Rigid molecular tripod with an adamantane framework and thiol legs. Synthesis and observation of an ordered monolayer on Au111

Tripod-shaped trithiols 1-3, containing CH2SH groups at the three bridgehead positions of the adamantane framework and a halogen-containing group [Br (1), p-BrC6H4 (2), or p-IC6H4 (3)] at the fourth bridgehead, were synthesized, and self-assembled monolayers (SAMs) were prepared on atomically flat Au111 surfaces. The three-point chemisorption of these tripods was confirmed by polarization modulation infrared reflection absorption spectroscopy, which showed the absence of a S-H stretching band. Scanning tunneling microscopy of the SAM of 1 exhibited a hexagonal arrangement of the adsorbed molecule with a lattice constant of 8.7 angstroms. A unidirectionally oriented, head-to-tail array of 1, which allows the close approach of neighboring molecules, is proposed as a reasonable model of the two-dimensional crystal, where the adsorbed sulfur atoms form a quasi-(radical3 x radical3)R30 degrees lattice. The charge of the electrochemical reductive desorption of the SAM of 1 was in good agreement with the expected surface coverage, while the SAMs of 2 and 3 showed somewhat less (ca. 70%) charge. The large negative reduction peak potentials, observed for the SAM of 1, are taken to indicate a tight anchoring of this tripod by three sulfur atoms.     

Blow‐up for a class of semilinear integro‐differential equations of parabolic type

In this paper, we study the following semilinear integro‐differential equation of the parabolic type that arise in the theory of nuclear reactor kinetics: under homogeneous Dirichlet boundary condition, where p, q⩾1. We first establish the local solvability of a large class of semilinear non‐local equations including the above equation. Next, we give the finite time blow‐up result by some modification of Kaplan's method and also the existence of global solutions by the comparison method. Copyright © 1999 John Wiley & Sons, Ltd.     

Dramatic structural rearrangements in porous coordination networks

With the use of ab initio X-ray powder diffraction, a family of isostructural crystalline porous coordination networks, [(ZnX(2))(3)(TPT)(2)](n)· (solvent) (X = I, Br, Cl), has been studied at elevated temperatures of 573-723 K. Upon heating, all three networks exhibited crystalline-to-amorphous-to-crystalline (CAC) phase transformations to three new networks, [(ZnI(2))(3)(TPT)(2)](n), [(ZnBr(2))(3)(TPT)(2)](n)·(H(2)O) and [(ZnBr(2))(μ-Br)(ZnBr)(TPT)](n), and [(ZnCl(2))(μ-Cl)(ZnCl)(TPT)](n), respectively. A set of control experiments was used to obtain detailed mechanistic aspects of the CAC transformations. We demonstrate how bonds are broken and formed in these significant molecular rearrangements and how the initial arrangement plays a crucial role in the formation of the new networks after the CAC transformations. The structural information in the amorphous phase is retained and passed from a metastable to a more stable crystal, thus, reinforcing the notion that coordination networks are flexible and chemically active.     

Effects of oxygen-vacancies in high-temperature cuprate superconductors

We investigate the effects of oxygen vacancies on the magnetic properties and superconducting transition temperature of high-temperature cuprate superconductors. Starting with the d-p Hamiltonian, we simultaneously employ the coherent potential approximation to account for the effects of oxygen vacancies, and the fluctuation-exchange scheme to address the copper-site Coulomb interactions. Our results show that the presence of oxygen vacancies weakens the antiferromagnetic spin fluctuations of d-electrons subsequently lowering the superconducting transition temperature.     

Topological structures of the sets of composition operators on the Bloch spaces

We study properties of the topological sets of composition operators on Bloch and little Bloch spaces in the operator topology.     

Femtosecond laser-induced crystallization of protein in gel medium

We succeeded in generating femtosecond laser-induced crystallization of hen egg-white lysozyme (HEWL) in the irradiated area by suppressing convection of the solution using a highly concentrated gel. When a laser pulse, whose energy was above the threshold energy for bubble formation, was focused along with a linear scanning of the stage, HEWL crystallization was enhanced at the surface of bubbles on the irradiated line. The relation between the bubble formation process and the crystallization is discussed.