Question of “bound” and “free” water

Summary The physical meaning of the correction for the binding of water by ions is clarified, and an equation is proposed for its accurate calculation.     

A comparative study in structure and reactivity of “FeO_x-on-Pt” and “NiO_x-on-Pt” catalysts

Oxide nanostructures grown on noble metal surfaces are often highly active in many reactions,in which the oxide/metal interfaces play an important role.In the present work,we studied the surface structures of Fe Ox-on-Pt and Ni Ox-on-Pt catalysts and their activity to CO oxidation reactions using both model catalysts and supported nanocatalysts.Although the active Fe O1x structure is stabilized on the Pt surface in a reductive reaction atmosphere,it is prone to change to an Fe O2x structure in oxidative reaction gases and becomes deactivated.In contrast,a Ni O1x surface structure supported on Pt is stable in both reductive and oxidative CO oxidation atmospheres.Consequently,CO oxidation over the Ni O1x-on-Pt catalyst is further enhanced in the CO oxidation atmosphere with an excess of O2.The present results demonstrate that the stability of the active oxide surface phases depends on the stabilization effect of the substrate surface and is also related to whether the oxide exhibits a variable oxidation state.     

Geminal interaction and “anomeric effect”

Quantum-chemical calculations by the methods of RHF/6-31G(d) and MP2/6-31+G(d) show equal ratio of the lengths of axial and equatorial bonds and electron density on the atoms forming them in cyclohexane and its mono derivatives and in six-membered heterocyclic molecules as well. This feature is due to the interaction of atoms in the chair form of these molecules regardless of the presence in them of a heteroatom. Introducing heteroatom to a cyclohexane ring leads only to increase in the difference between axial and equatorial bonds. This equation excludes the possibility to ascribe the elongation of axial bonds and increase in the electron density on atoms forming them in the heterocyclic molecules to the p,σ*-conjugation of the lone electron pair of the ring heteroatom with the antibonding orbital of the axial bond. Features of molecular geometry defined by the mutual influence of atoms in them, including inductive and non-inductive interaction of geminal atoms in triatomic groups Y-Z-M, result in energetic preference of gauche conformations of these molecules and “anomeric effect” in them.     

Syntheses and characterizations of trinuclear and dinuclear “half-sandwich” zirconocene phosphates and phosphonates

A series of six-coordinate “half-sandwich” zirconocene phosphates and phosphonates have been synthesized by the reaction of Cp₂ZrCl₂ with (diphenyl-, dibenzyl-)phosphate and methylphenylphosphinic acid under different conditions. All of the complexes were characterized by elemental analysis, FT-IR and NMR (¹H, ¹³C) spectroscopy. Except for complex 3, the structures of complexes 1, 2, 4, 5, and 6 were confirmed by X-ray crystallography. The structure analyses reveal that complexes 1, 2, and 3 are trinuclear complexes with fascinating μ₃-oxygen bridging ligands, central to a Zr–O backbone (Cp₂ZrCl₂:ligand is 1:1) while complexes 4, 5, and 6 are centrosymmetric dinuclear complexes built up about the trapezoidal Zr₂(μ₂-OH)₂ unit (Cp₂ZrCl₂:ligand is 1:2).     

Parameters of cation “hardness” and “softness” and application thereof for calculation of extraction constants

Analysis of published data was performed on the basis of solvation energies of a number of “transition” and “soft” cations. A dependence of the solvation energy of cations on the donor and acceptor numbers of the solvent was derived. Donor and acceptor ability parameters of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, and Tl⁺ were calculated. The resultant parameters were used to calculate the extraction constants of the specified cations with di-2-ethylhexyl-phosphoric acid (DEHPA) solution in neutral solvents; the model represented has a good predictive power.     

Radiation-induced luminescence from “dry” and hydrated DNA and related macromolecules

The radiation-induced luminescence from three types of fibrous DNA and a series of polydeoxynucleotides was measured under vacuum or in the presence of oxygen at 77 and 293 K. The “in pulse” emission spectra, generated by electrons with energies <260 keV, have been investigated in order to obtain an understanding of the effects of direct energy deposition within DNA. From a comparison of the observed emission spectra from “dry” DNA samples with different A + T/G + C ratios with those for the polydeoxynucleotides, it is inferred that the A + T/G + C ratio of DNA is an important factor in determining the wavelength dependence of the emission. The “in-pulse” emission characteristics of DNA and the polydeoxynucleotides were found to be independent of both temperature and the presence of oxygen. Investigations were extended to study the effect of hydration of DNA upon the resulting radiation induced emission spectra. It is apparent that with DNA thin films (15–20 μm) containing >50% water by wt (1.2:1 w/w, H₂O|DNA), the “in-pulse” luminescence spectrum is similar to that of “dry” DNA. These findings are discussed in terms of energy or charge migration induced in DNA upon irradiation and the possible effects of conformational changes, caused by hydration, on charge migration.     

Synthesis and study of “nonuniform” naphthylenephosphacyclophanes

A method for the preparation of nionuniform phosphacyclophanes with two different naphthylene radicals and two phosphoramidite, phosphoramidate, or thiophosphoramidate residues in the molecule is proposed. The “nonuniform” phosphacyclophanes containing trivalent phosphorus are stable systems. Their oxidation or addition of sulfur to them changes the overall configuration of the molecules and decreases the stability of such systems.     

Cyclometallaphosphiniminatopxosphane (and Arsane) Complexes of “Early” and “Late” Transition Metals Derived from Novel Heterodifunctional Phosphorus and Arsenic Ligands

Abstract

A new heterodifunctional ligand system Me₃EN=PPh₂(CH₂)_nQPh₂ (E - Si, Ge; Q = P, As; n ? 1, 2) has been developed. These heterodifunctional ligands provide hard (N) and soft (P, As) base character appropriate for combination with “early” and “late” transition metals respectively to form chelate and monodentate complexes. In addition M-N [sgrave] bond formation by means of metathetical Me₃EX elimination leads to a variety of useful functionalized phosphanes. Interactions with Ti(IV), Mo(O), W(O), Pd(II), Rh(I) and Ir(I) indicate the versatility of these ligands     

The XIth International symposium “polymers and light”

Information Congresses, Conferences, Symposia, Meetings, and Seminars in the Field of Chemical Sciences Held with the Participation of the Russian Academy of Sciences

The XIth International symposium polymers and light     

“Malonate Uptake and Metabolism in Saccharomyces cerevisiae”

Malonyl-CoA plays an important role in the synthesis and elongation of fatty acids in yeast Saccharomyces cerevisiae. Malonyl-CoA is at a low concentration inside the cell and is produced mainly from acetyl-CoA through the enzyme acetyl-CoA carboxylase. It would be beneficial to find an alternative source of malonyl-CoA to increase its intracellular concentration and overall synthesis of the fatty acids. MatB gene from the bacteria Rhizobium leguminosarium bv. trifolii encodes for a malonyl-CoA synthetase which catalyzes the formation of the malonyl-CoA directly from malonate and CoA. However, results from high-performance liquid chromatography (HPLC) proved that Saccharomyces cerevisiae itself does not contain enough cytoplasmic malonate within them and is unable to uptake exogenously supplied malonate in the form of malonic acid. A dicarboxylic acid plasma membrane transporter with the ability to uptake exogenous malonic acid was identified from another species of yeast known as Schizosaccharomyces pombe and the gene encoding this transporter is identified as the mae1 gene. From the experiments thus far, the mae1 gene had been successfully cloned and transformed into Saccharomyces cerevisiae. The expression and functional ability of the encoded plasma membrane dicarboxylic acid transporter were also demonstrated and verified using specialized technologies such as RT-PCR, yeast immunofluorescence, HPLC, and LC-MS.     

Elastic and thermoelastic properties of “inorganic rubber”

Polymerization of cyclic phosphonitrilic chloride trimer was carried out at sufficiently high temperatures and for sufficiently long periods to cause gelation of the poly(dichlorophosphazene) formed. The resulting crosslinked material, called “inorganic rubber”, was found to be stable enough in the absence of moisture to permit reliable stress-strain and stress-temperature (thermoelastic) measurements in elongation. The stress-strain isotherms at low and moderate values of the elongation, α, showed that the networks had relatively low degrees of crosslinking; at high α and low temperature, they underwent strain-induced crystallization. The thermoelastic data confirmed the occurrence of crystallization at high α and low T. Thermoelastic values of the fraction f_e/f of the force that is of energetic origin were negative and generally large, with a magnitude that increased with increase in α, presumably because of the crystallization. In any case, the experimental values of f_e/f are in at least qualitative agreement with rotational isomeric state theory, which predicts this ratio to be large and negative.     

Geminal interaction and effect of “positive charge”

Quantum-chemical calculations of the molecules containing Cl-C-M group (M=C, N, O, F) were carried out using RHF/6-31G(d) and MP2/6-31+G(d) methods. The calculations are aimed at verifying concept on “positive charge” effect of the central atom of the group suggested as understanding of non-inductive effect of heteroatom M on the Cl (Y) atom in Y-Z-M moieties (geminal interaction). It is shown that C atom in such systems bears negative or small positive charge, and hence “positive charge” effect is excluded. The non-inductive effect originates from the polarization of Cl-C (Y-Z) bonds due to the influence of the charge on any M atom directly through space on any Y and Z.     

Response to “About acceptance and rejection zones”

Desimoni and Brunetti raise some questions about the use of Eurachem/CITAC guide, because the Eurachem/CITAC guide does not discuss an ISO recommendation before performing a test, it should be decided whether it is to be a test for conformity or a test for non-conformity. In response, it is pointed out that although this recommendation is not discussed explicitly, it is of necessity covered by the decision rule that describes how the measurement uncertainty will be taken into consideration with regard to accepting or rejecting a product according to its specification and the result of a measurement. In addition, they propose the introduction of an ‘inconclusive’ zone. We do not think that this is necessary, since the Eurachem/CITAC guide takes the view that action on rejection should be covered by the ‘decision rule’ and this can make equivalent provision for confirmation or interpretation.