Characterization of Argentine Loess and Paleosols by Mössbauer Spectroscopy

Hyperfine Interactions - We have used Mössbauer spectroscopy to investigate iron-bearing mineral samples of loess and paleosols from a geologic section at La Plata, Argentina, 34°...     

Liquid-liquid extraction: A graphical method for equilibrium stage calculations for quaternary systems

Ruiz Beviá, F., Prats Rico, D. and Marcilla Gomis, A.F., 1984. Liquid-liquid extraction: a graphical method for equilibrium stage calculations for quaternary systems. Fluid Phase Equilibria, 15: 257-265.A very simple graphical method for stage calculations has been developed for quaternary systems. The calculation method is based on the equilibrium representation method proposed by Ruiz and Prats (1983a), and requires only two graphs for solution of the material balances. The method is based completely on experimental data and does not require any simplifying hypotheses.     

The palladium(0) Suzuki cross-coupling reaction as the key step in the synthesis of aporphinoids

We report a flexible approach to the total synthesis of 4,5-dioxoaporphines based on the palladium(0) catalyzed Suzuki cross-coupling of phenylboronic acids with sterically hindered 2-bromo phenyl acetates or bromo phenyl acetamides, followed by sequential bicyclization of biarylacetamides promoted by oxalyl chloride/Lewis acid. The reduction of 4,5-dioxoaporphines provides a chemoselective entry to aporphines, dehydroaporphines and 4-hydroxy-dehydroaporphines. A three-steps total synthesis for (±)-O,O′-dimethylapomorphine from readily accessible precursors is also reported.     

High Radix BKM Algorithm

In this paper, a high radix implementation of the BKM algorithm is introduced. The BKM algorithm is a shift-and-add CORDIC-like algorithm that performs fast computation of complex exponential and logarithm without any scalling factor. The proposed implementation reduces the number of iterations needed for the calculation. Compared to previous implementations of high radix BKM algorithm, it needs smaller lookup tables.     

Properties of the 69 150 Tm81 6− β-decaying isomer

Decay experiments for¹⁴⁸Ho 6^? and¹⁵⁰Tm 6^? were carried out at the GSI On-line mass separator using 5 MeV/A⁵⁸Ni-beams on⁹⁴Mo and⁹⁶Ru targets. Gammaγ-andγX-coincidences established the¹⁵⁰Tm 6^? decay scheme, and e^? gave firm I ^π assignments for¹⁴⁸Dy and¹⁵⁰Er levels fed in the decays. It was found that the previously unknown 6 ₁ ^? state in¹⁵⁰Er receives significantβ-strength, which strongly suggestsπh _11/2 νs ₁ ^2/?1 character for the¹⁵⁰Tm 6^? isomer. The results are discussed in terms of the expected GT strength function. Shell model calculations for theπh ₁₁ ^2/4 yrast states are presented.     

Simple Designs for the Construction of Complex Trans-Fused Polyether Toxin Frameworks. A Convergent Strategy Based on Hydroxy Ketone Cyclization of C-Linked Oxacycles

A single, unified convergent strategy for the stereocontrolled synthesis of trans-fused polyethers was developed. It was demonstrated that the epimerization and reductive intramolecular coupling of hydroxy ketones in reactions with silane-Lewis acids (SI-LA) to generate ethers in C-linked oxacycles is affected by its conformational preference in a predictable manner. The obtained results make evident that the influence of hydrogen bonding between a hemiketal hydroxyl and a 1,3-diaxial C-O bond is regular and predictable and that convergent synthesis of trans-fused polyethers may confidently be conducted on driving ring closure to oxane rings under thermodynamic conditions     

Analytical method for the representation of atoms-in-molecules densities

We present analytic refinements and applications of the deformed atomic densities method [Fernández Rico, J.; López, R.; Ramírez, G. J Chem Phys 1999, 110, 4213-4220]. In this method the molecular electron density is partitioned into atomic contributions, using a minimal deformation criterion for every two-center distributions, and the atomic contributions are expanded in spherical harmonics times radial factors. Recurrence relations are introduced for the partition of the two-center distributions, and the final radial factors are expressed in terms of exponential functions multiplied by polynomials. Algorithms for the practical implementation are developed and tested, showing excellent performances. The usefulness of the present approach is illustrated by examining its ability to describe the deformation of atoms in different molecular environments and the relationship between these atomic densities and some chemical properties of molecules.     

Calculation of the one-electron two-center integrals with STOS using recurrence-based algorithms

We present a new algorithm for the calculation of two-center one-electron integrals with STOS based on two sets of recurrence relations. The first one enables us to calculate any of these integrals in terms of a few “basic integrals.” Furthermore, these basic integrals are written in terms of certain auxiliary functions which can be obtained through the second set of relations from only two starting values. We give also simple formulas for these starting quantities. Finally, the numerical stability, accuracy, and speed of the different steps of the algorithm are analyzed.     

Long-Range multicenter integrals with slater functions: Gauss transform-based methods

The separation of the short- and long-range terms in the potentials generated by pairs of Slater functions is reformulated in the context of the Gauss transform method. Analytic expressions of the long-range potentials (in closed form) are derived for equal exponents and generalized (as expansion series) for different exponents. Additionally, the representation of these potentials from small sets of charges or lowest-order multipoles is examined, paying special attention to their values and optimal positions. Finally, numerical tests of the formal developments are presented. It is concluded that the long-range three- and four-center integrals can be calculated with high accuracy in a simple and relatively inexpensive manner. © John Wiley & Sons, Inc.