Evaluating the effects of hydrophobic and cationic residues on antimicrobial peptide self-assembly.

Antimicrobial peptides typically contain hydrophobic and cationic residues, which allow them to interact with microbial cells and induce cell death. In a previous study, we found that the hydrophobic and cationic residues could also help antimicrobial peptides self-assemble into hydrogels, and this could be used as a novel approach for the preparation of hydrogel wound dressings. Therefore, in this work, four PAF26 peptide derivatives with different hydrophobic and cationic residues were used to study the effects of hydrophobic and cationic residues on self-assembly behaviours. It was found that all the PAF26 peptide derivatives could self-assemble into hydrogels, but the storage moduli, microscopic structures, secondary structure transformations, and antimicrobial abilities varied. In particular, peptides with a greater number of hydrophobic and cationic residues tended to undergo an unordered coil transformation and form bent nanofibers, while peptides with a lower number of hydrophobic and cationic residues tended to undergo ß-sheet transformation and form straight nanofibers. In addition, antimicrobial experiments demonstrated that a strong crosslinked structure may have negative effects on the antimicrobial activity.

HPO42- enhanced catalytic activity of N, S, B, and O-codoped carbon nanosphere-armored Co9S8 nanoparticles for organic pollutants degradation via peroxymonosulfate activation: critical roles of superoxide radical, singlet oxygen and electron transfer.

In this study, we report a facile synthesis of a novel N, S, B, and O-codoped carbon nanosphere-armored Co9S8 nanoparticle composite (Co9S8@NSBOC) and its superior activation performance toward peroxymonosulfate (PMS) for methylene blue (MB) and ofloxacin degradation. The effects of various experimental parameters and the general applicability of the catalyst were investigated. Particularly, Co9S8@NSBOC exhibited high catalytic activity in a wide pH range of 3-12 and HPO42- exhibited a synergic catalytic effect with Co9S8@NSBOC in the degradation system. Radical quenching tests, EPR measurements and electrochemical analysis demonstrated that the degradation mechanism of pollutants in the Co9S8@NSBOC/PMS system included both radical and non-radical pathways, in which ˙O2-, 1O2 and electron transfer played dominant roles. Co2+, S2-, carbon defects, C[double bond, length as m-dash]O/C-O-C, pyridinic-N, graphitic-N, BC2O and C-S-C species on Co9S8@NSBOC, all contributed to PMS activation. The degradation pathways of MB and ofloxacin were proposed based on HPLC-MS/MS analysis of their degradation intermediates. This work not only presents a facile and practical synthetic method of cobalt sulfide-coupled multi-heteroatom-doped carbocatalysts, but also provides useful insights into their active sites and activation mechanisms toward PMS activation.

Co nanoparticle-embedded N,O-codoped porous carbon nanospheres as an efficient peroxymonosulfate activator: singlet oxygen dominated catalytic degradation of organic pollutants.

In this study, Co nanoparticle-embedded N,O-codoped porous carbon nanospheres (C@Co) with abundant N and O doping, high graphitization, large specific surface area (319 m2 g-1) and a well-developed mesoporous structure were synthesized and characterized thoroughly, and were applied to activate peroxymonosulfate (PMS) for the degradation of methylene blue (MB). Various influential factors affecting the catalytic performance including C@Co dosage, PMS dosage, MB concentration, initial pH, temperature, and co-existing common anions and humic acid (HA) on the MB degradation were systematically investigated. The increase of the C@Co dosage (15-60 mg), PMS dosage (25-100 mg) and reaction temperature (278-308 K) promoted the MB degradation in the C@Co/PMS system. The best performance of the C@Co/PMS system was observed under weakly acidic or nearly neutral conditions. Both the MB concentration (25-100 mg L-1) and Cl- (5-100 mM), NO3- (10-500 mM), CO32- (10-300 mM), HCO3- (1-30 mM) and HA (2-40 mg L-1) had an inhibitory effect on MB degradation, and the degree of decrease in MB degradation increased as their concentrations were enhanced. Interestingly, HPO42- (1-100 mM) had an overall inhibitory effect on the degradation process of MB; however, in comparison with lower concentrations (1-10 mM), an attenuation of the inhibitory effect at higher concentrations (50-100 mM) could be observed. Moreover, the C@Co/PMS system also exhibited general applicability in eliminating various organic pollutants from water such as methyl orange, malachite green, safranine T, Congo red, Rhodamine B, ofloxacin and tetracycline. Classical radical-quenching tests and EPR measurements showed that both the non-radical pathway (major route, involving 1O2) and radical pathway (minor route, involving ˙OH, ˙SO4- and ˙O2-) contribute to the MB degradation. DFT calculations disclosed that the combination of Co-C interactions with graphitic N doping brought in catalytically active sites in C@Co where the charge states of some C atoms were significantly increased. The degradation intermediates of MB during the catalytic reaction were also identified by HPLC-MS and the possible degradation pathway was proposed. Overall, the resultant C@Co can be developed as a novel and efficient heterogeneous catalyst for activating PMS to degrade organic pollutants, and has potential application in environmental remediation.

Evolution from Classical to Non-classical Aggregation-Based Crystal Growth of Calcite by Organic Additive Control.

Aggregation-based crystal growth is distinct from the classical understanding of solution crystallization. In this study, we reveal that N-stearoyl-l-glutamic acid (C18-Glu, an amphiphile that mimics a biomineralization-relevant biomolecule) can switch calcite crystallization from a classical ion-by-ion growth to a non-classical particle-by-particle pathway, which combines the classical and non-classical crystallization in one system. This growth mechanism change is controlled by the concentration ratio of [C18-Glu]/[Ca(2+)] in solution. The high [C18-Glu]/[Ca(2+)] can stabilize precursor nanoparticles to provide building blocks for aggregation-based crystallization, in which the interaction between C18-Glu and the nanoprecursor phase rather than that of C18-Glu on calcite steps is highlighted. Our finding emphasizes the enrollment of organic additives on metastable nano building blocks, which provides an alternative understanding about organic control in inorganic crystallization.

Realignment of Nanocrystal Aggregates into Single Crystals as a Result of Inherent Surface Stress.

Crystallization by particle attachment is widely observed in both natural and synthetic environments. Although this form of nonclassical crystallization is generally described by oriented attachment, random aggregation of building blocks to give single-crystal products is also observed, but the mechanism of crystallographic realignment is unknown. We herein reveal that random attachment during aggregation-based growth initially produces a nonoriented growth front. Subsequent evolution of the orientation is driven by the inherent surface stress applied by the disordered surface layer and results in single-crystal formation by grain-boundary migration. This mechanism is corroborated by measurements of orientation rate versus external stress, which demonstrated a predictive relationship between the two. These findings advance our understandings about aggregation-based growth via nanocrystal blocks and suggest an approach to material synthesis that takes advantage of stress-induced coalignment.

Virus capture and destruction by label-free graphene oxide for detection and disinfection applications.

Graphene oxide (GO) can efficiently capture viruses, destroy their surface proteins, and extract viral RNA in an aqueous environment by using the superficial bioreduction of GO. It follows from these phenomena that GO is an excellent nanomaterial for the high-throughput detection and disinfection of viruses, demonstrating its great potential for the prevention of environmental infections.

Silicification-induced cell aggregation for the sustainable production of H2 under aerobic conditions.

Photobiological hydrogen production is of great importance because of its promise for generating clean renewable energy. In nature, green algae cannot produce hydrogen as a result of the extreme sensitivity of hydrogenase to oxygen. However, we find that silicification-induced green algae aggregates can achieve sustainable photobiological hydrogen production even under natural aerobic conditions. The core-shell structure of the green algae aggregates creates a balance between photosynthetic electron generation and hydrogenase activity, thus allowing the production of hydrogen. This finding provides a viable pathway for the solar-driven splitting of water into hydrogen and oxygen to develop green energy alternatives by using rationally designed cell-material complexes.

Highly Efficient Photocatalytic Degradation of Tetracycline by Modifying UiO-66 via Different Regulation Strategies.

Wastewater containing organic pollutants cause potential harm to the environment and human health. A series of zirconium-organic frameworks (UiO-66) and their composites were synthesized by solvothermal methods, including band gap adjustment, heterojunction construction, and metal ion doping. For the model pollutant tetracycline (TC), all of the prepared catalysts could achieve effective degradation of it. Therein, the degradation efficiency of tetracycline could reach 95% under the UV irradiation with the aid of the catalyst, in which the UiO-66-NDC was modified with P-C3N4. The free radical capture experiments demonstrated that the superoxide radical (•O2-) was the main oxidizing species for the photodegradation of tetracycline. Hence, the improvement strategy of the catalyst would provide some enlightenment for the development of more efficient photocatalysts for the degradation of organic dyes in wastewater.

g-C3N4-modified Zr-Fc MOFs as a novel photocatalysis-self-Fenton system toward the direct hydroxylation of benzene to phenol.

In order to explore a green, economic, and sustainable phenol production process, a heterojunction semiconductor materials g-C3N4/Zr-Fc MOF was synthesized via an in situ synthesis method. With the synergistic effect of photocatalysis and the Fenton effect, the composite could effectively catalyze the direct hydroxylation of benzene to phenol under visible light irradiation. The yield of phenol and the selectivity were 13.84% and 99.38% under the optimal conditions, respectively, and it could still maintain high photocatalytic activity after 5 photocatalytic cycles. Therefore, the designed photocatalysis-self-Fenton system has great potential in the field of the direct hydroxylation of benzene to phenol.

Silkworm cocoon derived N, O-codoped hierarchical porous carbon with ultrahigh specific surface area for efficient capture of methylene blue with exceptionally high uptake: kinetics, isotherm, and thermodynamics.

Dyes are typical water contaminants that seriously affect water quality. In this study, silkworm cocoon derived N, O-codoped hierarchical porous carbon was successively developed via a facile pre-carbonization and chemical activation method, and characterized thoroughly by SEM, TEM, HRTEM, XRD, Raman, N2 adsorption and XPS. The as-prepared N, O-HPC showed a well-developed porous structure with an ultra-high specific surface area of 2270.19 m2 g-1, which proved to be a high-efficiency adsorbent. Batch adsorption experiments demonstrated that MB adsorption was highly dependent on contact time, initial MB concentration, temperature and initial solution pH. However, no remarkable effects of humic acid and ionic strength were observed. In the kinetic studies, the good applicability of a pseudo-second-order kinetic model was demonstrated. The adsorption isotherm study showed that a Langmuir isotherm model can describe the experimental data much more suitably with a maximum monolayer adsorption capacity value of 2104.29 mg g-1, which is among the highest in previously reported adsorbents and ascribed to multiple adsorption mechanisms including pore filling, π-π stacking interaction and electrostatic interaction between MB and N, O-HPC. Thermodynamic analyses suggested that MB adsorption onto N, O-HPC was spontaneous and endothermic. Furthermore, the as prepared adsorbent showed highly efficient adsorption for MB in tap water and synergistic adsorption performance toward MB and MO. Therefore, N, O-HPC derived from silkworm cocoon could be considered as an efficient, novel and advantageous material for wastewater remediation.

An injectable molecular hydrogel assembled by antimicrobial peptide PAF26 for antimicrobial application.

Wound infection is a crucial factor that inhibits wound recovery. A feasible measure to solve this problem is using antimicrobial biomaterials to suppress the microbial growth. In this work, an amphipathic antimicrobial peptide (Ac-RKKWFW-NH2, PAF26) was investigated to form the antimicrobial hydrogel. Triggered by pH, PAF26 peptide could self-assemble into a hydrogel, and the hydrogel formed was injectable and exhibited shear-thinning ability. Antimicrobial experiments demonstrated that the self-assembled hydrogel had an outstanding antimicrobial ability against pathogenic microbes such as Candida albicans, Staphylococcus aureus, and Escherichia coli via destroying the cell membrane structure. Thus, this study provides a novel method for preparing an injectable antimicrobial peptide hydrogel for antimicrobial therapies.

Multifunctional Gd,Ce,Tb co-doped ß-tricalcium phosphate porous nanospheres for sustained drug release and bioimaging.

Multifunctional Gd,Ce,Tb co-doped ß-tricalcium phosphate (TCP) porous nanospheres are prepared by a facile solvothermal strategy with trimethyl phosphate as the phosphorus source. The as-prepared nanomaterial (average diameter of 100 nm) has a multiple level pore size distribution with the specific surface area of 124.33 m2 g-1, which benefits drug loading. Its photoluminescent and magnetic multifunctions are realized by the co-doping of Gd3+, Ce3+ and Tb3+ ions, which make the nanomaterial promising for both fluorescence and magnetic resonance imaging techniques. Furthermore, the nanomaterial exhibits excellent cytocompatibility and a relatively high doxorubicin loading capacity as well as sustained pH-sensitive drug release behaviour. It is suggested that the Gd,Ce,Tb co-doped ß-TCP porous nanospheres are promising for applications in the biomedical fields such as multifunctional drug delivery systems and tissue engineering scaffolds with bioimaging guidance.

Robust glucose oxidase with a Fe3O4@C-silica nanohybrid structure.

Biomolecules, especially enzymes, usually have poor thermal and operational stability as well as limited reuse cycles, which greatly limit their industrial practices. Inspired by the biomineralization strategy evolved by natural organisms, we suggest nanohybrid enzyme formulation by in situ encapsulating enzyme loaded functional Fe3O4@C nanoparticles with silica. By using glucose oxidase (GOD) as an example, we demonstrate that the obtained enzyme-material hybrids are featured by their significantly enhanced operational and thermal stabilities, which exhibit a relatively steady catalytic ability in a board range of 25 °C to 65 °C. Even after 4 h of incubation at 55 °C, the GOD-material composites still retain 77% of their initial activity while the native ones only retain 30%. Besides, the nanohybrids show excellent reusability because the magnetic character of the integrated Fe3O4 particles facilitates the enzyme separation and recycle. This attempt provides a valuable approach for biological improvement by using functional materials.

The effect of amorphous calcium phosphate on protein protection against thermal denaturation.

The hybrid nanoparticles of amorphous calcium phosphate (ACP)-catalase (CAT) developed by in situ biomineralization can create a stable semi-aqueous nanoscale environment for entrapped proteins against thermal denaturation. This finding indicates the importance of an amorphous mineral phase in the preservation of organic macromolecules.

High efficient multifunctional Ag3PO4 loaded hydroxyapatite nanowires for water treatment.

Organic, inorganic, and biological pollutants are typical water contaminants and they seriously affect water quality. In this study, we suggested that a novel multifunctional Ag3PO4 loaded hydroxyapatite (HAP) material can remove the typical pollutants from water. The Ag3PO4/HAP composites were synthesized facilely via in-situ precipitation of Ag3PO4 on the pre-existing HAP nanowires. By optimizing the composition of Ag3PO4 and HAP, the material could achieve an optimal photocatalytic activity to decompose rhodamine B (RhB), methyl orange (MO) and methylene blue (MB) under visible light irradiations with enhanced pH stability. Besides, the adsorption of Pb(II) on the Ag3PO4/HAP reached a maximum capacity of 250 mg/g and this value was approximately three times as that of pure HAP. Furthermore, the composite material exhibited excellent antibacterial activities towards gram-negative bacterium (Escherichia coli) and gram-positive bacterium (Stphylococcus aureus). The results highlighted the cooperative effect between Ag3PO4 and hydroxyapatite (HAP). The simultaneous removals of dyes, toxic metal ions, and bacteria with a high efficiency followed an easy approach for the purification of contaminated water via the rationally designed material, in which the Ag3PO4/HAP composite might be developed as a general water treatment material with multiple functions.