Efficient photoredox catalysts containing transition metals, such as iridium and ruthenium, to initiate organic reactions and polymerization under visible light have recently emerged. However, these catalysts are composed of rare metals, which limit their applications. In this study, we report an efficient photoinduced living radical polymerization process that involves the use of chlorophyll as the photoredox biocatalyst. We demonstrate that chlorophyll a (the most abundant chlorophyll in plants) can activate a photoinduced electron transfer (PET) process that initiates a reversible addition-fragmentation chain transfer (RAFT) polymerization under blue and red LED light (λmax = 461 and 635 nm, respectively). This process controls a wide range of functional and non-functional monomers, and offers excellent control over molecular weights and polydispersities. The end group fidelity was demonstrated by NMR, UV-vis spectroscopy, and successful chain extensions for the preparation of diblock copolymers.

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Utilizing the electron transfer mechanism of chlorophyll a under light for controlled radical polymerization

Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global change, novel approaches that are rapid, repeatable and scalable are critical, especially in ecosystems for which information about species identity and the number of species is difficult to acquire. Here, we present 'spectral diversity'—a spectroscopic index of the variability of electromagnetic radiation reflected from plants measured in the visible, near-infrared and short-wave infrared regions (400–2,400 nm). Using data collected from the Cedar Creek biodiversity experiment (Minnesota, USA), we provide evidence that the dissimilarity of species' leaf spectra increases with functional dissimilarity and evolutionary divergence time. Spectral diversity at the leaf level explains 51% of total variation in productivity—a proportion comparable to taxonomic (47%), functional (51%) or phylogenetic diversity (48%)—and performs similarly when calculated from high-resolution canopy image spectra. Spectral diversity is an emerging dimension of plant biodiversity that integrates trait variation within and across species even in the absence of taxonomic, functional, phylogenetic or abundance information, and has the potential to transform biodiversity assessment because of its scalability to remote sensing.

Plant spectral diversity integrates functional and phylogenetic components of biodiversity and predicts ecosystem function.

Screening of functional compounds in supercritical fluid extracts from Spirulina platensis

JAM and MH thank MCYT for FPI grants. Authors thank MCYT (project AGL2002-04621-
C02-02) for financial support.

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Separation and characterization of antioxidants from Spirulina platensis microalga combining pressurized liquid extraction, TLC, and HPLC-DAD.

Three different parameters (temperature, solvent, and extraction time) were studied regarding to pressure liquid extraction (PLE) of antioxidant and antimicrobial compounds from Spirulina platensis. Two different antioxidant methods, β-carotene bleaching method and DPPH• (2,2-Diphenyl-1-picrylhydrazyl hydrate) free radical scavenging assay, were used to determine the optimal PLE conditions for antioxidants extraction. The selected conditions were as follows: extraction temperature equal to 115 °C, extraction time equal to 15 min and ethanol as extracting solvent. The main antioxidant compounds found in this extract were identified as zeaxanthin, a myxoxanthophyll-like compound and very polar phenolic compounds. Moreover, antimicrobial activity of different PLE fractions was tested against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 11775, Candida albicans ATCC 60193, and Aspergillus niger ATCC 16404. Data obtained showed the hexane and petroleum ether extracts were slightly more active than ethanolic extracts. As for water extracts, none of them were active against the microorganisms tested. Data indicated that both 115 and 170 °C were the best extraction temperatures conditions in order to optimize the extraction of antimicrobial compounds, whereas 9 min was the optimal extraction time. Besides, C. albicans was the most sensitive microorganism to all Spirulina PLE extracts.

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Functional characterization of pressurized liquid extracts of Spirulina platensis

A direct method of extracting plant pigments from spinach leaves into a dry organic solvent is presented. A powder is obtained by grinding a mixture of raw spinach, drying agent, and sand (1:1:2) that can be extracted directly into acetone in 10 minutes to provide a sample suitable for chromatographic analysis. This method avoids liquid–liquid extractions and subsequent drying as is found in previously reported methods. Removal of the magnesium ion from chlorophyll pigments was observed by treating the acetone extract with a strong ion-exchange resin for three minutes. The loss of magnesium ion is often observed as a degradation product of chlorophyll samples. An improved solvent system consisting of petroleum ether, cyclohexane, ethyl acetate, acetone, and methanol in 60%, 16%, 10%, 10%, and 4% quantities, respectively, is also reported. TLC separation using this extraction method and solvent system allows for the clear separation of chlorophyll a and b from all other extracted pigments.

Robert L. Steeper

Papers

An Improved Method for the Extraction and Thin-Layer Chromatography of Chlorophyll a and b from Spinach