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Neutron diffraction data have been collected at 12, 50, 150 and 295 K for the dipeptide glycyl-L-alanine, C5H10N2O3, in order to obtain accurate positional and anisotropic displacement parameters for the H atoms. The values of these parameters serve as a benchmark for assessing the equivalent parameters obtained from a so-called Hirshfeld-atom refinement of X-ray diffraction data described elsewhere [Capelli et al. (2014). IUCrJ, 1, 361-379]. The flexibility of the glycyl-L-alanine molecule in the solid and the hydrogen-bonding interactions as a function of temperature are also considered. [ABSTRACT FROM AUTHOR]

Reaction of [RuCl(CNN)(dppb)] ( 1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2P(CH2)4PPh2) with NaOCH2CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2CF3)(dppb)] ( 1-OCH2CF3), whose neutron diffraction study reveals a short RuO ⋅⋅⋅HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)] ⋅(EtOH) n ( 1-OEt⋅ n EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] ( 1-H) and acetaldehyde. Compound 1-OEt⋅ n EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt⋅ n EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2) of ketones to alcohols (turnover frequency (TOF) up to 6.5×104 h−1, 40 °C). DFT calculations were performed on the reaction of [RuH(CNN′)(dmpb)] ( 2-H) (HCNN′=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2P(CH2)4PMe2) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key 'amide' intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2; both pathways have low barriers and are alcohol assisted. [ABSTRACT FROM AUTHOR]

A novel vitreous carbon mount for macromolecular crystallography, suitable for neutron and X-ray crystallographic studies, has been developed. The technology described here is compatible both with X-ray and neutron cryo-crystallography. The mounts have low density and low background scattering for both neutrons and X-rays. They are prepared by laser cutting, allowing high standards of production quality, the ability to custom-design the mount to specific crystal sizes and large-scale production. [ABSTRACT FROM AUTHOR]

The title zwitterion (2 S)-2-azaniumyl-1-hydroxy-3-phenylpropan-1-olate, C9H11NO2, also known as L-phenylalanine, was characterized using synchrotron X-rays. It crystallized in the monoclinic space group P21 with four molecules in the asymmetric unit. The 0.62 Å resolution structure is assumed to be closely related to the fibrillar form of phenylalanine, as observed by electron microscopy and electron diffraction. The structure exists in a zwitterionic form in which π-π stacking and hydrogen-bonding interactions are believed to form the basis of the self-assembling properties. [ABSTRACT FROM AUTHOR]

The monoclinic C2 crystal structure of an α-cyclodextrin/1-undecanol host-guest inclusion complex was solved using single-crystal neutron diffraction. Large high-quality crystals were specially produced by optimizing temperature-controlled growth conditions. The hydrate crystallizes in a channel-type structure formed by head-to-head dimer units of α-cyclodextrin molecules stacked like coins in a roll. The alkyl chain of the guest lipid is entirely embedded inside the tubular cavity delimited by the α-cyclodextrin dimer and adopts an all- trans planar zigzag conformation, while the alcohol polar head group is outside close to the α-cyclodextrin primary hydroxyl groups. The cyclodextrin dimer forms columns, which adopt a quasi-square arrangement much less compact than the quasi-hexagonal close packing already observed in the less hydrated α-cyclodextrin channel-type structures usually found with similar linear guests. The lack of compactness of this crystal form is related to the high number of interstitial water molecules. The replacement of 1-undecanol by 1-decanol does not modify the overall crystal structure of the hydrate as shown by additional X-ray diffraction investigations comparing the two host-guest assemblies. This is the first study that analyses the entire hydrogen-bonding network involved in the formation of a cyclodextrin dimer surrounded by its shell of water molecules. [ABSTRACT FROM AUTHOR]

d-Xylose isomerase (XI) converts the aldo-sugars xylose and glucose to their keto analogs xylulose and fructose, but is strongly inhibited by the polyols xylitol and sorbitol, especially at acidic pH. In order to understand the atomic details of polyol binding to the XI active site, a 2.0 Å resolution room-temperature joint X-ray/neutron structure of XI in complex with Ni2+ cofactors and sorbitol inhibitor at pH 5.9 and a room-temperature X-ray structure of XI containing Mg2+ ions and xylitol at the physiological pH of 7.7 were obtained. The protonation of oxygen O5 of the inhibitor, which was found to be deprotonated and negatively charged in previous structures of XI complexed with linear glucose and xylulose, was directly observed. The Ni2+ ions occupying the catalytic metal site (M2) were found at two locations, while Mg2+ in M2 is very mobile and has a high B factor. Under acidic conditions sorbitol gains a water-mediated interaction that connects its O1 hydroxyl to Asp257. This contact is not found in structures at basic pH. The new interaction that is formed may improve the binding of the inhibitor, providing an explanation for the increased affinity of the polyols for XI at low pH. [ABSTRACT FROM AUTHOR]

Preliminary studies of perdeuterated crystals of human transthyretin (TTR) have been carried out using the LADI-III and D19 diffractometers at the Institut Laue-Langevin in Grenoble. The results demonstrate the feasibility of a full crystallographic analysis to a resolution of 2.0 Å using Laue diffraction and also illustrate the potential of using monochromatic instruments such as D19 for higher resolution studies where larger crystals having smaller unit cells are available. This study will yield important information on hydrogen bonding, amino-acid protonation states and hydration in the protein. Such information will be of general interest for an understanding of the factors that stabilize/destabilize TTR and for the design of ligands that may be used to counter TTR amyloid fibrillogenesis. [ABSTRACT FROM AUTHOR]

Heteromultimetallic hydride clusters containing both rare-earth and d-transition metals are of interest in terms of both their structure and reactivity. However, such heterometallic complexes have not yet been investigated to a great extent because of difficulties in their synthesis and structural characterization. Here, we report the synthesis, X-ray and neutron diffraction studies, and hydrogen addition and release properties of a family of rare-earth/d-transition-metal heteromultimetallic polyhydride complexes of the core structure type 'Ln4MHn' (Ln = Y, Dy, Ho; M = Mo, W; n = 9, 11, 13). Monitoring of hydrogen addition to a hydride cluster such as [{(C5Me4SiMe3)Y}4(?-H)9Mo(C5Me5)] in a single-crystal to single-crystal process by X-ray diffraction has been achieved for the first time. Density functional theory studies reveal that the hydrogen addition process is cooperatively assisted by the Y/Mo heteromultimetallic sites, thus offering unprecedented insight into the hydrogen addition and release process of a metal hydride cluster. [ABSTRACT FROM AUTHOR]

The article discusses a study on the structure of coenzyme cob (Cbl(2) determined from the monochromatic neutron data set gathered from the original D19 at the H11 thermal beam at the ILL to 0.92 A resolution. It reports preliminary studies of the feasibility of extending the structure's resolution further by gathering time-of-flight (TOF) neutron data during a short commissioning experiment on TOPAZ. It suggests that TOPAZ is an ideal instrument for developing new research based on ultra-high resolution neutron studies of biological macromolecules.

The article reports on the results of neutron diffraction studies that compare the structures of four metal-ion complexes of deuterated D-xylose isomerase, which represent the four stages in its biochemical catalytic reactions. An analysis of the structural changes provide insight on its biochemical mechanisms and the role of ionization. The variable charges in the substrate are important to the function of the metal ion in the isomerization.

Investigates the internal mean-square displacements of H atoms in xylitol using neutron diffraction study. Nuclear anisotropic displacement parameters; Rigid-body displacements; Molecular vibrations in xylitol.

Investigates the crystal structure of α-glycine during anomalous electrical behavior in the temperature range 288-427 K using neutron diffraction. Molecular structure; Expansion of the unit cell anisotropically with increasing temperature; Factors influencing the separation of antiferroelectric molecular layers with increasing temperature.

Studies the structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethyllan- thracene -9-ol using x-ray diffraction at room temperature and neutron diffraction at very low temperature. Presence of the two bifurcated hydrogen bonds; Evidence of very close pseudosymmetry in both molecules A and B.

Presents a study which determined the crystal structures of all five crystalline methyl D-pentofuranosides. Use of cryogenic X-ray and neutron crystallography; Role of hydrogen-bonding in of H-atom positions; Geometrical and conformational parameters of the structures of all five crystalline pentofuranosides.

The structure of H3Co2[C5H2(t-Bu)3]2 has been analyzed by low-temperature single-crystal neutron diffraction techniques, and shown to consist of two CoCp‡ moieties with three hydride ligands bridging the central Co–Co bond. Despite a fairly extensive twinning problem, the structure could be solved and successfully refined to a final R factor of 9.2% for 2024 reflections. Average molecular parameters in the H3Co2 core of the molecule are as follows: Co–Co=2.275(21) Å, Co–H=1.637(16) Å, H⋯H=2.050(20) Å, Co–H–Co=88.0(9)°, H–Co–H=77.0(7)°. Also included in this paper is a discussion on the molecular dimensions of symmetric hydride-bridged dinuclear systems (M(μ-H)nM, n=1, 2, 3, 4) that have been studied to date by neutron diffraction. [ABSTRACT FROM AUTHOR]

The crystal structures of ammonium tetraphenylborate, NH4+.BH4-, are determined by neutron diffraction at 20 and 293 K. At both temperatures, all four N - H vectors of the ammonium ion are time-average-oriented at the midpoints of the phenyl rings of neighboring anions. The N-H … Ph distances. H … M 2.067 and N … M 3.023 Å, are exceptionally short (M = aromatic midpoint). Even at 20 K the ammonium ion performs large amplitude motions which allow the N- H vectors to sample the entire face of the aromatic system. [ABSTRACT FROM AUTHOR]

The 1:1 and 2:1 cocrystals of benzene-1,2,4,5-tetra­carboxylic acid (BTA) and 4,4′-bipyridine (BPY) have been studied using neutron diffraction at 215 and 20 K, respectively. BTA and BPY crystallize in a 1:1 ratio with 1.8 mol­ecules of water, viz. 4,4′-bipyridinium 2,5-dicarboxy­benzene-1,4-dicarboxyl­ate 1.8-hydrate, C10H12N22+·C10H4O82−·1.8H2O, (I), in the space group P , with both BTA and BPY lying on inversion centres. BTA and BPY crystallize in a 2:1 ratio, viz. 4,4′-bipyridinium bis­(2,4,5-tricarboxy­benzoate), C10H12N22+·2C10H5O8−, (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short N—H⋯O hydrogen bond [N⋯O = 2.6047 (19) Å] and one intra­molecular O—H⋯O hydrogen bond [O⋯O = 2.423 (3) Å]. The crystal structure of the 2:1 cocrystal contains two N—H⋯O hydrogen bonds [N⋯O = 2.639 (3) and 2.674 (2) Å], and two intra­molecular [O⋯O = 2.404 (3) and 2.420 (3) Å] and four strong inter­molecular O—H⋯O hydrogen bonds [O⋯O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) Å]. [ABSTRACT FROM AUTHOR]