669 resultados para Ionic bonds
Resumo:
Magnetic interactions in ionic solids are studied using parameter-free methods designed to provide accurate energy differences associated with quantum states defining the Heisenberg constant J. For a series of ionic solids including KNiF3, K2NiF4, KCuF3, K2CuF4, and high- Tc parent compound La2CuO4, the J experimental value is quantitatively reproduced. This result has fundamental implications because J values have been calculated from a finite cluster model whereas experiments refer to infinite solids. The present study permits us to firmly establish that in these wide-gap insulators, J is determined from strongly local electronic interactions involving two magnetic centers only thus providing an ab initio support to commonly used model Hamiltonians.
Resumo:
The optical-absorption spectrum of a cationic Ag0 atom in a KCl crystal has been studied theoretically by means of a series of cluster models of increasing size. Excitation energies have been determined by means of a multiconfigurational self-consistent field procedure followed by a second-order perturbation correlation treatment. Moreover results obtained within the density-functional framework are also reported. The calculations confirm the assignment of bands I and IV to transitions of the Ag-5s electron into delocalized states with mainly K-4s,4p character. Bands II and III have been assigned to internal transitions on the Ag atom, which correspond to the atomic Ag-4d to Ag-5s transition. We also determine the lowest charge transfer (CT) excitation energy and confirm the assignment of band VI to such a transition. The study of the variation of the CT excitation energy with the Ag-Cl distance R gives additional support to a large displacement of the Cl ions due to the presence of the Ag0 impurity. Moreover, from the present results, it is predicted that on passing to NaCl:Ag0 the CT onset would be out of the optical range while the 5s-5p transition would undergo a redshift of 0.3 eV. These conclusions, which underline the different character of involved orbitals, are consistent with experimental findings. The existence of a CT transition in the optical range for an atom inside an ionic host is explained by a simple model, which also accounts for the differences with the more common 3d systems. The present study sheds also some light on the R dependence of the s2-sp transitions due to s2 ions like Tl+.
Resumo:
Charged and neutral oxygen vacancies in the bulk and on perfect and defective surfaces of MgO are characterized as quantum-mechanical subsystems chemically bonded to the host lattice and containing most of the charge left by the removed oxygens. Attractors of the electron density appear inside the vacancy, a necessary condition for the existence of a subsystem according to the atoms in molecules theory. The analysis of the electron localization function also shows attractors at the vacancy sites, which are associated to a localization basin shared with the valence domain of the nearest oxygens. This polyatomic superanion exhibits chemical trends guided by the formal charge and the coordination of the vacancy. The topological approach is shown to be essential to understand and predict the nature and chemical reactivity of these objects. There is not a vacancy but a coreless pseudoanion that behaves as an activated host oxygen.
Resumo:
The authors have developed a live-cell multimodality microscope combining epifluorescence with digital holographic microscopy; it has been implemented with a decoupling procedure allowing to separately measure from the quantitative phase important cell parameters including absolute volume, shape and integral intracellular refractive index. In combination with the numerous different specific fluorescent cellular probes, this multimodality microscopy can address important issues in cell biology. This is demonstrated by the study of intracellular calcium homeostasis associated with the change in cell volume, which play a critical role in the excitotoxicity-induced neuronal death.
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Audit report of the Schedule of Debt Service and Coverage for Iowa State University of Science and Technology for the Dormitory Revenue Refunding Bonds for the year ended June 30, 2012
Resumo:
A broad and simple method permitted halide ions in quaternary heteroaromatic and ammonium salts to be exchanged for a variety of anions using an anion exchange resin (A− form) in non-aqueous media. The anion loading of the AER (OH− form) was examined using two different anion sources, acids or ammonium salts, and changing the polarity of the solvents. The AER (A− form) method in organic solvents was then applied to several quaternary heteroaromatic salts and ILs, and the anion exchange proceeded in excellent to quantitative yields, concomitantly removing halide impurities. Relying on the hydrophobicity of the targeted ion pair for the counteranion swap, organic solvents with variable polarity were used, such as CH3OH, CH3CN and the dipolar nonhydroxylic solvent mixture CH3CN:CH2Cl2 (3:7) and the anion exchange was equally successful with both lipophilic cations and anions.
Resumo:
The Watershed Improvement Fund and the Watershed Improvement Review Board (WIRB) were created in 2005. This statute is now codified in Iowa Code Chapter 466A. The pmpose of the Watershed Improvement Fund is to enhance the water quality and flood prevention efforts in the state through a variety of impairment-based, locally directed watershed improvement projects. These projects are awarded grants through a competitive application process directed by the WIRB. Appropriations to the Fund do not revert. Interest earned on the moneys on the Fund are also retained in the Fund and are used to fund projects or pay per diem and expenses of the WIRB members. In state fiscal years 2009 (SFY2009) and 2010 (SFY2010), the Watershed Improvement Fund was appropriated $5,000,000 from the Rebuild Iowa Infrastructure Fund (RIIF). In SFY2011, the Watershed Improvement Fund was appropriated $2,000,000 from the Revenue Bonds Capitals II Fund (RBC2).
Resumo:
The Watershed Improvement Fund and the Watershed Improvement Review Board (WIRB) were created in 2005. This statute is now codified in Iowa Code Chapter 466A. The purpose of the Watershed Improvement Fund is to enlmnce the water quality and flood prevention efforts in the state through a variety of impairment-based, locally directed watershed improvement projects. These projects are awarded grants through a competitive application process directed by the WIRB. Appropriations to the Fund do not revert except for the Capital Revenue Bonds II (RCB2) appropriation. Interest eamed on the moneys on the Fund are also retained in the Fund and are used to fund projects or pay per diem and expenses of the WIRB members. Starting July 1, 2012, the Fund is also receiving Animal Agriculture Compliance Fund Penalties. In state fiscal years 2009 (SFY2009) and 2010 (SFY2010), the Watershed Improvement Fund was appropriated $5,000,000 from the Rebuild Iowa Infrastructure Fund (RIIF). In SFY2011, the Watershed Improvement Fund was appropriated $2,000,000 from the Revenue Bonds Capitals II Fund (RBC2). No appropriation was received in fiscal year 2012. In SFY 2013, the Watershed Improvement Fund was appropriated $1,000,000 from the RIIF.
Resumo:
The Watershed Improvement Fund and the Watershed Improvement Review Board (WIRB) were created in 2005. This statute is now codified in Iowa Code Chapter 466A. The purpose of the Watershed Improvement Fund is to enhance the water quality in the state through a variety of impairment-based, locally-directed watershed improvement projects. These projects are awarded grants through a competitive application process directed by the WIRB. Appropriations to the Fund do not revert except for the Capital Revenue Bonds II (RCB2) appropriation. Interest earned on the moneys on the Fund are also retained in the Fund and are used to fund projects or pay per diem and expenses of the WIRB members. Starting July 1, 2012, the Fund is also receiving Animal Agriculture Compliance Fund Penalties. In state fiscal years 2009 (SFY2009) and 2010 (SFY2010), the Watershed Improvement Fund was appropriated $5,000,000 from the Rebuild Iowa Infrastructure Fund (RIIF). In SFY2011, the Watershed Improvement Fund was appropriated $2,000,000 from the Revenue Bonds Capitals II Fund (RBC2). No appropriation was received in fiscal year 2012. In SFY 2013, the Watershed Improvement Fund was appropriated $1,000,000 from the RIIF.
Resumo:
The Watershed Improvement Fund and the Watershed Improvement Review Board (WIRB) were created in 2005. This statute is now codified in Iowa Code Chapter 466A. The purpose of the Watershed Improvement Fund is to enhance the water quality in the state through a variety of impairment-based, locally-directed watershed improvement projects. These projects are awarded grants through a competitive application process directed by the WIRB. Appropriations to the Fund do not revert except for the Capital Revenue Bonds II (RCB2) appropriation. Interest earned on the moneys on the Fund are also retained in the Fund and are used to fund projects or pay per diem and expenses of the WIRB members. Starting July 1, 2012, the Fund is also receiving Animal Agriculture Compliance Fund Penalties. In state fiscal years 2009 (SFY2009) and 2010 (SFY2010), the Watershed Improvement Fund was appropriated $5,000,000 from the Rebuild Iowa Infrastructure Fund (RIIF). In SFY2011, the Watershed Improvement Fund was appropriated $2,000,000 from the Revenue Bonds Capitals II Fund (RBC2). No appropriation was received in fiscal year 2012. In SFY 2013, the Watershed Improvement Fund was appropriated $1,000,000 from the RIIF.
Resumo:
This is the annual appropriations report submitted on behalf of the Watershed Improvement Review Board (WIRB).
Resumo:
Additions of lactams, imides, (S)-4-benzyl-1,3-oxazolidin-2-one, 2-pyridone, pyrimidine-2,4-diones (AZT derivatives), or inosines to the electron-deficient triple bonds of methyl propynoate, tert-butyl propynoate, 3-butyn-2-one, N-propynoylmorpholine, or N-methoxy-N-methylpropynamide in the presence of many potential catalysts were examined. DABCO and, second, DMAP appeared to be the best (highest reaction rates and E/Z ratios), while RuCl3, RuClCp*(PPh3)2, AuCl, AuCl(PPh3), CuI, and Cu2(OTf)2 were incapable of catalyzing such additions. The groups incorporated (for example, the 2-(methoxycarbonyl)ethenyl group that we name MocVinyl) serve as protecting groups for the above-mentioned heterocyclic CONH or CONHCO moieties. Deprotections were accomplished via exchange with good nucleophiles: the 1-dodecanethiolate anion turned out to be the most general and efficient reagent, but in some particular cases other nucleophiles also worked (e.g., MocVinyl-inosines can be cleaved with succinimide anion). Some structural and mechanistic details have been accounted for with the help of DFT and MP2 calculations.
Resumo:
Additions of lactams, imides, (S)-4-benzyl-1,3-oxazolidin-2-one, 2-pyridone, pyrimidine-2,4-diones (AZT derivatives), or inosines to the electron-deficient triple bonds of methyl propynoate, tert-butyl propynoate, 3-butyn-2-one, N-propynoylmorpholine, or N-methoxy-N-methylpropynamide in the presence of many potential catalysts were examined. DABCO and, second, DMAP appeared to be the best (highest reaction rates and E/Z ratios), while RuCl3, RuClCp*(PPh3)2, AuCl, AuCl(PPh3), CuI, and Cu2(OTf)2 were incapable of catalyzing such additions. The groups incorporated (for example, the 2-(methoxycarbonyl)ethenyl group that we name MocVinyl) serve as protecting groups for the above-mentioned heterocyclic CONH or CONHCO moieties. Deprotections were accomplished via exchange with good nucleophiles: the 1-dodecanethiolate anion turned out to be the most general and efficient reagent, but in some particular cases other nucleophiles also worked (e.g., MocVinyl-inosines can be cleaved with succinimide anion). Some structural and mechanistic details have been accounted for with the help of DFT and MP2 calculations.