Monolayer Fullerene Membranes for Hydrogen Separation

Hydrogen separation membranes are a critical component in the emerging hydrogen economy, offering an energy-efficient solution for the purification and production of hydrogen gas. Inspired by the recent discovery of monolayer covalent fullerene networks, here we show from concentration-gradient-driven molecular dynamics that quasi-square-latticed monolayer fullerene membranes provide the best pore size match, a unique funnel-shaped pore, and entropic selectivity. The integration of these attributes renders these membranes promising for separating H2 from larger gases such as CO2 and O2. The ultrathin membranes exhibit excellent hydrogen permeance as well as high selectivity for H2/CO2 and H2/O2 separations, surpassing the 2008 Robeson upper bounds by a large margin. The present work points toward a promising direction of using monolayer fullerene networks as membranes for high-permeance, selective hydrogen separation for processes such as water splitting.

Onggi's permeability to carbon dioxide accelerates kimchi fermentation

Since ancient times, Korean chefs have fermented foods in an onggi, a traditional earthenware vessel. The porous structure of the onggi mimics the loose soil where lactic acid bacteria is naturally found. This permeability has been purported to facilitate the growth of lactic acid bacteria, but the details of the process remain poorly understood. In this combined experimental and theoretical study, we ferment salted napa cabbage in onggi and hermetic glassware and measure the time course of carbon dioxide concentration, which is a signature of fermentation. We present a mathematical model for carbon dioxide generation rate during fermentation using the onggi's gas permeability as a free parameter. Our model provides a good fit for the data, and we conclude that porous walls help the onggi to 'exhale' carbon dioxide, lowering internal levels to those favoured by lactic acid bacteria. The positive pressure inside the onggi and the constant outflow through its walls act as a safety valve for bacteria growth by blocking the entry of external contaminants without mechanical components. We hope this study draws attention to the work of traditional artisans and inspires energy-efficient methods for fermenting and storing food products.

Surface of CuO Nanoparticles Modified by p-Benzoquinone for N2-Selective Membrane

In this study, CuO nanoparticles and p-benzoquinone (p-BQ) were added to a polyvinylpyrrolidone (PVP) matrix to increase N₂/CO₂ selectivity. The added p-BQ allowed CuO to be distributed in a uniform size in the PVP/CuO composite membrane and the matrix to be flexible by forming the interaction with PVP. The surface modification of CuO by p-BQ and the well-dispersed size affected the increase in the separation performance. The PVP/CuO/p-BQ composite membranes showed an N₂/CO₂ selectivity of about 23.1 with N₂ permeance of about 13.3 GPU, while the separation performance of PVP was not observed. The enhanced separation performance is attributable to the surface of CuO nanoparticles modified by p-BQ inducing CO₂ molecules to be relatively slowly transported by the adsorption properties in the polymer matrix. The chemical properties and coordinative interaction for PVP/CuO/p-BQ composite membrane were measured by FT-IR spectroscopy, thermogravimetric analysis, UV-vis, scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy.

Novel Polyelectrolyte Complex Membranes Containing Carboxymethyl Cellulose-Gelatin for Pervaporation Dehydration of Azeotropic Bioethanol for Biofuel

Polyelectrolyte complex membranes (PECMs) were prepared by combining sodium carboxymethyl cellulose (NaCMC) and gelatin (Ge) with variations in the Ge content in the NaCMC matrix. Characterization methods, such as infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), contact angle analysis (CA), and universal testing machines (UTM) were used to investigate the physicochemical studies of the prepared membranes. The pervaporation characteristics of membranes with Ge content were investigated using an azeotropic mixture of water and bioethanol. The obtained data revealed that the membrane with 15 mass% of Ge (M-3) showed a maximum flux of 7.8403 × 10^-2 kg/m²·h with separation selectivity of 2917 at 30 °C. In particular, the total and water flux of PECMs are shown as very close to each other indicating that the fabricated membranes could be employed to successfully break the azeotropic point of water-bioethanol mixtures. Using temperature-dependent permeation and diffusion data, the Arrhenius activation parameters were calculated, and the obtained values of water permeation (E_pw) were considerably smaller than bioethanol permeation (E_pE). Developed membranes showed the positive heat of sorption (ΔH_s), suggesting that Henry's sorption mode is predominant.

Trends and errors in reverse osmosis membrane performance calculations stemming from test pressure and simplifying assumptions about concentration polarization and solute rejection

A primary goal in the design of reverse osmosis (RO) membranes is to improve water-solute selectivity and water permeance. These transport properties are commonly calculated in the literature using the solution-diffusion model with selectivity (A/B, bar-1) defined as the ratio between water permeance (A, L.m-2.h-1.bar-1) and solute permeance (B, L.m-2.h-1). In calculating transport properties, researchers often use simplifying assumptions about concentration polarization (CP; i.e., assuming negligible CP or a certain extent of CP) and solute rejection (i.e., assuming solute rejection is approximately 1 to enable the explicit use of the CP modulus in solute permeance calculations). Although using these assumptions to calculate transport properties is common practice, we could not find a study that evaluated the errors associated with using them. The uncertainty in these errors could impede unequivocally identifying manufacturing approaches that break through the commonly plotted trade-off frontier between selectivity and water permeance (A/B vs. A); however, we did not find in the literature a study that quantified such errors. Accordingly, we aimed to: (1) quantify the error in transport properties (A, B, and A/B) calculated using common simplifying assumptions about CP and rejection; and (2) determine if using simplifying assumptions affects conclusions drawn about membrane performance or trends concerning the trade-off frontier. Results show that compared with the case where no simplifying assumptions were made, simplified calculations were least accurate at low pressures for water permeance (up to 78% overestimation) and high pressures for solute permeance (up to 188% overestimation). Accordingly, the corresponding selectivities were least accurate at low pressure (up to 111% overestimation) and high pressure (up to 66% underestimation), and conclusions drawn about membrane performance and trade-off trends were pressure-dependent. Importantly, even in the absence of simplifying assumptions, selectivity results were pressure-dependent, indicating the importance of standardizing test conditions for the continued use of current performance metrics (i.e., A/B and A). We propose a two-pressure approach-collecting data for A and B at a high and a low pressure, respectively-combined with simplifying assumptions for more accurate simplified estimations of selectivity (< 10% absolute error). Our work contributes to a better understanding of the effects of operating pressure and key simplifying assumptions commonly used in calculating RO membrane performance metrics and interpretation of corresponding results.

Graphene-Coated Halloysite Nanoclay Membrane for the Enhanced Separation of Hydrogen from a Hydrogen-Helium Mixture

This study highlights the separation of hydrogen from H₂-He mixture gas by a graphene-coated halloysite nanoclay membrane. The graphene-coated clay membrane along with its pure clay counterpart is successfully developed and studied for gas separation using hydrogen (H₂)-helium (He) single and mixture gases. Hydrothermal and nonhydrothermal methods were applied for the synthesis of a ″coated″ membrane on a porous alumina substrate from the graphene and halloysite clay. To date, nanoporous zeolites are the potential materials for gas separation based on a molecular sieving mechanism. A similar separation mechanism for hydrogen and helium from mixture gases may not work efficaciously due to the closeness of their kinetic diameter (H₂: 2.89 Å and He: 2.6 Å). The presence of defects and torn nanopores between graphene layers along with the different surface charges of the inner and outer layer of halloysite nanotubes facilitates the ″coated″ membrane to show an appreciable H₂/He separation factor of ∼4 using H₂-He (1:1) mixture gas compared to 2.86 for the pure halloysite membrane. The available charge layer of graphene also has a significant contribution for this increased H₂/He selectivity value. The permeate flux of H₂ and He through both the graphene-coated clay membrane and pure clay membrane has also been noted. The permeate flux of pure H₂ and He was 2 × 10^-7 and 1.3 × 10^-7 mol m^-2 s^-1 Pa^-1 for the clay membrane, whereas for the ″coated″ clay membrane, the values changed to 0.1 × 10^-7 and ∼0.05 × 10^-7 mol m^-2 s^-1 Pa^-1 at 100 kPa, respectively.

Ethanol dehydration performance of three types of commercial-grade zeolite permselective membranes

BACKGROUND

Many organic solvents form difficult-to-separate mixtures with water and have an affinity for water, making drying a potential reuse prerequisite. Pervaporation (PV) and vapor permeation (VP) membrane technologies hold promise for energy-efficient solvent drying. Several water-selective membrane materials are commercially available, but performance data is limited, particularly for two recently commercialized membrane materials: chabazite (CHA) and T-type zeolites. In this work, commercial-grade samples of CHA and T-type membranes, along with a NaA zeolite membrane, were evaluated for the removal of water from ethanol.

RESULTS

The CHA sample had the highest initial PV water permeance (6820 GPU) and water permselectivity (3430) with 5 wt% water in ethanol at 50 °C. Initial NaA membrane performance was slightly lower (6060 GPU and 3260), while the T-type membrane had the lowest initial permeance and selectivity (4260 GPU and 1090). Performance declined over time, most notably for the NaA membrane, for which water permeance fell over 50% through 39 days of testing. The T-type membrane exhibited the steadiest PV water permeance, but the most variable ethanol permeance.

CONCLUSION

The PV performance of the three membranes largely overlapped the predicted range for T-type membranes. That performance generally exceeds the anticipated ethanol drying performance of non-zeolitic PV membranes but is less than that predicted for NaA and CHA membranes. The present CHA membrane results, along with other recent reports, refine earlier predictions of the ethanol dehydration performance of that type of zeolite. The changing performance with time should be understood to properly design a solvent dehydration system.

Ultrahigh Water Permeance of Reduced Graphene Oxide Membrane for Radioactive Liquid Waste Treatment

Membrane methods exhibit great potential for application in radioactive liquid waste treatment. In this work, we prepared a reduced graphene oxide using the amino-hydrothermal method (AH-rGO) that exhibited effective rejection rates of 99.9% for CoCl2, ZnCl2, NiCl2, and radionuclide 60Co solutions with an ultrahigh water permeance of >71.9 L m-2 h-1 bar-1. The thickness of the AH-rGO membranes affects the water permeance, as the membrane with a thickness of ≈250 nm has the highest water permeance of up to 125.1 L m-2 h-1 bar-1 with the corresponding rejection rate of 86.8%. Importantly, this is the most permeable membrane with a satisfactory level of the rejection rate for typical radioactive ions of Co2+, Zn2+, and Ni2+. Moreover, the AH-rGO membranes presented excellent stability. These findings demonstrate the potential of reduced graphene oxide (rGO) membranes for radioactive liquid waste treatment.

Highly Permeable Reverse Osmosis Membranes via Molecular Layer-by-Layer Deposition of Trimesoyl Chloride and 3,5-Diaminobenzoic Acid

We present a series of polyamide membranes synthesized via molecular layer-by-layer (mLbL) deposition of trimesoyl chloride (TMC) and 3,5-diaminobenzoic acid (BA). These membranes exhibit superior NaCl rejection compared to previously reported TMC-BA membranes prepared via interfacial polymerization, with the improved performance of the mLbL films attributable to higher cross-link density facilitated by the stepwise deposition process in good solvents. We compare the TMC-BA series with membranes synthesized from TMC and m-phenylenediamine (MPD), a conventional reverse osmosis membrane chemistry. At the minimum thickness capable of 90 % NaCl rejection, mLbL TMC-BA membranes exhibit 50 % greater water permeance than mLbL TMC-MPD.

Synthesis and Characterization of Hybrid Metal Zeolitic Imidazolate Framework Membrane for Efficient H2/CO2 Gas Separation

In this paper, we propose mixed metal ions in the node of the zeolitic imidazolate framework (ZIF) structure. The hybrid metal ZIF is formed for the gas separation of hydrogen and carbon dioxide. In the first stage, the nanoparticles were prepared as a coating on a substrate, and acting as secondary growing nuclei. The hybrid metal ZIF structures were characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). N₂ adsorption–desorption isotherms determined surface area, and scanning electron microscopy (SEM) was used to observe the microstructure and surface morphology. The hybrid metal ZIF-8-67 powder had the largest surface area (1260.40 m² g⁻¹), and the nanoparticles (100 nm) could be fully dense-coated on the substrate to benefit the subsequent membrane growth. In the second stage, we prepared the hybrid metal ZIF-8-67 membrane on the pre-seeding substrate with mixed metal nanoparticles of cobalt and zinc, by the microwave hydrothermal method. Cobalt ions were identified in the tetrahedral coordination through UV–Vis, and the membrane structure and morphology were determined by XRD and SEM. Finally, a gas permeation analyzer (GPA) was used to determine the gas separation performance of the hybrid metal ZIF-8-67 membrane. We successfully introduced zinc ions and cobalt ions into the ZIF structure, where cobalt had a strong interaction with CO₂. Therefore, GPA analysis showed an excellent H₂/CO₂ separation factor due to lower CO₂ permeability. The CO₂ permeance was ~0.65 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹, and the separation factors for H₂/CO₂ and H₂/N₂ were 9.2 and 2.9, respectively. Our results demonstrate that the hybrid metal ZIF-8-67 membrane has a superior H₂/CO₂ separation factor, which can be attributed to its very high specific surface area and structure. Based on the above, hybrid metal ZIF-8-67 membranes are expected to be applied in hydrogen or carbon dioxide gas separation and purification.

Grafting Thin Layered Graphene Oxide onto the Surface of Nonwoven/PVDF-PAA Composite Membrane for Efficient Dye and Macromolecule Separations

This study investigates the permeance and rejection efficiencies of different dyes (Rhodamine B and methyl orange), folic acid and a protein (bovine serum albumin) using graphene oxide composite membrane. The ultrathin separation layer of graphene oxide (thickness of 380 nm) was successfully deposited onto porous polyvinylidene fluoride-polyacrylic acid intermediate layer on nonwoven support layer using vacuum filtration. The graphene oxide addition in the composite membrane caused an increased hydrophilicity and negative surface charge than those of the membrane without graphene oxide. In the filtration process using a graphene oxide composite membrane, the permeance values of pure water, dyes, folic acid and bovine serum albumin molecules were more severely decreased (by two orders of magnitude) than those of the nonwoven/polyvinylidene fluoride-polyacrylic acid composite membrane. However, the rejection efficiency of the graphene oxide composite was significantly improved in cationic Rhodamine B (from 9% to 80.3%) and anionic methyl orange (from 28.3% to 86.6%) feed solutions. The folic acid and bovine serum albumin were nearly completely rejected from solutions using either nonwoven/polyvinylidene fluoride-polyacrylic acid or nonwoven/polyvinylidene fluoride-polyacrylic acid/graphene oxide composite membrane, but the latter possessed anti-fouling property against the protein molecules. The separation mechanism in nonwoven/polyvinylidene fluoride-polyacrylic acid membrane includes the Donnan exclusion effect (for smaller-than-pore-size solutes) and sieving mechanism (for larger solutes). The sieving mechanism governs the filtration behavior in the nonwoven/polyvinylidene fluoride-polyacrylic acid/graphene oxide composite membrane.

Techno-Economic Assessment in a Fluidized Bed Membrane Reactor for Small-Scale H2 Production: Effect of Membrane Support Thickness

This paper investigates the influence of the support material and its thickness on the hydrogen flux in Palladium membranes in the presence of sweep gas in fluidized bed membrane reactors. The analysis is performed considering both ceramic and metallic supports with different properties. In general, ceramic supports are cheaper but suffer sealing problems, while metallic ones are more expensive but with much less sealing problems. Firstly, a preliminary analysis is performed to assess the impact of the support in the permeation flux, which shows that the membrane permeance can be halved when the H₂ diffusion through the support is considered. The most relevant parameter which affects the permeation is the porosity over tortuosity ratio of the porous support. Afterward, the different supports are compared from an economic point of view when applied to a membrane reactor designed for 100 kg/day of hydrogen, using biogas as feedstock. The stainless steel supports have lower impact on the hydrogen permeation so the required membrane surface area is 2.6 m² compared to 3.6 m² of the best ceramic support. This ends up as 5.6 €/kg H_2@20bar and 6.6 €/kg H_2@700bar for the best stainless steel support, which is 3% lower than the price calculated for the best ceramic support.

Surface-Controlled Water Flow in Nanotube Membranes

The independent effect of nanotube surface chemistry and structure on the flow of water under nanoscale confinement is demonstrated in this paper for the first time via the synthesis of novel carbon nitride nanotube (CNNT) membranes. Using a combination of experiments and high-fidelity molecular dynamics (MD) simulations, it is shown here that the hydrophilization of the sp² carbon structure, induced by the presence of the C-N bonds, decreases the pure water permeance in CNNTs when compared with pristine and turbostratic carbon nanotubes (CNTs). The MD simulations are based on a model true to the chemical structure of the synthesized nanotubes, built from spectroscopy measurements and calibrated potentials using droplet experiments. The effect on permeance is explained in terms of solid-liquid interactions at the nanotube wall with increased water viscosity and decreased surface diffusion near the CNNT wall, when compared to CNTs. A model directly linking the solid-liquid interactions to the water permeance is presented, showing good agreement with both experiments and MD simulations. This work opens the way to tailoring surface chemistry and structure inside nanotube membranes for a wide range of transport and separation processes.

The ecophysiology of leaf cuticular transpiration: are cuticular water permeabilities adapted to ecological conditions?

When the stomata are closed under drought, the only route for water loss from the leaf interior to the atmosphere is across the cuticle. Thus, the extent of cuticular transpiration in relation to the reservoirs of water in the plant and the water acquisition from the soil determines the fitness and survival of the plant. It is, therefore, widely assumed that the cuticular water permeability of plants regularly experiencing drought is comparatively low and, thus, adapted to the environment. To test this hypothesis, 382 measurements of cuticular permeability from 160 species were extracted from the literature published between 1996 and 2017. The data had been produced either by using isolated cuticles and astomatous leaf sides or by measuring the minimum leaf conductance under conditions assumed to induce maximum stomatal closure. The species were assigned to 11 life form groups. Except for two particular cases (epiphytes, and climbers and lianas), the cuticular permeabilities of all groups either did not differ significantly or the available data did not allow a statistical test. In conclusion, present knowledge either does not support the hypothesis that ecological adaptions of cuticular water permeability exist or the available data are insufficient to test it.

Quantitative characterization of cuticular barrier properties: methods, requirements, and problems

The interface between the atmosphere and leaves and fruits is formed by the lipophilic plant cuticle, which seals the outer epidermal cell walls, thus significantly reducing water loss and uptake of dissolved solutes deposited on the cuticle surface. Different experimental and theoretical approaches for quantifying barrier properties of cutinized leaf and fruit surfaces are presented and discussed in this review. Quantitative characterization of cuticle barrier properties requires (i) the measurement of diffusion kinetics, namely the amount diffusing versus time, (ii) accurate knowledge of driving forces, namely concentration gradients, acting across the barrier, and (iii) the calculation of permeances, namely diffusion velocity. We suggest that on the basis of permeances, which are independent from experimental boundary conditions such as driving forces, the time period of measurement, and area, cuticle barrier properties of different plant organs, different plant species, and different lines, as well as barrier properties of suberized root tissue or synthetic membranes, can be directly compared. This review provides a short and easy to understand manual on what should be kept in mind when quantifying barrier properties of cutinized and suberized transport barriers. This could be helpful for scientists working on cuticle biosynthesis and its regulation.

Perfluorinated Compounds as Test Media for Porous Membranes

We suggest a failure-free method of porous membranes characterization that gives the researcher the opportunity to compare and characterize properties of any porous membrane. This proposal is supported by an investigation of eight membranes made of different organic and inorganic materials, with nine different perfluorinated compounds. It was found that aromatic compounds, perfluorobenzene, and perfluorotoluene, used in the current study show properties different from other perfluorinated aliphatics. They demonstrate extreme deviation from the general sequence indicating the existence of π-π-interaction on the pore wall. The divergence of the flow for cyclic compounds from ideal e.g., linear compounds can be an indication of the pore dimension.

Nanofibrillated Cellulose Templated Membranes with High Permeance

One of the most challenging aspects of using nanofibrillated cellulose (NFC) for membranes production is their limited permeance. When NFC membranes are produced from aqueous suspensions, depending on their grammage, the permeances are in the range of a few decades of L/(hm²MPa) not matching satisfactory filtration times. We present a fast and sustainable solution to increase the permeances of such membranes through a combination of solvent exchange of the NFC suspension with ethanol and the use of a removable template, a mixture of calcium compounds (CC). The effect of the CC/NFC ratio was screened for various concentrations. The permeance of water could be increased by as much as 2-3 times as compared to nontemplated membranes. Further, the membranes showed the ability for penetration of water-soluble macromolecules, contaminant rejection of suspended solid particles, and thus fluids (such as orange juice) could be concentrated, with a view to applications in food industry.

Graphdiyne as a High-Efficiency Membrane for Separating Oxygen from Harmful Gases: A First-Principles Study

We theoretically explored the adsorption and diffusion properties of oxygen and several harmful gases penetrating the graphdiyne monolayer. According to our first-principles calculations, the oxidation of the acetylenic bond in graphdiyne needs to surmount an energy barrier of ca. 1.97 eV, implying that graphdiyne remains unaffected under oxygen-rich conditions. In a broad temperature range, graphdiyne with well-defined nanosized pores exhibits a perfect performance for oxygen separation from typical noxious gases, which should be of great potential in medical treatment and industry.

Synthesis of zeolite NaA membrane from fused fly ash extract

Zeolite-NaA membranes were synthesized from an extract of fused South African fly ash on a porous titanium support by a secondary growth method. The influence of the synthesis molar regime on the formation of zeolite NaA membrane layer was investigated. Two synthesis mixtures were generated by adding either aluminium hydroxide or sodium aluminate to the fused fly ash extract. The feedstock material and the synthesized membranes were characterized by X-diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). It was found by XRD and SEM that the cubic crystals of a typical zeolite NaA with a dense intergrown layer was formed on the porous Ti support. The study shows that the source of Al used had an effect on the membrane integrity as sodium aluminate provided the appropriate amount of Na(+) to form a coherent membrane of zeolite NaA, whereas aluminium hydroxide did not. Morphological, the single hydrothermal stage seeded support formed an interlocked array of zeolite NaA particles with neighbouring crystals. Also, a robust, continuous and well-intergrown zeolite NaA membrane was formed with neighbouring crystals of zeolite fused to each other after the multiple stage synthesis. The synthesized membrane was permeable to He (6.0 × 10(6) L m(-2)h(-1) atm(-1)) and CO2 (5.6 × 10(6) L m(-2)h(-1) atm(-1)), which indicate that the layer of the membrane was firmly attached to the porous Ti support. Membrane selectivity was maintained showing membrane integrity with permselectivity of 1.1, showing that a waste feedstock, fly ash, could be utilized for preparing robust zeolite NaA membranes on Ti support.

Self-supported fibrous porous aromatic membranes for efficient CO2/N2 separations

In this paper, we describe a new synthesis protocol for the preparation of self-supported hollow fiber membranes composed of porous aromatic framework PAF-56P and PSF. PAF-56P was facilely prepared by the cross-coupling reaction of triangle-shaped cyanuric chloride and linear p-terophenyl monomers. The prepared PAF-56P material possesses an extended conjugated network, the structure of which is confirmed by nuclear magnetic resonance and infrared characterizations, as well as a permanent porosity with a BET surface area of 553.4 m(2) g(-1) and a pore size of 1.2 nm. PAF-56P was subsequently integrated with PSF matrix into PAF-56P/PSF asymmetric hollow fiber membranes via the dry jet-wet quench method employing PAF-56P/PSF suspensions. Scanning electron microscopy studies show that PAF-56P particles are embedded in the PSF matrix to form continuous membranes. Fabricated PAF-56P/PSF membranes were further exploited for CO2 capture, which was exemplified by gas separations of CO2/N2 mixtures. The PAF-56P/PSF membranes show a high selectivity of CO2 over N2 with a separation factor of 38.9 due to the abundant nitrogen groups in the PAF-56P framework. A preferred permeance for CO2 in the binary CO2/N2 gas mixture is obtained in the range of 93-141 GPU due to the large CO2 adsorption capacity and a large pore size of PAF-56P. Additionally, PAF-56P/PSF membranes exhibit excellent thermal and mechanical stabilities, which were examined by thermal analysis and gas separation tests with the dependencies of temperatures and pressures. The merits of high selectivity for CO2, good stability, and easy scale up make PAF-56P/PSF hollow fiber membranes of great interest for the industrial separations of CO2 from the gas exhausts.

Antimicrobial Activity of Adenine-Based Inhibitors of NAD(+)-Dependent DNA Ligase

The relationship between enzyme inhibition and antimicrobial potency of adenine-based NAD(+)-dependent DNA ligase (LigA) inhibitors was investigated using a strain of the Gram-negative pathogen Haemophilus influenzae lacking its major AcrAB-TolC efflux pump and the Gram-positive pathogen Streptococcus pneumoniae. To this end, biochemical inhibitors not mediating their antibacterial mode of action (MOA) via LigA were removed from the analysis. In doing so, a significant number of compounds were identified that acted via inhibition of LigA in S. pneumoniae but not in H. influenzae, despite being inhibitors of both isozymes. Deviations from the line correlating antimicrobial and biochemical potencies of LigA inhibitors with the correct MOA were observed for both species. These deviations, usually corresponding to higher MIC/IC50 ratios, were attributed to varying compound permeance into the cell.