Morphological Diversity of Caffeine on Surfaces: Needles and Hexagons

Sarfraz, Adnan; Simo, Anne; Fenger, Robert; Christen, Wolfgang; Rademann, Klaus; Panne, Ulrich; Emmerling, Franziska

doi:10.1021/cg101358q

Cited by 20 publications

(19 citation statements)

References 33 publications

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“…On heterogeneous crystallization from solution two morphologies are typically evident, with long needles and the extended hexagonal structures. 38 The investigation of caffeine on mica surface prepared via HWE reveals similarly to bulk solutions solely needle type structures of caffeine in β-phase. Indication of another polymorph, especially the metastable α-phase was not noted, hence crystallization on mica is similar to the bulk.…”

Section: Discussionmentioning

confidence: 92%

Complex Behavior of Caffeine Crystallites on Muscovite Mica Surfaces

Röthel

Radziown

Resel

et al. 2015

Crystal Growth & Design

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Defined fabrication of organic thin films is highly desired in technological, as well as pharmaceutical, applications since morphology and crystal structure are directly linked to physical, electrical, and optical properties. Within this work, the directed growth of caffeine deposited by hot wall epitaxy (HWE) on muscovite mica is studied. Optical and atomic force microscopy measurements reveal the presence of caffeine needles exhibiting a preferable alignment in the azimuthal directions with respect to the orientation of the defined mica surface. Specular X-ray diffraction and X-ray diffraction pole figure measurements give evidence that the β-polymorphic form of caffeine forms on the mica surface. All results consent that caffeine molecules have an edge-on conformation i.e. minimizing their interaction area with the surface. Furthermore, the azimuthal alignment of the long caffeine needle axis takes place along the [11̅0], [100], and [110] real space directions of mica; needles are observed every 60° azimuthally. While mica has a complex surface structure with mirror planes and lowered oxygen rows, the slightly disturbed 3-fold symmetry dictates the crystal alignment. This is different to previous findings for solution cast caffeine growth on mica. For HWE the needles align solely along the mica main directions whereby solution cast needles show an additional needle splitting due to a different alignment of caffeine with respect to the surface.

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Section: Discussionmentioning

confidence: 92%

Complex Behavior of Caffeine Crystallites on Muscovite Mica Surfaces

Röthel

Radziown

Resel

et al. 2015

Crystal Growth & Design

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show abstract

“…In supramolecular chemistry, the studies dealing with solid-state structural properties of caffeine and its derivatives continued to emerge rapidly [16,17,18]. The polymorphic forms, solvates, co-crystals and inclusion complexes of caffeine have been well documented in the literature [19,20,21]. The first X-ray diffraction studies by June Sutor showed that caffeine readily crystallizes in its monohydrate form [22].…”

Section: Introductionmentioning

confidence: 99%

Caffeine as a Gelator

Nonappa

Kolehmainen

2016

Gels

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Caffeine (a stimulant) and ethanol (a depressant) may have opposite effects in our body, but under in vitro conditions they can "gel" together. Caffeine, being one of the widely used stimulants, continued to surprise the scientific community with its unprecedented biological, medicinal and physicochemical properties. Here, we disclose the supramolecular self-assembly of anhydrous caffeine in a series of alcoholic and aromatic solvents, rendering a highly entangled microcrystalline network facilitating the encapsulation of the solvents as illustrated using direct imaging, microscopy analysis and NMR studies.

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“…Two polymorphic forms and one hydrate form of caffeine were characterized. [20][21][22][23][24] Trask prepared one of the first caffeine containing cocrystals with glutaric acid as a coformer using the so called liquid-assisted grinding (LAG) method. 14 In this milling process a small amount of solvent is added to the solid reactant mixture to enhance the reaction rate.…”

Section: Introductionmentioning

confidence: 99%