The Role of Grain Boundary Diffusion in the Solute Drag Effect

Molecular dynamics (MD) simulations are applied to study solute drag by curvature-driven grain boundaries (GBs) in Cu–Ag solid solution. Although lattice diffusion is frozen on the MD timescale, the GB significantly accelerates the solute diffusion and alters the state of short-range order in lattice regions swept by its motion. The accelerated diffusion produces a nonuniform redistribution of the solute atoms in the form of GB clusters enhancing the solute drag by the Zener pinning mechanism. This finding points to an important role of lateral GB diffusion in the solute drag effect. A 1.5 at.%Ag alloying reduces the GB free energy by 10–20% while reducing the GB mobility coefficients by more than an order of magnitude. Given the greater impact of alloying on the GB mobility than on the capillary driving force, kinetic stabilization of nanomaterials against grain growth is likely to be more effective than thermodynamic stabilization aiming to reduce the GB free energy.

Evolution of the Hyaluronic Acid in Viscosupplementation – from Linear Particles to Hybrid Complexes

The discovery of unique properties of the hyaluronic acid and learning about the role of this aid in pathophysiology of extracellular matrices resulted in using this substance in pharmacological support in cases of tissue dysfunction due to numerous disease units. Therefore, the products containing this substance are now widely used in medicine including dermatology and aesthetic medicine, ophthalmology, facial-mandibular surgery and orthopedics, being among the most effective products used in the treatment of numerous cases of function impairment and deformation of tissues and organs. There are applied in both post-traumatic and post-inflammatory conditions as well as in symptoms due to chronic conditions. Their therapeutic effects result from joint surface moisturizing, reduction of the coefficient of friction (COF) and good bio-tolerance and biocompatibility confirmed by a low percentage of side effects and biocompatibility. The introduction of hyaluronic acid hybrid complexes with high and low molecular mass (H/L-HA) has increased the clinical usefulness of hyaluronic acid products thanks to their increased viscoelasticity, increased anti-inflammatory and chondroprotective properties and thermodynamic stabilization of the product guaranteeing its half-life. Thanks to the above mentioned pro­perties it becomes more effective in the non-surgical treatment of osteoarthritis.

A Quantitative Metric for Organic Radical Persistence Using Thermodynamic and Kinetic Features

<p>Long-lived organic radicals are promising candidates for the development of high-performance energy solutions such as organic redox batteries, transistors, and light-emitting diodes. However, “stable” organic radicals that remain unreactive for an extended time and that can be stored and handled under ambient conditions are rare<b>. </b>A necessary but not sufficient condition for organic radical stability is the presence of thermodynamic stabilization, such as conjugation with an adjacent p-bond or lone-pair, or hyperconjugation with a s-bond. However, thermodynamic factors alone do not result in radicals with extended lifetimes: many resonance-stabilized radicals are transient species that exist for less than a millisecond. Kinetic stabilization is also necessary for persistence, such as steric effects that inhibit radical dimerization or reaction with solvent molecules. We describe a quantitative approach to map organic radical stability, using molecular descriptors designed to capture thermodynamic and kinetic considerations. The comparison of an extensive dataset of quantum chemical calculations of organic radicals with experimentally-known stable radical species reveals a region of this feature space where long-lived radicals are located. These descriptors, based upon maximum spin density and buried volume are combined into a single metric, the Radical Stability Score, that outperforms thermodynamic scales based on bond dissociation enthalpies in identifying remarkably long-lived radicals. This provides an objective and accessible metric for used in future molecular design and optimization campaigns. </p><p>We demonstrate this approach in identifying Pareto-optimal candidates for stable organic radicals.</p>

A Quantitative Metric for Organic Radical Persistence Using Thermodynamic and Kinetic Features

<p>Long-lived organic radicals are promising candidates for the development of high-performance energy solutions such as organic redox batteries, transistors, and light-emitting diodes. However, “stable” organic radicals that remain unreactive for an extended time and that can be stored and handled under ambient conditions are rare<b>. </b>A necessary but not sufficient condition for organic radical stability is the presence of thermodynamic stabilization, such as conjugation with an adjacent p-bond or lone-pair, or hyperconjugation with a s-bond. However, thermodynamic factors alone do not result in radicals with extended lifetimes: many resonance-stabilized radicals are transient species that exist for less than a millisecond. Kinetic stabilization is also necessary for persistence, such as steric effects that inhibit radical dimerization or reaction with solvent molecules. We describe a quantitative approach to map organic radical stability, using molecular descriptors designed to capture thermodynamic and kinetic considerations. The comparison of an extensive dataset of quantum chemical calculations of organic radicals with experimentally-known stable radical species reveals a region of this feature space where long-lived radicals are located. These descriptors, based upon maximum spin density and buried volume are combined into a single metric, the Radical Stability Score, that outperforms thermodynamic scales based on bond dissociation enthalpies in identifying remarkably long-lived radicals. This provides an objective and accessible metric for used in future molecular design and optimization campaigns. </p><p>We demonstrate this approach in identifying Pareto-optimal candidates for stable organic radicals.</p>

Chemical Tuning of NaSICON Surfaces for Fast-Charging Na Metal Solid-State Batteries

<p>Solid-state batteries (SSBs) with alkali metal anodes hold great promise as energetically dense and safe alternatives to conventional Li-ion cells. Whilst, in principle, SSBs have the additional advantage of offering virtually unlimited plating current densities, fast charges have so far only been achieved through sophisticated interface engineering strategies. Here, we reveal that such interface engineering can be easily achieved by tuning the chemistry of NaSICON solid electrolytes (Na_3.4Zr₂Si_2.4P_0.6O₁₂) and taking advantage of the thermodynamic stabilization of a Na₃PO₄ layer on their surface upon thermal activation. The optimized planar Na|NZSP interfaces are characterized by their exceptionally low interface resistances (down to 0.1 Ω cm²at room temperature) and, more importantly, by their tolerance to large plating current densities (up to 10 mA cm^-2) even for extended cycling periods of 30 minutes (corresponding to an areal capacity 5 mAh cm^-2).</p>

Near quantitative synthesis of urea macrocycles enabled by bulky N-substituent

Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulky N-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promoting cis C = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulky N-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures.

Reversing the Irreversible: Thermodynamic Stabilization of Lithium Aluminum Hydride Nanoconfined Within a Nitrogen-Doped Carbon Host

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate a new approach to thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH4@NCMK-3 material releases H2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li3AlH6 intermediate. Moreover, >80% of LiAlH4 can be regenerated under 100 MPa H2, a feat previously thought to be impossible. The nitrogen sites lower the energy barrier for regenerating the hydride by changing the density of states in the vicinity of the Fermi level, effectively acting as solvation sites for lithium ions. Theoretical calculations provide a rationale for the unprecedented solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

Stabilization of telomeric G-quadruplex by ligand binding increases susceptibility to S1 nuclease

The extent of thermodynamic stabilization of telomeric G-quadruplex (G4) by isomers of G4 ligand L2H2-6OTD, a telomestatin analog, is inversely correlated with susceptibility to S1 nuclease. L2H2-6OTD facilitated the S1...