Self-Assembled Monolayers as Nucleating Surfaces to Study Early Formation Pathways of Crystallographic Polymorphs
look at early formation stages of crystallization.
to study polymorph selectivity in different solvents or solvent mixtures as well as to
appropriate conditions, nucleation and growth on SAMs can function as a model system
interpretations. Overall, the two-part project clearly established, however, that under
were the basis for the designs of all experiments conducted and associated
Covid-19 shutdown). This may have led to variations in the solubility curves, which
that only a small amount of ultrapure ROY was available (in part as a result of the
crystallization experiments reported with ROY on SAMS were also plagued by the fact
likely caused by crystals falling off of the substrate into the solution. Furthermore, all
phenyl SAMs). The growth possibility dropped as supersaturation increased, which was
secondary polymorphs typically increased with increasing supersaturation (exception:
observed as a function of SAM chemistry. The possibility of occurrence of these
dominant polymorph, irrespective of SAM. However, secondary polymorphs were
with longer incubation time. When the solvent changed to toluene, Y was still the
(exception: phenyl SAMs). The growth possibility showed an overall increasing trend
polymorphs were not frequently observed, even at higher supersaturation levels
benzyl alcohol, Y was the dominant polymorph, irrespective of SAM. Secondary
applied for polymorph characterization of the resulting nucleated crystals. For ROY in
induced on the SAM surface by generating temperature jumps. Raman microscopy was
part of the project. SAMs were placed vertically in the solution and the nucleation was
conducted instead of the solvent evaporation-based crystallization employed in the first
control the level of supersaturation, crystallization experiments upon cooling were
in toluene and benzyl alcohol were determined. In this part of the project, in order to
on polymorph selection in concert with SAMs. To that end, solubility curves for ROY
chemistry, and both polar and nonpolar solvents were again chosen to study their effects
different terminal (omega) functional groups were used to control nucleating surface
(ROY), was chosen for in depth studies. Alkane-thiols based SAMs on gold with
organic model system, 5-methyl-2-[(2-nitrophenyl) amino]-3-thiophenecarbonitrile
other model compounds. In the second part of the project, to that end a more complex
formation stages of the crystallization of ACM and may be used to extend to studies of
suggested, that our methodologies are effective to gain insights into the earliest
possible existence of structural transformations at these early stages. These results
occurring. Further analysis and corroboration via additional data sets pointed to the
nucleation, we identified unusual shifts along scattering vector, q, of the earliest peaks
totally in-plane orientation. Studying crystallization of Form I by spontaneous
crystallographic orientation, directing the (002) planes from slightly out-of-plane to a
(trichloro(phenyl)silane) terminated SAM surface has a strong influence over
the substrate-solution interface than in the bulk above, and that a PTS
crystallization of Form II by seeded nucleation, we verified that crystals grow faster at
of Form I and II crystallization events of ACM under these conditions. Studying
Cornell’s High Energy Synchrotron Source (CHESS) to study the early formation stages
We then introduced time-resolved in situ wide-angle X-ray scattering (WAXS) at
surface chemistry and solvent conditions work together to control crystal polymorph.
degree of supersaturation. Under these conditions, we first demonstrated that both SAM
and growth were induced by simple solvent evaporation, i.e. without control of the
predominant crystal forms, Form I and Form II, was investigated. In this part, nucleation
part of the project, a pharmaceutical compound, acetaminophen (ACM), with two
chosen to study their effects on polymorph selection in concert with SAMs. In the first
used to control nucleating surface chemistry. Both polar and nonpolar solvents were
gold or silanes on glass, each with different terminal (omega) functional groups, were
in order to control crystal polymorphs. To that end, either alkane-thiol based SAMs on
monolayers (SAMs) in conjunction with varying solvents or solvent mixtures
mechanisms are highly desirable. In this project, we used a combination of selfassembled
methods that lead to an advanced understanding of early crystal formation pathways and
industries. Since a polymorph is determined at the early stages during crystallization,
of organic compounds is scientifically and technologically important to several
Understanding and control of crystallographic polymorphism and crystal habit