Characterization of the conformational probability of N-acetyl-phenylalanyl-NH2 by RHF, DFT, and MP2 computation and AIM analyses, confirmed by jet-cooled infrared data

Computational and experimental determinations were carried out in parallel on the conformational probability of N-Acetyl-Phenylalanine-NH2 (NAPA). Ab initio computations were completed at the BLYP/6-311G(df,p), B3LYP/6-31G(d), B3LYP/6-31G(d,p), and B3LYP/6-31+G(d) levels of theory, labeled L/61fp, B/6, B/6p, and B/6+, respectively. Three experimentally identified conformers were compared with theoretical data, confirming their identities as the betaLanti, gammaLgauche+, and gammaLgauche- (BACKBONESIDECHAIN) conformers. Evidence comes from matching experimental and theoretical data for all three constituent N-H stretches of NAPA, with a Delta(Experimental-Theoretical) = approximately 1-3 cm(-1), approximately 0-5 cm(-1), and approximately 1-6 cm(-1), at the L/61fp and B/6+ levels, respectively. Corrected-ZPE relative energies were computed to be 0.14, 0.00, 0.26 and 0.00, 0.67, 0.57 (kcal*mol(-1)) for the betaLanti, gammaLgauche+, and gamma(Lgauche- conformers, respectively, at the L/61fp and B/6+ levels, respectively. The MP2/6-31+G(d) level of theory was subsequently found to give similar relative energies. Characterization of the intramolecular interactions responsible for red and blue shifting of the N-H stretches showed the existence of the following intramolecular interactions: C=O[i]- - -HN[i], (Ar[i])-Cgamma- - -HN[i+1], (Ar[i])-Cdelta-H- - -O=C[i-1] for betaLanti; C=O[i-1]- - -HN[i+1], (Ar[i])-Cgamma- - -HN[i+1], (Ar[i])-C-H- - -O=C[i] for gammaLgauche+; and C=O[i-1]- - -HN[i+1] for gammaLgauche-. Each of these interactions were further investigated and subsequently characterized by orbital population and Atoms-In-Molecules (AIM) analyses, with the identity of overlap and bond critical points (BCP) serving as 'scoring criteria', respectively. Experimental and theoretical carbonyl stretches were also compared and showed good agreement, adding further strength to the synergy between experiment and theory.     

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.