Quantification of the adhesion free energy between bacteria and hydrophobic and hydrophilic substrata

In this paper, the bacterial adhesion to hydrophilic glass and hydrophobic indium tin oxide (ITO) coated glass surfaces was investigated. The aim of this work was to examine the effect of the hydrophobicity of two bacterial strains (Pseudomonas stutzeri PS, and Staphylococcus epidermidis SE) and substrata surfaces on the adhesion mechanism. The hydrophobicity of the surfaces of the bacterial strains as well as of the surfaces of the tested materials was characterized using the contact angle measurement via sessile drop technique. The water contact angle measurements of the intrinsic cell hydrophobicity showed that the PS strain is more hydrophobic (θ = 40°) than SE strain (θ = 21°). For both tested materials, this angle was 12° for glass surface and 84° for ITO-coated glass surface. Based on the thermodynamic approach, the Lifshitz van der Waals interaction free energy, the hydrophobic interaction free energy and the total interaction free energy between the bacteria and the substratum through the suspending medium were quantified. In order to verify the thermodynamic approach predictions of the bacterial adhesion on each substratum, adhesion tests were carried out for each bacteria/substratum combination. The results revealed that for both materials surfaces, the adhesion energy of the hydrophobic PS strain (26.1 mJ/m² for glass and − 3.8 mJ/m² for ITO-coated glass) is higher than that of SE strain (31.8 mJ/m² for glass and 14.3 mJ/m² for ITO-coated glass). For both bacterial strains, the effect of the hydrophobicity property of the substratum seems more important in the initial adhesion step. However, the second step of adhesion involves the biological approach, since a discrepancy was found between physicochemical theoretical approach and adhesion tests for SE strain.     

Sequences of precipitate nucleation

Solid-solid nucleation theory, as recently extended to faceted nuclei, is applied to several problems in understanding experimentally observed sequences of precipitate nucleation involving transtion phases during isothermal ageing. Transition precipitates form due to a low interfacial energy resulting from a greater structural similarity to the matrix than the equilibrium phase or succeeding transition phases and in spite of a usually smaller driving force, ¦ΔG _v ¦, for nucleation than any of these competing phases. Transition phases formed after the first one are predicted to nucleate preferentially at the interphase boundaries of their predecessors, also on the basis of interfacial energy, rather than ΔG _v considerations. Most examples of precipitation sequences cited from the literature are in agreement with this prediction; the few exceptions found are noted and discussed. The preference of equilibrium phases for nucleating at high-energy grain boundaries and of transition precipitates for nucleation at dislocations and other lower energy sites is explained on the following basis. The high-energy boundaries reduce the net interfacial free energy needed for nucleation of either phase so much that the higher ¦ΔG _v ¦ for the equilibrium phase becomes dominant. At the lower energy sites, the smaller reduction in ΔG ^*, the free energy of activation for nucleation, provided makes the lower interfacial energy of the transition phases the dominant factor in causing such phases to nucleate more rapidly.     

Gamma radiation induced preparation of organic-inorganic composite material for sorption of cesium and zinc

A novel composite material, poly(acrylamide-acrylic acid-acrylonitrile)-N,N′-methylenediacrylamide/silicon oxide-zirconium oxide [P(AM-AA-AN)-DAM/SiO₂-ZrO₂], was prepared by γ-radiationinduced template copolymerization of acrylic acid (AA) with acrylonitrile (AN) on polyacrylamide P(AM) as a template polymer in presence of N,N′-methylenediacrylamide (DAM) as cross-linker in aqueous solution with water-insoluble mixed oxide of silicon and zirconium. The composite material was characterized by Fourier transform IR spectroscopy and by thermal analysis (synchronized TGA-DTA). The sorption of ¹³⁴Cs and ⁶⁵Zn(II) onto the prepared composite material was investigated using batch equilibrium technique with variation of pH, adsorbent weight, initial sorbate concentration, contact time, and temperature. The sorption equilibrium data were fitted with the Langmuir and Freundlich isotherm models. The isotherm is successfully fitted by the Langmuir equation over the entire concentration range studied. Lagergren pseudo-first- and pseudo-secondorder kinetic models were tested to describe the reaction mechanism. The experimental data are fitted well the pseudo-second-order model. The thermodynamic functions (free energy ΔG ⁰, enthalpy ΔH ⁰, entropy ΔS ⁰) of the sorption were calculated. These quantities show that the sorption of ¹³⁴Cs and ⁶⁵Zn onto the composite material is spontaneous and endothermic.     

Biosorption of uranium(VI) from aqueous solution using calcium alginate beads

In this paper, sorption potentials of uranium ions were studied using alginate polymer beads in diluted aqueous solutions. The ability of alginate beads to adsorb uranium(VI) from aqueous solution has been studied at different optimized conditions of pH, U(VI) concentration, contact time, biomass dosage and temperature. In order to determine the adsorption characteristics, Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherms were applied to the adsorption data. The thermodynamic parameters such as variations of enthalpy ΔH, entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of ln K_d vs. 1/T plots. The results suggested that alginate beads could be suitable as a sorbent material for adsorption and removal of uranium ions from dilute aqueous solutions.     

Synthesis and equilibrium studies of titanium vanadate and its use in the removal of some hazardous elements

Titanium vanadate was synthesized and characterized by X-ray diffraction, thermal analysis (TGA and DTA), X-ray fluorescence, and IR spectroscopy. The empirical formula of titanium vanadate is Ti₂V₂O₉·2.5H₂O. Titanium vanadate was tested as sorbent for removing some harmful ions such as Cs, Co, Cu, and Cd. The distribution coefficients (K _d) were determined. They decrease in the order Cs⁺ ? Cu²⁺ > Co²⁺ > Cd²⁺. The distribution coefficients increase with increasing pH and reaction temperature. The thermodynamic functions of sorption (ΔH ⁰, ΔS ⁰, ΔG ⁰) were calculated. Negative values of ΔG ⁰ and positive values of ΔH ⁰ show that the sorption is a spontaneous endothermic reaction.     

Kinetics of neptunium(V) reduction with iron(II) sulfamate in nitric acid solutions

The kinetics of chemical reduction of Np(V) with iron(II) sulfamate in HNO₃ solutions was studied by spectrophotometry. The reduction process can be described by the equation NpO ₂ ⁺ + Fe²⁺ + 4H⁺ ? Np⁴⁺ + Fe³⁺ + 2H₂O and follows the first- and zero-order rate law with respect to the Np(V) concentration. The reaction rate constants were determined in relation to the HNO₃ concentration (1–3 M), iron(II) sulfamate concentration [(0.59–2.94) × 10^?3 M], and temperature (298.2–319.2 K). The activation energy (E _a) and the thermodynamic functions of formation of the activated complex (activation free energy ΔG ^≠, enthalpy ΔH ^≠, entropy ΔS ^≠) were calculated.     

Characterization of a fracture specimen for crack growth in epoxy due to thermal fatigue

Finite element simulations are carried out to characterize a new fracture specimen, consisting of an outer circular epoxy ring bonded to an inner circular invar plate for accelerated thermal fatigue testing. Radial cracks are introduced in the epoxy ring. The growth of these radial cracks is correlated to the applied energy release rate G. We studied the dependence of G on the crack length, the specimen geometry and the elastic modulus. For short cracks, G is obtained in closed form. Analysis is carried out to determine the critical thermal buckling load the specimen can withstand. Experimental results show that the fatigue crack growth rate per thermal cycle da/dN is given by da/dN = 0.51(ΔG)^0.38 for cycling between 4 and 100 °C but by da/dN = 0.25(ΔG)^0.24 for cycling between 20 and 85 °C, where ΔG is the difference of the energy release rate between the highest and lowest temperatures during a thermal cycle. More severe thermal cycles produce considerably larger fatigue crack growth rates than less severe ones at the same ΔG. This result also implies that isothermal fatigue tests will probably be inadequate to predict thermal fatigue crack growth in epoxies.     

Investigation of Anti-Cancer Drug Nimustine Interaction with Calf Thymus DNA

Nimustine, a chloroethyl nitrosourea derivative (CENU), is an antineoplastic agent, which is used for the treatment of various types of cancer. The present study focuses on the prediction and investigation of binding properties of nimustine with DNA using molecular modeling and UV–Visible spectroscopic technique. The docking study show that nimustine plausibly binds within the major groove of DNA. Further analysis of docking suggests direct interaction of nimustine with the moieties of heterocyclic nitrogenous bases of DNA. The free binding energy value of the best nimustine-DNA docked conformer is predicted as ?4.31 kcal/mol using docking results.The molecular modeling study also reveals that the interaction between nimustine and DNA is majorly governed by van der Waals forces, hydrogen bonding and hydrophobic interactions, whereas the contribution of electrostatic forces stands negligible. Further, UV–Visible spectra of free calf thymus DNA and its complexes with varying concentration of nimustine indicate the binding constant (K _a ) value as 3.27 × 10³ M^?1, which suggests moderate interaction of nimustine with DNA. The spectroscopic results are further used to calculate the binding free energy of the complex using the relation ΔG = ?RT ln (K _a ). This accounts for a value of ?4.79 kcal/mol. It corroborates well with the docking outcomes. The results of present study may help in designing and synthesis of new chloroethyl nitrosourea derivatives with improved efficacy and specificity for the target molecules.     

Energetics and Escape of Interchain‐Delocalized Ion Pairs in Nonpolar Media

The electron acceptor F4TCNQ p‐dopes aggregates “nanowires” of poly(3‐hexylthiophene) in nonpolar solvents but does not dope unaggregated chains. The standard free energy change for the charge transfer to form an ion pair is ΔG°_et = ‐0.21 eV. The dissociation constant to produce free ions in toluene by DC conductivity is K°_d = 1 × 10^‐8 ± 50% (ΔG°_d = 0.48 ± 0.05 eV). This remarkably large K°_d, for ions in such a low polarity medium, may reflect interchain delocalization of the hole. The particular characteristics of this material system enables determination of both ΔG°_et and ΔG°_d, to find the overall free energy change from the two neutral species to completely separated ions in nonpolar media. It is endergonic by +0.27 ± 0.05 eV in contrast to ‐0.6 eV estimated from reported HOMO LUMO differences, illustrating the challenges that persist in determining such energetics. Steady state microwave conductivity experiments on doped aggregates confirm that holes in the aggregates cannot easily escape their dopant counterion, but at higher dopant concentrations, holes become mobile. These results provide insight into the mechanisms of charge separation involving intermolecularly delocalized charges in nonpolar media, an integral process in organic photovoltaic devices and doped molecular films.     

Thermodynamic properties of barium chromate

The standard free energy of formation of BaCrO₄ was determined in the temperature range 935 to 1187 K using barium fluoride as solid electrolyte and barium hexaferrite as reference electrode. The data obtained are represented by the equation ΔG_BaCrO4 = ?3.17T?81008(±340J)where ΔG_BaCrO4 is the free energy of formation of BaCrO₄ from BaO and Cr₂O₃.     

Growth kinetics and thermodynamic stability of octadecyltrichlorosilane self-assembled monolayer on Si (100) substrate

We have studied the growth kinetics and thermodynamic stability of octadecyltrichlorosilane (OTS) self-assembled monolayers on Si (100) substrate in order to understand its role in controlling the adhesion and surface hydrophobicity. Time-dependent contact angle measurements, using water as a function of OTS concentration, show rapid monolayer formation in the initial stage followed by a slow attainment of full coverage and the overall kinetics approximately follows the Langmuir adsorption isotherm. The adsorption rate constant (k_a = 150 M^− 1 s^− 1) is found to be significantly greater than the desorption rate constant (k_d = 0.156 s^− 1) while the Gibbs free energy (ΔG_ads) change amounts to − 4.2 kcal/mol suggesting thermodynamic stability of OTS monolayer on a silicon surface. Partial monolayer formation by a ‘uniform’ growth mechanism, even at low coverage, is revealed by atomic force microscopy (AFM) in conjunction with grazing angle FTIR spectroscopy. Analysis of the interfacial adhesion properties using Zisman plot suggests a critical surface tension (γ_c) of 20.7 dyn/cm for OTS monolayer on Si (100) surface.     

Adsorption and kinetic performance of Cs+, Co2+, and Ce4+ radionuclides on zirconium vanadate as a cation exchanger

Amorphous zirconium vanadate samples with different molar ratios have been prepared under optimum conditions. The experimental parameters such as the order of mixing and mixing ratios were established. The ion-exchange powders were characterized by X-ray diffraction, IR spectroscopy, and differential thermal analysis. The materials are thermally and chemically stable. The sorption behavior of Cs⁺, Co²⁺, and Ce⁴⁺ radionuclides was studied at varied values of Zr: V molar ratio, pH, and temperature. The thermodynamic equilibrium constants and the values of ΔG ₀, ΔH ₀, and ΔS ₀ for the exchange of Cs⁺, Co²⁺ and Ce⁴⁺ radionuclides at Zr: V = 1: 6 were calculated from the exchange isotherms. At Zr: V = 1: 6, the capability of the material to sorb Cs⁺, Co²⁺, and Ce⁴⁺ ions is the highest. The process kinetics can be descirbed by first- or second-order equations.     

Measurement of the intrinsic stress in thin films of silver by a new cantilevered plate technique

The intrinsic force per unit width S_Int in evaporated thin films of silver was determined from the instantaneous deformation of a cantilevered plate during film deposition from the early growth stages until a thickness of 800 Å was reached. The experimentally determined total bending force S_Tot is analysed as a sum of thermal bending forces and a bending force due to momentum transfer from the vapour. Formulae developed earlier are used to relate the thermal bending forces to the experimentally determined substrate temperature T and temperature differential ΔT between substrate faces, both of which are monitored during film deposition by means of thin film thermocouples. The bending force due to momentum transfer is obtained by simple calculation. The intrinsic bending force S_Int is then determined by subtraction. The results obtained by the present continuous technique are compared with earlier results obtained using a more usual sequential deposition technique.     

In vitro evaluation of artificial ageing on surface properties and early Candida albicans adhesion to prosthetic resins

Objective The aim of this in vitro study was to examine potential changes and influences of prosthetic resin surface properties on Candida albicans adhesion after surface treatment or artificial ageing. Materials and methods Standardized specimens of a denture base resin and a veneering composite were prepared, polished, and randomly subjected to different surface roughness treatments or artificial ageing protocols (storage in ethanol or artificial saliva for 7/90 d, thermocycling). Surface roughness (Ra) and surface free energy were determined prior and after each treatment. Specimens were incubated with phosphate buffered saline or whole saliva for 2 h at 37°C, and later with Candida albicans suspension (2.5 h, 37°C). Adherent viable fungi were quantified using a bioluminescence assay. Results Artifical ageing did not affect substratum surface roughness, yet slight increases in substratum surface free energy and significant increases in Candida albicans adhesion were observed. Saliva coating marginally influenced Candida albicans adherence to reference and surface treated specimens, yet more pronounced differences in Candida albicans adhesion between the various artificially aged specimens were found. Conclusion No correlation between substratum surface roughness or surface free energy and Candida albicans adhesion could be established.     

Removal of Congo Red from aqueous solution by cattail root

In this study, cattail root was used to remove Congo Red (CR) from aqueous solution. The effects of operation variables, such as cattail root dosage, contact time, initial pH, ionic strength and temperature on the removal of CR were investigated using batch adsorption technique. Removal efficiency increased with increase of cattail root dosage and ionic strength, but decreased with increase of temperature. The equilibrium data fitted well to the Langmuir model (R² > 0.98) and the adsorption kinetic followed the pseudo-second-order equation (R² > 0.99). Thermodynamics parameters such as standard free energy change (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were analyzed. The values of ΔG° were between ?7.871 and ?4.702 kJ mol^?1, of ΔH° was ?54.116 kJ mol^?1, and of ΔS° was ?0.157 kJ mol^?1 K^?1, revealing that the removal of CR from aqueous solution by cattail root was a spontaneous and exothermic adsorption process. The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61 mg g^?1 at 20, 30 and 40 °C, respectively. These results suggest that cattail root is a potential low-cost adsorbent for the dye removal from industrial wastewater.     

Adsorption of Cr(VI) from aqueous solution by hydrous zirconium oxide

A type of ZrO₂·nH₂O was synthesized and its Cr(VI) removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The Cr(VI) adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model. The adsorption capacity increased from 61 to 66 mg g^?1 when the temperature was increased from 298 to 338 K. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. The effective desorption of Cr(VI) on ZrO₂·nH₂O could be achieved using distilled water at pH 12.     

EPR and optical absorption studies of Cu ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu²⁺ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu²⁺ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures (T) and from the 1/χ-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the ²B_1g → ²B_2g transition of the Cu²⁺ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu²⁺ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (E_opt) and the Urbach energy (ΔE) are evaluated. The variation in E_opt and ΔE is explained based on the number of defect centers in the glass.     

A novel method for determination of T3 and T4 hormones, associated with its physicochemical studies

A novel method in the radioimmunoassay (RIA) technique was developed to attain the optimum conditions for the estimation of thyroid hormones, triiodothyronine (T₃) and thyroxin (T₄), by applying kinetic and thermodynamic studies. Polystyrene beads were coated by specific antibodies (Ab) of both T₃ and T₄ hormones at the same time, to create immobilized solid phase available for binding with antigens (Ag) and ¹²⁵I-labeled antigens (Ag*) by forming immunocomplexes according to RIA measurements. Kinetic investigations were conducted by applying the initial rate technique, with the orders determined and the rate equations deduced. Thermodynamic studies included the determination of ΔG ⁰, ΔH ⁰, and ΔS ⁰. They revealed that the reactions proceed spontaneously and are endothermic with entropy gain, which is characteristic of inner-sphere complexation. The positive ΔH ⁰ value matched with the determined activation energy (E _a). Forty samples of different thyroid status were assayed for T₃ and T₄ using the present system and with commercially available kits. The statistical analysis revealed good correlations between them. This work may offer an easier and more efficient method in diagnostics and treatment of thyroid dysfunctions.     

Development and experimental verification of a method for assessment of consistency of the thermodynamic and structural properties of binary coolants based on systems of alkali metals

The construction of correlation function of concentration fluctuations S _cc (0) = f(T, x _i ) is used to validate the criterion of assessment of the internal consistency of the thermodynamic and structural properties of liquid-metal alloys, as well as of the reliability of experimental data on the Gibbs energy of solution formation ΔG, methods of their approximation, and theoretical models which reproduce the behavior of ΔG. The method is verified for the Cs-Na, K-Na, and Cs-K systems of alkali metals using the data of thermodynamic experiment in determining the Gibbs energy of formation of liquid-metal solution ΔG which is the basis for construction of the function S _cc (0). The data on statistical structure factor S(0) uniquely related to function S _cc (0) are obtained using the results (available in the literature) of experiments in X-ray and neutron spectroscopy, including data on diffraction and small-angle inelastic scattering.