Ice chromatography: current progress and future developments

Ice chromatography, in which water-ice particles are employed as a chromatographic stationary phase, has proven an efficient technique for probing the solution/ice interface. The preparation of fine ice particles has allowed us to not only obtain higher-resolution separation but also investigate the molecular processes occurring on the ice surface in more detail. Chromatographic investigations have revealed that two or more hydrogen bonds are simultaneously formed between a solute and the dangling bonds on the ice surface when the solute gives measurable retention. Several compounds, including estrogens, amino acids, and acyclic polyethers, have been successfully separated by ice chromatography with a hexane-based mobile phase. In addition, this method effectively probes the surface melting of the ice stationary phase and the liquid phase that coexists with water ice at thermodynamic equilibrium. The thickness of the surface liquid layer and the size of the liquid phase that grows inside an ice particle have been evaluated. The perspectives of this method are also discussed.      

Ionic liquids in enhancing the sensitivity of capillary electrophoresis: Off‐line and on‐line sample preconcentration techniques

The popularity of ionic liquids (ILs) has grown during the last decade in enhancing the sensitivity of CE through different off‐line or on‐line sample preconcentration techniques. Water‐insoluble ILs were commonly used in IL‐based liquid phase microextraction, in all its variants, as off‐line sample preconcentration techniques combined with CE. Water‐soluble ILs were rarely used in IL‐based aqueous two phase system (IL‐ATPS) as an off‐line sample preconcentration approach combined with CE in spite of IL‐ATPS predicted features such as more compatibility with CE sample injection due to its relatively low viscosity and more compatibility with CE running buffers avoid, in some cases, anion exchange precipitation. Therefore, the attentions for the key parameters affecting the performance of IL‐ATPSs were generally presented and discussed. On‐line CE preconcentration techniques containing IL‐based surfactants at nonmicellar or micellar concentrations have become another interesting area to improve CE sensitivity and it is likely to remain a focus of the field in the endeavor because of their numerous to create rapid, simple and sensitive systems. In this article, significant contributions of ILs in enhancing the sensitivity of CE are described, and a specific overview of the relevant examples of their applications is also given.     

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

Regarding the surface phase of liquid mixtures as a thermodynamic phase, ideal surface phases are designed so that at fixed bulk‐phase composition, real and ideal surface phases have the same chemical composition and identical limiting slopes for the dependence of surface tension on mole fraction. Standard chemical potentials are introduced for surface phase components, and quasi‐exact expressions are worked out to compute ideal surface tensions and surface‐phase compositions of real liquid mixtures. Guidelines for choosing molecular models to estimate the molar surface area of pure constituents are given. Ideal and excess surface tensions are calculated by using literature data for aqueous ethanol solutions at 298 K. These results show treatment based on Butler’s equations grossly overestimate predicted surface tensions, thus leading to lower ethanol content in the surface phase. These inaccuracies are ascribed to the use of molar surface areas in model equations that are too small.     

Up to 4 orders of magnitude enhancement of crown ether complexation in an aqueous phase coexistent with ice

Ice chromatography measurements have revealed anomalous enhancements of crown ether complexation in a liquid phase coexistent with ice. The 4 orders of magnitude enhancement was confirmed for the complexation of dibenzo-24-crown-8 in sub-μm-sized liquid inclusions formed in ice doped with <1 mM NaCl or KCl. This enhancement became less pronounced with increasing dopant concentration.     

Transformation of ice in aqueous KCl solution to a high-pressure, low-temperature phase

The changes in in situ Raman spectra of ice in aqueous KCl solution have been measured as a function of pressure at liquid nitrogen temperature (77 K). The ice that is formed abruptly transforms to a crystalline phase at 800 MPa. It has a spectrum close to that of ice VII′ to which high density amorphous (hda) ice transforms at about 4 GPa. This behavior contrasts with that of the ice in aqueous LiCl solution, which transforms to an amorphous phase at 500 MPa, as in the case of pressure-induced amorphization of ice I_h to hda.     

Reversibly Thermosecreting Organogels with Switchable Lubrication and Anti‐Icing Performance

Synthetic gels with switchable interfacial properties have great potential in smart devices and controllable transport. Herein, we design an organogel by incorporating a binary liquid mixture with an upper critical solution temperature (UCST) into a polymer network, resulting in reversible modulation of lubrication and adhesion properties. As the temperature changes, the lubricating mechanism changes reversibly from boundary lubrication to hydrodynamic lubrication due to phase separation within the binary solution permeating the gel (friction coefficient 0.4–0.03). Droplets appear on the gel surface at low temperature and disappear with temperature higher than the critical phase separation temperature (T_ps) of the organogel. The organogel possesses a relatively low ice adhesive strength (less than 1 kPa). This material has potential applications in anti‐icing and smart devices, and we believe that this design strategy can be expanded to other systems such as aqueous solutions and hydrogels.     

Chemical signals of past climate and environment from polar ice cores and firn air

Chemical and isotopic records obtained from polar ice cores have provided some of the most iconic datasets in Earth system science. Here, I discuss how the different records are formed in the ice sheets, emphasising in particular the contrast between chemistry held in the snow/ice phase, and that which is trapped in air bubbles. Air diffusing slowly through the upper firn layers of the ice sheet can also be sampled in large volumes to give more recent historical information on atmospheric composition. The chemical and geophysical issues that have to be solved to interpret ice core data in terms of atmospheric composition and emission changes are also highlighted. Ice cores and firn air have provided particularly strong evidence about recent changes (last few decades to centuries), including otherwise inaccessible data on increases in compounds that are active as greenhouse gases or as agents of stratospheric depletion. On longer timescales (up to 800?000 years in Antarctica), ice cores reveal major changes in biogeochemical cycling, which acted as feedbacks on the very major changes in climate between glacial and interglacial periods.     

Hollow‐fiber‐supported liquid membrane microextraction of amlodipine and atorvastatin

A simple, environmentally friendly, and efficient method, based on hollow‐fiber‐supported liquid membrane microextraction, followed by high‐performance liquid chromatography has been developed for the extraction and determination of amlodipine (AML) and atorvastatin (ATO) in water and urine samples. The AML in two‐phase hollow‐fiber liquid microextraction is extracted from 24.0 mL of the aqueous sample into an organic phase with microliter volume located inside the pores and lumen of a polypropylene hollow fiber as acceptor phase, but the ATO in three‐phase hollow‐fiber liquid microextraction is extracted from aqueous donor phase to organic phase and then back‐extracted to the aqueous acceptor phase, which can be directly injected into the high‐performance liquid chromatograph for analysis. The preconcentration factors in a range of 34–135 were obtained under the optimum conditions. The calibration curves were linear (R² ≥ 0.990) in the concentration range of 2.0–200 μg/L for AML and 5.0–200 μg/L for ATO. The limits of detection for AML and ATO were 0.5 and 2.0 μg/L, respectively. Tap water and human urine samples were successfully analyzed for the existence of AML and ATO using the proposed methods.     

A reexamination of the ice III/IX hydrogen bond ordering phase transition

Ice III is a hydrogen bond disordered crystal which when cooled 1 K / min or faster transforms to an antiferroelectric hydrogen bond ordered structure, ice IX. Throughout its region of stability, experiments indicate that the H bonds in ice III are, in fact, partially ordered, i.e., some proton arrangements are preferred. In addition, there has been evidence that the structure of ice IX retains some residual disorder after the transition. Diffraction experiments and calorimetry apparently conflict with regard to the degree of ordering at the ice III/IX transition. Mean field statistical mechanical theories have been used to link partial occupations from diffraction data with thermodynamics. In this work, we investigate the ice III/IX proton ordering phase transition using electronic density functional theory calculations for small unit cells, extended to simulate the phase transition in a large unit cell using graph invariants. In agreement with experiment, we observe partial ordering over a wide range of temperatures as ice III transforms to partially disordered ice IX, near 126 K, which becomes fully ordered at lower temperatures. We compare our results from full statistical mechanical simulations with mean field models, finding small errors for the low-temperature ice IX phase and much larger errors for the high-temperature ice III phase. The failure of mean field theories may explain the apparent conflict between diffraction experiments and calorimetry.     

Quantum Control of Gas‐Phase and Liquid‐Phase Femtochemistry

Active control of chemical reactions on a microscopic (molecular) level, that is, the selective breaking or making of chemical bonds, is an old dream. However, conventional control agents used in chemical synthesis are macroscopic variables such as temperature, pressure or concentration, which gives no direct access to the quantum‐mechanical reaction pathway. In quantum control, by contrast, molecular dynamics are guided with specifically designed light fields. Thus it is possible to efficiently and selectively reach user‐defined reaction channels. In the last years, experimental techniques were developed by which many breakthroughs in this field were achieved. Femtosecond laser pulses are manipulated in so‐called pulse shapers to generate electric field profiles which are specifically adapted to a given quantum system and control objective. The search for optimal fields is guided by an automated learning loop, which employs direct feedback from experimental output. Thereby quantum control over gas‐phase as well as liquid‐phase femtochemical processes has become possible. In this review, we first discuss the theoretical and experimental background for many of the recent experiments treated in the literature. Examples from our own research are then used to illustrate several fundamental and practical aspects in gas‐phase as well as liquid‐phase quantum control. Some additional technological applications and developments are also described, such as the automated optimization of the output from commercial femtosecond laser systems, or the control over the polarization state of light on an ultrashort timescale. The increasing number of successful implementations of adaptive learning techniques points at the great versatility of computer‐guided optimization methods. The general approach to active control of light–matter interaction has also applications in many other areas of modern physics and related disciplines.     

<Emphasis Type="Italic">New Ideas and Hypotheses:</Emphasis> Acoustic emission on phase transformations in aqueous medium

Acoustic emission on phase transitions in aqueous medium, including ice melting, was experimentally studied. It was shown that the frequency, time, and other parameters of induced acoustic pulses depend on the nature of the substance and on outer conditions. Acoustic emission in melt water (homogeneous liquid) was reliably detected. This finding shows that acoustic emission can be used to control the technological processes involving metastable substances, and it can prove to be the only suitable technique for such processes.     

Linear Free‐Energy Relationships between a Single Gas‐Phase Ab Initio Equilibrium Bond Length and Experimental pKa Values in Aqueous Solution

Remarkably simple yet effective linear free energy relationships were discovered between a single ab initio computed bond length in the gas phase and experimental pK_a values in aqueous solution. The formation of these relationships is driven by chemical features such as functional groups, meta/para substitution and tautomerism. The high structural content of the ab initio bond length makes a given data set essentially divide itself into high correlation subsets (HCSs). Surprisingly, all molecules in a given high correlation subset share the same conformation in the gas phase. Here we show that accurate pK_a values can be predicted from such HCSs. This is achieved within an accuracy of 0.2 pK_a units for 5 drug molecules.     

Prediction of a phase transition to a hydrogen bond ordered form of ice VI

Ice VI is a hydrogen bond disordered crystal over its known region of stability. In this work, we predict that ice VI will transform into a hydrogen bond ordered phase near 108 K, and have identified the likely low-temperature phase as ferroelectric (space group Cc) with an antiferroelectric structure (space group P2(1)2(1)2(1)) close by in energy. Electronic density functional theory calculations provide input to our calculations, which are extended to cells large enough for statistical simulations by using graph invariants. A significant decrease in the configurational entropy is predicted as hydrogen bonds exhibit partial order above the transition, provided that the hydrogen bonds can equilibrate on an experimental time scale. Conversely, partial disorder is predicted at temperatures below the transition. Although some evidence for ordering of ice VI has been observed in experiments, a low-temperature proton ordered phase has not been identified experimentally.     

Formation of ice-like water structure on the surface of an antifreeze protein

Antifreeze proteins (AFPs) are found in different species from polar, alpine, and subarctic regions where they serve to inhibit ice crystal growth by adsorption to ice surfaces. Computational methods have the power to investigate the antifreeze mechanism in atomic detail. Molecular dynamics simulations of water under different conditions have been carried out to test our water model for simulations of biological macromolecules in extreme conditions: very low temperatures (200 K) and at the ice/liquid water interface. We show that the flexible F3C water model reproduces properties of water in the solid phase (ice I(h)), the supercooled liquid phase, and at the ice/liquid water interface. Additionally, the hydration of the type III AFP from ocean pout was studied as a function of temperature. Hydration waters on the ice-binding surface of the AFP were less distorted and more tetrahedral than elsewhere on the surface. More ice-like hydrating water structures formed on the ice-binding surface of the protein such that it created an ice-like structure in water within its first hydration layer but not beyond, suggesting that this portion of the protein has high affinity for ice surfaces.     

Probing the surfaces of core‐shell and hollow nanoparticles by solvent relaxation NMR

Measurement of the spin–spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core‐shell (titania–silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character.     

Temperature‐controlled liquid–liquid microextraction combined with high‐performance liquid chromatography for the simultaneous determination of diazinon and fenitrothion in water and fruit juice samples

A simple, environmentally benign, and rapid method based on temperature‐controlled liquid–liquid microextraction using a deep eutectic solvent was developed for the simultaneous extraction/preconcentration of diazinon and fenitrothion. The method involved the addition of deep eutectic solvent to the aqueous sample followed by heating the mixture in a 75°C water bath until the solvent was completely dissolved in the aqueous phase. Then, the resultant solution was cooled in an ice bath and a cloudy solution was formed. Afterward, the mixture was centrifuged and the enriched deep eutectic solvent phase was analyzed by high‐performance liquid chromatography with ultraviolet detection for quantification of the analytes. The factors affecting the extraction efficiency were optimized. Under the optimized extraction conditions, the limits of detection for diazinon and fenitrothion were 0.3 and 0.15 μg/L, respectively. The calibration curves for diazinon and fenitrothion exhibited linearity in the concentration range of 1–100 and 0.5–100 μg/L, respectively. The relative standard deviations for five replicate measurements at 10.0 μg/L level of analytes were less than 2.8 and 4.5% for intra‐ and interday assays, respectively. The developed method was successfully applied to the determination of diazinon and fenitrothion in water and fruit juice samples.     

Ionophore extrem hoher Lipophilie als selektive Komponenten für Flüssigmembranelektroden

Selective ionophores of extreme lipophilicity for liquid membrane electrodes Lipophilic ionophores of the type diether diamides have been prepared. Their lipophilicity is up to 7 orders of magnitude higher than the one of the most lipophilic ion carriers used as selective components in liquid membrane electrodes reported so far. For such ion carriers of extremely high lipophilicity kinetic limitations of the carrier induced ion transfer between aqueous and membrane phase usually dominate and heavily disturb the electromotive behavior of the membrane electrode. These limitations are absent only in those cases where most of the lipophilic segments of the carrier may remain in the membrane phase while the segments with the coordination sites are exposed to the aqueous phase during the transfer process.     

Aggregation of methylene blue in frozen aqueous solutions studied by absorption spectroscopy

The paper presents a qualitative as well as quantitative spectroscopic study of methylene blue (MB) aggregation that occurs upon freezing the aqueous solutions over a wide concentration range. The Gaussian curve analysis and the multivariate curve resolution-alternating least squares method were used to determine the number and concentration of chemical species responsible for the overlaying absorption visible spectra measured. The results show the extent of aggregation for the concentrations above 10(-7) mol L(-1), being dependent on the freezing rate and the initial concentration. While the local concentration of MB at the grain boundaries of polycrystalline ice increased by approximately 3 orders of magnitude upon fast freezing at 77 K compared to the liquid phase, the concentration raised at least by 6 orders of magnitude upon slow freezing at 243 K. Since enhancement of the local concentration of solutes plays an important role in (photo)chemical transformations in solid aqueous media, this work helps to understand how the initial conditions control the course of the process. The results are relevant in other interdisciplinary fields, such as environmental chemistry, cosmochemistry, or geochemistry.     

Electric‐Field Triggered Controlled Release of Bioactive Volatiles from Imine‐Based Liquid Crystalline Phases

Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N‐(4‐methoxybenzylidene)‐4‐butylaniline (MBBA, 1 ), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine‐based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal.     

Inhibition of solute crystallisation in aqueous H(+)-NH(4)(+)-SO4(2-)-H2O droplets

Ice clouds in the Earth's upper troposphere can form via homogeneous nucleation of ice in aqueous droplets. In this study we investigate the crystallisation, or lack of crystallisation, of the solute phase and ice in aqueous (NH(4))(3)H(SO(4))(2)/H(2)O and NH(4)HSO(4)/H(2)O droplets. This is done using in situ X-ray diffraction of emulsified solution droplets mounted on a cold stage. From the diffraction patterns we are able to identify the phases of crystalline solute and ice that form after homogeneous freezing in micrometer sized droplets. An important finding from this study is that crystallisation of the solute does not always occur, even when crystallisation is strongly thermodynamically favoured. The nucleation and growth of solute phase crystals becomes inhibited since the viscosity of the aqueous brine most likely increases dramatically as the brine concentration increases and temperature decreases. If ice nucleates below a threshold freezing temperature, the brine appears to rapidly become so viscous that solute crystallisation is inhibited. This threshold temperature is 192 K and 180 K, in (NH(4))(3)H(SO(4))(2) and NH(4)HSO(4), respectively. We also speculate that the formation of cubic ice within a highly viscous brine blocks the solvent mediated cubic to hexagonal phase transformation, thus stabilising the metastable cubic ice in the most concentrated solution droplets.