R￣d中Hausdorff维数和packing维数的确定

本文目的在于建立确定Ｒ￣ｄ中Ｈａｕｓｄｏｒｆｆ维数ｄｉｍ和ｐａｃｋｉｎｇ维数Ｄｉｍ的两个命题（定理１和定理２），进而寻求Ｒ￣ｄ中Ｈａｕｓｄｏｒｆｆ维数ｄｉｍ与ｐａｃｋｉｎｇ维数Ｄｉｍ相等的条件；这使得我们能够引入分形测度的测度论定义。     

Molecular weight dependence of diblock copolymer segregation at a polymer/polymer interface

Utilizing forward recoil spectrometry (FRES), we have determined the segregation isotherm which describes the interfacial excess z_i^* of diblock copolymers of poly (d₈-styrene-b-2-vinylpyridine) (dPS-PVP) at the interface between the homopolymers PS and PVP as a function of ?_∞, the volume fraction of diblock copolymer remaining in the host homopolymer. All the samples were analyzed after annealing at temperatures and times sufficient to achieve equilibrium segregation. The effect of the degree of polymerization of both the diblock copolymers and the host homopolymers on the segregation isotherm is investigated. When the degree of polymerization of the homopolymer is much larger than that of the diblock copolymer, the normalized interfacial excess (z_i^*/R_g), where R_g is the radius of gyration of an isolated block copolymer chain, is a universal function of that portion of the block copolymer chemical potential due to chain stretching. The existence of such a universal function is predicted by theory and its form is in good agreement with self-consistent mean field calculations. Using these results, one can predict important aspects of the block copolymer segregation (e.g., the saturation interfacial excess) without recourse to the time-consuming numerical calculations. © 1994 John Wiley & Sons, Inc.     

Preparation of dye-loaded SiO2 nanoparticles

A room temperature method for the encapsulation of pyrene in SiO₂ nanoparticles is described. The relation between alkoxysilane surfactant chain length, reactant molar ratios and the uptake of dye, sample morphology, photophysical properties, and the ability of the silicate matrix to protect the encapsulated dye was examined. The synthesis can easily be adapted for the encapsulation of other hydrophobic and thermolabile substances, and used in the development of nanostructured optically active coatings, films and monoliths.     

Analysis of the spin exchange interactions of ferromagnetic CdVO3 in terms of first principles and qualitative electronic structure calculations

First principles spin-polarized electronic band structure calculations were carried out for three ordered spin states of CdVO₃, and the strengths of its corner- and edge-sharing spin exchange interactions were estimated. To gain insight into why CdVO₃ exhibits ferromagnetism while CaV₂O₅ does not despite their apparent structural similarity, the spin exchange interactions of CdVO₃ and CaV₂O₅ were compared in terms of spin dimer analysis using extended Hückel tight binding calculations, and the local geometries of their V⁴⁺ ions were examined.     

Metal-ligand bonding and rutile- versus CdI2-type structural preference in platinum dioxide and titanium dioxide

First principles electronic structure calculations were carried out to determine the relative stabilities of the rutile- and CdI₂-type structures of platinum dioxide (PtO₂) and titanium dioxide (TiO₂). The orbital interactions between the transition metal d- and oxygen p-orbitals were analyzed to gain insight into why PtO₂ has both the rutile- and CdI₂-type structures, but TiO₂ has only the rutile-type structure. The cause for the large difference in the c/a ratios of the CdI₂-type structures of TiO₂ and PtO₂ was examined.     

Blue myoglobin reconstituted with an iron porphycene shows extremely high oxygen affinity

Myoglobin will be a good scaffold for engineering a function into proteins. To modulate the physiological function of myoglobin, almost all approaches have been demonstrated by site-directed mutagenesis, however, there are few studies which show a significant improvement in the function. In contrast, we focused on the replacement of heme in the protein with an artificial prosthetic group. Recently, we prepared a novel myoglobin reconstituted with an iron porphycene as a structural isomer of mesoheme. The bluish colored reconstituted myoglobin is relatively stable and the deoxymyoglobin reversibly binds ligands. Interestingly, the O2 affinity of the reconstituted myoglobin, 1.1 x 109 M-1, is a significant 1,400-fold higher than that of the native myoglobin. Furthermore, the unfavorable autoxidation kinetics show 7-fold decrease in rate for the reconstituted myoglobin relative to the native myoglobin, indicating the stable oxy-form against autoxidation. The net results come from the slow dissociation of the O2 ligand in the reconstituted myoglobin, koff = 0.11 s-1, because of the formation of strong hydrogen bond between His64 and negatively charged dioxygen. The present study indicates that the replacement of native heme with an artificially created prosthetic group will give us a unique function into a hemoprotein.     

Analysis of the Electron Localization, the Anisotropy of Electrical Conductivity, the Orbital Ordering, and Spin-Exchange Interactions in BaVS3 on the Basis of First Principles and Semi-empirical Electronic Structure Calculations

The electrical transport and magnetic properties of BaVS₃, made up of individual VS₃ octahedral chains, were examined on the basis of first principles and tight-binding electronic structure calculations. The electrical conductivity of BaVS₃ is nearly isotropic despite its one-dimensional structural feature, because of the orbital interactions associated with the short S···S contacts within each VS₃ chain and between adjacent VS₃ chains. The probable cause for the metal-insulator transition at ∼70 K was examined in terms of first principles electronic structure calculations, which indicate that the metallic and magnetic insulating states of BaVS₃ are nearly the same in energy. This is consistent with the observation that the metal-insulator transition at ∼70 K is caused by electron localization. The observed magnetic properties of BaVS₃ below ∼70 K are readily explained under the assumption that the symmetry-broken t_2g-orbitals act as the magnetic orbitals in the magnetic insulating state of BaVS₃. The probable cause for the latter was discussed.     

Structure of a de novo designed protein model of radical enzymes

The use of side chains as catalytic cofactors for protein mediated redox chemistry raises significant mechanistic issues as to how these amino acids are activated toward radical chemistry in a controlled manner. De novo protein design has been used to examine the structural basis for the creation and maintenance of a tryptophanyl radical in a three-helix bundle protein maquette. Here we report the detailed structural analysis of the protein by multidimensional NMR methods. An interesting feature of the structure is an apparent pi-cation interaction involving the sole tryptophan and a lysine side chain. Hybrid density functional calculations support the notion that this interaction raises the reduction potential of the W degrees /WH redox pair and helps explain the redox characteristics of the protein. This model protein system therefore provides a powerful model for exploring the structural basis for controlled radical chemistry in protein.