Conformational changes in aqueous

Similarly mono-(o-hydroxyphenyl)triphenylporphyrin (65) was covalently attached to a cyclodextrin unit, in the hope of preparing a water-soluble oxygen carrying model While 123 did not display the desired properties, guest inclusion in the cyclodextrin moiety appears to induce novel conformational changes in aqueous solutions. 

Polyelectrolyte Samples and Their Conformational Changes in Aqueous Solutions... 

Hydration of a neutral polymer can roughly be classified into two categories direct hydrogen bonds (referred to as H-bonds) between a polymer chain and water molecules (p-w), and the hydrophobic hydration of water molecules surrounding a hydrophobic group on a chain in a cage structure by water-water (w-w) H-bonds. In this section, we extend the combinatorial method for the partition function presented in the previous section to suit for the problem of solvent adsorption, and study polymer conformation change in aqueous solutions due to the direct p-w H-bonds. 

Interestingly, the conformational change in aqueous media does not go along with swelling phenomena which was shown by molecular dynamic simulations at low pH PAMAM forms a very dense shell, while at high pH it has a rather dense core. 

It is helpful to know the chemistry of fixatives in order to understand their action and avoid artifacts (4). Most commonly studied antigens are either proteins or carbohydrates. Many of these molecules are soluble in aqueous solutions and need to be fixed in place in cells. Insoluble antigens also need to be structurally preserved (/). All chemical fixatives will cause chemical and conformational changes in the protein structure of cells with lesser changes noted for carbohydrate antigens (5). Secondary and tertiary structures of proteins are the most important for eliciting antigenicity and chemical fixatives usually disturb these conformations (3). 

Water binding varies with the number and type of polar groups (5 ). Other factors that affect the mechanism of protein-water interactions include protein conformation and environmental factors that affect protein polarity and/or conformation. Conformational changes in the protein molecules can affect the nature and availability of the hydration sites. Transition from globular to random coil conformation may expose previously buried amino acid side chains, thereby making them available to interact with aqueous medium. Consequently, an unfolded conformation may permit the protein to bind more water than was possible in the globular form ( ). 

Glatzhofer et al.1281 describe the reduction of conductivity of polypyrrole films, doped with poly(styrene-p-sulfonate), as increasing concentrations of dioxane are added to the aqueous electrolyte. They claim that the solvent induces a conformational change in the counterion, which modifies the film morphology. 

The arrangement of the proteins within the membrane seems to depend to some extent on the electrostatic surface potential and interface permittivity. It is influenced by electrostatic interaction between the proteins, polar head groups of the phospholipid and ions within the aqueous medium of the membrane surface. This can be affected by exogenous molecules such as drugs. Phospholipid-induced conformational change in intestinal calcium-binding protein in the absence and presence of Ca2+ has been described [37]. There is, however, no doubt that hydrophobic interactions between peptides and membrane interfaces play an important role. A general frame-... 

In aqueous solution of the system PMAA-PVPo, AHM is positive and its absolute value is 1.4 kcal/mol. Assuming that the heat of conformational change in the complex formation is the same as that of PMAA in aqueous solution (obtained as heat of dilution), namely -0.6 kcal/mol, we obtain... 

Similar experiments were performed in different dioxane concentrations ranging from 60% to 100% v/v. No reaction was observed in pure dioxane or in dioxane supplemented with 1% aqueous buffer. All peroxidase reactions in dioxane concentrations below 95% v/v obeyed Michaelis-Menten kinetics (Fig. 3). The values of apparent Km and kcat are plotted in Figures 4 and 5, respectively. The maximum value of Km at 80% dioxane remains poorly understood. It is possible that the enzyme undergoes a conformational change in dioxane concentrations above 80% which enhances the binding of the p-cresol (and hence a drop in apparent values of Km above this concentration of dioxane). The significant drop in kcat above 80% dioxane is consistent with this speculation as conformational changes in the peroxidase would almost surely lead to diminished catalytic activity. 

The studies summarized in this section have proved particularly valuable, because they were conducted in (mostly aqueous) solution, enabling comparison with X-ray or neutron diffraction studies, for which crystalline material must be used. Although the conformation of a crystalline protein can be essentially the same as that in aqueous solution, it is not necessarily correct to make this assumption, since there may be large conformational changes in such solution, contingent on the variables of protein concentration, pH, ionic strength, and temperature. 

The direct simulation of the aqueous binding process is difficult because changes in solvation/desolvation that accompany association are slow and hard to sample, especially when hydrogen bonding patterns are coupled to conformational changes in the protein, or for recessed binding sites, where the associating substrate may hinder solvent escape. Another important kinetic factor is the differential stabilization (by enzyme vs. solvent) of the transition state of the... 

In many cases, soaking a compound into a crystal is not possible because of low solubility of the compound in the aqueous mother liquor. Soaking experiments can also be limited when the conformational space of the binding site is hindered, occupied by adjacent molecules in the crystal lattice, or if there are conformational changes in the binding site because of crystal packing effects. On the other hand, co-erystallization of the protein and li-... 

Titration data for wool have been available for more than two decades (Speakman and Stott, 1934 Steinhardt and Harris, 1940a,b) and have been the subject of various quantitative theoretical treatments and extensive controversy. Other more qualitative theories have been proposed to account for the effects of salts on chemical and conformational changes in animal fibers immersed in aqueous eIectrol3des. 

---