Water-binding sites

The previous calculation assumed that the solvation energy of ammonium was equal the solvation energy of a single water molecule times the number of water binding sites. Is this a valid assumption Compare the electrostatic potential maps of ammonium ion and ammonium ion+water. For which are the exposed hydrogens more acidic Did the calculation underestimate or overestimate the difference in solvation energies ... 

The authors offer a single sentence to explain the result RAMEB decreases the number of water-binding sites available in clay-rich soils. The authors offer this... 

The change in structure along the lanthanide series, going from La3+ to Lu3+, can be ascribed to the decrease in ionic radius of the metal center which causes an increase of the rigidity and in the steric constraint on the water binding site [35,36]. For this reason the 9-coordinate Gd complex shows a remarkably high water exchange rate. 

Fig. 4. Effect of protein binding on the water binding site, (a) The hydrophobic side chain of the ligand, bound to the protein is far from the Gd(III) chelate, thus protein binding does not influence water exchange, (b) The Gd(III) chelate is bound to the protein via electrostatic forces. The water binding site of the complex is partially blocked by the protein, thus the water exchange rate is diminished...

Rapatskiy L, Cox N, Ames W, et al. Detection of the water binding sites of the oxygen-evolving complex of photosystem II using W-band 170 ELDOR-detected NMR spectroscopy. J Am Chem Soc 2011 Epub date August 31, 2012. 

It is interesting to compare the hydration structure obtained by the 3D-RISM theory with crystallographic water sites of X-ray structure [30]. The crystallographic water molecules in the cavity are depicted in the right of Fig. 10.3, showing four water sites in the cavity, much as the 3D-RISM theory has detected. Moreover, the water distributions obtained from the theory and experiment are quite similar to each other. Thus the 3D-RISM theory can predict the water-binding sites with great success. 

It should be noted that one peak of the 3D-distribution function does not necessarily correspond to one molecule. If a water molecule transfers back and forth between two sites in the equilibrium state, two peaks correspondingly appear in the 3D-distribution function. In fact, the number of water molecules within the cavity calculated from the 3D-distribution function is 3.6. It is less than the number of water-binding sites and includes decimal fractions. To explain that, we carried out molecular dynamics (MD) simulation using the same parameters and under the same thermodynamic conditions as... 

An alternative approach to increasing k x is to modify the structure of the chelates. Complexes with a more steric water binding site or an increase in the basicity of the cyclic nitrogen on DOTA have a fast water exchange in 7d [39, 40]. The water exchange rate can be assessed by NMR, which measures the transverse relaxation rate of water both with and without Gd complexes. 

Ruloff, R., Toth, E., Scopelliti, R., et al. (2002) Accelerating water exchange for Gdlll chelates by steric compression around the water binding site. Chemical Communications, 2630-2631. 

If of Equation 3 is plotted against c, it is found that decreases hyperbolically with increasing c. On the other hand, Qp obeys the Langmuir-type adsorption formula, expressed by Equation 1. In a monomolecular layer of adsorbed protein, it may be assumed that the total number, N, of adsorptive sites on a material surface is constant, as indicated in Equation 4, and that the adsorbed protein molecules contribute n water-binding sites. 

The relaxometric measurement was determined at 10.1 and 18.6 s mM for dendrimer Gd-295e and G4, respectively (Table 2). Measurement of the relaxivity depended on the pH and was increased by a factor of 1.3 when the core amino group is protonated (14.8 and 25.8). The water residence life time was also increased from 16 ns for Gd-295b to 68 ns for G4 as the molecular size of the conjugate increased. It also appeared that the conjugation did not affect the water binding site. Their properties make them suitable for MRI. 

Korb el al. proposed a model for dynamics of water molecules at protein interfaces, characterized by the occurrence of variable-strength water binding sites. They used extreme-value statistics of rare events, which led to a Pareto distribution of the reorientational correlation times and a power law in the Larmor frequency for spin-lattice relaxation in D2O at low magnetic fields. The method was applied to the analysis of multiple-field relaxation measurements on D2O in cross-linked protein systems (see section 3.4). The reorientational dynamics of interfacial water molecules next to surfaces of varying hydrophobicity was investigated by Stirnemann and co-workers. Making use of MD simulations and analytical models, they were able to explain non-monotonous variation of water reorientational dynamics with surface hydrophobicity. In a similar study, Laage and Thompson modelled reorientation dynamics of water confined in hydrophilic and hydrophobic nanopores. 

Hiller W, Wydrzynski T (2000) The affinities for the two substrate water binding sites in the O2 evolving complex of photosystem II vary independently during S-state turnover. Biochemistry 39 4399-4405. 

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