between disparate condensates. Machine learning accurately predicts partitioning on the basis of physicochemical features, demonstrating the role of a hydrophobic environment in driving enrichment and exclusion.

We have calculated the distribution in a lipid bilayer of small molecules mimicking 17 natural amino acids in atomistic detail by molecular dynamics simulation. We considered both charged and uncharged forms for Lys, Arg, Glu, and Asp. The results give detailed insight in the molecular basis of the preferred location and orientation of each side chain as well the preferred charge state for ionizable residues. Partitioning of charged and polar side chains is accompanied by water defects connecting the side chains to bulk water. These water defects dominate the energetic of partitioning, rather than simple partitioning between water and a hydrophobic phase. Lys, Glu, and Asp become uncharged well before reaching the center of the membrane, but Arg may be either charged or uncharged at the center of the membrane. Phe has a broad distribution in the membrane but Trp and Tyr localize strongly to the interfacial region. The distributions are useful for the development of coarse-grained and implicit membrane potentials for simulation and structure prediction. We discuss the relationship between the distribution in membranes, bulk partitioning to cyclohexane, and several amino acid hydrophobicity scales.

Bacterial microcompartments are protein organelles with diverse metabolic capabilities. Their functional diversity is determined by an enzymatic core that is sequestered within a structurally conserved protein shell architecture. Segregation of protein cargo into the bacterial microcompartment is enabled by encapsulation peptides, which are short helical domains fused to core proteins through a disordered linker. Here, we investigate how encapsulation peptides drive multicomponent cargo assembly into biomolecular condensates. In vitro experiments supported by molecular dynamics simulations demonstrate the importance of both conserved hydrophobic packing and electrostatic interactions in stabilizing trimeric encapsulation peptide bundles. Topological rearrangements of encapsulation peptide domains can drive programmable liquid- or gel-like partitioning in vitro and in vivo. This partitioning is found to be encapsulation peptide-specific, modular, and can co-assemble at least three fluorescent reporters. In summary, we describe the molecular features necessary to drive biomolecular condensation using a widespread peptide tag. This work can serve as a blueprint for implementing encapsulation peptide biotechnology across diverse applications. Bacteria are increasingly known to employ internal organization strategies. Here, authors demonstrate that bacterial encapsulation peptides cause self-condensation of associated protein domains. These peptides may allow for programmable spatial control of metabolism.

Contamination of aquatic ecosystems by hydrophobic organic contaminants (HOCs) is often assessed based on their concentrations in riverbed sediment and suspended particulate matter (SPM). However, total HOC concentration (CTOT) in sediment or SPM is of limited value for evaluating the exposure of benthic or pelagic organisms. The accessible HOC concentration (CAS) presents a useful parameter quantifying the overall pool of HOC in sediment or SPM available for fast partitioning to the water phase or biota. We applied a novel approach of ex situ sequential equilibrium partitioning with silicone elastomer sampler at a high sampler/SPM phase ratio to measure CAS of HOC in SPM from the Danube River. We compared CTOT and CAS in SPM and surface layer sediment collected at the same sites to evaluate whether HOC monitoring in the two matrices provides equivalent information on environmental quality. At most sites, there was a good agreement and correlation of organic carbon (OC)-normalised CTOT in SPM and sediment for polychlorinated biphenyls (PCBs) and the majority of organochlorine pesticides (OCPs). In contrast, CTOT of polycyclic aromatic hydrocarbons (PAHs) in SPM were up to a factor 10 lower in SPM than in sediment. Site-specific differences of OC-normalised CAS concentrations in SPM and sediments were observed for PCBs and OCPs, with accessibility mostly lower in SPM than in sediment. The highest accessibility in SPM was observed for PCBs, ranging between 15 and 30%. The accessibility of OCPs varied from 0 to 23%. SPM and riverbed sediment samples provide complementary but not mutually interchangeable information on HOC contamination.

Engineered microbial ecosystems in bioscrubbers for the treatment of volatile organic compounds (VOCs) have been complicated by complex VOC mixtures from various industrial emissions. Microbial associations with VOC removal performance of the bioscrubbers are still not definitive. Here, one- and two-phase partitioning airlift bioreactors were used for the treatment of a complex VOC mixture. Microbial characteristics in both bioreactors were uncovered by high-throughput metagenomics sequencing. Results showed that dominant species with specialized VOC biodegradability were mainly responsible for high removal efficiency of relative individual VOC. Competitive enzyme inhibitions among the VOC mixture were closely related to the deterioration of removal performance for individual VOC. Relative to the mass transfer resistance, the specialized biodegrading functions of microbial inoculations and enzymatic interactions among individual VOC biodegradation also must be carefully evaluated to optimize the treatment of complex VOC mixtures in bioreactors.

Research during the last decade has led to several competing concepts of bioavailability and to many more methods to measure bioavailability. One reason for disagreement is the confusion of two fundamentally different parameters, accessible quantity and chemical activity. The accessible quantity describes a mass of contaminants, which can become available to, for example, biodegradation and biouptake. It can be determined with mild extraction schemes or depletive sampling techniques. The chemical activity, on the other hand, quantifies the potential for spontaneous physicochemical processes, such as diffusion, sorption, and partitioning. For instance, the chemical activity of a sediment contaminant determines its equilibrium partitioning concentration in sediment‐dwelling organisms, and differences in chemical activity determine the direction and extent of diffusion between environmental compartments. Chemical activity can be measured with equilibrium sampling devices and, theoretically, is closely linked to fugacity and freely dissolved concentration. The distinction between accessibility and chemical activity is outlined, and the benefits and limitation of both endpoints are provided. Finally, examples of how to measure and apply them are presented.

Perfluorooctane sulfonate (PFOS) is an emerging contaminant frequently detected in subsurface environments, raising significant concern due to its environmental persistence, mobility, and potential human health impacts. This study examines PFOS adsorption onto a range of solid substrates, including pure minerals, mineral assemblages, and natural soils. Specifically, the adsorption behavior of 2-line ferrihydrite, ferrihydrite-coated sand, and soil collected from a PFOS-impacted site in Killingworth, Connecticut was investigated to evaluate their capacity to retain PFOS under varying geochemical conditions. By integrating batch adsorption experiments with surface complexation modeling (SCM) and applying the component additivity approach, this study elucidates the reactive transport mechanisms governing PFOS behavior under a range of geochemical conditions. Our findings demonstrate that PFOS adsorption occurs significantly on both ferrihydrite and quartz surfaces, with the ferrihydrite-coated sand and soil exhibiting retention behavior attributable to contributions from both mineral phases. At lower pH values, sorption is predominantly governed by outer-sphere complexation driven by the surface charge characteristics of ferrihydrite. Specifically, under acidic conditions (pH < 5.5 for ferrihydrite-coated sand and pH < 6.0 for soil), PFOS retention is primarily facilitated through an outer-sphere hydrogen-bonded complex at ferrihydrite’s surface, while a secondary outer-sphere complex involving Na + co-adsorption contributes to a lesser extent. At elevated pH levels, however, electrostatic interactions become less favorable, and non-electrostatic hydrophobic interactions with quartz surfaces become increasingly dominant, highlighting the transition in sorption mechanisms from charge-driven to hydrophobic partitioning under neutral to alkaline conditions. A comparison with traditional partitioning coefficients (K d ) revealed that their variability closely corresponds with changes in dominant surface complexes across different pH conditions. Given the critical role of solid-phase partitioning in governing PFAS transport in the subsurface, enhanced predictive capabilities are essential for advancing site-specific risk assessments and informing management strategies aimed at protecting both public and private water resources. Graphical abstract

Fluorescent flippers have been introduced as small‐molecule probes to image membrane tension in living systems. While the hydrophilic headgroup region has been modified extensively for intracellular targeting, little is known about the hydrophobic interfacing with the surrounding membrane. To tackle this challenge, the design, synthesis and evaluation of a glutamine‐derived flipper collection is reported. Considering the importance of tension‐induced phase separation for tension imaging, this study is focused on how to modulate the distribution of functional flippers between ordered and disordered microdomains. Also of interest was control over intermembrane transfer without loss of function for the specific labeling of plasma and intracellular membranes. Evidence is presented for a two‐step insertion mechanism through more accessible disordered domains into better matching ordered domains. This process also explains differences between partition coefficients and bioimaging. It is further demonstrated that interdomain and intermembrane distribution can be regulated by hydrophobic interfacing to control brightness in fluorescence lifetime imaging microscopy and responsiveness to membrane tension. Irreversible partitioning inhibits intermembrane transfer and coincides with internalization into cells. These results demonstrate that hydrophobic interfacing can improve probe performance and provide guidelines on how to proceed. Hydrophobic interfacing is shown to improve the performance of mechanosensitive fluorescent flipper probes with regard to intermembrane transfer, microdomain and subphase recognition, two‐step partitioning, and their spectroscopic signature.