Abstract: We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime. A trapped gas of fermionic $^{40}\mathrm{K}$ atoms is evaporatively cooled to quantum degeneracy and then a magnetic-field Feshbach resonance is used to control the atom-atom interactions. The location of this resonance is precisely determined from low-density measurements of molecule dissociation. In order to search for condensation on either side of the resonance, we introduce a technique that pairwise projects fermionic atoms onto molecules; this enables us to measure the momentum distribution of fermionic atom pairs. The transition to condensation of fermionic atom pairs is mapped out as a function of the initial atom gas temperature $T$ compared to the Fermi temperature ${T}_{F}$ for magnetic-field detunings on both the BCS and BEC sides of the resonance.

Abstract: X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen– bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen– bonded tetrahedral structure in ice. Upon heating from 25°C to 90°C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen– bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.

Abstract: Five porous metal−organic frameworks based on linking zinc oxide clusters with benzene-1,4-dicarboxylate, naphthalene-2,6-dicarboxylate, 4,5,9,10-tetrahydropyrene-2,7-dicarboxylate, 2,3,5,6-tetramethylbenzene-1,4-dicarboxylate, or benzene-1,3,5-tris(4-benzoate) were synthesized in gram-scale quantities to measure their hydrogen uptake properties. Hydrogen adsorption isotherms measured at 77 K show a distinct dependence of uptake on the nature of the link. At 1 atm, the materials sorb between 4.2 and 9.3 molecules of H2 per formula unit. The results imply a trend in hydrogen uptake with the number of rings in the organic moiety.

Abstract: Nitrogen usually consists of molecules where two atoms are strongly triple-bonded. Here, we report on an allotropic form of nitrogen where all atoms are connected with single covalent bonds, similar to carbon atoms in diamond. The compound was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressures above 110 GPa using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The phase is a stiff substance with bulk modulus >or=300 GPa, characteristic of strong covalent solids. The polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which is most likely a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than five times that of the most powerfully energetic materials.

Abstract: We report now the first single molecule magnet (SMM) consisting of d−f elements. The present study demonstrates that the synthesis of the d−f polynuclear molecule is a very promising approach to SMMs. (1) The d−f polynuclear molecule can be easily synthesized by the assembly reaction of the d-component and the f-component, (2) the high-spin ground state can be generated by a smaller number of metal ions than the d complex, and (3) the molecular magnetic anisotropy is easily derived from the f-component.

Abstract: The design and synthesis of crystalline materials through the self-assembly of molecular building blocks and the pursuit of functional materials based upon this approach are usually classified under the banner Crystal Engineering. The field is interdisciplinary in nature involving synthetic, materials, structural and theoretical chemists. There are strong ties to modern crystallography which can offer rapid and accurate structure determination and, in particular, insight into molecular and intermolecular geometries. Illustrative examples that chart the development field and provide an assessment of the current state of the art will be reviewed with an emphasis on inorganic chemistry. Broadly speaking, two classes of compounds will be discussed: those based upon molecules or ions linked into networks via noncovalent interactions and those (coordination polymers) in which metal centres are linked using coordination bonds through bridging ligands into extended networks.

Abstract: The properties of materials can be created and improved either by confining their dimensions in the nanoscale or by controlling their nanostructure. We have combined these two concepts, and here we describe a new class of nanostructured nanosized materials that show ordered phase-separated domains at an unprecedented molecular length scale. Scanning tunnelling and transmission electron microscope images of monolayer-protected metal nanoparticles, with ligand shells composed of a mixture of molecules, show that the ligands phase-separate into ordered domains as small as 5 A. Importantly, the domain shape and dimensions can be controlled by varying the ligand composition or the metallic core size. We demonstrate that the formation of ordered domains depends on the curvature of the underlying substrate, and that novel properties result from this nanostructuring. For example, because the size of the domains is much smaller than the typical dimensions of a protein, these materials are extremely effective in avoiding non-specific adsorption of a variety of proteins.

Abstract: The diversity of mechanisms for enantiodiscrimination and of bond types that can be formed make Pd-catalyzed asymmetric allylic alkylation a powerful key step for simplification of synthetic strategy to complex molecular targets. Using a wide range of different classes of compounds including alkaloids, polyhydrofurans, nucleosides and carbanucleosides, cyclohexitols and cyclopentitols, chromanes, cyclopentanoids, amino acids, barbiturates, etc., novel synthetic strategies emerge that provide short efficient asymmetric syntheses.

Abstract: A gold(III)-catalyzed carbon−carbon bond formation reaction between arenes and electron-deficient alkynes or alkenes is described. Electron-rich arenes can be efficiently functionalized with the alkyne or alkene substrates. This reaction can be run with neat reactants at ambient temperature. Under the “solventless” conditions, clean product was obtained from a reaction of equal molar amounts of arene and alkyne substrates. The mild conditions and potential tolerance to different functional groups make this method practical for arene functionalization and for constructing complicated molecules. Efficient preparation of various coumarins from aryl alkynoates was demonstrated. Preliminary mechanistic studies were performed to probe the pathway of this reaction.

Abstract: Activation and Functionalization of C-H Bonds explores recent developments in the reaction chemistry of solution-phase transition-metal based systems with simple hydrocarbons and with more complex organic molecules. More than 20 internationally leading research groups contributed to this volume, and their chapters cover such topics as fundamental theoretical and mechanistic studies of C-H bond activation by metal complexes, catalytic systems for alkane functionalization, and new applications in synthetic organic chemistry. An introductory chapter offers an overview of stoichiometric and catalytic reactions of C-H bonds with transition metal complexes. The C-H bond is the most widespread linkage in organic chemistry, present in virtually every organic molecule. Unfortunately, C-H bonds are famously resistant to selective chemical transformations. The development of methods for their selective transformations has enormous potential value in fields ranging from the chemistry of fuels (for example, the conversion of methane to methanol) to the synthesis of the most complex organic molecules.

Abstract: A comprehensive picture of the interface between aqueous solutions and the (110) surface of rutile (α-TiO2) is being developed by combining molecular-scale and macroscopic approaches, including experimental measurements, quantum calculations, molecular simulations, and Gouy−Chapman−Stern models. In situ X-ray reflectivity and X-ray standing-wave measurements are used to define the atomic arrangement of adsorbed ions, the coordination of interfacial water molecules, and substrate surface termination and structure. Ab initio calculations and molecular dynamics simulations, validated through direct comparison with the X-ray results, are used to predict ion distributions not measured experimentally. Potentiometric titration and ion adsorption results for rutile powders having predominant (110) surface expression provide macroscopic constraints of electrical double layer (EDL) properties (e.g., proton release) which are evaluated by comparison with a three-layer EDL model including surface oxygen proton affini...

Abstract: Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH2 or M(H2) molecules so formed react further to form higher MH4, (H2)MH2, or M(H2)2, and MH6, (H2)2MH2, or M(H2)3 hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.

Abstract: The crystal and molecular structure, together with the hydrogen-bonding system in ammonia-mercerized cellulose IIII, has been determined using synchrotron X-ray and neutron fiber diffraction data. The structure has a one-chain monoclinic unit cell with an asymmetric unit that contains only one glucosyl residue and with the hydroxymethyl group in the gt conformation. The hydrogen-bonding system is well-defined with no evidence of disorder. A bifurcated hydrogen bond links a donating secondary alcohol O3 atom to a ring O5 atom (major) and a primary alcohol O6 atom (minor) of an adjacent residue in the same chain. Two hydrogen bonds are present between neighboring chains, perpendicular to the chain direction. A detailed comparison of the crystal structure and hydrogen-bonding system reported here for cellulose IIII and those reported previously for the other cellulose polymorphs is given. The conformation of the chain in cellulose IIII has features similar to that of the center chain in the highly stable cel...

Abstract: The chemical complexity and diversity of an Athabasca asphaltene sample was described using a series of molecular representations. The molecular representations were created with a Monte Carlo construction method that represented molecules with a series of aromatic and aliphatic groups. After the groups were randomly sampled for a molecule, a connection algorithm linked them together to form molecules consisting of aromatic groups connected by aliphatic chains and thioethers. A sequential nonlinear optimization algorithm was used to select a small subset of molecules that were consistent with elemental, molecular weight, and NMR spectroscopy (both 13C and 1H) data. To accurately represent the analytical data for the asphaltene sample, a minimum of five molecules was needed. On the basis of the results of the sequential optimization, at least 50 molecules in the starting population were required to produce an analytically consistent molecular representation.

Abstract: Threshold collision-induced dissociation of M+(AAA) with Xe is studied using guided ion beam tandem mass spectrometry M+ include the alkali metal ions Na+ and K+ The three aromatic amino acids are examined, AAA = phenylalanine, tyrosine, or tryptophan In all cases, endothermic loss of the intact aromatic amino acid is the dominant reaction pathway The threshold regions of the cross sections are interpreted to extract 0 and 298 K bond dissociation energies for the M+−AAA complexes after accounting for the effects of multiple ion−neutral collisions, internal energy of the reactant ions, and dissociation lifetimes Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of the neutral aromatic amino acids and their complexes to Na+ and K+ and to provide molecular constants required for the thermochemical analysis of the experimental data Theoretical bond dissociation energies are determined from single-point energy calculations at the B3LYP/6-311++

Abstract: Polyhedral clusters containing boron, alone or in combination with other elements, have been known for nearly a century, and intensive studies of their structures, bonding, and reactivity have been...

Abstract: A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions.

Abstract: Derivatized s-triazine (C3N3) precursors have seen significant recent use in the production of carbon nitride materials. Larger polycyclic molecular precursors, such as those containing an s-heptazine core (C6N7 or tri-s-triazine), may improve stability and order in carbon nitride products. In this Communication, we describe the synthesis and crystal structure of 2,5,8-triazido-s-heptazine (2). Synthesis of 2 was achieved from melon, an oligomeric s-heptazine synthesized by the pyrolysis of NH4SCN. Melon was converted to molecular 2,5,8-trichloro-s-heptazine, which was then transformed to the triazide upon reaction with (CH3)3SiN3. The crystal structure of 2 verifies that the s-heptazine is planar and the azides adopt a pinwheel-like C3h arrangement around the periphery. The s-heptazine core shows pi delocalization in the C-N bonds around the periphery (av. 1.33 A), while the internal planar C-N bonds are longer (1.40 A). The heptazine units pack into parallel, but offset, layered sheets in the crystal. The triazide 2 exhibits photoluminescence at 430 nm and rapidly and exothermically decomposes upon heating at 185 degrees C to produce a tan thermally stable carbon nitride powder with a formula near C3N4.

Abstract: The sterically crowded (C5Me5)3U complex reacts with KC8 or K/(18-crown-6) in benzene to form [(C5Me5)2U]2(-6:6-C6H6), 1, and KC5Me5. These reactions suggested that (C5Me5)3U could be susceptible to (C5Me5)1- substitution by benzene anions via ionic salt metathesis. To test this idea in the synthesis of a more conventional product, (C5Me5)3U was treated with KN(SiMe3)2 to form (C5Me5)2U[N(SiMe3)2] and KC5Me5. 1 has long U-C(C5Me5) bond distances comparable to (C5Me5)3U, and it too is susceptible to (C5Me5)1- substitution via ionic metathesis: 1 reacts with KN(SiMe3)2 to make its amide-substituted analogue {[(Me3Si)2N](C5Me5)U}2(-6:6-C6H6), 2. Complexes 1 and 2 have nonplanar C6H6-derived ligands sandwiched between the two uranium ions. 1 and 2 were examined by reactivity studies, electronic absorption spectroscopy, and density functional theory calculations. [(C5Me5)2U]2(-6:6-C6H6) functions as a six-electron reductant in its reaction with 3 equiv of cyclooctatetraene to form [(C5Me5)(C8H8)U]2(-3:3-C8H8), (C5Me5)2, and benzene. This multielectron transformation can be formally attributed to three different sources: two electrons from two U(III) centers, two electrons from sterically induced reduction by two (C5Me5)1- ligands, and two electrons from a bridging (C6H6)2- moiety.

Abstract: 6,12-Dimethylindolo[3,2-b]carbazoles were prepared by Cadogan ring closure using N-alkyl-2-substituted carbazole precursor. X-ray analyses on 5,11-dioctyl-6,12-dimethylindolo[3,2-b]carbazole have demonstrated a coplanar molecular structure with an interesting π-stacking of the molecules. Organic field-effect transistor using the same molecule as an active layer has revealed promising features.

Abstract: This paper describes a simple strategy for DNA immobilization on chemically modified and patterned silicon surfaces. The photochemical modification of hydrogen-terminated Si(111) with undecylenic acid leads to the formation of an organic monolayer covalently attached to the surface through Si-C bonds without detectable reaction of the carboxylic acid group, providing indirect support of a free radical mechanism. Chemical activation of the acid function was achieved by a simple chemical route using N-hydroxysuccinimide (NHS) in the presence of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride. Single strand DNA with a 5'-dodecylamine group was then coupled to the NHS-activated surface by amide bond formation. Using a previously reported chemical patterning approach, we have shown that DNA can be immobilized on silicon surfaces in spatially well-resolved domains. Methoxytetraethyleneglycolamine was used to inhibit nonspecific adsorption. The resulting DNA-modified surfaces have shown good specificity and chemical and thermal stability under hybridization conditions. The sequential reactions on the surface were monitored by ATR-FTIR, X-ray Photoelectron Spectroscopy, and fluorescence spectroscopy.

Abstract: The hydration of some of the alkaline earth divalent metal cations and first row transition metal cations is considered within the quasi-chemical theory of solutions. Quantum chemical calculations provide information on the chemically important interactions between the ion and its first-shell water molecules. A dielectric continuum model supplies the outer-shell contribution. The theory then provides the framework to mesh these quantities together. The agreement between the calculated and experimental quantities is good. For the transition metal cations, it is seen that the ligand field contributions play an important role in the physics of hydration. Removing these bonding contributions from the computed hydration free energy results in a linear decrease in the hydration free energy along the period. It is precisely such effects that molecular mechanics force fields have not captured. The implications and extensions of this study to metal atoms in proteins are suggested.

Abstract: From the experimental crystal structure and ab initio calculations on resveratrol and its derivatives, structural features of mechanistic importance are described. The molecular structure reveals the relative coplanarity of the trans-stilbene skeleton, and the molecular packing in the solid state shows an extensive hydrogen bond network that elucidates the flip-flop motion of the three hydroxyl groups that alternately form and break H bonds with each of the neighboring phenolic oxygens. The dynamic behavior provoked by the alternation of hydrogen bond formation and breaking can result in the ready mobility of up to three hydrogen atoms per resveratrol molecule that can be transferred to reactive oxidants that are rich in electron density. In addition, theoretical studies confirm the planarity of resveratrol as well as for half of the molecule of a condensation dimeric derivative of resveratrol, trans-σ-viniferin. Furthermore, these studies show the p-4‘-OH group to be more acidic compared to the other two...

Abstract: A new microcontainer for DNA delivery based on biocompatible poly[β-glucuronic acid-(1 → 3)-N-acetyl-β-galactosamine-6-sulfate-(1 → 4)](chondroitin sulfate)/poly(-l-arginine) microcapsules with 40 nm thick molecularly organized shell was proposed. DNA molecules were deposited as DNA/sperimidine complex on the surface of template 4 μm core particles followed by layer-by-layer nanoassembly of protective chondroitin sulfate/poly(-l-arginine) shell. After template core dissolution, DNA molecules were captured inside microcapsules retaining a natural double-helix structure. The developed DNA encapsulation approach can be employed for targeted delivery of plasmid DNA in living cells.