Phase transition effects: A crystallographic characterization of the temperature dependency of the crystal structure of the 1:1 charge transfer complex between anthracene and tetracyanobenzene in the temperature range 297 to 119 K

Crystal structures of the charge transfer complex between anthracene and tetracyanobenzene, A:TCNB, C14H10: C10H2N4, at three temperatures (297, 234 and 226 K) above the order–disorder phase transition at 206 K and at four temperatures (202, 170, 138, and 119 K) below it have been determined from x-ray diffraction data. The space group of the room temperature phase was assigned as Cm with a = 9.528(2), b =12.779(3), c = 7.441(2) Å and β=92.39(2) degrees at 297 K and for the low temperature phase is P21/a with a =9.457(1), b =12.689(2), c =7.325(1) Å and β=92.98(1)° at 119 K; Z = 2 in both phases. The electron densities, plotted for both the donor and acceptor molecules at each temperature, indicate that there is dynamic librational disorder in the A molecules that gives rise to a single average orientation in the room temperature phase. Below the phase transition, two temperature dependent, symmetry related, orientations are observed; the libration diminishes slowly as a function of temperature in this phase. There are also modest reorientations, relative to the room temperature phase, in the TCNB molecules as the crystal is cooled. Crystal packing indicates that a network of intermolecular dipole–dipole interactions between the heteroatomic acceptor molecules accounts for their lack of libration comparable to that of the donors

Phase transition effects: A crystallographic characterization of the temperature dependency of the crystal structure of the 1:1 charge transfer complex between anthracene and tetracyanobenzene in the temperature range 297 to 119 K

Crystal structures of the charge transfer complex between anthracene and tetracyanobenzene, A:TCNB, C14H10: C10H2N4, at three temperatures (297, 234 and 226 K) above the order–disorder phase transition at 206 K and at four temperatures (202, 170, 138, and 119 K) below it have been determined from x-ray diffraction data. The space group of the room temperature phase was assigned as Cm with a = 9.528(2), b =12.779(3), c = 7.441(2) Å and β=92.39(2) degrees at 297 K and for the low temperature phase is P21/a with a =9.457(1), b =12.689(2), c =7.325(1) Å and β=92.98(1)° at 119 K; Z = 2 in both phases. The electron densities, plotted for both the donor and acceptor molecules at each temperature, indicate that there is dynamic librational disorder in the A molecules that gives rise to a single average orientation in the room temperature phase. Below the phase transition, two temperature dependent, symmetry related, orientations are observed; the libration diminishes slowly as a function of temperature in this phase. There are also modest reorientations, relative to the room temperature phase, in the TCNB molecules as the crystal is cooled. Crystal packing indicates that a network of intermolecular dipole–dipole interactions between the heteroatomic acceptor molecules accounts for their lack of libration comparable to that of the donors

X-ray structure of the quinoprotein ethanol dehydrogenase from \u3ci\u3ePseudomonas aeruginosa\u3c/i\u3e: basis of substrate specificity

The homodimeric enzyme form of quinoprotein ethanol dehydrogenase from Pseudomonas aeruginosa ATCC 17933 crystallizes readily with the space group R3. The X-ray structure was solved at 2.6 Å resolution by molecular replacement. Aside from differences in some loops, the folding of the enzyme is very similar to the large subunit of the quinoprotein methanol dehydrogenases from Methylobacterium extorquens or Methylophilus W3A1. Eight W-shaped β-sheet motifs are arranged circularly in a propeller-like fashion forming a disk-shaped superbarrel. No electron density for a small subunit like that in methanol dehydrogenase could be found. The prosthetic group is located in the centre of the superbarrel and is coordinated to a calcium ion. Most amino acid residues found in close contact with the prosthetic group pyrroloquinoline quinone and the Ca2+ are conserved between the quinoprotein ethanol dehydrogenase structure and that of the methanol dehydrogenases. The main differences in the active-site region are a bulky tryptophan residue in the active-site cavity of methanol dehydrogenase, which is replaced by a phenylalanine and a leucine side-chain in the ethanol dehydrogenase structure and a leucine residue right above the pyrrolquinoline quinone group in methanol dehydrogenase which is replaced by a tryptophan side-chain. Both amino acid exchanges appear to have an important influence, causing different substrate specificities of these otherwise very similar enzymes. In addition to the Ca2+ in the active-site cavity found also in methanol dehydrogenase, ethanol dehydrogenase contains a second Ca2+-binding site at the N terminus, which contributes to the stability of the native enzyme

Preliminary X-ray diffraction studies of the transcriptional inhibitory antibody Fab41.4

The binding of transcription factor ATF-1 to DNA contributes to gene expression and regulation of cell growth. Antibody Mab41.4, raised against ATF-1, and its derivatives Fab41.4 and scFv41.4 inhibit specific DNA binding in vitro and induce apoptotic death of tumor cells in vivo. Structural studies of Fab41.4 were performed to gain insight into the mechanism of action of this potentially therapeutic antibody. The optimal conditions for crystallization of Fab41.4 were determined. Crystals were needle-like in appearance, displayed C2 space-group symmetry and diffracted to a resolution of 1.6 Å. The unit-cell parameters were determined to be a = 186.64, b = 40.22, c = 55.58 Å, α = γ = 90, β = 96.93°. The data set was 97.7% complete. Molecular replacement was performed, resulting in an R value of 44.6%

Preliminary X-ray diffraction studies of the transcriptional inhibitory antibody Fab41.4

The binding of transcription factor ATF-1 to DNA contributes to gene expression and regulation of cell growth. Antibody Mab41.4, raised against ATF-1, and its derivatives Fab41.4 and scFv41.4 inhibit specific DNA binding in vitro and induce apoptotic death of tumor cells in vivo. Structural studies of Fab41.4 were performed to gain insight into the mechanism of action of this potentially therapeutic antibody. The optimal conditions for crystallization of Fab41.4 were determined. Crystals were needle-like in appearance, displayed C2 space-group symmetry and diffracted to a resolution of 1.6 Å. The unit-cell parameters were determined to be a = 186.64, b = 40.22, c = 55.58 Å, α = γ = 90, β = 96.93°. The data set was 97.7% complete. Molecular replacement was performed, resulting in an R value of 44.6%

High-spin structures of 88Kr and 89Rb: Evolution from collective to single-particle behaviors

The high-spin states of the two neutron-rich nuclei, 88Kr and 89R have been studied from the 18O + 208Pb fusion-fission reaction. Their level schemes were built from triple gamma-ray coincidence data and gamma-gamma angular correlations were analyzed in order to assign spin and parity values to most of the observed states. The two levels schemes evolve from collective structures to single-particle excitations as a function of the excitation energy. Comparison with results of shell-model calculations gives the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines.Comment: 12 pages, 9 figures, Physical Review C (2013) in pres

Observation of the lowest energy gamma-ray in any superdeformed nucleus : 196Bi

New results on the superdeformed $^{196}$Bi nucleus a re reported. We have observed with the EUROBALL IV $\gamma$-ray spectrometer array a superdeformed trans ition of 124 keV which is the lowest observed energy $\gamma$-ray in any superdeformed nucleus. We have de velopped microscopic cranked Hartree-Fock-Bogoliubov calculations using the SLy4 effective force and a realistic surface p airing which strongly support the $K^\pi=2^-$($\pi$[651]1/2$\otimes \nu$[752]5/2) assignment of this su perdeformed band

Search for emission of unstable 8^8Be clusters from hot 40^40Ca and 56^56Ni nuclei

The possible occurence of highly deformed configurations is investigated in the $^{40}$Ca and $^{56}$Ni di-nuclear systems as formed in the $^{28}$Si + $^{12}$C and $^{28}$Si + $^{28}$Si reactions, respectively, by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments (A $\geq$ 6) and their associated light charged particles (p, d, t, and $\alpha$-particles) have been collected at the IReS Strasbourg VIVITRON Tandem facility with two bombarding energies $E_{lab}(^{28}$Si) = 112 and 180 MeV by using the ICARE charged particle multidetector array, which consists of nearly 40 telescopes. The measured energy spectra, velocity distributions, in-plane and out-of-plane angular correlations are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Although significant deformation effects at high spin are needed, the remaining disagreement observed in the $^{28}$Si + $^{12}$C reaction for the S evaporation residue suggests an unexpected large unstable $^{8}$Be cluster emission of a binary nature.Comment: 13 pages latex, 9 eps figures. Paper presented at the XXXIX International Winter Meeting on Nuclear Physics, Bormio(Italy) January 22-27, 2001 (to be published at Ricerca Scientifica ed Educazione Permanente