Date of Award

Spring 2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

Zafar Iqbal

Second Advisor

Tamara M. Gund

Third Advisor

Shirlynn Chen

Fourth Advisor

Rajesh N. Dave

Fifth Advisor

S. Mitra

Sixth Advisor

Carol A. Venanzi

Abstract

Experimental research on the use of Raman spectroscopy as an in- and on-line sensing tool and a complementary characterization technique for pharmaceutical applications is presented in this thesis. In the first chapter following a broad overview, the use of Raman spectroscopy, together with x-ray powder diffraction, scanning electron microscopy (SEM) and differential scanning calorimetry, for multilevel characterization of cryomilled powders, and the melt-grown amorphous phase of griseofulvin, a model active pharmaceutical ingredient (API), is presented and discussed in detail. A key feature was the observation of a broad inelastic background superimposed on the Raman spectra of cryomilled powders, which is attributed to lattice disorder and Mie scattering generated by mechanical processing and sub-micron particle interfaces. In the following chapter, polymorphs of another model API, acetaminophen (APAP), were studied by Raman spectroscopy with supporting information obtained from x-ray diffraction, SEM images and intrinsic dissolution profiles. An important result was the stabilization and characterization of the metastable type II orthorhombic phase of APAP which is highly desired for its unique tabletting properties which are important for pharmaceutical manufacturing. Stabilization of metastable type II APAP was achieved by micronizing or nanocoating stable monoclinic crystallites of type I APAP. In addition, as an Appendix to the thesis, micro-Raman spectroscopy of single crystal APAP as a function of crystal orientation and of temperature was measured to provide an understanding of the lattice properties of APAP for input into models to predict its behavior under mechanical milling conditions widely used in pharmaceutical processing. Molecular behavior obtained from the above studies guided simulated in-line and off-line characterization of griseofulvin as thin gel films made from micronized powders and nanosuspensions. By employing complementary near infrared and Raman imaging for newly developed films, it was possible to extract valuable information on the spatial distribution and crystallinity of the embedded particles in a polymeric matrix at different scales of scrutiny. Chemometrics processing of spectroscopic data for films and nanosuspensions allowed for qualitative and quantitative particle size determinations of the API’s in the films and nanosuspensions. In the final chapter a photonic crystal substrate for surface enhanced Raman spectroscopic (SERS) sensing was employed to detect and study griseofulvin and APAP down to 10-8 M levels with enhancement factors approaching 1099. Detection sensitivities of the aromatic griseofulvin and APAP molecules were also compared with those of less aromatic and non-aromatic energetic molecules in order to understand the Raman enhancement process.

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Chemistry Commons

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