A critical review on graphene and graphene-based derivatives from natural sources emphasizing on CO2 adsorption potential.

Accelerated release of carbon dioxide (CO2) into the atmosphere has become a critical environmental issue, and therefore, efficient methods for capturing CO2 are in high demand. Graphene and graphene-based derivatives have demonstrated promising potential as adsorbents due to their unique properties. This review aims to provide an overview of the latest research on graphene and its derivatives fabricated from natural sources which have been utilized and may be explored for CO2 adsorption. The necessity of this review lies in the need to explore alternative, sustainable sources of graphene that can contribute to the development of viable environmentally benign CO2 capture technologies. The review will aim to highlight graphene as an excellent CO2 adsorbent and the possible avenues, advantages, and limitations of the processes involved in fabricating graphene and its derivatives sourced from both industrial resources and organic waste-based naturally occurring carbon precursors for CO2 adsorption. This review will also highlight the CO2 adsorption mechanisms focusing on density functional theory (DFT) and molecular dynamics (MD)-based studies over the last decade.

Ln2Te6O15 (Ln = La, Gd, and Eu) "Anti-Glass" Phase-Assisted Lanthanum-Tellurite Transparent Glass-Ceramics: Eu3+ Emission and Local Site Symmetry Analysis.

The presence of lanthanide-tellurite "anti-glass" nanocrystalline phases not only affects the transparency in glass-ceramics (GCs) but also influences the emission of a dopant ion. Therefore, a methodical understanding of the crystal growth mechanism and local site symmetry of doped luminescent ions when embedded into the precipitated "anti-glass" phase is crucial, which unfolds the practical applications of GCs. Here, we examined the Ln2Te6O15 "anti-glass" nanocrystalline phase growth mechanism and local site symmetry of Eu3+ ions in transparent GCs produced from 80TeO2-10TiO2-(5 - x)La2O3-5Gd2O3-xEu2O3 glasses, where x = 0, 1, 2. A crystallization kinetics study identifies a unique crystal growth mechanism via a constrained nucleation rate. The extent of "anti-glass" phase precipitation and its growth in GCs with respect to heat-treatment duration is demonstrated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis. Qualitative analysis of XRD confirms the precipitation of both La2Te6O15 and Gd2Te6O15 nanocrystalline phases. Rietveld refinement of powder X-ray diffraction patterns reveals that Eu3+ ions occupy "Gd" sites in Gd2Te6O15 over "La" sites in La2Te6O15. Raman spectroscopy reveals the conversion of TeO3 units to TeO4 units with Eu2O3 addition. This confirms the polymerizing role of Eu2O3 and consequently high crystallization tenacity with increasing Eu2O3 concentration. The measured Eu3+ ion photoluminescence spectra revealed its local site symmetry. Moreover, the present GCs showed adequate thermal cycling stability (∼50% at 423 K) with the highest activation energy of around 0.3 eV and further suggested that the present transparent GCs would be a potential candidate for the fabrication of red-light-emitting diodes (LEDs) or red component phosphor in W-LEDs.

Chitosan and its derivatives: Promising biomaterial in averting fungal diseases of sugarcane and other crops.

Sugarcane (Saccharum officinarum)-a prominent cash crop accounts for around 80% production of sugar worldwide. However, the productivity of sugarcane is declining (~40%) due to the attack of a perilous fungus-Fusarium moniliforme responsible for pokkah boeng (PB) disease. Presently, chemical methods are incisive where their harmful effects on living organisms cannot be overlooked. Introduction of disease-resistant cultivars and other biocontrol measures protect sugarcane to some extent. The multifunctional biopolymers like chitosan (CH) and its derivatives (irradiated chitosan [IRC]), chitooligosaccharides (CO) and nanochiotosan (NCH) offer endless opportunities to spring numerous aids for crops. CH is a dynamic plant elicitor with multifarious antimicrobial properties. The current review unleashes information on CH and its derivatives in controlling PB and fungal diseases of sugarcane along with other crops. We highlight the strategies that deploy CH as "biofungicide" to mitigate F. moniliforme. CH delays the postharvest decay in fruits (apple, strawberry, mango, banana, papaya) and vegetables (tomato, finger millet, capsicum, fenugreek) (~500-1000 ppm). NCH has been utilized as a foliar spray successfully (0.1%-1%) to protect staple crops (wheat, rice, maize) as well. Overall, NCH based strategies are noteworthy to protect sugarcane and other crops.

Distributed Computing with Engineered Bacteria and Its Application in Solving Chemically Generated 2 × 2 Maze Problems.

This work presented an application of genetic distributed computing, where an abstract computational problem was mapped on a complex truth table and solved using simple genetic circuits distributed among various cell populations. Maze generating and solving are challenging problems in mathematics and computing. Here, we mapped all the input-output matrices of a 2 × 2 mathematical maze on a 4-input-4-output truth table. The logic values of four chemical inputs determined the 16 different 2 × 2 maze problems on a chemical space. We created six multi-input synthetic genetic AND gates, which distributed among six cell populations and organized in a single layer. Those cell populations in a mixed culture worked as a computational solver, which solved the chemically generated maze problems by expressing or not expressing four different fluorescent proteins. The three available "solutions" were visualized by glowing bacteria, and for the 13 "no solution" cases, no bacteria glowed. Thus, our system not only solved the maze problems but also showed the number of solvable and unsolvable problems. This work may have significance in cellular computation and synthetic biology.

Single-Cell, Time-Resolved Antimicrobial Effects of a Highly Cationic, Random Nylon-3 Copolymer on Live Escherichia coli.

Synthetic random copolymers based on the nylon-3 (ß-peptide) backbone show promise as inexpensive antimicrobial agents resistant to proteolysis. We present a time-resolved observational study of the attack of a particular copolymer MM63:CHx37 on single, live Escherichia coli cells. The composition and chain length of MM63:CHx37 (63% cationic subunits, 37% hydrophobic subunits, 35-subunit average length) were optimized to enhance antibacterial activity while minimizing lysis of human red blood cells. For E. coli cells that export GFP to the periplasm, we obtain alternating phase-contrast and green fluorescence images with a time resolution of 12 s over 60 min following initiation of copolymer flow. Within seconds, cells shrink and exhibit the same plasmolysis spaces that occur following abrupt external osmotic upshift. The osmoprotection machinery attempts to replenish cytoplasmic water, but recovery is interrupted by permeabilization of the cytoplasmic membrane (CM) to GFP. Evidently, the highly cationic copolymer and its counterions rapidly translocate across the outer membrane without permeabilizing it to GFP. The CM permeabilization event is spatially localized. Cells whose CM has been permeabilized never recover growth. The minimum inhibitory concentration (MIC) for cells lacking the osmolyte importer ProP is 4-fold smaller than for normal cells, suggesting that osmoprotection is an important survival strategy. In addition, at the time of CM permeabilization, we observe evidence of oxidative stress. The MIC under anaerobic conditions is at least 8-fold larger than under aerobic conditions, further implicating oxidative damage as an important bacteriostatic effect. Once the copolymer reaches the periplasm, multiple growth-halting mechanisms proceed in parallel.

Ternary nylon-3 copolymers as host-defense peptide mimics: beyond hydrophobic and cationic subunits.

Host-defense peptides (HDPs) are produced by eukaryotes to defend against bacterial infection, and diverse synthetic polymers have recently been explored as mimics of these natural peptides. HDPs are rich in both hydrophobic and cationic amino acid residues, and most HDP-mimetic polymers have therefore contained binary combinations of hydrophobic and cationic subunits. However, HDP-mimetic polymers rarely duplicate the hydrophobic surface and cationic charge density found among HDPs ( Hu , K. ; et al. Macromolecules 2013 , 46 , 1908 ); the charge and hydrophobicity are generally higher among the polymers. Statistical analysis of HDP sequences ( Wang , G. ; et al. Nucleic Acids Res. 2009 , 37 , D933 ) has revealed that serine (polar but uncharged) is a very common HDP constituent and that glycine is more prevalent among HDPs than among proteins in general. These observations prompted us to prepare and evaluate ternary nylon-3 copolymers that contain a modestly polar but uncharged subunit, either serine-like or glycine-like, along with a hydrophobic subunit and a cationic subunit. Starting from binary hydrophobic-cationic copolymers that were previously shown to be highly active against bacteria but also highly hemolytic, we found that replacing a small proportion of the hydrophobic subunit with either of the polar, uncharged subunits can diminish the hemolytic activity with minimal impact on the antibacterial activity. These results indicate that the incorporation of polar, uncharged subunits may be generally useful for optimizing the biological activity profiles of antimicrobial polymers. In the context of HDP evolution, our findings suggest that there is a selective advantage to retaining polar, uncharged residues in natural antimicrobial peptides.

Medium effects on minimum inhibitory concentrations of nylon-3 polymers against E. coli.

Minimum inhibitory concentrations (MICs) against E. coli were measured for three nylon-3 polymers using Luria-Bertani broth (LB), brain-heart infusion broth (BHI), and a chemically defined complete medium (EZRDM). The polymers differ in the ratio of hydrophobic to cationic subunits. The cationic homopolymer is inert against E. coli in BHI and LB, but becomes highly potent in EZRDM. A mixed hydrophobic/cationic polymer with a hydrophobic t-butylbenzoyl group at its N-terminus is effective in BHI, but becomes more effective in EZRDM. Supplementation of EZRDM with the tryptic digest of casein (often found in LB) recapitulates the LB and BHI behavior. Additional evidence suggests that polyanionic peptides present in LB and BHI may form electrostatic complexes with cationic polymers, decreasing activity by diminishing binding to the anionic lipopolysaccharide layer of E. coli. In contrast, two natural antimicrobial peptides show no medium effects. Thus, the use of a chemically defined medium helps to reveal factors that influence antimicrobial potency of cationic polymers and functional differences between these polymers and evolved antimicrobial peptides.

Two interdependent mechanisms of antimicrobial activity allow for efficient killing in nylon-3-based polymeric mimics of innate immunity peptides.

Novel synthetic mimics of antimicrobial peptides have been developed to exhibit structural properties and antimicrobial activity similar to those of natural antimicrobial peptides (AMPs) of the innate immune system. These molecules have a number of potential advantages over conventional antibiotics, including reduced bacterial resistance, cost-effective preparation, and customizable designs. In this study, we investigate a family of nylon-3 polymer-based antimicrobials. By combining vesicle dye leakage, bacterial permeation, and bactericidal assays with small-angle X-ray scattering (SAXS), we find that these polymers are capable of two interdependent mechanisms of action: permeation of bacterial membranes and binding to intracellular targets such as DNA, with the latter necessarily dependent on the former. We systemically examine polymer-induced membrane deformation modes across a range of lipid compositions that mimic both bacteria and mammalian cell membranes. The results show that the polymers' ability to generate negative Gaussian curvature (NGC), a topological requirement for membrane permeation and cellular entry, in model Escherichia coli membranes correlates with their ability to permeate membranes without complete membrane disruption and kill E. coli cells. Our findings suggest that these polymers operate with a concentration-dependent mechanism of action: at low concentrations permeation and DNA binding occur without membrane disruption, while at high concentrations complete disruption of the membrane occurs. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Tuning the biological activity profile of antibacterial polymers via subunit substitution pattern.

Binary nylon-3 copolymers containing cationic and hydrophobic subunits can mimic the biological properties of host-defense peptides, but relationships between composition and activity are not yet well understood for these materials. Hydrophobic subunits in previously studied examples have been limited mostly to cycloalkane-derived structures, with cyclohexyl proving to be particularly promising. The present study evaluates alternative hydrophobic subunits that are isomeric or nearly isomeric with the cyclohexyl example; each has four sp(3) carbons in the side chains. The results show that varying the substitution pattern of the hydrophobic subunit leads to relatively small changes in antibacterial activity but causes significant changes in hemolytic activity. We hypothesize that these differences in biological activity profile arise, at least in part, from variations among the conformational propensities of the hydrophobic subunits. The α,α,ß,ß-tetramethyl unit is optimal among the subunits we have examined, providing copolymers with potent antibacterial activity and excellent prokaryote vs eukaryote selectivity. Bacteria do not readily develop resistance to the new antibacterial nylon-3 copolymers. These findings suggest that variation in subunit conformational properties could be generally valuable in the development of synthetic polymers for biological applications.

Effects of Cyclic vs. Acyclic Hydrophobic Subunits on the Chemical Structure and Biological Properties of Nylon-3 Co-Polymers.

Nylon-3 co-polymers containing both hydrophobic and cationic subunits can mimic the activity profile of host-defense peptides, if subunit identity and proportion are carefully selected. These sequence- and stereo-random co-polymers inhibit bacterial growth at relatively low concentrations, apparently via disruption of bacterial membranes, but they are relatively non-disruptive toward eukaryotic cell membranes (low hemolytic activity). In all previous examples, the hydrophobic subunits have contained cycloalkyl groups that incorporate the backbone Cα-Cß bond. Here we have explored the effects of using analogous acyclic hydrophobic subunits. The results indicate that the replacing cyclic with acyclic hydrophobic subunits has a modest influence on biological properties. This influence appears to arise from differences in subunit flexibility.

Interplay among subunit identity, subunit proportion, chain length, and stereochemistry in the activity profile of sequence-random peptide mixtures.

Fmoc-based solid-phase synthesis methodology was used to prepare peptide mixtures containing one type of hydrophobic residue and one type of cationic residue. Each mixture was random in terms of sequence but highly controlled in terms of length. Analysis of the antibacterial and hemolytic properties of these mixtures revealed that selective antibacterial activity can be achieved with heterochiral binary mixtures but not homochiral binary mixture, if the proper amino acid residues are used.

Nylon-3 polymers with selective antifungal activity.

Host-defense peptides inhibit bacterial growth but show little toxicity toward mammalian cells. A variety of synthetic polymers have been reported to mimic this antibacterial selectivity; however, achieving comparable selectivity for fungi is more difficult because these pathogens are eukaryotes. Here we report nylon-3 polymers based on a novel subunit that display potent antifungal activity (MIC = 3.1 µg/mL for Candida albicans ) and favorable selectivity (IC10 > 400 µg/mL for 3T3 fibroblast toxicity; HC10 > 400 µg/mL for hemolysis).