J. Fraser Stoddart

Bio: J. Fraser Stoddart is an academic researcher from Northwestern University. The author has contributed to research in topics: Catenane & Supramolecular chemistry. The author has an hindex of 147, co-authored 1239 publications receiving 96083 citations. Previous affiliations of J. Fraser Stoddart include Zhejiang University & Northwest University (United States).

Folding of Oligoviologens Induced by Radical–Radical Interactions

Abstract: We report the synthesis of a series of homologous oligoviologens in which different numbers of 4,4′-bipyridinium (BIPY2+) subunits are linked by p-xylylene bridges, as a prelude to investigating how their radical cationic forms self-assemble both in solution and in the solid state. The strong radical–radical interactions between the radical cationic forms of the BIPY2+ units—namely, BIPY•+—in these oligoviologens induce intra- or intermolecular folding of these homologues. UV/Vis/NIR spectroscopic studies and DFT quantum mechanics indicate that the folding of the shorter oligoviologens is dominated by intermolecular radical–radical interactions. In addition to intermolecular interactions, strong intramolecular radical–radical interactions, which give rise to an NIR absorption band at 900 nm, tend to play a crucial role in governing the folding of the longer oligoviologens. The solid-state superstructure of the oligoviologen with three BIPY2+ units reveals that two intertwining chains fold together to form...

Molecular-Mechanical Switching at the Nanoparticle−Solvent Interface: Practice and Theory

Abstract: A range (Au, Pt, Pd) of metal nanoparticles (MNPs) has been prepared and functionalized with (a) redox-active stalks containing tetrathiafulvalene (TTF) units, (b) [2]pseudorotaxanes formed between these stalks and cyclobis(paraquat-p-phenylene) (CBPQT4+) rings, and (c) bistable [2]rotaxane molecules where the dumbbell component contains a 1,5-dioxynaphthalene (DNP) unit, as well as a TTF unit, encircled by a CBPQT4+ ring. It transpires that the molecules present in (a) and (c) and the supermolecules described in (b) retain their switching characteristics, previously observed in solution, when they are immobilized onto MNPs. Moreover, their oxidation potentials depend on the fraction, χ, of the molecules or supermolecules on the surface of the nanoparticles. A variation in χ affects the oxidation potentials of the TTF units to the extent that switching can be subjected to fine tuning as a result. Specifically, increasing χ results in positive shifts (i) in the oxidation potentials of the TTF unit in (a)−(...

Complexation between methyl viologen (paraquat) bis(hexafluorophosphate) and dibenzo[24]crown-8 revisited.

Abstract: Paraquat bis(hexafluorophosphate) undergoes stepwise dissociation in acetone. All three species-the neutral molecule, and the mono- and dications-are represented significantly under the experimental conditions typically used in host-guest binding studies. Paraquat forms at least four host-guest complexes with dibenzo[24]crown-8. They are characterized by both 1:1 and 1:2 stoichiometries, and an overall charge of either zero (neutral molecule) or one (monocation). The monocationic 1:1 host-guest complex is the most abundant species under typical (0.5-20 mM) experimental conditions. The presence of the dicationic 1:1 host-guest complex cannot be excluded on the basis of our experimental data, but neither is it unambiguously confirmed to be present. The two confirmed forms of paraquat that do undergo complexation-the neutral molecule and the monocation-exhibit approximately identical binding affinities toward dibenzo[24]crown-8. Thus, the relative abundance of neutral, singly, and doubly charged pseudorotaxanes is identical to the relative abundance of neutral, singly, and doubly charged paraquat unbound with respect to the crown ether in acetone. In the specific case of paraquat/dibenzo[24]crown-8, ion-pairing does not contribute to host-guest complex formation, as has been suggested previously in the literature.

Threading/dethreading processes in pseudorotaxanes. A thermodynamic and kinetic study

Abstract: Pseudorotaxanes are host–guest complexes made of a thread-like component penetrating a bead-like component. We have investigated, by a stopped-flow technique, the threading/dethreading kinetics of pseudorotaxanes formed between a tetracationic cyclophane, cyclobis(paraquat-p-phenylene), and thread-like compounds consisting of a naphthalene ring system with appended –(OCH2CH2)nOH groups (n from 0 to 3) on the 1 and 5 positions. The association and rate constants have been measured in MeCN (from 276 to 293 K) and H2O (from 276 to 313 K). In MeCN solution, the association constant increases with increasing length of the appended chain (e.g., Kass = 1.0 × 103 M−1 for n = 0 and Kass = 4.0 × 104 M−1 for n = 3, at 293 K); in H2O, the association constants are larger than in MeCN, but almost independent of the chain length. Both the threading (kt) and dethreading (kd) rate constants are larger in MeCN than in H2O and decrease with increasing chain length (e.g., kt > 108 and kt = 4 × 106 M−1 s−1 for n = 0 and n = 3, respectively, in H2O at 276 K). Thermodynamic and kinetic parameters have been obtained and the role played by the length of the chains appended to the naphthalene ring system is discussed.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

The Chemistry and Applications of Metal-Organic Frameworks

Abstract: Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.