IUCr 2005 (Florence, Italy) student award winners of the Larry Calvert CNC/IUCr Trust Fund Award

Sung Yeun Choi

(Department of Chemistry, University of Toronto)

By Sung Yeun Choi(1), Marc Mamak(2), Scott Speakman(3), Naveen Chopra(4), Geoffrey A. Ozin(1)
1. Materials Chemistry Research Group. Department of Chemistry, University of Toronto, 80 Saint George St, Toronto, Ontario, Canada M5S 3H6, (Canada), 2 Center for Nanostructure Imaging (CNI), Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, (Canada), 3 Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37830-6064 (USA), 4 Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, Ontario, L5K 2L1 (Canada).

Within the last few years, many periodic mesostructured forms of titania denoted meso-TiO2 have been produced based upon the self-assembly method. Besides the usual benefits of the self-assembly method including high surface area and uniform pore size and shape, the crystallinity and crystallite size of the anatase composing the channel walls of meso-TiO2 are an equally important factor since potential applications rely upon the intrinsic properties of titania governed by the extent and nature of its crystalline phase. Although crystallite growth, during the film calcination step, within the mesostructured titania framework should be considered the critical step in the formation of meso-TiO2 thin films, the issue of crystallite growth has yet to be identified as a major determining factor with respect to the properties of meso-TiO2 thin films and their applicability to electroactive and photoactive devices.

Herein we report the first kinetic study of the intrachannel wall phase-transition of amorphous titania to nanocrystalline anatase for periodic mesoporous titania thin films, monitored by time-resolved in-situ high temperature X-ray diffraction (HTXRD). Structural transformations associated with the phase transition are further probed by high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (HRTEM). The model found to be most consistent with the kinetic data involves 1-D diffusion controlled growth of nanocrystalline anatase within the spatial confines of the channel walls of the mesostructure. The observation of anisotropic, rod-shaped anatase nanocrystals preferentially aligned along the channel axis implies that the framework of the liquid crystal templated mesostructure guides the crystal growth.

Jason Dwyer

(Departments of Chemistry and Physics, University of Toronto, Toronto)

By Jason R. Dwyer, Robert E. Jordan, Christopher T. Hebeisen, Maher Harb, Ralph Ernstorfer and R.J. Dwayne Miller
1. Departments of Chemistry and Physics, University of Toronto, Toronto, Canada

Femtosecond (fs) lasers are an ideal tool to excite materials on timescales even shorter than vibrational periods, typically -100 fs. The ability to resolve all of the resulting structural dynamics depends on having a technique with femtosecond temporal resolution and capable of providing high structural resolution. Femtosecond electron diffraction satisfies both criteria and offer an unprecedented view of the fastest possible structural dynamics [1].

By using a femtosecond laser, one is able to very quickly deposit energy into a material - in these experiments, ultrathin films of gold and nickel. This leads to superheating of the metal and thereby permits the study of the familiar phenomenon of melting, only in this case the process is strongly driven. Even under these conditions, however, the material properties mediate the material response. In our first work [1], aluminum melted in 3.5 picoseconds (ps); under equivalent conditions, gold melts in 12 ps and nickel more quickly than gold. The difference in timescales is a consequence of a material parameter - the electron-phonon coupling constant - that differs by an order of magnitude between the gold and nickel and determines bow quickly the laser energy is transferred to nuclear motion. The observed structural changes, however, are the same for the two metals and thus allow for a generalized description of the molting mechanism.

(1) Siwick B,J. et at., Science, 2003, 302, 1382.

Jason Thomas Mayne

(Department of Biochemistry, University of Alberta, Edmonton)

By Jason T. Maynesa, Huu Anh Luua, Maia Cherneya, Charles F.B. Holmes and Michael N.G. James,
Department of Biochemistry, University of Alberta, Edmonton, Canada

Serine/Threonine Protein Phosphatases are important in many cellular processes including glycogen metabolism and immunosuppression. Many marine prokaryotic organisms produce structurally diverse phosphatase inhibitors that can be toxic. The surface of Ser/Thr Phosphatases contain an inhibitor-binding loop which is important in inhibitor activity. How this loop determines inhibitor-specificity is unknown. We have solved the structures of Protein Phosphatase-1 (PP1) bound to four marine natural product inhibitors: okadaic acid, motuporin, clavosine and microcystin-LA(2H)[1]. These inhibitors bind in a similar manner to the phosphatase, exhibiting analogous interactions and showing no structural rearrangement of the inhibitorbinding loop. A structure solved using a mutant PP1, where the inhibitor-binding loop from calcineurin has been substituted for the native loop, reveals repositioning of only specific amino acid sidechains. These results indicate that inhibitor specificity in Ser/Thr Phosphatases is most likely due to specific interactions within the inhibitor-binding loop and not structural rearrangements. There are observable differences in the binding of inhibitors to PP1 and the PP1-calcineurin hybrid, information that may be utilized in the design of new immunosuppressant calcineurin inhibitors.

[1] Maynes J.T., Perreault K.R., Cherney M.M., Luu H.A., James M.N.G., Holmes C.F.B., J. Biol. Chem., 2004, 279, 43198.

Elitza Tocheva

(Department of Microbiology and Immunology, University of British Columbia, Vancouver)

By Elitza Tocheva, Michael E. P. Murphy,
1. Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.

The process of denitrification involves the sequential reduction of nitrate (NO3-) to nitrite (NO2-), nitric oxide (NO), nitrous oxide (N2O) and finally dinitrogen (N2). The nitrite reductase from Alcaligenes faecalis S-6 (NiR) is a green 110 kDa periplasmic homotrimer with each monomer containing one type I and one type II copper sites. The type I is the site of electron transfer from the biological electron donor, pseudoazurin. Electrons are then donated internally to the type II Cu site, where NO2- is reduced to NO. Crystals of NiR are orthorhombic with a trimer in the asymmetric unit.

To visualize the product bound at the active site, ascorbate reduced crystals of NiR were exposed to a NO saturated solution and frozen in liquid N2 in the absence of oxygen. Data were collected at SSRL to 1.3 Å resolution. A difference electron-density map revealed elongated density at the apical position of the type II Cu. After refinement at full occupancy, the average B factor for NO is 29 Å2, similar to that observed for water bound to the resting state of the enzyme. The N (1.97 to 2.01 Å) and O (1.95 to 2.12 Å) atoms of NO are equidistant from the Cu, thus the Cu-nitrosyl of NiR is characterized with side-on coordination of a diatomic molecule (1).

To examine the ability of the enzyme to catalyze the reverse reaction (NO + H2O -> e- + NO2- + 2H+), oxidized crystals of NiR were exposed to a saturated NO solution. Refinement of the structure to 1.4 Å revealed nitrite bound to the copper via its oxygens, indicating completion of the reverse reaction in crystal. Spectroscopic studies which show that at alkaline pH, nitric oxide oxidation is faster than nitrite reduction (2) further support the conclusion that coppercontaining NiR can catalyze the reverse reaction.

[1]Tocheva, E. I., Rosell, F. I., Mauk, G. A., and Murphy, M. E. P. (2004). Science 304, 867-870. [2]Wijma, H. J., Canters, G. W., De Vries, S., and Verbeet, M. P. (2004). Biochemistry 43, 10467.