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Abstract Covalent bond cross-link networks endow rubber with unique resiliency enabling it to be widely used as a series of irreplaceable materials in modern life. However, the balance between rigidity [...]

Clay particle deposition in porous media is critical in many geotechnical applications that rely on filtration. The deposition of particles in the filter medium can result in clogging, which causes a reduction in the hydraulic conductivity of the filter medium. Particle attachment and detachment are a function of the interaction energy between clay particles and the filter bed material, which is frequently sand. These mechanisms are governed by the size of the clay particles as well as the solution chemistry. Batch kinetic adsorption tests were carried out to investigate the impact of ionic strength on the attachment of kaolinite to silica sand grains. Significant attachment of kaolinite was observed as ionic strength of the pore fluid increased and as the size of silica particles decreased. The short-term deposition of clay particles was not sensitive to ionic strength; however, in contrast, long-term deposition was a strong function of ionic strength. Key words: interaction energy, clogging, clay deposition, ionic strength, batch kinetic test, 1. Introduction Understanding the deposition of fine-grained particles in porous media is critical in hydraulic filtration applications as well as for quantifying the transport behavior of contaminants, such as heavy [...]

A new pyridine derivative l-(4-amino-3,5-dinitropyridin-2-yr) guanidine (ADG) was synthesized through nitration and substitution reaction using 4-amino-2-cholopyridine as raw material. Its structure was characterized by spectroscopy, nuclear magnetic resonance, and mass spectrometry. The crystal of ADG is monoclinic, space group Pbca with crystal parameters of a = 7.23 A, b = 14.56 A, c = 17.93 A, [alpha] = [beta] = [gamma] = 90 A, V = 1911 [A.sup.3], [micro], = 0.143 [mm.sup.-1], and Z = 8. This new molecule exhibits moderate density ([rho] = 1.677g [cm.sup.-3]), good thermal stability with a decomposition temperature of 217 [degrees]C, and moderate detonation property with detonation pressure of 20.83 GPa and detonation velocity of 7.00 km [s.sup.-1]. The Hirshfeld surface analysis revealed a significant contribution of weak interactions to the packing forces for molecules. Electron localization function analysis indicates that there is substantial electron localization in regions of C-H, N-H, and N-O covalent bond sites. Key words: organic synthesis, energetic materials, thermal analysis, theoretical calculation, 1. Introduction Detonation performance and safety are the first important factors to be considered in the field of practical application of energetic compounds. However, the essential contradiction of high-energy molecules [...]

The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the [P2.sub.1]/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the P1 space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine--nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 [A.sup.3]) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. [.sup.1]H [right arrow] [.sup.13]C and [.sup.19]F [right arrow] [.sup.13]C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds. Key words: solid-state NMR, X-ray diffraction, halogen bond, cocrystal, polymorphism, stoichiometry, stoichiomorphism. Nous avons etudie le concept de cocristallisation a stoechiometrie variable dans des systemes a liaison halogene. Nous avons prepare par evaporation lente trois nouveaux cocristaux de 1,4-diiodotetrafluorobenzene et de 3-nitropyridine avec des rapports molaires de 1:1, de 2:1 et de 1:2, respectivement. L'analyse par diffraction des rayons X sur monocristal revele des differences importantes entre les cocristaux theoriquement similaires. Par exemple, le cocrystal 1:1 cristallise selon le groupe d'espace [P2.sub.1]/n et presente une seule liaison halogene, sur les plans chimique et cristallographique, entre l'iode et l'azote du groupe pyridyle. Le cocrystal 2:1 cristallise selon le groupe d'espace P1 et presente une liaison halogene entre l'iode et l'un des oxygenes du groupe nitro, en plus de la liaison halogene iode-azote. Le cocristal 1:2 cristallise en formant une grande cellule unitaire (V = 9896 [A.sup.3]) selon le groupe d'espace Cc et presente 10 liaisons halogene iode-azote distinctes sur le plan cristallographique. Des experiences de diffraction des rayons X sur poudre realisees sur les cocristaux 1:1 et 2:1 confirment qu'un broyage leger ne modifie pas les formes cristallines. Nous avons utilise des experiences de RMN [.sup.1]H [right arrow] [.sup.13]C et [.sup.19]F [right arrow] [.sup.13]C a polarisation croisee en rotation a l'angle magique (CP/MAS, cross-polarization/magic angle spinning), realisees sur des echantillons de cocristaux 1:1 et 2:1 sous forme de poudre, comme outils d'edition spectrale pour selectionner l'accepteur ou le donneur de liaison halogene, respectivement. Les deplacements chimiques du carbone-13 dans les cocris-taux ne changent que de facon tres subtile par rapport au 1,4-diiodotetrafluorobenzene solide pur, mais le deplacement du carbone directement lie a l'iode augmente neanmoins, ce qui concorde avec la formation de liaisons halogene (p. ex., un deplacement de +1,6 ppm dans le cas du cocrystal 2:1). Ces travaux apportent de nouveaux exemples au domaine de l'ingenierie des cocristaux a stoechiometrie variable comportant des liaisons halogene. [Traduit par la Redaction] Mots-cles : RMN a l'etat solide, diffraction des rayons X, liaison halogene, cocristal, polymorphisme, stoechiometrie, stoechiomorphisme., Introduction Molecular and ionic solids can adopt a range of forms depending on how they are prepared. (1,2) Such forms include pure crystalline or amorphous phases, hydrates, or solvates. In [...]

Two-dimensional (2D) materials.sup.1-5 offer a unique platform from which to explore the physics of topology and many-body phenomena. New properties can be generated by filling the van der Waals gap of 2D materials with intercalants.sup.6,7; however, post-growth intercalation has usually been limited to alkali metals.sup.8-10. Here we show that the self-intercalation of native atoms.sup.11,12 into bilayer transition metal dichalcogenides during growth generates a class of ultrathin, covalently bonded materials, which we name ic-2D. The stoichiometry of these materials is defined by periodic occupancy patterns of the octahedral vacancy sites in the van der Waals gap, and their properties can be tuned by varying the coverage and the spatial arrangement of the filled sites.sup.7,13. By performing growth under high metal chemical potential.sup.14,15 we can access a range of tantalum-intercalated TaS(Se).sub.y, including 25% Ta-intercalated Ta.sub.9S.sub.16, 33.3% Ta-intercalated Ta.sub.7S.sub.12, 50% Ta-intercalated Ta.sub.10S.sub.16, 66.7% Ta-intercalated Ta.sub.8Se.sub.12 (which forms a Kagome lattice) and 100% Ta-intercalated Ta.sub.9Se.sub.12. Ferromagnetic order was detected in some of these intercalated phases. We also demonstrate that self-intercalated V.sub.11S.sub.16, In.sub.11Se.sub.16 and Fe.sub.xTe.sub.y can be grown under metal-rich conditions. Our work establishes self-intercalation as an approach through which to grow a new class of 2D materials with stoichiometry- or composition-dependent properties. The intercalation of native atoms into bilayer transition metal dichalcogenides during growth generates ultrathin, covalently bonded materials into which ferromagnetic ordering can be introduced., Author(s): Xiaoxu Zhao [sup.1] [sup.2] , Peng Song [sup.2] , Chengcai Wang [sup.3] , Anders C. Riis-Jensen [sup.4] , Wei Fu [sup.2] , Ya Deng [sup.5] , Dongyang Wan [sup.6] [...]

Post-translational protein modification by ubiquitin (Ub) and ubiquitin-like (Ubl) proteins such as small ubiquitin-like modifier (SUMO) regulates processes including protein homeostasis, the DNA damage response, and the cell cycle. Proliferating cell nuclear antigen (PCNA) is modified by Ub or poly-Ub at lysine (Lys)164 after DNA damage to recruit repair factors. Yeast PCNA is modified by SUMO on Lys164 and Lys127 during S-phase to recruit the anti-recombinogenic helicase Srs2. Lys164 modification requires specialized E2/E3 enzyme pairs for SUMO or Ub conjugation. For SUMO, Lys164 modification is strictly dependent on the E3 ligase Siz1, suggesting the E3 alters E2 specificity to promote Lys164 modification. The structural basis for substrate interactions in activated E3/E2Ub/Ubl complexes remains unclear. Here we report an engineered E2 protein and cross-linking strategies that trap an E3/E2Ubl/substrate complex for structure determination, illustrating how an E3 can bypass E2 specificity to force-feed a substrate lysine into the E2 active site., Author(s): Frederick C. Streich Jr [1]; Christopher D. Lima (corresponding author) [1, 2] Ub and Ubl proteins are conjugated to substrate proteins by dedicated three-enzyme cascades involving E1 activating enzymes, [...]

Author(s): Keriann M. Backus (corresponding author) [1]; Bruno E. Correia [1]; Kenneth M. Lum [1]; Stefano Forli [2]; Benjamin D. Horning [1]; Gonzalo E. Gonzlez-Pez [3]; Sandip Chatterjee [3]; Bryan [...]

In this work, the cooperative effects between anion-π and fluorine bond interactions are studied by ab initio calculations at the MP2/6-311++[G.sup.**] level. Cooperative effects are observed in complexes in which anion-π and fluorine bond interactions coexist. For each complex, the shortening of the binding distance in the fluorine bond is more prominent than that in the anion-π bond. Favorable cooperativity energies are found with values that range between -0.51 and -0.76 kcal/mol. The atoms in molecules and molecular electrostatic potential analyses are carried out for these complexes to understand the nature of anion-π and fluorine bond interactions and the origin of the cooperativity. Key words: anion-π, halogen bond, cooperativity, ab initio, molecular electrostatic potential. Dans le cadre des presents travaux, nous avons etudie les effets cooperatifs entre les interactions anion-π et les liaisons halogene du fluor par des calculs ab initio au niveau MP2/6-311++[G.sup.**]. Nous avons observe des effets cooperatifs dans les complexes dans lesquels existent fi la fois des interactions anion-π et des liaisons halogenes avec le fluor. Dans tous les complexes, la reduction de la longueur de la liaison halogene du fluor est plus importante que celle de la liaison anion-π. Nous avons observe des energies de cooperativite favorables dont les valeurs vont de -,51 a -0,76 kcal/mol. Nous avons modelise ces complexes selon la theorie quantique des atomes dans les molecules et calcule leur potentiel electrostatique moleculaire afin de comprendre la nature des interactions anion-π et des liaisons halogene du fluor ainsi que l'origine de la cooperativite. [Traduit par la Redaction] Mots-cles: anion-π, liaison halogene, cooperativite, ab initio, potentiel electrostatique moleculaire., Introduction In recent years, noncovalent interactions have received much attention due to their essential roles in many chemical and biological processes. (1-4) A halogen bond is defined as an attractive [...]

In this article, we describe the synthesis and characterization of a series of spiropyran containing copolymers that were used as colorimetric sensors for a series of divalent metal ions. The composition of spiropyran contained in the polymer backbone was varied from 10-100 mol % to investigate the influence of free volume and sterics on the photochromic response. Fourier transform-infrared (FT-IR) spectroscopy was used to characterize the photo-induced conversion, as well as the merocyanine--metal ion (MC-[M.sup.2+]) interaction. FT-IR spectra were analyzed using chemometric methods to elucidate the chemical binding environment between MC and [M.sup.2+] and to selectively identify different metal ions bound to MC. By means of UV--vis absorption spectroscopy, we also demonstrate that each metal ion gives rise to a unique colorimetric response that is dependent on the amount of spiropyran comonomer contained in the polymer backbone and that by increasing the concentration of chromophore in the copolymer, the selectivity between different metal ions decreases. With the use of chemometric methods, UV--vis spectra can be analyzed to quantitatively identify metal ions in a concentration range from 1 [micro]M to 100 mM. 10.1021/ac1001004

Recent advances in high-resolution solid-state NMR enabled us to resolve the previously unknown details of atomic configurations around quadrupolar nuclides such as O ([sup.17]O, spin 5/2) and aluminum ([sup.27]Al, spin 5/2) in phyllosilicates. Here, we report the [sup.17]O 1D and 2D NMR (MAS and MQMAS) spectra of synthetic kaolinite-montmorillonite mixtures. Various O sites in the mixtures revealed from O-17 NMR include apical O ([sup.VI]Si-O-[2.sup.IV]Al), multiple basal O atoms ([sup.VI]Si-O-[sup.VI]Si and two [sup.VI]Si-[O.sup.-VI]Al sites) in tetrahedral layers, and hydroxyl group with distinct ranges for NMR parameters (quadrupolar coupling constant, [C.sub.q] and isotropic chemical shift, [sup.17]O [[delta].sub.iso]). In particular, the structurally relevant NMR parameters ([sup.17]O [[delta].sub.iso], [C.sub.q], and asymmetry parameter, [eta]) for two resolved [sup.IV]Si-O-[sup.VI]Al sites are about 52 [+ or -] 2 ppm, 2.6 [+ or -] 0.2 MHz, and 0.5 for [sup.IV]Si-O-[sup.IV]Al (I) and about 44.5 [+ or -] 2 ppm, and 3.1 [+ or -] 0.2 MHz, and 0.5 for [sup.IV]Si-O-[sup.IV]Al (II), respectively. These sites may stem from crystallographically distinct [sup.IV]Si-O- [sup.IV]Al sites of varying bond length and [sup.IV]si-O-[sup.VI]Al bond angle or [sup.IV]Al-O-2[sup.VI]Al site in the montmorillonite. Keywords: High-resolution solid-state NMR, phyllosilicates, oxygen sites, 3QMAS NMR, montmorillonite

Ab initio study of six carbon-to-carbon identify proton transfers is described. There is no correlation between the transition state and the development of aromaticity and charge delocalization has lagged behind proton transfer as is commonly seen in nonaromatic systems involving [pi]-acceptor groups.

The synthesis of trisila analogues of allyl chlorides, chlorosilyl disilenes, and their reduction with lithium to cyclotrisilanides, the first anionic homonuclear three-membered silacycles, rather than open-chained allylic anions is described. The X-ay diffraction studies have shown that the Si-Si bond distance in cyclotrisilanes has depended on the electronegativity of the opposing silicon atom's substituents.

Pd-catalyzed aminocarbonylation in the presence of Xantphos as a ligand was used to transform lactam-, lactone-, and thiolactone-derived triflates into N-methoxy-N-methyl or morpholine Weinreb amides. The method could also be applied to synthesize dienones in which one of the double bonds is embedded in a heterocyclic moiety, as useful substrates for Nazarov cyclization.

A study was conducted to analyze the photoreactions of 4-nitroanisole and the 2-halo-4-nitroanisoles with the nucleophiles hydroxide ion and pyridine. The findings suggest that the efficiency-determining step to the halogen photosubstitution is attributed to simple formation of a [sigma]-complex through electron-paired bonding within the triplet manifold.

A combination of FTIR and molecular simulations were used to study the H-bond interactions between polyurethane with pendent carboxyl (PUc) and poly(4-vinylpyridine) (P4VP). The pyridyl N from P4VP was found to form two types of H-bond, while the formation of type I (COOH...P4VP) bond was 95.87%, thus proving it to be the primary force for the assembly between PUc and P4VP.

The structural correlation between aldopyranosyl ring saccharide structure and spin-spin coupling constants values was determined by using the density functional theory calculations. The couplings were observed to depend highly on the orientation and rotation of C-O bonds appended to the terminal coupled carbons.

Several new fluorescent chemosensors for heavy metal ions based on functionalized pendant arm derivatives of 7-anthracenylmethyl-1,4,10-trioxa-7,13-diazacyclopentadecane are synthesized. The topology and the nature of the binding domain are found to be highly significant in the process.

A facile and efficient method is described for the cleavage of the Ar-Si bond of various aryl trimethyl silanes. These arylsilanes have readily undergone a solvent-free protodesilylation to the corresponding arenes at room temperature, when adsorbed on montmorillonite KSF (mont KSF).

The reaction of [beta]-iodo-[alpha],[beta]-unsaturated [gamma]-sultones in aprotic polar solvents with soft nucleophiles has yielded an allenesulfonate by a very facile halophilic ring-opening [E.sub.2]-elimination. The results have shown the relative importance of the [beta]-halogen and the S-O(-C) bonds in increasing the acidity of the H-[C.sub.[alpha]]-S[(O).sub.2]-grouping.

The unsaturated D3C compounds were investigated at the molecular level using accurate quantum mechanical methods. The results indicated that the C=C double bond location imposes significant effects on the ionization potentials of D3C compounds and the inner shell binding energy spectral variations with respect to the C=C bond exhibit more site dependence.

A systematic study of the CH/[pi] interactions of methane with the purine and pyrimidine bases of nucleic acids and with the lateral chains of the four natural aromatic amino acids which showed two different kinds of clusters depending on number of CH bonds in the aromatic systems is presented.

Ab initio calculations were used to calculate the three adiabatic potential surfaces of the Br([super 2]P)-HCN complex that correlate to the [super 2]P ground state of the Br atom. It was found that Br-HCN occurs in two isomeric forms, Br-HCN and Br-NCH, both linear and the binding energy depends strongly on the CH bond length for the Br-HCN complex and less strongly for the Br-NCH complex.

The study of the structure and zinc binding properties of two ZnuA variants from Synechocystis 6803 suggest that ZnuA binds zinc via three histidine loop might be the region for sensor of high periplasmic levels of zinc.

The first principles calculations are performed to investigate the hydrogen storage characteristics of carbon based 3-D solid structures. The adsorption properties of hydrogen on the metal atoms dispersed inside the covalently bonded graphemes are also presented.

The steps leading to and involved in the C-H activation of benzene is investigated by using a combination of experimental kinetic studies and molecular reaction modeling based on density functional theory. It is shown that the Ti[triple bond]C linkage can engage in alkylidene-alkyl metathesis through multiple C-H activation reactions of tetramethylsilane and hydrocarbons by using a combination of 1,2-CH addition, [alpha]-hydrogen migration and [alpha]-hydrogen abstraction steps.

[Pt.sup.0] complexes of [[eta].sup.2]-coordinated diarylacetylenes are synthesized and characterized along with the corresponding C-C bond-activated [Pt.sup.II] complexes. It is shown that the C-C cleavage reaction in a substrate containing both electron-donating groups (EDG) and electron-withdrawing groups (EWG) as substituents has produced 55% activation product through the C-C bond adjacent to the EWG-substituted aryl ring and 45% activation product through the one adjacent to the EDG-substituted aryl.

A series of experiments are described that have elucidated the mechanism of N[double bond]N cleavage by an iron-hydride complex. It is shown that the high-spin iron(II) hydride can break N-N bonds through both nonradical and radical insertion mechanisms, which is a special feature that enables novel reactivity.

The bromination of 6,7,8,9-tetrahydro-5H-5,9-ethenobenzo[a][7]annulene has yielded regio- and stereospecifically formed dibromides arising from the alkyl shift where the bromine exclusively attacks the double bond from the endo face of the double bond. The results have shown that the pyramidalization of the double bond and steric repulsion caused by the methylene protons are responsible for the stereo- and regioselective addition of bromine.

A model is proposed for deriving protein reorganization energy from the approach based on a bond-length difference reaction coordinate, particularly on an electronically adiabatic surface with the aim to evaluate the applicability of the quadratic free-energy expression for the protein reorganization.

The dynamical correlation energy for diatomic hydrides of the first and second period is computed using Hartree-Fock-Heitler-London (HF-HL) method. Ab initio HF-HL configurations with inclusion of ionic structures yielded reasonable binding energies for hydrides as well as for the van der Waals HeH molecules and the computed total energies were in good agreement with exact non relativistic values.

The [S.sub.1]-[S.sub.0] internal conversion of 6-cyanozulebe (6CNAZ) was investigated by ab initio complete active-space self-consistent field (CASSCF) and second-order multireference Moller-Plesset perturbation (MRMP2) calculations. The stable geometry in [S.sub.0] is characterized by an aromatic bond-equalized structure in which all peripheral skeletal bond distances resemble an aromatic CC bond distance and stable geometry of [S.sub.1] is characterized by a nonaromatic [C.sub.2v] structure.

The preparation of a novel phosphapalladacycle derived from (di-tert-butyl)(diphenylmethyl)phosphine in the optically active form was observed to display a very strong tendency to remain in the ortho-palladated state with a palladacycle Pd-C bond which could not be permanently ruptured is presented.

The functional importance of the hydrogen bond network and ionic interaction in supporting the high thermostability of Aspergillus fumigatus phytase (Afp) and the feasibility of adopting these structural units to improve the thermostability of a homologous PhyA phytase are demonstrated.

The integration of semiporous membranes into poly(dimethylsiloxane) (PDMS) microfluidic devices is useful for mass transport control. Several methods such as plasma oxidation and manual application of PDMS prepolymer exist to sandwich such membranes into simple channel structures, but these methods are difficult to implement with reliable sealing and no leakage or clogging for devices with intricate channel features. This paper describes a simple but robust strategy to bond semiporous polyester and polycarbonate membranes between layers of PDMS microchannel structures effectively without channel clogging. A thin layer of PDMS prepolymer, spin-coated on a glass slide, is transferred to PDMS substrates with channel features as well as to the edges of the semiporous membrane by stamping. This thin PDMS prepolymer serves as 'mortar' to strongly bond the two PDMS layers and seal off the crevices generated from the thickness of the membranes. This bonding method enabled the fabrication of an 8 x 12 criss-crossing microfluidic channel array with 96 combinations of fluid interactions. The capability of this device for bioanalysis was demonstrated by measuring responses of cells to different color fluorescent reagents.

A study of the enolization of the [alpha], [beta]-unsaturated, bicyclic ketone [DELTA.sup.9,10]-octal-1-one (3, 4, 5, 6, 7, 8-hexahydro-1(2H)-naphthalenone), which can form the s-cis, endocyclic and s-trans, exocyclic dienolates, both of which have similar patterns of alkyl substitution at the [beta], [gamma] double bond is presented. The results have shown that the exocyclic dienolate is more stable than its endocyclic counterpart.