by Keyword: Photosynthesis

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Revilla-López, G., Sans, J., Casanovas, J., Bertran, O., Puiggalí, J., Turon, P., Alemán, C., (2020). Analysis of nitrogen fixation by a catalyst capable of transforming N2, CO2 and CH4 into amino acids under mild reactions conditions Applied Catalysis A: General 596, 117526

The processes related to the fixation of nitrogen in a catalyst able to produce glycine and alanine from a N2, CO2 and CH4 gas mixture at mild reaction conditions have been studied by combining experimental and theoretical investigations. Results have allowed to understand the role of different elements of the catalyst, which is constituted by permanently polarized hydroxyapatite (p-HAp), zirconia, and aminotris(methylenephosphonic acid) (ATMP). ATMP attracts N2 molecules towards the surface, maintaining them close to the zirconia and p-HAp components that are the most active from a catalytic point of view. On the other hand, the associative mechanism is thermodynamically favoured under mild reaction conditions with respect to the dissociative one, which is limited by the barrier associated to the Nsingle bondN bond cleavage. Because this reaction mechanism is similar to that employed in the nitrogen fixation by nitrogenase enzymes, these findings provide an opportunity to design new bioinspired catalysts.

Keywords: Artificial photosynthesis, Carbon fixation, Hydroxyapatite, N[sbnd]N bond cleavage

Lopez-Martinez, Montserrat, López-Ortiz, Manuel, Antinori, Maria Elena, Wientjes, Emilie, Nin-Hill, Alba, Rovira, Carme, Croce, Roberta, Díez-Pérez, Ismael, Gorostiza, Pau, (2019). Electrochemically gated long distance charge transport in photosystem I Angewandte Chemie International Edition 58, (38), 13280-13284

The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understand charge transport mechanisms, and to design bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Here, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current-distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions.

Keywords: Current decay, ECSTM, Electrochemical gate, Electron transfer, Photosynthesis

Pollastri, S., Jorba, I., Hawkins, T. J., Llusià , J., Michelozzi, M., Navajas, D., Peñuelas, J., Hussey, P. J., Knight, M. R., Loreto, F., (2019). Leaves of isoprene-emitting tobacco plants maintain PSII stability at high temperatures New Phytologist 223, (3), 1307-1318

At high temperatures, isoprene-emitting plants display a higher photosynthetic rate and a lower nonphotochemical quenching (NPQ) compared with nonemitting plants. The mechanism of this phenomenon, which may be very important under current climate warming, is still elusive. NPQ was dissected into its components, and chlorophyll fluorescence lifetime imaging microscopy (FLIM) was used to analyse the dynamics of excited chlorophyll relaxation in isoprene-emitting and nonemitting plants. Thylakoid membrane stiffness was also measured using atomic force microscope (AFM) to identify a possible mode of action of isoprene in improving photochemical efficiency and photosynthetic stability. We show that, when compared with nonemitters, isoprene-emitting tobacco plants exposed at high temperatures display a reduced increase of the NPQ energy-dependent component (qE) and stable (1) chlorophyll fluorescence lifetime; (2) amplitude of the fluorescence decay components; and (3) thylakoid membrane stiffness. Our study shows for the first time that isoprene maintains PSII stability at high temperatures by preventing the modifications of the surrounding environment, namely providing a more steady and homogeneous distribution of the light-absorbing centres and a stable thylakoid membrane stiffness. Isoprene photoprotects leaves with a mechanism alternative to NPQ, enabling plants to maintain a high photosynthetic rate at rising temperatures.

Keywords: (High) temperature, Atomic force microscopy (AFM), Chlorophyll fluorescence (quenching and lifetime), Fluorescence lifetime imaging microscopy (FLIM), Isoprene, Nonphotochemical quenching (NPQ), Photosynthesis