Crystallization Kinetics of an Amorphous Pharmaceutical Compound Using Fluorescence-Lifetime-Imaging Microscopy

Abstract

Pharmaceutical scientists are increasingly interested in amorphous drug formulations especially because of their higher dissolution rates. Consequently, the thorough characterization and analysis of these formulations are becoming more and more important for the pharmaceutical industry. Here, fluorescence-lifetime-imaging microscopy (FLIM) was used to monitor the crystallization of an amorphous pharmaceutical compound, indomethacin. Initially, we identified different solid indomethacin forms, amorphous and γ- and α-crystalline, on the basis of their time-resolved fluorescence. All of the studied indomethacin forms showed biexponential decays with characteristic fluorescence lifetimes and amplitudes. Using this information, the crystallization of amorphous indomethacin upon storage in 60 °C was monitored for 10 days with FLIM. The progress of crystallization was detected as lifetime changes both in the FLIM images and in the fluorescence-decay curves extracted from the images. The fluorescence-lifetime amplitudes were used for quantitative analysis of the crystallization process. We also demonstrated that the fluorescence-lifetime distribution of the sample changed during crystallization, and when the sample was not moved between measuring times, the lifetime distribution could also be used for the analysis of the reaction kinetics. Our results clearly show that FLIM is a sensitive and nondestructive method for monitoring solid-state transformations on the surfaces of fluorescent samples.

Indomethacin: The Interplay between Structural Relaxation, Viscous Flow and Crystal Growth

“…The particle size dependence of ΔH is shown in Figure 5 A, averaging ≈72.5 J·g −1 . The credibility of the ΔH data is supported by the simultaneous evaluation of the enthalpy of fusion ΔH m = 105.2 J·g −1 (37.6 kJ·mol −1 at the molecular weight of IMC M w = 357.8 g·mol −1 ), which is in perfect correspondence with the literature data [ 46 ]. With the knowledge that the IMC material subjected to the DSC crystallization measurements was fully amorphous, the discrepancy between ΔH and ΔH m can be explained by Kirchhoff’s law (the temperature evolution of c p ).…”

Biopolymer hydroxyapatite composite materials: Adding fluorescence lifetime imaging microscopy to the characterization toolkit

“…[ 54 ] FLIM has been used to investigate the crystallization kinetics of a pharmaceutical compound, with differing lifetimes of amorphous and crystalline materials and length scales on the tens of microns scale. [ 88 ] This differing crystallization kinetics could reveal heterogeneity on different length scales. Phase separation between two different materials may also impact material properties.…”

Quantifying Antibody Binding Kinetics on Fixed Cells and Tissues via Fluorescence Lifetime Imaging

“…25 It is useful to note that fluorescence lifetime depends only on the local properties of a sample, and thus, accounting for these properties is easier as compared to environmental factors such as temperature. The temporal analysis of such molecular environmental changes has successfully been used to calculate the reaction kinetics, 26 crystallization rates of pharmaceutical compounds, 27 and protein aggregation in animal models. 28 Additionally, it is interesting to note that FLIM has been used to characterize the binding of small molecules to kinases using the differences in the fluorescence decay time between bound and unbound states.…”