Graphene Oxide-Cytochrome c Multilayered Structures for Biocatalytic Applications: Decrypting the Role of Surfactant in Langmuir-Schaefer Layer Deposition

Valorization of Industrial Waste Graphite Fines into Graphene Oxide-Based Nanohybrids

The rapid growth of graphite market is highly coupled with the increasing demand for Li-ion grade graphite, the production of which results in significant losses of the graphitic material in the form of graphite fines. Herein, for the first time, we report an effective strategy to utilize industrial waste graphite fines through the development of graphene oxide-based nanohybrids as non-toxic and efficient antibacterial agents. To achieve this, graphene oxide (GO) was initially synthesized using industrial waste graphite fines as a graphitic precursor. Subsequently, hyperbranched polyethyleneimine (PEI), or either of its guanidinylated (GPEI) and N-sulfopropylated (SPEI) derivatives were successfully and homogenously attached onto GO, as confirmed by various characterization techniques, yielding GO-PEI, and novel GO-GPEI and GO-SPEI nanohybrids. The antibacterial activity of these nanohybrids was assessed against Gram (-) Escherichia coli and Gram (+) Staphylococcus Aureus bacteria. Both GO-GPEI and GO-SPEI were found to exhibit higher antibacterial activity, specifically against E. coli bacteria, compared to the pristine GO and GO-PEI nanohybrid, with GO-SPEI being more active than GO-GPEI. Finally, GO-GPEI and GO-SPEI were found to exhibit low cytotoxicity against mammalian cells, signifying that they can be used as potential antibacterial agents in various applications, including those in the disinfection industry.

Ultrahigh Surface Area Nanoporous Carbons Synthesized via Hypergolic and Activation Reactions for Enhanced CO2 Capacity and Volumetric Energy Density

We report a family of carbon sorbents synthesized by integrating hypergolics with activation reactions on a templated substrate. The materials design leads to nanoporous carbons with a BET area of 4800 m2 g-1 with an impressive total pore volume of 2.7 cm3 g-1. To the best of our knowledge, this BET area value is the highest reported in the literature. Electron spin resonance (ESR) measurements determined the number of radicals in an effort to provide a mechanistic understanding of the formation of ultrahigh surface area carbons. In combination with XPS, we propose a mechanism based on the synergistic effect between rim-based pentagonal rings and carbon radicals, which we believe can be exploited to produce other highly porous carbons. The CO2 capture capacity of the hyperporous carbon tested under dynamic CO2 capture conditions was ∼1.25 mmol g-1 versus 0.66 mmol g-1 of a conventionally activated carbon under similar conditions. The CO2 capture kinetics were extremely fast and reached 99% of the total capacity within 120 s. Lastly, supercapacitor electrodes deliver a high volumetric energy density of ∼60 W h L-1 and a volumetric power density of 1 kW L-1, which is the highest reported value for activated carbon.

CNT-FET for sensitive hydrogen peroxide biosensing via immobilized Cytochrome c

H₂O₂ is an effective substance in the body which contributes to gene expression, insulin metabolism and determining cell shapes. However, a high concentration of H₂O₂ is harmful to the body and can cause various diseases such as colitis wounds, sepsis disease, lymphocyte proliferation and macrophage apoptosis in systemic lupus erythematosus. In this study, a Cyt c/cMWCNTs/FET was designed to real-time detect H₂O₂ via immobilized Cyt c on the cMWCNTs/FET surface. The performance of the Cyt c/cMWCNTs/FET biosensor was studied under various parameters such as cMWCNTs and Cyt c concentrations, as well as different pH values. When H₂O₂ was added to the reaction chamber of the Cyt c/cMWCNTs/FET, the output current of the Bio-FET was reduced, which was attributed to H₂O₂ detection. The linear response range of this Cyt c/cMWCNT/FET was 10.0 fM to 1.0 nM. The limit of detection and response time of this platform were determined to be 9.13 fM and around 1.0 s, respectively. Also, the operation of the Cyt c/cMWCNTs/FET in the presence of glucose, leucine, tyrosine and ascorbic acid as interfering substances was selective towards H₂O₂.

One-Step Interfacial Integration of Graphene Oxide and Organic Chromophores into Multicomponent Nanohybrids with Photoelectric Properties

A one-step protocol for interfacial self-assembly of graphene oxide (GO), glutamine-substituted perylene diimide (PDI-glu), 10,12-pentacosadiynoic acid (PCDA), and zinc acetate into three- and four-component hybrid nanofilms through hydrogen and coordination bonding was developed. The hybrids deposited onto solid supports were studied after polymerization of PCDA by UV-vis absorption, fluorescence, and Raman spectroscopies, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results of spectroscopic studies suggest that the hybrids assembled through H-bonds can maintain the light-induced Förster energy transfer from the PDI-glu chromophore to the conjugated polymer and then to GO leading to fluorescence quenching. In the hybrids assembled through coordination bonding with zinc clusters, the energy transfer proceeds from PDI-glu to the PDA polymer, whereas the transfer from PDA to GO is quenched completely. Another important characteristic of these ultrathin hybrids is their stability with respect to photobleaching of chromophores due to the acceptor properties of GO. The as-assembled hybrid nanofilms were integrated with conventional photovoltaic planar architectures to study their photoelectric properties. The zinc-containing hybrids integrated with a hole transport layer exhibited photovoltaic properties. The cell with the integrated four-component hybrid comprising both PDI-glu and PDA showed a photocurrent/dark current ratio almost an order higher than that of the three-component hybrid assembled with PDA only. The supramolecular method based on the interfacial self-assembly can be extended to a wide variety of organic chromophores and polymerizable surfactants for integrating them into multicomponent functional GO-based nanohybrids with targeted properties for organic electronics.

Development of 3D Printed Enzymatic Microreactors for Lipase-Catalyzed Reactions in Deep Eutectic Solvent-Based Media

In this study, 3D printing technology was exploited for the development of immobilized enzyme microreactors that could be used for biocatalytic processes in Deep Eutectic Solvent (DES)-based media. 3D-printed polylactic acid (PLA) microwell plates or tubular microfluidic reactors were modified with polyethylenimine (PEI) and lipase from Candida antarctica (CALB) was covalently immobilized in the interior of each structure. DESs were found to have a negligible effect on the activity and stability of CALB, and the system proved highly stable and reusable in the presence of DESs for the hydrolysis of p-nitrophenyl butyrate (p-NPB). A kinetic study under flow conditions revealed an enhancement of substrate accessibility in the presence of Betaine: Glycerol (Bet:Gly) DES, while the system was not severely affected by diffusion limitations. Incubation of microreactors in 100% Bet:Gly preserved the enzyme activity by 53% for 30 days of storage at 60 °C, while the buffer-stored sample had already been deactivated. The microfluidic enzyme reactor was efficiently used for the trans-esterification of ethyl ferulate (EF) with glycerol towards the production of glyceryl ferulate (GF), known for its antioxidant potential. The biocatalytic process under continuous flow conditions exhibited 23 times higher productivity than the batch reaction system. This study featured an effective and robust biocatalytic system with immobilized lipase that can be used both in hydrolytic and synthetic applications, while further optimization is expected to upgrade the microreactor system performance.

Eco-Friendly Approach for Graphene Oxide Synthesis by Modified Hummers Method

The aim of this study is to produce graphene oxide using a modified Hummers method without using sodium nitrate. This modification eliminates the production of toxic gases. Two drying temperatures, 60 °C and 90 °C, were used. Material was characterized by X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and Scanning Electron Microscopy. FTIR study shows various functional groups such as hydroxyl, carboxyl and carbonyl. The XRD results show that the space between the layers of GO60 is slightly larger than that for GO90. SEM images show a homogeneous network of graphene oxide layers of ≈6 to ≈9 nm. The procedure described has an environmentally friendly approach.

Interaction of Lipophilic Cytarabine Derivatives with Biomembrane Model at the Air/Water Interface

Cell membrane models are useful for obtaining molecular-level information on the interaction of biologically active molecules whose activity is believed to depend also on their effects on the membrane. Cytarabine was conjugated with fatty acids to improve the drug lipophilicity and the interaction with the biomembrane model. Cytarabine was conjugated with fatty acids of different lengths to form the trimyristoyl cytarabine and the tristearoyl cytarabine derivatives. Their interaction with biomembrane models constituted by dimyristoylphosphatidylcholine (DMPC) monolayers was studied by employing the Langmuir-Blodgett technique. DMPC/cytarabine, DMPC/trimyristoyl cytarabine and DMPC/tristearoyl cytarabine mixed monolayers at increasing molar fractions of the compound were prepared and placed on the subphase. The mean molecular area/surface pressure isotherms were recorded at 37 °C. Between the molecules of DMPC and those of cytarabine or prodrugs, repulsive forces act. However, these forces are very weak between DMPC and cytarabine and stronger between DMPC and the cytarabine derivatives, thus avoiding the expulsion of the compounds at higher surface pressure and modifying the stability of the mixed monolayer. The fatty acid moieties could then modulate the affinity of cytarabine for biomembranes.

Novel Immobilized Biocatalysts Based on Cysteine Proteases Bound to 2-(4-Acetamido-2-sulfanilamide) Chitosan and Research on Their Structural Features

Briefly, 2-(4-Acetamido-2-sulfanilamide) chitosan, which is a chitosan water-soluble derivative, with molecular weights of 200, 350, and 600 kDa, was successfully synthesized. The immobilization of ficin, papain, and bromelain was carried out by complexation with these polymers. The interaction mechanism of 2-(4-acetamido-2-sulfanilamide) chitosan with bromelain, ficin, and papain was studied using FTIR spectroscopy. It was found that the hydroxy, thionyl, and amino groups of 2-(4-acetamido-2-sulfanilamide) chitosan were involved in the complexation process. Molecular docking research showed that all amino acid residues of the active site of papain formed hydrogen bonds with the immobilization matrix, while only two catalytically valuable amino acid residues took part in the H-bond formation for bromelain and ficin. The spectral and in silico data were in good agreement with the catalytic activity evaluation data. Immobilized papain was more active compared to the other immobilized proteases. Moreover, the total and specific proteolytic activity of papain immobilized on the carrier with a molecular weight of 350 kDa were higher compared to the native one due to the hyperactivation. The optimal ratio of protein content (mg × g ⁻¹ of carrier), total activity (U × mL⁻¹ of solution), and specific activity (U × mg⁻¹ of protein) was determined for the enzymes immobilized on 2-(4-acetamido-2-sulfanilamide) chitosan with a molecular weight of 350 kDa.