Advancing N-type doping in semiconductors through hydrogen-defect interactions

Probing the structural evolution and bonding properties of PtnC2−/0 (n = 1–7) clusters by density functional calculations

The unsaturated amides are traditionally synthesized by acylation of carboxylic acids or hydration of nitrile compounds but are rarely investigated by hydroaminocarbonylation of alkynes using heterogeneous single-metal-site catalysts (HSMSCs). Herein, single-Pd-site catalysts supported on N-doping carbon (NC) with different nitrogen dimensions inherited from corresponding metal-organic-framework precursors are successfully synthesized. 2D NC-supported single-Pd-site (Pd1/NC-2D) exhibited the best performance with near 100% selectivity and 76% yield of acrylamide for acetylene hydroaminocarbonylation with better stability, superior to those of Pd1/NC-3D, single-metal-site/nanoparticle coexisting catalyst, and nanoparticle catalyst. The coordination environment and molecular evolution of the single-Pd-site during the process of acetylene hydroaminocarbonylation on Pd1/NC-2D are detailly illuminated by various characterizations and density functional theoretical calculations (DFT). DFT also showed the energy barrier of rate-determining step on Pd1/NC-2D is lower than that of Pd1/NC-3D. Furthermore, Pd1/NC-2D catalyst illustrated the general applicability of the hydroaminocarbonylation for various alkynes.

Individual dopants in semiconductors are attracting considerable attention due to the prospect of using them in a wide range of applications. In particular, phosphorus donors in silicon have attracted significant interest owing to their weak interaction with the host crystal. However, harnessing their attributes toward the construction of scalable circuitry will require low resistive interconnects at a comparable scale as the dopant atoms. In this Rapid Communication, the authors investigate the transition from quantum coherent to the semiclassical diffusive transport in a 4.6-nm quasi-one-dimensional Si:P metal wire. Analyzing the temperature dependence of universal conductance fluctuations (UCF) the authors show that electron transport evolves from a quantum coherent to a semiclassical regime at temperatures as low as ~4 K and confirm that concepts of UCF and weak localization remain valid in metallic conductors at the atomic-scale.

As part of a search for new high energy density materials, we used density functional theoretical calculations to determine the thermochemical properties of various nitro-substituted borazine molecules. Optimized geometries, vibrational frequencies and spectra, and enthalpies of formation and combustion were determined for nitroborazine, dinitroborazine, trinitroborazine, and methyltrinitroborazine with substituents on either the boron atoms or the nitrogen atoms of the parent borazine ring. Our results indicate that the specific enthalpy of combustion ranged from 4 to 11 kJ g(-1), with increasing substitution of nitro groups lowering the energy of combustion per unit mass.

Electronic structure of cubic Er xGa 1−xN using the LSDA+ U approach

Chapter 8 - Optical hyperdoping

2-(5-Phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (Hptip) and its RuII complex [Ru(bpy)2(Hptip)](PF6)2 (where bpy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, 1H NMR spectroscopy, and mass spectrometry. The acid–base properties of the complex were studied by UV-visible and luminescence spectrophotometric pH titrations, and ground- and excited-state acidity ionization constants were derived. The DNA-binding properties of [Ru(bpy)2(Hptip)](PF6)2 were also investigated by means of UV-vis and emission spectroscopy, salt effects, steady-state emission quenching by [Fe(CN)6]4–, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. Density functional theoretical calculations were also carried out in order to understand the DNA binding properties.

Aromatic hydrocarbons are important components of polluted ambient air. The reaction of OH radicals with hexamethylbenzene (HMB) is a prototype system to study ipso addition leading eventually to dealkylation. We have investigated the OH + HMB and OD + HMB reactions between 323 and 433 K using a discharge fast-flow reactor coupled to a time-of-flight mass spectrometer with single-photon VUV photoionization (10.54 eV). The H atom abstraction channel has been found to be equal to (13.7 ± 4.4) % at 330 K leading to (11.1 ± 3.6) % at 298 K, higher than predicted by commonly used structure-reactivity relationships. The back dissociation rate constant has also been measured and has been found to be smaller than the rate of other aromatic hydrocarbons, in good agreement with density functional theoretical calculations. The dealkylation channel, leading to pentamethylphenol (PMP) + CH(3), is always found to be the minor channel, estimated inferior to 2% at 298 K.

Radioactvie waste forms for the future: Edited by Werner Lutze and Rodney C. Ewing. North Holland Publishing Co., Amsterdam/New York (1988), 778 pp.

Micellar liquid chromatographic method was developed for the enantioseparation of racemic amino alcohols. For that, diastereomeric derivatives of amino alcohols were prepared with activated ester of (S)-ketoprofen and separated on C18 column of RP-HPLC using the aqueous solution of surfactant (Brij-35 and SDS) as an alternative of the organic solvents. Also, chromatographic conditions were optimized by varying concentration of surfactant in aqueous solution, and by varying concentration and pH of the buffer. In addition, density functional theoretical calculations (DFT), validation [LOD (0.245 ng mL−1) and LOQ (0.735 ng mL−1)] and green-assessment score (82 score) were calculated for the developed method.

A phenylthiophenyl-bearing Ru(II) complex of [Ru(bpy)2(Hbptip)](PF6)2 {bpy = 2,2′-bipyridine, Hbptip = 2-(4-phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline} was synthesized and characterized by elemental analysis, 1H NMR spectroscopy, and electrospray ionization mass spectrometry. The ground- and excited-state acid–base properties of the complex were studied by UV–visible absorption and photoluminescence spectrophotometric pH titrations and the negative logarithm values of the ground-state acid ionization constants were derived to be pK a1 = 1.31 ± 0.09 and pK a2 = 5.71 ± 0.11 with the pK a2 associated deprotonation/protonation process occurring over 3 pK a units more acidic than thiophenyl-free parent complex of [Ru(bpy)2(Hpip)]2+ {Hpip = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline}. The calf thymus DNA-binding properties of [Ru(bpy)2(Hbptip)]2+ in Tris–HCl buffer (pH 7.1 and 50 mM NaCl) were investigated by DNA viscosities and density functional theoretical calculations as well as UV–visible and emission spectroscopy techniques of UV–visible and luminescence titrations, steady-state emission quenching by [Fe(CN)6]4−, DNA competitive binding with ethidium bromide, DNA melting experiments, and reverse salt effects. The complex was evidenced to bind to the DNA intercalatively with binding affinity being greater than those for previously reported analogs of [Ru(bpy)2(Hip)]2+, [Ru(bpy)2(Htip)]2+, and [Ru(bpy)2(Haptip)]2+ {Hip = 1H-imidazo[4,5-f][1,10]phenanthroline, Htip = 2-thiophenimidazo[4,5-f][1,10]phenanthroline, Haptip = 2-(5-phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}.

Focusing on the framework of how to realize the molecular spintronics in a single molecular magnet, we present theoretical studies on the spin-polarized quantum transport behavior through a single Mn12 molecular magnet. Our theoretical results were obtained by carrying out density functional theoretical calculation within the Keldysh nonequilibrium Green function formalism. The ultimate goal of the molecular spintronics is to develop single molecule transistors which generate spin-polarized currents through the molecular magnet. We obtained the densityof states, the transmission coefficients and the characteristic features of the current–voltage (I–V) on the spin-polarized transport properties of Mn12 by the theoretical calculation. These results show the possibility for the realization of molecular spintroinics using single molecular magnets.

S-Adenosylmethionine synthetase (ATP: L-methionine S-adenosyltransferase) catalyzes a two-step reaction in which tripolyphosphate (PPPi) is a tightly bound intermediate. Diimidotriphosphate (O(3)P-NH-PO(2)-NH-PO(3); PNPNP), a non-hydrolyzable analogue of PPPi, is the most potent known inhibitor of AdoMet synthetase with a K(i) of 2 nM. The structural basis for the slow, tight-binding inhibition by PNPNP has been investigated by spectroscopic methods. UV difference spectra reveal environmental alterations of aromatic protein residues upon PNPNP binding to form the enzyme.2Mg(2+).PNPNP complex, and more extensive changes upon formation of the enzyme.2Mg(2+).PNPNP.AdoMet complex. Stopped-flow kinetic studies of complex formation revealed that two slow isomerizations follow PNPNP binding in the presence of AdoMet, in contrast to the lower affinity, rapid-equilibrium binding in the absence of AdoMet. (31)P NMR spectra of enzyme complexes with PNPNP revealed electronic perturbations of each phosphorus atom by distinct upfield chemical shifts for each of the three phosphoryl groups in the enzyme.2Mg(2+).PNPNP complex, and further upfield shifts of at least 2 resonances in the complex with AdoMet. Comparison of the chemical shifts for the enzyme-bound PNPNP with the enzyme complexes containing either the product analogue O(3)P-NH-PO(3) or O(3)P-O-PO(2)-NH-PO(3) indicates that the shifts on binding are largest at the binding sites corresponding to those for the alpha and gamma phosphoryl groups of the nucleotide (-3.1 to -4.1 ppm), while the resonance at the beta phosphoryl group position shifts by -2.1 ppm. EPR spectra of Mn(2+) complexes demonstrate spin coupling between the two Mn(2+) in both enzyme.2Mn(2+).PNPNP and enzyme.2Mn(2+).PNPNP.AdoMet, indicating that the metal ions have comparable distances in both cases. The combined results indicate that formation of the highest affinity complex is associated with protein side chain rearrangements and increased electron density at the ligand phosphorus atoms, likely due to ionization of an -NH- group of the inhibitor. The energetic feasibility of ionization of a -NH- group when two Mg(2+) ions are bound to O(3)P-NH-PO(3) is supported by density functional theoretical calculations on model chelates. This mode of interaction is uniquely available to compounds with P-NH-P linkages and may be possible with other proteins in which multiple cations coordinate a polyphosphate chain.

The chemical vapor deposition method is widely used in preparation of graphene, hexagonal boron nitride (h-BN) and other 2D materials. To improve the quality of h-BN, it is essential to learn details of the growth mechanism including dissociation of precursors, the initial nucleation, the stabilities of various clusters and the origins behind them. Here, the dissociation process of ammonia borane (AB) and its later nucleation on the Ru(0001) surface were simulated with density functional theory. The results show that the key step before dissociation is the chemical adsorption of AB molecule on the Ru(0001) surface. In the approaching process of AB molecule to Ru(0001), all bonds connected with H, irrespective of B-H or N-H, are stretched by the underlying metal surface. The H atoms connected with boron prefer to be dissociated followed by those connected to nitrogen. After full dehydration, BN dimer accumulates by forming chain-like, ring-shaped and honeycomb clusters. The chain-like geometries are energy-favoured in BN clusters with size lower than 6. Beyond this, the honeycomb configuration becomes the energy-favoured one, resulting in a geometry evolution from chain-like to honeycomb. The nucleation barrier and the critical nuclei size of BN clusters on Ru(0001) at different chemical potentials are discussed, which can be realized by tuning ratios of B to N in the feedstock. The growth mode observed for h-BN on Ru(0001) can be easily extended to growth on other transition metals and other 2D materials, thus should provide important information in optimizing experimental schemes.

Chemical physics behind formation of effective and selective non-covalent interaction between fullerenes (C60 and C70) and a designed chiral monoporphyrin in solution