Selektive Umfunktionalisierung der terminalen Amidgruppe offenkettiger Polyamide via 2-Oxazolin-5-one als Zwischenstufen. Vorläufige Mitteilung

Selective Modification of the Terminal Amide Group of Linear Polyamides via 2-Oxazolin-5-ones as Intermediates Treatment of aqueous or alcoholic solutions of diamides of type 2 with HCl leads to the formation of amide-acids and amide-esters of type 3 (Scheme 1 and Table). It has been shown, that 2-oxazolin-5-ones of type 4 are intermediates of this selective transformation of the disubstituted terminal amide group. The selectivity of the transformation is demonstrated by the reaction sequence shown in Scheme 3. No selectivity has been observed in the acid-catalyzed hydrolysis of triamide 9 with a monosubstituted terminal amide group (Scheme 4). Hydrolysis of the optically active dipeptide derivatives (+)-(L )- 13 and (+)-(L )- 15 with HBr in nitromethane at 60–80° yields the pure enantiomer (+)-(L )- 14 and (+)-(L )- 16 , respectively (Scheme 5), i.e., no racemization takes place under the reaction conditions. These results show the usefulness of the dimethylamide group as a protecting group for carboxylic acids for example in the peptide synthesis.     

A refined algorithm to simulate latex colloid agglomeration at high ionic strength

This study is focussed on the simulation of particle agglomeration at relatively high ionic strength using a refined stochastic algorithm developed in the context of parcel-tracking approaches. For that purpose, experimental data of both diffusion-limited and reaction-limited aggregation of latex particles were obtained using dynamic light scattering techniques for different initial particle sizes (diameters ranging from 24 to 495 nm) and at various chemical conditions (ionic strength between 0.5 and 2 M with NaCl or CaCl\(_2\) solutions). The experimental data collected have been compared to numerical results obtained with the refined parcel-tracking algorithm for particle agglomeration which has been developed. Results show that the evolution of the aggregate diameters over time can be properly captured by the present model with the value of the aggregate fractal dimension that is extracted from experimental data.     

Dissolution Behavior and Varied Mesoporosity of Zeolites by NH4F Etching

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH₄F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano- and sub-nano scales. At the nano-scale, the hidden mosaics of zeolite structure predetermine the spatio-temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub-nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites.     

Remarks on a New Possible Discretization Scheme for Gauge Theories

We propose here a new discretization method for a class of continuum gauge theories which action functionals are polynomials of the curvature. Based on the notion of holonomy, this discretization procedure appears gauge-invariant for discretized analogs of Yang-Mills theories, and hence gauge-fixing is fully rigorous for these discretized action functionals. Heuristic parts are forwarded to the quantization procedure via Feynman integrals and the meaning of the heuristic infinite dimensional Lebesgue integral is questioned.     

Reaction Mechanisms of the Degradation of Fluoroethylene Carbonate,an Additive of Lithium-Ion Batteries,Unraveled by Radiation Chemistry

Numerous additives are used in the electrolytes of lithium-ion batteries, especially for the formation of an efficient solid electrolyte interphase at the surface of the electrodes. Understanding the degradation processes of these compounds is thus important; they can be seen through radiolysis. In the case of fluoroethylene carbonate (FEC), picosecond pulse radiolysis experiments evidenced the formation of FEC^.−. This radical is stabilized in neat FEC, whereas the ring opens to form more stable radical anions when FEC is a solute in other solvents, as confirmed by quantum chemistry calculations. In neat FEC, pre-solvated electrons primarily undergo attachment rather than solvation. On long timescales, the gases produced (H₂, CO, and CO₂) were quantified. A reaction scheme for both the oxidizing and reducing pathways at stake in irradiated FEC is proposed. This work shows that the nature of the primary species formed in FEC depends on the amount of FEC in the solution.