Apparent Free Energy Research Articles

Preparation of photocatalytic thin films with composition dependent wetting properties and self-healing ability

This paper presents the preparation of a multifunctional coating with triplet photoreactive, superhydrophobic and intelligent self-healing properties. Beside the structural and morphological behaviors of the hybrid thin films consist of fluoropolymer matrix and Ag-TiO2 photocatalyst particles, the wetting properties were also studied by static (Θ) and dynamic water contact angle measurements. The photoactivity of layers was evidenced both at solid/gas (S/G) and solid liquid (S/L) interfaces. The surface roughness (Rq = 3.7 ± 0.9 μm to 15.2 ± 1.2 μm) and thus the wetting properties and apparent surface free energy values (γstot) of the layers were adjustable from superhydrophilic (Θ = 0°; γstot = 70.2 mJ m−2) to superhydrophobic properties (Θ = 150.9°; γstot = 13.1 mJ m−2). At S/G interface the photoactivity of the layers was increased with the Ag-TiO2 photocatalyst content, however, at S/L interface the photocatalytic properties were tailored by the wetting of the films: 90% of the apolar SUDAN IV dye was photodegraded, while the aqueous Methylene Blue dye was not decomposed due to the inadequate surface adsorption. Moreover, it was also presented that the ambient moister catalysed hydrolysis/self-condensation reaction of the hydrophobic dodecyltrichlorosilane (DDSiCl3) molecules resulted self-assembled micro-protrusions on the surface of low energy photoreactive film and this mechanism resulted self-healing superhydrophobic surfaces with photocatalytic properties.

Forming nanostructured surfaces through Janus colloidal silica particles with nanowrinkles: A new strategy to superhydrophobicity

Proper nano-structuring coupled with low surface energy properties is exploited to obtain super-hydrophobic surfaces. A biomimicking hierarchically structured coating upon a material surface is obtained by depositing Janus nano-structured wrinkled colloidal particles. The morphology of the surface is thus ruled by different scales: the size of the wrinkles (few tens of nanometer), particle radius (several hundreds of nanometer) and interparticle distance. Janus wrinkled silica particles have one side exposing hydroxyl groups while the other side is partially silanized with dichlorodimethylsilane. To obtain these Janus particles, wax colloidosomes with surface covered by starting rough particles were successfully prepared. The exposed surface of rough wrinkled silica particles was then silanized, thus obtaining a Janus structure. The Janus character was prooved in different manners: the simple so called “visual test”, through Energy Filtered Transmission Electron Microscopy (was proven in different EFTEM) and by further functionalization with polypropylene grafted maleic anhydride (PPgMA).A glass microscope slide was covered by drop casting the particles obtaining super-hydrophobic features of the surface characterized by a high water contact angle (149°) and, more interestingly, by a very low water contact angle hysteresis (CAH = 2°) and roll-off angle (ROA = 1.8°). Superhydrophobicity is confirmed by the very low values of apparent surface free energy estimated with the OWRK (Owens-Wendt-Rabel e Kaelble) method. SEM and AFM analyses prove the multiple scale hierarchical roughness, from nano to micro size, that resembles the one present at the surface of the lotus leaves.

Measurement and modelling of solubility data for bosentan in 1-propanol + water mixtures at various temperatures

ABSTRACTThe experimental solubility determination of bosentan (BST) in 1-propanol + water mixtures within temperature range, T = (293.15–313.15) K were performed by applying the shake-flask method. The solubility data were correlated by four cosolvency models, which are the Jouyban-Acree, Jouyban-Acree-van’t Hoff, modified Wilson, and Yalkowsky equations. The back-calculated solubility using the Jouyban-Acree-van’t Hoff equation presents better compatibility with the experimental data than those by the other models. Thermodynamic properties such as apparent molar enthalpy, entropy, and Gibbs free energy change of BST dissolution process in the binary (1-propanol + water) mixtures were also calculated which indicative of the inspontaneous process of dissolution.

Measurement and relationships of density and viscosity of 1,2‑propylene glycol + dimethyl sulfoxide mixtures and spectral insight

The density (ρ) and viscosity (η) of 1,2‑propylene glycol (PPD) + dimethyl sulfoxide (DMSO) mixtures were measured at atmospheric pressure from (293.15 to 318.15) K. Based on experimental data, viscosity deviations, excess molar volumes values, partial molar volumes, apparent molar volumes and excessive Gibbs free energy were calculated by Redlich-Kister equation, Jouyban-Acree model, the least square method and other formulas. Meanwhile, FTIR, UV–Vis, and fluorescence spectroscopy were used to analyze the intermolecular interactions, which proved that the SO had a destructive effect on the hydrogen bond between OH and OH in PPD, and the SO also formed new hydrogen bond with OH, which expressed as (CH3)2SO⋯HOCH2CH(CH3)OH⋯OS (CH3)2.

Time-based changes in surface properties of poly(ethylene terephthalate) activated with air and argon-plasma treatments

This paper analyses the effects of time storage on the surface properties of plasma-treated poly(ethylene terephthalate) (PET) plates. For this purpose, optical profilometry-surface topography and surface composition (XPS technique) of the samples were studied before and after plasma treatment. Contact angles were measured using water, ethylen glycol and diiodomethane as liquid probes. Tadmor’s theory was used to calculate the equilibrium contact angles. Apparent surface free energy (SFE) was determined using two approaches, the hysteresis CAH approach and the acid-base LWAB. The results showed a significant increase in wettability after plasma treatment, especially in the case of argon-plasma activation. Surface roughness and the polar component of the SFE increased after activation, while the nonpolar component of the SFE did not change. It can be concluded that PET surface roughness is increased by air-plasma activation due to the polar groups originated by the treatment. The surface is not stable during storage time and becomes more hydrophobic because of surface layer reorganization. In the case of argon-plasma activation, the effects are stable over time, which was discussed using two different apparent surface free energy calculation approaches.

Kinetic study of gold nanoparticles synthesized in the presence of chitosan and citric acid

In this work colloidal gold nanoparticles (GNPs) are prepared using a citrate-reduction route, in which citric acid serves as reductive agent for the gold precursor HAuCl4. We demonstrate that a temperature variation on the one hand enables to tune the reaction rate of GNP formation and on the other hand allows modifying the morphology of the resulting metal nanoparticles. The use of chitosan, a biocompatible and biodegradable polymer with a multitude of functional amino and hydroxyl groups, facilitates the simultaneous synthesis and surface modification of GNPs in one pot. The resulting GNPs, which are stabilized by a network of chitosan and ß-ketoglutaric acid units, are characterized by UV–vis spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) as well as fluorescence correlation spectroscopy (FCS) and reveal an average diameter of about 10 nm at the end of the synthesis. The kinetics of GNP formation is studied by calculating activation parameters based on UV–vis and AFM data such as the apparent activation energy, entropy and free energy applying the concept of the Finke-Watzky model and harmonic transition state theory.

Lipid bilayer composition modulates the unfolding free energy of a knotted α-helical membrane protein

α-Helical membrane proteins have eluded investigation of their thermodynamic stability in lipid bilayers. Reversible denaturation curves have enabled some headway in determining unfolding free energies. However, these parameters have been limited to detergent micelles or lipid bicelles, which do not possess the same mechanical properties as lipid bilayers that comprise the basis of natural membranes. We establish reversible unfolding of the membrane transporter LeuT in lipid bilayers, enabling the comparison of apparent unfolding free energies in different lipid compositions. LeuT is a bacterial ortholog of neurotransmitter transporters and contains a knot within its 12-transmembrane helical structure. Urea is used as a denaturant for LeuT in proteoliposomes, resulting in the loss of up to 30% helical structure depending upon the lipid bilayer composition. Urea unfolding of LeuT in liposomes is reversible, with refolding in the bilayer recovering the original helical structure and transport activity. A linear dependence of the unfolding free energy on urea concentration enables the free energy to be extrapolated to zero denaturant. Increasing lipid headgroup charge or chain lateral pressure increases the thermodynamic stability of LeuT. The mechanical and charge properties of the bilayer also affect the ability of urea to denature the protein. Thus, we not only gain insight to the long-sought-after thermodynamic stability of an α-helical protein in a lipid bilayer but also provide a basis for studies of the folding of knotted proteins in a membrane environment.

Interfacial electrostatics of poly(vinylamine hydrochloride), poly(diallyldimethylammonium chloride), poly-l-lysine, and poly-l-arginine interacting with lipid bilayers.

Charge densities of cationic polymers adsorbed to lipid bilayers are estimated from second harmonic generation (SHG) spectroscopy and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The systems surveyed included poly(vinylamine hydrochloride) (PVAm), poly(diallyldimethylammonium chloride) (PDADMAC), poly-l-lysine (PLL), and poly-l-arginine (PLR), as well as polyalcohol controls. Upon accounting for the number of positive charges associated with each polyelectrolyte, the binding constants and apparent free energies of adsorption as estimated from SHG data are comparable despite differences in molecular masses and molecular structure, with ΔGads values of -61 ± 2, -58 ± 2, -57 ± 1, -52 ± 2, -52 ± 1 kJ mol-1 for PDADMAC400, PDADMAC100, PVAm, PLL, and PLR, respectively. Moreover, we find charge densities for polymer adlayers of approximately 0.3 C m-2 for poly(diallyldimethylammonium chloride) while those of poly(vinylamine) hydrochloride, poly-l-lysine, and poly-l-arginine are approximately 0.2 C m-2. Time-dependent studies indicate that polycation adsorption to supported lipid bilayers is only partially reversible for most of the polymers explored. Poly(diallyldimethylammonium chloride) does not demonstrate reversible binding even over long timescales (>8 hours).

Marginal stability drives irreversible unfolding of large multi-domain family 3 glycosylhydrolases from thermo-tolerant yeast

Protein folding is an extremely complex and fast, yet perfectly defined process, involving interplay of many intra and inter-molecular forces. In vitro, these molecular interactions are reversible for many proteins e.g., smaller and monomeric, organized into single domains. However, refolding of larger multi-domain/multimeric proteins is much more complicated, proceeds in a hierarchal way and is often irreversible. In a comparative study on two large, multi-domain and multimeric isozymes, β-glucosidase I (BGLI) and β-glucosidase II (BGLII) from Pichia etchellsii, we studied spontaneous and assisted refolding under three denaturing conditions viz. GdnHCl, alkaline pH and heat. During refolding, higher refolding yields were obtained for BGLII in case of pH induced unfolding (13.89%±0.25) than BGLI (6%±0.85) while for GdnHCl induced unfolding, refolding was marginal (BGLI=5%±0.5; BGLII=6%±0.69). Thermal unfolding was irreversible while assisted refolding also showed little structural gain for both proteins. When the apparent free energies of unfolding (ΔGUapp) were calculated from GdnHCl unfolding data, their values were strikingly found to be lower (BGLI ΔGUapp=3.02kcal/mol; BGLII ΔGUapp=2.99kcal/mol) than reported for globular (ΔGU=5–15kcal/mol)/multimeric proteins (ΔGU=23–29kcal/mol) indicating marginal stability results in low refolding.

Effect of gluten on the properties of ternary biopolymers based on gluten, whey protein concentrate, and kaolinite

The aim of the research was to investigate the effect of different gluten (Gl) concentration on ternary biopolymers with whey protein concentrate (WPC) and kaolinite (KAO). Distilled water dispersions of Gl (10–30%), WPC (7%), and KAO (5%) were heated at 80 °C for 30 min. The concentration of WPC and KAO was based on previous research with montmorillonite. Rheological properties of produced wet biopolymers were evaluated by dynamic rheology and ultrasound viscometry. The obtained biopolymers were dried in the thermostatic cabinet for 24 h at 45 °C. The texture was determined using the puncture test and the microstructure was analyzed by scanning electron microscopy. Surface properties of dried biopolymers were analyzed by surface wettability and roughness measurements. The increase in gluten concentration caused an increase in moduli and viscosity of the obtained wet biopolymers and in the puncture force for dry biopolymers. For the ternary biopolymer, layers with intercalation and exfoliation are observed in comparison with the biopolymer obtained without KAO. With the increasing Gl content in the biopolymer, the number of surface hydrophobic groups with carbon decreased and the number of surface hydrophilic groups increased. Higher Gl concentration produced less porous structure, although there are differences in the micro and nano-scale roughness. Water contact angle decreased with the increased Gl concentration, which is in agreement with less porous microstructure of the surface. The apparent surface free energy increased with the increasing of Gl concentration. The best plastic properties and the best shape of a pot were obtained for the ternary biopolymer with the 15% Gl concentration.

Solubility of sildenafil citrate in propylene glycol + water mixtures at various temperatures

ABSTRACTThe solubility of sildenafil citrate (SC) in aqueous mixtures of propylene glycol (PG) was investigated. This study was carried out at different mass fractions of PG ranging from 0.1 to 0.9 at T = 293.2–313.2 K. The solubility of SC in the mixed solutions increased with increasing temperature and PG mass fraction.The solubility values were correlated by two co-solvency models (Jouyban–Acree model and van’t Hoff–Jouyban–Acree model). The mean relative deviations (MRD) were 5.7% and 5.5%, respectively. Density of the SC-saturated solutions over the entire solvent composition and temperature range was also measured and the results correlated with the Jouyban–Acree model. Furthermore, the apparent thermodynamic properties, dissolution enthalpy, dissolution entropy and Gibbs free energy change of dissolution process of SC in all the mixed solvents were calculated according to van’t Hoff and Gibbs equations. Dissolution of SC in these mixed solvents is an endothermic process.

Solid–liquid phase equilibrium and thermodynamic analysis of prothioconazole in mono-solvents and binary solvents from 283.15 K to 313.15 K

Solid-liquid phase equilibrium solubility of prothioconazole in seven mono-solvents and (2-propanol±cyclohexane, 1-butanol±cyclohexane) binary solvent mixtures was determined by gravimetric method from 283.15 K to 313.15 K at atmospheric pressure. The solubility of prothioconazole increased with increasing temperature in all tested solvents. In mono-solvents, the solubility values at a fixed temperature ranked as: 1-butanol>1-propanol>2-propanol>methanol>2-butanol>acetonitrile>toluene. In binary solvent systems, the maximum solubility values were achieved at a certain solvent composition. The Apelblat equation, λh equation and NRTL model were employed to correlate the solubility data in mono-solvents, and the Apelblat equation in two binary solvent mixtures. The selected thermodynamic models can all give acceptable results. Furthermore, the apparent standard Gibbs free energy, enthalpy and entropy for the dissolution of prothioconazole were calculated, which indicates that the dissolution process of prothioconazole is an endothermic and entropy favorable process.

Crowding-facilitated macromolecular transport in attractive micropost arrays

Our study of DNA dynamics in weakly attractive nanofabricated post arrays revealed crowding enhances polymer transport, contrary to hindered transport in repulsive medium. The coupling of DNA diffusion and adsorption to the microposts results in more frequent cross-post hopping and increased long-term diffusivity with increased crowding density. We performed Langevin dynamics simulations and found maximum long-term diffusivity in post arrays with gap sizes comparable to the polymer radius of gyration. We found that macromolecular transport in weakly attractive post arrays is faster than in non-attractive dense medium. Furthermore, we employed hidden Markov analysis to determine the transition of macromolecular adsorption-desorption on posts and hopping between posts. The apparent free energy barriers are comparable to theoretical estimates determined from polymer conformational fluctuations.

Surface properties of ion-inducted whey protein gels deposited on cold plasma treated support

So far no studies have been undertaken on the influence of plasma processing of different solid surfaces on the properties of subsequently formed protein coat. Calcium chloride, magnesium chloride or iron (II) chloride inducing whey protein isolate gels were obtained on glass support previously treated with the plasma at the electric voltage 160 V per 1 min. Dynamic oscillatory and ultrasound viscosity measurements, scanning electron microscopy imaging, surface roughness and contact angles measurements have been performed. Apparent surface free energy was determined using the two approaches: van Oss, Good and Chaudchury (LWAB) and contact angle hysteresis (CAH). Gels surface roughness increased with the increasing of ions concentration. Both approaches used for determination of apparent surface free energy give comparable results. When the air plasma was applied for the support activation, polar groups deposited on the surface had a greater effect on the surface wettability than roughness. Plasma treatment of glass support caused the increase of hydrophobic properties of deposited layers. Wettability properties were affected by the electron donor parameter of energy whose value increased for the samples obtained on the plasma activated supports especially the air treated ones. Plasma treatment of glass plates might have an effect on food processing, production efficiency, microbiological aspects and cleaning process of the gels deposited on their surfaces.

Escherichia coli Biofilm Characteristics on Polymeric Heat Exchanger Surfaces

AbstractTime‐dependent effects on the apparent roughness and surface free energy of different polymeric surfaces and stainless steel were studied during the biofouling process for Escherichia coli K12. The surface roughness increases during primary adhesion of E. coli on the surfaces and is later reduced as the surface between scattered bacteria is completely covered, forming a uniform biofilm. During the fouling process, the polar fraction of the surface free energy significantly increased, whereas the dispersive fraction decreased for all substrates. The attachment of E. coli and subsequent bacterial production of extracellular polymeric substances increased the polarity of the initially nonpolar polymeric surfaces to increase wettability.

Wettability and thermal analysis of hydrophobic poly(methyl methacrylate)/silica nanocomposites

Hydrophobic poly(methyl methacrylate)/silica layers on the glass support activated with plasma were obtained. Wettability was investigated from the contact angle measurements and surface free energ...

Corrosion Inhibition of Steel (St 44-2) by Pomegranate Shells in Acidic Medium

Pomegranate shells were investigated as green inhibitors for steel 44-2 in 0.1M HCl at various temperatures (30, 40, 50, and 60) °C using electrochemical technique. Five concentrations of inhibitor were added 4, 8, 12, and 16 ppm. Corrosion tests were performed by Potentiostat at 5 mV.sec-1 scan rate and the data measured by Tafel extrapolation method such as Tafel slopes, corrosion current density and corrosion potential. Inhibition efficiencies were calculated and indicated that 8 ppm was the best concentration for inhibition especially at 60oC, where was 96.47%. Pomegranate Shells behaves as anodic inhibitor type and obeys Langmuir adsorption isotherm. The equilibrium constant of the adsorption-desorption process and the apparent free energy of adsorption confirm the physicsorption of Pomegranate shells. FTIR spectroscopy was used to test film formed on steel surface compared with FTIR spectrum of Pomegranate Shells. These spectra confirm the formation of Fe2+Pomegranate shells complex.

Influence of nitrogen plasma treatment on the wettability of polyetheretherketone and deposited chitosan layers

AbstractWettability properties of polyetheretherketone (PEEK) activated and non‐activated by nitrogen plasma have been investigated. Moreover, the PEEK plates were covered with antibacterial chitosan and its wettability properties were also investigated. Surface topography was determined using SEM and optical profilometry and surface composition by FT‐IR and XPS. For determination of apparent surface free energy, the hysteresis approach (CAH), acid base (LWAB), and Owens–Wendt (O–W) theory were used. The equilibrium contact angles were calculated from the Tadmor theory and further used for apparent surface energy calculation applying the above‐mentioned approaches. Due to the surface plasma activation both the roughness of the surface and the polar component of apparent surface free energy increased. It is shown that nitrogen plasma activation of PEEK surface increases the adhesion of chitosan to the surface due to the combination effect of: (i) the increase in surface roughness, (ii) introducing the polar groups onto the surface.

Temperature-Dependent Kinetic Studies of the Chlorine Evolution Reaction over RuO2(110) Model Electrodes

Ultrathin single-crystalline RuO2(110) films supported on Ru(0001) are employed as model electrodes to extract kinetic information about the industrially important chlorine evolution reaction (CER) in a 5M concentrated NaCl solution under well-defined electrochemical conditions and variable temperatures. A combination of chronoamperometry (CA) and online electrochemical mass spectrometry (OLEMS) experiments provides insight into the selectivity issue: At pH = 0.9, the CER dominates over oxygen evolution, whereas at pH = 3.5, oxygen evolution and other parasitic side reactions contribute mostly to the total current density. From temperature-dependent CA data for pH = 0.9, we determine the apparent free activation energy of the CER over RuO2(110) to be 0.91 eV, which compares reasonably well with the theoretical value of 0.79 eV derived from first-principles microkinetics. The experimentally determined apparent free activation energy of 0.91 eV is considered as a benchmark for assessing future improved theo...

Bip Binding Affects Integration of Transmembrane Domains

The Sec61 translocon mediates translocation of proteins into the endoplasmic reticulum (ER) and enables integration of hydrophobic (H) segments into the lipid bilayer via its lateral gate. The luminal chaperone BiP (Kar2 in yeast) has been shown to act as a molecular ratchet, recruited to the emerging polypeptide by the J-domain of Sec63, and to be involved in post- and cotranslational translocation. In this study, we address the question whether BiP binding to the nascent chain affects the process of membrane integration vs. translocation, i.e. whether integration is governed by thermodynamic equilibrium between pore and membrane. To determine the hydrophobicity threshold of membrane integration, a series of model proteins based on the sequence of dipeptidylaminopeptidase B (DPAPB) with oligo-alanine H-segments containing increasing numbers of leucines. The translocated loop preceding the H-segments was replaced by a sequence of similar length containing multiple copies of segments known to bind BiP with high affinity or not to interact with BiP. While H-segments preceded by the DPAPB sequence required ∼3.7 Leu for 50% integration, this threshold was reduced to ∼2.1 Leu with the BiP-binding sequence and increased to ∼5.2 Leu with the non-binding sequence. These results show that membrane integration of an H-segment is influenced by the already translocated sequence preceding it and suggest that BiP binding promotes membrane integration. We observed changes of the apparent free energy in integration between 1 to 3 kcal/mol. We propose a model in which Brownian motion of the translocated loop with bound chaperones preferentially promotes release of the H-segment into the lipid bilayer. The work was supported by grant W0125 of the Austrian science fund (FWF).