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101.
Andrew P. Mendham John Spencer Babur Z. Chowdhry Trevor J. Dines Muhammad Mujahid Rex A. Palmer Graham J. Tizzard Simon J. Coles 《Journal of chemical crystallography》2011,41(9):1323-1327
Abstract
The cyclic di-amino acid peptide N,N′-diacetyl-cyclo(Gly-Gly), C8H10N2O4, crystallizes in the triclinic space group P[`1] P\bar{1} with unit cell parameters a = 9.4855(4) ?, b = 10.0250(3) ?, c = 10.0763(4) ?, α = 73.682(2)°, β = 82.816(2)°, γ = 81.733(2)°, V = 906.40(6) ?3, Z = 4 (2 molecules, A and B, per asymmetric unit), Dc = 1.452 g cm−3 and linear absorption coefficient 0.118 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured at 120(2) K. In the final refinement cycle the data/restraints/parameter ratios were 4124/0/258 and goodness-of-fit on F2 = 1.0008. Final R indices for [I > 2σ(I)] were R1 = 0.0501, wR2 = 0.1007 and R indices (all data) R1 = 0.0864, wR2 = 0.11180. The largest electron density difference peak and hole were 0.241 and −0.232 e ?−3, respectively. The DKP rings in both molecules A and B have boat conformations with pseudo mm2 (C2v) symmetry if the N atoms and CH2 groups are considered identical. In each case, the prow and stern of the boat are the α-carbons C(3) and C(6). The overall molecular symmetry of molecules A and B is approximately C2 with the twofold symmetry axis of the DKP boat being maintained through the centre of the DKP ring. Details of the molecular geometry are compared with that of the parent compound cyclo(Gly-Gly) in which the DKP ring is planar with exact symmetry [`1] \bar{1} (Ci). 相似文献102.
Anna S. Gardberg Brian S. Potter Rex A. Palmer Garry J. McIntyre Dean A. A. Myles 《Journal of chemical crystallography》2011,41(4):470-480
Abstract
Single-crystal neutron diffraction data were collected at 20 K to a resolution of 1.05 ? on a crystal of the inverse formyl peptide receptor agonist cyclosporin H, CsH, (crystal form II, CsH-II) on the Laue diffractometer VIVALDI at the Institut Laue-Langevin (Grenoble). The solvent structure and hydrogen bonding network of CsH-II have been unambiguously determined by single-crystal neutron diffraction; the agreement factor R(F 2) is 13.5% for all 2726 reflections. All hydrogen atom positions, including methyl-group orientations, have been determined by crystallographic refinement. The neutron structure of cyclosporin provides unique and complementary insights into methyl orientation, hydrogen-bonding, and solvent interactions that are not available from X-ray analysis alone. 相似文献103.
We calculate branching ratios and the polarization in the decay ofB mesons to two vector mesons using heavy quark symmetries to evaluate the current matrix elements. 相似文献
104.
105.
In this paper we define tau functions for holonomic fields associated with the Dirac operator on the Poincaré disk. The deformation analysis of the tau functions is worked out and in the case of the two point function, the tau function is expressed in terms of a Painlevé function of type VI. 相似文献
106.
A white-light interferometric system, which comprises two Michelson interferometers linked by a 100 μm diameter core multimode step index fibre has been investigated, where a signal processing scheme, using curve fitting, has been introduced to suppress the noise induced in the system. The theoretical resolution of such a sensor with the use of an appropriate curve fitting signal processing scheme has been discussed. The experimental results obtained show the short term repeatability (to three standard deviations) to be better than 5 nm after signal processing, under conditions where the fibre is constantly vibrated in a known and reproducible way. 相似文献
107.
108.
109.
Michael H. Palmer 《Journal of Molecular Spectroscopy》2006,237(1):123-125
Early assignments of the vacuum UV photoabsorption spectrum of allene (1951-1972) gave a number of Rydberg series, but these series had limiting values for the ionization potential, which are incompatible (by up to 0.4 eV) with more recent adiabatic IPs from molecular beam and high resolution photoelectron spectra (UV-PES). We have performed a re-analysis of the VUV spectrum of allene by a combination of overlay of the VUV and UV-PES spectra which leads to new experimental assignments. Major differences in assignment to the early studies are reported, and these include the lowlying Rydberg states, which are now assigned as follows: 6.55 (3s), 7.2 (3p), 8.15 (3d), and 8.25 eV (4s), respectively, with further assignments up to 6s, 6p, and 6d. 相似文献
110.
F. Hegelund R. Wugt Larsen R.A. Aitken K.M. Aitken M.H. Palmer 《Journal of Molecular Spectroscopy》2007,246(2):198-212
The Fourier transform infrared spectrum of gaseous 1,3,4-oxadiazole, C2H2N2O, has been recorded in the 800–1600 cm−1 wavenumber region with a resolution around 0.0030 cm−1. The four fundamental bands ν9(B1; 852.5 cm−1), ν14(B2; 1078.5 cm−1), ν4(A1; 1092.6 cm−1), and ν2(A1; 1534.9 cm−1) are analyzed by the standard Watson model. Ground state rotational and quartic centrifugal distortion constants are obtained from a simultaneous fit of ground state combination differences from three of these bands and previous microwave transitions. Upper state spectroscopic constants are obtained for all four bands from single band fits using the Watson model. The ν4 and ν14 bands form a c-Coriolis interacting dyad, and the two bands are analyzed simultaneously by a model including first and second order Coriolis resonance using the ab initio predicted Coriolis coupling constant . An extended local resonance in ν2 is explained as higher order b-Coriolis type resonance with ν6 + ν10, which is further perturbed globally by the ν15 + ν10 level. A fit of selected low-J transitions to a triad model including ν2(A1), ν6 + ν10(B1), and ν15 + ν10(A2) using an ab initio calculated Coriolis coupling constant is performed.The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration–rotational constants (α-constants) predicted by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and α-constants for all fundamental levels of the molecule is given. 相似文献