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).

Template-Directed Syntheses of Rotaxanes

Abstract: Rotaxanes are molecules comprised of a dumbbell-shaped component encircled by one or more macrocyclic components. The early syntheses of rotaxanes were mainly based upon statistical threading or upon directed methodologies involving chemical conversion. However, with the advent of supramolecular chemistry, a series of host-guest and template-directed approaches to rotaxanes have been developed and employed successfully. We have devised a template-directed approach to rotaxanes incorporating π-electron deficient bipyridinium-based components and π-electron rich hydroquinone-based polyether components. The noncovalent bonding interactions responsible for the self-assembly of these molecular compounds are (i) π-π stacking interactions between the complementary aromatic units, (ii) hydrogen bonding interactions between the acidic hydrogen atoms in the α-positions with respect to the nitrogen atoms on the bipyridinium units and some of the polyether oxygen atoms, as well as, (iii) edge-to-face T-type interactions between some of the hydrogen atoms on the hydroquinone rings and the π-clouds of the aromatic spacers separating the bipyridinium units. By employing these methodologies, we have synthesised a range of [2]rotaxanes, [3]rotaxanes, and [4]rotaxanes. Furthermore, the dynamic processes involving the shuttling of the cyclic components along the dumbbell-shaped components associated with some of these rotaxanes have been investigated in some detail. The reversible control of the process via external stimuli - such as chemical and electrochemical - has been achieved in the case of a [2]rotaxane incorporating benzidine and biphenol recognition sites. These results suggest the possibility of generating, on the nanoscopic level, molecular devices in the shape of rotaxanes able to store and process informations, thus, affording molecular machines.

Polyviologen Dendrimers as Hosts and Charge‐Storing Devices

Abstract: Two dendrimers were designed and synthesized that contain a 1,3,5-trisubstituted benzenoid core and incorporate 9 and 21 viologen (4,4′-bipyridinium) units in their branches in addition to hydrophilic (aryloxy) terminal groups. For comparison purposes, model compounds containing one and two viologen units were also studied. These polycationic dendrimers form strong host–guest complexes with the dianionic form of the red dye eosin in dilute CH2Cl2 solutions. Titration experiments, based on fluorescence measurements, showed that each viologen unit in the dendritic structures becomes associated with an eosin dianion. Electrochemical (in MeCN) and photosensitization (in CH2Cl2) experiments revealed that only a fraction of the viologen units present in the dendritic structures can be reduced. This fraction corresponds to the number of viologen units present in the outer shells of the dendrimers. The reasons for incomplete charge pooling are discussed. Comparison with the behavior of polyviologen dendrimers that are terminated with bulky tetraarylmethane groups and were studied previously enabled the role played by the terminal groups in the redox and hosting properties to be elucidated. Sono stati progettati e sintetizzati due dendrimeri contenenti un'unita benzenica sostituita nelle posizioni 1,3,5 come core, 9 e 21 unita viologeno (4,4′-dipiridinio), rispettivamente, nelle ramificazioni e gruppi idrofilici di tipo arilossi come unita periferiche. In CH2Cl2 questi dendrimeri policationici interagiscono con la forma dianionica dell'eosina dando complessi host–guest in cui, come mostrato chiaramente dalle titolazioni basate su misure di fluorescenza, ogni unita viologeno contenuta nella struttura dendritica si associa con un anione eosina. Esperimenti di riduzione elettrochimica (in MeCN) e fotochimica (in CH2Cl2 e in presenza di un opportuno fotosensibilizzatore) hanno inoltre messo in evidenza che non tutte le unita viologeno contenute nei dendrimeri possono essere ridotte; in particolare, sembra che siano riducibili solo quelle presenti nel guscio dendritico piu esterno. Il confronto con il comportamento di composti modello, contenenti una e due unita viologeno, e di dendrimeri precedentemente investigati, che differiscono da quelli discussi in questo lavoro per la presenza di gruppi terminali piu ingombranti di tipo tetraarilmetano, ha fatto luce sui motivi che inibiscono la riduzione di tutte le unita viologeno contenute nelle strutture dendritiche e ha chiarito se e come la natura dei gruppi terminali influenza le proprieta redox e complessanti di questi dendrimeri.

Redox-driven switching in pseudorotaxanes

Abstract: Two donor–acceptor thread-like compounds incorporating viologen (V2+) units and 1,5-dihydroxynaphthalene (DNP) stations have been prepared Their ability to form self-assembled charge-transfer (CT) complexes with cucurbit[8]uril (CB[8]) is evidenced by UV-Vis and NMR spectroscopies, as well as by mass spectrometry Binding studies show the formation of 1 : 1 and 2 : 1 complexes between CB[8] and a thread-like compound containing two viologen units, while only a 1 : 1 inclusion complex was observed between CB[8] and a thread-like compound containing only a single viologen unit The switching behavior of the threads within their pseudorotaxane frameworks was investigated by using cyclic voltammetry (CV) and UV-Vis spectroscopy

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.