Hydrogen bonding dominated self-assembly mechanism of amphiphilic molecules in Chinese Baijiu.

Molecular mechanisms underlying the aging of Chinese Baijiu remained elusive. This study proposed the self-assembly behavior of amphiphilic molecules dominated by hydrogen bonds in Chinese Baijiu for the first time. The self-assembly degree of amphiphilic clusters gradually intensifies with the prolonged storage time of Baijiu, comprehensively characterized at both micro and macro levels. The results indicated that the blue-shift of the Raman hydrogen bond vibrational peak (about 11 cm-1 and 7 cm-1, respectively), the increase in viscosity (5.71% and 2.22%, respectively), and the rise in dielectric constant (95.63% and 94.99%, respectively) during the 17-year cellaring process of Strong-flavor Baijiu and Jiang-flavor Baijiu were consistent with the evolutionary trends observed in molecular dynamics simulations. The essential driving factors of cluster structure alteration of amphiphilic aroma substances in Chinese Baijiu during cellaring were demonstrated from molecular level. This study provided a research approach to comprehending the aging mechanism of Chinese Baijiu from the micro level.

Robust (hydrogen) phosphate sensing based on reversible redox of cobalt(II) hydroxide.

Response mechanism of the electrode is elucidated in terms of (hydrogen) phosphate accelerating oxidation of CoII to CoIII for the first time. Cyclic voltammetric techniques in conjunction with XRD, XPS and Raman characterizations have demonstrated unambiguously the response of cobalt (II) hydroxide electrode involves a phosphate and hydrogen ion dependent charge transfer process. Phosphate ions induce Co(OH)2 transformed into CoOOH within interlayer adsorption and restored the initial state after reduction. Meanwhile, the in common structural between Co(OH)2 and CoOOH prevents extensive structural convertibility upon cycling, result in the advantage of reversibility in phase transformation. Demonstrated sustainable technique offered the determination of phosphate with robust reproducibility (1000 cycles), long storage stability (6 months) and selectivity (potential interference: Cl-, NO3-, SO42- and HCO3-), achieving a detection limit of 5 × 10-8 M over a wide linear range up to 1.28 mM. Presented work provided insights into the unique selectivity towards phosphate in cobalt based sensors, which may inspire the rational design of Co(OH)2-based electrodes with superior electrochemical performance or extended applications.

Microplastic degradation methods and corresponding degradation mechanism: Research status and future perspectives.

Microplastics (MPs) pollution has become a global environmental concern because of their severe threat to biota. However, limited studies on the elimination of MPs pollution were reported. The conventional treatment methods were not suitable for MPs owing to their smaller size than plastic items. Hence many methods for MPs treatment have been examined. This review summarized the recently reported MPs degradation methods including AOPs (direct photodegradation, photocatalytic oxidation, and electrochemical oxidation) and biodegradation, corresponding degradation mechanism as well as current development state. The characteristics and limitations of each technique were discussed in detail. We found that all of them achieved almost satisfying degradation performance of MPs, but most of them exhibited that MPs can only be degraded partially into useful products or even CO2 and H2O under lab conditions. Given these, some recommendations for future research directions were proposed based on the knowledge gaps in these reported literatures. The aim of this review is to give a comprehensive introduction of several MPs degradation methods and acquaint the readers with the current research status of MPs degradation.

Simultaneously detecting ethyl carbamate and its precursors in rice wine based on a pH-responsive electrochemical impedance sensor.

Intensive efforts have been made to diminish ethyl carbamate in fermentation products. The presented research demonstrated an approach to simultaneously detecting ethyl carbamate and its precursors including urea, citrulline and arginine with nano Mn(Ⅱ)O modified composite working electrode via electrochemical impedance spectroscopy. Adjusting sample solutions at certain pH value leads the differentiated priority of protonation from nitrogen group in the ethyl carbamate (EC) and its precursors. Molecular recognition was achieved through attractive electrostatic interaction due to the negatively charged Mn(Ⅱ)O nanocrystal on the working electrode surface in aqueous sample solutions. Deconvolution and principle component analysis were applied to differentiate the specific scanning frequency for each analyte. The detection limits of EC, citrulline, urea and arginine are 0.8 ng L-1, 1.57 ng L-1, 0.54 ng L-1 and 1.56 ng L-1, respectively. The developed electrochemical sensor provides a sensitive and selective approach superior to the current reported label-free methodologies and offering a solution for ethyl carbamates in real time process control.

Enrichment-Free Rapid Detection of Phthalates in Chinese Liquor with Electrochemical Impedance Spectroscopy.

A non-invasive real-time detection technique for phthalates in Chinese liquor is proposed in this paper. This method is based on the measurement of Faradaic impedance in the presence of a redox probe, [Fe(CN)6]3-/4-, upon the absorption of phthalates to the graphene electrode surface. This absorption activity is according to the π-π stacking interactions between phthalates and the graphene working electrode which allows direct sampling and analyte preconcentration. The absorption of phthalates retards the interfacial electron-transfer kinetics and increases the charge-transfer resistance (Rct). Numerical values of Rct were extracted from a simulation of electrochemical impedance spectroscopy (EIS) spectra with the corresponding equivalent circuit. Cathodic polarization was employed prior to EIS measurements to effectively eliminate the metal ion interference. The results yielded a detection limit of 0.024 ng/L for diethyl phthalate (DEP) with a linear range from 2.22 ng to 1.11 µg. These results indicate a possibility of developing a household sensor for phthalate determination in Chinese liquor.

GUITAR-enhanced facile discrimination of aged Chinese Baijiu using electrochemical impedance spectroscopy.

The presented research demonstrated a method to evaluate aged Chinese Baijiu by measuring their electrochemical impedance spectrums (EIS) according to the distinctive colloidal impedance phenomena of verities' aged Baijiu. Graphite from the University of Idaho Thermolyzed Asphalt Reaction (GUITAR) electrode was employed for EIS data collection to achieve enhanced resolution. The obtained EIS Nyquist plots were simulated with the corresponding equivalent circuit to extract the numerical values of parameters which characterize the physicochemical properties of aged Baijiu. The curve fitting data were dimensionally reduced with principle components analysis (PCA). PCA score image originated from GUITAR electrode EIS measurement showed a more defined clustered profile in comparison to glassy carbon electrode. These results implicate GUITAR electrode based EIS is potentially available to develop a household device for aged Baijiu classification.

Characterization of a natural triple-tandem c-di-GMP riboswitch and application of the riboswitch-based dual-fluorescence reporter.

c-di-GMP riboswitches are structured RNAs located in the 5'-untranslated regions (5'-UTRs) of mRNAs that regulate expression of downstream genes in response to changing concentrations of the second messenger c-di-GMP. We discovered three complete c-di-GMP riboswitches (Bc3, Bc4 and Bc5 RNA) with similar structures, which are arranged in tandem to constitute a triple-tandem (Bc3-5 RNA) riboswitch in the 5'-UTR of the cspABCDE mRNA in Bacillus thuringiensis subsp. chinensis CT-43. Our results showed that this natural triple-tandem riboswitch controlled the expression of the reporter gene more stringently and digitally than the double-tandem or single riboswitch. A sandwich-like dual-fluorescence reporter was further constructed by fusing the Bc3-5 RNA gene between the two fluorescence protein genes amcyan and turborfp. This reporter strain was found to exhibit detectable fluorescence color changes under bright field in response to intracellular c-di-GMP level altered by induced expression of diguanylate cyclase (DGC) PleD. Using this system, two putative membrane-bound DGCs from B. thuringiensis and Xanthomonas oryzae were verified to be functional by replacing pleD with the corresponding DGC genes. This report represented the first native triple-tandem riboswitch that was applied to serve as a riboswitch-based dual-fluorescence reporter for the efficient and convenient verification of putative DGC activity in vivo.

Functional analysis of the sporulation-specific diadenylate cyclase CdaS in Bacillus thuringiensis.

Cyclic di-AMP (c-di-AMP) is a recently discovered bacterial secondary messenger molecule, which is associated with various physiological functions. In the genus Bacillus, the intracellular level and turnover of c-di-AMP are mainly regulated by three diadenylate cyclases (DACs), including DisA, CdaA and CdaS, and two c-di-AMP-specific phosphodiesterases (GdpP and PgpH). In this study, we demonstrated that CdaS protein from B. thuringiensis is a hexameric DAC protein that can convert ATP or ADP to c-di-AMP in vitro and the N-terminal YojJ domain is essential for the DAC activity. Based on the markerless gene knock-out method, we demonstrated that the transcription of cdaS was initiated by the sporulation-specific sigma factor σ(H) and the deletion of cdaS significantly delayed sporulation and parasporal crystal formation. These findings contrast with similar experiments conducted using B. subtilis, wherein transcription of its cdaS was initiated by the sigma factor σ(G). Deletion of all the three DAC genes from a single strain was unsuccessful, suggesting that c-di-AMP is an indispensable molecule in B. thuringiensis. Phylogenetic analysis indicated increased diversity of CdaS in the B. cereus and B. subtilis Bacillus subgroups. In summary, this study identifies important aspects in the regulation of c-di-AMP in the genus Bacillus.

Determination of 2-methylisoborneol and geosmin produced by Streptomyces sp. and Anabaena PCC7120.

A new sample preparation and enrichment technique, headspace liquid-phase microextraction (HS-LPME) linked to gas chromatography-mass spectrometry (GC-MS), was developed for the determination of the off-flavor odorants, 2-methylisoborneol and geosmin, produced by Streptomyces sp. and Anabaena PCC7120. Some of the factors that influence the extraction efficiency of HS-LPME, such as the type of extraction solvent, ionic strength of sample solution, and sample agitation rate, were studied and optimized by a single factor test. Other factors, including extraction temperature, extraction time, microdrop volume, and headspace volume were optimized by orthogonal array design. Extraction of 2-methylisoborneol and geosmin was conducted by exposing 2.5 microL of 1-hexanol for 9 min at 50 degrees C in the headspace of a 20 mL vial with a 10 mL of sample solution saturated by NaCl and stirred at 800 rpm. The developed protocol demonstrated good repeatability (relative standard deviations (RSDs) < 5%), wide linear ranges (10-5000 ng/L, r2 > 0.999), and low limits of detection (LODs) for 2-methylisoborneol and geosmin (0.05 ng/L for both analytes). Subsequently, the method was successfully applied to extract the analytes in bacterial cultures with high recoveries (from 94% to 98%). Compared with headspace solid-phase microextraction (HS-SPME), HS-LPME demonstrates better linearity, precision, and recovery. Importantly, the sensitivity is about 1 order of magnitude higher than that of most HS-SPME. The results showed that HS-LPME coupled with GC-MS is a simple, convenient, rapid, sensitive, and effective method for the qualitative and quantitative analysis of 2-methylisoborneol and geosmin.

Symbiotic abilities of Sinorhizobium fredii with modified expression of purL.

Previous reports showed that a transposon-induced PurL- mutant of Sinorhizobium fredii induced pseudonodules on Glycine max and the addition of 5-aminoimidazole-4-carboxamide-riboside or adenine to the plant could not restore the mutant to establish effective symbiosis. To gain a better understanding of the impact of the purL gene on symbiosis formation, we measured the effect of modified expression of this gene on the symbiotic abilities of S. fredii on soybean (G. max). A 1.98-kb in-frame deletion mutant in the purL gene of S. fredii was constructed. Transcriptional modification of the purL gene was conducted using several promoters such as those of lac, nifH, nifQ, and fixN. It was found that reduced expression of purL gene or suitable symbiotic expression of purL (such as with the promoter nifH or nifQ) can efficiently establish symbiosis of S. fredii on G. max without the exogenous supplementation of any adenine or purine precursor; at least a minimal level of expression of purL is essential for effective symbiosis with soybean.