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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: The overall topologies of MOf-1050 and MOF-1051, and the selective formation of stereoisomers and translational isomers during the kinetically driven crystallization, provide evidence that weak noncovalent bonding interactions play a significant role in the assembly of these extended (super)structures.
Abstract: We report the synthesis of two (2)catenane-containing struts that are composed of a tetracationic cyclo- phane (TC 4 + ) encircling a 1,5-dioxy- naphthalene (DNP)-based crown ether, which bears two terphenylene arms. The TC 4 + rings comprise either 1) two bipyridinium (BIPY 2 + ) units or 2) a BIPY 2 + and a diazapyrenium (DAP 2 + ) unit. These degenerate and nondegen- erate catenanes were reacted in the presence of CuA3)2·2.5 H2O to yield Cu-paddlewheel-based MOF-1050 and MOF-1051. The solid-state structures of these MOFs reveal that the metal clusters serve to join the heptaA A struts into grid-like 2D networks. These 2D sheets are then held together by infinite donor-acceptor stacks in- volving the (2)catenanes to produce in- terpenetrated 3D architectures. As a consequence of the planar chirality as- sociated with both the DNP and hydro- quinone (HQ) units present in the crown ether, each catenane can exist as four stereoisomers. In the case of the nondegenerate (bistable) catenane, the situation is further complicated by the presence of translational isomers. Upon crystallization, however, only two of the four possible stereoiso- A the enantiomeric RR and SS forms—are observed in the crystals. An additional element of co- conformational selectivity is present in MOF-1051 as a consequence of the substitution of one of the BIPY 2 + units by a DAP 2 + unit: only the translational isomer in which the DAP 2 + unit is en- circled by the crown ether is observed. The overall topologies of MOF-1050 and MOF-1051, and the selective for- mation of stereoisomers and transla- tional isomers during the kinetically driven crystallization, provide evidence that weak noncovalent bonding inter- actions play a significant role in the as- sembly of these extended (super)struc-

31 citations

Journal ArticleDOI
TL;DR: In this paper, the snug fit of two suitably spaced dialkylammonium centers within the cavity of the macrocyclic polyether bis-p-phenylene[34]crown-10 (BPP34C10) generates [2]pseudorotaxanes in which each cationic ammonium center “docks” with the macrocycle's two polyether loops.
Abstract: The snug fit of two suitably spaced dialkylammonium centers within the cavity of the macrocyclic polyether bis-p-phenylene[34]crown-10 (BPP34C10) generates [2]pseudorotaxanes in which each cationic ammonium center “docks” with one of the macrocycle's two polyether loops (right), for the most part by means of hydrogen bonds. One such doubly docked [2]pseudorotaxane forms the basis of a prototypical chromophoric supramolecular switch triggered by alterations to the surrounding pH.

31 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanisms of the formation of a [2]catenane and one of its molecular components from bipyridine (BP) and 1,4-bis(bromomethyl)benzene (BBB).
Abstract: The mechanisms of formation of a [2]catenane and one of its molecular components have been investigated. While the synthesis of the tetracationic cyclophane, [BBIPYBIXYCY]4+ from bipyridine (BP) and 1,4-bis(bromomethyl)benzene (BBB), directed by the template, 1,5–bis[2(2–hydroxyethoxy)ethoxy]naphthalene(1/5BHEEN) becomes less efficient (23 to 5%) under ultra-high pressure reaction conditions (12 kbars), the self-assembly of {[2]-[BPP34C10]-[BBIPYBIXYCY] catenane}4+ from BP and BBB in the presence of BPP34C10 can be achieved with increased efficiency (18 to 42%) at 12 kbars. This difference in the trends of the yields can be ascribed to the enhanced templating action of BPP34C10 relative to that of 1/5BHEEN when two moles of BP and two moles of BBB are being employed to construct the tetracationic cyclophane. The self-assembly of the [2]catenane from BP, BBB, and BPP34C10 has been followed by 1H NMR spectroscopy in D7-DMF solution. On the basis of this spectroscopic evidence and supporting chemical data, the formation of {[2]-[BPP34C10]-[BBIPYBIXYCY] catenane}4+ from two moles of BP, two moles of BBB, and one mole of BPP34C10 is believed to proceed via the monoquatemary intermediate, [MBXYBIPY]+, which has not been isolated, and the dicationic species, [BBIPYXY]2+, which has been isolated and shown to be an intermediate in the self-assembly process leading to the [2]catenane, presumably via the [BXYBBIPYXY]3+ trication — the final intermediate which again has not been isolated.

31 citations

Journal ArticleDOI
TL;DR: The described blockwise convergent approach allows assembly of a variety of 3,6-branched mannooligosaccharides and characterized the acylated and deprotected products were characterized, and the intersaccharide connections were elucidated by extensive one- and two-dimensional NMR spectroscopy.
Abstract: Glycosylation of sugar trityl ethers with sugar 1,2-O-(1-cyano)ethylidene derivatives (the trityl-cyanoethylidene condensation) has been applied to the synthesis of highly branched (dendritic) mannooligosaccharides incorporating a Manα1→3(Manα1→6)Man structural motif. The convergent synthetic strategy used to assemble these oligosaccharides was based on the use of glycosyl acceptors and/or a glycosyl donor already bearing this structural motif. The former were represented by mono- and ditrityl ethers of ManαOMe, Manα1→3ManαOMe, and Manα1→3(Manα1→6)ManαX, where X=OMe or SEt. The pivotal glycosyl donor was the peracetylated 1,2-O-(1-cyano)ethylidene-3,6-di-O-(α-D-mannopyranosyl)-β-D-mannopyranose (1), prepared by orthogonal Helferich glycosylation of the known 1,2-O-(1-cyano)ethylidene-β-D-mannopyranose with tetra-O-acetyl-α-D-mannopyranosyl bromide followed by O-acetylation. Glycosylation of acetates of methyl 6-O-trityl-α-D-mannopyranoside and methyl 3,6-di-O-trityl-α-D-mannopyranoside with one equivalent of the donor 1 gave rise to the isomeric tetrasaccharide derivatives, Manα1→3(Manα1→6)Manα1→6ManαOMe and Manα1→3(Manα1→6)Manα1→3ManαOMe, respectively. The latter derivative was further mannosylated at the remaining 6-O-trityl acceptor site to give the protected pentasaccharide Manα1→3(Manα1→6)Manα1→3(Manα1→6)ManαOMe. The isomeric pentasaccharide, Manα1→3(Manα1→6)Manα1→6(Manα1→3)ManαOMe, was prepared by reaction of 1 with the 6-O-trityl derivative of (Manα1→3)ManαOMe. In a similar fashion, 6′- and 6″-O-trityl derivatives of the branched trisaccharide Manα1→3(Manα1→6)ManαOMe served as precursors for two isomeric mannohexaosides. The 3,6-di-O-trityl ether of ManαOMe and the 6′,6″-di-O-trityl ether of Manα1→3(Manα1→6)ManαX (X=OMe or SEt) were efficiently bis-glycosylated with the donor 1 to give the corresponding protected mannoheptaoside and mannononaoside. The yields of these glycosylations with the donor 1 ranged from 50 to 66 %. Final deprotection of all the oligosaccharides was straightforward and afforded the target products in high yields. Both the acylated and deprotected products were characterized, and the intersaccharide connectivities were elucidated by extensive one- and two-dimensional NMR spectroscopy. The described blockwise convergent approach allows assembly of a variety of 3,6-branched mannooligosaccharides.

31 citations

Journal ArticleDOI
TL;DR: Electrochemical studies indicate that by replacing the BIPY2+ units in homo[2]catenane HC•7+-composed of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings-with "zero", one, and two more highly conjugated diazapyrenium dication units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF6
Abstract: Radical templation centered around a heterotrisradical tricationic inclusion complex DB•+⊂DAPQT2(•+), assembled from an equimolar mixture of a disubstituted 4,4'-bipyridinium radical cation (DB•+) and an asymmetric cyclophane bisradical dication (DAPQT2(•+)), affords a symmetric [2]catenane (SC·7PF6) and an asymmetric [2]catenane (AC·7PF6) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4'-bipyridinium (BIPY2+) units forming a mixed-valence (BIPY2)•3+ state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory. Electrochemical studies indicate that by replacing the BIPY2+ units in homo[2]catenane HC•7+-composed of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings-with "zero", one, and two more highly conjugated diazapyrenium dication (DAP2+) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF6 (0, 4+, 6+, 7+, and 8+), HC·7PF6 (0, 2+, 4+, 6+, 7+, and 8+), and AC·7PF6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique [2]catenanes present a promising prototype for the fabrication of high-density data memories.

31 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