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On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists - with their expertise in macrocyclic synthesis and measuring supramolecular interactions - have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists - with their expertise in macrocyclic synthesis and measuring supramolecular interactions - have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

Hydrophobic hydration, whereby water spontaneously structures around hydrophobic and amphiphilic molecules, plays a key role in the process of surfactant micelle formation and micellar oil solubilization. Using vibrational Raman multivariate curve resolution spectroscopy, we characterized changes in the hydrophobic hydration occurring within nonionic alkylphenol ethoxylate surfactant Tergitol NP‐12 micelles as a function of oil solubilization. We report trends in the changes of hydrophobic hydration depending on the chain length of the oil as well as the presence of a halogen atom in the oil chemical structure. Changes in hydrophobic hydration directly correlate to changes in the physical properties of the micellar solution, including cloud point and micelle hydrodynamic diameter. We compare hydrophobic hydration of Tergitol NP‐12 to nonionic linear alkyl ethoxylate surfactant Makon TD‐12 and ionic sodium dodecyl sulfate and observe similar trends; the molecular structure of the oil has the largest impact on the hydrophobic hydration. We believe these studies contribute to a fundamental understanding of the importance of hydrophobic hydration in surfactant and oil aggregates, especially as it relates to micellar oil solubilization, and provide insight into how the molecular solubilizate can impact micellar structure, size, and stability. [ABSTRACT FROM AUTHOR]

Byline: Yanjie Zhang; Paul S. Cremer, Department of Chemistry, Texas A&M University, College Station, Texas 77843; email: cremer@mail.chem.tamu.edu Keywords: hydrophobic collapse, lower critical solution temperature (LCST), liquid-liquid phase separation, vibrational sum frequency spectroscopy (VSFS), urea, protein denaturation Abstract The study of the interactions of salts and osmolytes with macromolecules in aqueous solution originated with experiments concerning protein precipitation more than 100 years ago. Today, these solutes are known to display recurring behavior for myriad biological and chemical processes. Such behavior depends both on the nature and concentration of the species in solution. Despite the generality of these effects, our understanding of the molecular-level details of ion and osmolyte specificity is still quite limited. Here, we review recent studies of the interactions between anions and urea with model macromolecular systems. A mechanism for specific ion effects is elucidated for aqueous systems containing charged and uncharged polymers, polypeptides, and proteins. The results clearly show that the effects of the anions are local and involve direct interactions with macromolecules and their first hydration shell. Also, a hydrogen-bonding mechanism is tested for the urea denaturation of proteins with some of these same systems. In that case, direct hydrogen bonding can be largely discounted as the key mechanism for urea stabilization of uncollapsed and/or unfolded structures.

Laser desorption/ionization (LDI) using silver nanoparticles (AgNPs) is shown to selectively ionize olefinic compounds, e.g., cholesterol, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and carotenoids. Selective AgNP LDI can be carried out from complex mixtures without the addition of an organic matrix, sample cleanup, or prefractionation. Results presented in this report are the first to demonstrate the selective ionization of specific compounds from a complex mixture using metal nanoparticles.

A method has been designed for patterning supported phospholipid bilayers (SLBs) on planar substrates and inside microfluidic channels. To do this, bovine serum albumin (BSA) monolayers were formed via adsorption at the liquid/solid interface. Next, this interfacial protein film was selectively patterned by using deep IN lithography. Subsequently, SLBs could be deposited in the patterned locations by vesicle fusion. By cycling through this process several times, spatially addressed bilayer arrays could be formed with intervening protein molecules serving as two-dimensional corrals. By employing this method, phospholipid bilayers containing various concentrations of ganglioside GM1 were addressed along the length of individual microfluidic channels. Therefore, the binding of GM 1 with pentameric cholera toxin B (CTB) subunits could be probed. A seven-channel microfluidic device was fabricated for this purpose. Each channel was simultaneously patterned with four chemically distinct SLBs containing 0, 0.2, 0.5, and 2.0 mol % GM1, respectively. Varying concentrations of CrB were then introduced into each of the channels. With the use of total internal reflection fluorescence microscopy, it was possible to simultaneously abstract multiple equilibrium dissociation constants as a function of ligand density for the CTB-GM1 system in a single shot.

The orientation of the isopropyl group at the liquid/vapor interface in 2-propanol/water binary mixtures was studied by vibrational sum frequency spectroscopy. The results indicated that the methyl groups lay down on the surface at low alcohol mole fraction and gradually twisted with increasing mole fraction.

Herein we demonstrate the ability to pattern Ag nanoparticle films of arbitrary geometry inside sealed PDMS/ Ti[O.sub.2]/glass microfluidic devices. The technique can be employed with aqueous solutions at room temperature under mild conditions. A 6 nm Ti[O.sub.2] film is first deposited onto a planar Pyrex or silica substrate, which is subsequently bonded to a PDMS mold. UV light is then exposed through the device to reduce [Ag.sup.+] from an aqueous solution to create a monolayer-thick film of Ag nanoparticles. We demonstrate that this on-chip deposition method can be exploited in a parallel fashion to synthesize nanoparticles of varying size by independently controlling the solution conditions in each microchannel in which the film is formed. The film morphology was checked by atomic force microscopy, and the results showed that the size of the nanoparticles was sensitive to solution pH. Additionally, we illustrate the ability to biofunctionalize these films with ligands for protein capture. The results indicated that this could be done with good discrimination between addressed locations and background. The technique appears to be quite general, and films of Pd, Cu, and Au could also be patterned.

We have developed a general method for photopatterning well-defined patches of enzymes inside a microfluidic device at any location. First, a passivating protein layer was adsorbed to the walls and floor of a poly(dimethylsiloxane)/glass microchannel. The channel was then filled with an aqueous biotin-linked dye solution. Using an [Ar.sup.+]/ [Kr.sup.+] laser, the fluorophore moieties were bleached to create highly reactive species. These activated molecules subsequently attached themselves to the adsorbed proteins on the microchannel walls and floor via a singlet oxygen-dependent mechanism. Enzymes linked to streptavidin or avidin could then be immobilized via (strept)avidin/biotin binding. Using this process, we were able to pattern multiple patches of streptavidin-linked alkaline phosphatase inside a straight microfluidic channel without the use of valves under exclusively aqueous conditions. The density of alkaline phosphatase in the patches was calculated to be ~5% of the maximum possible density by comparison with known standards. Turnover was observed via fluorogenic substrate conversion and fluorescence microscopy. A more complex two-step enzyme reaction was also designed. In this case, avidin-linked glucose oxidase and streptavidin-linked horseradish peroxidase were sequentially patterned in separate patches inside straight microfluidic channels. Product formed at the glucose oxidase patch became the substrate for horseradish peroxidase, patterned downstream, where fluorogenic substrate turnover was recorded.

The kinetics of formation of the aqueous two-phase system (ATPS) for alpha-elastin is studied by dark field microscopy in an on-chip linear temperature gradient. The formation rate of the ATPS could be fit as a first-order process and the apparent rate constant increased with protein concentration.

The independent generation of 5-(2'deoxycytidinyl)methyl radical and that this radical can give rise to the predicted novel intrastrand cross-link lesion in dinucleoside monophosphates of d(mCG) and D(GmC) is reported. The 5-(2'-deoxycytidinyl)methyl radical can be specifically generated by 254-nm irradiation of 5-(phenyl-thiomethyl)-2'-deoxycytidine in dinucleoside monophosphates d(mCSPLG) and D(GmCSPL).

A study which gives important insight into the electronic effects of alpha-helix dipoles in enzymes and provides experimentally based observations that have not been previously characterized in protein structure is reported. The study indicates that in a protein structure the ionic nature of a planar amide proposed by Wiberg appears to be a superior model than the resonance model historically used to describe a planar peptide group.

Vibrational sum frequency spectroscopy (VSFS), immunochemical assays and kinetic experiments for the human plasma fibrinogen (HPF) displacement mechanism is explained by employing a combination of techniques including atomic force microscopy. Results disclose that HPF can be readily displaced from the interface by other plasma proteins near neutral pH because the postively charged alpha C domains on HPF sit between the rest of the macromolecule and the underlying surface.

Investigations of ligand-receptor binding bivalent antibodies and membrane-bound ligands are presented. The purpose of the investigations is to explore binding as a function of Hapten density in a two-dimensionally fluid environment.

Sum frequency spectra of gramicidin A at the air/water interface in partially deuterated dimyristoylphosphatildycholine monolayers are collected as a function of surface pressure and mole fraction of the peptide. When the membrane peptide was added to the monolayer, changes in its orientation were noted at mole fractions below 0.5.

This paper describes a reusable platform that can apply a linear temperature gradient to a lab-on-a-chip device. When a planar microfluidic device with a series of micro-channels is placed on top of the platform with the channels perpendicular to the gradient, each channel is held at a discrete temperature. This allows temperature-dependent data for chemical or biochemical species flowed into the device to be obtained in a concurrent fashion. As a demonstration, a melting curve for dsDNA is performed by collecting all the data simultaneously. The gradient is stable enough to easily distinguish between 30-mers where the complement strand contains a single C--A mismatch or a single T--G mismatch or is a perfect match. On the other hand, a temperature gradient can be formed parallel to the direction of flow of the microchannels. This allows the temperature in each channel to vary continuously as the liquid flows downstream, If each microchannel in the array contains a distinct pH value, ionic strength, species concentration, or chemical composition, then a high-throughput two-variable experiment can be performed. We demonstrate this mode of data collection by measuring the fluorescence yield of fluorescein dye molecules in aqueous solution simultaneously as a function of concentration and temperature.

IR-visible sum frequency spectroscopy (SFS) was employed to investigate the molecular level details of the adsorption of the positively charged polyelectrolyte, polydiallyldimethylammonium chloride (PDDA) at the quartz/water interface. The behavior of PDDA at the quartz/water interface as a function of pH and ionic strength were explored.

Research has been conducted on the methods for combinatorial and array-based data obtaining. The microfluidics used in generating a linear temperature gradient across various samples which can be read off as a position function are discussed.

Herein we report the fabrication, characterization, and use of total analytical microsystems containing surface-immobilized enzymes. Streptavidin-conjugated alkaline phosphatase was linked to biotinylated phospholipid bilayers coated inside poly(dimethylsiloxane) microchannels and borosilicate microcapillary tubes. Rapid determination of enzyme kinetics at many different substrate concentrations was made possible by carrying out laminar flow-controlled dilution on-chip. This allowed Lineweaver--Burk analysis to be performed from a single experiment with all the data collected simultaneously. The results revealed an enzyme turnover number of 51.1 [+ or -] 3.2 [s.sup.-1] for this heterogeneous system. Furthermore, the same enzyme immobilization strategy was extended to demonstrate that multiple chemical reactions could be performed in sequence by immobilizing various enzymes in series. Specifically, the presence of glucose was detected by two coupled steps employing immobilized avidinD-conjugated glucose oxidase and streptavidin-conjugated horseradish peroxidase.

Author(s): Hagan Bayley (corresponding author) [1, 2, 3]; Paul S. Cremer [2, 3] Channels and pores that respond directly to molecules or to physical stimuli are found within sensory systems. [...]