Raman spectroscopic studies of a range of naturally occurring carotenoids in over 50 specimens of plant tissue and a range of standard extracts have been undertaken, and the characteristic bands of C C and C-C stretching and C-CH bending have been recorded. Comparison of the spectroscopic data with the chemical assignment of the carotenoids from chemical extraction of the plant tissues reveals that there is a problem in the interpretation of the spectroscopic data which can be attributed to significant wavenumber shifts, particularly in the C C stretching band wavenumber, for carotenoids in the organic tissues arising from molecular interactions between the carotenoid and its host matrix. The simple identification of carotenoids in biological tissues on the basis of comparison with the standard spectra of extracted material must be made with caution; the progressive shift in wavenumber of the C C stretching band in the conjugated polyene chain of carotenoids with the number of C C groups, and hence the identification of the carotenoid, cannot be unambiguously interpreted for the range of materials studied here.

In the present study, the inclusion processes of β-carotene, astaxanthin, lycopene, and norbixin (NOR) into the β-cyclodextrin (β-CD) cavity were investigated by means of Raman spectroscopy and quantum mechanics calculations. The Raman ν(1) band assigned to C═C stretching was sensitive to the host-guest interaction and in general undergoes a blue shift (3-13 cm(-1)) after inclusion takes place, which is the consequence of the localization of single and double bonds. This is supported by the molecular modeling prediction, which inclusion complexes show the ν(1) band blue shifted by 1-8 cm(-1). The calculated complexation energies was small for most of derivatives and was found to be -11.1 kcal mol(-1) for inclusion of AST and +0.27 kcal mol(-1) for NOR. The stability order was qualitatively correlated to topological parameters accounting for the opening angle of the chain. This means that after inclusion the guest molecules assume a slightly more extended conformation, which enhances the host-guest contact, improving the interaction energy. The results discussed here clearly demonstrate the matrix effect on the carotenes' spectroscopic profile and should contribute to fully characterize the raw samples.

The nature of the pigments in octocorals has been investigated by Raman spectroscopy, where laser excitation at 632.8 and 1064 nm were used to characterize the colored components present in the skeleton of the exotic pink-yellow soft coral Chromonephthea braziliensis, the reddish purple sea fan Leptogorgia punicea and the endemic deep violet red Leptogorgia violacea from the southeastern coast of Brazil. The observed positions of two major Raman bands at ca 1500 cm −1 [ν(C C)] and 1130 [ν(C-C)] for all specimens strongly suggest the presence of a mixtureof conjugated polyenes belonging to a class of compounds named parrodienes. The hemiketal steroidal feeding deterrent, 23-keto-cladiellin-A, isolated from C. braziliensis was identified in the crude extracts by the Raman analysis using 1064 nm excitation. The observation of the most important vibrational bands of this compound can be useful in future investigations to monitor its presence in crude extracts of C. braziliensis and or other species.

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