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  • 1. Cheuk, Dominic
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Seaton, Colin
    McArdle, Patrick
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Investigation into solid and solution properties of quinizarin2015In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 17, no 21, 3985-3997 p.Article in journal (Refereed)
    Abstract [en]

    Polymorphism, crystal shape and solubility of 1,4-dihydroxyanthraquinone (quinizarin) have been investigated in acetic acid, acetone, acetonitrile, n-butanol and toluene. The solubility of FI and FII from 20 degrees C to 45 degrees C has been determined by a gravimetric method. By slow evaporation, pure FI was obtained from n-butanol and toluene, pure FII was obtained from acetone, while either a mixture of the two forms or pure FI was obtained from acetic acid and acetonitrile. Slurry conversion experiments have established an enantiotropic relationship between the two polymorphs and that the commercially available FI is actually a metastable polymorph of quinizarin under ambient conditions. However, in the absence of FII, FI is kinetically stable for many days over the temperature range and in the solvents investigated. FI and FII have been characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission and ordinary powder X-ray diffraction (PXRD) at different temperatures. The crystal structure of FII has been determined by single-crystal XRD. DSC and high-temperature PXRD have shown that both FI and FII will transform into a not previously reported hightemperature form (FIII) around 185 degrees C before this form melts at 200-202 degrees C. By indexing FIII PXRD data, a triclinic P (1) over bar cell was assigned to FIII. The solubility of quinizarin FI and FII in the pure organic solvents used in the present work is below 2.5% by weight and decreases in the order: toluene, acetone, acetic acid, acetonitrile and n-butanol. The crystal shapes obtained in different solvents range from thin rods to flat plates or very flat leaves, with no clear principal difference observed between FI and FII.

  • 2.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    4-aminophenylacetic acid2005In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 61, no 6, O1536-O1537 p.Article in journal (Refereed)
    Abstract [en]

    Crystals of the title compound, C8H9NO2, were obtained from ethyl acetate. The structure consists of the acid in its zwitterionic form. In the crystal structure, each molecule interacts through strong N-H center dot center dot center dot O hydrogen bonds with six adjacent molecules, yielding a three-dimensional network.

  • 3. Jia, L.
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Crystal Growth of Salicylic Acid in Organic Solvents2017In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 17, no 6, 2964-2974 p.Article in journal (Refereed)
    Abstract [en]

    The crystal growth rate of salicylic acid has been determined by seeded isothermal desupersaturation experiments in different organic solvents (methanol, acetone, ethyl acetate, and acetonitrile) and at different temperatures (10, 15, 20, and 25 °C). In situ ATR-FTIR spectroscopy and principal component analysis (PCA) were employed for the determination of solution concentration. Activity coefficient ratios are approximately accounted for in the driving force determination. The results show that the dependence of the growth rate on the solvent at equal driving force varies with temperature; e.g., at 25 °C, the growth rate is highest in ethyl acetate and lowest in acetonitrile, while at 15 °C the growth rate is highest in acetonitrile. The growth rate data are further examined within the Burton Cabrera Franck (BCF) and the Birth and Spread (B+S) theories, and the results point to the importance of the surface diffusion step. Interfacial energies determined by fitting the B+S model to the growth rate data are well-correlated to interfacial energies previously determined from primary nucleation data.

  • 4. Kuhs, Manuel
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. SSPC, University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Thermodynamics of fenoxycarb in solution2013In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 66, 50-58 p.Article in journal (Refereed)
    Abstract [en]

    The solubility of fenoxycarb has been determined between 278 and 318 K in several organic solvents. The solid phase at equilibrium and some indication of polymorphism has been properly examined by powder XRD, DSC, Raman and ATR-FTIR spectroscopy, solution H-1 NMR and SEM. Using literature data the activity of the solid phase within a Raoult's law definition has been calculated, based on which solution activity coefficients have been estimated. In ethyl acetate, the van't Hoff enthalpy of solution is constant over the temperature range and equals the melting enthalpy. However, it is shown that the solution is slightly non-ideal with the heat capacity difference term compensating for the activity coefficient term. In toluene, the van't Hoff enthalpy of solution is constant as well but clearly higher than the melting enthalpy. In methanol, ethanol and isopropanol, van Hoff curves are strongly non-linear, the slope however clearly approaching the melting enthalpy at higher temperatures. In all solvents, positive deviations from Raoult's law are prevailing. The activity coefficients follow a decreasing order of isopropanol > ethanol > methanol > toluene > ethyl acetate, and in all solvents decrease monotonically with increasing temperature. The highest activity coefficient is about 18 corresponding to about 2.5 kJ/mol of deviation from ideality.

  • 5.
    Liu, Jin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Hippen, Perschia
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Solubility and Crystal Nucleation in Organic Solvents of Two Polymorphs of Curcumin2015In: Journal of Pharmaceutical Sciences, ISSN 0022-3549, E-ISSN 1520-6017, Vol. 104, no 7, 2183-9 p.Article in journal (Refereed)
    Abstract [en]

    Two crystal polymorphs of 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) have been obtained by crystallization from ethanol (EtOH) solution. The polymorphs have been characterized by differential scanning calorimetry, infrared spectroscopy, and X-ray powder diffraction and shown to be the previously described forms I and III. The solubility of both polymorphs in EtOH and of one polymorph in ethyl acetate (EA) has been measured between 10°C and 50°C with a gravimetric method. Primary nucleation of curcumin from EtOH solution has been investigated in 520 constant temperature crystallization experiments in sealed, magnetically stirred vials under different conditions of supersaturation, temperature, and agitation rate. By a thermodynamic analysis of the melting data and solubility of form I, the solid-state activity is estimated from 10°C up to the melting point. The solubility is lower in EtOH than in EA, and in both solvents, a positive deviation from Raoult's law is observed. Form I has lower solubility than form III and is accordingly thermodynamically more stable over the investigated temperature interval. Extrapolation of solubility regression models indicates that there should be a low-temperature enantiotropic transition point, below which form I will be metastable. By slurry conversion experiments, it is established that this temperature is below -30°C. All nucleation experiments resulted in the stable form I. The induction time is observed to decrease with increasing agitation rate up to a certain point, and then increase with further increasing agitation rate; a trend previously observed for other compounds. By correlating the induction time data obtained at different supersaturation and temperature, the interfacial energy of form I in EtOH is estimated to be 3.0 mJ/m(2) . 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:2183-2189, 2015.

  • 6.
    Liu, Jin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland .
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland .
    Influence of agitation and fluid shear on nucleation of m-Hydroxybenzoic acid polymorphs2014In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 11, 5521-5531 p.Article in journal (Refereed)
    Abstract [en]

    The influence of agitation and fluid shear on nucleation of m-hydroxybenzoic acid polymorphs from 1-propanol solution has been investigated through 1160 cooling crystallization experiments. The induction time has been measured at different supersaturations and temperatures in two different crystallizer setups: small vials agitated by magnetic stir bars, for which experiments were repeated 4080 times, and a rotating cylinder apparatus, for which each experiment was repeated five times. The nucleating polymorph has in each case been identified by FTIR spectroscopy. At high thermodynamic driving force for nucleation, only the metastable polymorph (form II) was obtained, while at low driving force both polymorphs were obtained. At equal driving force, a higher temperature resulted in a larger proportion of form I nucleations. The fluid dynamic conditions influence the induction time, as well as the polymorphic outcome. Experiments in small vials show that the agitation rate has a stronger influence on the induction time of form II compared to form I. The fraction of form I nucleations is significantly lower at intermediate agitation rates, coinciding with a reduced induction time of form II. In experiments in the rotating cylinder apparatus, the induction time is found to be inversely correlated to the shear rate. The difference in polymorphic outcome at different driving force is examined in terms of the ratio of the nucleation rates of the two polymorphs, calculated by classical nucleation theory using determined values of the pre-exponential factor and interfacial energy for each polymorph. A possible mechanism explaining the difference in the influence of fluid dynamics on the nucleation of the two polymorphs is based on differences between the two crystal structures. It is hypothesized that the layered structure of form II is comparatively more sensitive to changes in shear flow conditions than the more isotropic form I structure.

  • 7.
    Liu, Jin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Influence of Agitation on Primary Nucleation in Stirred Tank Crystallizers2015In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 15, no 9, 4177-4184 p.Article in journal (Refereed)
    Abstract [en]

    The influence of agitation on nucleation of butyl paraben and m-hydroxybenzoic acid polymorphs has been investigated through 330 cooling crystallization experiments. The induction time has been measured at different supersaturations and temperatures in three parallel jacketed vessels equipped with different overhead stirring agitators. In each case, the nucleating polymorph of m-hydroxybenzoic acid has been identified by infrared spectroscopy. The influences of agitation rate, impeller type, impeller diameter, impeller to bottom clearance, and the use of baffles have been investigated. A general trend in all of the experiments is that the induction time decreases with increasing agitation rate. Across all experiments with different fluid mechanics for the butyl paraben system, the induction time is correlated to the average energy dissipation rate raised to the power -0.3. It is shown that this dependence is consistent with a turbulent flow enhanced cluster coalescence mechanism. In experiments with m-hydroxybenzoic acid, the metastable form II was always obtained at higher nucleation driving force while both polymorphs were obtained at lower driving force. In the latter case, form I was obtained in the majority of experiments at low agitation rate (100 rpm) while form II was obtained in all experiments at higher agitation rate (>= 300 rpm).

  • 8. Mealey, Donal
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Castletroy, Ireland .
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Castletroy, Ireland .
    Thermodynamics of risperidone and solubility in pure organic solvents2014In: Fluid Phase Equilibria, ISSN 0378-3812, E-ISSN 1879-0224, Vol. 375, 73-79 p.Article in journal (Refereed)
    Abstract [en]

    The solid-liquid solubility of the thermodynamically stable form I of the drug risperidone has been determined by a gravimetric method in nine pure organic solvents in the temperature range 278.15-323.15 K. The melting temperature and associated enthalpy of fusion of risperidone form I has been determined by differential scanning calorimetry (DSC) to be 442.38 K and 43.94 kJ mol(-1), respectively. The heat capacity of the solid form I and the melt have been determined over a range of temperatures by temperature-modulated DSC, and extrapolated data has been used to calculate the Gibbs energy, enthalpy and entropy of fusion from ambient temperature up to the melting point. The ideal solubility within a Raoult's law framework is obtained from the Gibbs energy of fusion, and the solution activity coefficient at equilibrium in the nine solvents quantified. Solutions in all solvents exhibit positive deviation from Raoult's law, with the highest solubility (closest to ideality) in toluene, an aprotic apolar solvent. The solubility curves plotted in a van't Hoff graph show non-linear behaviour and are well-approximated by a second order polynomial.

  • 9. Nordström, Fredrik L
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Malmberg, Baldur
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Influence of Solution Thermal and Structural History on the Nucleation of m-Hydroxybenzoic Acid Polymorphs2012In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 9, 4340-4348 p.Article in journal (Refereed)
    Abstract [en]

    The influence of solution pretreatment on primary nucleation of m-hydroxybenzoic acid has been investigated through 550 cooling crystallization experiments. The metastable zone width has been determined at constant cooling rate, and the time and temperature of the preceding superheating step have been varied. m-Hydroxybenzoic acid has two polymorphs, and the influence of the polymorph used to prepare the solutions has also been investigated. There is an overall tendency in the experiments for the solution to exhibit a larger metastable zone width if it is superheated for a longer time and at a higher temperature, but under the investigated conditions this tendency is not very strong. The results show that the metastable form II preferentially crystallizes in all experiments and in particular when the solution has been more strongly superheated for several hours. However, when the time and/or the temperature of superheating is reduced, there is an increasing tendency to obtain the stable form I. This is most clearly found for solutions prepared by dissolving form I. When the solutions are prepared by dissolution of form II, this tendency is weaker in what appears to be a systematic way. It is hypothesized that, unless the solution is strongly superheated for several hours, it will contain for a significant period of time clusters of solute molecules that can retain some degree of structure from the dissolved crystal. This leads to "memory" effects in the solution, which may influence subsequent nucleation. The work includes a comprehensive review of previous published work on the influence of thermal history on nucleation in solutions and melts.

  • 10. Nordström, Fredrik L.
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Primary nucleation of salicylamide: the influence of process conditions and solvent on the metastable zone width2013In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 36, 7285-7297 p.Article in journal (Refereed)
    Abstract [en]

    The onset of nucleation of salicylamide in organic solvents has been measured for a total of 2911 nucleation experiments at a constant cooling rate. The experiments are divided into series of different experimental conditions and for each series, the mean values and distributions of the nucleation events have been recorded. Generally, a significant spread in the onset of nucleation among identical repeated experiments was observed. The solvent and the cooling rate were found to be the factors exerting the greatest influence on the onset of nucleation, whereas the expected effects of the solution volume and the saturation temperature were largely absent. A correlation is observed between the supersaturation ratio at the average onset of nucleation and a group of parameters extracted from the pre-exponential factor in the classical nucleation rate equation, which is in agreement with the concept that a higher attachment frequency facilitates nucleation. It is also found that there can be a profound difference in the metastable zone width between experiments in open and closed crystallizers.

  • 11.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Crystal Polymorphism of Substituted Monocyclic Aromatics2009Licentiate thesis, comprehensive summary (Other academic)
  • 12.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Structural, Kinetic and Thermodynamic Aspects of the Crystal Polymorphism of Substituted Monocyclic Aromatic Compounds2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work concerns the interrelationship between thermodynamic, kinetic and structural aspects of crystal polymorphism. It is both experimental and theoretical, and limited with respect to compounds to substituted monocyclic aromatics.

    Two polymorphs of the compound m-aminobenzoic acid have been experimentally isolated and characterized by ATR-FTIR spectroscopy, X-ray powder diffraction and optical microscopy. In addition, two polymorphs of the compound m-hydroxybenzoic acid have been isolated and characterized by ATR-FTIR spectroscopy, high-temperature XRPD, confocal Raman, hot-stage and scanning electron microscopy. For all polymorphs, melting properties and specific heat capacity have been determined calorimetrically, and the solubility in several pure solvents measured at different temperatures with a gravimetric method. The solid-state activity (ideal solubility), and the free energy, enthalpy and entropy of fusion have been determined as functions of temperature for all solid phases through a thermodynamic analysis of multiple experimental data. It is shown that m-aminobenzoic acid is an enantiotropic system, with a stability transition point determined to be located at approximately 156°C, and that the difference in free energy at room temperature between the polymorphs is considerable. It is further shown that m-hydroxybenzoic acid is a monotropic system, with minor differences in free energy, enthalpy and entropy.

    1393 primary nucleation experiments have been carried out for both compounds in different series of repeatability experiments, differing with respect to solvent, cooling rate, saturation temperature and solution preparation and pre-treatment. It is found that in the vast majority of experiments, either the stable or the metastable polymorph is obtained in the pure form, and only for a few evaluated experimental conditions does one polymorph crystallize in all experiments. The fact that the polymorphic outcome of a crystallization is the result of the interplay between relative thermodynamic stability and nucleation kinetics, and that it is vital to perform multiple experiments under identical conditions when studying nucleation of polymorphic compounds, is strongly emphasized by the results of this work.

    The main experimental variable which in this work has been found to affect which polymorph will preferentially crystallize is the solvent. For m-aminobenzoic acid, it is shown how a significantly metastable polymorph can be obtained by choosing a solvent in which nucleation of the stable form is sufficiently obstructed. For m-hydroxybenzoic acid, nucleation of the stable polymorph is promoted in solvents where the solubility is high. It is shown how this partly can be rationalized by analysing solubility data with respect to temperature dependence.

    By crystallizing solutions differing only with respect to pre-treatment and which polymorph was dissolved, it is found that the immediate thermal and structural history of a solution can have a significant effect on nucleation, affecting the predisposition for overall nucleation as well as which polymorph will preferentially crystallize.

    A set of polymorphic crystal structures has been compiled from the Cambridge Structural Database. It is found that statistically, about 50% crystallize in the crystallographic space group P21/c. Furthermore, it is found that crystal structures of polymorphs tend to differ significantly with respect to either hydrogen bond network or molecular conformation.

    Molecular mechanics based Monte Carlo simulated annealing has been used to sample different potential crystal structures corresponding to minima in potential energy with respect to structural degrees of freedom, restricted to one space group, for each of the polymorphic compounds. It is found that all simulations result in very large numbers of predicted structures. About 15% of the predicted structures have excess relative lattice energies of <=10% compared to the most stable predicted structure; a limit verified to reflect maximum lattice energy differences between experimentally observed polymorphs of similar compounds. The number of predicted structures is found to correlate to molecular weight and to the number of rotatable covalent bonds. A close study of two compounds has shown that predicted structures tend to belong to different groups defined by unique hydrogen bond networks, located in well-defined regions in energy/packing space according to the close-packing principle. It is hypothesized that kinetic effects in combination with this structural segregation might affect the number of potential structures that can be realized experimentally.

    The experimentally determined crystal structures of several compounds have been geometry-optimized (relaxed) to the nearest potential energy minimum using ten different combinations of common potential energy functions (force fields) and techniques for assigning nucleus-centred point charges used in the electrostatic description of the energy. Changes in structural coordinates upon relaxation have been quantified, crystal lattice energies calculated and compared with experimentally determined enthalpies of sublimation, and the energy difference before and after relaxation computed and analysed. It is found that certain combinations of force fields and charge assignment techniques work reasonably well for modelling crystal structures of small aromatics, provided that proper attention is paid to electrostatic description and to how the force field was parameterized.

    A comparison of energy differences for randomly packed as well as experimentally determined crystal structures before and after relaxation suggests that the potential energy function for the solid state of a small organic molecule is highly undulating with many deep, narrow and steep minima.

  • 13.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Gracin, Sandra
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Oiling out or molten hydrate-liquid-liquid phase separation in the system vanillin-water2007In: Journal of Pharmaceutical Sciences, ISSN 0022-3549, E-ISSN 1520-6017, Vol. 96, no 9, 2390-2398 p.Article in journal (Refereed)
    Abstract [en]

    Vanillin crystals in a saturated aqueous solution disappear and a second liquid phase emerges when the temperature is raised above 51 degrees C. The phenomenon has been investigated with crystallization and equilibration experiments, using DSC, TGA, XRD and hot-stage microscopy for analysis. The new liquid solidifies on cooling, appears to melt at 51 degrees C, and has a composition corresponding to a dihydrate. However, no solid hydrate can be detected by XRD, and it is shown that the true explanation is that a liquid-liquid phase separation occurs above 51 degrees C where the vanillin-rich phase has a composition close to a dihydrate. To our knowledge, liquid-liquid phase separation has not previously been reported for the system vanillin-water, even though thousands of tonnes of vanillin are produced globally every year.

  • 14.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Hjorth, Timothy
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Bohlin, Martin
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Calorimetric Properties and Solubility in Five Pure Organic Solvents of N-Methyl-D-Glucamine (Meglumine)2016In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 61, no 3, 1199-1204 p.Article in journal (Refereed)
    Abstract [en]

    The solid liquid solubility of the title compound has been measured by a gravimetric method in five pure organic solvents over the temperature range (283 to 323) K. The melting temperature and associated enthalpy of fusion have been determined by differential scanning calorimetry (DSC), and the heat capacity of the solid and the melt have been determined over a range of temperatures by means of temperature-modulated DSC. Melting data and the extrapolated difference in heat capacity between the melt and the solid have been used to calculate the Gibbs energy, enthalpy, and entropy of fusion and the ideal solubility from below ambient temperature to the melting point. On the basis of estimated activity coefficients at equilibrium, solutions in all the five solvents are shown to exhibit positive deviation from Raoult's law. The highest mole fraction solubility is observed in methanol, and all van't Hoff solubility curves are nonlinear. Solubility data is well correlated by a recently proposed semiempirical regression model.

  • 15.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Nordström, Fredrik L.
    Hoffmann, Eva-Maria
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Aziz, Baroz
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. Department of Chemical and Environmental Science, Solid State Pharmaceutical Cluster, Materials and Surface Science Institute, University of Limerick, Ireland .
    Thermodynamics and nucleation of the enantiotropic compound p-aminobenzoic acid2013In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 25, 5020-5031 p.Article in journal (Refereed)
    Abstract [en]

    In this work, the thermodynamic interrelationship of the two known polymorphs of p-aminobenzoic acid has been explored, and primary nucleation in different organic solvents investigated. The solubility of both polymorphs in several solvents at different temperatures has been determined and the isobaric solid-state heat capacities have been measured by DSC. The transition temperature below which form α is metastable is estimated to be 16°C by interpolation of solubility data and the melting temperature of form β is estimated to be 140°C by extrapolation of solubility data. Using experimental calorimetry and solubility data the thermodynamic stability relationship between the two polymorphs has been estimated at room temperature to the melting point. At the transition temperature, the estimated enthalpy difference between the polymorphs is 2.84 kJ mol-1 and the entropy difference is 9.80 J mol-1 K-1. At the estimated melting point of form β the difference in Gibbs free energy and enthalpy is 1.6 kJ mol-1 and 5.0 kJ mol-1, respectively. It is found that the entropic contribution to the free energy difference is relatively high, which explains the unusually low transition temperature. A total of 330 nucleation experiments have been performed, with constant cooling rate in three different solvents and with different saturation temperatures, and multiple experiments have been carried out for each set of conditions in order to obtain statistically significant results. All performed experiments resulted in the crystallization of the high-temperature stable α-polymorph, which is kinetically favoured under all evaluated experimental conditions. The thermodynamic driving force required for nucleation is found to depend chiefly on the solvent, and to be inversely correlated to both solvent polarity and to solubility.

  • 16.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Nordström, Fredrik L.
    Jasnobulka, Tanja
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Thermodynamics and Nucleation Kinetics of m-Aminobenzoic Acid Polymorphs2010In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 1, 195-204 p.Article in journal (Refereed)
    Abstract [en]

    The polymorphism of m-aminobenzoic acid has been investigated. Two polymorphs have been identified and characterized by X-ray powder diffraction (XRPD), Fourier transform IR (FTIR), microscopy, and thermal analysis. The melting properties and isobaric heat capacities of both polymorphs have been determined calorimetrically, and the solubility of each polymorph in several solvents at different temperatures has been determined gravimetrically. The solid-state activity (i.e., the Gibbs free energy of fusion) of each polymorph has been determined through a comprehensive thermodynamic analysis based on experimental data. It is found that the polymorphs are enantiotropically related, with a stability transition temperature of 156.1 °0C. The published crystal structure belongs to the polymorph that is metastable at room temperature. Energytemperature diagrams of both polymorphs have been established by determining the free energy, enthalpy, and entropy of fusion as a function of temperature. A total of 300 cooling crystallizations have been carried out at constant cooling rate using different saturation temperatures and solvents, and the visible onset of primary nucleation was recorded. The results show that for this substance the polymorph that will nucleate depends chiefly on the solvent. In water and methanol solutions, the stable form I was obtained in all experiments, whereas in acetonitrile, a majority of nucleation experiments resulted in the isolation of the metastable form II. It is shown how this can be rationalized by analysis of solubility, solution speciation, and nucleation relationships. The importance of carrying out multiple experiments at identical conditions in nucleation studies of polymorphic systems is demonstrated.

  • 17.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Thermodynamics and Nucleation of m-Hydroxybenzoic Acid Polymorphs in Pure SolventsManuscript (preprint) (Other academic)
  • 18.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Force Fields and Point Charges for Crystal Structure Modeling2009In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 48, no 6, 2899-2912 p.Article in journal (Refereed)
    Abstract [en]

    Molecular simulation is increasingly used by chemical engineers and industrial chemists in process and product development. In particular, the possibility to predict the structure and stability of potential polymorphs of a substance is of tremendous interest to the pharmaceutical and specialty chemicals industry. Molecular mechanics modeling relies on the use of parametrized force fields and methods of assigning point charges to the atoms in the molecules. In commercial molecular simulation software, a wide variety of such combinations are available, and there is a need for critical assessment of the capabilities of the different alternatives. In the present work, the performance of several molecular mechanics force fields combined with different methods for the assignment of atomic point charges have been examined with regard to their ability to calculate absolute crystal lattice energies and their capacity to identify the experimental structure as a minimum on the potential energy hypersurface. Seven small, aromatic monomolecular crystalline compounds are used in the evaluation. It is found that the majority of the examined methods cannot be used to reliably predict absolute lattice energies. The most promising results were obtained with the Pcff force field using integral charges, and the Dreiding force field using Gasteiger charges, both of which performed with an accuracy of the same order of magnitude as the variations in experimental lattice energies. Overall, it has been observed that the best results are achieved if the same force field method is used to relax the crystal structure and calculate the energy, and to optimize and calculate the energy of the gas phase molecule used for the correction for changes in molecular geometry. The Pcff and Compass force fields with integral charges have been found to predict relaxed structures closest to the experimental ones. In addition, five different methods for determining point charges fitted to the electrostatic potential (ESP charges), available in the same software, have been evaluated. For each method, the molecular geometries of 10 small, organic molecules were optimized, and ESP charges calculated and analyzed for linear correlation with a set of reference charges of an accepted standard method, HF/6-31G*. Dmol-3 gives charges that correlate well with the reference charge. The charges from Vamp are not linearly scalable to the HF/6-31G*-level, which is attributed partly to the geometry optimization but mainly to the calculation of the ESP and the subsequent charge fit.

  • 19.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    m-Hydroxybenzoic Acid: Quantifying Thermodynamic Stability and Influence of Solvent on the Nucleation of a Polymorphic System2013In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 13, no 3, 1140-1152 p.Article in journal (Refereed)
    Abstract [en]

    Nucleation of m-hydroxybenzoic acid crystals in different pure solvents has been investigated, and the thermodynamic interrelationship between two polymorphs was analyzed. The melting properties and specific heat capacities of both polymorphs have been determined by differential scanning calorimetry, and the solubility in several solvents at different temperatures was measured gravimetrically. Absolute values of the Gibbs free energy, enthalpy and entropy of fusion, and the activity of the polymorphs have been determined as functions of temperature. It is established that the polymorphs are monotropically related, with differences in enthalpy and Gibbs free energy of approximately 1 kJ/mol at room temperature. In a total of 539 nucleation experiments, in six solvents and with different cooling rates, the visible onset of nucleation was recorded and the nucleating polymorph was isolated. It is found that the degree of supersaturation required for nucleation and the polymorphic outcome depend strongly on the solvent. The metastable polymorph is kinetically favored under all evaluated experimental conditions, and for most of the conditions it is also statistically the most probable outcome. Nucleation of the stable polymorph is increasingly promoted in solvents of increasing solubility. It is shown how this can be rationalized by analysis of solubility and rate of supersaturation generation.

  • 20.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Molecular Simulations to Predict Experimental Polymorphs2008In: Proceedings of the 17th International Symposium on Industrial Crystallization / 8th Conference on Crystal Growth of Organic Materials (Maastricht, NL), 2008, 1631- p.Conference paper (Refereed)
  • 21.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. SSPC, University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. SSPC, University of Limerick, Ireland.
    (Solid + liquid) solubility of organic compounds in organic solvents: correlation and extrapolation2014In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 76, 124-133 p.Article in journal (Refereed)
    Abstract [en]

    A semi-empirical model is developed for the regression of solid-liquid solubility data with temperature. The model fulfils the required boundary conditions, allowing for robust extrapolation to higher and lower temperatures. The model combines a representation of the solid-state activity which accommodates a temperature-dependent heat capacity difference contribution with a scaled three-parameter Weibull function representing the temperature dependence of the solution activity coefficient at equilibrium. Evaluation of the model is based on previously published experimental calorimetric and solubility data of four organic compounds, fenoxycarb, fenofibrate, risperidone and butyl paraben, in five common organic solvents, methanol, ethyl acetate, acetone, acetonitrile, and toluene. The temperature dependence of the van’t Hoff enthalpy of solution and its components is analysed and discussed. Among the four compounds the influence of temperature on the enthalpy of fusion varies from moderate to substantial. Based on the semi-empirical model, a new equation containing three adjustable parameters is proposed for regression and extrapolation of solubility data for cases when only melting data and solubility data is available. The equation is shown to provide good accuracy and robustness when evaluated against the full semi-empirical model as well as against commonly used, more simple empirical equations. It is shown how such a model can be used to obtain an estimate of the heat capacity difference for cases where accurate solubility data is available in multiple solvents.

  • 22.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Structural and energetic aspects of the differences between real and predicted polymorphs2010In: Crystal research and technology (1981), ISSN 0232-1300, E-ISSN 1521-4079, Vol. 45, no 8, 867-878 p.Article in journal (Refereed)
    Abstract [en]

    In crystal structure prediction simulations based on lattice energy minimization, usually hundreds of structures within a reasonable range of lattice energy and density are found, whereas in practice, it is very rare to find more than a few polymorphs of the same compound. In the work presented here, this discrepancy is investigated from a structural and energetic point of view. 56 crystal structures of 26 polymorphic mono- and disubstituted aromatic compounds, extracted from the Cambridge Structural Database, have been analysed with respect to inter-polymorphic structural similarity. For comparison, potential crystal packing arrangements of the substances have been predicted with molecular mechanics simulations using a generic force field. The predicted structures are analysed with respect to structural features and similarity, and with respect to the number of structures and their lattice energy. It is found that the real polymorphs studied in this work tend to be structurally quite dissimilar with regard to hydrogen bonding and spatial packing of structural motifs, while many of the predicted structures of a given compound are very similar to each other. The results suggest that structure and lattice energy alone cannot explain why so few polymorphs are found in practice compared to the very large numbers predicted in simulations.

  • 23.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Valavi, Masood
    Khamar, Dikshitkumar
    Kuhs, Manuel
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Thermodynamic Stability Analysis of Tolbutamide Polymorphs and Solubility in Organic Solvents2016In: Journal of Pharmaceutical Sciences, ISSN 0022-3549, E-ISSN 1520-6017, Vol. 105, no 6, 1901-1906 p.Article in journal (Refereed)
    Abstract [en]

    Melting temperatures and enthalpies of fusion have been determined by differential scanning calorimetry (DSC) for 2 polymorphs of the drug tolbutamide: FIH and FV. Heat capacities have been determined by temperature-modulated DSC for 4 polymorphs: FIL, FIH, FII, FV, and for the supercooled melt. The enthalpy of fusion of FII at its melting point has been estimated from the enthalpy of transition of FII into FIH through a thermodynamic cycle. Calorimetric data have been used to derive a quantitative polymorphic stability relationship between these 4 polymorphs, showing that FII is the stable polymorph below approximately 333 K, above which temperature FIH is the stable form up to its melting point. The relative stability of FV is well below the other polymorphs. The previously reported kinetic reversibility of the transformation between FIL and FIH has been verified using in situ Raman spectroscopy. The solid-liquid solubility of FII has been gravimetrically determined in 5 pure organic solvents ( methanol, 1-propanol, ethyl acetate, acetonitrile, and toluene) over the temperature range 278 to 323 K. The ideal solubility has been estimated from calorimetric data, and solution activity coefficients at saturation in the 5 solvents determined. All solutions show positive deviation from Raoult's law, and all van't Hoff plots of solubility data are nonlinear. The solubility in toluene is well below that observed in the other investigated solvents. Solubility data have been correlated and extrapolated to the melting point using a semiempirical regression model.

  • 24.
    Valavi, Masood
    et al.
    University of Limerick, Ireland.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. University of Limerick, Ireland.
    Improving Estimates of the Crystallization Driving Force: Investigation into the Dependence on Temperature and Composition of Activity Coefficients in Solution2016In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 16, no 12, 6951-6960 p.Article in journal (Refereed)
    Abstract [en]

    The influence of temperature and composition on solution activity coefficients has been investigated. Under most conditions, the temperature dependence of the activity coefficient is much weaker than the composition dependence. A novel and more accurate approach to estimate crystallization driving forces is proposed, where, rather than neglecting the activity coefficient ratio, it can be estimated from solid−liquid equilibrium data.

  • 25. Valavi, Masood
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology. University of Limerick, Ireland.
    Prediction of the Solubility of Medium-Sized Pharmaceutical Compounds Using a Temperature-Dependent NRTL-SAC Model2016In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 55, no 42, 11150-11159 p.Article in journal (Refereed)
    Abstract [en]

    In this work, the NRTL-SAC and the Pharma UNIFAC models are evaluated with respect to the capability of prediction of solid liquid equilibria of pharmaceutical compounds in organic solvents. The original NRTL-SAC model is extended through the introduction of temperature-dependent binary interaction parameters, and the two versions of the model are parametrized using vapor liquid equilibrium (VLE) data. The performance of the NRTL-SAC models for correlation and prediction of the solubility of eight medium-sized flexible pharmaceutical or pharmaceutically similar molecules in multiple pure, organic solvents is examined: risperidone, fenofibrate, fenoxycarb, tolbutamide, meglumine, butyl paraben, butamben, and salicylamide. The performance of the Pharma UNIFAC model is evaluated using data for six of these compounds. In general, it is found that introducing a dependence on temperature to the binary interaction parameters of the NRTL-SAC model can improve its capability for modeling and prediction of the solubility of active pharmaceutical ingredients. For prediction of solubility data the Pharma UNIFAC model generally performs below the two NRTL-SAC models. Averaged over all evaluated systems where the solubility was predicted with each method, values of the root mean squared logarithmic error (RMSLE) in predicted mole fraction solubility obtained for Pharma UNIFAC (30 systems) and for the original and the modified temperature-dependent forms of the NRTL-SAC model (29 systems) are 1.64, 1.17, and 1.09, respectively. Comparing only those systems for which all models were evaluated (18 systems), the RMSLE values are 1.42, 1.06, and 0.87, respectively.

  • 26. Watterson, Samuel
    et al.
    Hudson, Sarah
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. SSPC, University of Limerick, Ireland.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Thermodynamics of fenofibrate and solubility in pure organic solvents2014In: Fluid Phase Equilibria, ISSN 0378-3812, E-ISSN 1879-0224, Vol. 367, 143-150 p.Article in journal (Refereed)
    Abstract [en]

    Calorimetric data on the melting of 1-methylethyl 2-[4-(4-chlorobenzoyl)-phenoxyl-2-methylpropanoate (fenofibrate) and the heat capacity of the solid and the melt have been determined, from which the Gibbs energy, enthalpy and entropy of fusion are calculated. Solid-liquid solubility data have been collected by a gravimetric method in seven pure solvents (methanol, ethanol, 1-propanol, 2-propanol, ethyl acetate, acetonitrile, and acetone) across a range of temperatures. Fenofibrate is much more soluble in ethyl acetate, acetonitrile and acetone compared to alcohols. In the alcohols the solubility increases with aliphatic chain length. The Gibbs energy of fusion is used to estimate the activity of the solid within a Raoult's law framework. Except for ethyl acetate solutions which are almost ideal, solutions in all evaluated solvents exhibit positive deviation from Raoult's law, and in the alcohols the activity coefficient ranges up to 25. It is shown that the heat capacity component of the enthalpy of fusion is not negligible at room temperature, in spite of the proximity to the melting point, and furthermore that the temperature dependence of the activity coefficient in the saturated solution has a governing influence on the van't Hoff enthalpy of solution in acetonitrile and the alcohols. Crystals obtained by two different methods from a range of solvents have been analysed by PXRD, FTIR and NMR spectroscopy, TGA and DSC, and have in all cases been shown to consist of the stable polymorph (form l).

  • 27.
    Yang, Huaiyu
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. Strathclyde Institute of Pharmacy and Pharmaceutical Sciences, University of Strathclyde3, United Kingdom .
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. Department of Chemical and Environmental Science, Materials and Surface Science Institute, University of Limerick, Ireland .
    Zeglinski, Jacek
    Rasmuson, Åke
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. Department of Chemical and Environmental Science, Materials and Surface Science Institute, University of Limerick, Ireland .
    Influence of Solvent and Solid-State Structure on Nucleation of Parabens2014In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 8, 3890-3902 p.Article in journal (Refereed)
    Abstract [en]

    In the present work, the induction time for nucleation of ethyl paraben (EP) and propyl paraben (PP) in ethanol, ethyl acetate, and acetone has been measured at different levels of supersaturation. The induction time shows a wide variation among repeat experiments, indicative of the stochastic nature of nucleation. The solid-liquid interfacial energy and the size of the critical nucleus have been determined according to the classical nucleation theory. Combined with previous results for butyl paraben (BP), the nucleation behavior is analyzed with respect to differences in the solid phase of the three pure compounds, and with respect to differences in the solution. The results indicate that the difficulty of nucleation in ethanol and acetone increases in the order BP < PP < EP but is approximately the same in ethyl acetate. For each of the three parabens, the difficulty of nucleation increases in the order acetone < ethyl acetate < ethanol. The Gibbs energy of melting increases in the order BP < PP < EP, but the crystal structures are quite similar resulting in the basic crystal shape being very much the same. The solid-liquid interfacial energy is reasonably well correlated to the solvation energy, and even better correlated to the deformation energy, of the solute molecule within the first solvation shell as obtained by density functional theory calculations.

  • 28. Zeglinski, Jacek
    et al.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Karpinska, Jolanta
    Kuhs, Manuel
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena. University of Limerick, Ireland.
    Analysis of the structure and morphology of fenoxycarb crystals2014In: Journal of Molecular Graphics and Modelling, ISSN 1093-3263, E-ISSN 1873-4243, Vol. 53, 92-99 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, we have explored the relationship between surface structure and crystal growth and morphology of fenoxycarb (FC). Experimental vs. predicted morphologies/face indices of fenoxycarb crystals are presented. Atomic-scale surface structures of the crystalline particles, derived from experimentally indexed single crystals, are also modelled. Single crystals of fenoxycarb exhibit a platelet-like morphology which closely matches predicted morphologies. The solvent choice does not significantly influence either morphology or crystal habit. The crystal morphology is dominated by the {0 0 1} faces, featuring weakly interacting aliphatic or aromatic groups at their surfaces. Two distinct modes of interaction of a FC molecule in the crystal can be observed, which appear to be principal factors governing the microscopic shape of the crystal: the relatively strong collateral and the much weaker perpendicular bonding. Both forcefield-based and quantum-chemical calculations predict that the aromatic and aliphatic terminated {0 0 1} faces have comparably high stability as a consequence of weak intermolecular bonding. Thus we predict that the most developed {0 0 1} surfaces of fenoxycarb crystals should be terminated randomly, favouring neither aliphatic nor aromatic termination.

1 - 28 of 28
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