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Hydrogen bonding interactions are essential in the structural stabilization and physicochemical properties of complex molecular systems, and carboxylic acid functional groups are common participants in these motifs. Consequently, the neutral formic acid (FA) dimer has been extensively investigated in the past, as it represents a useful model system to investigate proton donor–acceptor interactions. The analogous deprotonated dimers, in which two carboxylate groups are bound by a single proton, have also served as informative model systems. In these complexes, the position of the shared proton is mainly determined by the proton affinity of the carboxylate units. However, very little is known about the nature of the hydrogen bonding interactions in systems containing more than two carboxylate units. Here we report a study on the deprotonated (anionic) FA trimer. IR spectra are recorded in the 400–2000 cm−1 spectral range by means of vibrational action spectroscopy of FA trimer ions embedded in helium nanodroplets. Characterization of the gas-phase conformer and assignment of the vibrational features is achieved by comparing the experimental results with electronic structure calculations. To assist in the assignments, the 2H and 18O FA trimer anion isotopologues are also measured under the same experimental conditions. Comparison between the experimental and computed spectra, especially the observed shifts in spectral line positions upon isotopic substitution of the exchangeable protons, suggests that the prevalent conformer, under the experimental conditions, exhibits a planar structure that resembles the crystalline structure of formic acid.

Fatty acids are an abundant class of lipids that are characterised by wide structural variation including isomeric diversity arising from the position and configuration of functional groups. Traditional approaches to fatty acid characterisation have combined chromatography and mass spectrometry for a description of the composition of individual fatty acids while infrared (IR) spectroscopy has provided insights into the functional groups and bond configurations at the bulk level. Here we exploit universal 3-pyridylcarbinol ester derivatization of fatty acids to acquire IR spectra of individual lipids as mass-selected gas-phase ions. Intramolecular interactions between the protonated pyridine moiety and carbon–carbon double bonds present highly sensitive probes for regiochemistry and configuration through promotion of strong and predictable shifts in IR resonances. Gas-phase IR spectra obtained from unsaturated fatty acids are shown to discriminate between isomers and enable the first unambiguous structural assignment of 6Z-octadecenoic acid in human-derived cell lines. Compatibility of 3-pyridylcarbinol ester derivatization with conventional chromatography-mass spectrometry and now gas-phase IR spectroscopy paves the way for comprehensive structure elucidation of fatty acids that is sensitive to regio- and stereochemical variations and with the potential to uncover new pathways in lipid metabolism.

Ferrier reactions follow a mechanistic pathway whereby Lewis acid activation of a cyclic enol ether facilitates departure of an allylic leaving group to form a glycosyl Ferrier cation. Attack on the Ferrier cation provides a new acetal linkage concurrent with the transposition of the alkene moiety. The idiosyncratic outcomes of Ferrier reactions of seven-membered ring carbohydrate-based oxepines prompted an investigation of its corresponding septanosyl Ferrier cation. Experiments that characterized the ion, including gas-phase cryogenic IR spectroscopy matched with density functional theory-calculated spectra of candidate cation structures, as well as product analysis from solution-phase Ferrier reactions, are reported here. Results from both approaches revealed an inclination of the seven-membered ring cation to contract to five-membered ring structures. Gas-phase IR spectra matched best to calculated spectra of structures in which five-membered dioxolenium formation opened the oxepine ring. In the solution phase, an attack on the ion by water led to an acyclic enal that cyclized to a C-methylene-aldehydo arabinofuranoside species. Attack by allyl trimethylsilane, on the other hand, was diastereoselective and yielded a C-allyl septanoside.

Fucose is a signaling carbohydrate that is attached at the end of glycan processing. It is involved in a range of processes, such as the selectin-dependent leukocyte adhesion or pathogen-receptor interactions. Mass-spectrometric techniques, which are commonly used to determine the structure of glycans, frequently show fucose-containing chimeric fragments that obfuscate the analysis. The rearrangement leading to these fragments – often referred to as fucose migration – has been known for more than 25 years, but the chemical identity of the rearrangement product remains unclear. In this work, we combine ion-mobility spectrometry, radical-directed dissociation mass spectrometry, cryogenic-ion IR spectroscopy, and density-functional theory calculations to deduce the product of the rearrangement in the model trisaccharides Lewis x and blood group H2. The structural search yields the fucose moiety attached to the galactose with an α(1 → 6) glycosidic bond as the most likely product.

Photoelektronen-Zirkulardichroismus (im folgenden PECD, nach der englischen Bezeichnung) zeigt sich als eine Vorwärts-Rückwärts-Asymmetrie in der Photoemission nicht-razemischer Proben, ausgelöst durch zirkular polarisiertes Licht. Gegenüber anderen chiroptischen Methoden hat die PECD-Spektroskopie potentielle analytische Vorteile bei der Differenzierung chiraler Substanzen, da sie sehr sensitiv auf das chirale Potential von Molekülen ist. Anionen können für die PECD-Spektroskopie entsprechend ihrer Masse selektiert werden und ihr Einsatz eröffnet Wege zu einfachen experimentellen Aufbauten, die auf handlichen (table-top) Lasern basieren. Die Nachweise für den PECD von Anionen sind noch rar und das genaue Verständnis der Triebkräfte, welche die PECD-Elektronendynamik im Photodetachment bestimmen, sind unklar. Hier zeigen wir den PECD-Effekt im Photodetachment von massenselektierten, deprotonierten 1-Indanol-Anionen. Der PECD wird über einen großen Bereich von Photonenenergien mit einem Velocity-Map-Imaging(VMI)-Photoelektronenspektrometer energieaufgelöst analysiert. Ein PECD von bis zu 11 % wird nachgewiesen, was vergleichbar mit gemessenen Werten für neutrale Moleküle ist.

Photoelectron Circular Dichroism (PECD) is a forward-backward asymmetry in the photoemission from a non-racemic sample induced by circularly polarized light. PECD spectroscopy has potential analytical advantages for chiral discrimination over other chiroptical methods due to its increased sensitivity to the chiral potential of the molecule. The use of anions for PECD spectroscopy allows for mass-selectivity and provides a path to simple experimental schemes that employ table-top light sources. Evidence of PECD for anions is limited, and insight into the forces that govern PECD electron dynamics in photodetachment is absent. Here, we demonstrate a PECD effect in the photodetachment of mass-selected deprotonated 1-indanol anions. By utilizing velocity map imaging photoelectron spectroscopy with a tunable light source, we determine the energy-resolved PECD over a wide range of photon energies. The observed PECD reaches up to 11 %, similar to what has been measured for neutral species.

We present absolute frequency measurements of the 1P1←1S0 (229-nm) and 3P1←1S0 (326-nm) transitions for all naturally occurring isotopes of cadmium. The isotope shifts and hyperfine intervals of the fermionic isotopes are determined with an accuracy of 3.3 MHz. We find that quantum interference in the laser-induced fluorescence spectra of the 1P1←1S0 transition causes a variation of up to 29(5) MHz in determining the hyperfine splitting when not accounted for with an appropriate model. Using a King-plot analysis, we extract the field- and mass-shift parameters and determine nuclear charge radius differences for the fermions. The lifetime of the 1P1 state is determined to be 1.60(5) ns by measuring the natural linewidth of the 1P1←1S0 transition. These results resolve significant discrepancies among previous measurements., Physical Review Research, 5 (1), ISSN:2643-1564

Glycosaminoglycans (GAGs) are a family of complex carbohydrates vital to all mammalian organisms and involved in numerous biological processes. Chondroitin and dermatan sulfate, an important class of GAGs, are linear macromolecules consisting of disaccharide building blocks of N-acetylgalactosamine and two different uronic acids. The varying degree and the site of sulfation render their characterization challenging. Here, we combine mass spectrometry with cryogenic infrared spectroscopy in the wavenumber range from 1000 to 1800 cm-1. Fingerprint spectra were recorded for a comprehensive set of disaccharides bearing all known motifs of sulfation. In addition, state-of-the-art quantum chemical calculations were performed to aid the understanding of the differences in the experimental fingerprint spectra. The results show that the degree and position of charged sulfate groups define the size of the conformational landscape in the gas phase. The detailed understanding of cryogenic infrared spectroscopy for acidic and often highly sulfated glycans may pave the way to utilize the technique in fragment-based sequencing approaches.

Graphical abstract The position and configuration of carbon-carbon double bonds in unsaturated fatty acids is crucial for their biological functions and influences health and disease. However, double bond isomers are not routinely distinguished by classical mass spectrometry workflows. Instead, they require sophisticated analytical approaches usually based on chemical derivatization and/or instrument modification. In this work, a novel strategy to investigate fatty acid double bond isomers (18:1) without prior chemical treatment or modification of the ion source was implemented by non-covalent adduct formation in the gas phase. Fatty acid adducts with sodium, pyridinium, trimethylammonium, dimethylammonium, and ammonium cations were characterized by a combination of cryogenic gas-phase infrared spectroscopy, ion mobility-mass spectrometry, and computational modeling. The results reveal subtle differences between double bond isomers and confirm three-dimensional geometries constrained by non-covalent ion-molecule interactions. Overall, this study on fatty acid adducts in the gas phase explores new avenues for the distinction of lipid double bond isomers and paves the way for further investigations of coordinating cations to increase resolution. Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03334-3.

Although gold has become a well-known nonconventional hydrogen bond acceptor, interactions with nonconventional hydrogen bond donors have been largely overlooked. In order to provide a better understanding of these interactions, two conventional hydrogen bonding molecules (3-hydroxytetrahydrofuran and alaninol) and two nonconventional hydrogen bonding molecules (fenchone and menthone) were selected to form gas-phase complexes with Au

We present chemical kinetics measurements of the luminol oxydation chemiluminescence reaction at the interface between two aqueous solutions, using liquid jet technology. Free-flowing iquid microjets are a relatively recent development that has found its way into a growing number of applications in spectroscopy and dynamics. A variant thereof, called flat-jet, is obtained when two cylindrical jets of a liquid are crossed, leading to a chain of planar leaf-shaped structures of the flowing liquid. We here show that in the first leaf of this chain the fluids do not exhibit turbulent mixing, providing a clean interface between the liquids from the impinging jets. We also show, using the example of the luminol chemiluminescence reaction, how this setup can be used to obtain kinetics information from friction-less flow and by circumventing the requirement for rapid mixing but by intentionally suppressing all turbulent mixing and instead relying on diffusion.

The absolute-scale electronic energetics of liquid water and aqueous solutions, both in the bulk and at associated interfaces, are the central determiners of water-based chemistry. However, such information is generally experimentally inaccessible. Here we demonstrate that a refined implementation of the liquid microjet photoelectron spectroscopy (PES) technique can be adopted to address this. Implementing concepts from condensed matter physics, we establish novel all-liquid-phase vacuum and equilibrated solution–metal-electrode Fermi level referencing procedures. This enables the precise and accurate determination of previously elusive water solvent and solute vertical ionization energies, VIEs. Notably, this includes quantification of solute-induced perturbations of water's electronic energetics and VIE definition on an absolute and universal chemical potential scale. Defining and applying these procedures over a broad range of ionization energies, we accurately and respectively determine the VIE and oxidative stability of liquid water as 11.33 ± 0.03 eV and 6.60 ± 0.08 eV with respect to its liquid-vacuum-interface potential and Fermi level. Combining our referencing schemes, we accurately determine the work function of liquid water as 4.73 ± 0.09 eV. Further, applying our novel approach to a pair of exemplary aqueous solutions, we extract absolute VIEs of aqueous iodide anions, reaffirm the robustness of liquid water's electronic structure to high bulk salt concentrations (2 M sodium iodide), and quantify reference-level dependent reductions of water's VIE and a 0.48 ± 0.13 eV contraction of the solution's work function upon partial hydration of a known surfactant (25 mM tetrabutylammonium iodide). Our combined experimental accomplishments mark a major advance in our ability to quantify electronic–structure interactions and chemical reactivity in liquid water, which now explicitly extends to the measurement of absolute-scale bulk and interfacial solution energetics, including those of relevance to aqueous electrochemical processes., A generalised liquid-phase photoelectron spectroscopy approach is reported, allowing accurate, absolute energy scale ionisation energies of liquid water and aqueous solutions, as well as liquid water's work function to be reported.

1‐Deoxysphingolipide sind eine erst kürzlich beschriebene Klasse von Sphingolipiden, die in Zusammenhang mit verschiedenen Krankheiten wie diabetischer und erblicher Neuropathie gebracht werden. Die Identifizierung und Charakterisierung von 1‐Deoxysphingolipiden und deren Metaboliten ist in diesem Kontext sehr wichtig. Eine exakte Strukturbestimmung erfordert jedoch die Kombination von verschiedenen anspruchsvollen analytischen Techniken, da unterschiedliche Isomerentypen vorliegen können: Keton/Alkenol‐Isomere, Kohlenstoff‐Kohlenstoff‐Doppelbindungs(C=C)‐Isomere und Hydroxyl‐Regioisomere. Wir zeigen, dass kryogene Gasphasen‐Infrarot(IR)‐Spektroskopie von ionisierten 1‐Deoxysphingolipiden die Identifizierung und Unterscheidung von Isomeren anhand ihres einzigartigen spektroskopischen Profils ermöglicht. Insbesondere die Position und Konfiguration von C=C‐Bindungen können aufgrund von spezifischen Interaktionen zwischen dem geladenen Amin und der Doppelbindung bestimmt werden. Die Ergebnisse verdeutlichen das Potential der Gasphasen‐IR‐Spektroskopie, die Herausforderungen der Isomerenunterscheidung in der konventionellen Massenspektrometrie zu überwinden und den Weg für eine umfangreiche Analyse des Lipidoms zu ebnen.

Die stereoselektive Bildung von 1,2‐cis‐glykosidischen Bindungen ist bislang sehr anspruchsvoll. Häufig wird diese 1,2‐cis‐Selektivität durch Fernpartizipation (remote participation) von C4‐ oder C6‐Estergruppen herbeigeführt. Hierbei wird davon ausgegangen, dass ein ionisches Schlüsselintermediat, das Glykosylkation, gebildet wird. Obwohl derartige Mechanismen bereits vor Jahrzehnten postuliert wurden, konnte die exakte Struktur dieses Intermediats aufgrund seiner Kurzlebigkeit bisher nicht aufgeklärt werden. In dieser Studie nutzen wir kryogene Schwingungsspektroskopie und quantenchemische Rechnungen, um die Strukturen dieser Glykosylkationen aufzuklären. Acetylgruppen an der C4‐Position führen zur selektiven Bildung von α‐Galaktosiden, indem eine kovalente Bindung zum anomeren Kohlenstoff gebildet wird. Überraschenderweise können auch Benzylgruppen die stereoselektive Bildung von 1,2‐cis‐glykosidischen Bindungen durch Fernpartizipation herbeiführen.

We report on hyperfine-resolved laser spectroscopy of the A2Π ← X2Σ+ transition of magnesium monofluoride (MgF), relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines, and determined precise rotational, fine, and hyperfine structure parameters for the A2Π state. The radiative lifetime of the A2Π state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born–Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A2Π ← X2Σ+ transition by applying electric fields of up to 10.6 kV cm−1 and determined the permanent electric dipole moments of 24MgF in its ground X2Σ+ and first excited A2Π states to be μ X = 2.88(20) D and μ A = 3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition due to electric field induced parity mixing in the excited state. In order to scatter 104 photons, the electric field must be controlled to below 1 V cm−1.

Im Laufe der COVID-19 Pandemie haben mRNA-basierte Impfstoffe an immenser Bedeutung gewonnen. Massenspektrometrie ist für die Entwicklung und Analyse von modifizierten RNA Molekülen unerlässlich, setzt jedoch ein grundlegendes Verständnis über Fragmentierungsprozesse voraus. Analog zu der Zersetzung von RNA in Lösung durch Autohydrolyse, kann die Spaltung des RNA Rückgrats ebenso in der Gasphase stattfinden. Bislang sind die Fragmentierungsmechanismen jedoch unzureichend untersucht. In dieser Arbeit wurden Intermediate aus isolierten RNA Dinukleotiden in der Gasphase generiert und mittels kryogener Infrarotspektroskopie in Helium-Nanotröpfchen untersucht. Die experimentellen Daten, unterstützt durch Dichtefunktionaltheorie, liefern Hinweise dafür, dass die Bildung eines fünfgliedrigen zyklischen Phosphat-Intermediats begünstigt ist, während lineare oder sechsgliedrige Strukturen ausgeschlossen werden können. Weiterhin zeigen die Experimente, dass eine zusätzliche, bekannte Reaktion von RNA Nukleotiden in Lösung auch in der Gasphase induziert werden kann: die Tautomerisierung von Cytosin. Die beiden beobachteten Reaktionen spiegeln daher universelle und intrinsische Eigenschaften der untersuchten Moleküle wider.

Physical chemistry, chemical physics 24(14), 8081 - 8092 (2022). doi:10.1039/D1CP05748K special issue: "Festschrift Ivan Powis: Advances in Molecular Photoelectron Spectroscopy: Fundamentals & Application", We present an experimental X-ray photoelectron circular dichroism (PECD) study of liquid fenchone at the C 1s edge. A novel setup to enable PECD measurements on a liquid microjet [Malerz et al., Rev. Sci. Instrum., 2022, 93, 015101] was used. For the C 1s line assigned to fenchone's carbonyl carbon, a non-vanishing asymmetry is found in the intensity of photoelectron spectra acquired under a fixed angle in the backward-scattering plane. This experiment paves the way towards an innovative probe of the chirality of organic/biological molecules in aqueous solution., Published by RSC Publ., Cambridge

The stereoselective formation of 1,2-cis-glycosidic bonds is a major bottleneck in the synthesis of carbohydrates. We here investigate how the electron density in acyl protecting groups influences the stereoselectivity by fine-tuning the efficiency of remote participation. Electron-rich C4-pivaloylated galactose building blocks show an unprecedented α-selectivity. The trifluoroacetylated counterpart with electron-withdrawing groups, on the other hand, exhibits a lower selectivity. Cryogenic infrared spectroscopy in helium nanodroplets and density functional theory calculations revealed the existence of dioxolenium-type intermediates for this reaction, which suggests that remote participation of the pivaloyl protecting group is the origin of the high α-selectivity of the pivaloylated building blocks. According to these findings, an α-selective galactose building block for glycosynthesis is developed based on rational considerations and is subsequently employed in automated glycan assembly exhibiting complete stereoselectivity. Based on the obtained selectivities in the glycosylation reactions and the results from infrared spectroscopy and density functional theory, we suggest a mechanism by which these reactions could proceed.

Review of scientific instruments 93(1), 015101 (2022). doi:10.1063/5.0072346, We present a unique experimental design that enables the measurement of photoelectron circular dichroism (PECD) from chiral molecules in aqueous solution. The effect is revealed from the intensity difference of photoelectron emission into a backward-scattering angle relative to the photon propagation direction when ionizing with circularly polarized light of different helicity. This leads to asymmetries (normalized intensity differences) that depend on the handedness of the chiral sample and exceed the ones in conventional dichroic mechanisms by orders of magnitude. The asymmetry is largest for photon energies within several electron volts above the ionization threshold. A primary aim is to explore the effect of hydration on PECD. The modular and flexible design of our experimental setup EASI (Electronic structure from Aqueous Solutions and Interfaces) also allows for detection of more common photoelectron angular distributions, requiring distinctively different detection geometries and typically using linearly polarized light. A microjet is used for liquid-sample delivery. We describe EASI���s technical features and present two selected experimental results, one based on synchrotron-light measurements and the other performed in the laboratory, using monochromatized He-II �� radiation. The former demonstrates the principal effectiveness of PECD detection, illustrated for prototypic gas-phase fenchone. We also discuss the first data from liquid fenchone. In the second example, we present valence photoelectron spectra from liquid water and NaI aqueous solution, here obtained from a planar-surface microjet (flatjet). This new development features a more favorable symmetry for angle-dependent photoelectron measurements., Published by American Institute of Physics, [S.l.]

Over the course of the COVID-19 pandemic, mRNA-based vaccines have gained tremendous importance. The development and analysis of modified RNA molecules benefit from advanced mass spectrometry and require sufficient understanding of fragmentation processes. Analogous to the degradation of RNA in solution by autohydrolysis, backbone cleavage of RNA strands was equally observed in the gas phase; however, the fragmentation mechanism remained elusive. In this work, autohydrolysis-like intermediates were generated from isolated RNA dinucleotides in the gas phase and investigated using cryogenic infrared spectroscopy in helium nanodroplets. Data from both experiment and density functional theory provide evidence for the formation of a five-membered cyclic phosphate intermediate and rule out linear or six-membered structures. Furthermore, the experiments show that another prominent condensed-phase reaction of RNA nucleotides can be induced in the gas phase: the tautomerization of cytosine. Both observed reactions are therefore highly universal and intrinsic properties of the investigated molecules.

Tandem mass spectrometry is arguably the most important analytical tool for structure elucidation of lipids and other metabolites. By fragmenting intact lipid ions, valuable structural information such as the lipid class and fatty acyl composition are readily obtainable. The information content of a fragment spectrum can often be increased by the addition of metal cations. In particular, the use of silver ions is deeply rooted in the history of lipidomics due to their propensity to coordinate both electron-rich heteroatoms and C = C bonds in aliphatic chains. Not surprisingly, coordination of silver ions was found to enable the distinction of sn-isomers in glycerolipids by inducing reproducible intensity differences in the fragment spectra, which could, however, not be rationalized. Here, we investigate the fragmentation behaviors of silver-adducted sn- and double bond glycerophospholipid isomers by probing fragment structures using cryogenic gas-phase infrared (IR) spectroscopy. Our results confirm that neutral headgroup loss from silver-adducted glycerophospholipids leads to dioxolane-type fragments generated by intramolecular cyclization. By combining high-resolution IR spectroscopy and computational modelling of silver-adducted fragments, we offer qualitative explanations for different fragmentation behaviors of glycerophospholipid isomers. Overall, the results demonstrate that gas-phase IR spectroscopy of fragment ions can significantly contribute to our understanding of lipid dissociation mechanisms and the influence of coordinating cations. Graphical abstract

The proton-bound dimer of hydrogen sulfate and formate is an archetypal structure for ionic hydrogen-bonding complexes that contribute to biogenic aerosol nucleation. Of central importance for the structure and properties of this complex is the location of the bridging proton connecting the two conjugate base moieties. The potential energy surface for bridging proton translocation features two local minima, with the proton localized at either the formate or hydrogen sulfate moiety. However, electronic structure methods reveal a shallow potential energy surface governing proton translocation, with a barrier on the order of the zero-point energy. This shallow potential complicates structural assignment and necessitates a consideration of nuclear quantum effects. In this work, we probe the structure of this complex and its isotopologues, utilizing infrared (IR) action spectroscopy of ions captured in helium nanodroplets. The IR spectra indicate a structure in which a proton is shared between the hydrogen sulfate and formate moieties, HSO4-···H+···-OOCH. However, because of the nuclear quantum effects and vibrational anharmonicities associated with the shallow potential for proton translocation, the extent of proton displacement from the formate moiety remains unclear, requiring further experiments or more advanced theoretical treatments for additional insight.

Purpose The purpose of this paper is to explore the scientific nature of work-based learning (WBL) and research as operationalized in Professional Studies by examining first principles of scientific inquiry. Design/methodology/approach This paper introduces a Professional Studies program as it has been implemented at University of Southern Queensland in Australia and examines it from the perspective of five first principles of scientific inquiry: systematic exploration and reporting, use of models, objectivity, testability and applicability. The authors do so not to privilege the meritorious qualities of science or to legitimise WBL or its example in Professional Studies by conferring on them the status of science, but to highlight their systematised approach to learning and research. Findings If the authors define Professional Studies to mean the systematic inquiry of work-based people, processes and phenomena, evidence affirmatively suggests that it is scientific “in nature”. Originality/value WBL has been well documented, but its orientation to research, particularly mixed methods (MM) research through Professional Studies, and its adherence to first principles of science have never been explored; this paper begins to uncover the value of work-based pedagogical approaches to learning and research.

Es existieren über 100 Hydrophobieskalen für Aminosäuren, die auf unterschiedlichen Ansätzen basieren und einheitlich in kondensierter Phase ermittelt werden. Ein Vergleich der Hydrophobiewerte aus verschiedenen Methoden und die Ermittlung ihrer relativen Rangfolge sind jedoch anspruchsvoll, da die Wechselwirkungen zwischen der Umgebung und der Aminosäure in jeder Methode spezifisch sind. Hier überwinden wir diese Einschränkung, indem wir die Eigenschaften von Aminosäuren in der Reinraumumgebung der Gasphase untersuchen. In der Gasphase bleiben standardmäßig entropische Beiträge des hydrophoben Effektes aus, und nur die Polarität der Seitenkette ist für die Selbstorganisation entscheidend. Dies ermöglicht die Ableitung einer neuartigen Hydrophobieskala, die ausschließlich auf der Interaktion einzelner Aminosäureeinheiten innerhalb des Clusters basiert und somit die Eigenschaften der Seitenketten besser abbildet. Dieses Prinzip kann für die Klassifizierung von nicht‐natürlichen Derivaten angewendet werden, wie hier für fluorierte Aminosäurevarianten gezeigt ist.

The ubiquity of aqueous solutions in contact with charged surfaces and the realization that the molecular-level details of water–surface interactions often determine interfacial functions and properties relevant in many natural processes have led to intensive research. Even so, many open questions remain regarding the molecular picture of the interfacial organization and preferential alignment of water molecules, as well as the structure of water molecules and ion distributions at different charged interfaces. While water, solutes and charge are present in each of these systems, the substrate can range from living tissues to metals. This diversity in substrates has led to different communities considering each of these types of aqueous interface. In this Review, by considering water in contact with metals, oxides and biomembranes, we show the essential similarity of these disparate systems. While in each case the classical mean-field theories can explain many macroscopic and mesoscopic observations, it soon becomes apparent that such theories fail to explain phenomena for which molecular properties are relevant, such as interfacial chemical conversion. We highlight the current knowledge and limitations in our understanding and end with a view towards future opportunities in the field. What do a rock in a river, a red blood cell in our body and the electrodes inside a car battery have in common? Charged surfaces in contact with water. Although a unified approach to study such a variety of systems is not available yet, the current understanding — even with its limitations — paves the road to the development of new concepts and techniques.