Pyrolytic Behavior of Long-Chain Alkyl Quaternary Ammonium Bromide Inside Nanopores

The pyrolytic behavior of organic matter inside nanopores was studied by simultaneous thermogravimetric/differential scanning calorimetry analyzer coupled with Fourier transform infrared spectroscopy (STA/TG-FTIR). Nanoporous silica was prepared by a hydrothermal method using long-chain alkyl quaternary ammonium bromide (CnTAB, n = 12, 14) as a template. The pyrolytic behavior of CnTAB inside nanopores with different diameters was investigated and compared with that of CnTAB inside and outside nanopores. The results showed that the pyrolytic removal process consisted of the following features: 1) CnTAB underwent carbon chain decomposition and oxidation; 2) the DSC exothermal peak of CnTAB came mainly from its oxidative combustion, and the oxidative combustion temperature decreased with increasing pore size; 3) the CnTAB inside nanopores underwent crystallization–amorphous state phase transition, and CnTAB got trapped inside the calcined nanopores. In addition, the pyrolytic behavior of CnTAB inside the calcined nanopores was found to be similar to that of the uncalcined nanopores. This study aims to understand the storage and transformation processes of organic hydrocarbons under nanopore-confinement effect.

MspA Porin as a Local Nanopore Probe for Membrane-bound Proteins

Nanopore sensing is based on detection and analysis of nanopore transient conductance changes induced by analyte capture. We have recently shown that α-Synuclein (αSyn), an intrinsically disordered, membrane-active, neuronal protein implicated in Parkinson disease, can be reversibly captured by the VDAC nanopore. The capture process is a highly voltage dependent complexation of the two proteins where transmembrane potential drives the polyanionic C-terminal domain of αSyn into VDAC--exactly the mechanism by which generic nanopore-based interrogation of proteins and polynucleotides proceeds. The complex formation, and the motion of αSyn in the nanopore, thus may be expected to be only indirectly dependent on the pore identity. Here, we confirm this prediction by demonstrating that when VDAC is replaced with a different transmembrane pore, the engineered mycobacterial porin M2MspA, all the qualitative features of the αSyn/nanopore interaction are preserved. The rate of αSyn capture by M2MspA rises exponentially with the applied field, while the residence time displays a crossover behavior, indicating that at voltages >50 mV M2MspA-bound αSyn largely undergoes translocation to the other side of the membrane. The translocation is directly confirmed using the selectivity tag method, in which the polyanionic C-terminal and neutral N-terminal regions of αSyn alter the selectivity of the M2MspA channel differently, allowing direct discrimination of translocation vs retraction for single αSyn molecules. We thus prove that the physical model of the motion of disordered protein chains in the nanopore confinement and the selectivity tag technique are not limited to VDAC but are broadly applicable to nanopore-based protein detection, analysis, and separation technologies.

Profiling single-molecule reaction kinetics under nanopore confinement

The development of single-molecule reaction inside nanoconfinement is benefit to study the intrinsic molecular mechanism of a complex chemical reaction. However, the reaction kinetics model of single-molecule reaction inside confinement remains elusive. Herein we engineered the Aerolysin nanopore reactor to elaborate the single-molecule reaction kinetics inside nanoconfinement. By identifying bond forming and non-forming events directly, a four-state kinetics model is proposed for the first time. Our results demonstrated that the single-molecule reaction kinetics inside a nanopore depends on the voltage-dependent frequency of captured individual reactant and the fraction of effective collision inside nanopore confined space. This new insight will guide the design of nanoconfinement for resolving the single-molecule chemistry, and shed light on the mechanistic understanding of dynamic covalent chemistry in-side a nanopore

Nanopore Confinement Effect on the Phase Behavior of CO2/Hydrocarbons in Tight Oil Reservoirs considering Capillary Pressure, Fluid-Wall Interaction, and Molecule Adsorption

The pore sizes in tight reservoirs are nanopores, where the phase behavior deviates significantly from that of bulk fluids in conventional reservoirs. The phase behavior for fluids in tight reservoirs is essential for a better understanding of the mechanics of fluid flow. A novel methodology is proposed to investigate the phase behavior of carbon dioxide (CO2)/hydrocarbons systems considering nanopore confinement. The phase equilibrium calculation is modified by coupling the Peng-Robinson equation of state (PR-EOS) with capillary pressure, fluid-wall interaction, and molecule adsorption. The proposed model has been validated with CMG-Winprop and experimental results with bulk and confined fluids. Subsequently, one case study for the Bakken tight oil reservoir was performed, and the results show that the reduction in the nanopore size causes noticeable difference in the phase envelope and the bubble point pressure is depressed due to nanopore confinement, which is conductive to enhance oil recovery with a higher possibility of achieving miscibility in miscible gas injection. As the pore size decreases, the interfacial tension (IFT) decreases whereas the capillary pressure increases obviously. Finally, the recovery mechanisms for CO2 injection are investigated in terms of minimum miscibility pressure (MMP), solution gas-oil ratio, oil volume expansion, viscosity reduction, extraction of lighter hydrocarbons, and molecular diffusion. Results indicate that nanopore confinement effect contributes to decrease MMP, which suppresses to 650 psi (65.9% smaller) as the pore size decreases to 2 nm, resulting in the suppression of the resistance of fluid transport. With the nanopore confinement effect, the CO2 solution gas-oil ratio and the oil formation volume factor of the oil increase with the decrease of pore size. In turn, the oil viscosity reduces as the pore size decreases. It indicates that considering the nanopore confinement effect, the amount of gas dissolved into crude oil increases, which will lead to the increase of the oil volume expansion and the decrease of the viscosity of crude oil. Besides, considering nanopore confinement effect seems to have a slightly reduced effect on extraction of lighter hydrocarbons. On the contrary, it causes an increase in the CO2 diffusion coefficient for liquid phase. Generally, the nanopore confinement appears to have a positive effect on the recovery mechanisms for CO2 injection in tight oil reservoirs. The developed novel model could provide a better understanding of confinement effect on the phase behavior of nanoscale porous media in tight reservoirs. The findings of this study can also help for better understanding of a flow mechanism of tight oil reservoirs especially in the case of CO2 injection for enhancing oil recovery.