Molecular mechanisms of interaction between enzymes and Maillard reaction products formed from thermal hydrolysis pretreatment of waste activated sludge.

Thermal hydrolysis pretreatment (THP) is often used to improve the anaerobic digestion performance of waste activated sludge (WAS) in wastewater treatment plants (WWTPs). During the THP process, the proteins and polysaccharides in the biomass will undergo hydrolysis and Maillard reaction, producing biorefractory organic substances, such as recalcitrant dissolved organic nitrogen (rDON) and melanoidins. In this study, a series of spectroscopy methods were used to quantitatively analyze the Maillard reaction of glucose and lysine, and the interaction mechanisms of the Maillard reaction products (MRPs) and lysozyme were investigated. Results showed that the typical aromatic heterocyclic structures in MRPs, such as pyrazine and furan, were found to quench molecular fluorescence of lysozyme, resulting in an unfolding of standard protein structure and increase in lysozyme hydrophobicity. Significant loss of enzyme activity was detected during this process. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) confirmed that the interaction between MRPs and lysozyme occurred both exothermically and spontaneously. Density functional theory (DFT) calculations suggested that the molecular interactions of MRPs and protein included parallel dislocation aromatic stacking, T-shaped vertical aromatic stacking, H-bond and H-bond coupled to aromatic stacking.

Antioxidant Properties of Camphene-Based Thiosemicarbazones: Experimental and Theoretical Evaluation.

The thiosemicarbazone derivatives have a wide range of biological activities, such as antioxidant activity. In this study, the antiradical activities of six camphene-based thiosemicarbazones (TSC-1~6) were investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and peroxyl radical scavenging capacity (PSC) assays, respectively, and the results reveal that TSC1~6 exhibited good abilities for scavenging free radicals in a dose-dependent way. Compound TSC-2 exhibited the best effect of scavenging DPPH radical, with the lowest EC50 (0.208 ± 0.004 mol/mol DPPH) as well as the highest bimolecular rate constant Kb (4218 M-1 s-1), which is 1.18-fold higher than that of Trolox. Meanwhile, TSC-2 also obtained the lowest EC50 (1.27 µmol of Trolox equiv/µmol) of scavenging peroxyl radical. Furthermore, the density functional theory (DFT) calculation was carried out to further explain the experimental results by calculating several molecular descriptors associated with radical scavenging activity. These theoretical data suggested that the electron-donating effect of the diethylamino group in TSC-2 leads to the enhancement of the scavenging activities and the studied compounds may prefer to undergo the hydrogen atom transfer process.

Novel Colorimetric Method for Simultaneous Detection and Identification of Multimetal Ions in Water: Sensitivity, Selectivity, and Recognition Mechanism.

Accurate recognition and speciation analysis of heavy-metal ions in complex hydrological environments is always a serious challenge. In this work, we proposed a small-molecule-based ultrasensitive colorimetric detection strategy and successfully applied it to the accurate detection of Fe2+, Fe3+, Co2+, and Hg2+ in groundwater through the specific recognition of multiple ligands of different metal ions. The detection limits for Hg2+, Co2+, Fe2+, and Fe3+ are calculated to be 6.51, 0.34, 0.49, and 1.01 ppb, respectively, which are far below the drinking water standards and superior to most of the reported colorimetric sensors. Remarkably, the speciation analysis of Fe2+/Fe3+ also has been successfully realized by a one-step method without complex pretreatment. The speciation and concentration of Fe2+ and Fe3+ in actual water samples can be accurately identified and monitored. In addition, as an attempt of visual onsite detection, we have developed a simple test strip, which has been applied to visual monitoring of four metal ions with the detection limit estimated by the naked eye to be as low as ppb level. This proposed colorimetric method realizes the rapid, sensitive, and portable multiple metal ions recognition and Fe2+/Fe3+ speciation analysis, displaying great potential for onsite rapid water quality analysis.

Dye adsorption by self-recoverable, adjustable amphiphilic graphene aerogel.

A type of self-recoverable, adjustable amphiphilic graphene aerogel (GA) was prepared and applied to the dye adsorption. The GA with polyvinyl alcohol (PVA) as its cross-linking agent has the characteristics of adjustable amphiphilicity. By adjusting the PVA content in GA, the later can be used to adsorb dyes with different hydrophobic and hydrophilic properties. Four kinds of dyes (Malachite green, Rhodamine B, Methylene blue and Methyl orange) were applied as targets and the saturated adsorption amounts were calculated. The Langmuir adsorption model and the Lagrange pseudo-second-order equation mathematical model were used to study the behavior of dye adsorption by GA, and the experimental data was in full compliance with the mathematical models. The excellent mechanical properties (compressibility and recoverability) make the GA suitable for dye adsorption. A computational simulation was also performed to verify the adsorption energy of GA to dyes. The GA was able to retain 89.5% of its initial removal efficiency (for malachite green) after 10 cycles of application.

Smartphone Nanocolorimetric Determination of Hydrogen Sulfide in Biosamples after Silver-Gold Core-Shell Nanoprism-Based Headspace Single-Drop Microextraction.

In this work, the sensitive detection of hydrogen sulfide (H2S) was realized at low cost and high efficiency through the application of silver-gold core-shell nanoprism (Ag@Au-np) combined with headspace single-drop microextraction (HS-SDME). After SDME, smartphone nanocolorimetry (SNC), with the aid of a smartphone camera and color picker software, was used to detect and quantify the H2S. The method took advantage of the inhibition of the ultraviolet-visible (UV-vis) signal caused by H2S etching of the Ag@Au-np preadded to the SDME solvent to measure the H2S concentration. The coating of the gold layer not only ensured the high stability of the nanomaterial but also enhanced the selectivity toward H2S. The HS-SDME method was simple to process and required only a droplet of solvent for analysis to be realized. This HS-SDME-SCN approach exhibited a calibration graph linearity of between 0.1 and 100 µM and a limit of detection of 65 nM (relative standard deviations of N% ( n = 3) < 4.80). A comparison with UV-vis spectrophotometry was conducted. The practical applicability of HS-SDME-SNC was successfully demonstrated by determining H2S in genuine biosamples (egg and milk).

A novel turn-on fluorescent probe for selective sensing and imaging of glutathione in live cells and organisms.

We synthesized six 1-oxo-1H-phenalene-2,3-dicarbonitrile (OPD)-based probes with various leaving groups using an arylthioether linker and for the first time identified the probe O-NH2 capable of highly selective detection of glutathione over cysteine/homocysteine in vitro and in vivo based on an aromatic nuclear substitution reaction (SNAr) mechanism. The fluorescence of the probe O-NH2 was quenched because of the photoinduced electron transfer (PET) process, but switched on by a glutathione-triggered specific recognition reaction between the probe O-NH2 and glutathione. The recognition mechanism for glutathione was explored and verified by theoretical calculations and ESI-MS analysis. Using O-NH2 as the probe, the GSH fluorescence images were demonstrated in HeLa cells and the intracellular GSH levels in different imatinib-resistant K562 tumor cells were firstly determined. Further, O-NH2 was utilized to detect glutathione in D. magna and zebrafish embryos. The combined results indicate that O-NH2 can be applied as an effective tool for detecting glutathione in biological investigations.

In-syringe extraction using compressible and self-recoverable, amphiphilic graphene aerogel as sorbent for determination of phenols.

Graphene aerogels (GAs) have demonstrated great promise as sorbent materials. However, the intrinsically hydrophobic GAs are unsuitable for extraction of highly water-soluble analytes. Moreover, lack of compressibility limits the recyclability of GAs. In this work, an interesting type of water-induced self-recoverable amphiphilic GA was synthesized and employed as sorbent to extract nine priority phenols, listed as priority pollutants by the United States Environmental Protection Agency, from aqueous samples. The water-induced self-recoverability gives the GA the characteristic of a sponge, providing high recyclability and long-life. The aerogel was placed in a 2-mL microsyringe for in-syringe extraction of the phenols. The GA exhibits amphiphilicity due to the cross-linking by polyvinyl alcohol. At the same time, it exhibited selectivity to the water-soluble phenols. The extracted phenols were eluted with acetonitrile from the GA and the final extract was analyzed by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). The results showed that this method provided low limits of detection for the phenols (0.089-0.015 µg/L), good linearity (r2 ≥ 0.9956) and low relative standard deviations (≤6.8%). The optimized method was applied successfully to river water samples. The simple in-syringe extraction procedure in combination with HPLC-UV analysis was demonstrated to be efficient, fast and convenient.

Magnetic Ni/Fe layered double hydroxide nanosheets as enhancer for DNA hairpin sensitive detection of miRNA.

A new non-enzyme method based on hybridization chain reaction (HCR) and colorimetric reaction catalyzed by magnetic Ni/Fe layered double hydroxide (LDH) nanosheets was developed for detection of microRNA (miRNA), let-7b. The DNA hairpins from HCR were separated and adsorbed by Ni/Fe LDH. The peroxidase-like activity of Ni/Fe LDH was found to be enhanced by the DNA hairpins on the surface. The factors, such as ratio of Ni/Fe and concentration of DNA hairpins, related to the catalytic activity were evaluated and the mechanism was discussed. The results of this new detection method for let-7b provided low limit of detection (0.36 fM), wide linear range (0.01 pM to 200 pM) with good linearity (r2 = 0.9968). The optimized method was applied to analyze let-7b in real samples, lung cancer cells. This work demonstrated a new and cost-effective approach for efficient detection of miRNA.

pH-dependent selective ion exchange based on (ethylenediamintetraacetic acid-nickel)-layered double hydroxide to catalyze the polymerization of aniline for detection of Cu2+ and Fe3.

A pH-dependent selective ion exchange coupled with catalytic polymerization of aniline has been developed for sensitive detection of copper (Cu2+) and ferric ions (Fe3+). Ethylenediamintetraacetic acid (EDTA) chelated with nickel ion (Ni2+) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent for the enrichment of Cu2+ at pH 6.5 and Fe3+ at pH 4.5. Since both Cu2+ and Fe3+ have stronger complex formation constants with EDTA, Ni2+ exchanges with Cu2+/Fe3+ selectively. The resulting sorbent containing Cu2+/Fe3+ was transferred to catalyze the aniline polymerization reaction, since Cu2+/Fe3+ could be released by the sorbent effectively at different pH values and have high catalytic abilities for the polymerization reaction. The resulting polyaniline with different colors were produced at different pH values, an observation that was utilized to distinguish between the colorimetric signals of Cu2+ and Fe3+. The extraction temperature, extraction time, catalysis time and pH were optimized. The results showed that this method provided low limits of detection of 0.1 nM (6.4 ng/L) for Cu2+, 1 nM (56 ng/L) for Fe3+, wide linear ranges (0.0005-2.5 µM, and 0.005-5 µM, respectively), and good linearities (r2 values of 0.9904, and 0.9965, respectively). The optimized method was applied to river water samples. Using Cu2+/Fe3+ as examples, this work provided a new and interesting approach for the convenient and efficient detection of metal ions in aqueous samples.