Hydration dynamic measurements

With site-directed mutation and femtosecond-resolved fluorescence methods, we have used tryptophan as an excellent local molecular reporter for studies of a series of ultrafast protein dynamics, which include intraprotein electron transfer [64-68] and energy transfer [61, 69], as well as protein hydration dynamics [70-74]. As an optical probe, all these ultrafast measurements require no potential quenching of excited-state tryptophan by neighboring protein residues or peptide bonds on the picosecond time scale. However, it is known that tryptophan fluorescence is readily quenched by various amino acid residues [75] and peptide bonds [76-78]. Intraprotein electron transfer from excited indole moiety to nearby electrophilic residue(s) was proposed to be the quenching... 

The following paragraphs compare thermodynamic studies of hydration with other static measurements infrared, NMR, and x-ray diffraction. Dynamic measurements are considered in the next section. 

Comments. Dynamic properties show changes at hydration levels above 0.4 h, the point of completion of the changes in static properties. Because the later reflect a monolayer of water about the protein, the additional water seen in the dynamic measurements is "multi-layer" water. Furthermore, hydration affects the several rate properties differently. The more complex hydration dependence of dynamic compared with static properties is to be expected. Static properties, at least the thermodynamic, have a single molecular basis. In contrast, the various transition states governing the rate processes are necessarily different. 

A developing approach measures by NMR the local hydration dynamics around nitroxides at room temperature via Overhauser d3mamic nuclear polarization (DNP). 

An important dynamic measure of a hydration layer is provided by its survival correlation time, which is defined in the following way. First, we make a list of all the molecules present in the layer at the initial time. We can now proceed in two ways. First, we can assign decay to the hydration layer whenever any single water molecule leaves or enters the layer. We then average over all the molecules in the layer. Let us denote this fimction by Ssif). This can be defined in the following way... 

Lanthanum is the first element of the sixth-period transition metals. Its properties are close to those of the other rare earth elements and, as a consequence, the catalytic behavior of the lanthanum triflate is also very close to that of the entire series. An important example concerning the stability of these compounds in water is that indicating the capability of metal triflates, such as Yb(OTf)3, Eu(OTf)3, Sc(OTf)3 or La(OTf)3, to catalyze the hydration of alkynes to the corresponding ketones [56]. However, the interest in water-compatible lanthanide triflate-based catalysts is much larger and mainly includes the carbon-carbon bond-forming reactions. To increase the utility of these catalysts understanding of their aqueous mechanism is very important. For such a purpose, dynamic measurements of the water... 

There are several thermodynamic properties that are very useful for investigating solute-water interactions in aqueous solution. The partial molar compressibility of the solute is one such property. This quantity is particularly sensitive to the nature and extent of the intermolecular interactions between the solute and the solvent [74M, 94C1] and, as such, can be used to characterize the hydration of solutes in aqueous solution. The importance of compressibility measurements as a means to characterize the hydration of proteins and their constituent groups has been recognized and as a consequence of this, new results on biological compounds have been reported in recent years. In addition to this emphasis on hydration, compressibility measurements of proteins in aqueous solution are also of some importance in the study of the dynamics of globular proteins since the volume fluctuation of a protein is related to its isothermal coefficient of compressibility [76C],... 

Sodium octanoate (NaO) forms reversed micelles not only in hydrocarbons but also in 1-hexanol/water. The hydration of the ionogenic NaO headgroups plays an important role in this case too. For this reason Fujii et al. 64) studied the dynamic behaviour of these headgroups and the influence of hydration-water with l3C and 23Na NMR measurements. Below w0 = [H20]/[NaO] 6 the 23Na line-width... 

The main goal of the molecular dynamics computer simulation of ionic solvation and adsorption on a metal surface has been to test the above model and to provide more quantitative information about the different factors that influence the structure of hydrated ions at the interface. Unfortunately, most of the experimental information about these issues has been obtained from indirect measurements such as capacity and current-potential plots, although in recent years in situ experimental techniques have begun to provide an accurate test of the above model. For a recent review of experimental techniques and the theory of ionic adsorption at the water/metal interface, see the excellent paper by Philpott. ... 

Bo is the measurement frequency. Rapid exchange between the different fractions is assumed the bulk, water at the protein surface (s) and interior water molecules, buried in the protein and responsible for dispersion (i). In fact, protons from the protein surface exchanging with water lead to dispersion as well and should fall into this category Bulk and s are relevant to extreme narrowing conditions and cannot be separated unless additional data or estimations are available (for instance, an estimation of fg from some knowledge of the protein surface). As far as quadrupolar nuclei are concerned (i.e., and O), dispersion of Rj is relevant of Eqs. (62) and (63) (this evolves according to a Lorentzian function as in Fig. 9) and yield information about the number of water molecules inside the protein and about the protein dynamics (sensed by the buried water molecules). Two important points must be noted about Eqs. (62) and (63). First, the effective correlation time Tc is composed of the protein rotational correlation time and of the residence time iw at the hydration site so that... 

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