A Comparative IRMPD and DFT Study of Fe³⁺ and UO₂²⁺ Complexation with <i>N</i>‑Methylacetohydroxamic Acid

Iron­(III) and uranyl complexes of <i>N</i>-methylacetohydroxamic acid (NMAH) have been investigated by mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. A comparison between IRMPD and theoretical IR spectra enabled one to probe the structures for some selected complexes detected in the gas phase. The results show that coordination of Fe³⁺ and UO₂²⁺ by hydroxamic acid is of a very similar nature. Natural bond orbital analysis suggests that bonding in uranyl complexes possesses a slightly stronger ionic character than that in iron complexes. Collision-induced dissociation (CID), IRMPD, and ¹⁸O-labeling experiments unambiguously revealed a rare example of the UO bond activation concomitant with the elimination of a water molecule from the gaseous [UO₂(NMA)­(NMAH)₂]⁺ complex. The UO bond activation is observed only for complexes with one monodentate NMAH molecule forming a hydrogen bond toward one “yl” oxygen atom, as was found by DFT calculations. This reactivity might explain oxygen exchange observed for uranyl complexes

Azide Binding Controlled by Steric Interactions in Second Sphere. Synthesis, Crystal Structure, and Magnetic Properties of [Ni^II₂(L)­(μ_1,1-N₃)]­[ClO₄] (L = Macrocyclic N₆S₂ Ligand)

The dinuclear Ni^II complex [Ni₂(L²)]­[ClO₄]₂ (<b>3</b>) supported by the 28-membered hexaaza-dithiophenolate macrocycle (L²)^2– binds the N₃^– ion specifically <i>end-on</i> yielding [Ni₂(L²)­(μ_1,1-N₃)]­[ClO₄] (<b>7</b>) or [Ni₂(L²)­(μ_1,1-N₃)]­[BPh₄] (<b>8</b>), while the previously reported complex [Ni₂L¹­(μ_1,3-N₃)]­[ClO₄] (<b>2</b>) of the 24-membered macrocycle (L¹)^2– coordinates it in the <i>end-to-end</i> fashion. A comparison of the X-ray structures of <b>2</b>, <b>3</b>, and <b>7</b> reveals the form-selective binding of complex <b>3</b> to be a consequence of its preorganized, channel-like binding pocket, which accommodates the azide anion via repulsive CH···π interactions in the <i>end-on</i> mode. In contrast to [Ni₂L¹­(μ_1,3-N₃)]­[ClO₄] (<b>2</b>), which features a <i>S</i> = 0 ground state, [Ni₂(L²)­(μ_1,1-N₃)]­[BPh₄] (<b>8</b>) has a <i>S</i> = 2 ground state that is attained by competing antiferromagnetic and ferromagnetic exchange interactions via the thiolato and azido bridges with a value for the magnetic exchange coupling constant <i>J</i> of 13 cm^–1 (<b>H</b> = −2<i>JS</i>₁<i>S</i>₂). These results are further substantiated by density functional theory calculations. The stability of the azido-bridged complex determined by isothermal titration calorimetry in MeCN/MeOH 1/1 v/v (log <i>K</i>₁₁ = 4.88(4) at <i>I</i> = 0.1 M) lies in between those of the fluorido- (log <i>K</i>₁₁ = 6.84(7)) and chlorido-bridged complexes (log <i>K</i>₁₁ = 3.52(5)). These values were found to compare favorably well with the equilibrium constants derived at lower ionic strength (<i>I</i> = 0.01 M) by absorption spectrophotometry (log <i>K</i>₁₁ = 5.20(1), 7.77(9), and 4.13(3) for N₃^–, F^–, and Cl^– respectively)

Colorimetric Hg²⁺ Sensing in Water: From Molecules toward Low-Cost Solid Devices

A new colorimetric molecular sensor allowing for cheap, fast, sensitive, and highly selective naked-eye detection of Hg²⁺ in water is described. This molecule combines a 1,8-diaminoanthraquinone signaling subunit and phosphonic acid esters that confer the water solubility to the dye (R = H). A ready-to-use colorimetric solid sensor was obtained by incorporating an amphiphilic analog (R = OC₁₂H₂₅) exhibiting similar binding properties and optical responses in an agarose film

Colorimetric Hg²⁺ Sensing in Water: From Molecules toward Low-Cost Solid Devices

A new colorimetric molecular sensor allowing for cheap, fast, sensitive, and highly selective naked-eye detection of Hg²⁺ in water is described. This molecule combines a 1,8-diaminoanthraquinone signaling subunit and phosphonic acid esters that confer the water solubility to the dye (R = H). A ready-to-use colorimetric solid sensor was obtained by incorporating an amphiphilic analog (R = OC₁₂H₂₅) exhibiting similar binding properties and optical responses in an agarose film

Southern-blot analysis of RIPped and duplicated alleles of <i>AvrLm4-7</i> in virulent isolates.

<p><b>A.</b> schematic representation of the 4.5-kb region containing the <i>AvrLm4-7</i> gene. The restriction sites above the line are present in the control v23.1.3 isolate and are indicated as follows: <i>Xba</i>I, X; <i>Hpa</i>I, H; and <i>Spe</i>I, S. The <i>Xba</i>I and <i>Spe</i>I sites indicated below the <i>AvrLm4-7</i> gene are absent in v23.1.3 and are generated by RIP mutations in some RIPped alleles (see also Table S3 in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003020#ppat.1003020.s001" target="_blank">Text S1</a>). The thick black arrow indicates the <i>AvrLm4-7</i> gene and its direction of transcription. The location of the hybridization probe is indicated by the thick black bar. Red, green and blue lines indicate the location and size (in bp) of the restriction fragments generated by <i>Hpa</i>I, <i>Xba</i>I and <i>Spe</i>I, respectively, in the avirulent isolate v23.1.3 (upper double arrow(s)) and in representative RIPped isolates (lower double arrow(s)). <b>B.</b> Southern blot of the reference isolates v23.1.3 (<i>AvrLm7</i>) and Nz-T4 (<i>avrLm7</i>), along with <i>avrLm7</i> field isolates with different mutational events leading to virulence; G07-E1026, G07-E238, and G08-E1080, RIPped alleles; G08-E1474, G07-C484, and G08-C1052, RIPped alleles with duplicated copies of the gene, G08-E1167, lack of PCR amplification (for <i>Spe</i>I data, see Table S3 in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003020#ppat.1003020.s001" target="_blank">Text S1</a>). Size of the GeneRuler 1 kb Plus DNA ladder (in kb) is indicated on the right.</p

Estimates of genetic polymorphism revealed by seven minisatellites and mating type ratios in <i>AvrLm7</i> or <i>avrLm7</i> populations of <i>Leptosphaeria maculans</i> collected from the Grignon field experiment between autumn 2006 and 2008.

a<p>N, number of isolates; Na and Na Freq. ≥5%, mean number of different alleles and mean number of different alleles with frequency >0.05, respectively (± standard error); H, unbiased gene diversity averaged across loci (± standard error); MLG, number of multilocus genotypes; N_MLG, mean number of isolates per genotype (± standard error); <i>r</i>_d, standardized version of the index of association as calculated in Multilocus v3.1; Mat1-1/Mat1-2 is the ratio of the number of isolates carrying mating type 1 (Mat1-1) to isolates carrying mating type 2 (Mat1-2). (*) Significant deviation from a 1∶1 ratio was tested using a χ² with 1 degree of freedom; ns, P>0.05;</p>*<p>, P<0.05.</p

Changes in frequencies of isolates with different mutations leading to the <i>avrLm7</i> phenotype over three years in the experimental plot at Grignon.

<p>Dark blue diamonds, complete deletions; purple squares, RIP mutations; red triangles, partial deletions; pink squares, AA dinucleotide deletions and point deletions; black dots, Single Nucleotide Polymorphisms; green squares, unaltered gene sequence. In 2007 and 2008, isolates collected the same year at the phoma leaf spot stage and at the stem canker stage from the previous growing season residues have been pooled because they correspond to the same generation after the start of the experiment. In 2006, isolates were collected from phoma leaf spots only.</p

Changes in frequency of virulent <i>avrLm7</i> isolates in <i>Leptosphaeria maculans</i> populations before and during exposure to the <i>Rlm7</i> selection in a field experiment at Grignon and control plots at Grignon and Versailles.

a<p>The field experiment was established in autumn 2004 and the first samples from it were in autumn 2006.</p>b<p><i>rlm7</i> (without the <i>Rlm7</i> gene) plants were sown and used as trap cultivars to estimate the proportion of virulent isolates present in the air and landing on the crop at each site in each year.</p>c<p>Values in square brackets represent the exact confidence interval of the percentages at a 95% confidence level based on the total number of isolates and the percentage of virulent isolates in the sampling; values in brackets indicate the total number of isolates analysed for each sampling.</p>d<p>na, not applicable (the resistance gene was not yet released); nd, not determined.</p

Amino acid polymorphisms found in AvrLm4-7 proteins produced by different alleles of the avirulent <i>AvrLm7</i> form of the gene and their occurrence in populations sampled from the field experiment at Grignon.

a<p><i>avrLm4-AvrLm7</i>, isolates avirulent on <i>Rlm7</i> only; <i>AvrLm4-AvrLm7</i>, isolates avirulent on both <i>Rlm4</i> and <i>Rlm7</i>.</p>b<p>Comparisons are based on the sequence of the reference AvrLm4-7 protein of isolate v23.1.3 inducing avirulence towards <i>Rlm4</i> and <i>Rlm7</i> genotypes. Leu45Ser is due to a T to C mutation at base 134; Val74Ile is due to G to A mutation at base 220; Ile80Thr is due to a T to C mutation at base 239; Asp86Asn is due to a G to A mutation at base 256; Gly120Arg is due to a G to C mutation at base 358. The underlined amino acids are those showing polymorphism as compared to the reference sequence.</p>c<p>Number (frequency) of <i>AvrLm7</i> isolates showing a given combination of amino acid substitution at positions 45, 74, 80, 86 and/or 120.</p

Biomimetic Oxygen Reduction by Cofacial Porphyrins at a Liquid–Liquid Interface

Oxygen reduction catalyzed by cofacial metalloporphyrins at the 1,2-dichlorobenzene–water interface was studied with two lipophilic electron donors of similar driving force, 1,1′-dimethylferrocene (DMFc) and tetrathiafulvalene (TTF). The reaction produces mainly water and some hydrogen peroxide, but the mediator has a significant effect on the selectivity, as DMFc and the porphyrins themselves catalyze the decomposition and the further reduction of hydrogen peroxide. Density functional theory calculations indicate that the biscobaltporphyrin, 4,5-bis­[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene, Co₂(DPX), actually catalyzes oxygen reduction to hydrogen peroxide when oxygen is bound on the “exo” side (“dock-on”) of the catalyst, while four-electron reduction takes place with oxygen bound on the “endo” side (“dock-in”) of the molecule. These results can be explained by a “dock-on/dock-in” mechanism. The next step for improving bioinspired oxygen reduction catalysts would be blocking the “dock-on” path to achieve selective four-electron reduction of molecular oxygen