A Redox-Sensitive Cysteine Is Required for PIN1At Function

Parvulins are ubiquitous peptidyl-prolyl isomerases (PPIases) required for protein folding and regulation. Among parvulin members, Arabidopsis PIN1At, human PIN1, and yeast ESS1 share a conserved cysteine residue but differ by the presence of an N-terminal WW domain, absent in PIN1At. In this study, we have explored whether the cysteine residue of Arabidopsis PIN1At is involved in catalysis and subject to oxidative modifications. From the functional complementation of yeast ess1 mutant, we concluded that the cysteine at position 69 is mandatory for PIN1At function in vivo, unless being replaced by an Asp which is found in a few parvulin members. This result correlates with a decrease of the in vitro PPIase activity of non-functional PIN1At cysteinic variants. A decrease of PIN1At activity was observed upon H2O2 treatment. The in vitro oxidation of cysteine 69, which has an acidic pKa value of 4.9, leads to the formation of covalent dimers that are reduced by thioredoxins, or to sulfinic or sulfonic acid forms at higher H2O2 excess. These investigations highlight the importance of the sole cysteine residue of PIN1At for activity. The reversible formation of an intermolecular disulfide bond might constitute a protective or regulatory mechanism under oxidizing conditions.

Atomic-Scale Investigation of the Reversible alpha to omega-Phase Lithium Ion Charge – Discharge Characteristics of Electrodeposited Vanadium Pentoxide Nanobelts

Using an electrochemical potential pulse methodology in a mixed solvent system, electrochemical deposition of amorphous vanadium pentoxide (V2O5) nanobelts is possible. Crystallisation of the material is achieved using in air annealing with the temperature of crystallisation identified using in-situ heating transmission electron microscopy (TEM). The resulting alpha-phase V2O5 nanobelts have typical thicknesses of 10-20 nm, widths and lengths in the range 5-37 nm (mean 9 nm) and 15 - 221 nm (mean 134 nm), respectively. One-cycle reversibility studies for lithium intercalation (discharge) and de-intercalation (discharge) reveal a maximum specific capacity associated with three lithium ions incorporated per unit cell, indicative of omega-Li3V2O5 formation. Aberration corrected scanning TEM confirm the formation of omega-Li3V2O5 across the entirety of a nanobelt during discharge and also the reversible formation of the alpha-V2O5 phase upon full charge. Preliminary second cycle studies reveal reformation of the omega-Li3V2O5, accompanied with a morphological change in the nanobelt dimensions. Achieving alpha-V2O5 to omega-Li3V2O5 phase reversibility is extremely challenging given the large structural rearrangements required. This phenomenon has only been seen before in a very limited number of studies also employing nanosized V2O5 materials and never before with electrodeposited nanocrystals.

Dramatic Effect of A Ring Size of Alicyclic α-Dioximate Ligand Synthons on Kinetics of the Template Synthesis and of the Acidic Decomposition of the Methylboron-Capped Iron(II) Clathrochelates

Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximates—the clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthons—were compared. In the case of a macrobicyclic iron(II) tris-nioximate, the plausible pathway of its formation contains a rate-determining stage and includes a reversible formation of an almost trigonal-antiprismatic (TAP) protonated tris-complex, followed by its monodeprotonation and addition of CH3B(OH)2. Thus, the formed TAP intermediate undergoes a multistep rate-determining stage of double cyclization with the elimination of two water molecules accompanied by a structural rearrangement, thus giving an almost trigonal-prismatic (TP) iron(II) semiclathrochelate. It easily undergoes a cross-linking with CH3B(OH)2, resulting in the elimination of H+ ion and in the formation of a macrobicyclic structure. In contrast, the analogous scheme for its macrobicyclic tris-octoximate analog was found to contain up to three initial stages affecting the overall synthesis reaction rate. The rates of acidic decomposition of the above clathrochelates were found to be also affected by the nature of their ribbed substituents. Therefore, the single crystal XRD experiments were performed in order to explain these results. The difference in the kinetic schemes of a formation of the boron-capped iron(II) tris-nioximates and tris-octoximates is explained by necessity of the substantial changes in a geometry of the latter ligand synthon, caused by its coordination to the iron(II) ion, due to both the higher distortion of the FeN6-coordination polyhedra, and the intramolecular sterical clashes in the molecules of the macrobicyclic iron(II) tris-octoximates.

Reversible formation of coordination bonds in Sn-based metal-organic frameworks for high-performance lithium storage

Sn-based compounds with buffer matrixes possessing high theoretical capacity, low working voltage, and alleviation of the volume expansion of Sn are ideal materials for lithium storage. However, it is challenging to confine well-dispersed Sn within a lithium active matrix because low-melting-point Sn tends to agglomerate. Here, we apply a metal-organic framework (MOF) chemistry between Sn-nodes and lithium active ligands to create two Sn-based MOFs comprising Sn2(dobdc) and Sn2(dobpdc) with extended ligands from H4dobdc (2,5-dioxido-1,4-benzenedicarboxylate acid) to H4dobpdc (4,4’-dioxidobiphenyl-3,3’-dicarboxylate acid) with molecule-level homodispersion of Sn in organic matrixes for lithium storage. The enhanced utilization of active sites and reaction kinetics are achieved by the isoreticular expansion of the organic linkers. The reversible formation of coordination bonds during lithium storage processes is revealed by X-ray absorption fine structure characterization, providing an in-depth understanding of the lithium storage mechanism in coordination compounds.

Nitrosyl linkage photoisomerization in heteroleptic fluoride ruthenium complexes derived from labile nitrate precursors

Four complexes with trans-ON–Ru–F coordinate were synthesized from their nitrate precursors. Upon light irradiation, complexes I–III show reversible formation of highly stable linkage isomers MS2 which leads to a higher photogeneration temperature of MS1.

Temperature-induced liquid crystal microdroplet formation in a partially miscible liquid mixture

We demonstrate how, for a binary blend of a thermotropic liquid crystal and methanol, cooling from a miscible to an immiscible state induces the reversible formation of microdroplets, whose size, number and mesogen orientation can be controlled by the temperature protocol.