Effects of Charged Surfactants on Interfacial Water Structure and Macroscopic Properties of the Air-Water Interface

Surfactants are used to control the macroscopic properties of the air-water interface. However, the link between the surfactant molecular structure and the macroscopic properties remains unclear. Using sum-frequency generation spectroscopy and molecular dynamics simulations, two ionic surfactants (dodecyl trimethylammonium bromide, DTAB, and sodium dodecyl sulphate, SDS) with the same carbon chain lengths and charge magnitude (but different signs) of head groups interact and reorient interfacial water molecules differently. DTAB forms a thicker but sparser interfacial layer than SDS. It is due to the deep penetration into the adsorption zone of Br⁻ counterions compared to smaller Na⁺ ones, and also due to the flip-flop orientation of water molecules. SDS alters two distinctive interfacial water layers into a layer where H⁺ points to the air, forming strong hydrogen bonding with the sulphate headgroup. In contrast, only weaker dipole-dipole interactions with the DTAB headgroup are formed as they reorient water molecules with H⁺ point down to the aqueous phase. Hence, with more molecules adsorbed at the interface, SDS builds up a higher interfacial pressure than DTAB, producing lower surface tension and higher foam stability at a similar bulk concentration. Our findings offer improved knowledge for understanding various processes in the industry and nature.     

Increasing Complexity in Adamantyl Thioethers Characterized by Rotational Spectroscopy

We report on the synthesis and characterization using high-resolution rotational spectroscopy of three bulky thioethers that feature an adamantyl group connected to a sulfur atom. Detailed experimental and theoretical structures are provided and compared with the 1,1′-diadamantyl ether. In addition, we expand on previous findings concerning microsolvation of adamantyl derivatives by investigating the cluster formation between these thioethers and a water molecule. The investigation of such clusters provides valuable insights into the sulfur-centered hydrogen bonding in thioethers with increasing size and steric repulsion.     

亚微米电喷雾喷针在非变性质谱分析中的研究进展

非变性质谱技术已成为表征蛋白质结构的重要工具之一。与传统的电喷雾喷针(Electrospray emitter,ESI emitter)相比,亚微米电喷雾喷针具有改变离子电荷态分布和降低盐离子加合等多种特性,可在生理环境下直接解析蛋白质的结构。该文综述了亚微米电喷雾喷针的特性及其在非变性质谱分析中的应用,并对其未来的发展趋势进行了展望。     

ZSM-5分子筛酸位分布及其甲醇制烯烃催化性能的定向管理与调控

ZSM-5分子筛在甲醇制烯烃(MTO)过程中的催化性能和反应机理与其孔道中酸位点分布位置紧密相关. 本文证明在水热合成过程中加入适量的钠离子(Na⁺)可以增加ZSM-5分子筛交叉腔酸位点比例; 从而促进高级甲基苯的生成并加速芳烃循环, 有利于乙烯生成. 相反, 在合成过程中不添加钠离子, 所制备的ZSM-5分子筛直孔道和正弦孔道酸位点比例明显提高, 有利于促进烯烃循环并提高丙烯和C₃₊烯烃选择性.     

H-ZSM-5分子筛不同孔道处的酸位在甲醇制烯烃反应中的催化作用

甲醇制烯烃(MTO)作为一条由煤、天然气和生物质等含碳资源制备重要有机化学品的非石油路线,近年来备受关注.作为MTO催化剂,分子筛的骨架拓扑结构和酸性质对于其催化活性、反应路径和产物分布等具有重要的影响.H-ZSM-5分子筛是一种典型的MTO反应催化剂,酸位可以分布在MFI拓扑结构的直孔道、正弦孔道和交叉位点处.虽然目前已普遍认可MTO反应遵循芳烃/烯烃双循环烃池机理,分子筛的催化性能与其骨架中酸中心的位置相关,但对于H-ZSM-5分子筛不同孔道位置处的酸中心在甲醇制烯烃反应中的催化作用仍缺乏足够认识.本文采用密度泛函理论计算和分子动力学模拟方法,对H-ZSM-5分子筛不同孔道处(包括正弦孔道、直孔道和交叉腔)酸位中心上的MTO反应网络(包括芳烃循环、烯烃循环和芳构化)及甲醇原料和烯烃/芳烃产物的扩散行为进行了比较研究.结果表明,与正弦孔道和直孔道相比,芳烃循环和芳构化反应在交叉腔的酸中心上因具有较低的能垒而更易进行.相比之下,在正弦孔道和直孔道中,多甲基苯的生成受到显著限制,而烯烃循环却可以在三种酸中心(正弦孔道、直孔道和交叉腔)上以相近的能垒和相似的几率进行.芳烃循环生成乙烯和丙烯的几率相近,而烯烃循坏产物以丙烯和较高的烯烃产物为主.落位于H-ZSM-5交叉腔的酸中心能促进芳烃中间体如多甲基苯的生成,推动芳烃循环,提高乙烯选择性,而正弦孔道和直孔道中的酸中心则能增强烯烃循环,生成较多的丙烯和较高的烯烃产物.因此,H-ZSM-5分子筛对MTO的催化性能(包括活性和产物选择性等),可以通过有目的地调节酸中心在分子筛骨架中的位置分布(即铝落位)而得到有效调变和提升.本文阐明了H-ZSM-5分子筛酸中心在MTO反应中的催化作用与其骨架中的落位之间的有机联系,为高效甲醇转化分子筛催化剂的设计和性能提升提供了参考思路.     

SARS-CoV-2 virion physicochemical characteristics pertinent to abiotic substrate attachment

The structure, size, and main physicochemical characteristics of the SARS-CoV-2 virion with the spike transmembrane protein corona were discussed. Using these data, diffusion coefficients of the virion in aqueous media and in air were calculated. The structure and dimensions of the spike protein derived from molecular dynamic modeling and thorough cryo-electron microscopy measurements were also analyzed. The charge distribution over the molecule was calculated and shown to be largely heterogeneous. Although the stalk part is negatively charged, the top part of the spike molecule, especially the receptor binding domain, remains positively charged for a broad range of pH. It is underlined that such a charge distribution promotes the spike corona stability and enhances the virion attachment to receptors and surfaces, mostly negatively charged. The review is completed by the analysis of experimental data pertinent to the spike protein adsorption at abiotic surfaces comprising nanoparticle carrier particles. It is argued that these theoretical and experimental data can be used for developing quantitative models of virus attachment to surfaces, facilitating adequate analysis of future experimental results.     

How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct

The rotational spectrum of the weakly bound complex pentafluoropyridine⋅⋅⋅formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the ¹³C and ¹⁵N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the π-cloud of pyridine creating a π-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pair⋅⋅⋅π-hole interaction, reinforced by a weak C−H⋅⋅⋅N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridine⋅⋅⋅formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pair⋅⋅⋅π-hole and π⋅⋅⋅π stacking interactions.     

Synthesis of activated carbon foams with high specific surface area using polyurethane elastomer templates for effective removal of methylene blue

Carbon foams have gained significant attention due to their tuneable properties that enable a wide range of applications including catalysis, energy storage and wastewater treatment. Novel synthesis pathways enable novel applications via yielding complex, hierarchical material structure. In this work, activated carbon foams (ACFs) were produced from waste polyurethane elastomer templates using different synthesis pathways, including a novel one-step method. Uniquely, the produced foams exhibited complex structure and contained carbon microspheres. The ACFs were synthesized by impregnating the elastomers in an acidified sucrose solution followed by direct activation using CO₂ at 1000 ℃. Different pyrolysis and activation conditions were investigated. The ACFs were characterized by a high specific surface area (S_BET) of 2172 m²/g and an enhanced pore volume of 1.08 cm³/g. Computer tomography and morphological studies revealed an inhomogeneous porous structure and the presence of numerous carbon spheres of varying sizes embedded in the porous network of the three-dimensional carbon foam. X-ray diffraction (XRD) and Raman spectroscopy indicated that the obtained carbon foam was amorphous and of turbostratic structure. Moreover, the activation process enhanced the surface of the carbon foam, making it more hydrophilic via altering pore size distribution and introducing oxygen functional groups. In equilibrium, the adsorption of methylene blue on ACF followed the Langmuir isotherm model with a maximum adsorption capacity of 592 mg/g. Based on these results, the produced ACFs have potential applications as adsorbents, catalyst support and electrode material in energy storage systems.     

Plasmonic Pollen Grain Nanostructures: A Three-Dimensional Surface-Enhanced Raman Scattering (SERS)-Active Substrate

A new route has been developed to design plasmonic pollen grain-like nanostructures (PGNSs) as surface-enhanced Raman scattering (SERS)-active substrate. The nanostructures consisting of silver (Ag) and gold (Au) nanoparticles along with zinc oxide (ZnO) nanoclusters as spacers were found highly SERS-active. The morphology of PGNSs and those obtained in the intermediate stage along with each elemental evolution has been investigated by a high-resolution field emission scanning electron microscopy. The optical band gaps and crystal structure have been identified by UV-vis absorption and X-ray powder diffraction (XRD) measurements, respectively. For PGNSs specimen, three distinct absorption bands related to constituent elements Ag, Au, and ZnO were observed, whereas XRD peaks confirmed the existence of Ag, Au, and ZnO within the composition of PGNSs. SERS-activity of PGNSs was confirmed using Rhodamine 6G (R6G) as Raman-active dyes. Air-cooled solid-state laser kits of 532 nm were used as excitation sources in SERS measurements. SERS enhancement factor was estimated for PGNSs specimen and was found as high as 3.5×10⁶. Finite difference time domain analysis was carried out to correlate the electromagnetic (EM) near-field distributions with the experiment results achieved under this investigation. EM near-field distributions at different planes were extracted for s-, p- and 45° of incident polarizations. EM near-field distributions for such nanostructures as well as current density distributions under different circumstances were demonstrated and plausible scenarios were elucidated given SERS enhancements. Such generic fabrication route as well as correlated investigation is not only indispensable to realize the potential of SERS applications but also unveil the underneath plasmonic characteristics of complex SERS-active nanostructures.     

A New Approach for Controlling Mesoporosity in Activated Carbon by the Consecutive Process of Air Oxidation,Thermal Destruction of Surface Functional Groups,and Carbon Activation (the OTA Method)

A new and simple method, based entirely on a physical approach, was proposed to produce activated carbon from longan fruit seed with controlled mesoporosity. This method, referred to as the OTA, consisted of three consecutive steps of (1) air oxidation of initial microporous activated carbon of about 30% char burn-off to introduce oxygen surface functional groups, (2) the thermal destruction of the functional groups by heating the oxidized carbon in a nitrogen atmosphere at a high temperature to increase the surface reactivity due to increased surface defects by bond disruption, and (3) the final reactivation of the resulting carbon in carbon dioxide. The formation of mesopores was achieved through the enlargement of the original micropores after heat treatment via the CO₂ gasification, and at the same time new micropores were also produced, resulting in a larger increase in the percentage of mesopore volume and the total specific surface area, in comparison with the production of activated carbon by the conventional two-step activation method using the same activation time and temperature. For the activation temperatures of 850 and 900 °C and the activation time of up to 240 min, it was found that the porous properties of activated carbon increased with the increase in activation time and temperature for both preparation methods. A maximum volume of mesopores of 0.474 cm³/g, which accounts for 44.1% of the total pore volume, and a maximum BET surface area of 1773 m²/g was achieved using three cycles of the OTA method at the activation temperature of 850 °C and 60 min activation time for each preparation cycle. The two-step activation method yielded activated carbon with a maximum mesopore volume of 0.270 cm³/g (33.0% of total pore volume) and surface area of 1499 m²/g when the activation temperature of 900 °C and a comparable activation time of 240 min were employed. Production of activated carbon by the OTA method is superior to the two-step activation method for better and more precise control of mesopore development.