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Crystals growing via nonclassical crystallisation pathways often lose the shape factor and the mechanisms involved are often anomalous. This makes it difficult to predict the crystal growth kinetics using the conventional crystal growth kinetic models. A new pseudo second order growth kinetic expression to predict the anomalous growth behaviour of curcumin crystals is introduced. This model also allows several important parameters relevant to the kinetics of the crystal growth, such as mass crystallised with respect to time, overall crystal growth kinetic constant, the maximum number of active sites involved in the crystal growth process and the initial crystal growth rate, to be obtained. According to the pseudo second order kinetics, the activation energy for the nonclassical crystal growth of curcumin was found to be ∼69 kJ mol−1, which seems to agree with the activation energy for the classical crystal growth of organic compounds reported in the literature. The total number of active sites involved in the crystal growth process was found to be ∼1022 per gram of the seeds. [ABSTRACT FROM AUTHOR]

Crystallisation from solution is an important process in pharmaceutical industries and is commonly used to purify active pharmaceutical ingredients. Crystallisation involves phase change and the mechanisms involved are random which makes the process stochastic. This creates a variation in the time required to reach a fixed percentage of yield from batch to batch. It is essential to regulate the batch crystallisation process and make it more predictable for industrial applications for the ease of process chain scheduling of upstream and downstream unit operations. In this work, we propose a new technique called dotted crystallisation, where carbon dots are used to dictate and regulate events associated with nucleation and crystallisation processes. Following the rules of two-step nucleation theory, the carbon dots intentionally added to a supersaturated solution of curcumin anchors the crystallising compound to form prenucleation clusters that evolve into stable nuclei. Using curcumin as a model compound, we showed that the nucleation of this compound in isopropanol can be regulated, and the nucleation rate can be improved via addition of small quantities of carbon dots to the supersaturated solution. Our results confirmed that the nucleation rate of curcumin by dotted crystallisation was roughly four times higher than the nucleation rate by conventional cooling crystallisation and produced smaller sized crystals with a narrow size distribution. [ABSTRACT FROM AUTHOR]

During the growth of crystals in impure solution, impurities can pin the flow of the elementary steps and decrease the growth rate or even arrest the crystal growth. In this work, for the first time, we showed that curcumin crystals can grow in impure solution that contains two structurally similar impurities, following a non-classical crystallisation pathway that deviates from the pinning mechanism. We showed that, in a highly impure solution that contains 20 wt% of impurities, a high supersaturation can initiate the crystal growth via sympathetic nucleation that involves the formation of new growth surfaces on the seed crystals. These new surfaces formed on the seed crystals at the expense of higher supersaturation act like active growth surfaces and dictate the entire crystal growth kinetics especially at lower supersaturations. We showed that, if we can artificially create new surfaces that look like giant macrosteps at the micron scale on the crystal surface, then these macrosteps can not only speed-up the crystallisation rate but also control the rate of transfer of impurities into the bulk crystals. [ABSTRACT FROM AUTHOR]

Correction for 'Dotted crystallisation: nucleation accelerated, regulated, and guided by carbon dots' by Mayank Vashishtha et al., CrystEngComm, 2023, https://doi.org/10.1039/d3ce00574g. [ABSTRACT FROM AUTHOR]