Insights into Neutral vs. Deprotonated Phenol Adsorption on Graphene Oxide

The relationship between the chemical structure and biological activity (log IC50) of 40 derivatives of 1,4-dihydropyridines (DHPs) was studied using density functional theory (DFT) and multiple linear regression analysis methods. With the aim of improving the quantitative structure-activity relationship (QSAR) model, the reduced density gradient s( r) of the optimized equilibrium geometries was used as a descriptor to include weak non-covalent interactions. The QSAR model highlights the correlation between the log IC50 with highest molecular orbital energy (E HOMO), molecular volume (V), partition coefficient (log P), non-covalent interactions NCI(H4-G) and the dual descriptor [Δf(r)]. The model yielded values of R 2=79.57 and Q 2=69.67 that were validated with the next four internal analytical validations DK=0.076, DQ=-0.006, R P =0.056, and R N=0.000, and the external validation Q 2boot=64.26. The QSAR model found can be used to estimate biological activity with high reliability in new compounds based on a DHP series. Graphical abstract The good correlation between the log IC50 with the NCI (H4-G) estimated by the reduced density gradient approach of the DHP derivatives.

Lithium-ion (Li-ion) batteries have dominated the consumer electronics market for nearly two decades as an efficient energy storage device. However, for applications such as electric vehicles, conventional lithium ion batteries have not been able to cope with the taxing energy and power densities requirements. Lithium–sulfur (Li-S) battery, with much higher theoretical specific energy (~2600Wh/kg) than those (500-600Wh/kg) of Li-ion batteries, provides a promising alternative to meet these demands. However, low electrical conductivity of pure sulfur cathode and loss of active material due to dissolution of intermediate polysulfides from the cathode during battery operation limit the performance of Li-S batteries. Development of novel cathodes with enhanced electrical conductivity and capability to reduce the dissolution of intermediate polysulfides has been the major area of research in recent times. Graphene and graphene-based materials, which has superior electrical conductivity and mechanical flexibility, are considered as potential candidate for cathodes and cathode supports in Li-S batteries. In particular, graphene oxide (GO)–sulfur composite materials provide a more economical synthesis route compared to graphene. The functional groups (mostly epoxy and hydroxyl) present in GO could potentially act like anchors to sulfur particles and help reduce dissolution of polysulfides, leading to significantly improved performance of Li-S batteries. However, leveraging the advantages of both electrical conductivity and reducing polysulfide shuttle requires tuning the types and concentration of functional groups present in GO. In an effort to determine the favorable type and optimum concentration of functional groups in GO structure, we performed molecular dynamics (MD) simulations of a wide range of GO structures, with purely epoxy and hydroxyl functional groups, in contact with S8 2- polysulfides solvated in a standard electrolyte solvent DME – DOL in 1:1 v/v ratio. Only physical interactions between the polysulfides and the functional groups in GO were considered. Optimized potential for liquid simulations (OPLS) parameters were utilized to model GO and polysulfides along with solvent. Partial charge on carbon atoms in GO with epoxy and hydroxyl groups were evaluated from the optimized structures obtained using Density Functional Theory (DFT). Bond, angle and dihedral parameters along with partial charges on sulfur particles in polysulfide ion S8 2- were evaluated from the optimized structure using DFT. The calculated density of equilibrated solvent was within 5% of the experimental value. The time averaged distribution of polysulfides, normal to the surface of graphene oxide, was evaluated and showed that polysulfides tend to be closer to GO substrate with hydroxyl functional group as compared to ones with epoxy functional groups. The radial distribution (RDF) plots between H atom of hydroxyl functional group and S atoms of polysulfide ion suggested that a strong Coulombic interaction is responsible for physisorption of polysulfide onto the GO substrate. The diffusion co-efficients of polysulfides were also calculated and were observed to be significantly lower for GO as compared to pure graphene thus indicating a relatively stable deposition. For GO with epoxy functional groups, as the concentration of functional groups was reduced, the physisorption of polysulfides was observed to increase. The polysulfides tended to stabilize at a greater distance from the GO surface with epoxy functional groups. The study also analyzed the role of solvent molecules (especially DOL) in stabilizing polysulfides away from the GO substrate with epoxy functional groups. Overall, the results obtained in the present study show that GO with hydroxyl functional groups have a greater tendency to adsorb polysulfides onto the surface as compared to GO with epoxy groups. These results can potentially pave the way for design of molecularly-tailored cathode supports to mitigate polysulfide shuttle and therefore improve performance of Li-S batteries.

Lithium – sulfur (Li-S) battery, with highest predicted theoretical capacity of ~1675 mAh/g, is a promising technology meeting the demands of next-generation electric vehicles. Abundance of sulfur and environmental friendliness are major factors that make Li-S batteries interesting and important. However, Li-S battery is plagued by its own limitations, which include low electrical conductivity of pure sulfur cathode and loss of active material due to dissolution of intermediate polysulfides from the cathode during reduction reactions. These factors limit the performance of Li-S batteries. Developing superior cathode structures to mitigate these problems has been the major focus of research in recent times. Carbon-based materials such as fibers, nanospheres and nanotubes embedded with sulfur are being explored as cathodes for Li-S batteries. In particular, graphene, which has superior electrical conductivity and mechanical flexibility, has been studied as potential candidate for cathodes and cathode supports in Li-S batteries. However, economical synthesis of pure graphene is a major hurdle for their use in commercially-viable Li-S batteries. Graphene oxide – sulfur composite based structures are viable alternatives that could provide required electrical conductivity, based on the concentration of functional groups (epoxy and hydroxyl). Additionally, graphene oxides are believed to act like anchors to sulfur/polysulfides particles and help reduce their dissolution, leading to significantly improved performance of Li-S batteries. However, leveraging the advantages of enhanced electrical conductivity and reduced polysulfide shuttle requires tuning of the functional groups present in the graphene oxide. In an effort to determine the most favorable graphene oxide structure, we performed molecular dynamics (MD) simulations to calculate the mobility of polysulfide species in the vicinity of different graphene oxide structures with varying concentration of functional groups. Diffusion coefficients of polysulfides were calculated along the surface of these graphene oxide sheets using MD simulations. Initially graphene oxide sheets with pure epoxy and hydroxyl functional groups were simulated. Partial charge on carbon atoms in graphene oxide with epoxy and hydroxyl groups were evaluated from the optimized structures obtained using Density Functional Theory (DFT) calculations. Bond, angle and dihedral parameters along with partial charges on sulfur particles in polysulfides S8 2- were evaluated from the optimized structure using DFT. A standard electrolyte DME – DOL in 1:1 v/v ratio, modeled using OPLS force filed parameters, was used in all the MD simulations. The density of equilibrated solvent was within 5% of the experimental value. A system comprising graphene oxide solvated with electrolyte containing polysulfides was simulated at 300K. Overall charge neutrality of the system was maintained by incorporating counter ions, while using specific strategy to screen out long range electrostatic interactions between the polysulfides and counter ions. The surface diffusion coefficients of polysulfide was evaluated in the vicinity of graphene oxide and compared to that near pure graphene. Our simulations evaluated the effectiveness of various groups in reducing dissolution of polysulfides. The concentration of polysulfides in the vicinity of the graphene/graphene oxide structures tend to increase from graphene to graphene oxide with pure epoxy groups and maximizes for graphene oxide with pure hydroxyl functional groups. The relatively greater binding of polysulfides to graphene oxide structures leads to reduced surface diffusion coefficients for polysulfides on graphene oxide compared to that near graphene interfaces.

Experimental and density functional theory studies of laminar double-oxidized graphene oxide nanofiltration membranes

Variation in the bandgap by gradual reduction of GOs with different oxidation degrees: A DFT analysis

The effect of oxygen–containing functional groups on the H2 adsorption of graphene–based nanomaterials: experiment and theory

This study represents a comprehensive review about the structural features of graphene oxide (GO) and its significance in environmental applications. Two dimensional (2D) GO is tremendously focused in advanced carbon-based nanomaterials for environmental applications due to its tunable physicochemical characteristics. Herein, we report foundational structural models of GO and explore the chemical bonding of oxygen moieties, with graphite basal plane using various characterization tools. Moreover, the impact of these oxygen moieties and the morphology of GO for environmental applications such as removal of metal ions and catalytic, antibacterial, and gas sensing abilities have here been critically reviewed for the first time. Environmental applications of GO are highly significant because, in the recent era, the fast progress of industries, even in the countryside, results in air and water pollution. GO has been widely investigated by researchers to eradicate such environmental issues and for potential industrial and clinical applications due to its 2D structural features, large surface area, presence of oxygen moieties, nonconductive nature, intense mechanical strength, excellent water dispersibility, and tunable optoelectronic properties. Thence, particular emphasis is directed toward the modification of GO by varying the number of its oxygen functional groups and by coupling it with other exotic nanomaterials to induce unique properties in GO for potential environmental remediation purposes.

Nitrogen doping could improve the performance of carbon materials in electrocatalysis, CO2 adsorption, and energy storage. [1]However, the control of the doping type and the amount of nitrogen (N)-...

Covalently linked graphene oxide/reduced graphene oxide-methoxylether polyethylene glycol functionalised silica for scavenging of estrogen: Adsorption performance and mechanism

In recent years, graphene and its oxidized form, graphene oxide (GO), have emerged as a versatile material for various biomedical applications such as biosensing through graphene-quenched fluorescence, nucleic acid adsorption, gene/drug delivery, and photothermal therapeutics. These applications of GO are attributed to properties such as large surface area, excellent aqueous dispersibility, biocompatibility, acceptor of fluorescence resonance energy transfer (FRET) to quench dye fluorescence, and facile modification with functional groups. Importantly, GO exhibits preferential adsorption of single-stranded nucleic acid through π–π stacking interaction and hydrogen bonding between nucleobases and GO surfaces, whereas dsDNA adsorbs on GO with low affinity due to its stiffness and low diffusivity. Several biosensors for detection of a wide range of biomolecules have been developed utilizing GO as fluorescently labeled probes are almost completely quenched upon adsorption on GO’s surface. In the presence of complementary DNA, ds DNA is formed, and fluorescent probe is desorbed from the GO, resulting in florescence restoration which forms the basis for GO-based biosensor platforms. Understanding the fundamental mechanism of interaction between nucleic acid and the GO surface is important for the development of GO-based FRET sensors, gene/drug delivery systems, and biotherapeutics. This chapter provides theoretical considerations of DNA adsorption/desorption and fluorescence quenching of fluorescently labeled DNA by GO. It also summarizes the latest developments in the field of GO and functionalized GO with main applications in vitro and in vivo, including nucleic acid amplification, fluorescent nucleic acid biosensors, gene/drug delivery, and photothermal therapeutics.KeywordsGraphene oxideDNA adsorption and desorptionFluorescence resonance energy transfer (FRET)Fluorescence quenchingNucleic acid amplificationBiosensorNucleic acid aptamerGene deliveryPhotothermal therapeutics

Adsorption properties and mechanism of sepiolite to graphene oxide in aqueous solution

Drug designing is a crucial step in the exploration of novel drugs which requires potent methodologies. One of such methodologies is Quantitative Structure Activity Relationship (QSAR) which is a widely used statistical tool that correlates the structure of a molecule to a biological activity as a function of molecular descriptors, thereby, playing an essential role in the drug designing. QSAR utilizes Density Functional Theory (DFT) based chemical descriptors for this purpose. The selection of such significant molecular descriptors from various available descriptors is the foremost challenge in a QSAR as structural descriptors are representative of the molecular characteristics accountable for the relevant activity. Recently, new QSAR approaches have been introduced which further enhance the study of the activities. Further, the constructed QSAR models also need to be tested and validated for their efficiency and practical usage. As the QSAR models are structure specific, they may not be universally applicable. However, because of their high precision and efficacy, they have a promising future in the world of drug design. This review briefly summarizes the role of descriptor based QSAR in drug design in conjunction with existing QSAR approaches and also the utility as well as constraints of this approach in drug design.

Assessing the ecotoxicity of pharmaceuticals is of urgent need due to the recognition of their possible adverse effects on nontarget organisms in the aquatic environment. The reality of ecotoxicity data scarcity promotes the development and application of quantitative structure activity relationship (QSAR) models. In the present study, we aimed to clarify whether a QSAR model of ecotoxicity specifically for pharmaceuticals is needed considering that pharmaceuticals are a class of chemicals with complex structures, multiple functional groups, and reactive properties. To this end, we conducted a performance comparison of two previously developed and validated QSAR models specifically for pharmaceuticals with the commonly used narcosis toxicity prediction model, i.e., Ecological Structure Activity Relationship (ECOSAR), using a subset of pharmaceuticals produced in China that had not been included in the training datasets of QSAR models under consideration. A variety of statistical measures demonstrated that the pharmaceutical specific model outperformed ECOSAR, indicating the necessity of developing a specific QSAR model of ecotoxicity for the active pharmaceutical contaminants. ECOSAR, which was generally used to predict the baseline or the minimum toxicity of a compound, generally underestimated the ecotoxicity of the analyzed pharmaceuticals. This could possibly be because some pharmaceuticals can react through specific modes of action. Nonetheless, it should be noted that 95% prediction intervals spread over approximately four orders of magnitude for both tested QSAR models specifically for pharmaceuticals.

Graphene oxide in ceramic-based layered structure: Nanosheet optimization

Phenolic compound even at low concentrations, are considered to be priority pollutants due to their significant toxicity. Electrospinning was used to create a polyacrylonitril (PAN) nanofiber, which was then impregnated with graphene oxide (GO). After a preliminary investigation into the electrospinning parameters (e.g., using various voltages and polymer concentrations), the electrospun nanofibres were tuned, this study evaluated the effectiveness of these materials in removing phenolic compounds from wastewater through adsorption. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the synthesized nanofiber mats. The scanning electron microscopy (SEM) analysis revealed that the structure of nanofiber mats was altered by the addition of graphene oxide (GO) in different ratios. Specifically, the surface of the fibres exhibited increased roughness, and the diameter of the fibres also experienced an increase. The average diameter of the fibres was measured to be (134.9 ± 21.43 nm) for the PAN/2.5% GO composite and (198 ± 33.94 nm) for the PAN/5% GO composite. FTIR spectra of the PAN/GO nanocomposites nanofiber displayed distinct peaks associated with graphene oxide (GO). These included a wide peak at 3400 cm−1, related to the presence of hydroxyl (O–H) groups, as well as peaks on 1600 as well as 1000 cm−1, which indicated the existence of epoxy groups. In this study response surface methodology (RSM) was implemented. To enhance the efficiency of removing substances, it is necessary to optimise parameters such as pH, contact time, and dosage of the adsorbent. The optimum pH for removing phenol via all nanofiber mats was determined to be 7, while at a dose of 2 mg dose adsorbents maximum removals for pure PAN, PAN/2.5 GO, and PAN/5 GO were 61.3941, 77.2118, and 92.76139%, respectively. All the adsorbents obey Langmuir isotherm model, and the empirical adsorption findings were fitted with the second-order model kinetically, also non-linear Elovich model. The maximal monolayer adsorption capacities for PAN, PAN/2.5 GO, and PAN/5 GO were found to be 57.4, 66.18, and 69.7 mg/g, respectively. Thermodynamic studies discovered that the adsorption of phenol on all adsorbents nanofiber mats was exothermic, the adsorption of phenol on nanofiber mats decreases as the temperature increases. All the adsorbents exhibit negative enthalpy and entropy. The PAN/GO composite's superior phenol removal suggested that it could be used as a latent adsorbent for efficient phenol removal from water and wastewater streams.