Water assisted

DFT STUDY OF 8-MERCAPTOQUINOLINE INTRAMOLECULAR HYDROGEN BOND, SINGLE PROTON TRANSFER AND WATER-ASSISTED TAUTOMERIZATION... 

Some adverse reactions, such as dry mouth, episodes of orthostatic hypotension, and drowsiness, may need to be tolerated because drug therapy must continue. Nursing interventions to relieve some of these reactions may include offering frequent sips of water, assisting the patient out of the bed or chair, and supervising all ambulatory activities. 

These profiles clearly show that in the gas phase the alkylations of both ammonia and water by o-QM are assisted by an additional water molecule H-bonded to o-QM (water-catalyzed mechanism), since S4 and S5 TSs are favored over their uncatalyzed counterparts (SI and S2) by 5.6 and4.0 kcal/mol [at the B3LYP/6-311 + G(d,p) level], respectively. In contrast, the reaction with hydrogen sulfide in the gas phase shows a slight preference for a direct alkylation without water assistance (by 0.8 kcal/mol). 

The bulk solvent effect on the reaction energy, described by the lower portion of Scheme 2.3, significantly modifies the relative importance of the uncatalyzed and water-assisted alkylation mechanism by o-QM in comparison to the gas phase. 

FIGURE 2.2 Optimized TS geometries of the cytosine alkylation reaction by o-QM, without and with water assistance. Bond lengths (in A) and activation Gibbs free energies (in kcal/mol) in the gas phase and in aqueous solution (in parentheses) at the B3LYP/6-311 +G(d,p)// B3LYP/6-31G(d) level of theory with respect to the reactants have been taken from Ref. [14]. 

Further evidence for the OHb pairs is given in an STM movie recorded at approximately 187 K. The movie shows the OHb pairs separating across the Ob rows via proton exchange with water molecules [19]. Key frames from the movie are shown in Figure 8.5. This water-assisted OHb diffusion mechanism is supported by calculations, which show that the barrier to diffusion is lowered by the exchange with water. The same diffusion mechanism is also observed for isolated OHb and because of the misassignment of OHb and Ob-vacs by Schaub et al. [15], this water-mediated diffusion of OHb was incorrectly reported as oxygen-mediated diffusion of Ob-vacs [32, 33] via a mechanism inconsistent with subsequent isotope studies [34],... 

Barone, V. and C. Adamo. 1994. Theoretical study of direct and water-assisted isomerization of formaldehyde radical cation. A comparison between density functional and post-Hartree-Fock approaches. Chem. Phys. Lett. 224, 432. 

Jacobs, G., Patterson, P.M., Graham, U.M., Crawford, A.C., Dozier, A., and Davis, B.H. 2005. Catalytic links among the water-gas shift, water-assisted formic acid decomposition, and methanol steam reforming reactions over Pt-promoted thoria. J. Catal. 235 79. 

Hata, K. Futaba, D. N. Mizuno, K. Namai, T. Yumura, M. Iijima, S. 2004. Water-assisted highly efficient synthesis of impurity-free single-walled, carbon nanotubes. Science 306 1362-1364. 

Fig, 20 Water assisted proton transfer in an enamine intermediate... 

An emulsion may be obtained on further washing with water. A small amount of sodium chloride (2-3 g.) dissolved in the wash water assists in breaking such emulsions. 

The oxyl radicals resulting from the decomposition of organic peroxides are energy-rich intermediates and undergo a number of rapid reactions (Chap. 7). Here, it is briefly recalled that the tertiary oxyl radicals undergo facile (3-fragmentation [reaction (52)], and the primary and secondary oxyl radicals an equally fast water-assisted 1,2-H shift [reaction (53)]. 

This process must be water assisted (see also Elford and Roberts 1996), since this reaction requires a high activation energy in the gas phase (Batt et al. 1981 ... 

Unless a water-assisted disproportionation (cf. Wang et al. 1996) or a disproportionation by ET takes place, G has to dimerize. These dimers have escaped identification, but the various canonical mesomeric forms shown below indicate... 

The molecular mechanism of the Hoffmann elimination involving (iV-Cl)-N-methyl-ethanolamine has been theoretically characterized by using DFT at the B3LYP/ 6-31++G computing level.49 The role of water as a solvent has been analysed by using both discrete and hybrid discrete-continuum models. The rearrangement proceeds by a water-assisted asynchronous concerted mechanism. 

The results of a multiple isotope effect study of the acid-catalysed hydrolysis of HC02Me (Scheme 5) have provided a detailed picture of the transition-state structure for the reaction, which involves one hydronium ion and two water molecules (15).8 DFT calculations on the water-assisted neutral hydrolysis of MeC02Et indicated that a stepwise process involving four molecules of H20 is energetically favoured.9... 

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