The solute-rich mesoscopic precursors of crystal nuclei of olanzapine solid forms

Olanzapine (OZPN) is a BCS class II drug used to treat schizophrenia (bipolar disorder). OZPN exhibits rich solid-state diversity. To date, 60 distinct forms have been identified, including 3 polymorphs (I, II, III), 52 crystalline solvates, 3 dihydrates (DB, DD, DE), a disordered higher hydrate, plus an amorphous form. Atomic Force Microscopy (AFM) results suggest that the nucleation of OZPN DD on the surface of OZPN I in water may follow a non-classical mechanisms that includes formation of solute-rich mesoscopic clusters [1]. Since the solubility of OZPN I in water is very low, the kinetics of transformation are difficult to monitor. To increase the solubility of OZPN I, we added different ratios of a co-solvent, ethanol. AFM observations revealed that clusters similar to those seen in purely aqueous environments are present on the surface of OZPN:EtOH:H2O crystals in contact with both supersaturated and undersaturated EtOH/H2O solutions. To establish the mechanism of cluster formation, we monitored the dependence of the cluster size and volume fraction on time, OZPN concentration, and co-solvent concentration using Brownian Microscopy (BM). The characteristics of the cluster population were correlated with the standard enthalpy, entropy and free energy of crystallization obtained from temperature dependence of the solubility of OZPN:EtOH:H2O crystals. We verified, using small angle x-ray scattering, that the crystal form was preserved at all solvent compositions. We observed that the cluster radius was constant, at R ≈ 37 nm, in all solvent compositions tested and at all times. The volume of the cluster population φ mapped the non-monotonic dependence of the crystallization enthalpy on the EtOH content, indicating that φ is determined by the thermodynamics of the solute-solvent interactions. The decoupled behaviour of R suggests that, in contrast to φ, the cluster size is kinetically determined. These conclusions comply with the prediction of a model of mesoscopic solvent rich clusters, based on formation of transient solute oligomers in the solutions [3]. These are the first observations of solute-rich clusters in solutions of pharmaceutically active compounds and of their role in the nucleation of crystals and the transformations between crystal forms. The suggested cluster formation mechanism may point to means to control these behaviours that are crucial for the properties of pharmaceutical preparations.  References:[1] M. Warzecha, R. Guo, R. M. Bhardwaj, S. M. Reutzel-Edens, S. L. Price, D. Lamprou and A. J. Florence, In preparation 2017.[2] Gebauer, D., Kellermeier, M., Gale, J. D., Bergström, L. & Cölfen, H. Pre-nucleation clusters as solute precursors in crystallisation. Chem. Soc. Rev. 2014, 43, 2348 [3] Vekilov, P. G. The two-step mechanism of nucleation of crystals in solution. Nanoscale, 2010, 2, 2346

Study on Nucleation Kinetics of Lysozyme Crystallization

The nucleation kinetics of hen egg-white lysozyme crystallization was investigated using a hot stage cooling crystallizer and a microscope to monitor the solution crystallization process in real time. Images of crystals were continuously recorded under varied precipitant and protein concentrations. The nucleation rate was found to be higher at higher precipitant concentration, and increase monotonically with protein concentration if the precipitant concentration was held constant. Attempt was made to interpret the experimental data using classical nucleation theory. It was found that the model predictions are lower than the experimental values at low supersaturations but agree well with experimental data at high supersaturations. The trends in the experimental data suggest that two nucleation mechanisms might co-exist: heterogeneous nucleation seeming to be the dominant at low supersaturation while at higher supersaturation homogeneous nucleation seeming to play the major role

Early Onset of Kinetic Roughening due to a Finite Step Width in Hematin Crystallization

The structure of the interface of a growing crystal with its nutrient phase largely determines the growth dynamics. We demonstrate that hematin crystals, crucial for the survival of malaria parasites, transition from faceted to rough growth interfaces at increasing thermodynamic supersaturation Δμ. Contrary to theoretical predictions and previous observations, this transition occurs at moderate values of Δμ. Moreover, surface roughness varies nonmonotonically with Δμ, and the rate constant for rough growth is slower than that resulting from nucleation and spreading of layers. We attribute these unexpected behaviors to the dynamics of step growth dominated by surface diffusion and the loss of identity of nuclei separated by less than the step width w. We put forth a general criterion for the onset of kinetic roughening using w as a critical length scale.National Institutes of Health (U.S.) (Grant 1R21AI126215-01)National Science Foundation (U.S.) (Grant DMR-1710354)United States. National Aeronautics and Space Administration (Grant NNX14AD68G)United States. National Aeronautics and Space Administration (Grant NNX14AE79G)Robert A. Welch Foundation (Grant E-1794

Morphological Instability of Steps During Crystal Growth from Solution Flow

It is shown that step moving to meet solution flow can be unstable against lateral perturbations. The instability of long-wavelength perturbations occurs at values of the solution flow intensity less than some critical value depending on the step velocity. At given intensity of the solution flow, the instability comes at the step velocity exceeding a critical velocity. Decay of short-wavelength fluctuations is conditioned by the line tension of the step. The step moving along the solution flow is laterally stable at all values of the step velocity and the intensity of the solution flow. The overlapping diffusion field of the neighbour steps suppresses the lateral instability but it gives an instability of the step train against doubling of the period, i.e. neighbouring steps are attracted. The equidistant train moving to meet the solution flow is stable against the period variations.Comment: 22 pages, REVTEX (will be appeared in Journal of Crystal Growth

Design rules for the self-assembly of a protein crystal

Theories of protein crystallization based on spheres that form close-packed crystals predict optimal assembly within a `slot' of second virial coefficients and enhanced assembly near the metastable liquid-vapor critical point. However, most protein crystals are open structures stabilized by anisotropic interactions. Here, we use theory and simulation to show that assembly of one such structure is not predicted by the second virial coefficient or enhanced by the critical point. Instead, good assembly requires that the thermodynamic driving force be on the order of the thermal energy and that interactions be made as nonspecific as possible without promoting liquid-vapor phase separation.Comment: 5 pages, 4 figure

Growth from Solutions: Kink dynamics, Stoichiometry, Face Kinetics and stability in turbulent flow

1. Kink dynamics. The first segment of a polygomized dislocation spiral step measured by AFM demonstrates up to 60% scattering in the critical length l*- the length when the segment starts to propagate. On orthorhombic lysozyme, this length is shorter than that the observed interkink distance. Step energy from the critical segment length based on the Gibbs-Thomson law (GTL), l* = 20(omega)alpha/(Delta)mu is several times larger than the energy from 2D nucleation rate. Here o is tine building block specific voiume, a is the step riser specific free energy, Delta(mu) is the crystallization driving force. These new data support our earlier assumption that the classical Frenkel, Burton -Cabrera-Frank concept of the abundant kink supply by fluctuations is not applicable for strongly polygonized steps. Step rate measurements on brushite confirms that statement. This is the1D nucleation of kinks that control step propagation. The GTL is valid only if l* <Dk/vk, the diffusion path of a kink that has diffusivity Dk and average growth velocity vk. This is equivalent to supersaturations sigma less than approx. alpha/2l*, where alpha is the building block size. For lysozyme, sigma much less than (1%). Conventionally used interstep distance generated by screw dislocation, 19(omega)alpha/Delta(mu) should be replaced by the very different real one, approx.4l*. 2. Stoichiometry. Kink, and thus step and face rates of a non-Kossel complex molecular monocomponent or any binary, AB, lattice was found theoretically to be proportional to 1/(zeta(sup 1/2) + zeta(sup - 1/2)), where zeta = [B]/[A] is the stoichiometry ratio in solution. The velocities reach maxima at zeta = 1. AFM studies of step rates on CaOxalate monohydrate (kidney stones) from aqueous solution was found to obey the law mentioned above. Generalization for more complex lattice will be discussed. 3. Turbulence. In agreement with theory, high precision in-situ laser interferometry of the (101) KDP crystal face shows step bunching if solution flows parallel to the step flow. The bunch height increases with the distance the bunch travels, i.e. with the face size. However, when the flow rate, u, increases, at u greater than approx. 1 m / s , the average step bunch height decreases as 1/u. The pheonomenon is attributed to the turbulent rather than laminar viscous boundary layer where diffusivity Dt = 0.5u(sub tau),y, i.e. increases linearly with the distance y from the solid face. Friction velocity, u(sub tau) approx. u(sup 7/8). Dramatically larger rate of the mass/heat transport within the turbulent, as compared to the laminar, viscous layer will be discussed

The low-density/high-density liquid phase transition for model globular proteins

The effect of molecule size (excluded volume) and the range of interaction on the surface tension, phase diagram and nucleation properties of a model globular protein is investigated using a combinations of Monte Carlo simulations and finite temperature classical Density Functional Theory calculations. We use a parametrized potential that can vary smoothly from the standard Lennard-Jones interaction characteristic of simple fluids, to the ten Wolde-Frenkel model for the effective interaction of globular proteins in solution. We find that the large excluded volume characteristic of large macromolecules such as proteins is the dominant effect in determining the liquid-vapor surface tension and nucleation properties. The variation of the range of the potential only appears important in the case of small excluded volumes such as for simple fluids. The DFT calculations are then used to study homogeneous nucleation of the high-density phase from the low-density phase including the nucleation barriers, nucleation pathways and the rate. It is found that the nucleation barriers are typically only a few $k_{B}T$ and that the nucleation rates substantially higher than would be predicted by Classical Nucleation Theory.Comment: To appear in Langmui

On temperature- and space-dimension dependent matter agglomeration in a mature growing stage

Model matter agglomerations, with temperature as leading control parameter, have been considered, and some of their characteristics have been studied. The primary interest has been focused on the grain volume fluctuations, the magnitude of which readily differentiates between two commonly encountered types of matter agglomeration/aggregation processes, observed roughly for high- and low-density matter organizations. The two distinguished types of matter arrangements have been described through the (entropic) potential driving system. The impact of the potential type on the character of matter agglomeration has been studied, preferentially for (low density) matter agglomeration for which a logarithmic measure of its speed has been proposed. A common diffusion as well as mechanical relaxation picture, emerging during the mature growing stage, has been drawn using a phenomenological line of argumentation. Applications, mostly towards obtaining soft agglomerates of so-called jammed materials, have been mentioned