Matrix-assisted laser desorption ionization hydrogen/deuterium exchange studies to probe peptide conformational changes

AbstractHydrogen/deuterium (H/D) exchange chemistry monitored by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is used to study solution phase conformational changes of bradykinin, α-melanocyte stimulating hormone, and melittin as water is added to methanol-d4, acetonitrile, and isopropanol-d8 solutions. The results are interpreted in terms of a preference for the peptides to acquire more compact conformations in organic solvents as compared to the random conformations. Our interpretation is supported by circular dichroism spectra of the peptides in the same solvent systems and by previously published structural data for the peptides. These results demonstrate the utility of MALDI-TOF as a method to monitor the H/D exchange chemistry of peptides and investigations of solution-phase conformations of biomolecules

Theory of Π-N scattering in the strip approximation to the Mandelstam representation

The strip approximation to the Mandelstam representation is applied to the Π-N problem, and the basic equations given. The asymptotic behavior of the invariant amplitudes in the physical regions is discussed in terms of the unitarity condition on partial-wave amplitudes, the constancy of high-energy scattering cross sections, and the Pomeranchuk theorem, and it is shown to imply that no subtractions should be necessary except in the J=½ wave of the Π-N channel and the J=0 wave of the Π+Π→N+N̅ channel. This obviates the difficulties encountered by earlier workers when they subtracted higher waves

Nucleon as a Regge pole and the J=½, T=½ ΠN phase shifts

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Polaron self-energy and Bloch-Nordsieck method

By using the Bloch-Nordsieck method the self-energy of a polaron has been investigated in two limiting cases: (i) when the polaron velocity is low, i.e., mv<SUP>2</SUP>ħω, and (ii) when the velocity is high, i.e., mv<SUP>2</SUP>ħω. In case (i), this method gives results which are no better than those obtained by the use of the customary second-order perturbation theory, when the coupling constant is large. The contribution of the phonons of large momenta, if not more, is at least as much as that of the phonons of low momenta. However, in case (ii), we hope that our results are more satisfactory in view of the fact that the assumptions of the B-N method are better justified. In this case the self-energy is found to vary inversely as the velocity