A microstructural evaluation of friction stir welded 7075 aluminum rolled plate heat treated to the semi-solid state

Two rolled plates of 7075 aluminum alloy were used as starting material. The plates were welded using a simultaneous double-sided friction stir welding (FSW) process. One way of obtaining feedstock materials for Semi-solid processing or thixoforming is via deformation routes followed by partial melting in the semi-solid state. As both the base plate materials and the friction weld area have undergone extensive deformation specimens were subjected to a post welding heat-treatment in the semi-solid range at a temperature of 628 °C, for 3 min in order to observe the induced microstructural changes. A comparison between the microstructural evolution and mechanical properties of friction stir welded plates was performed before and after the heat-treatment in the Base Metal (BM), the Heat Affected Zone (HAZ), the Thermomechanically Affected Zone (TMAZ) and the Nugget Zone (NZ) using optical microscopy, Scanning Electron microscopy (SEM) and Vickers hardness tests. The results revealed that an extremely fine-grained structure, obtained in the NZ after FSW, resulted in a rise of hardness from the BM to the NZ. Furthermore, post welding heat-treatment in the semi-solid state gave rise to a consistent morphology throughout the material which was similar to microstructures obtained by the thixoforming process. Moreover, a drop of hardness was observed after heat treatment in all regions as compared to that in the welded microstructure

Towards in-cell structural study of light-harvesting complexes : an investigation with MAS-NMR

Light-Harvesting Complex II (LHCII) is responsible for light absorption and excitation energy transfer in plants and photosynthetic algae, while in high light it undergoes conformational changes by which it quenches excitations to prevent photodamage. The underlying molecular picture of these conformational changes has not yet been resolved. The main target of the research described in this thesis is to address the conformational dynamics of photosynthetic Light Harvesting Complex II and the role of the membrane environment. Hereto, I explored NMR-based methods that could eventually probe the molecular structure and dynamics of photosynthetic components in-vivo in functional membranes or cell systems.NWO CW-VIDI granted to Dr. Anjali Pandit, u-NMR-NL for the use of ultrahigh-field NMRSolid state NMR/Biophysical Organic Chemistr

In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

Article / Letter to editorLeiden Institute of Chemistry;Leiden Institute of Chemistr

In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

Article / Letter to editorLeiden Institute of Chemistry;Leiden Institute of Chemistr

In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

Article / Letter to editorLeiden Institute of Chemistry;Leiden Institute of Chemistr

In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

Solid state NMR/Biophysical Organic Chemistr

Towards in-cell structural study of light-harvesting complexes : an investigation with MAS-NMR

Light-Harvesting Complex II (LHCII) is responsible for light absorption and excitation energy transfer in plants and photosynthetic algae, while in high light it undergoes conformational changes by which it quenches excitations to prevent photodamage. The underlying molecular picture of these conformational changes has not yet been resolved. The main target of the research described in this thesis is to address the conformational dynamics of photosynthetic Light Harvesting Complex II and the role of the membrane environment. Hereto, I explored NMR-based methods that could eventually probe the molecular structure and dynamics of photosynthetic components in-vivo in functional membranes or cell systems.</p

In vivo NMR as a tool for probing molecular structure and dynamics in intact Chlamydomonas reinhardtii cells

Solid state NMR/Biophysical Organic Chemistr

Conformational Dynamics of Light-Harvesting Complex II in a Native Membrane Environment

Photosynthetic light-harvesting complexes (LHCs) of higher plants, moss, and green algae can undergo dynamic conformational transitions, which have been correlated to their ability to adapt to fluctuations in the light environment. Herein, we demonstrate the application of solid-state NMR spectroscopy on native, heterogeneous thylakoid membranes of Chlamydomonas reinhardtii (Cr) and on Cr light-harvesting complex II (LHCII) in thylakoid lipid bilayers to detect LHCII conformational dynamics in its native membrane environment. We show that membrane-reconstituted LHCII contains selective sites that undergo fast, large-amplitude motions, including the phytol tails of two chlorophylls. Protein plasticity is also observed in the N-terminal stromal loop and in protein fragments facing the lumen, involving sites that stabilize the xanthophyll-cycle carotenoid violaxanthin and the two luteins. The results report on the intrinsic flexibility of LHCII pigment-protein complexes in a membrane environment, revealing putative sites for conformational switching. In thylakoid membranes, fast dynamics of protein and pigment sites is significantly reduced, which suggests that in their native organelle membranes, LHCII complexes are locked in specific conformational states

Protein and lipid dynamics in photosynthetic thylakoid membranes investigated by in-situ solid-state NMR

Solid state NMR/Biophysical Organic Chemistr