Biomimetic Microdroplet Membrane Interface: Detection of the Lateral Localization of Amyloid Beta Peptides

Lateral membrane organization into domains, such as lipid rafts, plays an important role in the selective association of biological and nonbiological materials on heterogeneous membrane surfaces. The localization of such materials has profound influence on cellular responses. We constructed a biomimetic water-in-oil microdroplet membrane to study the lateral localization of these materials at heterogeneous biological interfaces. As a case study, we studied selective association of amyloid β peptide on the constructed membrane surface. Amyloid β peptide has attracted much attention as one of these membrane-associating proteins because of its “role” in Alzheimer’s disease pathology. Ternary lipid membranes covering microdroplets successfully produced lipid ordered structures, which mimicked biological lipid rafts. We revealed that amyloid β peptide selectively localizes within nonraft fluid membrane regions. The successful lateral organization in microdroplet membrane systems may lead to new opportunities for the study of molecular associations within heterogeneous membranes

Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties

Two new one-dimensional (1D) rhodium­(I)–semiquinonato complexes formulated as [Rh­(3,6-DBSQ-4,5-PDO)­(CO)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh­(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))­(CO)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds <b>4</b> and <b>5</b> comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are similar to those for <b>3</b> (3.09 Å); however, the molecules of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i>_trs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound <b>4</b> exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at <i>T</i>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 199 meV) in the LT phase. These behaviors are commonly observed for <b>3</b>. Alternating current susceptibility measurements of <b>4</b>, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for <b>3</b>, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound <b>5</b>, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10⁷ Ω cm

Multifunctional One-Dimensional Rhodium(I)–Semiquinonato Complex: Substituent Effects on Crystal Structures and Solid-State Properties

Two new one-dimensional (1D) rhodium­(I)–semiquinonato complexes formulated as [Rh­(3,6-DBSQ-4,5-PDO)­(CO)₂]_∞ (<b>4</b>; 3,6-DBSQ-4,5-PDO^•– = 3,6-di-<i>tert</i>-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh­(3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN))­(CO)₂]_∞ (<b>5</b>; 3,6-DBSQ-4,5-(<i>N</i>,<i>N</i>′-DEN)^•– = 3,6-di-<i>tert</i>-butyl-4,5-(<i>N</i>,<i>N</i>′-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>; 3,6-DBSQ-4,5-(MeO)₂^•– = 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds <b>4</b> and <b>5</b> comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh–Rh distances of 3.06 Å for <b>4</b> and 3.10 Å for <b>5</b>. These distances are similar to those for <b>3</b> (3.09 Å); however, the molecules of <b>5</b> are strongly dimerized in the 1D chain. Compound <b>4</b> undergoes a first-order phase transition at <i>T</i>_trs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound <b>4</b> exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at <i>T</i>_N = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (<i>E</i>_a = 31 meV) in the RT phase to a semiconductor with a large activation energy (<i>E</i>_a = 199 meV) in the LT phase. These behaviors are commonly observed for <b>3</b>. Alternating current susceptibility measurements of <b>4</b>, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for <b>3</b>, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound <b>5</b>, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10⁷ Ω cm

Bistable Multifunctionality and Switchable Strong Ferromagnetic-to-Antiferromagnetic Coupling in a One-Dimensional Rhodium(I)–Semiquinonato Complex

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV–vis−NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium­(I)–semiquinonato complex, [Rh­(3,6-DBSQ-4,5-(MeO)₂)­(CO)₂]_∞ (<b>3</b>), where 3,6-DBSQ-4,5-(MeO)₂^•– represents 3,6-di-<i>tert</i>-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound <b>3</b> comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh–Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228–207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C–H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound <b>3</b> exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature <i>T</i>_N of 14.2 K. The electrical conductivity of <b>3</b> at 300 K is 4.8 × 10^–4 S cm^–1, which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation