Photographic neutron diffraction study ofL-histidine.HCl.H₂O by the modified Laue method

Abstract

Film-recorded neutron intensities from modified Laue measurements (a convergent-beam technique) were evaluated quantitatively and a crystal structure was refined. About 4000 reflexions were collected on 60 films in altogether 30 hours 3 exposure of a 0.3 mm crystal of L-histidine. HC1. H20, space group P212121 with a = 15-36, b =8.92 and c= 6"88 A. The corrections necessary for this technique are described. The structure factors were derived from the optical densities scanned by an automatic microdensitometer and processed by computer programs. Refinement on 741 symmetry-independent reflexions yielded R(F 2) = 0.121. The parameters obtained are compared with those from conventional four-circle work. The mean differences in the positional parameters are 0.009 A for C, O and C1 and 0-022 A for H. For the anisotropic temperature factors U~ differences of 0.0054 and 0.0105 A 2 for heavy atoms and hydrogens respectively were observed between the results of the two techniques. A hydrogen atom misplaced in earlier X-ray work was located from film data collected in only 15 hours.

Multiple-spin analysis of chemical-shift-selective (13C, 13C) transfer in uniformly labeled biomolecules

“…In all cases, the QM transfer curves clearly remain sensitive to the distance of interest. Moreover, the interatomic distances predicted from the neutron diffraction study [53] most adequately describe in all cases the empirical data. For the relatively short (Ca, Cc) distance measured in (A), the accuracy suggested by our numerical results is better than AE0.2 A A.…”

“…Comparison between QM transfer curves simulated for different internuclear distances and experimental data points for three different spin pairs in His Á HCl. Bold curves correspond to distances as obtained from the neutron diffraction study [53].…”

“…In line with earlier studies [52], test simulations confirmed that the relative orientation of the anisotropic interactions is not relevant for the considered RR recoupling conditions. Distances defining the overall structure were taken from neutron diffraction studies (L L -His Á HCl [53]) and X-ray crystallography (ubiquitin [54]). Scalar ( 1 H, 13 C) and ( 13 C, 13 C) couplings were set to 140 and 35 Hz, respectively.…”

Topography of cyclodextrin inclusion complexes. XII. Hydrogen bonding in the crystal structure of α-cyclodextrin hexahydrate: the use of a multicounter detector in neutron diffraction

“…With these parameters the Lorentz factor for the modified Laue method is (Klar, 1973): L = 1/(sin2Ocosv + sin 0cos ~,sin v cos 0). This formula can be transformed into the expression given by Hohlwein (1977). The numerical values of L exhibit an asymptotic behaviour for 0 --, 90 °, showing the power of the modified Laue method in the high-angle region.…”

Combined use of monochromatic and Laue diffraction techniques for macromolecular structure determination

“…They were first employed in the neutron structure determination of small biological structures (Hohlwein, 1977;Klar, Hingerty & Saenger, 1980) using a modified Laue technique (Maier-Leibnitz, 1967). The same technique was used in the first (neutron) Laue diffraction study of a protein structure (Hohlwein & Mason, 1981).…”