Function Of Hydrophobicity Research Articles

Pyroglutamation of amyloid-βx-42 (Aβx-42) followed by Aβ1–40 deposition underlies plaque polymorphism in progressing Alzheimer’s disease pathology

Amyloid-β (Aβ) pathology in Alzheimer's disease (AD) is characterized by the formation of polymorphic deposits comprising diffuse and cored plaques. Because diffuse plaques are predominantly observed in cognitively unaffected, amyloid-positive (CU-AP) individuals, pathogenic conversion into cored plaques appears to be critical to AD pathogenesis. Herein, we identified the distinct Aβ species associated with amyloid polymorphism in brain tissue from individuals with sporadic AD (s-AD) and CU-AP. To this end, we interrogated Aβ polymorphism with amyloid conformation–sensitive dyes and a novel in situ MS paradigm for chemical characterization of hyperspectrally delineated plaque morphotypes. We found that maturation of diffuse into cored plaques correlated with increased Aβ1–40 deposition. Using spatial in situ delineation with imaging MS (IMS), we show that Aβ1–40 aggregates at the core structure of mature plaques, whereas Aβ1–42 localizes to diffuse amyloid aggregates. Moreover, we observed that diffuse plaques have increased pyroglutamated Aβx-42 levels in s-AD but not CU-AP, suggesting an AD pathology–related, hydrophobic functionalization of diffuse plaques facilitating Aβ1–40 deposition. Experiments in tgAPPSwe mice verified that, similar to what has been observed in human brain pathology, diffuse deposits display higher levels of Aβ1–42 and that Aβ plaque maturation over time is associated with increases in Aβ1–40. Finally, we found that Aβ1–40 deposition is characteristic for cerebral amyloid angiopathy deposition and maturation in both humans and mice. These results indicate that N-terminal Aβx-42 pyroglutamation and Aβ1–40 deposition are critical events in priming and maturation of pathogenic Aβ from diffuse into cored plaques, underlying neurotoxic plaque development in AD.

Chemical Functionalization of ZnS: A Perspective from the Ligand–ZnS Bond Character

Chemical functionalization of metal sulfides plays a critical role in many fields such as materials science and froth flotation. The commonly used thiol-bearing functionalized ligands are generally considered to bind with metal sulfides covalently, and the computational binding energy is widely used to evaluate the functionality of the ligands toward metal sulfides. Herein, we studied the surface chemistry of the model ZnS and its binding with typical S- and O-terminated ligands using density functional theory calculations with an emphasis on the resulting bond character. Surprisingly, it was found that the ligand–ZnS(110) bond is essentially ionic with limited covalency. This very fundamental finding was further extended to the hydrophobization of ZnS in the context of froth flotation and rationalized the previously unresolved phenomenon that the higher the ligand–ZnS(110) binding strength, the lower the hydrophobic functionality of the ligand toward ZnS. Meanwhile, instead of the binding energy, the ele...

Aldol Condensation of Cyclopentanone on Hydrophobized MgO. Promotional Role of Water and Changes in the Rate-Limiting Step upon Organosilane Functionalization

Aldol condensation is a key C—C coupling reaction for upgrading of biomass-derived oxygenates to fuels and chemicals. Here, we investigate the effects of added water on the condensation of cyclopentanone (CPO) on hydrophobized MgO catalysts. We have found that the role of water strongly depends on the degree of hydrophobic functionalization of the MgO surface. That is, on a nonfunctionalized (hydrophilic) high-surface-area MgO catalyst, the rate decreases with the addition of water, mostly due to active site blockage. By contrast, on MgO hydrophobized via silylation with octadecyltrichlorosilane (OTS), the rate actually increases with added water. A concomitant change in kinetics is observed from the pristine (hydrophilic) MgO to the hydrophobized sample. Specifically, on the hydrophilic sample, the reaction is first-order, as expected if the rate-limiting step is the formation of an enolate intermediate via α-H abstraction at a basic site, as widely reported in previous literature. By contrast, on the hy...

Molecular Transport through Self-Assembled DNA Nanofluidic Channels

Nanoscale channels are a fundamental mechanism for directed transport within living systems. Confinement of transport to one dimension makes transport rapid, and gating at channel entrances can make transport selective. However, little is known about the mechanisms and rates of transport of small molecules within nanoscale channels, particularly those that extend beyond the dimensions of lipid membranes and across hundreds of nanometers or microns. We have used techniques from structural DNA nanotechnology, which makes it possible to precisely control the geometry and chemical functionality of self-assembled structures, to construct synthetic nanoscale channels for molecular transport. The channel we have designed and constructed has an internal diameter of 4-6 nm and a length that can extend for multiple microns. It is composed of a DNA origami pore that penetrates and spans a lipid membrane and a DNA nanotube self-assembled from DAE-E double crossover tiles, consisting of five DNA oligomers that grows from the DNA origami pore. Membrane incorporation is facilitated by hydrophobic functionalization of DNA origami pore via 12 cholesterol moieties. These self-assembled channels can self-repair and can be grown such that their endpoints specifically attach at molecular landmarks, making them a promising biomolecular device for single-molecule biosensing, for studying intercellular signaling, and for drug delivery. We characterized molecular transport through these DNA channels by confocal microscopy and a dye influx assay, in which synthesized DNA channels spontaneously inserted onto giant unilamellar vesicles. The rates of fluorescent dye transport through the channels were quantified by time-lapse observation of intensities inside many vesicles through a confocal microscope and comparing to a diffusion-dominated molecular transport model. Our results indicate that transport of small molecules through these channels is diffusive and that molecule size determines the degree to which transport may occur.

Hydrophobic Functionalization of Polyacrylic Acid as a Versatile Platform for the Development of Polymer Lipid Nanodisks.

Polymer nanodisks have shown great potential as membrane mimetics that enable the study of functional membrane protein structural biology and also have a wider application in other fields such as drug delivery. To achieve these research goals, the ability to have a cheap, simple, fully customizable platform for future nanodisks technology applications is paramount. Here, a facile functionalization of polyacrylic acid (PAA) with varying hydrophobic groups that form nanodisks at different sizes is successfully demonstrated. The study shows that the choice of hydrophobic group can have a noticeable effect on the polymer solubilization properties and polymer-induced perturbation to the encased lipid bilayer. Due to this robust, tunable chemical synthesis method, PAA is an exciting platform for the future optimization of the hydrophobic, hydrophilic, or direct purposed functionalizations for polymer nanodisks.

Hydrophobic Functionalization of ZnO Nanosheets by In Situ Center‐Substituted Synthesis for Selective Photocatalysis under Visible Irradiation

AbstractThe selective degradation of specific substances in mixed contaminants is quite challenging. And a general approach for sensitized oxide semiconductor relies on dip‐coating method with sensitizer. Here, hydrophilic 2D, nest‐like architecture ZnO (ZnO NA) was hydrophobicly functioned by monomolecular–layer tetraphenylporphyrin zinc (ZnTPP), where ZnTPP was synthesized by means of an in situ center‐substituted (ISCS) process., i.e., the hydrogen atoms in the core of metal‐free tetraphenylporphyrin (H2TPP) are substituted by the unsaturated zinc ions in ZnO NAs. ZnTPP/ZnO NA was exhibited with significant hydrophobicity, benefitting to absorb hydrophobic phenol (PL). Further, it is realized to selectively photodegradate PL in the mixture by ZnTPP/ZnO NAs under visible irradiation. Note that the rate of degradation to hydrophobic PL by ZnTPP/ZnO NA is 9.17 times of that for ZnO NA within 150 min; on the contrary, the degradation rate of hydrophilic rhodamine B (RhB) by ZnTPP/ZnO is reduced by 40%. Radiative lifetime of photogenerated charges is obviously increased by ZnTPP/ZnO NA compared with that of ZnTPP, indicating the effective charge separation for ZnTPP/ZnO NAs. In addition, ZnTPP/ZnO NA produced more superoxide radicals (·O2−) in comparison to ZnO NA. With surface functionalization, the feasibility of selective photocatalysis under visible irradiation is demonstrated.

Hydrogenation of alkyl-anthraquinone over hydrophobically functionalized Pd/SBA-15 catalysts.

Organosilane-functionalized mesoporous silica SBA-15 was prepared by the co-condensation method and then applied as a support of Pd catalysts for hydrogenation of 2-alkyl-anthraquinone (AQ, alkyl = ethyl, tert-butyl and amyl). The as-prepared Pd catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, N2 adsorption–desorption, zeta potential, water contact angles measurement and transmission electron microscopy. By extending the pre-hydrolysis time of the silica source, the content of functional groups in the catalysts slightly increases. However, there is an initial increase in zeta potential and water contact angles up to a maximum at 2 h, followed by a decrease as the pre-hydrolysis time was further prolonged. The hydrophobicity created by organic functionalization has positive effects on AQ hydrogenation. The catalyst with the highest hydrophobicity exhibits the highest catalytic activity, with increments of 33.3%, 60.0% and 150.0% for hydrogenation of ethyl-, tert-butyl- and amyl-anthraquinone compared with the unfunctionalized one.

Interaction of functionalized nanoparticles with serum proteins and its impact on colloidal stability and cargo leaching.

The majority of effort in the area of polymeric nanocarriers is aimed at providing controlled drug delivery in vivo. Therefore, it is essential to understand the delicate interplay of polymeric NPs with serum proteins in order to forecast their performance in a biological system. In this study, the interaction of serum proteins with functionalized polymeric colloids as a function of particle charge and hydrophobicity was investigated. Moreover, impact on NP stability and cargo leaching was assessed. The hard protein corona of polymeric NPs with either uncharged methoxy groups (methoxy-NPs), positively charged amine groups (amine-NPs), negatively charged carboxylic acid groups (carboxyl-NPs) or zwitterionic NPs decorated with amine and carboxylic acid groups (zwitterion-NPs) was quantitatively and qualitatively analyzed and correlated with the respective colloidal stability using fluorescence resonance energy transfer. Positively charged amine-NPs displayed an enhanced interaction with serum proteins via electrostatic interactions resulting in a hard corona consisting of diverse protein components. As revealed by FRET and agarose gel electrophoresis, the enhanced adsorption of proteins onto the colloidal surface significantly altered the NP identity and severely impaired the colloidal integrity as the lipophilic cargo was continuously leached out of the hydrophobic NP core. These results highlight the importance of generating a profound knowledge of the bio-nano interface as adherence of biomolecules can severely compromise the performance of a colloidal drug delivery system by changing its identity and integrity.

Sustainable Extraction and Separation of Rhenium and Molybdenum from Model Copper Mining Effluents Using a Polymeric Aqueous Two-Phase System

A sustainable and flexible approach for the extraction and separation of rhenium and molybdate species based on a polymeric aqueous two-phase system (ATPS) is proposed in which the high metal content in concentrated copper effluents is directly used as the driver of phase demixing. The partition coefficient and selectivity of Re, Mo, and Cu are studied in the proposed polymer-CuSO4-H2O ATPS as a function of additive concentration and polymer hydrophobicity. The electrolyte selection and concentration have a marked influence on the partition of Mo to the polymer phase, while increasing the hydrophobicity of the polymeric agent significantly improves the extraction of Mo. A selective precipitation based on the addition of quaternary ammonium salts directly to the polymer-rich phase is subsequently used for the quantitative recovery of Mo. A final polyoxometallate [N2222]2Mo6O19 hybrid complex is obtained with high purity. The resulting process achieves high separation yields, relies exclusively on cheap chemicals with low toxicity and could be a more sustainable alternative for the extraction of Re and Mo from copper mine effluents. By using sulfate salts as the salting-out agent, the main component of the ore leachate drives the separation thereby avoiding the use of additional complexing agents.

A Review of Kinetic Hydrate Inhibitors from an Environmental Perspective

Kinetic hydrate inhibitors (KHIs) have been used in the upstream petroleum industry for about 25 years to prevent plugging of flow lines with gas hydrates. The main ingredients in current commercial KHI formulations are one or more water-soluble polymers which contain both hydrophobic and hydrophilic functionalities. Although the vast majority of KHIs are low in acute toxicity and bioaccumulation, very few commercial products show good biodegradability, and for that reason, there is always some concern of long-term chronic toxicity from partially degraded products if discharged into the environment. This report reviews all efforts to develop more biodegradable KHIs, and outlines the fact that some classes of so-called “green” chemicals are not necessarily readily biodegradable or low in toxicity. The review also covers methodologies to recover or destroy KHIs and reduce their discharge to the environment.

Characterization of Tween® Surfactants by MALDI TOF-MS and High Performance Liquid Chromatography in a Ternary Mobile Phase

AbstractDifferent hydrophobic and hydrophilic functionalities are produced in the reaction mixture of Tween® surfactants which affect the physiochemical properties of the final product. Only hydrophilic fractions and monoesters were separated in the binary mobile phase. MALDI TOF-MS of Tween® 40 revealed the identification of peaks separated in binary mobile phase (methanol-water). Liquid adsorption chromatography was performed on a gradient system on a SynergiTM fusion reverse phase column. Mobile phase composition used for this separation was a ternary phase gradient starting from 41 % methanol, 47 % acetone and going to 96 % acetone for the analysis time of 60 minutes. In the ternary mobile phase, gradient all the species such as polyethylene glycol, sorbitan and isosorbide ethoxylates, mono-, di- and triesters of sorbitan and isosorbide ethoxylates were well resolved in an of 60 minutes analysis time. The above separation mechanism can be employed for the analysis of polymeric multifunctional surfactant compositions.

Decoupling the Functional Roles of Cationic and Hydrophobic Groups in the Antimicrobial and Hemolytic Activities of Methacrylate Random Copolymers.

In this study, we report the antimicrobial and hemolytic activities of ternary statistical methacrylate copolymers consisting of cationic ammonium (amino-ethyl methacrylate: AEMA), hydrophobic alkyl (ethyl methacrylate: EMA), and neutral hydroxyl (hydroxyethyl methacrylate: HEMA) side chain monomers. The cationic and hydrophobic functionalities of copolymers mimic the cationic amphiphilicity of naturally occurring antimicrobial peptides (AMPs). The HEMA monomer units were used to separately modulate the compositions of cationic and hydrophobic monomers, and we investigated the effect of each component on the antimicrobial and hemolytic activities of copolymers. Our data indicated that increasing the number of cationic groups of the copolymers to be more than 30 mol % did not increase their antimicrobial activity against Escherichia coli. The number of cationic side chains in a polymer chain at this threshold is 5.5-7.7, which is comparable to those of natural antimicrobial peptides such as maginin (+6). The MIC values of copolymers with >30 mol % of AEMA depend on only the mol % of EMA, indicating that the hydrophobic interactions of the copolymers with E. coli cell membranes determine the antimicrobial activity of copolymers. These results suggest that the roles of cationic and hydrophobic groups can be controlled independently by design in the ternary copolymers studied here.

Hydrophobic ceramic capillary membranes for versatile virus filtration

In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardless of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of ~ 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiX174. The functionalized membranes allow a high membrane flux of ~ 150 L/(m2hbar), with throughput rates up to ~ 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.

Water-Soluble Leaving Group Enables Hydrophobic Functionalization of RNA.

Attachment of hydrophobic groups to RNA is challenging because of their poor aqueous solubility. One-step acylation of RNA 2'-OH groups in water using a water-soluble imidazole leaving group is described. The effect of the hydrophobic groups on hybridization is reported. Furthermore, propargyl-functionalized RNA is shown to be readily labeled with a fluorophore. Lastly, heptyl-functionalized RNA is found to exhibit the unusual property of solubility in organic solvents.

Control of Wettability Using Regularly Ordered Two-Dimensional Polymeric Wavy Substrates

Two-dimensional poly(dimethylsiloxane) (PDMS) films with wavy patterns were studied in order to investigate reversible and irreversible wetting effects. Pre-strained, surface oxidized layers of PDMS were used to form relieved wavy geometries, on which hydrophobic functionalization was carried out in order to produce irreversible wetting effects. Wavy-patterned PDMS films showed time-dependent reversible wetting effects. The degree of surface wettability could be tuned by the choice of wavy groove geometries. And the groove geometries were controlled via O2 plasma treatment and mechanical pre-straining. The pre-strained, buckled PDMS films were applied to the fabrication of hydrophobic polystyrene nano-patterns using colloidal self-assembly, where the colloids were arrayed in two-dimensional way. The wavy polystyrene films were found to be more hydrophobic relative to flat polystyrene films. The grooving methodology used in this study could be applied to enhancing the hydrophobicity of other types of polymeric thin films, eliminating the need for chemical treatment.

Rationally Engineered Tandem Facial Amphiphiles for Improved Membrane Protein Stabilization Efficacy.

A new family of tandem facial glucosides/maltosides (TFGs/TFMs) for membrane protein manipulation was prepared. The best detergent varied depending on the hydrophobic thickness of the target protein, but ether-based TFMs (TFM-C0E, TFM-C3E, and TFM-C5E) were notable for their ability to confer higher membrane protein stability than the previously developed amide-based TFA-1 (P. S. Chae, K. Gotfryd, J. Pacyna, L. J. W. Miercke, S. G. F. Rasmussen, R. A. Robbins, R. R. Rana, C. J. Loland, B. Kobilka, R. Stroud, B. Byrne, U. Gether, S. H. Gellman, J. Am. Chem. Soc. 2010, 132, 16750-16752). Thus, this study not only introduces novel agents with the potential to be used in membrane protein research but also highlights the importance of both the hydrophobic length and linker functionality of the detergent in stabilizing membrane proteins.

How does the use of surfactants in polymer-salt based aqueous two-phase systems affect the annatto dye (Bixa orellana L.) partitioning?

In this work, the partitioning of natural annatto pigments in aqueous two-phase systems formed by poly(ethylene) glycol polymers (1500 or 4000 or 6000 g mol−1) or triblock copolymer L35 (2000 g mol−1) + sodium citrate + water was studied in the presence of cetyltrimethylammonium bromide. The hypothesis investigated was that the use of surfactants as additives in traditional two-phase aqueous systems could improve the solubility of the annatto extract in the phases of these systems through a mechanism of mixed micelle formation. This would make it possible to implement the use of these systems in the annatto dye extraction process. For this, several experiments were conducted. The annatto extract partition coefficient was determined as a function of pH, surfactant concentration, molar mass and hydrophobicity of the polymer, tie-line length, and the nature of the electrolyte. These results showed the potential of surfactant as a modulation agent for dyes transfer between the aqueous two-phase systems phases. The effect of surfactant was attributed to its interaction with norbixin from annatto, which was studied by means of surface tension and spectrophotometric measurements. The driving force governing annatto extract partitioning was dependent on the system composition and the temperature. Lower partition constants values for annatto extract obtained in the presence of surfactant demonstrated the potential of the aqueous two-phase systems for the extraction or purification of annatto.

Design, manufacturing and testing of anti-fouling/foul-release (AF/FR) amphiphilic coatings

In this study, innovative strategies for the manufacturing of anti-fouling/foul-release (AF/FR) coatings based on the implementation of amphiphilic surfaces by the chemistry of silanes and polyurethanes were evaluated. The newly developed process for the synthesis of amphiphilic resins involved the introduction of hydrophobic functionalities by the sol-gel reaction of a fluorinate-alkyl bearing silanes (FTSi). Conversely, the introduction of hydrophilic PEG-ilate functionalities was alternatively implemented by the sol-gel reaction with PEG-ilate silanes (PEGSi) or PEG-ilate isocyanates. These synthesis processes were possible thanks to the adoption of a peculiar hydroxyl-rich hybrid resin, consisting in a polysiloxane resin modified by polyester domains. Manufacturing of the formulations was a rapid process (shorter than 3 h), and easily implementable thanks to the sole use of commercially available raw materials. The synthesis did not require any special technical arrangement such as reflux conditions, autoclave or inert atmosphere. The effectiveness of the synthesis was evaluated by FTIR analysis, while the amphiphilic character of the surfaces was ensured by wettability test against water. AF/FR properties were tested under severe conditions using a protein test probe (i.e., the so called “egg white” test) that well simulates the substances secreted by the bio-fouling organisms to adhere. All the samples tested showed amphiphilic character, with most of them featuring excellent AF/FR properties.

Facile, Scalable Spray-Coating of Stable Emulsion for Transparent Self-Cleaning Surface of Cellulose-Based Materials

Cellulose-based materials are vulnerable to moisture and microorganisms and thus lose their original mechanical properties and durability; meanwhile, self-cleaning technique as a disruptive nanotechnology of waterproofing is attracting tremendous interest. Here, we develop a facile, cheap, and scalable “top-down” strategy to fabricate a transparent self-cleaning surface for cellulose-based materials by spray-coating a stable emulsion of nano-SiO2 particles. The nanoparticles are precisely synthesized at an average diameter of ∼110 nm via a sol–gel way and finely tailored with hydrophobic function by successive modification of poly(dimethylsiloxane) (PDMS) and (heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane (17F). The modified nano-SiO2 particles well-distributed on the microscale rough surface of the cellulose-based materials by spray-coating to form a micro/nano two-tier structure to entrap air for water resistance, and thus build a superhydrophobic surface with static water contact angle (WCA) over...

Low-Bleed Silica-Based Stationary Phase for Hydrophilic Interaction Liquid Chromatography.

Bleeding of hydrophilic interaction liquid chromatographic (HILIC) phases is a major problem. A hydrophobic silica surface exhibits low bleeding but does not behave as a HILIC phase. A hydrophilic coating, such as that of poly(vinyl alcohol) (PVA) on a hydrophobic particle should result in a low-bleed hydrophilic phase. However, a silica particle functionalized in a hydrophobic manner is not wetted by PVA and cannot be coated with it. Coating with PVA becomes possible if one region of the hydrophobic functionality is polar. We describe a low-bleed HILIC stationary phase, PVA-coated benzylthioethyl-silica. The benzyl groups shield the silica from water erosion, while the thiol group provides sufficient local polarity for PVA to wet the material. The new stationary phase demonstrated good chromatographic performance and typical HILIC retention behavior. The measured silica concentration in the effluent was ∼80-fold lower than that from a bare silica column. The new stationary phase exhibited a lower background level, lower background noise, and lower background drift under gradient conditions than benchmark commercial columns.