Electronic and vibrational properties of carotenoids: from in vitro to in vivo

Abstract

Carotenoids are among the most important organic compounds present in Nature and play several essential roles in biology. Their configuration is responsible for their specific photophysical properties, which can be tailored by changes in their molecular structure and in the surrounding environment. In this review, we give a general description of the main electronic and vibrational properties of carotenoids. In the first part, we describe how the electronic and vibrational properties are related to the molecular configuration of carotenoids. We show how modifications to their configuration, as well as the addition of functional groups, can affect the length of the conjugated chain. We describe the concept of effective conjugation length, and its relationship to the S 0 ! S 2 electronic transition, the decay rate of the S 1 energetic level and the frequency of the n 1 Raman band. We then consider the dependence of these properties on extrinsic parameters such as the polarizability of their environment, and how this information (S 0 ! S 2 electronic transition, n 1 band position, effective conjugation length and polarizability of the environment) can be represented on a single graph. In the second part of the review, we use a number of specific examples to show that the relationships can be used to disentangle the different mechanisms tuning the functional properties of protein-bound carotenoids.

Modeling the photosynthetic system I as complex interacting network

“…all other types of nodes chromophores and the Cars nodes have only outgoing links (Figs 5-6) would indicate these types of chromophores as important light entry gate. This would confirm empirical evidences from literature, showing that Cars and LHCs have the primary function of light harvesting,and then perform energy transfer to other types of nodes throughout the outgoing links[6,35,53] .…”

“…In fact, Cars are long conjugated molecules with electrons delocalized in the entirety of the molecule, making the internal processes much faster than the external ones (i.e. energy transfer) [35]; so each Car can be considered almost like a point-node object delivering energy in the system. For this reason, we choose the C15 carbon, located in the middle of the molecule, to model the carotenoids.…”

Optical Projection and Spatial Separation of Spin Entangled Triplet-Pairs from the S1 (21Ag-) State of Pi-Conjugated Systems

“…Introducing an increasing number of conjugated oxygen atoms into the carotenoid backbone has also been shown to make these molecules more robust to conformational effects 88 , which guided our choice of AXT as a model carotenoid. Performing absorption measurements after each pump-push-probe scan further confirms there are no structural changes in the molecule during measurements (SI, Figure S12).…”

Colour in bivalve shells: Using resonance Raman spectroscopy to compare pigments at different phylogenetic levels

“…As such, the differently coloured shells may reflect both environment (dietary intake of different carotenoids) and genetics (heritable modifications of identical or differing carotenoid precursors). Factors affecting the effective conjugation length, and therefore colour, in carotenoids include binding to proteins, modifications to their configuration, the addition of functional groups, and isomerism . Differences in aggregation of carotenoproteins have also been shown to affect colour in lobsters and the effect of orientation in the shell matrix has been considered previously with respect to molluscan pigments .…”

“…Factors affecting the effective conjugation length, and therefore colour, in carotenoids include binding to proteins, modifications to their configuration, the addition of functional groups, and isomerism. [41,53,54] Differences in aggregation of carotenoproteins have also been shown to affect colour in lobsters [55] and the effect of orientation in the shell matrix has been considered previously with respect to molluscan pigments. [22] Unmodified carotenoids are commonly red, yellow, or orange, FIGURE 3 Graph of the C═C wavenumber (ν 1 ) versus C-C wavenumber (ν 2 ) as in other studies.…”