Ion distributions play a central role in various settings-from biology, where they mediate the electrostatic interactions between charged biomolecules in solution, to energy storage devices, where they influence the charging properties of supercapacitors. These distributions are determined by interactions dictated by the chemical properties of the ions and their environment as well as the long-range nature of the electrostatic force. Recent theoretical and computational studies have explored the role of correlations between ions, which have been suggested to underlie a number of counterintuitive results, such as like-charge attraction. However, the interdependency between ion correlations and other interactions that ions experience in solution complicates the connection between physical models of ion correlations and the experimental investigation of ion distributions. We exploit the properties of the liquid/liquid interface to vary the coupling strength Γ of ion-ion correlations from weak to strong while monitoring their influence on ion distributions at the nanometer scale with X-ray reflectivity and the macroscopic scale with interfacial tension measurements. These data are in agreement with the predictions of a parameterfree density functional theory that includes ion-ion correlations and ion-solvent interactions over the entire range of experimentally tunable correlation coupling strengths (from 0.8 to 3.7). This study provides evidence for a sharply defined electrical double layer for large coupling strengths in contrast to the diffuse distributions predicted by mean field theory, thereby confirming a common prediction of many ion correlation models. The reported findings represent a significant advance in elucidating the nature and role of ion correlations in charged soft matter.liquid surface scattering | ion density profile | surface excess charge | Poisson-Boltzmann | Debye-Hückel hole T he works by Gouy (1) and Chapman (2) introduced the Poisson-Boltzmann (PB) equation to describe the distribution of ions and the accompanying variation of electric potential at the interface between a charged planar electrode and an electrolyte solution (1, 2). This seminal theory considered point-like ions interacting through their mean electric field in a continuum solvent but neglected both chemically specific ion-solvent interactions and correlations between ions. Specific ion interactions are exemplified by the well-known Hofmeister series (3). The study of ion correlations has been motivated by observations of the reentrant condensation of DNA (4) and proteins (5) in solution, in which like-charged biomolecules aggregate in the presence of multivalent ions, and reports of charge reversal in colloidal suspensions, in which the sign of the screened charge on a colloid can be changed by varying the surrounding electrolyte solution (6, 7).Correlations between ions that are caused by their electrostatic interactions are expected to be important when the average electrostatic interaction energy between neighboring ions...

The interfacial behavior of a model solvent extraction liquid-liquid system, consisting of solutions of dihexadecyl phosphate (DHDP) in dodecane and SrCl2 in water, was studied to determine the structure of the interfacial ion-extractant complex and its variation with pH. Previous experiments on a similar extraction system with ErCl3 demonstrated that the kinetics of the extraction process could be greatly retarded by cooling through an adsorption transition, thus providing a method to immobilize ion-extractant complexes at the interface and further characterize them with X-ray interface-sensitive techniques. Here, we use this same method to study the SrCl2 system. X-ray reflectivity and fluorescence near total reflection measured the molecular-scale interfacial structure above and below the adsorption transition for a range of pH. Below the transition, DHDP molecules form a homogeneous monolayer at the interface with Sr(2+) coverage increasing from zero to saturation (one Sr(2+) per two DHDP) within a narrow range of pH. Experimental values of Sr(2+) interfacial density determined from fluorescence measurements are larger than those from reflectivity measurements. Although both techniques probe Sr(2+) bound to DHDP, only the fluorescence provides adequate sensitivity to Sr(2+) in the diffuse double layer. A Stern equation determines the Sr(2+) binding constant from the reflectivity measurements and the additional Sr(2+) measured in the diffuse double layer is accounted for by Gouy-Chapman theory. Above the transition temperature, a dilute concentration of DHDP-Sr complexes resides at the interface, even for temperatures far above the transition. A comparison is made of the structure of the interfacial ion-extractant complex for this divalent metal ion to recent results on trivalent Er(3+) metal ions, which provides insight into the role of metal ion charge on the structure of interfacial ion-extractant complexes, as well as implications for extraction of these two differently charged ions.

Complex interactions that determine ionic ordering in the bulk of electrolyte solutions are modified by surface-region inhomogeneities. We present results from an investigation of surface-ionic profiles that provide insights into the underlying physical chemistry in this region. X-ray reflectivity measurements from the liquid surfaces of aqueous ErCl3 solutions reveal in unprecedented detail a nonmonotonic electron density profile, which is interpreted in terms of a nonmonotonic surface distribution of cations (Er3+) and their relationship to the bulk. The combination of a heavy, multivalent Er3+ and a lighter, monovalent anion (Cl–) results in a significant cation depletion layer at the surface followed by a subsurface region of notably enhanced Er3+. Studying a series of solutions as a function of solute concentration reveals marked changes in Er3+ distribution, the most notable of which are the depletion layer thickness variation from 7.8 Å at 0.2 M to 5.5 Å at 1.0 M and the damped, oscillatory, cation concentrations indicative of solute multilayering in the subsurface region. This nonmonotonic profile is consistent with an analysis of surface tension measurements by the Gibbs adsorption equation that predicts negative adsorption. Molecular dynamics simulations provide physical insight into the observed behavior, implicating the high charge on erbium for its nonmonotonic variation with depth. This work suggests that future studies employing higher-valent cations will enhance the understanding of liquid/vapor interfaces and their widespread importance in areas ranging from atmospheric chemistry to metal-ion separations.

X-ray fluorescence near total reflection (XFNTR) is measured from the liquid/liquid interface between dodecane and an ErCl 3 aqueous solution by monitoring L shell Er emission lines. A custom sample cell is used to minimize absorption of the fluorescence x-rays that pass through dodecane on their way to the detector. The Er 3þ concentration near the interface is related to the fluorescence intensity by a scale factor that is extracted by fitting the incident-angle dependent Er La emission line intensities for different ErCl 3 bulk concentrations. As an application, we present the use of XFNTR to monitor the growth of interfacial crud in a model solvent extraction system consisting of an interface between a dodecane solution of bis(2-ethylhexyl) phosphate (HDEHP) and an ErCl 3 aqueous solution. V

An otherwise healthy, 35-year-old man was hospitalized for the management of acute respiratory failure due to coronavirus disease 2019 (COVID-19)-related severe bilateral pneumonia and acute respiratory distress syndrome (ARDS). The patient therapeutic regimen included the widely accepted standard combination of oxygen, anticoagulation therapy; corticosteroids, non-steroidal anti-inflammatory drugs (NSAIDs), and antibiotics. A novel combination of colchicine, hymecromone, and bromhexine inhalations was added to the therapeutic regimen as part of our unique COVID-19 management institutional protocol. COVID-19-related severe bilateral pneumonia and acute respiratory distress syndrome (ARDS). The patient therapeutic regimen included the widely accepted standard combination of oxygen, anticoagulation therapy, corticosteroids, NSAIDs, and antibiotics. A novel combination of colchicine, hymecromone, and bromhexine inhalations was added to the therapeutic regimen as part of our unique COVID-19 management institutional protocol.Rapid clinical response on day 2, with a significant improvement of radiographic pulmonary changes on day 5, and improvement of laboratory results on days 5-7 were observed. The administration of inhalatory bromhexine in combination with high-dose colchicine and hymecromone was crucial for the positive outcome of the disease. This treatment regimen resulted in a four to five-fold decrease in the mortality of hospitalized patients.