Neutron diffraction study at 37 K of sodium triaqua(ethylenediaminetetraacetato)samarate(III) pentahydrate, Na[Sm(C10H12N2O8)(H2O)3].5H2O

This is the publisher's version, also available electronically from http://scripts.iucr.org/cgi-bin/paper?S0108270184009173.See article for abstract

A leed analysis of the (2×1)H-Ni(110) structure

A monolayer of H atoms adsorbed on Ni(110) below 180 K forms a (2×1) structure. The unit cell exhibits a glide symmetry plane and contains two adsorbed atoms. Based on a quantitative comparison between experimental and calculated LEED I/V spectra using standard R-factors the following structure was derived: On the clean Ni(110) surface the separation between the first two atomic layers, d12, is contracted by 8.5%±1.5% with respect to the bulk value; those between the second and third and the third and fourth layer, d23 and d34, are expanded by 3.5%±1.5% and 1%±1.5%, respectively—in agreement with recent other results. In the presence of the H adlayer the contraction of d12 is reduced to 4.5%±1.5%, while the expansion of d23 is not affected within the limits of accuracy. The third interlayer spacing d34 returns to its bulk value. The H atoms occupy threefold-coordinated sites formed by two Ni atoms from the first layer and one Ni atom from the second layer which confirms previous more qualitative conclusions based on He diffraction and vibrational spectroscopy. The bond lengths between H and its neighbouring Ni atoms were determined to be equal, namely 1.72±0.1 Å

Structures of furanosides : geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha -D-arabinofuranoside (1), methyl beta -D-arabinofuranoside (2), methyl alpha -D-lyxofuranoside (3), methyl beta -D-ribofuranoside (4) and methyl alpha -D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate. unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C-1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations

An exemplar-based approach to risk assessment: Validating the risk management systems instrument

Using a sample of federal probationers, this study examines the predictive validity of the Risk Management Systems assessment instrument. The results indicate the RMS is predictive of arrest, technical violation, and unsuccessful termination from supervision

Inhibition of Protein Aggregation: Supramolecular Assemblies of Arginine Hold the Key

BACKGROUND: Aggregation of unfolded proteins occurs mainly through the exposed hydrophobic surfaces. Any mechanism of inhibition of this aggregation should explain the prevention of these hydrophobic interactions. Though arginine is prevalently used as an aggregation suppressor, its mechanism of action is not clearly understood. We propose a mechanism based on the hydrophobic interactions of arginine. METHODOLOGY: We have analyzed arginine solution for its hydrotropic effect by pyrene solubility and the presence of hydrophobic environment by 1-anilino-8-naphthalene sulfonic acid fluorescence. Mass spectroscopic analyses show that arginine forms molecular clusters in the gas phase and the cluster composition is dependent on the solution conditions. Light scattering studies indicate that arginine exists as clusters in solution. In the presence of arginine, the reverse phase chromatographic elution profile of Alzheimer's amyloid beta 1-42 (Abeta(1-42)) peptide is modified. Changes in the hydrodynamic volume of Abeta(1-42) in the presence of arginine measured by size exclusion chromatography show that arginine binds to Abeta(1-42). Arginine increases the solubility of Abeta(1-42) peptide in aqueous medium. It decreases the aggregation of Abeta(1-42) as observed by atomic force microscopy. CONCLUSIONS: Based on our experimental results we propose that molecular clusters of arginine in aqueous solutions display a hydrophobic surface by the alignment of its three methylene groups. The hydrophobic surfaces present on the proteins interact with the hydrophobic surface presented by the arginine clusters. The masking of hydrophobic surface inhibits protein-protein aggregation. This mechanism is also responsible for the hydrotropic effect of arginine on various compounds. It is also explained why other amino acids fail to inhibit the protein aggregation

Polymorphism: an evaluation of the potential risk to the quality of drug products from the Farmácia Popular Rede Própria

Polymorphism in solids is a common phenomenon in drugs, which can lead to compromised quality due to changes in their physicochemical properties, particularly solubility, and, therefore, reduce bioavailability. Herein, a bibliographic survey was performed based on key issues and studies related to polymorphism in active pharmaceutical ingredient (APIs) present in medications from the Farmácia Popular Rede Própria. Polymorphism must be controlled to prevent possible ineffective therapy and/or improper dosage. Few mandatory tests for the identification and control of polymorphism in medications are currently available, which can result in serious public health concerns

How an ideologically concentrated minority can trump a dispersed majority : Nonmedian voter results for plurality, run-off, and sequential elimination elections

In contrast to Downs' (1957) median voter result for two-candidate elections, we should not expect multicandidate elections to produce outcomes around the median, even on average. Rather the winning candidate will tend to be between the median voter and the mode. This is true whether we consider plurality, run-off, or sequential elimination elections, and whether or not the electorate is divided into factions that control the nomination of candidates. For an unfactionalized electorate, computer simulation with randomly positioned candidates is used to model various electoral systems. This is because no equilibrium solution exists for this case. For a factionalized electorate, a game-theoretic model of faction formation is used. The results suggest that an ideologically cohesive minority around the mode of the population distribution may have a disproportionate influence on the outcome. These results can be applied to party leadership in the U.S. House, following Grofman, Koetzle, and McGann (forthcoming)

Why party leaders are more extreme than their members : modeling sequential elimination elections in the US house of representatives

Grofman et al. (forthcoming) find that party leaders in the U. S. House of Representatives tend to be more extreme than the median member of their party, and that they tend to come from the party's ideological "heartland" between the median and the mode. This paper shows that if the distribution of preferences is skewed (as is the case with both parties in the House), then we should expect sequential elimination elections to choose on average leaders between the median and modal positions. We show that this is the case whether or not the party is factionalized

Experimental Determination of Anomalous Scattering Lengths of Samarium for Thermal Neutrons

Anomalous scattering lengths of natural Sm for thermal neutrons with wavelengths between 0.827 and 1.300 A have been determined using a single crysrtal of a Sm-complex of known structure. 140 selected reflections were measured at each wavelength and b/sub 0/ + b' and b'' refined in each case. The values obtained are in good agreement with theoretical values obtained from a Breit-Wigner calculation using tabulated resonance parameters for /sup 149/Sm. A value of b/sub 0/ = 4.3 +- 0.2 fm is deduced from the diffraction experiment