Lactiplantibacillus plantarum, a commensal lactic acid bacterium, is capable of performing mediated EET using flavins and quinones as small molecule redox mediators, together with its highly conserved FLEET gene locus encoding a type-II NADH dehydrogenase (Ndh2), flavin transport proteins, membrane demethylmenaquinone (DMK) synthesis proteins (DmkA, EetA, and EetB), and flavin mononucleotide (FMN) cofactor (PlpA). Recent studies by our group showed that Ndh2 is required for utilization of quinone mediators. Although L. plantarum has defined pathways that utilize quinones, it is incapable of producing them, and instead, must acquire quinones exogenously from its environment. Quinones are known to be abundant in many environmental niches, with high concentrations present in human gut. L. plantarum can convert exogenously acquired DHNA (1; 1,4-dihydroxy-2-naphthoic acid), an intermediate in the biosynthesis of menaquinone (vitamin K), to demethylmenaquinone through prenylation by DmkA. L. plantarum uses a variety of exogenous quinone mediators, though very little is known about their specificity for Ndh2. A small study that evaluated the Ndh2-dependent EET of six commercially available mediators indicated that reduction potential (E o ) and predicted free energy of binding (ΔGcomp) impacted EET activity. However, that study was limited in scope and only evaluated commercially available, structurally related 1,4-naphthoquinones, and one benzoquinone analog as mediators. For a mediator to be viable for EET, it must possess certain physicochemical properties and favorable biological interactions. In addition to binding favorably to Ndh2, mediators must have a favorable E o to accept an electron from Ndh2 and pass it to a given TEA. A mediator must also be lipophilic enough to diffuse through a lipid bilayer, yet have a diffusion coefficient (Dwater) that supports diffusion through aqueous environments to an insoluble TEA (Fig. ). However, a mediator's EET activity is unlikely to be equally dependent on each of these parameters as the timescale of each varies. Of the steps that a mediator must accomplish, the electron transfer is known to occur on the microto milli-second timescale and just requires an acceptable E o to facilitate the transfer of electrons. Meaning, the mediator must simply have a E o between that of Ndh2 and the TEA. We hypothesize that other physicochemical properties of the mediator, such as Dwater, lipophilicity (LogD), and topological polarization surface area (tPSA), have a larger impact on EET activity as they drive slower, potentially rate-limiting steps. Passive transport through a membrane and diffusion through an aqueous environment occur on the timescale of milliseconds for compounds with favorable properties but can be much slower for larger, charged compounds. This is up to an order of magnitude slower than the redox chemistry, thus we hypothesize these properties are likely very important for EET activity. Herein, we aim to better understand the chemical properties most important to mediating Ndh2-dependent EET in L. plantarum. A library of quinones, including naphtho-, anthra-, and benzoquinones, was designed to probe diverse chemical properties with a focus on polarity and lipophilicity. The mediator library was inspired by natural products that have previously exhibited shuttling properties. Our library was assembled using semi-synthesis to derivatize three scaffolds, isolated from natural sources, or acquired commercially. Examining the relationship between Ndh2-dependent EET activity with physicochemical and biochemical properties of the mediators revealed that LogD and ΔGcomp significantly correlates to increased EET activity (p < 0.0001 and p = 0.0115, respectively). Analysis of a subset of the mediators in a BES confirmed that select mediators can perform Ndh2-dependent EET using a carbon felt anode as the TEA, producing a stable current for duration of the experiment (up to 5 days).