Joint Center for Artificial Photosynthesis

The successive photosubstitution reaction from cis ‐[Ru(bpy) 2 (MeCN) 2 ] 2+ to cis‐ [Ru(bpy) 2 (pz)(pzH)] + was investigated under various conditions (bpy = 2,2′‐bipyridine, pzH = pyrazole). Temperature‐dependent studies revealed that distinct mechanistic features: the first step, conversion from cis ‐[Ru(bpy) 2 (MeCN) 2 ] 2+ to cis ‐[Ru(bpy) 2 (pzH)(MeCN)] 2+ , proceed in a temperature‐independent manner, whereas the second step, yielding cis‐ [Ru(bpy) 2 (pz)(pzH)] + , is strongly temperature‐dependent with an activation energy of 12.8 ± 1.4 kJ/mol. Transient absorption spectroscopy of the intermediate, cis‐ [Ru(bpy) 2 (pzH)(MeCN)] 2+ , determined an activation energy of 18.6 ± 0.3 kJ/mol for the transition from the 3 MLCT to 3 MC states, consistent with the activation energy observed for second photosubstitution reactions (MLCT: metal‐to‐ligand charge–transfer, MC: metal‐centered). The first photosubstitution was unaffected by the nature of incoming imine ligands, indicating that the photodissociation of acetonitrile occurs rapidly. In contrast, the second photosubstitution step was influenced by the σ‐donating ability of the pyrazole ligand and the basicity of the base, which facilitates deprotonation and promotes intramolecular hydrogen bonding between pyrazole ligands. The photosubstitution product, cis ‐[Ru(bpy) 2 (pz)(pzH)] + , exhibited 3 MLCT‐state lifetimes that were much shorter by nearly an order of magnitude compared to the intermediate, as determined from the transient absorption spectra.

Panchromatic dyes extending the absorption up to the near-infrared region stand out as excellent candidates for light harvesting and biological applications. One of the viable ways to construct panchromatic dyes involves the strategic selection of a molecular platform that can accommodate multiple chromophores absorbing at varied wavelength ranges. Even though azadipyrromethene (azaBODIPY) offers such a molecular skeleton, reports on broadband absorbing azaBODIPYs and related photoinduced interchromophore energy/electron transfer events intending to provide desirable functions such as electron migration and charge separation (CS) are still inadequate. In this context, multiheteroaromatic tethered azaBODIPY, (PTZ)2-AB-(TPA)2, containing phenothiazine (PTZ) and triphenylamine (TPA) integrated into azaBODIPY core has been synthesized and light-induced electron transfer events were explored. Parallely, control compounds involving azaBODIPYs with either TPA or PTZ moieties, (Ph)2-AB-(TPA)2 and (PTZ)2-AB-(Ph)2, and pristine Et-PTZ and TPA were synthesized, and the roles of the individual constituents in the photoinduced events are investigated. Optical absorption studies have revealed that the substitution of azaBODIPY skeleton with PTZ and TPA moieties at 1,7- and 3,5-positions enhanced the extended π-conjugation and resulted in broader absorption extending beyond 1000 nm. Electrochemical studies have displayed first oxidation from either TPA or PTZ, and first reduction from the azaBODIPY moieties indicating that TPA or PTZ would behave as electron donors and azaBODIPY as the electron acceptor, and computational studies have corroborated the results. Steady-state fluorescence studies in solvents of varied polarity, involving selective excitation of PTZ at 265 nm and TPA at 300 nm resulted in quenching of the PTZ or TPA emission indicating the occurrence of photoinduced electron transfer (PET) from 1PTZ* or 1TPA* to azaBODIPY. Time-correlated single photon counting studies confirmed the quenching of overall lifetimes of the azaBODIPYs indicating the presence of PET within these systems. Systematic femtosecond transient absorption studies revealed the optical signatures of TPA+• or PTZ+• displayed at 550 and 650 nm, respectively, authenticating the occurrence of PET from excited TPA or PTZ to azaBODIPY with a very short formation time of CS states (14, 61, and 7 ps for (PTZ)2-AB-(Ph)2, (Ph)2-AB-(TPA)2 and (PTZ)2-AB-(TPA)2, respectively), and a long charge recombination in the nanosecond time domain, and highlighted the versatility of azaBODIPY as an electron relay in light-induced events.

プラスチック原料の中でも，フマル酸は有用な不飽和ジカルボン酸であり，不飽和ポリエステル樹脂や生分解性ポリブチレンサクシネート（PBS），ポリプロピレンフマレート（PPF）等の前駆体である。フマル酸製造ではその一部がベンゼンのような石油由来の原料から製造されるため，バイオマス由来の再生可能な化合物を原料とし，太陽光のような外部再生可能エネルギーを用いて製造することが求められている。さらに，フマル酸製造にCO2を利用できれば，再生可能エネルギーによるCO2の回収・利用・貯蔵（CCUS）技術につながると期待される。本研究では，トリエタノールアミンを電子供与体，水溶性カチオン性亜鉛ポルフィリン，亜鉛テトラキス（4-N,N,N-トリメチルアミノフェニル）ポルフィリン（ZnTMAP4＋）を光増感剤およびロジウム錯体（[Cp∗Rh(bpy)(H2O)]2＋; Cp∗＝ペンタメチルシクロペンタジエニル，bpy＝2,2’-ビピリジル）を選択的NAD＋還元触媒としたNADH再生系とSulfobus tokodaii由来リンゴ酸デヒドロゲナーゼ（オキサロ酢酸脱炭酸酵素 ; MDH ; EC 1.1.1.38）とブタ心臓由来フマラーゼ（FUM; EC 4.2.1.2）からなる二元生体触媒を連携させたピルビン酸塩とCO2ガスを原料とする可視光駆動型フマル酸塩生成系を構築した。この系に可視光照射することによって定常的にピルビン酸塩とCO2ガスからフマル酸塩が生成した。可視光照射5時間後のピルビン酸塩からフマル酸への収率は2.0 %と見積もられた。

Plants photosynthesize with light that falls within the Photosynthetically Active Radiation (PAR, 400-700 nm) and this limits the rate of photosynthesis of leaves in the shade. In an agricultural field, where crops are usually grown in dense canopies, this is a severe loss factor for crop growth. In recent years, several cyanobacteria have been discovered that can perform oxygenic photosynthesis with near infrared (NIR, 700-800 nm) light that falls outside of the range of PAR. Their capacity to do so proves that it is possible to split water with photons of lesser energy, breaking the long-held paradigm of the scientific community that the fundamental energetic limit for this process was linked to the energy of the photons on the red edge of PAR. These discoveries have therefore sparked the idea of introducing these capabilities into plants, which – as discussed – would be especially beneficial for growing crops in dense canopies. The central goal of this research was to lay the groundwork for creating plants that, like these cyanobacteria, are proficient in far red photosynthesis. To start, we discuss which strategies several oxygenic photosynthetic organisms already use to harvest far-red light. Then, in more detail we have investigated the molecular mechanisms of light-harvesting of a particular antenna system that is capable of harvesting the far red and which is synthesized under low-light conditions during the so-called LoLiP response in some cyanobacteria. Using Cryo-electron microscopy we elucidate the unique helical shape of this antenna system, which we call far-red light allophycocyanin (FRL-AP). Using ultrafast transient absorption spectroscopy we show that excitation energy transfer between different FRL-AP subunits occurs within less than a picosecond. By using structure-based modelling of the transient absorption data it could be inferred that excitation energy diffusion between the low energy subunits should however be slow in FRL-AP, possibly making it a relatively inefficient antenna. Furthermore, it is shown that the FRL-AP far red absorption properties stem from the phycocyanobilins (PCBs) in the α-subunits that in the helical phycobilisome adopt a flattened conformation which increases their effective conjugation length, and is the result of the complexation of α-subunits with β-subunits. Next we investigated the natural capabilities of plant light-harvesting complexes to bind and function with redshifted chlorophylls (Chls). Both LHCII, which is the major antenna complex of PSII, and Lhca4, which is an antenna system of PSI, were reconstituted with pigment mixes containing redshifted Chls. In both LHCII and Lhca4 the redshifted Chls were functionally integrated in the Light-Harvesting Complex (LHC) protein scaffolds and both complexes were properly folded. Both reconstituted LHCs displayed significantly boosted absorption in the NIR region. Ultrafast time-resolved measurements revealed that the energy transfer dynamics were still ultrafast in these complexes. Furthermore, their excited state decay kinetics were not shortened. Interestingly, in both LHCII and Lhca4 the location of the lowest energy site was preserved and filled by Chl d. In Lhca4 this led to the combined action of red-shifting through the use of inherently lower energy absorbing pigments and of red-shifting by inducing exciton-CT mixing between the pigments, resulting in the red-most absorption properties ever reported for a plant LHC. Both studies clearly indicate that it is possible to obtain fully functional plant LHCs that bind red-shifted Chls, paving the way for their introduction into plants. Finally, using computational tools we investigated the Chl binding selectivity of LHCII for Chl a and b, using time-resolved spectroscopy we elucidated the excitation energy flows in the LHCII-CP24-CP29 PSII subcomplex and we showed the performance of our patented propagation synchronous integration scheme for streak camera’s that increases their sensitivity by a factor of ten.

Oxygen evolution reaction (OER) plays a crucial role as a counter half-reaction for both electrochemical hydrogen production through water splitting and the generation of valuable carbon compounds via CO2 reduction. To overcome the sluggish kinetics of the OER, significant efforts have been devoted to developing cost-effective, sustainable, and efficient electrocatalysts, with transition-metal-based catalysts emerging as promising candidates. Herein, we successfully synthesized a core-shell type nanostructure of Fe-doped CoMoOx/CoMoOx (CMFO), which exhibits excellent electrocatalytic properties for OER. The presence of an amorphous layer of Fe-doped CoMoOx with abundant oxygen vacancies, along with the stability of a key OER intermediate, *O, contributes to the enhanced activity of CMFO catalyst compared to pristine CoMoOx (CMO). The optimized catalyst of CMFO-550 achieved much lower overpotential and Tafel slope and also exhibited better remarkable long-term stability for over 90 h compared to CMO-550. These findings highlight the potential of CMFO-550 as a cost-effective and highly efficient electrocatalyst for the OER. The successful development of this core-shell nanostructure opens up a new opportunity for the design and synthesis of advanced electrocatalysts for the OER, with implications for various applications in energy conversion and storage.

Aloe vera-derived graphene (ADG) coupled system photocatalyst, mimicking natural photosynthesis, is one of the most promising ways for converting solar energy into ammonia (NH3 ) and nicotinamide adenine dinucleotide (NADH) that have been widely used to make the numerous chemicals such as fertilizer and fuel. In this study, we report the synthesis of the aloe vera-derived graphene-coupled phenosafranin (ADGCP) acting as a highly efficient photocatalyst for the generation of NH3 and regeneration of NADH from nitrogen (N2 ) and oxidized form of nicotinamide adenine dinucleotide (NAD+ ). The results show a benchmark instance for mimicking natural photosynthesis activity as well as the practical applications for the solar-driven selective formation ofNH3 and the regeneration of NADH by using the newly designed photocatalyst.

Two fundamental problems now are: the growing contamination of water throughout the world, and the progressive loss of fertility of agricultural soil. The lack of revenue is a significant impediment to financing water. Water pollution is a key part of the climate change. Unless the water sector addresses efficiently the challenges inhibiting creditworthiness, new sources of revenue aren´t likely to flow to the water sector. There are two ways to pay for water infrastructure: tariffs and taxes. Worldwide, there is the cycle of “building” water infrastructure, and then “neglecting” it by not maintaining or repairing these assets because the resources aren’t available. Specifically, when local governments, water utilities, and other providers can significantly expands their collection systems efficiently, improves significantly water quality, reducing the non-revenue water, and decrease energy costs, then they can become viable, efficient, safe, and bankable service providers. Current methods to improve water quality date back to the French Revolution, and to date they are carried out on a larger scale, with more sophistication, greater energy expenditure, more CO2 emissions, greater production of toxic sludge, and yet, the quality of the water is not better, on the contrary it is declining as the contamination of the water continues to be incessantly, increasingly, cumulative and more and more complex. Despite the centuries that have passed, one factor has gone relatively disregarded: the levels of dissolved oxygen in the water and in soil. The better the quality of the water, the higher the levels of dissolved oxygen, and vice versa. Which also applies to agricultural soil, because the more oxygen is present, the more fertile the soil and vice versa. Addressing the low levels of dissolved oxygen in the water, until now it seems that it is considered as something secondary, as if it were something accessory, something like a parameter that would even improve spontaneously as soon as the levels of contamination of the precious liquid improve. But this has not happened so far with any method and in any part of the world. In addition to a lack of interest in developing processes to raise dissolved oxygen levels in the water and soil, there is the problem that the few available to date are too expensive. But the discovery of the unsuspected capacity of the human body to extract oxygen from water, dissociating it like plants; it means a light at the end of the tunnel.

Journal of Clinical & Experimental Immunology, list of open access journals, open access, open access journals, open access publication, open access publisher, open access publishing, open access journal articles, Opast Publishing Group, Articles in Press

Electrochemical CO2 reduction provides a promising route to the sustainable generation of valuable chemicals and fuels. Tandem catalysts enable sequential CO2-to-CO and CO-to-multicarbon (C2+) product conversions on complementary active sites, to produce high C2+ Faradaic efficiency (FE). Unfortunately, previous tandem catalysts exhibit poor management of CO intermediates, which diminishes C2+ FE. Here, we design segmented gas-diffusion electrodes (s-GDEs) in which a CO-selective catalyst layer (CL) segment at the inlet prolongs CO residence time in the subsequent C2+-selective segment, enhancing conversion. This phenomenon enables increases in both the CO utilization and C2+ current density for a Cu/Ag s-GDE compared to pure Cu, by increasing the *CO coverage within the Cu CL. Lastly, we develop a Cu/Fe-N-C s-GDE with 90% C2+ FE at C2+ partial current density (jC2+) exceeding 1 A cm−2. These results prove the importance of transport and establish design principles to improve C2+ FE and jC2+ in tandem CO2 reduction.