The synthesis system for mesophase formation, using the diprotic anionic surfactant N‐myristoyl‐L ‐glutamic acid (C14GluA) as the structure‐directing agent (SDA) and N‐trimethoxylsilylpropyl‐N,N,N‐trimethylammonium chloride (TMAPS) as the co‐structure‐directing agent (CSDA), has been investigated and a full‐scaled synthesis‐field diagram is presented. In this system we have obtained mesophases including three‐dimensional (3D) micellar cubic Fmm, Pmn, Fdm, micellar tetragonal P42/mnm, two‐dimensional (2D) hexagonal p6mm and bicontinuous cubic Pnm, by varying the C14GluA/NaOH/TMAPS composition ratios. From the diagram it can be concluded that the mesophase formation is affected to a high degree by the organic/inorganic‐interface curvature and the mesocage–mesocage electrostatic interaction. Bicontinuous cubic and 2D‐hexagonal phases were found in the low organic/inorganic‐interface curvature zones, whereas micellar cubic and tetragonal mesophases were found in the high organic/inorganic‐interface curvature zones. Formation of cubic Fmm and tetragonal P42/mnm was favoured in highly alkaline zones with strong mesocage–mesocage interactions, and formation of cubic Pmn and Fdm was favoured with moderate mesocage–mesocage interactions in the less alkaline zones of the diagram. 相似文献
The effect of a layer of electrochemically grafted 4‐diazo‐N,N‐diethylaniline (DEA) groups on the electron transfer kinetics of redox systems, displaying fast and slow heterogeneous electron transfer rate constants at edge and basal planes of carbon, was investigated. The properties of the modified electrode were characterized by cyclic voltammetry using four different inorganic redox systems (Fe(CN) , Co(phen) , Ru(NH3) , and IrCl in acidic, neutral, and basic media. Two distinct blocking behaviors and electrostatic effects were observed. More precisely, a strong blocking effect of the grafted layer on Fe(CN) and Co(phen) was found, whereas Ru(NH3) and IrCl showed to be rather unaffected by the presence of the DEA grafted layer. 相似文献
Thermodynamic parameters obtained from studying the micellization of amphiphilic p‐sulfonatocalix[n]arenes were correlated with the alkyl chain length and with the number of monomeric units (n) in the calix[n]arene structure. The micellization Gibbs free energy (Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) becomes more negative upon increasing the alkyl chain length of the p‐sulfonatocalix[4]arene. This is in agreement with the trend generally observed for other surfactants. However, the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ value for transferring one CH2 group from the bulk aqueous medium to the micelle [Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH2)] is lower than the value generally observed for single‐chain surfactants, suggesting the existence of intramolecular interactions between the alkyl chains of the free unimers. On the other hand, the critical micelle concentration (cmc; per alkyl chain unit) increased with the increasing number of monomeric units. These results are explained on the basis of the conformation adopted by the calixarene in the bulk solution. The calix[4]arene derivatives are preorganized into the cone conformation, which is favorable for the formation of globular aggregates. The calix[6]arene and calix[8]arene derivatives do not adopt cone conformations. Changing these conformations to the more favorable cone conformer in the aggregates implies an energetic cost that contributes to making Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ less efficient. In the case of the calix[6]arene derivative this energetic cost is enthalpic, whereas in the case of the octamer it is both enthalpic and entropic. Both the Δ${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ (CH2) value and the change in heat capacity (ΔC${{\rm p}{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ ) seem to indicate that for the cone calix[4]arene derivatives all alkyl chains are solvated by the same hydration shell, whereas in the case of the highly flexible calix[8]arene derivative each alkyl chain is individually hydrated. 相似文献
Deviations from statistical binding, that is cooperativity, in self‐assembled polynuclear complexes partly result from intermetallic interactions ΔEM,M, whose magnitudes in solution depend on a balance between electrostatic repulsion and solvation energies. These two factors have been reconciled in a simple point‐charge model, which suggests severe and counter‐intuitive deviations from predictions based solely on the Coulomb law when considering the variation of ΔEM,M with metallic charge and intermetallic separation in linear polynuclear helicates. To demonstrate this intriguing behaviour, the ten microscopic interactions that define the thermodynamic formation constants of some twenty‐nine homometallic and heterometallic polynuclear triple‐stranded helicates obtained from the coordination of the segmental ligands L1 – L11 with Zn2+ (a spherical d‐block cation) and Lu3+ (a spherical 4f‐block cation), have been extracted by using the site binding model. As predicted, but in contrast with the simplistic coulombic approach, the apparent intramolecular intermetallic interactions in solution are found to be i) more repulsive at long distance ( > ), ii) of larger magnitude when Zn2+ replaces Lu3+ ( > ) and iii) attractive between two triply charged cations held at some specific distance ( <0). The consequences of these trends are discussed for the design of polynuclear complexes in solution. 相似文献
Pressure broadening and pressure shift of N2H+ rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions ${j = 3 \leftarrow 2}$ , ${4 \leftarrow 3}$ , ${5 \leftarrow 4}$ and ${6 \leftarrow 5}$ with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state‐to‐state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.相似文献
The sodium–sulfur (NAS) battery is a candidate for energy storage and load leveling in power systems, by using the reversible reduction of elemental sulfur by sodium metal to give a liquid mixture of polysulfides (Na2Sn) at approximately 320 °C. We investigated a large number of reactions possibly occurring in such sodium polysulfide melts by using density functional calculations at the G3X(MP2)/B3LYP/6‐31+G(2df,p) level of theory including polarizable continuum model (PCM) corrections for two polarizable phases, to obtain geometric and, for the first time, thermodynamic data for the liquid sodium–sulfur system. Novel reaction sequences for the electrochemical reduction of elemental sulfur are proposed on the basis of their Gibbs reaction energies. We suggest that the primary reduction product of S8 is the radical anion ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ , which decomposes at the operating temperature of NAS batteries exergonically to the radicals ${{\rm S}{{{{\bullet}}- \hfill \atop 2\hfill}}}$ and ${{\rm S}{{{{\bullet}}- \hfill \atop 3\hfill}}}$ together with the neutral species S6 and S5, respectively. In addition, ${{\rm S}{{{{\bullet}}- \hfill \atop 8\hfill}}}$ is predicted to disproportionate exergonically to S8 and ${{\rm S}{{2- \hfill \atop 8\hfill}}}$ followed by the dissociation of the latter into two ${{\rm S}{{{{\bullet}}- \hfill \atop 4\hfill}}}$ radical ions. By recombination reactions of these radicals various polysulfide dianions can in principle be formed. However, polysulfide dianions larger than ${{\rm S}{{2- \hfill \atop 4\hfill}}}$ are thermally unstable at 320 °C and smaller dianions as well as radical monoanions dominate in Na2Sn (n=2–5) melts instead. The reverse reactions are predicted to take place when the NAS battery is charged. We show that ion pairs of the types ${{\rm NaS}{{{{\bullet}}\hfill \atop 2\hfill}}}$ , ${{\rm NaS}{{- \hfill \atop n\hfill}}}$ , and Na2Sn can be expected at least for n=2 and 3 in NAS batteries, but are unlikely in aqueous sodium polysulfide except at high concentrations. The structures of such radicals and anions with up to nine sulfur atoms are reported, because they are predicted to play a key role in the electrochemical reduction process. A large number of isomerization, disproportionation, and sulfurization reactions of polysulfide mono‐ and dianions have been investigated in the gas phase and in a polarizable continuum, and numerous reaction enthalpies as well as Gibbs energies are reported. 相似文献
2,4‐Trifluoromethylquinoline (TFMAQ) derivatives that have amine ( 1 ), methylamine ( 2 ), phenylamine ( 3 ), and dimethylamine ( 4 ) substituents at the 7‐position of the quinoline ring were prepared and crystallized. Six crystals including the crystal polymorphs of 2 (crystal GB and YG) and 3 (crystal B and G) were obtained and characterized by X‐ray crystallography. In solution, TFMAQ derivatives emitted relatively strong fluorescence (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =418–469 nm and Φf(s)=0.23–0.60) depending on the solvent polarity. From Lippert–Mataga plots, Δμ values in the range of 7.8–14 D were obtained. In the crystalline state, TFMAQ derivatives emitted at longer wavelengths (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464–530 nm) with lower intensity (Φf(c)=0.01–0.28) than those in n‐hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =470 and 530 nm with Φf(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464 and 506 nm with Φf(c)=0.28 and approximately 0.28 for crystal B and G, respectively. In both crystal polymorphs of 2 and 3 , crystals GB and G showed emission color changes by heating/melting/cooling cycles that were representative. By following the color changes in heating at the temperature below the melting point with X‐ray diffraction measurements and X‐ray crystallography, the single‐crystal‐to‐single‐crystal transformations from crystal GB to YG for 2 and from crystal B to G for 3 were revealed. 相似文献
Broken‐symmetry DFT calculations on transition‐metal clusters with more than two centers allow the hyperfine coupling constants to be extracted. Application of the proposed theoretical scheme to a tetranuclear manganese complex that models the S2 state of the oxygen‐evolving complex of photosystem II yields hyperfine parameters that can be directly compared with experimental data. The picture shows the metal–oxo core of the model and the following parameters; exchange coupling constant Jij, the expectation value of the site‐spin operator , and the isotropic hyperfine coupling parameters.
The interaction between alkyl radicals and graphene was studied by means of dispersion‐corrected density functional theory. The results indicate that isolated alkyl radicals are not likely to be attached onto perfect graphene. It was found that the covalent binding energies are low, and because of the large entropic contribution, Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ is positive for methyl, ethyl, isopropyl, and tert‐butyl radicals. Although the alkylation may proceed by moderate heating, the desorption barriers are low. For the removal of the methyl and tert‐butyl radicals covalently bonded to graphene, 15.3 and 2.4 kcal mol?1 are needed, respectively. When alkyl radicals are agglomerated, the binding energies are increased. For the addition in the ortho position and on opposite sides of the sheet, the graphene–CH3 binding energy is increased by 20 kcal mol?1, whereas for the para addition on the same side of the sheet, the increment is 9.4 kcal mol?1. In both cases, the agglomeration turns the Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ <0. For the ethyl radical, the ortho addition on opposite sides of the sheet has a negative Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ , whereas for isopropyl and tert‐butyl radicals the reactions are endergonic. The attachment of the four alkyl radicals under consideration onto the zigzag edges is exergonic. The noncovalent adsorption energies computed for ethyl, isopropyl, and tert‐butyl radicals are significantly larger than the graphene–alkyl‐radical covalent binding energies. Thus, physisorption is favored over chemisorption. As for the Δ${G{{{\ominus}\hfill \atop 298\hfill}}}$ for the adsorption of isolated alkyl radicals, only the tert‐butyl radical is likely to be exergonic. For the phenalenyl radical we were not able to locate a local minimum for the chemisorbed structure since it moves to the physisorbed structure. An important conclusion of this work is that the consideration of entropic effects is essential to investigate the interaction between graphene and free radicals. 相似文献
The photopolymerization of methyl, ethyl, butyl, and hexyl methacrylates in solution was studied. The effect of initial initiator and monomer concentrations on the time evolution of polymer concentration, , and PDI was examined. The reversible chain addition and β‐scission, and primary radical termination steps were included in the mechanism along with the classical steps. The rate equations were derived using continuous distribution kinetics and solved numerically to fit the experimental data. The regressed rate coefficients compared well with the literature data. The model predicted the instantaneous increase in and PDI to steady state values. The rate coefficients exhibited a linear increase with the size of alkyl chain of the alkyl methacrylates.
