Valine, protonated

Figure 2. DQFCOSY spectrum of RpII in D2O. Cross peaks corresponding to a-P protons of various spin systems are labeled. The valine spin systems are shown explicitly.

FIGURE 7.34 Decomposition of the symmetrical anhydride of A-methoxycarbonyl-valine (R1 = CH3) in basic media.2 (A) The anhydride is in equilibrium with the acid anion and the 2-alkoxy-5(4//)-oxazolone. (B) The anhydride undergoes intramolecular acyl transfer to the urethane nitrogen, producing thelV.AT-fcwmethoxycarbonyldipeptide. (A) and (B) are initiated by proton abstraction. Double insertion of glycine can be explained by aminolysis of the AA -diprotected peptide that is activated by conversion to anhydride Moc-Gly-(Moc)Gly-0-Gly-Moc by reaction with the oxazolone. (C) The A,A -diacylated peptide eventually cyclizes to the IV.AT-disubstituted hydantoin as it ejects methoxy anion or (D) releases methoxycarbonyl from the peptide bond leading to formation of the -substituted dipeptide ester. 

The chemical shift may reveal the position of one atomic grouping with respect to another by anisotropic shielding. This is an effect likely to be sensitive to temperature and solvent changes as seen in the valine amide-proton resonance in Figure 3. 

H and 13C FT-NMR spectra of biomolecules. The lower spectra are for 1H showing a ppm scale of 0-10. TMS standard is at 0 ppm. The upper spectra are for 13C showing a ppm scale of 0-200. A L-Valine in D20 + DCI. Can you assign each peak to the correct protons and carbon atoms in the valine structure Hint The carboxyl carbon of valine has a peak at about 175 ppm. B Sucrose in D20. Carbon numbers in the chemical structure correspond to the following peaks in order from 0 to 120 ppm ... 

Study the H spectrum of valine in Figure 5.14A and match each peak to the corresponding proton in the chemical structure. Explain any spin-spin coupling. 

PROBLEM 16.19 Consider the titration of 40.0 mL of a 0.0250 M solution of the protonated form of the amino acid valine (H2A+) with 0.100 M NaOH. Calculate the pH after addition of the following volumes of 0.100 M NaOH ... 

The H NMR and X-ray crystallography results discussed in Section III have clearly shown that the environments of the heme pockets of the a and P chains of Hb as manifested by the conformations of proximal histidine (F8), distal histidine (E7), and distal valine (Ell), as well as the conformation of several porphyrin protons and the electronic structure of the heme group in both deoxy and ligated states, are not equivalent. It has not been clear what this difference in structure in the a and p heme pockets means in terms of differences in function, because there are discrepancies in the published results regarding the relative ligand affinities of the a and P chains of Hb A. 

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