Interfacial hydration

The NMR study by Wiithrich and coworkers has shown that there is a cavity between the protein and the DNA in the major groove of the Antennapedia complex. There are several water molecules in this cavity with a residence time with respect to exchange with bulk water in the millisecond to nanosecond range. These observations indicate that at least some of the specific protein-DNA interactions are short-lived and mediated by water molecules. In particular, the interactions between DNA and the highly conserved Gin 50 and the invariant Asn 51 are best rationalized as a fluctuating network of weak-bonding interactions involving interfacial hydration water molecules. 

The increased interfacial hydration in the presence of emulsifiers gives rise to a slight increase in the particle size of the fat globules in the ice cream mix (Figure 15). The volume of cream layers after centrifugation also increases up to 100% when lowering the temperature... 

The increased interfacial hydration at 5°C gives rise to an increased mix viscosity as described below. 

The properties of the water phase in whippable emulsions are important for product stability. The water phase is influenced by the soluble components of the systems, i.e., sugars, proteins and hydrocolloids. Interfacial hydration may also influence the properties of the water phase, particularly in high-fat systems. 

Figure 24 Viscosity of ice cream mix with different hydrocolloid types determined by the pipette method (flow time in seconds). Relation to interfacial hydration of fat globules (%H20).

When all hydrate cavities are filled, the three crystal types (I, n, and H) have remarkably high and similar concentrations of components 85 mol % water and 15 mol % guest(s). Hydrate formation is most probable at the interface of the bulk guest and aqueous phases because the hydrate component concentrations greatly exceed the mutual fluid solubilities. The solid hydrate film at the interface acts as a barrier to further contact of the bulk fluid phases, and fluid interface renewal is required for continued, rapid clathrate formation. Three phase interfacial hydrate formation occurs with equilibrium of gas, liquid, and hydrate phases in artificial situations such as laboratories or in man-made processes. 

Giovambattista, N., Rossky, P. J., and Debenedetti, P. G., 2007. Effect of Surface Polarity on Water Contact Angle and Interfacial Hydration Structure. J. Phys. Chem. 5111 9581. 

N. Giovambattista, P. G. Debenedetti and P. J. Rossky, Effect of surface polarity on water contact angle and interfacial hydration structure. /. Phys. Chem. B 111,9581-9587 (2007). 

Extensive theory and computer simulation work has been able to clarify the molecular mechanisms of solvation dynamics in bulk liquids over the past three decades.One of the most important conclusions from this body of work is that most of the contribution to polar solvation dynamics comes from the solute s first solvation shell. This conclusion and the earlier discussion about the prominent role the solute hydration shell plays in understanding vibrational and rotational dynamics at liquid interfaces suggest that surface effects on solvation dynamics will be muted as the solute s polarity is increased. An experimental validation of this are the similar solvation dynamics of C314 at the water liquid/vapor interface and in bulk water, mentioned above, where the highly polar excited state n = 12D) implicates an interfacial hydration structure similar to the bulk. 

F. Uhlig, J. M. Herbert, M. P. Coons, and P. Jungwirth,/. Phys. Chem. A, 118, 7507-7515 (2014). Optical Spectroscopy of the Bulk and Interfacial Hydrated Electron from ab Initio Calculations. 

Ganglioside Gmi at a concentration of 5 mol% stabilizes liposomes composed of a mixtiue of DOPE and transphosphatidylated-PE (TPE) [101], but Gm2, which differs from Gmi by lacking one galactose residue at the terminal position, does not make it stable at 5 mol%. Rapid lysis occms when Gmi-stabilized liposomes are treated with j8-galactosidase, an enzyme that converts Gmi to Gm2- Palmitoyl-immunoglubulin G (p-IgG) also stabilizes DOPE bilayers, where the hydrophilic Fab portion of a derivative antibody increases the interfacial hydration and, further, prevents interbilayer contact [115,117,118]. These PE immunoliposomes could be lysed by treatment with... 

Van Oss and Good [148] have compared solubilities and interfacial tensions for a series of alcohols and their corresponding hydrocarbons to determine the free energy of hydration of the hydroxyl group they find -14 kJ/mol per —OH group. 

Rapid e / h recombination, the reverse of equation 3, necessitates that D andM be pre-adsorbed prior to light excitation of the Ti02 photocatalyst. In the case of a hydrated and hydroxylated Ti02 anatase surface, hole trapping by interfacial electron transfer occurs via equation 6 to give surface-bound OH radicals (43,44). The necessity for pre-adsorbed D andM for efficient charge carrier trapping calls attention to the importance of adsorption—desorption equihbria in... 

Figure 5 Electron density distributions along the bilayer normal from an MD simulation of a fully hydrated liquid crystalline phase DPPC bilayer. (a) Total, lipid, and water contributions (b) contributions of lipid components in the interfacial region.

At each interface the interfacial potential will depend upon the chemical potentials of the species involved in the equilibrium. Thus at the Zn/Zn electrode there will be a tendency for zinc ions in the lattice to lose electrons and to pass across the interface and form hydrated ions in solution this tendency is given by the chemical potential of zinc which for pure zinc will be a constant. Similarly, there will be a tendency for hydrated Zn ions in solution to lose their hydration sheaths, to gain electrons and to enter the lattice of the metal this tendency is given by the chemical potential of the Zn ions, which is related to their activity. (See equation 20.155.) Thermodynamically... 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

It should be emphasized that the ester carbonyl group in the interfacial zone II is most crucial and susceptible to the anesthetic action of the drugs. In our NMR study, we have found that the ester carbonyl site in zone II is particularly susceptible to the extent of hydration [51]. Above the G/LC transition temperature, the carbonyl is the innermost site where the water can penetrate. The strong perturbation of the NMR signal of the... 

Alkali 10ns in aqueous solution are probably the most typical and most widely studied representatives of non-specific adsorption. The electrochemical term of non-specific adsorption is used to denote the survival of at least the primary hydration shell when an ion is interacting with a solid electrode. As pointed out previously, the generation of such hydrated ions at the gas-solid interface would be of great value because it would provide an opportunity to simulate the charging of the interfacial capacitor at the outer Helmholtz plane or perhaps even in the diffuse layer. 

---