Mass Spectrometry Study of Multiply Negatively Charged, Gas-Phase NaAOT Micelles: How Does Charge State Affect Micellar Structure and Encapsulation?

We report the formation and characterization of multiply negatively charged sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) aggregates in the gas phase, by electrospray ionization of methanol/water solution of NaAOT followed by detection using a guided-ion-beam tandem mass spectrometer. Singly and doubly charged aggregates dominate the mass spectra with the compositions of [Na_n-zAOT_n]^z– (n?=?1–18 and z?=?1–2). Solvation by water was detected only for small aggregates [Na_n-1AOT_nH₂O]^– of n?=?3–9. Incorporation of glycine and tryptophan into [Na_n-zAOT_n]^z– aggregates was achieved, aimed at identifying effects of guest molecule hydrophobicity on micellar solubilization. Only one glycine molecule could be incorporated into each [Na_n-zAOT_n]^z– of n?≥?7, and at most two glycine molecules could be hosted in that of n?≥?13. In contrast to glycine, up to four tryptophan molecules could be accommodated within single aggregates of n?≥?6. However, deprotonation of tryptophan significantly decrease its affinity towards aggregates. Collision-induced dissociation (CID) was carried out for mass-selected aggregate ions, including measurements of product ion mass spectra for both empty and amino acid-containing aggregates. CID results provide a probe for aggregate structures, surfactant-solute interactions, and incorporation sites of amino acids. The present data was compared with mass spectrometry results of positively charged [Na_n+zAOT_n]^z+ aggregates. Contrary to their positive analogues, which form reverse micelles, negatively charged aggregates may adopt a direct micelle-like structure with AOT polar heads exposed and amino acids being adsorbed near the micellar outer surface.      

Chemical Bonding and Interpretation of Time-Dependent Electronic Processes with Maximum Probability DomainsSCI北大核心CSCD

Tools have been designed obtain information about chemical bonds from quantum mechanical calculations. They work well for solutions of the stationary Schrödinger equation, but it is not clear whether Lewis electron pairs they aim to reproduce survive in time-dependent processes, in spite of the underlying Pauli principle being obeyed in this regime. A simple model of two same-spin non-interacting fermions in a one-dimensional box with an opaque wall, is used to study this problem, because it allows presenting the detailed structure of the wave function. It is shown that ⅰ) oscillations persisting after the Hamiltonian stopped changing produce for certain time intervals states where Lewis electron pairs are spatially separated, and ⅱ) methods (like density analysis, or the electron localization function) that are widely used for describing bonding in the stationary case, have limitations in such situations. An exception is provided by the maximum probability domain (the spatial domain that maximizes the probability to find a given number of particles in it). It is conceptually simple, and satisfactorily describes the phenomenon.     

Dramatic Enhancement of Binding Affinities Between Foldamer-Based Receptors and Anions by Intra-Receptor π-Stacking

As a synthetic model for intra-protein interactions that reinforce binding affinities between proteins and ligands, the energetic interplay of binding and folding was investigated using foldamer-based receptors capable of adopting helical structures. The receptors were designed to have identical hydrogen-bonding sites for anion binding but different aryl appendages that simply provide additional π-stacking within the helical backbones without direct interactions with the bound anions. In particular, the presence of electron-deficient aryl appendages led to dramatic enhancements in the association constant between the receptor and chloride or nitrate ions, by up to three orders of magnitude. Extended stacking within the receptor contributes to the stabilization of the entire folding structure of complexes, thereby enhancing binding affinities.     

Modifications and Electrochemical Properties of Graphite Fluoride北大核心CSCD

The commercial fluorinated graphite (CFx) was used as the raw material, which was modified by the reduction of hydrazine hydrate (N2H4·H2O). The effects of hydrazine hydrate contents on the electrochemical properties of fluorinated graphite were systematically studied. The crystal phases and electrochemical properties of the modified fluorinated graphite were analyzed by XRD, SEM, EDS, XPS, EIS techniques and constant current discharge measurement. The results showed that the voltage hysteresis response of Lithium-fluorocarbon battery prepared by the modified fluorinated graphite was obviously improved, while the amount of hydrazine hydrate had an important influence on the electrochemical performance of the materials. The H-CFx-2 material had the best overall performance (CFx:C2H6O: N2H4· H2O was 1:2:1). At 0.1C, the specific capacity of the material reached 794.5 mAh·g-1, the platform voltage was 2.53 V, and the low-wave voltage of the voltage hysteresis was 2.37 V. © Journal of Electrochemistry 2018.     

Effect of the Charge and the Nature of Both Cations and Anions on the Solubility of Zwitterionic Amino Acids,Measurements and Modeling

The effect of the charge and the nature of both the cations and the anions of some electrolytic salts: sodium fluoride (NaF), potassium fluoride (KF), sodium bromide (NaBr), potassium bromide (KBr), sodium iodide (NaI), potassium iodide (KI), sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), calcium chloride (CaCl₂), and barium chloride (BaCl₂), on the solubility of zwitterionic amino acids (glycine, DL-alanine, DL-valine, and DL-serine) in aqueous solutions at 298.15 K are studied and discussed. A salting-in effect is observed for all amino acids under investigation with all electrolytes used in the present study, except for DL-alanine and DL-valine in aqueous solutions containing sodium fluoride where a salting-out effect was observed. The orders of the effect of the nature and the charge of both the anions and the cations are: F^- < Cl^- < Br^- < I^- < NO₃^- < SO₄^2-\mathrm{F}^{-}<{}\mathrm{Cl}^{-}<{}\mathrm{Br}^{-}<{}\mathrm{I}^{-}<\mathrm{NO}_{3}^{-}<{}\mathrm{SO}_{4}^{2-} with both sodium and potassium cations; Na⁺<K⁺<Ca²⁺<Ba²⁺ with chloride anion.     

Preparation of biomass N-doped carbon dots and detection of tioproninEI北大核心CSCD

Nitrogen-doped carbon dots (N-CDs) were prepared by one-step hydrothermal synthesis with pomegranate seeds as the carbon source and urea as the nitrogen source. Observed by transmission electron microscopy (TEM), average particle size of N-CDs was 20 nm. Observed by atomic force microscopy (AFM), the thickness of N-CDs was 0. 6-1. 4 nm. Fourier transform infra-red (FT-IR) confirmed the presence of water-soluble functional groups such as amino groups on the surface of N-CDs. With the prepared N-CDs as the target fluorophore, Hg2 + can efficiently bind to the surface of N-CDs to form a complex, and achieve static quenching. The addition of tiopronin can bind the Hg2 + in the complex to make the Hg2 + detach from the surface of N-CDs and realize fluorescence recovery. The nano fluorescence switch constructed in this work is more accurate and sensitive than the traditional detection method. The optimum conditions were determined by optimizing the pH value, reaction time, the dosage of N-CDs and Hg2 +. The relative deviation (RSD) was 4. 7%, and the detection limit was 0. 2 μmol/L. The method was used to determine the content of tiopronin in human serum samples with the recoveries of 97. 2%-101. 3%. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Geometries, Electronic Structures, and Electron Detachment Energies of Small Boron Sulfide Anions： A Density Functional Theory Investigation

A density functional theory investigation on the geometries, electronic structures, and electron detachment energies of BS, BS2, B（BS）2 and B（BS）3 has been performed in this work. The linear ground-state structures of BS （C∞v, ^1∑^＋） and BS2^- （O∞h, ^1∑g^＋） prove to be similar to the previously reported BO and BO2 with systematically lower electron detachment energies. Small boron sulfide clusters are found to favor the formation of -B=S groups which function basically as a-radicals and dominate the ground-state structures of the systems. The perfect linear B（BS）2^-（D∞h, ^3∑g） and beautiful equilateral triangle B（BS）3^- （D3h,^2A1”） turn out to be analogous to the well-known C2v BH2 and O3h BH3, respectively. The electron affinities of BS, BS2, B（BS）2 and B（BS）3 are predicted to be 2.3, 3.69, 3.00 and 3.45 eV, respectively. The electron detachment energies calculated for BS^-, BS2^-, B（BS）2^-, and B（BS）3^- may facilitate future photoelectron spectroscopy measurements to characterize the geometrical and electronic structures of these anions.     

Why Are Proteins Charged? Networks of Charge–Charge Interactions in Proteins Measured by Charge Ladders and Capillary Electrophoresis

Almost all proteins contain charged amino acids. While the function in catalysis or binding of individual charges in the active site can often be identified, it is less clear how to assign function to charges beyond this region. Are they necessary for solubility? For reasons other than solubility? Can manipulating these charges change the properties of proteins? A combination of capillary electrophoresis (CE) and protein charge ladders makes it possible to study the roles of charged residues on the surface of proteins outside the active site. This method involves chemical modification of those residues to generate a large number of derivatives of the protein that differ in charge. CE separates those derivatives into groups with the same number of modified charged groups. By studying the influence of charge on the properties of proteins using charge ladders, it is possible to estimate the net charge and hydrodynamic radius and to infer the role of charged residues in ligand binding and protein folding.     

Preparation and Characterization of Self-Supporting Flexible Nitrogen-Doped Carbon Fabric Electrode北大核心CSCD

With the wide applications of intelligent wearable devices in various fields, developing a new generation of flexible energy storage devices has become a major challenge for the current technology. As a wide application of wearable flexible substrate, cotton fabric has the advantages over low price, non-toxic and environmental friendly, but the poor conductivity becomes a major problem limiting its development. As a nitrogen-containing conducting polymer, polypyrrole is traditionally used as electrode materials, but poor mechanical performance and cycle stability severely limit its application in electrode materials. In this article, a self-supporting flexible nitrogen-doped carbon fabric electrode was prepared by in situ polymerization-high temperature calcination method using cotton as a substrate and polypyrrole as a nitrogen source. The high temperature carbonization transformed the non-conductive cotton fabric into a good conductive carbon fabric while retaining its original three-dimensional structure and the nitrogen was mixed into carbon materials at the same time. The structure was characterized by Fourier infrared spectroscopy, specific surface area test, scanning electron microscopy and X-ray photoelectron spectroscopy. The results demonstrated that the cotton fiber was uniformly coated by polypyrrole that was subsequently carbonized into nanocarbon, the specific surface area of the obtained nitrogen-doped carbon (N-CT) electrode was 495.0 m2·g-1and the nitrogen content was 2.26%. The electrochemical performance test showed that the N-CT electrode had a capacitance of 256.2 F·g-1at a current density of 0.5 A·g-1. The stability test revealed that the capacitance retention was 98.3% and the coulomb effciency was about 98.8% after 5000 charge-discharge cycles. Meanwhile, the N-CT electrode exhibited good flexibility and mechanical properties. © Journal of Electrochemistry 2018.     

Progress in Synthesis，Detection and Clinical Application of Posaconazole北大核心CSCD

Posaconazole,as the second generation of triazole antifungal drugs,has a wide antifungal spectrum and strong antibacterial activity. It is widely used in clinical practice. However,it has been eight years since its publication before it is approved in China. In order to better understand posaconazole,a first-line drug with great clinical demand, this paper summarizes the pharmacokinetics, pharmacological properties,clinical application and synthetic route of posaconazole in the literature at home and abroad. It is hoped that it can fill the gap in the domestic API market,break the current situation that the API is completely dependent on import,and provide a useful reference for the industrial R & D. © 2022, Science Press (China). All rights reserved.