Relative Hydrophobicity Research Articles

Ligand binding remodels protein side-chain conformational heterogeneity.

While protein conformational heterogeneity plays an important role in many aspects of biological function, including ligand binding, its impact has been difficult to quantify. Macromolecular X-ray diffraction is commonly interpreted with a static structure, but it can provide information on both the anharmonic and harmonic contributions to conformational heterogeneity. Here, through multiconformer modeling of time- and space-averaged electron density, we measure conformational heterogeneity of 743 stringently matched pairs of crystallographic datasets that reflect unbound/apo and ligand-bound/holo states. When comparing the conformational heterogeneity of side chains, we observe that when binding site residues become more rigid upon ligand binding, distant residues tend to become more flexible, especially in non-solvent-exposed regions. Among ligand properties, we observe increased protein flexibility as the number of hydrogen bonds decreases and relative hydrophobicity increases. Across a series of 13 inhibitor-bound structures of CDK2, we find that conformational heterogeneity is correlated with inhibitor features and identify how conformational changes propagate differences in conformational heterogeneity away from the binding site. Collectively, our findings agree with models emerging from nuclear magnetic resonance studies suggesting that residual side-chain entropy can modulate affinity and point to the need to integrate both static conformational changes and conformational heterogeneity in models of ligand binding.

Recovery of β-carotene and astaxanthin from Phaffia rhodozyma biomass using aqueous solutions of cholinium-based ionic liquids

The red yeast Phaffia rhodozyma is a natural source of high-added value carotenoids such as β-carotene and astaxanthin, widely used in the cosmeceutical, chemical, feed/food and pharmaceutical industries. This yeast is characterized by a rigid cell wall mainly composed of biopolymers, being required an appropriate design of downstream processing to recovery these intracellular carotenoids. In this sense, a biocompatible alternative for the selective recovery of β-carotene and astaxanthin from P. rhodozyma cells by using ionic liquids (ILs) was proposed. The performance of different cholinium-based ILs to permeabilize the cell wall and recovery intracellular carotenoids from P. rhodozyma wet biomass was evaluated and the operational conditions were optimized. The recovery yields of β-carotene and astaxanthin increased with the increment of alkyl chain length of the anion (cf., increase of relative hydrophobicity of ILs), being cholinium octanoate [Ch][Oct] the most efficient (50 wt% in water, 45 °C and 60 min). The stability of carotenoids in ILs as well as the mechanisms behind the recoveries have also been investigated. Afterwards, it was developed for the best IL solution an integrative platform for the recycling of the solvents (up to three successive cycles without any make up) and recovery of β-carotene and astaxanthin using bio-based solvents. The results demonstrate the efficiency of cholinium-based ILs for the recovery of β-carotene and astaxanthin (≈ 40% w/w) from P. rhodozyma in one-step extraction, reinforcing the aptitude of ILs for the recovery of intracellular biomolecules from microbial-based biomass.

Sludge dewaterability enhancement under low temperature condition with cold-tolerant Bdellovibrio sp. CLL13

The dewatering performance of waste activated sludge (WAS) is generally deteriorated under low temperature due to the increase of viscosity, which would exacerbate the difficulties in sludge treatment and disposal. In this study, the cold-tolerant Bdellovibrio sp. CLL13 was successfully screened for efficient sludge biolysis, and it dramatically improved the sludge dewaterability while no significant biolysis effects were observed for the mesophilic BALO strain at 12 °C. The reduction rates of the sludge capillary suction time (CST), the specific resistance of filtration (SRF), the sludge dry weight, and the fecal coliform bacteria concentration at the optimal reaction time of 14 h were 40.1 ± 0.2%, 69.6 ± 0.7%, 7.7 ± 0.4%, and 78.5 ± 0.4%, respectively, when the mixed liquid suspended solids (MLSS) content was between 10.8 and 29.6 g/L, the input dosage of CLL13 was 8.8 × 106 PFU/mL sludge, and the DO level was 1.2 mg/L. Meanwhile, the viscosity reduction rate, the relative hydrophobicity increasement rate, and the bound water reduction rate were 20.3 ± 1.2%, 6.9 ± 0.7%, and 29.4 ± 1.0%, respectively. The ratios of protein content to polysaccharides content in the extracellular polymeric substances (EPS) decreased significantly. In addition, the degradation of the macromolecular substances in EPS and the increase of the soluble chemical oxygen demand, the total nitrogen, the total phosphorus, and the lactate dehydrogenase levels were observed. Therefore, the cold-tolerant CLL13 induced the sludge biolysis and compromised the negative effects of low temperature on the sludge dewatering performance, which should be beneficial for the efficient WAS biolysis treatment application in the near future under low temperature.

Fate of sloughed biomass in integrated fixed-film systems.

Fate of biofilm sloughing was assessed in a laboratory-scale (LS) integrated fixed-film sequencing batch reactor (IF-SBR) treating synthetic wastewater and in a full-scale (FS) integrated fixed-film activated sludge (IFAS) system treating municipal wastewater. It was observed that the properties of biofilms and flocs, including sludge volume index (SVI), mixed liquor suspended solids (MLSS), effluent suspended solids (ESS), relative hydrophobicity, and composition of extracellular polymeric substance (EPS) were associated with biofilm sloughing and formation of large granular flocs in the LS IF–SBR. In the FS IFAS system, the changes were studied at the molecular level. For example, the extracted EPS content results (the protein to polysaccharide ratio decreased in the flocs and increased in the biofilms, with biofilm sloughing) were complemented with the confocal laser scanning microscopy (CLSM) coupled with molecular specific staining. CLSM analyses revealed that micro-colonies rich in polysaccharides readily sloughed from the carriers. Live-dead staining revealed areas of the biofilm where the viability of biomass was a contributing factor associated with areas of the biofilm susceptible to sloughing. 16S rRNA gene sequencing (Illumina) of FS IFAS samples revealed greater diversity (α-diversity) in biofilms compared to flocs. Biofilm sloughing resulted in a decrease in diversity in biofilms and a corresponding increase in the flocs during sloughing. Microbial population dynamics revealed that bacteria known for denitrification (for example, Comamonadaceae) detached from the biofilms during sloughing, readily associated with the suspended biomass, and were retained in the bioreactors.

Uncover the secret of the stability and interfacial Gibbs free energy of aerobic granular sludge

Interfacial Gibbs free energy (IGFE) as a thermodynamic indicator characterize the stability of the natural system. For aerobic granular sludge (AGS), how IGFE determines the stability of sludge remains to be determined. The Gibbs free energy change at the AGS-water interface (ΔGswa) and AGS interfaces (ΔGsc) were selected as the main interfacial thermodynamic factors. Results indicated that the stable AGS was guaranteed with ΔGsc at the range of −31 to - 46 J m−2. Pearson correlation coefficients between ΔGswa/ ΔGsc and relative hydrophobicity, water content, SVI30, integrity coefficient were −0.9, 0.8, 0.85, and 0.84, which illustrated that the IGFE could be a more comprehensive thermodynamic indicator. Microbial community and EPS analysis verified the importance of denitrifiers, Amide III, protein-like substances for AGS stability. This work offers a new insight into the development of AGS stability based on IGFE.

New insight into filamentous sludge bulking: Potential role of AHL-mediated quorum sensing in deteriorating sludge floc stability and structure

The microcosmic mechanisms underlying filamentous bulking remain unclear. The role of extracellular polymeric substances (EPS) governed by quorum sensing (QS) in deteriorating sludge floc stability and structure during filamentous bulking and the feasibility of using quorum quenching (QQ) to maintain sludge floc stability and structure and sludge settling were investigated in this study. The results indicated that the concentration of C6HSL increased from 22.08±3.22 ng/g VSS to 81.42±5.98 ng/g VSS during filamentous bulking. The filamentous bacteria gradually evolved the hdtS gene related to the synthesis of C6HSL with increases in the population density. Triggered QS by filamentous bacteria proliferation induced variation in the composition and structure of EPS within the sludge flocs. The proteins (PN) content of the EPS increased evidently from 40.06 ± 2.41 mg/g VSS to 110.32 ± 4.32 mg/g VSS, and the polysaccharides (PS) content slightly increased during filamentous bulking. The upregulated proteins in the EPS led to a decrease in the relative hydrophobicity of the sludge and an increase in negative surface charge. The α-helix/(β-sheet+random coil) ratio evidently increased from 0.76 to 0.99 during filamentous bulking, revealing that the proteins were tightly structured, which prevented the exposure of inner hydrophobic groups. The total energy of the interaction (WT) between bacteria increased during sludge bulking, which resulted in the weakening of sludge aggregation. Variation in the physicochemical properties of EPS induced by QS in the filamentous bacteria markedly restrained adhesion between the filamentous bacteria and floc-forming bacteria. The production of PN in the EPS and the expression of the hdtS gene were inhibited by vanillin, which served as a QS inhibitor. The WT between bacteria with 50 mg/L of vanillin basically did not change. Filamentous bulking was significantly inhibited by the addition of vanillin. Therefore, QQ is a potential strategy for the prevention and control of filamentous bulking. This study provides new information regarding the microcosmic mechanisms of filamentous bulking.

Key factors controlling colloids–bulk soil distribution of polybrominated diphenyl ethers (PBDEs) at an e-waste recycling site: Implications for PBDE mobility in subsurface environment

Accumulation of polybrominated diphenyl ethers (PBDEs) in surface soils at elevated concentrations is common at e-waste recycling sites. Even though highly insoluble, migration of PBDEs into the vadose zone and groundwater is possible, due to their association with soil colloids. Here, we show that upon equilibration with artificial rainwater surface and subsurface soil samples collected at an e-waste recycling site release significant quantities of colloids, with the total concentrations of 14 PBDE congeners as high as 990 ng/g dw. The concentrations of different congeners vary markedly in the colloids, and that of BDE-209 is the highest in all the samples. Notably, even the colloids released from the soil collected at a depth of 95–105 cm contain high concentrations of PBDEs. Preferential binding of PBDEs to soil colloids is observed, with the colloids-soil distribution coefficients above 10 in certain cases. The extent of preferential binding displays no apparent correlation with the relative hydrophobicity of the PBDEs, nor can it be explained simply by considering the higher specific surface area, pore volume, and clay content of the soil colloids than the respective bulk soil. Principal component analysis shows that multiple soil properties are collectively responsible for the preferential distribution of PBDEs. Specifically, the differences in pore volume, soil organic carbon content, and pore size between colloids and soils are likely the major factors affecting the distribution of high-concentration PBDEs, whereas the differences in clay content, pore volume and specific surface area are the key factors affecting the distribution of low-concentration PBDEs. The findings clearly show that colloids are an important medium with which PBDEs are associated at contaminated sites, and underline the need of understanding colloid-facilitated transport of PBDEs at e-waste sites.

Modulation of micellization behavior of imidazolium based surface active ionic liquids by aromatic anions in aqueous medium

Surface active ionic liquids (SAILs) represent a class of ionic surfactants that many times display better surface-active properties as compared to conventional ionic surfactants. The micellization of SAILs can be further tailored by the addition of salts, and aromatic salts comprising hydrotropic anions have never been explored for altering the micellization of SAILs in low concentration range. Considering this, we have investigated the effect of addition of three aromatic salts i.e. Sodium 4-hydroxy benzenesulfonate, sodium benzenesulfonate, and sodium p-toluenesulfonate on the micellization of 1-dodecyl-3-methylimidazolium chloride, [C12mim][Cl] and its amide functionalized counterpart, 3-(2-(dodecylamino)−2-oxoethyl)−1-methyl-1H-imidazol-3-ium chloride, [C12Amim][Cl]. The surface-active behavior of SAILs has been investigated by tensiometry, whereas micellization in bulk has been probed through conductivity, steady-state fluorescence, dynamic light scattering (DLS) and zeta-potential measurements. The possible location of aromatic anions adsorbed on the micellar surface has been probed using 1H NMR measurements. Isothermal titration calorimetry has been utilized to gain insights into the thermodynamic aspects of micellization. The inferences gained from different techniques have been correlated and found to be in good agreement with each other. It has been observed that the functionalization of alkyl chain length of SAIL along with relative hydrophobicity and bulkiness of the aromatic anions control the characteristic properties of micellization.

Polyelectrolyte complexes of hyaluronic acid and diethylaminoethyl dextran: Formation, stability and hydrophobicity

Polyelectrolyte complexes (PECs) of hyaluronic acid (HA) and diethylaminoethyl dextran (DEAE-D), promising for biomedical applications, have been investigated with respect to physicochemical properties, mainly in terms of particle size and relative hydrophobicity as well as storage stability. Influences of charge ratio, polymer concentration, molar masses of HA, ionic strength and mixing methods have been particularly investigated. The complexation between HA and DEAED generally resulted in colloidal particles having mean hydrodynamic diameter of 150–350 nm, with larger particle size observed at negative to positive charge ratio (n-/n+) further from the unity. Higher polymer concentration or higher molar mass of HA also led to higher particle size of the PECs, whereas the increasing ionic strength led to a non-monotonic evolution in particle size. The effects of mixing mode and mixing order on particle size were interdependent and depended also on n-/n+. PECs at n-/n+ ≤ 0.4 showed lack of stability, which seemed not to be sensitive to storage temperature but significantly improved at higher salt concentration or lower polymer concentration. The relative hydrophobicity of such PECs was also confirmed by the fluorescence spectra of pyrene incorporated in PEC particles. Such results gave a better insight to polysaccharides-based PECs, especially as a potential system to encapsulate hydrophobic active molecules for drug delivery purposes.

Plant cell adhesion and growth on artificial fibrous scaffolds as an in vitro model for plant development.

Mechanistic studies of plant development would benefit from an in vitro model that mimics the endogenous physical interactions between cells and their microenvironment. Here, we present artificial scaffolds to which both solid- and liquid-cultured tobacco BY-2 cells adhere without perturbing cell morphology, division, and cortical microtubule organization. Scaffolds consisting of polyvinylidene tri-fluoroethylene (PVDF-TrFE) were prepared to mimic the cell wall’s fibrillar structure and its relative hydrophobicity and piezoelectric property. We found that cells adhered best to scaffolds consisting of nanosized aligned fibers. In addition, poling of PVDF-TrFE, which orients the fiber dipoles and renders the scaffold more piezoelectric, increased cell adhesion. Enzymatic treatments revealed that the plant cell wall polysaccharide, pectin, is largely responsible for cell adhesion to scaffolds, analogous to pectin-mediated cell adhesion in plant tissues. Together, this work establishes the first plant biomimetic scaffolds that will enable studies of how cell-cell and cell-matrix interactions affect plant developmental pathways.

Tetracycline removal in granulation: Influence of extracellular polymers substances, structure, and metabolic function of microbial community

Tetracycline is a potentially hazardous residual antibiotic detected in various sewages. High concentration (mg/L) of tetracycline is found in pharmaceutical/hospital wastewater and wastewater derived from livestock and poultry. So far, only antibiotics in μg/L level have been reported in granulation of aerobic sludge during wastewater treatment, but its effects in high concentration are rarely reported. In this study, the influence of tetracycline in high concentration (∼2 mg/L) on the formation of granular sludge, structure, and metabolic function of the microbial community during the granulation of aerobic sludge was investigated to improve the understanding of the aerobic granular sludge formation under high-level of tetracycline. The role of extracellular polymers substances (EPSs) derived from granular sludge in the granulation and tetracycline removal process was also investigated, showing that tetracycline improved the relative hydrophobicity, flocculability and protein/polysaccharide ratio of EPSs, accelerating the granulation of sludge. Succession of microbial communities occurred during the domestication of functional bacteria present in the sludge and was accompanied with regulation of metabolic function. The addition of tetracycline lead to an increase of tetracycline-degrading bacteria or antibiotic resistance genus. Those findings provide new perspectives of the influence of tetracycline on aerobic sludge granulation and the removal mechanism of tetracycline.

Reduction of biofilm adhesion strength by adjusting the characteristics of biofilms through enzymatic quorum quenching

Biofilm adhesion to the surface of a carrier plays an essential role during biofilm formation. Quorum quenching (QQ) has been shown to have great potential for delaying biofouling. However, little is known about whether QQ reduces the adhesion strength of biofilms during the formation process to inhibit biomass accumulation. In this study, we explored the effect of enzymatic QQ on the adhesion strength during biofilm development. In addition, a quantitative method was used to measure the adhesion strength of biofilms based on the shear force of water flow. Experimental results showed that QQ enzyme could reduce the adhesion strength of biofilms by at least 37% compared with the control. Furthermore, the biofilm accumulation rates were 0.05673 and 0.08762 h−1 with and without the QQ enzyme, illustrating a negative effect of QQ enzyme on biofilm accumulation. Specifically, QQ was confirmed to reduce extracellular polymeric substances, decrease the relative hydrophobicity, change the zeta potential by degrading signal molecules, and weaken the adhesion strength of biofilms. The successful reduction of the adhesion strength of the biofilm through QQ could provide a new strategy for the management and regulation of biofilm adhesion in the bioreactor.

Nitrogen removal and aggregation characteristics of Pseudomonas aeruginosa YL and its application capacity for ammonium-rich wastewater treatment

Pseudomonas aeruginosa YL, which was isolated and purified from activated sludge, performed a high-efficiency simultaneous nitrification and denitrification ability through the efficient utilization of sole and mixed N-sources. Kinetics analysis carried out by Gompertz model (R2 > 0.99) explicated the optimal condition of N-degradation, and its denitrification pathway was proposed as a sequential heterotrophic nitrification-aerobic denitrification process. Moreover, strain YL had higher flocculating ability, relative hydrophobicity and lower negative charges when NH4+-N used as N-source, which fully proved the stronger aggregation ability of the isolate during heterotrophic nitrification process. The formation mechanism of cell aggregates was explained by discussing the variations of extracellular polymeric substances (EPS) components, and exhibited an obviously relevance of EPS and bioflocculation. Furthermore, the great nutrients removal, stable existence of functional strain and the excellent flocculation-sedimentation performance in a sequencing batch reactor, further confirmed the good potential of strain YL for treating ammonium-rich wastewater.

Sequence-Based Prediction of Transmembrane Protein Crystallization Propensity.

Transmembrane proteins play a vital role in cell life activities. There are several techniques to determine transmembrane protein structures and X-ray crystallography is the primary methodology. However, due to the special properties of transmembrane proteins, it is still hard to determine their structures by X-ray crystallography technique. To reduce experimental consumption and improve experimental efficiency, it is of great significance to develop computational methods for predicting the crystallization propensity of transmembrane proteins. In this work, we proposed a sequence-based machine learning method, namely Prediction of TransMembrane protein Crystallization propensity (PTMC), to predict the propensity of transmembrane protein crystallization. First, we obtained several general sequence features and the specific encoded features of relative solvent accessibility and hydrophobicity. Second, feature selection was employed to filter out redundant and irrelevant features, and the optimal feature subset is composed of hydrophobicity, amino acid composition and relative solvent accessibility. Finally, we chose extreme gradient boosting by comparing with other several machine learning methods. Comparative results on the independent test set indicate that PTMC outperforms state-of-the-art sequence-based methods in terms of sensitivity, specificity, accuracy, Matthew's Correlation Coefficient (MCC) and Area Under the receiver operating characteristic Curve (AUC). In comparison with two competitors, Bcrystal and TMCrys, PTMC achieves an improvement by 0.132 and 0.179 for sensitivity, 0.014 and 0.127 for specificity, 0.037 and 0.192 for accuracy, 0.128 and 0.362 for MCC, and 0.027 and 0.125 for AUC, respectively.

Parallel comparison of functional and physicochemical properties of common pulse proteins

The demand for more functional plant-based proteins has greatly increased. The objective of this study was to provide a systematic understanding of the functional properties and physicochemical features of protein isolates extracted from common pulses. Chickpea protein (ChPI) was much less soluble compared to other extracted proteins. Pigeon pea protein (PiPI) and lab extracted soybean protein (SPI) possessed excellent emulsification capacity and stability of 0.71–0.73 and 0.70–0.71 cm/cm, respectively. Most proteins had foaming capacities greater than 1.20 mL/mL, except for ChPI. Lentil protein (LPI-W), pea protein, and PiPI showed greater water absorption capacity of 4.9, 3.5, and 3.6 g/g than other proteins and good oil absorption capacity. Pigeon pea protein had the greatest gelation capacity, with a least gelation concentration of 80 g/L. ChPI had a higher thermal denaturation peak temperature (169 °C) than the other proteins (145–154 °C). Commercial SPI was much less functional compared to the lab extracted SPI, which was due to intensive protein denaturation during commercial processing. The amino acid profiles, SDS-PAGE patterns, secondary structure composition, and relative surface hydrophobicity were analyzed to help elucidate the functional features. This study provides useful information in selecting appropriate protein sources to achieve more desirable functional applications.

Water‐repellent films from corn protein and tomato cutin

AbstractFlexible and hydrophobic biobased films were obtained using zein esterified with methanol and para‐toluene (p‐toluene) sulfonic acid, cutin from tomato peels and ethanol. Esterification was confirmed by proton nuclear magnetic resonance and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR‐FTIR). Non‐modified zein films were brittle and hydrophilic. ATR‐FTIR demonstrated that zein esterification increased zein hydrophobicity. Without cutin, esterified zein films were hydrophobic but brittle. Addition of cutin yielded films that were flexible and hydrophobic, as demonstrated by contact angle measurements. Principal component analysis (PCA) of ATR‐FTIR data showed that intensities at 3195 cm−1 and 3490 cm−1 were correlated to the relative hydrophobicity of zein films. PCA also showed that films of esterified zein and cutin were more hydrophobic than their counterparts (non‐modified zein without cutin). Optical and scanning electron microscopy demonstrated that esterified zein was compatible with cutin and yielded cohesive films, which did not fracture upon bending.

Precise control over supramolecular nanostructures via manipulation of H-bonding in π-amphiphiles.

Self-assembled supramolecular architectures are ubiquitous in nature. A synchronized combination of dynamic noncovalent interactions is the major driving force in forming unique structures with high-precision control over the self-assembly of supramolecular materials. Herein, we have achieved programmable nanostructures by introducing single/multiple H-bonding units in a supramolecular building block. A diverse range of nanostructures can be generated in aqueous medium by subtly tuning the structure of π-amphiphiles. 1D-cylindrical micelles, 2D-nanoribbons and hollow nanotubes are produced by systematically varying the number of H-bonding units (0-2) in structurally near identical π-amphiphiles. Spectroscopic measurements revealed the decisive role of H-bonding units for different modes of molecular packing. We have demonstrated that a competitive self-assembled state (a kinetically controlled aggregation state and a thermodynamically controlled aggregation state) can be generated by fine tuning the number of noncovalent forces present in the supramolecular building blocks. The luminescence properties of conjugated dithiomaleimide (DTM) provided insight into the relative hydrophobicity of the core in these nanostructures. In addition, fluorescence turn-off in the presence of thiophenol enabled us to probe the accessibility of the hydrophobic core in these assembled systems toward guest molecules. Therefore the DTM group provides an efficient tool to determine the relative hydrophobicity and accessibility of the core of various nanostructures which is very rarely studied in supramolecular assemblies.

Metal-semiconductor sorting of large-diameter single-wall carbon nanotubes by pH-dependent binding to a hydrophobic-interaction adsorbent

A batch adsorption method for sorting large-diameter single-walled carbon nanotubes (SWCNTs) is described that employs a hydrophobic-interaction chromatography (HIC) adsorbent and a single nonionic surfactant. The method is based on the creation of significant differences between metallic and semiconductor SWCNTs in their adsorption affinity to a HIC adsorbent. These differences are then used for the efficient separation of the electronic forms of large-diameter SWCNTs. To gain a better understanding of the mechanism involved, the effects of various HIC adsorbents under different pH conditions were studied. The results obtained demonstrate the importance of the type and density of the hydrophobic functional groups on the adsorbent in determining the relative strength of the adsorptive interactions for various electronic forms of SWCNTs. The results also show the effects of negatively charged adventitious functional groups on the nanotube on the relative hydrophobicity of the nanotubes. The method described here is implemented using widely-available HIC adsorbents, and only requires simple titration with HCl or NaOH to adjust the pH. Furthermore, the method is potentially suitable to be performed using liquid chromatography with a packed adsorbent column and with a liquid-phase pH gradient in order to achieve high-resolution separations.

Stickiness of extracellular polymeric substances on different surfaces via magnetic tweezers

Organic particle dynamics in the surface ocean plays a critical part in the marine carbon cycle. Aggregation of marine organic particles drives their downward transport to support various marine organisms on their transit to the sediments. Extracellular polymeric substances (EPS) from various microbes are a major contributor to the oceanic organic particle pool. The stickiness of EPS is expected to play a determining role in the aggregation process of particles; however, stickiness parameters are usually indirectly estimated through data fitting without direct assessment. Here a magnetic tweezer method was developed to quantitatively assess the stickiness of three model EPS produced by: Amphora sp., (diatom), Emiliania huxleyi (coccolithophore), and Sagittula stellata (bacteria), under different in vitro environmental conditions (salinity or EDTA complexed cations) and surface matrices (EPS-EPS and bare glass). Our results showed the stickiness of three microbial EPS decreasing for S. stellata > E. huxleyi > Amphora sp., in line with their decreasing protein-to-carbohydrate (P/C) ratios (related to their relative hydrophobicity). The data not only emphasize the importance of hydrophobicity on EPS stickiness, but also demonstrates that salinity and the nature of the substrate surface can influence the stickiness. Furthermore, we investigated stickiness between various types of EPS, and the observed selective stickiness of EPS between species may shed light on the interactions among heterogeneous marine microorganisms. Overall, this newly developed system provides a platform to assess the EPS stickiness to advance our understanding of the aggregation and sedimentation process of organic particles that are critical for the fate of organic carbon as well as for biofilm formation and microbial colonization of surfaces in the ocean.

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas.