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A silane coupling agent having a zwitterionic end group was covalently bound to a semi-cylindrical fused silica prism for sum-frequency generation (SFG) analyses and to a flat glass for estimating biological affinity. It was found that total intensity of the O H stretching region (3000–3600 cm −1 ) of the SFG spectrum derived from water in contact with a zwitterionic SAM-modified surface was smaller than that of SFG spectra derived from water in contact with a positively or negatively charged SAM-modified surface and a bare silica prism. These results indicated that water molecules in the vicinity of the zwitterionic SAM-modified surface are not strongly oriented in comparison with those of lopsidedly charged SAMs and bare silica. Moreover, the zwitterionic SAM surface suppressed non-specific adsorption of bovine serum albumin in contrast to the significant adsorption to lopsidedly charged SAMs and the bare cover glass. On the other hand, fibroblasts gradually adhered to the SAM surfaces and extended regardless of the electrical charge of the SAM, though the number of cells that adhered to the zwitterionic SAM was the smallest. The results strongly suggested that the charge neutralization of a solid material surface is very important for anti-biofouling properties. [ABSTRACT FROM AUTHOR]

Surfaces of both a cover glass and the flat plane of a semi-cylindrical quartz prism were modified with a mixture of positively and negatively charged silane coupling reagents (3-aminopropyltriethoxysilane (APTES) and 3-(trihydroxysilyl)propylmethylphosphonate (THPMP), respectively). The glass surface modified with a self-assembled monolayer (SAM) prepared at a mixing ratio of APTES:THPMP = 4:6 was electrically almost neutral and was resistant to non-specific adsorption of proteins, whereas fibroblasts gradually adhered to an amphoteric (mixed) SAM surface probably due to its stiffness, though the number of adhered cells was relatively small. Sum frequency generation (SFG) spectra indicated that total intensity of the O H stretching region (3000–3600 cm −1 ) for the amphoteric SAM-modified quartz immersed in liquid water was smaller than those for the positively and negatively charged SAM-modified quartz prisms and a bare quartz prism in contact with liquid water. These results suggested that water molecules at the interface of water and an amphoteric SAM-modified quartz prism are not strongly oriented in comparison with those at the interface of a lopsidedly charged SAM-modified quartz prism and bare quartz. The importance of charge neutralization for the anti-biofouling properties of solid materials was strongly suggested. [ABSTRACT FROM AUTHOR]

Highlights: [•] Zwitterionic copolymer film prepared by cast method on a quartz prism. [•] Sum frequency generation analysis of water in the vicinity of the film. [•] Weak orientation of water molecules in the vicinity of zwitterionic copolymer film. [•] Strong orientation of water molecules in the vicinity of lopsidedly charged copolymer films and bare prism. [•] Importance of charge balance to afford bio-inert surface. [Copyright &y& Elsevier]

Abstract: A zwitterionic poly(carboxymethylbetaine) (PCMB) brush was prepared on a fused quartz prism by the surface-initiated atom transfer radical polymerization (SI-ATRP) of CMB monomer. The conformation of PCMB brush and the state of water at the surface of the brush were examined using sum frequency generation (SFG) technique. The Cing band of the brush, indicating the gauche defect of the brush, was affected by the contact medium such as dry nitrogen, water vapor-saturated nitrogen and liquid water. The water molecules at the PCMB–water interfaces were not largely oriented in comparison with the interfacial water of both bare and the ATRP-initiator-modified quartz prisms. The similar tendency was previously observed for water in the vicinity of water-soluble zwitterionic polymers and polymer thin films using Raman and attenuated total reflection (ATR) infrared spectroscopies, respectively. The electrical neutralization between neighboring positive and negative charges might diminish the electrostatic adsorption of water molecules to the vicinity of zwitterionic polymer brushes. [Copyright &y& Elsevier]

Abstract: A polyampholyte brush was prepared on the surface of a quartz prism by surface-initiated reversible addition-fragmentation chain-transfer polymerization of methacrylic acid (MA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) at a monomer ratio of 1:1. The sum frequency generation method indicated that water molecules at the amphoteric polymer brush–water interfaces were not greatly oriented in comparison with those at the surfaces of bare quartz prisms, and negatively charged PolyMA and positively charged PolyDMAEMA brushes. The small perturbation effect of an amphoteric polymer brush on the structure of vicinal water was in accordance with the tendency of aqueous solution and thin films of amphoteric polymers observed by using Raman and infrared spectroscopies, respectively. [Copyright &y& Elsevier]

• Heat-treated Pt/Pd/C showed better PEFC performance than Pt/C. • Pd islands on the Pt shell induced by heat treatment are thought to play a role in catalytic activation. • The amount of Pt/Pd and PVP on catalyst can be controlled simultaneously by heat treatment. Among the various fuel cell electrocatalysts studied for the cathodic oxygen reduction reaction and anodic fuel oxidation reaction, platinum-based materials have attracted much attention over the past decade because of their high activity for both reactions. However, Pt-based catalysts suffer from several problems, such as their high cost, low abundance, and low long-term stability. Bimetallic Pt-based nanostructures with a core – shell structure have been considered as candidate cathode catalysts for polymer electrolyte fuel cells. In this study, a Pt/Pd/C catalyst was successfully synthesized by the hydrogen-sacrificial protection method to improve the performance of a membrane electrode assembly. Furthermore, on the basis of electrochemical spectroscopic findings, it was shown that control of the surface structure is an effective strategy to improve the cell performance of the Pt/Pd/C catalyst. [ABSTRACT FROM AUTHOR]

The effect of para-substituents on the NC bond of aryl isocyanide molecules adsorbed on Au, Ag, Pt, and Pd surfaces was examined by vibrational sum frequency generation (VSFG) spectroscopy. The frequency of NC stretching vibration, υNC, depended on the electronic property of the substituents. When the substituents were more electron-withdrawing and more electron-donating, υNC shifted to lower and higher frequencies, respectively. However, υNC shifted to lower frequency again when the substituents were too electron-donating. The strong dependence of υNC on metal substrates was also observed, reflecting the difference in metal d-band energies, which leads to the difference in the contributions of σ-donation and π back-donation of the NC-metal coupling., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Anode-free lithium metal batteries (AFLMBs) have attracted great attention owing to their higher energy density compared to conventional lithium metal batteries. Unfortunately, AFLMBs still suffer from poor Coulombic efficiency (CE) due to severe dendrite growth and the unstable solid-electrolyte interface (SEI) at the anode. Therefore, we explored the effect of concentration and LiNO 3 additive on the SEI layer and on Li plating/stripping efficiency using a low-concentration tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte in an AFLMB anode half-cell configuration. It was found that the formation of protective Li 2 O-based SEI layers when blocking the oxidative subsequent SEI formation (called "OSS") above 2.2 V vs. Li/Li + improved Li plating/stripping stability, while the LiNO 3 additive suppressed the oxidation of Li 2 O into Li 2 O 2 and sustained the existence of Li 2 O without blocking OSS, therefore improving CE performance. Although increasing the concentration (from 0.4 M to 2.0 M) did not have a major effect, the 2.0 M electrolyte with LiNO 3 additive shifted the dominant SEI species from Li 2 O to LiF, further enhancing CE performance.

In sharp contrast to conventional solid/hydrogel platforms, water-immiscible liquids, such as perfluorocarbons and silicones, allow the adhesion of mammalian cells via protein nanolayers (PNLs) formed at the interface. However, fluorocarbons and silicones, which are typically used for liquid cell culture, possess only narrow ranges of physicochemical parameters and have not allowed for a wide variety of cell culturing environments. In this paper, it is proposed that water-immiscible ionic liquids (ILs) are a new family of liquid substrates with tunable physicochemical properties and high solvation capabilities. Tetraalkylphosphonium-based ILs are identified as non-cytotoxic ILs, whereon human mesenchymal stem cells are successfully cultured. By reducing the cation charge distribution, or ionicity, via alkyl chain elongation, the interface allows cell spreading with matured focal contacts. High-speed atomic force microscopy observations of the PNL formation process suggest that the cation charge distribution significantly altered the protein adsorption dynamics, which are associated with the degree of protein denaturation and the PNL mechanics. Moreover, by exploiting dissolution capability of ILs, an ion-gel cell scaffold is fabricated. This enables to further identify the significant contribution of bulk subphase mechanics to cellular mechanosensing in liquid-based culture scaffolds., (© 2024 Wiley‐VCH GmbH.)

Lithium-air batteries (LABs) are considered one of the most promising energy storage devices because of their large theoretical energy density. However, low cyclability caused by battery degradation prevents its practical use. Thus, to realize practical LABs, it is essential to improve cyclability significantly by understanding how the degradation processes proceed. Here, we used online mass spectrometry for real-time monitoring of gaseous products generated during charging of lithium - oxygen batteries (LOBs), which was operated with pure oxygen not air, with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) tetraethylene glycol dimethyl ether (TEGDME) electrolyte solution. Linear voltage sweep (LVS) and voltage step modes were employed for charge instead of constant current charge so that the energetics of the product formation during the charge process can be understood more quantitatively. The presence of two distinctly different types of Li 2 O 2 , one being decomposed in a wide range of relatively low cell voltages (2.8-4.16 V) (l-Li 2 O 2 ) and the other being decomposed at higher cell voltages than ca. 4.16 V (h-Li 2 O 2 ), was confirmed by both LVS and step experiments. H 2 O generation started when the O 2 generation rate reached a first maximum and CO 2 generation took place accompanied by the decomposition of h-Li 2 O 2 . Based on the above results and the effects of discharge time and the use of isotope oxygen during discharge on product distribution during charge, the generation mechanism of O 2 , H 2 O, and CO 2 during charging is discussed in relation to the reactions during discharge.

Electrocatalytic activities for the oxygen reduction reaction (ORR) of Au electrodes modified by as prepared and size selected (0.45-1.0, 0.22-0.45, and 0.1-0.22 µm) h-BN nanosheet (BNNS), which is an insulator, were examined in O 2 saturated 0.5M H 2 SO 4 solution. The overpotential was reduced by all the BNNS modifications, and the smaller the size, the smaller the overpotential for ORR, i.e., the larger the ORR activity, in this size range. The overpotential was reduced by as much as ∼330 mV compared to a bare Au electrode by modifying the Au surface by the BNNS of the smallest size range (0.1-0.22 µm). The overpotential at this electrode was only 80 mV more than that at the Pt electrode. Both the rotation disk electrode experiments with Koutecky-Levich analysis and rotating ring disk electrode measurements showed that more than 80% of oxygen is reduced to water via the four-electron process at this electrode. These results strongly suggest and theoretical density functional theory calculations support that the ORR active sites are located at the edges of BNNS islands adsorbed on Au(111). The decrease in size of BNNS islands results in an effective increase in the number of the catalytically active sites and, hence, in the increase in the catalytic activity of the BNNS/Au(111) system for ORR.

Degradation products of lithium oxygen batteries with a tetraethylene glycol dimethyl ether (TEGDME) electrolyte solution during discharge/charge cycles were monitored by an online cold trap pre-concentrator-gas chromatography/mass spectroscopy system in real time. A total of 37 peaks were detected and 27 of them were assigned to specific molecules. Degradation compounds were generated and decomposed in very complex manners during discharge/charge cycles. Most molecules were generated during charge as a result of the degradation of TEGDME by active oxygen species and/or electrochemical oxidation. These molecules generated during charge were decomposed during discharge by active oxygen species., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Hypothesis: Interfacial water plays an essential role in natural phenomena and scientific applications despite causing many economic losses. Therefore, its real monitoring is no question mandatory; however, suitable techniques are quite rare and/or with limitations., Experiments: Moisture Sensor (MS) was used to detect the galvanic response current arising from the stacked interfacial water molecules between two dissimilar electrodes under controlled relative humidity (RH). Simultaneously, the frequency response was detected using QCM sensor as a quantitative tool. Bare and Hydrophilic (HP) sensor surfaces were used to examine the surface wettability. Moreover, sum frequency generation (SFG) was used to investigate the qualitative formation and the nature of stacked interfacial water molecules on bare and HP modified surfaces of quartz prism., Findings: Results revealed that, response current and frequency change were increased as the number of stacked water molecules increased. Correlating response current and frequency gave a clear quantitative estimation of stacked water molecules on the sensors' surfaces. Interfacial water molecules possessed strong H-bonding nature at the bare prism surface whereas, strong and weak H-bonding were existing at the HP/prism surface. Such findings provide feasible evaluation for the galvanic current source due to stacked interfacial water molecules at different levels of RH., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The selectivity rules of sum frequency generation spectroscopy were exploited to determine propyl chain order during the time-dependent oscillatory adsorption of propyltrimethoxysilane (PTMS) and Langmuir-type growth of propyldimethylmethoxysilane (PDMMS). During the early stages of film growth, molecular packing density determines the extent of propyl chain defects within both films with high surface coverage resulting in a film with fewer defects. Following this, an ordered monolayer-like film stabilizes on the Al 2 O 3 substrate for both silanes. Although this result is intuitive for the Langmuir-type growth of PDMMS, the stabilization of molecular ordering despite the continuing oscillation in PTMS surface coverage indicates the presence of a stable monolayer, while it is the oligomerized PTMS dendrimers which continue to desorb and readsorb to the substrate. We also reveal for the first time, the formation of a physisorbed bilayer during the self-assembly process of PTMS. The presence of this ordered, physisorbed bilayer on top of the covalently bound PTMS film plays a key role in the process of the molecular self-assembly mechanism and is proposed to enable further condensation of the covalently bound film.

For the development of lithium-air battery (LAB), which is one of the most promising next generation batteries, it is essential to understand the structure and properties of Li 2 O 2 , which is the discharged product at the positive electrode of a LAB, as well as the mechanism of Li 2 O 2 growth because its deposition limits the discharge capacity and is the origin of the high charging overpotential of LAB. Characterization of the structure and properties of the Li 2 O 2 formed in LABs is, however, difficult because it is usually in the form of poorly ordered small particles. In this study, we successfully grew well-aligned very long (∼80 μm) crystalline Li 2 O 2 nanowires (NWs: average diameter of 22 nm) electrochemically at a gold electrode covered with single-layer graphene (SLG/Au). Preferential growth of the NWs along c -axis was confirmed by X-ray diffraction, transmission electron microscopy with electron diffraction, and Raman scattering. Raman imaging indicated that the sites of NW growth were the grain boundaries of single-layer graphene. The long, crystalline Li 2 O 2 NWs provided the opportunity to investigate not only their structure and properties but also their growth mechanism during discharge. Raman measurements in the O-O stretching frequency region of the SLG/Au electrode at various depths of the discharge combined with exchange of oxygen in the solution from 18 O 2 to 16 O 2 during the discharge revealed that the growth took place at the bottom of the NWs, i.e., the Li 2 O 2 /electrode interface, not the top of the NWs, i.e., the solution/Li 2 O 2 interface. This growth mechanism can explain why such long NWs can be grown despite the insulating nature of Li 2 O 2 .

As one of the major impurities in the organic electrolyte, HF can react with the alkali components in the solid electrolyte interphase (SEI), such as lithium alkoxide and lithium carbonate, to form more LiF-rich SEI. Here, the effects of HF on the lithiation behavior of the single crystal Si(111) anode were studied using scanning electron microscopy, soft X-ray emission spectroscopy, and windowless energy-dispersive X-ray spectroscopy. When the Li-Si alloy is formed in 1.0 M LiPF 6 in the propylene carbonate solvent, it has a layered structure that contained the first layer of crystalline Li 15 Si 4 (c-Li 15 Si 4 ) alloy pyramids, the second layer of amorphous Li 13 Si 4 (a-Li 13 Si 4 ) alloy, and a third layer of Li-diffused Li x Si alloy. When the more concentrated HF is in the electrolyte solution, less amount of the c-Li 15 Si 4 alloy is formed in the first layer. It suggests that the Si lithiation can form only amorphous Li x Si alloy relative to the components in the electrolytes. The study also explains why only amorphous Li x Si alloy formation was observed in some previous studies., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI 3 , because upon exposure to ambient atmosphere the desired black orthorhombic phase CsSnI 3 would promptly lose single crystallinity and degrade to the inactive yellow phase, followed by irreversible oxidation into metallic Cs 2 SnI 6 . By alloying CsSnI 3 with CsPbI 3 , we herein report the synthesis of alloyed perovskite quantum dot (QD), CsSn 1-x Pb x I 3 , which not only can be phase-stable for months in purified colloidal solution but also remains intact even directly exposed to ambient air, far superior to both of its parent CsSnI 3 and CsPbI 3 QDs. Ultrafast transient absorption spectroscopy studies reveal that the photoexcited electrons in the alloyed QDs can be injected into TiO 2 nanocrystals at a fast rate of 1.12 × 10 11 s -1 , which enables a high photocurrent generation in solar cells.

In vivo, cells are immersed in an extracellular solution that contains a variety of bioactive substances including ions and water. Classical electrophysiological analyses of epithelial cells in the stomach and small intestine have revealed that within a distance of several hundred micrometers above their apical plasma membrane, lies an extracellular layer that shows ion concentration gradients undetectable in the bulk phase. This "unstirred layer", which contains stagnant solutes, may also exist between the bulk extracellular solution and membranes of other cells in an organism and may show different properties. On the other hand, an earlier study using a bacterial planar membrane indicated that H + released from a transporter migrates in the horizontal direction along the membrane surface much faster than it diffuses vertically toward the extracellular space. This result implies that between the membrane surface and unstirred layer, there is a "nanointerface" that has unique ionic dynamics. Advanced technologies have revealed that the nanointerface on artificial membranes possibly harbors a highly ordered assembly of water molecules. In general, hydrogen bonds are involved in formation of the ordered water structure and can mediate rapid transfer of H + between neighboring molecules. This description may match the phenomenon on the bacterial membrane. A recent study has suggested that water molecules in the nanointerface regulate the gating of K + channels. Here, the region comprising the unstirred layer and nanointerface is defined as the interphase between the plasma membrane and bulk extracellular solution (iMES). This article briefly describes the physicochemical properties of ions and water in the iMES and their physiological significance. We also describe the methodologies that are currently used or will be applicable to the interphase research.

Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface. We developed a series of ionic head groups-appended self-assembled monolayers with C2, C6, C8, and C12 space-filling alkyl chains, which capture a dendritic guest via the formation of multiple salt bridges. The guest release upon protonolysis is progressively suppressed when its distance from the background hydrophobe changes from 1.2 (C2) to 0.2 (C12) nanometers, with an increase in salt bridge strength of ~3.9 kilocalories per mole., (Copyright © 2015, American Association for the Advancement of Science.)

The potential dependence of the interfacial water structure at Pt and Au thin film electrodes was investigated by sum frequency generation (SFG) spectroscopy in internal reflection mode. In the case of the Pt electrode, two broad peaks were observed in the OH stretching region at ca. 3200 cm(-1) and ca. 3400 cm(-1), which are known to be due to the symmetric OH stretching (upsilon1) of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching (upsilon3) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively. In the case of the Au electrode, however, a 3400 cm(-1) band was dominant in the SFG spectrum, suggesting that the interaction between water molecules and Au and Pt are different, i.e., water molecules are more disordered at the Au surface. The potential dependence of interfacial water during the methanol oxidation reaction on a Pt electrode was also investigated. SFG intensity strongly depended on electrode potential. Several possibilities are suggested for the potential dependence of the SFG intensity.

Carboxylic acid-terminated monolayers on crystalline silicon surfaces can be readily modified with biological macromolecules for the fabrication of semiconductor-based biosensing devices. They were prepared by acid-catalyzed hydrolysis of alkoxycarbonyl (ester)-terminated monolayers and studied by vibrational sum frequency generation (SFG) spectroscopy. The C-H vibration region of the SFG spectra consists of strong methyl bands with significant contributions from methylene stretching modes, indicating that these monolayers are generally ordered but with considerable gauche defects in the alkyl chains in comparison with n-alkyl monolayers. After hydrolysis, the methylene stretching modes prevail, with "residues" of the methyl bands, indicating incomplete hydrolysis and disruption of the monolayer structure. This work demonstrates that SFG is capable of providing quantitative information on structure-reactivity correlations in organic monolayers.