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31.
Dr. Dominique Laniel Dr. Florian Trybel Dr. Adrien Néri Yuqing Yin Andrey Aslandukov Dr. Timofey Fedotenko Saiana Khandarkhaeva Dr. Ferenc Tasnádi Dr. Stella Chariton Dr. Carlotta Giacobbe Dr. Eleanor Lawrence Bright Dr. Michael Hanfland Dr. Vitali Prakapenka Prof. Dr. Wolfgang Schnick Prof. Dr. Igor A. Abrikosov Prof. Dr. Leonid Dubrovinsky Prof. Dr. Natalia Dubrovinskaia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202201998
Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. These properties mainly rely on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly attractive. In this study, the phosphorus–nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells, and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. δ-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two compounds are ultra-incompressible, having a bulk modulus of K0=322 GPa for δ-P3N5 and 339 GPa for PN2. Upon decompression below 7 GPa, δ-P3N5 undergoes a transformation into a novel α′-P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of α′-P3N5 underlines that a phase space otherwise inaccessible can be explored through materials formed under high pressure. 相似文献
32.
Chimera Spectrum Diagnostics for Peptides Using Two-Dimensional Partial Covariance Mass Spectrometry
Taran Driver Nikhil Bachhawat Leszek J. Frasinski Jonathan P. Marangos Vitali Averbukh Marina Edelson-Averbukh 《Molecules (Basel, Switzerland)》2021,26(12)
The rate of successful identification of peptide sequences by tandem mass spectrometry (MS/MS) is adversely affected by the common occurrence of co-isolation and co-fragmentation of two or more isobaric or isomeric parent ions. This results in so-called `chimera spectra’, which feature peaks of the fragment ions from more than a single precursor ion. The totality of the fragment ion peaks in chimera spectra cannot be assigned to a single peptide sequence, which contradicts a fundamental assumption of the standard automated MS/MS spectra analysis tools, such as protein database search engines. This calls for a diagnostic method able to identify chimera spectra to single out the cases where this assumption is not valid. Here, we demonstrate that, within the recently developed two-dimensional partial covariance mass spectrometry (2D-PC-MS), it is possible to reliably identify chimera spectra directly from the two-dimensional fragment ion spectrum, irrespective of whether the co-isolated peptide ions are isobaric up to a finite mass accuracy or isomeric. We introduce ‘3-57 chimera tag’ technique for chimera spectrum diagnostics based on 2D-PC-MS and perform numerical simulations to examine its efficiency. We experimentally demonstrate the detection of a mixture of two isomeric parent ions, even under conditions when one isomeric peptide is at one five-hundredth of the molar concentration of the second isomer. 相似文献
33.
To demonstrate a new paradigm of dynamical control of surface structure and reactivity, we perform density functional theory calculations of the adsorption of several molecules and atoms to the surface of ultrathin Pt(100) films supported on ferroelectric PbTiO3. We show that reorienting the polarization direction of the substrate can dramatically change the chemisorption energies of CO, O, C, and N and alter the reaction pathways for dissociation of CO, O2, N2, and NO. We discuss the structural and electronic effects of a polarized substrate on the metal surface, and we suggest potential applications in tunable catalysis. 相似文献
34.
We use first-principles density functional theory calculations to investigate the strongly nonlinear compositional trends in ferroelectric BiBO3-PbTiO3 solid solutions for a variety of cations on the perovskite B site. We demonstrate that previously tabulated crystal chemical parameters (extracted from other Pb-based perovskite alloys [Grinberg et al., J. Appl. Phys. 98, 094111 (2005)]) permit accurate prediction of cation displacements in these new Bi-Pb alloys. We find that observed transition temperatures in these materials are well correlated with computed polarization magnitudes. The presented model for coupling between compositional variation and cation displacements explains the highly nonlinear and often nonmonotonic dependence of the Curie temperature (T(C)) on composition observed in these solid solutions. 相似文献
35.
Given a sequence A = (a 1, …, a n ) of real numbers, a block B of A is either a set B = {a i , a i+1, …, a j } where i ≤ j or the empty set. The size b of a block B is the sum of its elements. We show that when each a i ∈ [0, 1] and k is a positive integer, there is a partition of A into k blocks B 1, …, B k with |b i ?b j | ≤ 1 for every i, j. We extend this result in several directions. 相似文献
36.
Characterizing Methyl‐Bearing Side Chain Contacts and Dynamics Mediating Amyloid β Protofibril Interactions Using 13Cmethyl‐DEST and Lifetime Line Broadening 下载免费PDF全文
Dr. Nicolas L. Fawzi Dr. David S. Libich Dr. Jinfa Ying Dr. Vitali Tugarinov Dr. G. Marius Clore 《Angewandte Chemie (International ed. in English)》2014,53(39):10345-10349
Many details pertaining to the formation and interactions of protein aggregates associated with neurodegenerative diseases are invisible to conventional biophysical techniques. We recently introduced 15N dark‐state exchange saturation transfer (DEST) and 15N lifetime line‐broadening to study solution backbone dynamics and position‐specific binding probabilities for amyloid β (Aβ) monomers in exchange with large (2–80 MDa) protofibrillar Aβ aggregates. Here we use 13Cmethyl DEST and lifetime line‐broadening to probe the interactions and dynamics of methyl‐bearing side chains in the Aβ‐protofibril‐bound state. We show that all methyl groups of Aβ40 populate direct‐contact bound states with a very fast effective transverse relaxation rate, indicative of side‐chain‐mediated direct binding to the protofibril surface. The data are consistent with position‐specific enhancements of 13Cmethyl‐${R{{{\rm tethered}\hfill \atop 2\hfill}}}$ values in tethered states, providing further insights into the structural ensemble of the protofibril‐bound state. 相似文献
37.
Ana Barragn Ane Sarasola Lucia Vitali 《Angewandte Chemie (International ed. in English)》2020,59(36):15599-15602
Efficiency in charge‐transport is a fundamental but demanding prerequisite to allow better exploitation of molecular functionalities in organic electronics and energy‐conversion systems. Here, we report on a mechanism that enables a one‐dimensional conductance structure by connecting discrete molecular states at 2.1 eV through the pores of a metal–organic network on Cu(110). Two adjacent, periodic and isoenergetic contributions, namely a molecular resonance and the confined surface‐state, add‐up leading to anisotropic structures, as channels, observable in real‐space conductance images. The adsorption configurations of Br atoms, inorganic byproduct of the redox‐reacted 4,7‐dibromobenzo[c]‐1,2,5‐thiadiazole (2Br‐BTD) molecules on the copper surface, drive the confinement of the Cu surface state within the pores and critically control the channel continuity. Small displacements of the Br atoms change the local surface potential misaligning the energy levels. This work visualizes the effect of order‐disorder transitions caused by the movement of single atoms in the electronic properties of two‐dimensional organic networks. 相似文献
38.
Jean-Marie Barbaroux Thomas Chen Vitali Vougalter Semjon Vugalter 《Annales Henri Poincare》2010,11(8):1487-1544
In this paper, we determine the exact expression for the hydrogen binding energy in the Pauli–Fierz model up to the order
α
5 log α
−1, where α denotes the fine structure constant, and prove rigorous bounds on the remainder term of the order o(α
5 log α
−1). As a consequence, we prove that the binding energy is not a real analytic function of α, and verify the existence of logarithmic
corrections to the expansion of the ground state energy in powers of α, as conjectured in the recent literature. 相似文献
39.
It is shown that radiation pressure can be profitably used to entangle macroscopic oscillators like movable mirrors, using present technology. We prove a new sufficient criterion for entanglement and show that the achievable entanglement is robust against thermal noise. Its signature can be revealed using common optomechanical readout apparatus. 相似文献
40.
Summary Phase separation and thermodynamic stability of water (W) — casein (C) — neutral polysaccharide (NPS) systems have been studied. Dextrans of different molecular weights D40, D150, D500 and D2000 (10–3
M
w
=40, 150, 500, 2000), ficoll (10–3
M
w
=400) and amylopectin (10-–6
M
w
= 38) have been used as neutral polysaccharides. Phase diagrams of W-C-NPS systems, as well as their effect on the thermodynamic stability of the molecular weight and structural features of polysaccharides, low-molecular salts, pH and temperature have been considered. There has been shown the similarity of conditions under which the stability of W-C-NPS systems is disturbed, resulting in their separation, as well as conditions favorable to self-association of casein. A decrease in the pH value, an increase in the ionic strength and a rise in temperature are favorable both to self-association of casein and separation of W-C-NPS systems. Proceeding from this fact and from the results obtained earlier for W-C-acidic polysaccharide and W-albumin-D-glucan systems, a conclusion is drawn as to the common nature of the relationship between self-association of polymers and their compatibility. At constant temperature and pH, the stability limit of W-C-NPS systems is determined by the concentrations of polymers (w
2 andw
3) and salt (C4). The totality of cloud points C
4
*
(pH) at givenw
2 andw
3 being considered as the stability limit. It is also shown that the relationship C
4
*
(pH) is an increasing function within the range of pH values from 6.5 to 11.5 and in all cases where lim C
4
*
(pH)=0. The sequence of values 947-1PHPH IEP C
4
*
is determined by the nature of the low-molecular salt (Na2SO4 NaCl KSCN) and the specific nature of the polysaccharides (D2000 amylopectin < D 150 < ficoll < D 40).W-C-NPS-NaCl have been found to possess a lower critical point in a system of coordinates: temperature-composition. W-C-NPS-urea (6M) systems feature, in a system of coordinates: pH-polymer concentration, two areas of separation, overlapping at sufficiently high total concentrations. This fact is indicative of the specific nature of interaction of casein macromolecules capable of association near the isoelectric point due to interaction of charge fluctuations and, in the acid region, due to interaction of non-ionized carboxyl groups. The obtained results are discussed with the stability limit being expressed in terms of second virial coefficients.With 13 figures and 2 tables 相似文献