NEW SURFACE-ACTIVE PETROCOLLECTING AND PETRODISPERSING REAGENT BASED ON STEARIC ACID AND TRYETHYLENETETRAAMINE

New surfactant was synthesized from stearic and triethylenetetraamine at room temperature, without utilizing any catalyst or solvent. Structure and composition of the salt was confirmed by using IR-, NMR- and UV- spectroscopies . Surface tension, conductivity measurements were performed on aqueous solutions of new surfactant. Its surface activity and colloidal-chemical parameters such as critical micelle concentration (CMC), surface pressure at CMC (πCMC), surface tension at CMC (γCMC), surface excess (Γmax), concentration required for 20 mN/m reduction of surface tension (C20), Gibbs energies of adsorption and micellization (ΔGad and ΔGmic) were determined. Moreover, corrosion properties and petrocollecting and petrodispersing properties of this salt was determined and maximum values of petrocollecting coefficients was calculated.

Weak Interactions of the Isomers of Phototrexate and Two Cavitand Derivatives

The interactions of two conformers of newly synthesized photoswitchable azobenzene analogue of methotrexate, called Phototrexate, with two cavitand derivatives, have been investigated in dimethyl sulfoxide medium. Photoluminescence methods have been applied to determine the complex stabilities and the related enthalpy and entropy changes associated to the complex formation around room temperature. Results show opposite temperature dependence of complex stabilities. The structure of the upper rims of the host molecules and the reordered solvent structure were identified as the background of the opposite tendencies of temperature dependence at molecular level. These results can support the therapeutic application of the photoswitchable phototrexate, because the formation of inclusion complexes is a promising method to regulate the pharmacokinetics of drug molecules.

Effect of the Temperature and Solvents on the Solvolysis of Barium Bromide in Aqueous-Organic Solutions: Volumetric and Viscometric Study

Volumetric and viscometric properties of solutions containing barium bromide in an aqueous solution of ethylene glycol and 1,4-dioxane have been discussed at different temperatures such as 298.15K 303.15K, 308.15K, and 313.15K. The Masson’s equation was used to determine the apparent molar volume, V_ϕ, standard partial molar volume, V_ϕ^0, molar expansibilities,E_ϕ^0 by taking the density data. The values of viscosity and density were used in the Jones-Dole equation to find the viscosity B coefficients, which were used to estimate the ion-solvent interactions. The values of Hepler’s constant (∂^2 V_ϕ^0/ ∂T2)p and the viscosity B-coefficients have been used to deduce the solvent structure-promoting or structure breaking tendency of the salt in the studied mixtures. In the current study, the positive values of Hepler’s constant and the negative values of dB/dT show that barium bromide in the considered solvents mainly behaves as a structure promoter.

Influence of solvent structure and hydrogen bonding on catalysis at solid–liquid interfaces

A pedagogical review that deconvolutes the excess free energy effects of several solvent phenomena and connects findings across a variety of catalytic reactions and materials.

Deflating the RNA Mg2+ bubble. Stereochemistry to the rescue!

Proper evaluation of the ionic structure of biomolecular systems remains challenging in X-ray and cryo-EM techniques but is essential for advancing our understanding of complex structure/activity/solvent relationships. However, numerous studies overestimate the number of Mg2+ in the deposited structures and underrate the importance of stereochemical rules to correctly assign these ions. Herein, we re-evaluate the PDBid 6QNR and 6SJ6 models of the ribosome ionic structure and establish that stereochemical principles should always be considered when evaluating ion binding features, even when K+ anomalous signals are available as it is the case for 6QNR. Assignment errors can result in misleading conceptions of the solvent structure of ribosomes and other RNA systems and should therefore be avoided. Our analysis resulted in a significant decrease of bound Mg2+ ions in the 6QNR structure, suggesting that K+ and not Mg2+ is the prevalent ion in the ribosome 1st solvation shell. We stress that the use of proper stereochemical guidelines is critical for deflating the current Mg2+ bubble witnessed in many ribosome and other RNA structures. Herewith, we would like to draw the attention of the researchers interested in the ionic structure of biomolecular systems on the importance and complementarity of stereochemistry and other ion identification techniques such as those pertaining to the detection of anomalous signals of transition metals and K+. We also stress that for the identification of lighter ions such as Mg2+, Na+, …, stereochemistry coupled with high resolution structures remain the best currently available option.