A Polar Copper–Boron One-Electron σ‑Bond

Virtually all chemical bonds consist of one or several pairs of electrons shared by two atoms. Examples of σ-bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas-phase cations such as H₂⁺ and Li₂⁺ and in highly unstable species generated in solid matrices. Only in the past decade was bona fide one-electron bonding observed for molecules in fluid solution. Here we report the isolation and structural characterization of a thermally stable compound featuring a Cu–B one-electron bond, as well as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners. This triad provides an excellent opportunity to study the degree of σ-bonding in a metalloboratrane as a function of electron count

A Polar Copper–Boron One-Electron σ‑Bond

Virtually all chemical bonds consist of one or several pairs of electrons shared by two atoms. Examples of σ-bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas-phase cations such as H₂⁺ and Li₂⁺ and in highly unstable species generated in solid matrices. Only in the past decade was bona fide one-electron bonding observed for molecules in fluid solution. Here we report the isolation and structural characterization of a thermally stable compound featuring a Cu–B one-electron bond, as well as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners. This triad provides an excellent opportunity to study the degree of σ-bonding in a metalloboratrane as a function of electron count

Synthesis and Characterization of Metal Iso-cyamelurate K_0.5In_0.5(H₂C₆N₇O₃)₂·9H₂O with Large Birefringence

In recent years, ultralarge planar π-conjugated groups were proposed for designing next-generation birefringent materials due to their strong structural anisotropy. Among the known π-conjugated groups, (HxC6N7O3)(3–x)– (x = 0−2) have been confirmed to hold considerablely strong anisotropic first-order polarizability, indicating their great potential for birefringent materials. In this work, we synthesized the first alkali main-group metal iso-cyamelurate single crystal of K0.5In0.5(H2C6N7O3)2·9H2O (I) by use of an aqueous solution method. In the crystal structure of I, (H2C6N7O3)– anions are layered, and K+ and In3+ cations fill in the interspace between the adjacent anion groups. I exhibits a wide band gap of ∼4.05 eV, and its estimated birefringence value reaches 0.35 at 1064 nm. The theoretical calculations have been performed to understand the origin of the optical properties of I featured with colossal planar π-conjugated groups

Activation of a Cryptic Gene Cluster in <i>Lysobacter enzymogenes</i> Reveals a Module/Domain Portable Mechanism of Nonribosomal Peptide Synthetases in the Biosynthesis of Pyrrolopyrazines

<i>Lysobacter</i> are considered “peptide specialists”. However, many of the nonribosomal peptide synthetase genes are silent. Three new compounds were identified from <i>L. enzymogenes</i> upon activating the six-module-containing <i>led</i> cluster by the strong promoter <i>P</i>_HSAF. Although <i>ledD</i> was the first gene under <i>P</i>_HSAF control, the second gene <i>ledE</i> was expressed the highest. Targeted gene inactivation showed that the two-module LedE and the one-module LedF were selectively used in pyrrolopyrazine biosynthesis, revealing a module/domain portable mechanism

Substrate Pathways in the Nitrogenase MoFe Protein by Experimental Identification of Small Molecule Binding Sites

In the nitrogenase molybdenum-iron (MoFe) protein, we have identified five potential substrate access pathways from the protein surface to the FeMo-cofactor (the active site) or the P-cluster using experimental structures of Xe pressurized into MoFe protein crystals from <i>Azotobacter vinelandii</i> and <i>Clostridium pasteurianum</i>. Additionally, all published structures of the MoFe protein, including those from <i>Klebsiella pneumoniae</i>, were analyzed for the presence of nonwater, small molecules bound to the protein interior. Each pathway is based on identification of plausible routes from buried small molecule binding sites to both the protein surface and a metallocluster. Of these five pathways, two have been previously suggested as substrate access pathways. While the small molecule binding sites are not conserved among the three species of MoFe protein, residues lining the pathways are generally conserved, indicating that the proposed pathways may be accessible in all three species. These observations imply that there is unlikely a unique pathway utilized for substrate access from the protein surface to the active site; however, there may be preferred pathways such as those described here

Hierarchically Structured MXene Nanosheets on Carbon Sponges with a Synergistic Effect of Electrostatic Adsorption and Capillary Action for Highly Sensitive Pressure Sensors

A highly sensitive pressure sensor with nanoscale features was developed based on the gradient concentration of Ti3C2Tx (MXene). The fabrication strategy involved electrostatic adsorption and capillary action utilizing a carbonized sponge as the substrate. In this approach, hexadecyl trimethyl ammonium bromide (CTAB) was added dropwise to the bottom of the carbonized melamine sponge, facilitating the self-assembly of MXene and achieving a gradient attachment of conductive fillers onto the substrate. Furthermore, a layer of polyvinyl alcohol fibers was electrospun between the sensor bottom and the electrode to enhance sensor sensitivity. The pressure-sensitive sensor prepared by this method exhibited an exceptionally strong response within the pressure range of 0–3 kPa. It demonstrated an ultrahigh sensitivity of 381.91 kPa–1, with a rapid deformation response of 100 ms and a quick recovery response of 30 ms. Notably, the sensor also demonstrated outstanding durability, enduring 8000 loading–unloading cycles without performance degradation. Moreover, it achieved a minimum detection limit as low as 0.1 Pa. Finite element numerical analysis confirmed that the MXene/CTAB/CMF composite prepared using this approach exhibited superior sensing performance under similar deformation conditions. Importantly, this pressure sensor’s exceptional sensing capabilities extended to detecting various physiological signals in the human body and daily work scenarios. When integrated with a microprocessor, it accurately processed complex data sets, highlighting its great potential for practical applications

Functional and Structural Analysis of Phenazine <i>O</i>‑Methyltransferase LaPhzM from <i>Lysobacter antibioticus</i> OH13 and One-Pot Enzymatic Synthesis of the Antibiotic Myxin

Myxin is a well-known antibiotic that had been used for decades. It belongs to the phenazine natural products that exhibit various biological activities, which are often dictated by the decorating groups on the heteroaromatic three-ring system. The three rings of myxin carry a number of decorations, including an unusual aromatic <i>N</i>5,<i>N</i>10-dioxide. We previously showed that phenazine 1,6-dicarboxylic acid (PDC) is the direct precursor of myxin, and two redox enzymes (LaPhzS and LaPhzNO1) catalyze the decarboxylative hydroxylation and aromatic <i>N</i>-oxidations of PDC to produce iodinin (1.6-dihydroxy-<i>N</i>5,<i>N</i>10-dioxide phenazine). In this work, we identified the <i>LaPhzM</i> gene from <i>Lysobacter antibioticus</i> OH13 and demonstrated that <i>LaPhzM</i> encodes a SAM-dependent <i>O</i>-methyltransferase converting iodinin to myxin. The results further showed that LaPhzM is responsible for both monomethoxy and dimethoxy formation in all phenazine compounds isolated from strain OH13. LaPhzM exhibits relaxed substrate selectivity, catalyzing <i>O</i>-methylation of phenazines with non-, mono-, or di-<i>N</i>-oxide. In addition, we demonstrated a one-pot biosynthesis of myxin by <i>in vitro</i> reconstitution of the three phenazine-ring decorating enzymes. Finally, we determined the X-ray crystal structure of LaPhzM with a bound cofactor at 1.4 Å resolution. The structure provided molecular insights into the activity and selectivity of the first characterized phenazine <i>O</i>-methyltransferase. These results will facilitate future exploitation of the thousands of phenazines as new antibiotics through metabolic engineering and chemoenzymatic syntheses

Labile Carbon from Artificial Roots Alters the Patterns of N₂O and N₂ Production in Agricultural Soils

Labile carbon (C) continuously delivered from the rhizosphere profoundly affects terrestrial nitrogen (N) cycling. However, nitrous oxide (N2O) and dinitrogen (N2) production in agricultural soils in the presence of continuous root C exudation with applied N remains poorly understood. We conducted an incubation experiment using artificial roots to continuously deliver small-dose labile C combined with 15N tracers to investigate N2O and N2 emissions in agricultural soils with pH and organic C (SOC) gradients. A significantly negative exponential relationship existed between N2O and N2 emissions under continuous C exudation. Increasing soil pH significantly promoted N2 emissions while reducing N2O emissions. Higher SOC further promoted N2 emissions in alkaline soils. Native soil-N (versus fertilizer-N) was the main source of N2O (average 67%) and N2 (average 80%) emissions across all tested soils. Our study revealed the overlooked high N2 emissions, mainly derived from native soil-N and strengthened by increasing soil pH, under relatively real-world conditions with continuous root C exudation. This highlights the important role of N2O and N2 production from native soil-N in terrestrial N cycling when there is a continuous C supply (e.g., plant-root exudate) and helps mitigate emissions and constrain global budgets of the two concerned nitrogenous gases

Stretchable and Transparent Heaters Based on Hydrophobic Ionogels with Superior Moisture Insensitivity

Flexible and stretchable transparent heaters (THs) have been widely used in various applications, including deicing and defogging of flexible screens as well as thermotherapy pads. Ionic THs based on ionogels have emerged as a promising alternative to conventional electronic THs due to their unique advantages in terms of transparency-conductance conflict, uniform heating, and interfacial adhesion. However, the commonly used hydrophilic ionogels inevitably introduce a moisture-sensitive issue. In this work, we present a stretchable and transparent hydrophobic ionogel-based heater that utilizes ionic current-induced Joule heating under high-frequency alternating current. This ionogel-based TH exhibits exceptional multifunctional properties with low hysteresis, a fracture strain of 840%, transmittance of 93%, conductivity of 0.062 S m–1, temperature resistance up to 165 °C, voltage resistance up to 120 V, heating rate of 0.1 °C s–1, steady-state temperature at 115 °C, and uniform heating even when bent or stretched (up to 200%). Furthermore, it maintains its heating performance when it is directly exposed to water. This hydrophobic ionogel-based TH expands the range of materials available for ionic THs and paves the way for their practical applications