Static and Dynamic Structure of Water in Hydrated Kaolinites. I. The Static Structure

Static and dynamic structure of water in hydrated kaolinites. II. The dynamic structure

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

CO2 Capture via Crystalline Hydrogen-Bonded Bicarbonate Dimers

Solid state characterization of mometasone furoate anhydrous and monohydrate forms

Sodium naproxen is an antiinflammatory nonsteroidal drug used in the treatment of rheumatoid and arthritic diseases. Three pseudopolymorphic forms have been reported in the literature, along with characterizations of anhydrous and dihydrated forms. In the present work, the monohydrated form of sodium naproxen was prepared by dehydration of the dihydrated form and investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and microscopy. Characteristic properties of the monohydrated form were compared to the anhydrous and the dihydrated forms, and the transformation of higher hydrated forms to lower ones was performed in an oven or a desiccator without generating other polymorphic forms. DSC and isothermal TGA experiments determined the structural characteristics and mechanisms by which two types of water were removed from the hydrated species.

Diclofenac Salts, Part 7: Are the Pharmaceutical Salts with Aliphatic Amines Stable?

Low-frequency depolarized Raman spectra of aqueous solutions of D-glucose and D-galactose have been investigated in the frequency region from −250 cm−1 to 250 cm−1 at 30.0 °C as a function of concentration up to 0.04 molar ratio. The dynamical structure of water in aqueous solution is analyzed by using the reduced Raman spectrum χ″(ν̄), which corresponds to the imaginary part of the dynamical susceptibility. The reduced spectrum is fitted with the superposition of one Cole–Cole type relaxation mode and two damped harmonic oscillator modes by a nonlinear least-squares fitting. The effects of D-glucose and D-galactose on the dynamical structure of water in aqueous solution are similar. The relaxation time of hydrogen bond among water molecules becomes slower with increasing sugar concentration. The characteristic frequencies of stretching-like and bending-like vibrations among water molecules do not change in both D-glucose and D-galactose aqueous solutions.

We attempted to obtain a large amount of solvates of 2,4,6-tris(isopropylamino)-1,3,5-trinitrobezene 1 and tried to embark on a systematic study (both experimentally and theoretically) of conformational effects of crystal packing. Here we describe their investigation by X-ray diffraction, thermal analysis, and computational methods (force field and ab-initio). The crystal and molecular structures were determined by X-ray diffraction. For thermal analysis investigations a combination of Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) measurements were done. In our work we have calculated the electrostatic potential (ESP) charges and the molecular energies of the experimental molecular structures after the correction of the hydrogen atomic positions, using the Density Functional Theory (DFT) electronic structure program DMOL3 (2.2), with DNP basis set and GGA-BLYP functional. The molecular structures with the calculated charges then have been used to calculate: the crystal, the lattice and individual interaction energies in each structure, within the molecular simulation program Discover, using COMPASS force field. A wide range of small molecules were found to be incorporated into crystals of 1.The crystal and molecular structures of the first dimorph 1a of 1 has been found previously. Six different packing arrangements, which have been divided into four groups, for the cosolvates of 1 were found. For the conformations of the six-membered ring of 1 in the different cosolvates, we have found that: three different conformations can be adopted by the host molecule 1: boat form with two short and four long C—C bonds in the six-membered ring (quinonoid character), twist form with two long and four short C—C bonds (cyanine character) and intermediate twisted-boat form. The following results were obtained from both DSC experiments and the theoretical calculations of the lattice energy: 1.Substantially high dissolution energy Ediss (obtained from DSC measurements) and lattice energy/molecule ELM (obtained from force field calculations) were found for the solvates that have host-guest intermolecular hydrogen bonds, for solvates that have methyl group in the para position and for inclusion crystals with benzonitrile and nitroethane. 2.Form 1a, which has chain character of the intermolecular hydrogen bonds system, is more stable than 1b, which have a dimer character of the intermolecular hydrogen bonds system. 3.The stabilities of the structures with isomeric inclusion molecules are in the following sequence: cosolvates with para > ortho > meta substitution pattern. 4.The close packing structure is always more stable then the other structure. For every structure powder diffraction measurements have been performed at room temperature and at temperature higher than the guest dissolution temperature. All the cosolvate structures changes to structure 1a after the evaporation of the solvent, except that of anisole which change to structure 1b. Detailed calculations of the interaction energies between the different molecules in each structure have been done to understand the factors affecting the crystal packing forces. The following results have been found: ·In the structures without solvent (the dimorphs) the largest interaction in the crystal has been calculated to be between the pair of molecules that connected with intermolecular hydrogen bonds. ·For the cosolvate structures in group 2, there are a dimer (two neighbouring molecules that are connected with intermolecular hydrogen bonds) or a pair (two neighbouring molecules sitting in the analogue position as the dimer but not connected with intermolecular hydrogen bonds) character structure of the host molecules. The largest interaction has been calculated to be between the host molecules of different dimers or pairs, which are not connected with intermolecular hydrogen bonds. This is because the intermolecular hydrogen bonds within the dimer are of week type, their lengths (NH—O) range between 3.20 A and 3.43 A. On the other hand, strong dispersion interactions in addition to considerable electrostatic interactions, have been calculated between the molecules of the different dimers or pairs, which can be attributed to the many close contacts between the methyl…methyl, nitro…methyl and nitro…nitro groups of these molecules. The nitro group free of intramolecular hydrogen bond and the methyl groups of the neighbouring isopropylamino groups are generally the groups that responsible for this interaction. ·The twist or the twisted boat six-membered ring conformations of the host 1, which are the forms adopted by 1 in the most cosolvates structures, are very suitable for the generation of many van der Waals interactions between the different layers within the packing patterns of our cosolvate structures.

This contribution addresses the role of water molecules in crystal engineering by studying the crystal structures and thermal stabilities of 11 new cocrystal hydrates, all of which were characterized by single crystal X-ray crystallography, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The cocrystal hydrates can be grouped into four categories based upon thermal stability: (1) water is lost at <100 °C; (2) water is lost between 100 and 120 °C; (3) water is lost at >120 °C; (4) dehydration occurs concurrently with the melt of the cocrystal. In order to address if there is any correlation between structure and stability, the following factors were considered: type of hydrate (tunnel hydrate or isolated hydrate); number of hydrogen bond donors and acceptors; hydrogen bond distances; packing efficiency. Category 1 hydrates exhibit water molecules in tunnels. However, no structure/stability correlations exist in any of the other categories of hydrate. To complement the cocrystal hydrates reported herein, a Cambridge Structural Database (CSD) analysis was conducted in order to address the supramolecular heterosynthons that water molecules exhibit with two of the most relevant functional groups in the context of active pharmaceutical ingredients, carboxylic acids, and alcohols. The CSD analysis suggests that, unlike cocrystals, there is great diversity in the supramolecular heterosynthons exhibited by water molecules when they form hydrogen bonds with carboxylic acids or alcohols. It can therefore be concluded that the promiscuity of water molecules in terms of their supramolecular synthons and their unpredictable thermal stability makes them a special challenge in the context of crystal engineering.

The amounts of three different types of water adsorbed on hydrolyzed lignin, which was obtained by acid hydrolysis of softwood meal in 1,4‐dioxane containing trace amounts of hydrochloric acid (in the following called DL), and on its derivatives, i.e., methylated and acetylated lignins, were determined by differential scanning calorimetry (DSC). The first type of water is non‐freezing water, the glass transition of which was detected by DSC. The second type of water corresponds to a kind of bound water which was detected from a crystallization peak in the vicinity of 225 K (peak II). This peak appeared when the water content exceeded a critical amount of non‐freezing water. The third type of water is free water, the crystallization peak (peak I) of which was found at the same temperature as that of pure water. From the enthalpies of crystallization of the above two types of water and the known weight of sorbed water, the amount of bound water in DL was determined to be 0,10 (weight of bound water/weight of dry sample). Furthermore, it was found that bound water breaks hydrogen bonds in DL and decreases its glass transition temperature (Tg) from 425 K to 330 K. The amount of hydroxyl groups, which varies with the degree of methylation or acetylation, was also found to affect the bound water content and inevitaby to decrease T g.

Effect of pulverization on dehydration behavior of crystals of GK-128, a serotonin3 receptor antagonist.

There are several types of water in inorganic salts. Those water molecules that are coordinated to the metal and retain their identity in solution —e.g., aquo-ions of the type [M(H2O)a] b —are termed coordinated water, and those water molecules that are hydrogen bonded to other water molecules or to the anion or to both are termed lattice water. The distinction, however, is not clear-cut, for some coordinated water may also engage in hydrogen bonds within the crystal. Confirmation of structures of this type has come from neutron diffraction studies of hydrates. Studies by Taylor et al. 1 with Th(NO3)4·5H2O showed coordinated water,1 water-water hydrogen bonds, and water hydrogen bonded to the nitrate. Figure 5–1 illustrates the structure of Th(NO3)4·5H2O. Uranyl nitrate hexahydrate exhibits similar types of environments for the water molecules.2 Stable solids containing the oxonium ion (H3O+) have also been reported.3–7 Recently, single-crystal neutron diffraction evidence for the diaquohydrogen ion in trans-[Co(en)2Cl2]+Cl-(H5O2)+Cl- has been found.8 The hydrogen bonding in the diaquohydrogen ion (trans.) is illustrated in Fig. 5–2. Complex structures of the aforementioned types (as illustrated by Th(NO3)4 · 5H2O and [Co(en)2Cl2]+Cl-(H5O2)+Cl-) should be considered to be typical of hydrates rather than exceptional.

Physicochemical Characterization of Nedocromil Bivalent Metal Salt Hydrates. 3. Nedocromil Calcium

A differential scanning calorimetric (DSC) study on the characteristics and behavior of water in low-rank coals

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding