Phase diagram of Na2S2O3 + ethanol + water at ambient pressure and temperature

In the present communication, we report the studies concerning liquid–liquid–solid equilibria for the ternary system sodium thiosulphate (Na₂S₂O₃) + ethanol + water at ambient pressure and at room temperature (303 ± 2 K). The solubility data of Na₂S₂O₃ are reported for solutions in water, ethanol and solutions of varying concentrations of ethanol in water. The phase diagram for the said system is developed, described and compared with similar system K₂CO₃ + methanol + water. These results have been explained in terms of structural properties of aqueous ethanol solutions and further discussed in terms of the effect of ions to cause phase separation.     

Hydrogen Bonding in Liquid Water and in the Hydration Shell of Salts

A near‐IR spectral study on pure water and aqueous salt solutions is used to investigate stoichiometric concentrations of different types of hydrogen‐bonded water species in liquid water and in water comprising the hydration shell of salts. Analysis of the thermodynamics of hydrogen‐bond formation signifies that hydrogen‐bond making and breaking processes are dominated by enthalpy with non‐negligible heat capacity effects, as revealed by the temperature dependence of standard molar enthalpies of hydrogen‐bond formation and from analysis of the linear enthalpy–entropy compensation effects. A generalized method is proposed for the simultaneous calculation of the spectrum of water in the hydration shell and hydration number of solutes. Resolved spectra of water in the hydration shell of different salts clearly differentiate hydrogen bonding of water in the hydration shell around cations and anions. A comparison of resolved liquid water spectra and resolved hydration‐shell spectra of ions highlights that the ordering of absorption frequencies of different kinds of hydrogen‐bonded water species is also preserved in the bound state with significant changes in band position, band width, and band intensity because of the polarization of water molecules in the vicinity of ions.     

Apparent and Transfer Molar Volumes for Aqueous Solution Containing Polyethylene Glycols and Amino Acid Ionic Liquids at 298.15 K

The densities of 1-n-butyl-3-methylimidazolium ([Bmim]) based amino acid ionic liquids (AAILs) prepared from glycine [Gly], alanine [Ala], and valine [Val], namely [Bmim][Gly], [Bmim][Ala] and [Bmim][Val], in aqueous?~?0.2 mol·kg^?1 polyethylene glycol (PEG400, PEG600 or PEG1000) and PEG400 solutions containing?~?(0.0946, 0.1891 and 0.3820) mol·kg^?1 of [Bmim][Gly], have been determined at 298.15 K. The experimental densities were used to evaluate the apparent molar volumes in the mixed solvent system and further used to obtain transfer molar volumes of AAILs for their transfer from water to aqueous PEG solutions and of PEG400 for its transfer from water to aqueous solutions containing (0.0946, 0.1891 and 0.3820) mol·kg^?1 of [Bmim][Gly]. The transfer molar volumes of AAILs and of PEG400 are found to be negative. The effects of alkyl chain-length variation on the anion of AAILs as well as the chain-length of PEG on transfer molar volumes are investigated and discussed in terms of hydrophobic–hydrophilic, hydrophobic–hydrophobic, and ion–hydrophobic interactions.     

Resonance-enhanced multiphoton ionisation photoelectron spectroscopy of the ClO radical: the C 2 sigma- state

A (2 + 1) one-colour resonance-enhanced multiphoton ionisation study is carried out on the C 2 sigma- state of the ClO radical in the one-photon energy range 29,500-31,250 cm-1. The ClO radical is produced by one-photon photolysis of ClO2 employing 359.2 nm photons derived from a separate laser. In this way a significant concentration of vibrationally excited ClO in its spin-orbit split X 2 pi omega (omega = 3/2 or 1/2) electronic ground state is produced. In addition to mass-resolved excitation spectra, kinetic-energy resolved photoelectron spectra for the X 3 sigma-(v+)<--C 2 sigma-(v' = 3-5) transitions are measured. These transitions are not completely Frank-Condon diagonal, and indicate a decrease in bond length on removal of the Rydberg electron from the C 2 sigma- state. In addition to an unambiguous assignment of the C 2 sigma- state, valuable information is obtained on the degree of vibrational excitation with which the nascent ClO radical is formed in the photolysis of ClO2. Analysis of the photoelectron spectra is supported by Franck-Condon calculations based on potential energy curves either from experimental spectroscopic parameters, or obtained by theoretical ab initio methods.     

Studies of Thermodynamic Properties of Binary and Ternary Methanolic Solutions Containing KBr and 18-Crown-6 at 298.15 K

Experimental measurements of the speed of sound, density and osmotic vapour pressure are reported for binary 18-Crown-6 (18C6) + CH₃OH, KBr + CH₃OH and ternary KBr + 18C6 + CH₃OH solutions at 298.15 K. The density and compressibility data were processed to obtain the apparent molar volume (ø _V ) and apparent molar isentropic compressibility ( $\phi _{K_S } Experimental measurements of the speed of sound, density and osmotic vapour pressure are reported for binary 18-Crown-6 (18C6) + CH₃OH, KBr + CH₃OH and ternary KBr + 18C6 + CH₃OH solutions at 298.15 K. The density and compressibility data were processed to obtain the apparent molar volume (? _V ) and apparent molar isentropic compressibility () of the solutes in methanol. Expansivity data were obtained for the 18C6 + CH₃OH system from density data at different temperatures and were used for calculation of the isothermal compressibility values at 298.15 K. The isothermal compressibility and expansivity data are further used to obtain the apparent molar isothermal compressibility () and apparent molar expansivity (? _E ) of 18C6 in methanolic solutions and as well as the energy-volume coefficient parameter (∂ U/∂ V) _T in methanol solutions. The volume and compressibility changes due to complexation of KBr with 18C6 are obtained at infinite dilution for ? _V and ? _K . The results are compared with the similar data obtained by us previously for aqueous and CCl₄ solutions. The osmotic coefficient data were used to calculate activities and activity coefficients of each component at 298.15 K as a function of the concentration of binary and ternary methanolic solutions containing KBr and 18C6. The activity and activity coefficient data are used to evaluate the pair and triplet interaction parameters by making appropriate use of the McMillan-Meyer theory of solutions. The calculation of the thermodynamic equilibrium constant (K) is made using the pair interaction parameter, g _NE (non-electrolyte – electrolyte pair interaction), for the complexation equilibria. The nature of interactions present in the CH₃OH solutions is discussed.     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.     

Phage display-derived inhibitor of the essential cell wall biosynthesis enzyme MurF

Background  

To develop antibacterial agents having novel modes of action against bacterial cell wall biosynthesis, we targeted the essential MurF enzyme of the antibiotic resistant pathogen Pseudomonas aeruginosa. MurF catalyzes the formation of a peptide bond between D-Alanyl-D-Alanine (D-Ala-D-Ala) and the cell wall precursor uridine 5'-diphosphoryl N-acetylmuramoyl-L-alanyl-D-glutamyl-meso-diaminopimelic acid (UDP-MurNAc-Ala-Glu-meso-A2pm) with the concomitant hydrolysis of ATP to ADP and inorganic phosphate, yielding UDP-N-acetylmuramyl-pentapeptide. As MurF acts on a dipeptide, we exploited a phage display approach to identify peptide ligands having high binding affinities for the enzyme.     

Thermodynamic studies of drug-alpha-cyclodextrin interactions in water at 298.15 K: promazine hydrochloride/chlorpromazine hydrochloride + alpha-cyclodextrin + H(2)O systems

Data on osmotic coefficients have been obtained for a binary aqueous solution of two drugs, namely, promazine hydrochloride (PZ) and chlorpromazine hydrochloride (CPZ) using a vapor pressure osmometer at 298.15 K. The observed critical micelle concentration (cmc) agrees excellently with the available literature data. The measurements are extended to aqueous ternary solutions containing fixed a concentration of alpha-cyclodextrin (alpha-CD) of 0.1 mol kg(-1) and varied concentrations (approximately 0.005-0.2 mol kg(-1)) of drugs at 298.15 K. It has been found that the cmc values increase by the addition of alpha-CD. The mean molal activity coefficients of the ions and the activity coefficient of alpha-CD in binary as well as ternary solutions were obtained, which have been further used to calculate the excess Gibbs free energies and transfer Gibbs free energies. The lowering of the activity coefficients of ions and of alpha-CD is attributed to the existence of host-guest (inclusion)-type complex equilibria. It is suggested that CPZ forms 2:1 and 1:1 complexed species with alpha-CD, while PZ forms only 1:1 complexed species. The salting constant (ks) values are determined at 298.15 K for promazine-alpha-CD and chlorpromazine-alpha-CD complexes, respectively, by following the method based on the application of the McMillan-Mayer theory of virial coefficients to transfer free energy data. It is noted that the presence of chlorine in the drug molecule imparts better complexing capacity, the effect of which gets attenuated as a result of hydrophobic interaction. The results are discussed from the point of view of associative equilibria before the cmc and complexed equilibria for binary and ternary solutions, respectively.