Protonation and Solvation Thermodynamics of Some Naphthol Derivatives in KCl Aqueous Solution of Different Ionic Strengths

The acid-base properties of naphthalen-1-ol (L1), naphthalene-1,5-diol (L2), and 4-amino-3-hydroxynaphthalene-1-sulphonic acid (L3) were characterized from pH-metric measurements in pure water and in different concentrations (0–4 mol kg−1) of aqueous KCl solutions at the temperature range of T = (293.15 to 213.15) K at 5 K intervals. The results reveal that naphthalen-1-ol and naphthalene-1,5-diol molecules have two ionisable protons (of the hydroxyl groups) while 4-amino-3-hydroxynaphthalene-1-sulphonic acid has three ionisable protons (hydrogen ion of the hydroxyl group, SO3H, and NH3+). Modeling of the data was done by applying Debye-Hückel model. The protonation and the solvation processes of all studied ligands are spontaneous and endothermic processes. Also the solubilities of naphthalen-1-ol, naphthalene-1,5-diol, and 4-amino-3-hydroxynaphthalene-1-sulphonic acid were determined. The data were analyzed using Setschenow equation and the values of Setschenow coefficients (km) were determined. From the solubility data, the activity coefficients were obtained. The values of the total solubilities (ST) for naphthalen-1-ol and naphthalene-1,5-diol were found equal to the values of their neutral species (S0). On the other hand, the total solubility for 4-amino-3-hydroxynaphthalene-1-sulphonic acid is different from that of its neutral species. The results also indicate solubility decrease in pure water from L1-L2-L3

Moringa oleifera plant extract as a copper corrosion inhibitor in binary acid mixture (HNO3 + H3PO4)

The behavior of Cu in 1 M mixture of nitric and phosphoric acids containing different concentrations of moringa oleifera leaves (MOL) extract has been studied by weight loss (WL) and electrochemical techniques [potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM)]. The maximum inhibition efficiency was found to be 89% at concentration 0.300 mol L-1 of the extract at 298K after 3 hours immersion period. The inhibition efficiency (IE) increased with increasing the extract concentration while decreased with increasing the temperature indicates that the extract is physically adsorbed on Cu surface. The adsorption of the extract follows Langmuir adsorption isotherm. Some thermodynamic parameters of activation and adsorption processes were also determined and discussed. Surface analysis was also studied

Esomeprazole Magnesium Trihydrate drug as a potential non-toxic corrosion inhibitor for mild steel in acidic media

The inhibiting effect of Esomeprazole Magnesium Trihydrate drug on the corrosion of mild steel (MS) in 1 M HCl was performed by chemical tests (weight loss (WL)) and electrochemical methods (Tafel polarization (TP), electrochemical frequency modulation (EFM) and AC impedance spectroscopy (EIS)). The adsorption isotherm of Esomeprazole Magnesium Trihydrate drug on the MS surface was found to follow Temkin adsorption isotherm. Some thermodynamic parameters were computed and discussed. The obtained data showed that the inhibition efficiency (IE) rises with increasing the dose of the Esomeprazole Magnesium Trihydrate and with raising the temperature. The morphology of MS surface was analyzed by using scanning electron microscope (SEM), atomic force microscopy (AFM), and Fourier transforms infrared spectroscopy (FTIR) techniques. All test methods were in good agreement with each other

A novel regulatory mechanism for the CRL4(DCAF1) RING ubiquitin ligase involving oligomerization

E3 ubiquitin ligases catalyze the transfer of ubiquitin (Ub) from E2~Ub to a substrate. Cullin RING E3 ubiquitin ligases (CRLs) are modular multi-subunit complexes that associate with several substrate-receptor subunits. CRL ligase activity is stimulated by the covalent attachment of the ubiquitin-like molecule NEDD8 (neddylation) to the cullin subunit. The COP9 signalosome complex reverses this activation process by the catalytic cleavage of NEDD8, leading to the inactivation of the ligase. CAND1 is the substrate adaptor-receptor exchange factor, which catalyzes the recruitment of new substrate receptors to the cullin subunit to bind substrates. The CRL4 (Cullin 4-DDB1-Rbx1) family of cullin-RING E3 ubiquitin ligases employs ~20 different substrate receptors, referred to as DCAFs (DDB1 and Cullin-4 Associated Factors). DCAF1 is a central member of the DCAF family, and found to be dysregulated in different types cancers. The activity of CRL4DCAF1 is suppressed when DCAF1 is bound to Merlin, a tumor suppressor protein that acts upstream of the Hippo pathway. CRL4DCAF1 recruits substrates implicated in DNA repair, cell cycle progression, and cell fate regulation. Viruses also hijack the CRL4 system by binding DCAF1, and drive the degradation of cellular proteins that facilitate viral infections. The regulatory mechanism underlying CRL4DCAF1 activity is currently poorly understood. We have used biochemical and structural approaches to study CRL4DCAF1 in vitro. The 8.2 Å cryo-EM map of CRL4DCAF1 finds the complex in a tetrameric arrangement, where DCAF1 WD40 domain mediates the interaction with the cullin C-terminal domain (CTD) and Rbx1. This architecture renders the RING domain of Rbx1, the catalytic subunit of the ligase, inaccessible to the E2. Upon activation of CRL4DCAF1 by neddylation, the interaction between the cullin CTD and DCAF1 is broken and the complex becomes dimeric and active. This dimeric state is also induced when the viral proteins VPR-UNG2 are bound to CRL4DCAF1, while the presence of Merlin is compatible with the tetrameric auto-inhibited state of the ligase. Moreover, the tetrameric conformation of CRL4DCAF1 seems to protect the ligase from the spontaneous exchange of adaptor-receptor modules in the absence of CAND1. These results suggest a novel mechanism by which the activity of isolated CRL4DCAF1 ligase is regulated

The effect of 18-crown-6 on the solubility and thermodynamic parameters of Li₂CO₃, Na2CO₃, NaCl, CH₃COONa and KCl in methanol and ethanol

1594-1596The effect of different concentrations of a cyclic polyether 18-crown-6 (18C6) on the solvation parameters of some alkali metal salts has been studied. The molal solubilities of Li2CO3, Na2CO3, NaCl, CH3COONa and KCl have been determined experimentally (using volumetric and precipitation titrations) in the absence and in presence of different concentrations of 18C6 in methanol and ethanol at 20, 25, 30 and 35oC. From the experimental results, the solvation thermodynamic parameters (the free energy, the enthalpy and the entropy) have been calculated and discussed. Also the effects of different concentrations of 18C6, temperature, anion, ionic radius and solvent on the parameters have been discussed