Water-induced formation of an alkali-ion dimer in cryptomelane nanorods

Tunneled metal oxides such as α-Mn₈O₁₆ (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K⁺ ions (which act as structure-stabilizing dopants) and H₂O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K⁺-doped α-Mn₈O₁₆ (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H₂O displaces K⁺ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K²⁺ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li⁺/Na⁺ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.

Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K²⁺) in the tunnels of hollandite.     

Reactivity of thienopyrroles. Synthesis of isomeric nitro and bromothienopyrroles

The preparation of ethyl 2-bromothieno[2,3-b]pyrrole-5-carboxylate, ethyl 2-bromothieno[3,2-b]pyrrole-5-carboxylate, ethyl 2-nitrothieno[2,3-b]pyrrole-5-carboxylate and ethyl 2-nitrothieno[3,2-b]pyrrole-5-carboxylate are described.     

FTIR investigation of the O-H[middle dot][middle dot][middle dot]Xe interaction in simple carboxylic acids in solid xenon

The O-H stretching region of the infrared spectra of a series of carboxylic acids in Xe matrices was investigated as a function of temperature. Upon increasing the temperature, the νO-H band site-components undergo reversible frequency blue-shifts, which are larger for the lowest-frequency components. This unprecedented observation indicates both that different types of O-H[middle dot][middle dot][middle dot]Xe specific interactions occur, depending on different trapping sites, and the prevalence of stronger interactions of this type for molecules trapped in sites corresponding to lower frequency νO-H band site-components. These results are in agreement with previous investigations pointing to an increased stabilization and larger νO-H frequency red-shifts in carboxylic acid∕Xe complexes bearing a specific H-bond like O-H[middle dot][middle dot][middle dot]Xe interaction. O-H[middle dot][middle dot][middle dot]Xe interaction energies were obtained theoretically and also estimated from the spectroscopic data. Changes in the interaction energies upon temperature variation were also evaluated.     

On the early stage of aluminum oxidation: An extraction mechanism via oxygen cooperation

We propose a barrierless mechanism for describing the oxidation of Al(111) in which oxygen atoms located on the outer surface extract aluminum atoms of the surface layers through local cooperation of other pre-adsorbed oxygen atoms. We show the details of this complex chemical process that kinetically competes with the non-destructive formation of an oxygen monolayer onto the Al surface, thus elucidating the initial aluminum oxidation regime. We demonstrate that further stripping of the complete surface Al layer is consistent with both (i) the formation of a defective alumina structure and (ii) an oxide capping layer preventing further oxidation at low temperature.     

Preserved conductance in covalently functionalized silicon nanowires

We study by means of ab initio simulations the Landauer conductance of covalently functionalized silicon nanowires. We show that in the case of alkyl side chains, the most common linkers, silicon nanowires remain quasiballistic over a large energy range. More reactive side molecules, such as alkenyl or phenyl conjugated radicals, amino and alkoxide groups, are less favorable as they induce resonant backscattering in the valence bands mainly. Such results provide strong support for the use of selectively functionalized nanowires in (opto)electronic devices and molecular sensors.     

Existence of multi-solitary waves with logarithmic relative distances for the NLS equation

We construct 2-solitary wave solutions with logarithmic distance to the nonlinear Schrödinger equation,

$\mathrm{i}{?}_{t}u+\mathrm{\Delta }u+|u{|}^{p?1}u=0,t\in \mathbb{R},x\in {\mathbb{R}}^d,$

in mass-subcritical cases $1<p<1+\frac{4}{d}$ and mass-supercritical cases $1+\frac{4}{d}<p<\frac{d+2}{d?2}$, i.e. solutions $u(t)$ satisfying

${6u(t)?{\mathrm{e}}^{\mathrm{i}\gamma (t)}\sum _{k=1}^{2}Q(??x_k(t))6}_{H^1}\to 0$

and

$|x_1(t)?x_2(t)|～2\log ?t,\text{as}t\to +\infty ,$

where Q is the ground state. The logarithmic distance is related to strong interactions between solitary waves.In the integrable case ($d=1$ and $p=3$), the existence of such solutions is known by inverse scattering (E. Olmedilla, Multiple pole solutions of the nonlinear Schrödinger equation, Physica D 25 (1987) 330–346; T. Zakharov, A.B. Shabat, Exact theory of two-dimensional self-focusing and one-dimensional self-modulation of waves in nonlinear media, Sov. Phys. JETP 34 (1972) 62–69). The mass-critical case $p=1+\frac{4}{d}$ exhibits a specific behavior related to blow-up, previously studied in Y. Martel, P. Raphaël (Strongly interacting blow up bubbles for the mass critical NLS, Ann. Sci. Éc. Norm. Supér. 51 (2018) 701–737).     

Enhancement of the reducing properties of metallic mercury in presence of complex forming ions

The reducing properties of metallic mercury in solutions containing ions forming precipitates or complexes with mercuric or mercurous ions have been studied.The reducing power of mercury in the presence of thiocyanate is greatly enhanced, and it is similar to that in the presence of hydrochloric acid. The effects of the thiocyanate and ferric concentrations have been examined. To reduce a 0.01 M solution of ferric ion without forming a precipitate of mercurous thiocyanate, a concentration of thiocyanate of at least 0.05 M is required. The action of mercurythiocyanate system on some oxidising substances has been studied. The most important reaction is the reduction of ferric ions. The method has been applied to the determination of iron on macro and semimicroscale and good results have been obtained.The reducing power of metallic mercury in the presence of cyanide has also been examined. In general it acts as a strong reducer in alkaline medium. Atmospheric oxygen is reduced partially to water and hydrogen peroxide. Ferricyanide is reduced quantitatively to ferrocyanide. The action of metallic mercury in the presence of cyanide on other oxidising substances has also been examined.     

Vibrational Spectroscopy and Conformational Structure of Protonated Polyalanine Peptides Isolated in the Gas Phase

The conformational structures of protonated polyalanine peptides, Ala(n)H(+), have been investigated in the gas phase for n = 3, 4, 5, and 7 using a combination of resonant-infrared multiphoton dissociation (R-IRMPD) spectroscopy in the NH and OH stretch regions and quantum chemical calculations. Agreement between theoretical IR and experimental R-IRMPD spectral features has enabled the assignment of specific hydrogen-bonded conformational motifs in the short protonated peptides and revealed their conformational evolution under elevated-temperature conditions, as a function of increasing chain length. The shortest peptide, Ala(3)H(+), adopts a mixture of extended and cyclic chain conformations, protonated, respectively, at a backbone carbonyl or the N-terminus. The longer peptides adopt folded, cyclic, and globular charge-solvated conformations protonated at the N-terminus, consistent with previous ion-mobility studies. The longest peptide, Ala(7)H(+), adopts a globular conformation with the N-terminus completely charge-solvated, demonstrating the emergence of "physiologically relevant" intramolecular interactions in the peptide backbone. The computed conformational relative free energies highlight the importance of entropic contributions in these peptides.