Aqueous solvation

Aqueous Solvation.—A review deals with ion solvation in both aqueous and non-aqueous media and covers thermodynamic aspects, electrical conductivity, viscosity, transport coefficients, and n.m.r. spectra. Factors affecting the 

Emel yanov and V. P. Yagodarov, Zhur. strukt. Khim., 1973, 14, 919. 

Some aqueous systems that have been investigated are listed in Table 

Aqueous Solvation.—A review, covering the 1968—1972 publications, deals with physical properties, thermodynamics, and structures of non-aqueous and aqueous-non-aqueous solutions of electrolytes, and complete hydration limits. Thermodynamic aspects of ionic hydration also reviewed include the thermodynamic theory of solvation the molecular interpretation of ionic hydration hydration of gaseous ions (AG s, H s, and AA s) thermodynamic properties of ions at infinite dilution in water, solvent isotope effect in hydration reference solvents and ionic hydration and excess properties. A third review on the hydration of ions emphasizes the structure of water in the gaseous, liquid, and solid states the size of ions and the hydration numbers of ions and the structure of the hydrated shell from measurements of mobility, compressibility, activity, and from n.m.r. spectra. Pure water and aqueous LiCl at concentrations up to saturation have been examined by neutron and X-ray diffraction. For the neutron studies LiCl and D2O are employed. The data are consistent with a simple model involving only 

Morachevskii, Elektrokhim. Rafinirovanie Tyazhelykh Legkoplavkikh Metal. 

however, Ca + does not have a dehydrating effect on Li+ since these ions possess similar enthalpies of hydration in saturated aqueous solutions. The nuclear magnetic relaxation rates and shifts of Li+ and Cs+ in aqueous solutions containing Fe + and various counter-anions are interpreted in terms of a dipolar attraction between Li+ and the unpaired electrons on the Fe + ion, and the formation of an ion pair between Cs+ and ferric halide complex. An increase of pressure in the range 0—1000 bar results in an enhancement in the hydration of the ions Na+ and K+ in their aqueous chloride solutions. The enhancement is more pronounced at 20 than at 45 °C. These conclusions 

Safford and P. S. Leung, U.S. Office Saline Water, Res. Develop. Progr. Kept., 1971, No. 708. 

Palfalvi-Rozsahegyi, and K. Burger, Proc. Symp. Co-ordination Chem. ird, 1970,1, 99. 

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Rick S W and B J Berne 1996. Dynamical Fluctuating Charge Force Fields The Aqueous Solvation of Amides, Journal of the American Chemical Society 118 672-679. 

Chambers C C, G D Hawkins, C J Cramer and D G Tmlilar 1996. Model for Aqueous Solvation Ba sed on Class IC Atomic Charges and First Solvation Shell Effects. Journal of Physical Chemistry 100 16385-16398. 

Fleischman S H and C L Brooks III 1987. Thermodynamics of Aqueous Solvation - Solution Properties of. Mcohols and Alkanes. Journal of Chemical Physics 87 3029-3037. 

It is possible that simple repulsion between parallel dipoles in 92 also plays a part in the greater stability of 93. It has been shown that aqueous solvation effects reduce anomeric stabilization in many systems, particularly for tetrahydropyranosyls. 

From the results described above it is clear that a different QSPR model can be obtained depending on what data is used to train the model and on the method used to derive the model. This state of affairs is not so much a problem if, when using the model to predict the solubility of a compound, it is clear which model is appropriate to use. The large disparity between models also highlights the difficulty in extrapolating any physical significance from the models. Common to all models described above is the influence of H-bonding, a feature that does at least have a physical interpretation in the process of aqueous solvation. 

Figure 4.11 Optimized structures of CH cO species, as indicated, over aqueous-solvated Pt(lll) as determined by DFT in Cao et al. [2005]. Horizontal and vertical arrows indicate C—H and O—H cleavage steps, respectively. Reaction energies are included for the aqueous phase [Cao et al., 2005] and the vapor phase (in parentheses) [Desai et al., 2002]. The thermodynamically preferred aqueous phase pathway is indicated by bold arrows (in blue). (See color insert.)...

Whitfield TW, Varma S, Harder E, Lamoureux G, Rempe SB, Roux B (2007) Theoretical study of aqueous solvation of K+ comparing ab initio, polarizable, and fixed-charge models. J Chem Theory Comput 3(6) 2068-2082... 

Rick SW, Berne BJ (1996) Dynamical fluctuating charge force fields The aqueous solvation of amides. J Am Chem Soc 118(3) 672—679... 

Two dendrimers based on Fe-porphyrin core carrying peptide-like branches of different sizes have been synthesized in order to have more open and a more densely packed (23) structures [43]. The electrochemical behavior has been examined in CH2C12 and in aqueous solution. In the less polar solvent, the two dendrimers show similar potentials for the Fem/Fen couple, suggesting that the iron porphyrins in both the more open and the more densely packed dendrimers experience similar microenvironments. On the contrary, in water the behavior of the two dendrimers is very different since the reduction from Fem to Fe11 is much easier for the densely packed dendrimer. This result can be explained considering that in the dendrimer with the relatively open structure the aqueous solvation of the iron porphyrin is still possible, whereas in the densely packed one the contact between the heme and the external solvent is signifi-... 

Sukumar, N., and G. A. Segal. 1986. Effect of Aqueous Solvation upon the Electronic Excitation Spectrum of the Glycine Zwitterion A Theoretical Cl Study Using a Fractional Charge Model. J. Am. Chem. Soc. 108, 6880-6884. 

Fleischman, S. H. Brooks III, C. L., Thermodynamics of aqueous solvation Solution properties of alchohols and alkanes, J. Chem. Phys. 1987, 87, 3029-3037... 

Liquid water is an essential component of most terrestrial chemical processes, including those of living organisms. The cooperativity of H-bonding in water clusters is therefore of primary importance for understanding the structure and dynamics of pure water, as well as a vast spectrum of aqueous solvation phenomena in biotic and abiotic systems. In the present section we examine cooperativity effects for a... 

The present authors, using the SMx series of models, have considered aqueous solvation effects on proton transfer for these same amines, together with several other bases, and have arrived at similar conclusions to those detailed... 

Using the same theoretical model, Karelson et al. [269] and later Rzepa et al. [270] examined 4-nitroimidazole. The latter work corrected incomplete geometry optimizations present in the former study. In this instance, AMI predicts 5 to be 1.4 kcal/mol lower in relative energy than 6. However, the D02 model predicts the aqueous solvation free energies to be -25.3 and -7.1 kcal/mol for 6 and 5, respectively, rendering 6 considerably lower in energy than 5 in solution, which agrees with the experimental situation. 

Parchment et al. [271] have provided more recent calculations on the 3-hydroxypyrazole equilibrium at the ab initio level. They noted that tautomer 9, which was not considered by Karelson et al. [268], is the lowest-energy tautomer in the gas phase at levels of theory (including AMI) up to MP4/6-31G //HF/3-21G [271], Although 8 is the dominant tautomer observed experimentally in aqueous solution, in the gas phase 8 is predicted to be nearly 9 kcal/mol less stable than 9 at the MP4 level [271], Using a DO model with an unphysically small cavity radius of 2.5 A, Parchment et al. [271] were able to reproduce at the ab initio level the AMI-DO prediction of Karelson et al. [268], namely that 8 is the most stable tautomer in aqueous solution. With this cavity, though, 8 is predicted to be better solvated than 9 by -22.2 kcal/mol [271], This result is inconsistent with molecular dynamics simulations with explicit aqueous solvation [271], and with PCM and SCME calculations with more reasonable cavities [271] these predict that 8 is only about 3 kcal/mol better solvated than 9. In summary, the most complete models used by Parchment et al. do not lead to agreement with experiment... 

Finally, we note that Karelson et al. [295] have used the D02 model with small cavity radii to consider aqueous solvation effects on other tautomeric equilibria of substituted pyridines. In particular, they examined methyllmethylene, amino/imino, hydroxy/oxo, and mercapto/thiono substitution at the 2-, 3, and 4-positions of pyridine. They observed methyl/methylene equilibria to be only slightly perturbed by aqueous solvation. Amino/imino equilibria were slightly more perturbed, followed by hydroxy/oxo equilibria. Mercapto/thiono equilibria were very significantly affected by aqueous solvation Karelson et al. predicted pK shifts of up to 16 units. This sensitivity of the thiono group to solvation is also discussed in the next section. Overall, the tautomeric equilibria of 3- and 4-substituted pyridines were more sensitive to aqueous solvation than were those of 2-substituted pyridines. 

Truhlar and coworkers [29, 232, 233] have proposed a quantum-mechanical-continuum dielectric model for aqueous solvation. This method is discussed by Truhlar and coworkers in Chapter I. 

From a theoretical viewpoint, the effect of aqueous solvation in organic reactions has received considerable attention in recent years. These studies have gone a step beyond analysis of simple models to consider reactions such as SN1, SN2, cycloaddition reactions and Claisen rearrangement, for instance, with more realistic models. 

Schwartz, B. J. and Rossky, P. J. Aqueous solvation dynamics with a quantum mechanical solute computer simulation studies of the photoexcited hydrated electron, J.Chem.Phys., 101 (1994), 6902-6916... 

Alfano, J. C., Walhout, P. K., Kimura, Y. and Barbara, P. F. Ultrafast transient-absorption spectroscopy of the aqueous solvated electron, J.Chem.Phys., 98 (1993), 5996-5998... 

The free energy of solvation is a key property of solute-solvent systems, since it quantifies the tendency of the solute to enter into solution. We have addressed this for aqueous solvation via the GIPF approach on several occasions.46 48 Our best correlation is Eq. (10), obtained using density functional B3P86/6-31+G Vs(r) 46... 

Some caution is required when comparing the association constants obtained from extraction experiments with those measured under anhydrous, homogeneous conditions. Iwachido et al. (1976, 1977) have shown that the extracted cation retains part of its aqueous solvation shell on complexation. In particular, the small univalent cations (Li+, Na+) and bivalent cations give high hydration numbers for their crown-ether complexes. Water molecules completing the co-ordination sphere of the cation have frequently been encountered in the solid state of crown-ether complexes (Bush and Truter, 1970, 1971). The effect of small amounts of water on the equilibria (1) has not been studied yet for crown ethers. However, it has been found that the presence... 

Figure 1 shows a reversed micelle where the bulk solvent is a hydrocarbon and the core is a water pool surrounded by surfactant. These systems possess unique features as the physical properties of the water pools only start to approach those of bulk water at high water content when the pool radii are >150 pools with radii as small as 15 can be constructed (1, 25). These systems have been used to investigate the nature of several inorganic reactions by stopped flow methods (26, 27). They have also been used to produce so-called naked ions, i.e., ions that possess a minimum of aqueous solvation (28). The system strongly promotes many reactions, a fact attributed to the unusual nature of the water in this system. 

We have examined the competing isomerization and solvolysis reactions of 1-4-(methylphenyl)ethyl pentafluorobenzoate with two goals in mind (1) We wanted to use the increased sensitivity of modern analytical methods to extend oxygen-18 scrambling studies to mostly aqueous solutions, where we have obtained extensive data for nucleophilic substitution reactions of 1-phenylethyl derivatives. (2) We were interested in comparing the first-order rate constant for internal return of a carbocation-carboxylate anion pair with the corresponding second-order rate constant for the bimolecular combination of the same carbocation with a carboxylate anion, in order to examine the effect of aqueous solvation of free carboxylate anions on their reactivity toward addition to carbocations. 

The nitrenium ion +NH2 has been the subject of a detailed, comprehensive calculation. Calculations on (48) with 15 different X substituents reveal a large substituent sensitivity, and also that aqueous solvation preferentially stabilizes the singlet state. This substiment sensitivity agrees with the results of a time-resolved IR study of the diphenylnitrenium ion (49), which shows that resonance contributors such as (50) and (51) are very important to the overall structure. Substituted 4-biphenyl nitrenium ions... 

Aqueous Solvation of Hyperbranched Polyfacrylic Acid) Films... 

In principle, it is a simple matter to include solvent water molecules directly in MD simulations, since appropriate intermolecular potential energy functions for water are available (1Z 37,38) one would just surround the solute molecules with a sufficient number of water molecules to approximate a bulk solution. Unfortunately, a "sufficient number of water molecules might be enormous, since many of the effects of aqueous solvation are long range or are due to entropic contributions arising from "structuring of the solvent, which may be cooperative in nature. 

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