Grzegorz Zajac

Raman microscopy as a novel tool to detect endothelial dysfunction

Raman microscopy, a label-free method with high spatial resolution, shows growing potential in various fields of medical diagnostics. Several proof-of-concept studies related to the application of Raman microscopy to detect endothelial dysfunction are summarized in this work. Both ex vivo measurements of the tissues in the murine models of endothelial pathologies, as well as in vitro investigations of the cell cultures in the context of cellular transport, drug action and inflammation processes are discussed. The future directions in application of Raman spectroscopy-based methods in such studies are also described.

Aggregation-Induced Resonance Raman Optical Activity (AIRROA): A New Mechanism for Chirality Enhancement

Raman optical activity (ROA) spectroscopy is hampered by low sensitivity, with limited possibilities for enhancing the signal. In the present study, we report a new mechanism whereby chirality is enhanced using the resonance resulting from supramolecular aggregation. We have named this mechanism aggregation-induced resonance Raman optical activity (AIRROA). As an example, we study J-aggregates of astaxanthin (AXT), which show strong absorption of circularly polarized light in the range of ROA excitation. The implications of aggregation-induced signal enhancement for chiroptical spectroscopy are discussed.

Aggregation-Induced Resonance Raman Optical Activity (AIRROA) and Time-Dependent Helicity Switching of Astaxanthin Supramolecular Assemblies

New methods for enhancing the Raman optical activity (ROA) signal are desirable due to the low efficiency of ROA, demanding otherwise high sample concentrations, high laser powers, and/or long acquisition times. Previously, we have demonstrated a new phenomenon, aggregation-induced resonance ROA (AIRROA), that produces significant enhancement of the ROA signal provided that the excitation wavelength coincides with the absorption of the measured species and that the electronic circular dichroism (ECD) signal in the range of this absorption is nonzero. In this work, analyzing three very different supramolecular astaxanthin aggregates (H1, H2, and J), we confirm the phenomenon and demonstrate that aggregation itself is not enough to enhance the ROA signal and that the above-mentioned conditions are necessary for induction of the resonance ROA effect. Additionally, by analyzing the changes in the ECD spectra of the H1 assembly, we demonstrate that the supramolecular helicity sign switches with time, which is dependent on the prevalence of kinetic or thermodynamic stabilization of the obtained aggregates.

Raman Optical Activity and Raman spectroscopy of carbohydrates in solution

This comprehensive study on selected 14 carbohydrates in water solution is an extension of previously published one focused only on solid state analysis. Here, Raman spectroscopy was used as a dedicated method for analysis of carbohydrates in solution, both using a normal effect (RS) and its chiral analogue: Raman Optical Activity spectroscopy (ROA). The compounds were selected as biologically important and representative of all groups: monosaccharides, disaccharides, trisaccharides, cyclodextrines and polysaccharides. RS and ROA spectra are presented together with an expanded discussion on various structures and conformations of studied carbohydrates in the solution taking into account particular regions, i.e. (1) low wavenumber region (250-600 cm-1), (2) anomeric region (600-950 cm-1), (3) fingerprint region (950-1200 cm-1) and (4) CH2and COH deformations region (1200-1500 cm-1). So, the following information can be obtained about: (1) the absolute configuration of the anomeric centre; (2) the configuration of the anomeric centre and the orientation of the anomeric hydroxyl group; (3) the ring structures and the relative orientation of substituents and (4) the conformation of the exocyclic CH2OH (4), respectively. Raman spectroscopy and Raman Optical Activity were shown as unique tools to study complex structures of carbohydrates.