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https://www.readbyqxmd.com/read/28732183/new-resins-for-dental-composites
#1
A P P Fugolin, C S Pfeifer
Restorative composites have evolved significantly since they were first introduced in the early 1960s, with most of the development concentrating on the filler technology. This has led to improved mechanical properties, notably wear resistance, and has expanded the use of composites to larger posterior restorations. On the organic matrix side, concerns over the polymerization stress and the potential damage to the bonded interface have dominated research in the past 20 y, with many "low-shrinkage" composites being launched commercially...
July 1, 2017: Journal of Dental Research
https://www.readbyqxmd.com/read/28732164/electrochemical-intercalation-of-mg-2-into-anhydrous-and-hydrated-crystalline-tungsten-oxides
#2
Ruocun Wang, Ching-Chang Chung, Yang Liu, Jacob L Jones, Veronica Augustyn
The reversible intercalation of multivalent cations, especially Mg(2+), into a solid-state electrode is an attractive mechanism for next-generation energy storage devices. These reactions typically exhibit poor kinetics due to a high activation energy for interfacial charge-transfer and slow solid-state diffusion. Interlayer water in V2O5 and MnO2 has been shown to improve Mg(2+) intercalation kinetics in non-aqueous electrolytes. Here, the effect of structural water on Mg(2+) intercalation in non-aqueous electrolytes is examined in crystalline WO3 and the related hydrated and layered WO3·nH2O (n = 1, 2)...
July 21, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28732154/ironing-out-genes-in-the-environment-an-experimental-study-of-the-dna-goethite-interface
#3
Michael P Schmidt, Carmen Enid Martinez
DNA fate in soil plays an important role in the cycling of genetic information in the environment. Adsorption onto mineral surfaces has great impact on this function. This study probes the kinetics, equilibrium behavior and bonding mechanisms associated with adsorption of DNA onto goethite, a common soil mineral. Surface sensitive ATR-FTIR and XPS approaches are applied to directly characterize the DNA-goethite interface. Adsorption kinetics follow a pseudo-first order model, suggesting adsorption rate is surface limited...
July 21, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28732033/spatial-and-simultaneous-representative-seroprevalence-of-anti-toxoplasma-gondii-antibodies-in-owners-and-their-domiciled-dogs-in-a-major-city-of-southern-brazil
#4
Aline do Nascimento Benitez, Felippe Danyel Cardoso Martins, Marcelle Mareze, Nelson Jessé Rodrigues Santos, Fernanda Pinto Ferreira, Camila Marinelli Martins, João Luis Garcia, Regina Mitsuka-Breganó, Roberta Lemos Freire, Alexander Welker Biondo, Italmar Teodorico Navarro
Toxoplasmosis, caused by Toxoplasma gondii, has traditionally been considered an important water and foodborne protozoonosis with important public health considerations. Although felids play a well-established role as definitive hosts, canine epidemiological involvement in the parasite's life cycle remains questionable and controversial. The increasing closeness of the human-dog bond, particularly seen in urban settings, has been recognized as a historically unprecedented worldwide movement. Sharing daily lives in the same households, dogs may be exposed to similar associated risks of T...
2017: PloS One
https://www.readbyqxmd.com/read/28731734/determining-potentials-of-zero-charge-of-metal-electrodes-versus-the-standard-hydrogen-electrode-from-density-functional-theory-based-molecular-dynamics
#5
Jiabo Le, Marcella Iannuzzi, Angel Cuesta, Jun Cheng
We develop a computationally efficient scheme to determine the potentials of zero charge (PZC) of metal-water interfaces with respect to the standard hydrogen electrode. We calculate the PZC of Pt(111), Au(111), Pd(111) and Ag(111) at a good accuracy using this scheme. Moreover, we find that the interface dipole potentials are almost entirely caused by charge transfer from water to the surfaces, the magnitude of which depends on the bonding strength between water and the metals, while water orientation hardly contributes at the PZC conditions...
July 7, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28731720/analytic-energy-gradients-for-variational-two-electron-reduced-density-matrix-driven-complete-active-space-self-consistent-field-theory
#6
Elvis Maradzike, Gergely Gidofalvi, Justin M Turney, Henry F Schaefer, A Eugene DePrince
Analytic energy gradients are presented for a variational two-electron reduced-density matrix (2-RDM)-driven complete active space self-consistent field (CASSCF) method. The active-space 2-RDM is determined using a semidefinite programing (SDP) algorithm built upon an augmented Lagrangian formalism. Expressions for analytic gradients are simplified by the fact that the Lagrangian is stationary with respect to variations in both the primal and dual solutions to the SDP problem. Orbital response contributions to the gradient are identical to those that arise in conventional CASSCF methods in which the electronic structure of the active space is described by a full configuration interaction (CI) wave function...
July 21, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28731717/hydrogen-bond-direction-enables-palladium-catalyzed-branch-and-enantioselective-allylic-aminations-and-beyond
#7
Ya-Ni Wang, Bao-Cheng Wang, Mao-Mao Zhang, Xiao-Wen Gao, Tian-Ren Li, Liang-Qiu Lu, Wen-Jing Xiao
The palladium-catalyzed branch- and enantioselective allylic amination of vinyl benzoxazinones was accomplished through controlling the hydrogen bond direction. This protocol provides a rapid and efficient route for synthesizing an important building block, chiral amino alkene, from widely available aliphatic amines in 64 → 99% yields with up to 99% ee. Furthermore, this transformation and the accompanying products were utilized to develop one-pot reactions through dual catalysis, affording chiral indolines with good synthetic efficiency and excellent enantiocontrol...
July 21, 2017: Organic Letters
https://www.readbyqxmd.com/read/28731710/computational-calorimetry-of-pnipam-cononsolvency-in-water-methanol-mixtures
#8
Cahit Dalgicdir, Francisco Rodriguez-Ropero, Nico F A van der Vegt
We revisit the mechanism for cononsolvency of PNIPAM in water/methanol mixtures. Using extensive molecular dynamics simulations we calculate the calorimetric enthalpy of the PNIPAM collapse transition and observe a unique fingerprint of PNIPAM cononsolvency which is analysed in terms of microscopic interactions. We find that polymer hydration is the determining factor for PNIPAM collapse in the cononsolvency regime. In particular, it is shown that methanol frustrates the ability of water to form hydrogen bonds with the amide proton and therefore causes polymer collapse...
July 21, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28731706/automated-construction-of-molecular-active-spaces-from-atomic-valence-orbitals
#9
Elvira R Sayfutyarova, Qiming Sun, Garnet Kin-Lic Chan, Gerald Knizia
We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multi-configuration and multi-reference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a redcoordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wavefunction (such as from a Hartree-Fock or Kohn-Sham calculations) based on projectors to targeted atomic valence orbitals...
July 21, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28731695/how-rhodopsin-tunes-the-equilibrium-between-protonated-and-deprotonated-forms-of-the-retinal-chromophore
#10
Siri Camee van Keulen, Alicia Solano, Ursula Rothlisberger
Rhodopsin is a photoactive G-protein-coupled receptor (GPCR) that converts dim light into a signal for the brain, leading to eyesight. Full activation of this GPCR is achieved after passing through several steps of the protein's photoactivation pathway. Key events of rhodopsin activation are the initial cis-trans photoisomerisation of the covalently bound retinal moiety followed by conformational rearrangements and deprotonation of the chromophore's protonated Schiff base (PSB), which ultimately lead to full activation in the meta II state...
July 21, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28731687/intramolecular-c-h-and-c-f-bond-oxygenation-by-site-differentiated-tetranuclear-manganese-models-of-the-oec
#11
Kurtis M Carsch, Graham de Ruiter, Theodor Agapie
The dangler manganese center in the oxygen-evolving complex (OEC) of photosystem II plays an important role in the oxidation of water to dioxygen. Inspired by the structure of the OEC, we synthesized a series of site-differentiated tetra-manganese clusters [LMn3(PhPz)3OMn][OTf]x (2: x = 2; 3: x = 1) that features an apical manganese ion-distinct from the others-that is appended to a trinuclear manganese core through an μ4-oxygen atom bridge. This cluster design was targeted to facilitate studies of high-valent Mn-oxo formation, which is a proposed step in the mechanism for water oxidation by the OEC...
July 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28731683/synthesis-and-optical-properties-of-cu6e6-snph-2-pph2et-6-e-s-se-te-cluster-molecules
#12
Andreas Eichhöfer, Michael Kühn, Sergei Lebedkin, Max Kehry, Manfred M Kappes, Florian Weigend
A homologous series of three copper-tin-chalcogenide cluster molecules [Cu6E6(SnPh)2(PPh2Et)6] (E = S, Se, Te) was synthesized by reactions of CuO(O)CCH3 and PhSnCl3 with E(SiMe3)2 in the presence of PPh2Et. The cluster cage structures are similar, with slight differences in the bridging modes of the respective chalcogenide ligands E. The onset of the optical absorption displays a significant decrease of ca. 1.1 eV on going from sulfur to tellurium. The differences in bonding and electronic excitations can be rationalized by DFT and TDDFT calculations...
July 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28731682/cold-adaptation-of-triosephosphate-isomerase
#13
Johan Åqvist
The main problem for enzymes from psychrophilic species, that need to work near the freezing point of liquid water, is the exponential decay of reaction rates as the temperature is lowered. Cold-adapted enzymes have solved this problem by shifting the activation enthalpy-entropy balance for the catalyzed reaction compared to their mesophilic orthologs. To understand the structural basis of this universal feature it is necessary to examine pairs of such orthologous enzymes, with known 3D structures, at the microscopic level...
July 21, 2017: Biochemistry
https://www.readbyqxmd.com/read/28731675/sustained-release-of-a-peptide-based-matrix-metalloproteinase-2-inhibitor-to-attenuate-adverse-cardiac-remodeling-and-improve-cardiac-function-following-myocardial-infarction
#14
Zhaobo Fan, Minghuan Fu, Zhaobin Xu, Bo Zhang, Zhihong Li, Haichang Li, Xinyu Zhou, Xuanyou Liu, Yunyan Duan, Pei-Hui Lin, Pu Duann, Xiaoyun Xie, Jianjie Ma, Zhenguo Liu, Jianjun Guan
Following myocardial infarction (MI), degradation of extracellular matrix (ECM) by upregulated matrix metalloproteinases (MMPs) especially MMP-2 decreases tissue mechanical properties, leading to cardiac function deterioration. Attenuation of cardiac ECM degradation at the early stage of MI has the potential to preserve tissue mechanical properties, resulting in cardiac function increase. Yet the strategy for efficiently preventing cardiac ECM degradation remains to be established. Current preclinical approaches have shown limited efficacy due to low drug dosage allocated to the heart tissue, dose-limiting side effects, and cardiac fibrosis...
July 21, 2017: Biomacromolecules
https://www.readbyqxmd.com/read/28731593/synthesis-characterization-and-efficient-catalytic-activities-of-a-nickel-ii-porphyrin-remarkable-solvent-and-substrate-effects-on-participation-of-multiple-active-oxidants
#15
Cheal Kim, Hye Ahn, Jeong Bae, Min Kim, Kwon Bok, Ha Jeong, Suk Lee
A new nickel(II) porphyrin complex, [NiII(porp)] (1) has been synthesized and characterized by 1H NMR, 13C NMR and mass spectrometry analysis. This NiII porphyrin complex 1 catalyzed quantitatively the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (MCPBA) under mild conditions. Reactivity and Hammett studies, H218O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants NiII-OOC(O)R 2, NiIV-Oxo 3, and NiIII-Oxo 4 in olefin epoxidation reactions by nickel porphyrin complex is markedly affected by solvent polarity and concentration and type of substrate...
July 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28731587/reversible-pressure-controlled-depolymerization-of-a-copper-ii-containing-coordination-polymer
#16
Jack Kay Clegg, Aidan Brock, Katrina Jolliffe, Simon Parsons, Leonard Lindoy, Peter Tasker, Fraser White
A unique pressure-induced Cu-N bond breaking/bond forming reaction is reported. The variation of pressure on a single crystal of a one-dimensional copper(II)-containing coordination polymer (Cu2L2(1-methylpiperazine)2]n, where H2L is 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione)), was monitored using single crystal X-ray diffraction with the aid of a diamond anvil cell. At a very low elevated pressure (~0.05 GPa) a remarkable reversible phase change was observed. The phase change results in the depolymerization of the material through the cleavage and formation of axial Cu-N bonds as well as "ring flips" of individual axially coordinated 1-methylpiperazine ligands...
July 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28731341/a-2d-coordination-network-that-detects-nitro-explosives-in-water-catalyzes-baylis-hillman-reactions-and-undergoes-unusual-2d%C3%A2-3d-single-crystal-to-single-crystal-transformation
#17
Vivekanand Sharma, Dinesh De, Sanchari Pal, Prithwidip Saha, Parimal K Bharadwaj
The solvothermal reaction of Zn(NO3)2·6H2O and a linear dicarboxylate ligand H2L, in the presence of urotropine in N,N'-dimethylformamide (DMF), gives rise to a new porous two-dimensional (2D) coordination network, {[Zn3(L)3(urotropine)2]·2DMF·3H2O}n (1), with hxl topology. Interestingly, framework 1 exhibits excellent emission properties owing to the presence of naphthalene moiety in the linker H2L, that can be efficiently suppressed by subtle quantity of nitro explosives in aqueous medium. Furthermore, presence of urotropine molecules bound to the metal centers, 1 is found to be an excellent heterogeneous catalyst meant for atom-economical C-C bond-forming Baylis-Hillman reactions...
July 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28731334/optical-spectra-and-magnetic-behavior-of-a-wide-range-of-europium-iii-oxo-compounds-analysis-of-the-ligand-field-effects
#18
Anna Bronova, Nils Kannengießer, Robert Glaum
The europium-oxygen interaction in nine different europium(III) oxo-compounds (including C-type Eu2O3) was investigated on the basis of powder reflectance spectra (near-IR/vis/UV) and temperature-dependent magnetic measurements. Computation of the transition energies and of the effective Bohr magneton numbers for Eu(3+) in the different ligand fields were performed within the framework of the angular overlap model (AOM) using the computer program BonnMag. These calculations show that all electronic transition energies in the optical spectra, the magnetic susceptibilities as well as their temperature dependence, are very well-accounted for by AOM...
July 21, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28731301/lead-ii-complexes-of-amino-acids-peptides-and-other-related-ligands-of-biological-interest
#19
Etelka Farkas, Péter Buglyó
Lead(II) forms (NH2,COO-)-chelated mono- and bis-complexes with simple amino acids, while mono-complexes with pH-dependent coordination modes exist with simple dipeptides. These mostly hemidirected complexes have moderate stability. While a weak interaction of side chain imidazole and carboxylate in lead(II)-aminoacidato complexes is found, the thiolate group has an exceptionally high affinity to this metal ion. For example, tridentate (NH2,COO-,S-)-coordination of penicillamine (Pen) and cysteine (Cys) results in an extremely strong interaction with lead(II), but, owing to the sterical effect of the 6s2 pair, a second ligand is not able to coordinate in the above mentioned tridentate way...
April 10, 2017: Metal Ions in Life Sciences
https://www.readbyqxmd.com/read/28731122/ligand-effect-on-the-rhodium-porphyrin-catalyzed-hydrogenation-of-2-2-paracyclophane-with-water-key-bimetallic-hydrogenation
#20
Chun Meng Tam, Ching Tat To, Kin Shing Chan
Rhodium porphyrin catalyzed hydrogenation of the aliphatic carbon-carbon σ-bond of [2.2]paracyclophane with water has been examined with a variety of tetraarylporphyrins and axial ligands. Mechanistic investigations show that Rh(III)(ttp)H, which can be derived from the reaction of [Rh(II)(ttp)]2 with water without a sacrificial reductant, plays an important role in promoting bimetallic reductive elimination to give the hydrogenation product.
July 21, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
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