Absorption and resonance Raman characteristics of β-carotene in water-ethanol mixtures, emulsion and hydrogel

Abstract

Absorption or resonance Raman scattering are often used to identify and even quantify carotenoids in situ. We studied the absorption spectra, the Raman spectra and their resonance behavior of β-carotene in different molecular environments set up as mixtures from lipid (emulsion) and non-polar (ethanol) solvents and a polar component (water) with regard to their application as references for in situ measurement. We show how both absorption profiles and resonance spectra of β-carotene strongly depend on the molecular environment. Most notably, our data suggests that the characteristic bathochromic absorption peak of J-aggregates does not contribute to carotenoid resonance conditions, and show how the Raman shift of the C=C stretching mode is dependent on both, the molecular environment and the excitation wavelength. Overall, the spectroscopic data collected here is highly relevant for the interpretation of in situ spectroscopic data in terms of carotenoid identification and quantification by resonance Raman spectroscopy as well as the preparation of reference samples. In particular, our data promotes careful consideration of appropriate molecular environment for reference samples.

Probing the changes of carotenoids in Microcystis flosaquae under environmental perturbations by two‐dimensional Raman correlation spectroscopy

“…Two‐dimensional Raman correlation spectroscopy was used to analyze the synchronicity and asynchronicity of the dynamic spectra of M. flosaquae , which were induced by dependent external perturbations such as nutrient changes, light fluxes, and water turbulence. The Raman spectra of the M flosaquae , without normalization except baseline correction, were used to conduct a cross correlation analysis with 2Dshige (Shigeaki Morita, Kwansei Gakuin University, 2004–2005) . Then, the synchronous and asynchronous correlation spectra were obtained by the calculation method based on linear algebra from the work of Noda and coworkers .…”

Raman Sensing and Its Multimodal Combination with Optoacoustics and OCT for Applications in the Life Sciences

“…The spectral map ( left ) quasi-continuously shows the transformation of the absorption characteristics of β-carotene emulsion in aqueous solution from 42% ethanol to 75% ethanol content. Three spectra from characteristic points of this series of measurements and an additional spectrum of β-carotene emulsion in pure water (from a different stock solution) are compiled in the graph on the right (reproduced with permission from [76]).…”

“…From top to bottom, the curves show resonance maps for 64 mg Altratene EM5% emulsion in 100 mL of water (green), a hydrogel stained with 11 mg Altratene EM5% emulsion in 100 mL of aqueous solution containing <12% ethanol (blue), and ethanol solutions with 20% (black) or 40% (gray) water content. Distance marks (arrows) at each 0-0 transition peak indicate the spectral shift between absorption and resonance maximum (reproduced with permission from (reproduced with permission from [76]).…”

“…Please note that all spectra were spectrally calibrated to the C-C vibration at a Raman shift of 1157 cm−1 due to lack of a common external standard. Therefore, peak-to-peak distances but not absolute peak positions are reliable (reproduced with permission from [76]).…”

“…The double image at the bottom right shows the same image (polymerized PVA hydrogel stained with β-carotene in emulsion) at two different carotenoid color scales to illustrate the large local variability of β-carotene concentration in the hydrogel. Each image shows a 100 µm wide sub-surface area of the gels (reproduced with permission from [76]).…”