We developed novel supramolecular gelators with simple molecular structures that could harden a broad range of solvents: aqueous solutions of a wide pH range, organic solvents, edible oil, biodiesel, and ionic liquids at gelation concentrations of 0.1-2 wt %. The supramolecular gelators were composed of a long hydrophobic tail, amino acids and gluconic acid, which were prepared by liquid-phase synthesis. Among seven types of the gelators synthesized, the gelators containing L-Val, L-Leu, and L-Ile exhibited high gelation ability to various solvents. These gelators were soluble in aqueous and organic solvents, and also in ionic liquids at high temperature. The gelation of these solvents was thermally reversible. The microscopic observations (TEM, SEM, and CLSM) and small-angle X-ray scattering (SAXS) measurements suggested that the gelator molecules self-assembled to form entangled nanofibers in a large variety of solvents, resulting in the gelation of these solvents. Molecular mechanics and density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers. Interestingly, the gelation of an ionic liquid by our gelator did not affect the ionic conductivity of the ionic liquid, which would provide an advantage to electrochemical applications.

The proximal heme axial ligand plays an important role in tuning the reactivity of oxoiron(IV) porphyrin π-cation radical species (compound I) in enzymatic and catalytic oxygenation reactions. To reveal the essence of the axial ligand effect on the reactivity, we investigated it from a thermodynamic viewpoint. Compound I model complexes, (TMP(+•))Fe(IV)O(L) (where TMP is 5,10,15,20-tetramesitylporphyrin and TMP(+•) is its π-cation radical), can be provided with altered reactivity by changing the identity of the axial ligand, but the reactivity is not correlated with spectroscopic data (ν(Fe═O), redox potential, and so on) of (TMP(+•))Fe(IV)O(L). Surprisingly, a clear correlation was found between the reactivity of (TMP(+•))Fe(IV)O(L) and the Fe(II)/Fe(III) redox potential of (TMP)Fe(III)L, the final reaction product. This suggests that the thermodynamic stability of (TMP)Fe(III)L is involved in the mechanism of the axial ligand effect. Axial ligand-exchange experiments and theoretical calculations demonstrate a linear free-energy relationship, in which the axial ligand modulates the reaction free energy by changing the thermodynamic stability of (TMP)Fe(III)(L) to a greater extent than (TMP(+•))Fe(IV)O(L). The linear free energy relationship could be found for a wide range of anionic axial ligands and for various types of reactions, such as epoxidation, demethylation, and hydrogen abstraction reactions. The essence of the axial ligand effect is neither the electron donor ability of the axial ligand nor the electron affinity of compound I, but the binding ability of the axial ligand (the stabilization by the axial ligand). An axial ligand that binds more strongly makes (TMP)Fe(III)(L) more stable and (TMP(+•))Fe(IV)O(L) more reactive. All results indicate that the axial ligand controls the reactivity of compound I (the stability of the transition state) by the stability of the ground state of the final reaction product and not by compound I itself.

Articles you may be interested inUnrestricted density functional theory based on the fragment molecular orbital method for the ground and excited state calculations of large systems Density functional theory with fractionally occupied frontier orbitals and the instabilities of the Kohn-Sham solutions for defining diradical transition states: Ring-opening reactions J. Chem. Phys. 111, 7705 (1999); 10.1063/1.480108Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit. III. Possibility of high-spin polymer Polyradicals comprised of m-phenylene-bridged organic radicals are well known as building blocks of organic ferromagnets, in which radical groups are connected with each other at the meta position in the benzene ring, and the parallel-spin configurations between radical sites are more stabilized than the antiparallel ones. Topological rules for spin alignments enable us to design organic high-spin dendrimers and polymers with the ferromagnetic ground states by linking various radical species through an m-phenylene unit. However, no systematic ab initio treatment of such spin dendrimers and magnetic polymers has been reported until now, though experimental studies on these materials have been performed extensively in the past ten years. As a first step to examine the possibilities of ferromagnetic dendrimers and polymers constructed of m-phenylene units with organic radicals, we report density functional and molecular orbital calculations of six m-phenylene biradical units with radical substituents and polycarbenes linked with an m-phenylene-type network. The relative stability between the spin states and spin density population are estimated by BLYP or B3LYP and Hartree-Fock calculations in order to clarify their utility for constructions of large spin denderimers and periodic magnetic polymers, which are final targets in this series of papers. It is shown that neutral polyradicals with an m-phenylene bridge are predicted as high-spin ground-state molecules by the computations, while m-phenylene-bridged ion-radical species formed by doping may have the low-spin ground states if zwitterionic configurations play significant roles to stabilize low-spin states. Ab initio computations also show an important role of conformations of polyradicals for stabilization of their high-spin states. The computational results are applied to molecular design of high-spin dendrimers and polymers. Implications of them are also discussed in relation to recent experimental results for high-spin organic molecules. d Standard geometries were assumed as CC and CH bond lengths and bond angles are 1.40 Å, 1.08 Å, and 120°, respectively. e J ab values by Eq. ͑11͒.

Discoveries of superconductivity of MgB 2 by Akimitsu et al. and high-T c cupurate superconductors by Bednorz and Muller have raised great interest for elucidation of the superconducting mechanism from both experimental and theoretical grounds. The transition temperature (T c ) was found to be 40 K for MgB 2 , while the very high-T c over 130 K was reported for doped copper oxides with layer structures. A crucial role of the electron-phonon (EP) interaction was pointed out as a common mechanism of the superconductivity of both materials. However, such high-T c superconductivity may indicate the possibility of cooperative mechanism of the EP interaction with others such as electron correlation (EC) and multiband (MB) effects discussed in part I (Int J Quantum Chem 1990, 37, 167) of this series. Here, as a continuation of part I, theoretical backgrounds are briefly described to select active orbital space for superconductivity and elucidate the nature of EP, EC, and MB effects for cooperative mechanisms. Next, molecular orbital calculations of Mg m B n and cagetype carbon cluster are carried out to elucidate contributions of the EP interaction using McMillan equation. The relative contributions of the EP and EC interactions are also discussed in relation to the screening of the Coulomb repulsion. Pair binding energies are calculated for cage-type carbon clusters. Finally, the cooperative mechanisms of the EP, EC, and MB effects are discussed to realize the high-T c superconductivity in molecule-based materials such as cage compounds and nanotubes. Several possible candidates are proposed on both experimental and theoretical grounds.

As a first step toward examination of ferromagnetic polymers and dendrimers by ab initio crystal orbital methods, we elucidated candidates for monomer units with the high-spin ground states in the previous study of Part I [J. Chem. Phys. 113, 4035 (2000)] by employing density-functional (DFT) methods using Becke’s and Becke’s three parameter exchanges with Lee–Yang–Parr correlation or Hartree–Fock (HF) molecular orbital and post HF approximations. However, it was found that further computations applying other DFT functionals should be carried out to clarify the level of approximations which appropriately describe the electronic structures of magnetic molecules. In this part II, we present details of numerical results concerning magnetic properties and electronic structures for m-phenylene molecules with three neutral and one cation radicals by spin-polarized density functional methods using variety of local and nonlocal functionals and unrestricted molecular orbital methods including Mo/ller–Plesset and coupled-cluster (CC) correlation corrections. The dependence of total, exchange and correlation energies, and spin densities on various approximated functionals is investigated thoroughly. The effective exchange integrals in the Heisenberg model are calculated by local and nonlocal DFT methods, and they are compared with those of complete active space (CAS) CI, CASSCF, and CASPT2. It is concluded that nonlocal DFT with density-gradient corrections can be used as a practical alternative to UCCSD(T) and CASPT2. The broken-symmetry Unrestricted Hartree–Fock (UHF) and DFT calculations of m-phenylene polyradicals with polar substituents are carried out to elucidate roles of superexchange interactions arising from the significant mixing of charge-transfer (CT) configurations. The resonance of covalent structures with CT or zwitterionic structures entails antiferromagnetic exchange interactions even in polyradicals with m-phenylene bridges; for example, substituted nitroxide polyradicals. Stable ferromagnetic polymers and dendrimers are designed on the basis of the theoretical grounds.