Fatty acid photodecarboxylase (FAP), a microalgal enzyme, is one of the rare photoenzymes found in nature. Since its discovery in 2017, FAP has made a huge impact in the field of photobiocatalysis, being so far the only photoenzyme with potential applicability for organic synthesis. Furthermore, among all studied enzymes to date, FAP is one of the most promising candidates for in vitro feasible biofuel production from oil. One field of study for FAP has been broadening its substrate scope and modulating substrate selectivity. In order to get insight into the enzyme’s substrate selectivity, as well as to generate a toolbox of mutant enzymes with distinct substrate preferences toward medium- and long-chain fatty acids, in this work, we carried out extensive mutagenesis of the active-site residues of FAP from Chlorella variabilis (CvFAP). Particularly, we performed partial-site saturation mutagenesis for the Y466 position due to its key location at the active site. Our experimental and computational analysis indicated a correlation between the exchanged amino acid type and the observed activity, demonstrating that the conventional binding mode of long-chain fatty acids is destabilized by charged amino acid residues, leading to a nonproductive binding conformation characterized by a compact folded form. Mutagenesis of other key residues around the substrate binding site led to variants with selectivity toward medium-chain or long-chain fatty acids. For example, we obtained enzyme variants that are highly selective toward either C12:0, C14:0, or C18:0/C18:1 fatty acids. Selectivity patterns agreed very well with the distances between the FAD cofactor and substrate, as calculated by our molecular dynamics simulations. Furthermore, we report unexplored activity of the wild-type CvFAP toward C20:1 and C22:1 fatty acids, which are major components of jojoba oil and rapeseed oil, respectively.

Spectrally tunable nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) are modified with titanium dioxide (TiO2) coatings via atomic layer deposition and used as model optoelectronic platforms to harness slow light for photocatalysis under visible-NIR illumination. Photocatalytic breakdown of methylene blue (MB) with a visible absorbance band is used as a benchmark reaction to unveil the mechanism of slow light-enhanced photocatalysis in TiO2-NAA-DBRs with a tunable photonic stop band (PSB) and thickness of TiO2. Assessment of the optical arrangement between MB's absorbance band and the PSB of TiO2-NAA-DBRs is used to identify and quantify slow light contributions in driving this model photocatalytic breakdown reaction. Our findings reveal that photodegradation rates rely on both the spectral position of PSB and thickness of the semiconductor. The performance of these photocatalysts is the maximum when the red edge of the PSB is spectrally close to the red or blue boundary of the MB's absorbance band and to dramatically decrease within the absorbance maximum of MB due to light screening by dye molecules. It is also demonstrated that TiO2-NAA-DBRs featuring thicker photoactive TiO2 layers can harvest more efficiently incident slow light by generating extra pairs of charge carriers on the semiconductor coating's surface. The crystallographic phase of TiO2 in the functional coatings is found to be critical in determining the performance of these model photocatalyst platforms, where the anatase phase provides ∼69% higher performance over its amorphous TiO2 form. This study provides opportunities toward the development of energy-efficient photocatalysts for environmental remediation and energy generation and other optoelectronic applications.

A direct synthesis of lactams (5-, 6-, and 7-membered) starting from amino-alcohols in a bienzymatic cascade is reported. Horse liver alcohol dehydrogenase together with the NADH oxidase from Streptococcus mutans were applied for the oxidative lactamization of various amino alcohols. Crucial parameters for the efficiency of this cascade reaction were elucidated. This report represents a direct approach for biocatalytic oxidative lactamization reaction.

Hot charge carriers from plasmonic nanomaterials currently receive increased attention because of their promising potential in important applications such as solar water splitting. While a number of important contributions were made on plasmonic charge carrier generation and their transfer into the metal's surrounding in the last decades, the local origin of those carriers is still unclear. With our study employing a nanoscaled bicontinuous network of nanoporous gold, we take a comprehensive look at both subtopics in one approach and give unprecedented insights into the physical mechanisms controlling the broadband optical absorption and the generation and injection of hot electrons into an adjacent electrolyte where they enhance electrocatalytic hydrogen evolution. This absorption behavior is very different from the well-known localized surface plasmon resonance effects observed in metallic nanoparticles. For small ligament sizes, the plasmon decay in our network is strongly enhanced via surface collisions of electrons. These surface collisions are responsible for the energy transfer to the carriers and thus the creation of hot electrons from a broad spectrum of photon energies. As we reduce the gold ligament sizes below 30 nm, we demonstrate an occurring transition from absorption that is purely exciting 5d-electrons from deep below the Fermi level to an absorption which significantly excites "free" 6sp-electrons to be emitted. We differentiate these processes via assessing the internal quantum efficiency of the gold network photoelectrode as a function of the feature size providing a size-dependent understanding of the hot electron generation and injection processes in nanoscale plasmonic systems. We demonstrate that the surface effect, compared with the volume effect, becomes dominant and leads to significantly improved efficiencies. The most important fact to recognize is that in the surface photoeffect presented here, absorption and electron transfer are both part of the same quantum mechanical event.

The use of oxidoreductases in organic-aqueous biphasic systems is advantageous (effective solvation of reactants, minimization of substrate/product-induced inhibition, improved volumetric productivity, and straightforward downstream processing). This paper explores the effects of organic solvents on horse liver alcohol dehydrogenase (HLADH) by combining experimental and computational studies. Various organic solvents displaying a broad range of hydrophobicity and functionalities are used, namely, ethyl acetate, 2-methyltetrahydrofuran, methyl tert-butyl ether, cyclopentyl methyl ether, toluene, cyclohexane, heptane, and dodecane. The catalytic performance of model enzyme horse liver alcohol dehydrogenase concerning its activity, stability, and selectivity is experimentally evaluated. The results are interpreted with molecular dynamics simulations by assessing the (i) protein location in biphasic media, (ii) organic solvent distribution, and (iii) enzyme conformation. Herein, the stability states the robustness of the enzyme while storing it in biphasic media without catalysis taking place. Overall, different toxicities of the solvent to the enzyme can be pinpointed: "molecular toxicity", related to the solvent functional groups, and "interfacial toxicity", related to the position of the enzyme at the interface. Likewise, some solvents are more prone to be located close to the active site of the enzyme, triggering other effects on the enzymatic performance. Thus, methyl tert-butyl ether resulted as an optimal option for the enzyme, whereas other solvents like toluene and 2-methyltetrahydrofuran were detrimental. The combined forces of experiments and simulations have been shown to be useful tools to study the effects of reaction media, thus guiding solvent selection.