Decontamination of Sr(II) on Magnetic Polyaniline/Graphene Oxide Composites: Evidence from Experimental, Spectroscopic, and Modeling Investigation

The interaction of Sr­(II) on magnetic polyaniline/graphene oxide (PANI/GO) composites was elucidated by batch, EXAFS, and surface complexation modeling techniques. The batch experiments showed that decreased uptake of Sr­(II) on magnetic PANI/GO composites was observed with increasing ionic strength at pH <5.0, whereas no effect of ionic strength on Sr­(II) uptake was shown at pH >5.0. The maximum uptake capacity of magnetic PANI/GO composites derived from the Langmuir model at pH 3.0 and 293 K was 37.17 mg/g. The outer-sphere surface complexation controlled the uptake of Sr­(II) on magnetic PANI/GO composites at pH 3.0 due to the similarity to the EXAFS spectra of Sr²⁺ in aqueous solutions, but the Sr­(II) uptake at pH 7.0 was inner sphere complexation owing to the occurrence of the Sr–C shell. According to the analysis of surface complexation modeling, uptake of Sr­(II) on magnetic PANI/GO composites was well simulated using a diffuse layer model with an outer-sphere complex (SOHSr²⁺ species) and two inner-sphere complexes (i.e., (SO)₂Sr­(OH)⁻ and SOSr⁺ species). These findings are crucial for the potential application of magnetic nanomaterials as a promising candidate for the uptake of radionuclides for environmental remediation

Development and Validation of a Method for the Determination of 159 Pesticide Residues in Tobacco by Gas Chromatography–Tandem Mass Spectrometry

A multiresidue gas chromatography–tandem mass spectrometry (GC-MS/MS) method was developed for the analysis of 159 multiclass pesticides in tobacco. A modified QuEChERS sample preparation technique, based on acetonitrile extraction and toluene dilution, followed by dispersive solid-phase extraction (d-SPE) cleanup using primary–secondary amine (PSA) and octadecyl (C18) sorbents, was used for sample treatment. Key performance parameters investigated were linearity, recovery, relative standard deviation (RSD), limit of detection, and limit of quantitation. With the exception of chinomethionate and folpet, recoveries for pesticides ranged from 69 to 141%, and the RSDs ranged from 2 to 27%. The validated method was applied to the analysis of 118 real samples, and positive results were obtained for 116 samples, with 25 different pesticides being detected

Structural Basis for the Selective Pb(II) Recognition of Metalloregulatory Protein PbrR691

The transcription regulator PbrR691, one of the MerR family proteins, shows extremely high sensitivity and selectivity toward Pb­(II) in <i>Ralstonia metallidurans</i> CH34. Here, we present the crystal structure of PbrR691 in complex with Pb­(II) at 2.0 Å resolution. The Pb­(II) coordinates with three conserved cysteines and adopts a unique trigonal-pyramidal (hemidirected) geometry. To our knowledge, the PbrR691-Pb­(II) structure provides the first three-dimensional visualization of a functional hemidirected lead­(II) thiolate coordinate geometry in a protein

Structural Basis for the Selective Pb(II) Recognition of Metalloregulatory Protein PbrR691

The transcription regulator PbrR691, one of the MerR family proteins, shows extremely high sensitivity and selectivity toward Pb­(II) in <i>Ralstonia metallidurans</i> CH34. Here, we present the crystal structure of PbrR691 in complex with Pb­(II) at 2.0 Å resolution. The Pb­(II) coordinates with three conserved cysteines and adopts a unique trigonal-pyramidal (hemidirected) geometry. To our knowledge, the PbrR691-Pb­(II) structure provides the first three-dimensional visualization of a functional hemidirected lead­(II) thiolate coordinate geometry in a protein

Mineralization of Few-Layer Graphene Made It Bioavailable in <i>Chlamydomonas reinhardtii</i>

Numerous studies have emphasized the toxicity of graphene-based nanomaterials to algae, however, the fundamental behavior and processes of graphene in biological hosts, including its transportation, metabolization, and bioavailability, are still not well understood. As photosynthetic organisms, algae are key contributors to carbon fixation and may play an important role in the fate of graphene. This study investigated the biological fate of 14C-labeled few-layer graphene (14C-FLG) in Chlamydomonas reinhardtii (C. reinhardtii). The results showed that 14C-FLG was taken up by C. reinhardtii and then translocated into its chloroplast. Metabolomic analysis revealed that 14C-FLG altered the metabolic profiles (including sugar metabolism, fatty acid, and tricarboxylic acid cycle) of C. reinhardtii, which promoted the photosynthesis of C. reinhardtii and then enhanced their growth. More importantly, the internalized 14C-FLG was metabolized into 14CO2, which was then used to participate in the metabolic processes required for life. Approximately 61.63%, 25.31%, and 13.06% of the total radioactivity (from 14CO2) was detected in carbohydrates, lipids, and proteins of algae, respectively. Overall, these results reveal the role of algae in the fate of graphene and highlight the potential of available graphene in bringing biological effects to algae, which helps to better assess the environmental risks of graphene

Structural basis of Zn(II) induced metal detoxification and antibiotic resistance by histidine kinase CzcS in <i>Pseudomonas aeruginosa</i>

<div><p><i>Pseudomonas aeruginosa</i> (<i>P</i>. <i>aeruginosa</i>) is a major opportunistic human pathogen, causing serious nosocomial infections among immunocompromised patients by multi-determinant virulence and high antibiotic resistance. The CzcR-CzcS signal transduction system in <i>P</i>. <i>aeruginosa</i> is primarily involved in metal detoxification and antibiotic resistance through co-regulating cross-resistance between Zn(II) and carbapenem antibiotics. Although the intracellular regulatory pathway is well-established, the mechanism by which extracellular sensor domain of histidine kinase (HK) CzcS responds to Zn(II) stimulus to trigger downstream signal transduction remains unclear. Here we determined the crystal structure of the CzcS sensor domain (CzcS SD) in complex with Zn(II) at 1.7 Å resolution. This is the first three-dimensional structural view of Zn(II)-sensor domain of the two-component system (TCS). The CzcS SD is of α/β-fold in nature, and it senses the Zn(II) stimulus at micromole level in a tetrahedral geometry through its symmetry-related residues (His55 and Asp60) on the dimer interface. Though the CzcS SD resembles the PhoQ-DcuS-CitA (PDC) superfamily member, it interacts with the effector in a novel domain with the N-terminal α-helices rather than the conserved β-sheets pocket. The dimerization of the N-terminal H1 and H1’ α-helices is of primary importance for the activity of HK CzcS. This study provides preliminary insight into the molecular mechanism of Zn(II) sensing and signaling transduction by the HK CzcS, which will be beneficial to understand how the pathogen <i>P</i>. <i>aeruginosa</i> resists to high levels of heavy metals and antimicrobial agents.</p></div

Data collection and refinement statistics for the structure of CzcS-Zn.

<p>Data collection and refinement statistics for the structure of CzcS-Zn.</p

Proposed molecular mechanism of Zn(II) signal transduction in HK CzcS.

<p>The two monomers in the CzcS functional dimer are shown in green and in cyan. When the Zn(II) binds to CzcS, the sensor domain will turn from monomer to dimer with the Zn(II) binding at the symmetrical N-terminal α-helices. The dimerization of sensor domain will drive the interactional rearrangement within the dimeric four-helical bundles in the transmembrane domain [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006533#ppat.1006533.ref047" target="_blank">47</a>], and autophosphorylation is activated at the conserved histidine residues in the cytoplasmic kinase domain [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006533#ppat.1006533.ref048" target="_blank">48</a>–<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006533#ppat.1006533.ref051" target="_blank">51</a>].</p

The identification of Co(II)-responsive mutant.

<p>Wild type <i>P</i>. <i>aeruginosa</i> and its derivative strains are examined on LB plates that contain Co(II) and MEPM antibiotic as follows: wild type <i>P</i>. <i>aeruginosa</i> with empty pAK1900 plasmid as the control (WT PAO1 pAK1900), <i>czcS</i>-deficient <i>P</i>. <i>aeruginosa</i> with the empty pAK1900 (PAO1△<i>czcS</i> pAK1900), <i>czcS</i>-deficient <i>P</i>. <i>aeruginosa</i> with wild type <i>czcS</i> encoded on pAK1900 (PAO1△<i>czcS</i> pCSAK), <i>czcS</i>-deficient <i>P</i>. <i>aeruginosa</i> complemented with the <i>czcS</i> mutants in pAK1900 (PAO1△<i>czcS</i> pCSAK D60C).</p

Cysteine substitution of residues in the linker region.

<p>(a) The schematic diagram of the linker region in the HK CzcS. The linker region, which connects the H1 and H1’ α-helices of the sensor domain to the transmembrane helices, is indicated by dashed lines. The amino acid sequence in the linker region is “Arg-Glu-Leu-Glu”. (b) Metal and antibiotic tolerance plate assay. Wild type <i>P</i>. <i>aeruginosa</i> and its derivative strains are examined on LB plates that contain Zn(II) and MEPM antibiotic as follows: wild type <i>P</i>. <i>aeruginosa</i> with the empty pAK1900 plasmid as the control (WT PAO1 PAK1900), <i>czcS</i>-deficient <i>P</i>. <i>aeruginosa</i> with empty pAK1900 (PAO1△<i>czcS</i> pAK1900), <i>czcS</i>-deficient <i>P</i>. <i>aeruginosa</i> with wild type <i>czcS</i> encoded on pAK1900 (PAO1△<i>czcS</i> pCSAK), <i>czcS</i> deficient <i>P</i>. <i>aeruginosa</i> complemented with <i>czcS</i> mutants in pAK1900 (PAO1△<i>czcS</i> pCSAK H55A, and PAO1△<i>czcS</i> pCSAK L38C H55A).</p