C-H...O interactions and stacking of water molecules between pyrimidine bases in 5-nitro-1-([beta]-D-ribosyluronic acid)-uracil monohydrate [1-(5-nitro-2,4-dioxopyrimidinyl)-[beta]-D-ribofuranoic acid monohydrate]: a neutron diffraction study at 80 K

This is the publisher's version, also available electronically from http://scripts.iucr.org/cgi-bin/paper?S0567740879006506.See article for abstract.Research carried out at Brookhaven National Laboratory under contract with the US Department of Energy, and supported by its Office of Basic Energy Sciences

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

The Protein Data Bank: Present status and future plans

The Protein Data Bank (PDB) archival database of dimensional structures of biological macromolecules, an international resource facility, contains information on protein, DNA, RNA, virus and carbohydrate structures. While the vast majority of PDB entries represent crystal structures, results from NMR and theoretical modeling strudies also are included. PDB, which in July 1992 contained 957 atomic coordinate entries, currently is experiencing a time of explosive growth. The present deposition rate is ca. 50 structures per month, doubling in less than two years. Responding to the challenge posed by this. rising data flow, over the past 18 months PDB has attracted increased funding to implement important enhancements of the resource. A rapid pre-release of entries pending for input was inaugurated in April 1992, and a substantial fraction of the accumulated backlog of pending entries is now available via FTP and e-mail in prerelease form. Extrapolation of current data rates suggests that by the year 2000 PDB may contain over 25,000 structures. PDB`s plans, to manage this voluminous amount of data, include the development of PDB-AUTHORIN software to allow depositors to do most of the preparation and validation of their own entries, and a comprehensive upgrade of PDB contents to add new data items and convert the current interchange format to the Crystallographic Information File (CIF) standard established by the International Union of Crystallography (IUCr)

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

Chemical crystallography at the High Flux Beam Reactor

A brief description is given of the neutron diffraction facilities at the Brookhaven High Flux Beam Reactor. Present instrumentation includes two fully automated four-circle diffractometers. Cryogenic refrigerators and furnaces make possible the collection of three-dimensional intensity data from single crystals over the full temperature range 10 to 1200/sup 0/K. Recent crystallographic research at the Reactor is illustrated by three representative studies on ferrocene, H/sub 3/Ni/sub 4/(C/sub 5/H/sub 5/)/sub 4/, and pyridine-2,3-dicarboxylic acid. A survey of important areas for future work is attempted: metal hydrides and charge-density studies by combined x-ray and neutron diffraction methods are included. 6 figures, 2 tables

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