Surface accumulation and acid-base equilibrium of phenol at the liquid-vapor interface.

We have investigated the surfactant properties of phenol in aqueous solution as a function of pH and bulk concentration using liquid-jet photoelectron spectroscopy (LJ-PES) and surface tension measurements. The emphasis of this work is on the determination of the Gibbs free energy of adsorption and surface excess of phenol and its conjugate base phenolate at the bulk pKa (9.99), which can be determined for each species using photoelectron spectroscopy. These values are compared to those obtained in measurements well below and well above the pKa, where pure phenol or phenolate, respectively, are the dominant species, and where the Gibbs free energy of adsorption determined from surface tension and LJ-PES data are in excellent agreement. At the bulk pKa the surface-sensitive LJ-PES measurements show a deviation of the expected phenol/phenolate ratio in favor of phenol, i.e., an apparent upward shift of the at the surface. In addition, the Gibbs free energies of adsorption determined by LJ-PES at the bulk pKa for phenol and phenolate deviate from those observed for the pure solutions. We discuss these observations in view of the different surface propensity of phenol and phenolate as well as potential cooperative interactions between them in the near-surface region.

The solvation shell probed by resonant intermolecular Coulombic decay.

Molecules involved in solvation shells have properties differing from those of the bulk solvent, which can in turn affect reactivity. Among key properties of these molecules are their nature and electronic structure. Widely used tools to characterize this type of property are X-ray-based spectroscopies, which, however, usually lack the capability to selectively probe the solvation-shell molecules. A class of X-ray triggered "non-local" processes has the recognized potential to provide this selectivity. Intermolecular Coulombic decay (ICD) and related processes involve neighbouring molecules in the decay of the X-ray-excited target, and are thus naturally sensitive to its immediate environment. Applying electron spectroscopy to aqueous solutions, we explore the resonant flavours of ICD and demonstrate how it can inform on the first solvation shell of excited solvated cations. One particular ICD process turns out to be a potent marker of the formation of ion pairs. Another gives a direct access to the electron binding energies of the water molecules in the first solvation shell, a quantity previously elusive to direct measurements. The resonant nature of the processes makes them readily measurable, providing powerful new spectroscopic tools.

Compression of a Stearic Acid Surfactant Layer on Water Investigated by Ambient Pressure X-ray Photoelectron Spectroscopy.

We present a combined Langmuir-Pockels trough and ambient pressure X-ray photoelectron spectroscopy (APXPS) study of the compression of stearic acid surfactant layers on neat water. Changes in the packing density of the molecules are directly determined from C 1s and O 1s APXPS data. The experimental data are fit with a 2D model for the stearic acid coverage. Based on the results of these proof-of-principle experiments, we discuss the remaining challenges that need to be overcome for future investigations of the role of surfactants in heterogeneous chemical reactions at liquid-vapor interfaces in combined Langmuir-Pockels trough and APXPS measurements.

Correction: Photoelectron angular distributions as sensitive probes of surfactant layer structure at the liquid-vapor interface.

Correction for 'Photoelectron angular distributions as sensitive probes of surfactant layer structure at the liquid-vapor interface' by Rémi Dupuy et al., Phys. Chem. Chem. Phys., 2022, 24, 4796-4808, https://doi.org/10.1039/D1CP05621B.

Core-Level Photoelectron Angular Distributions at the Liquid-Vapor Interface.

ConspectusPhotoelectron spectroscopy (PES) is a powerful tool for the investigation of liquid-vapor interfaces, with applications in many fields from environmental chemistry to fundamental physics. Among the aspects that have been addressed with PES is the question of how molecules and ions arrange and distribute themselves within the interface, that is, the first few nanometers into solution. This information is of crucial importance, for instance, for atmospheric chemistry, to determine which species are exposed in what concentration to the gas-phase environment. Other topics of interest include the surface propensity of surfactants, their tendency for orientation and self-assembly, as well as ion double layers beneath the liquid-vapor interface. The chemical specificity and surface sensitivity of PES make it in principle well suited for this endeavor. Ideally, one would want to access complete atomic-density distributions along the surface normal, which, however, is difficult to achieve experimentally for reasons to be outlined in this Account. A major complication is the lack of accurate information on electron transport and scattering properties, especially in the kinetic-energy regime below 100 eV, a pre-requisite to retrieving the depth information contained in photoelectron signals.In this Account, we discuss the measurement of the photoelectron angular distributions (PADs) as a way to obtain depth information. Photoelectrons scatter with a certain probability when moving through the bulk liquid before being expelled into a vacuum. Elastic scattering changes the electron direction without a change in the electron kinetic energy, in contrast to inelastic scattering. Random elastic-scattering events usually lead to a reduction of the measured anisotropy as compared to the initial, that is, nascent PAD. This effect that would be considered parasitic when attempting to retrieve information on photoionization dynamics from nascent liquid-phase PADs can be turned into a powerful tool to access information on elastic scattering, and hence probing depth, by measuring core-level PADs. Core-level PADs are relatively unaffected by effects other than elastic scattering, such as orbital character changes due to solvation. By comparing a molecule's gas-phase angular anisotropy, assumed to represent the nascent PAD, with its liquid-phase anisotropy, one can estimate the magnitude of elastic versus inelastic scattering experienced by photoelectrons on their way to the surface from the site at which they were generated. Scattering events increase with increasing depth into solution, and thus it is possible to correlate the observed reduction in angular anisotropy with the depth below the surface along the surface normal.We will showcase this approach for a few examples. In particular, our recent works on surfactant molecules demonstrated that one can indeed probe atomic distances within these molecules with a high sensitivity of ∼1 Šresolution along the surface normal. We were also able to show that the anisotropy reduction scales linearly with the distance along the surface normal within certain limits. The limits and prospects of this technique are discussed at the end, with a focus on possible future applications, including depth profiling at solid-vapor interfaces.

Photoelectron angular distributions as sensitive probes of surfactant layer structure at the liquid-vapor interface.

The characterization of liquid-vapor interfaces at the molecular level is an important underpinning for a basic understanding of fundamental heterogeneous processes in many areas, such as atmospheric science. Here we use X-ray photoelectron spectroscopy to study the adsorption of a model surfactant, octanoic acid, at the water-gas interface. In particular, we examine the information contained in photoelectron angular distributions and show that information about the relative depth of molecules and functional groups within molecules can be obtained from these measurements. Focusing on the relative location of carboxylate (COO-) and carboxylic acid (COOH) groups at different solution pH, the former is found to be immersed deeper into the liquid-vapor interface, which is confirmed by classical molecular dynamics simulations. These results help establish photoelectron angular distributions as a sensitive tool for the characterization of molecules at the liquid-vapor interface.

Low-energy constraints on photoelectron spectra measured from liquid water and aqueous solutions.

We report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV, on the photoemission spectra of liquid water. We show that the nascent photoelectron spectrum and, hence, the inferred electron binding energy can only be accurately determined if electron energies are large enough that cross sections for quasi-elastic scattering processes, such as vibrational excitation, are negligible. Otherwise, quasi-elastic scattering leads to strong, down-to-few-meV kinetic energy scattering losses from the direct photoelectron features, which manifest in severely distorted intrinsic photoelectron peak shapes. The associated cross-over point from predominant (known) electronically inelastic to quasi-elastic scattering seems to arise at surprisingly large electron kinetic energies, of approximately 10-14 eV. Concomitantly, we present evidence for the onset of indirect, autoionization phenomena (occurring via superexcited states) within a few eV of the primary and secondary ionization thresholds. These processes are inferred to compete with the direct ionization channels and primarily produce low-energy photoelectrons at photon and electron impact excitation energies below ∼15 eV. Our results highlight that vibrational inelastic electron scattering processes and neutral photoexcitation and autoionization channels become increasingly important when photon and electron kinetic energies are decreased towards the ionization threshold. Correspondingly, we show that for neat water and aqueous solutions, great care must be taken when quantitatively analyzing photoelectron spectra measured too close to the ionization threshold. Such care is essential for the accurate determination of solvent and solute ionization energies as well as photoelectron branching ratios and peak magnitudes.

Core level photoelectron spectroscopy of heterogeneous reactions at liquid-vapor interfaces: Current status, challenges, and prospects.

Liquid-vapor interfaces, particularly those between aqueous solutions and air, drive numerous important chemical and physical processes in the atmosphere and in the environment. X-ray photoelectron spectroscopy is an excellent method for the investigation of these interfaces due to its surface sensitivity, elemental and chemical specificity, and the possibility to obtain information on the depth distribution of solute and solvent species in the interfacial region. In this Perspective, we review the progress that was made in this field over the past decades and discuss the challenges that need to be overcome for investigations of heterogeneous reactions at liquid-vapor interfaces under close-to-realistic environmental conditions. We close with an outlook on where some of the most exciting and promising developments might lie in this field.

Photoexcited organic molecules en route to highly efficient autoionization.

The conversion of optical and electrical energies in novel materials is key to modern optoelectronic and light-harvesting applications. Here, we investigate the equilibration dynamics of photoexcited 2,7-bis(biphenyl-4-yl)-2',7'-ditertbutyl-9,9'-spirobifluorene (SP6) molecules adsorbed on ZnO(10-10) using femtosecond time-resolved two-photon photoelectron and optical spectroscopies. We find that, after initial ultrafast relaxation on femtosecond and picosecond time scales, an optically dark state is populated, likely the SP6 triplet (T) state, that undergoes Dexter-type energy transfer (rDex = 1.3 nm) and exhibits a long decay time of 0.1 s. Because of this long lifetime, a photostationary state with average T-T distances below 2 nm is established at excitation densities in the 1020 cm-2 s-1 range. This large density enables decay by T-T annihilation (TTA) mediating autoionization despite an extremely low TTA rate of kTTA = 4.5 ⋅ 10-26 m3 s-1. The large external quantum efficiency of the autoionization process (up to 15%) and photocurrent densities in the mA cm-2 range offer great potential for light-harvesting applications.

Proton dynamics in molecular solvent clusters as an indicator for hydrogen bond network strength in confined geometries.

Hydrogen bonding leads to the formation of strong, extended intermolecular networks in molecular liquids such as water. However, it is less well-known how robust the network is to environments in which surface formation or confinement effects become prominent, such as in clusters or droplets. Such systems provide a useful way to probe the robustness of the network, since the degree of confinement can be tuned by altering the cluster size, changing both the surface-to-volume ratio and the radius of curvature. To explore the formation of hydrogen bond networks in confined geometries, here we present O 1s Auger spectra of small and large clusters of water, methanol, and dimethyl ether, as well as their deuterated equivalents. The Auger spectra of the clusters and the corresponding macroscopic liquids are compared and evaluated for an isotope effect, which is due to proton dynamics within the lifetime of the core hole (proton-transfer-mediated charge-separation, PTM-CS), and can be linked to the formation of a hydrogen bond network in the system. An isotope effect is observed in water and methanol but not for dimethyl ether, which cannot donate a hydrogen bond at its oxygen site. The isotope effect, and therefore the strength of the hydrogen bond network, is more pronounced in water than in methanol. Its value depends on the average size of the cluster, indicating that confinement effects change proton dynamics in the core ionised excited state.

Electronic Decay of Singly Charged Ground-State Ions by Charge Transfer via van der Waals Bonds.

We report the observation of the radiative decay of singly charged noble gas ground-state ions embedded in heterogeneous van der Waals clusters. Electron-photon coincidence spectroscopy and dispersed photon spectroscopy are applied to identify the radiative charge transfer from Kr atoms to a Ne_{2}^{+} dimer, which forms after single valence photoionization of Ne atoms at the surface of a NeKr cluster. This mechanism might be a fundamental decay process of ionized systems in an environment.

Efficient Fluorescence Quenching by Distant Production of a Free Electron.

Energy and charge transfer processes play an important role in many fundamental reactions in chemistry, biochemistry, and even technology. If an entity that is part of a larger system is photoexcited, its energy will dissipate, for example, by rearrangement of electron density in a large molecule or by photon emission (fluorescence). Here, we report the experimental observation of free electrons from a heterogeneous van der Waals cluster, in which some sites act as electron emitters receiving their energy efficiently from other "antenna" sites that are resonantly excited in the UV range. By complementing electron spectroscopy with fluorescence detection, we can directly observe that electron emission via this mechanism completely quenches fluorescence once the channel opens. We suggest this mechanism to be important for both quenching of fluorescence as well as resonantly enhancing free electron production in a variety of systems.

Liver decompensation in HIV/Hepatitis B coinfection in the combination antiretroviral therapy era does not seem increased compared to hepatitis B mono-infection.

BACKGROUND & AIMS: HIV/hepatitis B virus (HBV) coinfected subjects are thought to have faster progression to end-stage liver disease (ESLD) than HBV mono-infected subjects. We assessed whether this remains in the current cART-era. METHODS: Data from subjects with follow-up completion post-2003 were compared between HIV/HBV coinfected subjects in the Dutch HIV Monitoring database and HBV mono-infected subjects from two centres. The primary outcomes of composite ESLD included portal hypertension, decompensated cirrhosis, hepatocellular carcinoma, liver transplantation and liver-related mortality. Outcomes were analysed using time-dependent cause-specific Cox regression models adjusted for follow-up time and relevant covariates. Subset-analyses were done in subjects with follow-up pre-2003. RESULTS: In the 1336 co- vs 742 mono-infected subjects, coinfected subjects had no increased probability for ESLD compared to mono-infected subjects (cHR 0.7 (95% CI 0.4-1.1), but had increased probabilities for all-cause (cHR 7.4 [4.9-11.1]) and liver-related mortality (cHR 3.4 [1.6-7.5]). In the current combined cohort, treatment with tenofovir or entecavir was inversely associated with ESLD, all-cause and liver-related mortality (cHR 0.4 [95% CI 0.3-0.7], cHR 0.003 [0.001-0.01]), cHR 0.007 [0.001-0.05]). Other predictors for ESLD were older age, being of Sub-Sahara African descent, increased alanine aminotransferase levels and hepatitis C virus coinfection. While the probability for all-cause mortality was increased in coinfected subjects, this rate decreased compared to pre-2003 (HR 40.2 (95% CI: 8.7-186.2). CONCLUSIONS: HIV/HBV coinfected patients no longer seem to be at increased risk for progression to ESLD compared to HBV mono-infected patients, likely due to widespread use of highly effective cART with dual HBV and HIV activity.

Competition between proton transfer and intermolecular Coulombic decay in water.

Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron-electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a1 ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40-50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12-52 fs for small water clusters.

High Treatment Uptake in Human Immunodeficiency Virus/Hepatitis C Virus-Coinfected Patients After Unrestricted Access to Direct-Acting Antivirals in the Netherlands.

Background: The Netherlands has provided unrestricted access to direct-acting antivirals (DAAs) since November 2015. We analyzed the nationwide hepatitis C virus (HCV) treatment uptake among patients coinfected with human immunodeficiency virus (HIV) and HCV. Methods: Data were obtained from the ATHENA HIV observational cohort in which >98% of HIV-infected patients ever registered since 1998 are included. Patients were included if they ever had 1 positive HCV RNA result, did not have spontaneous clearance, and were known to still be in care. Treatment uptake and outcome were assessed. When patients were treated more than once, data were included from only the most recent treatment episode. Data were updated until February 2017. In addition, each treatment center was queried in April 2017 for a data update on DAA treatment and achieved sustained virological response. Results: Of 23574 HIV-infected patients ever linked to care, 1471 HCV-coinfected patients (69% men who have sex with men, 15% persons who [formerly] injected drugs, and 15% with another HIV transmission route) fulfilled the inclusion criteria. Of these, 87% (1284 of 1471) had ever initiated HCV treatment between 2000 and 2017, 76% (1124 of 1471) had their HCV infection cured; DAA treatment results were pending in 6% (92 of 1471). Among men who have sex with men, 83% (844 of 1022) had their HCV infection cured, and DAA treatment results were pending in 6% (66 of 1022). Overall, 187 patients had never initiated treatment, DAAs had failed in 14, and a pegylated interferon-alfa-based regimen had failed in 54. Conclusions: Fifteen months after unrestricted DAA availability the majority of HIV/HCV-coinfected patients in the Netherlands have their HCV infection cured (76%) or are awaiting DAA treatment results (6%). This rapid treatment scale-up may contribute to future HCV elimination among these patients.

Sensitivity of Electron Transfer Mediated Decay to Ion Pairing.

Ion pairing in electrolyte solutions remains a topic of discussion despite a long history of research. Very recently, nearest-neighbor mediated electronic de-excitation processes of core hole vacancies (electron transfer mediated decay, ETMD) were proposed to carry a spectral fingerprint of local solvation structure and in particular of contact ion pairs. Here, for the first time, we apply electron-electron coincidence detection to a liquid microjet, and record ETMD spectra of Li 1s vacancies in aqueous solutions of lithium chloride (LiCl) in direct comparison to lithium acetate (LiOAc). A change in the ETMD spectrum dependent on the electrolyte anion identity is observed for 4.5 M salt concentration. We discuss these findings within the framework of the formation and presence of contact ion pairs and the unique sensitivity of ETMD spectroscopy to ion pairing.

Clinical impact of five large-scale screening projects for chronic hepatitis B in Chinese migrants in the Netherlands.

BACKGROUND & AIMS: In low-endemic countries it is debated whether first-generation migrants should be screened for chronic hepatitis B infection. We describe the clinical impact of five large-scale Dutch screening projects for hepatitis B in first-generation Chinese migrants. METHODS: Between 2009 and 2013 five independent outreach screening projects for hepatitis B targeting first-generation Chinese migrants were conducted in five main Dutch regions. To explore the relevance of our screening we defined clinical impact as the presence of an indication for: (i) antiviral therapy, (ii) strict follow-up because of high hepatitis B DNA levels and/or (iii) surveillance for hepatocellular carcinoma. RESULTS: In total, 4423 persons participated in the projects of whom 6.0% (n = 264) were HBsAg positive. One hundred and twenty-nine newly diagnosed HBsAg-positive patients were analysed in specialist care. Among these patients prevalence of cirrhosis was 6.9% and antiviral therapy for hepatitis B was started in 32 patients (25%). In patients without a treatment indication, strict follow-up because of high hepatitis B DNA levels and/or surveillance for hepatocellular carcinoma was considered indicated in 64 patients (50%). CONCLUSIONS: In our screening project in first-generation Chinese migrants, antiviral treatment, strict follow-up because of high hepatitis B DNA levels and/or surveillance for hepatocellular carcinoma were considered indicated in three of four analysed HBsAg-positive patients. These data show that detection of hepatitis B in Chinese migrants can have considerable impact on patient care.

Boceprevir, peginterferon and ribavirin for acute hepatitis C in HIV infected patients.

BACKGROUND & AIMS: Acute hepatitis C virus infections (AHCV) are prevalent among HIV positive men having sex with men and generally treated with pegylated interferon-alpha (PegIFN) and ribavirin (RBV) during 24weeks. The addition of a protease inhibitor could shorten therapy without loss of efficacy. METHODS: We performed an open-label, single arm study to investigate the efficacy and safety of a 12-week course of boceprevir, PegIFN and RBV for AHCV genotype 1 infections in 10 Dutch HIV treatment centers. The primary endpoint of the study was achievement of sustained virological response rate at week 12 (SVR12) in patients reaching a rapid viral response at week 4 (RVR4) and SVR12 in the intent to treat (ITT) entire study population was the most relevant secondary endpoint. RESULTS: One hundred twenty-seven AHCV patients were screened in 16 months, of which 65 AHCV genotype 1 patients were included. After spontaneous clearance in six patients and withdrawal before treatment initiation in two, 57 started therapy within 26 weeks after infection. RVR4 rate was 72%. SVR12 rate was 100% in the RVR4 group. SVR12 rate in the ITT group was 86% and comparable to the SVR12 rate of 84% in 73 historical controls treated for 24 weeks with PegIFN and RBV in the same study centers. CONCLUSION: With the addition of boceprevir to PegIFN and RBV, treatment duration of AHCV genotype 1 can be reduced to 12 weeks without loss of efficacy. Given the high drug costs and limited availability of interferon-free regimens, boceprevir PegIFN and RBV can be a considered a valid treatment option for AHCV. ClinicalTrials.gov, number NCT01912495.

Maraviroc Intensification of cART in Patients with Suboptimal Immunological Recovery: A 48-Week, Placebo-Controlled Randomized Trial.

OBJECTIVE: The immunomodulatory effects of the CCR5-antagonist maraviroc might be beneficial in patients with a suboptimal immunological response, but results of different cART (combination antiretroviral therapy) intensification studies are conflicting. Therefore, we performed a 48-week placebo-controlled trial to determine the effect of maraviroc intensification on CD4+ T-cell counts and immune activation in these patients. DESIGN: Double-blind, placebo-controlled, randomized trial. METHODS: Major inclusion criteria were 1. CD4+ T-cell count <350 cells/µL while at least two years on cART or CD4+ T-cell count <200 cells/µL while at least one year on cART, and 2. viral suppression for at least the previous 6 months. HIV-infected patients were randomized to add maraviroc (41 patients) or placebo (44 patients) to their cART regimen for 48 weeks. Changes in CD4+ T-cell counts (primary endpoint) and other immunological parameters were modeled using linear mixed effects models. RESULTS: No significant differences for the modelled increase in CD4+ T-cell count (placebo 15.3 CD4+ T cells/µL (95% confidence interval (CI) [1.0, 29.5] versus maraviroc arm 22.9 CD4+ T cells/µL (95% CI [7.4, 38.5] p = 0.51) or alterations in the expression of markers for T-cell activation, proliferation and microbial translocation were found between the arms. However, maraviroc intensification did increase the percentage of CCR5 expressing CD4+ and CD8+ T-cells, and the plasma levels of the CCR5 ligand MIP-1ß. In contrast, the percentage of ex-vivo apoptotic CD8+ and CD4+ T-cells decreased in the maraviroc arm. CONCLUSIONS: Maraviroc intensification of cART did not increase CD4+ T-cell restoration or decrease immune activation as compared to placebo. However, ex-vivo T-cell apoptosis was decreased in the maraviroc arm. TRIAL REGISTRATION: ClinicalTrials.gov NCT00875368.