In situgrazing incidence small-angle x-ray scattering real-time monitoring of the role of humidity during the structural formation of templated silica thin films

Within the scope of the comprehensive elucidation of the entire process chain for the production of highly functional thin films made of semiconducting aluminum-doped zinc oxide ( A Z O ) nanocrystals, this work deals with the detailed investigation of the stabilization sub-process, considering the requirements for the subsequent coating process. An innovative investigation procedure using non-invasive small angle X-ray scattering ( S A X S ) is developed, enabling an evaluation of qualitative and quantitative dispersion stability criteria of sterically stabilized A Z O nanocrystals. On the one hand, qualitative criteria for minimizing layer inhomogeneities due to sedimentation as well as aggregate formation are discussed, enabling a high particle occupancy density. On the other hand, a procedure for determining the A Z O concentration using S A X S , both in the stable phase and in the non-stabilized phase, is demonstrated to provide a quantitative evaluation of the stabilization success, having a significant impact on the final layer thickness. The obtained insights offer a versatile tool for the precise stabilization process control based on synthesis process using S A X S to meet coating specific requirements and thus a successful integration into the entire process chain for the production of functional A Z O thin films.

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The Role of Intersubunit Interactions for the Stabilization of the T State ofEscherichia coliAspartate Transcarbamoylase

Journal of Biological Chemistry ◽

10.1074/jbc.m208919200 ◽

2002 ◽

Vol 277 (51) ◽

pp. 49755-49760 ◽

Cited By ~ 10

Author(s):

Robin S. Chan ◽

Jessica B. Sakash ◽

Christine P. Macol ◽

Jay M. West ◽

Hiro Tsuruta ◽

...

Keyword(s):

Small Angle ◽

Structural State ◽

Aspartate Transcarbamoylase ◽

Wild Type ◽

X Ray ◽

X Ray Scattering ◽

Intersubunit Interactions ◽

T State ◽

Ray Scattering

Homotropic cooperativity inEscherichia coliaspartate transcarbamoylase results from the substrate-induced transition from the T to the R state. These two alternate states are stabilized by a series of interdomain and intersubunit interactions. The salt link between Lys-143 of the regulatory chain and Asp-236 of the catalytic chain is only observed in the T state. When Asp-236 is replaced by alanine the resulting enzyme exhibits full activity, enhanced affinity for aspartate, no cooperativity, and no heterotropic interactions. These characteristics are consistent with an enzyme locked in the functional R state. Using small angle x-ray scattering, the structural consequences of the D236A mutant were characterized. The unliganded D236A holoenzyme appears to be in a new structural state that is neither T, R, nor a mixture of T and R states. The structure of the native D236A holoenzyme is similar to that previously reported for another mutant holoenzyme (E239Q) that also lacks intersubunit interactions. A hybrid version of aspartate transcarbamoylase in which one catalytic subunit was wild-type and the other had the D236A mutation was also investigated. The hybrid holoenzyme, with three of the six possible interactions involving Asp-236, exhibited homotropic cooperativity, and heterotropic interactions consistent with an enzyme with both T and R functional states. Small angle x-ray scattering analysis of the unligated hybrid indicated that the enzyme was in a new structural state more similar to the T than to the R state of the wild-type enzyme. These data suggest that three of the six intersubunit interactions involving D236A are sufficient to stabilize a T-like state of the enzyme and allow for an allosteric transition.

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