Search

Framework AlFR Lewis sites represent a substantial portion of active sites in H-BEA zeolite catalysts activated at low temperatures. We studied their nature by 27Al WURST-QCPMG nuclear magnetic resonance (NMR) and proposed a plausible mechanism of their formation based on periodic density functional theory calculations constrained by 1H MAS, 27Al WURST-QCPMG, and 29Si MAS NMR experiments and FTIR measurements. Our results show that the electron-pair acceptor of AlFR Lewis sites corresponds to an AlTRI atom tricoordinated to the zeolite framework, which adsorbs a water molecule. This AlTRI–OH2 complex is reflected in 27Al NMR resonance with δiso = 70 ± 5 ppm and CQ = 13 ± 2 MHz. In addition, the AlTRI atom with adsorbed acetonitrile-d3 (the probe of AlFR Lewis sites in FTIR spectroscopy) exhibits a similar 27Al NMR resonance. We suggest that these AlFR Lewis sites are formed from Al–OH–Si–O–Si–O–Si–OH–Al sequences located in 12-rings (i.e., close unpaired Al atoms). [ABSTRACT FROM AUTHOR]

Recently, suitably sized polymer-based nanogels containing functional groups for the binding of biologically active substances and ultimately degradable to products that can be removed by glomerular filtration have become extensively studied systems in the field of drug delivery. Herein, we designed and tailored the synthesis of hydrophilic and biodegradable poly[N-(2-hydroxypropyl) methacrylamide-co-N,N′-bis(acryloyl) cystamine-co-6-methacrylamidohexanoyl hydrazine] (PHPMA-BAC-BMH) nanogels. The facile and versatile dispersion polymerization enabled the preparation of nanogels with a diameter below 50 nm, which is the key parameter for efficient and selective passive tumor targeting. The effects of the N,N′-bis(acryloyl) cystamine crosslinker, polymerization composition, and medium including H2O/MetCel and H2O/EtCel on the particle size, particle size distribution, morphology, and polymerization kinetics and copolymer composition were investigated in detail. We demonstrated the formation of a 38 nm colloidally stable PHPMA-BAC-BMH nanogel with a core–shell structure that can be rapidly degraded in the presence of 10 mM glutathione solution under physiologic conditions. The nanogels were stable in an aqueous solution modeling the bloodstream; thus, these nanogels have the potential to become highly important carriers in the drug delivery of various molecules. [ABSTRACT FROM AUTHOR]

It has been recognized that the C–H⋯O structural motif can be present in destabilizing as well as highly stabilizing intermolecular environments. Thus, it should be of interest to describe the strength of the C–H⋯O hydrogen bond for constant structural factors so that this intrinsic strength can be quantified and compared to other types of interactions. This description is provided here for C2h-symmetric dimers of acrylic acid by means of the calculations that employ the coupled-cluster theory with singles, doubles, and perturbative triples [CCSD(T)] together with an extrapolation to the complete basis set (CBS) limit. Dimers featuring the C–H⋯O and O–H⋯O hydrogens bonds are carefully investigated in a wide range of intermolecular separations by the CCSD(T)/CBS approach, and also by the symmetry-adapted perturbation theory (SAPT) method, which is based on the density-functional theory (DFT) treatment of monomers. While the nature of these two types of hydrogen bonding is very similar according to the SAPT-DFT/CBS calculations and on the basis of a comparison of the intermolecular potential curves, the intrinsic strength of the C–H⋯O interaction is found to be about a quarter of its O–H⋯O counterpart that is less than one might anticipate. [ABSTRACT FROM AUTHOR]

[sup.17]O solid-state NMR studies of waters of hydration in crystalline solids are presented. The [sup.17]O quadrupolar coupling and chemical shift (CS) tensors, and their relative orientations, are measured experimentally at room temperature for a-oxalic acid dihydrate, barium chlorate monohydrate, lithium sulfate monohydrate, potassium oxalate monohydrate, and sodium perchlorate monohydrate. The [sup.17]O quadrupolar coupling constants ([C.sub.Q]) range from 6.6 to 7.35 MHz and the isotropic chemical shifts range from -17 to 19.7 ppm. The oxygen CS tensor spans vary from 25 to 78 ppm. These represent the first complete CS and electric field gradient tensor measurements for water coordinated to metals in the solid state. Gauge-including projector-augmented wave density functional theory calculations overestimate the values of [C.sub.Q], likely due to librational dynamics of the water molecules. Computed CS tensors only qualitatively match the experimental data. The lack of strong correlations between the experimental and computed data, and between these data and any single structural feature, is attributed to motion of the water molecules and to the relatively small overall range in the NMR parameters relative to their measurement precision. Nevertheless, the isotropic chemical shift, quadrupolar coupling constant, and CS tensor span clearly differentiate between the samples studied and establish a 'fingerprint' [sup.17]O spectral region for water coordinated to metals in solids. Key words: nuclear magnetic resonance, water, quadrupolar coupling, hydrogen bonding, chemical shifts, density functional theory, [sup.17]O solid-state NMR. Nous presentons les resultats d'etudes de RMN de l'[sup.17]O a l'etat solide portant sur les molecules d'eau d'hydratation dans des solides cristallins. Nous avons mesure experimentalement a temperature ambiante le couplage quadripolaire de l'[sup.17]O et les tenseurs de deplacement chimique (DC) ainsi que leurs orientations relatives de l'acide a-oxalique dihydrate, du chlorate de baryum monohydrate, du sulfate de lithium monohydrate, de l'oxalate de potassium monohydrate et du perchlorate de sodium monohydrate. Les constantes de couplage quadripolaires ([C.sub.Q]) de l'[sup.17]O varient de 6,6 a 7,35 MHz et les deplacements chimiques isotropes de -17 a 19,7 ppm. L'envergure du tenseur de DC de l'oxygene varie de 25 a 78 ppm. Ces resultats representent les premieres mesures completes de DC et de tenseur de gradient de champ electrique effectuees sur des molecules d'eau coordonnees a des metaux en phase solide. Nous avons observe que les calculs de la theorie de la fonctionnelle de la densite par la methode<>surestiment les valeurs de [C.sub.Q], probablement a cause de la dynamique de libration des molecules d'eau. Les valeurs calculees des tenseurs de DC correspondent aux valeurs experimentales seulement sur le plan qualitatif. L'absence de fortes correlations entre les donnees experimentales et calculees, et entre ces donnees et toute caracteristique structurale, s'explique par le mouvement des molecules d'eau et la variation globale relativement faible des parametres de RMN par rapport a la precision de mesure de ceux-ci. Quoi qu'il en soit, le deplacement chimique isotrope, la constante de couplage quadripolaire et l'envergure des tenseurs de DC permettent de distinguer clairement les echantillons etudies les uns des autres et d'etablir une <> dans la region spectrale de l'[sup.17]O correspondant aux molecules d'eau coordonnees aux metaux dans les solides. [Traduit par la Redaction] Mots-cles: resonance magnetique nucleaire, eau, couplage quadripolaire, liaison hydrogene, deplacements chimiques, theorie de la fonctionnelle de la densite, [sup.17]O RMN a l'etat solide., Introduction Water is essential to life, innumerable biochemical and inorganic processes, chemical reactions, and the structure and properties of various materials. (1,2) Water molecules play key structural roles in organic, [...]