Molecular overtones and two-phonon combination bands in the near-infrared spectra of talc, brucite and lizardite

The near-infrared (NIR) spectra of hydrous minerals display absorption bands involving multiple excitations of vibrational modes. They usually involve OH stretching modes, but their interpretation is not straightforward due to the combined effects of bond anharmonicity and vibrational coupling. In the present study, the mid-infrared (MIR) and near-infrared spectra of well-ordered samples of trioctahedral layered hydrous minerals, talc, brucite and lizardite, have been measured on a spectral range extending from the fundamental vibrational modes to the second OH stretching overtones. The bands corresponding to molecular overtones are interpreted using an effective approach allowing us to infer the anharmonicity and coupling parameters controlling the OH stretching frequencies from spectroscopic data. They follow the usual relation between transition energy and quantum number of the excited state, which facilitates the comparison of NIR and MIR spectra. The results support the assignment of the main overtone bands to specific environments of OH groups and bring new constraints for the identification of the vibrational bands related to Fe and Al substitutions at octahedral sites in serpentines. The two-phonon absorption bands are theoretically analyzed at the density functional theory level by computing the absorption arising from the self-energy of the IR-active vibrational modes. The characteristics of the two-phonon OH stretching continuum between 7300 and 7400 cm−1 and of the combination bands between 4000 and 4800 cm−1 are related to the specificities of the one-phonon and two-phonon densities of states of the three minerals.</p

The CAF-1 and Hir Histone Chaperones Associate with Sites of Meiotic Double-Strand Breaks in Budding Yeast.

In the meiotic prophase, programmed DNA double-strand breaks (DSB) are introduced along chromosomes to promote homolog pairing and recombination. Although meiotic DSBs usually occur in nucleosome-depleted, accessible regions of chromatin, their repair by homologous recombination takes place in a nucleosomal environment. Nucleosomes may represent an obstacle for the recombination machinery and their timely eviction and reincorporation into chromatin may influence the outcome of recombination, for instance by stabilizing recombination intermediates. Here we show in budding yeast that nucleosomes flanking a meiotic DSB are transiently lost during recombination, and that specific histone H3 chaperones, CAF-1 and Hir, are mobilized at meiotic DSBs. However, the absence of these chaperones has no effect on meiotic recombination, suggesting that timely histone reincorporation following their eviction has no influence on the recombination outcome, or that redundant pathways are activated. This study is the first example of the involvement of histone H3 chaperones at naturally occurring, developmentally programmed DNA double-strand breaks

Recombination in CAF-1 mutants does not rely more of the class II crossover pathway.

<p>DSB formation and CO frequency at <i>HIS4LEU2</i> in <i>mms4 slx4 yen1</i> triple mutant (VBD1444) and in <i>mms4 slx4 yen1 cac1Δ</i> (VBD1443) monitored by Southern blot. The graph shows DSB and CO quantification from the same time-courses.</p

Melting curve and phase diagram of ammonia monohydrate at high pressure and temperature

International audienceThe phase diagram and melting behavior of the equimolar water-ammonia mixture have been investigated by Raman spectroscopy, x-ray diffraction, and visual observations from 295 K to 675 K and up to 9 GPa. Our results show non-congruent melting behavior of ammonia monohydrate (AMH) solid below 324 K and congruent melting at higher temperatures. The congruent melting is associated with the stability of a previously unobserved solid phase of AMH, which we named AMH-VII. Another, presumably water-rich, hydrate has also been detected in the range 4 GPa-7 GPa at 295 K on decompression of the high pressure disordered ionico-molecular alloy (DIMA) phase. Comparing our melting data to the literature suggests that non-congruent melting extends from 220 K to 324 K and that the solid phase that borders the fluid between 220 K and 270 K, called AMH-III, is not a proper phase of AMH but a solid solution of ammonia hemihydrate and ice. These results allow us to propose a revised and extended experimental phase diagram of AMH. Published under license by AIP Publishing. https://doi.org/10.1063/5.0021207 .,

CAF-1 large subunit is recruited to Spo11 and VDE meiotic DSB, independently of strand invasion and of its interaction with PCNA.

<p>(A) VDE DSB formation upon a time course of VDB1206 (VRS::<i>ARE1/</i>VRS mut::<i>ARE1 dmc1Δ)</i> monitored by Pulse-Field Gel Electrophoresis of whole chromosomes followed by Southern blot and hybridization with a <i>CHA1</i> probe at the left end of chromosome III (left panel) or by regular Southern blot after restriction digest with <i>Bgl</i>II (right panel). (B) Cac1-3HA association with the VDE DSB site and a Spo11 DSB site (<i>GAT1</i> promoter) relative to the negative control site in a <i>dmc1Δ</i> strain. ChIP is from a VBD1206 meiotic time course. (C) Cac1 is recruited to the donor DNA (uncut allele) in wild-type but not in <i>dmc1Δ</i>. Cac1-3HA association with VDE DSB site and the uncut VRS site relative to the control site. ChIP from VBD1115 (VRS::<i>ARE1/</i>VRS mut::<i>ARE1</i>) and VBD1206 (VRS::<i>ARE1/</i>VRS mut::<i>ARE1 dmc1Δ</i>) meiotic time course. (D) Cac2 is recruited to the VDE and Spo11 DSBs, in wild-type and <i>dmc1Δ</i>. ChIP from VBD1331 (VRS::<i>ARE1</i>/VRS mut::<i>ARE1</i>) and from VBD1349 (<i>dmc1Δ</i> VRS::<i>ARE1</i>/VRS mut::<i>ARE1</i>) meiotic time courses. (E) Cac1 is recruited to VDE and Spo11 DSBs, independently of its interaction with PCNA. ChIP from a VBD1314 (VRS::<i>ARE1</i>/VRS mut::<i>ARE1 cac1-20-3HA</i>) meiotic time-course. (F) Cac1 is recruited to VDE and Spo11 DSBs, independently of the Cac2 subunit. ChIP from VBD1281 (VRS::<i>ARE1</i>/VRS mut::<i>ARE1 cac2Δ</i>) from a meiotic time course.</p

Boron carbide under torsional deformation: evidence of the formation of chain vacancies in the plastic regime

International audienceWe report a combined experimental and theoretical study of boron carbide under stress/deformation. A special rotating anvil press, the rotating tomography Paris Edinburgh cell (RoToPEC), has been used to apply torsional deformation to boron carbide under a pressure of 5 GPa at ambient temperature. Subsequent damages and point defects have been analysed at ambient pressure by energy dispersive X-ray microdiffraction at the synchrotron and by Raman spectroscopy, combined with calculations based on the density functional theory (DFT). We show that apart from the signals due to B4C, new peaks appear in both characterisation methods. The DFT calculations of atomic structures and phonon frequencies enable us to attribute most of the new peaks to boron vacancies in the intericosahedral chains of boron carbide. Some of the Raman spectra also show three peaks that have been attributed to amorphous boron carbide in the literature. Deformed boron carbide thus shows small inclusions of clusters of boron carbide with chain vacancies, and/or small zones interpreted as amorphous zone

Cac1 deletion does not affect crossover levels nor spore viability.

<p>(A) Meiotic progression was followed by DAPI staining in WT (VBD1311), <i>cac1Δ</i> (VBD1341) and <i>cac2Δ</i> (VBD1262) strains. Past Meiosis I: nuclei having passed the first meiotic division. (B) Spore viability in WT (VBD1311; 155 tetrads), <i>cac1Δ</i> (VBD1341; 175 tetrads) and <i>cac2Δ</i> (VBD1262; 213 tetrads) strains. (C) Cac1-3HA association with <i>HIS4LEU2</i>, <i>GAT1</i> (DSB1) and <i>BUD23</i> (DSB2) Spo11 sites relative to negative control site. ChIP was performed in a VBD1379 meiotic time course. (D) DSB formation and CO frequency at <i>HIS4LEU2</i> in WT (VBD1311) and <i>cac1Δ</i> (VBD1341) monitored by Southern blot. The graph shows DSB and CO quantification from the same time-courses. (E) CO frequency at the <i>EST3-FAA3</i> locus in <i>ZIP3</i> (VBD1229), <i>zip3-4AQ </i>(VBD1113), <i>cac2Δ ZIP3</i> (VBD1282) and <i>cac2Δ zip3-4AQ</i> (VBD1283) monitored by Southern blot. The positions of parental bands (P1 and P2) and of the recombinant crossover products (CO1 and CO2) are indicated. The graph shows mean CO2 frequency between the 12h and 13h time-points ± standard deviation.</p