Primary protons

Step 1 Assume that only H3P04 significantly affects the pH. The primary proton transfer equilibrium is... 

Most aliphatic ketones can lose a proton from either of two carbon atoms adjacent to the carbonyl. The question of which of the possible carbanions or salts is the effective reagent in a given base-catalyzed reaction depends on the nature of the electrophilic reagent with which the ion subsequently reacts. Thus alkyl methyl ketones lose a primary proton in their reactions with alkali and iodine, alkali and an aldehyde, or alkali and carbon dioxide, but lose a secondary proton in certain other reactions. 

The reactions in which the methyl ketone loses a primary proton are all fast reactions, and the direction of the reaction is determined by the fact that an electron-releasing alkyl group slows down the removal of the secondary proton from the methylene group. On the other hand a slow reaction, like the base-catalyzed reaction of ketones with dimethyl sulfate in ether, gives a product corresponding to the removal of a proton from the more alkylated carbon.418... 

Site-directed mutagenesis and the crystal structure analysis of a proteasome-inhibitor complex identified the amino-terminal threonine (Thrl) of Thermoplasma P subunits as both, the catalytic nucleophile and the primary proton acceptor (Seemiiller et al. 1995 Lowe et al. 1995). 

The acceleration of the initial stage of the epoxy compound polymerization under the action of the TA in the presence of the primary amine is explained by the role of the proton donor of primary proton amine activating the epoxy ring. The initial polymerization rate increases linearly with increasing concentration of the primary amine 46). 

On the other hand, IR data suggested that some silatrane-4-carboxylic acids might be present in solution as an equilibrium mixture of the acid (42) and the salt (42a) forms (equation 58). These results, combined with the stability of the protonated equatorial Si—O bond of these acids in their crystals, was regarded as favoring the primary protonation of... 

Thus, the three-center potential integrals are not retained. Ferenczy et al. found that the AMI MEP maps are able to reproduce the main characteristics of the HF/STO-3G MEP maps for the water, formaldehyde, formamide and the cytosine molecules and for the cyanate ion [40]. However, the NDDO AMI MEP maps gave deeper minima which were closer to the molecules than those in the HF/STO-3G MEP maps. The contour plots of MEP for the cytosine molecule are displayed in Fig. 2. It can be seen that the NDDO AMI MEP map correctly predicts the N3 nitrogen atom as a primary protonation center instead of the 02 oxygen atom. This finding is in agreement with the HF/STO-3G MEP map [28] and the experimental as well as the theoretical proton affinities [29, 30]. Similar results were also obtained by Luque et al. based on the quasi ab initio MNDO MEP map [37], INDO/S, HF/4-31G and HF/6-31G calculations showed an opposite order of protonation [27, 31] as discussed earlier. 

In the presence of potassium hydroxide, cellulose adds to carbon disulfide (Figure 8.4). In this way potassium xanthate A is produced. It is soluble in water, but restores the water-insoluble cellulose upon addition of acid. The primary protonation product is the dithiocarbonic acid O-cellulose ester B. B reacts just like the unstable carbonic acid derivatives in Figure 8.3, namely via a zwitterion (C) and its decomposition into cellulose (a heteroatom nucleophile)... 

An increase in primary proton-beam intensity by a factor of 200 as compared with the CERN experiment. 

An essential feature of reactions catalyzed by metal-sulfur oxidoreductases is the coupling of proton- and electron-transfer processes. In this context, an important question is how primary protonation of metal-sulfur sites influences the metal-sulfur cores, small molecules bound to them, and the subsequent transfer of electrons. In order to shed light upon this question, protonations, isoelectronic alkylations, and redox reactions of [M(L) (S )] complexes were investigated (M = Fe, Ru, Mo L = CO, NO S = Sj, US24 ). The CO and NO ligands served as infrared (IR) probe for the electron density at the metal centers. Resulting complexes were characterized as far as possible by X-ray crystallography. Scheme 23 shows examples of such complexes. 

The upheld signal at 1.2 8 is due to saturated primary protons. The downfield signal at 3.5 5 is due to protons on carbon adjacent to an electronegative atom - in this case, oxygen. 

Asp 85, to approach closer to the positively charged primary proton donor, the Schiff base. The primary proton transfer event would then neutralize these two groups, canceling their electrostatic attraction and facilitating a relaxation of helix C to a less strained geometry. 

After it became clear that the reduction of CH3-S-C0M to CH4 consists of two reactions, one of these, the reduction of the heterodisulfide of CoM-S-H and H-S-HTP with H2 (Reaction 7 of Table 2), was considered to be the coupling site for ATP synthesis [14,71], Indeed, it was shown that everted vesicles of G61 also catalyzed the reduction of the heterodisulfide with H2 or with chemically reduced factor F420, F420H2, to H-S-CoM and H-S-HTP and that this reaction was coupled with the synthesis of ATP via the mechanism of electron transport phosphorylation [114-117] (Fig. 5) (i) the reduction of the heterodisulfide was associated with primary proton translocation at a ratio of up to 2H /CoM-S-S-HTP proton translocation was inhibited by protonophores rather than by DCCD (ii) reduction of the heterodisulfide was stimulated by protonophores and inhibited... 

The sterically hindered base would be more likely to remove the primary proton, because it would not be able to reach the crowded tertiary proton. Bearing these factors in mind, which proton is most likely to be removed when CH3C0CHC02Et is treated with a general base ... 

The primary cosmic rays propagate through the interstellar medium (ISM) until they either escape into extragalactic space, or are removed by interaction or energy losses in the ISM. Their interstellar equilibrium intensity may be recorded with a detector which is usually carried above the earth s atmosphere on spacecraft or balloon. Secondary cosmic rays are those that are generated as products from interactions of the primaries in the ISM positrons and antiprotons mostly come from interactions of primary protons, while the secondary nuclei such as Li, Be, B, and the elements just below iron, which cannot be produced by primary nucleosynthesis, are the products of spallation reactions of heavier primaries in the ISM. The overall arriving cosmic-ray intensity represents a mix of primary and secondary particles. 

Fig. 4 also shows the spectrum of primary protons, which has been derived from the flux of unaccompanied hadrons measured with the KASCADE experiment Antoni et al. 2004c. The spectrum is compatible with the proton flux as obtained from the unfolding procedure when using the QGSJET model. The EAS-TOP experiment published two sets of spectra with different assumptions about the contribution of protons and helium nuclei derived from the measurements of the electromagnetic and muonic shower components Navarra et al. 

For the pyridine complexes, effects due to complexation observed at the pyridine molecule (such as N chemical shifts) can also be used . Low temperature measurements have clearly been very useful in elucidating these reactions. An approach using N and H chemical shifts as well as deuterium isotope effects on N chemical shifts and primary proton isotope effects (see Section n.F.7) at very low temperature in freons showed in the N spectrum three different species AHB, AHAHB and AHAHAHB. For the 1 1 complex an asymmetric single well potential is assumed , different from the approach taken above. Furthermore, a linear correlation was found between the N chemical shift and the one-bond 7(N,H) coupling constant. This type of reaction has also been studied using fractionation factors (See Section n.O). 

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