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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).


Papers
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Journal ArticleDOI
TL;DR: Two molecular shuttles/switches in the shape of dumbbells have been synthesized and characterized in this paper, one is a slow one and the other is a fast one, which can act as recognition sites for the tetracationic cyclophane, cyclobis(paraquat-p-phenylene).
Abstract: Two molecular shuttles/ switches-a slow one and a fast one- in the shape of amphiphilic, bistable [2]rotaxanes have been synthesized and characterized. Both [2]rotaxanes contain a hydrophobic, tetraarylmethane and a hydrophilic, dendritic stopper. They are comprised of two π-electron-rich stations-a monopyrrolotetrathiafulvalene unit and a 1,5-dioxynaphthalene moiety-which can act as recognition sites for the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), to reside around. In addition, a model [2]rotaxane, incorporating only a monopyrrolotetrathiafulvalene unit in the rod section of the amphiphilic dumbbell component and cyclobis(paraquat-p-phenylene) as the ring component, has been investigated. The dumbbell-shaped components were constructed using conventional synthetic methodologies to assemble 1) the hydrophobic, tetraarylmethane stopper and 2) the hydrophilic, dendritic stopper. Next, 3) the hydrophobic stopper was fused to the 1,5-dioxynaphthalene moiety and/or the monopyrrolotetrathiafulvalene unit by appropriate alkylations, followed by 4) attachment of the hydrophilic stopper, once again by alkylation to give the dumbbell-shaped compounds. Finally, 5) the [2]rotaxanes were self-assembled by using the dumbbells as templates for the formation of the encircling cyclobis(paraquat-p-phenylene) tetracations. The two [2]rotaxanes differ in their arrangement of the π-electron-rich units, one in which the SMe group of the monopyrrolotetrathiafulvalene unit points toward the 1,5-dioxynaphthalene moiety (2 . 4PF 6 ) and another in which it points away from the 1,5-dioxynaphthalene moiety (3 . 4PF 6 ). This seemingly small difference in the orientation of the monopyrrolotetrathiafulvalene unit leads to profound changes in the physical properties of these rotaxanes. The bistable [2]rotaxanes were both isolated as brown solids. 1 H NMR and UV-visible spectroscopy, and electrochemical investigations, reveal the presence of both possible translational isomers at ambient temperature. As a consequence of the existence of both possible translational isomers in these bistable [2]rotaxanes, they exhibit a complex electrochemical behavior, which is further complicated by the presence of folded conformations wherein the monopyrrolotetrathiafulvalene unit is involved in an "alongside" interaction with the tetracationic cyclophane. In the molecular shuttle/switch 2 . 4PF 6 a "knob", in the shape of the SMe group, is situated between the monopyrrolotetrathiafulvalene and the 1,5-dioxynaphthalene recognition sites, making it possible to isolate both translational isomers (2 . 4 PF 6 . GREEN and 2 . 4 PF 6 . RED) and to investigate the kinetics of the shuttling of the cyclobis(paraquat-p-phenylene) tetracation between the two recognition sites. The shuttling processes, which are accompanied by clearly detectable color changes, can be followed by 'H NMR and UV-visible spectroscopy, allowing the rate constants and energies of activation for the translation of the cyclobis(paraquat-p-phenylene) tetracations between the two recognition sites to be determined. In the molecular shuttle/switch 3 . 4PF 6 , there is no "knob" situated between the 1,5-dioxynaphthalene and the monopyrrolotetrathiafulvalene recognition sites, resulting in a considerably faster shuttling of the cyclobis(paraquat-p-phenylene) tetracation between these two sites, making the separation of the two possible translational isomers of 3 . 4PF 6 impractical. However, the shuttling of the cyclobis(paraquat-p-phenylene) tetracation can be followed by dynamic 1 H NMR spectroscopy. At low temperatures, the major translational isomer is 3 . 4 PF 6 . RED, while 3 . 4 PF 6 . GREEN is the major isomer at higher temperature. In the bistable [2]rotaxanes shuttling of the cyclobis(paraquat-p-phenylene) tetracations can be driven by electrochemical oxidation of the monopyrrolotetrathiafulvalene unit. In complexes in which one of the two dumbbell stoppers is missing, electrochemical oxida

107 citations

Journal ArticleDOI
TL;DR: Direct evidence for the self-organization was obtained from AFM investigations which have shown that both of the [2]rotaxane and its dumbbell precursor form linear superstructures which the authors propose are helical in nature.
Abstract: The switching properties, gelation behavior, and self-organization of a cholesterol-stoppered bistable [2]rotaxane containing a cyclobis(paraquat-p-phenylene) ring and tetrathiafulvalene/1,5-dioxynaphthalene recognition units situated in the rod portion of the dumbbell component have been investigated by electrochemical, spectroscopic, and microscopic means. The cyclobis(paraquat-p-phenylene) ring in the [2]rotaxane can be switched between the tetrathiafulvalene and 1,5-dioxynaphthalene recognition units by addressing the redox properties of the tetrathiafulvalene unit. The organogels can be prepared by dissolving the [2]rotaxane and its dumbbell precursor in a CH2Cl2/MeOH (3:2) mixed solvent and liquified by adding the oxidant Fe(ClO4)3. Direct evidence for the self-organization was obtained from AFM investigations which have shown that both of the [2]rotaxane and its dumbbell precursor form linear superstructures which we propose are helical in nature.

107 citations

Journal ArticleDOI
TL;DR: This minireview traces the development of artificial molecular machines from their prototypes in the form of shuttles and switches to their emergence as motors and pumps where supplies of energy become a minimum requirement for them to function away from equilibrium.
Abstract: The past quarter of a century has witnessed an increasing engagement on the part of physicists and chemists in the design and synthesis of molecular machines de novo. This minireview traces the development of artificial molecular machines from their prototypes in the form of shuttles and switches to their emergence as motors and pumps where supplies of energy in the form of chemical fuel, electrochemical potential and light activation become a minimum requirement for them to function away from equilibrium. The challenge facing this rapidly growing community of scientists and engineers today is one of putting wholly synthetic molecules to work, both individually and as collections. Here, we highlight some of the recent conceptual and practical advances relating to the operation of wholly synthetic rotary and linear motors.

106 citations

Journal ArticleDOI
TL;DR: Under mild conditions, orthogonal recognition motifs have been shown to lead to templation with positive cooperativity that is fast and all but quantitative, as well as being green and efficient.
Abstract: After the manner in which coenzymes often participate in the binding of substrates in the active sites of enzymes, pillar[5]arene, a macrocycle containing five hydroquinone rings linked through their para positions by methylene bridges, modifies the binding properties of cucurbit[6]uril, such that the latter templates azide–alkyne cycloadditions that do not occur in the presence of only the cucurbit[6]uril, a macrocycle composed of six glycoluril residues doubly linked through their nitrogen atoms to each other by methylene groups. Here, we describe how a combination of pillar[5]arene and cucurbit[6]uril interacts cooperatively with bipyridinium dications substituted on their nitrogen atoms with 2-azidoethyl- to 5-azidopentyl moieties to afford, as a result of orthogonal templation, two [4]rotaxanes and one [5]rotaxane in >90% yields inside 2 h at 55 °C in acetonitrile. Since the hydroxyl groups on pillar[5]arene and the carbonyl groups on cucurbit[6]uril form hydrogen bonds readily, these two macrocycles...

106 citations


Cited by
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01 May 1993
TL;DR: 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.
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.

29,323 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组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�ly.
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。

18,940 citations

Journal ArticleDOI
TL;DR: A review of gold nanoparticles can be found in this article, where the most stable metal nanoparticles, called gold colloids (AuNPs), have been used for catalysis and biology applications.
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

11,752 citations

Journal ArticleDOI
30 Aug 2013-Science
TL;DR: Metal-organic frameworks are porous materials that have potential for applications such as gas storage and separation, as well as catalysis, and methods are being developed for making nanocrystals and supercrystals of MOFs for their incorporation into devices.
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.

10,934 citations