Sonolysis of high macroviscosity systems: hen albumen hydrogel.

To understand molecular effects of ultrasound on protein gels (cross-linked, hydrated macromolecular systems of immeasurably high macroviscosity, but low microviscosity), the thick fraction of hen albumen was sonicated. The immeasurably high viscosity of the intact thick fraction decreased to 2.5-4.

Effects of microviscosity, dry electron scavenging, and protein mobility on the radiolysis of albumen hydrogel.

Nanosecond pulse radiolysis experiments performed on the oxygen and nitrogen saturated thick fraction of egg white (which has an immeasurably high macroviscosity) produced a rate constant for hydrated electron reaction with oxygen equal to 1.7 × 10(10) M(-1) s(-1) at 18 °C, indicating that, due to the very low microviscosity, hydrated electrons are as mobile and reactive in the albumen hydrogel as in neat water. Also, the radiolytic yield for the hydrated electron (G-value) in the thick fraction of egg white (measured at the end of a 14 ns electron pulse) was found to be 86% of that determined in neat water, which can be attributed to the reaction of dry electrons with the protein constituents.

Mobility of molecules and ions solubilized in protein gels: diffusion in the thick fraction of hen egg white.

The thick fraction of hen egg white is a protein hydrogel with an immeasurably high viscosity composed of ∼90% water that can serve as a model system for mammalian mucous membrane. Measurements of the rate constants of diffusion-controlled reactions occurring within the gel (and corresponding activation energies) and electric conductivity revealed that the thick fraction of egg white can be envisioned as a 3D network comprising hydrated protein molecules (held by intermolecular S-S bridges) surrounded by water pools and channels (of nonuniform diameters) that have a microviscosity that is very similar to that of bulk water. This was corroborated by differential scanning calorimetry measurements that revealed that 16% of water is bound to proteins.

Macro- and microscale rheological properties of poly(vinyl alcohol) aqueous solutions.

Electric conductivity measurements indicated that microviscosities of poly(vinyl alcohol), PVA, solutions [up to 10% (w/w)] are comparable to that of pure water (contrary to Walden's rule), but are different (25%) from those determined from diffusion-controlled reaction measurements that coincide with the values obtained using pure water. Energies of activation of fluidity of PVA solutions are found to increase with PVA concentration, whereas those of the diffusion-controlled reactions are independent of PVA concentration. By comparing the macro- and microviscosities, it was concluded that PVA aqueous solutions can be envisioned as dynamic systems comprising hydrated PVA molecules (that affect the macroviscosity) and "interconnected water pools" (located between macromolecules), the rheological properties of which are very similar to that of pure water.

Analysis and improvement of rate constant determination of reactions involving charged reactants.

Kinetics of tris(2,2'-bipyridine)ruthenium(ii), Ru(bpy)(3)(2+), luminescence quenching by copper(ii) (in the form of chloride, nitrate, sulfate and perchlorate salt) was studied using pulse laser photolysis technique. The pseudo-first order rate constant versus quencher concentration plots obtained were found to be nonlinear, bending upward. The ionic strength effect contribution was evaluated by applying the Debye-Hückel extended law and was found to be as important as other effects such as cation-counter anion complex and ion-pairing complex formation which were all found to be dependent on the counter anion.

Molecular perspective of antigen-mediated mast cell signaling.

Antigen-mediated cross-linking of the high affinity receptor for IgE (Fc epsilon RI), in the plasma membrane of mast cells, is the first step in the allergic immune response. This event triggers the phosphorylation of specific tyrosines in the cytoplasmic segments of the beta and gamma subunits of Fc epsilon RI by the Src tyrosine kinase Lyn, which is anchored to the inner leaflet of the plasma membrane. Lyn-induced phosphorylation of Fc epsilon RI occurs in a cholesterol-dependent manner, leading to the hypothesis that cholesterol-rich domains, or "lipid rafts," may act as functional platforms for IgE receptor signaling.