Crystal Growth Mechanism in a Solution of Hollow Whiskers of Molecular Compounds

Mallet, Franck; Petit, Samuel; Lafont, Sylvaine; Billot, Pascal; Lemarchand, D.; Coquerel, Gérard

doi:10.1021/cg030046e

Cited by 33 publications

(35 citation statements)

References 13 publications

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“…After the observation in literature that crystalline hollow needles can be produced from many crystalline substances [2,3,5,6] and the demonstration of a case in which the ends of those needles can be closed [1], it was shown here that the hollow (this was again verified by an indirect method), closed needles could also be filled. It was demonstrated by two indirect methods that substances can be enclosed inside the needles, i.e., by the use of a fluorescence dye and the detection of a pharmaceutically active agent using UV spectroscopy.…”

Section: Discussionmentioning

confidence: 56%

“…By changing the thermodynamic conditions, e.g., temperature, pressure or concentration (solvent), a phase transformation of solvates can be seen to occur [1][2][3], e.g., a monohydrate crystal immerged into an organic solvent in which the anhydrate represents the thermodynamically stable form. During solvent mediated phase transformation [4], the crystal water is transferred into the organic solvent due to the higher affinity of the incorporated water to the solvent.…”

Section: Introductionmentioning

confidence: 99%

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Closed Crystalline Tubes as a Container System

et al. 2010

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Hollow crystalline glucose anhydrate needles are produced based on a technique to produce hollow crystal needles by phase transformation of solvate crystals into non-solvates. The fascinating characteristic of the glucose anhydrate needles is the possibility of closing them by a simple drying process. This creates great potential for future applications as a container system, e.g., for pharmaceutical substances. The hollowness of the needles has already been proven, but the filling of the needles has not been investigated. Due to the lack of a direct method to demonstrate the possibility of filling the needles, two indirect methods are presented to demonstrate a successful technique to enclose substances in these needles. On the one hand, the filling is proven by fluorescence microscopy of glucose anhydrate needles with enclosed rhodamine 6G. Here it is possible to visualize the fluorescence dye by observation of the broken needles. On the other hand, the concentration of included ibuprofen is examined by the means of UV spectroscopic measurements. A significant concentration of the enclosed drug is detected following the extraction out of the needle interior.

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Section: Discussionmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Closed Crystalline Tubes as a Container System

et al. 2010

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“…A number of authors [28][29][30][31][32][33] have reported solvent-mediated phase transitions between different crystalline phases of a given material that result in the formation of hollow needles emanating from the original crystal (see Fig. 9).…”

Section: Example 4: Phase Transitions For Product Design -Generating mentioning

confidence: 99%

“…The resulting phase is generally the desolvated phase; in other words, and in the specific case of a crystal hydrate as starting material, the resulting phase is the anhydrate. One notable exception is the formation of hollow needles by solvent exchange as observed for dexamethasone acetate [32,33]. Although the presence of the anti-solvent is not a necessary condition for the transition to a desolvated phase, it is required for the formation of the hollow needles.…”

Section: Example 4: Phase Transitions For Product Design -Generating mentioning

confidence: 99%

Design of Crystalline Solids

2009

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Product design is an active area of research. In a top-down approach to product design, the required product properties dictate product development from the very basic choice of the functional material to use for a defined task up to the processing required to render the material in a suitable form. This article focuses on processing crystalline solids with a particular field of application in mind and shows how process conditions can be used both to generate a material with particular properties and to tailor these properties. The examples selected are biased towards novel pharmaceutical applications; the principles of the processes and the resulting product properties discussed can, however, be transferred to other areas where materials with similar functions are required. The case studies presented pertain to in situ coating of solid particles (cases 1 and 2) with a crystalline coating of a different chemical nature, to freeze casting for generating porous particles and, finally, to the potential for exploiting phase transformations to generate tubular crystalline solids that can function as micro-delivery devices for other materials. Potential advantages of all four processing techniques are the delivery of well-defined products with tailored properties that can be controlled by judicious choice of the process conditions. Example 1: Forming and Coating the Solid Drug Simultaneously by Drop SolidificationAn in situ coating process [1][2][3] has the following prerequisites. The multi-component system from which the pastilles are formed must behave as a eutectic. For eutectic systems, one component can be isolated with a high degree of purity [4,5]. If a drop of this multi-component system is brought into contact with a colder environment, crystallization (nucleation and crystal growth) will commence on its surface [6]. If this drop is allowed to solidify in its entirety, the eutectic behavior ensures that the components are spatially separated. From this it follows that the higher-melting component, i.e., the component that crystallizes first, will preferentially accumulate on and near the surface of the pastille. As a consequence, the lower-melting components accumulate in the interior of the pastille. It is then conceivable that a eutectic mixture of an active pharmaceutical ingredient (drug substance) and a suitable coating material can be found that fulfils the above requirements. It then becomes possible to design and control the solidification in such a manner that a pastille is formed (see Fig. 1a) the exterior of which is predominantly composed of the coating material whereas the drug substance accumulates in the center of the pastille.In the following, the solidification of a drop of a binary melt will be described in detail. Matsuoka [7] summarized the binary solid-liquid equilibrium phase diagram types found in the International Critical Tables [8]. According to Matsuoka, it is

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“…For example, an ethanolic saturated solution of DMA injected in water (anti-solvent) [1] leads to the formation of hollow needlelike crystals called whiskers. At present, the mechanism of formation of these "whiskers" remains not fully understood [1,2]. In order to understand the mechanism of crystallization, it was first decided to characterize the solid phases of DMA in water.…”

Section: Introductionmentioning

confidence: 99%