Surfactant aggregation in hydrophobic ionic liquid to formulate microemulsions for the enhancement of the solubility of enzymes and their catalytic performance

Room temperature ionic liquids (ILs) are molten salts at room temperature or below 100 °C. They are composed of organic cations and inorganic/organic anions. ILs have many advantages such as low volatility, high stability, good miscibility with organic compounds and unique constituents designability. Compared to traditional organic solvents, ILs are usually considered as “green” solvents. The use of ILs as media for enzyme catalysis was tried as early as 2000, and since then, many endeavours have been devoted to the studies. Previous studies indicate that an enzyme usually has catalytic activity in ILs if the enzyme is active in an organic solvent. Also it has been found that the [email protected] performance of enzymes in ILs is correlated with the hydrophilicity/hydrophobicity of ILs. In hydrophobic ILs, such as [Bmim][PF6] and [Bmim][NTf2], enzymes are not soluble, and usually their powders are suspended in ILs. The suspended enzymes exhibit catalytic activity and even good stability, but only small portions are available for catalysis due to their poor dispersion. By contrast, in hydrophilic ILs, enzymes are soluble, but their activity is poor due to the unfavourable interaction between enzymes and ILs. It follows that the major problem for the utilization of ILs as media for enzyme catalysis is how to reconcile the contradiction between the maintenance of the enzyme activity and the solubility of the enzyme in ILs. Reviewing the evolution of the medium engineering for enzyme catalysis, we get a good idea. For hydrophobic ILs (HILs), a good solution to the problem is to create a microenvironment suitable for the dispersion of an enzyme as well as the maintenance of the enzyme activity by dispersing water into HILs; i.e., the so-called microemulsification of HILs with surfactants. The microemulsification results in larger surface area than in the HIL/water two-phase system and makes the reactions of hydrophobic substrates with a hydrophilic enzyme go easily. Moreover, the formed water pool can restrict the change of the conformation of the enzyme. Studies have shown that most enzymes can maintain their catalytic activity and stability in HIL-based microemulsions. In this talk, we make a brief description of the recent progress made in my group in the enzyme catalysis in HIL- based microemulsion. To be relevant to the themes of the Conference, the talk is focused on the aggregation behaviour of different surfactants in HILs as well as the microstructural effect of the formed aggregates on solubilized enzymes. The aggregation of surfactants of different types will be summarized. To circumvent the poor solubility of most ionic surfactants such as NaAOT in HILs, a new strategy has been developed; i.e., the substitution of the inorganic counter ion by its organic counterpart. For example NaAOT, the replacement of the counter ion Na+ by [Bmim]+ not only increases the surface activity of AOT- in water, but also significantly improve its solubility in [Bmim]Tf2N. Also it is found the exchange of the cations helps to formulate a W/HIL microemulsion without any additives. In addition to the construction strategy, we will present detailed studies on the regulation of the microstructure and the consequent water solubilization capacity by salts and alcohols. The catalytic performance of enzymes hosted in HIL-based microemulsions has been characterized. It is found that the formation of the microdroplet of water in HIL facilitates the dispersion of enzymes such as laccase on a molecular level and also greatly reduces the negative effect of the ionic liquid on the enzyme. The catalytic activity of an enzyme hosted in the droplet depends upon the size of the droplets, the interfacial components and charge density. For a given enzyme, an optimal microenvironment could be created via the formulation optimization. All results indicate that HIL-based reverse micelles or microemulsions, which are homogeneous macroscopically but microscopically heterogeneous, are promising media for an enzyme catalyzed reaction

An optical method for carbon dioxide isotopes and mole fractions in small gas samples: Tracing microbial respiration from soil, litter, and lignin

Rationale Carbon dioxide isotope (δ13C value) measurements enable quantification of the sources of soil microbial respiration, thus informing ecosystem C dynamics. Tunable diode lasers (TDLs) can precisely measure CO2 isotopes at low cost and high throughput, but are seldom used for small samples (≤5 mL). We developed a TDL method for CO2 mole fraction ([CO2]) and δ13C analysis of soil microcosms. Methods Peaks in infrared absorbance following constant volume sample injection to a carrier were used to independently measure [12CO2] and [13CO2] for subsequent calculation of δ13C values. Using parallel soil incubations receiving differing C substrates, we partitioned respiration from three sources using mixing models: native soil organic matter (SOM), added litter, and synthetic lignin containing a 13C label at Cβ of the propyl side chain. Results Once-daily TDL calibration enabled accurate quantification of δ13C values and [CO2] compared with isotope ratio mass spectrometry (IRMS), with long-term external precision of 0.17 and 0.31‰ for 5 and 1 mL samples, respectively, and linear response between 400 and 5000 μmol mol−1CO2. Production of CO2 from native soil C, added litter, and lignin Cβ varied over four orders of magnitude. Multiple-pool first-order decay models fitted to data (R2 \u3e 0.98) indicated substantially slower turnover for lignin Cβ (17 years) than for the dominant pool of litter (1.3 years) and primed soil C (3.9 years). Conclusions Our TDL method provides a flexible, precise, and high-throughput (60 samples h−1) alternative to IRMS for small samples. This enables the use of C isotopes in increasingly sophisticated experiments to test biogeochemical controversies, such as the fate of lignins in soil

Electrical Detection of Ferroelectric-like Metals through Nonlinear Hall Effect

Ferroelectric-like metals are a relatively rare class of materials that have ferroelectric-like distortion and metallic conductivity. LiOsO$_3$ is the first demonstrated and the most investigated ferroelectric-like metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using the symmetry analysis and first-principles calculations, we demonstrate that the ferroelectric-like transition of LiOsO$_3$ can be probed by a kind of electrical transport method based on nonlinear Hall effect. The Berry curvature dipole exists in the ferroelectric-like phase, and it can lead to a measurable nonlinear Hall conductance with a conventional experimental setup. However, the symmetry of the paraelectric-like phase LiOsO$_3$ vanishes the Berry curvature dipole. The Berry curvature dipole shows a strong dependence on the polar displacement, which might be helpful for the detection of polar order. The nonlinear Hall effect provides an effective method for the detection of phase transition in the study of the ferroelectric-like metals and promotes them to be applied in the ferroelectric-like electronic devices

Electrical detection of ferroelectriclike metals through the nonlinear Hall effect

Ferroelectriclike metals are a relatively rare class of materials that have ferroelectriclike distortion and metallic conductivity. LiOsO3 is the first demonstrated and the most investigated ferroelectriclike metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using symmetry analysis and first-principles calculations, we demonstrate that the ferroelectriclike transition of LiOsO3 can be probed by a kind of electrical transport method based on nonlinear Hall effect. The Berry curvature dipole exists in the ferroelectriclike phase and it can lead to a measurable nonlinear Hall conductance with a conventional experimental setup. However, the symmetry of the paraelectriclike phase LiOsO3 vanishes the Berry curvature dipole. The Berry curvature dipole shows a strong dependence on the polar displacement, which might be helpful for the detection of polar order. The nonlinear Hall effect provides an effective method for the detection of phase transition in the study of the ferroelectriclike metals and promotes them to be applied in ferroelectriclike electronic devices

A Safety Control Method of Car-Following Trajectory Planning Based on LSTM

This paper focuses on the potential safety hazards of collision in car-following behaviour generated by deep learning models. Based on an intelligent LSTM model, combined with a Gipps model of safe collision avoidance, a new, Gipps-LSTM model is constructed, which can not only learn the intelligent behaviour of people but also ensure the safety of vehicles. The idea of the Gipps-LSTM model combination is as follows: the concept of a potential collision point (PCP) is introduced, and the LSTM model or Gipps model is controlled and started through a risk judgment algorithm. Dataset 1 and dataset 2 are used to train and simulate the LSTM model and Gipps-LSTM model. The simulation results show that the Gipps-LSTM can solve the problem of partial trajectory collision in the LSTM model simulation. Moreover, the risk level of all trajectories is lower than that of the LSTM model. The safety and stability of the model are verified by multi-vehicle loop simulation and multi-vehicle linear simulation. Compared with the LSTM model, the safety of the Gipps-LSTM model is improved by 42.02%, and the convergence time is reduced by 25 seconds

Impaired 26S Proteasome Assembly Precedes Neuronal Loss in Mutant UBQLN2 Rats.

Proteasomal dysfunction is known to be associated with amyotrophic lateral sclerosis and frontotemporal degeneration (ALS/FTD). Our previous reports have shown that a mutant form of ubiquilin-2 (UBQLN2) linked to ALS/FTD leads to neurodegeneration accompanied by accumulations of the proteasome subunit Rpt1 in transgenic rats, but the precise pathogenic mechanisms of how this mutation impairs the proteasome remains to be elucidated. Here, we reveal that this UBQLN2 mutation in rats disrupted the proteasome integrity prior to neurodegeneration, that it dissociated the 26S proteasome in vitro, and that its depletion did not affect 26S proteasome assembly. During both disease progression and in an age-dependent manner, we found that proteasome subunits were translocated to the nucleus, including both of the 20S core particles (PSMA1 and PSMB7) and the 19S regulatory particles (Rpt1 and Rpn1), suggesting that defective proteasome function may result from the proteasome-subunit mislocalization. Taken together, the present data demonstrate that impaired proteasome assembly is an early event in the pathogenesis of UBQLN2-associated neurodegeneration in mutant UBQLN2 rats