Temperature and Solvent Dependent Catalytic Transfer Hydrogenolysis in Aromatic Aldehydes and Ketones Via Ammonium Formate

Temperature control and solvent specification are used to reduce aromatic aldehydes and ketones to intermediate alcohols rather than methylene derivatives using HCO₂NH₄ as a catalytic hydrogen transfer agent. A mechanism for the catalytic reduction is proposed.     

Synthesis and proton conductivity of sulfonated,multi‐phenylated poly(arylene ether)s

A series of sterically‐encumbered, sulfonated, poly(arylene ether) copolymers were synthesized and their proton conductivity examined. The series was prepared by copolymerizing a novel monomer, 2″,3″,5″,6″‐tetraphenyl‐[1,1′:4',1″:4″,1″':4″',1″″‐quinquephenyl]‐4,4″″‐diol, with 4,4'‐difluorobenzophenone and bisphenol A. Subsequent sulfonation and solution casting provided membranes possessing ion exchange capacities of 1.9 to 2.7 mmol/g and excellent mechanical properties (Young's modulus, 0.2–1.2 GPa; tensile strength, 35–70 MPa; elongation at break, 62–231%). Water uptake ranged from 34 to 98 wt% at 80 °C/100% RH. Proton conductivities ranged between 0.24 to 16 mS/cm at 80 °C/60% RH, and 3 to 167 mS/cm at 80 °C/95% RH. TEM analysis of the polymers, in the dehydrated state, revealed isolated spherical aggregates of ions, which presumably coalesce when hydrated to provide highly conductive pathways. The strategy of using highly‐encumbered polymer frameworks for the design of mechanically‐robust and dimensionally‐stable proton conducting membranes is demonstrated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2579‐2587     

The first metals in Mendeleiev’s table: further arguments to place He above Ne and not above Be

In a recent paper in this Journal, one of us argued against placing He above Be in Mendeleiev’s system of the elements. In it the goal was to dispute the notion that in Mendeleiev’s system of the elements the location of He should in fact lie above Be, which has a very similar electronic configuration, rather than above the noble gas column. That paper was based on rather old, Hartree–Fock limit studies on the strikingly limited non-additive contributions in the He₃ and He₄ systems in contrast with the much larger non-additivity obtained for the Be₃, Be₄ and Be₅ oligomers. In a recent benchmark multireference Averaged Quadratic Coupled Cluster results on Be₂ and Be₃ we showed that the delocalized non-additive contribution comprises 94 % of the binding energy of Be₃. Here we use this and other pertinent information (drawn from the same paper) to conclude that He may not be associated with Be in Mendeleiev’s Table, despite their quite similar spectroscopic ground states. Furthermore, we use the new results to show that the large non-additivity implies that less than 2 % of the Be₃ binding is located in each Be pair contained within the Be trimer. The rest of the interaction energy is necessarily delocalized over all three Be atoms. This might actually announce the bulk properties (i.e. “the electron gas”) that in solid-state physics explain the large electric and heat conduction for the solid Be metal. Thus, in the case of beryllium the metallic characteristics are already evident in Be₃, a far cry from the monoatomic helium gas.     

Conformational landscape of l-threonine in neutral,acid and basic solutions from vibrational circular dichroism spectroscopy and quantum chemical calculations

The biological relevance of amino acids is well known. They can be used as zwitterionic, cationic or anionic forms according to the pH of the medium where they are. Thus, our aim herein was to study the conformational preference of the polar amino acid l-threonine [C₄H₉NO₃, (2S,3R)-2-amino-3-hydroxybutyric acid] under different pH conditions. A conformational study in an aqueous solution of the dissociation equilibrium of the amino acid l-threonine was carried out for this purpose. We recorded, at room temperature, the Mid-IR, Far-IR, Raman and VCD spectra of l-threonine from the aqueous solutions at pH values 5.70 (zwitterionic species), 1.00 (protonated species) and 13.00 (deprotonated species). The number of conformers found with the conformational search was 9 zwitterions, 27 anions and 52 cations. Both the study of the conformational landscape and the theoretical analysis of the vibrational features were accomplished by using DFT and ab initio calculations, that is, B3LYP/6-311++G(d,p) level of theory for all the conformers obtained from the conformational search, M062X/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory for the most stable conformers. The presence of water was included with the IEF-PCM implicit hydration model. With regard to the zwitterion, the importance of the analysis of the low frequency region (700–30 cm^–1) in the Far-IR spectra should be noted, because it provides relevant information that can be used to determine the presence of the most stable structures.     

Equilibrium theory of molecular fluids: Structure and freezing transitions

In this article we review equilibrium theory of molecular fluids which includes structure and freezing transitions. The application of the theory to evaluate the pair correlation functions using Integral Equation methods and Computer Simulations have been discussed. Freezing of classical complex fluids based on the density functional approach is also discussed and compare a variety of its versions. Transitions discussed are sensitive to the value of direct correlation functions of the effective liquid which is required as an input information in the theory. Accurate evaluation of pair correlation functions is emphasized. Calculation of these correlation functions which pose problems in the case of ordered phases is discussed. The pair correlation functions of the ordered phase, which are supposed to be made up of two contributions, one that preserves the symmetry of the isotropic phase and a second that breaks it, are discussed. A new free-energy functional developed for an inhomogeneous system that contains both symmetry conserved and symmetry broken parts of the direct pair correlation function is discussed. The most useful three dimensional reference interaction site model (3D-RISM) and its extension done recently by many workers is discussed. Application of this theory to a large variety of complex systems in combination with the density functional theory method implemented in the Amsterdam density functional software package is discussed. Coupling of the 3D-RISM salvation theory with molecular dynamics in the Amber molecular dynamics package is also given.     

High temperature enthalpy increment and thermodynamic functions of U2Ti

This study investigated thermodynamic properties of uranium–titanium alloy to determine its suitability for storage of hydrogen isotopes. The enthalpy increments of U₂Ti were measured using a high temperature inverse drop calorimeter in the temperature range of 299–1,169 K. Temperature dependence of the molar enthalpy increment and molar heat capacity is expressed in the form $ H^\circ_{\text{m}} (T) - H^\circ_{\text{m}} (298.15\,{\text{K}})({\text{J }}\,{\text{mol}}^{ - 1} ) = 23.236(T/{\text{K}}) + 53.292 \times 10^{ - 3} (T/{\text{K}})^{2} - 21.294 \times 10^{5} ({\text{K}}/T) - 4523 $ and $ C^\circ_{\text{p,m}} ({\text{J}}\,{\text{K}}^{ - 1} \,{\text{g}}^{ - 1} ) = 23.236 + 10.6584 \times 10^{ - 2} (T/{\text{K}}) + 21.294 \times 10^{5} ({\text{K}}/T)^{2} (300 \le T/{\text{K}} \le 900) $ , respectively. A set of self consistent thermodynamic functions such as entropy, Gibbs energy function, heat capacity, and Gibbs energy and enthalpy values for U₂Ti have been computed using data obtained in this study and required data from the literature.     

Computational studies on the structures and energies of the tautomers of 1-amino-3-nitrotriazol-5-one-2-oxide

Molecular orbital calculations at the DFT-B3LYP/aug-cc-pVDZ level were performed for the possible tautomers of 1-amino-3-nitro-1,2,4-triazol-5-one-2-oxide. We have examined the substitution effects of amino and nitro groups by comparing calculated geometries, relative energies, and electrostatic potentials of model molecules. The optimized structures, vibrational frequencies, and thermodynamic values for triazol-5-one-N-oxides were obtained in their ground state. The results show 1H, 4H tautomers to be most stable. Detonation velocity and detonation pressure were evaluated by the Kamlet and Jacob equations based on the predicted density and the calculated heat of explosion. Explosive properties appear to be promising compared with those of 1,3,5-trinitro-1,3,5-triazine (D = 8.75 km/s, P = 34.7 Gpa) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (D = 8.96 km/s, P = 35.96 Gpa), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s, P = 42.0 Gpa) and octanitrocubane (D = 9.90 km/s, P = 48.45 GPa). The designed triazol-5-one-N-oxides satisfy the criteria of high energy density materials.     

Separation and Analysis of Nucleic Acids and Their Constituents by Ion-Exclusion and Ion-Exchange Column Chromatography

The recent commercial development of high pressure liquid chromatographic instruments, and the availability of small and uniformly sized resin beads has enhanced the role of column chromatography for the rapid assay of nucleic acid components. A major advancement in the purification and analysis has been due to the recent demonstration that the ion exclusion is more or equally effective than the ion exchange as a separation principle for the resolution of purine and pyrimidine bases, nucleosides, deoxynucleosides and nucleotides^1–3. This article deals with the recent applications of separation principles that have been employed for the separation of nucleic acid constituents. The reader is referred to two review articles of Cohn for the earlier works on this subject^{4, 5}. Separations by chromatography and electrophoresis on paper and thin layers are not described here; several monographs and review articles are available in the literature^6–12.The reader is also referred to a recent methodological study for the base analysis of ribopolynucleotides by chemical tritium labeling which utilizes two dimensional chromatography on thin layers of cellulose as a separation means^{13, 14}.