Alteration of polymorphic selectivity through different crystallization mechanisms occurring in the same crystallization solution

We report a case in which two different crystallization mechanisms occurring in the same crystallization experiment are found to yield different polymorphic outcomes. In particular, we focus on crystallization of glycine from neutral aqueous solution. Crystallization in the bulk solution gives only the metastable R-polymorph, as observed in previous studies, whereas crystallization by evaporation of a thin film of the solution on the walls of the crystallization vessel is found to give rise to the thermodynamically stable ç-polymorph, and furthermore produces an uncharacteristic crystal morphology for this polymorph. A detailed set of control experiments are described that elucidate mechanistic details relating to the latter crystallization process. The fact that crystallization on the walls of a crystallization vessel can yield a different polymorphic outcome from crystallization in the bulk solution in the same experiment has potentially much wider significance with regard to other polymorphic systems

Altering the Polymorphic Product Distribution in a Solid-State Dehydration Process by Rapid Sample Rotation in a Solid-State NMR Probe

There is currently considerable interest in the phenomenon of polymorphism in organic molecular solids, and a key issue in this field is to understand the experimental techniques and procedures that may be employed to obtain new polymorphic forms of a given molecule. This paper demonstrates that the polymorphic form of a material (sodium acetate) obtained by a solid-state dehydration process (starting from sodium acetate trihydrate) can be altered by carrying out the dehydration process under conditions of rapid (several kilohertz) sample rotation in a solid-state magic-angle-spinning NMR probe. This observation suggests a new opportunity to influence the outcome of solid-state dehydration/desolvation processes and, in particular, to alter the polymorphic form of the product obtained

Triple-quantum Na-23 MAS NMR spectroscopy as a technique for probing polymorphism in sodium salts

Triple-quantum 23Na MAS NMR spectroscopy has been applied to characterize the three polymorphs of sodium acetate. The crystallographically distinct sodium sites in each of these polymorphs are uniquely identified from the triple-quantum 23Na MAS NMR spectra. These data provide access to the 23Na quadrupole interaction parameters (quadrupole coupling constant and asymmetry parameter) for each sodium site, which provide a quantitative measure of the local structural properties of the sodium cations in each polymorphic form

Crystal structure determination by the combined analysis of NMR and powder diffraction data

Powder diffraction and solid-state NMR are complementary approaches for probing the structural properties of solids, and provide complementary types of information. There are thus considerable potential benefits to be gained by employing these techniques in tandem in the structural characterization of solids. This article is focused on the combined analysis of solid-state NMR data and powder X-ray diffraction data during the process of crystal structure determination. The article covers both the wide-ranging uses of solid-state NMR in providing information to assist the process of structure determination from powder X-ray diffraction data, as well as recent advances toward ab initio crystal structure determination from solid-state NMR data (which generally relies on the combined use of information from powder X-ray diffraction data for the material of interest)

Study of Generalized Interaction Wake Models Systems with ELM Variation for Off-Shore Wind Farms

This paper reports a novel frandsen generalized wake model and its variation model-frandsen generalized normal distribution wake model for off-shore wind farms. Two different new wake models in off-shore wind farms have been studied comparatively. Their characteristics have been analyzed through mathematical modeling and derivation. Meanwhile, simulation experiments show that the proposed two new wake models have different properties. Furthermore, the distributions of wind speed and wind direction are modeled by the statistical methods and Extreme Learning Machine through the off-shore wind farms of Yangshan Deepwater Harbor in the Port of Shanghai, China. In addition, the data of wind energy are provided to verify and test the correctness and effectiveness of the proposed two models. Wind power has been demonstrated by wind rose and wind resources with real-time data. These techniques contribute to enhance planning, utilization and exploitation for wind power of off-shore wind farms

In situ solid-state 1H NMR studies of hydration of the solid acid catalyst ZSM-5 in its ammonium form

Hydration of the ammonium form of the solid acid catalyst ZSM-5 is investigated by applying a technique that has been developed recently for carrying out in situ solid-state NMR studies of adsorption processes. From 1H MAS NMR spectra recorded as a function of time and temperature during the hydration process, insights are established on the nature of the interaction between the adsorbed water molecules and the ammonium cations in the ZSM-5 material. The change in isotropic chemical shift for the ammonium cations is consistent with the formation of N–H⋯O hydrogen bonding with the water molecules. Studies of the adsorption of deuterated water, and dehydration of the hydrated material, are also reported

Preferential Clustering of Water Molecules During Hydration of the Ammonium Form of the Solid Acid Catalyst ZSM-5

Hydration of the ammonium form of the solid acid catalyst ZSM-5 is investigated by applying a technique developed recently for in situ solid-state NMR studies of adsorption processes. From high-resolution solid-state 1H NMR spectra recorded as a function of time during the hydration process, insights are established concerning the nature of the interaction between the adsorbed water molecules and the ammonium cations in the ZSM-5 host material. In particular, quantitative information is established regarding the clustering of water molecules during the hydration process, and indicates the preferential formation of clusters comprising two water molecules associated with each hydrated ammonium cation