Insight into the Nucleation Mechanism of p-Methoxybenzoic Acid in Ethanol-Water System from Metastable Zone Width

The metastable zone width (MSZW) of p-methoxybenzoic acid (PMBA) in an ethanol-water system was measured using the polythermal method. The nucleation order m obtained by the Nývlt’s model indicates the nucleation of PMBA following a progressive nucleation mechanism at low saturation temperature (m = 3.18–7.50) and an instantaneous nucleation mechanism at high saturation temperature (m = 1.46–2.55). Then, combined with the metastable zone experiment and the Sangwal model, we found that the MSZW and the interfacial energy reached the maximum when the mass fraction of ethanol was 0.8, which resulted in the smallest crystal product size. Meanwhile, the maximum rcrit and ΔGcrit obtained based on the modified Sangwal model indicating the PMBA needs to overcome a higher nucleation barrier in the ethanol mass fraction of 0.8. Finally, we proposed a preferential strategy for adjusting MSZW by correlating the interfacial energy with the change in ethanol mass fraction, saturation temperature, and cooling rate, respectively.

Effects of Various Inhibitors on the Nucleation of Calcium Oxalate in Synthetic Urine

A new synthetic urine was adopted in this work to study the nucleation kinetics of calcium oxalate using a batch crystallizer for various supersaturations at 37 °C. In the studied new synthetic urine, three additional components (urea, uric acid and creatinine) within the normal physiological ranges were added to the commonly-used synthetic urine to simulate human urine more closely. The interfacial energy for the nucleation of calcium oxalate was determined based on classical nucleation theory using the turbidity induction time measurements. The effects of various inhibitors, including magnesium, citrate, hydroxycitrate, chondroitin sulfate, and phytate, on the nucleation of calcium oxalate were investigated in detail. Scanning electron microscopy was used to examine the influences of these inhibitors on the preferential nucleation of the different hydrates of calcium oxalate crystals.

A Linear Regression Model for Determining the Pre-Exponential Factor and Interfacial Energy Based on the Metastable Zone Width Data

A linear regression model is presented in this study to determine the pre-exponential factor and interfacial energy of the crystallized substance based on classical nucleation theory using the metastable zone width data. The nucleation event is assumed corresponding to a point at which the total number density of the nuclei has reached a fixed (but unknown) value. One equation is derived for any temperature-dependent functional form of the solubility. Another equation is derived for the van’t Hoff solubility expression. The pre-exponential factor and interfacial energy obtained from these two equations are found consistent for the studied systems, including glutamic acid, glycine, and 3-nito-1,2,4-triazol-5-one. The results obtained from these two equations are also compared with those obtained from the integral method and classical 3D nucleation theory approach.

Investigations into the Influence of Solvents on the Nucleation Kinetics for Isonicotinamide, Lovastatin, and Phenacetin

A new method of data interpretation based on classical nucleation theory is proposed in this work to elucidate the influence of solvents on the pre-exponential nucleation factor and interfacial energy using the induction time data for three crystallization systems, including isonicotinamide, lovastatin, and phenacetin. In this method, the pre-exponential nucleation factor is replaced by the intrinsic nucleation factor multiplied by temperature and divided by solution viscosity. The proposed method is applied to study the nucleation kinetics of isonicotinamide, lovastatin, and phenacetin among various solvents using the induction time data measured in this work. The results indicate that the intrinsic nucleation factor increases linearly with increasing square root of interfacial energy in various solvents for each system.

Modelling of the Polymorph Nucleation based on Classical Nucleation Theory

To elucidate the relative nucleation rates of different polymorphs, a competitive kinetic model is developed based on classical nucleation theory to describe the time evolution of two different polymorphic cluster size distributions controlled by the association and dissociation of the solute molecules during polymorph nucleation. Although there is only one type of the solute molecules, the agglomerated solute clusters are divided into two types–A form and B form, which resemble the structures and morphologies of the different mature polymorphs and eventually lead to the formation of two polymorphic crystals. A dissociation kernel is incorporated into the proposed model to account for gradual dissolution of the solute clusters smaller than a critical nucleus size due to the thermodynamic instability. By fitting the experimental induction period data and the final measured weight fractions of eflucimibe polymorphs with the proposed model, the association and dissociation rate constants for two polymorphs are determined. The developed model is satisfactory to explain the competitive mechanism of polymorph nucleation for eflucimibe that B form dominates at higher supersaturation while A form dominates at lower supersaturation. The results also indicate that A form is more stable than B form with a transition energy of 3.1kJ/mole at 35°C.

Determination of the Nucleation and Growth Kinetics for Aqueous L-glycine Solutions from the Turbidity Induction Time Data

As the turbidity induction time measurements are influenced by the size distribution of the nuclei at the detection point, these data should provide important information on both nucleation and growth. A model is developed in this work to determine the nucleation and growth kinetics of aqueous L-glycine solutions using the turbidity induction time data for various supersaturations from 293.15 K to 313.15 K. The photomicroscopic growth experiments of aqueous L-glycine solutions are also conducted to determine the growth kinetics of nuclei under the same conditions for comparison. The results indicate that the interfacial energy obtained from this model is consistent with that obtained based on the traditional method by assuming t i − 1 ∝ J . The growth kinetics, including the growth activation energy and the kinetic growth parameter, obtained from this model using the induction time data are close to those obtained from the photomicroscopic growth experiments performed in this work.

Relating induction time and metastable zone width

A relation between MSZW and induction time reveals nucleation happens when nucleation potential accumulates up to a constant value in a system. The MSZW and induction time can be estimated from each other with this relation.

Comment on “Relation between metastable zone width and induction time of butyl paraben in ethanol” by H. Yang, CrystEngComm, 2015, 17, 577

An integral equation is developed to predict MSZW from the induction time results based on the classical nucleation theory.

Reply to the “Comment on ‘Relation between metastable zone width and induction time of butyl paraben in ethanol’” by L.-D. Shiau, CrystEngComm, 2015, 17, DOI: 10.1039/C5CE00101C

The accumulated “nucleation potential” and “crystal density”, in the interpretations describing relation between metastable zone width and induction time, reach a critical value, respectively, at the nucleation in cooling crystallization.