Tight approximations to total scattering intensities from electron-pair density quantities

Three different mathematical techniques (maximum-entropy, Stieltjes-type and Padé-like approximants) are used to obtain tight approximations to scattering intensities in terms of a few local and/or global quantities related to the electron-pair density. The accuracy of the approximations is analyzed and compared by means of Hylleraas-type atomic wavefunctions.     

Isotopic dependence of electron screening in fusion reactions

The fusion reactions⁶Li(p, )³He,⁶Li(d, )⁴He, and⁷Li(p, )⁴He have been studied over the c.m. energy rangeE=10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomicp ord projectiles compared to the case of molecularH ₂ orD ₂ gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.Supported in part by the Landesamt Nordrhein-Westfalen (IVA5-10600387), the Deutsche Forschungsgemeinschaft (Ro429/ 18-2 and Ro429/21-1), and the Comision Interministerial de Ciencia y Tecnologia (AEN90-0932)     

Compton profiles and momentum space inequalities

Rigorous upper and lower bounds to the atomic Compton profileJ(q) are obtained for any value of the momentum transferredq in terms of radial expectation values 〈p ⁿ 〉 of the atomic momentum density γ(p). In doing so, a procedure based on moment-theoretic techniques and Chebyshev inequalities has been used. This type of results can be employed to study the compatibility of diverse information obtained by using different models, techniques, numerical calculations or experimental data. The same method allows also to obtain approximations to the Compton profile and to bound other relevant characteristics ofJ(q). A comparison of the approximations with some previously known Maximum Entropy Approximations is done. In order to test the accuracy of the bounds, a numerical study of the results is carried out in a Hartree-Fock framework for atomic systems.     

Site-specific solvation determined by intermolecular nuclear Overhauser effect--measurements and molecular dynamics

Site-specific solvation has been determined by intermolecular NOE measurements between solvent and solute. The experimental effect is shown on the four compounds 2-butanol, L-alanyl-L-tryptophan (Ala-Trp), adenosine and the disodium salt of adenosine 5'-monophosphate (5'-AMP) in the two solvents water and dimethyl sulfoxide (DMSO). The strength of NOE transfer correlates with the average distribution of solvent molecules around the corresponding solvation sites represented by the number of solvent molecules in a first solvation sphere, which can be obtained from molecular dynamics simulations in water. Saturation transfer between exchanging protons explains some deviations from this correlation. The NOE transfer measurements provide information on specific solute-solvent interactions and contribute to a better understanding of solvation phenomena. On the basis of a distinct relationship between steric solvation hindrance and the strength of NOE transfer, the application of such measurements for conformational analysis has been demonstrated for the first time.     

Electrosynthesis of a Bis-Ketenedithioacetal Disulphide Derivative From 1-Phenyl-3-Methyl-4-Butyldithiocarboxylate-5-Pyrazolone Using a Glassy Carbon Electrode

The electrooxidation of 1-phenyl-3-methyl-4-butyldithiocarboxylate-5-pyrazolone 1 has been studied in ethanol/water solution, using a glassy carbon electrode surface. The electrochemical and spectroscopic data are in agreement with a bis-ketenedithioacetal disulphide compound 2 as the only product of the reaction.     

Prediction and Conditional Simulation of a 2D Lognormal Diffusion Random Field

This paper describes techniques for estimation, prediction and conditional simulation of two-parameter lognormal diffusion random fields which are diffusions on each coordinate and satisfy a particular Markov property. The estimates of the drift and diffusion coefficients, which characterize the lognormal diffusion random field under certain conditions, are used for obtaining kriging predictors. The conditional simulations are obtained using the estimates of the drift and diffusion coefficients, kriging prediction and unconditional simulation for the lognormal diffusion random field.      

Chemoenzymatic Synthesis of Fluorinated Cellodextrins Identifies a New Allomorph for Cellulose-Like Materials**

Understanding the fine details of the self-assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft-matter materials with specific properties. Enzymatically synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self-assemble into particles resembling the antiparallel cellulose II crystalline packing. We have prepared and characterised a series of site-selectively fluorinated cellodextrins with different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. Bearing in mind the potential disruption of the hydrogen-bond network of cellulose II, we have prepared and characterised a multiply 6-fluorinated cellodextrin. In addition, a series of single site-selectively fluorinated cellodextrins was synthesised to assess the structural impact upon the addition of one fluorine atom per chain. The structural characterisation of these materials at different length scales, combining advanced NMR spectroscopy and microscopy methods, showed that a 6-fluorinated donor substrate yielded multiply 6-fluorinated cellodextrin chains that assembled into particles presenting morphological and crystallinity features, and intermolecular interactions, that are unprecedented for cellulose-like materials.     

Antiprotozoal 6-substituted-5,6-dihydro-alpha-pyrones from Raimondia cf. monoica

Dichloromethane extracts of both the roots and the leaves of Raimondia cf. monoica showed in vitro antiplasmodial and leishmanicidal activities against Plasmodium falciparum and Leishmania panamensis, respectively. Three 6-substituted 5,6-dihydro-2H-pyran-2-ones were isolated. (1) and (2) were identified as (6S)-(5'-oxohepten-1'E,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (1) and (6R)-(5'-oxohepten-1'Z,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (2), respectively. (-)-Arentilactone (3) was also isolated. The structure of the new compound (1) was determined by spectroscopic methods; additional spectroscopic data for (2) are reported for the first time.     

Analysis of bulk and inorganic degradation products of stones,mortars and wall paintings by portable Raman microprobe spectroscopy

This work reports the use of a portable Raman microprobe spectrometer for the analysis of bulk and decaying compounds in carbonaceous materials such as stones, mortars and wall paintings. The analysed stones include limestone, dolomite and carbonaceous sandstone, gypsum and calcium oxalate, both mono- and dihydrated, being the main inorganic degradation products detected. Mortars include bulk phases with pure gypsum, calcite and mixtures of both or with sand, soluble salts being the most important degradation products. The pigments detected in several wall paintings include Prussian blue, iron oxide red, iron oxide yellow, vermilion, carbon black and lead white. Three different decaying processes have been characterised in the mortars of the wall paintings: (a) a massive absorption of nitrates that reacted with calcium carbonate and promoted the unbinding of pigment grains, (b) the formation of black crusts in the vault of the presbytery and (c) the thermodecomposition of pigments due to a fire.