Coupled-cluster, Möller Plesset (MP2), density fitted local MP2, and density functional theory examination of the energetic and structural features of hydrophobic solvation: water and pentane

The interaction potentials between immiscible polar and non-polar solvents are a major driving force behind the formation of liquid:liquid interfaces. In this work, the interaction energy of water-pentane dimer has been determined using coupled-cluster theory with single double (triple) excitations [CCSD(T)], 2nd order M?ller Plesset perturbation theory (MP2), density fitted local MP2 (DF-LMP2), as well as density functional theory using a wide variety of density functionals and several different basis sets. The M05-2X exchange correlation functionals exhibit excellent agreement with CCSD(T) and DF-LMP2 after taking into account basis set superposition error. The gas phase water-pentane interaction energy is found to be quite sensitive to the specific pentane isomer (2,2-dimethylpropane vs. n-pentane) and relative orientation of the monomeric constituents. Subsequent solution phase cluster calculations of 2,2-dimethylpropane and n-pentane solvated by water indicate a positive free energy of solvation that is in good agreement with available experimental data. Structural parameters are quite sensitive to the density functional employed and reflect differences in the two-body interaction energy calculated by each method. In contrast, cluster calculations of pentane solvation of H(2)O solute are found to be inadequate for describing the organic solvent, likely due to limitations associated with the functionals employed (B3LYP, BHandH, and M05-2X).     

Nested Log-Concavity

We give conditions on the coefficients of a polynomial p(x) so that p(x + t) be log-concave or strictly log-concave. Several applications are given: if p(x) is a polynomial with nonnegative and nondecreasing coefficients, then p(x + t) is strictly log-concave for all t ≥ 1; for any polynomial p(x) with positive leading coefficient, there is t ₀ ≥ 0 such that for any t ≥ t ₀ it holds that the coefficients of p(x + t) are positive, strictly decreasing, and strictly log-concave; if p(x) is a log-concave polynomial with nonnegative coefficients and no internal zeros, then p(x + t) is strictly log-concave for all t > 0; Betti numbers of lexsegment monomial ideals are strictly log-concave.     

The Group of Automorphisms of the Rational Group Algebra of a Finite Metacyclic Group

We investigate the group of automorphisms Aut(? G) of a rational group algebra ? G of a finite metacyclic group G by first describing the simple components of the Wedderburn decomposition of ? G and then investigating when two of these simple components are isomorphic.     

Predicting Inclusion Behaviour and Framework Structures in Organic Crystals

We have used well‐established computational methods to generate and explore the crystal structure landscapes of four organic molecules of well‐known inclusion behaviour. Using these methods, we are able to generate both close‐packed crystal structures and high‐energy open frameworks containing voids of molecular dimensions. Some of these high‐energy open frameworks correspond to real structures observed experimentally when the appropriate guest molecules are present during crystallisation. We propose a combination of crystal structure prediction methodologies with structure rankings based on relative lattice energy and solvent‐accessible volume as a way of selecting likely inclusion frameworks completely ab initio. This methodology can be used as part of a rational strategy in the design of inclusion compounds, and also for the anticipation of inclusion behaviour in organic molecules.     

New metal(II) complexes with ceftazidime Schiff base

Complexes of Co(II), Ni(II) and Cu(II) with the Schiff base (LH) derived from ceftazidime and salicylaldehyde were synthesized. The proposed structures of the new metal complexes based on the results of elemental analyses, molar conductivity, IR, DRUV and ¹H NMR spectra, effective magnetic moment and thermal analysis were discussed. The surface morphology of Schiff base and metal complexes was studied by SEM. The composition of the metal complexes was ML₂, where L is the deprotonated Schiff base ligand and M = Co(II), Ni(II) and Cu(II). IR spectral data indicated the Schiff base ligand being bidentately coordinated to the metallic ions with N and O atoms from azomethine and phenolic groups. All the complexes have square-planar geometry and are nonelectrolytes. The thermal analysis recorded that TG, DTG, DTA and DSC experiments confirmed the assigned composition and gave information about the thermal stability of complexes in dynamic air atmosphere. Theoretical investigation of the molecular structure of Schiff base ligand and its complexes was studied using programs dedicated to chemical modeling and quantomolecular calculation of chemical properties. The newly synthesized complexes were tested for in vitro antibacterial activity against selected Gram-negative and Gram-positive bacterial strains, and they exhibited an antibacterial activity superior to that of the Schiff base ligand.     

Volumetric properties of dilute aqueous solutions of cobalt-amine-type salts. Part I. Densities at 25°C

The densities of dilute aqueous solutions of [CoL₃]X₃ [L=1,2-diaminoethane(en), 1,2-diaminopropane(pn), 1,3-diaminopropane(tn) X=Cl^–, Br^– and (ClO₄)^–] have been measured at 25°C from 0 to 5×10^–2m. The apparent molar volumes were calculated and extrapolated to infinite dilution. Ion-solvent interactions were detected from the change of the ionic partial molar volumes with concentration. These interactions depend both on the properties of the ion (polarization charge density at the surface, hydrophobic groups, etc.) and the characteristics and structure of the solvent.     

Carbonyl cationic rhodium(I) and iridium(I) complexes with sulphur donor and triphenylphosphine ligands

Summary The reaction of previously reported Rh^I and Ir^I cationic complexes towards carbon monoxide and triphenylphosphine has been studied. Carbonyl rhodium(I) mixed complexes of the formulae [Rh(CO)L₂(PPh₃)]ClO₄, (L=tetrahydrothiophene(tht), trimethylene sulfide(tms), SMe₂, or SEt₂), [(CO)(PPh₃)Rh{-(L-L)}₂Rh(PPh₃)(CO)](ClO₄)₂ (L-L= 2,2,7,7-tetramethyl-3,6-dithiaoctane (tmdto), (MeS)₂(CH₂)₃ (dth), or 1,4-dithiacyclohexane (dt), [Rh(CO)L(PPh₃)₂]ClO₄ (L= tht, tms, SMe₂, or SEt₂), and carbonyl iridium(I) complexes of the formulae [Ir(CO)₂(COD)(PPh₃)]ClO₄, [Ir(CO)(COD)(PPh₃)₂]ClO₄, [(CO)(COD)(PPh₃) Ir{-(L-L)} Ir(PPh₃)(COD)(CO)](ClO₄)₂ (L-L = tmdto or dt), [(CO)₂ (PPh₃)Ir(-tmdto)Ir(PPh₃)(CO)₂](ClO₄)₂, [(CO)₂(PPh₃) Ir(-dt)₂Ir(PPh₃)(CO)₂](ClO₄)₂, were prepared by different synthetic methods.     

Evaluation of the analytical performance of inductively coupled plasma mass spectrometry for the simultaneous determination of major and minor elements in basic slags

The application of inductively coupled plasma mass spectrometry to the analysis of basic slags has been studied. A conventional dissolution-fusion procedure and a microwave digestion system were used for sample dissolution. Suitable selection of the analyte isotopes and the use of appropriate instrument settings and of internal standardization makes it possible to determine the major and minor elements in the same test sample dilution. Use of the omnirange device and low-abundance isotopes for the determination of the major elements is evaluated. The influence of the attack reagents is tested and the interferences caused by polyatomic ions are studied and corrected by applying elementary mathematical equations. For the major and minor elements considered, precision was found to be better than 1% (RSD). Results are presented for three basic slag reference materials and the agreement between the certified and found values shows the capacity of the method accurately to determine elemental concentrations in basic slags.