Effect of Oil Polarity on the Protein Adsorption at Oil-Water Interfaces.

Protein adsorption at oil-water interfaces has received much attention in applications of food emulsion and biocatalysis. The protein activity is influenced by the protein orientation and conformation. The oil polarity is expected to influence the orientation and conformation of adsorbed proteins by modulating intermolecular interactions. Hence, it is possible to tune the protein emulsion stability and activity by varying the oil polarity. Martini v3.0-based coarse-grained molecular dynamics (CGMD) simulations were employed to investigate the effect of oil polarity on the orientation and conformation of hydrophobin (HFBI) and Candida antarctica lipase B (CALB) adsorbed at triolein-water, hexadecane-water, and octanol-water interfaces for the first time. The protein adsorption orientation was predicted through the hydrophobic dipole, indicating that protein adsorption exists in preferred orientations at hydrophobic oil interfaces. The conformation of the adsorbed HFBI is well conserved, whereas relatively larger conformational changes occur during the CALB adsorption as the oil hydrophobicity increases. Comparisons on the adsorption interaction energy of proteins with oils confirm the relationship between the oil polarity and the interaction strength of proteins with oils. In addition, CGMD simulations allow longer time scale simulations of the behaviors of protein adsorption at oil-water interfaces.

Zwitterion-Modified Nanogel Responding to Temperature and Ionic Strength: A Dissipative Particle Dynamics Simulation.

The self-assembly and stimuli-responsive properties of nanogel poly(n-isopropylacrylamide) (p(NIPAm)) and zwitterion-modified nanogel poly(n-isopropylacrylamide-co-sulfobetainemethacrylate) (p(NIPAm-co-SBMA)) were explored by dissipative particle dynamics simulations. Simulation results reveal that for both types of nanogel, it is beneficial to form spherical nanogels at polymer concentrations of 5-10%. When the chain length (L) elongates from 10 to 40, the sizes of the nanogels enlarge. As for the p(NIPAm) nanogel, it shows thermoresponsiveness; when it switches to the hydrophilic state, the nanogel swells, and vice versa. The zwitterion-modified nanogel p(NIPAm-co-SBMA) possesses thermoresponsiveness and ionic strength responsiveness concurrently. At 293 K, both hydrophilic p(NIPAm) and superhydrophilic polysulfobetaine methacrylate (pSBMA) could appear on the outer surface of the nanogel; however, at 318 K, superhydrophilic pSBMA is on the outer surface to cover the hydrophobic p(NIPAm) core. As the temperature rises, the nanogel shrinks and remains antifouling all through. The salt-responsive property can be reflected by the nanogel size; the volumes of the nanogels in saline systems are larger than those in salt-free systems as the ionic condition inhibits the shrinkage of the zwitterionic pSBMA. This work exhibits the temperature-responsive and salt-responsive behavior of zwitterion-modified-pNIPAm nanogels at the molecular level and provides guidance in antifouling nanogel design.

Finely tuned water structure and transport in functionalized carbon nanotube membranes during desalination.

Molecular dynamics simulations were performed to tune the transport of water molecules in nanostructured membrane in a desalination process. Four armchair-type (7,7), (8,8), (9,9) and (10,10) carbon nanotubes (CNTs) with pore diameters around 1 nm were chosen, their interior surfaces were modified with -OH, -CH3 and -F groups. Simulation results show that water transport in nanochannel depends on confined water structures which could be regulated by precisely controlled channel diameter and chemical functionalization. Increasing CNT diameter changes water structures from single-file-like to be square and hexagonal-like, then into a disordered pattern, resulting in a concave-shaped trend of water permeance. The -OH functional groups promote structural ordering of water molecules in (7,7) CNT, but disrupt water structures in (8,8) and (9,9) CNTs, and reduce the order degree of water molecules in (10,10) CNT, moreover, exert an attraction to enhance surface friction inside channel. The -CH3 groups induce more strictly single-file movement of water molecules in (7,7) CNT, turning water structures in (8,8) and (9,9) CNTs into two and triangular column arrangements, improving water transport, however, causing again square-like water structure in (10,10) CNT. Fluorinations of CNT make water structure more disordered in (7,7), (9,9) and (10,10) CNTs, while enhance the square water structure in (8,8) CNT with a lower water permeance. Through changing channel diameter and functionalization, the low tetrahedral order corresponds to a more single-file-like water structure, associated with rapid water diffusion and high permeability; an increase in tetrahedrality results in more ice-like water structures, lower water diffusion coefficients, and permeability. The results of this study demonstrate that water transport could be finely regulated via a functionalized CNT membrane.

Prediction and Interpretability of Melting Points of Ionic Liquids Using Graph Neural Networks.

Ionic liquids (ILs) have wide and promising applications in fields such as chemical engineering, energy, and the environment. However, the melting points (MPs) of ILs are one of the most crucial properties affecting their applications. The MPs of ILs are affected by various factors, and tuning these in a laboratory is time-consuming and costly. Therefore, an accurate and efficient method is required to predict the desired MPs in the design of novel targeted ILs. In this study, three descriptor-based machine learning (DBML) models and eight graph neural network (GNN) models were proposed to predict the MPs of ILs. Fingerprints and molecular graphs were used to represent molecules for the DBML and GNNs, respectively. The GNN models demonstrated performance superior to that of the DBML models. Among all of the examined models, the graph convolutional model exhibited the best performance with high accuracy (root-mean-squared error = 37.06, mean absolute error = 28.79, and correlation coefficient = 0.76). Benefiting from molecular graph representation, we built a GNN-based interpretable model to reveal the atomistic contribution to the MPs of ILs using a data-driven procedure. According to our interpretable model, amino groups, S+, N+, and P+ would increase the MPs of ILs, while the negatively charged halogen atoms, S-, and N- would decrease the MPs of ILs. The results of this study provide new insight into the rapid screening and synthesis of targeted ILs with appropriate MPs.

Coarse-grained simulations of lysozyme-silica-nanoparticle corona.

Protein coronas, formed by proteins and nanomaterials, have various applications in the biomedical field. Here, large-scale simulations of protein coronas have been carried out by an efficient mesoscopic coarse-grained method with the BMW-MARTINI force field. The effects of protein concentration, size of silica nanoparticles (SNPs), and ionic strength on the formation of lysozyme-SNP coronas are investigated at the microsecond time scale. Simulations results indicate that (i) an increase in the amount of lysozyme is favorable for the conformation stability of adsorbed lysozyme on SNPs. Moreover, the formation of ringlike and dumbbell-like aggregations of lysozyme can further reduce the conformational loss of lysozyme; (ii) for a smaller SNP, the increase of protein concentration exhibits a greater effect on the adsorption orientation of lysozyme. The dumbbell-like lysozyme aggregation is unfavorable for the stability of lysozyme's adsorption orientation; however, the ringlike lysozyme aggregation can enhance the orientation stability; (iii) the increase of ionic strength can reduce the conformation change of lysozyme and accelerate the aggregation of lysozyme during their adsorption process on SNPs. This work provides some insights into the formation of protein coronas and some valuable guidelines for the development of novel biomolecule-NP conjugates.

Factors affecting microbiological quality of household drinking water supplied by small-scale ultrafiltration systems: A field study.

Small scale ultrafiltration (UF) systems have been increasingly used in rural areas for drinking water supply, but their effectiveness in guarantying microbiological water safety at household level has rarely been assessed. Therefore, this study surveyed six representative villages where UF was utilized for full-scale drinking water supply for at least four years. At each village, the influent and the effluent from every stages of the treatment, as well as household tap water, were sampled and analyzed for microbiological indicating parameters, including total coliform count, Escherichia coli count, and heterotrophic plate count. The results were further assessed against current drinking water quality guidelines and standards. It was found that: (1) the qualification rate of household tap water samples varied substantially in the studied villages (0-75%), mainly due to the lack of post-disinfection and the occurrence of fecal contamination during water distribution; (2) UF appeared to be effective in controlling microbial contamination for small-scale systems with high-quality source water, while for systems using inferior source water, fecal contamination during water distribution necessitated continuous post-disinfection; and, (3) existing monitoring of membrane operational parameters cannot ensure microbial quality of treated water, and therefore, routine monitoring of microbial indicators in household water is recommended.

[Control of Coagulant Dosing for Humic Substances Based on Ultraviolet Spectrum Analysis].

Humic substance (HS) is a main component of dissolved organic matter in the aquatic environment and significantly affects water treatment processes. To investigate the applicability and principle of UV spectrum analysis for coagulation control, laboratory jar tests were conducted with synthetic waters that had varying concentrations of HS and kaolinite. Thus, the influence of water quality conditions on the optimal coagulant dose (OCD) was determined and further correlated to Specific Ultraviolet Absorbance (SUVA254) and the ultraviolet spectral slopes of the coagulated water. Subsequently, the relationship between the UV spectral slopes and organic fractionation was further identified by using size exclusion chromatography (SEC). The results showed that the coagulant demands of the synthetic waters were positively related to dissolved organic carbon (DOC). Consequently, a stoichiometric relationship (0.61 mg·mg-1 calculated as Al/DOC) was found between the coagulant demand and initial DOC of the synthetic water. As the coagulant dose increased, SUVA254 decreased from 8.9 L·(mg·m)-1 to a steady level of 2.0 L·(mg·m)-1 and the removal efficiency of DOC was positively correlated with SUVA254. Spectral slopes in different wavelength ranges had showed similar tendencies, with S275-295 having the best correlation with SUVA254 (R2=0.81). Furthermore, SEC results demonstrated that coagulation preferentially removed humic substances, leading to reduced humification. As a result, S275-295 had the highest correlation with the portion of UVA254 contributed by humic substances in water. Therefore, online measurement of ultraviolet spectral slopes was an important aspect in the control of coagulant dosing.

Preparation and application of a novel bioflocculant by two strains of Rhizopus sp. using potato starch wastewater as nutrilite.

A complex bioflocculant MBF917 was prepared by Rhizopus sp. M9 and M17 using potato starch wastewater (PSW) as nutrilite, and its flocculation characteristics of treating PSW were studied. Culture conditions of the two strains were optimized, and flocculating conditions of the bioflocculant for treating PSW were also investigated. The optimal and economical culture conditions were determined as COD of about 1600 mg/L, 0.3 g/L urea and 0.04 g/L potassium dihydrogen phosphate, with no need of adding carbon sources or adjusting pH. When the bioflocculant was used to flocculate PSW, the optimal dosage was 0.1 mL/L with addition of 5 mL/L 10% CaCl2 as coagulant aid, and there was no need to adjust pH. After flocculation, COD and turbidity removal rates of the PSW could reach 54.09% and 92.11%, respectively, and 1.1g/L proteic substance was recycled from the PSW as a byproduct that could be used for animal feed.