Self-organizing maps in chemotaxonomic studies of Asteraceae: a classification oftribes using flavonoid data

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Abstract

Flavonoids have shown good chemical markers for Asteraceae. In this paper, 4,700 occurrences of flavonoids (about 800 compounds) were considered in an expert system developed for taxonomic purposes. Through the use of Self-Organizing Maps (SOM) phylogenetic relationships among the subfamilies and tribes of Asteraceae were established. These taxa were classified on the basis of their occurrences and oxidation patterns of the flavonoids. The obtained results show the separation between the two subfamilies of Asteraceae the correlation among the tribes of the Cichiroideae subfamily according to the topological tree proposed by Karis the clustering of the tribes according to the tree proposed by Jansen based on CpDNA and the separation of the tribes classified in the Asteroideae subfamily as well as the tribes based on the methoxylation x glycosylation level in flavonoids. From these results one can affirm that the method applied with chemical data can be used as a complementary tool in plant classification.

Translated abstract

Flavonóides são considerados bons marcadores químicos da família Asteraceae. Nesse artigo 4700 ocorrências de flavonóides (cerca de 800 substâncias) foram utilizadas em um sistema especialista desenvolvido para estudos taxonômicos. Através do uso de Mapas Auto-Organizáveis foram estabelecidas relações filogenéticas entre as subfamílias e as tribos de Asteraceae, as quais foram classificadas com base no número de ocorrências e nos padrões de oxidação de flavonóides. Os resultados obtidos permitiram a diferenciação das duas subfamílias de Asteraceae a correlação de tribos na subfamília Cichiroideae de acordo com a árvore topológica proposta por Karis o agrupamento de tribos de acordo com a árvore baseada em dados de CpDNA proposta por Jansen e separar as subtribos de Asteroideae bem como as tribos de acordo com o grau de metoxilação x glicosilação de flavonóides. A partir desses resultados pode-se afirmar que o método descrito com dados químicos pode ser utilizado como uma ferramenta complementar na classificação de plantas.

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Is Open Access

Level alignment of a prototypical photocatalytic system: Methanol on TiO2(110)

Hrvoje Petek, Angel Rubio, Duncan Mowbray … (2013)

Photocatalytic and photovoltaic activity depends on the optimal alignment of electronic levels at the molecule/semiconductor interface. Establishing level alignment experimentally is complicated by the uncertain chemical identity of the surface species. We address the assignment of the occupied and empty electronic levels for the prototypical photocatalytic system of methanol on a rutile TiO2 (110) surface. Using many-body quasiparticle (QP) techniques we show that the frontier levels measured in ultraviolet photoelectron and two photon photoemission spectroscopy experiments can be assigned with confidence to the molecularly chemisorbed methanol, rather than its decomposition product, the methoxy species. We find the highest occupied molecular orbital (HOMO) of the methoxy species is much closer to the valence band maximum, suggesting why it is more photocatalytically active than the methanol molecule. We develop a general semi-quantitative model for predicting many-body QP energies based on the appropriate description of electronic screening within the bulk, molecular or vacuum regions of the wavefunctions at molecule/semiconductor interfaces.