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Why does vacuum drive to the loading of halloysite nanotubes? The key role of water confinement

Lisuzzo L, Cavallaro G, Pasbakhsh P, Milioto S, Lazzara G

J Colloid Interface Sci, 2019 Jul 01;547:361-369.
PMID: 30974251 DOI: 10.1016/j.jcis.2019.04.012

The filling of halloysite nanotubes with active compounds solubilized in aqueous solvent was investigated theoretically and experimentally. Based on Knudsen thermogravimetric data, we demonstrated the water confinement within the cavity of halloysite. This process is crucial to properly describe the driving mechanism of halloysite loading. In addition, Knudsen thermogravimetric experiments were conducted on kaolinite nanoplates as well as on halloysite nanotubes modified with an anionic surfactant (sodium dodecanoate) in order to explore the influence of both the nanoparticle morphology and the hydrophobic/hydrophilic character of the lumen on the confinement phenomenon. The analysis of the desorption isotherms allowed us to determine the water adsorption properties of the investigated nanoclays. The pore sizes of the nanotubes' lumen was determined by combining the vapor pressure of the confined water with the nanoparticles wettability, which was studied through contact angle measurements. The thermodynamic description of the water confinement inside the lumen was correlated to the influence of the vacuum pumping in the experimental loading of halloysite. Metoprolol tartrate, salicylic acid and malonic acid were selected as anionic guest molecules for the experimental filling of the positively charged halloysite lumen. According to the filling mechanism induced by the water confinement, the vacuum operation and the reduced pressure enhanced the loading of halloysite nanotubes for all the investigated bioactive compounds. This work represents a further and crucial step for the development of halloysite based nanocarriers being that the filling mechanism of the nanotube's cavity from aqueous dispersions was described according to the water confinement process.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext Wheat Germ Agglutinin-Conjugated Disulfide Cross-Linked Alginate Nanoparticles as a Docetaxel Carrier for Colon Cancer Therapy

Chiu HI, Lim V

Int J Nanomedicine, 2021;16:2995-3020.
PMID: 33911862 DOI: 10.2147/IJN.S302238

PURPOSE: In chemotherapy, oral administration of drug is limited due to lack of drug specificity for localized colon cancer cells. The inability of drugs to differentiate cancer cells from normal cells induces side effects. Colonic targeting with polymeric nanoparticulate drug delivery offers high potential strategies for delivering hydrophobic drugs and fewer side effects to the target site. Disulfide cross-linked polymers have recently acquired high significance due to their potential to degrade in reducing colon conditions while resisting the upper gastrointestinal tract's hostile environment. The goal of this project is, therefore, to develop pH-sensitive and redox-responsive fluorescein-labeled wheat germ agglutinin (fWGA)-mounted disulfide cross-linked alginate nanoparticles (fDTP2) directly targeting docetaxel (DTX) in colon cancer cells.
METHODS: fDTP2 was prepared by mounting fWGA on DTX-loaded nanoparticles (DTP2) using the two-step carbodiimide method. Morphology of fDTP2 was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Dynamic light scattering (DLS) study was carried out to determine the mean diameter, polydispersity index (PDI) and zeta potential of fDTP2. Cellular uptake efficiency was examined using fluorescence microplate reader. Biocompatibility and active internalization of fDTP2 were conducted on HT-29.
RESULTS: fDTP2 was found to exhibit a DTX loading efficiency of 19.3%. SEM and TEM tests revealed spherical nanoparticles. The in vitro DTX release test showed a cumulative release of 54.7%. From the DLS study, fDTP2 reported a 277.7 nm mean diameter with PDI below 0.35 and -1.0 mV zeta potential. HT-29 which was fDTP2-treated demonstrated lower viability than L929 with a half maximal inhibitory concentration (IC50) of 34.7 µg/mL. HT-29 (33.4%) internalized fDTP2 efficiently at 2 h incubation. The study on HT-29 active internalization of nanoparticles through fluorescence and confocal imaging indicated such.
CONCLUSION: In short, fDTP2 demonstrated promise as a colonic drug delivery DTX transporter.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Water-Soluble Dioxidovanadium(V) Complexes of Aroylhydrazones: DNA/BSA Interactions, Hydrophobicity, and Cell-Selective Anticancer Potential

Sahu G, Banerjee A, Samanta R, Mohanty M, Lima S, Tiekink ERT, et al.

Inorg Chem, 2021 Oct 18;60(20):15291-15309.
PMID: 34597028 DOI: 10.1021/acs.inorgchem.1c01899

Five new anionic aqueous dioxidovanadium(V) complexes, [{VO2L1,2}A(H2O)n]α (1-5), with the aroylhydrazone ligands pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H2L1) and furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H2L2) incorporating different alkali metals (A = Na+, K+, Cs+) as countercation were synthesized and characterized by various physicochemical techniques. The solution-phase stabilities of 1-5 were determined by time-dependent NMR and UV-vis, and also the octanol/water partition coefficients were obtained by spectroscopic techniques. X-ray crystallography of 2-4 confirmed the presence of vanadium(V) centers coordinated by two cis-oxido-O atoms and the O, N, and O atoms of a dianionic tridentate ligand. To evaluate the biological behavior, all complexes were screened for their DNA/protein binding propensity through spectroscopic experiments. Finally, a cytotoxicity study of 1-5 was performed against colon (HT-29), breast (MCF-7), and cervical (HeLa) cancer cell lines and a noncancerous NIH-3T3 cell line. The cytotoxicity was cell-selective, being more active against HT-29 than against other cells. In addition, the role of hydrophobicity in the cytotoxicity was explained in that an optimal hydrophobicity is essential for high cytotoxicity. Moreover, the results of wound-healing assays indicated antimigration in case of HT-29 cells. Remarkably, 1 with an IC50 value of 5.42 ± 0.15 μM showed greater activity in comparison to cisplatin against the HT-29 cell line.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Use of cellulose acetate/polyphenylsulfone derivatives to fabricate ultrafiltration hollow fiber membranes for the removal of arsenic from drinking water

Kumar M, RaoT S, Isloor AM, Ibrahim GPS, Inamuddin, Ismail N, et al.

Int J Biol Macromol, 2019 May 15;129:715-727.
PMID: 30738161 DOI: 10.1016/j.ijbiomac.2019.02.017

Cellulose acetate (CA) and cellulose acetate phthalate (CAP) were used as additives (1 wt%, 3 wt%, and 5 wt%) to prepare polyphenylsulfone (PPSU) hollow fiber membranes. Prepared hollow fiber membranes were characterized by surface morphology using scanning electron microscopy (SEM), surface roughness by atomic force microscopy (AFM), the surface charge of the membrane was analyzed by zeta potential measurement, hydrophilicity by contact angle measurement and the functional groups by fourier transform infrared spectroscopy (FTIR). Fouling resistant nature of the prepared hollow fiber membranes was evaluated by bovine serum albumin (BSA) and molecular weight cutoff was investigated using polyethylene glycol (PEG). By total organic carbon (TOC), the percentage rejection of PEG was found to be 14,489 Da. It was found that the hollow fiber membrane prepared by the addition of 5 wt% of CAP in PPSU confirmed increased arsenic removal from water as compared to hollow fiber membrane prepared by 5 wt% of CA in PPSU. The removal percentages of arsenic with CA-5 and CAP-5 hollow fiber membrane was 34% and 41% with arsenic removal permeability was 44.42 L/m2h bar and 40.11 L/m2h bar respectively. The increased pure water permeability for CA-5 and CAP-5 hollow fiber membrane was 61.47 L/m2h bar and 69.60 L/m2 h bar, respectively.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext Ultraviolet A and Ultraviolet C Light-Induced Reduction of Surface Hydrocarbons on Titanium Implants

Naauman Z, Rajion ZAB, Maliha S, Hariy P, Muhammad QS, Noor HAR

Eur J Dent, 2019 Feb;13(1):114-118.
PMID: 31170762 DOI: 10.1055/s-0039-1688741

OBJECTIVE: The carbon, titanium, and oxygen levels on titanium implant surfaces with or without ultraviolet (UV) pretreatment were evaluated at different wavelengths through X-ray photoelectron spectroscopy (XPS).
MATERIALS AND METHODS: This interventional experimental study was conducted on nine Dio UFII implants with hybrid sandblasted and acid-etched (SLA) surface treatments, divided equally into three groups. Control group A samples were not given UV irradiation, while groups B and C samples were given UVA (382 nm, 25 mWcm2) and UVC (260 nm, 15 mWcm2) irradiation, respectively. The atomic ratio of carbon, titanium, and oxygen was compared through XPS.
RESULTS: Mean carbon-to-titanium ratio and C1 peaks considerably increased in Group A compared to those in experimental Groups B and C. The intensity of Ti2p and O1s peaks was more pronounced for group C compared to that for groups A and B.
CONCLUSIONS: Although the decrease in surface hydrocarbons was the same in both UV-treated groups, the peak intensity of oxygen increased in the UVC-treated group. Thus, it can be concluded that compared with UVA irradiation, UVC irradiation has the potential to induce more hydrophilicity on SLA-coated implants.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext UV induced surface modification on improving the cytocompatibility of metallocene polyethylene

Jaganathan SK, Prasath MM

An Acad Bras Cienc, 2018 4 12;90(1):195-204.
PMID: 29641759 DOI: 10.1590/0001-3765201820170736

Demand for medical implants is rising day by day as the world becomes the place for more diseased and older people. Accordingly, in this research, metallocene polyethylene (mPE), a commonly used polymer was treated with UV rays for improving its biocompatibility. Scanning electron microscopy (SEM) images confirmed the formation of crests and troughs, which depicts the improvement of surface roughness of mPE substrates caused by UV etching. Accordingly, the contact angle measurements revealed that the wettability of mPE-2.5 J/cm2 (68.09º) and mPE-5 J/cm2 (57.93º) samples were found to be increased compared to untreated mPE (86.84º) indicating better hydrophilicity. Further, the UV treated surface exhibited enhanced blood compatibility as determined in APTT (untreated mPE- 55.3 ± 2.5 s, mPE-2.5 J/cm2 - 76.7 ± 4.1 s and mPE-5 J/cm2 - 112.3 ± 2 s) and PT (untreated mPE - 24.7 ± 1.5 s, mPE- 2.5 J/cm2 - 34.3 ± 1.1 s and mPE-5 J/cm2 - 43 ± 2 s) assay. Moreover, the treated mPE-2.5 J/cm2 (4.88%) and mPE-5 J/cm2 (1.79%) showed decreased hemolytic percentage compared to untreated mPE (15.40%) indicating better safety to red blood cells. Interestingly, the changes in physicochemical properties of mPE are directly proportional to the dosage of the UV rays. UV modified mPE surfaces were found to be more compatible as identified through MTT assay, photomicrograph and SEM images of the seeded 3T3 cell population. Hence UV-modified surface of mPE may be successfully exploited for medical implants.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext Two-Step Dopamine-to-Polydopamine Modification of Polyethersulfone Ultrafiltration Membrane for Enhancing Anti-Fouling and Ultraviolet Resistant Properties

Mulyati S, Muchtar S, Arahman N, Syamsuddin Y, Mat Nawi NI, Yub Harun N, et al.

Polymers (Basel), 2020 Sep 09;12(9).
PMID: 32916778 DOI: 10.3390/polym12092051

Polydopamine has been widely used as an additive to enhance membrane fouling resistance. This study reports the effects of two-step dopamine-to-polydopamine modification on the permeation, antifouling, and potential anti-UV properties of polyethersulfone (PES)-based ultrafiltration membranes. The modification was performed through a two-step mechanism: adding the dopamine additive followed by immersion into Tris-HCl solution to allow polymerization of dopamine into polydopamine (PDA). The results reveal that the step of treatment, the concentration of dopamine in the first step, and the duration of dipping in the Tris solution in the second step affect the properties of the resulting membranes. Higher dopamine loadings improve the pure water flux (PWF) by more than threefold (15 vs. 50 L/m2·h). The extended dipping period in the Tris alkaline buffer leads to an overgrowth of the PDA layer that partly covers the surface pores which lowers the PWF. The presence of dopamine or polydopamine enhances the hydrophilicity due to the enrichment of hydrophilic catechol moieties which leads to better anti-fouling. Moreover, the polydopamine film also improves the membrane resistance to UV irradiation by minimizing photodegradation's occurrence.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Two new monofunctional platinum(II) dithiocarbamate complexes: phenanthriplatin-type axial protection, equatorial-axial conformational isomerism, and anticancer and DNA binding studies

Imran M, Rehman ZU, Hogarth G, Tocher DA, Chaudhry GE, Butler IS, et al.

Dalton Trans, 2020 Nov 10;49(43):15385-15396.
PMID: 33140800 DOI: 10.1039/d0dt03018j

The syntheses of two platinum(ii) dithiocarbamate complexes (1 and 2) that show quinoplatin- and phenanthriplatin-type axial protection of the Pt-plane are described. The Pt-plane of complex 2 is axially more protected than that of complex 1. Furthermore, both complexes adopt two different stereochemical conformations in the solid state (based on single-crystal X-ray structures) owing to the structurally flexible piperazine backbone; i.e., C-e,e-Anti (1) and C-e,a-Syn (2), where "C" stands for the chair configuration, "e" and "a" stand for the equatorial and axial positions and "Anti" (opposite side) and "Syn" (same side) represent the relative orientations in space of the terminal substituents on the piperazine ring. In complex 2, the C-e,a-Syn conformation may provide additional steric hindrance to the Pt-plane. Despite the lower lipophilicity of 2 as compared to that of 1, the in vitro anticancer action against selected cancer cell lines is better for the former revealing the superior role of the axial protection over lipophilicity in modulating anticancer activity. The activity against the cancer promoting protein NF-κB signifies that the mode of cancer cell death may be the result of hindering the activity of NF-κB in the initiation of apoptosis. The apoptotic mode of cell death has been established earlier in a study using Annexin V-FITC. Finally, DNA binding studies revealed that the complex-DNA adduct formation is spontaneous and the mode of interaction is non-intercalative (electrostatic/covalent).

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Triggering Mechanisms of Thermosensitive Nanoparticles Under Hyperthermia Condition

Dabbagh A, Abdullah BJ, Abdullah H, Hamdi M, Kasim NH

J Pharm Sci, 2015 Aug;104(8):2414-28.
PMID: 26073304 DOI: 10.1002/jps.24536

Nanoparticle-based hyperthermia is an effective therapeutic approach that allows time- and site-specific treatment with minimized off-site effects. The recent advances in materials science have led to design a diversity of thermosensitive nanostructures that exhibit different mechanisms of thermal response to the external stimuli. This article aims to provide an extensive review of the various triggering mechanisms in the nanostructures used as adjuvants to hyperthermia modalities. Understanding the differences between various mechanisms of thermal response in these nanostructures could help researchers in the selection of appropriate materials for each experimental and clinical condition as well as to address the current shortcomings of these mechanisms with improved material design.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Toluene promotes lid 2 interfacial activation of cold active solvent tolerant lipase from Pseudomonas fluorescens strain AMS8

Yaacob N, Mohamad Ali MS, Salleh AB, Rahman RNZRA, Leow ATC

J Mol Graph Model, 2016 07;68:224-235.
PMID: 27474867 DOI: 10.1016/j.jmgm.2016.07.003

The utilization of cold active lipases in organic solvents proves an excellent approach for chiral synthesis and modification of fats and oil due to the inherent flexibility of lipases under low water conditions. In order to verify whether this lipase can function as a valuable synthetic catalyst, the mechanism concerning activation of the lid and interacting solvent residues in the presence of organic solvent must be well understood. A new alkaline cold-adapted lipase, AMS8, from Pseudomonas fluorescens was studied for its structural adaptation and flexibility prior to its exposure to non-polar, polar aprotic and protic solvents. Solvents such as ethanol, toluene, DMSO and 2-propanol showed to have good interactions with active sites. Asparagine (Asn) and tyrosine (Tyr) were key residues attracted to solvents because they could form hydrogen bonds. Unlike in other solvents, Phe-18, Tyr-236 and Tyr-318 were predicted to have aromatic-aromatic side-chain interactions with toluene. Non-polar solvent also was found to possess highest energy binding compared to polar solvents. Due to this circumstance, the interaction of toluene and AMS8 lipase was primarily based on hydrophobicity and molecular recognition. The molecular dynamic simulation showed that lid 2 (residues 148-167) was very flexible in toluene and Ca(2+). As a result, lid 2 moves away from the catalytic areas, leaving an opening for better substrate accessibility which promotes protein activation. Only a single lid (lid 2) showed the movement following interactions with toluene, although AMS8 lipase displayed double lids. The secondary conformation of AMS8 lipase that was affected by toluene observed a reduction of helical strands and increased coil structure. Overall, this work shows that cold active lipase, AMS8 exhibits distinguish interfacial activation and stability in the presence of polar and non-polar solvents.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext Thermal and UV Hydrosilylation of Alcohol-Based Bifunctional Alkynes on Si (111) surfaces: How surface radicals influence surface bond formation

Khung YL, Ngalim SH, Scaccabarozi A, Narducci D

Sci Rep, 2015 Jun 12;5:11299.
PMID: 26067470 DOI: 10.1038/srep11299

Using two different hydrosilylation methods, low temperature thermal and UV initiation, silicon (111) hydrogenated surfaces were functionalized in presence of an OH-terminated alkyne, a CF3-terminated alkyne and a mixed equimolar ratio of the two alkynes. XPS studies revealed that in the absence of premeditated surface radical through low temperature hydrosilylation, the surface grafting proceeded to form a Si-O-C linkage via nucleophilic reaction through the OH group of the alkyne. This led to a small increase in surface roughness as well as an increase in hydrophobicity and this effect was attributed to the surficial etching of silicon to form nanosize pores (~1-3 nm) by residual water/oxygen as a result of changes to surface polarity from the grafting. Furthermore in the radical-free thermal environment, a mix in equimolar of these two short alkynes can achieve a high contact angle of ~102°, comparable to long alkyl chains grafting reported in literature although surface roughness was relatively mild (rms = ~1 nm). On the other hand, UV initiation on silicon totally reversed the chemical linkages to predominantly Si-C without further compromising the surface roughness, highlighting the importance of surface radicals determining the reactivity of the silicon surface to the selected alkynes.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext The identification of novel Mycobacterium tuberculosis DHFR inhibitors and the investigation of their binding preferences by using molecular modelling

Hong W, Wang Y, Chang Z, Yang Y, Pu J, Sun T, et al.

Sci Rep, 2015;5:15328.
PMID: 26471125 DOI: 10.1038/srep15328

It is an urgent need to develop new drugs for Mycobacterium tuberculosis (Mtb), and the enzyme, dihydrofolate reductase (DHFR) is a recognised drug target. The crystal structures of methotrexate binding to mt- and h-DHFR separately indicate that the glycerol (GOL) binding site is likely to be critical for the function of mt-DHFR selective inhibitors. We have used in silico methods to screen NCI small molecule database and a group of related compounds were obtained that inhibit mt-DHFR activity and showed bactericidal effects against a test Mtb strain. The binding poses were then analysed and the influence of GOL binding site was studied by using molecular modelling. By comparing the chemical structures, 4 compounds that might be able to occupy the GOL binding site were identified. However, these compounds contain large hydrophobic side chains. As the GOL binding site is more hydrophilic, molecular modelling indicated that these compounds were failed to occupy the GOL site. The most potent inhibitor (compound 6) demonstrated limited selectivity for mt-DHFR, but did contain a novel central core (7H-pyrrolo[3,2-f]quinazoline-1,3-diamine), which may significantly expand the chemical space of novel mt-DHFR inhibitors. Collectively, these observations will inform future medicinal chemistry efforts to improve the selectivity of compounds against mt-DHFR.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
The effect of p-nitrophenol toward the structural characteristics and antioxidant activity of oil palm fronds (OPF) lignin polymers

Sa'don NA, Rahim AA, Hussin MH

Int J Biol Macromol, 2017 May;98:701-708.
PMID: 28174085 DOI: 10.1016/j.ijbiomac.2017.01.137

This article reports on the structural characteristics and antioxidant activity of unmodified autohydrolyzed ethanol organosolv lignin (AH EOL) extracted from oil palm fronds (OPF) and modified autohydrolyzed ethanol organosolv lignin via incorporation of p-nitrophenol (AHNP EOL). The isolated lignin were analyzed by FTIR, (1)H and (13)C NMR spectroscopy, 2D NMR; HSQC and HMBC, CHN analysis, molecular weight distribution using GPC analyzer, thermal analysis; TGA and DSC. The chemical modification by utilizing an organic scavenger during delignification process provided smaller lignin fragments and enhanced the solubility of lignin by reducing its hydrophobicity properties. It was revealed that the antioxidant properties increased as compared to the unmodified organosolv lignin. Additionally, the modified lignin has better solubility in water (DAHNP EOL=35%>DAH EOL=25%).

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
The effect of Piper betle and Psidium guajava extracts on the cell-surface hydrophobicity of selected early settlers of dental plaque

Razak FA, Othman RY, Rahim ZH

J Oral Sci, 2006 Jun;48(2):71-5.
PMID: 16858135

The adhesion of early settlers of dental plaque to the tooth surface has a role in the initiation of the development of dental plaque. The hydrophobic surface properties of the bacteria cell wall are indirectly responsible for the adhesion of the bacteria cell to the acquired pellicle on the tooth surfaces. In this study, the effect of aqueous extract of two plants (Psidium guajava and Piper betle) on the cell-surface hydro-phobicity of early settlers of dental plaque was determined in vitro. Hexadecane, a hydrocarbon was used to represent the hydrophobic surface of the teeth in the oral cavity. It was found that treatment of the early plaque settlers with 1 mg/ml extract of Psidium guajava reduced the cell-surface hydrophobicity of Strep. sanguinis, Strep. mitis and Actinomyces sp. by 54.1%, 49.9% and 40.6%, respectively. Treatment of these bacteria with the same concentration of Piper betle however, showed a comparatively lesser effect (< 10%). It was also observed that the anti-adhesive effect of the two extracts on the binding of the early plaque settlers to hexadecane is concentration dependent.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
The anti-adherence effect of Piper betle and Psidium guajava extracts on the adhesion of early settlers in dental plaque to saliva-coated glass surfaces

Razak FA, Rahim ZH

J Oral Sci, 2003 Dec;45(4):201-6.
PMID: 14763515

The aqueous extracts of Piper betle and Psidium guajava were prepared and tested for their anti-adherence effect on the adhesion of early plaque settlers (Strep. mitis, Strep. sanguinis and Actinomyces sp.). The saliva-coated glass surfaces were used to simulate the pellicle-coated enamel surface in the oral cavity. Our results showed that the anti-adherence activities of Piper betle and Psidium guajava extracts towards the bacteria were different between the bacterial species. Psidium guajava was shown to have a slightly greater anti-adherence effect on Strep. sanguinis by 5.5% and Actinomyces sp. by 10% and a significantly higher effect on Strep. mitis (70%) compared to Piper betle. The three bacterial species are known to be highly hydrophobic, and that hydrophobic bonding seemed to be an important factor in their adherence activities. It is therefore suggested that the plant extracts, in expressing their anti-adherence activities, could have altered the hydrophobic nature of the bonding between the bacteria and the saliva-coated glass surfaces.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
The True Amphipathic Nature of Graphene Flakes: A Versatile 2D Stabilizer

Kuziel AW, Milowska KZ, Chau PL, Boncel S, Koziol KK, Yahya N, et al.

Adv Mater, 2020 Aug;32(34):e2000608.
PMID: 32672882 DOI: 10.1002/adma.202000608

The fundamental colloidal properties of pristine graphene flakes remain incompletely understood, with conflicting reports about their chemical character, hindering potential applications that could exploit the extraordinary electronic, thermal, and mechanical properties of graphene. Here, the true amphipathic nature of pristine graphene flakes is demonstrated through wet-chemistry testing, optical microscopy, electron microscopy, and density functional theory, molecular dynamics, and Monte Carlo calculations, and it is shown how this fact paves the way for the formation of ultrastable water/oil emulsions. In contrast to commonly used graphene oxide flakes, pristine graphene flakes possess well-defined hydrophobic and hydrophilic regions: the basal plane and edges, respectively, the interplay of which allows small flakes to be utilized as stabilizers with an amphipathic strength that depends on the edge-to-surface ratio. The interactions between flakes can be also controlled by varying the oil-to-water ratio. In addition, it is predicted that graphene flakes can be efficiently used as a new-generation stabilizer that is active under high pressure, high temperature, and in saline solutions, greatly enhancing the efficiency and functionality of applications based on this material.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext The Toxic Truth About Carbon Nanotubes in Water Purification: a Perspective View

Das R, Leo BF, Murphy F

Nanoscale Res Lett, 2018 Jun 18;13(1):183.
PMID: 29915874 DOI: 10.1186/s11671-018-2589-z

Without nanosafety guidelines, the long-term sustainability of carbon nanotubes (CNTs) for water purifications is questionable. Current risk measurements of CNTs are overshadowed by uncertainties. New risks associated with CNTs are evolving through different waste water purification routes, and there are knowledge gaps in the risk assessment of CNTs based on their physical properties. Although scientific efforts to design risk estimates are evolving, there remains a paucity of knowledge on the unknown health risks of CNTs. The absence of universal CNT safety guidelines is a specific hindrance. In this paper, we close these gaps and suggested several new risk analysis roots and framework extrapolations from CNT-based water purification technologies. We propose a CNT safety clock that will help assess risk appraisal and management. We suggest that this could form the basis of an acceptable CNT safety guideline. We pay particular emphasis on measuring risks based on CNT physico-chemical properties such as diameter, length, aspect ratio, type, charge, hydrophobicity, functionalities and so on which determine CNT behaviour in waste water treatment plants and subsequent release into the environment.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext The Role of Solvent-Accessible Leu-208 of Cold-Active Pseudomonas fluorescens Strain AMS8 Lipase in Interfacial Activation, Substrate Accessibility and Low-Molecular Weight Esterification in the Presence of Toluene

Yaacob N, Ahmad Kamarudin NH, Leow ATC, Salleh AB, Raja Abd Rahman RNZ, Mohamad Ali MS

Molecules, 2017 Aug 12;22(8).
PMID: 28805665 DOI: 10.3390/molecules22081312

The alkaline cold-active lipase from Pseudomonas fluorescens AMS8 undergoes major structural changes when reacted with hydrophobic organic solvents. In toluene, the AMS8 lipase catalytic region is exposed by the moving hydrophobic lid 2 (Glu-148 to Gly-167). Solvent-accessible surface area analysis revealed that Leu-208, which is located next to the nucleophilic Ser-207 has a focal function in influencing substrate accessibility and flexibility of the catalytic pocket. Based on molecular dynamic simulations, it was found that Leu-208 strongly facilitates the lid 2 opening via its side-chain. The KM and Kcat/KM of L208A mutant were substrate dependent as it preferred a smaller-chain ester (pNP-caprylate) as compared to medium (pNP-laurate) or long-chain (pNP-palmitate) esters. In esterification of ethyl hexanoate, L208A promotes a higher ester conversion rate at 20 °C but not at 30 °C, as a 27% decline was observed. Interestingly, the wild-type (WT) lipase's conversion rate was found to increase with a higher temperature. WT lipase AMS8 esterification was higher in toluene as compared to L208A. Hence, the results showed that Leu-208 of AMS8 lipase plays an important role in steering a broad range of substrates into its active site region by regulating the flexibility of this region. Leu-208 is therefore predicted to be crucial for its role in interfacial activation and catalysis in toluene.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Fulltext Tensile properties of alkaline treated coconut meat husk reinforced polyester composites

Muhammad Faiz Ghazali, Mohamad Juraidi Jamal, Syed Azuan Syed Ahmad

Journal of Engineering and Science Research, 2017;1(1):4-7.
MyJurnal

Synthetic fibers such as glass fiber and carbon fiber are traditionally used as reinforcement in engineering composites. The increasing of environmental concerns has led to the use of natural fibers as renewable alternatives reinforcement. Among them, coconut meat husk fiber which abundant availability can be used as reinforcement fiber. However, the coconut meat husk fiber, same as other natural fibers, has the issues of fiber/matrix bonding and moisture absorption. Chemical treatments are needed to modify the surface of fiber, aiming at improving the adhesion with polymer matrix and reducing the hydrophilicity of the fiber. Alkalization was used in this study to treat the coconut meat husk fiber. The effects of chemical treatments for 1hr and 24 hr treatment time on the coconut meat husk fibers reinforced composites were investigated. A result showed that the 24 hr alkali treatment gave the highest tensile stenght compared to the 1hr treatment and RO water.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions
Tensile and water absorption properties of biodegradable composites derived from cassava skin/polyvinyl alcohol with glycerol as plasticizer

Dayangku Intan Munthoub, Wan Aizan Wan Abdul Rahman

Sains Malaysiana, 2011;40:1179-1186.

Natural organic and abundant resources biopolymers received more attention due to their low cost, availability and degradability after usage. Cassava skin was used as natural fillers to the polyvinyl alcohol (PVA). Cassava skin/poly vinyl alcohol blends were compounded using melt extrusion twin screw extruder and test samples were prepared using the compression method. Various ratios of cassava skin and glycerol were investigated to identify suitable composition based on the water absorption and tensile properties. The water absorption of the cassava skins/PVA samples increased at higher composition of cassava skin due to their hydrophilic properties but decrease with glycerol content. The strength of the cassava skins/PVA samples increased with the higher composition of cassava skin up to 70 wt% while gradually decreased with the increasing composition of glycerol. The Young modulus increased with glycerol content but decreased with fibre loading up to 70 wt%. Elongation at break decreased with fibre loading and glycerol up to 70 wt% and 30 phr, respectively.

Matched MeSH terms: Hydrophobic and Hydrophilic Interactions

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