Water unique solvent

Besides these special physical properties, hydrogen-bonded liquid water also has unique solvent and solution properties. One feature is high proton (H ) mobility due to the ability of individual hydrogen nuclei to jump from one water molecule to the next. Recalling that at temperatures of about 300 K, the molar concentration in pure water of H3O ions is ca. 10 M, the "extra" proton can come from either of two water molecules. This freedom of to transfer from one to an adjacent "parent" molecule allows relatively high electrical conductivity. A proton added at one point in an aqueous solution causes a domino effect, because the initiating proton has only a short distance to travel to cause one to pop out somewhere else. 

Water is a unique solvent because of its high polarity and ability to form a network of H-bonds. It is immiscible with many organic solvents and is therefore a suitable solvent for use in biphasic reactions in which catalysts are made preferentially soluble in the aqueous phase. Phase transfer catalysis allows the use of aqueous reagents with substrates that have low solubility in water. That water is abundant and totally non-toxic make it the perfect clean solvent, provided that solubility issues can be overcome, and it is in use as a solvent on an industrial scale for polymerization, hydroformylation, and a range of organic chemistry involving PTC. These applications are discussed further in Chapters 7-11. 

The half-wave potentials of K+, Tl+ and Ca2+ in water are slightly more negative and thosefor Zn2+, Cd2+, Mn2+, Ni2+ and Co2+ considerably more negative than is expected according to the donicity rule. It has been shown in the previous sections that water is a rather unique solvent. The effect in question may be interpreted by the so-called Katzin-effect according to which water forms a royal core of coordinated water molecules which are hooked together by hydrogen bonds 70,71>122,1231. 

It was postulated that the differences in enzyme activity observed primarily result from interactions between enzyme-bound water and solvent, rather than enzyme and solvent. As enzyme-associated water is noncovalently attached, with some molecules more tightly bound than others, enzyme hydration is a dynamic process for which there will be competition between enzyme and solvent. Solvents of greater hydrophihcity will strip more water from the enzyme, decreasing enzyme mobility and ultimately resulting in reversible enzyme deactivation. Each enzyme, having a unique sequence (and in some cases covalently or noncovalently attached cofactors and/or carbohydrates), will also have different affinities for water, so that in the case of PPL the enzyme is sufficiently hydrophilic to retain water in all but the most hydrophilic solvents. 

That the traits of B. m aterium can be transferred to B. subtilis by plasmid transfer techniques has been established. These traits are increased resistance to naphthalene, parachlorbiphenyl, and dibenzofuran, and increased ability to degrade C-naphthalene. The transformants increased degradative abilities were demonstrated by the accumulation of greater quantitites of water soluble metabolite and the presence of a unique solvent soluble metabolite. 

Water is a unique solvent, which also happens to be ubiquitous to life on Earth. Paradoxical as it may seem, any discussion on enzymatic catalysis in organic sol-... 

A class of solutions where the combined properties of water make it a rather unique solvent is micellar solutions. These solutions arise from the dissolution of surfactants in water at above a certain concentration (the critical micelle concentration, CMC). The micelles are structures that contain a few tens to a few hundreds of surfactant molecules, arranged so as to have the hydrophobic long... 

For the same reason as above, excess solvent molecules in the cavitation bubble also seriously limit the applicability of many volatile organic solvents as a medium for sonochemical reactions [2,25,26]. In fact, water becomes a unique solvent in many cases, combining its low vapor pressure, high surface tension, and viscosity with a high yield of active radical output in solution. Its higher cavitation threshold results in subsequently higher final temperatures and pressures upon bubble collapse. Most environmental remediation problems deal with aqueous solutions, whereas organic solvents are mostly used in synthesis and polymer modifications processes. 

The different catalytic responses of peroxidase in dioxane and methanol versus acetone are intriguing. It is clear that the effects of water-miscible solvents on enzymatic catalysis are not equivalent and for the first time quantitative kinetic data have been obtained which highlight this. However, the cause of this effect remains unresolved. We are continuing and expanding this kinetic study to include other solvents, both water-miscible and immiscible, and other phenols. This future study will enable rational and quantitative approaches for peroxidase-catalyzed phenolic polymerizations to be based on optimal solvent and phenol choices. From a more fundamental standpoint, this work has shown that enzymes may be more active in organic media than in water as long as optimal conditions are employed. There is no reason to believe peroxidase is unique in this respect. 

Supercritical fluids are unique solvents and reaction media due to liquid like density and gas like viscosity. Diffusion is not limited by any interface. Under ambient conditions hydrocarbons and water are nearly unmiscible. Phase equilibrium changes significantly in the supercritical region of water (Tc = 647 K, pc = 22.1 MPa). Hydrocarbons and supercritical water become miscible at any ratio, whereas supercritical carbon dioxide and hydrocarbons still have a broad miscibility gap [4],... 

For an in-depth understanding of the formulation of solvent inks for CIJ printers, we need to look at how CIJ technology works, the product applications and the history of ink formulation within the CIJ technology area. Although there are a few aqueous formulations used in CIJ printers, the vast majority of inks are indeed solvent-based, even if they are solvent/water or solvent/UV inks. Thus, solvent inks form the backbone of this industry and there are literally hundreds of unique solvent-based ink formulations being sold and used each day. 

This sample preparation method involves steam distillation of the volatile organic components of a sample followed by preconcentration by LEE using a water-insoluble solvent. SDE served as unique clean-up and preconcentration step before derivatization, in the GC-MS determination of polycyclic aromatic hydrocarbons, phenols and aromatic amines in particulate phase mainstream cigarette smoke . Preconcentration by the SDE... 

The influence of water as solvent on the rate of Diels-Alder reactions is likely the best example of the close relationship between the unique properties of liquid water and its strongly accelerative effect. This is probably due to the large negative value of the activation voliune of Diels-Alder reactions this value (ca. 30 cm mol" ) is even somewhat more negative in water versus organic solvents [28]. 

These two surface forces are observed in thin aqueous films. Their appearance is somehow connected with the unique properties of the water as solvent small molecular size, large dipole moment, high dielectric constant, and formation of an extensive hydrogen bonding network. " " ... 

Water, as we know, is a unique solvent. One of its special properties is its ability to act either as an acid and as a base. Water functions as a base in reactions with acids such as HCI and CH3COOH, and it functions as an acid in reactions with bases such as NH3. Water is a very weak electrolyte and therefore a poor conductor of electricity, but it does undergo ionization to a small extent ... 

Describe why the chemical and physical properties of water make It a truly unique solvent. 

The above results and analysis on the low A in mononuclear and dinuclear cupredoxins have also been supported by numerous structural analyses of both oxidized and reduced cupredoxins. Both X-ray crystallography and XAS " of the metal-binding sites in the cupredoxins clearly show minimal difference between the oxidized and reduced proteins. Finally, in addition to the unique geometry and valence delocalization discussed above, which affect inner-sphere reorganization energy, other factors that may influence outer-sphere reorganization energy may also play an important role in cupredoxins. The factors include exclusion of water or solvent from the copper center in the folded proteins. This factor rules out electron transfer as a putative function for the red copper protein nitrosocyanin because its copper center is solvent accessible. 

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