Crystalline Solid Phase Research Articles

Crystallization Kinetics of Phosphonium Ionic Liquids: Effect of Cation Alkyl Chain Length and Thermal History.

The effects of alkyl chain length on the crystallization kinetics and ion mobility of tetraalkylphosphonium, [P666,n][TFSI], (n = 2, 6, 8, and 12) ionic liquids were studied by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) over a wide temperature range. The liquid-glass transition temperature (Tg) and ion dynamics examined over a broad T range were almost insensitive to structural modifications of the phosphonium cation. In contrast, the crystallization kinetics were strongly affected by the length of the fourth alkyl chain. Furthermore, the thermal history of the sample (cold vs melt crystallization) significantly impacted the crystallization rate. It has been found that the nature of crystallization phenomena is the same across the homologous series, while the kinetic aspect differs. Finally, electric conductivity in supercooled liquid and crystalline solid phases was measured for all samples, revealing significant ionic conductivity, largely independent of the cation structure.

Influence of structural Fe content in clay minerals on selenite redox reactions: Kinetics and structural transformations

Redox reactions control the environmental fate of selenium, an element of concern due to its small gap between beneficial and detrimental effects on human health and due to the longevity of the radionuclide 79Se produced in nuclear reactors. Fe-bearing clay minerals are major redox-active ingredients of Earth’s critical zone and constitute an important component of the barrier in (radioactive and other) waste repositories. Here we systematically investigate selenite (Se(IV)O32−) sorption and reduction by Fe-bearing clay minerals of the smectite group, using batch experiments and X-ray absorption fine structure (XAFS) spectroscopy to elucidate reaction mechanisms and kinetics up to 720 or 3600 h. We found a linear relationship between structural Fe(II) content and selenite reduction rate. Selenite reduction depends also on redox potential and pH, with pH 7 showing a slower reduction rate than at pH 5. Selenite first sorbs to clay edge sites by forming an inner-sphere sorption complex, before being reduced to Se(0). The first redox product was amorphous (red) Se(0), which gradually transformed into trigonal (grey) Se(0), indicative of a kinetically hindered conversion of an amorphous (or less crystalline) solid phase into the thermodynamically stable and more crystalline form of the solid. Despite an Fe2+aq concentration of up to 6·10−4 M in the clay suspension, and their thermodynamic prediction for the clays at lower Eh, we did not observe formation of iron selenides. These insights into the selenite reduction mechanisms by Fe-bearing clays provides valuable information for the development of effective approaches for selenite immobilization.

Formation of Peroxynitrite, [O-N-O-O]-, via a Cascade of Reactions between Ozonide and Ammonia.

We report on an unexpected reaction between ammonia and potassium ozonide dissolved in liq. NH3 resulting in the formation of peroxynitrite, [ONOO]-, which exclusively happens in the presence of a specific partially fluorinated aniline-based ammonium cation. High-resolution structural data of the peroxynitrite anion in cis-conformation have been obtained. We further studied this molecule anion by single crystal Raman spectroscopy. The cis and trans isomers of peroxynitrite were analysed computationally with respect to their relative energies, the cis-trans transition barrier and their decomposition pathways to the nitrate anion. By experimentally examining cations decorated with fluorine ligands to different degrees, we demonstrate that fluorine specific interactions play a crucial role in the unexpected formation of peroxynitrite and as a conspicuously structure directing factor for the underlying crystalline solid phases, exhibiting distinct micro-separations of fluorine and hydrogen enriched regions.

High-resolution and high-accuracy calorimetry of order–disorder and melting transitions in the n-alkanes n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane and n-eicosane

In this work, a Peltier-element-based adiabatic scanning calorimeter was used to investigate, with high-resolution and accuracy, the temperature dependence of the specific heat capacity and specific enthalpy difference of a series of linear alkanes. More specifically, results are reported for the even n-alkanes; namely n-eicosane, n-octadecane, n-hexadecane and for the odd n-alkanes, namely n-nonadecane, n-heptadecane and n-pentadecane. The measurements cover a temperature range from well in the crystalline solid phase across the solid–solid transitions (when present) in to the liquid phase across the melting transition. Accurate transition temperatures and heat of transitions were derived from the direct experimental data in view of the potential use of n-alkanes as phase change materials.

Simulation studies on the dynamic heterogeneity of organic ionic plastic crystals

AbstractOrganic ionic plastic crystals (OIPCs) are one of promising solid‐state electrolytes (SSEs) for all‐solid‐state batteries. OIPCs consist of organic ions that form crystalline solid phases. It is a challenging but critical task in the development of SSEs to improve the ion conductivity of lithium ions in such crystalline solid phases. We discuss our recent simulation studies on the transport mechanism of ions in OIPCs and show that the dynamic heterogeneity should be a key to the transport mechanism. We aim to show that both translational and rotational dynamic heterogeneities should play an important role in understanding the ionic conductivity in SSEs. We found from our simulations that the introduction of dopants and defects into OIPCs facilitated both the dynamic heterogeneity and the ion conductivity significantly. We also found that the polarizability of matrix organic ions could contribute to the rotational and conformational relaxations of organic ions in OIPCs.

Solid-amorphous transition is related to the waterlike anomalies in a fluid without liquid-liquid phase transition.

The most accepted origin for the water anomalous behavior is the phase transition between two liquids (LLPT) in the supercooled regime connected to the glassy first order phase transition at lower temperatures. Two length scale potentials are an effective approach that has long been employed to understand the properties of fluids with waterlike anomalies and, more recently, the behavior of colloids and nanoparticles. These potentials can be parameterized to have distinct shapes, as a pure repulsive ramp, such as the model proposed by de Oliveira et al. [J. Chem. Phys. 124, 64901 (2006)]. This model has waterlike anomalies despite the absence of LLPT. To unravel how the waterlike anomalies are connected to the solid phases, we employ molecular dynamics simulations. We have analyzed the fluid-solid transition under cooling, with two solid crystalline phases, BCC and HCP, and two amorphous regions being observed. We show how the competition between the scales creates an amorphous cluster in the BCC crystal that leads to amorphization at low temperatures. A similar mechanism is found in the fluid phase, with the system changing from a BCC-like to an amorphous-like structure in the point where a maxima in kT is observed. With this, we can relate the competition between two fluid structures with the amorphous clusterization in the BCC phase. These findings help to understand the origins of waterlike behavior in systems without the liquid-liquid critical point.

Mechanochemistry-Directed Ligand Design: Development of a High-Performance Phosphine Ligand for Palladium-Catalyzed Mechanochemical Organoboron Cross-Coupling

Mechanochemical synthesis that uses transition-metal catalysts has attracted significant attention due to its numerous advantages, including low solvent waste, short reaction times, and the avoidance of problems associated with the low solubility of starting materials. However, even though the mechanochemical reaction environment is largely different from that of homogeneous solution systems, transition-metal catalysts, which were originally developed for use in solution, have been used directly in mechanochemical reactions without any molecular-level modifications to ensure their suitability for mechanochemistry. Alas, this has limited the development of more efficient mechanochemical cross-coupling processes. Here, we report a conceptually distinct approach, whereby a mechanochemistry-directed design is used to develop ligands for mechanochemical Suzuki-Miyaura cross-coupling reactions. The ligand development was guided by the experimental observation of catalyst deactivation via the aggregation of palladium species, a problem that is particularly prominent in solid-state reactions. By embedding the ligand into a poly(ethylene glycol) (PEG) polymer, we found that phosphine-ligated palladium(0) species could be immobilized in the fluid phase created by the PEG chains, preventing the physical mixing of the catalyst into the crystalline solid phase and thus undesired catalyst deactivation. This catalytic system showed high catalytic activity in reactions of polyaromatic substrates close to room temperature. These substrates usually require elevated temperatures to be reactive in the presence of catalyst systems with conventional ligands such as SPhos. The present study hence provides important insights for the design of high-performance catalysts for solid-state reactions and has the potential to inspire the development of industrially attractive, almost solvent-free mechanochemical cross-coupling technologies.

Computational Procedure for Analysis of Crystallites in Polycrystalline Solids of Quasilinear Molecules

In the current work, a comprehensive procedure for structural analysis of quasilinear organic molecules arranged in a polycrystalline sample generated by molecular dynamics is developed. A linear alkane, hexadecane, is used as a test case because of its interesting behavior upon cooling. Instead of a direct transition from isotropic liquid to the solid crystalline phase, this compound forms first a short-lived intermediate state known as a "rotator phase". The rotator phase and the crystalline one are distinguished by a set of structural parameters. We propose a robust methodology to evaluate the type of ordered phase obtained after a liquid-to-solid phase transition in a polycrystalline assembly. The analysis starts with the identification and separation of the individual crystallites. Then, the eigenplane of each of them is fit and the tilt angle of the molecules relative to it is computed. The average area per molecule and the distance to the nearest neighbors are estimated by a 2D Voronoi tessellation. The orientation of the molecules with respect to each other is quantified by visualization of the second molecular principal axis. The suggested procedure may be applied to different quasilinear organic compounds in the solid state and to various data compiled in a trajectory.

Experimental Determination of a Chiral Ternary Solubility Diagram and Its Interpretation in Gas Antisolvent Fractionation

Although crystallization has been widely applied for the enantiomeric enrichment of non-racemates both in research and in industrial applications, the physical-chemical background of chiral crystallizations is not as frequently discussed. A guide for the experimental determination of such phase equilibrium information is lacking. In the current paper, the experimental investigation of chiral melting phase equilibria, chiral solubility phase diagrams and their application in atmospheric and supercritical carbon dioxide-assisted enantiomeric enrichment is described and compared. Benzylammonium mandelate is a racemic compound; it shows eutectic behavior when molten. A similar eutonic composition was observed in its methanol phase diagram at 1 °C. The influence of the ternary solubility plot could be unequivocally discovered in atmospheric recrystallization experiments, which proved that the crystalline solid phase and the liquid phase were in an equilibrium. The interpretation of the results obtained at 20 MPa and 40 °C, using the methanol-carbon dioxide mixture as a pseudo-component, was more challenging. Although the eutonic composition was found to be the limiting enantiomeric excess value in this purification process as well, the high-pressure gas antisolvent fractionation results were only clearly thermodynamically controlled in certain concentration ranges.

Disentangling the Effect of Pressure and Mixing on a Mechanochemical Bromination Reaction by Solid-State NMR Spectroscopy.

Mechanical forces, including compressive stresses, have a significant impact on chemical reactions. Besides the preparative opportunities, mechanochemical conditions benefit from the absence of any organic solvent, the possibility of a significant synthetic acceleration and unique reaction pathways. Together with an accurate characterization of ball-milling products, the development of a deeper mechanistic understanding of the occurring transformations at a molecular level is critical for fully grasping the potential of organic mechanosynthesis. We herein studied a bromination of a cyclic sulfoximine in a mixer mill and used solid-state nuclear magnetic resonance (NMR) spectroscopy for structural characterization of the reaction products. Magic-angle spinning (MAS) was applied for elucidating the product mixtures taken from the milling jar without introducing any further post-processing on the sample. Ex situ 13 C-detected NMR spectra of ball-milling products showed the formation of a crystalline solid phase with the regioselective bromination of the S-aryl group of the heterocycle in position 4. Completion is reached in less than 30 minutes as deduced from the NMR spectra. The bromination can also be achieved by magnetic stirring, but then, a longer reaction time is required. Mixing the solid educts in the NMR rotor allows to get in situ insights into the reaction and enables the detection of a reaction intermediate. The pressure alone induced in the rotor by MAS is not sufficient to lead to full conversion and the reaction occurs on slower time scales than in the ball mill, which is crucial for analysing mixtures taken from the milling jar by solid-state NMR. Our data suggest that on top of centrifugal forces, an efficient mixing of the starting materials is required for reaching a complete reaction.

НАНОБИОТЕХНОЛОГИЧЕСКИЙ ПОДХОД К ВЫЯВЛЕНИЮ И ИССЛЕДОВАНИЮ МЕТАБОЛИЧЕСКИ АКТИВНЫХ ПРИРОДНЫХ МИКРОБНЫХ СООБЩЕСТВ КАК НОВЫЙ ВИД ЭКОЛОГИЧЕСКОГО МОНИТОРИНГА

An innovative nanobiotechnological express method for the detection of metabolically active microorganisms in natural water samples based on the ability of microbial cells to generate metal nanoparticles during the reduction reaction of cations introduced into the test samples as precursor (Detection of Biogenic Nanoparticles Growth/Generation ― DBNG method) is proposed. Metallic nanoparticles generated de novo form a new solid crystalline phase and can be detected with high accuracy by various physical methods. The DBNG method was tested on model psychrotolerant bacteria and proved to be effective in studying the metabolic activity of microbial communities in samples from various cold Arctic and Antarctic ecosystems. This approach can be used in ecology for monitoring changes in the ecological state of natural ecosystems.

Crystal and mesophase structure of a bicyclohexyl cyano mesogen.

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C-H or aliphatic C-H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

Nanobiotechnological Method for Studying Metabolically Active Natural Microbial Communities

An innovative nanobiotechnological express method for the detection of metabolically active microorganisms is proposed. The method is based on the inherent feature of microbial cells to generate metal nanoparticles during their metabolic activity in the process of reducing cations added in the system. The resulting nanoparticles are a new solid crystalline phase and can be detected with high accuracy by various physical methods. The technique was successfully tested and proved to be effective in the study of microbial activity in both samples from various cold ecosystems and pure psychoactive cultures from the genera Cryobacterium Methylophilus, Mycobacterium and Rhodococcus. This methodology can be used in ecology for monitoring the ecological state of natural ecosystems, in biotechnology for screening active samples when isolating industrially important microorganisms, and in astrobiology for identifying living metabolizing microbial cells in extraterrestrial environments

Corrosion and mechanical behavior of amorphous-nanocrystalline NiCrMo coatings

To develop a high-performance coating for marine engineering equipment, we successfully designed amorphous-nanocrystalline NiCr0.25Mox (x = 0, 0.02, 0.05, 0.1, 0.2, 0.4) alloy coatings via direct current (DC) magnetron sputtering. The compositional, microstructural, corrosion and mechanical properties, specifically the relationship between the coating structure and performance were discussed in detail. The results showed that the amorphous phase sharply alleviated grain boundary corrosion, and the addition of Cr and Mo was beneficial to improve repassivation ability with the formation of a dense passive film. In the nanoindentation and micro-scratch tests, the nanohardness and adhesion strength of the coatings first increased remarkably with Mo content and then declined due to the formation of an amorphous phase. The enhancement of strength was caused by nanocrystals hindering the formation of shear banding, while the addition of Mo improved the tendency of amorphous formation due to the difference in atomic size and lattice distortion. Most importantly, the NiCr0.25Mo0.1 coating exhibited excellent corrosion performance and mechanical behavior through the formation of a dense passivation film composed of Cr2O3 and Cr(OH)3. These ductile solid solution crystalline phases promoted homogeneous plastic deformation and decelerated crack propagation during the scratching process.

Encapsulation of catechin into nano-cyclodextrin-metal-organic frameworks: Preparation, characterization, and evaluation of storage stability and bioavailability

This study, nanoscale α-, β-, γ-cyclodextrin (CD)-metal–organic frameworks (MOFs) were successfully prepared using solvothermal assisted ultrasound method. CD-MOFs were used as nanocarriers to encapsulate catechin (CA), and their encapsulation capacities were evaluated. Encapsulation capacities of CD-MOFs to incorporate CA followed the order: β-CD-MOFs > γ-CD-MOFs > α-CD-MOFs. CA/CD-MOFs were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). DSC and SEM results provided evidence for the formation of CA/CD-MOFs. XRD results indicated the new solid crystalline phases formed in CA/CD-MOFs complex. Results of FT-IR showed that CA was combined with CD-MOFs through hydrogen bonding and van der Waals forces. Current research demonstrated that encapsulation of CA within CD-MOFs provided it against light, oxygen and temperature. Moreover, encapsulation by CD-MOFs improved storage stability and bioavailability of CA. Thus, these CA/CD-MOFs have potential to be used as nutritional supplements and functional foods.

Characterisation of the progression of salts in walls of earthen architecture heritage

AbstractTwo hundred years (1750–1950) of earthen architecture represents an important period of construction in the central region of Portugal. Earthen architecture is usually built close to the coast or to rivers and placed in sandy ground. The impact of rising damp is a general problem and efflorescences are a common cause of damage decay. This problem was studied in a building with two types of earthen construction, adobe masonry walls and formed masonry walls. The aim of this research was to characterise the conditions for the appearance and phase transitions of thénardite and mirabilite, and determine how to prevent progression of salt effects in the two types of wall to support future conservation measures. Laboratory capillarity and porosimetry tests with dolomitic air lime mortar and hygrothermal monitoring were pursued along with in situ tests. Visual assessment showed that the progression of salts depends on the composition of the earthen materials. To understand these differences, all crystalline solid phases were analysed by powder X-ray diffraction, and building interior hygrothermal conditions were monitored. An investigation into the influence of surface lime water painting and sacrificial mortar application on the crystallisation of sodium sulfates concluded that these also depend on the wall's composition. Data allowed us to conclude that inside the building the temperature and humidity [relative humidity (RH = 100 pw/p°w > 70)] conditions led to the adobe breakdown by the fast conversion from thénardite to mirabilite. Therefore, contact with wet atmospheres should be avoided and interior hygrothermal conditions should be controlled. Laboratory and in situ tests showed that the environmental conditions of the spaces had effects on the results. The results contribute to understanding of the salt progression and pattern of decay, as well as supporting future recommendations for building conservation, based on the identification of environmental conditions proper to their occurrence.

QUANTAS: a Python software for the analysis of thermodynamics and elastic behavior of solids from ab initio quantum mechanical simulations and experimental data.

Mineralogy, petrology and materials science are fundamental disciplines not only for the basic knowledge and classification of solid phases but also for their technological applications, which are becoming increasingly demanding and challenging. Characterization and design of materials are of utmost importance and usually need knowledge of the thermodynamics and mechanical stability of solids. Alongside well known experimental approaches, in recent years the advances in both quantum mechanical methods and computational power have placed theoretical investigations as a complementary useful and powerful tool in this kind of study. In order to aid both theoreticians and experimentalists, an open-source Python-based software, QUANTAS, has been developed. QUANTAS provides a fast, flexible, easy-to-use and extensible platform for calculating the thermodynamics and elastic behavior of crystalline solid phases, starting from both experimental and ab initio data.

Multicomponent Crystal of Trimethoprim and Citric Acid: Solid State Characterization and Dissolution Rate Studies

BACKGROUND: Trimethoprim is a broad spectrum antimicrobial agent with low solubility in water which causes low bioavailability in systemic circulation.
 AIM: The purpose of this study was to prepare multicomponent crystals of trimethoprim and citric acid to increase the solubility and dissolution rate of trimethoprim.
 MATERIALS AND METHODS: Multicomponent crystals were prepared by solvent evaporation method. Characterizations of multicomponent crystalline solid phase properties were carried out by powder X-ray diffraction (PXRD) analysis, differential scanning calorimetry (DSC), FT-IR spectroscopy, scanning electron microscopy (SEM). Solubility and dissolution rate tests were carried out in aqueous medium.
 RESULTS: The PXRD characterization results showed a new X-ray diffraction pattern in the multicomponent crystal phase. DSC analysis showed the formation of a new endothermic peak. This indicates the formation of a multicomponent crystal phase between trimethoprim and citric acid. The results of the SEM analysis indicate the formation of a new crystal habit. Solubility of multi-component crystal phase of trimethoprim increased 7 times compared to intact trimethoprim. The dissolution of trimethoprim and multicomponent crystals in 0.1 N HCl medium at 60 minutes was 56.36% and 95.57% and CO2-free distilled water medium was 43.03% and 88.26%, respectively.
 CONCLUSIONS: From the results of the study, it can be concluded that the multicomponent phase of trimethoprim crystals with citric acid successfully increase the solubility and dissolution rate of trimethoprim significantly.

Enantiotropic inconstancy, crystalline solid solutions and co-crystal in the salicylic acid-anthranilic acid system.

The phase boundaries and thermodynamic properties of crystal phases in the salicylic acid (SA) - anthranilic acid (AA) system have been determined experimentally. The complete binary T-X diagram reveals a total of four crystalline phases, including a co-crystal and three crystalline solid solutions. The two eutectics were determined through triplicate DSC analyses at 33 compositions. By adding a liquid solvent and generating a ternary phase diagram, a methodology is introduced to determine the solid-state miscibility limits of the solid solutions at 20 and 55 °C. The crystalline solid solutions exhibit substantial differences in physical properties relative to the pure components, including solubility enhancements that are relevant for chemical processing and material properties. The thermodynamic relationships of the three polymorphs of AA have been resolved showing an enantiotropic transition temperature of 50-55 °C between Form I and III of pure AA. However, as a result of the solid solutions with SA, the enantiotropic transition temperature was suppressed by around 30 °C at the eutectoid. In addition, a co-existence envelope is formed, wherein the two AA polymorph solid solutions exist in equilibrium with one another over a wide range of temperatures and compositions.

Hard and electrically conductive multicomponent diboride-based films with high thermal stability

We report high-quality, hard (31–41 GPa), crack-resistant (hardness-to-effective Young's modulus ratio of 0.13–0.16) and electrically conductive (2.8–4.2 × 105 S m−1) HfB2-based ceramic materials with high thermal stability. The materials were prepared in the form of well adhesive films using a simple deposition process: pulsed magnetron sputtering (B4C target overlapped by metal stripes) onto floating substrates. We go through a wide range of compositions resulting from incorporating five other metals (Ti, Y, Zr, Ho or Ta) which partially replace Hf, and focus on the effect of the number and characteristics of elements in the metal sublattice. Regardless of the number of incorporated elements, no segregation to more than one AlB2-type crystalline phase was observed. Growing number of metal elements leads to decreasing crystal size as indicated by the width of diffraction peaks, strongly decreasing compressive stress to less than 2 GPa and slightly decreasing hardness and electrical conductivity. The experimental data are explained by Monte-Carlo calculations of the energy delivered into the growing films. The thermal stability of septenary diboride-based films Hf8Zr4Ti4Ta4Y5B60C9 and Hf10Zr4Ti4Ta4Ho5B58C9 was superior to that of quaternary films Hf22Y5B58C9 and Hf22Ho5B58C9 when annealed to 1300 °C. Both the single solid solution crystalline phase (X-ray diffraction) and the dense and pinhole-free structure (scanning electron microscopy) were observed for the septenary films not only before but also after annealing. The results are important for the design and industry-friendly preparation of thin-film materials combining multiple functional properties for various technological applications.