Proton high mobility

As will be seen from Table 2, the mobility of the hydrogen ion is even greater than that of (OH)-. This high mobility is ascribed to successive proton jumps of the kind... 

The viscosity of pure H2SO4 at 25°C is 27.6 times greater than that of water consequently the normal migration of ions is extremely slow. The comparatively high mobility of the (IISO4)- ion undoubtedly arises from successive proton transfers to the ion from an adjacent solvent molecule 2... 

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. 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

When water undergoes self-ionization, a range of cationic species are formed, the simplest of which is the hydronium ion, HjO (Clever, 1963). This ion has been detected experimentally by a range of techniques including mass spectrometry (Cunningham, Payzant Kebarle, 1972), as have ions of the type H+ (HaO) with values of n up to 8. Monte-Carlo calculations show that HjO ions exist in hydrated clusters surrounded by three or four water molecules in the hydration shell (Kochanski, 1985). These ions have only a short lifetime, since the proton is highly mobile and may be readily transferred from one water molecule to another. The time taken for such a transfer is typically of the order of 10 s provided that the receiving molecule of water is correctly oriented. 

Proton conductivities of 0.1 S cm at high excess water contents in current PEMs stem from the concerted effect of a high concentration of free protons, high liquid-like proton mobility, and a well-connected cluster network of hydrated pathways. i i i i Correspondingly, the detrimental effects of membrane dehydration are multifold. It triggers morphological transitions that have been studied recently in experiment and theory.2 .i29.i ,i62 water contents below the percolation threshold, the well-hydrated pathways cease to span the complete sample, and poorly hydrated channels control the overall transports ll Moreover, the structure of water and the molecular mechanisms of proton transport change at low water contents. 

The proton-olefin complex is probably responsible for the unusually high cisjtrans ratio 47, 92). These intermediates have to be considered as hydrogen bond-like structures and evidence has been presented for an extremely high mobility of the proton in these structures 98, 99). 

This is a reasonable assumption in view of the high mobility of protons in zeolites. 

The yield of strand breaks appears to be relatively independent of sample irradiation temperature, as discussed above. This implies that competing processes do not have much impact on reactions 1,2, 5, and 8. That is, the competitions between holes tunneling from the solvent to DNA and deprotonation of HsO " and between hole tunneling form the sugar phosphate to the bases and deprotonation of the sugar are fairly temperature-insensitive (from 4 to 300 K). In contrast, the mobility of the holes and excess electrons centered on the bases is very temperature-sensitive, zero at 4 K, onset at —40 K, and highly mobile at 180 K. By our model, the mobility is controlled by the proton transfer... 

Lunsford et al. (202) used trimethylphosphine as a probe molecule in their 31P MAS NMR study of the acidity of zeolite H-Y. When a sample is activated at 400°C, the spectrum is dominated by the resonance due to (CH3)3PH+ complexes formed by chemisorption of the probe molecule on Bronsted acid sites. At least two types of such complexes were detected an immobilized complex coordinated to hydroxyl protons and a highly mobile one, which is desorbed at 300°C. (see Fig. 45)... 

Three different states of protons are detected by solid-state H MAS NMR spectroscopy for H3PWi2O40 nH2O at room temperature, as shown in Fig. 10 (77). A sharp h resonance observed for n = 17 shows that the protons are in a uniform state and highly mobile. Much broader and weaker lines for less hydrated states indicate lower mobility of protons. The chemical shifts for n = 17 and n = 6 (7.3-7.5 ppm) correspond to clusters of hydrated water, as in Fig. 2a. The resonance at 9.2 ppm, for anhydrous H3PWi204o was assigned to protons attached to the most basic bridging oxygen atoms, on the basis of 1R results (78) and the basicity estimated by nO NMR spectroscopy (see below). 

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