Aggregation Of Chlorophyll a Probed By Resonance Light Scattering Spectroscopy

We report the resonance light scattering (RLS) spectra of chlorophyll a aggregated in a 9:1 solution of formamide and pH 6.8 phosphate buffer. The aggregate formed after 2 h of mixing, referred to as Chl(469), shows a strong scattering feature at 469 nm (Soret band) and a much weaker feature at 699 nm (Q(y) band). A kinetic investigation confirmed that the aggregation process is cooperative, and also detected one intermediate (Chl(458)) with a strong RLS spectrum but only a weak CD spectrum. We propose that aggregation proceeds via at least three steps: 1) formation of a nucleating species, probably a dimer of chlorophylls; 2) formation of large aggregates with little or no secondary structure (e.g., Chl(458)); and 3) conformational change to form helical aggregate (Chl(469))

Chirality in optical trapping and optical binding

Optical trapping is a well-established technique that is increasingly used on biological substances and nanostructures. Chirality, the property of objects that differ from their mirror image, is also of significance in such fields, and a subject of much current interest. This review offers insight into the intertwining of these topics with a focus on the latest theory. Optical trapping of nanoscale objects involves forward Rayleigh scattering of light involving transition dipole moments; usually these dipoles are assumed to be electric although, in chiral studies, magnetic dipoles must also be considered. It is shown that a system combining optical trapping and chirality could be used to separate enantiomers. Attention is also given to optical binding, which involves light induced interactions between trapped particles. Interesting effects also arise when binding is combined with chirality

Towards artificial photosynthesis : resolving supramolecular packing of artificial antennae chromophores through a hybrid approach

Photosynthesis is a highly cross linked process. However, we can distinguish a set of fundamental building blocks like chlorophylls, which interact to form photosystem, which performs the complex function of water splitting. The key challenge in artificial photosynthesis is to learn how to design systems that can adapt and optimize their topologies in line with self-assembly of natural photosystem. In this thesis I combine different techniques of cross polarization Magic angle spinning Nuclear Magnetic Resonance and Transmission Electron Microscopy with simulation and modeling, to resolve the global packing of molecules which are potential candidates for efficient solar fuel cell devices. This thesis focuses on the packing analysis of three-dimensional structures, which are heterogeneous in nature. I demonstrate a new and general structure determination approach that, in combination with first-principles quantum chemical calculations, establishes the structures of molecularly ordered antenna complexes that lack long-range 3D atomic crystalline order. This is possible despite the absence of a priori information on the space group or atomic coordinates. Chapter 2 describes DATZnS(3ʹ-NMe) parallel stacking in an antiparallel framework with the P2/c space group. 13C CP/MAS NMR yields number of asymmetric sites in the structure and recognition motif. This in conjunction with unit cell parameters and diffraction spots from the Fourier transformation of a TEM image is used to resolve the structure. Supramolecular recognition motif is a characteristic of the packing of the DATZnS(3ʹ-NMe) molecule. The molecular recognition and molecular symmetry steer the packing into a racemic mixture with a c-glide plane and inversion symmetry to release the steric hindrance. Simulation of the LGCP build up curve between specific pairs and electron diffraction were used to validate the proposed packing. Chapter 3 describes the centerosymmetric dimer formation with NMI extending outwards to capture the solar energy. MAS NMR chemical shifts were used to generate a truncated 1,7-perylene-3,4,9,10-tetracarboxylic monoimide dibutylester motif. This motif is further optimized and used for molecular replacement approach to generate a partial 3D electron density approach. The P-1 symmetry obtained from Electron Nano Crystallography is used to graft the naphathelene monoimide substituents. The alkyl chains are modeled using the intermolecular correlation observed in HETCOR. Naphthalene monoimide antennas projecting out from the rows of dimers formed out of rod type D1A2 could capture the light energy and transfer to dimers through FRET. Finally, in chapter 4 C2 molecular symmetry obtained from MAS NMR and DFT modeling is used as the core motif to propose the packing of the DATZnS(4H). Intermolecular correlations obtained from the HETCOR shows the folding of the tails along the phenazine moiety. The analogous modeling showed how the packing could be steered by the NCH3 functional group between antiparallel and parallel dipoles. This understanding opens the way for the evidence based design of light harvesting antenna. In summary, a novel methodology to resolve the structure of chromophore antenna from a structural background with static and dynamic heterogeneity that strongly limits the diffraction response is shown. Furthermore, I anticipate that the insights into packing of the antenna are key to the design of the organic solar fuel cell device in the future.Bio-organic Synthesi

Chlorophyll-Inspired Tunable Metamaterials with Multi-Negative Refractive Index Bands: The Porphyrin Ring and Hydrophobic Tail Effect

Tunable negative electromagnetic properties: permittivity, permeability, and refractive index, in mimic Chlorophyll metamaterial structures in the X- and Ku-band regimes are theoretically and numerically demonstrated. A very broad negative permeability covering the majority of the X- and Ku bands, from 8GHz to 16GHz, is observed, while five negative permittivity bands are found within the same range. The two aforementioned properties result in a broad, greater than 25% bandwidth, low-loss negative-refractive index transmission band. These negative electromagnetic properties can be effectively tailored within the low-loss multi-transmission and the high-loss multi-absorption bands in the operating frequency range by modifying the structure’s tiller part or the artificial hydrophobic or Phytol tail. By focusing either on the transmission or the absorption bands, these passive always-on bio-inspired metamaterials could be utilized in microelectronic, communication and photonic, and optic devices

Mutations in the SmAPRR2 transcription factor suppressing chlorophyll pigmentation in the eggplant fruit peel are key drivers of a diversified colour palette

[EN] Understanding the mechanisms by which chlorophylls are synthesized in the eggplant (Solanum melongena) fruit peel is of great relevance for eggplant breeding. A multi-parent advanced generation inter-cross (MAGIC) population and a germplasm collection have been screened for green pigmentation in the fruit peel and used to identify candidate genes for this trait. A genome-wide association study (GWAS) performed with 420 MAGIC individuals revealed a major association on chromosome 8 close to a gene similar to APRR2. Two variants in SmAPRR2, predicted as having a high impact effect, were associated with the absence of fruit chlorophyll pigmentation in the MAGIC population, and a large deletion of 5.27 kb was found in two reference genomes of accessions without chlorophyll in the fruit peel. The validation of the candidate gene SmAPRR2 was performed by its sequencing in a set of MAGIC individuals and through its de novo assembly in 277 accessions from the G2P-SOL eggplant core collection. Two additional mutations in SmAPRR2 associated with the lack of chlorophyll were identified in the core collection set. The phylogenetic analysis of APRR2 reveals orthology within Solanaceae and suggests that specialization of APRR2-like genes occurred independently in Cucurbitaceae and Solanaceae. A strong geographical differentiation was observed in the frequency of predominant mutations in SmAPRR2, resulting in a lack of fruit chlorophyll pigmentation and suggesting that this phenotype may have arisen and been selected independently several times. This study represents the first identification of a major gene for fruit chlorophyll pigmentation in the eggplant fruit.This work has been funded by grants RTI-2018-094592-BI00 and PID2021-128148OB-I00 funded by MCIN/AEI/10.13039/501100011033/and by "ERDF A way of making Europe", and by European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement No. 677379 (G2P-SOL project: Linking genetic resources, genomes and phenotypes of Solanaceous crops). AA is grateful to Spanish Ministerio de Ciencia, Innovacio ' n y Universidades for a predoctoral (FPU18/01742) contract. PG is grateful to Spanish Ministerio de Ciencia e Innovacion for a post-doctoral grant (FJC2019-038921-I/AEI/10.13039/501100011033). Funding for open access charge: Universitat Politecnica de Valencia.Arrones-Olmo, A.; Mangino, G.; Alonso-Martín, D.; Plazas Ávila, MDLO.; Prohens Tomás, J.; Portis, E.; Barchi, L.... (2022). Mutations in the SmAPRR2 transcription factor suppressing chlorophyll pigmentation in the eggplant fruit peel are key drivers of a diversified colour palette. Frontiers in Plant Science. 13:1-14. https://doi.org/10.3389/fpls.2022.10259511141