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.

Polyenic pigments in octocorals have been investigated by Raman spectroscopy using laser excitation at 532, 785 and 1064 nm. The spectral features suggest the structural nature of carotenoids from Phyllogorgia dilatata, Leptogorgia punicea, Muricea atlantica, Carijoa riisei and conjugated polyenals from L. punicea, L. setacea, Muricea flamma and Renilla muelleri. The observed vibrational bands at ca. 1540–1520 ν1(C=C), 1159 ν2(C–C) and 1005 cm−1 ρ3(C–CH3) were assigned to carotenoids, whereas the identification of non‐methylated conjugated polyenals have been proposed due to two major Raman bands at ca. 1500 and 1120 cm‐1, assigned to ν(C=C) and ν(C–C), respectively. Copyright © 2012 John Wiley & Sons, Ltd.

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.

Phyllogorgia dilatata is a Brazilian endemic gorgonian with a natural color ranging from white to pale yellow. An unusual violet pigmentation has been observed in colonies with tissue damage and skeleton anomalies. In order to investigate the chemical composition of these pigments, we have used in situ Raman spectroscopy to characterize the white/cream and violet tissues as well as sclerites, a skeletal component consisting of calcite, from both samples. Violet/purple pigmentation surrounding tissue necrosis is characterized as purpling, in response to fungus infection and allelopathic interactions. The spectroscopic analysis of the white-cream tissues, designated as healthy, has revealed the presence of the carotenoid peridinin, typical of the endosymbiont that harbors this species; however, peridinin was not observed in the colorless sclerites analysis, presenting bands exclusively of calcite. In contrast, the violet coloration of damaged tissue has also been observed in the sclerites. Both showed Raman bands corresponding to unmethylated polyunsaturated aldehyde, besides calcite bands. This is the first report of purpling in a Brazilian octocoral, identified as a derivative of the biochromes named psittacofulvins, which have been reported as exclusive in parrots.

This review is centered on the linear conjugated polyenes, which encompasses chromatic biomolecules, such as carotenoids, polyunsaturated aldehydes and polyolefinic fatty acids. The linear extension of the conjugated double bonds in these molecules is the main feature that determines the spectroscopic properties as light‐absorbing. These classes of compounds are responsible for the yellow, orange, red and purple colors which are observed in their parent flora and fauna in nature. Raman spectroscopy has been used as analytical tool for the characterization of these molecules, mainly due to the strong light scattering produced by the delocalized pi electrons in the carbon chain. In addition, conjugated polyenes are one of the main target molecular species for astrobiology, and we also present a brief discussion of the use of Raman spectroscopy as one of the main analytical tools for the detection of polyenes extra‐terrestrially.

Recebido em 19/11/08; aceito em 27/3/09; publicado na web em 26/8/09 OXOCARBONS, PSEUDO-OXOCARBONS AND SQUARAINES. Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.Keywords: oxocarbons; pseudo-oxocarbons; squaraines. INTRODUÇÃOOxocarbonos são compostos orgânicos formados essencialmente por carbono e oxigênio, apresentam-se como diácidos em sua forma neutra e seus ânions possuem fórmula geral C n O n 2-onde n varia de 3 a 6. Os ânions croconato (n=5) e rodizonato (n=6) Os oxocarbonos apresentam características particulares muito interessantes, tais como, estruturas cíclicas planares, elevada simetria molecular, sistemas π-deslocalizados e espectros eletrônicos singulares por apresentarem o efeito Jahn-Teller. 4 Uma evidência experimental acerca da estrutura de ressonância destes compostos foi obtida por Hirata e colaboradores através da espectroscopia de absorção no infravermelho.5 Nestes estudos foi verificada a ausência da banda referente ao ν(CO) que ocorre na região ~1850-1710 cm -1. Em estudos posteriores constatou-se que a variação do tamanho do anel promove uma interessante modificação na deslocalização eletrônica do respectivo oxocarbono: quanto maior o anel menor a deslocalização eletrônica. 5Deste ponto de vista , o íon deltato é o único oxocarbono considerado realmente aromático apresentando uma maior estabilidade, devida à maior distribuição de carga, quando comparado aos demais oxocarbonos, e esta estabilidade diminui com o aumento do tamanho do anel. Os demais oxocarbonos são considerados, formalmente, não-aromáticos, porém, apresentando a elevada conjugação eletrônica característica.Estas espécies apresentam elevado valor de constante de dissociação, evidenciando a elevada estabilidade conseguida através da ressonância de seus respectivos ânions. Por exemplo, os valores de pK 1 e pK 2 para o íon croconato são 0,8 e 2,2, respectivamente, para o íon esquarato são 0,5 e 3,5 e para o rodizonato são 4,3 e 4,7, respectivamente. 6A elevada simetria molecular é verificada através de seus espectros eletrônicos, onde o perfil espectroscópico evidencia a presença do efeito Jahn-Teller característico destas espécies (Figura 2). O dupleto observado ocorre devido à dupla degenerescência do primeiro estado eletrônico excitado presente nestas molécul...

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