Browse
Submit Data
Databases
API
Help

Dataset Information

26 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Orientation of Methylguanidinium Ions at the Water-Air Interface.

ABSTRACT: We use heterodyne-detected vibrational sum-frequency generation (HD-VSFG) to determine the orientation of the molecular plane of methylguanidinium ions at the surface of aqueous solutions. We measure the VSFG response of the symmetric and antisymmetric methyl stretch vibrations of the methylguanidinium ion with different polarization combinations. We find that for at least 50% of the methylguanidinium ions the molecular plane is at an angle >20° with respect to the surface plane. Hence, for only a minor fraction of the ions does the molecular plane have an orientation (near-)parallel to the surface plane, in contrast to the predictions of recent molecular dynamics simulation studies.

SUBMITTER: Strazdaite S

PROVIDER: S-EPMC5677249 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Orientation of Methylguanidinium Ions at the Water-Air Interface.

Strazdaite S S Versluis J J Ottosson N N Bakker Huib J HJ

The journal of physical chemistry. C, Nanomaterials and interfaces 20170914 42

We use heterodyne-detected vibrational sum-frequency generation (HD-VSFG) to determine the orientation of the molecular plane of methylguanidinium ions at the surface of aqueous solutions. We measure the VSFG response of the symmetric and antisymmetric methyl stretch vibrations of the methylguanidinium ion with different polarization combinations. We find that for at least 50% of the methylguanidinium ions the molecular plane is at an angle >20° with respect to the surface plane. Hence, for only ...[more]

PMID: 29129985

Similar Datasets

Ions Speciation at the Water-Air Interface.

Project description:In typical aqueous systems, including naturally occurring sweet and salt water and tap water, multiple ion species are co-solvated. At the water-air interface, these ions are known to affect the chemical reactivity, aerosol formation, climate, and water odor. Yet, the composition of ions at the water interface has remained enigmatic. Here, using surface-specific heterodyne-detected sum-frequency generation spectroscopy, we quantify the relative surface activity of two co-solvated ions in solution. We find that more hydrophobic ions are speciated to the interface due to the hydrophilic ions. Quantitative analysis shows that the interfacial hydrophobic ion population increases with decreasing interfacial hydrophilic ion population at the interface. Simulations show that the solvation energy difference between the ions and the intrinsic surface propensity of ions determine the extent of an ion's speciation by other ions. This mechanism provides a unified view of the speciation of monatomic and polyatomic ions at electrolyte solution interfaces.

| S-EPMC10197129 | biostudies-literature

Water Orientation at the Calcite-Water Interface.

Project description:Mineral-water interfaces play an important role in many natural as well as technological fields. Fundamental properties of these interfaces are governed by the presence of the interfacial water and its specific structure at the surface. Calcite is particularly interesting as a dominant rock-forming mineral in the earth's crust. Here, we combine atomic force microscopy, sum-frequency generation spectroscopy, and molecular dynamics simulations to determine the position and orientation of the water molecules in the hydration layers of the calcite surface with high resolution. While atomic force microscopy provides detailed information about the position of the water molecules at the interface, sum-frequency generation spectroscopy can deduce the orientation of the water molecules. Comparison of the calcite-water interface to the interfaces of magnesite-water, magnesite-ethanol, and calcite-ethanol reveals a comprehensive picture with opposite water orientations in the first and second layer of the interface, which is corroborated by the molecular dynamics simulations.

| S-EPMC8365774 | biostudies-literature

Molecular Orientation of Carboxylate Anions at the Water-Air Interface Studied with Heterodyne-Detected Vibrational Sum-Frequency Generation.

Project description:The carboxylate anion group plays an important role in many (bio)chemical systems and polymeric materials. In this work, we study the orientation of carboxylate anions with various aliphatic and aromatic substituents at the water-air interface by probing the carboxylate stretch vibrations with heterodyne-detected vibrational sum-frequency generation spectroscopy in different polarization configurations. We find that carboxylate groups with small aliphatic substituents show a large tilt angle with respect to the surface normal and that this angle decreases with increasing size of the substituent. We further use the information about the orientation of the carboxylate group to determine the hyperpolarizability components of this group.

| S-EPMC10226120 | biostudies-literature

Water orientation and hydrogen-bond structure at the fluorite/water interface.

Project description:Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the "free OH" signature in the VSFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of CaF2/water interfaces and state-of-the-art ab initio molecular dynamics simulations which include electronic structure effects.

| S-EPMC4828669 | biostudies-literature

SPOT-RASTR-A cryo-EM specimen preparation technique that overcomes problems with preferred orientation and the air/water interface.

Project description:In cryogenic electron microscopy (cryo-EM), specimen preparation remains a bottleneck despite recent advancements. Classical plunge freezing methods often result in issues like aggregation and preferred orientations at the air/water interface. Many alternative methods have been proposed, but there remains a lack a universal solution, and multiple techniques are often required for challenging samples. Here, we demonstrate the use of lipid nanotubes with nickel NTA headgroups as a platform for cryo-EM sample preparation. His-tagged specimens of interest are added to the tubules, and they can be frozen by conventional plunge freezing. We show that the nanotubes protect samples from the air/water interface and promote a wider range of orientations. The reconstruction of average subtracted tubular regions (RASTR) method allows for the removal of the nanotubule signal from the cryo-EM images resulting in isolated images of specimens of interest. Testing with β-galactosidase validates the method's ability to capture particles at lower concentrations, overcome preferred orientations, and achieve near-atomic resolution reconstructions. Since the nanotubules can be identified and targeted automatically at low magnification, the method enables fully automated data collection. Furthermore, the particles on the tubes can be automatically identified and centered using 2D classification enabling particle picking without requiring prior information. Altogether, our approach that we call specimen preparation on a tube RASTR holds promise for overcoming air-water interface and preferred orientation challenges and offers the potential for fully automated cryo-EM data collection and structure determination.

| S-EPMC11303004 | biostudies-literature

Bronsted basicity of the air-water interface.

Project description:Differences in the extent of protonation of functional groups lying on either side of water-hydrophobe interfaces are deemed essential to enzymatic catalysis, molecular recognition, bioenergetic transduction, and atmospheric aerosol-gas exchanges. The sign and range of such differences, however, remain conjectural. Herein we report experiments showing that gaseous carboxylic acids RCOOH(g) begin to deprotonate on the surface of water significantly more acidic than that supporting the dissociation of dissolved acids RCOOH(aq). Thermodynamic analysis indicates that > 6 H(2)O molecules must participate in the deprotonation of RCOOH(g) on water, but quantum mechanical calculations on a model air-water interface predict that such event is hindered by a significant kinetic barrier unless OH(-) ions are present therein. Thus, by detecting RCOO(-) we demonstrate the presence of OH(-) on the aerial side of on pH > 2 water exposed to RCOOH(g). Furthermore, because in similar experiments the base (Me)(3)N(g) is protonated only on pH < 4 water, we infer that the outer surface of water is Brønsted neutral at pH ?3 (rather than at pH 7 as bulk water), a value that matches the isoelectric point of bubbles and oil droplets in independent electrophoretic experiments. The OH(-) densities sensed by RCOOH(g) on the aerial surface of water, however, are considerably smaller than those at the (>1 nm) deeper shear planes probed in electrophoresis, thereby implying the existence of OH(-) gradients in the interfacial region. This fact could account for the weak OH(-) signals detected by surface-specific spectroscopies.

| S-EPMC3503180 | biostudies-literature

SPOT-RASTR - a cryo-EM specimen preparation technique that overcomes problems with preferred orientation and the air/water interface

Project description: Not available

| EMPIAR-12179 | biostudies-other

Alpha-synuclein in alpha-helical conformation at air-water interface: implication of conformation and orientation changes during its accumulation/aggregation.

Project description:Alpha-synuclein, a natively unstructured protein important in the neuropathology of Parkinson's disease, was found to form a Langmuir monolayer in an alpha-helical conformation with its helical axis parallel to the air-water interface. This study sheds light on the role of vesicles in neuronal cells in the accumulation/aggregation of alpha-synuclein.

| S-EPMC3186058 | biostudies-literature

Self-propelled ion gel at air-water interface.

Project description:We report on a self-propelled gel using ionic liquid as a new type of self-propellant that generates a powerful and durable motion at an air-water interface. The gel is composed of 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)). A long rectangular ion gel piece placed on the interface shows rapid rotation motion with maximum frequency close to 10?Hz, corresponding to the velocity over 300 mms-1 at an outmost end of the piece. The rotation continues for ca. 102?s, followed by a reciprocating motion (<~103?s) and a nonlinear motion in long-time observations (>~103?s). The behaviours can be explained by the model considering elution of EMIM-TFSI to the air-water interface, rapid dissolution into water, and slow diffusion in an inhomogeneous polymer gel network. Because the self-propellants are promptly removed from the interface by dissolution, durable self-propelled motions are observed also at limited interface areas close in size to the gel pieces. A variety of motions are induced in such systems where the degree of freedom in motion is limited. As the ion gel possesses formability and processability, it is also advantageous for practical applications. We demonstrate that the gel does work as an engine.

| S-EPMC5571170 | biostudies-literature

Ion pair particles at the air-water interface.

Project description:Although the role of methanesulfonic acid (HMSA) in particle formation in the gas phase has been extensively studied, the details of the HMSA-induced ion pair particle formation at the air-water interface are yet to be examined. In this work, we have performed Born-Oppenheimer molecular dynamics simulations and density functional theory calculations to investigate the ion pair particle formation from HMSA and (R1)(R2)NH (for NH3, R1 = R2 = H; for CH3NH2, R1 = H and R2 = CH3; and for CH3NH2, R1 = R2 = CH3) at the air-water interface. The results show that, at the air-water interface, HMSA deprotonates within a few picoseconds and results in the formation of methanesulfonate ion (MSA-)??H3O+ ion pair. However, this ion pair decomposes immediately, explaining why HMSA and water alone are not sufficient for forming stable particles in atmosphere. Interestingly, the particle formation from the gas-phase hydrogen-bonded complexes of HMSA with (R1)(R2)NH on the water droplet is observed with a few femtoseconds, suggesting a mechanism for the gas to particle conversion in aqueous environments. The reaction involves a direct proton transfer between HMSA and (R1)(R2)NH, and the resulting MSA-??(R1)(R2)NH2+ complex is bound by one to four interfacial water molecules. The mechanistic insights gained from this study may serve as useful leads for understanding about the ion pair particle formation from other precursors in forested and polluted urban environments.

| S-EPMC5703292 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data