Nanosized Water Channels Associated with Hydrophobic and Hydrophilic Fibrillar Arrangements Formed on Nafion Surfaces in Confined Regions.

Herein, the origin of interfacial water nanosized channel distributions attached onto Nafion surfaces is investigated. The surface fibrillary hydrophilic and hydrophobic arrangements were observed on AFM images scanned on Nafion surfaces immersed in water. Then, by analyzing the force vs separation curves, it is possible to map arrays of interfacial water channels and their locations. Nafion surface profiles and the water interfacial patterns are then combined using this AFM technique. As there are no reported experimental techniques to measure water nanochannel cross sections, presented measurements report on their dimensions. Water nanochannels characterized by ε < 7 attached to hydrophilic fibrillary sections form aggregated water domains, a highly organized water structure compared with bulk water. Channels are attached to Nafion surface hydrophilic fibrillary domains in confined sites.

The spike protein of SARS-CoV-2 can be detected by electrochemical impedance spectroscopy using antibody desorption from iron magnetic nanoparticles.

SARS-CoV-2 is a matter of concern. Here, biosensors were prepared using iron magnetic nanoparticles containing antibodies against the receptor binding domain (RBD) of the spike protein. Antibodies were adsorbed to nanoparticles in three configurations, including direct adsorption without functionalization (DANPs). Nanoparticles were added to a glassy carbon electrode and connected to an electrochemical cell. Electrochemical impedance spectroscopy and ELISA experiments indicated that antibodies were desorbed from the DANPs upon the addition of the RBD. DANPs-based biosensors produced linear curves with decreasing charge transfer resistance due to the removal of antibodies. Thus, a detection method can be based on antibody desorption.

Removal of p-cresol using wash waters from lipopeptide production.

This work shows the efficiency of wash waters from lipopeptide production as a remediation strategy to treat urban water samples contaminated with p-cresol. The harvesting step in surfactin production involved a centrifugation step, generating a major soluble fraction and a fraction that is adsorbed to the biomass. The adsorbed fraction was recovered by washing steps. These wash waters containing lipopeptides (mostly surfactins), were successfully used to adsorb and solubilize p-cresol. The method of decontamination applied to an artificially contaminated natural water was monitored using a biosensor based on laccase/magnetic nanoparticles. Given the amount of surfactin within the wash water, the removal of p-cresol from artificially contaminated water was approximately 46.0%. This result confirms the successful and sustainable application of surfactin-rich wash waters to remove p-cresol from artificially contaminated natural water. The adsorption mechanism is potentially based on a multi-layer adsorption process, considering Langmuir and Freundlich adsorption isotherms.

Fibrillary Arrangement of Elongated, Almost Parallel Aggregates of Hydrophobic and Hydrophilic Domains Forming the Nafion Surface Structure Improved Contrast Atomic Force Microscopy Images.

A significant improvement in spatial resolution is reported in Nafion surface maps when compared to previous atomic force microscopy images of the Nafion surface scanned in air. The technique ability is to generate maps showing approximately few nanometer (∼2-5 nm) patterns to the long fiber length (>2 µm). Atomic force microscopy force vs separation curve profiles registered in water are used to characterize the surface hydrophobic and hydrophilic domains. Initially, Nafion surfaces were imaged in air for comparison and then immersed in water. Nafion surfaces immersed in water display a matrix of hydrophilic and hydrophobic regions with fibrillary structure dimensions of ∼40 nm formed by fiber pairs. Ribbons formed by two pairs with diameters of ∼83 nm are separated by larger channels.

Variable Interfacial Water Nanosized Arrangements Measured by Atomic Force Microscopy.

While there seems to be broad agreement that cluster formation does exist near solid surfaces, its presence at the liquid/vapor interface is controversial. We report experimental studies we have carried out on interfacial water attached on hydrophobic and hydrophilic surfaces. Nanosized steps in the measured force vs distance to the surface curves characterize water cluster profiles. An expansion of the interfacial structure with time is observed; the initial profile extent is typically ∼1 nm, and for longer times expanded structures of ∼70 nm are observed. Our previous results showed that the interfacial water structure has a relative permittivity of ε ≈ 3 at the air/water interface homogeneously increasing to ε ≈ 80 at 300 nm inside the bulk, but here we have shown that the interfacial dielectric permittivity may have an oscillating profile describing the spatial steps in the force vs distance curves. This low dielectric permittivity arrangements of clusters extend the region with ε ≈ 3 inside bulk water and exhibit a behavior similar to that of water networks that expand in time.

Residual biomass from surfactin production is a source of arginase and adsorbed surfactin that is useful for environmental remediation.

Lipopeptides are important secondary metabolites produced by microbes. They find applications in environmental decontamination and in the chemical, pharmaceutical and food industries. However, their production is expensive. In the present work we propose three strategies to lower the production costs of surfactin. First, the coproduction of surfactin and arginase in a single growth. Second, extract the fraction of surfactin that adsorbs to the biomass and is removed from the growth medium through centrifugation. Third, use microbial biomass for the remediation of organic and inorganic contaminants. The coproduction of surfactin and arginase was evaluated by factorial design experiments using the LB medium supplemented with arginine. The best conditions for surfactin production were 22 h of growth at 37 °C using LB supplemented with arginine 7.3 g/L. Almost similar conditions were found to produce highest levels of arginase, 24 h and 6.45 g/L arginine. Decontamination of phenol and copper from artificial samples was attained by treatment with residues from lipopeptide production. Thus, cell suspensions and wash-waters used to extract surfactin from the biomass. Cell suspensions were used to successfully remove hydroquinone. Cell suspensions and wash-waters containing surfactin were successfully used to recover copper from solution. Specific monitoring methods were used for phenol and metal solutions, respectively a biosensor based on tyrosinase and either atomic absorption flame ionization spectrometry or absorbance coupled to the Arduino™ platform. Therefore, we report three alternative strategies to lower the production costs in lipopeptide production, which include the effective recovery of copper and phenol from contaminated waters using residues from surfactin production. Sustainable and profitable production of surfactin can be achieved by a coproduction strategy of lipopeptides and enzymes. Lipopeptides are collected in the supernatant and enzymes in the biomass. In addition, lipopeptides that coprecipitate with biomass can be recovered by washing. Lipopeptide wash-waters find applications in remediation and cells can also be used for environmental decontamination.

Hydrated excess protons and their local hydrogen bond transport network as measured by translational, librational, and vibrational frequencies.

A clear molecular description of excess hydrated protons and their local hydrogen bond transport network remains elusive. Here, the hydrogen bond network of excess hydrated protons in water bridges was probed by measuring their Raman spectra and comparing them to the spectra of protons in ice and water. The proton vibrational spectrum and the hydrogen bond network translational and librational spectra were recorded. The spectra of the water bridge and water exhibit clear differences, indicating the presence of a structure in water bridges when subjected to an electric field of ∼106 V/m that has not been previously reported. The intermolecular Raman spectrum of the floating water bridge exhibits a hydrogen bond stretching band at 150-250 cm-1, librational bands within the 300-1000 cm-1 spectral range, and a large band at 1500-3000 cm-1, which corresponds to the vibrational signature of excess hydrated protons in the water bridge structure. The excess protons are shown to move predominantly at the air/water interface, and the effect of this distribution is a measurable change in the air/water interfacial tension from ∼80 to ∼32 N/m. Therefore, hydrated protons must have a unique water arrangement that enables them to propagate without sinking into bulk water. This local polarized hydrogen bond network in the interfacial water region is characterized by a translational spectrum similar to that of ice V.

Physical properties of water near a gold surface: a nanorheological analysis.

Water at room temperature is not simply a medium for which uniform properties can always be assumed. Water close to solid hydrophobic or hydrophilic surfaces has elasticity, which is measured by monitoring the quartz crystal microbalance (QCM) resonant frequency and resistance. Small additions of salt are shown to modify this elasticity. Furthermore, near the hydrophobic QCM gold electrode, undersaturated aqueous NaCl solutions present a high concentration of ion pairs, which is confirmed by atomic force microscopy through force versus distance measurements.