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).

Dual-mode "co-conformational" switching in catenanes incorporating bipyridinium and dialkylammonium recognition sites.

Abstract: Three [2]catenanes and three [3]catenanes incorporating one or two π-electron-rich macrocyclic polyethers and one π-electron-deficient polycationic cyclophane have been synthesized in yields ranging from 4 to 38 %. The π-electron-rich macrocyclic components possess either two 1,4-dioxybenzene or two 1,5-dioxynaphthalene recognition sites. The π-electron-deficient cyclophane components incorporate two bipyridinium and either one or two dialkylammonium recognition sites. The template-directed syntheses of these catenanes rely on i) π⋅⋅⋅π stacking interactions between the dioxyarene and bipyridinium recognition sites, ii) C−H⋅⋅⋅O hydrogen bonds between some of the bipyridinium hydrogen atoms and some of the polyether oxygen atoms, and iii) C-H⋅⋅⋅π interactions between some of the dioxyarene hydrogen atoms and the aromatic spacers separating the bipyridinium units. The six catenanes were characterized by mass spectrometry and by both 1H and 13C NMR spectroscopy. The absorption spectra and the electrochemical properties of the catenanes have been investigated and compared with those exhibited by the component macrocycles and by related known catenanes. Broad and weak absorption bands in the visible region, originating from charge-transfer (CT) interactions between electron-donor and electron-acceptor units, have been observed. Such charge-transfer interactions are responsible for the quenching of the potentially fluorescent excited states of the aromatic units of the macrocyclic polyether components. The redox behavior of these novel compounds has been investigated and correlations among the observed redox potentials are illustrated and discussed. The catenanes undergo co-conformational switching upon one-electron reduction of the two bipyridinium units. One of them—in its reduced form—can be also switched by acid/base inputs and exhibits AND logic behavior. The co-conformational rearrangements induced by the redox and acid/base stimulations lend themselves to exploitation in the development of molecular-level machines and logic gates. Sono stati sintetizzati tre [2]catenani e tre [3]catenani contenenti un ciclofano policationico π elettron accettore e, rispettivamente, uno e due polieteri macrociclici π elettron donatori, con rese comprese fra 4 e 38 %. I componenti macrociclici π donatori possiedono due unita 1,4-diossibenzene o due unita 1,5-diossinaftalene, mentre il componente π accettore contiene due gruppi dipiridinio ed uno o due gruppi dialchilammonio. La sintesi templata di questi catenani si basa su i) interazioni π⋅⋅⋅π fra i siti di riconoscimento diossiaromatici e dipiridinio, ii) legami a idrogeno C−H⋅⋅⋅O fra atomi di idrogeno dei gruppi dipiridinio ed atomi di ossigeno delle catene polieteree e iii) interazioni C−H⋅⋅⋅π fra atomi di idrogeno delle unita diossiaromatiche e gli spaziatori p-fenilenici che separano i gruppi dipiridinio. I sei catenani sono stati caratterizzati mediante spettrometria di massa e spettroscopia 1H e 13C NMR. Il comportamento elettrochimico e gli spettri di assorbimento dei catenani sono stati esaminati e confrontati con quelli dei componenti macrociclici e di altri catenani simili studiati in precedenza. Si osservano bande di assorbimento deboli e allargate nella regione del visibile, attribuite alle interazioni di trasferimento di carica fra le unita π elettron donatrici e quelle π elettron accettrici. Tali interazioni sono responsabili anche dello spegnimento degli stati eccitati, potenzialmente fluorescenti, localizzati sulle unita aromatiche dei polieteri macrociclici. Dalle correlazioni fra i potenziali dei processi redox osservati si puo concludere che i catenani subiscono riarrangiamenti co-conformazionali in seguito a riduzione monoelettronica dei due gruppi dipiridinio. Uno dei catenani esaminati, nella forma ridotta, da luogo a riarrangiamenti strutturali anche a seguito di stimoli chimici di tipo acido/base, evidenziando un comportamento logico di tipo AND. I movimenti co-conformazionali indotti mediante stimoli redox e acido/base suggeriscono la possibilita di impiegare questi nuovi catenani per la realizzazione di macchine e porte logiche a livello molecolare.

Aromatic hydrocarbon belts.

Abstract: Aromatic hydrocarbon belts (AHCBs) have fascinated scientists for over half a century because of their aesthetically appealing structures and potential applications in the field of carbon nanotechnology. One of the enduring challenges in synthesizing AHCBs is how do we cope with the build-up of energy in the highly strained structures during their synthesis? Successful preparations of AHCBs offer the prospect of providing well-defined templates for the growth of uniform single-walled carbon nanotubes-a long-standing interest in nanocarbon science. In this Review, we revisit the protracted historical background involving the rational design and synthesis of AHCBs and highlight some of the more recent breakthroughs, with emphasis being placed on the different strategies that have been used for building up curved and fused benzenoid rings into molecular belts. We also discuss the scientific challenges in this fledgling field and provide some pointers as to what could transpire in years to come.

Molecular Meccano, 27. A Template‐directed Synthesis of a Molecular Trefoil Knot

Abstract: A design logic for the self-assembly of a molecular trefoil knot and of its isomeric trivial knot is described. The approach relies on the formation of a double-stranded supramolecular complex between an acyclic π-electron rich 1,5-di-oxynaphthalene-based polyether and an acyclic π-electron deficient bipyridinium-based tetracation. The reversible complexation of the two acyclic complementary components in solution is followed by the irreversible formation of covalent bonds connecting the termini of these two precursors within the supramolecular complex, affording both a trefoil knot and a trivial knot, though only in extremely low yields. The isomers were separated by preparative high-performance liquid chromatography and characterized by liquid secondary ion mass spectrometry which revealed the binding of up to two ammonium ions in the case of only one of the two isomers – namely, the trivial knot. In addition, we have performed binding studies between some model acyclic and macrocyclic 1,5-dioxynaphthalene-based polyethers and the bipyridinium based precursor of the knots. One of the complexes was also characterized in the solid state by X-ray crystallography which revealed the formation of a [2]pseudorotaxane in the solid state.

Second-Sphere Coordination

Abstract: The design and synthesis of artifical receptors, able to recognize and bind transition metal complexes, is an area of growing interest in supramolecular chemistry. Macrocyclic hosts such as crown ethers, cyclodextrins, and cyclophanes have been employed to generate second-sphere adducts with numerous transition metal complexes as a result of nonconvalent bonding interactions, such as hydrogen bonding, π-π stacking, and hydrophobic interactions. The effect of second-sphere coordination on the chemical, electrochemical, and photochemical properties of the adducts, as well as on their geometries in solution and in the solid state, has been investigated; these investigations have demonstrated the potential of second-sphere coordination in modulating the behavior of transition metal complexes by designed external intervention.

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.