Assembly Behavior of Iron Oxide-Capped Janus Particles in a Magnetic Field

Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O₂ atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies

Assembly Behavior of Iron Oxide-Capped Janus Particles in a Magnetic Field

Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O₂ atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies

Assembly Behavior of Iron Oxide-Capped Janus Particles in a Magnetic Field

Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O₂ atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies

Assembly Behavior of Iron Oxide-Capped Janus Particles in a Magnetic Field

Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O₂ atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies

Theoretical Study on Thermodynamic and Spectroscopic Properties of Electro-Oxidation of <i>p</i>‑Aminothiophenol on Gold Electrode Surfaces

The electro-oxidation of <i>p</i>-aminothiophenol (PATP) on gold electrodes has been investigated by means of density functional theory. A combination of thermodynamic calculations and surface Raman and infrared (IR) spectral simulations has allowed us to reveal the electro-oxidation mechanism and reaction products of PATP on gold electrodes in acidic, neutral, and basic solutions. PATP can be first oxidized to the radical cation PATP­(NH₂^•+) or the neutral radical PATP­(NH^•) depending on the pH of aqueous solutions, and this is the rate-determining step. The radical cation or neutral radical can then transform to the dimerized products through a radical coupling reaction. In the acidic medium, the radical cation reacts with its resonance hybrid through a N–C4 coupling to form 4′-mercapto-<i>N</i>-phenyl-1,4-quinone diimine (D1), which can further undergo hydrolysis to yield 4′-mercapto-<i>N</i>-phenyl-1,4-quinone monoimine (D2). In the neutral medium, the neutral radical reacts with its resonance hybrid through the N–C2(6) coupling to form 4,4′-dimercapto-<i>N</i>-phenyl-1,2-quinone diimine (D3). In the basic medium, the neutral radical reacts with its resonance structure through the N–N coupling to form 4,4′-di­mercapto­azo­benzene (D4). The adsorbed dimer products exhibit reversible redox properties. The calculated standard electrode potentials of the above four species decrease in the order D3, D1, D2, and D4. Finally, the characteristic bands for the surface Raman and IR spectra of D1 to D4 redox pairs are clearly assigned. This study provides mechanistic insight into the electrochemical reaction properties of PATP on metal electrodes

The <i>phzA2-G2</i> Transcript Exhibits Direct RsmA-Mediated Activation in <i>Pseudomonas aeruginosa</i> M18

<div><p>In bacteria, RNA-binding proteins of the RsmA/CsrA family act as post-transcriptional regulators that modulate translation initiation at target transcripts. The <i>Pseudomonas aeruginosa</i> genome contains two phenazine biosynthetic (<i>phz</i>) gene clusters, <i>phzA1-G1</i> (<i>phz1</i>) and <i>phzA2-G2</i> (<i>phz2</i>), each of which is responsible for phenazine-1-carboxylic acid (PCA) biosynthesis. In the present study, we show that RsmA exhibits differential gene regulation on two <i>phz</i> clusters in <i>P. aeruginosa</i> M18 at the post-transcriptional level. Based on the sequence analysis, four GGA motifs, the potential RsmA binding sites, are found on the 5′-untranslated region (UTR) of the <i>phz2</i> transcript. Studies with a series of <i>lacZ</i> reporter fusions, and gel mobility shift assays suggest that the third GGA motif (S3), located 21 nucleotides upstream of the Shine-Dalgarno (SD) sequence, is involved in direct RsmA-mediated activation of <i>phz2</i> expression. We therefore propose a novel model in which the binding of RsmA to the target S3 results in the destabilization of the stem-loop structure and the enhancement of ribosome access. This model could be fully supported by RNA structure prediction, free energy calculations, and nucleotide replacement studies. In contrast, various RsmA-mediated translation repression mechanisms have been identified in which RsmA binds near the SD sequence of target transcripts, thereby blocking ribosome access. Similarly, RsmA is shown to negatively regulate <i>phz1</i> expression. Our new findings suggest that the differential regulation exerted by RsmA on the two <i>phz</i> clusters may confer an advantage to <i>P. aeruginosa</i> over other pseudomonads containing only a single <i>phz</i> cluster in their genomes.</p></div

Activities of transcriptional and translational <i>lacZ</i> fusions for <i>phzA1</i> and <i>phzA2</i> in strain M18 and its <i>rsmA</i> mutant M18ΔRA.

<p>β-gal activities of the two transcriptional fusions of pMP1C (<i>phzA1-lacZ</i>) and pMP2C-2 (<i>phzA2-lacZ</i>) are shown in (A) and (B), and the activities of the two translational fusions of pMP1L (<i>phzA1′-’lacZ</i>) and pMP2L (<i>phzA2′-’lacZ</i>) are shown in (C) and (D) both in wild-type strain M18 (squares) and <i>rsmA</i> mutant M18ΔRA (triangles) in PPM broth at 28°C. Values are the means ± standard deviations of triplicate cultures.</p

Secondary structures and free energies of WT and mutant <i>phz2</i> leader regions.

<p>The RNA structures of the <i>phz2</i> upstream region from nt +160 to +205 in the three plasmids of pMP2L (A), pMP2L-M1 (B), pMP2L-M2 (C) were predicted by M-fold and their folding free energies were -18.5 kcal/mol, -14.5 kcal/mol, and-7.1 kcal/mol, respectively. RABS: RsmA binding site.</p

Effects of RsmA on PCA production and the growth of strain M18 and its mutants.

<p>Growth curves (open symbols) and PCA production (solid symbols) were determined for (A) the wild-type strain M18 (squares) and its <i>rsmA</i> mutant M18ΔRA (triangles), (B) M18ΔRA/p-rsmA (squares) and M18ΔRA/pME6000 (triangles), (C) triple-mutant M18ΔMSP1 (squares) and quadruple-mutant M18ΔMSAP1 (triangles), and (D) triple-mutant M18ΔMSP2 (squares) and quadruple-mutant M18ΔMSAP2 (triangles) in PPM broth at 28°C. M18ΔRA/pME6000 indicates <i>rsmA</i> mutant M18ΔRA harbouring an empty pME6000 plasmid. M18ΔRA/p-rsmA indicates <i>rsmA</i> mutant M18ΔRA harbouring recombinant pME6000 that expressed the <i>rsmA</i> gene. Values are the means ± standard deviations of triplicate cultures.</p

Structure prediction of the <i>phz2</i> transcript and putative model of RsmA mediated activation of <i>phz2</i> translation.

<p>(A) A predicted 5′-UTR secondary structure from +160 to +205 nucleotides of the <i>phz2</i> transcript generated by <i>RNA structure.</i> (B) A putative direct activation model of the <i>phz2</i> transcript mediated by RsmA in <i>P. aeruginosa</i> M18. In the <i>rsmA</i>-deleted mutant (right), base-paired nucleotides between the SD with its flanking sequence and the RABS resulted in a relatively stable stem-loop structure, which prevented ribosome access and translation initiation. However, in the WT strain (left), the loose stem-loop structure caused by RsmA binding resulted in easy access to the ribosome and translation activation of the <i>phz2</i> transcript. RABS: RsmA binding site.</p