Lignin-Induced CaCO3 Vaterite Structure for Biocatalytic Artificial Photosynthesis

Bio-Inspired Photosynthesis Platform for Enhanced NADH Conversion and L-Glutamate Synthesis

Inspired by the layered structure, light absorption, and charge carrier pathway of chloroplast thylakoids in natural photosynthesis, we propose a novel artificial photosynthesis platform, which is composed of layered structured vaterite as the scaffold with gold nanoparticles (AuNPs), photosensitizer eosin Y (EY), and redox enzyme L-glutamate dehydrogenase (GDH) as the functional components. The EY exhibited significantly enhanced light absorption and charge carrier generation due to the localized surface plasmon resonance (LSPR) around the AuNPs and light refraction within the layers. This artificial photosynthesis platform can regenerate reduced nicotinamide adenine dinucleotide (NADH) under visible light and promote the rapid conversion of α-ketoglutarate to L-glutamate (0.453 Mm/h). The excellent biocompatibility of layered vaterite significantly enhances the resistance of GDH to harsh conditions, including high pH (pH = 10) and elevated temperatures (37-57 °C).

Review on Microreactors for Photo-Electrocatalysis Artificial Photosynthesis Regeneration of Coenzymes

In recent years, with the outbreak of the global energy crisis, renewable solar energy has become a focal point of research. However, the utilization efficiency of natural photosynthesis (NPS) is only about 1%. Inspired by NPS, artificial photosynthesis (APS) was developed and utilized in applications such as the regeneration of coenzymes. APS for coenzyme regeneration can overcome the problem of high energy consumption in comparison to electrocatalytic methods. Microreactors represent a promising technology. Compared with the conventional system, it has the advantages of a large specific surface area, the fast diffusion of small molecules, and high efficiency. Introducing microreactors can lead to more efficient, economical, and environmentally friendly coenzyme regeneration in artificial photosynthesis. This review begins with a brief introduction of APS and microreactors, and then summarizes research on traditional electrocatalytic coenzyme regeneration, as well as photocatalytic and photo-electrocatalysis coenzyme regeneration by APS, all based on microreactors, and compares them with the corresponding conventional system. Finally, it looks forward to the promising prospects of this technology.

Size and phase preservation of amorphous calcium carbonate nanoparticles in aqueous media using different types of lignin for contrast-enhanced ultrasound imaging

HYPOTHESIS

Calcium carbonate (CaCO3) nanoparticles could have great potential for contrast-enhanced ultrasound imaging (CEUS) due to their gas-generating properties and sensitivity to physiological conditions. However, the use of nano CaCO3 for biomedical applications requires the assistance of stabilizers to control the size and avoid the fast dissolution/recrystallization of the particles when exposed to aqueous conditions.

EXPERIMENTS

Herein, we report the stabilization of nano CaCO3 using lignin, and synthesized core-shell amorphous CaCO3-lignin nanoparticles (LigCC NPs) with a diameter below 100 nm. We have then investigated the echogenicity of the LigCC NPs by monitoring the consequent generation of contrast in vitro for 90 min in linear and non-linear B-mode imaging.

FINDINGS

This research explores how lignin type and structure affect stabilization efficiency, lignin structuration around CaCO3 cores, and particle echogenicity. Interestingly, by employing lignin as the stabilizer, it becomes possible to maintain the echogenic properties of CaCO3, whereas the use of lipid coatings prevents the production of signal generation in ultrasound imaging. This work opens new avenue for CEUS imaging of the vascular and extravascular space using CaCO3, as it highlights the potential to generate contrast for extended durations at physiological pH by utilizing the amorphous phase of CaCO3.

Enhanced Photocatalytic Efficiency in Visible-Light-Induced NADH Regeneration by Intramolecular Electron Transfer

Inspired by natural photosynthesis, photocatalytic NADH regeneration has drawn increasing interest in the recent decade as it provides a perfect approach for NAD⁺ reduction into NADH, which can be further consumed by oxidordeuctase for enzymatic redox reactions. However, two issues still remain unsolved in this procedure. First, the photocatalytic efficiency in NAD⁺ hydrogenation requires further improvement. Second, the rhodium electron mediator [Cp*Rh(bpy)H₂O]²⁺ (M), which is always required for selective 1,4-NADH regeneration, is difficult to recover because of its good solubility in aqueous solution. Given the high price of M, it is highly wasteful and inefficient if it only spends once. Here, we report a Cp*Rh(bpy)Cl implanted conjugated microporous polymer DTS/Rh@CMPs which can be employed as a highly effective visible light photocatalysts for in situ NADH regeneration without using additional M. In addition, the insertion of Rh complex into a polymer skeleton, as demonstrated in UV-vis, fluorescence, photocurrent and electrochemical impedance, dramatically improves the light absorption capacity and the electron separation and transfer efficiency. Compared with that of DTS@CMP-1 with M, an enhanced reaction yield of 33% was determined in DTS/Rh@CMP-1 suggesting that intramolecular electron transfer has a better activity than that of intermolecular electron transfer in photocatalytic NAD⁺ reduction. Moreover, as the Rh complex is rooted firmly in a polymer framework, negligible Rh loss and conversion decrease in NADH regeneration are observed. When the DTS/Rh@CMP-1 was coupled with yeast alcohol dehydrogenase (YADH, from Saccharomyces cerevisiae), 1.36 mM of methanol was accumulated, implying an excellent biocompatibility of DTS/Rh@CMP-1 and a high feasibility of photobiocatalysis for formaldehyde hydrogenation.

Unbiased Photoelectrode Interfaces for Solar Coupling of Lignin Oxidation with Biocatalytic C═C Bond Hydrogenation

The pulp and paper manufacturers generate approximately 50 million metric tons of lignin per annum, most of which has been abandoned or incinerated because of lignin's recalcitrant nature. Here, we report bias-free photoelectrochemical (PEC) oxidation of lignin coupled with asymmetric hydrogenation of C═C bonds. The PEC platform consists of a hematite (α-Fe₂O₃) photoanode and a silicon photovoltaic-wired mesoporous indium tin oxide (Si/mesoITO) photocathode. We substantiate a new function of photoelectroactivated α-Fe₂O₃ to extract electrons from lignin. The extracted electrons are transferred to the Si/mesoITO photocathode for regenerating synthetic nicotinamide cofactor analogues (mNADHs). We demonstrate that the reduction kinetics of mNAD⁺s depend on their reduction peak potentials. The regenerated mNADHs activate ene-reductases from the old yellow enzyme (OYE) family, which catalyze enantioselective reduction of α,β-unsaturated hydrocarbons. This lignin-fueled biocatalytic PEC system exhibits an excellent OYE's turnover frequency and total turnover number for photobiocatalytic trans-hydrogenation through cofactor regeneration. This work presents the first example of PEC regeneration of mNADHs and opens up a sustainable route for bias-free chemical synthesis using renewable lignin waste as an electron feedstock.

Microfluidic artificial photosynthetic system for continuous NADH regeneration and l-glutamate synthesis

Artificial photosynthesis coenzyme regeneration and photoenzymatic synthesis of l-glutamate by glutamate dehydrogenase.