Search

We reversibly controlled phase conversion between a microdroplet of a NaClO3 unsaturated aqueous solution and a metastable single crystal, which is usually a short-lived phase in spontaneous crystallization, simply by irradiating a tightly focused visible continuous-wave (CW) laser to the microdroplet. The laser irradiation allowed the metastable crystal to generate and stably grow without a polymorphic transformation. This successful metastable phase control is attributed to the combination of the advantage of optical trapping-induced nucleation that nucleation takes place from unsaturated mother solution and the advantage of microdroplet method, which suppresses additional nucleation leading to the transformation. In situ observation shows the crystal dissolves when the laser irradiation is stopped, whereas the laser irradiation stabilizes the crystal even if the size of the crystal becomes larger than that of focal spot. These observations indicate that a change in the relative magnitudes of chemical potentials between solution/crystalline phases. This change is possibly promoted via crystal growth by trapping of crystalline clusters in optical potential well formed on a crystal surfaces originating from “light propagation” through the crystal. Our results shed a light not only on polymorph control but also on a method to prepare a longer-lived achiral precursor for analysis on achiral–chiral transition by “freezing” a kinetic pathway of chiral crystallization. [ABSTRACT FROM AUTHOR]

This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p-n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment. [ABSTRACT FROM AUTHOR]

Silk fibroin fiber is a well-knowntextile, but is also used asbiomaterial that is of interest for use in a variety of applications,usually in a hydrated state. Thus, the determination of the hydratedsilk fibroin structure is important for understanding the functionand in designing novel biomaterials. In this work, 13Cdipolar decoupling/magic angle spinning NMR was used to determinethe local conformation of [3-13C]Ala-, [3-13C]Ser-, and [3-13C]Tyr -Bombyx morisilkfibroin in a hydrated state. Ser residues are present predominantlyin the crystalline domains, Tyr predominantly in the noncrystallinedomains and Ala residues in both domains. The fraction of β-sheetand two random coil distributions with fast and slow chain dynamicscould be determined for all these residues by 13C conformation-dependentchemical shift. The fraction of β-sheet of these residues inthe fiber and the crystalline fraction did not change significantlybefore and after hydration. The fraction of random coil conformationswith fast motion in total random coil fraction of the hydrated fiberwas 25%, 22%, and 11% for Ala, Ser, and Tyr residues, respectively.Thus, Tyr residues tend to hydrate relatively little among these residues.This information is the first detailed study of the effects of hydrationon site-specific crystalline and noncrystalline domains of silk. [ABSTRACT FROM AUTHOR]

Torsional-tapping AFM with supersharpcarbon-whisker tips is usedto explore the molecular conformations at the surface of a semicrystallinepolymer. Images of the crystal–amorphous interface of orientedpolyethylene have allowed us to measure hitherto inaccessible parametersthat can be directly compared to polymer crystallization theoriesand molecular simulations, such as the length of stem-to-stem overhang.It has also been possible to identify both first- and second-neighborfolds and to determine the surface roughness of lamellae which wefind approximately doubles the interfacial area. Finally, we calculatethe interfacial density profile from the images and find it to besigmoidal but narrower than values reported by SAXS measurements. [ABSTRACT FROM AUTHOR]

Three families of ZnTe magic-sized nanoclusters (MSNCs) were obtained exclusively using polytellurides as a tellurium precursor in a one-pot reaction by simply varying the reaction temperature and time only. Different ZnTe MSNCs exhibit different self-assembling or aggregation behavior, owing to their different structure, cluster size, and dipole--dipole interactions. The smallest family of ZnTe MSNCs (F323) does not reveal a crystalline structure and as a result assembles into lamellar triangle plates. Continuous heating of as synthesized ZnTe F323 assemblies resulted in the formation of ZnTe F398 MSNCs with wurzite structure and concomitant transformation into lamellar rectangle assemblies with the organization of nanoclusters along the <002> direction. Further annealing of ZnTe F398 assembled lamellar rectangles leads to full organization of MSNCs in all directions and formation of larger ZnTe F444 NCs that spontaneously form ultrathin nanowires following an oriented attachment mechanism. The key step in control over the size distribution of ZnTe ultrathin nanowires is, in fact, the growth mechanism of ZnTe F398 MSNCs; namely, the step growth mechanism enables formation of more uniform nanowires compared to those obtained by continuous growth mechanism. High yield of ZnTe nanowires is achieved as a result of the wurzite structure of F398 precursor. Transient absorption (TA) measurements show that all three families possess ultrafast dynamics of photogenerated electrons, despite their different crystalline structures. [ABSTRACT FROM AUTHOR]

The self-assembly of [CuII(dien)(H2O)2]2+ and [WV(CN)8]3- in aqueous solution leads to the formation (H3O){[CuII(dien)]4[WV(CN)8]}[WV(CN)8]2·6.5H2O (1). The crystal structure of 1 consists of an unprecedented {[CuII(dien)]4[WV(CN)8]}5+∞ chain of (2,8) topology, nonbridging [W(CN)8]3- anions, and crystallization water molecules. The analysis of magnetic behavior of 1 was performed by the density functional theory (DFT) method and magnetic susceptibility measurements. The DFT broken symmetry approach gave two JCuW coupling constants: Jax = +2.9 cm-1 assigned to long and strongly bent W-CN-Cu linkage, and the Jeq = +1.5 cm-1 assigned to short and less bent W-CN-Cu linkage, located at the axial and the equatorial positions of square pyramidal CuII centers, respectively, in the hexanuclear {W2Cu4} chain subunit. The dominance of weak-to-moderate ferromagnetic coupling within the chain was confirmed by magnetic calculations. Zero-field susceptibility of the full chain segment {WCu4}n was calculated by a semiclassical analytical approach assuming that only one WV out of five 1/2 spins of the chain unit WCu4 is treated as a classical commuting variable. The calculation of the field dependence of the magnetization was performed separately by replacing the same spin with the Ising variable and applying the standard transfer matrix technique. The intermolecular coupling between the chain segments and off-chain [W(CN)8]3- entities was resolved using the mean-field approximation set to be of antiferromagnetic character. The magnetic coupling parameters are compared with those of other low dimensional {CuII-[MV(CN)8]} systems. [ABSTRACT FROM AUTHOR]

Direct simulations of laminar solid−liquid flow in microchannels with full resolution of the solid−liquid interfaces have been performed. The solids phase consists of simple agglomerates, assembled of monosized, spherical particles. The flow of the interstitial liquid is solved with the lattice-Boltzmann method. Solids and fluid dynamics are two-way coupled. The simulations keep track of the flow-induced forces in the agglomerates. The effects of agglomerate type (doublets, triplets, and quadruplets), solids loading, and channel geometry on (the statistics of the) flow and collision-induced forces has been investigated. By comparing these forces with agglomerate strength, we would be able to assess the potential of microchannels as agglomerate breakage devices. [ABSTRACT FROM AUTHOR]

1,3,5,7-Telramethyl-1 ,3,5,7-tetrahydroxycycloletrasiloxane has been synthesized in good yield from tetrapotassium tetramethytcyclotetrasiloxanolate. Methods for isolation of all-cis-somer I and cis-trans-cis-isomer II as Ihe only crystalline product have been developed. Both isomers have been characterized by single-crystal X-ray diffraction analysis (XRD), elemental analysis, NMR (1H, 13C, 13Si), and IR. The stability of these compounds in solutions and the solid state has been investigated. [ABSTRACT FROM AUTHOR]

As a member of the small heat shock protein superfamily, α-crystallin has a chaperone-like ability to recognize and bind denatured or unfolded proteins and prevent their aggregation. Recent studies suggest that α-crystallin may also interact with a variety of proteins under native conditions in vitro. To identify potential binding partners for α-crystallin in the intact ocular lens, we conducted cross-linking studies in transgenic mouse lenses designed for overexpression of His-tagged human αA-crystallin. Interacting proteins were copurified with the epitope-tagged crystallin complexes and were identified by tandem mass spectrometry. This approach identified GRIFIN (galectin-related interfiber protein) as a novel binding partner. Consistent with results from cross-linking, GRIFIN subunits copurified with α-crystallin complexes during size exclusion chromatography of nontrans- genic mouse lens extracts prepared without chemical cross-linking. Equilibrium binding to GRIFIN was studied using native α-crystallin isolated from calf lenses as well as oligomeric complexes reconstituted from recombinant αA- and αB-crystallin subunits. Calf lens α-crystallin binds GRIFIN with relatively high affinity (Kd = 6.5 ± 0.84 μM) at a stoichiometry of 0.25 ± 0.01 GRIFIN monomer/ α-crystallin subunit. The binding interaction between α-crystallin and GRIFIN is enhanced up to 5-fold in the presence of 3 mM ATP. These binding data support the hypothesis that GRIFIN is a novel binding partner of α-crystallin in the lens. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is an important material for hybrid inorganic−organic devices in which the characteristics of the interface can dominate both the structural and electronic properties of the system. These characteristics can be modified through chemical functionalization of the ZnO surface. One of the possible strategies involves covalent bonding of the modifier using silane chemistry. Whereas a significant body of work has been published regarding silane attachments to glass and SiO2, there is less information about the efficacy of this method for controlling the surface of metal oxides. Here we report our investigation of molecular layers attached to polycrystalline ZnO through silane bonding, controlled by an amine catalyst. The catalyst enables us to use triethoxysilane precursors and thereby avoid undesirable multilayer formation. The polycrystalline surface is a practical material, grown by sol−gel processing, that is under active exploration for device applications. Our study included terminations with alkyl and phenyl groups. We used water contact angles, infrared spectroscopy, and X-ray photoemission spectroscopy to evaluate the modified surfaces. Alkyltriethoxysilane functionalization of ZnO produced molecular layers with submonolayer coverage and evidence of disorder. Nevertheless, a very stable hydrophobic surface with contact angles approaching 106° resulted. Phenyltriethoxysilane was found to deposit in a similar manner. The resulting surface, however, exhibited significantly different wetting as a result of the nature of the end group. Molecular layers of this type, with a variety of surface terminations that use the same molecular attachment scheme, should enable interface engineering that optimizes the chemical selectivity of ZnO biosensors or the charge-transfer properties of ZnO−polymer interfaces found in oxide−organic electronics. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the structural and spatial considerations in the N,N'-Diacyl- and Bis(alkoxycarbonyl)bispidinone series. It discourses on the structural distinctiveness and involution to other compounds of the bispidinone framework which believed to have been eluded notice. It offers details which considers the experiments and procedures where the given compound is further elaborated.

Members of the adenylate-forming family of enzymes play a role in the metabolism of halogenated aromatics and of short, medium, and long chain fatty acids, as well as in the biosynthesis of menaquinone, peptide antibiotics, and peptide siderophores. This family includes a subfamily of acyl- and aryl-CoA ligases that catalyze thioester synthesis through two half-reactions. A carboxylate substrate first reacts with ATP to form an acyl-adenylate. Subsequent to the release of the product PP1, the enzyme binds CoA, which attacks the activated acyl group to displace AMP. Structural and functional studies on different family members suggest that these enzymes alternate between two conformations during catalysis of the two half-reactions. Specifically, after the initial adenylation step, the C-terminal domain rotates by ~140° to adopt a second conformation for thioester formation. Previously, we determined the structure of 4-chlorobenzoate:CoA ligase (CBL) in the adenylate forming conformation bound to 4-chlorobenzoate. We have determined two new crystal structures. We have determined the structure of CBL in the original adenylate-forming conformation, bound to the adenylate intermediate. Additionally, we have used a novel product analogue, 4-chlorophenacyl-CoA, to trap the enzyme in the thioester-forming conformation and determined this structure in a new crystal form. This work identifies a novel binding pocket for the CoA nucleotide. The structures presented herein provide the foundation for biochemical analyses presented in the accompanying manuscript in this issue [Wu et al. (2008) Biochemistry 47, 8026-8039]. The complete characterization of this enzyme allows us to provide an explanation for the use of the domain alternation strategy by these enzymes. [ABSTRACT FROM AUTHOR]

[(n-C4H9)4N]2[Mo6O18(N-1-C10H6-2-CH3)] (1) has been prepared by the reaction of 1-amino-2-methylnaphthalene hydrochloride with [(n-C4H9)4N]4[α-Mo8O26] in the presence of 1,3-dicyclohexylcarbodiimide. Three solvent-free crystalline phases are isolated from the mixed solvents of acetone and acetic ether. The X-ray single-crystal structures of the three phases have been determined, showing the packing and supramolecular assembly characters (pseudohigher symmetry, helical chains, and π-π stacking) by which the effect of solvent polarity and crystallization speed on polymorphism in organic-inorganic hybrids has been demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, (1) a simple and controllable method to synthesize single crystalline nanoribbons of CuTCNQ in a large area was demonstrated by using a physical and chemical vapor combined deposition technique. (2) Nanoribbons synthesized by this method were identified to belong to phase I. (3) Devices and device arrays of nanoribbons were in situ fabricated by this method using gap electrodes and gap electrode arrays. (4) Current-voltage characteristics of crystalline devices and device arrays of nanoribbons exhibited semiconductor properties, and this conclusion was further confirmed by the results of devices based on an individual nanoribbon or microribbon of CuTCNQ (phase I). The controllable synthesis of nanoribbons for the in situ fabrication of crystalline nanodevices and device arrays will be attractive for nanoelectronics. Moreover, semiconductor current-voltage characteristics of the nanoribbons will be beneficial to the understanding of CuTCNQ. [ABSTRACT FROM AUTHOR]

Subnanometric cobalt metallic particles, with an average size of 0.8 nm and an estimated number of 50 atoms, have been stabilized in the confined spaces within the nanopores of crystalline molecular sieves. Remarkably, these clusters show a rapid vanishing of the magnetization as the temperature is increased from 10 to 20 K because of the ferromagnetic–paramagnetic transition together with thermal fluctuations of the remaining moment. This dramatic reduction of the transition temperature is due to strong finite size effects. Such behavior, predicted for very small metallic particles, was never observed before due to the inherent difficulty in achieving subnanometric stable metallic particles. [ABSTRACT FROM AUTHOR]

Upon dehydration, trehalose dihydrate transforms either toward a glassy amorphous state or toward a polymorphic crystalline phase depending on the dehydration protocol. Although this duality is now admitted, its origin remains an open question. We present here calorimetric and thermogravimetric experiments clearly showing that the main pertinent physical parameter governing this duality is the instantaneous rate of water release and not the thermal treatment used to dehydrate the sample. The latter, by acting on the rate of water loss, has only an indirect influence on the structure of the dehydrated product. A threshold rate of water removal, above which dehydration produces an amorphous state and below which it produces a polymorphic phase, is also defined. [ABSTRACT FROM AUTHOR]

Focuses on the synthesis and detailed characterization of a series of crystalline R-phases in the magnesium-zinc-aluminum system. Chemical bonding properties in complex aluminides; Quasicrystalline phases; Structural characterization by X-ray diffraction; Neutron powder diffraction; Magnetic susceptibility measurements; Electronic structure calculations.

We present a robust solid-state NMR approach for the accurate determination of molecular interfaces in insoluble and noncrystalline protein-protein complexes. The method relies on the measurement of intermolecular 13C-13C distances in mixtures of [1-13C]glucose- and [2-13C]glucose-labeled proteins. We have applied this method to Parkinson's disease-associated α-synuclein fibrils and found that they are stacked in a parallel inregister arrangement. Additionally, intermolecular distance restraints for the structure determination of the fibrils at atomic resolution were measured. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the fundamental relationships between the nature of chemical bonding and the anisotropic mechanical responses of crystalline hybrid framework materials that incorporate both inorganic and organic moieties. It analyzes the deformation characteristics of a lanthanide mixed-ligand hybrid cerium oxalate-formate. Evidence shows that crystal orientation dominated by inorganic chains is not strong enough to withstand from the mechanical properties.

Examines the functional layer of solid using tetrakis(imidazolyl)borate coordinating anion. Potential anion exchange in the solid state with retention of crystallinity; Assessment on the stoichiometric exchange of nitrate; Confirmation on the retention of crystallinity by powder XRD diffraction.

The article presents a setup which combines SAXS, WAXS and XAFS to study the crystallization processes of inorganic solids in depth. The purpose of this study is to follow the changes that occur with time at the molecular, nanoscopic and crystalline level with a time resolution in the order of a few minutes. The setup enables the observation of the various stages of zinc-substituted microporous aluminophosphate formation in one experiment and represents the first data of its kind.

The article presents the study which shows the synthesis and stabilization of monodisperse iron nanoparticles and their dispersion. The nanoparticles are more efficiently stabilized by the crystalline Fe3O4 shell and are readily functionalized and dispersed in phosphate-buffered saline. It has been concluded that monodisperse Fe nanoparticles are synthesized through a simple one-pot thermal decomposition of Fe(CO)5 in the presence of oleylamine.

The article reports on the synthesis, structure, and adsorption properties of a novel 2D pillared-bilayer open framework of Cu(lI), using a mixed ligand system {[Cu(pyrdc)(bpp)](5H2O)}n, where pyrdc = pyridine-2,3-dicarboxylate; bpp = 1 ,3-bis(4-pyridyl)- propane, which shows reversible sponge-like dynamic behavior with centric-to-acentric structural transformation upon dehydration- rehydration with retention of single crystallinity. It presents that this is a first observation of porous to nonporous phase transition of a dynamic framework, with retention of single crystallinity and introducing asymmetry into the framework upon dehydration.

The article describes a method for the generation of relief features with vertical dimensions ranging from the micro scale to the atomic scale using partially fractured, single-crystalline silicon substrates. The generation of cracks using this procedure is straightforward and high yielding. The wide availability of high-quality Silicon wafers and the ease of generation of the crack and step make this approach attractive for wide use in nanoscience. This type of method, accurate, quick, and inexpensive, is attractive because it is highly accessible to the general scientific community.

If a molecule with electronic excitation in the infrared region can be designed, then the molecular system is expected to have unprecedented electronic properties. To develop a metallic crystal that consists of single-component molecules, molecules with unprecedentedly low electronic excitations have been synthesized. It may be said that the recent developments in single-component molecular metals were realized by successfully designing molecules with unprecedentedly small highest⁄lowest occupied molecular orbital gaps.