Values Of Standard Free Energy Research Articles

Effect of antidiabetic drug metformin hydrochloride on micellization behavior of cetylpyridinium bromide in aqueous solution

Herein, the interaction of an antidiabetic drug, metformin hydrochloride (MHCl), and a cationic surfactant, cetylpyridinium bromide (CPB) is investigated in an aqueous medium. The critical micellar concentration (CMC) of CPB is estimated through conductivity experiments and found to be reduced on adding MHCl and further decreased in the presence of NaCl. The reduced CMC is attributed to the solubilization of MHCl by CPB through micellization and the micellization is found to be thermodynamically spontaneous that experiences an augmentation in the presence of NaCl. This is identified from the negative value of standard free energy ( Δ G0 m). The higher negative value of Δ G0 m (-55.41 kJ mol−1) for CPB + MHCl + NaCl than CPB (-37.89 kJ mol−1) and CPB + MHCl (-34.08 kJ mol−1) is suggestive of the above phenomenon. The positive values of Δ S0 m in all three cases confirm that the micellization is entropy driven. The binding of MHCl on CPB is quantified by estimating binding constant using the Benesi-Hildebrand (B-H) plot through UV-visible spectral methods. The binding constant values were calculated to be 2.70 M−1 for CPB + MHCl + NaCl compared to 1.258 M−1 for CPB + MHCl predicting a favoring of micellization in the presence of NaCl which is higher than that in the presence of co-solvents. The molecular interaction of MHCl and CPB is justified using FT-IR and NMR techniques. The surface properties of drug surfactant interactions are assessed using SEM techniques. The point of interaction between the drug and surfactant is visualized through the molecular docking approach. The results suggest that CPB would be an effective solubilizer for developing MHCl drug formulations. Communicated by Ramaswamy H. Sarma

Influence of Lanthanum on Stern Layer Conductance in the Nanochannel.

In this report, high-frequency electric impedance spectroscopy was performed to investigate ionic transport through nanochannels. Special attention was focused on (i) conductance behaviors depending on the role of cation valence in three background electrolytes (XCln): monovalent 1-1 (K+ and Cl-), divalent 2-1 (Mg2+ and 2Cl-), and trivalent 3-1 (La3+ and 3Cl-), (ii) the effects of proton and bicarbonate ions on bulk and surface conductance, and (iii) the connected microchannel dimension (surface/height ratio aspect) within the nanochannel apparent conductance. The results highlight a net quantitative increase in surface silanol density and a strong decrease in surface ionization degree when lanthanum cations are employed. The results also demonstrate that La3+ strongly interacts with the silica surface, leading to negative values of standard free energy for ion-site interactions and chemical potential for ion-ion correlations in the Stern layer of -0.8 and -10.2 kT, respectively. We ascribed the evolution of surface charge density to the balance between the mole ratios of water molecules and adsorbed cations at equilibrium. We found that La3+ behaves as an acidic cation (Lewis conceptualization) that neutralizes the negative silica surface accompanying water molecule expulsion due to steric hindrance. This study constitutes a new contribution to ion-site interactions and to ion-ion correlation phenomena on the planar silica surface to explain charge inversion observation in micro-nanofluidic devices.

Investigations on the effect of 2-[(furan-3ylmethylene)-amino]-benzenethiol on corrosion in carbon steel

A Schiff base namely, 2-[(furan-3ylmethylene)-amino]-benzenethiol (2-FAB) was synthesized and its influence on the inhibition of corrosion in carbon steel immersed in 0.5 M H2SO4 was investigated by weight loss analysis, potentiodynamic polarization studies, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and FT-IR spectroscopy. The weight loss measurements showed that 2-FAB has an excellent inhibiting efficiency of 95.51% at a concentration of 250 ppm. The inhibitor efficiency was found to depend on both the concentration and molecular structure of the inhibitor. Potentiodynamic polarization curves revealed that the studied inhibitors represent a mixed-type, predominantly cathodic control. An equivalent circuit is suggested based on an analysis of EIS data. Surface analysis using scanning electron microscope (SEM) and atomic force microscopy (AFM) show a significant morphological improvement on the mild steel surface with the addition of 2-FAB. The negative value of standard free energy of adsorption in the presence of inhibitor suggests the spontaneous adsorption of inhibitors on the carbon steel surface. The Temkin and Langmuir adsorption isotherms were found to provide a accurate description of the adsorption behavior of the inhibitor. Taken as a whole, this work demonstrates that 2-FAB shows promising results in resisting the deterioration of carbon steel in 0.5 M H2SO4 environment. The inhibitor forms a protective film on the surface of the carbon steel, significantly reducing its corrosion rate.

Physicochemical insights into the micellar delivery of doxycycline and minocycline to the carrier protein in aqueous environment

Physicochemical understanding of the micellar drug delivery is essential for designing efficient drug carrier molecules. An in-depth analysis of the partitioning mechanism of drugs in a quantitative manner and the effects of partitioning on the delivery of drugs through micellar media is a subject of enormous research. This paper focuses on the quantitative measurements of the binding of two antibiotic drugs from tetracycline family, doxycycline and minocycline with the carrier protein human serum albumin (HSA). The partitioning of both the drugs in the micellar system of hexadecyltrimethylammonium bromide (HTAB) and their delivery to HSA through this micellar system was also studied applying spectroscopy and calorimetry. A combination of fluorescence spectroscopy, isothermal titration calorimetry (ITC) and docking studies suggest that both the drugs bind close to Site I of HSA. The ITC results establish that the association of drugs with the protein occurs with an affinity of 103-104 M−1 and the binding is mainly entropy driven. The partitioning mechanisms have been evaluated in terms of the values of the changes in values of standard molar Gibbs free-energy, enthalpy, entropy, and partitioning stoichiometry. The thermodynamic signatures associated with the drug-HSA binding in the presence of HTAB micelles suggest that the partitioning of doxycycline/minocycline in the micelles of HTAB changes their interaction behavior with HSA. These findings provide deep understanding about the micellar drug delivery systems, thereby suggesting their potential applications in strategies for more effective therapeutics.

Choline amino acid ionic liquids as green corrosion inhibitors of mild steel in acidic medium

The corrosion inhibition performance of three choline amino acid ionic liquids ([Ch][AA]ILs) for mild steel in 1 M HCl solution was evaluated by electrochemical analysis, gravimetric measurement, and surface morphological characterization in the temperature range of 298–328 K in this paper. The results of the polarization experiments show that [Ch][AA]ILs affect the cathode and anode reaction processes, proving that [Ch][AA]ILs are mixed corrosion inhibitors. Choline phenylalanine ionic liquids ([Ch][Phe]) exhibit the highest corrosion prevention efficiency among the three chosen corrosion inhibitors, as proven by SEM/EDS scanning, XPS analysis, and molecular dynamics simulation. The values of standard free energy of adsorption ΔGads range between − 20 kJ·mol-1 and − 40 kJ·mol-1, showing that inhibitor molecule adsorption on the metal surface involves both physical and chemical adsorption. According to the results of XPS research and quantum chemical calculations, the adsorption of corrosion inhibitor molecules on the metal surface is strongly related to the anions. The corrosion inhibitor molecules form a thick monolayer adsorption layer on the metal surface, preventing metal-corrosive media interaction. The molecular dynamics simulation findings reveal that the corrosion inhibitor molecules replace the solvent water or any other ions pre-adsorbed on the metal surface during the adsorption process, protecting the metal from corrosion.

Removal of Orange G dye using peanut shells activated carbon: a green synthesis approach

ABSTRACT The use of activated carbon (AC) to remove heavy metals and dyestuffs from heavy industry waste is widely preferred. In this study, a novel adsorbent AC obtained from peanut shell (PS)s by the green chemical activation (sodium thiosulphate and potassium chloride) method was used in the adsorbing process of Orange G (OG) from aqueous solutions. The surface area of the activated carbon was determined as 930.1 m2 g−1. Several parameters, such as pH, dye concentration, adsorbent amount, and temperature, were investigated in relation to the adsorption process. Isotherm, kinetic and thermodynamic analyses were performed using experimental adsorption data. Accordingly, the most appropriate isotherm model which described the system was the Langmuir isotherm (R2 = 0.999), and the most efficient kinetic model was pseudo-second order (R2 = 0.999). It was discovered that the adsorbent with a maximum adsorption capacity (qmax) of 294.12 mg g−1 is suitable for sustainable OG adsorption (RL = 0.044). The standard free energy (∆G°) values of the system were between −7.5 and −10.6 kJ mol−1 and negative ∆G° values increased in the negative direction, revealing that the adsorption process takes place by spontaneous physical adsorption. It was found that the adsorption process with positive enthalpy (∆H°) (14.5 kJ mol−1) was endothermic and with positive entropy (∆S°) (57.9 J mol−1 K−1) value increased the disorder at the solid-liquid interface.

Insight into the inhibition performance of thiosemicarbazones as efficient inhibitors for copper in acidic environment: Combined experimental and computational investigations

The corrosion resistance of copper makes it a popular material. Despite this, the Cu metal is prone to corrosion, and pitting corrosion is frequently observed which leads to application restrictions. In this work, we devolved three efficient corrosion inhibitor types of thiosemicarbazone derivatives namely, (2E,2′E)−2,2′-(1,4-phenylenebis(methanylylidene))bis(N-benzylhydrazine-1-carbothioamide) (BBCT), (2E,2′E)−2,2′-(1,4-phenylenebis(methanylylidene))bis(N-allylhydrazine-1-carbothioamide) (BACT) and (E)−2-(5-azido-2-hydroxybenzylidene)-N-benzylhydrazine-1-carbothioamide (HBCT)that can inhibit the copper corrosion in 0.5 M sulfuric acid. The chemical structure of these materials were confirmed by FT-IR, HRMS,1HNMR and 13CNMR spectroscopic techniques. Moreover, their inhibition performance were evaluated by using various electrochemical techniques i.e. potentiodynamic polarization, AC impedance method, along with the density functional theory (DFT) and Monte Carlo (MC) simulations. The maximum inhibition efficiency (η) obtained by electrochemical techniques was 98.37% at 298 K for 150 ppm BBCT. The synthesized compounds were adsorbed via Langmuir adsorption model with physiochemical adsorption as inferred from the standard free energy (∆G°ads) values and the favorable performance was ascribed to the formation of BBCT adsorption films on the surface of the copper. Finally, the experimental results were correlated with the theoretical calculations using DFT theory which revealed the interaction between the assembled compounds and the copper surface.

Experimental studies on the corrosion inhibition performance of 2-(2-aminophenyl)benzimidazole for mild steel protection in HCl solution

BackgroundMild steel is one of the most widely used material in industry. However, this metal easily corrodes specifically in acidic solutions. Therefore, protection of this metal in this solutions is essential. There are many protection methods. The use of corrosion inhibitors is one of the widely them, which is a rapid, relatively easy and economical method. The choice of 2-(2-aminophenyl)benzimidazole (APBI) for this aim was based on its molecular structure, which bringing three N atoms and conjugated bonds as adsorption centers, and being a friendly compound. MethodsThe corrosion inhibition and adsorption properties of APBI on mild steel (MS) in 1 M HCI were studied by potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The MS surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The potential of zero charge (Epzc) of the steel in the presence of the inhibitor was determined by EIS method and an adsorption process was discussed. The effects of temperature and exposure time on the corrosion of MS were also reported. Significant findingsIt was found that the average inhibition efficiency of ABPI on the corrosion of MS determined from three electrochemical techniques is 98.8% in 1 M HCl solution. The high inhibition efficiency was assigned to its adsorption on the steel surface and forming a protective organic film. The PP studies showed that the corrosion current densitiy reduced almost 99% and open circuit potential moved from -0.48 V to -0.439 V in the presence of 10 mM inhibitor, which indicates a mixed type corrosion inhibition effect. SEM images showed good surface coverage of the inhibitor. The average percentage ratios of N and CI− on the metal which exposed to the inhibited solution were 0.97 % and 2.44 %, respectively. EDX mapping images indicated that the inhibitor distributed very homogenously. The adsorption of APBI on the mild steel surface in the corrosive solution was found to obey the Langmuir adsorption isotherm. The average value of equilibrium constant (Kads) and standard free energy of adsorption of the inhibitor (∆Goads) were found as 20.58 M−1 and -34.56 kJ mol−1, respectively. The activation energy (Ea) values are 77.28 kJ mol−1 and 78.00 kJ mol−1 for the corrosion process in the presence and absence of APBI, respectively. The CA and CV results clearly show that the inhibitor molecules are tightly adsorbed on the steel surface and form a very stable film.

Use of Ionic Liquid Pretreated and Fermented Sugarcane Bagasse as an Adsorbent for Congo Red Removal

A large amount of industrial wastewater containing pollutants including toxic dyes needs to be processed prior to its discharge into the environment. Biological materials such as sugarcane bagasse (SB) have been reported for their role as adsorbents to remove the dyes from water. In this study, the residue SB after fermentation was utilized for the dye removal. A combined pretreatment of NaOH and methyltrioctylammonium chloride was given to SB for lignin removal, and the pretreated SB was utilized for cellulase production from Bacillus aestuarii UE25. The strain produced 118 IU mL−1 of endoglucanse and 70 IU mL−1 of β-glucosidase. Scanning electron microscopy and FTIR spectra showed lignin and cellulose removal in fermented SB. This residue was utilized for the adsorption of an azo dye, congo red (CR). The thermodynamic, isotherm and kinetics studies for the adsorption of CR revealed distinct adsorption features of SB. Untreated SB followed Langmuir isotherm, whereas pretreated SB and fermented SB obeyed the Freundlich isotherm model. The pseudo-second-order model fitted well for the studied adsorbents. The results of thermodynamic studies revealed spontaneous adsorption with negative standard free energy values. Untreated SB showed a 90.36% removal tendency at 303.15 K temperature, whereas the adsorbents comprised of pretreated and fermented SB removed about 98.35% and 97.70%, respectively. The study provided a strategy to utilize SB for cellulase production and its use as an adsorbent for toxic dyes removal.

Application of a polymer-magnetic-algae based nano-composite for the removal of methylene blue – Characterization, parametric and kinetic studies

The potential ability of synthesized PPy-Fe3O4-SW nano-composite to remove Methylene Blue (MB) from synthetic textile dye solution was investigated under batch conditions. Through parametric studies, the influence of process parameters namely solution pH, on the effective performance of nano-composite was studied. PPy - Fe3O4– SW nano-composite removed 99.14% of MB at the optimized conditions of pH-10, temperature – 25 °C, initial MB concentration – 50 mg/L, nano-composite dosage - 20 mg and contact time - 20 min. PPy - Fe3O4– SW nano-composite has a maximum sorption capacity of 666.66 mg/g. The kinetics and isotherm study revealed that the chromium adsorption obeys pseudo second order (PSO) model (R2 = 0.9941) and Freundlich isotherm (R2 = 0.9910) respectively. The PSO kinetic constant (K2) was found to be 0.000442 (g/mg) min. The thermodynamic feasibility was confirmed through negative values of standard free energy at all tested conditions. The characteristics of adsorption study were analyzed and the results of FTIR, SEM and EDS confirmed the uptake of MB by PPy-Fe3O4-SW nano-composite.

Long-term differences in nutrient management under intensive cultivation alter potassium supplying ability of soils

Despite removal of potassium (K) by crops in large quantities, often exceeding that of nitrogen (N), K fertilization has long been neglected compared with N and phosphorus (P) in Indian agriculture leading to mining of soil K. We, therefore, studied the effect of long-term fertilization (with or without K) on K supplying ability of two major soil orders of India, viz. Inceptisol and Vertisol after more than four decades of cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 43 (Inceptisol) or 42 (Vertisol) cropping cycles from on-going long-term experiments located at New Delhi (Inceptisol) and Jabalpur (Vertisol), India, from six treatments, viz. no-fertilization (control), recommended N (N), N and P (NP), N, P and K (NPK), 150% NPK and NPK + farmyard manure (NPK + FYM), along with adjacent uncultivated land. Ammonium acetate extractable K (Kex), non-exchangeable K (NEK), quantity-intensity relationship and K release kinetics along with grain yields and K uptake by crops were studied. The Kex and K-saturation of exchange complex in both soils and NEK in the Inceptisol were the lowest under NP followed by N. Cropping without K input resulted in lower quantity (non-specifically and specifically held K i.e. –ΔK0 and Ks) and intensity (equilibrium activity ratio i.e. AReK) of K in both soils. More negative values of standard free energy of exchange (ΔG0) under cultivation without K in both soils indicated increased affinity of soil solids for K+ owing to K omission. The gap between equilibrium exchangeable K (EK0) and minimum exchangeable K (EKmin) was significantly lower under cropping without K than with K in the Vertisol. Imbalanced fertilization (N or NP) also showed noticeably smaller cumulative K releases and slower rates of replenishment of solution K by solid phase K in both soils. Interestingly, even under cropping with K fertilization at either experimental site, several K supply parameters showed decline compared with adjacent uncultivated soil. Grain yields of wheat and total K uptake by all crops (maize and wheat in Inceptisol; soybean and wheat in Vertisol) showed significant and positive response to K application. The study showed variable effect of long-term intensive cropping with or without K input on the K supplying ability of an Inceptisol and a Vertisol. The findings underlined inadequacy of the existing K fertilizer recommendations, and the need for their refinement to minimize native K mining and sustain K supplying ability of soils.

Experimental and computational study for X-65 steel corrosion mitigation effect of a synthesized cationic surfactant in 1 M HCl.

New cationic surfactant, named as N-(2-hydroxypropyl)-N, N-dimethyldodecan-1-aminium bromide (DPC12), was prepared, followed by characterization using FT-IR and 1HNMR spectroscopic techniques. DPC12 performance evaluated by several electrochemical analyses, including potentiodynamic polarization and AC impedance methods, confirmed the inhibition proprieties of the prepared cationic surfactant. Tafel curves presented that the prepared DPC12 served as a corrosion inhibitor with mixed-type. Inhibition efficiency is directly proportional to cationic surfactant concentration. By increasing concentration, efficiency increases until reaching 72.27% at 10-4M. DPC12 inhibition action was due to its adsorption over X65 surface and followed Langmuir isotherm model having chemisorption adsorption mode as provided by values of standard free energy (ΔG°ads).cationic adsorption affinity over X-65 steel corrosion in HCl (1 M) was proved via surface morphology studies with SEM analyses. Finally, the quantum chemical calculations supported the experimental findings with Materials Studio software 6.0 using density function (DFT) theory and monte carlo molecular simulation technique (MC).

Use of Aluminium Metal Embedded ThujaOccidentalis Leaves Carbon (AMETLC) for Fluoride Removal from Water: Equilibrium and Kinetic Studies

In this research work, Aluminum metal embedded Thuja Occidentalis leaves carbon (AMETLC) is used an adsorbent for the removal of fluoride from water. On batch technique, under key factors like pH, the dosage of adsorbent, variation of fluoride concentration and contact time, 92% of fluoride removal is observed at room temperature under optimum experimental conditions with an adsorbent particle size of <75 µm. The impact of existing negative ions on percentage removal of fluoride is studied, and it is noticed in the direction of PO43- > HCO3-> SO42- > NO3- > Cl-. The adsorbent is characterized by using FTIR, SEM, EDX, and XRD techniques. Experimental data reveal that the Langmuir isotherm model(maximum adsorption capacity obtained is 0.625 mg g-1) provided the best correlation (R2 = 0.988) and is well fit followed by pseudo-second-order kinetic model represents mono-layered, and chemisorptions are the rate-determining step for fluoride adsorption. Thermodynamic studies reveals better adsorption is attained at lower temperatures. The standard free energy (ΔH0) is observed as negative and the negative value of standard free energy (ΔH0) represents that the adsorption process is exothermic. Moreover, desorption study reveals that fluoride leaching takes place at a pH 13.0. In addition, succinct cost estimation was done for the AMETLC which offered one of the best alternatives for the removal of fluoride. The application of AMETLC is helpful to decrease the fluoride concentration in groundwater samples to meet the permissible limit according to BIS-2012 standards.

Adsorption, kinetics, and thermodynamic studies of cacao husk extracts in waterless sustainable dyeing of cotton fabric

Natural dyes exhibit a low dye uptake when cellulosic fiber dyeing is carried out using a conventional water bath dyeing process. In this research, cotton fabric was exhaust dyed in a microemulsion dyebath containing cacao husk extracts dye and decamethylcyclopentasiloxane (D5) to achieve higher dye exhaustion percentage on cotton fiber, which is an environmentally beneficial dyeing process. The adsorption behavior of cacao husk extract dye in a D5 microemulsion system was investigated under conditions of varied dye mass (1–8% o.w.f), dyeing time (5–500 min), and dyeing temperatures (333–373 K). Kinetic modelling of cacao husk extracts dye/D5 adsorption on cotton fiber was studied by fitting experimental data to pseudo first-order and pseudo second-order kinetics, and the intraparticle diffusion model. Early results indicated that the kinetic model of adsorption of cacao husk extracts dye on cotton fiber followed the pseudo second-order model. Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherm models were employed to analyze the adsorption isotherms, and the results showed that the adsorption process fit well with the Langmuir model compared to the Freundlich isotherm. The mean adsorption energy from the Dubinin–Radushkevich isotherm model implied that adsorption of the cacao husk extracts onto cotton was accompanied with a physical process. The values of standard enthalpy (ΔH° > 0), standard entropy (ΔS° > 0), and Gibbs free energy (ΔG° < 0) strongly reflected that the adsorption of the cacao husk extracts onto cotton was thermodynamically favourable and feasible. Thus, waterless dyeing of cotton fabric using a natural dye/D5 system explores a sustainable dyeing technology with higher dye exhaustion percentage.

Improvement and characterization of alum sludge by nano-iron oxide and rice husk for removal of methylene blue dye from aqueous solution

In the present study, the adsorption characteristics of the alum sludge (AS) waste from Rod El-Farag water treatment plant was improved by treatment with acidic rice husk (RH) and Nano-Magnetite (N.M) to form Nano-Magnetite composite (ASRHNMC). This composite gained new characteristics of large surface area, mesoporous structure and magnetic properties and it was used as a low cost adsorbent for the removal of methylene blue (MB) as a cationic dye from aqueous solution. (AS) and (ASRHNMC) were characterized by FT-IR, XRD, BET N2, EDX, SEM, TEM and XRF and were compared to adsorption ability against MB dye. The pH of the solution, sorbent dose, initial dye concentration, contact time and temperature were investigated using batch sorption technique for (MB) dye. The experimental results have pointed out that the adsorption equilibrium data is fitted well to the Langmuir isotherm reflecting favor formation of monolayer of MB dye on composite surface. The value of enthalpy change indicating that the removal process is endothermic. The adsorption process follows pseudo-second order rate equation and the negative values of standard free energy (DG◦) suggested that the adsorption process is spontaneous. The repeatability and regeneration studies of (ASRHNMC) for adsorption of MB were investigated and the results indicated the ability of reuse this composite several times in removal of MB from aqueous solutions.

Physico-chemical study of the interaction between levofloxacin hemihydrate Drug with Cetylpyridinium chloride in aqueous medium: conductometric and spectrophotometric investigation

Herein, the interaction between levofloxacin hemihydrate (LFH), a fluoroquinolone antibiotic drug, and cetylpyridinium chloride (CPC), a cationic surfactant, has been studied by applying conductometric and spectrophotometric techniques at various temperatures. The binding constant of LFH to various types of micelles has also been calculated by means of the Benesi-Hildebrand Equation. (CPC+LFH) mixed system exhibits lower critical micelle concentration (cmc) values in magnitude compared to the pure CPC in aqueous solution at a particular temperature as confirmed by the conductometric measurements. The profound change in the cmc values of the (CPC+LFH) mixtures by varying the concentration of LFH signify the synergistic (attractive) interaction between CPC and LFH. In addition, The negative values of standard free energy demonstrate the stability of the (CPC+LFH) mixture. Furthermore, the other thermodynamic parameters such as the standard enthalpy and standard entropy data suggest the existence of hydrophobic interaction between LFH and surfactants.

Role of carbonate electrolytes on interaction of quinolone drug with anionic surfactant at various temperatures: A conductometric study

AbstractThe role of different carbonate salts on the interaction of anionic surfactant sodium dodecyl sulfate (SDS) with employed quinolone antibiotic drug (ciprofloxacin hydrochloride [CFH]) was explosively inspected through measuring specific conductivity (κ) of the investigated system. The drug, CFH, is an excellent antibiotic for the treatment of different bacterial infections like skin, urinary tract, and respiratory infections. The estimated critical micelle concentrations (cmc) of SDS were observed to be dwindled in the attendance of electrolytes and cmc reduction continues with the escalation of the electrolyte's concentration. The magnitudes of cmc for the SDS + CFH mixture were reduced with the elevation of temperature in K2CO3 and CaCO3 medium while increased with the rise of the temperature in the Na2CO3 medium. The magnitudes of counterion binding to micelles (β) were increased with the increase of the concentration of Na2CO3 and K2CO3 up to definite value and then reduced with the increase of successive rise of concentration of both salts at all temperatures while decreased monotonically with the rise of electrolyte concentration in CaCO3 medium. The values of standard free energy ( ) were achieved to be negative in each case suggesting spontaneous self‐assembly formation. The standard entropy change ( ) along with enthalpy change ( ) was also assessed and discussed elaborately.

Electrochemical behavior of Cu-10Al-10Zn alloy in seawater in the presence of cationic surfactants benzotriazole derivatives

The behavior of Cu-10Al-10Zn alloy in seawater was studied in absence and presence of different concentrations of different surfactants (1-hexyl-5-methyl-1H-benzo[d][1,2,3]triazole-1- ium bromide (HBT(6)), 1-dodecyl-5-methyl-1H-benzo[d][1,2,3]triazole-1- ium bromide, (DBT(12)), and 1-octadecyl-5-methyl-1H-benzo[d][1,2,3]triazole-1- ium bromide, (OBT(18)) as corrosion inhibitors. These inhibitors were synthesized and their structures, (HBT) as a representative compound, were confirmed using 1HNMR and FTIR techniques. Conventional electrochemical techniques such as polarization methods and electrochemical impedance spectroscopy (EIS) were used. The inhibition efficiency increased by increasing the concentration of the prepared cationic surfactants in the medium. The curves of potentiodynamic polarization technique showed that, the performance of all prepared compounds act as mixed type. The standard free energy (〖∆G〗_ads^°) values indicate that the three prepared cationic surfactants adsorbed via physicochemical adsorption and obeyed to Langmuir adsorption model. AFM technique observed the decrease of surface roughness due to the protective film formed on Cu-10Al-10Zn alloy surface.

Gemini Surfactant Performance Evaluation as Inhibitive action of PAPM for Treatment of AISI steel Corrosion and Studying Temperatures Influence in Acidic Medium

To inhibit corrosion of the AISI 4130 steel in 1M H2SO4 solution at different temperatures, the gemini surfactant was used, namely N,N'-((1,4-phenylenebis(azanediyl)) bis (2-hydroxy propane-3,1-diyl)) bis (N,N-dimethyldecan-1-aminium) (PAPM). The gemini surfactant by electrochemical impedance spectroscopy technique and weight loss method has been evaluated at different temperatures 30, 40 and 50°C. The gemini surfactant showed a very good performance as a corrosion inhibitor in acidic solution, and inhibition efficiency increases with increase inhibitor concentration but decreased with increasing temperatures. Impedance technique results shown, that studied molecule act as mixed-type inhibitor toward AISI steel, also values of standard free energy of adsorption suggest the physisorption and chemisorption were occurred for inhibitor molecules on AISI surface. In addition, the inhibitor adsorption behavior on the AISI surface was investigated at specified temperatures and it coincide with Langmuir’s adsorption isotherm. Furthermore, time effect on corrosion inhibition efficiency was studied where results shown that influence was slight. From quantum calculations, the inhibitor act as soft molecule were noted, also it was shown that the inhibitor more responding for reacting with the AISI surface and prefer the electrophilic attack because it contains on a nucleophilic centers. Experimental inhibition efficiency obtained from both two methods are on a good agreement to each other where optimum efficiency reached 90.32% for weight loss method and 87.17% for EIS technique. On other hand, theoretical inhibition efficiency and experimental inhibition efficiency were in a good agreement to each other, where as theoretical efficiency reached 92.35%.

Can All-Atom Molecular Dynamics Simulations Quantitatively Describe Homeodomain-DNA Binding Equilibria?

We systematically investigate the applicability of a molecular dynamics-based setup for the calculations of standard binding free energies of biologically relevant protein-DNA complexes. The free energies are extracted from a potential of mean force calculated using umbrella sampling simulations. Two protein-DNA systems derived from a homeodomain transcription factor complex are studied in order to investigate the binding of both disordered and globular proteins. Free energies and trajectories obtained using two modern molecular mechanical force fields are compared to each other and to experimental data. The temperature dependence of the calculated standard binding free energies is investigated by performing all simulations over a range of temperatures. We show that the values of standard binding free energies obtained from these simulations are overestimated compared to experimental results. Significant differences are observed between the two protein-DNA systems and between the two force fields, which are explained by different propensities to form inter- and intramolecular contacts. The number of protein-DNA contacts increases with increasing temperature, in agreement with the experimentally known temperature dependence of enthalpies of binding. However, conclusions about the temperature dependence of the standard binding free energies cannot be made with confidence, as the differences among the values are on the order of statistical uncertainty.