Energies of OH⋯X− hydrogen bonds in the gas phase and proton affinities

The energies of hydrogen-bond formation (−ΔH⁰_HX) between hydroxy derivatives and halide ions in the gas phase obey the following relationship: −ΔH⁰_HX = 0 (ΔPA > 0)+32 e^{−0.0156&mid;ΔPA&mid;}, or −ΔH⁰_HX = −ΔPA (ΔPA < 0) + 32 e^{−0.0156∣ΔPA∣}, where ΔPA is the difference between the heterolytic dissociation energy of the -OH and HX bonds. This relation is discussed as a function of the different factors (electrostatic, repulsion, polarization and charge transfer) contributing to the protonation reaction or hydrogen-bond formation.     

Géométrie de l'intermittence en turbulence développée

A geometrical interpretation of intermittency in fully developed turbulence is realized through an hierarchy of fractal structures Ω_p of dimensions Δ_p linked each other by the relations Ω_{p + 1} − Ω_p (i.e. Δ_{p + 1} < Δ_p) and γ = (Δ_{p + 1} − Δ_∞)/(Δ_p − Δ_∞) with γ = ((1 + 3/√8)^1/3 + (1 − 3/√8)^1/3)³ and Δ_∞ = 1 and Δ_∞ = 1. This is obtained by the introduction of an entropy jump, defined at the scale r, ΔS_p(r) = (Δ_{p + 1} − Δ_p) ln (r/r₀) characterizing the order level of each sub-structure Ω_p and verifying a linear relation ΔS_p(r) = γ ΔS_{p − 1}(r).     

Halon thermochemistry: Ab initio calculations of the enthalpies of formation of fluoroethanes

The ab initio G2, G2(MP2), CBS-4 and CBS-Q quantum mechanical protocols and the parameterized BAC-MP4 procedure were used to calculate the enthalpies of formation (Δ_fH⁰) of ethane and the complete series of fluoroethanes, C₂H_xF_6−x, x = 0−5. Results from all methods exhibited significant negative deviations from experiment. With the exception of the CBS-4 and BAC-MP4 procedures, the negative errors in the calculated enthalpies were observed to be linearly dependent upon the number of CF bonds in the molecule. Application of a bond additivity correction (BAC) parameter, Δ_CF, derived in an earlier investigation of fluoro- and chlorofluoromethanes, removed some although not all of the systematic deviations. Introduction of a heavy atom interaction parameter, representing the effect of an attached carbon on the CF bond error, yielded corrected enthalpies which agree with experiment to within the reported uncertainties. The BAC-MP4 method, which has already been parameterized with generalized BACs, yields calculated enthalpies which average approximately 10 kJ mol⁻¹ below the experimental values of Δ_fH⁰ in the fluoroethanes.     

Gas-phase ion equilibria studies of protons and chloride ions in propanol and acetone

The gas-phase clustering reactions of proton in propanol and acetone, and chloride ions in acetone were investigated. The −ΔH_n−1,n values obtained for clustering reactions (n−1,n) were as follows: H⁺ (C₃H₇OH)_n−1 + C₃H₇OH ⇄ H⁺ (C₃H₇OH)_n, (2, 3) 18.9 kcal mol⁻¹, (3, 4) 14.2 kcal mol⁻¹, (4, 5) 11.7 kcal mol⁻¹; H⁺ (CH₃COCH₃)₂ + CH₃COCH₃ ⇄ H⁺ (CH₃COCH₃)₃, 14.2 kcal mol⁻¹; and Cl⁻ + CH₃COCH₃ ⇄ Cl⁻ (CH₃COCH₃), 12.4 kcal mol.⁻¹. For clustering reactions, Cl⁻ (CH₃COCH_3n−1 + CH₃COCH₃ ⇄ Cl⁻ (CH₃COCH₃)_n where n ≥ 2, the equilibria could not be established; probably due to the isomerization of ligand acetone molecules from the keto to enol form.     

Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

A multi-channel sensor based on 8-hydroxyquinoline ferrocenoate for probing Hg(II) ion

A new sensing molecule 8-hydroxyquinoline ferrocenoate (Fc-Q) which combines ferrocene and 8-hydroxyquinoline moieties was synthesized and applied as a multi-channel sensor for the detection of Hg²⁺ ion. Fc-Q can coordinate with Hg²⁺ to give colorimetric, fluorescent and electrochemical responses. Upon complexation with Hg²⁺ ion, the characteristic absorption peak is red-shifted (Δλ = 45 nm), the fluorescent intensity is quenched at 303 nm, and the oxidation peak is cathodic shifted (ΔE_1/2 = −149 mV). Quantitatively analyzed Hg²⁺ ions at the range of ppb level could be achieved by electrochemical response. For the practical application of sensing Hg²⁺ in real world water, Fc-Q modified screen-printed carbon electrodes were obtained for facile, sensitive, and on-site analysis of Hg²⁺.     

Enthalpy and entropy of transfer of hydrogen ion from water to mixed solvents

Attempts have been made to determine the enthalpy and entropy of transfer of H⁺ ion from water to mixed solvents using the calorimetric data of earlier experiments. The results are in qualitative agreement with the facts that ΔH _t ⁰ (H⁺) passes through an exothermic maximum andTΔS _t ⁰ passes through a minimum at about 20 to 30 wt% of organic solvent indicating the initial structure formation and the ultimate breakdown of the solvent structure with the addition of organic solvent.     

Thermodynamic properties of potassium metasilicate (K2SiO3)

The standard enthalpy of formation of potassium metasilicate (K₂SiO₃), determined by hydrofluoric acid solution calorimetry, was found to be ΔH^o_f,298 = −363.866±0.421 kcal mol⁻¹ (−1522.415±1.762 kj mol⁻¹). The standard enthalpy of formation from the oxides was found to beΔH^o₂₉₈ = −64.786±0.559 kcal mol⁻¹ (−271.065±2.339 kJ mol⁻¹).These experimentally determined data were combined with data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the literature data. The standard enthalpies of formation and Gibbs energies of formation are given as functions of temperature. The standard Gibbs energy of formation is ΔG_f,298.15⁰ = −341.705 kcal mol⁻¹ (−1429.694 kJ mol⁻¹).     

Studies on the adsorption of peptides of glycine/alanine on montmorillonite clay with or without co-ordinated divalent cations

The adsorption of simple peptides of glycine/alanine from their aqueous solutions onto montmorillonite, Ca²⁺ and Mg²⁺ exchanged montmorillonite clay studied UV spectrophotometrically at constant pH 7.02 and temperature 23 °C. The percent binding of Gly², Gly³, Gly⁴ and Gly-ala is calculated in terms of their optical density. The adsorption parameters, i.e. X_m and K_L have been calculated from Langmuir adsorption isotherm. Similar adsorption behaviour was observed with or without divalent cation exchanged adsorbent, but the percent binding and monolayer capacity appear to depend on the molecular weight, i.e. number of aliphatic carbon atoms of the adsorbates. The adsorption was significantly affected by the concentration of peptide, pH and temperature of the system. Equilibrium constant (K) and the free energies of adsorption (−ΔG) were determined from the isotherm measured under static conditions. Tetra glycine (Gly⁴) has positive −ΔG and K>1 showing greater adsorptibility, whereas for other peptides, −ΔG values were negative and K<1, thus showing very weak adsorption. A linear dependence of −ΔG on the number of aliphatic carbon atoms (n_c) from Gly² to Gly⁴ in adsorbate molecule was found. Thermodynamic data strongly support the quantitative data obtained from Langmuir adsorption isotherm. Ca²⁺ montmorillonite exhibited relatively better adsorption as compared to Mg²⁺ exchanged form or montmorillonite without Ca²⁺ or Mg²⁺. Results have shown that clay minerals might have played a significant role in prebiotic formation of proteins via adsorption of simple bio-oligomers on their surface.     

Enthalpy of formation and magnetic susceptibility of californium sesquioxide,Cf2O3

The enthalpy of formation of cubic (b.c.c., a₀ = 1.0839 ± 0.0004 nm) Cf₂O₃, Δ_fH° (298 K), has been determined to be −1652.6 ± 10.3kJ mol⁻¹ by solution microcalorimetry. The magnetic susceptibilities of two samples have been measured between 1.5 and 300 K. Cf₂O₃ obeys the Curie-Weiss law between 90 and 300 K with _eff = 9.7 ± 0.2 μ_B and gq = −80 ± 10 K.     

High resolution Fourier transform spectroscopy of the PbO molecule from investigation of the O2(1Δg)—Pb reaction

From the reaction of Pb with metastable oxygen O₂(¹Δ_g) in a Broida type oven we have analysed at high resolution some vibrational levels of the X0⁺, a1, A0⁺ and B1 states of the ²⁰⁸PbO molecule. The rotational parameters determined allowed us to recalculate the position of the various isotope lines to within 0.01 cm⁻¹. We have found a negative value of ω_eχ_e (−0.123 (25) cm⁻¹) in A0⁺, contrary to previous observations. The Ω type doubling in a1 varies from +1.8 × 10⁻⁴ cm⁻¹ (υ′ = 2) to +2.3 × 10⁻⁴ cm⁻¹ (υ′ = 9) and in B1 from −1.17 × 10⁻⁴ cm⁻¹ (υ′ = 0) to −0.97 × 10⁻⁴ cm⁻¹ (υ′ = 2).     

Volumes of activation for anion-diazonium ion recombination

Anion-cation recombination reactions between aryldiazonium ions and anionic nucleophiles have volumes of activation which are small or even negative against expectations of considerably positive values resulting from release of electrostricted solvent. Various interpretations of these results are considered.Volumes of activation for reactions: X-C₆H₄-N₂⁺ + Nu⁻ → X-C₆H₄-NN-Nu have been measured by high pressure stopped-flow kinetics. Values of (X, Nu⁻, solvent ΔV^≠/cm³ mol⁻¹, ) are: H,N₃⁻, water, +2.2; H, HSO₃⁻, water,−9.1; H,SO₃⁼,−8.9, water; p-NO₂, PhSO₂⁻, −1.7 water; p-OMe, p-nitrobenzoate, DMSO, −15; . None of the reactions show the large positive values expected for ion-neutralisations. Various interpretations are discussed.     

Thermochemistry of adducts of some bivalent transition metal bromides with aniline

The compounds [MBr₂(an)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); an = aniline) were synthesized and characterized by melting points, elemental analysis, thermal studies, and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and aniline in methanol, aqueous 1.2 M HCl or 25% (v/v) aqueous 1.2 M HCl in methanol were measured. The following thermochemical parameters for the adducts have been determined by thermochemical cycles: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds () and the enthalpies of formation of the adducts from the ions in the gaseous phase: M²⁺_(g) + Br⁻_(g) + an_(g) → [MBr₂(an)₂]_(g), (Δ_fiH°) have been estimated.     

Thermochemistry of adducts of some transition metals(II) bromides with pyridine N-oxide

The compounds [MBr₂(pyNO)_n] (where M: Mn, Fe, Co, Ni, Cu or Zn; pyNO is pyridine N-oxide and n=2, 3 or 6) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyNo in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-oxygen bonds () have been estimated.     

Ion association and solvation behavior of some alkali metal acetates in aqueous 2-butanol solutions at T = 298.15, 303.15 and 308.15 K

Molar conductance of lithium acetate, sodium acetate and potassium acetate were studied in aqueous 2-butanol solutions with an alcohol mass fraction (w₂) of 0.70, 0.80 and 0.90 at 298.15, 303.15 and 308.15 K. The conductance data were analyzed with the Fuoss conductance-concentration equation to evaluate the limiting molar conductances (Λ₀), association constants (K_A,c) and cosphere diameter (R) for ion-pair formation. Gibbs energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) for ion-association reaction were derived from the temperature dependence of K_A,c. Activation energy for ionic movement (ΔH^#) was derived from the temperature dependence of Λ₀. Based on the composition dependence of Walden products (Λ₀η₀) and different thermodynamic properties (ΔG⁰,ΔH⁰, ΔS⁰ and ΔH^#), the influence of the solvent composition on ion-association and solvation behavior of ions were discussed in terms of ion-solvent, ion-ion interactions and the structural changes in the mixed solvent media.     

Intense turquoise colors of apatite-type compounds with Mn5+ in tetrahedral coordination

The solid solutions of chlorapatite compounds Ba₅Mn_3−xV_xO₁₂Cl (x = 0–3.0) and Ba₅Mn_3−xP_xO₁₂Cl (x = 0–3.0) have been synthesized through solid state reactions and Pechini or sol–gel method using citric acid. The colors of the samples change from white (x = 3.0) through turquoise (x = 1.5) to dark green (x = 0) with increasing amount of manganese. Optical measurements reveal that the origin of the color is presumably a combination of d–d transitions of Mn⁵⁺ and cation-anion charge transfer from transition metals to oxygens. Near IR reflectance measurements indicate that synthesized compounds are promising materials for “cool pigments” applications. Magnetic measurements verify that manganese has two unpaired electrons and exhibits 5 + oxidation state. The IR spectra change systematically with sample compositions and the fingerprint region (700 cm⁻¹ to 1100 cm⁻¹) indicates characteristic bands belonging to (MnO₄)³⁻, (VO₄)³⁻ and (PO₄)³⁻ functional groups. Structure refinements using neutron data confirm that Mn⁵⁺, V⁵⁺ and P⁵⁺ cations occupy the tetrahedral sites in the apatite structure.     

Intensities of lines in the band a 1Δg (v′= 0) − X3Σ−g (v″ = 0) of 16O2 in absorption

Line-strengths in the band a¹Δ_g (v′= 0) − X³Σ⁻_g (v″ = 0) of gaseous ¹⁶O₂ in absorption near 7.9 × 10⁵ m⁻¹ have been remeasured in the laboratory under conditions of pressure less than 101,000 Pa and temperature near 300 K. The band-strength is estimated to be (2.1 ± 0.3) × 10⁻²⁶ m, and the coefficient for self-broadening of individual lines near the band centre is (10 ± 1) m⁻¹ bar⁻¹. No evidence of an underlying continuum was found.     

Localization of electrons and excitations

Electrons, electron holes, or excitations in finite or infinite ‘multimer systems’ may be localized or delocalized. In the theory of Hush, localization depends on the ratio Δ/λ (Δ/2 = coupling; λ = reorganization energy). The latter theory has been extended to the infinite system [S. Larsson, A. Klimkāns, Mol. Cryst. Liq. Cryst. 355 (2000) 217]. The metal/insulator transition often takes place abruptly as a function of Δ/λ. It is argued that localization in a system with un-filled bands cannot be determined on the basis of Mott–Hubbard U alone, but depends on the number of accessible valence states, reorganization energy λ and coupling Δ (=2t). In fact U = 0 does not necessarily imply delocalization. The analysis here shows that there are many different situations for an insulator to metal transition. Charge transfer in doped NiO is characterized by Ni²⁺ − Ni³⁺ exchange while charge transfer in pure NiO is characterized by a disproportionation 2Ni²⁺ → Ni⁺ + Ni³⁺. In spite of the great differences between these two cases, U has been applied without discrimination to both. The relevant localization parameters appear to be Δ and λ in the first case, with only two oxidation states, and U, Δ and λ in the second case with three oxidation states. The analysis is extended to insulator-metal transitions, giant magnetic resistance (GMR) and high T_c superconductivity (SC). λ and Δ can be determined quite accurately in quantum mechanical calculations involving only one and two monomers, respectively.     

Theoretical studies of halocarbene cycloaddition selectivities: A new interpretation of negative activation energies and entropy control of selectivity

Ab initio RHF calculations with the 3–21G basis set have been carried out on cycloadditions of CF₂ and CCl₂ with ethylene. Although π-complex intermediates are predicted for both reactions at this level, MP2/3-21G calculations imply that there are no complexes in reactions of CCl₂ or more reactive carbenes with ethylene or substituted alkenes. Nevertheless, negative activation energies can be observed, since ΔG reaches a maximum due to the increase in —TΔS for these bimolecular reactions. The apparent “entropy control” for reactive carbenes results from the rapid decrease in ΔH. As the reactivity of the alkene increases, the transition state shifts to an earlier point on the free energy surface, where —TΔS³ is lower, but ΔH³ is higher than for less reactive alkenes. Model potentials are developed for ΔH and —TΔS which reproduce experimental behavior, without the assumption of intermediates.     

Localization of cyclopropyl groups and alkenes within glycerophospholipids using gas-phase ion/ion chemistry

Shotgun lipid analysis using electrospray ionization tandem mass spectrometry (ESI-MS/MS) is a common approach for the identification and characterization of glycerophohspholipids GPs. ESI-MS/MS, with the aid of collision-induced dissociation (CID), enables the characterization of GP species at the headgroup and fatty acyl sum compositional levels. However, important structural features that are often present, such as carbon–carbon double bond(s) and cyclopropane ring(s), can be difficult to determine. Here, we report the use of gas-phase charge inversion reactions that, in combination with CID, allow for more detailed structural elucidation of GPs. CID of a singly deprotonated GP, [GP − H]⁻, generates FA anions, [FA − H]⁻. The fatty acid anions can then react with doubly charged cationic magnesium tris-phenanthroline complex, [Mg(Phen)₃]²⁺, to form charge inverted complex cations of the form [FA − H + MgPhen₂]⁺. CID of the complex generates product ion spectral patterns that allow for the identification of carbon–carbon double bond position(s) as well as the sites of cyclopropyl position(s) in unsaturated lipids. This approach to determining both double bond and cyclopropane positions is demonstrated with GPs for the first time using standards and is applied to lipids extracted from Escherichia coli.