Crystal Solvates Research Articles

Properties of solutions of poly-(p-phenylenebenzobisthiazole) in polyphosphoric acids of different composition

The possibility of hydrolytic degradation of an oligomeric solvent—polyphosphoric acid—in finished spinning solution was established. The viscosity of the polymer solution can be decreased by decreasing the proportion of phosphoric anhydride in the solvent with a small change in the concentration of polymer in the solution; the properties of the fibre fabricated from such a solution do not worsen. When the degree of polymerization of the polyphosphoric acid decreases (up to its conversion to orthophosphoric acid), poly-(p-phenylenebenzobisthiazole) crystal solvates are crystallized into single crystals hundreds of micrometers in size.

Red, orange and yellow crystals of 4,5-bis(4-methoxyphenyl)-2-(3-nitrophenyl)-1H-imidazole

Red non-solvate crystals of the title compound from ethanol, C23H19N3O4, orange solvate crystals from tert-butanol, C23H19N3O4·C4H10O, yellow solvate crystals from dioxane–water, C23H19N3O4·0.5C4H8O2, and intense yellow solvate crystals from benzene–N,N′-dimethylformamide, C23H19N3O4·C6H6, differ from each other in their molecular conformation and hydrogen-bonding scheme. The bathochromic shifts of the crystal color are explained by the molecular planarity and charge-transfer effect among the imidazole mol­ecules.

Improved synthesis of paroxetine hydrochloride propan-2-ol solvate through one of metabolites in humans, and characterization of the solvate crystals.

Paroxetine, a potent and selective inhibitor of 5-hydroxytryptamine (serotonin) uptake, was prepared through a piperidine derivative, which was reported to be one of the paroxetine metabolites in humans. Thus, the piperidine derivative was converted to its N-tert-butoxycarbonyl (N-Boc) derivative, which was then converted to N-Boc paroxetine. Paroxetine hydrochloride propan-2-ol (isopropyl alcohol (IPA)) solvate crystals were directly obtained from the N-Boc paroxetine by adding hydrogen chloride to the N-Boc paroxetine IPA solution. The amount of IPA content in the crystals was reduced by drying with a continuous change of powder X-ray diffraction patterns. Other characterizations of the solvate crystals were also conducted.

Crystal Structures and Solvate Formation of Two Conformationally Frozen Isomers of a Bridged Calix[6]arene

Crystal Structures and Solvate Formation of Two Conformationally Frozen Isomers of a Bridged Calix[6]arene

Effects of lyophilization on the physical characteristics and chemical stability of amorphous quinapril hydrochloride.

To prepare amorphous quinapril hydrochloride (QHCl) by lyophilization and to compare its physical characteristics and chemical stability as a function of the initial pH of the pre-lyophilized solution. Amorphous QHCl samples were prepared by lyophilization from aqueous solutions. Solid-state characteristics were evaluated by DSC, PXRD, and optical microscopy. Chemical degradation was monitored by an HPLC assay. Amorphous QHCl samples obtained from lyophilization exhibited variable glass transition temperatures, depending on the pH and/or concentration of the starting aqueous solutions. Neutralized quinapril (Q) in the amorphous form, which has a Tg of 51 degrees C, lower than that of its HCl salt (91 degrees C), was significantly more reactive than QHCl at the same temperature. The Tg of lyophilized samples prepared at various initial pH values correlated well with values predicted for mixtures of QHCl and Q. Their different reaction rates were related to their glass transition temperature, consistent with the results from earlier studies obtained with amorphous samples made by precipitation from an organic solution and grinding of the crystal solvate. Lyophilization of different QHCl solutions produces mixtures of amorphous QHCl and its neutralized form Q, with Tg values intermediate to the values of QHCl and Q. As the fraction of Q increases the overall rate of chemical degradation increases relative to QHCl alone, primarily due to the increase in molecular mobility induced by the plasticizing effects of Q.

13C-MAS-NMR investigation of solutions saturated with fullerenes: study of the anomalous solubility behaviour

A simple and very efficient procedure for investigating the solubility of any organic compound in organic solvents at different temperatures is described. Applying pulsed nuclear magnetic resonance and magic angle spinning, saturated solutions of C 60 fullerene in o-dichlorobenzene were studied in a wide range of temperatures. This work was made to develop a better understanding of the anomalous solubility behaviour, i.e. the presence of a maximum in the solubility curve and an exothermic dissolution of fullerenes at high temperatures. These results relate the first direct observation of the phase transition between solvated crystals and pure C 60 by NMR. The temperature of this transition was found to be around 313 K which corresponds to the maximum of the solubility of C 60 in o-dichlorobenzene. The transition is quite reversible and the equilibrium between the two phases occurs within a few hours.

Thermoanalytical characterization of pseudopolymorphs of sulphadimidine and sulphadimidine–trimethoprim molecular complexes

In recrystallization experiments of sulphadimidine from water, dioxane and their mixtures aimed at preparing the unstable hydrate, a non-stoichiometric solvate with dioxane C 12H 14N 4O 2S· 1 5 C 4H 8O 2 and a pseudopolymorph with similar X-ray powder diffraction and infrared absorption properties but different thermal behaviour (DSC, TG) were isolated. In co-crystallization experiments of trimethoprim and sulphadimidine, a monohydrate of the respective 1 : 2 molecular complex and a methanol solvate of the equimolecular complex were obtained from aqueous ethanol and anhydrous methanol, respectively. The thermal stability of both pseudopolymorphic complexes is reflected by the high DSC and TG onset temperatures of solvent escape from the crystal lattice ( T e≈163°C and T e≈144°C, respectively, for water and methanol) and is consistent with the important role of water in the hydrated crystal packing and the very strong hydrogen-bonding interaction of methanol with a sulphonamido oxygen atom in the methanol solvate crystal.

Rheology and phase behavior of the system PBZT-phosphoric acid-water

Solutions of poly-p-phenylenebisbenzthiazole (PBZT) in phosphorous acid were examined in a rheogoniometer for shear response and relaxation as a function of concentration and temperature based on knowledge of the phase diagram of the system. It was found that the various regions of the phase diagram (i.e., the isotropic, the nematic, and the biphasic regions) and the various kinds of crystal solvates were reflected by their rheological behavior. This shows that rheological properties can be used to map, at least, the broad features of phase diagrams; conversely, the knowledge of the phase diagram is a prerequisite for the appreciation of rheological behavior. At the same time, the stress involved in the rheological tests themselves can modify, to a lesser extent, the positions of the phase dividing lines compared to those in the static system, which at appropriate points in the phase space can lead to stress-induced phase transitions. The principal rheological effect, here used diagnostically, is in itself novel; it is a spontaneous stress buildup in the stationary state of the rheometer after the stresses generated by the preceding shearing have decayed following stoppage of the rotor. The effect itself will be followed up in a separate study.

Thermochemistry of solvated crystals of C60 and C70 with o-xylene

Differential scanning calorimetry (DSC) was used to study the binary systems of C60-o-xylene and C70-o-xylene and the ternary system C60-C70-o-xylene. Fullerene C60 formed solvated crystals C60·2C8H10 with incongruent melting point 320 K and with enthalpy of decomposition 31±3 kJ (mol of C60)-1. Two solvated crystals of C70 with incongruent melting points 283 and 369 K, and with decomposition enthalpies 18.5±2.2 and 23.0±1.5 kJ (mol of C70)-1, were formed from o-xylene solutions. Three ternary compositions with C60/C70 mole ratios of 3:1, 1:1 and 1:3 were scanned by DSC.

Phase Transition C60−C60*4C6H6 in Liquid Benzene

The results of the first direct observations of the transition between solvated C60*C6H6 and pure fcc C60 in benzene solution with optical microscopy and combined with X-ray powder diffraction are presented. It is shown that the solvated C60*4C6H6 structure at room temperature is significantly different from the low-temperature structure described before. The temperature of phase transition was found to be between 40 and 41.5 °C. A new method of growth of solvated crystals based on recrystallization of face-centered cubic C60 to solvated form is described.

Triterpenoids fromAbies species

The structure and the absolute configuration of 25,26,27-trinor-17,13-frido-9β-lanostane hydroxyketonep-bromobenzoate were established by X-ray structural analysis. This compound readily forms a 1∶1 crystal solvate withn-pentane.

Radical Dissociation of 2,2′-Bis(2-aryl-3-benzothiophenonyl)s by Mechanical Energy

Abstract On applying pressure with a press in the solid state, the title compounds undergo homolysis of the central C–C bond to give green-colored radicals. X-Ray structure analysis for p-chloro derivative showed that the central C(2)–C(2′) bond was not elongated but had a normal distance (1.576 Å) as a hexa-substituted Csp3–Csp3 bond. The amount of the radical formed by mechanical energy depended on the substituents on the 2-phenyl rings and on the solvent of crystallization. As for the crystals containing no solvent, p-bromo and p-chloro derivatives showed higher reactivity than the unsubstituted compound, probably due to smaller dissociation enthalpy. The radical dissociation was suppressed by the presence of some solvent of crystallization. In the solvated crystals, the excess energy supplied by external mechanical energy would be transferred mainly to vibrational modes of the solvent molecules rather than to the substrate.

Crystal-solvate phases of poly(p-phenylene benzobisoxazole)

The crystal structure and morphology in oriented solutions of the rigid polymer poly(p-phenylene benzobisoxazole) (PBZO) in polyphosphoric acid (PPA), at different degrees of exposure to moisture, were studied by transmission electron microscopy and X-ray diffraction. Two crystal solvate forms, crystalline complexes of PBZO and PPA, were found. The form I crystal solvates exhibit several sharp equatorial reflections, whereas only a few broad reflections are observed in the form II state. All crystal solvate phases studied exhibit three-dimensional crystallinity evident in sharp off-meridional reflections. This is considered to be due to unique associations between the protonated PBZO polycations and the PPA anions. Endothermic transitions observed upon heating the crystal solvates are interpreted as dissolution of the form I crystals at about 70°C and crystal-crystal transformation of the form II crystal solvate to PBZO crystals, due to deprotonation above 300°C. A microfibrillar morphology is observed in the oriented PBZO fibre coagulated by immersion in water. Similar microfibrils, less than 10 nm in width, are already observed in the form II crystal solvate state, obtained from the oriented solution by absorption of moisture.

Crystal structure of tris(4,4′-dimethoxy-2,2′-bipyridine)iron (II) bis (hexafluorophosphate) , solvate with N-methyl-2-pyrrolidone

The crystal study of tris(4,4′-dimethoxy-2,2′-bipyridine)iron(II)bis(hexafluorophosphate) (crystal solvate with N-methyl-2-pyrrolidone) was performed at 295 K. The crystals are triclinic, a = 11.721(4), b = 12.864(6), c =15.664(7) A ̊ , α = 77.14(4),β = 85.03 (3), γ = 81.76(3)° , space group P 1, Z = 2, R = 0.0679 for 4694 reflections. The average FeN distances of 1.967 Å agrees well with those observed in other tris(2,2-bipyridine) complexes of hexacoordinated Fe(II) with a large low-spin fraction. A small difference of the individual FeN distances in the dication (which are shorter for one of the bipyridine ligands) may be explained by crystal packing effects. A very specific orientation of dications [Fe(DMO-bpy) 3] 2+ in the crystal is worthy of note (the vector of one of the moieties N…(Fe)…N of the dication coincides in fact with direction [011] of the crystal). The possible interaction of the trication of tris(4,4′-dimethoxy-2,2′-bipyridine)iron (III) with the active site of glucose oxidase (i.e. the metal complex acting as an oxidant/electron-transfer mediator) is discussed.

Study of the mechanism of optical resolutions via diastereoisomeric salt formation

Racemic malic acid (I) was resolved by R-α-phenylethylamine(II). The S-(−)-I.R-(+)-II diastereoisomer was in excess in the precipitated salt. DSC curves and X-ray powder diffractograms proved that the diastereoisomeric salt mixture precipitated during the resolution was isomorphous with the optically pure S-(−)-I.R-(+)-II salt. The diastereoisomeric salt mixture containing the R-(−)-I.R-(+)-II salt in abundance bound crystal solvate (water or methanol) when produced by the total evaporation of the mother liquor, while the optically pure R-(−)-I.R-(+)-II salt crystallized without solvate. It is generally assumed that solid solution formation takes place when the two diastereoisomers are alike and the high similarity results in less efficient enantiomer separation. This paper demonstrates that efficient resolution can be accomplished in case of solid solution formation too. The diastereoisomeric salt mixtures can crystallize in isomorphic form even when the physico-chemical properties of the optically pure diastereoisomeric salts are quite different.

Interactions of C60 with organic molecules in solvate crystals studied by infrared spectroscopy

Infrared absorption spectra (400–4000 cm−1) of C60 solvate crystals in benzen, toluene, chlorobenzen, decalin and n-decane have been measured in the temperature range 90–300 K. Chemical reactions of C60 with decalin and n-decane are observed. Interactions between C60 and solvent molecules have an influence on the infrared bands assigned to the CH stretching vibrations. Solvent effects are also observed in the temperature dependence of the C60 infrared bands.

Characterization of Fullerenes Obtained from Boron Nitrite Containing Graphite Electrodes: Electronic Structure of C60-X-YBXNYand Deformed C60

Abstract The electronic structure of C60 molecules with carbon substituted by other elements such as boron or nitrogen has been calculated for molecules in the singlet state with even number of electrons. Therefore, in the case of boron and nitrogen substituents, calculations have been performed for ionized molecules. The results obtained from our density functional calculations prove than in the C60-x-yBxNy molecules both HOMO and LUMO levels are split due to the lower symmetry of the molecule Influence of deformation of C60 molecules on electronic states, which is interesting because fullerenes may undergo deformation in solvate crystals, is also shown These C59B and C59N, as well as C58BN molecules are of special interest because samples containing such species can be prepared The Electron Spin Resonance (ESR) in those samples differs from the results obtained in pure C60 samples, it consists of several lines which are very sensitive to the temperature.

Some Enthalpies of Solution of C60 and C70. Thermodynamics of the Temperature Dependence of Fullerene Solubility

The enthalpy of solution of C60 in toluene, carbon disulfide, decalin, and N,N-diethylaniline and of C70 in CS2 has been measured using an isoperibol solution calorimeter. Exothermic heats of solution are observed in all cases. The heat of solution of C60 in toluene is −8.6 ± 0.7 kJ mol-1; in carbon disulfide it is −20 ± 1 kJ mol-1. In decalin, slow dissolution prevents an accurate determination, but the heat of solution is less than −5 kJ mol-1. In N,N-diethylaniline, a fast exothermic step comparable to that observed in other systems is followed by a much larger heat evolution, implying that a chemical reaction is occurring. The heat of solution of C70 in CS2 is −9 ± 1 kJ mol-1. A thermodynamic theory of the temperature dependence of fullerene solubility is presented. The central idea is that the unusual temperature dependence of the solubilities of fullerenes is caused by the formation of solvated crystals. Conditions are derived under which a temperature maximum of solubility, caused by an incongruent...

Stoichiometry and phase behavior of carbon tetrachloride solvates of C 60

Two solvated crystals of C 60 were formed from CCl 4 solutions. It was found that the cubic solvated crystal is composed of a C 60(CCl 4) 13 formula unit while the hexagonal crystal has a C 60(CCl 4) 2 unit. These solvates have phase behavior comparable with that of cyclohexane solvates of C 60, being closely related to binary sphere mixtures with a characteristic diameter ratio of 0 .58. The present calorimetric study strongly suggests that the C 60(CCl 4) 13 crystal has an AB 13-type structure, in which icosahedron clusters of CCl 4 like those in the cyclohexane analogue are formed.

Thermochemical reactivity of a solvate crystal studied by thermal analysis and in situ X-ray absorption spectroscopy

A solvate compound of rubidium bromoacetate and bromoacetic acid (1:1) was prepared and characterized. Its thermochemical reactivity was studied with thermal analysis (DSC and thermogravimetry combined with mass spectroscopy) and time-resolved in situ X-ray absorption spectroscopy at the K-edges of both bromine and rubidium. The reaction leads first to decomposition of the solvate crystal into bromoacetic acid and rubidium bromoacetate. Bromoacetic acid evaporates, and rubidium bromoacetate eliminates rubidium bromide and partially forms polyglycolide, a polyester. After the completed reaction, crystalline rubidium bromide remains.