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).

Making Molecular Borromean Rings. A Gram-Scale Synthetic Procedure for the Undergraduate Organic Lab.

Abstract: Borromean rings (BRs) have long fascinated scholars of all disciplines for their wide cultural appeal and unique topology. Undergraduate students are no exception and so we have modified our published experimental procedure for the synthesis of molecular BRs to turn it into a lab instruction experiment suitable for undergraduate students to pursue in an organic chemistry laboratory course. Herein, we describe a procedure that requires seven 4-hour blocks of time to allow an undergraduate student to prepare the molecular BRs on a gram-scale in 90% yield. Just as important as engaging students in the BRs is the fact that the making of the molecular BRs incorporates several important, yet nonetheless overlooked, areas of chemistry. They include synthetic organic, physical organic, inorganic and metallo-organic chemistry, supramolecular, and dynamic covalent chemistry, all packaged up under the same umbrella in one project.

Substrate-directed synthesis: The rapid assembly of novel macropolycyclic structures via stereoregular diels-alder oligomerizations

Abstract: An increasing appreciation of molecular architecture and design will provide a greater impetus to tackle the exciting and elaborate structural targets that will confront chemistry in the twenty-first Century. It is, therefore, of the upmost importance that methods by which outwardly complex chemical systems can be assembled selectively, rapidly, and efficiently, are devised. Towards this goal, a trebly diastereoselective tandem Diels-Alder reaction sequence has been developed. Subsequently, we have demonstrated how this synthetic methodology can be utilized for the synthesis of novel macropolycyclic molecular structures. In each cycloaddition, the stereoelectronic characteristics, that are inherent in part of the rigid bicyclic frameworks of both bisdienophile and bisdiene building blocks, are used to dictate their respective modes of reaction. The outcome of this substrate-directed approach to organic synthesis allows the rapid and highly-controlled assembly of an increasing range of apparently complex molecular structures. The diastereoselectivities that are witnessed in each cycloaddition are rationalized as involving kinetically-controlled transition-state effects. The rationalization is based upon maximal vicinal staggering and the subsequent minimization of torsional strain within the rigid bicyclic framework in the transition state. In this survey, the application of the repetitive Diels-Alder approach for the synthesis of a wide range of macropolycyclic molecular structures is examined. The potential of these compounds as ideal precursors in the preparation of intriguing hydrocarbons is revealed. The pivotal role played by the sequential use of mild and forcing conditions — most notably the use of thermally- and high pressure-promoted Diels-Alder reactions — to produce oligomeric compounds in a predictable and stepwise manner is documented. Throughout these discussions, special attention has been given to the methods employed for the purification and characterization of this new class of unnatural products.

Crystal and supramolecular structures of complexes of BF3NH3 and BH3NH3 with 18-crown-6

Abstract: The macrocyclic polyether 18-crown-6 (C12H24O6) readily forms crystalline 1 : 1 complexes with the adducts BF3NH3 and BH3NH3 Crystals of the solvates BF3NH3·C12H24O6·CH2Cl2 and BH3NH3·C12H24O6·MeOH were suitable for X-ray crystallographic investigation In both cases, the crystal structures reveal that 18-crown-6 adopts an all-gauche conformation with pseudo D3d symmetry in which the intermolecular N–H ⋯ O hydrogen-bonding interactions between the macrocyclic polyether and the adducts are associated directly with the triangle of oxygen atoms on the complexing face of the crown

Allosteric Modulation of Substrate Binding within a Tetracationic Molecular Receptor

Abstract: The synthesis and recognition phenomena of a tetracationic molecular receptor that possesses a nanometer-sized molecular cavity are described. The host-guest properties of the molecular receptor can be tuned and modulated allosterically, where the association of a heterotropic effector at the periphery of the molecule serves to modulate its affinity for the globular, electron-rich guest that resides within its molecular cavity. This stimuli-responsive host-guest behavior was observed in both the solution phase and the crystalline solid state, and can be reversed with high fidelity by sequestration of the effector molecule.

Selective Photodimerization in a Cyclodextrin Metal-Organic Framework.

Abstract: For the most part, enzymes contain one active site wherein they catalyze in a serial manner chemical reactions between substrates both efficiently and rapidly. Imagine if a situation could be created within a chiral porous crystal containing trillions of active sites where substrates can reside in vast numbers before being converted in parallel into products. Here, we report how it is possible to incorporate 1-anthracenecarboxylate (1-AC-) as a substrate into a γ-cyclodextrin-containing metal-organic framework (CD-MOF-1), where the metals are K+ cations, prior to carrying out [4+4] photodimerizations between pairs of substrate molecules, affording selectively one of four possible regioisomers. One of the high-yielding regioisomers exhibits optical activity as a result of the presence of an 8:1 ratio of the two enantiomers following separation by high-performance liquid chromatography. The solid-state superstructure of 1-anthracenecarboxylate potassium salt (1-ACK), which is co-crystallized with γ-cyclodextrin, reveals that pairs of substrate molecules are not only packed inside tunnels between spherical cavities present in CD-MOF-1, but also stabilized-in addition to hydrogen-bonding to the C-2 and C-3 hydroxyl groups on the d-glucopyranosyl residues present in the γ-cyclodextrin tori-by combinations of hydrophobic and electrostatic interactions between the carboxyl groups in 1-AC- and four K+ cations on the waistline between the two γ-cyclodextrin tori in the tunnels. These non-covalent bonding interactions result in preferred co-conformations that account for the highly regio- and enantioselective [4+4] cycloaddition during photoirradiation. Theoretical calculations, in conjunction with crystallography, support the regio- and stereochemical outcome of the photodimerization.

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.