Comment on: "Disentangling density and temperature effects in the viscous slowing down of glass forming liquids" [J. Chem. Phys. 120, 6135 (2004)

Recently, Tarjus et al. [G. Tarjus, D. Kivelson, S. Mossa, and C. Alba-Simionesco, J. Chem. Phys. 120, 6135 (2004)] concluded from a review of data for a variety of glass formers that the supercooled dynamics are almost invariably dominated by temperature T, rather than by density rho. By including additional published data into such a compilation, we show that for van der Waals molecular liquids, the dynamics near T(g) are in fact governed as much by density as by temperature. Moreover, relaxation times measured at various temperatures and pressures can be superimposed by plotting as a function rho(gamma)/T. This scaling form can arise from an assumed inverse power law for the intermolecular repulsive potential, with gamma a material constant. (c) 2004 American Institute of Physics.     

Molecular dynamics investigation of a density-driven glass transition in a liquid crystal system

Molecular dynamics simulations are carried out to address the density-driven glass transition in a system of rodlike particles that interact with the Gay-Berne potential. Since crystallization occurs in this system on the time scale of the simulations, direct simulation of the glass transition is not possible. Instead, glasses with isotropic orientational order are heated to a temperature T, and the relaxation times by which nematic orientational order develops are determined. These relaxation times appear to diverge at a critical density rho(c); i.e., the system can equilibrate at rhorho(c) (at the temperature T). The relaxation times follow a power-law scaling as the critical density is approached, suggesting that this density-driven glass transition concurs with mode coupling theory.     

A study of the decay of atoms in chlorine plasma on aluminum films

The possibility of using the relaxation technique for monitoring the time dependence of the number density of chlorine atoms in a discharge in the presence of aluminum specimens was shown. The decay kinetics of chlorine atoms on aluminum was studied in detail, and it was shown that the mechanism of the decay of chlorine atoms follows the first-order rate law in their concentration. The probability of the decay of chlorine atoms on aluminum immediately in the plasma zone was experimentally measured (γ = 9.3 × 10⁻³); its value is three times that known from the literature for the afterglow region.     

Thermodynamic scaling of diffusion in supercooled Lennard-Jones liquids

The manner in which the intermolecular potential u(r) governs structural relaxation in liquids is a long standing problem in condensed matter physics. Herein, we show, in agreement with recent experimental results, that diffusion coefficients for simulated Lennard-Jones m-6 liquids (8 < or = m < or = 36) in normal and moderately supercooled states are a unique function of the variable rhogamma/T, where rho is density and T is temperature. The scaling exponent gamma is a material specific constant whose magnitude is related to the steepness of the repulsive part of u(r), evaluated around the distance of closest approach between particles probed in the supercooled regime. Approximations of u(r) in terms of inverse power laws are also discussed.     

Reactions of organochlorosilanes with chloro-and organogermanes in the presence of aluminum chloride

The effect of substituents at the silicon and germanium atoms in reactions of organochlorosilanes with chloro-and organogermanes in the presence of aluminum chloride was studied. The only occurring process is the exchange of the chlorine atoms at Ge for the phenyl groups from Si; an increase in the number of methyl groups or chlorine atoms at Si promotes formation of phenyltrichlorogermane, and an increase in the number of phenyl groups or replacement of the chlorine atom at the Si atom by hydrogen leads to the formation of di-and triphenylchlorogermanes. Neither phenyl nor other radicals are transferred back from Ge to Si in the course of reactions of phenylgermanes with methylchlorosilanes in the presence of aluminum chloride; the only occurring processes are the exchange of the phenyl or methyl radicals bonded to Ge for the Cl atom bonded to Al and the disproportionation of phenylchlorogermanes.     

Atomic correlation energy from the electron density at the nucleus

Ground-state atomic correlation energies, and their kinetic energy and potential energy components, are shown to be well-represented by empirical formulas of the form CNrho(0)Z(-gamma), where C and gamma are constants that are largely invariant within various sets of atoms and positive ions, Z is the atomic number, N is the number of electrons, and rho(0) is the electron density at the nucleus. Results are given for neutral atoms, singly charged positive ions, and many isoelectronic series-315 atomic species in all.     

Features of Sulfonation of Polychlorinated Biphenyl Congeners

Sulfonation of polychlorinated biphenyls (PCBs) and their commercial mixture (Trichlorobiphenyl) with oleum has been studied. General sulfonation patterns have been revealed for PCB congeners having no substituents in the ortho positions. The sulfonation of PCBs with chlorine atoms in only one aromatic ring gives exclusively the corresponding polychlorobiphenylmonosulfonic acids. The sulfonation of PCBs with chlorine atoms in both aromatic rings is accompanied by side formation of polychlorodibenzothiophene S,S-dioxides.     

Beiträge zur Chemie der Pyrrolpigmente, 31. Mitt.: Die Spin-Gitter-Relaxation in den1H-NMR-Spektren von Bilatrienen-abc

The¹H-NMR spin lattice relaxation times of aetiobiliverdin-IV- and biliverdindimethylester were determined using the inversion recovery technique. The relaxation times of protons attached to the terminal rings A and D are longer than those situated at the rings B and C which points to a higher mobility of rings A and D. Moreover these measurements allowed an independent assignment of the¹H-NMR-signals of the methyl groups of biliverdindimethylester.

30. Mitt.:H. Falk undT. Schlederer, Ann. Chem., im Druck.     

Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids

Viscosities eta and their temperature T and volume V dependences are reported for seven molecular liquids and polymers. In combination with literature viscosity data for five other liquids, we show that the superpositioning of relaxation times for various glass-forming materials when expressed as a function of TV(gamma), where the exponent gamma is a material constant, can be extended to the viscosity. The latter is usually measured to higher temperatures than the corresponding relaxation times, demonstrating the validity of the thermodynamic scaling throughout the supercooled and higher T regimes. The value of gamma for a given liquid principally reflects the magnitude of the intermolecular forces (e.g., steepness of the repulsive potential); thus, we find decreasing gamma in going from van der Waals fluids to ionic liquids. For some strongly H-bonded materials, such as low molecular weight polypropylene glycol and water, the superpositioning fails, due to the nontrivial change of chemical structure (degree of H bonding) with thermodynamic conditions.     

How do the substituents affect and regulate the relative retention times of polychlorinated biphenyls during gas chromatography?

The effects and regulatory actions of the polychlorinated biphenyls (PCBs) substituent characteristics on their relative retention times (RRTs) during gas chromatography were analyzed based on known experimental RRTs of 209 PCB congeners and biphenyl; the substituent characteristics used for this analysis included the total amount of substituents, the similarity between two phenyl rings in a single PCB congener, the substituents distribution in single phenyl ring, the main/second‐order interactions effects at each position, and the combined effect of two phenyl rings. At last, the universality of regulation was validated on other experimental conditions. Among them, the full factorial experimental design included 10 factors correlated with each substituent position and two levels (0, 1) were initially applied to the domains of the substituent characteristics. The obtained results have revealed that increasing the total amount of substituents can increase the RRTs of PCBs linearly, but similarities between the two rings cannot control the RRTs effectively. Meanwhile, the more compact the substituent distributions on a single phenyl ring are, the bigger the RRTs of PCBs are. Based on a full factorial experimental design, the overall important trend for each position is as follows: para > meta > ortho and the main regulatory substituents for the second‐order interaction effects are distributed in the same phenyl ring in the following sequence: N_o > N_m > N_p. The congener with two perpendicular phenyl rings exhibits a milder combined effect on RRTs and smaller RRT relatively. The regulation has a good universality among different experimental conditions, revealing the dominant effect of substituent characteristics on RRTs of PCBs. Copyright © 2015 John Wiley & Sons, Ltd.     

Dipole relaxation, intramolecular mobility, and molecular self-organization in solutions of alternating polymers with phenylazomethine and siloxane fragments

Dielectric relaxation in solutions of polyesters containing flexible siloxane and rigid phenylazomethine fragments of various structures is studied. For these polymers in solution, five relaxation processes that reflect the mobility of certain portions of the macrochain are observed. The kinetic rigidity of the macrochain increases with increasing length of the siloxane spacer. This trend is associated with rearrangement of the electronic structure of silicon atoms and phenyl rings and with ordering of rigid phenylazomethine fragments.     

Hydrogen nuclear spin relaxation in hydrogen-ice clathrate

H2 in D2O ice clathrate has been studied by hydrogen NMR. In a previous report, the H2 line shape was shown to be due to incompletely averaged intramolecular dipolar interactions. Here the relaxation times T1, T1rho, and T2 are reported. T1 passes through a minimum at 10 K, indicating that the rotational transition rate Gamma between the three sublevels of J = 1 passes through the resonance frequency at this temperature. On the cold side, T1 varies as T(-2.6); on the hot side, the rate T1(-1) varies as T(-2) plus a constant (due to paramagnetic impurities). These indicate a two-phonon process drives the rotational transitions Gamma. The spin-echo T2 is nearly independent of temperature and in reasonable agreement with the Van Vleck intermolecular H2-H2 second moment. T1rho deviates from the expected T1rho = T1 behavior above 85 K, revealing an additional slow-motion source of relaxation. The deviation is driven by the hopping of H2 between large cages. Ortho-para conversion is measured to be much slower in the clathrate than in the bulk solid, reflecting the greater distances between the H2 molecules.     

Correlation between electron capture negative chemical ionization mass spectrometric fragmentation and calculated internal energies for polychlorinated biphenyls

Correlationbse tween molecular structure and fragmentation observed in electron capture negative chemical ionization mass spectra (moderator gas = methane) of 49 selected tetrachlorinated, pentachlorinated, and hexachlorinated biphenyls have been investigated by using molecular modeling. The semiempirical general molecular orbital program MOPAC was used to calculate molecular properties for biphenyl and the 209 polychlorinated biphenyls. The mass spectrometric ionization and fragmentation processes were found to be linked to the number of chlorine atoms present on the biphenyl, and to the number of those chlorine atoms in the ortho (2, 2′, 6, and 6′) positions. The intensity of molecular ions increased with the number of chlorine atoms present, but this was counteracted by enhanced fragmentation as the number of ortho position chlorine atoms increased. The molecular parameters that were most closely linked with the number of ortho chlorine atoms were the twist angle between the phenyl rings and the energy of the lowest unoccupied molecular orbital (LUMO). It is suggested that fragmentation occurs when the energy of the ionizing electron exceeds the energy difference between the LUMO and LlJMO + 1 orbitals.     

Approximate scaling properties of the density functional theory Tc for atoms

Revealed are scaling properties for T(c)[rho], the kinetic-energy component of the correlation energy density functional for atoms, in terms of the total number of electrons N, the nuclear charge Z, and the total electron density at the nucleus rho(0). T(c) scales well as Nrho(0)/Z(8/3) for both neutral atoms up to Z=18 and the four-electron Be-like cationic species. A model is given that describes these findings, involving a density encoding the cusp information and an effective potential going like r(-4/3).     

Theoretical electron density distributions for Fe- and Cu-sulfide earth materials: a connection between bond length, bond critical point properties, local energy densities, and bonded interactions

Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, rho(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, rho(rc), the Laplacian, triangle down2rho(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of rho(rc) and triangle down2rho(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of rho(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the high-spin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the rho(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides.     

Density scaling and relaxation of the Pauli principle

The relaxation of the Pauli principle associated with density scaling is examined. Scaling the density has been investigated in the development of density functional computational methods with higher accuracy. Scaling the density by rho(r)(zeta)=rho(r)zeta reduces the number of electrons to M=Nzeta when zeta>1. The minimum kinetic energy of the scaled density, T(s)[rhozeta], can be scaled back to the N-electron system by multiplying the M-electron Kohn-Sham-type occupation numbers by zeta to produce T(zeta)[rho]. This relaxes the Pauli principle when the orbital occupation numbers are greater than 1 in the N-electron system. The effects of antisymmetry on solutions to the Kohn-Sham equations are examined for Ne and the Be isoelectronic series. The changes in T(zeta)[rho] and the exchange energy E(xzeta)[rho] when zeta is varied show that these two quantities are inextricably linked.     

Synthesis of new haloderivatives of benzo[<Emphasis Type="Italic">f</Emphasis>]quinoline and 4,7-phenanthroline

By condensations of 2-naphthylamine and 6-aminoquinoline with halogen-substituted benzaldehydes, 3-acetylpyridine and acetophenone derivatives new 1,3-diaryl(heteryl)benzo-[f]quinolines and 4,7-phenanthrolines were synthesized containing atoms of fluorine, bromine, and chlorine in the phenyl rings.     

Electron density distributions calculated for the nickel sulfides millerite, vaesite, and heazlewoodite and nickel metal: a case for the importance of ni-ni bond paths for electron transport

Bond paths and the bond critical point properties (the electron density (rho) and the Hessian of rho at the bond critical points (bcp's)) have been calculated for the bonded interactions comprising the nickel sulfide minerals millerite, NiS, vaesite, NiS(2), and heazlewoodite, Ni(3)S(2), and Ni metal. The experimental Ni-S bond lengths decrease linearly as the magnitudes of the properties each increases in value. Bond paths exist between the Ni atoms in heazlewoodite and millerite for the Ni-Ni separations that match the shortest separation in Ni metal, an indicator that the Ni atoms are bonded. The bcp properties of the bonded interactions in Ni metal are virtually the same as those in heazlewoodite and millerite. Ni-Ni bond paths are absent in vaesite where the Ni-Ni separations are 60% greater than those in Ni metal. The bcp properties for the Ni-Ni bonded interactions scatter along protractions of the Ni-S bond length-bcp property trends, suggesting that the two bonded interactions have similar characteristics. Ni-Ni bond paths radiate throughout Ni metal and the metallic heazlewoodite structures as continuous networks whereas the Ni-Ni paths in millerite, a p,d-metal displaying ionic and covalent features, are restricted to isolated Ni(3) rings. Electron transport in Ni metal and heazlewoodite is pictured as occurring along the bond paths, which behave as networks of atomic size wires that radiate in a contiguous circuit throughout the two structures. Unlike heazlewoodite, the electron transport in millerite is pictured as involving a cooperative hopping of the d-orbital electrons from the Ni(3) rings comprising Ni(3)S(9) clusters to Ni(3) rings in adjacent clusters via the p-orbitals on the interconnecting S atoms. Vaesite, an insulator at low temperatures and a doped semiconductor at higher temperatures, lacks Ni-Ni bond paths. The net charges conferred on the Ni and S atoms are about a quarter of their nominal charges for the atoms in millerite and vaesite with the net charge on Ni increasing with increasing Ni-S bond length. Reduced net charges are observed on the Ni atoms in heazlewoodite and are related to its Ni-Ni metal bonded interactions and to the greater covalent character of its bonds. Local energy density and bond critical point properties of the electron density distributions indicate that the Ni-S and Ni-Ni bonded interactions are intermediate in character between ionic and covalent.     

1H and 13C nmr studies of salicylalanilines

Several substituted salicylanilines (I) are studied by ¹H (chemical shifts) and ¹³C (chemical shifts and T₁ relaxation times) NMR in order to obtain information on molecular geometry changes and the transmission of the electronic effects due to substituents, as well as on the relative rates of the overall molecular tumbling and of the flipping of the phenyl rings. In particular, a good linear correlation of the OH proton shifts (affected by intramolecular hydrogen bonding) with Hammett's σ constants for p-substitution in the aniline moiety is found. Changes in rigidity of the rings expected as a result of the OH...N interaction and of p-substitution are reflected on the phenyl carbon relaxation times.