Proton functions

Metal centers bound to surface chelate, or surrounded by n protonated functional groups... 

Alper and coworkers investigated the influence of more bulky bases (2,2 -bipyridine, 1,10-phenanthroline, and 6,7-dihydro-5,8-dimethyldibenzo[b,j]-l,10-phenantroline) and para-toluene sulfonic acid (p-TsOH) as proton source (proton functions as a Lewis acid). In the presence of p-TsOH a molecular weight up to 10,000 g/mol was reported. This could be slightly increased by the use of benzylbromide instead of p-TsOH, forming PhCH2COCo(CO)4 as catalyst in situ. In this case, a molecular weight comparable to that found in Rieger s work was achieved, but the polymers remain atactic [69]. 

One general statement may be made If a molecule MX (X is a functional group) is protonated by the reagent ion to give the quasimolecular ion MXH+, fragmentation usually produces the neutral protonated functional group XH and the fragment ion M+. 

Harbury HA, Loach PA (1960) Oxidation-linked proton functions in heme octa- and undecapeptides from mammalian cytochrome c. J Biol Chem 235 3640-3645... 

In this mechanism, the second ring is formed early. The carbonyl oxygen of the amide is protonated, and then the oxygen of the aldehyde adds to this protonated functional group to form a new ring. 

The assignment of structure on the basis of NMR spectra requires knowledge of the relationship between chemical shifts and functional groups. Normally, both proton and carbon spectra are recorded and analyzed. This section considers the relationship between proton resonances and structure. Figure 3-9 summarizes the resonance ranges for common proton functionalities. 

Figure 5.7. Extent of dissociation of the protonated functional groups (expressed as the fraction, a) of an acid peat soil, in the presence of AP" " (as AICI3) or of (as KCI). (Adapted from P. Bloom and M. B. McBride. 1979. Metal ion binding and exchange with hydrogen ions in acid-washed peat. Soil Sci. Soc. Am.. 43 687-692.)...

The chemical interpretation of o-in measured by the Schofield method depends sensitively on the type and concentration of probe electrolyte used. If these properties are chosen so that the cation in the reacting electrolyte neutralizes precisely the exposed functional group charge associated with isomorphic substitutions and dissociated hydroxyls and so that the anion neutralizes only the exposed protonated functional groups, then q+ and q. will have optimal magnitude for the chosen pH value and CTjn will be truly an intrinsic surface charge density. On the other hand, if the cation in the probe electrolyte is not able to displace all of the native adsorbed cations in, e.g., inner-sphere surface complexes, or if the anion cannot displace all of the native anions bound to protonated functional groups, or if either ion does not form only neutral surface complexes in the soil clay, then Ojn will differ from its optimal value. 

Phenol functions as a nucleophile, and formaldehyde (activated by protonation) functions as an electrophile in an electrophilic aromatic substitution reaction. The resulting alcohol then functions as an electrophile (again activated by protonation) and reacts with phenol in another electrophilic aromatic substitution reaction. 

In addition to its protonating function, the NH4 ion can solvate the sample molecules [reaction (b) above], producing an abundant [M + 18] peak for some natural product classes (particularly carbohydrates and their derivatives). Ammonia is now well established in such cases as an alternative to methane and isobutane as a positive Cl reagent gas (9). Nitrous oxide has also been used with success to generate abundant [M + NO] ions from a variety of compounds, including natural terpenes 10). The fragmentations were characteristic. 

The low pH of these reaction solutions indicates that protons are being produced in the system. There are several possible sources. First, displacement of a proton from one of the protonated functional groups in the amino acid by the metal ion is necessary for coordination at the metal site. The reactions of K2PtCl4 with amino acids has been extensively studied by Volshtein and others. According to Volshtein, reaction of the simple amino acid in the zwitterion form, AH, proceeds according to the following equations ... 

Scheme 4.15 Alkox5mines and nitroxides with protonable functions.

---