Finite perturbation theory-density functional theory calculation of the spin-dipolar contribution to NMR spin-spin coupling constants

In this work an implementation of the FPT-DFT approach for calculating the spin-dipolar contribution to NMR spin-spin coupling constants is presented. This method was tested in a set of small molecules, giving results in excellent agreement when comparing them with values taken from the literature, which were obtained with state-of-the-art calculations. To obtain an insight into the relative importance of the spin-dipolar contribution in unsaturated compounds, calculations of J(F,C), J(F,F) and J(F,H) couplings in 1,2-, 1,3-, and 1,4-difluorobenzenes were performed. An important spin-dipolar contribution to ³ J(F, F) and ⁵ J(F,F) was found, suggesting that this term might be important in some cases. When performing DFT calculations the non-singlet instabilities usually found in unsaturated compounds are overcome.     

Hyperfine Interactions in the Sr0.88Ba0.12HfO3 Compound

The temperature dependence of the hyperfine parameters in a powder sample of the Sr_0.88Ba_0.12HfO₃ compound has been investigated for the first time using perturbed angular correlation spectroscopy. The time spectra were measured as a function of the temperature from 293 to 1273 K. Activated ¹⁸¹Ta nuclei were used as hyperfine probes at the Hf sites. The analysis of the time spectra indicates the presence of two different surroundings for the Ta probes. The most populated site (f ₁≈75% at laboratory temperature) was fitted with the usual static quadrupole hyperfine interactions found in most perovskite-type compounds. The resulting quadrupole frequency is ω _Q ≈24 Mrad/s at this temperature. This frequency continuously decreases to nearly 9 Mrad/s at 1273 K. Its line width temperature dependence displays three regions and the changes observed probably correspond to phase transitions. The other site has a large and temperature independent quadrupole frequency ω _Q ≈120 Mrad/s that reversibly transforms into the first at high temperatures and probably originates from some defect in the structure. This revised version was published online in September 2006 with corrections to the Cover Date.     

Increasing returns economics and generalized Pólya processes

This article extends the traditional Pólya scheme consisting of one urn with two colors to the schemes where multiple independent and/or interdependent urns with multiple additions and/or withdraws and several independent and/or interdependent colors are considered. It also argues that with these schemes many complex economic systems subject to increasing returns can be formalized mathematically, for they allow for positive and negative feedbacks among many variables, “jumps,” “bad” behaved dynamics, dis continuities, and interrelation among systems. © 2013 Wiley Periodicals, Inc. Complexity 19: 21–37, 2013     

Mössbauer and X-ray Study of Fe1−x Al x , 0.2≤x≤0.5, Samples Produced by Mechanical Alloying

In this work we report the magnetic and structural properties obtained by Mössbauer spectroscopy and X-ray diffraction, of the Fe_1?x Al _x , 0.2≤x≤0.5, alloys produced by mechanical alloying. Alloys with x=0.2, 0.3, 0.4 and 0.5, were for milled 12, 24, 36, and 48 hours. All the obtained alloys are in the bcc phase. The obtained Mössbauer spectra are characteristic of disordered ferromagnetic system. The lattice parameter remains nearly constant (～2.91 Å) for all the milling times and compositions. The mean grain sizes in the (110) and (211) direction are nearly constants with the milling time but vary from 15.5 to 11 nm and from 10.5 to 8.5 nm when Al content grow between x=0.2 to x=0.4, respectively. The difference between the mean grain sizes in these two directions shows that the grains are of prolate spheroid form.

     

Electric Fields Gradients at 111In Sites in CdIn2O4 Spinel

The perturbed angular correlation (PAC) technique was applied to study the electric field gradients at ¹¹¹In sites in CdIn₂O₄. The measurements were carried out at temperatures in the range 150–1073 K. The aims of the study were both to characterize the quadrupole interactions of the tracers and to determine the distribution of indium ions among the available sites in the spinel structure. Room temperature measurements corresponding to samples cooled at different rates are also reported. ^aAlso at Comisión de Investigasiones Científicas de la Provincia de Buenos Aires, Argentina.     

Ring-Opening Metathesis Polymerization Kinetics of Cyclooctene with Second Generation Grubbs’ Catalyst

A kinetic study of the ring-opening metathesis polymerization (ROMP) of cis-cyclooctene using the ruthenium initiator benzylidene [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]-dichloro-(tricyclohexylphosphine) (second generation Grubbs’ catalyst) was carried out by ¹H-NMR. The dependence on the reaction rate with the temperature and the influence of the addition of a chain transfer agent were evaluated. Some kinetic constants are also reported for this system.     

Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Using ¹H and ¹³C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d ₃. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H₃O⁺ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H₃O⁺ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.     

Interpolation of Limited and Weakly Compact Operators on Families of Banach Spaces

In this paper, we study how the limited and weakly compact properties of operators are preserved by interpolation of the real method for infinite families of Banach spaces introduced by Carro in Studia Math. 109 (1994). We apply these results to the case of Sparr, Fernández and Cobos–Peetre methods of interpolation for finite families.     

Effect of short and long range forces on the thermodynamic properties of water. A simple short range reference system

Three realistic potential models of water, the non-polarizable ST2 and TIP4P models, and the polarizable TIP4P/P model, were used in computer simulations to study the effect of the range of intermolecular interactions on the thermodynamic properties of water. Following the results of recent studies, a short range system is constructed to the full pair potential u(1,2) in such a way that a perturbation expansion can be formulated in powers of the dipole-dipole interaction only. Computations of low density properties and computer simulations performed for several densities on three subcritical and one supercritical isotherms show that the short range reference not only reproduces the structure but approximates also the internal energy and pressure of water surprisingly well. Differences in the internal energy between the full and short range water do not exceed 5% for all models used over the entire range of the thermodynamic conditions considered.     

Thermodynamics of binding of Zn2+ to carbonic anhydrase inhibitors

The Becke3LYP functional of DFT theory and the two-layered ONIOM (B3LYP/6–311 + G(d,p): MNDO) method were used to characterize 46 gas-phase complexes of 34 neutral and anionic ligands (H₂O, CH₃OH, CH₃COOH, CH₃CONH₂, HOSO₂NH₂, CO₂, HSO₂NH₂, CH₃SO₂NH₂, CH₃C(= O)NHOH, imidazole, NH₂SO₂NH₂, anions of 4-aminobenzenesulphonamide, saccharin, 1I9L, brinzolamide, dorzolamide, acetazolamide, further HO^(?), CH₃CO^(?), CH₃COO^(?), CH₃CONH^(?), N = N = N^(?), S = C = N^(?), CH₃C(= O)NHO^(?), HOCOO^(?), imidazoleN^(?), phenol-O^(?), HOSO₂NH^(?), ^(?)OSO₂NH^(?), ^(?)OSO₂NH₂, H₂NSO₂NH^(?), HSO₂NH^(?), CH₃SO₂NH^(?), and CF₃SO₂NH^(?), respectively) with Zn²⁺. Proton dissociation enthalpies and Gibbs energies of acidic inhibitors in the presence of zinc were computed. Their gas-phase acidity considerably increases upon chelation. Of the bases investigated, the weakest zinc affinity is exhibited by carbon dioxide (- 313.5 kJ mol^?1). Deprotonated inhibitors have higher affinities for zinc than the neutral ones. Compared to the other mono-deprotonated ligands the acetohydroxamic acid anion has the highest affinity for zinc (- 1872.7 kJ mol^?1). The zinc affinity of the acetazolamide anion computed using the hybrid ONIOM (B3LYP/6-311 + G(d,p): MNDO) method is in very good agreement with the full DFT ones and this method can be adopted to model large complexes of inhibitors with the active site of carbonic anhydrase.